Oxidative Coupling of Methane over Mn/Na2WO4 Catalyst Supported by Monolithic SiO2

In this study, oxidative coupling of methane (OCM) to ethane and ethylene was investigated over Mn/Na2WO4 catalyst supported by monolithic silica. Monolithic silica (monosil), which was prepared using sol-gel method, composed of white whole-structural rods with meso and macroporosities; 2 wt.% Mn and 5 wt.% Na2WO4 were impregnated respectively to the monolithic silica by dropping the precursor solution over the support by injection needle. OCM reaction was carried out by using a 10 mm ID quartz reactor. After the catalyst bed, inside diameter of the reactor was reduced to 2 mm in order to hinder the non-selective gas phase reactions. For comparison particulate catalyst prepared by incipient to wetness impregnation method and wash-coated catalyst over the commercial cordierite monolith was also tested. The results have shown that performance of monosil (about 16% C2 yield) is comparable with particulate catalyst, which have given the best results (about 19% C2 yield); the wash coated catalyst over the commercial cordierite monolith did not worked well (maximum yield was about 6%). Besides, the C2+ selectivity and yield over the monosil catalyst remained the same for a long time on stream indicating that the monosil catalyst is very stable for OCM reaction. It was also observed that monosil regained its activity, after increasing the temperature from and then decreasing to the optimum temperature (no hysteresis effect). Therefore, it was concluded that Mn/Na2WO4 catalyst over monosil can be a promising alternative for the OCM process.