Partial oxidation of toluene to benzaldehyde ovser vanadium antimonate catalysts doped with itanium. The influence of the antimony content over the deactivation proces

S.A. LARRONDO.; M. MATRANGA; N.E. AMADEO

STUDIES IN SURFACE SCIENCE AND CATALYSIS

ELSEVIER SCIENCE BV

Lugar: Amsterdam, The Netherlands; Año: 2001 vol. 139 p. 383 - 389

0039-3037

In this work the effect of Sb or V substitution by Titanium over the redox properties and the catalyst behaviour of solids with nominal composition VSbO4, Vo.sSbTio.204, VSbo.sTio.204 is studied. In addition, the effect of the Sb content on the deactivation of the catalysts is analysed. The solids have been prepared by solid-state reaction in air, of pure V(V), Sb(III) y Ti(IV)oxides. Fresh samples have been characterised by Temperature programmed reduction (TPR)and catalytic tests. For vo.sSbTio.204 catalysts, elemental C-H-N-O analysis was performed on flesh and used samples. The TPR profiles of the samples were noticeably different. The larger separation between the temperatures of the two centres of reduction would be related to an efficient electron transfer, necessary to have a good performance as a catalyst for partial oxidation. Therefore, for sample VSbo.sTio.204 only oxidation products are obtained during the toluene oxidation. For sample VSbO4, both oxidation products and residue are observed, without deactivation of the catalyst during a typical run of 12 hours. In addition, sample V0.sSbTi0.204, presenting only one peak with a shoulder in the TPR profile, has shown an enhancement in the residue formation and a deactivation process, as a consequence of carbonaceous compounds adsorbed over the catalyst surface. The higher Sb content of this sample appears to ease the adsorption of the heavy compounds over the active sites of the catalysts, probably due to a strong Pi-bonding of the aromatic ring with the active site. Kinetic experiments performed under stable-conditions and under unsteady-state regime have shown that both toluene and benzaldehyde are precursors in the residue production.