Continuous oxidation of methane into methanol by N2O over Cu-Zeolite: A combined experimental and theoretical study

The direct oxidation of methane to methanol (DMTM) constitutes a great challenge of C-1 chemistry. Herein, we investigate the continuous DMTM by utilizing N2O as the oxidant over a series of Cu modified zeolite (CHA, MFI, MOR), attempting to taking advantage of low-temperature generated active oxygen to promote CH3OH production. Considering that the Cu cation has been recognized as the active center for N2O-DMTM, a solid-state ion exchange strategy with H-Zeolite and Cu precursor (CuCl) being heated under NH3 center dot H2O atmosphere (SSIENH3 center dot H2O) has been developed to enhance Cu+ cation internal diffusion. It is solidly verified that the SSIE-NH3 center dot H2O prepared Cu-Zeolites exhibit higher Cu+ cation loadings and CH3OH generation rate than those of SSIE-N-2 prepared samples (heated under the N-2 atmosphere) according to the H-2-TPR, XPS, CO-probed FTIR and activity measurement. Among the SSIE-NH3 center dot H2O prepared Cu-Zeolites, the 0.3 %Cu-SSZ-13 displays the highest CH3OH yield (232.4 mu mol gcat(-1) h(-1)), which can be closely related to its low Si/Al ratio as well as small pore-size structure that favors higher amounts of Cu+ loadings. The DFT mechanism simulation combined with a comprehensive microkinetic modeling was further constructed, based on which the N2O-DMTM mechanism over monomeric [Cu](+) site of Cu-SSZ-13 was clarified and it is indicated that the N2O dissociation step with an energy barrier of 1.31 eV and reaction rate of 2.70E+02 s(-1) constitutes the rate-determining step. Generally, present work develops an efficient method of SSIE-NH3 center dot H2O favoring internal dispersion of Cu cations, which would favor other highly efficient zeolitic catalyst design for N2O-DMTM.