Zinc Addition Influence on the Properties of Pd/Sibunit Catalyst in Selective Acetylene Hydrogenation

A series of bimetallic Pd–Zn catalysts supported on the carbon material Sibunit was synthesized for selective hydrogenation of acetylene. XRD, XPS, XAFS and TEM data revealed that the structure and dispersion of bimetallic particles in Pd–Zn/Sibunit samples depend on the molar ratio Pd:Zn. The active component of the Pd–Zn(1:0.25)/Sibunit sample is a substitutional solid solution. In the catalysts with Pd:Zn ≤ 1, the interaction proceeds more completely with the transformation of FCC lattice of the solid solution into the tetragonal structure of intermetallic phase with the composition close to PdZn, whereas an excess of zinc forms the individual ZnO phase. It was found that an increase in the zinc content in Pd–Zn/Sibunit catalysts from Pd:Zn = 1:0 to 1:4 leads to dispergation of the deposited mono- and bimetallic particles from d av = 7.2 to 2.0 nm. The formation of the PdZn intermetallic compound with increasing the zinc content from Pd:Zn = 1:0 to 1:1 is accompanied by a gradual increase in selectivity to ethylene from 42% for Pd/Sibunit to 67% for Pd–Zn(1:1)/Sibunit (the reaction temperature is 95 °C), and also by a decrease in activity. The introduction of a zinc excess (Pd:Zn < 1), on the contrary, decreases the hydrogenation selectivity to ~ 62%, presumably owing to a high dispersion of bimetallic particles.