Catalytic and kinetic study of the liquid-phase hydrogenation of acetophenone over Cu/SiO2 catalyst

The liquid-phase hydrogenation of acetophenone (AP)to 1-phenylethanol (PhE) was studied on Cu(6.8%)/ SiO2 catalyst. Catalytic tests were carried out in a batch reactor by varying temperature, total pressure and AP initial concentration between 353-373 K, 5-20 bar, and 0.038-0.251 M, respectively, and using four different solvents: isopropylic alcohol (IPA), cyclohexane, toluene and benzene, The selectivity to PhE was about 100% irrespective of the solvent used, but the initial AP conversion rate followed the order IPA > cyclohexane > toluene > benzene. The differences in catalyst activity when changing the solvent were interpreted by considering the effect of the solvent-rnetal interaction on the relative coverage of adsorbed reactant species. Experimental data were well interpreted by kinetic modeling only when assuming that: (i) the adsorption of AP and H-2 is competitive; (ii) AP adsorption is strong; (iii) copper surface is saturated in AP; (iv) the PhE coverage on the catalyst is negligible. These assumptions were consistent with the fact that the reaction was negative order with respect to AP and first order in H-2. The highly selective AP hydrogenation to PhE was explained by considering that the strong electrostatic repulsion between metallic Cu and the phenyl group tilts the AP molecule thereby favoring its adsorption via the carbonyl group and the formation of the unsaturated alcohol. Also, PhE was not consecutively converted via hydrogenolysis or other acid catalyzed reactions since the support was inert. (c) 2008 Elsevier B.V. All rights reserved.