CO₂ capture from wet flue gas using transition metal inserted porphyrin-based metal-organic frameworks as efficient adsorbents

CO₂ capture from large point sources is indispensable for achieving 1.5 degree target as long as fossil fuels are still in use. Selective adsorption of CO₂ from flue gas constitutes a promising CO₂ capture technology, thanks to the development of numerous fascinating solid adsorbents in the past three decades. However, very few adsorbents can retain their required performance in the presence of moisture which is unfortunately always the case in reality. In this study, we elevated the CO₂ adsorption and separation performance of a water-stable aluminum-based porphyrin metal-organic frameworks (Al-PMOF) by inserting transition metals as adsorption sites. Compared with the pristine Al-PMOF and other four transition metals (TMs) incorporated PMOFs (Al-PMOF(M)), the Co-inserted Al-PMOF (Al-PMOF(Co)) exhibited the highest CO₂ adsorption capacity (3.32 mmol/g) and highest CO₂/N₂ and CO₂/CH₄ selectivity (87 and 20, respectively) at 273 K and 1.0 bar. After three consecutive cyclic moisture treatments, the CO₂ adsorption capacity of Al-PMOF(Co) remained almost unchanged. More importantly, the dynamic binary CO₂/N₂ breakthrough adsorption of Al-PMOF(Co) exhibited negligible differences in CO₂ adsorption capacities between dry and wet flue gas conditions, suggesting that TMs incorporated Al-PMOF possess excellent moisture-resistant properties. Mechanistic studies using the combined in situ synchrotron infrared spectroscopic and powder X-ray diffraction together with density functional theory calculations unambiguously revealed the inserted metals are the dominant CO₂ adsorption sites. This study materializes the rational design of efficient adsorbents for CO₂ capture and contributes to mitigating climate change.