Enhancing Selectivity of La─Ce─O Catalyst in Oxidative Coupling of Methane by Na2WO4 Doping

Abstract La─Ce─O catalyst doped with 5, 10, and 15 wt% of Na 2 WO 4 prepared by wet impregnation was characterised by XRD, N 2 ‐sorption, Raman spectroscopy, TPD‐CO 2 , and SEM‐EDX and tested in the oxidative coupling of methane (OCM) reaction between 400 and 800 °C. In the presence of La─Ce─O and doped with 5 wt% Na 2 WO 4 catalysts, the reaction starts at 450 °C while the catalysts with 10 and 15 wt% Na 2 WO 4 are inactive below 600 °C. Moreover, doping with Na 2 WO 4 improves the selectivity to C 2 hydrocarbons (ethane and ethylene). Over the catalysts with 15 wt% Na 2 WO 4 content 65% selectivity to C 2 hydrocarbons with a methane conversion of 25% were obtained at 650 °C (CH 4 /O 2 = 3.8). Changes in the catalytic properties of the Na 2 WO 4 doped La─Ce─O catalysts are accompanied by significant changes in their physicochemical properties. It has been proposed that the modification of the chemical and phase composition and blocking the strong basic sites are primarily responsible for improving the selectivity, while the activity is also influenced by the reduction of the surface area and increase in the particle size caused by the Na 2 WO 4 doping.