TEM study of the microstructural modifications of an alumina-supported palladium combustion catalyst

Journal Article · Mon Oct 25 04:00:00 EDT 1999 · Journal of Catalysis

DOI:https://doi.org/10.1006/jcat.1999.2545· OSTI ID:20003833

Lyubovsky, M; Pfefferle, L; Datye, A; Bravo, J; Nelson, T

An {alpha}-alumina-supported Pd catalyst was studied for the catalytic combustion of methane. Changes in catalyst activity due to variations in the oxygen partial pressure were correlated with corresponding changes in the catalyst oxidation state, particle size, and morphology. At a temperature of 1,070 K, the apparent catalyst activity increased with time under the reaction conditions where decomposition of the PdO phase occurs. The formation of large, faceted crystallites of metallic Pd, 200--300 nm in size, was observed by TEM during this process. The increase in activity with increasing particle size is counterintuitive and suggests that metallic Pd surfaces formed under reaction conditions are highly reactive. Since the activation energy for methane oxidation over Pd metal is greater than that over PdO, their results can only be explained by an increase in the pre-exponential factor for this reaction on metal surfaces. To gain insight into the changes in morphology, a model Pd/{alpha}-alumina catalyst was subjected to similar thermal treatments. It was found that decomposition of PdO leads to the formation of large Pd metal particles. Upon cooling, these Pd particles re-oxidize by the formation of rough polycrystalline PdO particles rather than by the formation of uniform layers of Pd oxide on the Pd metal. Observations suggest a mechanism to explain the phenomenon on Pd catalyst activation observed in their previous research and by other research groups.

• Research Organization: Yale Univ., New Haven, CT (US)
• Sponsoring Organization: US Department of Energy
• OSTI ID: 20003833
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 2 Vol. 187; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

33 ADVANCED PROPULSION SYSTEMS
54 ENVIRONMENTAL SCIENCES
CATALYSTS
CATALYTIC COMBUSTORS
CATALYTIC EFFECTS
CHEMICAL ACTIVATION
METHANE
MICROSTRUCTURE
MORPHOLOGICAL CHANGES
PALLADIUM