Methane Activation over Zn-Modified MFI Zeolite: NMR Evidence for Zn-Methyl Surface Species Formation

The early stages of methane activation over Zn-modified H-MFI catalysts obtained by high-temperature reaction with zinc vapor have been studied by C-13 MAS NMR in situ. Methane 99.9% enriched with C-13 was used as labeled reactant. The spectroscopic data pointed to formation of zinc methyl species at ambient temperature just after methane adsorption onto the zeolite sample. The results suggest that methane activation occurs via dissociative adsorption over acid-base Zn-O pairs involving Zn2+ cations and negatively charged oxygen atoms of the zeolite framework. The nature of the sites responsible for the dissociation is discussed.