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), Vol. 93:15; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
02 PETROLEUM
33 ADVANCED PROPULSION SYSTEMS
CATALYTIC CONVERTERS
RHODIUM COMPOUNDS
INFRARED SPECTRA
ADSORPTION
CARBON MONOXIDE
CATALYSTS
DATA ANALYSIS
EXPERIMENTAL DATA
MEASURING INSTRUMENTS
MEASURING METHODS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
DATA
EQUIPMENT
INFORMATION
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
POLLUTION CONTROL EQUIPMENT
REFRACTORY METAL COMPOUNDS
SORPTION
SPECTRA
TRANSITION ELEMENT COMPOUNDS
400201* - Chemical & Physicochemical Properties
025000 - Petroleum- Combustion
330700 - Advanced Propulsion Systems- Emission Control