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Supported rhodium catalysts. Support effects on state and dispersion of the rhodium
Author(s) -
Zaki M. I.,
Tesche B.,
Kraus L.,
Knözinger H.
Publication year - 1988
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.740120403
Subject(s) - rhodium , nucleation , dispersion (optics) , catalysis , chemistry , particle (ecology) , metal , temperature programmed reduction , adsorption , oxidation state , transmission electron microscopy , inorganic chemistry , chemical engineering , materials science , nanotechnology , organic chemistry , engineering , physics , oceanography , optics , geology
Using SiO 2 , γ‐Al 2 O 3 as typical examples for acidic, amphoteric and basic oxides, the effect of the support nature on the behaviour of Rh was studied by temperature‐programmed reduction, transmission electron microscopy and IR spectroscopy of adsorbed CO. Reduction is much easier on SiO 2 than on Al 2 O 3 and MgO. The highest metal dispersion is stabilized on Al 2 O 3 , while particle aggregation to particles with diameters of up to 6 nm occurs on SiO 2 , during severe reduction and on MgO even under mild reduction conditions. The mobility of RH o atoms and the nucleation rates seem to be larger on MgO than on the other supports. In the presence of CO, the very small particles are disrupted with formation of Rh + (CO) 2 complexes at temperature below 300 K; at higher temperatures CO acts as a reducing agent and induces particle growth. It seems that particle disruption is favoured on the supports having the more acidic OH groups. Apart from the support nature, the nature of the precursor complex in solution and the solvent play a decisive role for the reducibility of rhodium.