Oxidative coupling of methane over La-promoted CaO catalysts： Influence of precursors and catalyst preparation method

The oxidative coupling of methane to C2 hydrocarbons has been studied over a series of La-promoted CaO (La/Ca = 0.05) catalysts, prepared using different precursor salts for CaO and La2O3 (viz. acetates, carbonates, nitrates and hydroxides) and catalyst preparation methods (viz. physical mixing of precursors, co-precipitation using ammonium carbonate/sodium carbonate as a precipitating agent), under different reaction conditions (temperature: 700-850℃, CH4/O2 ratio: 4.0 and 8.0, and GHSV: 51360 cm3 g-1 h-1)...

Oxidative coupling of methane over La-promoted CaO catalysts: Influence of precursors and catalyst preparation method

The oxidative coupling of methane to C2 hydrocarbons has been studied over a series of La-promoted CaO (La/Ca = 0.05) catalysts, preparedusing different precursor salts for CaO and La2O3 (viz. acetates, carbonates, nitrates and hydroxides) and catalyst preparation methods (viz.physical mixing of precursors, co-precipitation using ammonium carbonate/sodium carbonate as a precipitating agent), under different reactionconditions (temperature: 700–850 ◦C, CH4/O2 ratio: 4.0 and 8.0, and GHSV: 51360 cm3.g−1.h−1). The surface area and surface basicity/basestrength distribution of the catalysts have also been investigated. The surface properties and catalytic activity/selectivity of the La-promotedCaO catalysts vary from catalyst to catalyst depending on the catalyst precursors used and catalyst preparation method. The basicity/basestrength distribution is strongly influenced by the precursors (for CaO and La2O3) and catalyst preparation method. Basicity (total and strongbasic sites measured in terms of CO2 chemisorbed at 50 ◦C and 500 ◦C, respectively) observed for the catalyst prepared by co-precipitationmethod is higher than that of the catalysts prepared by physical mixing method. The catalysts prepared by the nitrates of La- and Ca- and coprecipitatedby the solution of sodium carbonate and ammonium carbonate exhibit different catalytic performance in OCM. The finding that nodirect relationship between the surface basicity and catalytic activity/selectivity in OCM exists indicates that basicity is not solely responsiblefor obtaining high selectivity to C2 hydrocarbons.