Teams develop CO₂ capture-conversion tandem system adaptable to a wide range of CO₂ concentrations

CO₂ concentrations vary widely depending on the source, ranging, for example, from about 0.04% in the atmosphere to about 10% in flue gases. Moreover, these gas streams contain a significant amount of O₂ (about 10%), a potent oxidizing agent. To achieve carbon neutrality, it is necessary to develop a robust process that can convert CO₂ over a wide concentration range, even in the presence of O₂. However, current technology does not offer a single unified approach that can efficiently handle CO₂ conversion from trace to high concentrations. To meet this challenge, researchers at Hokkaido University and collaborators developed a tandem CO₂ capture and conversion system free of precious metals that accommodates a wide range of CO₂ concentrations under oxygen-rich conditions. Their work is published in the journal Industrial Chemistry & Materials on June 13, 2025.

"We aim to develop a unified process capable of efficiently converting CO₂ and NO_x contained in combustion exhaust gases from thermal power plants and other sources into resources with high yields," explains Ken-ich Shimizu, a professor at Hokkaido University. Among various carbon capture, utilization, and storage (CCUS) strategies, integrated CO₂ capture and reduction (CCR) with hydrogen using dual-functional materials (DFMs) has recently gained attention as a promising approach for utilizing low-concentration CO₂ in O₂-rich conditions such as air or flue gases. However, this method remains unsuitable for treating high-concentration CO₂ streams exceeding 10%. This limitation stems from the inherent properties of conventional DFMs, which typically contain basic metal oxides such as CaO. Although these materials capture CO₂ via a bulk diffusion mechanism and exhibit substantial CO₂ uptake capacity, only the surface carbonates participate in the reaction, while the carbonates within the bulk remain largely inaccessible, thereby constraining the overall efficiency of CO₂ utilization. To overcome these challenges, the developed tandem configuration separates the two functions. The zeolite adsorbent allows for rapid CO₂ adsorption and complete desorption under controlled temperature changes. After desorption, the released CO₂ flows into a separate catalytic reactor where it reacts with H₂. Unlike conventional CCR designs, the strength of the tandem system design is its flexibility to independently optimize the active sites and reaction conditions for each step.

In evaluations using simulated flue gas (10% CO₂, 10% O₂), the Ni/CeO₂ catalyst achieved 92% CH₄ yield and over 99% selectivity at 300 °C, outperforming more than 100 conventional CCR systems that are intolerant to O₂. In parallel experiments, the Cu/ZnO/Al₂O₃ catalyst achieved 93% CO yield and an H₂/CO ratio of 3.7 at 650 °C, providing an H₂/CO ratio suitable for downstream syngas applications. The system was also evaluated in terms of direct air capture (DAC), producing CH₄ from atmospheric CO₂ (0.04%) with a maximum CH₄ concentration of 0.7% and an average CH₄ concentration of about 0.4%. The results show that 10 times the concentration of CH₄ is produced from atmospheric CO₂. From an efficiency perspective, the tandem system showed an energy efficiency (η) of 46% and a fuel production efficiency (FPE) of 83%, outperforming a comparable CCR system. The ability to operate continuously under normal pressure and high O₂ concentration conditions is a significant technical advantage.

The research team proposes that this platform can be expanded to methanol synthesis and LPG synthesis in the future by combining it with an FT catalyst or a methanol synthesis catalyst. The combination of a modular design and a simple thermal cycle is expected to be applicable not only to large point sources, namely fossil-fuel-fired power gasification plants, but also to small distributed sources such as home and office. “In the future, we plan to continue improving the system and extend its applicability to real exhaust gases, including other acid gases such as NO_x, as well as challenging conditions involving coexisting species like water vapor and SO₂,” said Shimizu.

The research team includes Shinta Miyazaki, Akihiko Anzai, Masaki Yoshihara, Hsu Sheng Feng, Takashi Toyao, and Ken-ichi Shimizu from Institute for Catalysis, Hokkaido University, and Shinya Mine from National Institute of Advanced Industrial Science and Technology.

This research is funded by the “Moonshot Research and Development Program” (JPNP18016), commissioned by the New Energy and Industrial Technology Development Organization (NEDO), KAKENHI (23K20034, and 21H04626) from the Japan Society for the Promotion of Science (JSPS), the Joint Usage/Research Center for Catalysis, and the Grant-in-Aid for JSPS Fellows (24KJ0267).

Industrial Chemistry & Materials is a peer-reviewed interdisciplinary academic journal published by Royal Society of Chemistry (RSC) with APCs currently waived. ICM publishes significant innovative research and major technological breakthroughs in all aspects of industrial chemistry and materials, especially the important innovation of the low-carbon chemical industry, energy, and functional materials. Check out the latest ICM news on the blog.