Plasma-catalytic Direct Oxidation of Methane to Methanol over Cu-MOR:
Revealing the Zeolite-confined Cu 2+ Active Sites
Abstract
Efficient methane conversion to methanol remains a significant challenge
in chemical industry. This study investigates the direct oxidation of
methane to methanol under mild conditions, employing a synergy of
non-thermal plasma and Cu-MOR (Copper-Mordenite) catalysts. Catalytic
tests demonstrate that the Cu-MOR IE-3 catalyst (i.e., prepared by three
cycles of ion exchange) exhibits superior catalytic performance (with
51% methanol selectivity and 7.9% methane conversion). Conversely, the
Cu-MOR catalysts prepared via wetness impregnation tend to over-oxidize
CH 4 to CO and CO 2. Through systematic
catalyst characterizations (XRD, TPR, UV-Vis, HRTEM, XPS), we elucidate
that ion exchange mainly leads to the formation of zeolite-confined Cu
2+ species, while wetness impregnation predominantly
results in CuO particles. Based on the catalytic performance, catalyst
characterizations and in-situ FTIR spectra, we conclude that
zeolite-confined Cu 2+ species serve as the active
sites for plasma-catalytic direct oxidation of methane to methanol.