日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

It is crucial to develop CO₂ recovery and utilization methods toward the realization of carbon neutrality by 2050. The physisorption process using porous materials is one of the CO₂ recovery processes expected from the viewpoint of energy cost and operationality. Microporous materials, such as zeolites and metal-organic frameworks (MOFs), have attracted attention as CO₂ adsorbents due to their high adsorption capacity and separation selectivity. MOFs with structural flexibility, called flexible MOFs, exhibit gate-type adsorption performance, which results in a stepwise change in the amount of CO₂ adsorbed at specific pressures. This adsorption performance can obtain a large working capacity in the narrow pressure range compared to adsorbents showing type-I adsorption isotherms. Meanwhile, nowadays it has been obvious that zeolites exhibit the stepwise adsorption isotherms derived from gate-type adsorption. In addition, it is expected to develop the energy-saving CO₂ recovery process using zeolites. Our study clarified that Cs⁺-type PHI zeolite showed gate-type adsorption performance for CO₂. This paper describes the unique adsorption mechanisms and the control of the CO₂ adsorption behavior using the composition of heterogeneous zeolite frameworks.