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Structural Characterization of Alumina‐Supported Rh Catalysts: Effects of Ceriation and Zirconiation by using Metal–Organic Precursors
Author(s) -
Kroner Anna B.,
Newton Mark A.,
Tromp Moniek,
Russell Andrea E.,
Dent Andrew J.,
Evans John
Publication year - 2013
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201300537
Subject(s) - rhodium , x ray photoelectron spectroscopy , catalysis , x ray absorption fine structure , chemistry , extended x ray absorption fine structure , calcination , materials science , metal , inorganic chemistry , analytical chemistry (journal) , absorption spectroscopy , spectroscopy , chemical engineering , organic chemistry , physics , quantum mechanics , engineering
Abstract The effects of the addition of ceria and zirconia on the structural properties of supported rhodium catalysts (1.6 and 4 wt % Rh/γ‐Al 2 O 3 ) are studied. Ceria and zirconia are deposited by using two preparation methods. Method I involves the deposition of ceria on γ‐Al 2 O 3 from Ce(acac) 3 , and the rhodium metal is subsequently added, whereas method II is based on a controlled surface reaction technique, that is, the decomposition of metal–organic M(acac) x (in which M=Ce, x =3 and M=Zr, x =4) on Rh/γ‐Al 2 O 3 . The structures of the prepared catalyst materials are characterized ex situ by using N 2 physisorption, transmission electron microscopy, high‐angle annular dark‐field scanning transmission election microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray photoelectron spectroscopy (XPS), and X‐ray absorption fine structure spectroscopy (XAFS). All supported rhodium systems readily oxidize in air at room temperature. By using ceriated and zirconiated precursors, a larger rhodium‐based metallic core fraction is obtained in comparison to the undoped rhodium catalysts, suggesting that ceria and zirconia protect the rhodium particles against extensive oxidation. XPS results indicate that after the calcination and reduction treatments, a small amount of chlorine is retained on the support of all rhodium catalysts. EXAFS analysis shows significant RhCl interactions for Rh/Al 2 O 3 and Rh/CeO x /Al 2 O 3 (method I) catalysts. After reaction with H 2 /He in situ, for series of samples with 1.6 wt % Rh, the EXAFS first shell analysis affords a mean size of approximately 30 atoms. A broader spread is evident with a 4 wt % rhodium loading (ca. 30–110 atoms), with the incorporation of zirconium providing the largest particle sizes.