Controlled Hydrogenation of Acetophenone Over Pt/CeO₂-MO x (M = Si, Ti, Al, and Zr) Catalysts

Vapour phase selective hydrogenation of acetophenone has been performed over a series of Pt/CeO₂-MO x (MO x = SiO₂, Al₂O₃, TiO₂, and ZrO₂) catalysts. The controlled hydrogenation was carried out in the 453-533 K temperature range at normal atmospheric pressure. The ceria-based mixed oxides were prepared through a co-precipitation or deposition-precipitation route. Platinum was deposited by a wet impregnation method. The obtained catalysts were calcined at 773 K and characterized by means of X-ray diffraction, Raman spectroscopy, BET surface area, temperature programmed reduction, temperature programmed desorption, thermogravimetry, and scanning electron microscopy. XRD analyses suggest that CeO₂-SiO₂ and CeO₂-Al₂O₃ primarily consist of CeO₂ nanoparticles dispersed over the amorphous silica or alumina surface. In the case of CeO₂-TiO₂, presence of segregated nanocrystalline CeO₂ and TiO₂-anatase phase were noted. Formation of cubic Ce₀.₇₅Zr₀.₂₅O₂ solid solution was observed in the case of CeO₂-ZrO₂. No peaks pertaining to platinum could be detected from XRD profiles. Formation of zirconia rich tetragonal phase (Ce₀.₄Zr₀.₆O₂) was observed in the case of Pt/CeO₂-ZrO₂ sample. Raman measurements revealed the fluorite structure of ceria and presence of oxygen vacancies in all samples. TPR results suggest that the presence of Pt facilitates the reduction of ceria. The catalytic performance of Pt-based catalysts was found to depend strongly on the nature of the support oxide employed. Among various catalysts investigated, the Pt/CeO₂-SiO₂ catalyst exhibited better product yields.