Mechanistic Insights on the Direct Conversion of Methane into Methanol over Cu/Na–ZSM-5 Zeolite: Evidence from EPR and Solid-State NMR

Abstract

The selectively direct conversion of methane to methanol on Cu-exchanged zeolites has attracted a lot of interest because of the abundant availability of methane. A detailed reaction mechanism of the transformation of methane to methanol aimed to improve the catalyst design has been long expected. On the basis of EPR and solid-state NMR studies, we demonstrate that CH4 activates on the [Cu2O]2+ core of the Cu/Na–ZSM-5 zeolite, producing a ·CH3 radical and an ·OH radical. The generated methanol molecule, which formed from the combination of ·CH3 and the ·OH radicals, adsorbs on the Cu+ species and forms the copper methoxy species (−Cu–O–CH3) and the −Al–OH group. Through the process of hydration, the copper methoxy species and the adsorbed methanol transform into free methanol. We expect that our mechanistic understanding of the methane to methanol process could pave the way for catalyst design.