Selective hydrogenation of p-chloronitrobenzene over Ni-P-B amorphous catalyst and synergistic promoting effects of B and P

Ni-P-B amorphous alloy catalyst was prepared by chemical reduction of Ni2+ with KBH4 and NaH2PO2 as co-reducing agents. During liquid-phase hydrogenation of p-chloronitrobenzene (p-CNB), Ni-P-B exhibited higher activity and better selectivity to p-chloroaniline (p-CAN) than either Ni-B or Ni-P, obviously owing to the synergistic promoting effects of both the P and the B co-alloying with the metallic Ni. The P promoted hydrogenation activity via enhancing the intrinsic activity (R-H(S)) since the Ni active sites alloying with P became more highly unsaturated, which could adsorb hydrogen more strongly, taking into account that p-CNB hydrogenation was first-order with respect to hydrogen. The B promoted hydrogenation activity via enhancing the dispersion degree of Ni active sites. The higher selectivity to p-CAN could be attributed to the inhibition of hydrodehalogenation since the metallic Ni alloying with P could adsorb the nitro group preferentially against the chlorine atom in p-CNB. Meanwhile, the presence of the alloying B could further enhance the adsorption strength for nitro group via side-bonding and also protected Ni active sites from poisoning by the amine resulting from p-CNB hydrogenation. (c) 2008 Elsevier B.V. All rights reserved.