Hydrogenation of p-chloronitrobenzene over NiPtB nanoalloy catalysts

NiPtB nanoalloy catalysts with various Ni contents were prepared by chemical reduction method at room temperature using NaBH4 as reducing agent. Pt and Ni cations were completely reduced to metals, and small amount of boron was also reduced and form alloy with metals. NiPtB formed nanosized alloy structure and X-ray diffraction patterns showed its amorphous nature. The particle size distribution and the surface composition were affected by Ni/Pt ratio in the starting materials and the temperature of heat treatment. The catalytic activity of the nanoalloys was tested for hydrogenation of p-chloronitrobenzene (p-CNB). The activity and selectivity to p-chloroaniline (p-CAN) were affected by the content of Ni in the catalyst. For NiPt0.01B catalyst, the occurrence of surface segregation of B was driven by the strain energy at high reaction temperature. For NiPt0.03B and NiPt0.01B catalysts, Pt segregated to the surface by H2 affinity. Ni/Pt ratio decreased as the reaction temperature increased. The activity was essentially affected by the addition of Ni on Pt in the NiPtB catalyst, as expected, because Pt is more active than Ni for this reaction. The hydrogenation of p-CNB was very selective and yielded p-CAN exclusively on NiPtB catalysts than that on Pt catalyst.