Reversibility of hydrogen chemisorption on a ceria-supported rhodium catalyst

• Published in: Journal of catalysis 1992-09, Vol.137 (1), p.1-11
• Main Authors: Bernal, S., Calving, J.J., Cifredo, G.A., Rodríguez-Izquierdo, J.M., Perrichon, V., Laachir, A.
• Format: Article
• Language: English
• Subjects: 330700 - Advanced Propulsion Systems- Emission Control; 400201 - Chemical & Physicochemical Properties; ADVANCED PROPULSION SYSTEMS; AMBIENT TEMPERATURE; CATALYSIS; CATALYSTS; Catalysts: preparations and properties; CATALYTIC CONVERTERS; CATALYTIC EFFECTS; CERIUM COMPOUNDS; CERIUM OXIDES; CHALCOGENIDES; CHEMICAL REACTIONS; Chemical Sciences; CHEMISORPTION; Chemistry; ELEMENTS; Exact sciences and technology; General and physical chemistry; HYDROGEN; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; METALS; NONMETALS; OXIDES; OXYGEN COMPOUNDS; PLATINUM METALS; POLLUTION CONTROL EQUIPMENT; RARE EARTH COMPOUNDS; REDUCTION; RHODIUM; SEPARATION PROCESSES; SORPTION; SORPTIVE PROPERTIES; SURFACE PROPERTIES; TEMPERATURE RANGE; TEMPERATURE RANGE 0273-0400 K; TEMPERATURE RANGE 0400-1000 K; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; TRANSITION ELEMENTS; VALENCE
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/0021-9517(92)90134-4

This work reports on some new aspects of the chemistry of hydrogen-ceria systems. It is shown that, at room temperature, in the presence of highly dispersed rhodium, ceria chemisorbs large amounts of hydrogen. As deduced from magnetic measurements carried out in situ, this spillover process leads to the reduction of ceria to an extent of 21% of the total amount of cerium ions present in the sample, which is roughly equivalent to the complete surface reduction of the oxide. It is found that over a highly hydroxylated sample the reduction of ceria induced by the spillover process is partly reversible even at 295 K. If the sample is pumped off at 773 K, the initial oxidation state of ceria is almost completely recovered. Both the rate and extent of hydrogen chemisorption on ceria were found to be sensitive to the specific pretreatment applied to the catalyst. Over bare ceria, hydrogen chemisorption at 298 K was negligible, temperatures as high as 473 K being necessary to activate the process. In contrast to the rhodium-containing catalyst, over pure ceria the desorption of hydrogen leads to a much larger extent to water formation, thus revealing a deeper irreversible reduction of the oxide.