关键词: 密度泛函理论, 水煤气变换反应, 机理, 二元铜团簇

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 Cu₆TM is easier than that of H₂O. WGSR mechanism involves the redox, carboxyl and formate pathways, which correspond to CO^*+O^*→CO₂(g), CO^*+OH^*→COOH^*→CO₂(g)+H^*, and CO^*+H^*+O^*→CHO^*+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 Cu₆TM (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 Cu₆TM (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.

Key words: density functional theory, water-gas shift reaction, mechanism, binary copper cluster