V-Ti-O (rutile) catalysts were prepd. by hydrolysis of VIV-TiIV solns. and calcination at 673 K. The catalysts were characterized by chem. analyses, x-ray diffraction, ESR, and Fourier transform IR spectroscopies, and thermogravimetry. They were tested in the oxidn. of o-xylene to phthalic anhydride and in the ammoxidn. of toluene to benzonitrile. Different vanadia species were identified: (i) a VIV species present in substitutional solid soln. within the rutile lattice, which is stable to both oxidn. and redn., (ii) a VV species, chem. interacting with the rutile surface and constituting the monolayer which is easily reducible to VIV, (iii) surface VO2+ ions, and (iv) highly disordered and poorly cryst. V2O5. The VO2+ surface ions formed during the catalytic tests are the active sites of hydrocarbon activation during both oxidn. and ammoxidn. A comparison with V-Ti-O (anatase) samples suggests that the cryst. structure of TiO2 does not influence the activity of the V-Ti-O catalysts, but possibly the no. of surface VO2+ ions does, and is strongly related to the method of prepn. and to the activation procedure. [on SciFinder(R)]
Surface structure and reactivity of vanadium oxide supported on titanium dioxide: vanadium pentoxide/titania (rutile) catalysts prepared by hydrolysis
CENTI, Gabriele;
1988-01-01
Abstract
V-Ti-O (rutile) catalysts were prepd. by hydrolysis of VIV-TiIV solns. and calcination at 673 K. The catalysts were characterized by chem. analyses, x-ray diffraction, ESR, and Fourier transform IR spectroscopies, and thermogravimetry. They were tested in the oxidn. of o-xylene to phthalic anhydride and in the ammoxidn. of toluene to benzonitrile. Different vanadia species were identified: (i) a VIV species present in substitutional solid soln. within the rutile lattice, which is stable to both oxidn. and redn., (ii) a VV species, chem. interacting with the rutile surface and constituting the monolayer which is easily reducible to VIV, (iii) surface VO2+ ions, and (iv) highly disordered and poorly cryst. V2O5. The VO2+ surface ions formed during the catalytic tests are the active sites of hydrocarbon activation during both oxidn. and ammoxidn. A comparison with V-Ti-O (anatase) samples suggests that the cryst. structure of TiO2 does not influence the activity of the V-Ti-O catalysts, but possibly the no. of surface VO2+ ions does, and is strongly related to the method of prepn. and to the activation procedure. [on SciFinder(R)]Pubblicazioni consigliate
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