La-promoted Na2WO4/Mn/SiO2 catalysts for the oxidative conversion of methane simultaneously to ethylene and carbon monoxide

Abstract

A series of La-promoted 5 wt% Na₂WO₄/2 wt% Mn/SiO₂ catalysts were prepared by varying the impregnation sequence and the concentration of La promoter, and their catalytic performance for the oxidative conversion of methane was investigated in a micro-quartz-tube reactor. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was found that the existence of Mn ions was in favor of the dispersion of La species on the catalyst, and the addition of La promoter could increase the dispersion of Na₂WO₄, which enriched the amount of surface oxygen species connected with the metal atoms. This oxygen species was found to be active for the oxidative coupling of methane to C₂ hydrocarbons. The selectivity and yield of C₂ hydrocarbons with a C₂H₄/CO ratio of 1/1 reached the optimized value of about 56% and 25%, respectively, at 800 °C, over the 5 wt% Na₂WO₄/2 wt% La–2 wt% Mn/SiO₂ catalyst prepared by co-impregnation of La and Mn.