Youssef Belmabkhout , Renjith S. Pillai , Dalal Alezi , Osama Shekhah , Prashant M. Bhatt , Zhijie Chen , Karim Adil , Sebastien Vaesen , Guy De Weireld , Maolin Pang , Mikhail Suetin , Amy J. Cairns , Vera Solovyeva , Aleksander Shkurenko , Omar El Tall , Guillaume Maurin , Mohamed Eddaoudi
Structure/properties relationships for a series of isostructural (MOFs) with the soc topology were explored for various gas separation applications.
A cooperative experimental/modeling strategy was used to unveil the structure/gas separation performance relationship for a series of isostructural metal–organic frameworks (MOFs) with soc-topology (square-octahedral) hosting different extra-framework counter ions (NO 3 −, Cl − and Br −). In 3+-, Fe 3+-, Ga 3+- and the newly isolated Al( iii)-based isostructural soc-MOF were extensively studied and evaluated for the separation-based production of high-quality fuels ( i.e., CH 4, C 3H 8 and n-C 4H 10) and olefins. The structural/chemical fine-tuning of the soc-MOF platform promoted equilibrium-based selectivity toward C 2+ (C 2H 6, C 2H 4, C 3H 6 C 3H 8 and n-C 4H 10) and conferred the desired chemical stability toward H 2S. The noted dual chemical stability and gas/vapor selectivity, which have rarely been reported for equilibrium-based separation agents, are essential for the production of high-purity H 2, CH 4 and C 2+ fractions in high yields. Interestingly, the evaluated soc-MOF analogues exhibited high selectivity for C 2H 4, C 3H 6 and n-C 4H 10. In particular, the Fe, Ga and Al analogues presented relatively enhanced C 2+/CH 4 adsorption selectivities. Notably, the Ga and Al analogues were found to be technically preferable because their structural integrities and separation performances were maintained upon exposure to H 2S, indicating that these materials are highly tolerant to H 2S. Therefore, the Ga- soc-MOF was further examined for the selective adsorption of H 2S in the presence of CO 2- and CH 4-containing streams, such as refinery-off gases (ROG) and natural gas (NG). Grand canonical Monte Carlo (GCMC) simulations based on a specific force field describing the interactions between the guest molecules and the Ga sites supported and confirmed the considerably higher affinity of the Ga- soc-MOF for C 2+ (as exemplified by n-C 4H 10) than for CH 4. The careful selection of an appropriate metal for the trinuclear inorganic molecular building block (MBB), i.e., a Ga metal center, imbues the soc-MOF platform with the requisite hydrolytic stability, H 2S stability, and exceptional gas selectivity for ROG and NG upgrading. Finally, the soc-MOF was deployed as a continuous film on a porous support, and its gas permeation properties as a membrane were evaluated.