CHARACTERIZATION OF TITANIA-SUPPORTED V2O5 CATALYSTS BY REDUCTION ANDSUBSEQUENT OXYGEN-ADSORPTION

The aim of this study was to test the suitability of oxygen uptake mea surements for the characterization of titania-supported vanadia cataly sts. Before oxygen uptake measurements, the two catalysts (EL10V1 and EL10V8) were reduced in flowing hydrogen (623 K, 2 and 6 h). The subse quent oxygen adsorption at different temperatures was determined by us ing a static (microbalance) and a dynamic (GC pulse experiments) metho d. There was only a significant influence of reduction time on oxygen uptake for catalyst EL10V8. Considering the oxygen uptake of the two c atalysts (mumol O2/mumol V2O5), EL10V1 shows a higher degree of reduct ion for all temperatures, which is explained by the higher dispersion of the vanadia leading to stronger support interaction and easier redu cibility of these species. The static and the dynamic method are both suitable for oxygen uptake measurements for characterizing supported v anadia catalysts. However, it seems unlikely that the reduction and ox idation processes are confined to the outermost surface layer of vanad ia. The following reference conditions are proposed: reduction of the catalyst for 6 h at 623 K and subsequent exposure to oxygen at the sam e temperature.