New review outlines advances in dual-functional materials that combine atmospheric carbon removal with in-situ conversion

Atmospheric CO₂ concentrations reached 420 μmol/mol in 2022, escalating at 2.4 μmol/mol annually and driving urgent calls for carbon-negative solutions. While direct air capture (DAC) technology can remove CO₂ from ambient air, conventional systems require energy-intensive, separate processes for capture, desorption, compression, and transportation before utilization. This fragmentation dramatically increases costs and energy consumption, hindering large-scale deployment. Researchers from Shanghai Jiao Tong University and Queen's University Belfast examined how integrated direct air CO₂ capture and utilization (IDACU) could transform this paradigm by capturing and converting CO₂ in a single system.

This mini-review systematically analyzes IDACU technologies that employ dual-functional materials (DFMs) to adsorb atmospheric CO₂ and catalytically convert it into fuels and chemicals in-situ. The study categorizes three primary technical routes: solid-based DFMs via thermo-catalysis, liquid sorbent systems with thermo-catalysis, and emerging non-thermal conversion methods including photocatalysis and electrocatalysis. The review examines reaction mechanisms, material characteristics, and performance metrics for producing methane, methanol, formic acid, and carbon monoxide directly from air-captured CO₂. Special attention is given to distinguishing material requirements for IDACU versus conventional flue gas capture, given the ultra-low CO₂ concentration (≈400 μmol/mol) in ambient air.

Key technological breakthroughs highlighted in the review include:

1. Solid-Based DFMs: Novel unsupported NiCa-based materials achieved exceptional CO₂ capture capacity exceeding 7 mmol/g with over 95% conversion to methane at 450°C. These use Ca(OH)₂ sorbents that prevent CO₂ release during heating, addressing a critical limitation of supported systems. Supported Ru/Al₂O₃ systems demonstrated stable operation for 250+ hours under ambient conditions.
2. Liquid Sorbent Systems: Homogeneous catalytic systems using KOH solutions and Ru-PNP catalysts achieved 100% methanol yield from air-captured CO₂ under relatively mild conditions (140-155°C, 50 bar). Heterogeneous systems with non-noble Cu/ZnO/Al₂O₃ catalysts reached 90% CO₂ hydrogenation to methanol at 170-200°C.
3. Non-Thermal Routes: Photocatalytic systems using carbonate-type CuCoAl-layered double hydroxides enabled simultaneous CO₂ capture and conversion at 34-37°C, producing both reduction (CO) and oxidation products. Electrochemical systems at room temperature achieved formate production using enzyme-inspired catalysts.
4. Catalyst-Free Innovation: Hydroxide-based ionic liquids captured CO₂ as bicarbonates and converted it to cyclic carbonates with 100% selectivity under mild conditions (60°C), eliminating expensive metal catalysts.

IDACU technology represents a paradigm shift that could dramatically reduce the energy footprint of carbon removal by eliminating the most costly step—CO₂ desorption and compression. By integrating capture and conversion, these systems enable direct production of carbon-neutral fuels and chemicals while avoiding complex logistics. The review demonstrates that overcoming the challenge of ultra-dilute atmospheric CO₂ requires specialized materials with enhanced adsorption kinetics, tunable pore structures, and resistance to oxidation. While still in early development, IDACU shows particular promise for renewable energy storage and distributed fuel production. The technology could enable modular, on-site conversion of air-captured CO₂ into methane for heating, methanol for transport fuel, or formic acid for fuel cells, creating a closed carbon loop. Success hinges on developing robust, low-cost materials and optimizing system-level integration, but the review provides a clear roadmap for advancing this transformative approach toward climate mitigation and sustainable energy systems.

JOURNAL: ENGINEERING Energy (formerly Frontiers in Energy)

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Cite this article Zhang, Y., Feng, J., Li, L. et al. Integrated direct air CO₂ capture and utilization via in-situ catalytic conversion to fuels and chemicals using dual functional materials: Recent progresses and perspectives. Front. Energy 19, 586–598 (2025). https://doi.org/10.1007/s11708-025-0977-5

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