Spectroscopic Studies of Catalysis by Vanadium Pentoxide

Abstract

Abstract The role of the V=O bond in V2O5 in the adsorption of several gases was studied by measuring the electron spin resonance (ESR) and the infrared (IR) spectra. The ESR spectra of V2O5 supported on γ-Al2O3 were similar to those of VOSO4 on γ-Al2O3. When such electron-donating gases as CO, SO2 and C2H4 were adsorbed on this V2O5-γ-Al2O3, the signal intensity of ESR increased and the splitting of the h.f.s. became clear. Upon treatment with an electron-accepting gas such as O2, a reverse change was observed. In the case of V2O5 supported on SiO2, similar ESR spectra were observed by the adsorption of CO after a mild reduction. The IR spectra of V2O5 have a sharp absorption peak at 1023 cm−1 due to the stretching vibration of the (V=O)3+ bond; this peak became broader by adsorption of such gases as CO and SO2. Simultaneously, the center of the peak shifted to the red region and a weak hump appeared at 980–990 cm−1, probably due to (V=O)2+. These results of the ESR and IR measurements reveal that these electron-donating gases are adsorbed on the (V=O)3+ bonds on the surface of V2O5, and that the increase in electron densities in the adsorption sites results from adsorption of these gases. Furthermore, the role of this (V=O)3+ bond in oxidation reaction was also discussed.