Studies on the V 2 O 5 -TiO 2 System. IV. Oxygen Chemisorption

Abstract

The chemical adsorption of oxygen on V₂O₅ and V₂O₅ -TiO₂ over the temperature range 100–450°C and at pressures between 10⁻² and 3 Torr has been studied. Assays have been performed using a volumetric method, the isotherms obtained being in accordance with Langmuir's adsorption model.

Isobaric plots at 1.5 Torr of these isotherms exhibit two maxima, at 250 and 400°C, respectively. These maxima have been interpreted in terms of the surface chemisorption of O²⁻ and its diffusion into the bulk solid.

The amount adsorbed at the 250°C maximum depends on the sample composition in the following decreasing adsorption order: VT80, VT50, VT10, VT20 and VT0.

At the 400°C maximum, the same amount of O₂ is adsorbed experimentally by all the TiO₂-containing samples, this value being quite different from that corresponding to pure V₂O₅ (VTO). Possible explanations for this observation are based on (i) the relative magnitudes of the V/Ti surface ratios and (ii) the presence of Ti⁴⁺ in V₂O₅ crystals.