Propene hydrogenation on low-temperature reduced Pt/TiO2. Effects of TiO2 phases and H2 treatment on specific catalytic activity

TiO₂ gel obtained by hydrolysis of titanium tetra-n-butoxide was heated at various temperatures, providing poorly crystallized TiO₂, disordered anatase and a well crystallized anatase—rutile mixture. Platinum dispersion was obtained on these TiO₂ supports by the reduction of platinum—allyl species with H₂ at 278 K. These catalysts and a Pt/SiO₂-gel sample were used for propene hydrogenation at various temperatures and H₂/propene molecular ratios. Fresh and run catalysts were subjected to X-ray diffraction analysis for the study of extant phases and determination of average size of platinum particles. In all cases, results obtained for catalysts as prepared or after H₂ treatment at 493 K indicated that the ordinary hydrogenation mechanism was maintained but that important changes of specific catalytic activity were observed, depending on H₂ treatment and nature of the support. TiO₂ morphology was assumed to be responsible for the specific activity decrease in Pt on the rutile—anatase mixture and for the opposite effect found for platinum on anatase.