Oscar E. Médina, Diana López, Andrés A. Amell, Alexander Santamarı́a
In this work, the development of Ni-containing, Ce-promoted hydrotalcite-derived geopolymers is reported as a strategy to engineer structured catalysts for CO 2 methanation. Catalysts were synthesized via in situ formation of Ni–Mg–Al layered double hydroxides (LDHs) within a metakaolin-based geopolymer matrix and modified with cerium using two strategies: preimpregnation (MK-NiMgAl-Ce pre ) and postimpregnation (MK-NiMgAl-Ce post ). The MK-NiMgAl-Ce pre catalyst demonstrated the highest CO 2 conversion (73.2%) and CH 4 selectivity (98.4%) at 350 °C and atmospheric pressure, corresponding to a 17.5% improvement in conversion compared with the undoped MK–NiMgAl catalyst (63.3%) and a 10.4% enhancement over the postdoped analogue (66.3%). Textural analysis showed the MK-NiMgAl-Cepre maintained a BET surface area of 185.4 m 2 g –1, while XRD and H 2 –Temperature-Programmed Reduction (TPR) confirmed improved Ni dispersion and enhanced reducibility, with metallic Ni crystallite size reduced from 9.12 nm (undoped) to 6.12 nm and H 2 uptake increasing from 2616 to 2952 μmol g –1 . CO 2 –Temperature-Programmed Desorption (TPD) analysis revealed enrichment in moderate basic sites (155.0 μmol g –1 ), which are key for CO 2 activation. During 10-cycle redox testing, MK-NiMgAl-Ce pre preserved ∼75% after the fifth cycle and nearly recovered its original performance following H 2 regeneration, evidencing reversible redox behavior. XPS analysis further confirmed dynamic redox behavior of Ce 3+ /Ce 4+ and reversible Ni 2+ /Ni 0 transitions, confirming the role of CeO 2 as a redox buffer. Overall, the MK-NiMgAl-Ce pre catalyst combines high activity, selectivity, and regenerability, highlighting the synergistic effect of LDH–geopolymer integration and cerium modification. These findings offer a promising route toward durable, structured catalysts for efficient CO 2 valorization in power-to-methane applications.