Novel Ni-Containing Ce-Promoted Hydrotalcite Derived Geopolymers (MK-Ni _3-x Mg _<i>x</i> Al–Ce) as Structured Catalysts for CO ₂ Methanation

In this work, the development of Ni-containing, Ce-promoted hydrotalcite-derived geopolymers is reported as a strategy to engineer structured catalysts for CO2 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-Cepre) and postimpregnation (MK-NiMgAl-Cepost). The MK-NiMgAl-Cepre catalyst demonstrated the highest CO2 conversion (73.2%) and CH4 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 m2 g–1, while XRD and H2–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 H2 uptake increasing from 2616 to 2952 μmol g–1. CO2–Temperature-Programmed Desorption (TPD) analysis revealed enrichment in moderate basic sites (155.0 μmol g–1), which are key for CO2 activation. During 10-cycle redox testing, MK-NiMgAl-Cepre preserved ∼75% after the fifth cycle and nearly recovered its original performance following H2 regeneration, evidencing reversible redox behavior. XPS analysis further confirmed dynamic redox behavior of Ce3+/Ce4+ and reversible Ni2+/Ni0 transitions, confirming the role of CeO2 as a redox buffer. Overall, the MK-NiMgAl-Cepre 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 CO2 valorization in power-to-methane applications.