Effect of pretreatment with hydrogen on the structure and properties of carbon-supported Pd-Ag-nanoalloys for ethylene production by acetylene hydrogenation

Abstract

• Pd-Ag/Sibunit catalysts are promising in C 2 H 4 production by acetylene hydrogenation. • ~ Pd 0.6 Ag 0.4 particles are formed during treatment in H 2 at t = 400–500 °C. • The Pd-Pd distance in the ~ Pd 0.6 Ag 0.4 particles is 2.78–2.80 Å. • The sample treated in H 2 at t = 400 °C have an average particle size of 2.9 nm. • The ethylene selectivity of the Pd-Ag/Sibunit treated with H 2 at 400–500 °C is 77–78%. The formation process of the active component of 0.5%Pd-0.5%Ag catalysts supported on the carbon black/pyrolytic synthetic carbon composite «Sibunit», which were synthesized by joint impregnation, was studied. XRD and EXAFS studies revealed that heating of the Pd-Ag/Sibunit catalyst in hydrogen at 400–500 °C results in the formation of bimetallic solid solution Pd 0.6 Ag 0.4 . The bimetallic particles are characterized by an increased distance between neighboring palladium atoms (2.78–2.80 Å), as compared to metallic palladium and by an increase in the electron density on palladium atoms under the action of silver (according to XPS data). The synthesized samples with supported Pd-Ag nanoparticles make it possible to obtain С 2 Н 4 by ethyne hydrogenation with the selectivity of 77–78%.