The Electron Spin Resonance of Oxovanadium Sulfate Dispersed on Porous Materials

Oxovanadium sulfate was fixed on silica and alumina gel bases as a model of the oxidation catalyst. On silica gel the ESR spectra showed an exchange narrowing without hyperfine lines as a result of the formation of small crystallites. In this case, axially-symmetrical g factors were obtained: g⊥=1.969±0.001 and g||=1.915±0.005. When sulfuric salts of alkali metals were added to the system, the dispersion of VO2+ ions became homogeneous and a hyperfine structure was observed in the ESR spectra. On an alumina gel base the spectrum resembled that of the frozen aqueous solution of VOSO4 and showed the hyperfine structure, A⊥=(7.0±0.2)×10−3cm−1 and A||=(1.85±0.05)×10−2cm−1. It may be considered that VO2+ ions are distributed homogeneously in the surfase layer of alumina. In the alumina gel and silica gel with alkali sulfate, the decrease in the V4+ ions with heat treatment was slower than in the silica gel system.