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

Soclium-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 degrees C, a gas hourly space velocity (GHSV) of 23,947 cm(3)/g h, a catalyst pretreatment period of 2 h, a dilution ratio of 0.2, and a CH4/O-2 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 alpha-cristobalite to quartz and the loss of manganese oxide from the catalyst surface. (C) 2008 Elsevier B.V. All rights reserved.