Methanol can be used as a liquid fuel and is a value-adding intermediate in the petrochemical industry. Given the abundance of natural gas (mostly methane), there is strong interest in developing efficient and low-temperature catalysts for achieving methane-to-methanol conversion (MMC) with atmospheric oxygen. However, managing the reaction selectivity is a big challenge as methane C-H activation processes often produce a series of side products, via over-oxidation. To this extent, copper-exchanged zeolites [e.g. copper-exchanged mordenite zeolite, MOR] have been found to be promising mild-temperature (~200 °C) catalysts with high selectivity (80-90 %) for methanol. We are interested in using quantum mechanical calculations to develop new catalytic platforms that can also facilitate MMC at low temperatures but with higher efficiencies than existing systems. In this work, we have used density functional theory (DFT) calculations to examine the C-H activation steps of the MMC pathway as well as competing side reactions on tri-metal trio-oxo complexes that are reminiscent of the Cu3O32+ species identified by Grundner et al. (Nature Communications 2015, 6, 7546) in MOR. We describe correlations between the hydrogen abstraction energies, spin densities, bond angles and bond distances for the methane C-H activation step as well as the oxidation of methanol oxidation to formic acid. We show how differences in the chemical natures of the tri-metal trio-oxo complexes can affect the methanol selectivity and the suitability of the various descriptors. These descriptors provide us an opportunity to screen various materials in the future.

Development of descriptors for methane-to-methanol conversion and side-reactions on zeolite-supported tri-metal tri-oxo catalysts

255th National Meeting (2018)

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