焙烧温度对低温水煤气变换AuFe 2O3催化剂性能的影响

物理化学学报(Wuli Huaxue Xuebao )
Acta Phys.鄄Chim.Sin .,2008,24(6)：932-938
Received:January 23,2008;Revised:March 3,2008;Published on Web:April 7,2008.English edition available online at
∗
Corresponding author.Email:qizheng2005@.
国家自然科学基金(20271012)和福建省科技计划项目(2002H026)资助
ⒸEditorial office of Acta Physico ⁃Chimica Sinica
[Article]
June
焙烧温度对低温水煤气变换Au/Fe 2O 3催化剂性能的影响
李锦卫
詹瑛瑛
林性贻
郑
起∗
(福州大学化肥催化剂国家工程研究中心,福州
350002)
摘要：采用改性沉积⁃沉淀法制备了系列低温水煤气变换Au/Fe 2O 3催化剂,发现经300℃焙烧的样品具有较好的催化活性和稳定性.并运用N 2物理吸附、原位X 射线粉末衍射(in situ XRD)、程序升温还原(H 2⁃TPR)和X 射线光电子能谱(XPS)等技术,探讨焙烧温度对催化剂性能的影响机制,同时对样品的失活原因进行了分析.结果表明,催化剂性能与焙烧温度引起的金和载体氧化铁的相互作用以及载体还原性质的变化密切相关.XPS 表征结果说明,尽管反应后在催化剂表面有碳酸盐或类碳酸盐物种生成,但半定量分析表明这些物种的形成不是催化剂失活的主要原因;根据在低温水煤气变换反应过程中Au/Fe 2O 3催化剂的比表面积明显下降,载体的结晶度也明显提高,推断Au/Fe 2O 3催化剂载体的结构性质的变化才是其失活的主要原因.关键词：水煤气变换;焙烧温度;失活;Au/Fe 2O 3催化剂
中图分类号：O643
Influence of Calcination Temperature on Properties of Au/Fe 2O 3
Catalysts for Low Temperature Water Gas Shift Reaction
LI Jin ⁃Wei ZHAN Ying ⁃Ying LIN Xing ⁃Yi ZHENG Qi ∗
(National Engineering Research Center of Chemical Fertilizer Catalysts,Fuzhou University,Fuzhou
350002,P.R.China )
Abstract ：A series of Au/Fe 2O 3catalysts for the water gas shift (WGS)reaction were prepared by modified deposition ⁃precipitation method.The sample calcined at 300℃showed higher catalytic activity and better stability than other ing N 2physisorption,in situ XRD,H 2⁃TPR,and XPS techniques,the influence of calcination temperature on properties of Au/Fe 2O 3catalyst was explored,and the cause of deactivation was analyzed as well.The results showed that the catalytic behaviors were related to the interaction between Au and Fe 2O 3,and the reductive property of support,both of which were significantly affected by calcination temperature.Furthermore,according to the results of XPS,although stable carbonate and carbonyl surface species were found on the spent catalysts,the semiquantitative analysis of these species indicated that they were not the main cause of the deactivation.In fact,the deactivation of Au/Fe 2O 3was sensitive to the structure change of support.During the water gas shift reaction,Fe 3O 4particle would aggregate and crystallize leading to increase in the crystallinity of support and a significant reduction in the surface area of the catalysts,which resulted in the deactivation of Au/Fe 2O 3.Key Words ：Water gas shift;Calcination temperature;
Deactivation;
Au/Fe 2O 3catalyst
The water gas shift (WGS)reaction is a key reaction in the pro duction of hydrogen for a number of process,including petroleum refining and chemical synthesis.An emerging application for the WGS is in the production of hydrogen for proton exchange membrane (PEM)fuel cells.This reaction is important because
it removes CO,a poison to the fuel cell electrocatalysts,which is produced during the steam reforming and/or partial oxidation re-actions.Cu ⁃based and Fe ⁃Cr ⁃based WGS catalysts are commer-cially used in current chemical plants.However,they are unsuit-able for PEM system because they are pyrophoric and they do
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No.6LI Jin⁃Wei et al.：Influence of Calcination Temperature on Properties of Au/Fe2O3Catalysts for Low Temperature
not have sufficient activity at low temperature.So,there is sub-
stantial interest in development of better performance and more
durable WGS catalysts[1-5].
Recently,it has been reported that Au supported catalysts are
interesting candidates for novel WGS reaction[6-11].High activities
of Au/Fe2O3and Au/CeO2for WGS reaction have been observed
by Andreeva[6]and Fu[7]et al.It is generally known that high catalytic activity of the gold/metal oxide catalysts depends
strongly on the dispersion of gold particles and the interaction
between gold and support.Therefore,most of the interest in gold
catalysis has geared to the study of preparation method[6,12-14],the
synthesis parameters[15,16],pretreatment conditions[17,18],and the
choice of supports[19,20],all affecting the dispersion of the gold
particles.However,there is relatively little work devoted to the
effect of the state and structure of support in the WGS reaction.
Zhang et al.[21]reported the remarkable nanosize effect of zirco-
nia in Au/ZrO2catalyst for CO oxidation.In addition,supported
gold catalysts have been reported to be susceptible to deactiva-
tion.There are several reports describing deactivation mecha
nisms for gold⁃based CO oxidation catalysts[22-26].Some of the
studies have considered sintering of Au particles as a reason for
the deactivation[24-26].Change of Au particle size from4to5.5nm
has been taken as a significant change influencing the catalytic
performance[26].For WGS reaction,catalysis process of gold⁃
containing systems generally involves the formation of carbonyl
or carbonate-like species on ultrafine gold particles.Kim et al.[27]
reported that it is these species blocking the active surface sites
that contribute to the deactivity of Au/CeO2catalyst.There is
only one another work[28],which is devoted to the study of deacti
vation mechanisms of the gold⁃based WGS catalyst.With the
help of DRIFTS,MS,TGA,TEM,N2physisorption,ICP,and
XRD,Silberova et al.[28]put forward that the decrease of the sur-
face area can almost solely explain the decrease on the activity
when Au/Fe2O3catalyst was exposed to a steam with0.5%CO,
1.5%H2O,and98%He.Because WGS gas composition in the
production of hydrogen for proton exchange membrane(PEM)
fuel cells is typically with10%CO,furthermore work is needed
to clarify whether the decrease of the surface area is the essential
reason for the deactivation of Au/Fe2O3catalysts in higher CO
concentration.
In this article,temperature⁃programmed and long⁃term stabili-
ty tests of Au/Fe2O3catalysts calcined at different temperatures
for the WGS reactions were studied.The influence of calcina-
tion temperature on the structure and catalytic performance of
Au/Fe2O3catalysts for WGS reaction were investigated by apply
ing different characterization techniques(e.g.in situ XRD,N2physi-
cal adsorption,TPR,and XPS).Finally,all of above characteri-
zations of the physical and chemical properties of the fresh and
used catalysts helped to define the deactivation mechanism.
1Experimental
1.1Catalyst preparation
Supported gold catalysts used in this article were designed with mass fraction of4.0%Au and prepared by the following general route.The aqueous solutions of1.0mol·L-1Fe(NO3)3 and1.0mol·L-1K2CO3were simultaneously added dropwise to 20mL deionized water at60℃and at a constant pH value of 8.0under vigorous stirring.After being centrifuged and washed with deionized water several times,the obtained precipitate was redispersed into30mL deionized water at60℃.Then the0.2 mol·L-1HAuCl4was pumped into the support slurry under vig-orous stirring at ca8.0cm·min-1.And the base(0.5mol·L-1 K2CO3)was pumped in at a variable rate to maintain pH as close as possible to8.0throughout the addition of gold chloric acid. After the aqueous solution addition was complete,stirring was continued for a further1h at60℃.The acquired samples were alternatively centrifuged and washed with deionized water until no Cl-ion was detected by AgNO3solution.Following that,the samples were dried at110℃for8h,then heated to desired tem-perature(200,300,400or500℃)in air at a rate of5℃·min-1and held at concerned temperature for2h.The as-prepared samples were labeled as Au/Fe⁃200,300,400,or500,respectively.For comparison,Fe2O3was prepared in a similar way.
1.2Catalyst characterization
The textures of the samples were obtained from nitrogen ab-sorption⁃desorption isotherms which were measured at liquid ni-trogen temperature,using‘OMINSORP100CX’instrument.Be-fore analysis,the samples were degassed at150℃to final pres-sure of1×10-3Pa.
Powder X⁃ray diffraction(XRD)data of all samples were col-lected via a Panalytical X′Pert Pro diffractometer with X′Celera-tor Detector,using the Co Kαradiation(0.1790nm)at a voltage and current of40kV and40mA,respectively.Diffraction patterns were recorded at room temperature(25℃)in the step scanning mode,with a2θstep of0.0333°and every step standing for10s in the range of20°≤2θ≤80°.
Temperature⁃programmed reduction(TPR)of the catalysts in fine powder form was carried out in a‘Micromeritics Autochem 2910’instrument equipped with a thermal conductivity detector (TCD).About100mg of the fresh sample was packed into a re-actor with quartz tubing of6mm i.d.(inner diameter),and pretreat-ed with high purity helium gas at120℃for1h.Then TPR traces of samples were pursued in a reductive flow of30mL·min-110%(φ)H2in helium,on raising the system temperature linearly from room temperature to700℃at a ramp rate of5℃·min-1.
In addition,the chemical transformation of uncalcined Au/Fe2O3catalyst was studied with in situ XRD by heating the samples in a gas mixture of H2/N2(φ(H2)=10%)at a rate of2℃·min-1.Diffraction patterns were recorded within2θ=30°-50°during the reduction process since most intense diffraction peaks of Fe2O3phases are located in this2θrange.
The X⁃ray photoelectron spectroscopy(XPS)measurements were performed with a Phi Quantum2000spectrophotometer with Al Kαradiation(1486.6eV).The samples were preliminari-ly pressed into pellets and reduced at150℃for9h in H2/N2
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Acta Phys.鄄Chim.Sin.,2008Vol.24
mixture(φ(H2)=10%),then transferred to a test chamber.An
electron takeoff angle of45°was used.The vacuum in the test
chamber was maintained below1.33×10-7Pa during the collec-
tion.Binding energies were corrected for surface charging by
referencing them to the energy of C1s peak of contaminant car-
bon at284.8eV.
1.3Activity and stability measurements
The catalytic activity of the samples in the WGS reaction was
measured using‘CO⁃CMAT9001apparatus(Beijing Hangdun,
China)’at atmospheric pressure.A stainless steel tube with an
inner diameter of9mm was used as the reactor tube.The sam-
ples were all0.5cm3(20-40mesh size)in volume and prelimi-
narily reduced at150℃for9h in H2/N2mixture(φ(H2)=10%).
The mixture reactant gas,containing10%(φ)CO diluted by ni-
trogen,passed through a vaporizer(82℃)before being fed into the reactor.Catalysts were tested in the range of150-300℃with a step size of50℃.At each test point the reaction temperature re-mained unchanged for5h.The flow rate was91mL·min-1 (space velocity:11000h-1).The tail gas was directed through a condenser and then sent to an online gas chromatograph(Shi-madzu GC⁃8A),where the CO content was analyzed.The catalytic activity was expressed by the degree of conversion of CO,which was defined as X(CO)=((1-V′C O/V CO)/(1+V′C O))×100%,where V CO and V′C O were the inlet and outlet contents of CO,respectively.
2Results and discussion
2.1Influence of calcination temperature
The conversion of CO shift to CO2obtained via the water gas shift reaction over the Au/Fe2O3catalysts uncalcined(only dried at120℃)and calcined at different temperatures is presented as a function of temperature in Fig.1.The uncalcined sample dis-plays considerable activity at150℃,reaches a maximum at200℃,but declines to a lower value with further increasing test tem-perature.The catalysts calcined at200and300℃also show high activity and the similar tendency.However,upon further in-creasing the calcination temperature(400and500℃),we find that the catalytic activity decreases distinctly.Especially for the sample calcined at500℃,the catalytic activity decreases most observably and almost loses the activity at150℃.
Structural characteristics of the samples under study have been investigated by the nitrogen absorption⁃desorption isotherms and X⁃ray diffraction(XRD).The pore size distributions of the fresh catalysts are presented in Fig.2.And the detailed data for all samples are given in Table1.
Comparing with the uncalcined samples,Au/Fe⁃200series samples show higher surface area and lower pore diameter except the reduced sample.On further increasing the calcination temper-ature,the surface area decreased remarkably,whereas the pore di-ameter increased on the contrary.To our interest,as we can see in the last column of Table1,the particle size of supports shows the regular change,i.e.,it increases with the increase in calcination temperature and the further reduction and use.
XRD patterns of all fresh Au/Fe2O3catalysts are reported in Fig.3.According to Au Mössbauer spectra for the uncalcined material studied by Hodge et al.[29],a considerable portion of AuOOH·x H2O may also be contained.However,in our case,as can be seen in Fig.3,the uncalcined sample only presents several weak peaks related to hematite(JCPDS03⁃0800)and
metallic Fig.1CO conversion obtained during the temperature鄄
programmed test of WGS reaction over Au/Fe2O3catalysts
calcined at different temperatures
(a)uncalcined,(b)Au/Fe⁃200,(c)Au/Fe⁃300,(d)Au/Fe⁃400,(e)Au/Fe⁃500
Fig.2Pore size distribution of Au/Fe2O3catalysts calcined
at different temperatures
(a)uncalcined,(b)Au/Fe⁃200,(c)Au/Fe⁃300,(d)Au/Fe⁃400,(e)Au/Fe⁃500
BET
2·g-1pore-1pore d Fe2O3/nm
790.236 4.5not detected
reduced750.2067.410.9
spent280.18126.019.6
Au/Fe⁃200fresh1780.257 2.28.3
reduced940.24815.514.8
spent330.18122.021.2
Au/Fe⁃300fresh1320.223 3.013.1
reduced700.2178.212.5
spent330.19023.021.9
Au/Fe⁃400fresh470.220 6.515.8
reduced360.18013.018.7
spent12.70.0329.937.3
Au/Fe⁃500fresh250.16210.518.6
reduced180.14216.326.7
spent13.50.03410.034.6
uncalcined fresh
Table1Physicochemical properties of Au/Fe2O3catalysts
treated under different conditions
934
No.6LI Jin ⁃Wei et al .：Influence of Calcination Temperature on Properties of Au/Fe 2O 3Catalysts for Low Temperature gold (JCPDS 01⁃1172).The characteristic peak of gold (111)over-laps with the diffraction peak of hematite,which indicates that Au(OH)3of precipitate gold species is thermally unstable at 120℃and tends to decompose to metallic gold during the drying pretreatment:2Au(OH)3➝2Au+3H 2O+3/2O 2[30].With the increase in calcination temperature,the characterization peaks diffracted from both hematite and gold become more distinct,indicating that the gold particle size and the degree of crystallinity of the support increased.
Fig.4gives the H 2⁃TPR profiles of the investigated catalysts.For comparison,the profile of Fe 2O 3prepared by the same method (calcined at 300℃)is also showed in Fig.4.The TPR spectra of Au/Fe 2O 3catalysts calcined at lower temperature (below 300℃)are composed of three main peaks:one located in the lower tem-perature region is related to partial reduction of amorphous Fe 2O 3➝Fe 3O 4and/or hydroxy groups.Ilieva et al .[31]reported that the hydroxyl coverage on Au/Fe 2O 3was about two times higher than that on pure Fe 2O 3.The second peak at about 180℃is at-tributed to the reduction of crystalline Fe 2O 3➝Fe 3O paring with that of the same transition in the absence of gold,it de-creased by ca 200℃,indicating that the metal ⁃support interac-tion between the gold crystallites and the hematite particle is very strong.This interaction has also been reported by Andreeva et al.[6].The last wide peak at about 600℃is attributed to the re-
duction of Fe 3O 4➝FeO ➝Fe [32,33].Their intensity and position are independent to the calcination temperatures and doping of gold.For the sample calcined at 400and 500℃,the first reduction peak disappears because of dehydroxylation by calcination and furthermore crystallization of support at high temperature,and the second peak being attributed to the reduction of crystalline Fe 2O 3➝Fe 3O 4shifts to higher temperature zone (200-350℃).Based on the results of XRD,we find that the position of the second peak shifts to high temperature region with the increase in crystallization extent of the supports,indicating the reducibili-ty of Au/Fe 2O 3influenced by the crystallinity of support.We think that the amorphous iron oxide material contained much more surface defect that would strengthen Au ⁃support interac-tions,and a higher calcination temperature would lead to a well crystallized iron oxide and a weaker interaction between gold and iron oxide.It is likely that the intimate interaction between gold and the support is crucial for water gas shift activity.
In order to further confirm the attribution of the TPR peaks,the in situ XRD experiments were carried out.The in situ XRD patterns in Fig.5show the transformation of uncalcined Au/Fe 2O 3during the heating in a gas mixture of H 2/N 2(φ(H 2)=10%).The three peaks at 38.5°,41.4°,and 47.7°are the characteristic (104),(110),and (113)diffraction peaks of Fe 2O 3(JCPDS 03⁃0800),and the peak of Fe 2O 3at 44.7°overlaps with the (111)diffraction peak of gold (JCPDS 01⁃1172).All peaks of the sam-ple do not change significantly between room temperature and 160℃,but in the TPR profiles (Fig.4),during this temperature zone,there is a strong reduction peak (near 100℃)for samples calcined under low temperature.This confirms the analysis of TPR that the low temperature reduction peak (near 100℃)is the reduction of surface hydroxyl groups and/or reduction of amor-phous Fe 2O 3➝Fe 3O 4.When the detected temperature is increased to 170℃,the relative intensities of Fe 2O 3diffraction peaks de-crease,and a new diffraction peak rises at 35.1°corresponding to the (220)reflection of FeFe 2O 4phase (JCPDS 19⁃06292).Fur-ther increasing the detected temperature,the phase of Fe 2O 3van-ishes at 200℃and the 41.4°peak corresponding to the (311)re-flection of FeFe 2O 4phase (JCPDS 19⁃06292)becomes more in-tense with the increase in temperature.All results acquired by
in
Fig.3XRD patterns of Au/Fe 2O 3catalysts calcined at
different temperatures
(a)uncalcined,(b)Au/Fe ⁃200,(c)Au/Fe ⁃300,(d)Au/Fe ⁃400,(e)Au/Fe ⁃
500
Fig.4H 2⁃TPR profiles of Fe 2O 3calcined at 300℃and Au/Fe 2O 3catalysts calcined at different temperatures
(a)uncalcined,(b)Au/Fe ⁃200,(c)Au/Fe ⁃300,(d)Au/Fe ⁃400,(e)Au/Fe ⁃
500
Fig.5In situ XRD patterns of uncalcined Au/Fe 2O 3catalysts
during temperature ⁃programmed reduction
935
Acta Phys.鄄Chim.Sin.,2008Vol.24
situ XRD support the attribution for the TPR peaks and hint that the Fe3O4phase is likely to be further crystallized at redox atmo-
sphere.
On the basis of the results discussed above,it can be conclud-
ed that the presence of gold in Au/Fe2O3sample,giving rise to
interaction between gold and iron oxide,leads to a considerable
lowering of the temperature of the reduction step Fe2O3➝Fe3O4. However,the increase in calcination temperature causes the
gradual increase in the crystallinity of Au and support,leading to
the weakening of their interaction,and resulting in the serious
decreasing of the catalytic activity.
2.2Deactivation properties
2.2.1Isothermal test at200℃
Fig.1shows that Au/Fe2O3catalysts exhibit high activity for
water gas shift reaction,but the stability of catalysts under oper-
ating conditions is important for commercial applications,too.
In fact,the difficulty of preparing highly active gold catalysts is
mirrored in the problem of maintaining this activity.However,
this aspect was rarely examined,and it is not clear whether sup-
ported gold catalysts do have sufficient stability for practical ap-
plication.So,the long⁃term experiments were performed at200℃and the results are presented in Fig.6.The results show that fast deactivation phenomenon occurs in the first5h for all cata-lysts,independent of the calcination temperature.The deactiva-tion degree of low⁃temperature treatment(uncalcined and cal-cined at200℃)catalysts is higher than that of samples calcined at300,400or500℃.The lowest activity but the best stability is obtained with the catalyst calcined at500℃.The highest activi-ty with an excellent stability for water gas shift reaction is achieved with the catalyst calcined at300℃.
2.2.2Microstructural properties
Table1lists the measured values of the specific surfaces and
pore diameters of the fresh samples and after various treatments,
i.e.,reduction by H2/N2(φ(H2)=10%)at150℃for9h and after
catalytic operation.From Table1,it can be seen that the BET
surface area and pore volume of every sample decrease remark-
ably when Fe2O3is reduced to magnetite(Fe3O4)by H2/N2(φ(H2)=
10%).This phenomenon accompanied by the enlargement of pore diameter is more distinct for the sample suffering the catalytic operation.All used samples show a surface area less than20m2·g-1,indicating that distinct restructure of the supports occurred during the catalytic operation.This inference is consis-tent with the evolvement of the sample′s crystalline structure as revealed by XRD.When the fresh and used samples were com-pared(Fig.7and Fig.3),we had not observed obvious changes of intensities of characteristic(111)and(200)diffraction peaks of gold.This indicated that the gold particles had not changed dur-ing the catalytic process.So in our case,the deactivation of cata-lyst do not essentially relate to the gold particle size.This phe-nomenon was consistent with the results reported by Silberova et
al.[28].On the contrary,the supports of all investigated catalysts have been changed after reduction and WGS reaction,the hematite structure in fresh catalysts was transformed into the magnetite structure,and the particle size of the support was in-creased remarkably(Table1).The above discussion suggests that the deactivation is accompanied by a change in texture proper-ties.The support of used Au/Fe2O3catalyst for water gas shift re-action was severely transformed.Although the support was pre-treatment by H2/N2(φ(H2)=10%)at150℃for9h,the reduction of support and the growth of magnetite crystals did not stop dur-ing the catalytic process.A significant reduction in the surface area of the catalysts and increase in the crystallinity of support took place during the water gas shift reaction.This change is likely to be the main cause for the deactivation of Au/Fe2O3cata-lysts.
2.2.3Surface characterization of the deactivated catalyst
To better understand the mechanism of deactivation,the sur-face properties of Au/Fe2O3catalysts calcined at300℃was characterized.X⁃ray photoelectron spectroscopy(XPS)was used to characterize chemical species on the reduced and deactivated catalysts.XPS spectra for C1s and Au4f regions are shown in Fig.8.Features in the Au4f regions were nearly identical for the reduced and deactivated catalysts and indicated the presence of gold in the metallic state.Deconvolution of the C1s spectra in-dicated that there were four different carbon species on the cata-lyst surface:adventitious carbon(284.7eV),carbon associated
with Fig.6CO conversion obtained during the isothermal
stability test of WGS reaction over Au/Fe2O3catalysts
calcined at different temperatures
(a)uncalcined,(b)Au/Fe⁃200,(c)Au/Fe⁃300,(d)Au/Fe⁃400,(e)Au/Fe⁃500
Fig.7XRD patterns of Au/Fe2O3catalysts calcined at
different temperatures after WGS reaction
(a)uncalcined,(b)Au/Fe⁃200,(c)Au/Fe⁃300,(d)Au/Fe⁃400,(e)Au/Fe⁃500 936
No.6LI Jin⁃Wei et al.：Influence of Calcination Temperature on Properties of Au/Fe2O3Catalysts for Low Temperature
R—OH(286.1eV),adsorbed CO2(292.6eV),and—COOR/CO2-3 (288.3eV,its existence was ever interpreted for the deactivation of Au/CeO x water gas shift reaction catalysts)[27,34].Comparing the peaks of the reduced and spent catalysts,we found that the peak of R—OH(286.1eV)was observed on both samples,and the peak area increased obviously in the spent catalyst.The out-let gas under the WGS condition was detected by IR instrument. However,methanol or other byproduct produced was not detect-ed for the investigated catalysts[4].So,the reason for the peak of R—OH(286.1eV)increase is not explained in this study.At the same time,we found that the peak of—COOR/CO2-
3
(288.3eV) also increased to some extent but not as obviously as described in the published work[27].Moreover,the gold⁃base catalysts supported on carbonate also show high activity for low⁃tempera-ture CO oxidation in the presence of water in the feed steam[35]. Therefore,the formation of carbonate and carbonyl species during the water gas shift reaction could not be taken as the main cause of the Au/Fe2O3deactivation.
3Summary
The catalytic activity and stability of Au/Fe2O3catalysts de-pend strongly on the calcination temperatures and crystallinity of the support.Increasing calcination temperature causes the gradu-al increase of the crystallinity of gold and the support,leading to the serious weakening of the interaction between gold and sup-port,and the decrease of the catalytic activity.
The fast deactivation phenomenon was observed in the first5 h for all Au/Fe2O3catalysts,independent of the calcination tem-perature and crystalline structure of the support.By XRD and XPS analyses,we exclude the possibility of the increase in Au particles and the formation of carbonate and carbonyl species during the water gas shift reaction as the main cause of the Au/Fe2O3deactivation.Whereas,the in situ and/or normal XRD, and N2physisorption characterization disclose that the support suffers severe changes during the water gas shift reaction,i.e., Fe3O4particle would aggregate and crystallize leading to the in-crease in the crystallinity of Fe3O4and the decrease in the sur-face area of the catalysts,and ultimately,this change causes the deactivation of Au/Fe2O3catalyst.
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