二元铜团簇催化水煤气变换反应机理的理论研究  

Theoretical Study on Menchanism of Water-Gas Shift Reaction Catalyzed by Binary Copper Cluster

作　　者：任宁宁[1,2] 郭玲[1,2] 董晓娜[1,2] 文彩霞[1,2] 

机构地区：[1]山西师范大学化学与材料科学学院 [2]山西师范大学现代文理学院,山西临汾041004

出　　处：《化学学报》2015年第4期343-348,共6页Acta Chimica Sinica

基　　金：山西省自然科学基金(No.2013011009-6);山西省高等学校131领军人才工程项目;山西省高等学校大学生创新创业训练项目(No.2015537)资助~~

摘　　要：水煤气变换反应是一个重要的反应体系,它可以去除H2中少量的CO而被应用在质子膜燃料电池中.然而关于水煤气变换的反应机理还存在一定的争议,为阐明其反应机理,本文采用密度泛函理论PBE方法,金属元素采用Lanl2dz基组,非金属元素采用6-311++G(d,p)基组,对系列二元铜团簇Cu6TM(TM=Co,Rh,Ir,Ni,Pd,Pt,Ag,Au)催化水煤气变换反应机理进行了研究.结果表明:CO分子比H2O分子更容易吸附到团簇上.水煤气变换反应包括三种反应机理:羧基反应机理,氧化还原反应机理,甲酸反应机理,相对应的基元反应分别为CO*+O*→CO2(g),CO*+OH*→COOH*→CO2(g)+H*,和CO*+H*+O*→CHO*+O*→HCOO**→CO2(g)+H*.甲酸根是实验中最可能检测到的中间物,这是由于生成甲酸根有较低的能垒以及甲酸根解离有较高的解离能.Co,Rh,Ni,Pd掺杂在Cu7团簇中对水煤气转化反应的催化效果明显比纯Cu7团簇催化效果好.采用CO的初始消耗率以及最终CO2的产率进一步研究了在Cu6TM(TM=Co,Rh,Ni,Pd)表面甲酸根是反应过程中的旁观者还是一种重要的中间物.计算结果还表明,对于Cu6TM(TM=Ni,Pd),由于CO较低的反应能垒,水煤气变换反应主要按照氧化还原反应机理进行反应,而对于Cu6TM(TM=Co,Rh),水煤气变换反应三种反应机理均可进行反应.本文的结果有助于理解水煤气变换反应和设计更好的催化剂.The water-gas shift reaction （WGSR） is an important reaction system and can be applied for removing small amounts of CO from H2-rich gases for polymer electrolyte membrane fuel cells. However, the mechanism of the reaction is still in dispute. In order to clarify the mechanism of WGSR, the detailed mechanisms of WGSR on a series of binary clusters Cu6TM （TM=Co, Rh, Ir, Ni, Pd, Pt, Ag, Au） were investigated by density functional theory, using the PBE functional along with the Lanl2dz basis for metals and 6-311＋ ＋G（d,p） for non-metals in this paper. The computational results indicated that the absorption of CO molecules on CurTM is easier than that of H2O WGSR mechanism involves the redox, carboxyl and formate pathways, which correspond to CO＊→O＊→CO2（g）, CO＊q-OH＊→COOH＊→CO2（g）＋H＊, and CO＊q→H＊→q→O＊→ CHO＊→q→O＊→HCOO＊＊→CO2（g） ＋H＊, respectively. The experimentally most observed formate can be attributed to its lower formation and higher dissociation barriers. And dopant Co, Rh, Ni and Pd on copper cluster can have more beneficial effects than pure copper on the catalytic activity. Furthermore, the role of formate, a spectator or key intermediate, on CurTM （TM= Co, Rh, Ni, Pd） surfaces has been investigated. WGSR activity has been determined from the initial CO consumption and final CO2 product rates. The calculation results show that WGSR is mostly follows the redox pathway on Cu6TM （TM=Ni, Pd） surface due to the lower CO oxidation barriers; on the other hand, all the three pathways contribute similarly in WGSR on CurTM （TM=Co, Rh） surfaces. The results can help us to understand the catalytic behavior in experiment, design better catalysts, and, therefore, move one step forward to enable hydrogen economy to the practical application.

关 键 词：密度泛函理论 水煤气变换反应 机理 二元铜团簇 

分 类 号：O643.12[理学—物理化学]