Liquid-Phase Selective Hydrogenation of p-Chloronitrobenzene on Ni-P-B Nanocatalysts

A series of Ni-P-B catalysts were prepared by liquid-phase reduction. Nickel acetate and sodium hypophosphite were mixed in ethanolic solution. The solution of sodium borohydride in excess amount was then added dropwise into the aforementioned mixture to ensure full reduction of the Ni cations. The Ni:P:B ratios in the mother solution was fixed at 1:3:3. These catalysts were characterized by powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, and X-ray photoelectron spectroscopy. The effects of preparation conditions such as temperature, stirring speed, and sheltering gas on the particle size, surface compositions, oxidation states of surface atoms, and catalytic activities of the Ni-P-B catalysts were studied. The catalysts were tested by liquid-phase hydrogenation of p-chloronitrobenzene at 393 K and 1.2 MPa hydrogen pressure in a batch reactor. Raney nickel catalyst was included for comparison. The preparation condition had significant influence on the particle size and surface compositions of the catalyst. All of the catalysts prepared in this study had nanosized particles. Boron, combined with nickel metal in the Ni-P-B powder, donated electrons to the nickel metal and phosphorus accepted electrons from the nickel metal. Under specific preparation conditions, one was able to prepare a catalyst that was more active than the Raney nickel catalyst. The catalyst with the lower concentration of nickel on the surface seemed to have higher activity. The reaction conditions also have a pronounced effect on the catalytic activity. Using methanol as the reaction medium significantly increased the conversion of p-chloronitrobenzene, compared to that using ethanol as the reaction medium. The selectivity of p-chloroaniline was >99% on the Ni-P-B Catalyst. In contrast, the Raney nickel catalyst had a lower selectivity to p-chloroaniline.