Dynamic states of V-oxide species:: reducibility and performance for methane oxidation on V2O5/SiO2 catalysts as a function of coverage

Temperature-programmed in situ Raman spectroscopy is used to understand the effect of surface vanadia coverage on the structure, reducibility and performance for the oxidation of methane on V2O5/SiO2 catalysts. The vanadia coverage on silica has no effect on its structure below its dispersion-limit loading ("monolayer" coverage); however, the interactions among surface vanadia species under reducing conditions become increasingly important. This interaction appears to operate through the sharing of oxygen sites facilitating the reduction, but it does not alter the total reducibility. The probability for this interaction to take place increases with vanadium oxide surface coverage. It is therefore expected that under reaction conditions the catalyst with higher vanadia coverage would have a greater capacity to release oxygen. This would increase the activity per vanadium site.