Colloidal palladium protected with poly(N-vinyl-2-pyrrolidone) for selective hydrogenation of cyclopentadiene

Colloidal dispersions of palladium were prepared by refluxing solutions of palladium(II) chloride and poly(N-vinyl-2-pyrrolidone) in alcohols. The average diameter of the palladium particles was controlled in the range 18–56 Å by using appropriate species of alcohols and additives. The colloidal palladium exhibited high activity and selectivity as a catalyst for hydrogenation of cyclopentadiene to cyclopentene in methanol at 30°C under 1 atm of hydrogen. Effects of particle size of the colloidal palladium and the polymer used as a protective colloid upon the selectivity of monoene formation and the kinetics of the reaction were studied. The high selectivity of the colloidal palladium for monoene formation is discussed in terms of selective adsorption of the diene on the catalytic site. poly(N-vinyl-2-pyrrolidone) plays an important role in stabilizing the colloidal dispersion as a protective colloid and in increasing the hydrogenation selectivity through the interaction with the palladium particles.