An investigation of the thermal stability and performance of wet-incipient WO3/V2O5/TiO2 catalysts and a comparison with flame aerosol catalysts of similar composition for the gas-phase oxidation of methanol

WO3/V2O5/TiO2 catalysts prepared using the wet-incipient and the flame aerosol methods are compared. The wet-incipient catalysts were dried and calcined; the flame aerosol catalysts were used as prepared. The key conclusion of this study is that surface V coverage on anatase TiO2 is the most important factor regarding both thermal stability and performance, and the synthesis method did not have significant effects on observed trends.For the wet-incipient catalysts, this study represents a systematic investigation on the effects of V and W loading on anatase TiO2 with respect to sintering, crystal structure changes, and catalyst performance. Both sintering and crystal phase conversion were promoted by surface V loadings greater than one monolayer. However, a high degree of sintering did not necessarily correspond with crystal phase conversion from anatase to rutile TiO2. The presence of W on the surface inhibits sintering, strongly inhibits crystal structure changes in the TiO2 support, and has very little effect on the performance of the catalysts. An optimum catalyst performance was observed at approximately one monolayer of surface V coverage on anatase TiO2. At sub-monolayer surface V loadings, the flame aerosol catalysts performed better than the wet-incipient catalysts. The better dispersion of V over the surface of TiO2 at low V loadings in the flame aerosol catalysts is likely the reason for this observation. Overall, the performance of the flame aerosol catalysts was comparable to the best wet-incipient catalysts with similar composition for the oxidation of methanol.