Ru/ZrO{sub 2} catalysts. 1. O{sub 2}, CO, and NO adsorption and reactivity
The Ru/ZrO{sub 2} catalyst's surface properties have been studied by quantitative chemisorption experiments on carbon monoxide and oxygen at different temperatures, by FTIR studies of oxygen, carbon monoxide, and nitric oxide adsorptions, and by FTIR studies of the CO-NO reaction. On the oxidized sample at least three FTIR absorptions are evident at 1008, 980, and 950--940 cm{sup {minus}1}. All the observed bands can be assigned to Ru-O surface species, differing in the oxidation state of ruthenium directly bonded to oxygen, the degree of metal-oxygen {pi} bonding, and the coordination of the Ru atoms with the support. The larger heterogeneity of the bands observed on Ru/ZrO{sub 2} catalyst, with respect to that previously detected on Ru/ZnO, can be taken as an indication that a significant role is played by the coordination properties and the surface features of the support. The strong increase of the band at 1008 cm{sup {minus}1} at temperatures higher than 573 K can be ascribed to the increase of the surface concentration of Ru-O surface species bonded to an Ru atom with an oxidation state higher than 4. The CO adsorption on the oxidized sample evidences the full reactivity of Ru-O species toward CO between room temperature (RT) and 473. CO and NO chemisorptions on reduced samples show that the two molecules are both molecularly and dissociatively adsorbed on the catalysts. The NO admission on preadsorbed CO produces immediately a significant modification of the adsorbed CO spectrum, i.e., a reduction of the intensity of the band assigned to CO adsorbed on Ru{degree} sites and the appearance of additional bands that can be assigned to N{sub 2}O, NO, and carbonate species. These features indicate that NO is immediately dissociated on Ru already in the presence of preadsorbed CO and gives rise to N{sub 2}O and CO{sub 2} already at RT. Upon heating at 373 K the N{sub 2}O absorptions and the bands ascribed to CO adsorbed species are depleted and that of CO{sub 2} increases, indicating that the reaction 2CO + 2NO {yields} N{sub 2} + 2CO{sub 2} may prevail on the catalyst.
- Research Organization:
- Univ. degli Studi di Torino (IT)
- OSTI ID:
- 20076100
- Journal Information:
- Journal of Catalysis, Vol. 192, Issue 1; Other Information: PBD: 15 May 2000; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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