An XPS study of interactions in thin films containing a noble metal with valence-invariant and reducible oxides

Journal Article · Tue Sep 01 00:00:00 EDT 1992 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1016/0021-9517(92)90143-6· OSTI ID:7142212

Shelef, M; Haack, L P; Soltis, R E; DeVries, J E; Logothetis, E M ^[1]

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1. Ford Motor Co., Dearborn, MI (United States)

X-ray photoelectron spectroscopy was employed to examine the reducibility of oxides possessing multiple oxidation states (titania, niobia, and ceria) in the presence of palladium and a valence-invariant oxide (lanthana). The materials consisted of sputter-deposited ultra-thin films containing Pd with either titania, niobia, or ceria, with and without lanthana, on a sapphire substrate. For lanthana/Pd films, no reduction of the lanthana surface was observed after in situ treatment in hydrogen up to 600 C. After similar treatment, in the absence of lanthana a partial reduction to the lower oxidation states of niobia and titania and a total reduction to the lower oxidation state of ceria was observed. The presence of lanthana in the films inhibits the reduction of the titania completely and that of the niobia and ceria partially. Also, in a complementing set of films containing ceria an overlayer of high-surface-area {gamma}-Al{sub 2}O{sub 3}, was put over the smooth sapphire surface before the deposition of the other film components. In this case, the inhibiting effect on ceria-reducibility was attenuated. This points to the redistribution of lanthana over the available oxide surfaces. The preponderant portion of the lanthana accommodated on the porous {gamma}-Al{sub 2}O{sub 3} has rendered a significant part of the ceria unprotected and, in the presence of Pd, susceptible to reduction by H{sub 2} at 600 C. The results of these studies are a further manifestation of the known surface reactivity of lanthana, which while remaining itself irreducible, may strongly affect the behavior of other irreducible oxides such as alumina, or as presently shown, of reducible oxides such as titania, niobia, and ceria.

• OSTI ID: 7142212
• Journal Information: Journal of Catalysis; (United States), Vol. 137:1; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CATALYST SUPPORTS
CONFIGURATION INTERACTION
CATALYSTS
CERIUM OXIDES
REDUCTION
NIOBIUM OXIDES
PALLADIUM
CATALYTIC EFFECTS
TITANIUM OXIDES
ALUMINIUM OXIDES
ENERGY BEAM DEPOSITION
HYDROGEN
LANTHANUM OXIDES
PHOTOELECTRON SPECTROSCOPY
SAPPHIRE
SPUTTERING
SURFACE AREA
THIN FILMS
VALENCE
X-RAY SPECTROSCOPY
ALUMINIUM COMPOUNDS
CERIUM COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
CORUNDUM
DEPOSITION
ELECTRON SPECTROSCOPY
ELEMENTS
FILMS
LANTHANUM COMPOUNDS
METALS
MINERALS
NIOBIUM COMPOUNDS
NONMETALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
RARE EARTH COMPOUNDS
REFRACTORY METAL COMPOUNDS
SPECTROSCOPY
SURFACE COATING
SURFACE PROPERTIES
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
400201* - Chemical & Physicochemical Properties