The-Reactivity-Series-of-Metals

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九江24年小学四年级上册第七次英语第三单元真题(含答案)

九江24年小学四年级上册英语第三单元真题(含答案)考试时间：80分钟（总分:120）A卷考试人：_________题号一二三四五总分得分一、综合题(共计100题共100分)1. 选择题：What is the capital of Norway?A. OsloB. BergenC. TrondheimD. Stavanger2. 选择题：What is the capital of France?A. BerlinB. MadridC. RomeD. Paris答案: D3. 听力题：The _____ (fruit/vegetable) is fresh.4. 填空题：The __________ (火灾) affected the forest area.5. 填空题：The ______ (狼) hunts for food at night.6. 听力题：The chemical properties of metals include conductivity and ______.7. 选择题：What do bees produce?A. MilkB. HoneyC. SugarD. Jam8. 填空题：The firefly glows in the ________________ (黑暗).9. 填空题：The sunset is _______ (动人的).10. 填空题：The cat's whiskers are sensitive to ______ (触觉).11. 听力题：I want to be a ___ (scientist/artist).12. 填空题：My brother is a _____ (学生) participating in competitions.13. 填空题：A cheetah is the fastest _______ on land, running swiftly.14. 填空题：I have a pet _______ (仓鼠) that runs on a wheel.15. 听力题：A chemical change can be indicated by a change in ______.16. 填空题：The cake smells _______ (甜美).17. 填空题：__________ (实验) help scientists understand chemical principles.18. 听力题：The __________ is the largest ocean on earth.19. 填空题：I enjoy _______ (与家人一起)度假.20. 选择题：What do you call a person who designs clothes?A. TailorB. Fashion designerC. StylistD. Seamstress答案: B21. 选择题：What is the name of the famous clock tower in London?A. Big BenB. Eiffel TowerC. Tower of LondonD. London Bridge答案: A22. 选择题：What is the name of the famous wizard in Harry Potter?A. DumbledoreB. VoldemortC. HarryD. Sirius答案: C23. 听力题：A ______ is a type of fish that can glow.24. 听力题：The picture is on the ___. (wall)25. 填空题：A _____ (植物探险) can lead to discovering new species.26. 填空题：The ________ (地壳) is constantly changing.27. 填空题：My _____ (姐姐) helps me with homework.28. 填空题：My sister’s favorite animal is a _______ (我姐姐最喜欢的动物是_______).29. 选择题：What is 100 75?A. 15B. 25C. 35D. 45答案: BWhat is the name of the famous American landmark located in New York City?A. Statue of LibertyB. Golden Gate BridgeC. Mount RushmoreD. Empire State Building答案：A31. 听力题：The cake is very ________.32. 听力题：The chemical symbol for manganese is ________.33. 填空题：The __________ is the capital city of Mexico. (墨西哥城)34. 听力题：The _______ of an object is related to its mass and speed.35. 填空题：The _______ (Machu Picchu) is an ancient Incan city located in Peru.36. 填空题：My brother loves __________ (音乐) and plays guitar.37. 听力题：The chemical symbol for iodine is ______.38. 填空题：I can ______ (调整) my schedule as needed.39. 听力题：Elements can be metals, nonmetals, or _____.40. 听力题：I can ________ (adapt) to changes quickly.41. 选择题：Which holiday falls on October 31st?A. ChristmasB. HalloweenC. ThanksgivingD. New YearI can ______ (画画) well.43. 填空题：Have you seen a _____ (黑猩猩) at the zoo?44. 填空题：When I answer the phone at home, I usually say, "Hello, this is __." (当我在家接电话时，我通常说：“你好，我是。

专业英语

questions
How
do you distinguish steel from cast iron? How do you distinguish low alloy steel from high alloy steel?
1.1.1 Iron and Steel
The earth contains a large number of metals which are useful to man. One of the most important of these is iron. Modern industry needs considerable quantities of this metal, either in the form of iron or in the form of steel.
Mechanical Engineering materials
Organic polymer materials Inorganic non-metallic materials
plastic rubber Synthetic Fibers Traditional ceramics Special Ceramics Metal Matrix Composites
1.1.1 Iron and Steel
The ore becomes molten, and its oxides combine with carbon from the coke. The non-metallic constituents of the ore combine with the limestone to form a liquid slag. This floats on top of the molten iron, and passed out of the furnace through a tap. The metal which remains is pig iron.

有机合成（孟祥豹）ch5有机金属试剂

Organometallic Compounds有机金属试剂有机金属试剂主族金属试剂：Li,Na, Mg, Cu, Zn, Cd过渡金属有机化合物：Pd,W,Mo,Ni,Sn稀土金属有机化合物: Sm,La,Yb,Ru,Rh,ScI. Concepts and principles Compounds with C-M bond. M = metalAs electrophilic reagents,attacked by nucleophilesAs nucleophilicreagents, attackelectrophiles Organometellic compoundsOrganometellic compoundsThe reactivity depends on the nature of the metal atom. Electropositive characterA. Preparation1. From metals and organic halides2. Metal-halogen exchangeSolventEquilibrium 利于形成与电负性更大的碳原子相连的有机金属试剂3. Metal-metal exchange4. Metalation of hydrocarbonsEquilibrium/ 利于形成含更小电正性金属的试剂A acidic C-H bond, formation a stable carbanionB. General reactions of organometallic compounds1. Substitution ( nucleophilic )2. Addition to double bondsNucleophiliesII. Organomagnesium compounds(Grignard reagents)♣1901, Grignard reagent was discovered; ♣1912, Nobel PrizeX = Cl, Br, IR = alkyl, aryl, alkenylPreparation:Order of reactivity: RI > RBr > RCl >> RF ♦Magnesium metal♦Alkyl halide: ♦Solvent: 乙醚, THF ，（丁醚, 异戊醚），甲基叔丁基醚⨯♦O 2, CO 2, H 2O should be rigorously excluded 1o RX > 2o RX > 3o RX♦反应的引发：碘或者CH 2Br 2♦反应的淬灭：氯化铵水溶液Vinyl halidesAcetylenic halidesAlkyl Chlorides Reactions of Grignard reagentsA. Formation of carbon-carbon bonds 1. Formation of Hydrocarbons 延长碳链烷基化卤代烃、磺酸酯、硫酸酯2. Formation of AlcoholsTertiary alcoholPrimary alcoholSecondary alcohol酮甲醛醛格氏试剂与醛酮的反应提供了一条由简单醇制备复杂醇的路线收率-----电性因素立体因素√Less bulky Grignard reagent is preferableAlternative methods for synthesizing alcoholsa. With acyl halides控制投料比,可控制产物的结构状态低温, 等当量投料立体位阻？b. With carboxylic esters3o 醇有两个相同烃基的醇甲酸酯对称的仲醇2o 醇六甲基磷酰胺HMPA有两个相同取代基的二醇c. With epoxide增加两个碳的醇不对称环氧化物3. Formation of Aldehydes原酸酯4. Formation of Ketones腈酰胺5. Formation of Caboxylic acids 与CO 2的反应B. Reaction at elements other than carbon1. Hydroperoxides 氢过氧化物2. Thiols过氧醇硫醇3. Sulfinic acids4. Alkyl Iodides烷基亚磺酸5. Amines6. Derivatives of phosphorus, boron, and siliconC. Some abnormal reactions of Grignard reagents1. Allylic and Benzylic Grignard reagentMajorminorAllyl Grignard reagentAllylic-type Grignard reagentReaction through six-membered cyclic transition stateBenzylic Grignard reagentsPyrrole2-position3-positionIndole2. 1,4 -Additionα, β-不饱和醛, 1,2-additionGrignard reagent, with a large bulky group1, 2-addition1,4-addition75%25%α, β-不饱和酮, 1,4-additionOrganic SynthesisA large bulky group in 4-positionA large bulky group in α-positionCu +, Cu 2+催化1,4-加成反应CuCl, Cu(OAc)2,CuCN3. Undesirable reactions of Grignard reagentDecomposition of Grignard reagentα-Hydrogen atomenolizationAs a baseReductionA hydrogen atom at β-carbonHydride-ion transferSix-memberedCyclic transition stateStereoselectivityMechanism of Grignard Reaction Barbier reactionIII. Organolithium compounds♦作为强碱;♦作为强的亲核试剂, 活性高于Grignard 试剂;♦发生一些不同于Grignard 试剂的反应Wurtz coupling reaction♦RX/Li干燥, 溶剂, 隔绝空气, 温度低温反应♦金属-卤素交换芳基、乙烯基卤代物♦锂-氢交换较强酸性的烃C-H键涉及有机锂试剂的实验装置RLi 过滤、转移装置反应装置无水溶剂蒸馏转移装置涉及有机锂试剂的实验装置B. ReactionsSimilar as the Grignard reagents, but more effective.The differences from Grignard reagentsLess readily prevented by steric hindrance from reacting at carbonyl groups.1. Reaction with Carbonyl Groups2. 1,2-addition , with unsaturated ketones1,4-addition1,2-addition3. Wurtz coupling 烃基取代反应4. Carbon dioxide 形成羧酸、酮的反应羧酸5. Addition to cyclic ether6. Reaction with Carboxylic DerivativesIV. Organocopper compoundsA. PreparationOrganocoper compoundsLithium organocuprates二烷基铜锂试剂R = alkyl, alkenyl, arylB. Reactions1. With alkyl halides较少重排、消除副反应2. Coupling reaction with Carbonyl halides形成酮，温和，收率较高3. Reaction with α-Bromo-ketones酮的α-烃化碱催化, 与卤代烃反应/ 消除, 缩合烷基铜锂试剂仅与卤代烃反应, 而不与醛酮羰基反应4. With α,β-unsaturated carbonyl compoundsReacts exclusively by 1,4-addition, Michael addition---------高度的区域选择性, 将烷基、芳基引入α、β-不饱和羰基化合物的β-位RMgBr: 1,2-and 1,4-additionRLi: 1,2-addition R2CuLi: 1, 4-additionCis-加成5. Addition to Epoxides反应条件温和，生成增加2个碳的醇；加成反应的位点α, β-不饱和环氧化物1, 4-additionTrans-addition活性顺序：酰氯> 醛> 环氧化物>RX>酮>酯>腈6. Copper(I) catalyzed formation of cyclopropanesA copper-carbene complex may be involved V. Organocadmium compoundsA. Preparation金属试剂与金属离子交换, 生成更稳定的金属试剂R = alkyl, aryl 反应活性比RMgX, RLi低, 毒性B. ReactionDo not react with ketones and esters.分子中引入酮基, 对其它功能团没有影响VI. Organozinc compounds A. Preparation1. With acyl chlorideB. ReactionsKetones2. With aldehydes and ketonesReformatsky reaction3. With nitriles4. The Simmons-Smith reactionCarbenoidZinc-copper alloyVII. Organonickel compoundsA. PreparationThe 3-allyl complex dimerizationAllyl halideB. ReactionsCoupling reaction with alkyl halidesDihydrocoumarinsTerpenesB. ReactionsVIII. Organoferric compoundsA. PreparationCollman’s reagentCarbonyl complexSynthesis of cyclic ketonesFerrocene二茂铁。

化学中英双语全面Review

travel by car 乘坐汽车 cook with gas使用天然气 animal husbandry 畜牧业 farming 种植业 Carbon dioxide and methane are greenhouse gases.Greenhouse gases keep the Earth warm enough for life.But now their increasing amounts are warming it too much. 二氧化碳和甲烷都是温室气体。温室气体能够保证地球上的生物的热度需求。但是，现在温室气体的增加太多，导致温度过高了。
7.2 metals and water
金属和水反应
metals react with water 金属与水的反应
sodium Na +H2O----NaOH +H2 ( chemical equation 化学方程式) NaOH(sodium hydrate氢氧化钠) 2Na +2H2O===2NaOH +H2(balanced equation) Only reactive metals, for example, Li Na K Ca Mg, can react with water. 只有非常活泼的金属，比如锂、钠、钾、钙、镁，能够与水发生反应。
6.5 Inside solids
What are solids like? 固体是什么样子的
A lump of solid contains millions of atoms ,all held together tightly in a regular pattern. 一小块固体通常就含有上百万个原子，所有的原子之间都以有规律的模式相互紧密结合在一起。

化学专业英语(竞赛)

化学专业英语一、无机化学1. periodic table 元素周期表element 元素metal 金属nonmetal 非金属transition metal 过渡金属group / family 族alkali metal 碱金属alkaline earth metal 碱土金属chalcogen 氮族元素halogen 卤素noble gas 稀有气体period 周期lanthanide 镧系元素actinide 锕系元素block 区s-block s区（H、He、碱金属、碱土金属）p-block p区（IIIA~VIIA族、稀有气体(He除外)）d-block d区（过渡金属）f-block f区（镧系元素、锕系元素）2. electron configuration 电子排布，电子构型electron shell 电子层shell （电子）层subshell （电子）亚层atomic orbital 原子轨道structure 结构molecule 分子molecular 分子的atom 原子atomic nucleus 原子核electron 电子electron cloud 电子云ion 离子anion /ˈæn.aɪ.ən/ 阴离子cation /ˈkæt.aɪ.ən/ 阳离子3. quantum number 量子数principal quantum number 主量子数（n）1≤nazimuthal quantum number 角量子数（ℓ）0≤ℓ≤n-1magnetic quantum number 磁量子数（m）- ℓ≤m ≤ℓspin quantum number 自旋量子数（s或m s）±1/2Pauli exclusion principle（泡利不相容原理）：Two electrons cannot occupy the same quantum state within a quantum system simultaneously.Hund’s principle / Hund’s rule（洪特规则）：If two orbitals of equal energy are available, electrons will occupy them singly before filling them in pairs.4. chemical bond 化学键ionic bond 离子键ionization energy 电离能electron affinity 电子亲和能ionic polarization 离子极化dipole 偶极covalent bond 共价键metallic bond 金属键(=metallic bonding)intermolecular force 分子间作用力van der Waals force 范德华力5. Lewis structure 路易斯结构lone pairs 孤电子对，孤对电子valence electron 价电子single bond 单键multiple bond 多重键（double bond 双键，triple bond 三键）6. chemical reaction 化学反应四种基本反应类型（four basic types）：combination reaction 化合反应 C + O2= C O2decomposition reaction 分解反应Cu(OH)2 = CuO + H2Odisplacement reaction (single displacement reaction) 置换反应Fe + CuSO4 = FeSO4 + Cumetathesis reaction (double displacement reaction) 复分解反应AgNO3 + NH4I = NH4NO3+ AgI↓precipitation 沉淀（作用）precipitate 沉淀物其它反应：reduction-oxidation reaction (=redox reaction) 氧化还原反应oxidation 氧化reduction 还原combustion 燃烧（=burning）stoichiometry /ˌstɔɪkiˈɒmɪtri/ 化学计量stoichiometric ration 化学计量比reactivity series of metals / activity series of metals 金属活动性顺序standard electrode potential 标准电极电势（符号Eθ）chemical stability 化学稳定性acid-base reaction 酸碱（中和）反应conjugated acid 共轭酸conjugated base 共轭碱Lewis acid 路易斯酸Lewis base 路易斯碱Brønsted acid Brønsted酸Brønsted base Brønsted碱7. solution 溶液solute 溶质solvent 溶剂concentration 浓度concentrated 浓的dilute 稀的molality 质量摩尔浓度(mol溶质/kg溶剂) mole fraction 摩尔分数mass fraction 质量分数mass concentration 质量浓度(kg/m3)osmotic pressure 渗透压molar concentration 摩尔浓度(mol/L)solubility 溶解度solubility product 溶度积（K sp）soluble 可溶的slightly soluble 微溶的insoluble 难溶的，不溶的solvation 溶剂化作用solvate 溶剂合物（如CaCl2·C2H5OH）hydration 水合作用hydrate 水合物（如CuSO4·5H2O）hemihydrate 半水合物monohydrate 一水合物dihydrate 二水合物(tri- 3, tetra- 4, penta- 5, hexa- 6, hepta- 7, octa- 8, nona- 9, deca- 10, undeca- 11, dodeca- 12)8. compound (=chemical compound) 化合物inorganic compound 无机化合物organic compound 有机化合物nomenclature /nəˈmenklətʃə(r)/ 命名法chemical formula 化学式empirical formula 实验式，简式structural formula 结构式molecular formula 分子式macromolecule 高分子polymer 聚合物coordination complex 配合物，络合物元素名以ium（或um）结尾的，去掉后缀，某化物加ide，如硫化钠sodium sulfide。

专英第三章翻译(直译)

（P139）3.1晶界生长与外延正如前面第一章所讨论的那样，在分立器件和集成电路中最重要的两种半导体是硅和砷化镓，在这一章我们叙述这两种半导体的常用的单晶生长技术，基本的工艺流程是从原料到抛光晶片，原料经过化学处理做成一个用来生长单晶的高纯多晶半导体。

单晶硅锭铸形，以定义材料的直径，这些晶片经过腐蚀和抛光来提供一个光滑的特定的且器件将做在上面的表面。

一种和单晶生长密切相关的技术包含一个单晶半导体层在一个单晶半导体衬底的生长，这叫外延，它是从希腊语epi和taxis得来的，外延工艺提供了一种重要的控制掺杂形貌的技术，以至于器件和电流性能可以被优化。

例如，一个掺杂浓度相当低的半导体层可以在一个同型掺杂而浓度很高的衬底外延生长，通过这种方式和衬底相关联的体电阻将被充分地减少，许多新的器件结构，特别是微波和光学器件，可以通过外延工艺制得。

在这章的后面我们将考虑讨论一些重要外延生长技术。

（p140）3.2从熔体生长单晶重要：从熔体生长单晶有两种基本方法，直拉法和布里奇曼法，用于半导体行业的充足百分比的硅单晶是通过直拉法制备的，实际上所有的用于集成电路制造的硅都是用这方法制备的。

大部份的砷化镓，在另一方面，是通过布里奇曼法生长的。

然而，直拉法在生长大直径的砷化镓方面变得越来越流行。

3.2.1原始材料硅的起始材料是一种相当纯的叫做石英的沙子形式。

它和各种形式的碳被置于炉中，当很多反应在炉中发生时，总的反应式是SI+SIO2=这种工艺生产出纯度98%的冶金及的硅。

下一步，硅被磨碎和******反应生成三氯氢硅（SIHCL3）SI + 2HCL三氯氢硅在温室下是液体，液体分馏除去不要的杂质，净化过后的SIHCL3用于与氢气反应。

制备电子级的硅（EGS）：SIHCL3+这个反应在包括为硅的沉积提供晶体成核点的电阻加热硅棒的反应堆中发生，纯度为电子级别的硅，也就是一个高纯的多晶硅材料，是用于制备器件级质量的单晶硅的未加工材料。

超导现象-英汉双语

Superconductivity超导现象One of the earliest properties investigated in the laboratories at Leiden was the resistance of metal wires. It was measured by finding the voltage, or potential difference, between the ends of a wire when a known current was flowing through it. Whenever the current is doubled, the voltage is also doubled according to Ohm's law, and the resistance is voltage over current (R=v/c). With some metals such as copper, iron and platinum, the resistance dropped smoothly down with falling temperature, until at 40°K it was only perhaps a hundredth of its value at 0℃. With others, notably lead, mercury and tin, there was a temperature, different for each one but well below 20°K, at which the resistance dropped to nothing at all. A hundredth of a degree above this critical temperature the resistance was normal, like those of copper, iron and platinum; but a hundredth of a degree below, it was zero or too small to measure.参考译文：金属丝的电阻是莱顿实验室最早研究的金属特性之一。

翻译2

P223塑性变形的变形是永久性的,超出弹性范围内的物质。

通常,金属塑性变形而产生作用的,因为有益的效果赋予的力学性能。

必要的变形金属可以达到应用大量的机械力的唯一或加热金属,然后应用一个很小的力。

金属的变形,这是由于原子位移的获得是通过一个或两个的过程称为滑的友好。

详细的微观变形方法,可以发现,在教材冶金。

宏观尺度上的时候,发生塑性变形、金属似乎流沿着固态特定的方向,这依赖于类型的加工和应用方向的力量。

晶体的金属颗粒的方向是延长的金属流动。

金属的流动显微镜下可以看到和合适的蚀刻,抛光后的金属表面。

这些被称为流线、实线、虚线、剖面线、一些有代表性的标本Fig.7.1,都在比较中呈现。

由于谷物是延长的水流方向,他们将可以提供更多的抗应力在他们。

表演作为结果,机械金属锻造产品称为工作能够达到较好的机械强度在特定方向,流向。

因为它有可能控制这些流纹线方向在任何特定的小心推拿,如图Fig.7.1受力时,就有可能实现最佳的力学性能。

金属,当然,就会削弱沿水流线。

metal-working损耗材料过程要么是微不足道的,或者非常小,生产率在一般都非常高。

这两个因素引起的经济生产。

热加工和寒冷的工作传统的metal-working过程分为热加工处理而被称为cold-working下面的过程。

热的作用下,迫使,当原子达到一定的能量较高的水平,形成新的晶体开始,称为再结晶。

再结晶晶粒结构变形破坏旧机械工作,全新的晶体,strain-free就形成了。

颗粒,事实上,开始成核点的最严重的变形。

所定义的再结晶温度由美国社会的金属是“近似最低温度的时间里,完成再结晶冷塑性变形金属发生在一个指定的时间”。

再结晶温度的三分之一到一半一般也不同熔点的大多数的金属。

再结晶温度的典型值给于表格7.1。

再结晶温度也取决于总数的冷工作目前已收到的材料。

更高的寒冷的工作,降低再结晶温度将在Fig.7.2如图所示。

在热加工过程,可以携带以上的再结晶温度有或没有实际供暖。

九江2024年01版小学5年级下册第14次英语第5单元测验卷[有答案]

4. 选择题： Which planet is known as the Red Planet? A. Earth B. Mars C. Jupiter D. Venus
5. 填空题： I saw a _______ (小鹿) in my yard.
6. 填空题： The ancient Egyptians built their temples to honor _____.
22. 填空题： My __________ (玩具名) always brings me __________ (名词).
23. 听力题： The _____ (music/dance) is fun.
24. 选择题： Which bird is known for its colorful feathers and ability to mimic sounds? A. Crow B. Parrot C. Sparrow D. Eagle 答案:B
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45. 选择题： How many days are there in a week? A. 5 B. 6 C. 7 D. 8

化学专业考研英语词汇

苯环上上甲醛

Radical and migratory insertion reaction mechanisms in Schiﬀbase zirconium alkylsPaul D.Knight a ,Guy Clarkson a ,Max L.Hammond a ,Brian S.Kimberley b ,Peter Scott a,*a Department of Chemistry,University of Warwick,Gibbett Hill Road,Coventry CV47AL,UK bResearch &Technology Centre,BP Chemicals snc,Boite Postale No.6,13117Lavera,FranceReceived 9February 2005;received in revised form 22March 2005;accepted 23March 2005Available online 4May 2005AbstractFour salicylaldimine derivatives H 2L 4–7of 2,20-diamino-6,60-dimethylbiphenyl,where the C @N bond is sterically protected by substituents on the phenol ring,form alkyls of zirconium,cis -a -[Zr L 4–7(CH 2Ph)2].Rather than decomposing via the established pathway of 1,2-migratory insertion of an alkyl group to imine,they undergo a radical mechanism.This is evidenced by the large number of products observed,kinetic and thermodynamic data (Rice-Herfeld,3/2order,positive D S à),response to steric factors,and the fact that switching to a less stable radical leaving group inhibits the reaction.In contrast,the 1,2-migratory insertion is a clean,ﬁrst-order intramolecular process with negative D S à.The steric modiﬁcation of the ligands nevertheless transforms an inac-tive precatalyst into a stable system for the polymerisation of ethene.Closely related unbridged salicylaldimine catalysts are known to be highly active catalysts,but in most cases they appear to suﬀer from high temperature instability.The ﬁrst examples of zirco-nium alkyls of this class are isolated,and it is found that they are inherently much more resistant to decomposition by either path-way (migratory insertion or radical).Structural studies are used to interpret this variance in behaviour;the biaryl-bridged complexes are pre-organised for both reactions,while the unbridged systems would have to undergo signiﬁcant ordering prior to activation.Correspondingly,the unbridged systems are not noticeably aﬀected by the same steric modiﬁcation of the ligand,and it is concluded that the more likely mechanism of catalyst death in the latter is ligand loss (i.e.transfer to aluminium from co-catalyst).Ó2005Elsevier B.V.All rights reserved.Keywords:Mechanism kinetics;Zirconium;Alkene polymerisation1.IntroductionA fundamental concern for those using Schiﬀbase complexes in catalytic applications is the reactivity of the C @N bond,speciﬁcally where this limits the number of turnovers.This issue is particularly important in early transition chemistry,where coordination of the imine unit renders it highly electrophilic [1].We have sought to avoid this issue through the replacement of theC @N units with less reactive linkers,and while this has met with some successes in enantioselective catalysis [2],the favourable properties of Schiﬀbase systems –strong ligand–metal bond,ease of synthesis,tunability,crystallinity,structural rigidity –have encouraged us to investigate the possibilities for improvement of their stability in early transition complexes.In this context,salicylaldimine (SA)complexes of the group 4metals,[M(SA)2Cl 2](Fig.1),which when combined with,e.g.methylaluminoxane (MAO)yield extremely active or otherwise useful catalysts for the polymerisation of alk-enes,are of particular interest [3].It is assumed that me-tal alkyls are involved in these catalyses,and evidence0022-328X/$-see front matter Ó2005Elsevier B.V.All rights reserved.doi:10.1016/j.jorganchem.2005.03.043*Corresponding author.Tel.:+442476523238;fax:+442476572710.E-mail address:peter.scott@ (P.Scott).Journal of Organometallic Chemistry 690(2005)5125–5144/locate/jorganchemhas been presented that alkyl cation species [M(SA)2Me]+are formed on treatment of [M(SA)2Cl 2]with MAO [4].Coates has mentioned that analogous ketimino ligands form stable alkyl complexes on treat-ment with [Ti(CH 2Ph)4][5].In contrast with many other oleﬁn polymerisation systems however an alkyl cation has not been isloated.We have recently shown that biaryl-bridged salicyl-aldimine derivatives H 2L 1–3(Fig.2)form,under appro-priate conditions,isolable alkyls of zirconium [Zr L 1–3R 2]with cis -a geometry (C 2-symmetric with cis alkyl ligands)[7].Subsequently,however,they decompose via 1,2-migratory insertion of an alkyl group to imine (Scheme 1)followed in some instances by a second sim-ilar reaction.This provides an explanation for their complete inactivity in oleﬁn polymerisation.Here we re-port a detailed kinetic investigation of this reaction,an attempt to prevent the process by ligand modiﬁcation,discovery of a new decomposition mechanism,and the development of a stable polymerisation catalyst system.We also describe some attempts to apply the lessons learned to the SA catalyst system.Part of this work has been brieﬂy communicated [6].2.Results and discussion 2.1.Ligand designsReducing the steric demand in the phenolate 2-posi-tion (R 0in Scheme 1)reduces the rate of 1,2-migratory insertion in the metal benzyl complexes [Zr L n (CH 2Ph)2](i.e.L 3<L 1<L 2)[7].This is however an unsatisfactory resolution of the problem of complex stability for two reasons;(i)even when this group is hydrogen the 1,2-migratory insertion pathway is still accessible and occurs over a short period of time (<48h),(ii)it is known that group 4iminophenolate complexes require sterically demanding substituents (e.g.t Bu)in this position to fur-nish highly active catalysts for alkene polymerisation [3].We thus sought other modiﬁcations.A space-ﬁlling model of the molecular structure of [Zr L 1(CH 2Bu t )2][7]is shown in Fig.3(a),with the elec-trophilic imine carbon atom indicated *.We envisaged that notionally moving the 4-methyl substituent to the 5-position [Fig.3(b)]would eﬀectively block the ap-proach of a zirconium bound alkyl group to the imine carbon atom.The series of ligands L 1,L 4,L 5was de-signed to examine the eﬀect of steric demand in this 5-position.In addition,it was envisioned that the series L 6,L 4,L 7would allow investigation of the eﬀect of steric demand in the 2-position for this unusual salicylaldi-mine substitutionpattern.Fig. 3.Space-ﬁlling models of (a)[Zr L 1(CH 2CMe 3)2]from X-ray molecular structure and (b)[Zr L 4(CH 2CMe 3)2]based on (a);phenolate 4and 5positions and imine carbon atom (*)indicated.5126P.D.Knight et al./Journal of Organometallic Chemistry 690(2005)5125–51442.2.Synthesis of zirconium alkyl complexesThe synthesis of[Zr L1(CH2Ph)2]was reported previ-ously[7].Reaction of H2L4with zirconium tetrabenzyl in acetonitrile yielded a precipitate which was found to be mainly unreacted H2L4.This was probably due to the low solubility of H2L4in acetonitrile.The complex [Zr L4(CH2Ph)2]was successfully synthesised in dichlo-romethane atÀ78°C.The reaction of the more soluble proligand H2L5with[Zr(CH2Ph)4]in acetonitrile pro-ceeded cleanly giving[Zr L5(CH2Ph)2]in high purity. The complexes[Zr L6(CH2Ph)2]and[Zr L7(CH2Ph)2] were prepared similarly.The NMR spectra of freshly prepared solutions of these complexes were consistent with cis-a geometry.2.3.Solution stability of[Zr L4–7(CH2Ph)2]:initial observationsWe were surprised toﬁnd that the four complexes [Zr L4–7(CH2Ph)2]underwent fairly rapid decomposition in solution,although the spectra of the products were markedly diﬀerent from those expected for1,2-migra-tory insertion processes.After ca.3h at298K,the1H NMR spectrum of a solution of[Zr L4(CH2Ph)2]in d2-dichloromethane displayed a very large number of new peaks in the imine(d7.5–9.5ppm)and aliphatic regions. These features,which were similar for all four complexes with a5-substituent,are consistent with radical decom-position processes.Attempts at isolation of one of the many decomposition products were unsuccessful.2.4.Kinetic studies of the decomposition processesThe decomposition of[Zr L1(CH2Ph)2]in d2-dichloro-methane was followed by1H NMR spectroscopy be-tween283and303K.Values for the integration of the complex imine peak relative to the residual protio sol-vent resonance were obtained over ca.two half-lives where possible.First-order plots were satisfactory over the whole temperature range(Fig.4).Similar vari-able temperature kinetic studies on the complexes [Zr L4–7(CH2Ph)2]showed that they did not decompose viaﬁrst-order processes and after much experimentation it was found that the only satisfactoryﬁt was via1.5or-der plots(e.g.Fig.5).This unusual order was conﬁrmed using VanÕt Hoﬀplots of the data.Activation parameters(Table1)were subsequently obtained via Eyring plots.The uncertainties recorded were calculated using standard methods[8].1The negative value of entropy of activation for the decomposition of[Zr L1(CH2Ph)2]is consistent with the formation of an ordered(four-membered)cyclic transition state in an intramolecular1,2-migratory inser-tion process.As we had proposed,placing a methyl group in the5-position as in complex[Zr L4(CH2Ph)2] inhibits the formation of this cyclic transition state, but unexpectedly a new mechanistic pathway is opened up as evidenced by the number of products formed and by a change in the order of reaction to3/2.Both observations are consistent with Rice–Herzfeld radical propagation kinetics[9,10](vide infra).We propose an initiation step involving homolyticﬁs-sion of the Zr–CH2Ph bond,leading to formation of two radical species(Eq.(1),Bn=CH2Ph).2The benzyl rad-ical can then attack the ligand(e.g.at an imine position) on another complex molecule to form a new radical spe-cies(Eq.(2)).We have previously described a very clo-sely related reaction at a Nb(IV)Schiﬀbase system (Scheme2)leading to oxidation to diamagnetic Nb(V) [11].In the case of Zr the radical character is retained by the ligands(Eq.(2)),and the system may react to form a closed shell complex and a further benzyl radical (Eq.(3)).The lack of a higher oxidation state for zirco-nium thus enables a radical propagation process that terminates when two radicals combine(Eq.(4)).Assum-ing steady state conditions,Eq.(5)is eventually ob-tained[10].We note that the observed rate constant k obs(Eq.(6))and thus the thermodynamic values ob-tained from the Eyring analysis for the process of‘‘acti-vation’’are actually composite parameters arising from initiation,propagation and termination.The positive entropies of activation for the complexes of L4–7(Table 1)are nevertheless consistent with a radical process. Initiation½Zr LðBnÞ2!k1½Zr LðBnÞ ÅþBnÅð1ÞPropagationBnÅþ½Zr LðBnÞ2!k2½ZrðBn–LÞðBnÞ2Åð2Þ½ZrðBnÀLÞðBnÞ2Å!k3½ZrðBn–LÞðBnÞ þBnÅð3ÞTerminationBnÅþBnÅ!k4Bn2ð4ÞRate¼k2k1k40.5½Zr LðBnÞ21.5ð5ÞRate¼k obs½Zr LðBnÞ21.5ð6Þ1Standard error in the slope,SEm ¼s e=ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃTSS xpand standard error inthe intercept,SE c¼s eﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃð1=nÞþð X2=TSS xqÞ.These were computedusing the LINEST function in Microsoft Excel.2These equations are representative examples of the type of process described.P.D.Knight et al./Journal of Organometallic Chemistry690(2005)5125–51445127Returning to the initiation step,we propose that the proximity of a benzylic H atom to the imine carbon may facilitate the homolytic ﬁssion of the metal–benzyl bond (Fig.6).We note that the observed rate of decom-position of the L 5complex is almost twice that of L 4and this diﬀerence arises in the main from the much greater positive D S àin the former where the proposed H atom donor unit is i Pr rather than Me.Subject to the caveat mentioned above regarding the composite nature of the thermodynamic parameters,wealso note that the enthalpies of activation decrease for the complexes in the order L 6>L 4>L 7,with steric bulk in the phenolate 2-position increasing in the same order (H <Me <i Pr).This is the same trend as observed for the ﬁrst order 1,2-migratory insertion process and is consistent with greater steric compression in the more substituted complexes.The large increase in k rel onTable 1Activation parameters and relative rates for decomposition of [Zr L n (CH 2Ph)2]Complex k rel (298K a )D H à(kJ mol À1)D S à(J K À1mol À1)[Zr L 1(CH 2Ph)2]–+88(±2)–32(±7)[Zr L 4(CH 2Ph)2] 1.0+101(±5)+16(±16)[Zr L 5(CH 2Ph)2] 1.8+113(±10)+62(±34)[Zr L 6(CH 2Ph)2]0.3+108(±7)+29(±23)[Zr L 7(CH 2Ph)2]1.1+91(±5)+17(±16)aRelative rate constant versus [Zr L 4(CH 2Ph)2].5128P.D.Knight et al./Journal of Organometallic Chemistry 690(2005)5125–5144moving from L6to L4is not continued on moving to L7 however,principally because the general trend in D Sàis acting against this.2.5.Reaction of H2L4with[Zr(CH2CMe3)4]We explored brieﬂy the eﬀect of the presence of a less stable radical leaving group on the decomposition pro-cess.Reaction of H2L4with zirconium tetrakis(neopen-tyl)in dichloromethane proceeded smoothly,and a high purity sample of the complex[Zr L4(CH2CMe3)2]was obtained by crystallisation from pentane.This complex only began to show traces of decomposition in solution after leaving for several days at room temperature.2.6.Synthesis and polymerisation activity of[Zr L1À7Cl2]Since the benzyl complexes were prone to decomposi-tion,we attempted to generate the chloride complexes as these had previously been observed to be far more ro-bust[12].Treatment of the ligands with sodium hydride followed by[ZrCl4(THF)2]proceeded without problem. The zirconium chloride complexes,[Zr L1–7Cl2],were then puriﬁed by sublimation at ca.300°C,10À6mm Hg in all cases and found to possess C2symmetry.However, treatment with MAO in toluene in the presence of ethyl-ene at ambient temperature and1.2bar led to very low uptake of gas.This lack of activity may be attributed to the lack of steric bulk in the phenolate2-position[3,13].2.7.Synthesis of[Zr L8,9Cl2]and polymerisation catalysisThese zirconium chloride complexes were synthesised and characterised as before.Ethylene polymerisation re-sults are summarised in Table2.As can be seen,the presence of the phenolate2-tert-butyl group in[Zr L9Cl2] does not give rise to signiﬁcant polymerisation activity on its own.In combination with5-methyl substituent, as in[Zr L8Cl2],polymerisation activity was observed for theﬁrst time using this type of ligand,albeit moder-ate according to GibsonÕs classiﬁcation[14].The catalyst is unusually stable,and there is no noticeable loss of activity at25and50°C over at least a period of1h (Fig.7).The lower average productivity and activity at 50°C is due to the reduced solubility of ethylene in tol-uene at higher temperatures.2.8.Structural implications of phenolate5-methyl substitutionWe obtained X-ray molecular structures(Table3)of [Zr L7Cl2]and[Zr L9Cl2]via crystals obtained from sam-ples of the pure complexes in d2-dichloromethane.The molecular structures are shown in Fig.8with selected bond lengths and angles given in Table4.The view along the Zr–O axes(Fig.9)highlights the inﬂuenceofTable2Polymerisation activity of complexes[Zr L8,9Cl2]:precatalyst,1.39·10À2mmol;toluene(500ml);ethene pressure,1.2bar;MAO:Zrmolar ratio,1000:1Precatalyst Temperature(°C)Average productivity(1h)(kg PE/mol–Zr bar–C2h)[Zr L8Cl2]2565[Zr L9Cl2]25–[Zr L8Cl2]5040[Zr L9Cl2]50–P.D.Knight et al./Journal of Organometallic Chemistry690(2005)5125–51445129the5-methyl substituent;steric compression between this group and the imine-CH has led to a twist in the plane of coordination of the phenolate ring,such that the phenolate–CH3lies between the imine group and the adjacent Zr–Cl group.This increases the hindrance of the pathway for1,2-migratory insertion between the imine carbon and a metal bound alkyl group(in place of Cl).This twisting of the phenolate ring may have an additional consequence in that the phenolate2-alkyl substituent has been directed away from the‘‘active sites’’of the catalyst.This may reduce steric compres-sion at these sites resulting in reduced propensity for decomposition as well as opening the sites for increased catalytic activity.2.9.Synthesis and stability of active species in polymerisation catalysisThe question remained as to whether zirconium alkyl complexes of L8and L9decompose via diﬀerent path-ways.All attempts failed at generating the desired com-plexes by reaction of proligands with zirconium tetrabenzyl and zirconium tetrakis(neopentyl).1H NMR spectra indicated that the reaction was much slower than for less bulky ligands;resonances corre-sponding to unreacted and mono-deprotonated ligand were evident for the neopentyl reaction,and several other products were evident for the benzyl.Attempts at alkylation of the zirconium chloride complexes using Grignard and lithium reagents produced a number of unidentiﬁed products.Reactions of[Zr L8Cl2]and [Zr L9Cl2]in NMR tubes with previously dried MAO (10molar equivalents)in d8-toluene resulted inTable3Experimental data for the X-ray diﬀraction studies[Zr L7Cl2][Zr L9Cl2]ÆCH2Cl2[Zr L11Cl2] Colour Yellow Yellow YellowHabit Block Block BlockMolecular formula C36H38Cl2N2O2Zr C39H44Cl4N2O2Zr C36H40Cl2N2O2Zr Crystal system Monoclinic Monoclinic Monoclinic Space group C2/c C2/c C2/ca(A˚)19.975(4)13.349(3)21.166(4)b(A˚)10.551(2)14.379(3)7.925(2)c(A˚)15.521(3)20.131(4)20.282(4)b(°)97.95(3)96.74(3)100.770(19)Cell volume(A˚3)3239.7(11)3837.4(13)3342.2(14)Z444l(mmÀ1)0.5390.6010.523Total reﬂections10,36412,48113,587 Independent reﬂections[R(int)]3987[0.0183]4650[0.1109]4189[0.0182]R1,wR2[I>2r(I)]0.0235,0.06170.0768,0.19160.0225,0.0585Table4Selected bond lengths(A˚)and angles(°)for molecular structures of[Zr L7Cl2],[Zr L9Cl2]and cis-a-[Zr(L11)2Cl2](vide infra)[Zr L7Cl2][Zr L9Cl2][Zr(L11)2Cl2]Zr–O 1.9987(11) 1.986(3) 1.981(9)Zr–Cl 2.4246(6) 2.4313(17) 2.432(5)Zr–N 2.3221(12) 2.347(4) 2.348(11)O–Zr–O165.30(6)172.2(2)157.40(5)N–Zr–N75.09(6)72.9(2)84.31(6)Cl–Zr–Cl103.82(3)108.36(10)94.38(3) 5130P.D.Knight et al./Journal of Organometallic Chemistry690(2005)5125–5144consumption of the starting complexes and signiﬁcant broadening of the spectra,but no unambiguous indica-tions of the formation of alkyl or alkyl cation species.Since we could not generate zirconium alkyl com-plexes of L 8and L 9,we decided to use complexes of L 4and L 1as models.An NMR tube was charged with [Zr L 1(CH 2Ph)2]and B(C 6F 5)3,and d 2-dichloromethane was distilled into it at À78°C.The 1H NMR spectra were then recorded at À80°C and then at increments of +10°C up to room temperature.A similar reaction was carried out using [Zr L 4(CH 2Ph)2].In both cases,the 1H NMR spectra indicated formation of [B(C 6F 5)3(CH 2Ph)]À[15].Below ca.À40°C,two imine peaks were observed that do not correspond to the start-ing complexes,and the presence of six methyl reso-nances indicate that the species formed were C 1symmetric.For both reactions,new pairs of doublets oc-curred in the region d 2.0–3.5ppm,and we tentatively assign all these features to the desired cationic species [Zr L (CH 2Ph)]+.Upon warming the solution containing the proposed L 4complex cation,signiﬁcant decomposi-tion occurred between À30and 0°C;a large number of new imine peaks are generated and the pair of doublets disappeared.The solution containing the L 1complex also decomposes signiﬁcantly within the same tempera-ture range,however three major new imine peaks are observed along with the disappearance of the pair of doublets.No clear evidence for 1,2-migratory insertion processes was observed in either case.2.10.Application to other catalyst systemsWe sought to investigate the eﬀect of 5-alkyl substitu-tion on Fujita Õs zirconium iminophenolate catalysts.Four proligands H L 10–13(Fig.10)were synthesisedviaFig.9.Salicylaldimine–Zr–Cl fragments of (a)[Zr L 7Cl 2]and (b)[Zr L 9Cl 2]extracted from X-ray molecular structures,highlighting eﬀects of substituents ortho to the iminecarbon.P.D.Knight et al./Journal of Organometallic Chemistry 690(2005)5125–51445131condensation of the appropriate salicylaldehydes with aniline in ethanol.Two of these ligands(H L10,12)have a methyl group in the5-position and two control ligands H L11,13have the traditional2,4-substitution(H L11has previously appeared)[16].Reactions of H L10and H L11with sodium hydride in THF followed by[ZrCl4(THF)2]resulted in the produc-tion of yellow/orange solids which were sublimated at ca.300°C,10À6mm Hg to yield yellow solids of stoichi-ometry[Zr(L10,11)2Cl2],as indicated by mass spectrome-try and CHN analysis.1H NMR spectra revealed that two isomeric complexes were present in both cases. The major products were C2-symmetric,as indicated by the presence of single imine,phenolate methyl and tert-butyl resonances.The minor products(ca.27%for½Zr L102Cl2 and ca.36%for½Zr L112Cl2 )had broad1HNMR spectra at room temperature,but cooling(253K for½Zr L102Cl2 and203K for[Zr L11Cl2])gave riseto sharp resonances.Two imine peaks and two pheno-late methyl and tert-butyl resonances were observed in both complexes.We therefore assigned these species as having the C1-symmetric cis-b topography.The ratio of cis-a to cis-b remains unchanged over a period of days.Interestingly,Fujita and coworkers[16]did not note the presence of cis-b isomers of[Zr L11Cl2], although their NMR data are possibly consistent with this.Coates[5]has noted the presence of cis-b isomers of ketimino titanium complexes and others.Crystals of cis-a-½Zr L112Cl2 were grown from toluenesolution.X-ray analysis revealed that the C2-symmetric complex(Fig.11)crystallises as a dimer via a face-face p–p stacking interaction between N-aryl rings(Fig.12).The distance between H(16A)and the centroid of the proximal aryl ring is ca.3.37A˚[17].The bond dis-tances and angles about Zr(1)are unremarkable for this type of complex[16]and are discussed in more detail through comparison with those of a biaryl-bridged com-plex in Section2.12.Samples of½Zr L102Cl2 and½Zr L112Cl2 were tested at BP laboratories under supported gas-phase conditions with MAO co-catalyst.Both complexes had similarly high activities and catalytic lifetimes were<10min at 50–80°C in both instances.Thus,while substitution of the ligand with a methyl group ortho to the imine carbon atom does not signiﬁcantly alter the intrinsic polymeri-sation activity of the complexes,it fails to increase lon-gevity of the catalyst in this instance.In the hope of shedding further light on the issue of iminophenolate catalyst stability we undertook a study of some alkyl derivatives.2.11.Synthesis and properties of[Zr(L10–13)2(CH2Ph)2]In NMR tube scale experiments,the reactions between two equivalents each of H L10–13with[Zr(CH2-Ph)4]were shown to give cleanly[Zr(L10–13)2(CH2Ph)2]. One example,[Zr L102(CH2Ph)2],was synthesised on a preparative scale and was characterised in the usual way.Attempts to grow single crystals for X-ray analysis were unsuccessful.The1H NMR spectrum of½Zr L102ðCH2PhÞ2indi-cated the adoption of the cis-a structure;in particular the appearance of the C H2Ph as a pair of AB doublets indicated that interconversion between the chiral-at-metal structures(Fig.13)is slow onthis5132P.D.Knight et al./Journal of Organometallic Chemistry690(2005)5125–5144timescale.The spectrum of½Zr L112ðCH2PhÞ2wassimilar.For[Zr(L12,13)2(CH2Ph)2]these C H2Ph reso-nances appeared as a broad singlet.This trend in con-ﬁgurational stability is consistent with an N-dissociative mechanism since bulky groups in the phenolate2-posi-tion would cause steric compression on lengthening of the N–Zr bond,and hence hinder isomerisation[18].All the above complexes were found to be relatively stable with respect to the decomposition reactions de-tailed above.After several days in solution at ambient temperature,samples of the bulky ligand complexes [Zr(L10,11)2(CH2Ph)2]began to show signs of formation of1,2-migratory insertion products,viz.a new single imine peak and a set of three quartets in the regionca.parison of the molecular structures of cis-a-½Zr L9Cl2 and cis-a-½Zr L112Cl2 .P.D.Knight et al./Journal of Organometallic Chemistry690(2005)5125–51445133d 2.5–6.5ppm[1a].Solutions of the complexes [Zr(L12À13)2(CH2Ph)2]showed very little,if any,decom-position over a period of several days.2.12.Stability of[Zr L102CH2Ph]þWe attempted to generate an alkyl cation complex byreaction of½Zr L102ðCH2PhÞ2with B(C6F5)3in an NMRtube atÀ78°C,using d2-dichloromethane as solvent.1H NMR spectra were recorded atÀ80°C and at+10°C increments up to room temperature.Resonances for [B(CH2Ph)(C6F5)3]Àwere observed at low temperature [15],indicating that a reaction had taken place,but while some resonances assignable to a cationic species [Zr(L10)2(CH2Ph)]+were observed,byÀ40°C extensive decomposition had occurred.This result and the at-tempts to form[Zr L1,4(CH2Ph)]+(Section2.8),do not bode well for isolation of a stable alkyl cationic species such as that implicated in oleﬁn polymerisation catalyses by these complexes.Fujita[4]has also detected NMR resonances consistent with such a species on treatment of a dichloride complex with dried MAO.2.13.Biaryl-bridged complexes vs.non-bridged complexesComplexes of our biaryl-bridged ligands above and the non-bridged salicylaldimine type ligands are similar in terms of functionality.Nevertheless,considerable dif-ferences are observed for polymerisation activity.We can see that in comparison to the constrained structure of the biaryl complex[Zr L9Cl2][Fig.14(a)],the N-arylunits in the non-bridged ligand complex½Zr L112Cl2 (b)are directed away from one another.The presence of the biaryl unit also constrains the N–Zr–N0angle toca.72.9°compared with84.3°for½Zr L112Cl2 ,(Table4),and perhaps most importantly reduces the size of the active site by forcing the phenolate units forwards;the O–Zr–O0angles for[Zr L9Cl2]and½Zr L112Cl2 are172.2°and157.4°,respectively.The top view of the com-plexes shows that the phenolate tert-butyl substituents are positioned directly above the zirconium chloride sites in the L9complex,whereas in the L11complex these tert-butyl groups are situated above the zirconium cen-tre.The resultant steric compression in[Zr L9Cl2]forces the chlorides farther apart(108.4°)than in the L11com-plex(94.4°).Given these structural diﬀerences,the vari-ance in intrinsic catalytic activity between[Zr L8Cl2]and½Zr L102Cl2 is not surprising.The variance in response of the two catalysts systems to attempted steric blocking of the1,2-migratory inser-tion reaction also requires comment.For the biaryls, the geometry is essentially pre-organised for the approach of metal-coordinated alkyl towards the carbon atom. Steric compression from phenolic ortho substituents (top view,Fig.14)encourages this further.Nevertheless, the constrained biaryl ligand geometry also dictates that a methyl group ortho to the imine consistently impedes this reaction,thus leading to the remarkable increase in catalyst stability detailed above.The unbridged com-plexes are not pre-organised for this reaction,and as a result the1,2-migratory insertion is inherently slower for these compounds.The observation that phenolate 5-methyl substitution does not aﬀect catalyst longevity suggests that either;(i)despite the fact that complexes [Zr(L10–13)2(CH2Ph)2]appear to be rather stable with respect to1,2-migratory insertion,the greaterﬂexibility allows for imine migratory insertion even in the modiﬁed catalyst,or perhaps more likely(ii)that other processes are responsible for catalyst deactivation(vide infra). 3.ConclusionsOur attempt here to block sterically the1,2-migratory insertion process in our Schiﬀbase group4alkyl com-plexes was successful principally because of the lack of ﬂexibility of the system.This also results however in the complexes being pre-organised for decomposition via a radical process.Kinetic analysis and1H NMR spec-troscopy data highlight the diﬀerences between the two pathways.For the1,2-migratory insertion mechanism a single product was formed in a highly diastereoselective intramolecular manner to give an unstable intermediate. The reaction displayedﬁrst order reaction kinetics with a negative entropy of activation associated with ordered transition state.The radical process gave many products in a1.5order Rice–Herzfeld reaction with positive entro-py of activation,but was inhibited through the use of a less stable radical leaving group(neopentyl)at the metal, thusﬁnally giving a stable metal alkyl.The eﬀect on polymerisation catalysis using the bia-ryl-bridged complexes with this ligand modiﬁcation is signiﬁcant as we transformed an inactive system to one that displays activity(albeit moderate)and also demon-strated that the catalyst is long lived.Application of this simple ligand modiﬁcation to the unbridged salicylaldimine systems did not lead to an in-crease in polymerisation catalyst lifetime at higher tem-peratures.At least two explanations are available which are consistent with observations to date.If imine reac-tivity is at the heart of the instability of the unbridged systems,then the lack of success in inhibiting1,2-migra-tory insertion by our method might be traced to the dif-ferences in precatalyst structure detailed in Section2.13. If on the other hand,loss of a salicylaldimine ligand(e.g. via transfer to aluminium from MAO)causes catalyst death,then this steric modiﬁcation would not be ex-pected to make a signiﬁcant diﬀerence.We note the growing body of evidence for the latter picture,such as the relatively poor polymerising capabilities of mono-salicylaldimine complexes[19]and improved sta-bility of more electron-rich phenolate systems[20].5134P.D.Knight et al./Journal of Organometallic Chemistry690(2005)5125–5144。

关于金属材料的英语作文

关于金属材料的英语作文英文回答：Metals are materials that possess specific properties, including high thermal and electrical conductivity, luster, malleability, and ductility. They are widely used in various applications due to their unique characteristics and versatility.The properties of metals are primarily determined by their atomic structures and composition. Metals typically exhibit a metallic bond, where valence electrons are delocalized and can move freely within the material. This delocalization of electrons allows metals to conduct heat and electricity efficiently.The thermal conductivity of metals varies depending on the specific material. Metals with higher thermal conductivity, such as copper and aluminum, are commonly used in heat sinks and other applications where efficientheat dissipation is critical. Metals with lower thermal conductivity, such as stainless steel and titanium, areoften used in applications where heat retention is desired.Similarly, the electrical conductivity of metals varies widely. Metals with high electrical conductivity, such as copper and silver, are used in electrical wiring, conductors, and other applications where efficient current flow is required. Metals with lower electrical conductivity, such as iron and nickel, are used in applications such as magnets and electromagnetic devices.The mechanical properties of metals are also important considerations for various applications. Metals aregenerally strong and durable, but their specific strengths vary depending on the alloy composition and heat treatment processes. Malleability and ductility are desirable properties for metals that need to be shaped or formed into specific geometries.Metals are relatively easy to form and shape using techniques such as casting, forging, rolling, and extrusion.This versatility makes them suitable for a wide range of manufacturing processes and applications.In addition to their inherent properties, metals can be further enhanced through alloying and surface treatments. Alloying involves combining different metals or non-metals to create materials with specific properties tailored for particular applications. Surface treatments, such as anodizing, plating, or coating, can improve the corrosion resistance, wear resistance, or other surface characteristics of metals.中文回答：金属材料是具备特定性质的一类材料，包括高导热性、高导电性、光泽、延展性和可锻性。

访第四统计力学创建者金日光教授发现陶瓷金字塔顶部使水中的一些元素引起常温下的核反应1.doc

访第四统计力学创建者金日光教授发现陶瓷金字塔顶部使水中的一些元素引起常温下的核反应1.doc访第四统计力学创建者金日光教授发现陶瓷金字塔顶部使水中的一些元素引起常温下的核反应联合国友好画报社总编胡多多女士访金日光教授的访谈录胡多多总编之言：据我所知，当代高能核物理学理论是绝不承认在常温下发生融核反应的，所以若有人说在常温下能发生融核反应（cold?fision），肯定认为是“精神异常”。

但是中国有一位在国际上创建第四统计力学理论的金日光教授，早年专门学习过量子化学、量子统计力学，他从多年前开始用电荷间作用力来统一了“强作用力”、“电磁作用力”、“弱作用力”、“万有引力”。

这一统一场论，引起了世界华人华侨及欧美科学界的震憾。

近几年他如今一直在研究宇宙空间能量的聚焦和应用的问题。

他发现用陶瓷做的金字塔能够聚焦空间中的中微子，使塔顶上所放的塑料瓶中水的各种元素含量发生显著的变化，看来显然是发生了常温下的原子核的融合反应。

这是国际上首次发现的、非常惊人的事情，现在下面请金教授论述他的最新发现。

上世纪90年代中国北京化工大学金日光教授继国际上Maxwell-Boltzmann统计力学，Fermi-Dirac统计力学，Bose-Einstein统计力学之后，在国际上首次提出了第四统计力学理论，成功地研究了同时具有吸引和排斥的各种体系的统计问题，发表了许多论文，著有《第四统计力学》、《模糊群子论》、《当代中医药生命动力学》等专著。

上世纪美国ABI500人影响人物的书及维基百科（https:///wiki/%E9%87%91%）里给予了专门的介绍。

金日光教授，一直关注金字塔结构所引起的各种现象，在这些现象中他特别关注了一些故事：捷克电技工程师K.Drbal组装了一个金字塔，把钝了的胡须刀放到其中，过了一星期，发现胡须刀变得非常锋锐了，而且使用次数增加到400次，于是金日光教授认为刀刃上可能出现了新的“金属元素”，也就是出现了新的原子核了，基于这样的想法，设计了一种金字塔，用一些陶瓷原料，经1250℃加以烧结成三个金字塔型陶瓷（见图），并造了一些瓷粒（见图），分别用量子微弱场检测仪（WF-3）来测它们的辐射量，大体上有8～10微特斯拉（μT），当把瓷粒装到金字塔内1/3高度时，再测顶部辐射值，其结果表明～30μT。

小学上册U卷英语第六单元期中试卷

小学上册英语第六单元期中试卷英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.I enjoy playing with my toy ________ (玩具名称) at the park.2.Learning new languages is very ________ (有趣).3.The movie starts at ________.4.My favorite hobby is ______ (摄影). I love capturing beautiful ______ (瞬间).5.The baby is ______ (crying).6.The chemical symbol for manganese is __________.7.My brother is great at ____.8.My favorite season is ______. I love this time of year because the weather is ______. In spring, the flowers start to ______ and the trees become ______. It is also a great time to go outside and enjoy nature.9.My favorite _____ is a soft, cozy blanket.10.ai were warriors in ________ (日本). The Silk11.This ________ (玩具) brings smiles to my face.12. A reaction that produces a gas and a solid is called a ______ reaction.13.What is the main theme of the story "Little Red Riding Hood"?A. FriendshipB. AdventureC. DangerD. Love14.My uncle loves to __________ (看书) in his spare time.15.What is 5 + 3?A. 10B. 8C. 7D. 9B16.The reactivity of elements is based on their _______ structure.17.The chemical symbol for indium is ______.18.Which shape has three sides?A. SquareB. CircleC. TriangleD. RectangleC19.My cousin is very __________ (聪明的) in math.20.What do you call the process of planting seeds?A. GrowingB. HarvestingC. SowingD. WateringC21.The _____ is the distance between two celestial bodies.22.What do we call a sweetened beverage made from tea?A. Iced TeaB. Sweet TeaC. LemonadeD. Fruit Punch23.The tree is ______ (full) of ripe fruit.24.The main component of air is _____.25.The walrus has whiskers on its ________________ (脸).26.My grandma has a lovely _____ at her house.27.I love to ride my ______ (bike) in the park.28.My sister has a ________ (毛绒玩具), and she takes it everywhere, even to ________ (学校).29.The chemical formula for copper sulfate is _____.30.We will go to the ___. (circus)31.My mom loves to make ____ (soups) in winter.32.The _____ (小马) runs very fast.33. A squirrel finds nuts to store for ________________ (冬天).34. A simple machine like a lever helps us to ______ (lift) heavy things.35.What instrument do you play to make music with your mouth?A. FluteB. GuitarC. ViolinD. TambourineA36. A __________ is a place where magma reaches the earth's surface.37. A ______ (果汁机) can extract healthy drinks from fruits.38.Which of these is a mode of transportation?A. TreeB. CarC. HouseD. BookB39.What is the name of the fairy tale character with long hair?A. CinderellaB. RapunzelC. Snow WhiteD. BelleB40.The chemical formula for calcium hydroxide is ______.41.The first woman to fly in space was _______ Ride.42.The capital of France is __________.43. A __________ (合金) is a mixture of metals.44.The _______ of a pendulum can be affected by the length of the string.45.What do you call the act of reading aloud?A. WhisperB. ShoutC. SpeakD. Recite46.My pet _____ loves to play outside.47.Certain plants can _____ (繁殖) quickly in warm weather.48.The __________ (历史的博物馆) showcase artifacts from the past.49.What do you call a person who studies the universe?A. AstronomerB. AstrophysicistC. CosmologistD. All of the aboveD50.The llama is known for its soft _________ (毛).51.My brother has a teddy _______ (我哥哥有一个泰迪_______).52. A metal reacts with an acid to produce a _____ and hydrogen gas.53.Which animal is known for its ability to mimic sounds?A. DogB. ParrotC. CatD. CowB Parrot54.My ______ is very inspiring and motivates others.55.What do you call a small, soft fruit?A. GrapeB. CherryC. RaspberryD. All of the above56.The parrot can learn to _______ (说话) easily.57.My grandma always says, “Call me !” (我奶奶总是说：“叫我！”)58.The Earth's surface is subject to changes from both natural and ______ factors.59.What do we call a collection of books published together?A. AnthologyB. CompilationC. SeriesD. VolumeA60.What do we call the time when leaves change color and fall from trees?A. SpringB. SummerC. FallD. WinterC61.What is the name of the largest reptile in the world?A. Komodo DragonB. Saltwater CrocodileC. Green AnacondaD. Leatherback TurtleB62.How many hours are in a day?A. 20B. 22C. 24D. 2663.The ______ (花期) of a plant varies with species.64.I like to ______ (参加) environmental activities.65.I have a toy _______ that hops around and plays with me all day long.66.I need to ________ my homework.67.What is the largest mammal in the world?A. ElephantB. Blue WhaleC. GiraffeD. RhinocerosB68. A force applied to an object can cause it to _______.69.What is the capital city of Malta?A. VallettaB. MdinaC. SliemaD. St. Julian'sA70.The chemical formula for calcium sulfate is ______.71. A solution is a type of ______.72.What do we call the study of the human mind and behavior?A. SociologyB. PsychologyC. AnthropologyD. PhilosophyB73.What is the name of the fairy in "Peter Pan"?A. CinderellaB. Tinker BellC. Snow WhiteD. AuroraB74.I like to go ______ (滑雪) during winter vacations.75.The ______ is a predator of many small animals.76. A solubility test determines how much solute can ______.77.I want to _______ (学习) about marine life.78.The __________ is a famous mountain located in South America. (安第斯山脉)79.What can you find in a library?A. FoodB. BooksC. ClothesD. Toys80.The sun is _____ (shining/raining) today.81.They are ___ (talking/listening) to music.82.The __________ (历史的同情) can bridge divides.83. A _______ is a substance that speeds up a chemical reaction.84.The country known for its historical landmarks is ________ (意大利).85.I like to spend my evenings ______.86.The ________ (土壤成分) affects fertility.87.The eagle has sharp ______ (爪子).88.The ____ has a colorful shell and is often seen in the garden.89.I have a _______ (challenge) for you.90.The __________ (历史的纪录片) provide visual representations.91.What is the name of the famous cartoon character known for his catchphrase, "What's up, Doc?"A. Daffy DuckB. Bugs BunnyC. Porky PigD. Elmer Fudd92.What do we call the maximum number of individuals that an environment can support?A. Carrying capacityB. Population limitC. Resource limitD. Environmental thresholdA Carrying capacity93.What is the capital city of Italy?A. ParisB. RomeC. MadridD. Berlin94.The __________ can indicate the health of an ecosystem.95.The ancient Egyptians made ______ (木乃伊) as part of their burial practices.96.What is the largest organ in the human body?A. HeartB. BrainC. SkinD. LiverC Skin97.What do you call a piece of furniture to sit on?A. TableB. ChairC. BedD. Couch98. A ______ (观赏植物) can beautify any space.99.The walrus has whiskers on its _________ (脸).100.The garden is _______ (生机勃勃).。

光于金属的英语作文

光于金属的英语作文Title: The Interaction of Light with Metals: A Fascinating Phenomenon.Light, the invisible force that bathes our world in brightness and color, interacts with matter in a myriad of ways, creating a spectrum of phenomena. Among these, the interaction of light with metals is particularly intriguing,展现出一系列 unique properties and applications that have fascinated scientists and artists alike.Metals, being composed of densely packed atoms, possess a unique electronic structure that allows them to interact strongly with electromagnetic radiation, particularly visible light. When light strikes a metal surface, it can either be reflected, absorbed, or transmitted, depending on the metal's properties and the wavelength of the light.Reflection is a common outcome when light interactswith metals. Metals are generally good reflectors ofvisible light, which is why they appear shiny and glossy. The reflection of light from metal surfaces is often specular, meaning that the reflected light maintains the same polarization and phase as the incident light,resulting in a clear and sharp reflection. This specular reflection is responsible for the mirror-like appearance of many metals.However, not all light incident on a metal surface is reflected. A portion of the light is absorbed by the metal, causing it to heat up. The absorption of light by metals is determined by their optical properties, which are influenced by factors such as the metal's work function, electron density, and the presence of impurities or alloys. Certain metals, such as gold and silver, absorb visible light strongly, giving them their characteristic golden or silvery hues.Transmission of light through metals is a less common occurrence, as metals are typically opaque due to their dense atomic packing. However, under certain conditions, such as when the metal is thin enough or when the light hasa specific wavelength, transmission can occur. This phenomenon is known as metal transparency, and it is observed in thin films of certain metals, such as aluminumor silver, at specific wavelengths of the electromagnetic spectrum.In addition to these basic interactions, metals also exhibit a range of optical effects when light interactswith them. One such effect is plasmonics, which involvesthe interaction of light with free electrons in metal nanostructures. Plasmonics has led to the development of novel optical devices and sensors that utilize the unique optical properties of metals to enhance or manipulate light.Another fascinating effect is the photoelectric effect, which occurs when light striking a metal surface ejects electrons from the metal. This effect, first observed by Albert Einstein in 1905, underlies the operation of photoelectric cells and other photoelectric devices that convert light into electrical energy.The interaction of light with metals also findsapplications in various fields. In jewelry and art, metals are used to create beautiful and intricate designs that are enhanced by their optical properties. In the field of photonics, metals are employed in optical devices such as mirrors, lenses, and filters to manipulate and controllight. In addition, metals play a crucial role in the development of optoelectronic devices, such as solar cells and LEDs, that convert light into electricity or vice versa.In conclusion, the interaction of light with metals isa rich and multifaceted phenomenon that has captivated scientists and artists for centuries. The unique optical properties of metals, their ability to reflect, absorb, and transmit light, and the various effects they exhibit when interacting with light have led to a diverse range of applications in various fields. As technology continues to advance, we can expect to see even more innovative uses of metals in optical and photonic devices, further expanding our understanding and appreciation of the fascinating interaction between light and matter.。

单交换反应英语

单交换反应英语Here is an essay on the topic of "Single Displacement Reaction" with a word count of over 1000 words, written in English without any extra punctuation marks.Chemical reactions are fundamental processes that occur in the natural world and in various industrial applications. One type of chemical reaction that is particularly important is the single displacement reaction. In this essay, we will explore the concept of single displacement reactions, their characteristics, and some practical applications.A single displacement reaction, also known as a substitution reaction, is a type of chemical reaction where one element in a compound is replaced by another element. The general form of a single displacement reaction can be written as:A + BC → A C + Bwhere A is the replacing element, and BC is the original compound. The product of the reaction is a new compound AC, and B is the element that is displaced or replaced.One of the key characteristics of single displacement reactions is that they typically involve the rearrangement of atoms or ions within a compound. This rearrangement occurs due to the differences in the reactivity of the elements involved. The more reactive element, A, is able to displace the less reactive element, B, from the original compound, BC.The reactivity of elements is often determined by their position on the periodic table. Elements on the left side of the periodic table, such as the alkali metals and alkaline earth metals, are generally more reactive than elements on the right side, such as the halogens and noble gases. This reactivity difference is a crucial factor in determining the direction and feasibility of a single displacement reaction.Another important aspect of single displacement reactions is the concept of the activity series or reactivity series. The activity series is a list of elements arranged in order of decreasing reactivity. This series can be used to predict the direction and likelihood of a single displacement reaction. In general, the more reactive element will displace the less reactive element from a compound.One common example of a single displacement reaction is the reaction between iron and copper sulfate (CuSO4) solution. When apiece of iron is placed in a copper sulfate solution, the iron will displace the copper from the compound, resulting in the formation of iron sulfate (FeSO4) and solid copper metal. The reaction can be written as:Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)In this reaction, the more reactive iron (Fe) displaces the less reactive copper (Cu) from the copper sulfate (CuSO4) compound.Single displacement reactions have numerous practical applications in various fields, including chemistry, metallurgy, and environmental science. In the field of metallurgy, single displacement reactions are used in the extraction and purification of metals. For example, the Mond process, which is used to extract nickel from its ores, involves a single displacement reaction between nickel and carbon monoxide gas.Another important application of single displacement reactions is in the field of electrochemistry. The activity series of elements can be used to determine the direction and feasibility of electrochemical reactions, such as those involved in the operation of batteries and fuel cells.Furthermore, single displacement reactions play a crucial role inenvironmental remediation processes. For instance, the use of zero-valent iron (Fe0) in groundwater treatment is based on a single displacement reaction, where the iron reduces and removes contaminants such as chlorinated organic compounds and heavy metals from the water.In conclusion, single displacement reactions are a fundamental type of chemical reaction that involve the replacement of one element in a compound by another more reactive element. These reactions have a wide range of practical applications, from metallurgy and electrochemistry to environmental remediation. Understanding the principles of single displacement reactions, including the activity series and the factors that govern their feasibility, is essential for chemists, engineers, and scientists working in various fields.。

The properties and applications of metal nitrides

The properties and applications ofmetal nitridesMetal nitrides are a class of inorganic compounds that contain nitrogen and ametallic element. They have excellent physical and chemical properties, which makethem widely used in various fields, such as catalysis, electronics, and materials science.In this article, we will discuss the properties and applications of metal nitrides.Properties of Metal NitridesMetal nitrides have unique properties, including high melting point, hardness, and thermal stability. They also exhibit excellent mechanical, electrical, magnetic, and optical properties, which make them suitable for various applications.One of the most important properties of metal nitrides is their high melting point. For example, tungsten nitride (WN) and titanium nitride (TiN) have melting points of 2,810℃and 2,930℃, respectively. This high melting point makes them ideal for applications that require high-temperature stability, such as in catalysis and thermal barrier coatings.Another property of metal nitrides is their hardness. Metal nitrides are typically harder than their corresponding metals. For example, TiN is harder than titanium metal. This property makes them ideal for use as wear-resistant coatings in tools and manufacturing equipment.Metal nitrides also exhibit high thermal stability. They can withstand high temperatures without decomposing or degrading. For example, aluminum nitride (AlN) has a thermal conductivity of 320 W/mK, making it suitable for use in high-temperature electronic applications.Applications of Metal NitridesMetal nitrides have a wide range of applications in different fields, including catalysis, electronics, and materials science.In catalysis, metal nitrides are used as catalysts because of their high surface area, high thermal stability, and catalytic activity. For example, molybdenum nitride (MoN) and niobium nitride (NbN) have been used as catalysts for ammonia synthesis and hydrodesulfurization, respectively.In electronics, metal nitrides are used in the fabrication of semiconductors, optoelectronic devices, and integrated circuits. For example, gallium nitride (GaN) has demonstrated high electron mobility, making it suitable for use in high-frequency electronic devices.In materials science, metal nitrides have been used in coatings, composites, and nanomaterials. For example, TiN is commonly used as a coating for cutting tools because of its wear resistance and hardness. AlN has been used as a substrate for growing high-quality GaN films.ConclusionMetal nitrides are a class of inorganic compounds with unique properties that make them suitable for a wide range of applications. They have high melting points, hardness, thermal stability, and excellent mechanical, electrical, magnetic, and optical properties. Metal nitrides have been used in catalysis, electronics, and materials science to improve the performance of various applications. As new applications are developed, metal nitrides will continue to play an important role in shaping our world.。

CO2制甲醇

Discovery of a Ni-Ga catalyst for carbon dioxide reduction to methanolFelix Studt 1,Irek Sharafutdinov 2,Frank Abild-Pedersen 1,Christian F.Elkjær 2,Jens S.Hummelshøj 1,Søren Dahl 2,Ib Chorkendorff 2and Jens K.Nørskov 1,3*The use of methanol as a fuel and chemical feedstock could become very important in the development of a more sustainable society if methanol could be efﬁciently obtained from the direct reduction of CO 2using solar-generated hydrogen.If hydrogen production is to be decentralized,small-scale CO 2reduction devices are required that operate at low pressures.Here,we report the discovery of a Ni-Ga catalyst that reduces CO 2to methanol at ambient pressure.The catalyst was identiﬁed through a descriptor-based analysis of the process and the use of computational methods to identify Ni-Ga intermetallic compounds as stable candidates with good activity.We synthesized and tested a series of catalysts and found that Ni 5Ga 3is particularly active and parison with conventional Cu/ZnO/Al 2O 3catalysts revealed the same or better methanol synthesis activity,as well as considerably lower production of CO.We suggest that this is a ﬁrst step towards the development of small-scale low-pressure devices for CO 2reduction to methanol.Nature reduces CO 2photochemically to store energy,and devising an artiﬁcial process to replicate this remains one of the grand challenges in modern chemistry 1–4.One possibility,which is currently the subject of very active research,is a photo-elec-trochemical process,but ﬁnding an electrocatalyst that is selective and has a low overpotential is challenging 5–11.An alternative approach would be to ﬁrst generate molecular hydrogen via a photo-electrochemical process or an electrochemical process using electrical power from photovoltaic cells or wind turbines 12,13.If the hydrogen were then used in a heterogeneously catalysed process to reduce CO 2to methanol,a sustainable source of liquid fuel would be established.Today,methanol is produced in large facilities from CO,CO 2and H 2(derived from fossil resources)in a high-pressure (50–100bar)process using a Cu/ZnO/Al 2O 3catalyst 14.If hydrogen production is to be distributed and produced in small-scale devices,it would be attractive if the subsequent conversion of H 2into a liquid fuel could also be performed in simpler,low-pressure decentralized units.This is not,however,simply a case of reengineering the technol-ogy currently optimized for high-pressure conversion of syngas into methanol,because a low-pressure CO 2reduction process may require a different catalyst.Another challenge arises with the use of CO-free CO 2,which will lead to CO as a by-product of methanol via the reverse water–gas shift (rWGS)reaction.The production of CO not only reduces the yield of methanol—it also has a negative effect when methanol is used in fuel cells because CO poisons the Pt catalyst ing the industrial Cu/ZnO/Al 2O 3catalyst (which is optimized for different reaction conditions including a CO-rich feed)in low-pressure methanol synthesis leads to signiﬁcant CO production,so new catalysts are needed to advance this ﬁeld.In the present Article,we report the discovery of a new,non-precious metal catalyst working at low pressure with similar or higher methanol yield than the current Cu/ZnO/Al 2O 3methanol synthesis catalyst 15–17.We use a computational descriptor-based approach to guide us towards a new class of Ni-Ga catalysts andshow experimentally that it has the unique property that it reduces CO 2to methanol without producing large amounts of CO via the rWGS reaction.ResultsA large literature exists about the methanol synthesis reaction over supported copper catalysts 18–28.Here,we consider the direct CO 2reduction to methanol.Grabow and Mavrikakis have considered many different reaction paths and suggested the following to be most likely 29,30:H 2(g )+2*↔2H*(1)CO 2(g )+H*↔HCOO*(2)HCOO*+H*↔HCOOH*+*(3)HCOOH*+H*↔H 2COOH*+*(4)H 2COOH*+*↔H 2CO*+OH*(5)H 2CO*+H*↔H 3CO*+*(6)H 3CO*+H*↔CH 3OH (g )+2*(7)OH*+H*↔H 2O (g )+2*(8)The symbol *represents a surface site or an adsorbed species.A simple mean-ﬁeld kinetic model is used to elucidate trends in reactivity.The model treats all reaction steps as being potentially rate-determining and solves the rate of methanol production under steady-state conditions,similar to those described for other reactions 31,32.There are a total of eight activation energies for the forward elementary steps.Together with the eight elementary reac-tion energies,these deﬁne the complete energy-space of the1SUNCAT Center for Interface Science and Catalysis,SLAC National Accelerator Laboratory,2575Sand Hill Road,Menlo Park,California 94025,USA,2Centre for Individual Nanoparticle Functionality (CINF),Department of Physics,Building 307T echnical University of Denmark,DK-2800Lyngby,Denmark,3SUNCAT Center for Interface Science and Catalysis,Department of Chemical Engineering,Stanford University,Stanford,California 94305,USA.*e-mail:norskov@reaction.These energies have been calculated with density func-tional theory (DFT)using the RPBE exchange-correlation energy functional 33for a selected set of metals (see Supplementary Tables 1and 2for a table of all the energies).In each case we chose a stepped face-centred cubic fcc(211)surface to represent the active site 30,34.We have shown that van der Waals (vdW)interactions can be important for the energetics of CO 2reduction for Cu(211)using the BEEF–vdW functional 35,36.In the following we include such effects by assuming that the extra effect of van der Waals inter-actions is the same as on copper for all the other metals considered.Given the non-speciﬁc nature of the dispersion interactions,and the fact that the catalytically interesting metals are close in bonding to copper,this is a very reasonable approximation.We will now describe the approach we have taken to reduce the number of energy parameters in the methanol synthesis from 16to only 1.In doing so we lose some accuracy,but it is important to build such a model for at least two reasons.First,it allows us to understand the trends in catalytic activity among the metals.Second,it is a very efﬁcient way of identifying new catalyst leads 37,38.We ﬁnd that scaling relations exist between the oxygen adsorption energy,D E O ,and the adsorption energies and tran-sition-state energies of all the hydrogenated forms of CO 2when we compare different metal surfaces (see Supplementary Figs.1and 2for the complete set of scaling relations).The result is a com-plete mapping of all the relevant energies in the methanol kinetics onto only one parameter,D E O .To a ﬁrst approximation this par-ameter characterizes the catalytic properties uniquely.Solving the steady-state microkinetic model with the input of these scaling relations yields the calculated rate of CO 2hydrogen-ation as a function of D E O at ambient pressure and 500K,as shown in Fig.1.Values of D E O for the elemental metals copper,pal-ladium and nickel are included in this volcano plot.The optimum in reaction rate is a result of competition between having a too weak interaction with oxygen (resulting in too unstable intermediates and high reaction barriers)and a too strong coupling to oxygen (giving rise to surface poisoning by formate,and possibly other species bound through oxygen).At atmospheric pressure,elemental copper is closest to the top,while nickel and palladium bind oxygen too strongly and weakly,respectively.In the ﬁgure we have also included zinc doping in a copper step to model the active site of the ZnO promoted commer-cial catalyst.This has been shown theoretically and experimentally to be a good description 30,and the model captures the near-optimal activity of such a site.Our one-descriptor model therefore provides a good starting point for discovering other potential cata-lysts.We note that even though the zinc promoted copper steps have close to optimal activity,the density of such sites is small in a doped system 30,and a more homogeneous catalyst with the same activity per site but more active sites would be advantageous.In Fig.1we have included predictions of the simple models for the mixed-metal system Ni-Ga.We chose Ni-Ga because this com-prises a series of stable intermetallic compounds with large ordering energies (for example,Ni-Ga is calculated to have a heat of for-mation of 20.64eV/formula unit (two atoms)).This increases the chance that the surfaces exhibit a truncated bulk structure,making modelling simpler.Several of the Ni-Ga intermetallic compounds show active sites with oxygen adsorption energies close to the optimum.We synthesized a series of Ni-Ga catalysts with different Ni:Ga ratios sup-ported on silica using incipient wetness co-impregnation followed by high-temperature reduction in H 2.The Ni-Ga catalysts were charac-terized using X-ray diffraction (XRD)together with transmission electron microscopy (TEM)(Fig.2).As can be seen from the XRD diffraction patterns,all three different Ni-Ga intermetallic com-pounds,Ni 3Ga,NiGa and Ni 5Ga 3,could be prepared rather phase-pure,which can be attributed to the high formation energy of the different phases and the very sharp lines in the Ni-Ga phase diagram 39.The TEM images presented in Fig.2a reveal an average particle size of 5.1nm for the Ni 5Ga 3and 6.2nm for theNiGa.l o g (T O F /T O F C u )ΔE O – ΔE O Cu(eV)Figure 1|Theoretical activity volcano for CO 2hydrogenation to methanol.T urnover frequency (TOF)is plotted as a function of D E O ,relative toCu(211).D E O for the stepped 211surfaces of copper,nickel and palladium is depicted as open black circles,and Cu þZn is depicted in orange.D E O for Ni-Ga intermetallic compounds is depicted in red.Closed circles indicate nickel-rich sites,open circles gallium-rich sites and half-open circles mixed sites.Reaction conditions are 500K,1bar,and a CO 2:H 2ratio of 1:3.Ni 5Ga 3NiGa405060702θ (deg)α-Ni 3Gaδ-Ni 5Ga 3Cu/ZnO/Al 2O 3β-NiGa8090I n t e n s i t y (a .u .)In situ XRDafter reduction/alloying10 nm 10 nmabFigure 2|Characterization of the catalysts studied.a ,TEM images of Ni 5Ga 3and NiGa.b ,In situ XRD patterns of Ni 3Ga,Ni 5Ga 3and NiGa intermetallic compounds as well as Cu/ZnO/Al 2O 3.DOI:10.1038/NCHEM.1873We tested the Ni-Ga catalysts with CO 2hydrogenation at a pressure of 1bar in a tubular ﬁxed-bed reactor.For comparison,a conventional Cu/ZnO/Al 2O 3catalyst was synthesized following the procedure described in ref.40.This procedure has been shown to produce catalysts that are at least as good as the commer-cial catalysts for short-term testing 17.The XRD pattern of the Cu/ZnO/Al 2O 3catalyst is also shown in Fig.2b.The measured Brunauer-Emmet-Teller surface area of this catalyst (92m 2g 21)is comparable to that reported in ref.40.Figure 3shows the measured activity and selectivity towards methanol synthesis as a function of temperature for the different SiO 2supported Ni-Ga catalysts.The amount of active metal (Ni þGa or Cu),in moles,was the same for all catalysts under investi-gation.The corresponding values of the active surface area,esti-mated from XRD and TEM analysis,can be found in Supplementary Table 3.Ni 5Ga 3/SiO 2stands out as being particu-larly active towards methanol synthesis.In fact,at temperatures above 2208C,the yield of methanol is considerably higher than with Cu/ZnO/Al 2O 3.The selectivity,including all products except CO,is very high for Cu-Zn,Ni 5Ga 3and NiGa.Only Ni 3Ga produces signiﬁcant amounts of methane.Notably,the CO-to-methanol ratio of Ni 5Ga 3is signiﬁcantly lower than that of Cu/ZnO/Al 2O 3(Fig.3c).The selectivity towards CO compared to methanol,that is,the rate of the rWGS versus the rate of methanol synthesis is animportant consideration for the present group of catalysts.A CO 2reduction process that mainly produces methanol and water is highly desirable,because the CO will need to be recycled or burned.The conventional Cu-Zn catalyst has a high rate of rWGS.The data in Fig.3show that this is not the case for the Ni-Ga catalysts.DiscussionThe experimental data raise two interesting questions:(1)what is the relationship between the activity volcano in Fig.1and the ranking of the activity data in Fig.3;(2)why is the rWGS activity of the Ni-Ga catalysts lower than for the copper-based catalyst.Part of the answer to the ﬁrst question is related to the obser-vation made earlier that there are two factors affecting the rate,the activity and number of active sites.The copper particles will be most active at the relatively few places where they are promoted by zinc,whereas the active sites on the intermetallic compounds do not need the presence of a promoter.The difference in activity between Cu-Zn and the intermetallic compounds is therefore prob-ably masked by differences in the number of active sites.When it comes to the ranking of the different Ni-Ga catalysts,the main dis-crepancy between the volcano in Fig.1and the experimental data in Fig.3is the Ni 3Ga mixed sites catalyst,which is predicted to be very active,but found not to be so.The reason for this,we suggest,is that the nickel sites become poisoned by adsorbed CO and eventually (through dissociation)by carbon (see the following and the Supplementary Fig.3)and subsequent phase separation.In fact,if we distinguish between nickel-rich sites and gallium-rich sites (as done in Fig.1by using different symbols),it can be seen that the gallium-rich sites follow the ordering observed experimentally very well.The difference in rWGS and methanol synthesis activity can be understood with the same picture.The gallium-rich sites facilitate methanol synthesis and the nickel-rich sites do rWGS (and metha-nation)until they become self-poisoned by CO and carbon.It is different for Cu-Zn,where both rWGS and methanol synthesis proceed at the same surface site.Because CO does not bind strongly enough to copper,no poisoning effect will be observed,which translates into a higher rWGS activity and hence lower methanol selectivity.A more detailed analysis supporting this argument can be found in the Supplementary Section ‘Reverse water-gas-shift volcano’.We note that the high activity ofthe0.100.150.25abcm o l [M e O H]/m o l [a c t i v e m e t a l ]*h0.050.20100Temperature (°C)Temperature (°C)Temperature (°C)C O /M e O H r a t i o M e O H +D ME s e l e c t i v i t y (%)10080604020101Figure 3|The measured activity and selectivity towards methanolsynthesis as a function of temperature for the studied catalysts.a ,Yield of methanol of a series of Ni x Ga y catalysts compared with Cu/ZnO/Al 2O 3as a function of temperature at atmospheric pressure.Gas composition:75%H 2and 25%CO 2.Gas hourly space velocity ¼6,000h 21.b ,CO-free selectivity towards methanol and dimethyl ether in per cent.c ,Comparison of the CO to MeOH ratio of Cu/ZnO/Al 2O 3with Ni 5Ga 3.Time on stream (h)5 × 10P r o d u c t (g [p r o d u c t ]/g [c a t ]*h )Figure 4|Deactivation of Ni 5Ga 3with time on stream.The reaction was carried out at 2008C,atmospheric pressure and with a CO 2to H 2ratio of 1:3.Regeneration of the catalyst in H 2at 3508C is shown.Asterisks mark temperature crashes for several hours that have not been accounted for in the total time on stream.DOI:10.1038/NCHEM.1873Ni-Ga catalysts at high temperatures is related to the low rWGS activity.The amount of water in the gas is smaller,shifting the equi-librium concentration of methanol up,hence substantially reducing the backwards reaction.We performed stability tests for the best catalyst,Ni5Ga3/SiO2, under reaction conditions.Figure4shows the production of metha-nol,CO,dimethyl ether and methane of Ni5Ga3/SiO2as a function of time on stream,at2008C and atmospheric pressure.After initial deactivation of the catalyst,the activity with respect to all products remains quite constant,with CO and methane activity dropping most,supporting the notion developed above that there are two different sites,one for rWGS and methanation(nickel-rich site) and one for methanol formation(gallium-rich site).Ni5Ga3was tested for a period of over60h,after which we tried to regenerate the catalyst through reduction with hydrogen at3508C for2h. As can be seen in Fig.4,the catalyst could be successfully regener-ated to its original activity.Reduction with hydrogen yields an amount of methane equivalent to poisoning of 10%of the catalyst surface area(see Supplementary Table3for details),again conﬁrming our analysis above.Concluding remarksThe Ni-Ga catalysts are not optimized but already show interesting activity,selectivity and stability for ambient-pressure CO2reduction. Importantly,they are superior to the existing Cu/ZnO/Al2O3catalyst with respect to their ability to reduce the rWGS activity in favour of methanol production.A process producing mainly methanol and water would provide an excellent fuel for a fuel cell41,42and could be interesting in connection with a decentralized use of solar-or wind-generated hydrogen.There are many challenges to be overcome to make such a process viable.A process to efﬁciently separate CO2 from air may be the largest43–46,followed by process design and,of course,optimization and test,including stability and resistance to poi-soning of the catalysts.The Ni-Ga catalysts provide a good starting point for a new catalyst system based on non-precious metals showing new and interesting effects of suppressing the rWGS. MethodsDensity functional theory(DFT)calculations for the intermediates and transition states were carried out on the(211)surfaces of copper,silver,palladium,platinum and rhodium using the Dacapo code(http://wiki.fysik.dtu.dk/dacapo).The computational set-up and model surfaces used are identical to those described in ref.47.Determination of NiGa and Ni3Ga intermetallic compound stability was performed as described in ref.47.D E C and D E O were retrieved from ref.47,as found in CatApp48.Further information about calculations regarding Ni5Ga3as well as CO adsorption can be found in the Supplementary Fig.4.Gas-phase values obtained for CO2and HCOOH were corrected as described in refs35and49. Contributions from van der Waals interactions were included as estimated by comparison to calculations performed with the BEEF–vdW functional described elsewhere.35Steady-state solutions to the microkinetic model were found as described in ref.32.Ni-Ga catalysts were prepared using incipient wetness impregnation of a mixed aqueous solution of nickel and gallium nitrates(Sigma Aldrich)on silica(Saint-Gobain NorPro).The samples were directly reduced in H2for2h at7008C.The conventional Cu/ZnO/Al2O3catalyst was prepared following the procedure described in ref.40.Activity measurements were carried out at a totalﬂow rate of100Nml min21in a tubularﬁxed-bed reactor with a CO2to H2ratio of3:1at atmospheric pressures. Catalyst loading was0.472g for Ni3Ga,0.476g for NiGa,0.474g for Ni5Ga3and 0.167g for Cu/ZnO/Al2O3,ensuring that the total amount of nickel and gallium in moles matched the amount of copper in Cu/ZnO/Al2O3.The metal loading of the Ni-Ga and Cu/ZnO/Al2O3catalysts was17wt%and48wt%, respectively.The outlet stream was sampled every15min using a gas chromatograph (Agilent7890A).TEM measurements were performed using a FEI Technai TEM operating at 200kV.XRD patterns were recorded with a PANalytical X’Pert PRO diffractometer equipped with an Anton Paar XRK in situ cell and a gasﬂow control system. 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具刺激性的有机酸

THE MATERIAL WORLDAcetic (ethanoic) acid醋酸无色，具刺激性的有机酸,为食用醋的主要成分。

化学式是CH3COOH。

Acid 酸能在水中溶解并形成酸性溶液的物质。

(substances which dissolve in water forming an acidic solution.)能在水溶液中产生氢离子(H﹢)的化合物。

形容词形式为acidic。

Acid rain 酸雨当不同的非金属氧化物溶解在降水中。

(forms when various oxides dissolve in atmospheric water.)Acidic solution 酸性溶液包含水和离子，尤其是氢离子。

(containing water and ions, particularly hydrogen ions.)Activity series (reactivity series) 反应性序列根据金属的反应性所列出的表。

（list of metals in order of how easily they react.）Alcohol醇（酒精）每分子含有一个氢氧离子, OH。

(hydroxy group)Alkali（base）碱能在水溶液中电离而生成氢氧离子（OHˉ）的化合物。

形容词形式为alkaline (basic)。

Alkane 烷烃公式为C n H2n+2的碳氢化合物。

(saturated hydrocarbons with general formula C n H2n+2.)Alkene 烯烃公式为C n H2n的碳氢化合物。

(unsaturated hydrocarbons with general formula C n H2n.)Alloy 合金金属和其他金属或非金属溶解混合而成的融合物，例如：铅和锌合金的黄铜。

（a mixture of two or more metals.）Aluminiumoxide(Alumina)氧化铝（矾土）铝的氧化物，从铁矾土中可以制造出铝。

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