Applied Catalysis A: General 246 (2003) 49–68 Oxidative dehydrogenation of isobutane over V 2 O 5 -based catalysts prepared by grafting vanadyl alkoxides on TiO 2 –SiO 2 supports V. Iannazzo a , G. Neri a , S. Galvagno a , M. Di Serio b , R. Tesser b , E. Santacesaria b,∗ a Dipartimento di Chimica Industriale e Ingegneria dei Materiali dell’Università di Messina, Salita Sperone 31, Messina 98166, Italy b Dipartimento di Chimica dell’Università di Napoli “Federico II”, Complesso di M. te S. Angelo, Via Cinthia, Napoli 80126, Italy Received 31 July 2002; received in revised form 9 December 2002; accepted 10 December 2002 Abstract 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 TiO 2 –SiO 2 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 TiO 2 environment has been largely simplified by avoiding the use of a TiO 2 –SiO 2 support obtaining, in the meantime, a remarkable improvement in the selectivity. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Isobutane; Oxidative dehydrogenation; Grafting alkoxides; V 2 O 5 ; Hydrolysis 1. Introduction Isobutene is an important feedstock for petrochem- ical, polymer and chemical industries [1,2]. Light olefins can be produced by dehydrogenation, at high temperature, of the corresponding alkanes. However, the catalytic dehydrogenation still suffers from a number of limitations including high energy input and catalyst deactivation. The light alkane oxidative dehy- drogenation (ODH) represents an alternative for the production of these chemicals, provided that highly selective catalysts are developed. A number of studies on the ODH of isobutane to isobutene are reported ∗ Corresponding author. in the literature [3–9]. It can be pointed out that sup- ported V 2 O 5 , a well-established catalyst for the ODH of propane [10–16], was less investigated in the ODH of isobutane. With conventional supported V 2 O 5 cat- alysts, low selectivity to the desired olefines were reported. Hoang et al. [17] obtained over V 2 O 5 /Al 2 O 3 catalysts a selectivity of less than 15%, at 7% of isobutane conversion. However, a very recent paper of Zhang et al. [18] reports that vanadium-containing MCM-41 catalysts prepared by a direct hydrothermal (DHT) method show selectivities to isobutene higher than 40%, at a conversion of about 10%. On the other hand, it has been clearly shown that activities and selectivities of vanadia-based catalysts in the ODH of alkane strongly depend on the VO x environment, 0926-860X/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0926-860X(02)00668-3