Oxidative dehydrogenation of isobutane over V2O5-based catalysts prepared by grafting vanadyl alkoxides on TiO2-SiO2 supports

Following four different procedures many vanadium-based catalysts have been prepared by using the grafting technique and have been tested on the oxidative dehydrogenation of isobutane. The best results of selectivity have been obtained with catalysts prepared by grafting bimetallic vanadium-titanium alkoxides directly on silica. The alkoxide precursors have been obtained by partially hydrolysing titanium alkoxide, dissolved in isopropanol, with a stoichiometric amount of water and reacting then with vanadyl tri-isopropoxide, or alternatively by mixing the two mentioned alkoxides in isopropanol and submitting both to controlled partial hydrolysis. The bimetallic alkoxide grafted on silica show a prevalence of isolated V-O-Ti bonds with respect to polyvanadylic V-O-V bonds that are prevalent, on the contrary, when vanadyl tri-isopropoxide dissolved in n-hexane is grafted on a TiO2-SiO2 support. Catalysts characterised by the prevalence of V-O-Ti bonds are slightly less active but two times more selective than catalysts in which V-O-V bonds prevail. The preparation of vanadium-based catalysts with a favourable TiO2 environment has been largely simplified by avoiding the use of a TiO2-SiO2 support obtaining, in the meantime, a remarkable improvement in the selectivity