Liquid-phase hydrogenation of acetophenone over silica-supported Ni, Co and Cu catalysts: Influence of metal and solvent

ANDRÉS F. TRASARTI; NICOLÁS M. BERTERO; CARLOS R. APESTEGUÍA; ALBERTO J. MARCHI

APPLIED CATALYSIS A-GENERAL

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2014 vol. 475 p. 282 - 291

0926-860X

In this work, we studied the influence of solvent and metal nature on the liquid-phase hydrogenation of acetophenone (AP) over Ni/SiO2, Co/SiO2 and Cu/SiO2. Catalysts were prepared by wetness impregnation method with metal loads of about 7-8 wt. %. Catalytic tests were performed in a batch reactor, at 363 K and 10 bar (H2), using 2-propanol (IPA), cyclohexane (CHX), toluene (TOL) and benzene (BEN) as solvents. Considering the three catalysts, the general pattern for the initial hydrogenation rate was: Ni/SiO2 > Co/SiO2 > Cu/SiO2, whereas the trend for selectivity to 1-phenylethanol (PHE) was just de opposite. AP can interact with nickel metal surface through both ‒C=O group and aromatic ring and thus the aromatic alcohol and saturated compounds were obtained. Instead, cobalt and copper metal surfaces interact preferentially with the ‒C=O group leading to selective hydrogenation of AP into PHE. In addition, an important interaction between the ‒C‒OH group of PHE and Co/SiO2 surface takes place, leading to rapid alcohol hydrogenolysis into ethylbenzene. The general activity pattern found with the four solvents was: IPA > CHX ³ TOL ³ BEN. The magnitude of solvent influence on the catalytic performance strongly depended on the metal nature. The most significant solvent effect took place with Ni/SiO2, whereas the less noticeable influence was observed in the case of Cu/SiO2. From pseudo-homogenous kinetic modeling and temperature-programmed desorption, the following noteworthy observations arose: 1) IPA has a positive contribution by hydrogen transfer and/or AP activation by polarization; 2) the magnitude of the positive IPA influence on AP hydrogenation rate follows the trend: Ni/SiO2 > Co/SiO2 > Cu/SiO2; 3) CHX has a neutral contribution because of its weak adsorption on the metal phase and low interaction with reactant and products; 4) the effect of TOL and BEN is clearly negative for Ni/SiO2 due to active site blockage by strong adsorption of solvent on the metallic surface; 5) the effect due to strong adsorption of TOL and BEN is much less noticeable on Co/SiO2 and Cu/SiO2; 6) as a consequence, the pattern for AP hydrogenation rates in BEN and TOL is Cu/SiO2 > Co/SiO2 > Ni/SiO2. Selectivity to PHE was less influenced by solvent nature. However, in the case of Ni/SiO2 and Co/SiO2, PHE yields and selectivities increased with the solvent-metal interactions, mainly due to inhibition of the alcohol hydrogenolysis. Cu/SiO2 was always 100% selective to PHE in all of the solvents. These results are clearly indicating that solvent effect on catalytic performance strongly depends on the metal nature.