The effect of palladium particle size on the kinetics of hydrogenation of acetylene-ethylene mixtures over Pd/SiO2 catalysts

The kinetics of hydrogenation of acetylene-ethylene mixtures over the Pd/SiO2 catalysts has been studied over a wide range of Pd particle sizes (d = 42-262 Angstrom). The size d was found to have no influence on the mechanism of the reaction and on the adsorption strengths of acetylene and ethylene molecules (the electronic effect was not observed to occur). The observed antipathetic structure sensitivity originates from two geometric effects: (i) statistics of faces in Pd crystallites, (ii) surface-site statistics in the crystallite faces carrying carbonaceous deposits. A general kinetic model of hydrogenation of acetylene-ethylene mixtures on Pd/SiO2 catalysts has been developed. The model describes the relation of turnover frequency to size d at various partial pressures of the reactants.