Catalytic behaviour of V-Sb-Ti mixed oxides in the vapour-phase reaction of ethylbenzene with air

The objective of this work is to study the behaviour of V-Sb-Ti mixed oxides in the ODH of ethylbenzene and to compare these results with those previously reported for the partial oxidation of toluene with the same catalysts. The solids, with nominal compositions VSbO4, VSb0.8Ti0.2O4 and V0.8SbTi0.2O4, were prepared by solid-state reaction. Catalytic tests were carried out in a fixed-bed reactor using ethylbenzene and air as reactants. A relation between the dehydrogenation function of the solids and their Sb/V surface ratios was established. The higher Sb/V surface ratio the higher selectivity to styrene but pointing out the participation of Sb sites in the H-abstraction step. Comparison between toluene and ethylbenzene oxidation results has confirmed that the reaction rate is independent of the hydrocarbon used in the feed and controlled by the reoxidation of the catalyst. Besides, at the same conversion level, selectivity to total oxidation products is lower when ethylbenzene is used as reactant, due to the formation of a stable dehydrogenated product, styrene, which competes with oxygen for the chemisorption on Lewis acid sites.