Hydrogenation of p-chloronitrobenzene on Ni-P-B nanoalloy catalysts

Wei Jye Wang, Jia Huei Shen, Yu Wen Chen

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A series of nanosized NiPB amorphous alloy catalysts with various concentrations was prepared by chemical reduction of nickel acetate with sodium hypophosphite and sodium borohydride in aqueous solution at 298 K under N 2 curtain gas with vigorous stirring. The catalysts were characterized with inductively coupled plasma-atomic emission spectroscopy, nitrogen sorption, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalysts were tested for liquid-phase hydrogenation of p-chloronitrobenzene at 1.2 MPa hydrogen pressure, 353 and 393 K reaction temperature, absolute ethanol as a reaction medium, 500 rpm stirring speed, 0.2 M p-CNB, and 2 mmol of Ni catalyst. The initial Ni/P/B molar ratio of starting materials affected the concentration of boron and phosphorus bound to the nickel metal, resulting in a change of surface area, amorphous structure, and hydrogenation activity of the catalyst. The XPS results revealed that boron combined with nickel metal in the NiPB powder donates electrons to nickel metal and that phosphorus withdraws electrons from nickel metal. The sample NiPB(1:3:3) (the values in parentheses are Ni/P/B ratios in the starting materials) prepared at 298 K under N2 flow with vigorous stirring had the highest surface area of 28.2 m2/g. The BET surface area increased with an increase of phosphorus content in the sample. The XPS results revealed that boron could donate electrons to the nickel metal and that phosphorus could accept electrons from the nickel metal in the NiPB catalysts. By regulating the concentrations of boron and phosphorus, one could regulate the electron denisity of nickel, which in turn could influence the activity of the catalyst. The order of activity per weight of the catalyst was NiPB(1:0.3:3) > NiPB(1:1:3) > NiB(1:3) > NiPB (1:3:3). The activities per surface area and turnover frequencies of the catalysts also decreased in the same order. NiPB catalysts prepared with suitable Ni/P/B ratios in the starting materials had higher activities than the NiB catalyst. Small amounts of phosphorus in the NiB catalyst can increase the surface area and turnover frequency. Both are beneficial for promoting the reaction. However, an overdose of phosphorus became a poison for the Ni catalyst.

Original languageEnglish
Pages (from-to)8860-8865
Number of pages6
JournalIndustrial and Engineering Chemistry Research
Issue number26
StatePublished - 20 Dec 2006


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