HYDROGENATION OF CROTONALDEHYDE ON PT TIO2 CATALYSTS - INFLUENCE OF THE PHASE-COMPOSITION OF TITANIA ON ACTIVITY AND INTRAMOLECULAR SELECTIVITY/

The hydrogenation of crotonaldehyde in the gas phase at 413 K and 2 MP a over Pt/TiO2 catalysts reduced at 473 K (LTR) or 773 K (HTR) was inv estigated in order to examine if the catalytic properties could be alt ered by the phase composition of TiO2. The catalysts prepared by ion-e xchange or sol-gel technique were characterized by physisorption, chem isorption, EPR, TEM and XRD measurements. It was found that the phase composition of the support has a strong influence on the activity whic h decreased with increasing anatase fraction (xi(ANA)) Furthermore, th e specific activities on a per g Pt basis were higher in the case of t he HTR catalysts than those of their LTR counterparts, The selectivity to crotyl alcohol ranged from 30 to 40% at crotonaldehyde conversions up to 50% independent of the catalyst support used, However, at highe r conversions up to 80% the highest selectivity of 53% to crotyl alcoh ol was obtained over a Pt catalyst with xi(ANA) = 65%. Both the observ ed behavior in selectivity which corresponds to the TOF data for produ ct formation on individual Pt catalysts as well as the catalytic prope rties of physical mixtures of the catalysts suggest that the differenc es in selectivities are connected with different degrees of competitiv e adsorption and readsorption of the products which depend on the TiO2 phase composition, In addition, the sol-gel derived Pt catalyst gave a selectivity of 51% for crotyl alcohol which shows that the SMSI effe ct could be more pronounced by the close contact of Pt with the anatas e matrix. (C) 1997 Elsevier Science B.V.