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–metal 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 H2 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 H2. 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.
Graphical abstractThe liquid-phase hydrogenation of acetophenone into 1-phenylethanol over Cu/SiO2 catalyst was studied. Results obtained in different conditions were interpreted by kinetic modeling employing heterogeneous Langmuir–Hinshelwood–Hougen–Watson (LHHW)-type and non-stationary models. A reaction mechanism (see pictogram), based on the interactions acetophenone-Cu0 explains: (1) the high selectivity to 1-phenylethanol; (2) the negative order respect to acetophenone and first order in H2; (3) solvent influence.Figure optionsDownload full-size imageDownload as PowerPoint slide
Journal: Applied Catalysis A: General - Volume 349, Issues 1–2, 31 October 2008, Pages 100–109