Carbon Dioxide Hydrogenation to Methane on Hydrogen Boride Sheet: A Density Functional Theory Study

Abstract

The conversion of CO2 into valuable chemicals has attracted considerable attention as a strategy to address two major global challenges: the production of renewable energy and the reduction of CO2 emissions. Experimental studies have demonstrated that hydrogen boride sheets exhibit promising potential for CO2 hydrogenation, producing methane and ethane, while uniquely supplying hydrogen directly from its lattice without requiring external H2. However, the underlying reaction mechanism remains poorly understood. In this study, we employ density functional theory calculations to investigate the reaction pathways of CO2 conversion to CH4 on hydrogen-deficient HB sheets, where H-vacancy sites serve as the active centers for CO2 activation. Our results reveal that the conversion of CO2 proceeds via a CO-mediated dissociative mechanism. We further consider the effect of O* participation as a reactant following C–O bond cleavage and show that coadsorbed OH* lowers the barrier for HCO* formation, making the associative pathway more kinetically favorable than the route proceeding via C*. The rate-determining step is identified as the hydrogenation of CH* to CH2*, with a barrier of 2.02 eV, consistent with the experimentally observed negligible CH4 yield under dry conditions. These findings provide mechanistic insight and complement existing experimental observations.