Stability of Adsorbents for Direct Air Capture (DAC): Challenges and Perspectives

Direct air capture (DAC) technologies, particularly adsorption-based systems, are advancing rapidly as a form of negative emission technologies (NETs). DAC technologies represent a promising engineering approach to addressing diffuse CO2 emissions and provide several deployment advantages, including flexibility and scalability. However, a critical yet often overlooked challenge of adsorption-based DAC is the limited stability of CO2 sorbent materials, which undermines sustainability and hinders large-scale deployment. While most research has focused on developing adsorbents with high CO2 selectivity and capacity, stability remains a crucial criterion, investigated in some studies through multi-cycle testing and exposure to accelerated degradation environments. This review provides a brief overview of DAC adsorbent types, followed by a detailed analysis of existing studies on the stability of solid sorbents under DAC operating conditions, highlighting key findings and research gaps. The thermal, oxidative, and hydro(thermal) stability of different adsorbents are discussed, along with the influence of operational variables on degradation mechanisms. Findings indicate that, while thermal degradation is generally not the primary concern at the moderate regeneration temperatures typical of DAC, oxidative degradation in the presence of oxygen can be severe, particularly for amine-based sorbents. Hydro(thermal) stability is found to depend largely on the properties of the support material. Ultimately, this review aims to guide the development of efficient and durable CO2 adsorbents, contributing to the design of more sustainable DAC systems.