Hydrogenation of p-chloronitrobenzene on Mo, La, Fe, and W-modified NiCoB nanoalloy catalysts

A series of NiCoB catalysts with various modifiers (Mo, La, Fe and W) were prepared by chemical reduction method using NaBH4 as the reducing agent at 303 K. The catalysts were characterized with nitrogen sorption, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The catalytic properties of these catalysts for p-chloronitrobenzene (p-CNB) hydrogenation were studied. All of the modified catalysts possessed amorphous structure. The modifiers acted as the spacer to prevent the NiCoB particles from aggregation, so the particle sizes of the modified catalysts were less than that of the unmodified NiCoB catalyst. XPS results showed that the modifiers existed both in elemental and oxidized states. Different modifiers had various effects on the surface composition of NiCoB catalyst. The elemental state of the modifier formed nano-alloy with Ni and Co and affected their electron densities. The oxidized state of each modifier had its unique Lewis acidity which influenced the products distributions (the relative contents of p-chloronitroaniline, aniline and nitrobenzene) in the p-CNB hydrogenation. These effects were responsible for the different behaviors of Mo-, La-, Fe- and W-modified NiCoB catalysts in the p-CNB hydrogenation.