Room temperature activation of methane over Zn modified H-ZSM-5 zeolites: Insight from solid-state NMR and theoretical calculations

Abstract

Room temperature activation of methane over a Zn modified H-ZSM-5 zeolite catalyst was investigated by solid-state NMR spectroscopy in combination with other spectroscopic methods and DFT theoretical calculations. We found for the first time that the activation of methane resulted in the preferential formation of surface methoxy intermediates at room temperature, which mediated the formation of methanol and its further conversion to hydrocarbons. Experimental and theoretical calculation results demonstrated that an oxygen-containing dizinc cluster center in an open shell was responsible for homolytic cleavage of the C–H bond of methane at room temperature, leading to the formation of methyl radicals. The zeolite matrix readily trapped the methyl radicals by forming the surface methoxy intermediates for further selective conversion. In parallel to the homolytic cleavage pathway, heterolytic dissociation of methane was also observed on isolated Zn²⁺ ions at room temperature, which gives rise to zinc methyl species.