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

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 C-2 hydrocarbons. The selectivity and yield of C-2 hydrocarbons with a C2H4/CO ratio of 1/1 reached the optimized value of about 56% and 25%, respectively, at 800 degrees C, over the 5 wt% Na2WO4/2 wt% La-2 wt% Mn/SiO2 catalyst prepared by co-impregnation of La and Mn. (C) 2007 Elsevier B.V. All rights reserved.