Influence of ceria on alumina-supported rhodium: Observations of rhodium morphology made using FTIR spectroscopy
- General Motors Research Labs., Warren, MI (USA)
The adsorbed states of carbon monoxide on a 0.5% Rh/10% Ce/Al{sub 2}O{sub 3} catalyst were investigated by infrared spectroscopy in order to better understand the promotional effects ceria exerts on rhodium in automobile catalysts. It was found that the IR spectra of freshly prepared catalysts were dominated by the dicarbonyl species Rh(CO){sub 2} - indicative of a high degree of atomic dispersion. Prolonged exposures to CO at 473 K effectively agglomerated the rhodium as evidenced by the simultaneous growth of linear- and bridged-carbonyl IR bands (Rh-CO and Rh{sub 2}(CO), respectively) and disappearance of the dicarbonyl features. However, the total integrated absorbance of all adsorbed CO species did not decrease significantly, suggesting that the Rh is coalescing from an atomically dispersed state to one of high dispersion. The agglomerated state would presumably be characterized by small or flat Rh{sup 0} particles. Brief exposures to O{sub 2} at 673 K followed by exposure to CO at 373 K showed that the catalyst could be returned to a state of {approximately} 100% atomic dispersion, again suggesting that the particles are small or flat and easily oxidized. Ceria primary role as a promoter may be the maintenance of high Rh dispersions; other reputed benefits such as increased water-gas shift activity may be secondary effects arising from small Rh particle sizes.
- OSTI ID:
- 6985577
- Journal Information:
- Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 93:15; ISSN 0022-3654; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ADSORPTION
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYSTS
CATALYTIC CONVERTERS
CHALCOGENIDES
DATA
DATA ANALYSIS
EQUIPMENT
EXPERIMENTAL DATA
INFORMATION
INFRARED SPECTRA
MEASURING INSTRUMENTS
MEASURING METHODS
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
POLLUTION CONTROL EQUIPMENT
REFRACTORY METAL COMPOUNDS
RHODIUM COMPOUNDS
SORPTION
SPECTRA
TRANSITION ELEMENT COMPOUNDS