Hydrogen can be oxidized by recombination with atmospheric oxygen over a catalyst, such as Pt/Al2O3, at a temperature much lower than that required for thermal oxidation generating heat and water vapor. However, there is potential for the passive autocatalytic recombiner to generate volatile forms of iodine, namely molecular iodine, by catalytic dissociation of various iodine compounds too. The dissociated atomic iodine on the surfaces of the Pt/Al2O3 catalyst is mainly measured at ambient temperature as I 3d peaks in X-ray photoelectron spectroscopy. It seems that dissociation of iodine compounds on the catalyst surfaces and then production of gaseous I-2 by recombination of the dissociated iodine occur prior to the oxidation or reduction of iodine compounds under air or H-2. Atomic iodine is predominant on the surfaces of the catalyst in H-2 and air conditions, and it is stable even with exposure to H2O. Adsorbed iodine prevents the adsorption of H-2 or O-2 for recombination to H2O, but it can be desorbed completely at a high temperature.