Partial Oxidation of Methane to Synthesis Gas over Rhodium Vanadate, RhVO4: Redispersion of Rh Metal during the Reaction

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Abstract
Partial oxidation of methane to synthesis gas (CO+H2) has been carried out over both RhVO4/SiO2 and unpromoted Rh/SiO2 catalysts at temperatures between 300 °C and 720 °C and 1 atomosphere pressure, with a CH4 : O2 of 2 : 1 under nitrogen dilution. It is found that the RhVO4 compound supported on SiO2 was reduced to Rh metal and V2O3 during the reaction, and the catalyst showed onset of activity to CO and H2 around 500 °C reaching a maxium conversion in excess of 90% at 650 °C, while the unpromoted Rh/SiO2 catalyst showed the onset of activity at the higher temperature (above 600 °C) reaching almost 100% conversion at around 700 °C. The different catalytic activity may be ascribed to both the morphology change (Rh dispersion) and the Rh–vanadia interaction after the reduction of the RhVO4 compound.