Effects of high-temperature aging on the dispersion of Rh/Al[sub 2]O[sub 3]

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

DOI:https://doi.org/10.1006/jcat.1993.1331· OSTI ID:5041411

Beck, D D; Carr, C J ^[1]

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1. General Motor Research and Development, Warren, MI (United States)

The effect of high-temperature treatment in relatively simple gas mixtures of 1% O[sub 2]/N[sub 2], 1% H[sub 2]/N[sub 2], and an environment which alternates between these two gases on the dispersion of 0.5 wt% Rh/Al[sub 2]O[sub 3] were characterized using temperature-programmed desorption (TPD) of D[sub 2]. The TPD data were used to determine the relative changes in the Rh metal dispersion as a result of treatment. These treatments were selected as they are believed to model the oxidation and reduction environments in the typical automotive exhaust. When the fresh catalyst was aged in reducing environments at 600, 700, or 800[degrees]C, the dispersion decrease is directly related to the treatment temperature. When the catalyst was aged in oxygen at 600, 700, or 800[degrees]C, the Rh was rapidly and completely oxidized. At the lower aging temperatures, most of the Rh could be recovered to the metallic state using a reduction treatment at 200[degrees]C, but at 800[degrees]C, only a small amount of the Rh was recovered to the metal using this mild reduction treatment. Subsequent reduction treatments at high temperature resulted in near complete recovery of Rh in the form of large metal particles. Treatment in alternating oxygen/hydrogen environments at low frequency produced Rh[sub 2]O[sub 3] after each oxidation treatment and Rh metal particles after each reduction treatment. The higher temperature treatments produced sintered Rh metal particles, even in the alternating environment. Treatment in alternating oxygen/hydrogen environments at high frequency resulted in incomplete oxidation of Rh after the oxidation cycle, but did result in more rapid sintering of the Rh metal as the treatments in the pure gases at the same temperature. 47 refs., 9 figs., 4 tabs.

• OSTI ID: 5041411
• 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
CHALCOGENIDES
COMPLEXES
DEUTERIUM
HEAT TREATMENTS
HYDROGEN ISOTOPES
ISOTOPES
LIGHT NUCLEI
NUCLEI
ODD-ODD NUCLEI
OXIDES
OXYGEN COMPOUNDS
RHODIUM COMPLEXES
SORPTIVE PROPERTIES
STABLE ISOTOPES
SURFACE PROPERTIES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
TRANSITION ELEMENT COMPLEXES