Abstract
Pd metal supported on Zn-II-Cr-III mixed oxide is an efficient bifunctional catalyst for the one-step synthesis of methyl isobutyl ketone (MIBK) from acetone and H-2 in the gas and liquid phases. The reaction involves acid-catalysed condensation of acetone to mesityl oxide, followed by its hydrogenation to MIBK. Diisobutyl ketone (DIBK) is a useful byproduct in this process. Zn-Cr oxides (Zn/Cr = 20: 1-1:30) are prepared by coprecipitation of Zn-II and Cr-III hydroxides. The texture and acid properties (i.e., the nature, density, and strength of acid sites) of Zn-Cr oxides, as well as the Pd dispersion in the catalysts, are thoroughly characterised. For both the continuous gas-phase process and the batch liquidphase process, the preferred catalyst formulation is 0.3 wt% Pd on the amorphous Zn-(:r (1:1) oxide (S-BET = 132 m(2)/g) having Lewis acid sites (1.2 mmol/g density) with an enthalpy of NH3 adsorption of -155 kJ/mol. Both processes produce MIBK with a selectivity of 70-78% and 90% MIBK + DIBK total selectivity at 38-40% acetone conversion. Evidence is provided that hydrogenation of mesityl oxide to MIBK is the rate-limiting step in the gas-phase process. (c) 2008 Elsevier Inc. All rights reserved.