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Monitoring Transport Phenomena of Paramagnetic Metal‐Ion Complexes Inside Catalyst Bodies with Magnetic Resonance Imaging
Author(s) -
Bergwerff Jaap A.,
Lysova Anna A.,
EspinosaAlonso Leticia,
Koptyug Igor V.,
Weckhuysen Bert M.
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700990
Subject(s) - chemistry , yolk , catalysis , paramagnetism , metal , eggshell , electron paramagnetic resonance , ion , analytical chemistry (journal) , nuclear magnetic resonance , chromatography , organic chemistry , ecology , physics , food science , quantum mechanics , biology
An indirect magnetic resonance imaging (MRI) method has been developed to determine in a noninvasive manner the distribution of paramagnetic Co 2+ complexes inside Co/Al 2 O 3 catalyst extrudates after impregnation with Co 2+ /citrate solutions of different pH and citrate concentrations. UV/Vis/NIR microspectroscopic measurements were carried out simultaneously to obtain complementary information on the nature of the Co 2+ complexes. In this way, it could be confirmed that the actual distribution of Co 2+ inside the extrudates could be derived from the MRI images. By combining these space‐ and time‐resolved techniques, information was obtained on both the strength and the mode of interaction between [Co(H 2 O) 6 ] 2+ and different Co 2+ citrate complexes with the Al 2 O 3 support. Complexation of Co 2+ by citrate was found to lead to a stronger interaction of Co with the support surface and formation of an eggshell distribution of Co 2+ complexes after impregnation. By addition of free citrate and by changing the pH of the impregnation solution, it was possible to obtain the rather uncommon egg‐yolk and egg‐white distributions of Co 2+ inside the extrudates after impregnation. In other words, by carefully altering the chemical composition and pH of the impregnation solution, the macrodistribution of Co 2+ complexes inside catalyst extrudates could be fine‐tuned from eggshell over egg white and egg yolk to uniform.