How Hydration Drastically Improves Adsorption Selectivity for CO₂ over CH₄ in the Flexible Chromium Terephthalate MIL‐53

Abstract

One of the technological problems that face society today is the environmentally friendly and economically feasible separation, recovery, and recovery/reuse of vapors and gases. Several examples are currently of interest: the selective recovery of solvents, the recovery of greenhouse gases, and the purification of hydrogen. Many processes include an adsorption step in which microporous adsorbents, such as activated carbon and zeolites, are used. Recently a new class of porous materials have found interest: these metal organic frameworks (MOFs) [1,2] or metal coordination polymers [3] are built up from inorganic subnetworks and organic complexing molecules (phosphonates, carboxylates, sulfonates). These subnetworks often contain divalent or trivalent cations connected by organic groups such as carboxylates. Such structures possess tunnels or cavities with pore sizes between 3 and 35 . Several of these organic-inorganic hybrid porous solids [4][5][6][7][8][9][10][11] have the interesting feature of being selectively flexible during the adsorption process by means of a breathing [12] or gate-opening process, [9] which depends on the nature of the adsorptive. Examples discovered by Ferey and coworkers include flexible porous carboxylates formed by chains of metallic centers (MIL-53, -69) [13,14] and with metalcenter trimers (MIL-88A).[15] These solids have shown to "breath" with unprecedented increases in volume between 50 and 85 % depending on the nature of the fluid. A consequence of this particular property is the possibility to develop novel selective separation and storage processes that could be less expensive than existing processes.In many adsorption processes since the presence of water is detrimental, it is often removed using a precolumn. In the [*] Dr.

Cu2(pzdc)2L [L=dipyridyl-based ligands] porous coordination polymers: Hysteretic adsorption and diffusion kinetics of CO2 and CH4

“…Many flexible MOFs exhibit an interesting gate-opening phenomenon where the framework structures suddenly changes from a relatively closed structure to an open one and due to guest-induced framework transition [44,[58][59][60][61]. Kitagawa Inspection of Fig.…”

Chemistry of coordination space of porous coordination polymers

“…The MIL-53 solids exhibit a large breathing phenomenon upon hydration and dehydration [92,133,146]. In addition, the MIL-53 shows an unusual step in the CO 2 adsorption isotherm which may be due to the presence of interactions between the CO 2 molecules and the OH groups [147]. A three-dimensional iron(III) fumarate framework MIL-88, Fe 3 3 OH, exhibits an exceptionally large swelling structural transformation, almost doubling its cell volume [148] (Fig.…”

Natural gas treating by selective adsorption: Material science and chemical engineering interplay

“…This phenomenon, usually named gate opening arises mainly from the flexibility of the networks. For instance, carbon dioxide and methane adsorptions on MIL-53 are strongly affected by the presence of water which causes drastic changes in the pore shapes [101,102]. • Very high adsorption capacities per mass unit due to very large micro-, mesoporous volumes.…”

“…3. Carbon dioxide adsorption isotherms measured at about 300 K for various MOFs and reference materials: Cu(dhbc)2(4,4 -bpy) [107], MIL-96 (Al) [108], MIL-102 [109], MIL-53 (Al) [98], MIL-53 (Cr) [101], HKUST-1 [110], HKUST-1 [111], Ni-STA-12 [99], MIL-53 (Al)-NH2 [112], MOF-508b [113], MIL-101c [114] and SWNTs [115].…”