Abstract:Integrated carbon dioxide (CO2) capture and methanation (ICCM) is a crucial technology for achieving carbon neutrality, as it converts waste CO2 into synthetic natural gas through the utilization of dual-functional materials (DFMs). This review systematically synthesizes recent progress in nickel-based DFMs, aiming to clarify the relationships among material design, reaction mechanisms in complex flue gas environments, and engineering challenges associated with process scale-up. The discussion covers various synthesis strategies for adsorbents, including calcium-, magnesium-, and alkali metal-based systems. It critically examines the roles of promoters as well as the influence of reactor configuration and operational parameters. Emphasis is placed on multi-scale structural effects, ranging from macroscopic bed configurations to nanoscale interfacial engineering. Furthermore, deactivation mechanisms caused by realistic flue gas components such as O2, H2O, NOx, and SO2 are thoroughly summarized. In terms of material optimization, while CaO-based DFMs exhibit exceptional theoretical capacities, their real-world applications are frequently hindered by sintering and thermodynamic limitations. Strategies such as the incorporation of inert supports (e.g., γ-Al2O3), the use of layered double hydroxide (LDH) precursors, and alkali-metal doping have proven effective in enhancing component dispersion and cyclic stability. Similarly, MgO-based materials, which often suffer from surface passivation, show significantly improved CO2 uptake kinetics through the addition of alkali nitrate molten salts. Moreover, the review highlights the important roles played by transition-metal promoters (such as Ru, Zr, Ce) in facilitating low-temperature reduction, refining Ni crystallite size, and generating oxygen vacancies (Ovs) or frustrated Lewis pairs (FLPs) that enhance surface activation. A critical analysis reveals that the proximity between adsorption and catalytic sites is paramount in determining overall reaction efficiency. Constructing nanoscale interfaces with buffer layers (e.g., CeO2, AlOx) or employing core-shell structures can proficiently balance mass-transfer efficiency with active site accessibility. Regarding the influence of impurities, the presence of O2 leads to temporary Ni oxidation, which can assist in coke removal; however, H2O and NOx impede the process through competitive adsorption. Notably, SO2 acts as a significant poison, forming stable sulfates that occupy basic sites and kinetically inhibit the decomposition of critical formate (HCOO*) intermediates, thus blocking hydrogenation pathways. This review also concludes that the successful industrial implementation of ICCM technology requires a shift in emphasis from laboratory-scale material screening toward integrated engineering-system design. Future research should focus on: (1) the development of highly active, stable, and anti-toxic DFMs; (2) the elucidation of deactivation mechanisms in complex atmospheres using in situ characterization techniques; (3) the design of synergistic multi-pollutant control strategies, such as integrated CO2/SO2 and CO2/NOx treatment systems; and (4) the engineering of specialized reactors capable of handling the rapid thermal cycling and strongly exothermic nature of the ICCM process. Close-