Study of selective hydrogenation of acetophenone on Pt/SiO2

The competitive hydrogenation between phenyl and carbonyl groups of acetophenone (AP) and the reaction pathway were investigated by gas phase hydrogenation, infrared (IR) spectra and TPD experiments on reduced and oxidized Pt/SiO2. The reduced Pt/SiO2 offers good catalytic activity for carbonyl and phenyl hydrogenation to produce I-phenylethanol (PE) and cyclohexylethanol at room temperature, but the formation rate and reaction selectivity of I-phenylethanol are gradually boosted with decreasing formation rate of cyclohexylethanol. The catalytic selectivity of acetophenone hydrogenation is proposed to be dominated by some fragments from acetophenone dissociation and by I-phenylethanol product strongly adsorbed on the surface. The fragments formed from acetophenone dissociation during reaction will inhibit the bonding between phenyl group and Pt surface leading to a decrease in the rate of cyclohexylethanol formation. On the other hand, the large amount of I-phenylethanol product with strong adsorption ability remaining on the surface without desorption also leads to suppressing hydrogenation of phenyl group. Oxidized Pt catalyst can provide lower catalytic activity than reduced Pt. but reaction selectivity shifts to formation of I-phenylethanol and ethylbenzene (EB). The hydrogenation of aromatic ring was almost suppressed by oxygen. The oxidized Pt surface induces the activation of C=O; this is more advantageous for C=O hydrogenation than for C=C hydrogenation. Formation of both main products is proposed to follow the route: acetophenone --> 1-phenylethanol --> cyclohexylethanol. (C) 2003 Elsevier Science B.V. All rights reserved.