A study on structural features of bimetallic Pd-M/C (M: Zn, Ga, Ag) catalysts for liquid-phase selective hydrogenation of acetylene

The present work is devoted to the study of doping effects of zinc, gallium and silver on the structure of active sites and catalytic properties of carbon-supported 0.5 wt% Pd catalysts in the liquid-phase selective hydrogenation of acetylene to ethylene. Carbonaceous graphite-like material Sibunit was used as a support. The reaction was performed in a medium of N-methyl-2-pyrrolidone at 55 °C. It was shown that the bimetallic Pd-Zn/C, Pd-Ga/C and Pd-Ag/C catalysts exhibit better activity and selectivity towards target product if compare with the monometallic Pd/C catalyst. The ethylene yield increases in a row as follows: Pd/C (19%) < Pd-Ag/C (34%) < Pd-Ga/C (42%) < Pd-Zn/C (53%). Using X-ray absorption spectroscopy and transmission electron microscopy it was found that an improvement of the selectivity is stipulated by the formation of bimetallic PdZn, Pd_xGa_y and PdAg nanophases. In the case of Pd-Zn/C and Pd-Ag/C systems, an increased distance between neighboring Pd atoms (2.82–2.89 Å) in relation with monometallic Pd/C, where this distance is 2.72 Å, was observed. The higher activity of modified bimetallic systems is connected with increased number of active sites due to enhanced dispersity of supported palladium doped with second metal.