Oxidative coupling of methane over sodium-chloride-promoted zirconia supported on sodium-preimpregnated silica Original Research Article

Supported Na+single bondZrO2single bondCl− catalysts were prepared by impregnating sodium-preimpregnated silica with a mixed solution of zirconyl chloride and sodium carbonate, and the optimum amounts of sodium preimpregnation and the mixed-solution impregnation were investigated for the oxidative coupling of methane (OCM). The supported catalyst showed a better performance than the unsupported catalyst, and the highest C2 selectivity, yield and ethene/ethane ratio obtained over the optimum catalyst at 1073 K were 67%, 24.6% and 5, respectively. The sodium preimpregnation effectively suppressed the combustion activity of silica by both the scavenging of the acidic sites and reduction of the surface area, and the former is considered to be more important. With the optimum amount of preimpregnated sodium, further interaction of sodium in the mixed solution with the silica is considered to be minimized, resulting in effective incorporation of sodium and chlorine into ZrO2 from the mixed solution. It is suggested that the high C2 selectivity and yield of the optimum catalyst is due to a combination of a low surface concentration of ZrO2 which is primarily responsible for the deep oxidation and high surface concentrations of sodium and lower-binding-energy chlorine species which are associated with the active sites for the production of methyl radicals.