Fe-modified MgAl2O4 makes a surprisingly active catalyst support, likely linked to a structural effect of the Fe incorporation. Two catalyst supports, MgAl2O4 and MgFeAlO4, have been studied in fresh and reduced state to determine the effect of high-temperature H2 reduction upon ion distribution in the lattices. To this end, an X-ray Raman scattering study has been performed, focusing on the oxygen K edge and magnesium and aluminum L2,3 and iron M2,3 soft edges. MgAl2O4 shows a random cation distribution and only small changes occur at the Mg L2,3 and Al L2,3 edges upon reduction at 1073 K. The main oxygen signal does lose intensity and its simulation points to a lower O covalency and more confined state after reduction. Introducing 8.9 wt % Fe into the spinel pushes Mg towards mostly tetrahedral position in the MgFeAlO4 lattice, whereas Fe and Al share the octahedral sites. Concomitant lattice distortion is observable in the O signal. Reduction of MgFeAlO4 leads to enhanced distortion visible in the O and Al signals and the presence of 50% Fe2+. Both disorder and reduction lead to partial segregation of MgFeO x from the MgFeAlO4 lattice. This combination of distortion and phase restructuring in the Fe-modified MgFeAlO4 material facilitates the lattice oxygen mobility and hence its catalytic activity.

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MgAl2O4-supported Ni materials are highly active and cost-effective CO2 conversion catalysts, yet their oxidation by CO2 remains dubious. Herein, NiO/MgAl2O4, prepared via colloidal synthesis (10 wt % Ni) to limit size distribution, or wet impregnation (5, 10, 20, and 40 wt % Ni), and bare, i.e., unsupported, NiO are examined in H2 reduction and CO2 oxidation, using thermal conductivity detector-based measurements and in situ quick X-ray absorption spectroscopy, analyzed via multivariate curve resolution-alternating least-squares. Ni reoxidation does not occur for bare Ni but is observed solely on supported materials. Only samples with the smallest particle sizes get fully reoxidized. The Ni-MgAl2O4 interface, exhibiting metal–support interactions, activates CO2 and channels oxygen into the reduced lattice. Oxygen diffuses inward, away from the interface, oxidizing Ni entirely or partially, depending on the particle size in the applied oxidation time frame. This work provides evidence for Ni oxidation by CO2 and explores the conditions of its occurrence and the importance of metal–support effects.

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MgAl2O4 and its Fe-modified analogue (MgFexAl2−xO4) were synthesized as supports with a nanostructure by a hydrothermal process, and employed as supports for Ni catalysts in methane dry reforming (DRM). All...