Unveiling the Origin of Alkali Metal (Na, K, Rb, and Cs) Promotion in CO2 Dissociation over Mo2 C Catalysts

Abstract

Molybdenum carbide (Mo2 C) is a promising and low-cost catalyst for the reverse water−gas shift (RWGS) reaction. Doping the Mo2 C surface with alkali metals can improve the activity of CO2 conversion, but the effect of these metals on CO2 conversion to CO remains poorly understood. In this study, the energies of CO2 dissociation and CO desorption on the Mo2 C surface in the presence of different alkali metals (Na, K, Rb, and Cs) are calculated using density functional theory (DFT). Alkali metal doping results in increasing electron density on the Mo atoms and promotes the adsorption and activation of CO2 on Mo2 C; the dissociation barrier of CO2 is decreased from 12.51 on Mo2 C surfaces to 9.51–11.21 Kcal/mol on alkali metal-modified Mo2 C surfaces. Energetic and electronic analyses reveal that although the alkali metals directly bond with oxygen atoms of the oxides, the reduction in the energy of CO2 dissociation can be attributed to the increased interaction between CO/O fragments and Mo in the transition states. The abilities of four alkali metals (Na, K, Rb, and Cs) to promote CO2 dissociation increase in the order Na (11.21 Kcal/mol)