Review and Outlook of CO2 Capture Using Alkali and Alkaline Earth Metal Oxide-Based Adsorbents: Powder Synthesis, Pelletization, and Reactor Design

Abstract Alkali and alkaline earth metal oxide-based adsorbents have attracted significant attention in the field of CO2 capture due to their good thermal stability, strong resistance to oxidative degradation, and low cost. This paper systematically reviews the research progress of the adsorbents from low-, medium-, to high-temperature regions in three parts: material synthesis, particle forming, and reactor application. In the material part, modification strategies such as alkali metal doping and defect engineering have proven highly effective in enhancing adsorption capacity. However, the sintering of active components and pore collapse during cycling remain the key bottlenecks limiting the material’s lifespan. There is an urgent need to overcome these challenges through structural optimization and synergistic design of multiple components. At the particle-forming part, methods such as tableting, extruding-rounding, spray drying, gel-droplet, and 3D printing each have their own applicable systems and limitations. There is no universal solution for the trade-off between mechanical strength, porosity, and adsorption capacity of binders. In the reactor part, fixed beds, fluidized beds, and moving beds respectively face differentiated deactivation mechanisms such as irreversible phase change, wear, and thermal sintering, which put forward targeted requirements for the mechanical properties of adsorbent particles. At present, challenges such as the independent design of materials, molding, and reactors, and insufficient research on the competitive adsorption of multiple components in real flue gas are prominent. In the future, it is necessary to strengthen multiscale collaborative optimization to promote these alkali and alkaline earth metal oxide-based adsorbents from the laboratory to industrial applications.