Key words: palladium, copper, hexafluoroacetylacetone, acetylene hydrogenation, bimetallic catalysts, supercritical CO2
The catalytic properties of palladium and palladium-copper composite deposited on γ-Al2O3 from a supercritical carbon dioxide (SC-CO2) medium have been studied in the reaction of selective hydrogenation of acetylene into ethylene. Palladium and copper complexes with hexafluoroacetylacetone were used as precursors of the active component. Acetylene hydrogenation was studied in a reaction mixture (in vol. %): 1.0 C2H2, 93.7 C2H4, 5.3 H2, simulating a mixture used in the industrial process of acetylene removal from ethylene obtained by pyrolysis of various hydrocarbons. It is shown that the Pd/Al2O3 sample obtained by deposition of palladium from a SC-CO2 medium with subsequent reduction in hydrogen has an «egg-shell» type of distribution of the active component — it is concentrated in a thin (about 0.07 ± 0.01 mm) outer layer of a spherical carrier granule with a diameter of ∼1 mm. In the case of the PdCu/Al2O3 composite, an uneven distribution of the deposited component is also observed, but to a considerable depth along the diameter of the pellet. The Pd/Al2O3 sample showed high activity and moderate selectivity in the hydrogenation of acetylene to ethylene. After crushing and loading the fraction of 0.2—0.4 mm into the reactor, the same sample shows higher selectivity while maintaining high activity. The PdCu/Al2O3 sample showed substantially lower activity and selectivity in the target process. The results obtained demonstrate a high sensitivity of the catalytic properties to the method of deposited palladium-containing systems synthesis and a significant effect of the transfer processes in the grain and in the catalyst layer on the parameters of the acetylene hydrogenation in an acetylene-ethylene mixture.