Reaction mechanism of water gas shift over Au n clusters: A density functional theory study

Abstract The stability and catalytic activity of Au 10 , Au 13 and Au 20 clusters in water gas shift (WGS) reaction were investigated by density functional theory (DFT); the adsorption behavior of reaction species and the reaction mechanism of WGS on various Au n clusters were explored. The results indicated that the stability of three Au n clusters follows the order Au 10 13 20 , whereas their electron delocalization and adsorption capacity decreases in the sequence of Au 13 > Au 10 > Au 20 . Three Au n clusters exhibit the same rate-determining step for WGS, i.e. H 2 O dissociation; however, they are quite different in the actual reaction routes. Over Au 10 cluster, the WGS reaction follows the carboxyl mechanism, characterized by the direct dissociation of COOH*; over Au 13 cluster, the redox mechanism applies, suggested by the disproportionation of two OH*; over Au 20 cluster, the WGS reaction proceeds via the carboxyl mechanism, represented by the disproportionation of COOH* and OH*. A comparison for the optimal reaction paths over three Au n clusters suggests that the Au 13 cluster has the highest catalytic activity in the WGS reaction at low temperature.