Gas-Phase Catalytic Oxidation of Methane into Methanol over Copper-Exchanged Zeolites with Molecular Oxygen

The direct catalytic conversion of methane to liquid oxygenated compounds, such as methanol or dimethyl ether, using molecular oxygen at low temperature is a grand challenge in C-H activation that has never been met. We report the first demonstration of direct, catalytic oxidation of methane into methanol with molecular oxygen over copper-exchanged zeolites at low reaction temperatures. Reaction kinetics studies show sustained catalytic activity and high selectivity over copper-exchanged ZSM-5 under mild conditions. Transient and steady state measurements with isotopically labeled molecules confirm catalytic turnover. Catalytic activity is observed for a variety of commercially available zeolite topologies. The catalytic rates and apparent activation energies are significantly affected by the zeolite topology, with caged-based zeolites (e.g., Cu-SSZ-13) showing the highest rates. Reactivity and characterization data demonstrate that the mono-(μ-oxo) dicupric site in copper exchanged ZSM-5 active for stoichiometric methane oxidation is not the catalytic site.