Phase Relations in the System TiO2-V2O x under Oxidizing and Reducing Conditions

Abstract

The target of this work was to investigate the phase development in the catalyst system consisting of TiO 2 (Anatase) and V 2 O 5 (Shcherbinaite) under several gas atmospheres. Thus a set of V 2 O 5 / TiO 2 specimens was prepared by ball milling and exposed to subsequent annealing in air and feed gas in the temperature range from 400 to 700°C. The XRD-results showed that the initial phases Anatase and Shcherbinaite remain stable for all atmospheres containing oxygen. In the temperature range above 525°C the formation of a Rutile solid solution (Rutile-ss) containing VO x species takes place. However, under reducing conditions (lower oxygen partial pressure) the reduction of V 2 O 5 to V 2 O 3 was found by X-ray diffraction measurements. There is no miscibility up to 1300°C followed by the formation of V 2 TiO 5 (Berdesinskiite). SEM images underline the reduction by monitoring the change in morphology with respect to the V-containing phases. TiO 2 remains without much alteration. The two phases V 2 Ti 7 O 17 and V 2 Ti 3 O 9 (Schreyerite) as described in mineralogy have not been observed in these experiments. The knowledge of phase relations helps to find the appropriate processing conditions and to understand the aging phenomena of catalysts.

Phase equilibria and thermodynamic evaluation of the Ti-V-O system in air

“…Little liquidus and solidus data have been reported for the Ti-V-O system in air (see Table 1). However, in two recent studies by Habel et al [4,5] a wide solubility range of V 2 O 5 in rutile crystal structure was reported. The focus of their work was on phase development during catalyst processing under oxidizing conditions.…”

“…In this study, we investigate the Ti-V-O system in air, which in turn will contribute to thermochemical database for M-V-O systems (where M refers to metallic elements like Na, K, Ca, Mg, Ti, Cr, Mn, Fe, Al, and Si) under oxidizing conditions. Only a few studies have partially investigated phase equilibria of Ti-V-O in air and at lower oxygen partial pressures [2,3,4,5]. Nevertheless, the Ti-V-O system was thermodynamically evaluated by Enomoto [6] and later again by Yang et al [7] in response to new experimental phase diagram data obtained under relatively reducing conditions [4,5,8].…”

“…Applications of the Ti−V−O system under oxidizing conditions were reported by numerous studies [9,10,4,5]. One such application of the Ti-V-O system under oxidizing conditions is its effect as supportive promoter for catalyst during the selective oxidation of butadiene, 1-butene, and benzene to maleic anhydride, and of naphtalene and ooxylene to phthalic anhydride [9].…”

Structural properties of transparent Ti-V oxide semiconductor thin films

“…[17,21,22], doping with vanadium should provide realization of transparent and semiconducting films based on a TiO 2 matrix. Ti-V oxides can form either n or p type conduction depending on revealed phases [23,24]. In previous authors' work [18] in TiO 2 -V 2 O 5 phase composition, semiconducting properties with the p-type of electrical conductivity rarely found in transparent electronics has been achieved [18] ion concentration, acting as a donor impurity.…”

Structural, electrical and surface static charge investigation of TiO<inf>2</inf> thin films doped with different amount of vanadium

“…Thus, in this paper studies of the structural, electrical and antistatic properties of Ti0 2 thin films have been presented. For modification of dielectric nature of Ti0 2 and obtain semiconductive, dissipative thin films doping with different amount of vanadium [6,7] has been applied.…”