Selective hydrogenation of acetylene in an ethylene-rich stream over silica supported Ag-Ni bimetallic catalysts

Abstract

Semi-hydrogenation of acetylene in an ethylene-rich stream is an industrially important process. Recent work on the purification of ethylene mainly focuses on the modification of Pd catalysts; little attention has been paid to the development of alternative catalysts with low-cost metals. Herein, a series of Ag-Ni/SiO2 bimetallic catalysts, with varied Ni/Ag atomic ratios, were prepared by wetness co-impregnation method. Their activity for the selective hydrogenation of acetylene in an ethylene-rich stream was evaluated, which showed that the introduction of Ag decreased the formation of both ethane and methane, thus increased the ethylene selectivity. The ethylene selectivity over the AgNi0.25/SiO2 catalyst was increased by >600% when compared with the corresponding monometallic Ni0.25/SiO2 as well as the simple physical mixture of the monometallic Ag/SiO2 and Ni0.25/SiO2 catalysts. As was verified by a combination of the X-ray diffraction, high angular annular dark field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy under scanning transmission electron microscopy results, decreased Ni content induced the sintering of the bimetallic nanoparticles while with uniform dispersion. Temperature-programmed reduction results demonstrated that, compared with the corresponding monometallic catalysts, both the reduction of AgOx and NiOx were promoted in the Ag-Ni/SiO2 bimetallic catalysts. In-situ Fourier-transform infrared spectroscopy results also illustrated obvious interaction between Ag and Ni. The contact between Ag and Ni may account for the enhanced ethylene selectivity.