Factors controlling the selectivity of V2O5 supported catalysts in the oxidative dehydrogenation of propane

The surface properties of a series of V2O5 catalysts supported on different oxides (Al2O3, H-Na/Y zeolite, MgO, SiO2, TiO2 and ZrO2) were investigated by transmission electron microscopy and FTIR spectroscopy augmented by CO and NH3 adsorption. In the case of the V2O5/SiO2 system TEM images evidence d the presence of V2O5 crystallites, whereas such segregated phase was not observed for the other samples. VOx species resulted widely spread on the s urface of Al2O3 H-Na/Y zeolite, MgO and SiO2, whereas on Tier and ZrO2 they are assembled in a layer covering almost completely the support, Furthermo re, evidences for the presence in this layer of V-OH Bronsted acid sites cl ose to the active centres were found. It is proposed that propene molecules primarily produced by oxydehydrogenation of propane can be adsorbed on thi s acid centres and then undergo an overoxidation by reaction with redox cen tres in the neighbourhood. This features could account for the low selectiv ity of V2O5/TiO2 and V2O5/ZrO2 catalysts. (C) 2000 Elsevier Science B.V. Al l rights reserved.