Catalytic Properties of Silica-Supported Monometallic and Palladium-Containing Bimetallic Catalysts in the Selective Hydrogenation of Acetylene

The kinetics of acetylene hydrogenation in the presence of supported catalysts containing transition metals (Fe, Co, Ni, Cu, Ag) and palladium has been studied. The catalysts have been synthesized by depositing palladium hexafluoroacetylacetonate from solution in a supercritical carbon dioxide medium onto a silicon-based support and subsequently subjecting the samples to heat treatment and reduction in a hydrogen stream at 500°C. The support has been preimpregnated with solutions of transition metal nitrates. The catalytic properties of bimetallic systems and monometallic systems containing the same components have been compared. It has been shown that palladium and the transition metal used affect the catalytic properties of each other. It has been found that the kinetics of formation of acetylene hydrogenation products (ethylene, methane) changes with an increase in temperature, and the changes are different in the presence of bimetallic catalysts containing Cu and Ag and the catalysts containing Fe, Co, and Ni. In the latter case, a minimum acetylene conversion rate is observed at a temperature of about 100°C, and the ethylene selectivity abruptly increases with a further increase in temperature. The observed relationships are interpreted in terms of the existence of various adsorbed species of reactants (hydrogen and unsaturated hydrocarbons), which differ in adsorption strength and reactivity, on the surface of complex multicomponent catalyst systems.