A partially reduced Pd/gamma-Fe2O3 nanocomposite catalyst (Pd/gamma-Fe2O3-PR) was prepared using PdO and ferric hydroxide colloidal particles as starting materials. This catalyst exhibited excellent catalytic properties for the selective hydrogenation of para-chloronitrobenzene (p-CNB) to para-chloroaniline (p-CAN). The selectivity to p-CAN reached 99.2% at complete conversion of the Substrate and intermediates, and the hydrodechlorination of p-CAN was fully suppressed over Pd/gamma-Fe2O3-PR. The byproduct aniline was derived from the hydrodechlorination of p-CNB and 4,4'-dichloroazobenzene intermediate, a new hydrodechlorination route. X-ray photoelectron spectroscopy characterization indicated ail electron transfer from the partially reduced gamma-Fe2O3 nanoparticles to the Pd particles in Pd/gamma-Fe2O3-PR. IR-CO probe and CO chemisorption experimental results revealed that CO could hardly be chemisorbed on the Pd particles in Pd/gamma-Fe2O3-PR Under our experimental conditions, implying ail electronic interaction between the Pd particles and gamma-Fe2O3-PR nanoparticles, which may be a Cause of the observed superior selectivity to p-CAN over Pd/gamma-Fe2O3-PR. (C) 2009 Elsevier B.V. All rights reserved