Substituent Effects in Heterogeneous Catalysis. IV. Adsorption Estimations during Competitive Hydrogenation of Cyclohexanone and Its 2-Alkyl Derivatives

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Abstract
Cyclohexanone (1) and its 2-alkyl derivatives (2-methyl-, 2-ethyl-, and 2-propylcyclohexanone (2m, 2e, and 2p)) were hydrogenated both individually and competitively in pairs (1+2) in cyclohexane using Ru/Al2O3, Rh/Al2O3, and Pt/Al2O3 as catalysts. For all the catalysts, the reaction rates in competitive reaction decreased in the sequence, l>>2m>2e>2p, while those in individual reaction were in the relation, 1>2m≈2e≈2p. By the analysis of these kinetic data, the relative values of adsorption equilibrium constants have been estimated for 2m, 2e, and 2p. These experimental values are in good agreement with the theoretical ones which have been derived on the basis of statistical mechanics using an adsorption model characterized by immobile adsorption of the substrate ketones.