Enhancement of methanol selectivity in the products of direct selective oxidation of methane in CH4-O2-NO with Cu-ZnO/Al2O3

Enhancement of methanol selectivity in the products of the direct selective oxidation of methane with CH4-O-2-NO in a gas-phase reaction was examined using a Cu-ZnO/Al2O3 catalyst. Three distinct reaction paths over the Cu-ZnO/Al2O3 catalyst were detected in the gas-phase selective oxidation of methane in CH4-O-2-NO. The formation of CH3OH from CH2O-H-2 and the water-gas shift reaction of CO-H2O progressed chiefly at around 250 degreesC over CuZnO/Al2O3 catalyst. The steam reforming reaction of CH3OH progressed over the same Cu-ZnO/Al2O3 catalyst at around 350 degreesC and higher. Both CH3OH and CH2O were observed as C-1-oxygenates at 550 degreesC in the gas-phase selective oxidation of methane in CH4-O-2-NO, but only CH3OH was observed as a C-1-oxygenate in the presence of Cu-ZnO/Al2O3 catalyst in addition to the gas-phase selective oxidation of methane. The complete exhaustion of oxygen in the gas-phase selective oxidation of methane in CH4-O-2-NO was a key to the effective use of Cu-ZnO/Al2O3 catalyst. Of the two reactions, CH3OH formation and water-gas shift over Cu-ZnO catalyst, the water-gas shift reaction progressed more over the catalyst with a higher surface area and with a lower surface Cu/Zn atomic ratio. (C) 2001 Academic Press.