Water-Involved Methane Selective Catalytic Oxidation by Dioxygen over Copper-Zeolites
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The selective oxidation of methane to methanol is a dream reaction of
direct methane functionalization, which remains a key challenge in catalysis
and a hot issue of controversy. Herein, we report the water-involved methane
selective catalytic oxidation by dioxygen over copper-zeolites. At 573 K, a
state-of-the-art methanol space-time yield of 543 mmol/molCu/h with
methanol selectivity of 91 % is achieved with Cu-CHA catalyst. Temperature-programmed
surface reactions with isotope labelling determine water as the dominating oxygen
and hydrogen source of hydroxyl in methanol while dioxygen participates in the
reaction through reducing to water. Spectroscopic analyses reveal the fast redox cycle of Cu2+-Cu+-Cu2+ during methane selective oxidation, which is closely related to the high catalytic activity of Cu-CHA. Density functional theory calculations
suggest that both CuOH monomer and dimer in Cu-CHA can catalyze the selective
oxidation of methane to methanol with Cu-OOH as the key reaction intermediate, and meanwhile, various copper sites undergo
interconversion under reaction conditions.