Effects of high-temperature oxidation and reduction on the structure and activity of Rh/Al sub 2 O sub 3 and Rh/SiO sub 2 catalysts

Journal Article · Fri Sep 01 04:00:00 EDT 1989 · Journal of Catalysis; (USA)

DOI:https://doi.org/10.1016/0021-9517(89)90133-4· OSTI ID:7124182

Wong, C; McCabe, R W ^[1]

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1. General Motors Research Laboratories, Warren, MI (USA)

The effects of high-temperature oxidizing and reducing treatments on the structure and activity of Rh/Al{sub 2}O{sub 3} and Rh/SiO{sub 2} catalysts were examined using the techniques of temperature-programmed reduction, H{sub 2} chemisorption, infrared spectroscopy, transmission electron microscopy, and CO oxidation kinetic analysis. Sequential treatments in O{sub 2} and H{sub 2} at 1075 K had little effect on the Rh/SiO{sub 2} catalysts beyond increasing the mean particle size from {approx}4 nm to greater than 12 nm. No interactions between the Rh and the support were observed for the Rh/SiO{sub 2} catalysts. In contrast, 1075 K oxidation of the Rh/Al{sub 2}O{sub 3} catalysts caused most of the Rh to diffuse into the bulk of the alumina and resulted in a five- to tenfold decrease in CO oxidation activity. Nearly all of the Rh could be restored to the surface of the alumina by a subsequent 1075-K 1-h H{sub 2} reduction followed by a reoxidation at 775 K for 1 h. The reactivated catalyst oxidized CO at greater rates than the fresh catalyst and with an apparent activation energy of {approx}22 kcal/g mol compared to {approx}30 kcal/g mol for the fresh catalyst. The data suggest that the most active form of Rh in the reactivated catalyst is small clusters whereas most of the active Rh in the fresh catalyst is present in larger Rh particles which are more bulk-like in character.

• OSTI ID: 7124182
• Journal Information: Journal of Catalysis; (USA), Journal Name: Journal of Catalysis; (USA) Vol. 119:1; ISSN 0021-9517; ISSN JCTLA
• Country of Publication: United States
• Language: English

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ACTIVATION ENERGY
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYST SUPPORTS
CATALYSTS
CATALYTIC CONVERTERS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISORPTION
CONTROL
CRYSTAL STRUCTURE
ELECTRON MICROSCOPY
ELEMENTS
ENERGY
EQUIPMENT
HYDROGEN
HYDROGENATION
INFRARED SPECTRA
KINETICS
METALS
MICROSCOPY
MICROSTRUCTURE
MINERALS
NITRIC OXIDE
NITROGEN COMPOUNDS
NITROGEN OXIDES
NONMETALS
OXIDATION
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PARTICLE SIZE
PLATINUM METALS
POLLUTION CONTROL EQUIPMENT
REACTION KINETICS
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REGENERATION
RHODIUM
SEPARATION PROCESSES
SILICA
SILICON COMPOUNDS
SILICON OXIDES
SIZE
SORPTION
SPECTRA
SYNTHESIS
TEMPERATURE CONTROL
TRANSITION ELEMENTS
TRANSMISSION ELECTRON MICROSCOPY