Oxidative coupling of methane for the production of ethylene over sodium-tungsten-manganese-supported-silica catalyst (Na-W-Mn/SiO2)

Abstract

Abstract Sodium-tungsten-manganese (Na-W-Mn)-supported SiO2 catalyst is one of the widely studied catalysts in oxidative coupling of methane (OCM) reaction. Na, W and Mn have individual roles during the OCM reaction, in providing the stability and activity of the catalyst system. The interaction effects of the component–component and component–support on the methane conversion and C2+ yield were investigated with the aid of thermal gravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectroscopy, Fourier transformed infrared (FTIR) spectroscopy, nitrogen adsorption analysis and catalytic activity tests. The catalyst performance was studied at an operating temperature of 850 °C, a gas hourly space velocity (GHSV) of 23,947 cm3/g h, a catalyst pretreatment period of 2 h, a dilution ratio of 0.2, and a CH4/O2 ratio of 7. During the stability test, methane conversion was maintained at 40–50% throughout a 30 h run. The catalyst was regenerated by allowing oxygen flow through the catalyst bed for 3–5 h once the catalyst was deactivated. C2+ selectivity was recovered to almost 60%, whereas methane conversion did not change after the regeneration. Both Na2WO4 and Mn2O3 crystalline phases contributed to achieving high selectivity of C2+ products. The catalyst activity dropped due to the phase transformation of the support from α-cristobalite to quartz and the loss of manganese oxide from the catalyst surface.