Catalytic Properties of Pd and a Pd–Cu Composite, Deposited on Alumina from Supercritical CO2, in the Reaction of Selective Hydrogenation of Acetylene

The catalytic properties of palladium and a palladium–copper composite, both deposited on γ-Al2O3 from a supercritical carbon dioxide (SC CO2) medium, were studied in the selective hydrogenation of acetylene to ethylene. Complexes of palladium and copper with hexafluoroacetylacetone were used as precursors of the active component. The acetylene hydrogenation process was studied in a reaction mixture comprising 1.0 vol % C2H2, 93.7 vol % C2H4, and 5.3 vol % H2, which imitated the mixture used in the industrial process of acetylene removal from ethylene produced by the pyrolysis of hydrocarbon feedstock. It was shown that the Pd/Al2O3 sample obtained by depositing palladium from a SC CO2 medium with subsequent reduction in hydrogen had an “egg-shell” type of distribution of the active component: it was concentrated in a thin (about 0.07 ± 0.01 mm) outer layer of a spherical support granule with a diameter of 1 mm. In the case of the PdCu/Al2O3 composite, the active component was deposited to a significant depth along the granule diameter and had an uneven distribution. The Pd/Al2O3 sample exhibited high activity and moderate selectivity in acetylene hydrogenation to ethylene. The same sample after crushing and loading into the reactor (fraction 0.2–0.4 mm) demonstrated higher selectivity while maintaining high activity. The PdCu/Al2O3 sample exhibited lower activity and selectivity in the target process. The catalyst properties were shown to depend on the method of obtaining the supported palladium-containing systems, and the transfer processes in the grain and catalyst layer were found to have a significant influence on the performance of the acetylene hydrogenation in an acetylene–ethylene mixture.