Preparation of SnO2 and Nb2O5 Supported Vanadium Oxide Catalysts by a Column-Exchange Adsorption Method and Dispersed States of Vanadia Species

SnO2 and Nb2O5-supported monolayer or sub monolayer vanadium oxide catalysts were prepared by an impregnation method such as the column-exchange adsorption of oxovanadium ion at various pH(=2, 4, and 7). The deposited states of the vanadia species on SnO2 and Nb2O5 surfaces were examined by ESR spectrometry using V4+ ion as a probe. The catalytic features were studied by measuring the 2-propanol decomposition rate as a test reaction. The deposited states of the vanadia species differed to a small extent between SnO2 and Nb2O5 carriers depending upon the difference in the symmetry of the surface field. The deposited states, however, did not vary with pH upon impregnation, although the amounts of vanadium oxide deposited (coverage, θ) were much affected by the pH. The activation energy (Ea) for the dehydration of 2-propanol over these catalysts was linearly related to the reciprocal of the coverage (1⁄θ). When both curves were extended to 1⁄θ=0, they crossed at around 5–6 kcal·mol−1 which was the minimum value, although the inclination differed largely between the carriers. This low activation energy was regarded as an intrinsic value that was caused by the multi-layered vanadium oxide deposited on the carriers. Through the discussion it is clearly shown that the most effective catalyst, a monolayer catalyst, was prepared on impregnation at pH=2 and the vanadia species were dispersed widely, keeping a weak interaction with the SnO2 and Nb2O5 surfaces.