Partial oxidation of methane on silica-supported vanadia catalysts. The relevance of catalyst BET area and gas-phase activation

Silica-supported vanadium oxide catalysts with different BET areas have been used in partial oxidation of methane to formaldehyde. The BET area of the silica support not only plays an important role in the activation of methane but also in promoting the degradation of reaction intermediates. A reaction scheme is proposed where HCHO and CO2 are primary products, whereas CO is a secondary product from the degradation of formaldehyde and hydrocarbons. A large BET area led to degradation of hydrocarbons to CO, whereas on low-BET-area catalysts, this side reaction is partially inhibited with the simultaneous formation of C-2 hydrocarbons. The general trend observed is that the activity decreases with decreasing BET areas. Gas-phase reactivity increases the initial activation of methane, but does not increase the degradation of reaction intermediates as much as surface area does thus providing a selective activation for methane.