Pd supported on ZnII–CrIII mixed oxide as a catalyst for one-step synthesis of methyl isobutyl ketone

Pd metal supported on ZnII–CrIII mixed oxide is an efficient bifunctional catalyst for the one-step synthesis of methyl isobutyl ketone (MIBK) from acetone and H2 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 ZnII and CrIII 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 liquid-phase process, the preferred catalyst formulation is 0.3 wt% Pd on the amorphous Zn–Cr (1:1) oxide (SBET=132 m2/gSBET=132 m2/g) having Lewis acid sites (1.2 mmol/g density) with an enthalpy of NH3 adsorption of −155 kJ/mol−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.