Hofmann-type metal-organic frameworks with dual open nickel centers for efficient capture of CO2 from CH4 and N2

The capture of CO 2 from flue gas or natural gas plays a significant role in mitigating global warming and improving the energy level of natural gas. However, it is still challenging to design energy-efficient adsorbents that combine high uptake and selectivity. Herein, two Hofmann-type MOFs, Co(Pyz)[Ni(CN) 4 ] and Ni(Pyz)[Ni(CN) 4 ] (termed CoNi-Pyz and NiNi-Pyz ), are used to capture and separate CO 2 . Due to the difference in nodal metals, NiNi-Pyz shows a smaller pore size than CoNi-Pyz . This subtle difference resulted in higher volumetric uptake of CO 2 and higher selectivity of CO 2 /N 2 and CO 2 /CH 4 . Molecular simulations reveal a closer binding interaction of CO 2 with NiNi-Pyz . Finally, the dynamic breakthrough experiment verified that NiNi-Pyz enables the effective separation of binary mixtures of CO 2 /N 2 (v/v ​= ​15/85) and CO 2 /CH 4 (v/v ​= ​50/50). Capture and separation of CO 2 is achieved in Hofmann-type MOFs with open metal sites. The high CO 2 uptake and selectivity make it a potential high-performance physical adsorbent. • A Hofmann-type MOF NiNi-Pyz shows a CO 2 volumetric uptake of 92.5 ​cm 3 ​cm −3 at 298 ​K and 1 ​bar. • The high CO 2 /N 2 uptake ratio (17.8) and selectivity (60.3) of NiNi-Pyz at 298 ​K and 1 ​bar make it a potential high-performance physical adsorbent. • The dynamic breakthrough tests show that NiNi-Pyz can effectively separate binary mixtures of CO 2 /N 2 and CO 2 /CH 4 with separation rates of 33 and 2.5, respectively.