酸洗Pt-Fe和Pt-Co催化剂在CO氧化反应中的对比研究（英文）

发布时间：2018-05-26 02:19

本文选题：铂-铁 + 铂-钴　；参考：《催化学报》2017年07期

【摘要】：负载型纳米催化剂表面结构与其催化性能之间关系的研究一直受到广泛关注.由于其结构复杂使得人们在研究催化剂构效关系时遇到了很多困难.近年来,大量研究发现反转催化剂在众多反应中表现出优越的催化性能.反转催化剂是将过渡金属氧化物负载于其它金属表面.和传统金属/氧化物催化剂相比,反转催化剂更能突出氧化物在催化反应中的重要作用.众多研究表明,在氧化物-金属界面处存在特殊的作用,这种作用可以改变氧化物的电子特性和化学性质,进而产生较高的催化性能.傅强等人创建了金属氧化物负载于Pt表面的反转催化体系,其表现出了高的低温CO氧化反应性能.在氧化物和Pt之间的界面限域效应可以稳定氧化物中配位不饱和的金属阳离子.这种配位不饱和的氧化物提供了活化O_2的活性位.目前,反转催化剂的研究主要集中在单晶模型体系中,在负载型催化剂中的研究还较少.我们以炭黑(CB)为载体,将还原后的Pt-Fe和Pt-Co催化剂经过酸洗制备了一种表面富Pt核为合金的结构.考察了酸洗后的Pt-Fe和Pt-Co催化剂经过不同温度氧化后的结构变化,并讨论了其结构与CO完全氧化反应(COOX)和CO选择氧化反应(CO-PROX)性能的关系.X射线粉末衍射(XRD),电感耦合等离子体发射光谱(ICP),透射电镜(TEM)和X射线光电子能谱(XPS)表征结果表明,还原后的Pt基催化剂经过酸洗可以选择性去除纳米粒子表面的3d过渡金属,形成表面富Pt体相为合金的结构.将酸洗后的Pt-Fe和Pt-Co催化剂在不同温度下空气中氧化,发现近表层的Fe(Co)会扩散到粒子表面上,形成过度氧化的Fe_2O_3(Co_3O_4)表面结构.氧化后的催化剂在COOX和CO-PROX反应中表现出截然不同的催化性能.酸洗后的Pt-Fe(Pt-Co)催化剂经过不同温度氧化后在COOX反应中活性都较差,室温下的CO转化率只有不到30%,CO完全转化的温度超过100 ℃,相当于纯Pt催化剂的活性.这说明Pt表面过度氧化的Fe_2O_3(Co_3O_4)对CO氧化反应的促进作用不明显.而氧化后的催化剂在CO-PROX反应中表现出较高的活性,250 ℃(或350 ℃)氧化后的酸洗Pt-Fe催化剂室温下的CO转化率接近100%,250 ℃(或350 ℃)氧化后的酸洗Pt-Co催化剂室温下的CO转化率也达到了70%.结合表征和反应结果,我们认为氧化处理形成的表面过度氧化的金属氧化物(Fe_2O_3,Co_3O_4)在COOX的催化性能较差.通入CO-PROX反应气后,气氛中大量H_2的存在和Pt表面的氢溢流效应可以使得表面Fe_2O_3,Co_3O_4在室温下被还原成配位不饱和的FeO,CoO.这种配位不饱和的氧化物在表面Pt的限域作用和大量H_2气氛下比较稳定,并且具有较强的活化解离O_2的能力,进而提高了CO-PROX反应的活性.为了进一步证实催化剂表面氧化物与其催化性能的关系,我们在室温下进行了两种反应气的循环实验测试.测试结果表明,对于氧化后的酸洗Pt-Fe催化剂,COOX反应中的表面Fe_2O_3和CO-PROX反应中的表面FeO可以通过变换反应气氛实现两种氧化物的相互转变,并表现出完全不同的催化性能.对于氧化后的酸洗Pt-Co催化剂,CO-PROX反应中形成的CoO表面结构在COOX反应中也比较稳定,在两种反应气中表现出相似的催化性能.
[Abstract]:The study of the relationship between the surface structure and the catalytic performance of the supported nano catalyst has been widely concerned. Because of its complex structure, many difficulties have been encountered in the study of the structure effect relationship of the catalyst. In recent years, a large number of studies have found that the reverse catalyst has shown superior catalytic performance in many reactions. The transition metal oxide is loaded on the other metal surface. Compared with the traditional metal / oxide catalyst, the reverse catalyst can highlight the important role of the oxide in the catalytic reaction. Many studies have shown that there is a special role in the oxide metal interface, which can be used to change the electronic and chemical properties of the oxide. Fu Qiang et al. Created a reverse catalytic system with a metal oxide loaded on the Pt surface, showing a high low temperature CO oxidation reaction. The interface limit effect between oxide and Pt can stabilize the metal ionized metal ionon in the oxide, which is unsaturated. At present, the active sites of O_2 are activated. The research on the reverse catalyst is mainly concentrated in the single crystal model system, and the research on the supported catalyst is still less. We use carbon black (CB) as the carrier to prepare a Pt-Fe and Pt-Co catalyst after the reduction by acid washing. The Pt-Fe and Pt-Co catalysis after acid pickling are investigated. The structure changes after the oxidation of different temperatures, and the relationship between the structure and the properties of CO complete oxidation (COOX) and CO selective oxidation reaction (CO-PROX),.X ray powder diffraction (XRD), inductively coupled plasma emission spectroscopy (ICP), transmission electron microscopy (TEM) and X ray photoelectron spectroscopy (XPS) indicate that the Pt radical after reduction is shown. After pickling, the 3d transition metal on the surface of the nanoparticles can be selectively removed and the structure of the surface rich Pt phase is formed. The Pt-Fe and Pt-Co catalysts after acid washing are oxidized at different temperatures in the air. It is found that the near surface Fe (Co) will spread to the surface of the particles and form the surface structure of the over oxidation of Fe_2O_3 (Co_3O_4). After oxidation, the oxidation of Fe (Co_3O_4) is formed. The catalyst shows very different catalytic performance in the reaction of COOX and CO-PROX. After the acid washing, the Pt-Fe (Pt-Co) catalyst has poor activity in the COOX reaction after different temperatures, the CO conversion rate at room temperature is only less than 30%, the temperature of CO is more than 100 degrees C, and the activity of the pure Pt catalyst. This shows that the Pt surface is over. The oxidation of Fe_2O_3 (Co_3O_4) has no obvious promotion effect on CO oxidation, and the catalyst after oxidation shows high activity in CO-PROX reaction. The CO conversion rate of Pt-Fe catalyst after oxidation at 250 C (or 350 C) is close to 100% at room temperature and CO conversion rate at room temperature at 250 C (or 350 C) for acid washing Pt-Co catalyst at room temperature 70%. combined with characterization and reaction results, we believe that the catalytic performance of overoxidized metal oxides (Fe_2O_3, Co_3O_4) formed by the oxidation process is poor in COOX. After entering the CO-PROX reactant gas, the existence of a large number of H_2 in the atmosphere and the hydrogen overflow effect on the Pt surface can make the surface Fe_2O_3 and Co_3O_4 be reduced to match at room temperature. The unsaturated FeO, CoO., the ligand unsaturated oxides are stable in the confinement of the surface Pt and in a large number of H_2 atmospheres, and have strong ability to dissolve the O_2, and thus improve the activity of the CO-PROX reaction. In order to further confirm the relationship between the oxide of the catalyst surface and its catalytic performance, we conduct the reaction at room temperature. Two kinds of reactant gas cycle tests have been carried out. The results show that the surface FeO in the surface Fe_2O_3 and CO-PROX reaction in the COOX reaction can be converted to each other by changing the reaction atmosphere in the COOX reaction after the oxidation of the acid washing Pt-Fe catalyst, and shows a completely different catalytic performance. The surface structure of CoO formed by CO-PROX reaction is also stable in COOX reaction, showing similar catalytic performance in the two reaction gases.
【作者单位】：安徽工业大学化学与化工学院;
【基金】：supported by the National Natural Science Foundation of China(21403004,21403003)~~
【分类号】：O643.36

【相似文献】