title: Monitoring transport phenomena of paramagnetic metal-ion complexes inside catalyst bodies with magnetic resonance imaging.
abstract: An indirect magnetic resonance imaging (MRI) method has been developed to determine in a noninvasive manner the distribution of paramagnetic Co2+ complexes inside Co/Al2O3 catalyst extrudates after impregnation with Co2+/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 Co2+ complexes. In this way, it could be confirmed that the actual distribution of Co2+ 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(H2O)6]2+ and different Co2+ citrate complexes with the Al2O(3) support. Complexation of Co2+ by citrate was found to lead to a stronger interaction of Co with the support surface and formation of an eggshell distribution of Co2+ 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 Co2+ inside the extrudates after impregnation. In other words, by carefully altering the chemical composition and pH of the impregnation solution, the macrodistribution of Co2+ complexes inside catalyst extrudates could be fine-tuned from eggshell over egg white and egg yolk to uniform.
authors.affiliation: Inorganic Chemistry and Catalysis Group, Department of Chemistry, Faculty of Science, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands.
authors.forename: Jaap A
authors.initials: JA
authors.lastname: Bergwerff
authors.forename: Anna A
authors.initials: AA
authors.lastname: Lysova
authors.forename: Leticia
authors.initials: L
authors.lastname: Espinosa-Alonso
authors.forename: Igor V
authors.initials: IV
authors.lastname: Koptyug
authors.forename: Bert M
authors.initials: BM
authors.lastname: Weckhuysen