Hydrogen for use in fuel cells is produced in a fuel processor by the catalytic reforming of hydrocarbons. Experimental results from synthetic diesel and JP8 autothermal reforming activity tests performed over a commercial Pt/ceria catalyst was presented in part I of this paper. A reversible-irreversible poisoning phenomenon affected the catalyst's activity. The objective of this paper is to present the results of characterization studies on these catalysts. Temperature programmed reduction (TPR) studies suggest that the oxidation-reduction properties of ceria are affected by poisoning. Temperature programmed desorption (TPD) and XPS analysis confirmed the formation of chemisorbed sulfur entities (irreversible poisoning). Based on these findings, a global deactivation mechanism is proposed. Experiments confirmed that the poisoning is reversible and is enhanced at higher temperatures in presence of a reducing environment. (c) 2005 Elsevier B.V. All rights reserved.