Preparation of gold-containing binary metal clusters by co-deposition-precipitation method and for hydrogenation of chloronitrobenzene

Abstract

Nano-gold catalyst has been reported to have high activity and selectivity for liquid phase hydrogenation reaction. In this study, gold-containing bimetals were loaded on TiO2. For bimetallic catalysts, gold and different metals were prepared by the deposition-precipitation method, and then used NaBH4 to reduce metal cations. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalytic properties of these catalysts were tested by hydrogenation of p-chloronitrobenzene (p-CNB) in a batch reactor at 1.1 MPa H2 pressure, 373 K and 500 rpm. Cu, Ag, Ru, and Pd formed nano-alloy with Au. In addition, Cu–Au, Ag–Au, and Ru–Au alloy had Cu-, Ag-, and Ru-enriched surface, respectively. Instead, Pd–Au alloy had Pd-enriched surface. There are two kinds of alloy effects: (1) geometric effects, i.e., the surface-enriched metal would change the distance of Au–Au atoms that is required for facilitating the hydrogenation of chloronitrobenzene; and (2) electronic effects, which involve charge transfer between the metals. The activity decreased in the following order: PdAu/TiO2 > Au/TiO2 > NiAu/TiO2 > AgAu/TiO2 > RuAu/TiO2 > CuAu/TiO2. Comparing with other metals, adding Pd in Au showed a higher activity. Adding palladium could reduce gold-valence state, and increased active sites for reaction.