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 MPa over Pt/TiO2 catalysts reduced at 473 K (LTR) or 773 K (HTR) was investigated in order to examine if the catalytic properties could be altered by the phase composition of TiO2. The catalysts prepared by ion-exchange or sol-gel technique were characterized by physisorption, chemisorption, EPR, TEM and XRD measurements. It was found that the phase composition of the support has a strong influence on the activity which decreased with increasing anatase fraction (xi(ANA)) Furthermore, the specific activities on a per g Pt basis were higher in the case of the 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 higher conversions up to 80% the highest selectivity of 53% to crotyl alcohol was obtained over a Pt catalyst with xi(ANA) = 65%. Both the observed behavior in selectivity which corresponds to the TOF data for product formation on individual Pt catalysts as well as the catalytic properties of physical mixtures of the catalysts suggest that the differences in selectivities are connected with different degrees of competitive 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 effect could be more pronounced by the close contact of Pt with the anatase matrix. (C) 1997 Elsevier Science B.V.