Temperature-programmed reduction and oxidation experiments with V2O5/TiO2 catalysts

Temperature-programmed reduction (TPR) and oxidation (TPO) experiments were performed with V2O5/TiO2 catalysts with vanadia loadings of 1 wt.% (Euroca t EL10V1) and 8 wt.% (Eurocat EL10V8) and with unsupported It was possible to correlate the redox properties with the presence of different vanadia sp ecies : crystalline and polymeric vanadia species known to be present on EL 10V8 were found to be the most difficult to reduce but the easiest to reoxi dize. Monomeric vanadyl species known to be present on EL10V1 were the easi est to reduce but the most difficult to reoxidize. In a further set of expe riments toluene was used as reducing agent under isothermal conditions at 6 23 K to probe the catalytic properties of the various vanadia species. In t he subsequent TPO experiments the oxygen mass balance including O-2, CO, CO 2 and H2O was solved thus allowing us to distinguish between the oxidative degradation of adsorbates and the reoxidation of the catalyst. The O-2 cons umption at lower temperatures was shown to originate from the total oxidati on of adsorbates, observed for all three samples, whereas the O-2 consumpti on at higher temperatures, observed only for EL10V8 and V2O5, was caused by the reoxidation of these catalysts. Thus, monomeric vanadyl species were a ble to adsorb toluene dissociatively, but no oxygenated products were relea sed into the gas phase. In contrast, fast oxygen insertion into toluene and desorption of oxygenates occurred when crystalline and polymeric vanadia s pecies were present.