Gold catalysts supported on CeO2 and CeO2–Al2O3 for NOx reduction by CO

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第３４卷第４期化㊀学㊀研㊀究Ｖｏｌ．３４㊀Ｎｏ．４２０２３年７月ＣＨＥＭＩＣＡＬ㊀ＲＥＳＥＡＲＣＨＪｕｌ．２０２３载体效应与镍晶粒尺寸对ＣＯ２甲烷化低温催化性能的影响李㊀倩１，苏兵雷１，吉永红１，邵莹莹１，李㊀玥２∗（１．河南省洛阳生态环境监测中心，河南洛阳４７１０００；２．河南工程学院化工与印染工程学院，河南郑州４５１１９１）收稿日期：２０２２⁃１１⁃２２基金项目：河南省自然科学基金面上项目（２１２３００４１０３３６）作者简介：李倩（１９８６－），女，化学工程硕士，主要从事生态环境保护与监测研究工作㊂∗通信作者，Ｅ⁃ｍａｉｌ：ｌｉｙｕｅ０１２８＠１６３．ｃｏｍ摘㊀要：采用等体积浸渍法制备ＭｇＯ和ＣｅＯ２负载的一系列不同镍含量催化剂，对其进行了二氧化碳甲烷化催化性能评价㊂研究结果表明ＮｉＯ／ＣｅＯ２基催化剂具有优异的低温催化活性，其中８０％ＮｉＯ／ＣｅＯ２催化剂，在１８Ｌ／（ｇ㊃ｈ）㊁Ｈ２／ＣＯ２＝４和３５０ħ反应条件下甲烷产率为６７％㊂探究了镍含量对ＮｉＯ／ＭｇＯ和ＮｉＯ／ＣｅＯ２催化剂活性的影响，结果表明，随着镍含量增加，二氧化碳转化率㊁甲烷产率升高，在镍负载量为５０％８０％时催化性能最佳㊂通过Ｘ射线衍射（ＸＲＤ）㊁氢气程序升温还原（Ｈ２⁃ＴＰＲ）㊁拉曼（Ｒａｍａｎ）㊁ＣＯ２⁃ＴＰＤ表征探究不同载体和Ｎｉ晶粒大小对ＮｉＯ／ＭｇＯ，ＮｉＯ／ＣｅＯ２催化剂催化活性的影响㊂本研究可为设计具有优异低温催化性能的二氧化碳甲烷化催化剂提供参考㊂关键词：甲烷化；载体；催化性能；晶粒大小；负载量中图分类号：Ｏ６４３文献标志码：Ａ文章编号：１００８－１０１１（２０２３）０４－０３５２－０８ＥｆｆｅｃｔｏｆｓｕｐｐｏｒｔａｎｄｎｉｃｋｅｌｃｒｙｓｔａｌｓｉｚｅｏｎｌｏｗｔｅｍｐｅｒａｔｕｒｅｃａｔａｌｙｔｉｃｐｅｒｆｏｒｍａｎｃｅｏｆｃａｒｂｏｎｄｉｏｘｉｄｅｍｅｔｈａｎａｔｉｏｎＬＩＱｉａｎ１ＳＵＢｉｎｇｌｅｉ１ＪＩＹｏｎｇｈｏｎｇ１ＳＨＡＯＹｉｎｇｙｉｎｇ１ＬＩＹｕｅ２∗１．ＬｕｏｙａｎｇＥｃｏｌｏｇｉｃａｌＥｎｖｉｒｏｎｍｅｎｔＭｏｎｉｔｏｒｉｎｇＣｅｎｔｅｒｏｆＨｅｎａｎＰｒｏｖｉｎｃｅＬｕｏｙａｎｇ４７１０００ＨｅｎａｎＣｈｉｎａ２．ＳｃｈｏｏｌｏｆＣｈｅｍｉｃａｌａｎｄＰｒｉｎｔｉｎｇ⁃ｄｙｅｉｎｇＥｎｇｉｎｅｅｒｉｎｇＨｅｎａｎＵｎｉｖｅｒｓｉｔｙｏｆＥｎｇｉｎｅｅｒｉｎｇＺｈｅｎｇｚｈｏｕ４５１１９１ＨｅｎａｎＣｈｉｎａＡｂｓｔｒａｃｔＡｓｅｒｉｅｓｏｆｃａｔａｌｙｓｔｓｗｉｔｈｄｉｆｆｅｒｅｎｔｎｉｃｋｅｌｃｏｎｔｅｎｔｓｓｕｐｐｏｒｔｅｄｂｙＭｇＯａｎｄＣｅＯ２ｗｅｒｅｐｒｅｐａｒｅｄｂｙｔｈｅｅｑｕａｌｖｏｌｕｍｅｉｍｐｒｅｇｎａｔｉｏｎｍｅｔｈｏｄａｎｄｅｖａｌｕａｔｅｄｆｏｒｔｈｅｉｒｍｅｔｈａｎａｔｉｏｎｃａｔａｌｙｔｉｃｒｅａｃｔｉｏｎ．ＴｈｅｒｅｓｅａｒｃｈｒｅｓｕｌｔｓｓｈｏｗｔｈａｔｔｈｅＮｉＯ／ＣｅＯ２⁃ｂａｓｅｄｃａｔａｌｙｓｔｈａｓｂｅｔｔｅｒｌｏｗ⁃ｔｅｍｐｅｒａｔｕｒｅｒｅａｃｔｉｏｎｐｅｒｆｏｒｍａｎｃｅ，ａｎｄｔｈｅ８０％ＮｉＯ／ＣｅＯ２ｃａｔａｌｙｓｔｈａｓａｍｅｔｈａｎｅｙｉｅｌｄｏｆ６７％ｕｎｄｅｒｔｈｅｒｅａｃｔｉｏｎｃｏｎｄｉｔｉｏｎｓｏｆ１８Ｌ／（ｇ㊃ｈ），Ｈ２／ＣＯ２＝４，ａｎｄ３５０ħ．ＴｈｅｅｆｆｅｃｔｏｆｎｉｃｋｅｌｃｏｎｔｅｎｔｏｎｔｈｅｃａｔａｌｙｔｉｃａｃｔｉｖｉｔｙｏｆＮｉＯ／ＭｇＯａｎｄＮｉＯ／ＣｅＯ２ｃａｔａｌｙｓｔｓｗａｓａｌｓｏｅｘｐｌｏｒｅｄ．Ｔｈｅｒｅｓｕｌｔｓｓｈｏｗｔｈａｔｗｉｔｈｔｈｅｉｎｃｒｅａｓｅｏｆｎｉｃｋｅｌｃｏｎｔｅｎｔ，ｔｈｅｃａｒｂｏｎｄｉｏｘｉｄｅｃｏｎｖｅｒｓｉｏｎｒａｔｅａｎｄｔｈｅｍｅｔｈａｎｅｙｉｅｌｄｉｎｃｒｅａｓｅ，ａｎｄｗｈｅｎｔｈｅｎｉｃｋｅｌｌｏａｄｉｎｇｉｓ５０％－８０％ｔｈｅｃａｔａｌｙｔｉｃｐｅｒｆｏｒｍａｎｃｅｉｓｏｐｔｉｍａｌ．ＢｙＸ⁃ｒａｙｄｉｆｆｒａｃｔｉｏｎ（ＸＲＤ），ｈｙｄｒｏｇｅｎｔｅｍｐｅｒａｔｕｒｅｐｒｏｇｒａｍｍｅｄｒｅｄｕｃｔｉｏｎ（Ｈ２⁃ＴＰＲ），ＲａｍａｎａｎｄＣＯ２⁃ＴＰＤｃｈａｒａｃｔｅｒｉｚａｔｉｏｎ，ｉｔｉｓｆｏｕｎｄｔｈａｔＮｉｃｒｙｓｔａｌｓｉｚｅａｎｄｃｏｎｔｅｎｔａｒｅｔｈｅｋｅｙｆａｃｔｏｒｓｔｈａｔａｆｆｅｃｔｉｎｇｔｈｅｃａｔａｌｙｔｉｃａｃｔｉｖｉｔｙｏｆＮｉＯ／ＭｇＯａｎｄＮｉＯ／ＣｅＯ２ｃａｔａｌｙｓｔｓ．Ｔｈｉｓｓｔｕｄｙｃａｎｐｒｏｖｉｄｅｇｕｉｄａｎｃｅｆｏｒｔｈｅｄｅｓｉｇｎｏｆｃａｒｂｏｎｄｉｏｘｉｄｅｍｅｔｈａｎａｔｉｏｎｃａｔａｌｙｓｔｓｗｉｔｈｅｘｃｅｌｌｅｎｔｃａｔａｌｙｔｉｃｐｅｒｆｏｒｍａｎｃｅａｔｌｏｗｔｅｍｐｅｒａｔｕｒｅ．Ｋｅｙｗｏｒｄｓ：ｍｅｔｈａｎａｔｉｏｎ；ｓｕｐｐｏｒｔ；ｃａｔａｌｙｔｉｃｐｅｒｆｏｒｍａｎｃｅ；ｃｒｙｓｔａｌｓｉｚｅ；ｌｏａｄｉｎｇ㊀㊀目前，中国每年天然气和石油燃料消费所排放的二氧化碳高达２１．１亿吨，并且呈现逐年增长趋势㊂在我国２０６０年碳中和目标号召下，为推动实现碳达峰㊁碳中和目标，碳减排㊁碳零排和碳负排这三方面是石化行业切实有效的技术路径㊂其中将二氧化碳捕获利用，转化为高附加值化学品是碳负排的重要方面㊂二氧化碳甲烷化技术是将工业废气ＣＯ２转化为高附加值燃料ＣＨ４，可实现碳资源的有效循环利用［１－５］，对积极推动碳中和具有重要作用㊂自从第４期李㊀倩等：载体效应与镍晶粒尺寸对ＣＯ２甲烷化低温催化性能的影响３５３㊀１９０２年Ｓａｂａｔｉｅ等［６］报道了甲烷化反应（ＣＯ＋３Ｈ２＝ＣＨ４＋Ｈ２Ｏ）以后，人们研制了很多种甲烷化催化剂㊂近年来研究比较多的催化剂活性组分有Ｒｕ㊁Ｎｉ㊁Ｃｏ㊁Ｆｅ等，不同的活性组分在活性和选择性有所差异㊂活性：Ｒｕ＞Ｆｅ＞Ｎｉ＞Ｃｏ＞Ｒｈ＞Ｐｄ＞Ｐｔ＞Ｉｒ；选择性：Ｐｄ＞Ｐｔ＞Ｉｒ＞Ｎｉ＞Ｒｈ＞Ｃｏ＞Ｆｅ＞Ｒｕ㊂众所周知，在二氧化碳甲烷化反应中，Ｒｕ基催化剂活性最高，但Ｒｕ资源稀缺且价格昂贵限制了其工业化应用前景［７］㊂Ｎｉ基催化剂具有一定的催化活性，价格低廉，得到了广泛的应用［８－１０］㊂二氧化碳甲烷化反应是一个强放热反应（主反应，１），如果反应温度太高，容易朝副反应方向进行（副反应，２）且容易造成Ｎｉ烧结，进而导致催化剂催化活性明显下降；而反应温度过低，催化反应性能不理想㊂为了提高低温性能，大量科研工作者致力于催化剂的改性，主要包括活性金属的负载量，载体性质改良，活性组分的筛选，焙烧温度，金属颗粒大小，活性金属与氧化物载体界面效应调控等方面的研究［７，１１－１３］㊂然而二氧化碳甲烷反应不仅受到热力学限制，高温下活性组分Ｎｉ容易烧结，催化剂容易产生积碳㊂因此本文着力提升二氧化碳的低温活性㊂ＣＯ２＋４Ｈ２ңＣＨ４＋２Ｈ２ＯΔＨ２９８Ｋ＝－１６５ｋＪ／ｍｏｌ（主反应，１）ＣＯ２＋Ｈ２ңＣＯ＋Ｈ２ＯΔＨ２９８Ｋ＝４１ｋＪ／ｍｏｌ（副反应，２）㊀㊀在二氧化碳甲烷化反应中，一个普遍接受的反应机理为：载体吸附活化二氧化碳，金属镍解离Ｈ２成Ｈ原子通过氢溢流与载体吸附的二氧化碳耦合，最后生成甲烷［８－１０］㊂本文基于甲烷化反应机理，设计㊁组合㊁优化载体和活性主分，筛选构筑具有高低温反应性能的甲烷化催化剂㊂本文以探究载体效应和Ｎｉ晶粒大小对催化性能为切入点提升ＣＯ２甲烷化低温反应性能㊂表１为已报道的研究中Ｎｉ／ＭｇＯ，Ｎｉ／ＣｅＯ２催化剂与本工作的二氧化碳甲烷化催化活性进行比较，从表１可以看出，该工作制备出的Ｎｉ／ＣｅＯ２催化剂展示出良好的催化活性，可为设计具有优异低温性能的二氧化碳甲烷化催化剂提供参考㊂表１㊀已报道的研究与本工作中二氧化碳甲烷化活性统计结果Ｔａｂｌｅ１㊀ＳｔａｔｉｓｔｉｃａｌｒｅｓｕｌｔｓｏｆＣＯ２ｍｅｔｈａｎａｔｉｏｎａｃｔｉｖｉｔｙｉｎｌｉｔｅｒａｔｕｒｅａｎｄｔｈｉｓｗｏｒｋ催化剂反应温度／ʎＣＣＯ２转化率／％甲烷产率／％参考文献Ｎｉ／ＣｅＯ２⁃ｎｒｓ３５０６５６０［１４］Ｎｉ／ＣｅＯ２⁃Ｍ１３２５６５６２［１５］Ｎｉ／ＣｅＯ２⁃ＨＭ３５０５２４８［１６］ＭｏｎｏｌｉｔｈＮｉ／ＣｅＯ２３５０６５５８［１７］Ｎｉ／ＣｅＯ２２９０５８５４［１８］Ｎｉ／ＣｅＯ２３００６７６４［１９］Ｎｉ／ＣｅＯ２⁃ＺｒＯ２３００４６４１［２０］Ｎｉ⁃ＣｅＯ２／ＭＣＭ⁃４１３２０１５１２［２１］Ｎｉ／ＭｇＯ３００６１５８［２２］Ｎｉ⁃ＭｇＯ／ＳｉＯ２２８０１０９［２３］Ｎｉ⁃Ｌａ／Ｍｇ⁃Ａｌ３００５６５２［２４］Ｎｉ／ＣｅＯ２３５０６９６７本文１㊀实验部分１．１㊀试剂㊀㊀Ｃｅ（ＮＯ３）３㊃６Ｈ２Ｏ（Ａ．Ｒ．伊诺凯），ＮＨ３㊃Ｈ２Ｏ（２５％，国药），Ｍｇ（ＮＯ３）２㊃６Ｈ２Ｏ（Ａ．Ｒ．国药），Ｎｉ（ＮＯ３）２㊃６Ｈ２Ｏ（Ａ．Ｒ．国药）１．２㊀制备ＭｇＯ通过沉淀法制备ＭｇＯ，首先将ＮＨ３㊃Ｈ２Ｏ逐滴加入Ｍｇ（ＮＯ３）２㊃６Ｈ２Ｏ溶液，磁力搅拌（８００ｒ／ｍｉｎ），控制溶液ｐＨ＝１０，静置陈化１２ｈ，经多次过滤直至水中溶解性固体总量（ＴＤＳ）＜２０，然后８０ħ干燥过夜，在马弗炉中空气气氛下，５５０ħ焙烧４ｈ㊂１．３㊀制备ＣｅＯ２通过沉淀法制备ＣｅＯ２，首先将ＮＨ３㊃Ｈ２Ｏ逐滴加入Ｃｅ（ＮＯ３）３㊃６Ｈ２Ｏ溶液，磁力搅拌拌（８００ｒ／ｍｉｎ），控制溶液ｐＨ＝１０，静置陈化１２ｈ，经多次过滤直至ＴＤＳ＜２０，然后８０ħ干燥过夜，在马弗炉中空气气氛下，５５０ħ焙烧４ｈ㊂１．４㊀制备ＮｉＯ通过沉淀法制备ＮｉＯ，首先将ＮＨ３．Ｈ２Ｏ逐滴加入Ｎｉ（ＮＯ３）２．６Ｈ２Ｏ溶液，磁力搅拌（８００ｒ／ｍｉｎ），控制溶液ｐＨ＝１０，静置陈化１２ｈ，经多次过滤直至ＴＤＳ＜２０，然后８０ħ干燥过夜，在马弗炉中空气气氛下，５５０ħ焙烧４ｈ㊂３５４㊀化㊀学㊀研㊀究２０２３年１．５㊀制备Ｎｉ／ＭｇＯ和Ｎｉ／ＣｅＯ２采用等体积浸渍法将活性组分Ｎｉ负载ＭｇＯ载体上，具体方法如下：称取１ｇＭｇＯ载体和相当量的Ｎｉ（ＮＯ３）２．６Ｈ２Ｏ溶液，室温下充分搅拌６ｈ，然后８０ħ水浴蒸干，１１０ħ下干燥过夜，随后在马弗炉中以２ħ／ｍｉｎ的升温速率升至５００ħ，并在此温度下焙烧４ｈ，得到ｘ％ＮｉＯ／ＭｇＯ（ｘ＝２０，５０，８０），最后在５００ħ，１０％Ｈ２／Ａｒ混合气中还原２ｈ，得到ｘ％Ｎｉ／ＭｇＯ㊂ｘ％ＮｉＯ／ＣｅＯ２（ｘ＝２０，５０，８０）催化剂的制备方法与ＮｉＯ／ＭｇＯ一样，除了载体不同㊂１．６㊀催化剂的反应性能评价二氧化碳甲烷化反应性能评价在固定床石英管反应器（ＩＤ＝６ｍｍ）中进行㊂称取１００ｍｇ催化剂，先在流速为３０ｍＬ㊃ｍｉｎ－１的（Ｈ２／Ａｒ＝１／９）混合气中５００ħ原位还原２ｈ，随即自然冷却至室温，然后通入原料气高纯ＣＯ２和高纯Ｈ２（Ｈ２／ＣＯ２＝４）经气体混合器，使原料气混合均匀，维持混合气流速为３０ｍＬ㊃ｍｉｎ－１的条件下测试催化剂活性㊂反应尾气经冷却水冷却后，进入ＧＣ９３１０气相色谱在线分析㊂色谱以高纯氩气为载气，用ＴＤＸ⁃０１（ＩＤ＝２ｍｍ，Ｌ＝３ｍ）分子筛色谱柱分离Ｈ２㊁ＣＯ㊁ＣＨ４和ＣＯ２㊂尾气依次通过有ＴＤＸ⁃０１色谱柱的气相色谱，采用碳守恒面积归一法计算反应转化率㊂使用ＧＣ９３１色谱热导池（ＴＣＤ）对经色谱柱分离后的物质（反应物和产物），进行检测㊂ＣＯ２转化率㊁甲烷选择性和甲烷收率计算公式如下所示：Ｘ（ＣＯ２）＝ｎ（ＣＨ４）ｏｕｔ＋ｎ（ＣＯ）ｏｕｔｎ（ＣＨ４）ｏｕｔ＋ｎ（ＣＯ２）ｏｕｔ＋ｎ（ＣＯ）ｏｕｔˑ１００％（３）Ｓ（ＣＨ４）＝ｎ（ＣＨ４）ｏｕｔｎ（ＣＨ４）ｏｕｔ＋ｎ（ＣＯ）ｏｕｔˑ１００％（４）Ｙ（ＣＨ４）＝Ｘ（ＣＯ２）∗Ｓ（ＣＨ４）（５）１．７㊀催化剂表征ＸＲＤ物相分析采用ＢｒｕｋｅｒＤ８，管电流３０ｍＡ，管电压４０ｋＶ，Ｃｕ靶Ｋα辐射（λ＝０．１５４０５ｎｍ），２θ扫描角度范围为１０ʎ ９０ʎ，扫描速度为２ʎ／ｍｉｎ㊂Ｎ２等温吸附脱附采用Ｍｉｃｒｏｍｅｒｉｔｉｃｓ公司的ＡＳＡＰ⁃２０２０比表面积分析仪进行测试㊂所有催化剂样品在测试前，预先在２５０ħ温度下真空脱气处理６ｈ，然后在液氮温度－１９６ħ下吸附脱附Ｎ２，得到Ｎ２吸脱附等温曲线和催化剂的比表面积㊂Ｈ２⁃ＴＰＲ测试在Ｍｉ⁃ｃｒｏｍｅｒｉｔｉｃｓＡｕｔｏｃｈｅｍ２９２０化学吸附仪上进行㊂取５０ｍｇ催化剂，在１２０ħ高纯氩气氛下预处理３０ｍｉｎ，随即冷却至室温，之后切换成Ｈ２／Ａｒ混合气以３０ｍＬ㊃ｍｉｎ－１流速吹扫至基线稳定，待基线稳定后，以１０ħ／ｍｉｎ的升温速率从室温升至７００ħ，尾气经空气冷阱除水分后进入检测器检测，记录实验结果㊂拉曼测试在Ｒｅｎｉｓｈａｗ光谱仪上测定，激光器波长为５３２ｎｍ，探测器为ＲｅｎｉｓｈａｗＲｅｎＣａｍＣＣＤ㊂扫描的拉曼位移范围从２００到９００ｃｍ－１㊂ＣＯ２⁃ＴＰＤ采用Ｍｉｃｒｏｍｅｒｉｔｉｃｓ公司生产的ＡｕｔｏＣｈｅｍ２９２０化学吸附仪进行测试分析㊂高纯氦作为预处理气和载气，ＣＯ２为吸附气㊂取５０ｍｇ催化剂，先在氦气氛中以１０ħ／ｍｉｎ的升温速率升至４００ħ，在此温度下预处理３０ｍｉｎ，之后自然降温至５０ħ㊂催化剂在气体流速为３０ｍＬ／ｍｉｎ的高纯ＣＯ２气氛下吸附１ｈ至饱和状态，随后用氦气吹扫６０ｍｉｎ除去催化剂上表面物理吸附的ＣＯ２，最后程序升温从５０ħ升到７００ħ（升温速率１０ħ／ｍｉｎ）㊂２㊀实验结果与分析２．１㊀催化剂物化性质㊀㊀为了考察ＮｉＯ／ＭｇＯ，ＮｉＯ／ＣｅＯ２催化剂的结构和物相组成，对所有样品进行ＸＲＤ测试，样品的特征衍射峰如图１（ａ）和（ｂ）所示㊂从图１（ａ）中可见，图１㊀ＮｉＯ／ＭｇＯ（ａ），ＮｉＯ／ＣｅＯ２（ｂ）的ＸＲＤ衍射图Ｆｉｇ．１㊀ＸＲＤｐａｔｔｅｒｎｏｆＮｉＯ／ＭｇＯ（ａ），ＮｉＯ／ＣｅＯ２（ｂ）第４期李㊀倩等：载体效应与镍晶粒尺寸对ＣＯ２甲烷化低温催化性能的影响３５５㊀ＭｇＯ在２θ为３７．３０ʎ㊁４３．３０ʎ和６２．８８ʎ分别对应（１１１）㊁（２００）和（２２０）晶面特征衍射峰，表明成功合成了ＭｇＯ（ＰＤＦ＃８９⁃７７４６）㊂图１（ｂ）中可以观察到ＣｅＯ２在２θ为２８．９０ʎ㊁４７．７７ʎ和５６．７６ʎ的三强峰，依次对应（１１１）㊁（２００）和（２２０）晶面特征衍射峰，表明成功地合成了具有立方萤石结构ＣｅＯ２［２５－２６］（ＰＤＦ＃８９⁃８４３６）㊂在图１（ａ）中，随着ＮｉＯ的负载量增加其衍射峰（１１１晶面）增强，而ＭｇＯ衍射峰减弱；在图１（ｂ）中，随着ＮｉＯ的负载量增加其衍射峰增强，ＣｅＯ２衍射峰减弱㊂在二氧化碳甲烷化反应中，金属ＮｉＯ／Ｎｉ晶粒大小是影响二氧化碳转化率和甲烷产率的重要因素之一［８－１０］㊂通过Ｓｃｈｅｒｒｅｒ公式计算ＮｉＯ（１１１）晶粒大小，计算结果如表２所示㊂２０％ＮｉＯ／ＭｇＯ催化剂，ＮｉＯ晶粒大小为１４．１ｎｍ（六配位Ｎｉ２＋，离子半径为０．０６９ｎｍ，六配位Ｍｇ２＋离子半径为０．０７２ｎｍ，离子半径相接近，晶型相同，导致Ｎｉ和Ｍｇ作用力增加，抑制了自由态ＮｉＯ颗粒的形成，因此ＮｉＯ颗粒较小），在２０％ＮｉＯ／ＣｅＯ２催化剂中ＮｉＯ晶粒大小为１６．５ｎｍ㊂这一系列ＮｉＯ／ＭｇＯ，ＮｉＯ／ＣｅＯ２催化剂中随着ＮｉＯ负载量增加，ＮｉＯ晶粒大小都呈现增加趋势，ＮｉＯ／ＣｅＯ２催化剂中的ＮｉＯ晶粒增加幅度比ＮｉＯ／ＭｇＯ大㊂表２㊀催化剂ＮｉＯ／Ｎｉ性质Ｔａｂｌｅ２㊀ＴｈｅｐｒｏｐｅｒｔｉｅｓｏｆＮｉＯ／Ｎｉｃａｔａｌｙｓｔｓ催化剂ＮｉＯ晶粒ａ／ｎｍＨ／Ｎｉ原子比ｂ２０％ＮｉＯ／ＭｇＯ１４．１１．９５５０％ＮｉＯ／ＭｇＯ１４．８２．０３８０％ＮｉＯ／ＭｇＯ１５．７２．０４２０％ＮｉＯ／ＣｅＯ２１６．５１．８９５０％ＮｉＯ／ＣｅＯ２１７．６２．０５８０％ＮｉＯ／ＣｅＯ２１８．８２．０３ＮｉＯ２０．１１．８９㊀㊀ａ基于ＸＲＤ衍射ＮｉＯ（１１１）晶面；ｂ基于Ｈ２⁃ＴＰＲ２．２㊀反应性能测试在二氧化碳甲烷化反应中，ＭｇＯ作为碱性载体可以很好地提供碱中心，ＣｅＯ２中丰富的氧空位也可以提供中等强度碱中心㊂而金属Ｎｉ本身也可以解离吸附氢气，具有一定的催化活性㊂为了探究这两种载体负载不同含量ＮｉＯ催化剂的构效关系，对所有催化剂进行ＣＯ２甲烷化活性评价㊂在图２（ａ）ＮｉＯ／ＭｇＯ二氧化碳转化率图中，在低温区（２００３５０ħ）随着温度的上升二氧化碳转化率逐渐升高㊂而在高温区（３５０５００ħ）随着温度的上升，由于该反应受热力学限制反应二氧化碳转化率逐渐降低㊂其中，二氧化碳转化率趋势为２０％ＮｉＯ／ＭｇＯ＜ＮｉＯ＜５０％ＮｉＯ／ＭｇＯ＜８０％ＮｉＯ／ＭｇＯ㊂这说明在二氧化碳甲烷化反应中，较大的金属颗粒可以提高二氧化碳转化率和甲烷选择性［２５］㊂在图２（ｂ）中，甲烷的产率也是随着ＮｉＯ负载量增加而增加，呈现与二氧化碳转化率类似趋势㊂图２（ｃ）ＮｉＯ／ＣｅＯ２二氧化碳转化率图中，在低温区（２００３５０ħ）随着温度的上升二氧化碳转化率逐渐升高㊂在高温区（３５０５００ħ）随着反应温度的上升二氧化碳转化率逐渐降低㊂其中二氧化碳转化率趋势为ＮｉＯ＜２０％ＮｉＯ／ＣｅＯ２＜５０％ＮｉＯ／ＣｅＯ２＜８０％ＮｉＯ／ＣｅＯ２㊂在２（ｄ）中，甲烷的产率也是随着ＮｉＯ负载量增加而增加，呈现与二氧化碳转化率类似趋势，在镍负载量为５０％８０％时趋于饱和㊂相比于ＮｉＯ／ＭｇＯ催化剂，ＮｉＯ／ＣｅＯ２呈现较好的低温反应性能㊂２．３㊀ＮｉＯ／ＭｇＯ和ＮｉＯ／ＣｅＯ２催化剂物理化学性质对比分析２．３．１㊀催化剂还原性能分析㊀㊀为了分析催化剂中ＮｉＯ／Ｎｉ物种，金属Ｎｉ与载体间相互作用以及载体的还原能力㊂对ＮｉＯ／ＭｇＯ，ＮｉＯ／ＣｅＯ２都进行了Ｈ２⁃ＴＰＲ表征测试㊂在图３（ａ）中，ＭｇＯ作为刚性载体，没有还原峰㊂３５５３８７ħ的还原峰归属于ＮｉＯңＮｉ的还原，且随着ＮｉＯ负载量增加，ＮｉＯ的还原峰向低温方向迁移［１３，２６］㊂ＮｉＯ／ＭｇＯ相比于ＮｉＯ／ＣｅＯ２样品，其还原峰向高温方向迁移，有可能是由于六配位Ｎｉ２＋，离子半径为０．０６９ｎｍ；六配位Ｍｇ２＋离子半径为０．０７２ｎｍ，其离子半径相接近，晶型相同，导致Ｎｉ和Ｍｇ作用力增加㊂在图３（ｂ）中，未改性的ＣｅＯ２在４８０ħ和７８ħ处有两个还原峰，依次归属于表面的Ｃｅ４＋ңＣｅ３＋与体相中ＣｅＯ２ңＣｅ２Ｏ３的还原［２７－２８］㊂３４８３６４ħ的还原峰归属归属于ＮｉＯңＮｉ的还原，且随着ＮｉＯ负载量增加，ＮｉＯ的还原峰向低温迁移（由于随着负载量增加，未与载体直接接触的ＮｉＯ，更加容易还原）㊂此外，通过定量计算这一系列催化剂的Ｈ／Ｎｉ比来分析ＮｉＯ的还原程度，从表２中可知，所有催化剂维持Ｈ／Ｎｉ约等于２，说明ＮｉＯ基本都还原成金属Ｎｉ单质㊂Ｈ２⁃ＴＰＲ测试结果表明ＮｉＯ在两种载体上还原程度呈现截然相反趋势，ＮｉＯ／ＣｅＯ２样品相比于ＮｉＯ／ＭｇＯ，其还原峰向低温方向迁移，ＣｅＯ２载体可以促进ＮｉＯ还原；ＭｇＯ载体抑制了ＮｉＯ还原，ＮｉＯ与ＭｇＯ载体作用力更强㊂３５６㊀化㊀学㊀研㊀究２０２３年图２㊀ＮｉＯ／ＭｇＯ催化剂二氧化碳转化率（ａ），甲烷产率（ｂ）；ＮｉＯ／ＣｅＯ２催化剂二氧化碳转化率转化率（ｃ），甲烷产率（ｄ）Ｆｉｇ．２㊀Ｃａｒｂｏｎｄｉｏｘｉｄｅｃｏｎｖｅｒｓｉｏｎ（ａ），ｍｅｔｈａｎｅｙｉｅｌｄ（ｂ）ｏｆＮｉＯ／ＭｇＯｃａｔａｌｙｓｔ；ｃａｒｂｏｎｄｉｏｘｉｄｅｃｏｎｖｅｒｓｉｏｎ（ｃ）ｍｅｔｈａｎｅｙｉｅｌｄ（ｄ）ｏｆＮｉＯ／ＣｅＯ２ｃａｔａｌｙｓｔ图３㊀（ａ）ＮｉＯ／ＭｇＯ，（ｂ）ＮｉＯ／ＣｅＯ２催化剂Ｈ２⁃ＴＰＲ图Ｆｉｇ．３㊀Ｈ２⁃ＴＰＲｓｐｅｃｔｒａｏｆ（ａ）ＮｉＯ／ＭｇＯａｎｄ（ｂ）ＮｉＯ／ＣｅＯ２ｃａｔａｌｙｓｔｓ２．３．２㊀催化剂物理吸附性能为了考察ＮｉＯ／ＭｇＯ和ＮｉＯ／ＣｅＯ２催化剂的催化剂比表面积及孔道结构，对催化性能最好的８０％ＮｉＯ／ＭｇＯ和８０％ＮｉＯ／ＣｅＯ２催化剂进行了Ｎ２吸脱附测试㊂从图４可知所有样品在０．７１．０ｐ／ｐ０压力下都呈现典型的ＩＶ型等温线，Ｈ３型回滞环㊂其中８０％ＮｉＯ／ＭｇＯ（２８ｍ２／ｇ，０．１４ｃｍ３／ｇ），８０％ＮｉＯ／ＣｅＯ２（３２ｍ２／ｇ，０．１６ｃｍ３／ｇ），可见８０％ＮｉＯ／ＭｇＯ与８０％Ｎｉ／ＣｅＯ２具有相似的比表面积和孔容㊂Ｎ２⁃ＢＥＴ测试结果表明ＮｉＯ／ＭｇＯ与ＮｉＯ／ＣｅＯ２比表面积相近，说明比表面积不是决定这两类催化剂催化性能差异的因素㊂２．３．３㊀催化剂化学吸附性能ＣＯ２⁃ＴＰＤ表征用于考察催化剂表面碱中心的类型㊁数量和强度㊂图５中，２００ħ以下的脱附峰归属于弱碱位吸附的ＣＯ２，由表面ＯＨ产生；２００４００ħ区间的脱附峰归属于中等碱性位，由缺位氧产生［２９］㊂而在ＮｉＯ／ＭｇＯ催化剂中，６００８００ħ脱附峰归属于强碱性位，由于ＮｉＯ／ＣｅＯ２具有较多中等碱性位，ＮｉＯ／ＭｇＯ没有中等碱性位，６００８００ħ归属第４期李㊀倩等：载体效应与镍晶粒尺寸对ＣＯ２甲烷化低温催化性能的影响３５７㊀于强碱性位不能对反应起到作用（反应温度低于５００ħ）㊂图４㊀催化剂的Ｎ２吸附脱附曲线Ｆｉｇ．４㊀Ｎ２ａｄｓｏｒｐｔｉｏｎａｎｄｄｅｓｏｒｐｔｉｏｎｃｕｒｖｅｓｏｆｔｈｅｃａｔａｌｙｓｔ图５㊀催化剂的ＣＯ２⁃ＴＰＤ图Ｆｉｇ．５㊀ＣＯ２⁃ＴＰＤｃｕｒｖｅｏｆｃａｔａｌｙｓｔＹａｎ等［３０］研究发现中等强度碱中心可以提升二氧化碳甲烷化的低温反应性能，弱碱中心对低温反应性能所起的作用不显著㊂Ｐａｎ等［３１］通过对比Ｎｉ／ＣｅＯ２㊁Ｎｉ／Ａｌ２Ｏ３催化ＣＯ２甲烷化原位红外实验发现中等强度碱位吸附的ＣＯ２更易转化为ＨＣＯＯ∗，可以显著提升ＣＯ２催化性能㊂ＣｅＯ２中的氧空位可以作为吸附活化二氧化碳位点，充当中等强度碱中心，同时也促进金属ＮｉＯңＮｉ，从而展现优异的低温反应性能㊂ＣＯ２⁃ＴＰＤ测试结果及结合文献观点，表明了ＣｅＯ２中具有丰富的中等强度碱中心位点，ＭｇＯ没有中等强度碱中心位点；中等强度碱中心是决定低温反应性能的关键因素之一㊂２．３．４㊀催化剂拉曼谱图分析Ｒａｍａｎ表征用于探究ＮｉＯ掺杂对ＣｅＯ２氧空位的影响㊂图６中，对于纯ＣｅＯ２样品，４６０和５７０ｃｍ－１依次归属于氧化铈的Ｆ２ｇ振动峰㊁表面氧空位［３２］㊂随着ＮｉＯ含量增加，ＣｅＯ２的Ｆ２ｇ振动峰逐渐宽化，且样品８０％ＮｉＯ／ＣｅＯ２宽泛最明显㊂在５７０ｃｍ－１处，ＣｅＯ２样品的表面氧空位随着ＮｉＯ含量增加而增加㊂图６㊀ＮｉＯ／ＣｅＯ２催化剂拉曼谱图Ｆｉｇ．６㊀ＲａｍａｎｓｐｅｃｔｒａｏｆＮｉＯ／ＣｅＯ２ｃａｔａｌｙｓｔｓＲａｍａｎ测试结果表明，８０％ＮｉＯ／ＣｅＯ２具有最多的氧空位，ＮｉＯ掺杂使得立方萤石结构ＣｅＯ２的Ｆ２ｇ振动峰逐渐宽化，形成更多氧空位㊂ＮｉＯ掺杂构筑的表面氧空位是决定ＮｉＯ／ＣｅＯ２催化剂具有优异低温反应性能的因素之一㊂２．４㊀反应机制分析图７是该工作的作用机制图㊂两种不同载体负载Ｎｉ催化剂呈现不同的构效关系，在表面积几乎相同情况下，Ｎｉ／ＣｅＯ２催化剂相比于Ｎｉ／ＭｇＯ具有更好的ＮｉＯ－Ｎｉ还原能力，且具有更丰富的中等强度碱中心，可以更好地吸附活化二氧化碳，进而体现优异的二氧化碳甲烷化低温性能㊂Ｎｉ／ＣｅＯ２催化剂在３００ħ下甲烷收率达到６３％，而Ｎｉ／ＭｇＯ仅有２５％㊂通过对比两种不同载体，发现Ｎｉ／ＣｅＯ２可以显著提升二氧化碳甲烷化催化剂的低温反应性能，在低温下能够具有优异性能可以减少反应热力学的限制，避免高温下反应朝副反应方向进行㊂更加证实了，在实际应用中我们可以选择合适的载体，优化活性组分负载量，使催化剂具有更丰富的碱中心和氧化还原能力，从而设计出具有优异低温二氧化碳甲烷化催化活性的催化剂㊂３５８㊀化㊀学㊀研㊀究２０２３年图７㊀Ｎｉ／ＭｇＯ和Ｎｉ／ＣｅＯ２的二氧化碳甲烷化反应机理图Ｆｉｇ．７㊀ＭｅｃｈａｎｉｓｍｄｉａｇｒａｍｏｆｃａｒｂｏｎｄｉｏｘｉｄｅｍｅｔｈａｎａｔｉｏｎｒｅａｃｔｉｏｎｏｆＮｉ／ＭｇＯａｎｄＮｉ／ＣｅＯ２３㊀结论１）采用浸渍法分别以ＭｇＯ和ＣｅＯ２为载体制备了一系列不同镍负载量的二氧化碳甲烷化催化剂，活性评价结果表明ＮｉＯ／ＣｅＯ２催化剂相比ＮｉＯ／ＭｇＯ具有更好的低温反应性能，８０％ＮｉＯ／ＣｅＯ２催化剂具有最佳催化性能（ＣＯ２转化率，甲烷选择性）㊂２）ＮｉＯ／ＭｇＯ和ＮｉＯ／ＣｅＯ２具有较好的催化活性，尽管在５００ħ时出现活性轻微下降㊂３）Ｎｉ含量是影响ＮｉＯ／ＭｇＯ和ＮｉＯ／ＣｅＯ２催化剂的关键因素之一，随着Ｎｉ含量的增加，二氧化碳转化率提高，甲烷产率提升，在５０％８０％的负载量时产率趋于稳定㊂４）综合各表征表明ＣｅＯ２具有丰富的中等强度碱中心位点，ＭｇＯ没有中等强度碱中心位点；且ＮｉＯ／ＣｅＯ２基催化剂中ＮｉＯ晶粒大，提高了二氧化碳转化率及甲烷产率，中等强度碱中心位点和ＮｉＯ晶粒大小是ＮｉＯ／ＣｅＯ２催化剂催化性能优于ＮｉＯ／ＭｇＯ的两个关键因素㊂参考文献：［１］刘昌俊，郭秋婷，叶静云，等．二氧化碳转化催化剂研究进展及相关问题思考［Ｊ］．化工学报，２０１６，６７（１）：６⁃１３．ＬＩＵＣＪ，ＧＵＯＱＴ，ＹＥＪＹ，ｅｔａｌ．ＰｅｒｓｐｅｃｔｉｖｅｏｎｃａｔａｌｙｓｔｉｎｖｅｓｔｉｇａｔｉｏｎｆｏｒＣＯ２ｃｏｎｖｅｒｓｉｏｎａｎｄｒｅｌａｔｅｄｉｓｓｕｅｓ［Ｊ］．ＣＩＥＳＣＪｏｕｒｎａｌ，２０１６，６７（１）：６⁃１３．［２］ＹＡＮＧＨＹ，ＺＨＡＮＧＣ，ＧＡＯＰ，ｅｔａｌ．Ａｒｅｖｉｅｗｏｆｔｈｅｃａｔａｌｙｔｉｃｈｙｄｒｏｇｅｎａｔｉｏｎｏｆｃａｒｂｏｎｄｉｏｘｉｄｅｉｎｔｏｖａｌｕｅ⁃ａｄｄｅｄｈｙｄｒｏｃａｒｂｏｎｓ［Ｊ］．ＣａｔａｌｙｓｉｓＳｃｉｅｎｃｅ＆Ｔｅｃｈｎｏｌｏｇｙ，２０１７，７（２０）：４５８０⁃４５９８．［３］ＺＨＯＵＷ，ＣＨＥＮＧＫ，ＫＡＮＧＪＣ，ｅｔａｌ．ＮｅｗｈｏｒｉｚｏｎｉｎＣ１ｃｈｅｍｉｓｔｒｙ：ｂｒｅａｋｉｎｇｔｈｅｓｅｌｅｃｔｉｖｉｔｙｌｉｍｉｔａｔｉｏｎｉｎｔｒａｎｓｆｏｒｍａｔｉｏｎｏｆｓｙｎｇａｓａｎｄｈｙｄｒｏｇｅｎａｔｉｏｎｏｆＣＯ２ｉｎｔｏｈｙｄｒｏｃａｒｂｏｎｃｈｅｍｉｃａｌｓａｎｄｆｕｅｌｓ［Ｊ］．ＣｈｅｍｉｃａｌＳｏｃｉｅｔｙＲｅｖｉｅｗｓ，２０１９，４８（１２）：３１９３⁃３２２８．［４］马园园，李锦涛，刘小静，等．ＣＯ２／ＣＯ甲烷化催化剂及其反应机理研究进展［Ｊ］．现代化工，２０２０，４０（１０）：３０⁃３４．ＭＡＹＹ，ＬＩＪＴ，ＬＩＵＸＪ，ｅｔａｌ．ＣａｔａｌｙｓｔｓｆｏｒｍｅｔｈａｎａｔｉｏｎｏｆＣＯ２／ＣＯａｎｄｒｅｓｅａｒｃｈａｄｖａｎｃｅｓｉｎｉｔｓｒｅａｃｔｉｏｎｍｅｃｈａｎｉｓｍ［Ｊ］．ＭｏｄｅｒｎＣｈｅｍｉｃａｌＩｎｄｕｓｔｒｙ，２０２０，４０（１０）：３０⁃３４．［５］宋鹏飞，单彤文，李又武，等．氢气与二氧化碳甲烷化在现代能源体系中的新应用［Ｊ］．现代化工，２０２０，４０（１０）：４⁃９．ＳＯＮＧＰＦ，ＳＨＡＮＴＷ，ＬＩＹＷ，ｅｔａｌ．Ｓｅｖｅｒａｌｎｅｗａｐｐｌｉｃａｔｉｏｎｓｃｅｎａｒｉｏｓｏｆｍｅｔｈａｎａｔｉｏｎｂｅｔｗｅｅｎｈｙｄｒｏｇｅｎａｎｄｃａｒｂｏｎｄｉｏｘｉｄｅｉｎｍｏｄｅｒｎｅｎｅｒｇｙｓｙｓｔｅｍ［Ｊ］．ＭｏｄｅｒｎＣｈｅｍｉｃａｌＩｎｄｕｓｔｒｙ，２０２０，４０（１０）：４⁃９．［６］ＢＲＯＯＫＳＫＰ，ＨＵＪＬ，ＺＨＵＨＹ，ｅｔａｌ．ＭｅｔｈａｎａｔｉｏｎｏｆｃａｒｂｏｎｄｉｏｘｉｄｅｂｙｈｙｄｒｏｇｅｎｒｅｄｕｃｔｉｏｎｕｓｉｎｇｔｈｅＳａｂａｔｉｅｒｐｒｏｃｅｓｓｉｎｍｉｃｒｏｃｈａｎｎｅｌｒｅａｃｔｏｒｓ［Ｊ］．ＣｈｅｍｉｃａｌＥｎｇｉｎｅｅｒｉｎｇＳｃｉｅｎｃｅ，２００７，６２（４）：１１６１⁃１１７０．［７］ＷＡＮＧＷ，ＧＯＮＧＪＬ．Ｍｅｔｈａｎａｔｉｏｎｏｆｃａｒｂｏｎｄｉｏｘｉｄｅ：ａｎｏｖｅｒｖｉｅｗ［Ｊ］．ＦｒｏｎｔｉｅｒｓｏｆＣｈｅｍｉｃａｌＳｃｉｅｎｃｅａｎｄＥｎｇｉｎｅｅｒｉｎｇ，２０１１，５（１）：２⁃１０．［８］ＬＩＷＨ，ＷＡＮＧＨＺ，ＪＩＡＮＧＸ，ｅｔａｌ．ＡｓｈｏｒｔｒｅｖｉｅｗｏｆｒｅｃｅｎｔａｄｖａｎｃｅｓｉｎＣＯ２ｈｙｄｒｏｇｅｎａｔｉｏｎｔｏｈｙｄｒｏｃａｒｂｏｎｓｏｖｅｒｈｅｔｅｒｏｇｅｎｅｏｕｓｃａｔａｌｙｓｔｓ［Ｊ］．ＲＳＣＡｄｖａｎｃｅｓ，２０１８，８（１４）：７６５１⁃７６６９．［９］ＦＡＬＢＯＬ，ＭＡＲＴＩＮＥＬＬＩＭ，ＶＩＳＣＯＮＴＩＣＧ，ｅｔａｌ．ＫｉｎｅｔｉｃｓｏｆＣＯ２ｍｅｔｈａｎａｔｉｏｎｏｎａＲｕ⁃ｂａｓｅｄｃａｔａｌｙｓｔａｔｐｒｏｃｅｓｓｃｏｎｄｉｔｉｏｎｓｒｅｌｅｖａｎｔｆｏｒＰｏｗｅｒ⁃ｔｏ⁃Ｇａｓａｐｐｌｉｃａｔｉｏｎｓ［Ｊ］．ＡｐｐｌｉｅｄＣａｔａｌｙｓｉｓＢ：Ｅｎｖｉｒｏｎｍｅｎｔａｌ，２０１８，２２５：３５４⁃３６３．［１０］ＲＯＹＳ，ＣＨＥＲＥＶＯＴＡＮＡ，ＰＥＴＥＲＳＣ．ＴｈｅｒｍｏｃｈｅｍｉｃａｌＣＯ２ｈｙｄｒｏｇｅｎａｔｉｏｎｔｏｓｉｎｇｌｅｃａｒｂｏｎｐｒｏｄｕｃｔｓ：ｓｃｉｅｎｔｉｆｉｃａｎｄｔｅｃｈｎｏｌｏｇｉｃａｌｃｈａｌｌｅｎｇｅｓ［Ｊ］．ＡＣＳＥｎｅｒｇｙＬｅｔｔｅｒｓ，２０１８，３（８）：１９３８⁃１９６６．［１１］ＦＲＯＮＴＥＲＡＰ，ＭＡＣＡＲＩＯＡ，ＦＥＲＲＡＲＯＭ，ｅｔａｌ．ＳｕｐｐｏｒｔｅｄｃａｔａｌｙｓｔｓｆｏｒＣＯ２ｍｅｔｈａｎａｔｉｏｎ：ａｒｅｖｉｅｗ［Ｊ］．Ｃａｔａｌｙｓｔｓ，２０１７，７（２）：５９．［１２］ＡＺＩＺＭＡＡ，ＪＡＬＩＬＡＡ，ＴＲＩＷＡＨＹＯＮＯＳ，ｅｔａｌ．ＣＯ２ｍｅｔｈａｎａｔｉｏｎｏｖｅｒｈｅｔｅｒｏｇｅｎｅｏｕｓｃａｔａｌｙｓｔｓ：ｒｅｃｅｎｔｐｒｏｇｒｅｓｓａｎｄｆｕｔｕｒｅｐｒｏｓｐｅｃｔｓ［Ｊ］．ＧｒｅｅｎＣｈｅｍｉｓｔｒｙ，２０１５，１７（５）：２６４７⁃２６６３．［１３］ＪＩＡＸＹ，ＺＨＡＮＧＸＳ，ＲＵＩＮ，ｅｔａｌ．ＳｔｒｕｃｔｕｒａｌｅｆｆｅｃｔｏｆＮｉ／ＺｒＯ２ｃａｔａｌｙｓｔｏｎＣＯ２ｍｅｔｈａｎａｔｉｏｎｗｉｔｈｅｎｈａｎｃｅｄａｃｔｉｖｉｔｙ［Ｊ］．ＡｐｐｌｉｅｄＣａｔａｌｙｓｉｓＢ：Ｅｎｖｉｒｏｎｍｅｎｔａｌ，２０１９，２４４：１５９⁃１６９．［１４］ＭＡＹ，ＬＩＵＪ，ＣＨＵＭ，ｅｔａｌ．Ｅｎｈａｎｃｅｄｌｏｗ⁃ｔｅｍｐｅｒａｔｕｒｅａｃｔｉｖｉｔｙｏｆＣＯ２ｍｅｔｈａｎａｔｉｏｎｏｖｅｒＮｉ／ＣｅＯ２ｃａｔａｌｙｓｔ［Ｊ］．第４期李㊀倩等：载体效应与镍晶粒尺寸对ＣＯ２甲烷化低温催化性能的影响３５９㊀ＣａｔａｌｙｓｉｓＬｅｔｔｅｒｓ，２０２２，１５２（３）：８７２⁃８８２．［１５］ＴＡＮＧＲ，ＵＬＬＡＨＮ，ＨＵＩＹＪ，ｅｔａｌ．ＥｎｈａｎｃｅｄＣＯ２ｍｅｔｈａｎａｔｉｏｎａｃｔｉｖｉｔｙｏｖｅｒＮｉ／ＣｅＯ２ｃａｔａｌｙｓｔｂｙｏｎｅ⁃ｐｏｔｍｅｔｈｏｄ［Ｊ］．ＭｏｌｅｃｕｌａｒＣａｔａｌｙｓｉｓ，２０２１，５０８：１１１６０２．［１６］ＲＡＴＣＨＡＨＡＴＳ，ＳＵＲＡＴＨＩＴＩＭＥＴＨＡＫＵＬＳ，ＴＨＡＭＵＮＧＫＩＴＡ，ｅｔａｌ．ＣａｔａｌｙｔｉｃｐｅｒｆｏｒｍａｎｃｅｏｆＮｉ／ＣｅＯ２ｃａｔａｌｙｓｔｓｐｒｅｐａｒｅｄｆｒｏｍｄｉｆｆｅｒｅｎｔｒｏｕｔｅｓｆｏｒＣＯ２ｍｅｔｈａｎａｔｉｏｎ［Ｊ］．ＪｏｕｒｎａｌｏｆｔｈｅＴａｉｗａｎＩｎｓｔｉｔｕｔｅｏｆＣｈｅｍｉｃａｌＥｎｇｉｎｅｅｒｓ，２０２１，１２１：１８４⁃１９６．［１７］ＧＡＲＣÍＡ⁃ＭＯＮＣＡＤＡＮ，ＮＡＶＡＲＲＯＪＣ，ＯＤＲＩＯＺＯＬＡＪＡ，ｅｔａｌ．ＥｎｈａｎｃｅｄｃａｔａｌｙｔｉｃａｃｔｉｖｉｔｙａｎｄｓｔａｂｉｌｉｔｙｏｆｎａｎｏｓｈａｐｅｄＮｉ／ＣｅＯ２ｆｏｒＣＯ２ｍｅｔｈａｎａｔｉｏｎｉｎｍｉｃｒｏ⁃ｍｏｎｏｌｉｔｈｓ［Ｊ］．ＣａｔａｌｙｓｉｓＴｏｄａｙ，２０２２，３８３：２０５⁃２１５．［１８］ＺＨＥＮＧＨ，ＬＩＡＯＷＱ，ＤＩＮＧＪＱ，ｅｔａｌ．ＵｎｖｅｉｌｉｎｇｔｈｅｋｅｙｆａｃｔｏｒｓｉｎｄｅｔｅｒｍｉｎｉｎｇｔｈｅａｃｔｉｖｉｔｙａｎｄｓｅｌｅｃｔｉｖｉｔｙｏｆＣＯ２ｈｙｄｒｏｇｅｎａｔｉｏｎｏｖｅｒＮｉ／ＣｅＯ２ｃａｔａｌｙｓｔｓ［Ｊ］．ＡＣＳＣａｔａｌｙｓｉｓ，２０２２，１２（２４）：１５４５１⁃１５４６２．［１９］ＺＨＡＮＧＹ，ＺＨＡＮＧＴＦ，ＷＡＮＧＦ，ｅｔａｌ．Ｎｉ／ＣｅＯ２ｃａｔａｌｙｓｔｓｆｏｒｌｏｗ⁃ｔｅｍｐｅｒａｔｕｒｅＣＯ２ｍｅｔｈａｎａｔｉｏｎ：ｉｄｅｎｔｉｆｙｉｎｇｅｆｆｅｃｔｏｆｓｕｐｐｏｒｔｍｏｒｐｈｏｌｏｇｙａｎｄｏｘｙｇｅｎｖａｃａｎｃｙ［Ｊ］．ＧｒｅｅｎｈｏｕｓｅＧａｓｅｓ：ＳｃｉｅｎｃｅａｎｄＴｅｃｈｎｏｌｏｇｙ，２０２１，１１（６）：１２２２⁃１２３３．［２０］ＦＵＫＵＨＡＲＡＣ，ＨＡＹＡＫＡＷＡＫ，ＳＵＺＵＫＩＹ，ｅｔａｌ．Ａｎｏｖｅｌｎｉｃｋｅｌ⁃ｂａｓｅｄｓｔｒｕｃｔｕｒｅｄｃａｔａｌｙｓｔｆｏｒＣＯ２ｍｅｔｈａｎａｔｉｏｎ：ａｈｏｎｅｙｃｏｍｂ⁃ｔｙｐｅＮｉ／ＣｅＯ２ｃａｔａｌｙｓｔｔｏｔｒａｎｓｆｏｒｍｇｒｅｅｎｈｏｕｓｅｇａｓｉｎｔｏｕｓｅｆｕｌｒｅｓｏｕｒｃｅｓ［Ｊ］．ＡｐｐｌｉｅｄＣａｔａｌｙｓｉｓＡ：Ｇｅｎｅｒａｌ，２０１７，５３２：１２⁃１８．［２１］ＷＡＮＧＸＬ，ＺＨＵＬＪ，ＬＩＵＹＣ，ｅｔａｌ．ＣＯ２ｍｅｔｈａｎａｔｉｏｎｏｎｔｈｅｃａｔａｌｙｓｔｏｆＮｉ／ＭＣＭ⁃４１ｐｒｏｍｏｔｅｄｗｉｔｈＣｅＯ２［Ｊ］．ＳｃｉｅｎｃｅｏｆｔｈｅＴｏｔａｌＥｎｖｉｒｏｎｍｅｎｔ，２０１８，６２５：６８６⁃６９５．［２２］ＴＡＮＪＪ，ＷＡＮＧＪＭ，ＺＨＡＮＧＺＹ，ｅｔａｌ．ＨｉｇｈｌｙｄｉｓｐｅｒｓｅｄａｎｄｓｔａｂｌｅＮｉｎａｎｏｐａｒｔｉｃｌｅｓｃｏｎｆｉｎｅｄｂｙＭｇＯｏｎＺｒＯ２ｆｏｒＣＯ２ｍｅｔｈａｎａｔｉｏｎ［Ｊ］．ＡｐｐｌｉｅｄＳｕｒｆａｃｅＳｃｉｅｎｃｅ，２０１９，４８１：１５３８⁃１５４８．［２３］ＧＵＯＭ，ＬＵＧＸ．ＴｈｅｅｆｆｅｃｔｏｆｉｍｐｒｅｇｎａｔｉｏｎｓｔｒａｔｅｇｙｏｎｓｔｒｕｃｔｕｒａｌｃｈａｒａｃｔｅｒｓａｎｄＣＯ２ｍｅｔｈａｎａｔｉｏｎｐｒｏｐｅｒｔｉｅｓｏｖｅｒＭｇＯｍｏｄｉｆｉｅｄＮｉ／ＳｉＯ２ｃａｔａｌｙｓｔｓ［Ｊ］．ＣａｔａｌｙｓｉｓＣｏｍｍｕｎｉｃａｔｉｏｎｓ，２０１４，５４：５５⁃６０．［２４］ＷＩＥＲＺＢＩＣＫＩＤ，ＭＯＴＡＫＭ，ＧＲＺＹＢＥＫＴ，ｅｔａｌ．Ｔｈｅｉｎｆｌｕｅｎｃｅｏｆｌａｎｔｈａｎｕｍｉｎｃｏｒｐｏｒａｔｉｏｎｍｅｔｈｏｄｏｎｔｈｅｐｅｒｆｏｒｍａｎｃｅｏｆｎｉｃｋｅｌ⁃ｃｏｎｔａｉｎｉｎｇｈｙｄｒｏｔａｌｃｉｔｅ⁃ｄｅｒｉｖｅｄｃａｔａｌｙｓｔｓｉｎＣＯ２ｍｅｔｈａｎａｔｉｏｎｒｅａｃｔｉｏｎ［Ｊ］．ＣａｔａｌｙｓｉｓＴｏｄａｙ，２０１８，３０７：２０５⁃２１１．［２５］ＧＵＯＹ，ＭＥＩＳ，ＹＵＡＮＫ，ｅｔａｌ．Ｌｏｗ⁃ｔｅｍｐｅｒａｔｕｒｅＣＯ２ｍｅｔｈａｎａｔｉｏｎｏｖｅｒＣｅＯ２⁃ｓｕｐｐｏｒｔｅｄＲｕｓｉｎｇｌｅａｔｏｍｓ，ｎａｎｏｃｌｕｓｔｅｒｓ，ａｎｄｎａｎｏｐａｒｔｉｃｌｅｓｃｏｍｐｅｔｉｔｉｖｅｌｙｔｕｎｅｄｂｙｓｔｒｏｎｇｍｅｔａｌ－ｓｕｐｐｏｒｔｉｎｔｅｒａｃｔｉｏｎｓａｎｄＨ⁃ｓｐｉｌｌｏｖｅｒｅｆｆｅｃｔ［Ｊ］．ＡＣＳＣａｔａｌｙｓｉｓ，２０１８，８（７）：６２０３⁃６２１５．［２６］ＷＡＮＧＢ，ＸＩＯＮＧＹＹ，ＨＡＮＹＹ，ｅｔａｌ．ＰｒｅｐａｒａｔｉｏｎｏｆｓｔａｂｌｅａｎｄｈｉｇｈｌｙａｃｔｉｖｅＮｉ／ＣｅＯ２ｃａｔａｌｙｓｔｓｂｙｇｌｏｗｄｉｓｃｈａｒｇｅｐｌａｓｍａｔｅｃｈｎｉｑｕｅｆｏｒｇｌｙｃｅｒｏｌｓｔｅａｍｒｅｆｏｒｍｉｎｇ［Ｊ］．ＡｐｐｌｉｅｄＣａｔａｌｙｓｉｓＢ：Ｅｎｖｉｒｏｎｍｅｎｔａｌ，２０１９，２４９：２５７⁃２６５．［２７］ＸＵＪＷ，ＰＥＮＧＬ，ＦＡＮＧＸＺ，ｅｔａｌ．Ｄｅｖｅｌｏｐｉｎｇｒｅａｃｔｉｖｅｃａｔａｌｙｓｔｓｆｏｒｌｏｗｔｅｍｐｅｒａｔｕｒｅｏｘｉｄａｔｉｖｅｃｏｕｐｌｉｎｇｏｆｍｅｔｈａｎｅ：ｏｎｔｈｅｆａｃｔｏｒｓｄｅｃｉｄｉｎｇｔｈｅｒｅａｃｔｉｏｎｐｅｒｆｏｒｍａｎｃｅｏｆＬｎ２Ｃｅ２Ｏ７ｗｉｔｈｄｉｆｆｅｒｅｎｔｒａｒｅｅａｒｔｈＡｓｉｔｅｓ［Ｊ］．ＡｐｐｌｉｅｄＣａｔａｌｙｓｉｓＡ：Ｇｅｎｅｒａｌ，２０１８，５５２：１１７⁃１２８．［２８］ＬＩＮＸＴ，ＬＩＳＪ，ＨＥＨ，ｅｔａｌ．ＥｖｏｌｕｔｉｏｎｏｆｏｘｙｇｅｎｖａｃａｎｃｉｅｓｉｎＭｎＯｘ⁃ＣｅＯ２ｍｉｘｅｄｏｘｉｄｅｓｆｏｒｓｏｏｔｏｘｉｄａｔｉｏｎ［Ｊ］．ＡｐｐｌｉｅｄＣａｔａｌｙｓｉｓＢ：Ｅｎｖｉｒｏｎｍｅｎｔａｌ，２０１８，２２３：９１⁃１０２．［２９］ＷＡＮＧＦ，ＷＥＩＭ，ＥＶＡＮＳＤＧ，ｅｔａｌ．ＣｅＯ２⁃ｂａｓｅｄｈｅｔｅｒｏｇｅｎｅｏｕｓｃａｔａｌｙｓｔｓｔｏｗａｒｄｃａｔａｌｙｔｉｃｃｏｎｖｅｒｓｉｏｎｏｆＣＯ２［Ｊ］．ＪｏｕｒｎａｌｏｆＭａｔｅｒｉａｌｓＣｈｅｍｉｓｔｒｙＡ，２０１６，４（１６）：５７７３⁃５７８３．［３０］ＹＡＮＹ，ＤＡＩＹＨ，ＨＥＨ，ｅｔａｌ．ＡｎｏｖｅｌＷ⁃ｄｏｐｅｄＮｉ⁃ＭｇｍｉｘｅｄｏｘｉｄｅｃａｔａｌｙｓｔｆｏｒＣＯ２ｍｅｔｈａｎａｔｉｏｎ［Ｊ］．ＡｐｐｌｉｅｄＣａｔａｌｙｓｉｓＢ：Ｅｎｖｉｒｏｎｍｅｎｔａｌ，２０１６，１９６：１０８⁃１１６．［３１］ＰＡＮＱＳ，ＰＥＮＧＪＸ，ＳＵＮＴＪ，ｅｔａｌ．ＩｎｓｉｇｈｔｉｎｔｏｔｈｅｒｅａｃｔｉｏｎｒｏｕｔｅｏｆＣＯ２ｍｅｔｈａｎａｔｉｏｎ：ｐｒｏｍｏｔｉｏｎｅｆｆｅｃｔｏｆｍｅｄｉｕｍｂａｓｉｃｓｉｔｅｓ［Ｊ］．ＣａｔａｌｙｓｉｓＣｏｍｍｕｎｉｃａｔｉｏｎｓ，２０１４，４５：７４⁃７８．［３２］ＰＵＺＹ，ＬＵＪＱ，ＬＵＯＭＦ，ｅｔａｌ．ＳｔｕｄｙｏｆｏｘｙｇｅｎｖａｃａｎｃｉｅｓｉｎＣｅ０．９Ｐｒ０．１Ｏ２⁃δｓｏｌｉｄｓｏｌｕｔｉｏｎｂｙｉｎｓｉｔｕＸ⁃ｒａｙｄｉｆｆｒａｃｔｉｏｎａｎｄｉｎｓｉｔｕＲａｍａｎｓｐｅｃｔｒｏｓｃｏｐｙ［Ｊ］．ＴｈｅＪｏｕｒｎａｌｏｆＰｈｙｓｉｃａｌＣｈｅｍｉｓｔｒｙＣ，２００７，１１１（５０）：１８６９５⁃１８７０２．［责任编辑：吴文鹏］。

氮化硼负载的钌基合成氨催化剂的制备及浸渍顺序对其表面性能的影响

氮化硼负载的钌基合成氨催化剂的制备及浸渍顺序对其表面性能的影响赵梦婷;邬晨旭;霍超【摘要】采用等体积浸渍法制备了一系列用于合成氨的BN负载钌基催化剂,其结构和性能经SEM,EDS,XRD和H2-TPD表征.研究了助剂Ba、K与活性组分Ru的浸渍顺序对催化剂表面性能的影响.结果表明:浸渍顺序依次为Ba,Ru,K时,在10 MPa,475℃,10000 h-1条件下,Ba-Ru-K/BN催化剂的氨合成反应速率最高可达33.95 mmol·g-1·h-1.【期刊名称】《合成化学》【年(卷),期】2019(027)004【总页数】5页(P279-283)【关键词】氨合成;氮化硼;等体积浸渍法;钌基催化剂;制备;性能【作者】赵梦婷;邬晨旭;霍超【作者单位】浙江工业大学化学工程学院,浙江杭州 310014;浙江工业大学化学工程学院,浙江杭州 310014;浙江工业大学化学工程学院,浙江杭州 310014【正文语种】中文【中图分类】O643;O626在低温低压条件下，钌基催化剂较传统铁基催化剂的氨合成活性更高，被誉为“第二代氨合成催化剂”。

载体是影响负载型催化剂活性的重要因素之一。

Jacobsen等[1]发现，Ru颗粒的大小及形态是影响其催化剂性能的主要原因，载体的表面性质对Ru颗粒的形态及大小有决定性影响。

目前，氨合成催化剂采用的载体主要有：活性炭[2-6]、氧化物(主要包括氧化镁、氧化铝、氧化铈等)[7-13]、分子筛[14]、氮化硼[15]和复合载体[16-18]等。

其中，活性炭虽然具有较高的比表面积和丰富的孔结构，对活性组分的高度分散有利，但由于活性组分Ru同时也是甲烷化的催化剂，容易造成活性炭载体的流失而导致催化剂失活；氧化物载体表面虽具有较高的碱性，有利于N2的活化，但因其负载的Ru的分散度较低而催化活性较低；以分子筛为载体的Ru基氨合成催化剂同样活性偏低。

氮化硼(BN)表面结构与石墨结构类似，性能较稳定，受氨浓度的影响较小，已成为最有潜力的氨合成催化剂载体之一。

gold指南分组依据

gold指南分组依据英文回答：Gold classification can be based on various criteria, such as its physical properties, its chemical properties, and its uses. In terms of physical properties, gold can be classified based on its color, hardness, and density. For example, pure gold is yellow in color, relatively soft, and has a high density. On the other hand, gold alloys, which are mixtures of gold with other metals, can have different colors, hardness, and density. In terms of chemical properties, gold can be classified based on its reactivity and corrosion resistance. For example, gold is known forits resistance to corrosion and its inertness towards most chemicals, which makes it suitable for use in jewelry and electronics. In terms of uses, gold can be classified based on its applications in various industries, such as jewelry, electronics, medicine, and finance. For example, gold is widely used in jewelry for its beauty and rarity, in electronics for its conductivity and corrosion resistance,in medicine for its use in treating certain medical conditions, and in finance as a store of value and a hedge against inflation.Gold指南的分组可以基于其物理性质、化学性质和用途等各种标准。

贵金属orr催化剂

贵金属orr催化剂英文回答：Gold is a precious metal that has been used for various purposes throughout history. One of its important applications is in catalysis, where gold nanoparticles are used as catalysts to facilitate chemical reactions. This field of research, known as gold catalysis, has gained significant attention in recent years.Gold catalysts have unique properties that make them highly effective in certain reactions. For example, gold nanoparticles can act as excellent catalysts for the oxidation of carbon monoxide (CO) to carbon dioxide (CO2) at low temperatures. This reaction is crucial in the purification of exhaust gases from automobiles and industrial processes. Gold catalysts are also used in the selective hydrogenation of unsaturated compounds, such as alkenes, to produce valuable chemicals.One of the key advantages of gold catalysts is their high selectivity. Selectivity refers to the ability of a catalyst to direct a reaction towards a specific product, while minimizing the formation of unwanted by-products. Gold nanoparticles have been found to exhibit remarkable selectivity in various reactions, such as the oxidation of alcohols and the synthesis of pharmaceutical intermediates.Gold catalysts also offer excellent stability and recyclability. Unlike many other catalysts, gold nanoparticles do not undergo significant changes in their structure or activity over multiple reaction cycles. This makes them highly attractive for industrial applications, where catalysts need to be robust and cost-effective.Furthermore, gold catalysts can operate under mild reaction conditions, which is advantageous from an energy consumption perspective. Many reactions that traditionally required harsh conditions, such as high temperatures and pressures, can be efficiently catalyzed by gold nanoparticles at ambient conditions. This not only reduces the energy input but also minimizes the environmentalimpact of the process.In addition to their technical advantages, gold catalysts have also become a subject of fascination for scientists due to their unique behavior at the nanoscale. The size and shape of gold nanoparticles can significantly influence their catalytic activity and selectivity. Researchers have been exploring various synthetic methods to control the size and shape of gold nanoparticles, aiming to optimize their catalytic performance.中文回答：贵金属催化剂是一种重要的催化剂，其应用广泛。

211086490_甲烷蒸汽重整制氢技术及进展浅析

甲烷蒸汽重整制氢技术及进展浅析采用ZnO与H2S反应生成ZnS以深度脱除S。

制氢过程中预重整、蒸汽重整、中温变换使用的催化剂（预重整和蒸汽重整催化剂为Ni/Al2O3，中温水气变换催化剂为Fe3O4/Cr2O3或ZnO/ZnAl2O4）容易被硫化物中毒失活，为深度脱除原料中的硫化物，保护下游过程的催化剂，常在预重整前进行加氢脱硫，保证整个制氢体系的长周期稳定运行。

预重整（PR）是将C2+饱和烃转化为C1和H2，避免进料温度过高造成C2+烃热分解积炭，使预重整后的C1和H2可以预热到更高温度。

预重整还可以将微量S充分脱除，保护后续催化剂长周期稳定运行。

此外，预重整的部分原料为合成气（CO+H2），可降低后续高温蒸汽重图1 甲烷蒸汽重整制氢工艺流程198研究与探索Research and Exploration ·工程技术与创新中国设备工程 2023.04 (上）温度约200℃，催化剂为Cu/ZnO/Al 2O 3，产品干气中CO 分数为0.25%。

变压吸附（PSA）是一种应用广泛的低成本氢气提纯工艺，利用不同气体分子在一些高比表面积吸附材料表面的吸附能力差异，通过多次反复吸附-脱附，最终将不同吸附能力的组分分离出来。

变压吸附包含吸附（A-Adsorption）、降压/均压（E 1-Pressure equalization）、顺放（PP-Provide purge）、逆放（D-Dump）、冲洗（P-Purging/Regeneration）、升压/均压（R 1/R 0-Repressurization）等六个步骤。

常规的吸附分离具有能耗低、压损小、纯度高、投资小、流程短、操作弹性范围大、原料适应性强等众多优点，但收率较低。

采用变压吸附后，氢气回收率提高到75~95%，氢气纯度提高到99.9%以上。

若氢气价值高，还可以采用真空变压吸附（VPSA）提高氢气回收率至95%以上。

甲烷蒸汽重整制氢技术经百年发展，工艺成熟，装置完善，经济可靠，制氢能力强，适合规模化生产，但也存在原料利用率不高和工艺复杂、操作难度大的缺点，不容忽视。

CeO2 supported Ni-Rh bimetallic catalysts for reforming of bio-ethanol to produce hydrogen for fuel

Novel CeO2 supported Ni-Rh bimetallic catalysts for reforming of bio-ethanol to produce hydrogen for fuelcellsJunichiro Kugai, S. Velu, Chunshan Song*Clean Fuels and Catalysis Program, The Energy Institute, andDepartment of Energy and Geo-Environmental EngineeringThe Pennsylvania State University209 Academic Projects Building, University Park, PA 16802.*E-mail: csong@IntroductionRecently, there is a growing interest worldwide in the development of fuel cells for automobiles and stationary power plants because they have the potential to offer unique opportunities for significant reduction in energy use and emissions of environmental pollutants. Polymer electrolyte membrane fuel cell (PEMFC), which operates at low temperature, is considered as promising candidate for automobile applications. However, the PEMFC uses pure H2 or H2-rich gas as a fuel and this needs to be produced on-board a vehicle from a suitable liquid hydrocarbon fuels. Owing to the high energy density and ready availability, methanol and gasoline are considered as preferred fuels, and methods for the catalytic reforming of these fuels to H2-rich gas has been reported.1-4 On the other hand, bio-ethanol, which is a mixture of water and ethanol, produced from fermentation of biomass, is a renewable raw material and could be used as an alternative primary fuel for the on-board production of H2 for fuel cells. Some of the advantages of using bio-ethanol to produce H2 for fuel cell applications are; (i) Bio-ethanol is a renewable raw material and can be cheaply obtained from sugarcane, corn or cellulose feedstock such as wood chips. (ii) The process is CO2 neutral as the CO2 produced in the reforming reaction can be consumed for the biomass growth. The system therefore offers a closed carbon loop. (iii) Unlike methanol, the bio-ethanol is non-toxic, and (iv) Unlike gasoline, the bio-ethanol is sulfur-free, and this avoids the risk of sulfur poisoning on the reforming and fuel cell electrode catalysts.Unlike methanol reforming, the catalytic methodology for ethanol reforming is not well developed, and more efficient and highly active catalysts are needed. Steam reforming of ethanol has been reported to occur relatively at high temperature, around 700˚C. In lower temperature, the reaction produces a wide range of liquid and gaseous products, including H2, CO, CO2, CH4, CH3CHO, CH3COOH, C2H5OC2H5, ethylene depending on the nature of metal and support.5-7 Oxidative steam reforming of ethanol has also been reported to be more efficient for the low temperature reforming of ethanol for H2 production.8The objective of the present study was to develop a novel highly efficient catalyst system for the on-board reforming of bio-ethanol to produce fuel cell grade H2 gas at relatively lower temperature. A detailed literature review reveals that C—C bond cleavage is an important step in the reforming of ethanol to produce H2 and carbon oxides5-8. Both Ni and Rh are known to favor the C—C bond rupture effectively.9 In addition, since Ni has hydrogenation ability, it is expected to combine chemisorbed hydrogen to form H2 gas. Thus, a series of Ni-Rh bimetallic catalysts with different Ni/Rh atomic ratios have been synthesized. The nature of support also plays an important role in the ethanol reforming. Acidic and basic supports are known to favor dehydrogenation / dehydration and condensation reactions. Hence, in the present study, redox supports such as CeO2, ZrO2 and CeO2-ZrO2 mixed oxides having high surface area, above 100 m2 g—1 have been chosen. The effect of combination of Rh and Ni, and the nature of support on the catalytic performance in the steam reforming and oxidative steam reforming of ethanol are studied over these catalysts for the first time.ExperimentalIn order to optimize the Ni/Rh atomic ratio for the better catalytic performance in the ethanol reforming, commercially available high surface area CeO2 (BET surface area = 148 m2g—1) obtained from Rhodia Co. Three catalysts, 10wt%Ni/CeO2, 2wt%Rh/CeO2, and 2wt%Rh-10wt%Ni/CeO2 were prepared by the incipient wetness impregnation method. The catalysts were calcined at 450˚C for 3 h in air, palletized, crushed and sieved to 18-35 mesh. About 0.5g of catalyst was loaded in the reactor. Steam reforming of ethanol was performed in a fixed bed stainless-steel down-flow reactor. A premixed ethanol-water mixture with a water/ethanol molar ratio of 4 was fed into the reactor through a vaporizer and the mixed with Ar carrier gas. Prior to the catalytic reaction, the catalysts were reduced in-situ in a H2 flow (10% H2 in Ar). Effluent of the reaction was analyzed using an on-line GC equipped with a sampling loop injector, 30 feet Hayesep DB packed column, and a TCD detector.Results and DiscussionSteam reforming of ethanol has been performed at 335 and 395˚C over Rh-Ni/CeO2 catalysts synthesized in the present study. Fig. 1 compares the conversion of ethanol in the steam reforming over these catalysts at 335 and 395˚C. It can be seen that at 335˚C, the Rh-Ni/CeO2 catalyst exhibited slightly higher activity than Rh/CeO2 catalyst. The Ni/CeO2 catalyst is much less active compared to other two catalysts. On the other hand, all catalysts exhibited almost complete conversion, close to 100 %, at 395˚C. These results indicate that Rh is more active than Ni in the low temperature range though Ni becomes as active as Rh in the high temperature range. The high activity of Rh can be attributed to the ease of C—C bond cleavage of ethanol on Rh metal surface9. The support CeO2 exhibits very poor performance under the present experimental conditions, indicating that the metals supported on the CeO2display active sites for the ethanol reforming.Figure 1 Comparison of ethanol conversion at 335 and 395˚C over CeO2-based Bimetallic catalysts. Left bar; 335˚C and right bar;395˚CH2, CO, CO2, CH4, and acetaldehyde are the major products obtained in the steam reforming of ethanol in the present study. The selectivities of H2 and carbon containing products at 335˚C and 395˚C are shown in the Table 1. Hydrogen selectivity was indicatedby molar ratio of produced hydrogen in all the products. Carbon selectivity was indicated by molar ratio of carbon included in each carbon-containing products to carbon included in all carbon-containing products. From the table, it can be seen that H2, CO, CO2, CH4 are main products and acetaldehyde is only produced at 335˚C, which is insufficient temperature for complete C—C bond cleavage. Acetaldehyde can be considered to be an intermediate in the steam reforming of ethanol.5-8 Higher selectivity of H2 has been observed Rh/CeO2 catalyst despite the highest ethanol conversion obtained over Rh-Ni/CeO2.Table 1 Product selectivity of ethanol reforming at335 and 395˚C unit: %CatalystTemp. H2 CO CO2 CH4 acetaldehydeacetoneRh-Ni 335 33.4 21.8 34.6 30.4 13.3 0395 34.5 8.6 55.0 33.5 2.9 0Rh335 35.4 46.9 14.6 30.8 7.7 0395 38.8 8.2 62.3 29.5 0 0Ni335 29.1 14.0 40.8 6.1 23.5 10.8395 29.7 4.9 56.0 39.0 0 0At 335˚C, the selectivity for CO2 decreases in the order, Ni/CeO2 > Rh-Ni/CeO2 > Rh/CeO2. When taking the ratio of CO2 selectivity to CO selectivity into account, it is clear that the presenceof Ni causes the reaction of CO to CO2. At 395˚C, CO2 selectivity over all three catalysts increases and becomes closer to each other. This means under the present experimental conditions, water-gas shift reaction also takes place over these catalysts. It should be that Ni has higher water-gas shift reactivity than Rh at 335˚C, but Rh also exhibits as high water-gas shift reactivity as Ni at 395˚C. Diagne et. al.10 reported that Rh/CeO2-ZrO2 catalyst has much higher CO2/CO ratio than Rh/CeO2 and Rh/ZrO2 in the selectivity of ethanol steam reforming reaction. Therefore it is anticipated that using CeO2-ZrO2 support with Rh and Ni metals leads to further increase in CO2/CO ratio.Suppressing methane production is one of the interests of this work. Ni was added to promote the combination of atomic hydrogen species on the metal surface into molecular hydrogen. But Ni functioned as a promoter for water-gas shift reaction and hydrogenation of surface CHx species rather than a promoter for dehydrogenation of surface hydrogen. It is reported that ethanol is dehydrogenated to adsorbed acetaldehyde species, then further dehydrogenated to H2, CO, and CHx(x=2,3) on Ni surface11. Therefore CHx species is considered to be hydrogenated easily to produce methane in the presence of molecular or adsorbed hydrogen and more methane is produced on Ni surface. On Rh surface, on the other hand, ethanol is dehydrogenated into oxametallacycle species, which is readily decomposed to H2, CO, CHx(x<2) and suppress the production of methane12. Some amount of ethanol is converted via acetaldehyde intermediate according to the fact that acetaldehyde was observed on Rh/CeO2 catalyst in low temperature in our work. This might be a cause of a lot of methane production even on Rh-containing catalysts.ConclusionsThe steam reforming of ethanol on Rh-Ni/CeO2 bimetallic catalyst exhibited high ethanol conversion and CO2 selectivity. It is concluded that Ni has higher water-gas shift activity than Rh. However its hydrogen selectivity was slightly lower than Rh/CeO2 catalyst. AcknowledgementThis work was supported by Nippon Shokubai Co., Ltd. and by the Pennsylvania State University.References(1) Song, C. Catal.Today, 2002, 77, 17.(2) Velu, S.; Suzuki, K.; Okazaki, M.; Kapoor, M.P.; Osakai, T.;Ohashi, F. J.Catal. 2000, 194, 373.(3) Ming, Q.M.; Healey, T.; Allen, L.; Irving, P. Catal.Today, 2002,77, 51.(4) Moon, D.J.; Sreekumar, K.; Lee, S.D.; Lee, B.G.; Kim. H.S.Appl.Catal. A General, 2001, 215, 1.(5) Marino, F.; Boveri, M.; Baronetti, G.; Laborde, M. Int. J.Hydrogen Energy, 2001, 26, 665.(6) Breen, J. P., Burch, R., Coleman, H. M., Appl. Catal. BEnvironmental, 2002, 39, 65.(7) Fierro, V.; Akdim, O.; Mirodatos, C.; Green Chemistry, 2003, 5,20.(8) Velu, S., Satoh, N., Gopinath, C. S., Suzuki, K., Catal. Lett., 2002,82, 145.(9) Sheng, P.-Y.; Yee, A.; Bowmaker, G.A.; Idriss, H. J.Catal. 2002,208, 393.(10) Diagne, C., Idriss, H., Kiennemann, A., Catal. Commun., 2002,3, 565.(11) Takezawa, N., Iwasa, N., Catal. Today, 1997, 36, 45.(12) Brown, N. F., Barteau, M. A., Langmuir, 1992, 8, 862.。

不同形貌CeO2的制备及其在乙醇水蒸气重整反应中的应用

内蒙古工业大学硕士学位论文
traditional nanoparticles catalysts, special pore structure in short-range of CeO2 enhance the interaction between cobalt and CeO2, which are essential for superior activity and selectivity of the mesoporous catalysts. Moreover, Co/Ce-CMK-3 also have a preferable carbon resistance property. CeO2 with different morphologies and particle size were prepared through hydrothermal. We studied the impacts of CeO2 morphologies (Flowerlike, Polyhedron, Prism, Fusiformis, Bouquet, Ricelike and Spindle) on SRE performance. Characterization results showed that flowerlike CeO2 have unique 3D opened pore structures and expose the most active (100) planes and more active (110) planes, which make them own the best oxygen storage capacity, promote reduction of catalysts active components, and improve ethanol conversion as well as carbon resistance capacity. Catalysts test indicated that the H2 production is higher than 68% in the whole reaction, which illustrates the mainly exposed planes (100) and (110) of supports optimize the distrubution of products. The relative results of supports morphologies, catalysts structures and catalytic performance indicated that there are different exposed planes, oxygen storage capacities and ineraction between Co and CeO2 for supports with different morphologies and structures, thus affects ethanol conversion and products distribution, which results in differences of carbon deposition types. CeO2(flowerlike) own the largest specific surface area and uniforn pore size distribution focused on 3.5nm. They have more oxygen vacancies due to the most reactive (100) and (110) planes they exposed. For catalysts, there are more Co ions entering into CeO2 lattice, which enhance the interaction between Co and ceria. It is easier to reduce Co species to active components, and enhance ethanol conversion as well as carbon resistance capacity, then optimize products distribution.

Goldair Platinum Dehumidifier 使用说明书

Thank you for choosing a Goldair Platinum Dehumidifier.This Goldair appliance has been designed and manufactured to high standards of engineering and with proper use and care,as described in this booklet,will give you years of useful service.Please read these instructions carefully and keep for future reference.YOUR SAFETY IS IMPORTANT TO US. PLEASE ENSURE YOU TAKE NOTE OF THEINSTRUCTIONS AND WARNINGS OUTLINED IN THIS MANUAL.1.WARNING you must not cover this appliance.Covering this appliance presents fire risk.2.Use only the voltage specified on the rating label of the appliance.3.Keep all objects at least 1metre from the front,sides and rear of the appliance.4.This appliance is intended for household use only and not for commercial or industrial use.5.Indoor use only.6.Do not use abrasive cleaning products on this appliance.Clean with a damp cloth (not wet)rinsed in hot soapy wateronly.Always remove plug from the mains supply beforecleaning.7.The common cause of overheating is deposits of dust or fluffin the appliance.Ensure these deposits are removedregularly by unplugging the appliance and vacuum cleaningthe air vents and grills.8.Always unplug appliance when not in use.9.When the appliance has been unpacked,check it fortransport damage and ensure all parts have been delivered.If parts are missing or the appliance has been damaged,contact the Goldair Customer Services Team.10.If your appliance does not work,or is not working properly,contact the place of purchase or the Goldair CustomerServices Team.11.Do not connect the appliance to mains supply untilcompletely assembled and adjusted.12.Ensure hands are dry before handling the plug or main unit.13.Do not locate the appliance directly below any power socketoutlet.14.Ensure appliance is on a flat,stable,heat-resistant surface.15.Do not operate with cord set coiled up as a heat build up islikely,which could be sufficient to become a hazard.16.Carry out regular checks of the supply cord to ensure nodamage is evident.17.Do not operate this appliance with a damaged cord,plug orafter the appliance malfunctions or has been dropped ordamaged in any manner.Return to a qualified electricalperson for examination,electrical service or repair.18.Do not remove plug from power socket by pulling cord;always grip plug.19.Do not twist,kink or wrap the cord around the appliance,as this may cause the insulation to weaken and split.Always ensure that all cord has been removed from any cord storage area and is unrolled before use.20.It is recommended that this appliance is plugged directly into the wall socket.The use of power boards is not recommended as many power boards are not designed to supply power to high wattage appliances.21.A correctly specified,undamaged extension cord may be used with this appliance provided it is used in a safe e this appliance only as described in this manual.Any other use is not recommended by the manufacturer and may cause fire,electric shock or injury.23.Do not remove plug from power socket until the appliance has been switched off.24.Do not place cord under carpet or cover with rugs or furniture.Arrange the cord so it cannot be tripped over.25.Do not place appliance on bedding.26.Switch off and use handle provided when moving.27.Do not place appliance close to radiant heat source.28.Never use the appliance to dry clothes.29.Do not insert or allow foreign objects to enter any ventilation or exhaust opening,as this may cause an electric shock,fire or damage to the appliance.30.Do not sit on the appliance.31.Do not operate in areas where petrol,paint or other flammable liquids are used or stored.32.This appliance is not intended for use by persons (including children)with reduced physical,sensory or mental capabilities or lack of experience and knowledge,unless they are supervised or have been given instruction concerning the use of the appliance by a person responsible for their safety.33.Children should be supervised to ensure that they do not play with the appliance.34.Do not use this appliance in the immediate surrounds of a bath,a shower,or a swimming pool or other liquids.The appliance must not be immersed in any liquids.35.There are no user serviceable parts installed in the unit.36.Do not place the unit in wardrobes or other enclosed spaces as this may cause fire hazards.37.This unit is not supposed to be used in or around locations where foodstuffs,works of art or delicate articles ofscience,etc are stored.General Care and Safety GuideThe LCD display shows the ambient humidity and temperature (The variation of relative humidity can be 5%).To turn off,press the “ON/OFF”button again;the dehumidifier will stop working and the louvre will close.DEHUMIDIFY Press the key “〈”or “〉”to choose your humidity setting.You can choose the continuous dehumidification option or your preferred humidity required in the range of 50-70%.When the machine is set in automatic dehumidification,the desired humidity setting and fan Speed is indicated on the LCD display.When ambient humidity is 5%lower than your setting,compressor shuts off and fan works at low speed.If ambient humidity is 5%higher than the setting,the dehumidification is activated again.When the machine is set in continuous dehumidification,the continuous dehumidification mode and corresponding fan speed will be displayed on LCD.In this mode,the ambient humidity has no effect on the operation of the dehumidifier.In automatic dehumidification mode (50%RH,60%RH,70%RH),or continuous dehumidification mode press “Speed”to select the fan speed either “Mid speed”or “Low speed”.When in dry mode,you cannot adjust the humidity setting.You need to come out of the dry mode to set desired humidity.WARNING:Keep all objects at least 1metre from thefront,sides and rear of the appliance.WARNING:In order to avoid overheating or risk offire,do not cover the appliance.WARNING:Never leave this appliance unattendedwhen in use.WARNING:Do not use this appliance with aprogrammer,remote-control system,separate timeror any other device that switches the appliance onautomatically.Note:When the appliance is turned on for the firsttime,it may release a slight odour.This odour is anormal occurrence caused by the initial starting ofthe unit and should not occur again.Leave the appliance to stand for one hour aftertransport or after the unit has been on its side beforeconnecting it to the mains supply to let the refrigerantsettle.Ensure all external windows and doors are closedbefore turning on the unit.Ensure that the water container is positionedcorrectly.OPERATIONPlug into power supply and switch on at the mains.When plugged into power socket,3beep signals willbe heard.2.Press the “ON/OFF”button to turn on the unit.Thelouvre opens automatically and the unit goes into thedefault mode of continuous dehumidification and midspeed running.Always choose a safe location for your appliance,keeping in mind the safety precautions outlined.Ensure all packaging has been removed from the unit before use.This appliance requires no installation,it should be used solely as a portable appliance.CONTROL PANELTIMER OFF When the unit is operating press the TIMER button to set the length of time that you would like the unit to run for before turning off.Each press of the TIMER button will adjust the length of time by 1hour increments from 1–24hours.To turn off the Timer function,set the Timer back to “0”hours or simply turn the unit off.TIMER ON When the unit is Off press the TIMER button to set the length of time that you would like the unit to remain off before turning on.Each press of the TIMER button will adjust the length of time by 1hour increments from 1–24hours.To turn off the Timer function,set the Timer back to “0”hours or simply turn the unit on manually.WARNING!Take care in positioning your appliance,using the timer will mean the unit will come on automatically.Fire may result if placed next to combustible material.WATER TANK FULL ALARM When the water tank is full a buzzer will sound 10times and the symbol of water full is shown on the LCD screen,all other symbols disappear.The dehumidifier stops working and louver closes.Carefully remove the water tank and empty the water,and then reinstate the water tank.The dehumidifier will start working in the previously set conditions.If you do not reinstate the bucket within 3minutes,the dehumidification process will start and there may be water spillage.Hence it is recommended to switch off the dehumidifier completely from the power socket and then remove the waterbucket.DRYPress this key to start or stop dry mode.Press “dry”,the dry pattern is displayed on LCD,thedehumidifier runs in dry mode and in continuousdehumidification.The fan works at “high speed “level .The louver swings automatically press the “swing”button stops the swing function.SPEEDPress this key to select the fan speed at “mid speed”level or “Low speed”.In automatic dehumidification mode or continuousdehumidification mode,press “Speed”to select thefan at “Mid speed”or “Low speed”.In dry mode,you cannot select the fan mode.It runs inhigh speed by default.When in automatic defrost,the fan works at “Midspeed”.When the sensor detects ambient temperatureexceeding 32°C,it automatically moves to “Midspeed”and when sensor detects ambienttemperature lower than 30°C,it returns back toprevious speed setting.SWINGWhen the dehumidifier runs,press this key to startswing and the louvre oscillates automatically,and theswing pattern is displayed on LCD.Press this key againand the louvre will stop at that position.DEFROSTWhen the dehumidifier works in low temperature,frost will be produced on the surface of evaporator.To ensure the dehumidifier performs well,theautomatic defrost function is designed with thedehumidifier.1When the temperature sensor detects thetemperature of the evaporator i ≤-1°C ，thedehumidifier moves to defrost mode automaticallyand after defrosting,it automatically startsdehumidifying.When defrosting,the red defrost indicator lightilluminates.When defrosting,the compressor will turn off and thefan runs at mid speed.Care and CleaningCARE AND CLEANINGThe appliance requires regular cleaning to ensure trouble free operation:Unplug the appliance from the mains supply before cleaning.Ensure that the appliance has been allowed to cool down completely before cleaning.Use a damp cloth(not wet)to wipe the exterior of the appliance to remove dust and dirt.Never use solutions such as benzene,thinners or polishing agents.Use a vacuum cleaner to remove dust and fluff from around the grills and fins.Ensure the appliance is dry before plugging back into the mains supply.Do not attempt to dismantle the appliance.There are no user serviceable parts.For service or repair,contact an authorised electrical service technician.TO CLEAN THE AIR FILTER:Unplug the appliance from the mains supply. Remove the filter.Clean the filter with a vacuum or with water.Dry the filter.Ensure the filter is completely dry before placing back in the unit.Never use unit without the air filter.STORAGETo store the unit,remove the plug from the socket and empty the water container.Allow the container and the appliance to dry completely.Clean the air filter.Store the device in a dust-free location, preferably covered with a sheet of plastic.PERMANENT WATER DRAINAGEIt is possible to connect a drainage tube(not supplied) to the appliance for permanent water drainage.If this option is desired,you will need to purchase a suitable PVC tube from your local hardware retailer (Goldair does not hold tubes as spare parts). Connect the drainage hose to the drain spout.Place the end of the drainage hose in a drainage outlet. Ensure that the end of the hose is lower than the drain opening,otherwise the water will not drain and flooding may occur.Also ensure the water tank is positioned in the unit otherwise the continuous drainage will not operate.It will also catch any overflow.When you no longer wish to use the permanent water drainage,disconnect the drainage tube from the device and water will be collected in tank again.Trouble Shooting your DehumidifierGoldair–New Zealand Monday –Friday 8am-5pm Phone +64 (0)9 917 4000 Phone 0800 232 633***********.nzGoldair–Australia Monday –Friday 8am-5pm Phone +61 (0)3 9365 5100 Phone 1300 465 324 *******************.auProblem Cause SolutionThe Dehumidifier will not turn on The power is not connectedInsert plug into mains powersupply and turn unit onThe Dehumidifier is not extracting water The water tank is fullRemove the water tank andempty waterThe water tank is not in itscorrect positionRemove water tank andreplace it correct positionThe air filter is cloggedClean the air filter as perinstructions in user manualThe temperature or relativehumidity in the room is toolowIt is normal for theDehumidifier not to operatein low humidity or lowtemperaturesThe Dehumidifier operates, but reduces the relative humidity in the room by small amounts The room which theDehumidifier is operating inis too largeRecommend using aDehumidifier with a largercapacityThere are too many sourcesof humidityRecommend using aDehumidifier with a largercapacityThe room has too muchventilationReduce the number ofventilation sources (i.e. closewindows, doors, etc.SUPPORT AND TECHNICAL ADVICEPROOF OF PURCHASETo receive warranty retain receipt as proof of purchase. TECHNICAL SPECIFICATIONModel No:GPDH380Supply:220-240VAC50HzWattage:385WUnit Capacity:20.0L/day max(30℃/80%RH)Tank Capacity: 5.0LRefrigerant:R134a150gThank you for purchasing this Goldair Platinum product.Your product is warranted against faults and manufacture when used in normal domestic use for a period of three years.In non-domestic use Goldair limits the voluntary warranty to three months.Goldair undertake to repair or replace this product at no charge if found to be defective due to a manufacturing fault during the warranty period.This warranty excludes damage caused by misuse,neglect,shipping accident,incorrect installation,or work carried out by anyone other than a qualified electrical service technician.PLEASE KEEP YOUR RECEIPT AS THIS WILL HELP VERIFY YOUR WARRANTY.The benefits given to you by this warranty are in addition to other rights and remedies available to you under law in relation to the goods or services to which this warranty relates.In Australia,our goods come with guarantees that cannot be excluded under the Australian Consumer Law.You are entitled to a replacement or refund for a major failure and compensation for any other reasonably foreseeable loss or damage.You are also entitled to have the goods repaired or replaced if the goods fail to be of acceptable quality and the failure does not amount to a major failure.In New Zealand this warranty is additional to the conditions and guarantees of the Consumers Guarantee Act (1993).Three Year WarrantyGoldair Three Year Warranty (IMPORTANT: Please complete and retain this warranty card)NameAddressPlace Of Purchase Date Of PurchaseName Of ProductModel NumberAttach a copy of the purchase receipt to this warranty card Due to continual design improvements, the product illustrated in this User Manual may differ slightly from the actual product.Goldair –New ZealandCDB GoldairPO Box 100-707N.S.M.CAucklandPhone +64 (0)9 917 4000Phone 0800 232 633 Goldair –Australia CDB Goldair Australia Pty PO Box 574South Morang Victoria, 3752Phone +61 (0)3 9365 5100Phone 1300 GOLDAIR (1300 465 324).au。

Water Gas Shift in Microreactors at Elevated Pressure

Water Gas Shift in Microreactors at Elevated Pressure:Platinum-Based Catalyst Systems and Pressure EffectsP.Piermartini •T.Schuhmann •P.Pfeifer •G.SchaubPublished online:2August 2011ÓSpringer Science+Business Media,LLC 2011Abstract A new lab-scale microstructured reactor was used for investigations on enhancing the H 2/CO ratio in synthesis gas from biomass feedstocks via the water gas shift reaction.A model mixture of carbon monoxide,car-bon dioxide,water,and hydrogen was used to reproduce the typical synthesis gas composition from dry biomass gasiﬁcation.Catalyst layers were prepared and character-ized;a combined incipient wetness impregnation and sol–gel technology was applied.The catalytic activities of Pt/CeO 2and Pt/CeO 2/Al 2O 3ﬁlms were determined at temperatures of 400–600°C and pressures of up to 45bars.Increased pressure leads to higher values of CO conversion and to increased formation of hydrocarbons (CH 4,C 2H 6,etc.)and coke.Methane is the main by-product,and coke formation was attributed to the catalytic activity of peripheral reactor components.Keywords Water gas shift ÁMicrostructured reactor ÁBiomass feedstock ÁSyngas conditioning ÁPlatinum-ceria catalyst1IntroductionBiomass is the only renewable energy source containing carbon that can be used in the long term as a feedstock for the generation of chemicals and fuels [1].For the chemical conversion of biomass to synthesis gas (‘‘syngas’’)via gasiﬁcation and subsequent fuel synthesis,microstructured reactors may be used in the catalytic reaction steps.They offer unique options for temperature control including user-deﬁned temperature gradients [2],efﬁcient heat transfer [3,4],and offer the potential of modular design [5].An innovative approach suggested for biomass conver-sion includes a pyrolysis step to generate an oil/char slurry to be fed into the gasiﬁcation reactor [6].Thermal decomposition occurs at 500°C,and a twin screw mixer reactor can be applied to rapidly heat-up and pyrolyze the biomass in order to generate stable slurries [7,8].These slurries can be pumped into the gasiﬁer [9]and converted to syngas at temperatures above 1100°C and elevated pressures between 30and 80bar.For an entrained ﬂow gasiﬁer,the H 2/CO ratio in the gas is typically too low to meet the requirements of a downstream synthesis plant [10].However,the high temperature and high pressure conditions produce a tar-free syngas and avoid compres-sion before synthesis.The hydrogen content of syngas can be increased via the water gas shift reaction at high pres-sures above the temperature of the synthesis step.According to Eq.1the water gas shift reaction is a weakly exothermic,reversible reaction that is nearly independent of pressure:H 2O þCO $H 2þCO 2D H 0R ¼À41:3kJ molð1ÞAccording to calculations using slightly modiﬁed kinetics of a copper catalyst [11],the CO-conversionDedicated to the 70th birthday of Professor Holmen.P.Piermartini (&)ÁT.Schuhmann ÁP.PfeiferInstitute for Micro Process Engineering (IMVT),Karlsruhe Institute of Technology (KIT),Hermann-von-Helmholtz-Platz 1,76344Eggenstein-Leopoldshafen,Germany e-mail:paolo.piermartini@G.SchaubEngler-Bunte-Institute Division of Fuel Chemistry and Technology,Karlsruhe Institute of Technology (KIT),Engler-Bunte-Ring 1,76131Karlsruhe,GermanyTop Catal (2011)54:967–976DOI 10.1007/s11244-011-9717-7may be rate limited at temperatures of about 350°C,whereas at higher temperatures the reaction rate at the entrance of a reactor is high but the CO conversion is limited due to thermodynamic equilibrium [12].If a temperature proﬁle decreasing along the reactor length is deﬁned,these calculations indicate that the reaction rate along the reactor can be increased.It was shown previously that linearly decreasing temperature proﬁles of up to 150K can be deﬁned for a microreactor with 8cm reactor length [13].A microreactor with a decreasing temperature proﬁle could be part of a compact and easy-to-operate reactor concept for water gas shift reaction in the synthesis gas.Equilibrium calculations (taking into account species present in the synthesis gas)show that H 2/CO ratios between 2and 3could be reached at low temperatures,between 100and 350°C,when the syngas contains only 18mol%of steam.Taking into account some driving force for enhancing the reaction rate especially for the microreactor concept,these temperatures are below those applied to most reactions utilizing syngas as a chemical feedstock.Low temperature Fischer–Tropsch synthesis may be the only exception.With a higher H 2O content of 28mol%(Fig.1),H 2/CO ratios above 2could be obtained over a wide temperature range,i.e.,below 500°C.Higher temperatures offer more ﬂexibility with respect to the temperature range over which a temperature proﬁle can be applied.Even if no H 2O was present in the raw synthesis gas,an energy balance shows that sufﬁcient steam would be generated by using water to quench from 1100°C to a shift reaction temperature of 500°C.Equilibrium calculations taking into account methane,carbon,and C 2?species show that parallel reactions such as methane synthesis (Eq.2),coke formation (Eq.3),and hydrocarbon formation (with consequently a large number of by-products,Eq.4)occur at temperatures below 500°Cand pressures between 30and 50bars.Figure 2shows the equilibrium compositions when methane,ethane,and car-bon are included in addition to the species involved in the water gas shift reaction.An understanding of potential by-product formation is necessary for catalyst selection and deﬁnition of optimal operating conditions.CO þ3H 2$CH 4þH 2O D H 0R ¼À205:8kJmolð2Þ2CO ðg Þ$C ðs ÞþCO 2ðg ÞD H 0R ¼À172:45kJ mol ð3ÞCO þ2H 2$ðÀCH 2ÀÞþH 2OD H 0R ¼À158:5kJ molð4ÞWGS catalysts should tolerate a limited level of impurities and poisons generated during biomass gasiﬁcation (typi-cally H 2S,COS,Alkali,HCl,NH 3)in addition to providing a high activity and suppressing the formation of by-prod-ucts.Catalyst regeneration and replacement,are important characteristics of the materials applied.Many catalysts have been reported in literature to facilitate the water gas shift reaction at different tempera-tures.Iron catalysts have conventionally been applied [14–16],but novel catalytic materials have also been investigated.For example,gold nanoparticles supported on TiO 2and CeO 2have been successfully used over a wide range of temperatures,between 50and 400°C [17].Au/TiO 2also exhibits good CO-conversion at temperatures below 300°C,while Au/CeO 2was most active at tem-peratures above 300°C.Co-precipitated bimetallic gold catalysts have also been studied.Gold catalysts containing ceria as support showed a good activity in the low tem-perature range of 200–350°C,especially an Au–Pt/ceria catalyst [18].An increase in the conversion of the carbon monoxide and a reduction of surface oxygen at lower1002504005507008501000Temperature / °C — — H2O(g)H2(g)N2(g)- - CO2(g)CO(g)Equilibrium concentrations of the WGS reaction at 50bar for synthesis gas composition from a entrained ﬂow gasiﬁer i.e.,temperatures was observed for co-precipitation of gold and metal catalysts[18].Noble metals(Rh,Pt,Pd and Ru)supported on CeO2–Al2O3were investigated for the water gas shift at relatively high temperatures(500–700°C)in order toﬁnd an active catalyst that could be directly coupled with the biomass gasiﬁcation process[19].Pt-CeO2/Al2O3catalyst showed the highest CO-conversion at temperatures of700°C,and the ceria support seemed to improve the catalyst performance.Noble metal catalysts have been incorporated in mic-roreactors and applied to the WGS reaction in literature. The microreactor systems have been exclusively applied to ambient pressures for fuel cell applications[20,21].These studies showed that the Pt/CeO2/Al2O3catalyst is one of the best candidates with respect to selectivity and activity. The catalysts showed a high CO2-productivity[21].In aprevious study[22]Ru catalysts supported on ZrO2coated microstructured foils were applied to the water gas shift reaction at temperatures of250–300°C at ambient pres-sure.Neither the typical low-temperature catalysts such as copper–zinc or ruthenium–zirconia nor the iron–chrome catalysts seemed to be adequate for our selected tempera-ture range(400–600°C).Only the Pt/CeO2/Al2O3-based catalyst promised a remarkable activity at the desired temperatures[19].For this reason,two catalyst systems were examined in this paper.A Pt/CeO2/Al2O3catalyst was prepared via an alumina sol–gel and a ceria aqueous solution.And,a Pt/CeO2based on a ceria sol–gel was produced.Ceria is a less acidic support compared to alu-mina and should improve the catalytic activity through better contact between platinum and ceria.The catalysts were applied as coating on microstructured metal foils.The coated foils were pressed together in a novel clamping reactor and the identical reaction conditions were used for the testing of both catalysts.The effects of pressure,tem-perature and residence time on the product distribution are presented.Particular attention is given to the selectivity of secondary reactions and by-product generation.2Experimental2.1MicroreactorThe reactor(Fig.3)was built of Nicrofer3220H/Alloy 800H.This material was chosen for its satisfactory pressure resistance at temperatures of up to600°C.Special graphite seals were used to prevent leaks at high pressure under the low totalﬂow rates applied to the reactor.And,two sides of the reactor could be opened,one for the foil integration (i.e.,a full opening)and one side for inserting powder catalyst from the top while having aﬁxed foil stack.The housing of the reactor is225mm long andﬁts microstructured foils25mm wide.The narrow foil dimension was chosen to avoid back mixing phenomena, i.e.,axial mass transport,which could occur at the low gas velocities used in these investigations.Fourteen stainless steel foils structured with micro-channels were coated on one side with catalyst and suc-cessively stacked in the reactor.The dimensions of the microchannels are given in Table1.The geometric surface area is the sum of the channel bottom,the side channel walls,and the top of theﬁn.This is the area coated by the catalyst.2.2Catalyst PreparationThe foils wereﬁrst cleaned in water and then in isopropyl alcohol for30min in an ultrasonic bath and then annealed in air at500°C for5h.Annealing stainless steal foils generates a chromium oxide layer,which improves the adhesion of the oxide catalyst to the foil surface[22].The Pt/CeO2/c-Al2O3was prepared from an alumina-sol–gel[23].24.8g aluminium tri-sec-butyl acetate Al(OC4H9)3were dissolved in80ml ethyl alcohol.10g acetyl acetone in40ml ethyl alcohol and3.6g H2O in 20ml ethyl alcohol were added.To dissolve the precipitate formed,HNO3was added until the pH reached4.5.A speciﬁc quantity of sol–gel solution was applied to the stainless steel foils,using the capillary effect for equal distribution in the microchannels.The foils were dried at 80°C for24h and then calcined at500°C for5h.Two coatings were applied before reaching the desired foil loading with catalyst.An aqueous Ce(NH4)2(NO3)6solution containing7g/l CeO2and a0.01mol/l aqueous platinum nitrate solution were used for impregnation of the deposited sol–gel layer. Drying and calcination occurred under the sameconditions Fig.3Reactor for testing of the coated foilsas for the sol–gel deposition.A total amount of0.2g catalyst was placed on the14foils and the composition was 5wt.%Pt/12wt.%CeO2/83wt.%c-Al2O3.Prior to testing the catalyst was reduced in situ the reactor with2vol.%H2 in N2at500°C for2h.For the preparation of the Pt/CeO2a different sol–gel process was used[24].2.7g Ce(NH4)2(NO3)6were sus-pended in pre-mixed30ml ethyl alcohol and0.7ml diethanolamine while stirring under N2-atmosphere.After 1h1.5ml HNO3were added as a stabilizing agent.The sol–gel solution was stirred for24h.The cerium oxide content was1.6*10-4mol/ml.500l l ceria sol–gel were dropped onto the surface of each foil.The foils were dried at80°C for24h and calcinated at500°C for5h.The foils were successively coated with a0.02mol/l aqueous platinum nitrate solution and again dried and calcinated.A total amount of0.2g catalyst was distributed among the14 foils and the composition was5wt.%Pt/95wt.%CeO2.2.3Catalyst CharacterizationThe morphology of the catalysts was determined by scan-ning electron microscopy(JEOL6300)applying a sec-ondary electron detector(SED)and a backscattering detector(BSD).An acceleration voltage of20kV was used.Secondary electron images(SE)were used to examine the sol–gel coating.Backscattering of primary electron(BSE)was used for material contrast,i.e.,in order to distinguish the metal phase(Pt)from the oxide layer(the detector gives higher signals for higher molecular weight components,i.e.,a brighter pixel results for Pt).Sorption measurements were conducted in an Autosorb 1C machine from Quantachrome.The total catalyst surface area was determined through nitrogen adsorption using the BET method for the calculation of the surface area(S BET). The values of the speciﬁc surface area are given as the surface enlargement ratio(E)of the layer[22]to the geo-metric surface area of the foil(S geom.):E¼S BETS geom:ð5ÞThe active metal surface area per mass or volume of cat-alyst and the dispersion of the active metal particles on the surface were determined from chemical adsorption mea-surement with hydrogen in the Autosorb1C machine.The chemisorption was carried out at40°C,and a stoichiom-etry of2was used(dissociative adsorption of H2on the metal).The sample was reduced with H2at400°C and outgassed at120°C prior to measurement.The‘‘Extrap-olation to P=0Method’’was used applying the data points from strong adsorption.A pressure between40and 300mTorr hydrogen was used for the isotherm.2.4Reaction ConditionsThe following experimental conditions were used for investigating the water gas shift reaction in the micro-structured reactors:A feed gas of32vol.%CO,10vol.%CO2,18vol.%H2, 10vol.%N2and30vol.%H2O was applied to the catalysts at three modiﬁed residence times s mod(8000,12000, 24000g s/m3),see Eq.6.The reactor wall temperature ranged from400to550°C,and the pressure was increased from1bar up to45bars.Hence,the total gasﬂow varied between0.5and1.5l/min(STP).s mod:¼m cat:_VðSTPÞ¼catalyst massvolume flow rateðSTPÞð6ÞFrom the measured inlet concentration[CO]in and end concentration[CO]end,the conversion of carbon monoxide X(CO)could be determined:XðCOÞ¼½CO inÀ½CO end½CO inð7ÞFrom the measured outlet concentrations of all the products of the water gas shift reaction,the concentration ratio K can be deﬁned:K¼CO2½ vol:ÃH2½ vol:CO½vol:ÃH2O½vol:ð8Þ2.5Test Setup and AnalyticsMassﬂow controllers(Brooks)were used for feeding the gas components:nitrogen,hydrogen,carbon monoxide, and carbon dioxide.The water used for the reaction was pressurised with nitrogen and dosed through a liquid mass ﬂow controller(Brooks).A microstructured nozzle was employed[25]for atomizing and evaporating the water:theTable1Geometry data of the microstructured foil stack Geometric dimensions of the microstructured foilsChannel width(l m)200 Channel height(l m)200 Fin width(l m)100 Channels per foil50 Length of foil(mm)150 Width of foil(mm)25 Geometric surface area of one foil(mm2)5235 Number of foils14 Height of stack(mm) 4.2 Channel volume of stack(mm3)1125required quantity of water was accelerated with extra nitrogen in the micronozzle and sprayed into the premixed and heated gases(H2,CO,CO2).The pipes were heated with electrical resistance coils.Constant and pulsation-free evaporation was achieved.The mixture then entered the reactor via a heated and insulated connection pipe with an inner diameter of4mm.The reactor housing was also heated electrically using three groups of resistance wires. The temperature of the housing was measured with6 thermocouples.An isothermal temperature proﬁle along the reactor was provided.Two additional thermocouples measured the inlet and outlet gas temperature,upstream and downstream of the microreactor.A marginal temper-ature gradient between the inlet and outlet of the reactor was detected.The pressure drop within the microstructured reactor was measured by a pressure transducer.Measured and calculated reactor pressure drop showed good agree-ment.The high system pressure was controlled with a pneumatic control valve.The inlet concentration of the gases(corresponding to the bypass concentrations)and the product concentrations were determined with a gas chromatograph(Agilent 6890N).The conversion was determined from the differ-ences between the inlet and outlet concentrations(Eq.7). 3Results and Discussion3.1Catalyst CharacterisationSEM-micrographs of the catalyst foils impregnated with Pt/CeO2/c-Al2O3are shown in Fig.4.The coating exhibits cracks in the channel corners,i.e.,is inhomogeneous in thickness at the channel perimeter.The resultingﬂakes appear to be only loosely attached to the surface,butmaterial loss(even from the calculation of expected alu-mina weight resulting from the sol–gel)was not observed in the experiments.Some artifacts of large platinum crys-tals in the range of1l m can be observed on top of theﬁns at high magniﬁcation in b),which is possible due to the higher backscattering radiation(white spots)of the plati-num metal.The SEM-micrographs of the Pt/CeO2catalyst are shown in Fig.5.The results in terms of coating quality are similar except that fewer cracks are present.No platinum crystals were observed in the different micrographs,which might indicate a better distribution of smaller platinum particles and thus higher platinum surface area or a better inﬁltration of the support.The results of physisorption and chemisorption analysis are presented in Table2.The alumina support provides a higher enlargement ratio of the surface area,but the values of metal dispersion and active metal surface area are quite similar—even though there are some artifacts of large crystals in the layer of Pt/CeO2/c-Al2O3.So the large crystals on theﬁn surface of the alumina-based layers do not strongly contribute to the reaction rate.The catalyst on top of theﬁns may anyway be subject to mass transport limi-tations as the residual gap between the individual foils is dependent on the burrs and roughness of the metal surfaces.The catalysts were inspected with the same methods after reaction and no change was observed.No loss of catalyst layer was observed.3.2Reaction Experiments3.2.1Pt/CeO2/Al2O3The conversion of carbon monoxide is plotted versus the reactor wall temperature for the Pt/CeO2/Al2O3catalyst in Fig.6.It reveals a considerable inﬂuence of thepressure Fig.4SEM-micrographs of Pt/CeO2/Al2O3.a Front view on theﬁn and the channels(SED).b Contrast picture(BSD):dark surface is c-Al2O3sol–gel-coating and white spots are platinum crystalsas CO conversion increases with increasing pressure.At 550°C reactor wall temperature and a reaction pressure of 45bar,the CO conversion reaches a maximum value of 70%for the range of values studied,while at ambient pressure and similar temperatures,only 40%CO-conver-sion was measured.At elevated temperature and pressure,the CO conver-sion exceeds the conversion calculated at thermodynamic equilibrium for the species present in the synthesis gas(only water gas shift reaction considered).This can be explained due to byproduct formation as shown in the introduction.Signiﬁcant formation of methane and C 2?hydrocar-bons at high pressure and high temperature was observed,as shown in Table 3.The amount of all detectable by-products and the sum of all the calculated yields do not adequately explain the difference between the CO con-version and the water gas shift equilibrium calculation.A considerable amount of coke was observed at the end of each experiments series at reactor entrance in front of the microstructured foils.The weight of the coke remaining in the reactor approximately closes the material balance.Blank tests,on the other hand,showed that the coke for-mation does not signiﬁcantly inﬂuence the inlet composi-tion.Meanwhile,we found that coke formation can mainly be attributed to the stainless steel frit and the high content of nickel in the ﬁller material used for welding the tubes to the reactor.A homogeneous reaction can not be fully excluded yet.As predicted by the pressure dependence of the Boudouard reaction,coke formation was noticed at the end of each experiment conducted at a pressure higher than ambient pressure.No coke was observed on the catalyst foils,and no deactivation was measured during the duration of the experiments ([100h).Fig.5SEM-micrographs of Pt/CeO 2.a Perspective view of the channels of the coated foils.b Top view of the coated foils Table 2Physisorption and chemisorption analysis results CatalystPt/CeO 2/c -Al 2O 3Pt/CeO 2Surface enlargement ratio (m 2/m 2)312216Active metal surface area (m 2/g cat.) 1.72Active metal surface area (m 2/m cat 3)0.5E71E7Metal dispersion (%)1416Table 3Methane and C 2?hydrocarbons volume fractions at 550°C for the Pt/CeO 2/Al 2O 3catalyst Pressure CH 4/vol.%R C 2?/vol.%1bar ––5bar ––15bar 0.82–30bar 2.170.4545bar2.820.91In order to get information about the shift activity of the catalyst,the reactor efﬂuent composition can be used for calculation of the water gas shift equilibrium by treating all byproducts as inert gas(e.g.,additional nitrogen).In Fig.7 the concentration ratio K is plotted as function of the reactor wall temperature.The experimental results obtained at24000g s/m3modiﬁed residence time reach the thermodynamic equilibrium at a pressure of45bars at high temperatures(500–550°C)within the experimental error.Figure8shows the inﬂuence of modiﬁed residence time and pressure on the CO conversion for the Pt/CeO2/Al2O3 catalyst.For constant temperature and pressure,the CO conversion is almost constant at ambient pressure,whereas for higher pressure(45bars)there is a trend of higher conversion with higher residence time.In the experiments conducted at450°C,the CO-conversion increases from a value of30%at8000g s/m3modiﬁed residence time to 40%at12000g s/m3and reaches a maximum value of 60%at24000g s/m3s mod.The inﬂuence of byproduct formation on the CO con-version is excluded in the same way as in Fig.7.Figure9 shows the shift activity as K for two of the curves from Fig.8.The experiments conducted at450°C reveal that K approaches the equilibrium value with increasing modiﬁed residence time and increasing pressure.This result shows that not only byproduct formation is enhanced by higher residence times.3.2.2Pt/CeO2Pressure variation experiments at constant residence time (24000g s/m3)were carried out with the Pt/CeO2catalyst. The results were similar to those of the alumina supported system(not shown).The difference in the CO conversion among the different pressures increases with the reactor wall temperature:at400°C the difference between ambi-ent pressure and45bars amounts to just10%,while at 550°C this difference rises to25%.At550°C,45bar system pressure,and a modiﬁed residence time of 24000g s/m3,a maximum value for the range of temper-ature and pressures examined of70%CO conversion is reached.This suggests that byproduct formation increases at elevated pressure.Table4lists the concentration values at the different operating points.Formation of methane, C2?hydrocarbons,and also coke was observed for the Pt/CeO2catalyst too.No coke was observed on the catalyst foils and no deactivation was measured during the duration of the experiment([100h).The analysis of the concentration ratio K for the water gas shift reaction(again considering the byproduct as inertgas)is plotted as a function of the wall temperature in Fig.10.The values of K approach the calculated equilib-rium at a pressure of45bar and temperatures between500 and550°C.The inﬂuence of the modiﬁed residence time was investigated and is shown in Fig.11.In the case of the Pt/ CeO2catalyst the effect of the s mod-variation is more pronounced at low pressure than at high pressure.This is different than for the Pt/CeO2/Al2O3catalyst.At a reactor wall temperature of450°C and ambient pressure,the CO-conversion reaches a value of ca.13%at8000g s/m3 modiﬁed residence time and a value of ca.35%at 24000g s/m3s mod.The approach to equilibrium(compare Fig.9)for the shift activity,however,is not different for the two catalysts(not shown).We suppose that this effect could be due to the cerium oxide interaction with the platinum for oxygen exchange and less acidity of the cerium oxide compared to c-Al2O3.Due to the step-wise impregnation of the alumina with components ceria and platinum in the Pt/CeO2/Al2O3catalyst,the platinum is not necessarily in contact with cerium oxide in the three component mixture and interaction between ceria and platinum may be hin-dered compared to the Pt/CeO2catalyst.3.3Catalysts ComparisonFigure12shows a direct comparison of the two catalyst systems with respect to CO conversion.The difference in CO conversion between ambient pressure and high pres-sure(45bars)is more signiﬁcant for the c-Al2O3supported system than for the Pt/CeO2catalyst.The CO conversion is higher at ambient pressure for the Pt/CeO2system than for the Pt/CeO2/Al2O3system.At high pressure(45bars)the activity is opposite,i.e.,the Pt/CeO2/Al2O3shows the higher conversion.The results suggest a lower dependence of the CO-conversion on pressure for the platinum metal catalyst with CeO2support.Table5reveals that lower byproduct formation was obtained with the Pt/CeO2catalyst.The reason for the lower byproduct generation may be based on the less acidic nature of this system in comparison with the c-Al2O3 catalyst.Table4Methane and C2?hydrocarbons volume fractions at550°C for the Pt/CeO2catalystPressure CH4/vol.%R C2?/vol.%1bar––5bar0.08–15bar0.23–30bar 1.360.2945bar 2.450.594ConclusionTwo different platinum catalysts,Pt/CeO2/Al2O3and Pt/ CeO2,with different metal-oxide carriers were coated on microstructured foils.It was possible to measure high shift activity for increasing the ratio between hydrogen and car-bon monoxide of a model gas mixture,which represents the typical gas product composition of an entrainedﬂow gasiﬁer.Higher carbon monoxide conversion was observed at higher pressures.At a modiﬁed residence time of 24000g s/m3,pressure of45bar,and reactor wall tem-peratures between500and550°C,the water shift reaction was at equilibrium.A H2/CO ratio of2was reached at a pressure of45bar and reactor wall temperature of450°C Byproduct formation was detected at high temperature and high pressure.Methane up to3vol.%and traces of C2?species were measured in the gas stream.Coke was detected in the reactor entrance caused by some high nickel containing reactor components.The formation of hydro-carbons and coke did not affect the performance of the catalysts.The coke formation at the entrance of the reactor did not signiﬁcantly(within standard deviation)alter the reactant composition observed from blank runs.Each cat-alyst was tested for more than100h and in this time no deactivation was observed.The coating was also checked after the reaction,and no differences were observed.Fur-ther experiments varying the inlet gas composition will be carried out to study the effect of gas composition on reaction kinetics.Interesting results are expected in the near future from experiments with temperature proﬁles deﬁned along the microreactor.Acknowledgments Theﬁnancial support of the Baden-Wuerttemberg Stiftung for the project Bio11is gratefully acknowledged. 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CO低温氧化催化剂研究进展

CO低温氧化催化剂研究进展杨德强;周庆华【摘要】The CO oxidation,which involving duwhstrial, environmental, military, and many aspects of human life, has been one of the hot catalytic field. Noble metal catalysts have high activity, good stability, long life, etc., but with the very expensive price,it is necessary to search for the non-noble metal catalyst which have good catalytic activity and lower price. This paper gives a review of CO oxidation catalysts which including noble metal and non-noble metal catalysts.%CO催化氧化涉及工业、环保、军事和人类生活的多个方面,一直是催化领域的热点之一.贵金属催化剂有活性高,稳定性好,寿命长等优点,但价格昂贵,研究开发价格低廉,活性较好的非贵金属催化剂也越来越受到了人们的重视.本文将CO氧化催化剂分为贵金属和非贵金属两类进行了综述.【期刊名称】《化学工程师》【年(卷),期】2011(000)008【总页数】3页(P36-38)【关键词】CO氧化;贵金属;非贵金属【作者】杨德强;周庆华【作者单位】黑龙江中医药大学,黑龙江哈尔滨150040;黑龙江中医药大学,黑龙江哈尔滨150040【正文语种】中文【中图分类】O643.32空气污染是当今社会的重要环境问题之一，CO又是释放到空气中最多的气态染物之一。

非均相钌催化高铁酸盐氧化降解苯酚

DOI:10.7524/j.issn.0254-6108.2022081301于永强, 何佳豪, 张静. 非均相钌催化高铁酸盐氧化降解苯酚[J ]. 环境化学, 2024, 43（3）: 783-789.YU Yongqiang, HE Jiahao, ZHANG Jing. Enhanced ferrate oxidation by ruthenium nanoparticles for degradation of phenol [J ]. Environmental Chemistry, 2024, 43 （3）: 783-789.非均相钌催化高铁酸盐氧化降解苯酚 *于永强1　何佳豪1　张静1,2 **（1. 重庆大学环境与生态学院，重庆，400045；2. 哈尔滨工业大学环境学院，哈尔滨，150090）摘　要　本研究开发了以ZSM-5、TiO 2和CeO 2为载体的非均相钌（Ru ）催化剂，并检验了其催化高铁酸盐（Fe(Ⅵ)）氧化苯酚的性能. 随着Ru/ZSM-5、Ru/TiO 2或Ru/CeO 2催化剂投加量的增加，Fe(Ⅵ)氧化苯酚的伪一级反应速率常数（k obs ，min -1）呈线性增长趋势. 催化剂的效能主要取决于载体上钌纳米颗粒的分散情况，受钌负载量的影响不明显. 虽然Ru/ZSM-5的Ru 载量最低，但ZSM-5的比表面积较高，且Ru 在ZSM-5表面的分散性好，使其催化效能与另外两种催化剂相当. 非均相钌催化性能受pH 影响很大，在pH 5.0—9.0时显著提高了苯酚的去除率. Ru 的催化机理为Ru III 被Fe(Ⅵ)氧化为Ru Ⅶ中间体，Ru Ⅶ具有较高活性和氧化能力，可以快速氧化苯酚，从而促进Fe(Ⅵ)氧化苯酚的速率. 研究通过连续10次重复使用实验考察了3种催化剂的稳定性，证明Ru/CeO 2和Ru/TiO 2的稳定性优于Ru/ZSM-5，Ru/ZSM-5稳定性下降的主要原因是ZSM-5比表面积较大，更容易吸附Fe(Ⅵ)的还原产物——氢氧化铁，从而使得Ru 活性位点被氢氧化铁掩盖.关键词　钌，高铁酸盐，动力学，机理，苯酚.Enhanced ferrate oxidation by ruthenium nanoparticles fordegradation of phenolYU Yongqiang 1 HE Jiahao 1 ZHANG Jing 1,2 **（1. College of Environment and Ecology, Chongqing University, Chongqing, 400045, China ；2. School of Environment, HarbinInstitute of Technology, Harbin, 150090, China ）Abstract In this study, we developed ruthenium-based (Ru-based) catalysts with ZSM-5, TiO 2 and CeO 2 as supports, and examined their performance for catalyzing ferrate (Fe(Ⅵ)) oxidation of caffeine or phenol. With the introduction of Ru/ZSM-5, Ru/TiO 2, and Ru/CeO 2, the pseudo-first-order reaction rate constants (k obs , min -1) of Fe(Ⅵ) oxidation of phenol increase linearly with the dosage of each catalyst. The enhancement from each catalyst depends more on the dispersion of ruthenium nanoparticles on the supports than the loading of ruthenium. Hence, we observed comparable catalytic performance for these three catalysts with Ru/ZSM-5 having the highest dispersion, but the lowest loading of ruthenium nanoparticles. Ruthenium nanoparticles significantly increased the removal of phenol at pH 5.0—9.0, while its catalytic performance was greatly affected by pH. Ru intermediate with higher oxidation state, Ru Ⅶ, was proved to be the major active species in ruthenium catalyzed Fe(Ⅵ) oxidation. To investigate the stability of catalysts, we used Ru/CeO 2,2022 年 8 月 13 日收稿（Received ：August 13，2022）．* 国家自然科学基金（22076016，51878095）和中央高校基本科研业务费（2021CDJQY-006）资助.Supported by National Natural Science Foundations of China (22076016，51878095) and Fundamental Research Funds for the Central Universities (2021CDJQY-006).* * 通信联系人 Corresponding author ，E-mail ：******************.cn784环境化学43 卷Ru/TiO2 and Ru/ZSM-5 for ten consecutive times under same reaction conditions. It was found that the stability of Ru/CeO2 and Ru/TiO2 are better than Ru/ZSM-5, which would favor their application in pilot or engineering practice. The depressed performance of Ru/ZSM-5 may be mainly associated with masking active sites by the deposited ferric hydroxide.Keywords　ruthenium，ferrate，kinetics，mechanism，phenol.高铁酸盐（Fe（Ⅵ））是一种环境友好的氧化剂[1]，与含有富电子基团的有机微污染物（例如胺类[2 − 3]、硫醇硫酯类[4]、酚类[5]）具有较高的反应活性. 与二氧化氯、高锰酸盐、臭氧和次氯酸盐等常见氧化剂相比[6]，Fe（Ⅵ）在酸性pH值下具有最高的氧化还原电位，且会减少溴代和氯代消毒副产物的生成[7]. 然而，Fe（Ⅵ）生产成本较高、在水溶液中的稳定性较低，这阻碍了其在水处理中的广泛应用. 因此，通过催化Fe（Ⅵ）氧化，提高Fe（Ⅵ）的利用效率具有重要意义.在各种催化剂中，钌（Ru）因其多功能性而占有特殊的地位. ZSM-5（一种具有规整结构的微孔晶态硅铝酸盐分子筛）、TiO2和CeO2作为钌基催化剂的载体，在高锰酸盐氧化体系中性能稳定，钌能很好地附着到载体表面. 另外，ZSM-5、TiO2和CeO2作为载体，本身不会对催化效果产生影响. 因此本文选择ZSM-5、TiO2和CeO2作为载体. 已有研究证明在常见水处理pH范围内，催化剂Ru/ZSM-5、Ru/TiO2或Ru/CeO2能显著提高高锰酸盐氧化速率[8 − 9]. 此外，Ru/CeO2和Ru/TiO2具有良好的稳定性，在连续6次重复试验中其催化活性基本保持不变[8]；但在连续10次重复试验中，Ru/ZSM-5的催化效能迅速下降，其稳定性比Ru/CeO2和Ru/TiO2差[9]. Ru作为催化剂在高铁酸盐氧化中的应用却鲜有报道.因此，本研究以CeO2、TiO2和 ZSM-5为载体的非均相钌催化剂，并考察了其在不同pH条件下催化Fe（Ⅵ）氧化苯酚的性能，提出了Ru催化Fe（Ⅵ）氧化中的机理并评估了催化剂的稳定性.1 材料与方法（Materials and methods）1.1 试验药剂水合三氯化钌（RuCl3·x H2O, 37% Ru）购自J&K化学公司；CeO2、TiO2、苯酚以及甲醇、甲酸等有机溶剂购自国药化学试剂有限公司；咖啡因购自Sigma公司；ZSM-5购自南开大学催化剂厂. 实验中所有溶液均使用超纯水配制.采用湿式化学合成法[10]制备固体高铁酸钾（K2FeO4，纯度>95%）. 将固体K2FeO4溶解在超纯水中制备K2FeO4储备溶液，然后用0.45 μm亲水性滤头过滤，通过紫外分光光度计在510 nm测量浓度，并在30 min内使用，以减少其自分解的影响.1.2 实验流程将装有200 mL一定浓度有机物和一定量催化剂的溶液调节至指定pH值，投加高铁酸钾储备液后，反应开始计时，定时取样，采用硫代硫酸钠或者盐酸羟胺淬灭，水样经醋酸纤维膜（孔径0.22 μm）过滤后定量分析.1.3 催化剂的制备与表征将RuCl3的干固体溶于pH 2.0的盐酸溶液中，配置成浓度为1 mol·L−1的RuCl3酸性溶液，弱酸环境可以有效防止三价钌被空气氧化为四价钌. 然后在室温条件下（约20 ℃）向RuCl3酸溶液投加载体，在磁力搅拌器上进行剧烈搅拌，使之达到均匀混合的状态，搅拌过程持续4 h. 然后通过高速离心机将固体从溶液中分离开来，用超纯水对催化剂进行反复冲洗，直至冲洗液的pH约为近中性，再将最终离心的固体置于温度为40 ℃的真空干燥箱中进行干燥. 待催化剂彻底干燥以后，即可进行实验.利用场发射扫描电子显微镜（SEM，型号HITACHIS-4800）观察催化剂的表面形貌. 采用高分辨透射电子显微镜（TEM，型号为JEM-2100）和能量色散X射线光谱仪（EDAX）对催化剂表面的钌氢氧化物的颗粒形貌进行观察，同时对选定区域进行元素分析. 采用 Coulter SA 3100 吸附分析仪进行氮吸附-解吸，测定催化剂的比表面积和孔体积. 新合成的催化剂和使用后的催化剂分别经硝酸微波消解，采用电感耦合等离子体发射光谱法（ICP-AES）测定其Ru含量.1.4 分析方法采用超高效液相色谱仪（UPLC ，型号H-Class ）测定苯酚和咖啡因的浓度. 采用BEH C18柱子，柱温控制在35 ℃；测定苯酚时流动相为水：甲醇=65:35，测定咖啡因时流动相为水（0.1%甲酸）：甲醇=70:30；检测波长是254 nm （苯酚）和273 nm （咖啡因）.2 结果与讨论（Results and discussion）2.1 非均相钌催化剂的表征新合成的Ru/ZSM-5、Ru/CeO 2和Ru/TiO 2催化剂中Ru 的含量分别为0.69‰、0.80‰和0.94‰.SEM 、TEM 和EDAX 的结果均证明载体上存在Ru 颗粒（图1）. 图1表面ZSM-5和TiO 2为球形，CeO 2为立方体形状. TEM 结果表明，在Ru/ZSM-5、Ru/CeO 2和Ru/TiO 2中，Ru 以粒径约为2.5 nm 的颗粒存在于ZSM-5、TiO 2和CeO 2的表面. 制备过程中载体与RuCl 3酸溶液反应结束后，通过离心将固体从溶液中分离，然后用超纯水对催化剂进行反复冲洗，因此在冲洗过程中RuCl 3可能会发生水解，生成相应的氢氧化钌，推测载体表面的纳米颗粒为氢氧化钌的颗粒 [8]. 在Ru/ZSM-5中，ZSM-5的比表面积较高，通过TEM 观测到Ru 在ZSM-5表面的分散性也更好（表1）. Ru/ZSM-5的区域EDAX 分析表明Ru 被成功负载（图1b ）.图 1 （a ） Ru/ZSM-5的TEM 图，（b ）Ru/ZSM-5表面黄色方框内的EDAX 图，（c ） Ru/CeO 2的TEM 图，（d ） Ru/TiO 2的TEM 图；载体的SEM 图像显示在（a ）、（c ）和（d ）的插图中.Fig.1 （a ） TEM image of Ru/ZSM-5, （b ） EDAX image of Ru/ZSM-5 surface in the yellow box, （c ） TEM image of Ru/CeO 2, and （d ） TEM image of Ru/TiO 2. The SEM images of supports were shown in the insets of （a ）, （c ） and （d ）.表 1 催化剂及其载体的性质Table 1 Characteristics of synthesized catalysts and supports 平均粒径/μm Average diameter 比表面积/（m 2·g −1）BET Surface area 微孔表面积/（m 2·g −1）Micropore surface area 外比表面积/（m 2·g −1）External surface area 孔径/nm Pore size 孔体积/（m 3·g −1）Pore volume 微孔体积/（m 3·g −1）Micropore volumeZSM-50.54613231380.50.3860.132Ru/ZSM-50.54072801270.50.2720.0883 期于永强等：非均相钌催化高铁酸盐氧化降解苯酚785续表 1平均粒径/μm Average diameter 比表面积/（m 2·g −1）BET Surface area 微孔表面积/（m 2·g −1）Micropore surface area 外比表面积/（m 2·g −1）External surface area 孔径/nm Pore size 孔体积/（m 3·g −1）Pore volume 微孔体积/（m 3·g −1）Micropore volumeTiO 20.15 4.87—————Ru/TiO 20.15 4.70—————CeO 230 4.53—————Ru/CeO 230 4.87—————2.2 非均相钌催化剂的催化性能已有研究证明Fe （Ⅵ）氧化有机微污染物符合二级反应动力学，因此本研究假设在有催化剂或没有催化剂的情况下，Fe （Ⅵ）氧化苯酚的反应在初始阶段遵循二级反应. 苯酚降解可能发生在溶液中（即非催化反应）和/或催化剂表面（即催化反应）. 反应动力学方程1为简化的动力学模型，该模型同时考虑了催化反应和非催化反应.式中，k u （L·mol −1·min −1）为非催化反应的二级速率常数，k c （L·mol −1·min −1）为催化反应的二级速率常数；k T （L·mol −1·min −1）是整个反应的表观二级速率常数；k obs （min −1）等于k T [Fe （Ⅵ）]. 在以前的研究中，Fe （Ⅵ）浓度随时间的变化是通过紫外分光光度计在510 nm 测量的，但在本研究中，由于固体催化剂的干扰，无法测定溶液中Fe （Ⅵ）的浓度.如图2所示，Ru/ZSM-5、Ru/CeO 2和Ru/TiO 2催化剂加入后，k obs 随催化剂用量的增加呈线性增加.当Ru/ZSM-5的投加量从0增加到0.5 g·L −1时，k obs 几乎增加了10倍. Ru/ZSM-5的Ru 载量最低（0.69‰），但其催化效能与另外两种催化剂相当. 由于ZSM-5比表面积远高于TiO 2和CeO 2，且钌纳米颗粒在ZSM-5载体上有良好分散性. 已有研究证明CeO 2、TiO 2和 ZSM-5作为载体，本身不会对钌催化效果产生影响[11]. 虽然载体本身对非均相钌催化剂的性能影响不大，但决定了钌纳米颗粒的分散性[8]，而钌的分散性对其催化性能起着决定性作用.图 2 催化剂Ru/ZSM-5、Ru/CeO 2、Ru/TiO 2的用量对其催化Fe （Ⅵ）氧化苯酚的影响反应条件：[phenol]0 = 5 μmol·L −1, [Fe （Ⅵ）]0 = 50 μmol·L −1, pH = 7.0, T = 23 ℃.Fig.2 Effect of catalysts dosage on the oxidation of phenol by Fe （Ⅵ） in the presence of Ru/ZSM-5, Ru/CeO 2, and Ru/TiO 2respectively786环境化学43 卷2.3 pH 值的影响不同pH 值下，Fe （Ⅵ）存在不同酸碱形态（p K a1 = 3.5，p K a2 = 7.3）[12]，且不同形态的Fe （Ⅵ）活性不同.苯酚（PhOH ）也存在分子态和电离态（p K a = 10），在pH 5.0—9.0范围内，苯酚主要以分子态PhOH 存在，因此可以忽略其电离态. 假设不同形态的Fe （Ⅵ）通过平行反应对PhOH 进行氧化（反应 2—4）：在不投加催化剂的情况下，当pH 从5.0升高到7.0时，k obs 从3.74×10−2 min −1增加到7.89×10−2 min −1，随着pH 进一步升高到9.0，k obs 从7.89×10−2 min −1下降到6.40×10−2 min −1（图3）. 以往的研究证明HFeO 4−比FeO 42−的反应活性更高，但在pH 5.0和6.0下k obs 相对较低，这可能是由于在低pH 条件下Fe （Ⅵ）会快速自分解[12].图 3 pH 对Fe （Ⅵ）氧化苯酚的影响（空心为催化体系，实心为非催化体系）反应条件：[phenol]0 = 5 μmol·L −1, [Fe （Ⅵ）]0 = 50 μmol·L −1, [Ru/ZSM-5]0 = 0.5 g·L −1, and T = 23 ℃Fig.3 Influence of pH on Fe （Ⅵ） oxidation of phenol在3种催化剂中，选择Ru/ZSM-5作为模型催化剂来评估pH 对Fe （Ⅵ）氧化苯酚性能的影响. 如图3所示，Ru/ZSM-5催化Fe （Ⅵ）氧化苯酚的动力学也表现出很强的pH 依赖性. 在pH 5.0—9.0范围内，Ru/ZSM-5极大地提高了苯酚的去除速率. 除pH 7.0外，Ru/ZSM-5催化Fe （Ⅵ）氧化苯酚的k obs （min −1）随pH 升高而降低. 这是由于随着pH 的升高，Fe （Ⅵ）氧化电位逐渐降低，因此生成的Ru x +的量也就相应逐渐下降，最终使得催化效果下降. 在pH 7.0时，Ru/ZSM-5催化效能升高，这可能是因为在pH 7.0时，钌的催化活性较高[13].2.4 催化机理研究表明，在Fe （Ⅵ）氧化过程中，可能有中间态Fe （Ⅳ）、Fe （Ⅴ）和羟基自由基（HO·）等反应活性中间体[14]. 高铁酸盐氧化咖啡因过程中，主要是中间价态铁Fe （Ⅴ）和Fe （Ⅳ）在发挥氧化效能，而Fe （Ⅵ）不能降解咖啡因[15]. 因此，本文选择咖啡因作为探针化合物，检测和评估Fe （Ⅴ）和Fe （Ⅳ）对Fe （Ⅵ）-Ru/ZSM-5体系的贡献. 如图4所示，由于Ru/ZSM-5的存在，Fe （Ⅵ）对咖啡因的降解被完全抑制. 因此，可以排除 Fe （Ⅵ）-Ru/ZSM-5体系中Fe （Ⅴ）和Fe （Ⅳ）的贡献. 已有研究证明[16]，Fe （Ⅵ）氧化过程中产生的HO·对有机物的降解作用可以忽略不计. 因此，排除了HO·对苯酚降解的贡献.3 期于永强等：非均相钌催化高铁酸盐氧化降解苯酚787788环境化学43 卷图 4 pH值对未催化和Ru/ZSM-5催化Fe（Ⅵ）氧化咖啡因的影响（a） pH 6.0，（b） pH 7.0，（c） pH 8.0反应条件：[caffeine]0 = 5 μmol·L−1, [Fe（Ⅵ）]0 = 50 μmol·L−1, [Ru/ZSM-5]0 = 0.5 g·L−1, T = 23 ℃Fig.4 Influence of pH on the uncatalyzed and Ru/ZSM-5 catalyzed Fe（Ⅵ） oxidation of caffeine 在高锰酸钾氧化的过程中，钌纳米颗粒具有电子穿梭的作用[8]. 简而言之，RuⅢ被高锰酸盐氧化成更高的氧化态RuⅦ，其作为氧化物种被有机微污染物还原到其初始状态RuⅢ. 因此，本研究假设Ru催化Fe（Ⅵ）氧化过程中的活性物种也是RuⅦ. 本文通过投加KRuO4，评估了RuⅦ对Fe（Ⅵ）氧化苯酚的影响. 在pH 7.0下，单独RuⅦ降解苯酚速率比Fe（Ⅵ）更高，但其对咖啡因的降解几乎没有影响（图5）. Fe（Ⅵ）/RuⅢ降解苯酚的动力学规律与Fe（Ⅵ）/RuⅦ相同，但Fe（Ⅵ）/RuⅦ的反应速率常数更大. 这是因为Fe（Ⅵ）/RuⅦ中的Fe（Ⅵ）和RuⅦ都参与苯酚降解，而Fe（Ⅵ）/RuⅢ中部分Fe（Ⅵ）用于转化RuⅢ为中间态RuⅦ. 可以确定RuⅦ是Ru催化Fe（Ⅵ）氧化的主要活性物种，也是降解有机微污染物的选择性氧化剂[12].图 5 RuⅦ在（a）苯酚和（b）咖啡因降解中的氧化能力和催化作用反应条件：[phenol]0=[caffeine]0= 5 μmol·L−1, pH=7.0 ，T=23 ℃Fig.5 Oxidative capacity and catalytic effect of RuⅦ in （a） phenol and （b） caffeine degradation2.5 催化剂的稳定性在催化反应和工业应用中，催化剂的可重复使用性和稳定性至关重要. 因此本文评估了Ru/CeO2、Ru/TiO2和Ru/ZSM-5连续使用10次的稳定性（图6）. 在Ru/CeO2和Ru/TiO2催化体系中，苯酚的去除率始终高于92%；而当催化剂为Ru/ZSM-5时，在前6次实验中苯酚的去除率保持不变，但从第6次到第10次循环实验中，苯酚的去除率从98.1%逐渐下降到80.0%. 经过10次循环使用后，Ru/ZSM-5、Ru/CeO2和Ru/TiO2中Ru负载量分别从0.69‰降至0.65‰、0.80‰至0.77‰、0.94‰至0.84‰. 因此，Ru的泄露并不是Ru/ZSM-5性能下降的主要原因. Fe（Ⅵ）的主要还原产物是Fe（Ⅲ），即氢氧化铁沉淀物，这些沉淀物可能吸附在催化剂表面，导致催化剂部分活性位点被覆盖. ZSM-5是一种中孔沸石，具有较高的表面积，因此对氢氧化铁的吸附能力更高（表1）. ICP结果证实在使用后的Ru/ZSM-5上存在Fe元素，质量占比为0.04‰，而Ru/CeO2和Ru/TiO2上的Fe可以忽略不计. 因此，Ru/ZSM-5 性能下降可能主要与沉积的氢氧化铁掩盖了Ru/ZSM-5表面的活性位点有关. Ru/TiO2和Ru/CeO2稳定性好，有利于其工程或中试应用，但应尽量避免氢氧化铁在催化剂表面沉积.图 6 Ru/ZSM-5、Ru/CeO 2和Ru/TiO 2催化Fe （Ⅵ）连续10次氧化降解苯酚反应条件：[phenol]0 = 5 μmol·L −1, [Fe （Ⅵ）]0 = 50 μmol·L −1, pH = 7.0, reaction time 40 min, T = 23 ℃Fig.6 Phenol removed by Fe （Ⅵ） oxidation in the presence of Ru/ZSM-5, Ru/CeO 2, and Ru/TiO 2 respectively in ten consecutive runs.3 结论（Conclusion）Ru/ZSM-5、Ru/CeO 2和Ru/TiO 2可以有效催化Fe （Ⅵ）氧化降解苯酚，且催化效能随催化剂用量线性增加. 钌纳米颗粒的良好分散性是其获得较好催化性能的关键，因此，在未来研究中，单原子钌基催化剂具有广阔前景. Ru 催化Fe （Ⅵ）氧化降解苯酚的动力学表现出很强的pH 依赖性. Ru 催化Fe （Ⅵ）氧化降解苯酚过程中的主要活性物质为Ru Ⅶ和Fe （Ⅵ）. Ru/TiO 2和Ru/CeO 2的稳定性优于Ru/ZSM-5，有利于其中试或工程实践中的应用.参考文献(References)ZHENG L, DENG Y. Settleability and characteristics of ferrate(Ⅵ)-induced particles in advanced wastewater treatment [J ]. WaterResearch, 2016, 93: 172-178.［ 1 ］SUN S F, LIU Y L, MA J, et al. Transformation of substituted anilines by ferrate(Ⅵ): Kinetics, pathways, and effect of dissolvedorganic matter [J ]. Chemical Engineering Journal, 2018, 332: 245-252.［ 2 ］JOHNSON M D, HORNSTEIN B J. Oxidation of aniline by ferrate(Ⅵ): Formation of an iron-imido species [J ]. Abstracts of Papers ofthe American Chemical Society, 2000, 219: U843-U843.［ 3 ］SHARMA V K, CHEN L, ZBORIL R. Review on high valent Fe VI (ferrate): A sustainable green oxidant in organic chemistry andtransformation of pharmaceuticals [J ]. ACS Sustainable Chemistry & Engineering, 2016, 4（1）: 18-34.［ 4 ］LEE Y, YOON J, von GUNTEN U. Kinetics of the oxidation of phenols and phenolic endocrine disruptors during water treatment withferrate (Fe(Ⅵ)) [J ]. Environmental Science & Technology, 2005, 39（22）: 8978-8984.［ 5 ］张静, 张宏龙, 王定祥, 等. 强化高锰酸钾氧化体系中自由基的产生与利用研究进展 [J ]. 环境化学, 2021, 40（2）: 487-496.ZHANG J, ZHANG H L, WANG D X, et al. Generation and utilization of radicals during enhanced permanganate oxidation: A review [J ]. Environmental Chemistry, 2021, 40（2）: 487-496（in Chinese ）.［ 6 ］LI C, LUO F, DONG F L, et al. Chlorine decay and trihalomethane formation following ferrate(Ⅵ) preoxidation and chlorination ofdrinking water [J ]. Chemosphere, 2017, 187: 413-420.［ 7 ］ZHANG J, SUN B, GUAN X H, et al. Ruthenium nanoparticles supported on CeO 2 for catalytic permanganate oxidation ofbutylparaben [J ]. Environmental Science & Technology, 2013, 47（22）: 13011-13019.［ 8 ］ZHANG J, SUN B, HUANG Y Y, et al. Catalyzing the oxidation of sulfamethoxazole by permanganate using molecular sievessupported ruthenium nanoparticles [J ]. Chemosphere, 2015, 141: 154-161.［ 9 ］THOMPSON G W, OCKERMAN L T, SCHREYER J M. Preparation and purification of potassium ferrate( Ⅵ) [J ]. Journal of theAmerican Chemical Society, 1951, 73（3）: 1379-1381.［10］张静. Ru Ⅲ催化KMnO 4氧化去除水中新兴微污染物的效能与机理[D ]. 哈尔滨: 哈尔滨工业大学, 2014.ZHANG J. Performance and mechanism of Ru ⅲ-catalyzed permanganate oxidation of emerging micropollutants in water [D ]. Harbin:Harbin Institute of Technology, 2014(in Chinese).［11］HU L H, MARTIN H M, ARCE-BULTED O, et al. Oxidation of carbamazepine by Mn(VII) and Fe(Ⅵ): Reaction kinetics andmechanism [J ]. Environmental Science & Technology, 2009, 43（2）: 509-515.［12］OUNKHAM W L, WEEDEN J A, FROST B J. Aqueous-phase nitrile hydration catalyzed by an in situ generated air-stable rutheniumcatalyst [J ]. Chemistry - A European Journal, 2019, 25（42）: 10013-10020.［13］LEE Y, KISSNER R, von GUNTEN U. Reaction of ferrate(Ⅵ) with ABTS and self-decay of ferrate(Ⅵ): Kinetics and mechanisms [J ].Environmental Science & Technology, 2014, 48（9）: 5154-5162.［14］ZHU J H, YU F L, MENG J R, et al. Overlooked role of Fe(Ⅳ) and Fe(Ⅴ) in organic contaminant oxidation by Fe(Ⅵ) [J ].Environmental Science & Technology, 2020, 54（15）: 9702-9710.［15］WANG D X, LIANG J L, ZHANG H L, et al. Reinvestigation of ferrate(Ⅵ) oxidation of bisphenol A over a wide pH range [J ]. ACSES& T Water, 2022, 2（1）: 156-164.［16］3 期于永强等：非均相钌催化高铁酸盐氧化降解苯酚789。

CeO2-Cu2O_2D

物理化学学报Acta Phys. -Chim. Sin. 2023, 39 (12), 2302051 (1 of 10)Received: February 28, 2023; Revised: April 7, 2023; Accepted: April 10, 2023; Published online: April 17, 2023. *Correspondingauthors.Emails:**************.cn(Z.J.);********************.ac.jp(N.T.)The project was supported by the National Natural Science Foundation of China (22062001), the Innovative Team for Transforming Waste Cooking Oil into Clean Energy and High Value-Added Chemicals, Ningxia Low-Grade Resource High Value Utilization and Environmental Chemical Integration Technology Innovation Team Project.国家自然科学基金(22062001), 宁夏废弃食用油转化为清洁能源高附加值化学品创新团队和低品位资源高值化利用及环境化工一体化技术创新团队资助项目© Editorial office of Acta Physico-Chimica Sinica[Article]doi: 10.3866/PKU.WHXB2023020512D/3D S-Scheme Heterojunction Interface of CeO 2-Cu 2O Promotes Ordered Charge Transfer for Efficient Photocatalytic Hydrogen EvolutionLijun Zhang 1,2, Youlin Wu 1, Noritatsu Tsubaki 2,*, Zhiliang Jin 1,*1 School of Chemistry and Chemical Engineering, North Minzu University, Yinchuan 750021, China.2 Department of Applied Chemistry, Graduate School of Engineering, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan.Abstract: Rapid intrinsic carrier recombination severely restricts the photocatalytic activity of CeO 2-based catalytic materials. In this study, a heterogeneous interfacial engineering strategy is proposed to rationally perform interface modulation. A 2D/3D S-scheme heterojunction with strong electronic interactions was constructed. A composite photocatalyst was synthesized for the 3D Cu 2O particles anchored at the edge of 2D CeO 2. First-principles calculations (based on density functional theory) and the experimental results show that a strongly coupled S-scheme heterojunction electron transport interface is formed between CeO 2 and Cu 2O, resulting in efficient carrier separation and transfer. The photocatalytic hydrogen evolution activity of thecomposite catalyst is significantly improved in the system with triethanolamine as the sacrificial agent and is 48 times as that of CeO 2. In addition, the resulting CeO 2-Cu 2O photocatalyst affords highly stable photocatalytic hydrogen activity. This provides a general technique for constructing unique interfaces in novel nanocomposite structures. Key Words: CeO 2; Cu 2O; DFT; S-scheme heterostructure; Photocatalytic hydrogen evolutionCeO 2-Cu 2O 2D/3D S 型异质结界面促进有序电荷转移以实现高效光催化析氢张利君1,2，吴有林1，Noritatsu Tsubaki 2,*，靳治良1,*1北方民族大学化学与化学工程学院，银川 7500212富山大学工学部，应用化学系，五福3190，富山 930-8555，日本摘要：快速的本征载流子复合严重限制了CeO 2基催化材料的光催化活性。

甲醇氧化羰基合成碳酸二甲酯原位红外研究

甲醇氧化羰基合成碳酸二甲酯原位红外研究马新宾;李振花;王保伟;许根慧【摘要】采用原位红外技术对甲醇氧化羰基合成碳酸二甲酯反应机理进行了系统的研究.原位红外实验结果表明,氧气在负载的Cu基催化剂上发生解离吸附,CO在催化剂表面的吸附为弱吸附,氧气与CO在催化剂表面发生共吸附,甲醇在催化剂表面吸附后产生甲氧基,压力提高有助于甲氧基的生成.吸附态的甲氧基诱导弱吸附的CO进行插入反应是生成碳酸二甲酯的途径.同时,原位红外技术研究结果表明,在碳酸二甲酯合成过程中,存在甲氧基与离解的氧进一步作用生成副产物CO2和H2O 的可能,因此,应控制原料中O2的浓度为适宜值.【期刊名称】《天津大学学报》【年(卷),期】2002(035)004【总页数】5页(P459-463)【关键词】碳酸二甲酯;一氧化碳;甲醇;铜【作者】马新宾;李振花;王保伟;许根慧【作者单位】天津大学一碳化学与化工国家重点实验室,天津,300072;天津大学一碳化学与化工国家重点实验室,天津,300072;天津大学一碳化学与化工国家重点实验室,天津,300072;天津大学一碳化学与化工国家重点实验室,天津,300072【正文语种】中文【中图分类】TQ032.41碳酸二甲酯（DMC）是一种十分重要的有机合成中间体，可替代有毒的硫酸二甲酯和光气用作甲基化剂或羰基化剂.经典的合成DMC的方法是光气甲醇法［1］.该法存在工艺复杂，原料（光气）有剧毒，副产大量HCI等缺点，因而限制了该法的进一步发展.醇钠法和酯交换法［2，3］在我国尚不具备工业化开发的条件.甲醇氧化羰基合成DMC的方法由于具有反应条件温和、对设备无腐蚀等优点而成为DMC合成的新方法［4，5］，其反应式为1.1催化剂的制备负载于γ-Al2O3载体的铜催化剂的制备与负载于活性炭载体的铜催化剂的制备方法相同，采用等体积浸渍法制备催化剂.用CuCl2的乙醇溶液以等体积浸渍法浸渍，于100℃N2气氛中焙烧3h.待冷却到室温后用氢氧化钠水溶液以等体积浸渍法浸渍，于300℃N2气氛中焙烧 3h，得到含铜量OH/Cu摩尔比为1.0的催化剂，编号记为Cu（9.0）/Al2O3（1.0T300）.1.2 原位红外实验将催化剂与KBr（或γ-Al2O3）以一定比例混合后，压成直径为12mm、厚约0.1mm的催化剂薄片，置于快速应答的原位红外池中.原位红外实验装置如图1所示.原位红外反应池连接在一套加压反应装置中，使用高压四通阀进行气体的切换，利用气体夹带将甲醇带入原位红外反应池.用PE System FT-IR仪实现原位红外池中催化剂表面物种的特征红外吸收峰的快速应答.分辨率为4cm-1，扫描次数20～50次.原位红外池操作压力为0.7MPa，反应温度130℃.2.1 催化剂的活性测定结果在加压微反实验装置上，在相同反应条件下，对催化剂 Cu（9.0）/C（1.0T300）和 Cu（9.0）/Al2O3（1. 0T300）进行活性测定.实验结果见表1.表1的实验数据表明，负载于γ-Al2O3载体的铜催化剂的反应活性与负载于活性炭载体的铜催化剂相比，甲醇的转化率和DMC选择性、转化数均下降.2.2 负载于氧化铝的铜催化剂的原位红外实验研究由于活性炭载体的红外透过率低，且在催化剂制片时要加入大量的KBr，导致原位红外实验中未能得到有关催化反应的信息，因此重点对负载于氧化铝的铜催化剂进行了原位红外实验研究.将催化剂Cu（9.0）/Al2O3（1.0T300）与氧化铝载体按重量比1з2的比例混合，仔细研磨粉碎，压成透光性良好的薄片，置于原位红外反应池中.在氮气气氛吹扫下，将反应池温度以5℃/min的升温速率升温至200℃，停留10min，然后降温至130℃，目的是清洁催化剂表面.然后切换各种气体进行原位吸附的原位反应的研究.2.2.1 O2在催化剂上的吸附将催化剂片在氮气气氛下依上述方法处理后，切入氧气，考察氧在催化剂表面的吸附情况，结果如图2所示.从图2中可以看到，随着吸附时间的增加，谱峰1 292 cm-1的强度逐渐增加，而谱峰1 186cm-1基本不变化.李灿等人［6，7］曾报道O2在真空处理的CeO2上吸附时极易形成吸附物种，其红外特征谱为2 237其中峰锐而强，归属为的O—O伸缩振动频率一般较弱，归属为的倍频.在NiO催化剂［8］的红外吸收峰为1 140和催化剂上［9］物种的红外吸收波数为范围.L.Andrews等人［10］研究了惰性气体基质中的O2-物种，其红外吸收波数为1 097cm-1.以同样的条件考察O2在Al2O3表面的吸附情况，发现谱峰1 186 cm-1，而谱峰1 292 cm-1未出现.因此谱峰1 186 cm-1可以归属于O2在Al2O3载体上的吸附峰，而波数1 292 cm-1为O2在催化剂活性组分上的吸附位.Christe等人研究认为固态状态下O-Cl的伸缩振动峰为1 290 cm-1.根据这些研究结果，谱峰1 292 cm-1可归属于氧在催化剂活性组分上以双氧形式吸附，由于卤素C1的强电负性进一步离解O2在催化剂表面产生O—Cl键的伸缩振动峰.2.2.2 CO在催化剂上的吸附将催化剂片在氮气气氛下依上述的方法处理以后，切入一氧化碳考察一氧化碳在催化剂表面的吸附情况.结果在实验过程中未得到任何表明CO在催化剂表面吸附的信息，可参考图3中先引入CO时的红外谱图.再次切换为氮气进行吹扫，也未得到任何信息，其中有两种可能性：1）CO在催化剂表面的吸附可能需要与其它分子进行共吸附；2）CO在催化剂表面弱吸附，由于气相一氧化碳的影响未能观察到吸附状态的一氧化碳的红外伸缩振动峰.2.2.3 CO与O2在催化剂上的共吸附催化剂在氮气气氛下处理以后，先切入CO气体，然后切入O2考察CO与O2同时吸附的情况.结果如图3所示.由图3可见，引入CO后，无明显的吸附峰出现，当引入O2后，发现除氧在催化剂表面吸附产生的红外吸收峰1 292 cm-1外，同时在1585cm-1和1418cm-1处出现吸附峰.说明O2与CO在该催化剂表面存在共吸附.前人研究指出［11］CO+O2在不同催化剂表面的吸附可分为图4所示的3种情况.其中结构Ⅰ的C‖O非对称伸缩振动峰和结构Ⅱ的C‖O对称伸缩振动峰其红外吸收特征谱带分别为1540、1390cm-1，而属于双齿配位碳酸盐Ⅲ的C‖O伸缩振动峰和非对称伸缩振动峰其红外吸收特征谱带为 1560cm-1和1330cm-1.根据以上研究结果，和得到的有关氧在催化剂表面是以双氧方式吸附的结论，认为CO与O2在催化剂表面的共吸附是以图4中结构Ⅲ的方式存在的，谱峰1585cm-1和谱峰1418cm-1分别归属于所形成的双齿配位碳酸盐Ⅲ的C‖O的伸缩振动峰和非对称伸缩振峰.2.2.4 甲醇在催化剂上的吸附将催化剂片在氮气气氛下处理以后，用氮气夹带甲醇进入原位红外反应池，考察甲醇在催化剂表面的吸附情况.图5为甲醇吸附后的红外谱图.可以发现谱峰1111cm-1的强度随时间增加逐渐增大，这应归属于表面甲氧基的C—O键吸收峰［12-14］.1056和1032cm-1为气相甲醇的振动峰.降低系统压力并用氮气吹扫后，气相甲醇的伸缩振动峰仍存在，但表面甲氧基的C—O键伸缩振动峰消失，表明高压有利于甲醇在催化剂表面吸附产生甲氧基. 2.2.5 甲醇氧化羰基合成碳酸二甲酯反应的原位红外研究图6为甲醇氧化羰基合成碳酸二甲酯反应的原位红外谱图.甲醇由一氧化碳和氧气的混合气带入原位反应池.由图6可以看出随着反应进行，碳酸二甲酯的特征峰1771cm-1（C‖O的伸缩振动峰）出现，一些表面中间物的特征红外峰，参考有关资料一一认定，结果列于表2.根据原位红外实验所得的结果，推测甲醇氧化羰基合成碳酸二甲酯的反应机理为：1）甲醇在催化剂表面吸附产生甲氧基；2）CO在催化剂表面为弱吸附，CO的插入反应，使表面甲氧基与CO反应生成碳酸二甲酯3）分子氧在催化剂活性组分表面吸附后，进一步离解.甲氧基可以进一步与离解的氧作用生成副产物CO2和水，历程如下：4）CO可与催化剂表面离解的氧相结合生成二氧化碳一氧化碳的插入反应是生成碳酸二甲酯的途径，高压有利于甲醇在催化剂表面吸附产生甲氧基，而甲氧基的深度氧化导致副产物CO2和H2O的产生，因此在反应过程中需恰当地控制反应物中氧的浓度，防止甲醇的深度氧化.1）O2在催化剂活性组分上吸附，并进一步发生离解.CO在催化剂表面的吸附为弱吸附，甲醇在催化剂表面吸附产生甲氧基，高压有利于甲醇在催化剂表面吸附产生甲氧基.2）一氧化碳的插入反应是生成碳酸二甲酯的途径.3）在原位反应过程中，表面中间物==的存在，表明甲氧基与离解的氧进一步作用可生成副产物CO2和H2O.【相关文献】［1］赵天生，韩怡卓，孙予罕，碳酸二甲酯合成方法的研究进展［J］，石油化工，1998，27（6）：457-462.［2］方云进，肖文德，绿色工艺的原料—碳酸二甲酯［J］，化学通报2000，63（9）：19-29. ［3］ Jo Ann Gilpin，Albert H Emmons.Synthesis of dimethyl carbonate［P］.US：3803201，1974.［4］ Romano Ugo，Tesei Renato，Cipriani Gioacchino，et at.Method for the preparation of esters of carbonic acid［P］.US：4218391，1979.［5］ Short Glyn David，Spencer Michael Staines.A process for the production of di-alkyl carbonate［P］.EP：134668，1985.［6］ Li C，Domen K，Maruya K，et al.IR spectra of dioxygen species formed on CeO2at room temperarure［J］.J Chem Soc Chem Commum，1988，23：1541-1545.［7］李灿，辛勤，郭燮贤.乙烯和乙烷在CeO2上温和条件下表面氧化反应的原位FT-IR研究［J］.分子催化，1991，5（3）：193-201.［8］ Tsyganenko A A，Rodionova TA，Filimonov VN.Infrared studies of low temperature adsorption of oxygen on NiO surface［J］.React Kinet Catal Lett，1979，11（2）：113-117.［9］ Zecchina A，Spoto G，Coluccia S.Surface dioxygen adducts on Mg-CoO solid solutions：Analogy with cobalt-based homogeneous oxygen carriers［J］.J Mol Catal，1982，14；351-354.［10］ Andrews L，Smardzewski R R.Argon matrix raman spectrum of LiO2：bonding in the M+molecules and the ionic model［J］. J Chem Phys，1973，58（6），2258-2261. ［11］ Eischens R P，Pliskin W A，Advance in Catalysis［M］.New York：Academic Press Inc.1957 IX.［12］黄伟，阴丽华，王常有.Cu-Co催化剂催化CO2合成醇的原位红外表征及其反应机理［J］.分子催化，1995，9（1）：37-42.［13］ Clarke D B，Bell A T，An infrared study of methanol synthesis from CO2on clean and Potassium-promoted Cu/SiO2［J］.J Catal.1995 154（2）：314-328.［14］ Schild C，Wokaun A，Baiker A.On the mechanism of CO and CO2hydrogenation reactions on zirconia-supported catalysts：a diffuse reflectance FTIR study part I：Identification of surface species and mechanism reactions on palladium/zirconia catalysts［J］.J Mol Catal，1990，63（2）：223-242.［15］许世科，刘金尧，朱起明.低碳醇合成反应的中间物及其衍变动态研究［J］.分子催化，1992，6（1）：38-43.。

二氧化碳加氢逆水汽变换反应的研究进展

化工进展CHEMICAL INDUSTRY AND ENGINEERING PROGRESS 2016年第35卷第10期·3180·二氧化碳加氢逆水汽变换反应的研究进展徐海成，戈亮（海军装备部装备采购中心，北京 100071）摘要：化石能源的热能利用产生大量的CO2，破坏了地球生态系统中的碳平衡，严重威胁人类的可持续发展。

利用可再生能源产生的氢气与CO2通过逆水汽变换（RWGS）反应产生CO可以作为F-T合成的主要原料，有望部分替代煤制合成气路线，与此同时还是解决“弃风”、“弃光”等问题的有效方案之一。

本文归纳了近年来研究RWGS反应所使用的催化体系，包括负载型金属催化剂、复合氧化物催化剂和过渡金属碳化物催化剂；介绍了在不同催化剂上RWGS反应的反应机理。

重点分析了影响CO2加氢制CO选择性的因素，包括催化剂活性组分的颗粒尺寸、载体效应、助剂、反应条件等以及如何提高催化剂的高温稳定性。

总结了RWGS反应在不同催化体系上的优缺点，可为进一步设计高性能的RWGS反应催化剂提供借鉴。

关键词：二氧化碳；加氢；逆水汽变换；催化剂中图分类号：TQ 032.4 文献标志码：A 文章编号：1000–6613（2016）10–3180–10DOI：10.16085/j.issn.1000-6613.2016.10.023Progress on the catalytic hydrogenation of CO2via reverse water gas shiftreactionXU Haicheng，GE Liang（Naval Equipment Procurement Center，Beijing 100071，China）Abstract：The excess emission of CO2 through the combustion of fossil fuels，have triggered a severe crisis to the carbon balance in the earth’s ecological system and thus threatened the sustainable development of our economy and society. An attractive way to mitigate the problem is to utilize CO2 and the excess H2 generated from renewable energy sources，to produce CO via the reverse water gas shift reaction (RWGS)，which can be used as feedstock in the successive Fischer-Tropsch synthesis，and therefore could replace partially the coal-to-syngas route. Meanwhile，this strategy could provide a reference to the abandoned wind and light energy issues. In this review，the catalytic systems for the study of RWGS reaction in recent years were summarized，including supported metal catalysts，metal oxide catalysts and transition metal carbide catalysts. We also introduced the reaction mechanisms of RWGS reaction over different types of catalysts. The factors affecting the selectivity of CO2 hydrogenation to CO were analyzed，mainly including the particle size of active component，supports，promoters，reaction conditions，as well as the strategy to improve the catalyst stability when exposed toa high temperature environment. Moreover，the advantages and disadvantages of different catalysts inthe RWGS reaction were discussed，which can provide a guidance for the development of high-performance RWGS catalysts with increases CO selectivity and life.Key words：carbon dioxide；hydrogenation；reverse water gas shift reaction；catalyst收稿日期：2016-01-19；修改稿日期：2016-03-23。

SiO2负载CeO2催化氧化芴制备芴酮

2017年第36卷第6期 CHEMICAL INDUSTRY AND ENGINEERING PROGRESS·2183·化工进展SiO 2负载CeO 2催化氧化芴制备芴酮王季茹1，2，郭少青3，康荷菲1，2，宋毛宁4，赵亮富1（1中国科学院山西煤炭化学研究所，应用催化与绿色化工实验室，山西太原 030001；2中国科学院大学，北京 100049；3太原科技大学环境与安全学院，山西太原030024；4太原理工大学化学与化工学院，山西太原 030024）摘要：由于在工业上液相催化氧化法制备芴酮无法连续生产以及产生大量废水的缺点，本文以SiO 2为载体，分别采用浸渍法、沉淀法和溶胶凝胶法制备了CeO 2/SiO 2催化剂，用于空气气相催化氧化芴制备芴酮。

通过X 射线衍射（XRD ）、氢气程序升温还原（H 2-TPR ）、二氧化碳程序升温脱附（CO 2-TPD ）、高分辨率透射电子显微镜（HRTEM ）等手段对所制备的催化剂进行表征，考察了不同方法制备的CeO 2/SiO 2对芴选择性催化氧化的影响，结果表明芴在CeO 2活性组分上的转化率与CeO 2还原温度、表面氧空位浓度以及表面氧浓度有关。

芴酮在CeO 2活性组分上的选择性与CeO 2表面碱量以及碱性有关。

在3种制备方法中，采用溶胶凝胶法制备的CeO 2/SiO 2分散性最好，催化活性最佳，在反应温度370℃、质量空速0.5h –1、气液比250时，芴的转化率可达到83%，选择性可达到60%。

关键词：二氧化硅；催化剂；固定床；氧化；制备中图分类号：TQ244.2 文献标志码：A 文章编号：1000–6613（2017）06–2183–07 DOI ：10.16085/j.issn.1000-6613.2017.06.031Aerobic oxidation of 9H-fluorene to 9-fluorenone using SiO 2-supportedCeO 2 catalystWANG Jiru 1，2，GUO Shaoqing 3，KANG Hefei 1，2，SONG Maoning 4，ZHAO Liangfu 1（1Laboratory of Applied Catalysis and Green Chemical Engineering ，Institute of Coal Chemistry ，Chinese Academy ofSciences ，Taiyuan 030001，Shanxi ，China ；2University of Chinese Academy of Sciences ，Beijing 100049，China ；3School of Environment and Safe ，Taiyuan University of Science and Technology ，Taiyuan 030024，Shanxi ，China ；4College ofChemistry and Chemical Engineering ，Taiyuan University of Technology ，Taiyuan 030024，Shanxi ，China ）Abstract: The catalytic liquid-phase oxidation of fluorene to 9-fluorenone is limited by the difficultiesof continuous production for industrialization and waste water generated in production. CeO 2/SiO 2 catalysts were prepared by impregnation method ，precipitation method and sol-gel method ，respectively. Their activities for oxidation of fluorene to 9-fluorenones were investigated. The catalysts were characterized by XRD ，H 2-TPR ，CO 2-TPD and HRTEM. The catalytic performances of catalysts for oxidation of fluorene to 9-fluorenone were examined. The experimental results indicate that the conversion of fluorene on CeO 2 is determined by the reduction temperature of CeO 2，the concentration of oxygen vacancies and the concentration of surface oxygen. The selectivity of fluorenone on CeO 2 is related to the amount and intensity of surface basicity. The catalysts prepared by the sol-gel method have第一作者：王季茹（1991—），女，硕士研究生，主要研究煤焦油精细化学品加工方向。

沉淀法制备介孔二氧化铈

ＰｒｅｐａｒａｔｉｏｎｏｆｍｅｓｏｐｏｒｏｕｓＣｅＯ２ｂｙｐｒｅｃｉｐｉｔａｔｉｏｎｍｅｔｈｏｄ
ＴＡＮＮｉｎｇ－ｈｕｉ，ＬＩＵＹｉｎｇ－ｌｉａｎｇ，ＸＵＬｉ
（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｓｔｒｙ，ＮａｎｏｃｈｅｍｉｓｔｒｙＩｎｓｔｉｔｕｔｅ，ＪｉｎａｎＵｎｉｖｅｒｓｉｔｙ，Ｇｕａｎｇｚｈｏｕ５１０６３２，Ｃｈｉｎａ）
图４反应物配比与介孔ＣｅＯ２比表面积的关系
图５反映了反应温度与介孔ＣｅＯ２比表面积的关系，如图所示，反应在８０ ℃进行最为合适，温度过高或过低都不利于反应的进行．这是因为：在沉淀
图６氨水的量对介孔ＣｅＯ２比表面积的影响
溶液的ｐＨ值通常对介孔材料的比表面积产生
反应中，温度会对晶粒的生成和长大有一定影响．当温度较低时，过饱和度较大，成核的速度快，一般得到细小的颗粒，颗粒太小，则难以过滤和洗涤，容易团聚而形成更大的颗粒，升高温度则能使沉淀反应的反应常数增大，反应速率加快，同时也使布朗运动加速，从而使质点间碰撞的频率增大［１５］．
图５反应温度与介孔ＣｅＯ２比表面积的关系
反应物配比与介孔ＣｅＯ２比表面积的关系如图４，从图中可以看出，当二乙烯三胺与硫酸高铈的摩尔比为２ ∶１时，介孔ＣｅＯ２的比表面积最大，高达１１７ｍ２／ｇ，这是因为：当表面活性剂浓度增大时，将导致溶液中表面活性剂胶束增多，有利于介孔ＣｅＯ２的形成；表面活性剂或无机物的浓度太大时，一方面会影响无机物和表面活性剂的有效结合；另一方面会堵塞介孔ＣｅＯ２的孔道，从而使介孔ＣｅＯ２的比表面积降低．
图１样品的低角度Ｘ线衍射图
图２样品的ＸＲＤ图谱

硫酸酸化膨润土负载Au及Au-Ce催化剂的制备及其催化性能

硫酸酸化膨润土负载Au及Au-Ce催化剂的制备及其催化性能张荣斌;姚刘晶;张宁;蔡建信;敖志勇;居艳【摘要】采用硫酸对膨润土(Ben)进行改性处理,通过沉积-沉淀法(DP)制备活化后膨润土负载的金催化剂,以CO氧化作为探针反应对催化剂的催化性能进行研究.采用CTAB修饰载体表面并添加Ce作为助剂制备Au-Ce催化剂,并用BET、XRD、ICP和TPD等对催化剂进行了表征.结果表明:经过简单酸处理后的膨润土比表面积和孔体积有了大幅度的提高,质量分数30％的硫酸对膨润土的改性效果更好.以硫酸酸化膨润土作为载体,Au-Ce复合催化剂相比Au催化剂性能有较大提高.%The bentonite was modified with H2SO4 in this paper. The Au catalysts supported on acid-activated bentonite had been prepared by the methods of deposition-precipitation. CO oxidation was used as a probe reaction to characterize the catalytic performance. The surface of acid-activated bentonite was modified by CTAB, and then adding Ce as assistant to prepare Au-Ce catalyst. The samples were characterized by BET,XRD and TPD. The results showed that the surface area and pore volume had a substantial improvement. Ω(H2SO4) =30% can modify bentonite better than others. When using the bentontie activated by H2SO4 as supporter, the activity of Au-Ce catalyst was better than that of Au catalyst.【期刊名称】《南昌大学学报（工科版）》【年(卷),期】2011(033)003【总页数】5页(P205-209)【关键词】酸化膨润土;Au;Au-Ce;催化性能【作者】张荣斌;姚刘晶;张宁;蔡建信;敖志勇;居艳【作者单位】南昌大学化学系,江西南昌330031;南昌大学化学系,江西南昌330031;南昌大学化学系,江西南昌330031;南昌大学化学系,江西南昌330031;南昌大学化学系,江西南昌330031;南昌大学化学系,江西南昌330031【正文语种】中文【中图分类】O643.3自从Haruta等［1-2］发现高分散的Au催化剂对于CO低温完全氧化反应具有很高催化活性后，Au催化剂才成为人们的研究热点。

金属-载体相互作用对多相催化反应的影响

金属-载体相互作用对多相催化反应的影响王珍【摘要】多相催化反应体系中,金属催化剂与载体之间通过电荷转移、物质输运等机理产生相互作用.这种金属-载体相互作用对催化反应性能的影响具有多样性,既可以抑制或促进某个反应的发生,造成选择性的不同;也可以在反应中诱导活性中心的生成,提高反应活性,因此在实际研究中需要对特定催化体系进行充分了解,并加以有效利用.【期刊名称】《广州化工》【年(卷),期】2013(041)024【总页数】4页(P20-23)【关键词】金属-载体相互作用;SMSI;电荷转移;物质输运【作者】王珍【作者单位】神华准能资源综合开发有限公司,内蒙古鄂尔多斯010300【正文语种】中文【中图分类】O643.32+21 金属－载体相互作用 (SMSI)概念在催化科学发展的初期，催化剂载体一直被认为是惰性的，只起到支撑、分散活性组分的简单作用，不会影响到催化剂的性能。

但随着研究的深入，人们逐渐认识到，催化剂性能通常会不可避免地受到所用载体的影响［1－2］。

Tauster等［3－5］于1978年首先提出金属－载体强相互作用 (Strong Metal－Support Interaction，SMSI)的概念，他们研究了TiO2载体上负载的第八族贵金属催化剂(Pt、Pd、Ir、Ru、Rh等)对CO和H2的吸附能力，实验发现低温(473 K)氢气还原对气体吸附没有影响，而高温(＞700 K)还原之后，CO和H在金属表面的吸附几乎为零，表明高温还原降低了金属对气体的吸附能力。

利用X射线衍射、电镜等测试分析，首先排除了金属烧结、载体包覆、还原不完全等因素的影响，Tauster等由此提出金属与载体之间可能存在着某种相互作用，从而在一定程度上减弱了气体的吸附。

随后，他们将此项研究拓展到十余种氧化物载体上，发现这种抑制效应在不同载体负载的金属催化剂上表现不同，在一些可被还原的氧化物载体上作用比较明显，如 TiO2、V2O5、Nb2O5和Ta2O5，而且这种吸附性能随处理温度的变化是可逆的。

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Gold catalysts supported on CeO2and CeO2–Al2O3forNO x reduction by COL.Ilieva a,*,G.Pantaleo b,I.Ivanov a,A.M.Venezia c,D.Andreeva aa Institute of Catalysis,BAS,‘‘Acad.G.Bonchev’’Str.bl.11,1113Soﬁa,Bulgariab Dipart.Chim.Inorg.e Analitica,Universita`di Palermo,V.le delle Scienze,Parco D’Orleans,I-90128Palermo,Italyc Istituto per lo Studio di Materiali Nanostrutturati,CNR,Via Ugo La Malfa,I-90146Palermo,ItalyReceived30September2005;received in revised form15December2005;accepted23December2005Available online23February2006AbstractThe reduction of NO x by CO was studied over gold catalyst supported on ceria and ceria–alumina.The mixed supports with different CeO2/ Al2O3ratios were prepared by co-precipitation.The catalysts were characterized by means of XRD,TPR,XPS and Raman spectroscopy.The addition of alumina led to a slight enlargement of the gold particles,while the ceria particle size was decreased.Deeper oxygen vacancies formation in the presence of alumina was detected by TPR,XPS and Raman spectroscopy,compared to the pure ceria support.The samples exhibited a high and stable activity and100%selectivity towards N2was reached at2008C.#2006Published by Elsevier B.V.Keywords:Gold;Ceria;Ceria–alumina;NO x reduction by CO;XRD;TPR;XPS;Raman spectroscopy1.IntroductionCatalysis is a key technology providing an effective solution of many environmental problems,and the most important one among them is the removal of NO x.This is a major pollutant in the exhaust gases of various combustion processes.A widely applied method for NO x removal is the catalytic reduction, using different reducing agents such as CO,hydrogen or hydrocarbons.In practice,there are two different sets of conditions for the catalytic reduction of exhaust gases produced,at the stoichiometric air-to-fuel ratio and under oxygen rich exhaust gases conditions.Diesel and lean-burn gasoline engines operate at high air-to-fuel ratios,as oxygen is fed in excess.Currently,the selective catalytic reduction is one possible solution of the NO x problem;another one is the NO x storage concept recently developed by Toyota[1].The operating conditions of internal combustion engines,equipped with three-way catalysts(TWCs)areﬁxed around the stoichiometric air-to-fuel ratio,where the amount of supplied air is maintained on a level just sufﬁcient for the complete combustion of the fuel.The supported noble metals—rhodium,platinum or palladium are currently used as the active components in the commercial TWCs.Oxides like ceria are used as supports,which enable widening of the operating air/ fuel window,due to their high oxygen storage capacity(OSC). The efforts to optimize the performance of TWCs are mainly related to improvement of the OSC and catalytic stability under normal operating conditions.Recently,gold has also been reported as a catalyst for NO reduction with H2,CO or hydrocarbons[2–5].Gold is not able to match the high temperature performance of the platinum group metal(PGM) TWCs;however,a high activity during the catalytic operation at relatively low temperatures is characteristic of supported gold catalysts.To enhance the performance of the TWCs at low temperatures is still a challenging problem.It is needed in order to decrease the emissions immediately following the start-up of the vehicle’s engine(‘‘cold start’’phase).The present study is focused on the NO x reduction by CO over gold catalysts supported on CeO2and CeO2–Al2O3.The presence of alumina is aimed,on the one hand,to improve the gold and ceria dispersion and stability and,on the other hand,to study the effect of oxygen vacancies formation due to Al3+ions on the catalytic activity.An interestingﬁnding in the literature [6]is the doping of CeO2with metal(3+)oxides soluble in it, causing the creation of the so-called extrinsic oxygen vacancies in the mixed oxide support.The extrinsic oxygen vacancy/locate/apcatb *Corresponding author.Tel.:+35929792572;fax:+35929712967.E-mail address:luilieva@ic.bas.bg(L.Ilieva).0926-3373/$–see front matter#2006Published by Elsevier B.V.formation caused by the presence of Al3+in ceria structure has already been conﬁrmed by some of us in the case of gold/ceria–alumina catalyst synthesized by a method different from that in the present study[7].These vacancies are different from the intrinsic oxygen vacancies,formed by the reduction of Ce4+to Ce3+and removal of oxygen leading to an improvement of the oxygen transport characteristics.The prerequisite for the enhancement of the intrinsic oxygen vacancies is the presence of a noble metal,which promotes the redox behaviour of ceria. In the review by Trovarelli[6]it was shown that oxygen vacancies are associated with reduced ceria in the proximity of platinum metal particles.These have been supposed by many researchers as active sites for NO and CO conversion mainly due to their effective role in promoting NO dissociation.In the present study the gold-based catalysts were characterised by several techniques—XRD,Raman,XPS,TPR.The aim was to look for a relationship between the structural features and catalytic behaviour and especially to clarify the role of alumina for the catalytic activity and stability in NO x reduction by CO.2.Experimental2.1.Sample preparationA series of three catalysts was studied:gold supported on ceria(AuCe);Au supported on ceria–alumina mixed support containing10wt.%alumina in ceria(AuCeAl10)and20wt.% alumina in ceria(AuCeAl20).The ceria–alumina mixed oxide supports were prepared by co-precipitation of the correspond-ing nitrates at a desired ratio with a solution of K2CO3.The gold was then loaded by deposition–precipitation under full control of the synthesis parameters(pH,temperature,stirring speed, etc.).Afterﬁltering and carefully washing,the samples were dried and calcined in air at4008C for2h.The amount of gold was determined by gravimetric analysis.The initial salts used HAuCl4Á3H2O,Ce(NO3)3Á6H2O,Al(NO3)3Á9H2O and K2CO3 were of analytical grade purity.2.2.Sample characterizationThe BET surface area of the samples was determined on a Micromeritics‘Flow Sorb II-2300’device with30%N2,70%He mixture at atmospheric pressure and N2boiling temperature.The X-ray diffraction patterns were obtained on a DRON-3 automatic powder diffractometer,using Cu K a1radiation.The crystal size of gold,ceria and alumina particles was calculated on the basis of the peak broadening using‘‘Powder Cell’’program.The program gives the possibility ofﬁtting the expe-rimental XRD spectra,based on the corresponding theoretical structures.The instrumental broadening effect was taken into consideration.The XRD proﬁles were approximated by Lorentz functions.The Raman spectra were recorded using a SPEX1403 double spectrometer with a photomultiplier,working in the photon counting mode.The488nm line of an Ar+ion laser was used for excitation.The laser power on the samples was60mW.measurements by increasing the size of the focused laser spot. The optimal conditions were chosen,checking the intensity, position and the width of the464cmÀ1Raman line of CeO2. The spectral slit width was4cmÀ1.The X-ray photoelectron spectroscopy analyses were performed with a VG Microtech ESCA3000Multilab, equipped with a dual Mg/Al anode.The spectra were excited by a non-monochromatized Mg K a source(1254.4eV) operated at14kV and15mA.The analyzer operated in the constant analyzer energy(CAE)mode.Pass energy of20eV was used across the hemispheres for the individual peak energy regions.The survey spectra were measured at50eV pass energy.The samples,analyzed as prepared,were pelletized and then attached on a double-sided adhesive tape.The pressure in the analysis chamber was in the range of10À8Torr during the data collection process.The binding energies of the support electrons were referenced with respect to the energy of the C1s peak at285.1eV arising from adventitious carbon.The peaks wereﬁtted by a non-linear least squareﬁtting program using a properly weighed sum of Lorentzian and Gaussian component curves after background subtraction according to Shirley and Sherwood[8,9].The binding energy values are given with a precision ofÆ0.15eV.The surface atomic concentration was evaluated based on peak areas using appropriate sensitivity factors set in the VG software.The TPR measurements were carried out by means of an apparatus described elsewhere[10].A cooling trap(À408C) for removing the water formed during reduction was mounted in the gas line prior to the thermal conductivity detector.A hydrogen–argon mixture(10%H2),dried over a molecular sieve5A(À408C),was used to reduce the samples at aﬂow rate of24ml minÀ1.The temperature was linearly raised at a rate of158minÀ1.The sample mass charged was0.05g.It was selected based on the criterion proposed by Monti and Baiker[11].The hydrogen consumption during the reduction processes was calculated using a previous calibration of the thermo-conductivity detector.2.3.Catalytic activity measurementsThe catalytic activity in NO x reduction by CO was tested using a quartz glass U-shaped reactor,equipped with a temperature programmed controller.All the reactants and products were monitored by IR and UV analysers.The MS analysis of the reaction products was also performed using on-line Pffeffer quadrupole mass spectrometer and Balzers Quadstar software.The steady-state tests were made upon increasing the reaction temperature,waiting at each tempera-ture for a constant conversion value.The catalysts were tested in a wide temperature interval charging0.05g of the sample at aﬂow rate of50ml minÀ1corresponding to WHSV of 60,000ml gÀ1h.The catalytic behaviour of AuCe,AuCeAl10and AuCeAl20 samples pretreated using5%H2in helium for30min at1208C was compared.Two series of experiments were performed using3000or2000ppm H2feed concentration in addition toL.Ilieva et al./Applied Catalysis B:Environmental65(2006)101–109 1023.Results3.1.Sample characterizationThe XRD diffraction patterns are represented in Fig.1.The chemical composition,BET surface area and the average size of gold,ceria and alumina particles before and after the catalytic test,estimated by XRD,are shown in Table1.The addition of 10wt.%alumina did not inﬂuence the average size of ceria particles.The increase of Al content to20wt.%results in a decrease of the particle size of ceria,which remains unchanged in the spent catalyst(4nm for the fresh and spent AuCeAl20 compared to7nm for the fresh and,respectively,14nm for the spent AuCe sample).Moreover it is seen that the presence of alumina leads to an increase of the average size of gold particles in the fresh samples but it stabilizes them during the catalytic test.A strong line of CeO2,characteristic ofﬂuorite structure materials,is present in the Raman spectra.In the presence of alumina the main line of ceria was shifted.To obtain the information about oxygen vacancies creation,the full width at half maximum(FWHM)of the main line of ceria was calculated.The data are represented in Table2.An increase of the FWHM in the presence of alumina is clearly seen.The gold loading leads to an additional increase in this value.Fig.2represents the experimentally measured andﬁtted Au 4f spectra of AuCe and AuCeAl catalysts before and after catalytic test are represented.Fig.3illustrates the Ce3d spectra of gold on pure ceria and gold on20%alumina doped ceria.The XPS data in terms of the Au4f7/2,O1s and Ce3d5/2binding energies and the corresponding Au atomic percentage are summarized in Table3.A binding energy at84.6Æ0.2eV,typical of metallic gold was found in all samples.As it is seen in the spectra another component at86.3Æ0.3eV typical of ionic gold is also present.After catalytic reaction the ionic component decreases in all the samples.The presence of alumina seems to determine a decrease of the FWHM of each gold component from2.2eV in the pure ceria supported catalyst to1.8eV in the AuCeAl20 sample.A lower differential charging of the gold particles could be a possible explanation.The O1s spectra contain three components:one at about529.6Æ0.2eV typical of the lattice oxygen of CeO2,another one at about531.5Æ0.1eV typical of hydroxide species and the third one at533.4Æ0.3eV due to the presence of Ce3+surface defects[12,13].The increase of the O1s component at531.5eV with the alumina content in the mixed oxide samples is due to the presence of alumina characterized by an O1s peak at this energy value.No signiﬁcant modiﬁcation of the oxygen spectra occurs after catalytic operation.The experimentally measured Ce3d spectra of the pure ceria and those of the20%alumina doped ceria catalysts,shown in Fig.3,have beenﬁtted with several components arising from the multiplicity ofﬁnal states reached during the Ce3d photoionization process[12].The Ce3d spectrum of the AuCe catalyst is typical of the pure CeO2.It should be noted that the pure ceria always contains a small percentage(about3%)of Ce(III)oxide characterized by the presence of peaks,generally indicated by V0and U0,attributed to the Ce3d5/2and Ce3d3/2components of Ce(III).Moreover some reduction is generally induced by the exposure to X rays [13].It has to be mentioned also that such Ce(III)related components increase upon increasing the alumina content in the paring the XPS derived surface Al/Ce atomicL.Ilieva et al./Applied Catalysis B:Environmental65(2006)101–109103Fig.1.X-ray diffraction patterns of gold-containing samples.Table2Full width at half maximum(FWHM)of the CeO2line in the Raman spectra of the non-promoted and promoted by gold catalystsCatalysts CeO2line position(cmÀ1)FWHM(cmÀ1) AuCe46213.5AuCeAl1045448.5AuCeAl2045565.2CeO246412.0CeAl1045946.4CeAl2045565.1Table1Chemical composition,BET surface area and the average size of gold,ceria and alumina particlesCatalyst Chemical composition(wt.%)S BET(m2gÀ1)Average size(nm)Au CeO2Al2O3Au Au b CeO2CeO2b Al2O3 AuCe 3.097.0–108<5.0a9.37.014.0–AuCeAl10 2.887.59.71037.07.07.07.08.0 AuCeAl20 2.977.719.41408.07.0 4.0 4.0 5.0a Estimated by HRTEM.ratios with the corresponding bulk ratios a surface segregation of alumina over ceria is established.The segregation is founded to a large extent in the AuCeAl20sample.The alumina enriched ceria surface is in agreement with the observation of energetically favourable(3+)ions migration to the surface,observed in the case of the cubicﬂuorite structure[14]. Moreover a decrease of the surface gold amount is observed in the alumina doped samples,in agreement with the larger particle size.However a decrease of this concentration after catalytic reaction is observed only in the absence of alumina. This result is in accordance with the XRD determined particle size.Indeed alumina prevents the sintering of gold.The TPR proﬁles of AuCe,AuCeAl10and AuCeAl20 catalysts are shown in Fig.4.The proﬁles of the corresponding supports without gold are shown in the inset.The TPR pattern of pure ceria contains two peaks:a low temperature(LT)peak at T max=5108C assigned to the surface layer reduction and a high temperature(HT)peak at T max=8558C connected to the bulk reduction of ceria[15].Only one peak was registered in the range up to8008C in the spectra of both ceria–alumina supports.The peak maximum in the spectrum of CeAl10sample was located at5358C and the intensity of this peak is higher compared to that of pure ceria.In the case of CeAl20sample a complex peak having the highest intensity was recorded with a maximum at about5508C.This behaviour could be connected with the enhanced reduction of deeper ceria layers in the presence of alumina.In the case of gold containing samples,the peaks assigned to ceria surface layer reduction were locatedL.Ilieva et al./Applied Catalysis B:Environmental65(2006)101–109104Fig.2.Experimental andﬁtted Au4f spectra of fresh and spent AuCe,AuCeAl10and AuCeAl20samples.Fig.3.Experimental andﬁtted Ce3d spectra of fresh AuCe and AuCeAl20samples.Table3Au4f7/2,O1s and Ce3d5/2binding energies of the studied catalysts along with the component percentagesSample Au4f7/2(eV)O1s(eV)Au(at%)Al/Ce Ce3d5/2(eV) Fresh(%)Spent(%)Fresh(%)Spent(%)Fresh Spent Fresh(%)Spent(%) AuCe84.8(72)84.6(89)529.5(75)529.0(70)0.50.4881.6(97)881.9(97)86.32(28)85.8(11)531.5(20)531.1(27)884.4(3)884.6(3)533.7(5)532.7(3)AuCeAl1084.5(85)84.3(95)529.4(62)529.6(59)0.40.4881.9(94)881.9(94)86.5(15)86.0(5)531.4(30)531.6(29)0.640.62884.9(6)884.7(6)533.1(8)533.3(12)AuCeAl2084.5(85)84.6(80)529.8(49)529.8(49)0.30.3881.9(80)881.7(93)86.5(15)86.8(20)531.6(45)531.6(45) 2.8 2.5885.0(20)884.8(7)533.5(6)533.5(6)within the temperature interval 120–1508C.The observed signiﬁcant lowering of the temperature of ceria surface layers reduction is in agreement with the results already obtained with gold supported on ceria [16–18]and ceria–alumina synthesized by a different method of support preparation [7].Complex peaks are recorded in the HT interval.The hydrogen consumption corresponding to the ﬁrst TPR peak was calculated.The results for the gold containing catalysts and the initial supports are represented in the Table 4.The experimentally measured hydrogen consumption concern-ing the pure ceria was 16.9%of the stoichiometric amount of hydrogen for the reduction 2CeO 2+H 2!Ce 2O 3+H 2O (145.2m mol).Signiﬁcantly bigger hydrogen consumption was registered with mixed ceria–alumina supports,especially with the AuCeAl20sample.The experimental H 2consumption related to the stoichiometric amount (130.7m mol)for CeO 2reduction in the case of support with 10%alumina is 27.4%andL.Ilieva et al./Applied Catalysis B:Environmental 65(2006)101–109105Fig.4.TPR patterns of gold-containing samples.Inset—TPR patterns of pure supports.Table 4Hydrogen consumption corresponding to the ﬁrst TPR peak in the spectra of samples studied Sample Hydrogen consumption (LT peak)(m mol)Ce 24.6CeAl1035.8CeAl2050.3AuCe 23.1AuCeAl1026.4AuCeAl2028.6in the case of20%alumina in the support is43.3%,respectively (116.2m mol of H2amount needed).These results show that due to the presence of Al3+in the ceria structure,theﬁrst TPR peaks in the spectra of CeO2–Al2O3samples have to be connected not only with the ceria surface layers reduction.Sanchez and Gazquez have considered that CeO2can be reduced up to17% without changing theﬂuorite structure to the hexagonal Ce2O3 structure[19].Laachir et al.have observed that when the reduction is limited only to the surface of ceria,this leads to a 20%reduction degree[20].Based on these observations,the bulk reduction of ceria–alumina samples,leading to structural changes has to be considered.The bulk ceria reduction is increased when the amount of alumina is higher.This enhancement of ceria reduction can be connected with increased oxygen mobility in the defective ceria structure generated by the introduction of alumina.For the gold containing samples theﬁrst peaks were recorded at very low temperature and a higher OSC due to the presence of alumina was observed as well.The H2consumption associated with the LT TPR peaks was the highest for AuCeAl20catalyst.The experimental values with respect to the stoichiometric amount,neglecting any gold contribution,are as follows:15.9%in the case of AuCe,20.2and24.6%for AuCeAl10and AuCeAl20,respectively.The reduction process involves mainly a surface layer reduction,because a small amount of hydrogen is retained in ceria based on our preliminary results of TPD measurements[21].Hydrogen incorporation into the bulk has been observed as well[20]and the formation of H y CeO2Àx bronze-like species could be the reason[22].3.2.Catalytic activityThe steady-state activities at different temperatures are represented in Fig.5(3000ppm H2in the feed)and Fig.6 (2000ppm H2in the feed).The highest activity(conversion degree of NO and CO)is shown by the AuCe sample in the whole temperature range of the catalytic test and the lowest was shown of AuCeAl10sample.The differences in the catalytic activities of all the samples are larger at lower temperatures, while they decrease at high temperatures.Moreover the catalytic activity of the samples is higher when the hydrogen content in the feed is higher.It was observed with all the studied catalysts that at temperatures of high CO conversion(even 100%)the CO2formation was only65–70%.Depending on the temperature,in addition to the reduction of NO by CO to N2,L.Ilieva et al./Applied Catalysis B:Environmental65(2006)101–109106parallel reactions are taking place.With all the samples a small amount of N2O formed below2008C was registered.At temperatures of2508C and higher,the NH3formation was detected by MS analysis.To estimate the catalyst stability after the activity test,the catalysts were kept in the reaction mixture for14h at5008C and14h at6008C.Under these extreme conditions the catalytic activity of the catalysts practically remains the same.4.DiscussionThe catalytic activity of the samples follows the order: AuCe>AuCeAl20>AuCeAl10The presence of alumina leads to a decrease in the catalytic activity.However,comparing the catalysts with different amount of alumina,it is seen that the sample with higher amount of alumina(AuCeAl20sample)shows higher activity than that of the sample with lower Al amount(AuCeAl10 sample).Table5summarizes the data on the catalytic activity and selectivity over all studied catalysts,registered at2008C. At this relatively low temperature,100%selectivity to N2and a comparably high conversion degree of NO and CO was reached.At temperatures of2508C and higher,the produced NH3could participate in the NO reduction,as well.As it was mentioned above,at the temperatures of high CO conversion degree,the CO2formation was only65–70%.This experi-mental result could be related to a strong CO2adsorption,as conﬁrmed by preliminary TPD measurements[21].It is also seen that the activity of the catalysts increases upon increasing the hydrogen content in the feed.This result conﬁrms the role of hydrogen concerning not only the surface catalyst reduction but also its active participation in the NO reduction.Studying the NO reduction by H2,Nieuwenhuys and coworkers[23]have also observed that alumina supported multicomponent gold catalysts convert NO to N2O at low temperatures(<1008C) and NO to ammonia at high temperatures(>2008C).The maximum selectivity of86%towards N2formation has been detected at intermediate temperatures.It has to be noted also that the results presented by Nieuwenhuys and coworkers[23] have been provided at signiﬁcantly lowerﬂow rate compared to those in the present study.The100%selectivity to N2at2008C makes the studied gold catalysts promising for‘‘cold-start’’application.The results on sample characterization gave us a possibility toﬁnd a relationship between the structure and reactivity of the catalysts.The X-ray analysis data have shown that the addition of alumina inhibits the crystallization process of ceria.The amorphous character of ceria prevails when the amount of alumina increases.The addition of10wt.%alumina causes a slight increase of the Au average particle size,while the ceria average particle size does not change.The increase of alumina to20wt.%leads to a higher ceria dispersion,while the gold particle size remains almost the same(Table1).It is known that the dispersion of gold plays a key role for the catalytic activity of supported gold catalysts,which is in agreement with the catalytic results obtained in this study.As far as the CeO2 dispersion is concerned,some authors put the accent on the nanosize ceria responsible for the high activity of gold catalysts.Fu et al.have shown that the reactivity of surface ceria oxygen in gold-ceria catalysts is controlled by the crystal size of ceria[24].Nunan et al.[25]have established that the decrease of CeO2crystallite size is reﬂected on the Pt/CeO2 interaction leading to a subsequent improvement in the TWCs performance.In the case of AuCeAl20catalyst the lowest average particle size of both ceria and alumina was estimated. Concerning these results a possible explanation of the highest catalytic activity of AuCe catalyst could be based on the lowest gold particle size of this sample,while the higher activity of AuCeAl20catalyst compared to the AuCeAl10one could be explained by the lowest average particle size of ceria.After stability test under extreme conditions(high temperature and reaction mixture medium)gold and ceria dispersion were maintained in the presence of alumina.The calculated FWHM values of the main CeO2line of the Raman spectra show a signiﬁcant increase in the presence of alumina(Table2).Such an increase can be related to the average crystal size of ceria and/or to defects formation in the ceria structure.Graham et al.have observed a correlation between the Raman line-width and the inverse particle size of ceria,pointing out that the defects in ceria lattice have also to be considered[26].Kosacki et al.discussing the relationship between the lattice disorder and the form of ceria Raman spectra,have found a direct correlation between the defects and absence of stoichiometry in CeO2[27].Studying gold catalysts, supported on ceria–alumina prepared by a different method (deposition of ceria onto alumina)an increase in the FWHM values of the main ceria line has already been observed by some of us[7].The explanation in this case was related to the oxygen vacancies formation in the presence of alumina.The gold loading leads to an additional increase in this value.In the present study,the highest FWHM value was registered for AuCeAl20catalyst and the reason could be both the lowest ceria particle size and the highest number of oxygen vacancies.L.Ilieva et al./Applied Catalysis B:Environmental65(2006)101–109107 Table5Conversion of NO and CO and selectivity to N2at2008C upon adding different amount of H2to the gas feed compositionSample NO conversion(%)CO conversion(%)Selectivity to N2(%) 3000ppm H22000ppm H23000ppm H22000ppm H23000ppm H22000ppm H2 AuCe78.067.181.673.1100100 AuCeAl1051.528.046.225.210095.2This consideration is in accordance with the TPR results obtained.In the case of gold-based catalysts the highest OSC of ceria is observed with the sample containing20%alumina (Table4).The calculated OSC of the corresponding initial support(CeAl20)is even higher,but this peak is registered in HT region(5508C,compared to1508C for AuCeAl20).The oxygen vacancy formation is giving rise to the increased oxygen mobility.Another explanation could be the lowest ceria particle size in agreement with the results of Usmen et al.[28]. They have established that the high OSC of Pt containing ceria doped with lantana can be attributed to the higher dispersion of Pt and CeO2.The higher ceria dispersion and the enhanced oxygen vacancy formation,due to the presence of20%of alumina in the mixed ceria–alumina support,can be the reason for the higher catalytic activity and reducibility of AuCeAl20 compared to the AuCeAl10catalyst.Our preliminary TPD measurements have shown,that there is no trace of N2 formation,e.g.no dissociative NO adsorption over the studied gold catalysts,both supported on ceria and ceria–alumina[21]. These results are in contrast to that already reported over PGM/ CeO2[29–32].This probably means that the NO reduction mechanism on gold-based catalysts,compared with the catalysts based on platinum group metals,is completely different.The obtained XPS data show the presence of both metallic and ionic gold species(Table3).The decrease of the average size of gold particles leads to the emerging of speciﬁc sites such as coordinative-unsaturated gold surface atoms.As the gold average size is smaller,the fraction of the particles with more coordinative sites is higher;therefore,the interaction between gold and the support becomes stronger.This is in accordance with the slightly increased Au4f BE in XPS spectra of the AuCe compared to the other samples.Moreover gold particles in close contact with oxygen vacancies become electron enriched because of a charge transfer from the support to the gold particles[33].Indeed upon increasing the alumina content, a tendency of electron enrichment of gold,associated with a negative binding energy shift of the Au4f components,is observed.This effect is caused by the presence of higher amount of oxygen vacancies in ceria–alumina support, probably having an important role for the catalytic activity. In support of the above consideration,Bond and Thompson [34],describing the mechanism of CO oxidation and the nature of the active sites for this reaction,have indicated the important role of oxidized/ionic gold.5.ConclusionsIt was established that gold-supported catalysts on ceria and ceria–alumina exhibited high catalytic activity in NO+CO reduction in the low temperature interval.Several factors are of crucial importance for the higher activity—the gold and ceria particles size as well as the formation of oxygen vacancies.The addition of alumina leads to high ceria dispersion and enhanced oxygen vacancies formation and to a slight increase of gold particle sizes.The diminishing intensity of the ionic gold observed by XPS with the AuCeAl20catalyst are indicative of the oxygen vacancies creation.This corresponds with the higher catalytic activity comparing to AuCeAl10sample. 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