Factors influencing the temperature-programmed reduction profiles of vanadium pentoxide

Abstract

The temperature-programmed reduction (t.p.r.) of bulk V₂O₅ has been examined as part of a study of the reducibility of V₂O₅-containing catalysts. T.p.r. profiles have been studied as a function of flow rate, heating rate and sample weight. From experiments at different flow rates it is concluded that the order of the reduction rate in hydrogen is low or even zero. A rule of thumb has been derived to provide an easy check on possible exhaustion of hydrogen in the feed. The influence of sample weight and heating rate is explained in terms of the formation of water in the sample during reduction. The reduction of bulk V₂O₅ to V₂O₃ proceeds in several steps; intermediate species include V₆O₁₃ and VO₂. The apparent activation energy of ca. 200 kJ mol^–1 indicates that solid-state diffusion influences the reduction process of V₂O₅.