Theoretical Study into Water Promoted CO₂ Hydrogenation to Methanol over PdMo Alloy

CO₂ hydrogenation to methanol is generally considered one of the most promising approaches in CO₂ utilization. However, how to design highly efficient catalysts still remains a significant challenge. In this paper, density functional theory as well as microkinetic modeling is employed to systematically investigate the reaction mechanism and catalytic performance of methanol formation over two surface models, hcp-PdMo, i.e., st_PdMo and fl_PdMo. On the basis of our calculation results, the adsorption and activation behavior of CO₂ and H₂ are closely related to the catalyst surface they are binding to. For both surfaces, CO₂ hydrogenation is controlled by different reaction pathways, which further leads to their different catalytic performances in CH₃OH formation. By comparison with fl_PdMo, st_PdMo exhibits the higher catalytic activity and product selectivity in methanol formation. The catalytic performance of st_PdMo could be further improved by explicitly introducing an H₂O molecule into the catalyst system. Based on the electronic structure analysis, H₂O inclusion could promote the electron transfer within the TS configuration of the O-H formation step, which thereby lowers the kinetic barrier of the corresponding step. Overall, our study offers a new perspective on the factors that influence the reaction mechanism of CO₂ hydrogenation on the bimetallic catalyst.