Preparation Of Alumina Supported Platinum Nanoclusters And The Catalytic Performance In The Hydrogenation Of Acetophenone

Catalytic hydrogenation of organic compounds containing carbonyl groups is an important field in a variety of chemical processes for the synthesis of fine chemical and Pharmaceuticals. The supported metal catalysts consisting of Ni, Pt, Pd and Rh have been studied for the hydrogenation of acetophenone and its derivatives. However the selectivity to a desired product is not satisfactory since many side products form during the course of hydrogenation, while the hydrogenation of acetophenone can form the optically active secondary alcohol which is the intermediate for the synthesis of some natural products and physiologically active substances. The asymmetric hydrogenation of carbonyl groups has become a rapidly growing field, but the asymmetric hydrogenation of simple achiral ketones is more difficult.We study alumina supported and PVP stabilized platinum nanoclusters under gentle conditions. The effect of reaction parameters, such as solvent, temperature, hydrogen pressure, reduction time on the hydrogenation of acetophenone have been investigated. The catalyst exhibited very high activity in acetophenone hydrogenation and the selectivity of 100% for a-phenylethanol. Under the optimum reaction conditions: 60℃, PH2 =5MPa, the concentration of KOH in isopropanol is over 0.04mol/L, the conversion of acetophenone and TOF can reach 97.0% and 101.6 mol/mol-min, respectively.In the asymmetric hydrogenation, the homogeneous catalysts are bearing chiral ligands, while the heterogeneous catalysts are modified by chiral reagents. However, we found that when the concentration of KOH in isopropanol is over0.04mol/L, the PVP (polyvinylpyrrolidone) stabilized and alumina supported platinum nanoculster catalyst exhibits the enantioselectivity for (S)-1-phenylethanol in hydrogenation of acetophenone in the absence of any chiral modifier. The data of XRD show that Y -Al2O3 has been changed after the treatment with high concentration of KOH solution. The effect of the concentration of KOH, the different base, temperature, hydrogen pressure, reduction time on the asymmetric hydrogenation of acetophenone have been investigated. Under the optimum condition: acetophenone: Pt: KOH =10000:1:78, 60℃, P H2=5Mpa, 3h, the conversion of acetophenone and the ee value of the 1-phenylethanol can reach 100% and 22.2%,respectively.