水煤气变换反应(WGSR)AuFe2O3催化剂的相关影响因素

.2011－2012 学年第二学期《专外与文献检索》 课程考查成绩细则成绩组成及比重具体项目及分数检索策略（15）基本格式（5）摘要（5）关键词（5）论文（80％）前言、正文、结论（30） 文中是否按顺序标明文献出处（5）参考文献的编排格式（10）中英文文献数量（5）摘要原文及翻译（20）合计（100）作业（10％）出勤（10％）成绩：得分..《专外与文献检索》课程考查课题名称（2 分）中文 低温水煤气变换反应研究进展 英文 Low-Temperature Water-Gas ShiftReactionResearchProgress一．课题简介（4 分）水煤气变换反应( Water- Gas Shift Reaction, 简称 WGSR) 的工业应用已有90 多年历史，在以煤、石油和天然气为原料的制氢工业和合成氨工业具有广泛的应用，在合成气制醇、制烃催化过程中，低温水气变换反应通常用于甲醇重整制氢反应量 CO 的去除，同时在环境科学甚至在民用化学方面所起作用也不可忽视，如汽车尾气的处理、家用煤气降低 CO 的含量等。

近年来由于在燃料电池电动车上的应用,这一经典化学反应的研究再次引起国外同行极大关注。

近年来近年来，负载型催化剂一直是低温水煤气变换反应催化剂研究的热点，尤其是负载金超微粒子催化剂研究，因此，探究低温水煤气变换反应研究进展，研究起催化剂发展状况具有重要意义。

二．中文检索词及基本检索策略（列出检索字段及逻辑运算关系）（3 分）中国知网 具体日期 2005.1.1-今天..题名：水煤气变换反应 并含主题：低温三．英文检索词及基本检索策略（列出检索字段及逻辑运算关系）（3 分）数据库：Elsevier Science 电子期刊检索方法："water-gas shift reaction" orWGSR or "WGS reaction" （title）（一行）AND "low temperature"（title）（一行）Data range： 2005 to present数据库：ISI Web of Knowledge 检索方法："water-gas shift reaction" orWGSR or "WGS reaction" （title）（一行） AND "low temperature"（title）（一行）时间跨度 2005 到 2012数据库：EI(工程索引)—compendexWebSearch forsearch in"water-gas shift reaction"titleOr WGSR or "WGS reaction"title"low temperature"title Limit by 2005-2012 注释：引号在英文半角输入四．所用电子资源名称及最终检出结果数（3 分）.电子资源名称 中国知网 Elsevier Science 电子期刊 ISI Web of Knowledge EI(工程索引)—compendexWeb.检出结果数 11 篇 43 篇 66 篇 56 篇低温水煤气变换反应研究进展摘要：低温水煤气变化反应由于它在许多工业过程起着重要作用，引起了研究者的极大兴趣， 一直是研究领域的一个热点问题。

水煤气变换反应催化研究作者：***摘要：能源问题是全球人民关注日益密切的问题，能源的高效利用和开发发新能源成为各国科学家要努力攻破的课题。

氢能是一种很好的替代能源,并且燃料电池制氢系统具有高效、可靠、灵活、低污染、操作性能优良等特点,而且燃烧过程不产生任何环境污染物,使氢成为真正最清洁的燃料, 氢能无疑是最环保的能源，没有之一，所以各国都在大力开发氢燃料电池技术。

制氢技术的发展有利于氢能源的广泛利用，目前水煤气变换反应(WGS, CO+H2O=CO2+H2, kJ/mol)能够有效的使等量的CO与H20反应,转变成C02和H2,因此水煤气变换反应在制氢工业中有着广泛的应用。

关键词：水煤气变换反应低温催化剂前言：随着新型燃料电池工业的兴起, 负载型金催化剂在水煤气变换 (WGS)反应中的应用逐渐成为研究热点[1]。

燃料电池具有能量效率高、环境友好等优点, 作为固定式电源和移动式电源具有广阔的应用前景。

其中, 质子交换膜燃料电池被认为是最适宜的动力电源。

烃类和醇类 (如天然气、甲醇 )等富氢燃料通过现场重整的方式为燃料电池提供氢源, 是近期乃至中期最现实的燃料电池氢源解决方案[2]。

正文：水煤气变换(WGS)反应主要用于精华合成气，为合成氢的反应过程提供洁净的H2来源，近年来，，由于以纯氢为原料的车载质子交换膜燃料电池（PEMPC）技术的兴起，是的这一静电反应再次引起研究者的极大兴趣，负载Au催化剂具有较高的低温活性、较宽的活性温区、较好的抗氧化性能及抗水性能，因而被认为是最适合用于PEMFC苛刻操纵环境的WOS催化剂之一。

目前，具有较好WGS催化活性的负载Au 催化体系包括Au/Fe2O3, Au/TiO2, Au/ThO2, Au/Cu x Mn y O z,Au/CeZrO4及Au/ZrO2等。

其中，Au/ZrO2因性能友谊而成为近年来的研究热点。

研究发现，ZrO2的晶型、颗粒及晶粒大小、表面羟基的浓度以及比表面积等性质对Au/ZrO2催化剂的性能有显著影响。

水煤气变换催化剂摘要：水煤气变换反应（WGRS)在化工生产中起着积极而重要的作用，一是人们研究的课题之一。

催化反应进行的催化剂是近年来的研究热点。

本文对各种催化剂的制备及性能、影响因素做了详细的阐述，并就我国低温水煤气变换催化剂的研发提出了一些见解。

关键词：水煤气；催化剂；发展0 引言众所周之，氢是工业领域中一种至关重要的天然材料，它已经在合成氨工业中广泛应用，分解高分子的天然油脂和脱硫。

除此之外，氢也是一种不平常的燃料，它的能量密度或者发热量远高于其他气体或者液体燃料。

氢的天然存在量很少，需要工业大量合成，水煤气变换反应是工业用氢气的主要来源。

水煤气变换反应(CO+H2O==CO+H2，△H=一41．9 Kmol／mo1),在合成氨、合成甲醇等制氢工业中)是一重要的反应过程。

水煤气变换反应速度相对较慢，需高性能的催化剂使放映得以进行。

工业化的变换催化剂均是固体催化剂，如铁系高温变换催化剂、铜锌系低温变换催化剂、钴钼系耐硫宽温变换催化剂等，且均采用固定床反应器[1]。

国外对气一水溶液体系水煤气变换反应一直没有间断过研究，研究主要从两个方面进行。

一是对各种无机化合物作为催化剂反应系统的效能进行考察，另一方面是对各种贵金属有机化合物作为催化剂进行研究，无机化合物作为催化剂的反应体系适用性较好，对氧气有一定的承受能力，而金属有机化合物作为催化剂的反应体系，对氧非常敏感，几乎要求在无氧条件下进行，PPM 级的杂质氧就能使催化剂失活[2]，国内在这方面的研究也在不断进行。

1 水煤气变换反应关于水煤气变换反应的反应机理，目前普遍接受的是表面氧化还原机理，可表示为[3]：H 2O(g)一H2O(S) (1)H2O(S)一OH(S)+H(S) (2) OH(S)一O(S)+H(S) (3)2H(S)一H2(g) (4)CO(g)一CO(S) (5)CO(S)+O(S)一CO(S) (6)CO2(S)一CO2(g) (7)式中，g表示气态，S表示表面吸附态。

2025届高考化学一轮复习专题卷： 晶体结构与性质一、单选题1．下列推论正确的( )A.的沸点高于，可推测的沸点高于B.为正四面体结构，可推测出也为正四面体结构C.晶体是分子晶体，可推测晶体也是分子晶体，D.是碳链为直线型的非极性分子，可推测也是碳链为直线型的非极性分子2．有四种不同堆积方式的金属晶体的晶胞如图所示，有关说法正确的是( )A.①为简单立方堆积②为六方最密堆积③为体心立方堆积④为面心立方最密堆积B.每个晶胞含有的原子数分别为：①1个，②2个，③2个，④4个C.晶胞中原子的配位数分别为：①6，②8，③8，④12D.空间利用率的大小关系为：①<②<③<④3．下列叙述错误的是( )A.金属键无方向性和饱和性，原子配位数较高B.晶体尽量采取紧密堆积方式，以使其变得比较稳定C.因共价键有饱和性和方向性，所以原子晶体不遵循“紧密堆积”原理D.金属铜和镁均以ABAB…方式堆积4．环六糊精（D-吡喃葡萄糖缩合物）具有空腔结构，腔内极性较小，腔外极性较大，可包合某些分子形成超分子。

图1、图2和图3分别表示环六糊精结构、超分子示意图及相关应用。

下列说法错误的是( )4SiH 4CH 3PH 3NH 4NH +4PH +2CO 2SiO 26C H 38C HA.环六糊精属于寡糖B.非极性分子均可被环六糊精包合形成超分子C.图2中甲氧基对位暴露在反应环境中D.可用萃取法分离环六糊精和氯代苯甲醚5．下列反应的离子方程式正确的是( )A.去除废水中的：B.过氧化钠在潜水艇中作为的来源：C.沉淀溶于氨水：D.在溶液中滴加少量溶液：6．碳硼烷酸是一类超强酸，也是唯一能质子化富勒烯(如)但不会将其分解的酸，2Na S 2Hg +2+2-Hg +S HgS ↓2O 22222O 2H O 4OH O --++↑AgCl ()332AgCl 2NH Ag NH Cl⎡⎤+⎣⎦NaOH ()442NH AlSO ()34Al 4OHAl OH -+-⎡⎤+⎣⎦60C其结构如图所示。

费-托合成中的水煤气变换反应蔡丽萍 沈菊李 唐浩东 刘化章* 杨霞珍(浙江工业大学工业催化研究所 杭州 310014)摘 要 评述了近年来有关费-托合成中的水煤气变换反应的研究进展，着重介绍了费-托反应条件下发生的水煤气变换反应的热力学分析、反应机理和动力学。

同时介绍了催化剂制备、操作参数等因素对水煤气变换反应的影响。

关键词 水煤气变换反应 费-托合成 机理 动力学The Water Gas Shift Reaction in Fischer-Tropsch SynthesisCai Liping, Shen Juli, Tang Haodong, Liu Huazhang *, Yang Xiazhen(Catalysis Institute of Zhejiang University of Technology, Hangzhou 310014)Abstract In this paper, the development of research on the water gas shift(WGS) reaction in theFischer-Tropsch synthesis (FTS) was reviewed. The WGS reaction is important when synthesis gas with nonstoichiometric amounts of hydrogen is used, whereas CO efficiency is decreased accordingly. Its thermodynamic analysis, reaction mechanism and kinetics in conjunction with the FTS are presented. The WGS reaction is equilibrium or close to equilibrium reaction under Fischer-Tropsch conditions on catalysts with a high water gas shift activity such as iron-based FTS catalysts, which may operate via a mechanism with a formate species or via a direct oxidation mechanism. The kinetic studies assumed that the WGS reaction proceeds on a different catalytic site than the FTS. The effects of catalyst preparation and operation parameters on the WGS reaction activity are also summarized. The importance and prospect of research on the WGS reaction under the Fischer-Tropsch conditions are proposed.Key words Water gas shift reaction(WGS reaction), Fischer-Tropsch synthesis(FTS), Mechanism,Kinetics21世纪，世界能源的需求量仍将继续增长，费-托合成(Fischer-Tropsch synthesis ，简称为FTS)作为一个清洁利用煤炭和天然气资源的途径，受到各国能源部门的重视。

催化剂设计对提高碳氢化合物转化反应效率影响因素分析催化剂是化学反应中起到催化作用的物质，能够加速反应发生并提高反应的效率。

在碳氢化合物转化反应中，催化剂的设计起着至关重要的作用。

本文旨在分析催化剂设计对提高碳氢化合物转化反应效率的影响因素。

1. 催化剂的成分和结构催化剂的成分和结构对碳氢化合物转化反应的效率有重要影响。

首先，催化剂的活性材料应具有适合的能级结构，以提高反应发生的能力。

对于氢化反应而言，催化剂通常由贵金属（如铂）或过渡金属（如镍、钴）组成，这些金属具有较好的催化性能。

其次，催化剂的结构也需要考虑。

催化剂的表面形貌、晶格结构和孔结构等都会影响反应物质在催化剂表面的吸附和扩散行为，进而影响反应的速率和选择性。

2. 催化剂的活性位点在催化剂设计中，活性位点的选择是非常重要的。

合理设计催化剂的活性位点可以增强催化剂与反应物之间的相互作用，提高反应速率和选择性。

常见的活性位点包括吸附位点、活性中心和晶体缺陷等。

通过在催化剂表面引入适当的活性位点，可以提供与反应物分子之间的相互作用所需的键合能，从而改善反应效率。

3. 催化剂的尺寸效应尺寸效应是指催化剂颗粒尺寸对反应性能的影响。

研究表明，催化剂颗粒的尺寸对反应速率和选择性有明显影响。

较小的催化剂颗粒具有更大的比表面积和更多的晶格缺陷，有利于提高反应物吸附和扩散速率，从而增强反应效率。

此外，尺寸效应还会影响反应物质在催化剂表面的吸附位点的可访性和反应活性，进一步改变反应过程。

4. 催化剂的修饰催化剂的修饰是通过向催化剂表面引入特定的功能基团或异质原子来改变催化剂的性质。

修饰可以改变催化剂的吸附性能、电子状态以及酸碱性等重要特性，从而影响反应速率和选择性。

例如，通过在催化剂表面修饰金属或半导体颗粒，可以调节反应物在催化剂表面的吸附等特性，提高催化剂的活性和稳定性。

5. 反应条件的优化除了催化剂设计外，反应条件的优化也非常重要。

反应温度、气体流速、反应物浓度等条件会对反应速率和选择性产生明显影响。

水煤气变换催化剂研究新进展【文献综述】毕业论文文献综述化学工程与工艺水煤气变换催化剂研究新进展一、前言部分水煤气是通过炽热的焦炭而生成的气体，主要成份是一氧化碳，氢气，燃烧后排放水和二氧化碳，有微量CO、HC和NO X。

燃烧速度是汽油的7.5倍，抗爆性好，据国外研究和专利的报导压缩比可达12.5。

热效率提高20－40％、功率提高15％、燃耗降低30％，尾气净化近欧IV标准，还可用微量的铂催化剂净化。

比醇、醚简化制造和减少设备，成本和投资更低。

压缩或液化与氢气相近，但不用脱除CO，建站投资较低。

还可用减少的成本和投资部分补偿压缩(制醇醚也要压缩)或液化的投资和成本。

有毒，工业上用作燃料，又是化工原料。

二、主题部分（阐明有关主题的历史背景、现状和发展方向，以及对这些问题的评述）1负载金超微粒子WGS催化剂金由于化学惰性和难于高度分散，一般不用作催化剂。

传统上金催化剂的制备大多采用浸渍法，无法制得具有高活性的金超微粒子。

因此，并未显示出较其它金属催化剂更好的催化性能。

80年代以来，人们通过改变制备方法获得高度分散态金催化剂，显示出其超常的催化性能。

它对许多反应都具有极高的催化活性，如CO，H2氧化、烃类完全氧化、N0直接分解或用CO还原、CO加氢反应等；而且催化反应温度较低，如在200K 就能催化氧化CO。

亦适宜作金属和载体相互作用及其催化反应机理的研究模型。

因此，近年来有关金催化剂的研究和开发日趋活跃。

本节简述负载型金催化剂在水煤气变换反应方面的研究进展。

1.1载体种类的影响采用不同载体制备负载型金催化剂，其催化活性、选择性及稳定性都表现出很大的差异。

文献【14～24】中采用的载体有α -Fe2O3,Al2O3,TiO2,ZnO,ZrO2,CeO2,Ni(OH)2,Co3O4和沸石分子筛等。

研究发现，以Fe2O3，CeO2，ZrO2或TiO2为载体制备的负载型金催化剂具有较好的催化性能。

Andreeva等比较了Au/Fe2O3，Au/Al2O3，CuO/ZnO/Al2O3催化剂的水煤气变换反应活性。

物理化学学报(Wuli Huaxue Xuebao )Acta Phys.鄄Chim.Sin .,2008,24(6)：932-938Received: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：O643Influence of Calcination Temperature on Properties of Au/Fe 2O 3Catalysts for Low Temperature Water Gas Shift ReactionLI Jin ⁃Wei ZHAN Ying ⁃Ying LIN Xing ⁃Yi ZHENG Qi ∗(National Engineering Research Center of Chemical Fertilizer Catalysts,Fuzhou University,Fuzhou350002,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 3catalystThe 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 becauseit 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 do932No.6LI Jin⁃Wei et al.：Influence of Calcination Temperature on Properties of Au/Fe2O3Catalysts for Low Temperaturenot have sufficient activity at low temperature.So,there is sub-stantial interest in development of better performance and moredurable WGS catalysts[1-5].Recently,it has been reported that Au supported catalysts areinteresting candidates for novel WGS reaction[6-11].High activitiesof Au/Fe2O3and Au/CeO2for WGS reaction have been observedby Andreeva[6]and Fu[7]et al.It is generally known that high catalytic activity of the gold/metal oxide catalysts dependsstrongly on the dispersion of gold particles and the interactionbetween gold and support.Therefore,most of the interest in goldcatalysis has geared to the study of preparation method[6,12-14],thesynthesis parameters[15,16],pretreatment conditions[17,18],and thechoice of supports[19,20],all affecting the dispersion of the goldparticles.However,there is relatively little work devoted to theeffect 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,supportedgold catalysts have been reported to be susceptible to deactiva-tion.There are several reports describing deactivation mechanisms for gold⁃based CO oxidation catalysts[22-26].Some of thestudies have considered sintering of Au particles as a reason forthe deactivation[24-26].Change of Au particle size from4to5.5nmhas been taken as a significant change influencing the catalyticperformance[26].For WGS reaction,catalysis process of gold⁃containing systems generally involves the formation of carbonylor carbonate-like species on ultrafine gold particles.Kim et al.[27]reported that it is these species blocking the active surface sitesthat contribute to the deactivity of Au/CeO2catalyst.There isonly one another work[28],which is devoted to the study of deactivation mechanisms of the gold⁃based WGS catalyst.With thehelp of DRIFTS,MS,TGA,TEM,N2physisorption,ICP,andXRD,Silberova et al.[28]put forward that the decrease of the sur-face area can almost solely explain the decrease on the activitywhen Au/Fe2O3catalyst was exposed to a steam with0.5%CO,1.5%H2O,and98%He.Because WGS gas composition in theproduction of hydrogen for proton exchange membrane(PEM)fuel cells is typically with10%CO,furthermore work is neededto clarify whether the decrease of the surface area is the essentialreason for the deactivation of Au/Fe2O3catalysts in higher COconcentration.In this article,temperature⁃programmed and long⁃term stabili-ty tests of Au/Fe2O3catalysts calcined at different temperaturesfor the WGS reactions were studied.The influence of calcina-tion temperature on the structure and catalytic performance ofAu/Fe2O3catalysts for WGS reaction were investigated by applying 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 andused catalysts helped to define the deactivation mechanism.1Experimental1.1Catalyst preparationSupported 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 characterizationThe 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/N2933Acta Phys.鄄Chim.Sin.,2008Vol.24mixture(φ(H2)=10%),then transferred to a test chamber.Anelectron takeoff angle of45°was used.The vacuum in the testchamber was maintained below1.33×10-7Pa during the collec-tion.Binding energies were corrected for surface charging byreferencing them to the energy of C1s peak of contaminant car-bon at284.8eV.1.3Activity and stability measurementsThe catalytic activity of the samples in the WGS reaction wasmeasured using‘CO⁃CMAT9001apparatus(Beijing Hangdun,China)’at atmospheric pressure.A stainless steel tube with aninner 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 discussion2.1Influence of calcination temperatureThe 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)andmetallic Fig.1CO conversion obtained during the temperature鄄programmed test of WGS reaction over Au/Fe2O3catalystscalcined at different temperatures(a)uncalcined,(b)Au/Fe⁃200,(c)Au/Fe⁃300,(d)Au/Fe⁃400,(e)Au/Fe⁃500Fig.2Pore size distribution of Au/Fe2O3catalysts calcinedat different temperatures(a)uncalcined,(b)Au/Fe⁃200,(c)Au/Fe⁃300,(d)Au/Fe⁃400,(e)Au/Fe⁃500BET2·g-1pore-1pore d Fe2O3/nm790.236 4.5not detectedreduced750.2067.410.9spent280.18126.019.6Au/Fe⁃200fresh1780.257 2.28.3reduced940.24815.514.8spent330.18122.021.2Au/Fe⁃300fresh1320.223 3.013.1reduced700.2178.212.5spent330.19023.021.9Au/Fe⁃400fresh470.220 6.515.8reduced360.18013.018.7spent12.70.0329.937.3Au/Fe⁃500fresh250.16210.518.6reduced180.14216.326.7spent13.50.03410.034.6uncalcined freshTable1Physicochemical properties of Au/Fe2O3catalyststreated under different conditions934No.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 byinFig.3XRD patterns of Au/Fe 2O 3catalysts calcined atdifferent temperatures(a)uncalcined,(b)Au/Fe ⁃200,(c)Au/Fe ⁃300,(d)Au/Fe ⁃400,(e)Au/Fe ⁃500Fig.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 ⁃500Fig.5In situ XRD patterns of uncalcined Au/Fe 2O 3catalystsduring temperature ⁃programmed reduction935Acta Phys.鄄Chim.Sin.,2008Vol.24situ 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 tointeraction between gold and iron oxide,leads to a considerablelowering of the temperature of the reduction step Fe2O3➝Fe3O4. However,the increase in calcination temperature causes thegradual increase in the crystallinity of Au and support,leading tothe weakening of their interaction,and resulting in the seriousdecreasing of the catalytic activity.2.2Deactivation properties2.2.1Isothermal test at200℃Fig.1shows that Au/Fe2O3catalysts exhibit high activity forwater 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 ismirrored 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 propertiesTable1lists the measured values of the specific surfaces andpore diameters of the fresh samples and after various treatments,i.e.,reduction by H2/N2(φ(H2)=10%)at150℃for9h and aftercatalytic operation.From Table1,it can be seen that the BETsurface 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 etal.[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 catalystTo 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 associatedwith Fig.6CO conversion obtained during the isothermalstability test of WGS reaction over Au/Fe2O3catalystscalcined at different temperatures(a)uncalcined,(b)Au/Fe⁃200,(c)Au/Fe⁃300,(d)Au/Fe⁃400,(e)Au/Fe⁃500Fig.7XRD patterns of Au/Fe2O3catalysts calcined atdifferent temperatures after WGS reaction(a)uncalcined,(b)Au/Fe⁃200,(c)Au/Fe⁃300,(d)Au/Fe⁃400,(e)Au/Fe⁃500 936No.6LI Jin⁃Wei et al.：Influence of Calcination Temperature on Properties of Au/Fe2O3Catalysts for Low TemperatureR—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.3SummaryThe 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.References1Andreeva,D.;Idakiev,V.;Tabakova,T.;Andreevk,A.;Giovanoli,R.Appl.Catal.A:Gen.,1996,134:2752Bond,G.C.;Thompson,D.T.Catal.Rev.鄄Sci.Eng.,1999,41:3193Venugopal,A.;Scurrell,M.S.Appl.Catal.A:Gen.,2004,258:2414Zhang,F.;Zheng,Q.;Wei,K.;Lin,X.;Zhang,H.;Li,J.;Cao,Y.Catal.Lett.,2006,108:1315Zhang,Q.;Zhan,Y.;Lin,X.;Zheng,Q.Catal.Lett.,2007,115:1436Andreeva,D.;Tabakova,T.;Idakiev,V.;Chrestov,P.;Giovanoli, R.Appl.Catal.A:Gen.,1998,169:97Fu,Q.;Kudriavtseva,S.;Saltsburg,H.;Stephanopoulous,M.F.Chem.Eng.J.,2003,93:418Hua,J.;Wei,K.;Zheng,Q.;Lin,X.Appl.Catal.A:Gen.,2004,259:1219Jacobs,G.;Williams,L.;Graham,U.;Thomas,G.A.;Spark,D.E.;Davis,B.H.Appl.Catal.A:Gen.,2003,252:10710Li,J.;Chen,C.;Lin,X.;Zheng,Q.J.Fuel Chem.Technol.,2006, 34(6):712[李锦卫,陈崇启,林性贻,郑起.燃料化学学报,2006,34(6):712]11Hua,J.M.;Zheng,Q.;Lin X.Y.;Wei,K.M.Chin.J.Catal.,2003, 24(12):957[华金铭,郑起,林性贻,魏可镁.催化学报,2003, 24(12):957]12Bamwenda,G.R.;Tsubota,S.;Nakamura,T.;Haruta,M.Catal.Lett.,1997,44:8313Grisel,R.J.H.;Kooyman,P.J.;Nieuwenhyus,B.E.J.Catal., 2000,191:43014Fu,Q.;Weber,A.;Flytzani⁃Stephanopoulos,M.Catal.Lett.,2001, 77:8715Wolf,A.;Schuth,F.Appl.Catal.A:Gen.,2002,226:116Jain,A.;Zhao,X.;Kjergaard,S.;Stagg⁃Williams,S.M.Catal.Lett.,2005,104:19117Su,Y.S.;Lee,M.Y.;Lin,S.D.Catal.Lett.,1999,57:4918Kang,Y.M.;Wan,B.Z.Catal.Today,1995,26:5919Haruta,M.Catal.Surv.Jpn.,1997,1:6120Schubert,M.M.;Hackenberg,S.;Veen,A.C.;Muhler,M.;Plzak, V.;Behm,R.J.J.Catal.,2001,197:11321Zhang,X.;Wang,H.;Xu,B.Q.J.Phys.Chem.B,2005,109: 967822Costello,C.K.;Kung,M.C.;Oh,H.S.;Wang,Y.;Kung,H.H.Appl.Catal.A:Gen.,2002,232:159Fig.8X鄄ray photoelectron spectra in the Au4f region for the(a)reduced and(b)spent Au/Fe2O3catalysts and in the C1sregion for the(c)reduced and(d)spent catalysts937Acta Phys.鄄Chim.Sin.,2008Vol.2423Valden,M.;Pak,S.;Lai,X.;Goodman,D.W.Catal.Lett.,1998, 56:724Konova,P.;Naydenov,A.;Venkov,C.;Mehandjiev,D.;Andreeva,D.;Tabakova,T.J.Mol.Catal.A:Chem.,2004,213:23525Haruta,M.Catal.Today,1997,36:15326Luengnaruemitchai,L.;Osuwan,S.;Gulari,mun., 2003,4:21527Kim,C.H.;Thompson,L.T.J.Catal.,2005,230:6628Silberova,B.A.A.;Makkee,M.;Moulijin,J.A.Top Catal.,2007, 44:20929Hodge,N.A.;Kiely,C.J.;Whyman,R.;Siddigui,M.R.H.;Hutchings,G.J.;Pankhurst,Q.A.;Wagner,F.E.;Rejaram,R.R.;Golunshki,S.E.Catal.Today,2002,72:13330Chen,Y.J.;Yeh,C.T.J.Catal.,2001,200:5931Ilieva,L.I.;Andreeva,D.H.;Andreev,A.A.Thermochim.Acta, 1997,292:16932Neri,G.;Visco,A.M.;Galvagno,S.;Donato,A.;Panzalorto,M.Thermochim.Acta,1999,329:3933Minico,S.;Scire,S.;Crisafulli,C.;Maggiore,R.;Galvagno,S.Appl.Catal.B,2000,28:24534Moulder,J.F.;Sticke,W.F.;Sobol,P.E.;Bomben,K.D.Handbook of X⁃ray photoelectron spectroscopy.Eden Prairie:Pariss Perkin⁃Elmer,199235Lian,H.;Jia,M.;Pan,W.;Li,Y.;Zhang,W.;Jiang,D.Catal.Commun.,2005,6:47938。