Catalytic direct oxidation of methane to methanol by redox of copper mordenite

Abstract

Expectations for industrial implementation of direct conversion of CH₄ to CH₃OH are growing with the increasing demand for energy-efficient chemical processes. In this study, catalytic production of CH₃OH by direct oxidation of CH₄ with O₂ was performed using Cu zeolite catalysts in a CH₄/O₂/H₂O flow reaction. Among the various Cu zeolites investigated, the Cu-MOR catalyst exhibited relatively high CH₃OH production with a turnover number of 7.4 mol_CH3OH mol_Cu⁻¹ over 24 h (CH₄ conversion: 0.011%). The catalytically active Cu species and catalytic cycle were investigated by in situ simultaneous X-ray absorption and infrared spectroscopy. The results suggest that the key to the catalytic cycle over Cu-MOR is the redox of Cu(I)/Cu(II) species. Furthermore, H₂O-adsorption-included dynamic Cu species are revealed to be catalytically active.