Growth/restructuring of Pd clusters induced by CO adsorption

Journal Article · Thu Aug 22 04:00:00 EDT 1991 · Journal of Physical Chemistry; (United States)

DOI:https://doi.org/10.1021/j100170a042· OSTI ID:7163607

Anderson, S L; Mizushima, Takanori; Udagawa, Yasuo ^[1]

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1. Inst. for Molecular Science, Okazaki (Japan)

Highly dispersed palladium catalysts supported on {gamma}-alumina and silica were prepared and studied by EXAFS spectroscopy, IR spectroscopy, X-ray diffraction, and CO uptake. The Pd-Pd EXAFS oscillations for the freshly reduced catalysts are only about 1/4th as strong as those observed for bulk Pd, indicating that the Pd particles in the catalysts are either very small, highly disordered, or both. Exposure to CO at room temperature causes the Pd-Pd EXAFS intensity to increase dramatically, in some cases to nearly to bulk Pd value. This increase is irreversible with respect to CO removal. IR spectra show CO binding only in the expected 2-fold bridging and linear sites. The increase was observed on both SiO{sub 2} and Al{sub 2}O{sub 3} supports but varied in magnitude with support and support condition. Exposure to water vapor did not affect the Pd-Pd EXAFS. Several possible explanations for the EXAFS intensity increases are discussed. The most likely appears to be that CO increases the mobility of Pd atoms over the support, and allows growth of the Pd clusters present after reduction. These results have implications for the interpretation of the commonly used CO adsorption method for measuring catalyst dispersion.

• OSTI ID: 7163607
• Journal Information: Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 95:17; ISSN 0022-3654; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ABSORPTION SPECTRA
ADSORPTION
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL PROPERTIES
CRYSTAL GROWTH
DATA
ELEMENTS
EXPERIMENTAL DATA
INFORMATION
INFRARED SPECTRA
METALS
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
PALLADIUM
PLATINUM METALS
SORPTION
SORPTIVE PROPERTIES
SPECTRA
SURFACE PROPERTIES
SYNTHESIS
TRANSITION ELEMENTS