Magnetic resonance imaging studies on catalyst impregnation processes: discriminating metal ion complexes within millimeter-sized γ-Al2O3 catalyst bodies

Magnetic resonance imaging (MRI) was used to study the impregnation step during the preparation of Ni/γ-Al2O3 hydrogenation catalysts with Ni2+ metal ion present in different coordinations. The precursor complexes were [Ni(H2O)6]2+ and [Ni(edtaHx)](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(edtaHx)](2−x)− were visualized applying T2 or T1 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(edtaHx)](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 γ-Al2O3 catalyst bodies. These phenomena yielded nonuniform Ni distributions after impregnation, which are interesting for certain industrial applications.