OXIDATIVE COUPLING OF METHANE OVER Y2O3-CAO CATALYSTS

Binary oxides of Y2O3CaO were evaluated as catalysts in the oxidative coupling of methane to C2+ (sum of C2H6, C2H4, C3H8, and C3H6) hydrocarbons. Passing a mixture of CH4/O2 and He gases (at 6, 3 and 31 ml/min respectively) in a fixed-bed flow reactor 13% and 7.5% of C2+ yields were achieved at 750°C and 650°C, respectively, over 0.5 g of 10 mol-% Y2O3CaO catalyst prepared by calcining a coprecipitate of their oxalates at 800°C. The C2+ yields on 10 mol-% Y2O3CaO, prepared by physical mixing, were lower than those on the coprecipitated catalyst. With increasing Y2O3 content in the coprecipitated catalyst, the C2+ selectivity at 700°C was significantly enhanced even at ca. 3 mol-%, whereas at 600°C such a change was not observed. A similar dependence on the Y2O3 content was found in the way both surface areas and basicities decreased. Those changes were attributed to the formation of a solid solution accompanying the production of interstitial oxygen ions. Electron-spin resonance (ESR) studies indicated that the ion is a superoxide ion which is responsible for the generation of methyl radical from methane. At low reaction temperatures, 700°C, it was found that a lattice distortion of Y2O3 in the binary oxides also affected the C2+ selectivity. © 1990.