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Actual constitution of the mixed oxide promoter in a Rh/Ce 1− x Pr x O 2− y /Al 2 O 3 catalyst. Evolution throughout the preparation steps
Author(s) -
Aboussaïd Karima,
Bernal Serafín,
Blanco Ginesa,
Calvino José Juan,
Cifredo Gustavo Aurelio,
LópezHaro Miguel,
Pintado José María,
el Begrani Mohamed Soussi,
Stéphan Odile,
Trasobares Susana
Publication year - 2008
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/sia.2773
Subject(s) - x ray photoelectron spectroscopy , praseodymium , crystallite , oxide , cerium , analytical chemistry (journal) , cerium oxide , non blocking i/o , calcination , desorption , lanthanide , catalysis , mixed oxide , chemistry , materials science , crystallography , inorganic chemistry , adsorption , chemical engineering , ion , chromatography , biochemistry , organic chemistry , engineering
The evolution of the ceria‐praseodymia mixed oxide promoter throughout the successive steps involved in the preparation of a 3% Rh/25% Ce 0.8 Pr 0.2 O 2− x /Al 2 O 3 –3.5% SiO 2 catalyst is studied with the help of X‐ray diffraction (XRD), spatially resolved electron energy loss spectroscopy (EELS), XPS, and thermal programed desorption (TPD) techniques. Incipient wetness impregnation has been used to obtain the appropriate loading of this promoter. As revealed by XRD, EELS, and XPS data, the alumina‐supported CeO 2 PrO 2− x mixed oxide sample consisted of a bimodal distribution of the particles of the promoter. XRD shows two fluorite‐like phases: cerium‐rich particles with a mean crystallite size greater than 6 nm and smaller praseodymium‐rich crystals, about 3.5 nm size. Surface Ce/Pr ratio obtained by XPS was consistent with a higher dispersion of the praseodymium‐rich oxide particles. The final Rh catalyst was prepared in a second step, by impregnation of the CePrO x /Al 2 O 3 system with an acidic solution of Rh(NO 3 ) 3 . The low pH of this solution is responsible for further modifications of the lanthanide oxides distribution. Thus, there is a redispersion of the praseodymium‐rich phase, which is evidenced by EELS and XPS data. Likewise, CO 2 desorption from samples exposed to the atmosphere is consistent with an enhanced basicity of the sample due to the increase of Pr 3+ content at the surface of the catalyst. The observed changes on the nanostructure of the mixed oxide promoter can be attributable to a partial dissolution of the oxide, selectively leaching Pr 3+ cations from the lattice, which are finally deposited as small particles after the drying steps of the preparation. Copyright © 2008 John Wiley & Sons, Ltd.