Alkali (Na, K)-promoted Ru/hydrotalcite dual function materials for integrated CO2 capture and methanation: A parametric study

Integrated CO2 capture and methanation (ICCM) is attracting growing interest as a circular net-zero technology to convert dilute waste CO2 into synthetic natural gas using green hydrogen. However, its effective deployment requires dual-function materials (DFMs) that balance high CO2 adsorption capacity with fast, selective methanation kinetics under realistic cyclic conditions. This work systematically evaluates Ru-based DFMs supported on hydrotalcite-derived (Mg-Al) oxides promoted by K or Na. The effect of alkali promotion on CO2 uptake, hydrogenation kinetics and cyclic ICCM performance is investigated under both ideal (5% CO2/N2) and realistic feeds containing H2O and O2 during the capture stage. DFM performance is correlated with surface chemistry through combined transient ICCM experiments in the fixed-bed reactor and operando DRIFTS studies. The Ru/Na-Mg-Al is identified as the most balanced DFM, capturing as much as 550 μmol CO2 g−1DFM in the presence of water vapour and converting it to CH4 with high selectivity and remarkable stability across cycles at 340–400 °C. Particular emphasis is placed on methane productivity under cyclic operation, as a key performance indicator for material development and process intensification under realistic feed conditions.