Characterization and catalytic properties of Ni–Sn intermetallic compounds in acetylene hydrogenation

Abstract

The surface and catalytic properties of Ni–Sn intermetallic compounds (IMCs), Ni₃Sn, Ni₃Sn₂ and Ni₃Sn₂ and Ni₃Sn₄, were studied by X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR) and catalytic reactions, such as the hydrogenation of acetylene, H₂–D₂ equilibration and H–D exchange between C₂D₄ and H₂. The XPS results clarified that nickel and tin atoms near the surface were reduced into Ni⁰ and Sn⁰ by the hydrogen treatment at 873 K. The surface of each Ni–Sn IMC had specific nickel compositions and Ni3d valence band spectra. The TPR results showed that each Ni–Sn IMC had a different peak temperature from pure nickel and each other. These results revealed that Ni–Sn IMCs had the genuine surface of each IMC phase. Ni₃Sn and Ni₃Sn₂ catalysts showed the high selectivity for the partial hydrogenation of acetylene into ethylene and did not catalyze the ethane formation. The high selectivity of Ni–Sn IMCs resulted from the very low activity of Ni₃Sn and inactivity of Ni₃Sn₂ for the ethylene hydrogenation. The H–D exchange between deuterized ethylene and hydrogen, however, proceeded even over Ni₃Sn₂. The cause of the low activity of Ni–Sn IMC for the ethylene hydrogenation was discussed in view of the reaction mechanism.