Identifying the crucial role of water and chloride for efficient mild oxidation of methane to methanol over a [Cu2(μ-O)]2+-ZSM-5 catalyst

Abstract

Controllable methane oxidation to methanol is a challenging in catalysis, usually suffering from over-oxidation. We report that a single-metal [Cu2(μ-O)]2+-ZSM-5 catalyst can activate methane to methanol with superior high selectivity up to 91.3% in C1 oxygenates and 12.31 molmethanol kgcat-1h−1 by avoiding over-oxidation. Density functional theory (DFT) calculations combined with in situ FT-IR and EPR demonstrated that methanol forms via direct dissociation of strongly adsorbed *CH3OOH generated by *CH3 spontaneously reacting with H2O2 rather than OH. It was found that water plays a crucial role in enhancing methanol formation as other solvents ethanol and acetone show negligible activity. DFT calculations and TPD results confirmed that adsorbed H2O* facilitates active site regeneration and accelerate methanol desorption via H migration between H2O* and [Cu2(μ-OH)2]2+. In addition, the introduction of chloride is favorable for the formation of active [Cu2(μ-O)]2+ species owing to a decrease in binding energy between active sites and ZSM-5, and can promote methanol production by weakening the interaction between methanol and active sites by accepting electron from Cu.