Gas chromatographic determinations of adsorption and kinetic properties of Wilkinson's catalyst chemically bonded to silica



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A gas chromatographic method is used to determine adsorption and kinetic properties of Wilkinson's catalyst [tris-triphenylphosphine chloro rhodium(I)] chemically bonded to silica. Adsorption isotherms were determined for cyclohexane, benzene and cyclohexene. All three compounds exhibited Type I isotherms. The heat of adsorption for all three compounds was approximately 10 kcal per mole which is a borderline value between physical and chemical adsorption. Since the catalyst represented only a small portion (~ 3%) of the surface area, it was assumed the adsorption shown was physical adsorption. However at low coverage the heat of adsorption for benzene and cyclohexene rose much faster than cyclohexane. The heat of adsorption at zero coverage was determined to be 9.65, 13.75, and 14.25 kcal per mole for cyclohexane, benzene and cyclohexene respectively. The support catalyst was found to be an effective hydrogenation catalyst. Using plots of product concentration vs contact time at temperatures of 58, 100 and 120°C, an activation energy of approximately 5 kcal per mole was obtained for the hydrogenation of cyclohexene. The gas chromatographic method proved to be a simple and satisfactory method to obtain both adsorption and kinetic data.