A comprehensive DFT study of CO2 catalytic conversion by H2 over Pt-doped Ni catalysts

Abstract

PtNi bimetallic catalysts show superior performance for CO2 catalytic conversion by hydrogen, but the underlying mechanism and the key elementary steps in controlling the activity and selectivity of CO2 hydrogenation remain unclear. In present work, the complete reaction network for CO2 hydrogenation has been investigated systematically over Pt/Ni (111) surface based on periodic density functional theory, and active sites and reaction mechanism have been determined. It is found that HCOOH is mainly produced by undergoing the HCOO pathways while synthesis of CH3OH and CH4 via RWGS+CO hydrogenation is the dominant reaction pathway, and their selectivity are determined by the competitive reaction between hydrogenation and CO bond scission of H2COH species. The dissociation of COOH is regarded as the rate-determining step as it has the highest barrier (2.07 eV) in RWGS+CO hydrogenation. Moreover, it is observed that the doping of Pt on Ni surface can promote the transformation of CO2 into chemisorbed CO2δ− and reduce the barrier in H2 dissociation, which further facilitate the activation and hydrogenation of CO2. More importantly, the doped Pt atom could promote HxCO hydrogenation to HxCOH, meanwhile, suppress HxCOH dissociation into CHx. Especially, the activation barrier and reaction energy for C formation is markedly enhanced, and the ability for C hydrogenation is promoted over Pt/Ni (111) surface, which could lower the possibility of coke formation. These results provide helpful information in understanding the process of CO2 hydrogenation at atomic scale, and could benefit for the synthesis of Ni-based bimetallic catalysts.