Preparation of Pd-B/TiO₂ amorphous alloy catalysts and their performance on liquid-phase hydrogenation of p-nitrophenol

The Pd-B/TiO₂ amorphous alloy catalyst were prepared by the liquid-phase chemical reduction with KBH₄ aqueous solution. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC) and high reaction transmission electron microscopy (HRTEM). Analysis results show that the active metal clusters Pd-B are homogeneously dispersed on the surface of the TiO₂ particles and the size of most metal clusters is below 10 nm. The as-prepared Pd-B/TiO₂ catalysts exhibit higher catalytic properties (activity, selectivity, and stability) than the corresponding Pd-based catalysts and Ni-based catalysts during the liquid-phase p-nitrophenol (PNP) hydrogenation to p-aminophenol (PAP), which indicates the promoting effect of the alloying B and TiO₂ support. Enriched electron state of Pd active sites and high dispersion of the Pd-B active sites on TiO₂ support are mainly attributed to the improvement of catalytic activity of Pd-B/TiO₂ amorphous alloy catalyst. The effects of different reaction parameters such as support, pH value, Pd loading and the thermal treatment on the catalytic activity of the Pd-B/TiO₂ amorphous alloy catalyst were studied in detail. The maximum preparation condition is achieved by using TiO₂ (P25), pH 12 and 0.5% amount of Pd loading.