Theoretical investigation on the promotional role of Ag for reverse water-gas shift reaction on Ni catalysts during CO2 reduction

Abstract

Catalytic reduction of CO2 to CO via reverse water-gas shift reaction on Ni-based catalysts is challenging due to the competing methanation reaction. In this work, the reduction of CO2 toward CO and CH4 has been studied by density functional theory calculation and microkinetic simulations on Ni(211) and Ag@Ni(211) surfaces. On both surfaces, direct CO2 dissociation is more favorable over formate and carboxyl pathways toward CO, and direct CO dissociation is the major pathway toward CH4. The presence of Ag shifts the d-band center of adjacent Ni atoms away from the Fermi level, resulting in reduced affinity to CO2/CO/intermediates and slightly increased barriers for most elementary steps. In particular, the apparent barrier for direct CO2 dissociation is slightly reduced by ∼0.1 eV while direct CO dissociation is strongly inhibited by ∼0.3 eV along the reaction coordinate, leading to CO as the predominant product on Ag@Ni(211), which agrees well with the experimental results.