Hydrogen Redistribution of Acetone on ZnO Catalysts

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Abstract
The hydrogen redistribution reaction between d0-acetone and d6-acetone was carried out at −10–60 °C over ZnO catalysts subjected to various modes of pretreatment. The activity of ZnO was several times larger than that of Zn metal, being hardly affected by the conditions of pretreatment below 350 °C and illumination with a mercury lamp. The rate of hydrogen redistribution was proportional to the amount of chemisorbed acetone which obeys the Langmuir adsorption isotherm. The activation heat of redistribution and the heat of acetone chemisorption were estimated to be 14±2 and 10±1 kcal/mol, respectively. The time course of the relative amounts of dn-acetones, independent of the catalyst or its activity, was reproducible by a calculation based on the stepwise exchange model for the hydrogen exchange of acetone. About half of the chemisorbed acetone was found to be active for the redistribution or exchange of hydrogen. From the results and IR spectrometric study of acetone adsorbed on ZnO, the hydrogen redistribution of acetone was concluded to proceed via a chemisorbed acetone with an enol type configuration on a pair of sites, Zn2+–O2−, of ZnO surface.

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