Theoretical study of methanol decomposition mediated by Au_3 ~+, Au_3 and Au_3 ~-: Mechanism and effect of charge state of gold on its catalytic activity

摘要

By performing density functional theory calculations, we studied methanol decomposition promoted by neutral, anionic and cationic Au trimers, which represent the three simplest prototypes of Au-cluster-based catalysts with different charge states. The results show that the Au_3 ~- and Au_3 ~+-mediated reactions proceed via four successive single dehydrogenation steps, CH_3OH→CH_3O → CH_2O → CHO → CO, while the Au_3 ~--mediated reaction occurs through two double dehydrogenation steps, CH_3OH → CH_2O → CO. The additional negative charge reduces remarkably the binding capability of CO (the completely dehydrogenated product of methanol) on the cluster, and is thus beneficial in reducing poisoning of the catalyst by CO. In contrast, the neutral and positively charged clusters present strong interactions with CO, making the catalyst readily poisoned by CO. Furthermore, the reaction promoted by the cationic cluster shows a much higher energy barrier than those by the neutral and anionic clusters. So selecting suitable substrates that make Au nanoparticles negatively charged may be a promising strategy for promoting methanol oxidation.