Density functional theory study of water-gas shift reaction on TM@Cu12 core-shell nanoclusters

Abstract

The mechanism of water-gas shift reaction on the transition metal of Co, Ni, Cu (from the 3d row), Rh, Pd, Ag (from the 4d row), Ir, Pt, and Au (from the 5d row) @Cu₁₂ bimetallic clusters have been studied using density functional theory (DFT) calculations. Three reaction mechanisms including redox, carboxyl, and formate mechanisms, which are equal to CO* + O* → CO₂ (g), CO* + OH* → COOH* → CO₂ (g) + H*, and CO* + H* + O* → CHO* + O* → HCOO** → CO₂ (g) + H*, respectively, have been studied. The result revealed that the WGSR prefer to follow the carboxyl mechanism on the TM@Cu₁₂ surfaces. The rate-controlling step of WGS reaction is H₂O dissociation into OH and H or COOH decomposition into CO and OH. The transition metal additive in Cu cluster could enhance the activity of water dissociation, which is beneficial for WGS reaction. Especially, doping Ni has the largest promotion effect in reducing the active barrier, the reason is electronic effect. The calculation indicates that Ni@Cu₁₂ is thus the promising candidates for improved WGSR catalysts. In addition, The TOF values are studied to estimate effectively activity of the TM@Cu₁₂ cluster. To get insight into conclusion, reaction mechanism and structure of cluster was elucidated by the relative energy profiles and detailed electronic local density of states (LDOS).