CO₂ Hydrogenation with High Selectivity by Single Bi Atoms on MXenes Enabled by a Concerted Mechanism

Developing efficient catalysts for the capture and direct conversion of CO2 into various chemicals is essential to alleviate CO2 emissions and minimize the negative environmental effects of fossil fuels. Combining density functional theory calculations and microkinetic analysis, we propose that single Bi atoms supported on V2CO2 MXenes (Bi@V2CO2) are promising single-atom catalysts (SAC) for CO2 hydrogenation. The catalytic performance of Bi SACs is ensured by the stable single-atom dispersion of Bi atoms on V2CO2 and enhanced adsorption of CO2. Of importance, Bi@V2CO2 exhibits remarkable selectivity toward the synthesis of formic acid (HCOOH), in which the main competing reaction, namely, the reverse water gas shift (RWGS) and the formation of CO, is strictly prohibited. In contrast to conventional Cu or In2O3 catalysts, CO2 hydrogenation exhibits a unique mechanism on Bi@V2CO2, in which the formic acid is directly generated via a concerted pathway. As a result, the formation of both intermediate HCOO and COOH is prevented, leading to high selectivity (nearly 100%) toward HCOOH on Bi@V2CO2. Moreover, analysis of the kinetic behavior suggests that the stabilization of HCOOH adsorption would be an effective approach to promote catalyst performance toward methanol synthesis.