Limitations of free energy diagrams to predict the catalytic activity: the reverse water gas shift reaction catalyzed by Ni/TiC

Abstract

The temporal evolution at the catalyst surface is a result of an intricate interplay between all involved microscopic events such as adsorption, desorption, diffusion, and bond breaking/formation steps, and the interaction with the surrounding environment. By properly including these effects, kinetic Monte Carlo (kMC) simulations can accurately describe the complexity of real catalysts, unravel the dominant reaction mechanisms and provide fundamental understanding towards the rational design of novel catalysts. In this work, we combine density functional theory (DFT) calculations, statistical thermodynamics and kMC simulations to study the reverse water–gas shift (RWGS) reaction on Ni/TiC, a bifunctional catalyst. The predictions from DFT energy profiles do not coincide with the outcome of the kMC simulations, evidencing the limitations of the former, especially in including the effect of coverage of surface species, which plays a crucial role. The kMC simulations results are in remarkable agreement with the experimental data, proving that the kMC simulations are able to describe the complex chemistry of the RWGS reaction on a bifunctional catalyst.