CO desorption and oxidation on CeO₂-supported Rh: Evidence for two types of Rh sites

Journal Article · Sun Jan 01 04:00:00 EST 2006 · Journal of Catalysis

DOI:https://doi.org/10.1016/j.jcat.2006.07.008· OSTI ID:931302

Xu, Jun ^[1]; Mullins, David R ^[1]

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1. ORNL

Previous co-adsorption studies of CO and oxygen on Rh single-crystal surfaces have shown that formation of CO{sub 2} is the dominant pathway during temperature-programmed desorption and that the reaction limits the competing pathway of CO and O{sub 2} desorption. The present work finds that this selectivity is altered on CeO{sub 2}-supported Rh islands. In addition to facile CO oxidation, a new CO adsorption state is found that is associated with the Rh but is observed only in the presence of both the CeO{sub 2} support and pre-adsorbed oxygen. This state is characterized by its low desorption temperature (140-250 K), well below the CO{sub 2} formation temperatures of 290 K ({beta}2) and 360 K ({beta}1), and by its IRAS frequency of 2100 cm-1, higher than observed for either CO adsorbed on the supported Rh islands (2057-2066 cm-1) or CO co-adsorbed with O on Rh islands (2074 cm-1). The data suggest that oxygen and subsequent CO exposure of CeO{sub 2} supported Rh creates atomically dispersed gem-dicarbonyl, Rh(CO){sub 2}, from the edge of Rh islands. As temperature increases, part of the dicarbonyl desorbs at low temperature, and the remainder is converted to CO{sub 2}. The low-temperature desorption pathway has a selectivity as high as 46%, with the remaining CO oxidized to CO{sub 2}.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 931302
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Vol. 243; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ADSORPTION
CARBON MONOXIDE
CARBONYLS
CATALYST SUPPORTS
CATALYTIC EFFECTS
CERIUM OXIDES
DESORPTION
OXIDATION
RHODIUM
RHODIUM COMPOUNDS