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

Journal article, 2025

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.