Magnetic Resonance Imaging Studies on Catalyst Impregnation Processes: Discriminating Metal Ion Complexes within Millimeter-Sized gamma-Al2O3 Catalyst Bodies

Magnetic resonance imaging (MRI) was used to study the impregnation step during the preparation of Ni/gamma-Al2O3 hydrogenation catalysts with Ni2+ metal ion present in different coordinations. The precursor complexes were [Ni(H2O)(6)](2+) and [Ni(edtaH(x))]((2-x)-) (where x = 0, 1, 2 and edta = ethylenediaminetetraacetic acid), representing a nonshielded and a shielded paramagnetic complex, respectively. Due to this shielding effect of the ligands, the dynamics of [Ni(H2O)(6)](2+) or [Ni(edtaH(X))]((2-x)-) were visualized applying T-2 or T-1 image contrast, respectively. MRI was applied in a quantitative manner to calculate the [Ni(H2O)(6)](2+) concentration distribution after impregnation when it was present alone in the impregnation solution, or together with the [Ni(edtaH(x))]((2-x)-) species. Moreover, the combination of MRI with UV-vis microspectroscopy allowed the visualization of both species with complementary information on the dynamics and adsorption/desorption phenomena within gamma-Al2O3 catalyst bodies. These phenomena yielded nonuniform Ni distributions after impregnation, which are interesting for certain industrial applications.