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XPS analysis and microstructural characterization of a Ce/Tb mixed oxide supported on a lanthana‐modified transition alumina
Author(s) -
Galtayries A.,
Blanco G.,
Cifredo G. A.,
Finol D.,
Gatica J. M.,
Pintado J. M.,
Vidal H.,
Sporken R.,
Bernal S.
Publication year - 1999
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/(sici)1096-9918(199910)27:10<941::aid-sia657>3.0.co;2-y
Subject(s) - x ray photoelectron spectroscopy , materials science , lanthanum oxide , oxide , cerium oxide , calcination , mixed oxide , fourier transform infrared spectroscopy , analytical chemistry (journal) , chemical engineering , chemistry , catalysis , metallurgy , biochemistry , engineering , chromatography
In the framework of a research project aimed at developing alternative materials for application in three‐way catalysis, this work reports on the preparation and characterization of a ceria– terbia mixed oxide supported on a lanthana‐modified transition alumina. This complex multicomponent oxide system has been characterized by combining x‐ray diffraction (XRD), high‐resolution electron microscopy (HREM), temperature‐programmed desorption mass spectrometry (TPD‐MS), Fourier transform infrared spectroscopy (FTIR) and x‐ray photoelectron spectroscopy (XPS). Following a dry impregnation procedure, the lanthana‐containing phase was deposited first, the ceria– terbia oxide being dispersed on the modified alumina in a subsequent step. The structural and chemical characterization studies carried out on the La 2 O 3 /Al 2 O 3 binary system provide no evidence of a crystalline lanthana‐containing phase. Neither lanthanum oxide nor the phases resulting from its aging in air could be identified. Likewise, no lanthana– alumina mixed oxide phases could be deduced from analysis of the HREM micrographs, selected‐area electron diffraction (SAED) or XRD patterns. As deduced from the H 2 O and CO 2 TPD studies, the chemisorptive properties of the La 2 O 3 /Al 2 O 3 are significantly different from those of the alumina and the bulk lanthana. We conclude, accordingly, that the supported lanthana consists of a highly dispersed oxide in strong interaction with the alumina support. By contrast, after deposition and further calcination of the cerium– terbium nitrate precursors, the presence of fluorite microcrystals of average size 5 nm could be identified both by XRD and HREM. The XPS studies carried out on the alumina support, La 2 O 3 /Al 2 O 3 and CeTbO x /La 2 O 3 /Al 2 O 3 , as well as a series of reference systems consisting of aged‐in‐air lanthana, CeLaO x and CeTbO x mixed oxides, have revealed the presence in the ternary system (CeTbO x /La 2 O 3 /Al 2 O 3 ) of at least two different types of chemical environments for the lanthanum ions. With the help of the La 3d 5/2 spectra recorded for the different reference systems, we conclude that these two environments correspond to highly dispersed lanthana strongly interacting with OH − and/or CO 3 2− groups, and to La 3+ species incorporated in the Ce/Tb mixed oxide phase. Copyright © 1999 John Wiley & Sons, Ltd.