A partially reduced Pt/gamma-Fe2O3 magnetic nanocomposite catalyst (Pt/gamma-Fe2O3-PR) exhibited excellent catalytic properties in the selective hydrogenation of 2,4-dinitrochlorobenzene and iodonitrobenzenes. The selectivity to 4-chloro-m-phenylenediamine (4-CPDA), meta-iodoaniline (m-IAN), and para-iodoaniline (p-IAN) reached 99.9%, 99.8%, and 99.4%, respectively, at complete conversion of the substrates. The hydrodehalogenation of 4-CPDA and IANs was fully suppressed for the first time over Pt/gamma-Fe2O3-PR. It was found that CO chemisorption on the Pt nanoparticles deposited on the partially reduced gamma-Fe2O3 and Fe3O4 nanoparticles was very weak, implying a weak tendency of the electronic back-donation from the Pt nanoparticles to the pi* antibonding orbitals of the adsorbed molecules. We believe that this is a cause of the superior selectivity to the haloanilines in the hydrogenation reactions of interest over the Pt/gamma-Fe2O3-PR catalyst. (c) 2008 Elsevier Inc. All rights reserved.