COMPLETE OXIDATION OVER NOBEL METAL-CATALYSTS .2. BEHAVIORS OF CARBON-MONOXIDE AND OXYGEN OVER A SUPPORTED PALLADIUM CATALYST AND EFFECT OF HALIDE-IONS

Behaviors of carbon monoxide and oxygen adsorbed on supported palladium catalysts were studied using a pulse reaction technique. The effects of sodium halides added to the catalyst were also studied. Adsorbed carbon monoxide reacted rapidly with oxygen in the gas phase in the temperature range from 50°C to 300°C. The amount of oxygen adsorbed was almost constant between 100 and 200°C and it corresponded to the monolayer coverage of palladium surface with atomic oxygen. A remarkable increase in adsorption of oxygen on palladium was observed above 250°C. This increase is probably attributed to the formation of palladium oxide. Although the amount of carbon monoxide adsorbed was not affected by the addition of any other sodium halide than sodium iodide in the catalyst, the reactivity of carbon monoxide decreased in the following order : Pd(216) >Pd-NaCl(100)>Pd-NaBr(31)>Pd-NaI (2). The amount of oxygen adsorbed on those catalysts at 200°C decreased in the following order : Pd(271)>Pd-NaCl(100)>Pd-NaBr(27)>Pd-NaI(4). Relative values in the product of the value of the reactivity of carbon monoxide adsorbed and the amount of oxygen adsorbed on each catalyst agreed well with the relative reactivities of the catalyst. It suggests that the role of halide ion as an inhibitor on CO oxidation is based on the poisoning of catalytic sites which are capable of adsorbing dissociated oxygen and active carbon monoxide. © 1979, The Chemical Society of Japan. All rights reserved.