Molecular Mechanism and Microkinetic Analysis of the Reverse Water Gas Shift Reaction Heterogeneously Catalyzed by the Mo2C MXene

Abstract

The potential of the Mo2C MXene to catalyze the reverse water gas shift (RWGS) reaction has been investigated by a combination of density functional theory (DFT)-based calculations, atomistic thermodynamics, and microkinetic simulations. Different catalytic routes are explored including redox and associative (carboxyl and formate) mechanisms at a high temperature at which the RWGS reaction is exothermic. The present study predicts that, on the Mo2C MXene, the RWGS reaction proceeds preferentially through the redox and formate catalytic routes, the rate-limiting step being the formation of the OH intermediate followed by the H2O formation, whereas the carboxyl route to form the carboxyl intermediate is hindered by a large energy barrier. Microkinetic simulations confirm the formation of carbon monoxide (CO) under relatively mild conditions (i.e., ∼400 °C and 1 bar). The CO formation is not affected either by the total pressure or by the CO2/H2 ratio. However, water formation requires high temperatures of ∼700 °C and pressures above 5 bar. In addition, an excess of hydrogen in the CO2/H2 ratio favors water formation. Shortly, the present study confirms that the Mo2C MXene emerges as a heterogeneous catalyst candidate for generating a CO feedstock that can be used for subsequent transformation into methanol through the Fischer−Tropsch process.