Oxidative coupling of methane over Y2O3CaO catalysts

Abstract Binary oxides of Y 2 O 3 CaO were evaluated as catalysts in the oxidative coupling of methane to C 2+ (sum of C 2 H 6 , C 2 H 4 , C 3 H 8 , and C 3 H 6 ) hydrocarbons. Passing a mixture of CH 4 /O 2 and He gases (at 6, 3 and 31 ml/min respectively) in a fixed-bed flow reactor 13% and 7.5% of C 2+ yields were achieved at 750°C and 650°C, respectively, over 0.5 g of 10 mol-% Y 2 O 3 CaO catalyst prepared by calcining a coprecipitate of their oxalates at 800°C. The C 2+ yields on 10 mol-% Y 2 O 3 CaO, prepared by physical mixing, were lower than those on the coprecipitated catalyst. With increasing Y 2 O 3 content in the coprecipitated catalyst, the C 2+ 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 Y 2 O 3 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 Y 2 O 3 in the binary oxides also affected the C 2+ selectivity.