INFLUENCE OF THE PREPARATION MODE ON METAL-SUPPORT INTERACTIONS IN PT/TIO2 CATALYSTS

Pt/TiO2 catalysts in which the support was either a pure TiO2 or a TiO2 containing small amounts of K2O, P2O5, and Nb2O5 were prepared either by the microemulsion method, in which the metal particles are formed before depositing on the support, or by the incipient wetness method, where the particles are formed directly on the support following adsorption of the metal precursor and reduction. The catalysts, independently of the preparation mode, were additionally reduced at low and high temperature, 200 and 390°C, respectively. Reduction at 390°C implies that strong metal-support interactions (SMSI) begin to be noticeable. Isomerisation and cracking reactions of 2-methylpentane and hydrogenolysis reactions of methylcyclopentane have been studied over these catalysts. 13C-labelling experiments allowed the determination of the relative contributions of cyclic and of bond-shift mechanisms towards the isomerisation reactions. In the absence of support additives, whatever the reduction temperature, catalysts prepared from microemulsions were more active and selective in the isomerisation reactions than those prepared by the incipient wetness method. The doped catalysts, reduced at high temperature, presented additive-platinum interactions, as observed by XPS analyses. In addition, they were less active and behaved like catalysts in the SMSI state. The metal-support interactions were not observed for the microemulsion-prepared catalysts and the effect of additives was less important for them than for those prepared by the incipient wetness method. © 1993 by Academic Press, Inc.