Catalysis Today 91–92 (2004) 259–264 Synthesis, characterization and evaluation as catalysts for propane ammoxidation of VMoSbO systems with rutile-type structure M. Cimini a,b , J.M.M. Millet a , N. Ballarini b , F. Cavani b,∗ , C. Ciardelli b , C. Ferrari b a Institut de Recherches sur la Catalyse, CNRS, 2 av. A. Einstein, 69626 Villeurbanne, France b Dipartimento di Chimica Industriale e dei Materiali, Viale Risorgimento 4, 40136 Bologna, Italy Abstract Monophasic, rutile-type Mo/V/Sb mixed oxides were synthesized with the co-precipitation procedure; Mo 6+ replaced for V 4+ in the lattice of V antimonate, and the (Mo + V)/Sb ratio remained approximately constant. The addition of Mo increased the catalytic activity in propane ammoxidation, but the catalysts became less selective to acrylonitrile, due to the increased contribution of combustion, and more active in ammonia oxidation to molecular nitrogen. This was attributed to an enhanced Lewis acidity, which increased the interaction of the catalyst with ammonia and favored its unselective transformation. © 2004 Elsevier B.V. All rights reserved. Keywords: Propane ammoxidation; Acylonitrile; Mo/V/Sb mixed oxides; Rutile-type mixed oxides 1. Introduction Rutile-based systems, including V/Sb/(W, Al)/O [1–6], Fe/V/Sb/O [7,8], Sn/V/Sb/O [9], Cr/Sb/O [10], Ga/Sb/O [11] and V/Nb/Sb/O [12], are known to be efficient catalysts for the ammoxidation of propane to acrylonitrile. The partic- ular properties of these systems arise from the following chemical–physical features: (i) formation of mixed oxides in which the components essential for the activation of paraf- fins (i.e., V, but also Fe, Ga or Cr) and those which are active in the O/N insertion on the allylic-type intermediate, belong to the same structure and can effectively co-operate in the transformation of the alkane, and (ii) ability to disperse an- timony oxide on its surface, in the form of a supra-surface layer above quasi-VSbO 4 [13], which also plays an impor- tant role in the reaction mechanism. The rutile structure in some cases is surface-enriched in Sb [10,14], and this also may provide the development of specific sites (Sb 5+ =O, Sb 3+ –O–Sb 5+ ) which have been proposed to be the active species involved in the allylic ammoxidation of the unsatu- rated intermediate [15]. ∗ Corresponding author. Tel.: +39-051-2093680; fax: +39-051-2093680. E-mail address: cavani@ms.fci.unibo.it (F. Cavani). A second class of catalysts active and selective in the am- moxidation of propane are those based on V/Mo/Nb/Sb(Te) mixed oxides [16,17], which first were developed by Mit- subishi and later were claimed as catalysts for several dif- ferent reactions of alkanes oxidation, including oxidation of ethane to acetic acid, oxidation of propane to acrylic acid, and oxidehydrogenation of ethane to ethylene. The catalytic properties of these materials derive from the development of specific structures, in which cooperation between V, Mo and co-elements is particularly effective [18,19]. In these classes of catalytic materials, Mo is supposed to play the role of NH 2- -insertion onto the allylic intermediate, in the same way as it happens in Bi molybdates for propylene am- moxidation. Starting from the classification of catalysts for propane ammoxidation, and with reference to the specific role which has been assigned in literature to each element in these mul- tifunctional systems, we have decided to study the possibil- ity of formation of V/Mo/Sb/O systems, by investigation of the nature of crystalline compounds formed. The investiga- tion was focussed on compositions in which the ratio be- tween elements are far from compositions claimed for the Mitsubishi systems. In the present work we report about the catalytic performance, in propane ammoxidation and oxida- tion, of monophasic V/Mo/Sb mixed oxides characterized by the rutile-type structure, never described before in liter- 0920-5861/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2004.03.059