Dynamic Catalysis Multiscale Simulations for Nonoxidative Coupling of Methane Using Light and Heat

Abstract

Methane (CH₄) activation and conversion under mild reaction conditions are a great challenge for the chemical industry. Photocatalysis is attractive for activating inert C–H bonds of CH₄ at room temperature. Specifically, photocatalytic nonoxidative coupling of CH₄ (NOCM) is a promising process to produce ethane (C₂-hydrocarbon) and H₂. Different oxide-based photocatalysts have been used for room-temperature NOCM, and TiO₂ is a potential photocatalyst with a bandgap that can capture photons in the UV region. However, a fundamental understanding of the NOCM mechanism on TiO₂ is still missing. Herein, we apply multiscale modeling, combining density functional theory (DFT) calculations with kinetic Monte Carlo (kMC) simulations to investigate the photocatalytic NOCM on a rutile TiO₂(110) surface. DFT calculations revealed that the photogenerated holes mediate the homolytic activation of CH₄ via the formation of methyl radicals with an activation barrier that is 70% lower than that of the conventional thermocatalytic route. The generated methyl radicals further recombine to form ethane. The detailed reaction pathway energetics investigated with DFT-based kMC simulations revealed that ethane can be formed at 315.15 K, but the dissociated hydrogens poison the catalyst surface. Further thermocatalytic simulations revealed that increasing the temperature by thermal heating (ca. 690.15 K) facilitated H₂ formation and catalyst regeneration. Importantly, we demonstrate how photo- and thermocatalytic modes can be combined, facilitating NOCM on TiO₂ and a route to enable dynamic catalysis simulations through multiscale modeling, opening alternative avenues in computational catalyst discovery.