JOURNAL OF CATALYSIS 106, 251-262 (1987) Nature of Active Species in the Ammoxidation of Toluene over V205/Ti02 Catalysts Prepared by Flash-Drying FABRIZIO CAVANI, ELISABETTA FORESTI, FERRUCCIO TRIFIR~,’ AND GUIDO BUSCA” Rcccivcd August ?I. 1986: rcviscd Deccmhcr 17. lY8h VITiIO catalysts we,-e prepared by flash-drying of solutions containing V(IV) and Ti(lV) ion\. thus with contemporaneous hydrolysis and precipitation of V20i and TiO!. as anatase. The catalysts were characterized by means of X-ray diffraction. (XRII). chemical annlyses. Fouricl transform infrared spectrometry. (FTIR) and thermogravimetl-y. The result\ indicate that at least three different forms of vanadium are present in the calcined sample\: (1) a V(IV) stabilized as regards oxidation. but reducible to V(III), which stl-ongly interacts with the support. and probably constitutes the so-called monolayer spread over the anatase surface: this species is chaf-acterized by an IR absorption at Y40 cm ‘; (2) u V(V) spccicz, easily reducible to V(IV). and to V(III). chWacterized by an IR band at 980 cm ‘; this species also strongly Inlcracts with the Ti02: and (3) vanadia weakly interacting with the TiOl. present as amorphous V,Oi. Catalysts containing different amounts of vanadium were tested in the ammoxidation of toluene to benzonitrile. and in the dehydrogenation of isopropyl alcohol to acetone. The correlation between the amounts of the different vanadia species and the activities indicated that species I possesses the active sites responsible for toluene activation and alcohol dehydrogenation: species ? instead is responsible fat the parallel undesired combustion of ammonia to nitrogen; while the third specie\ is inactive in all reactions. (’ IYX7 Acwlcmc I’I.cI\ Inc INTRODUCTION V/Ti/O catalysts have been widely stud- ied and characterized for oxidation reac- tions of different organic substrates, such as aromatic hydrocarbons (especially o- xylene) (1-6) and olefins, and in the ammoxidation of some alkylaromatics, such as alkylpyridine. or xylenes (7-12). These catalysts are usually prepared by the wet impregnation technique, thus by deposition of vanadium from a V(V) solu- tion onto preformed TiO? (IS-IS). Other methods which have been used are the grafting technique (16/7), flame hydroly- sis (18), and mixing of the two oxides followed by heating (7, 8). A completely different preparation tech- ’ To whom correspondence should bc addrcsscd. nique has been used in previous studies in order to prepare catalysts active and selec- tive for the ammoxidation of aromatic com- pounds and oxidation of o-xylene to phthalic anhydride, by the contem- poraneous precipitation of Ti and V oxo- hydrates (10-12, 19). The coprecipitation has been carried out by flash-drying, that is. by dropping a solution of titanium and vanadium (IV) ions on a hot ceramic plate at high temperature. The aim of this research was to gain some insights on the nature of active sites in the ammoxidation of toluene to benzonitrile, and to compare the results and the model proposed with those for catalysts prepared by impregnation or grafting techniques. In the case of catalysts prepared by impregnation or grafting methods it has been established that the surface structure