ESR study of the stabilization of V4+ ions in TiO2 (anatase)

Abstract

ESR data on vanadium-titanium oxide heated at 300-550"C indicate that V 4+ ions are stabilized in the substitution sites ofTiO2 (anatase).

ESR study of reduced vanadium-titanium oxide catalysts

“…According to the XRD data [12], the oxidized vanadium-titanium oxide sample contained a mixture of anatase and V205 phases. This sample exhibited An unusual ESR spectrum of type T ( Fig.…”

“…[12] and calcined in air at 500~ was reduced in hydrogen in the temperature range of 150-450~ First, the sample was heated in the air flow up to the reduction temperature. Then, it was reduced in the hydrogen flow for 2 h, and, finally, cooled in helium to room temperature.…”

“…The accuracy of the line width measurement was + 10 G. The number of V 4+ ions observed by ESR was evaluated by comparison of the integral intensity of ESR spectra with a reference VOC204 sample prepared according to ref. [12]. Relative integral intensities of the ESR spectra measured at 77 K and assigned to associates of V 4+ ions in anatase (type III spectra) were determined as a ratio of the integral intensity of these ESR spectra to that of the initial oxidized sample.…”

“…For VTi-1 sample, the formation of ordered clusters of V 4+ ions in the rutile structure was observed after calcination in air at 550-950~ [12,14]. The appearance of the spectrum of isolated V 4+ ions in the rutile structure after reduction at 400~ is likely to indicate that the mechanisms of the rutile formation in vanadium-titanium oxide samples under oxidizing and reducing conditions are different.…”

“…The formation of vanadium-titanium coherent boundary in vanadium-titanium oxide samples synthesized by the mixing technique with the use of low-temperature anatase has been shown by electron microscopy [11]. For these samples containing low-temperature anatase it has been shown by ESR [12] that under 0133-1736/99/US$12.00. 9 Akad~mJai Kiad6, Budapest.…”