Understanding the Reverse Water Gas Shift Reaction over Mo2C MXene Catalyst: A Holistic Computational Analysis

The catalytic performance of Mo₂C MXene for reverse water gas shift (RGWS) reaction is computationally assessed on an holistic fashion, unveiling the reaction mechanism and its thermodynamics through density functional theory (DFT) calculations on suitable models, and gaining information about kinetics, and dynamics aspects by means of mean-field microkinetic modelling (MKM), and kinetic Monte Carlo (kMC) simulations.

Abstract

Pristine Mo₂C MXene has been proposed as an heterogeneous catalysis of the reverse water gas shift (RWGS) reaction. The present computational study aims at understanding its catalytic performance and reaction mechanisms tackling its thermodynamics, kinetics, and surface dynamic effects, combining Gibbs free energy profiles gained by density functional theory (DFT), mean-field kinetics by microkinetic modeling, and rare-event steps by kinetic Monte Carlo (kMC). The RWGS endergonicity goes for the use of high temperatures and reactants partial pressures to make the reaction exergonic. Gibbs free energy profiles show a preference for redox mechanism, whereas microkinetic simulations favor a low-temperature preference of formate mechanism. The kMC reveals simultaneous operating redox and formate pathways, where surface coverage disfavors redox favoring the formate pathway. A peak performance is found at 700 K, in line with reported experiments, where the formation of surface O₂* is found to be key, acting as a reservoir for O* adatoms while freeing surface sites upon O₂* formation. Even though high turnover frequencies are predicted, the system could benefit from swing operando conditions, alternating CO production steps with H₂ reduction regeneration steps, and/or ways to reduce the surface O₂* and so to have more active catalytic sites.

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