Plasma-catalytic one-step steam reforming of methane to methanol: Revealing the catalytic cycle on Cu/mordenite

Direct CH4 to CH3OH conversion is a long-standing grand challenge in catalysis. We present one-step steam reforming of methane to methanol (OSRMtM) by combining an atmospheric pressure CH4/H2O/Ar plasma with a Cu/Mordenite (Cu/MOR) catalyst at 170 degrees C, achieving 77% CH3OH selectivity with 3.0% CH4 conversion. Catalyst characterization and plasma diagnostics, as well as D2O and H218O-labeled isotope tracer experiments reveal that the excellent reaction performance is attributed to Cu-O active sites confined by MOR zeolite. During plasma-catalytic OSRMtM, both CH4 and H2O are activated in the plasma and dissociated to produce radicals (CH3, OH, and H). These radicals drive the redox process between Cu2+ and Cu+, playing an important role in plasma-catalytic OSRMtM. Although a gradual reduction of Cu2+ to Cu+ leads to slow deactivation, the catalytic performance can be completely recovered through simple calcination, which enables a continuous plasma-catalytic OSRMtM process using a fluidized-bed reactor.