Catalytic properties of silver-exchanged zeolites for propene production by conversion of methane in the presence of ethene

Conversion of 13C-labeled methane (13CH4) in the presence of ethene (C2H4) over Ag+-exchanged zeolites (Ag–A, Ag–Y and Ag-ZSM-5) at 673 K affords a mixture of 13C-labeled propene (13CC2H6) and unlabeled propene (C3H6) at a ratio of approximately 80/20. The same reaction over Ag3PW12O40 and proton-exchanged zeolites (H-ZSM-5 and H–Y) yields only unlabeled propene. The role of silver species in the activation of methane in this system is examined by proton nuclear magnetic resonance analysis, and it is revealed that silver cationic clusters (Agn+ in Ag+-exchanged zeolites are responsible for the activation of methane to form silver hydride species (Agn–H) and highly polarized CH3δ+, which reacts with ethene to form propene and acidic protons. Regeneration of Agn+ proceeds by reaction of acidic protons with Agn–H accompanied by the formation of H2. Silver cations in Ag3PW12O40, a silver salt, do not dissociate the C–H bond of CH4 and thus cannot catalyze the reaction of methane and ethene.