Hierarchically Structured Porous Spinels via an Epoxide-Mediated Sol-Gel Process Accompanied by...

Enhancing the activity and stability of catalysts is a major challenge in scientific research nowadays. Previous studies showed that the generation of an additional pore system can influence the catalytic performance of porous catalysts regarding activity, selectivity, and stability. This study focuses on the epoxide-mediated sol-gel synthesis of mixed metal oxides, NiAl₂O₄ and CoAl₂O₄, with a spinel phase structure, a hierarchical pore structure, and Ni and Co contents of 3 to 33 mol % with respect to the total metal content. The sol-gel process is accompanied by a polymerization-induced phase separation to introduce an additional pore system. The obtained mixed metal oxides were characterized with regard to pore morphology, surface area, and formation of the spinel phase. The Brunauer-Emmett-Teller surface area ranges from 74 to 138 m²·g^-1 and 25 to 94 m²·g^-1 for Ni and Co, respectively. Diameters of the phase separation-based macropores were between 500 and 2000 nm, and the mesopore diameters were 10 nm for the Ni-based system and between 20 and 25 nm for the cobalt spinels. Furthermore, Ni-Al spinels with 4, 5, and 6 mol % Ni were investigated in the dry reforming of CH₄ (DRM) with CO₂ to produce H₂ and CO. CH₄ conversions near the thermodynamic equilibrium were observed depending on the Ni content and reaction temperature. The Ni catalysts were further compared to a noble metal-containing catalyst based on a spinel system showing comparable CH₄ conversion and carbon selectivity in the DRM.