XAFS characterization of Rh/Al[sub 2]O[sub 3] after treatment in high-temperature oxidizing environments

Journal Article · Mon Nov 01 04:00:00 EST 1993 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1993.1332· OSTI ID:5091468

Beck, D D; Capehart, T W; Wong, C; Belton, D N ^[1]

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1. General Motors Research, Warren, MI (United States)

The effect of high-temperature oxygen aging on the local structure of Rh oxide particles in a Rh/Al[sub 2]O[sub 3] catalyst has been characterized using X-ray absorption fine structure (XAFS) measurements. Thermal aging of the catalyst was performed at various temperatures and for different lengths of time at selected temperatures. Following treatment in 5% oxygen at or above 500[degrees]C, the supported Rh is completely oxidized to orthorhombic Rh[sub 2]O[sub 3]. The coordination of the dominant shells in the radial distribution function increases with treatment temperature, reaching a maximum at 800[degrees]C for an extended period results in an increase in coordination of the first three dominant shells. Most of this increase takes place during the initial 1-2h of treatment, but proceeds more slowly thereafter. Extended treatment at lower temperatures (600[degrees]C) results in slow and gradually increasing coordination in these shells, while at much higher temperatures (1000[degrees]C) the coordination initially increases but then decreases over extended treatment periods. The latter behavior is coincident with an apparent change in the structure as well. Since XAFS provides insight about single crystallite domains, the results suggest that at 800[degrees]C, Rh[sub 2]O[sub 3] crystallite growth or consolidation is more favored than at lower or higher temperatures. The behavior of the supported Rh[sub 2]O[sub 3] at high temperatures indicates a strong interaction with the support; however, this interaction does not appear to involve formation of a spinel or dissolution of Rh cations into the alumina lattice. Alternative explanations for these observations are discussed. 46 refs., 8 figs., 5 tabs.

• OSTI ID: 5091468
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 144:1; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CATALYST SUPPORTS
CATALYSTS
CHALCOGENIDES
CHEMICAL REACTIONS
COMPLEXES
CRYSTAL GROWTH
CRYSTAL LATTICES
CRYSTAL STRUCTURE
HEAT TREATMENTS
ORTHORHOMBIC LATTICES
OXIDATION
OXIDES
OXYGEN COMPOUNDS
RHODIUM COMPLEXES
SPECTROSCOPY
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
TRANSITION ELEMENT COMPLEXES
X-RAY SPECTROSCOPY