Investigating the Composition of the Metal Dimer Site in Chabazite for Direct Methane-to-Methanol Conversion

Journal article, 2024

Methanol is a liquid energy carrier that has the potential to reduce the use of fossil fuels. Industrial production of methanol is currently a multistep high-temperature/high-pressure synthesis route. Direct conversion of methane to methanol under low-temperature and low-pressure conditions is an interesting but challenging alternative, which presently lacks suitable catalysts. Here, the complete reaction cycle for direct methane-to-methanol conversion over transition-metal dimers in the chabazite zeolite is studied by using density functional theory calculations and microkinetic modeling. In particular, a reaction mechanism previously identified for the Cu2 dimer is explored under dry and wet conditions for dimers composed of Ag, Au, Pd, Ni, Co, Fe, and Zn and the bimetallic dimers AuCu, PdCu, and AuPd. The density-functional-theory-based microkinetic modeling shows that Cu2, AuPd, and PdCu dimers have reasonable turnover frequencies under technologically relevant conditions. The adsorption energy of atomic oxygen is identified as a descriptor for the reaction landscape as it correlates with the adsorption and transition-state energies of the other reaction intermediates. Using the established scaling relations, a volcano plot of the rate is generated with its apex close to the Cu2, AuPd, and PdCu dimers.