A Pd on Ni-B (Pd/Ni-B) bimetallic nanoparticle catalyst was prepared through a replacement reaction of amorphous Ni-B nanoparticles with Pd2+ ions. In the hydrodechlorination of chlombenzene, the Pd/Ni-B bimetallic catalyst exhibited better activity than a Pd catalyst supported on polyvinylpolypyrrolidone, a mixture of Pd and Ni-B nanoparticles, and a Pd on Ni catalyst obtained by the replacement reaction of nanocrystalline Ni with Pd2+ ions. The properties of the Pd/Ni-B catalyst were studied in detail by XRD, TEM, XPS, and H-2 chemisorptions. The characterizations demonstrated that a Pd-Ni-B surface alloy occurred on the Pd/Ni-B catalyst with heating treatment. The resulting surface alloy promoted resistance to chlorine poisoning, adsorption of the reactants (chlorobenzene and hydrogen), and desorption of products, explaining the better catalytic activity and stability of the Pd/Ni-B bimetallic catalyst. (c) 2008 Elsevier Inc. All rights reserved.