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

Abstract

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 Cu 2 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 densityfunctional-theory-based microkinetic modeling shows that Cu 2 , 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 Cu 2 , AuPd, and PdCu dimers.