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Computational high-throughput screening was carried out to assess a large number of experimentally reported metal-organic frameworks (MOFs) and zeolites for their utility in hexane isomer separation. Through the work, we identified many MOFs and zeolites with high selectivity (SL+M > 10) for the group of n-hexane, 2-methylpentane, and 3-methylpentane (linear and monobranched isomers) versus 2,2-dimethylbutane and 2,3-dimethylbutane (dibranched isomers). This group of selective sorbents includes VICDOC (Fe2(BDP)3), a MOF with triangular pores that is known to exhibit high isomer selectivity and capacity. For three of these structures, the adsorption isotherms for a 10-component mixture of hexane and heptane isomers were calculated. Subsequent simulations of column breakthrough curves showed that the DEYVUA MOF exhibits a longer process cycle time than VICDOC MOF or MRE zeolite, which are previously reported, high-performing materials, illustrating the importance of capacity in designing MOFs for practical applications. Among the identified candidates, we synthesized and characterized a MOF in a new copper form with high predicted adsorbent capacity (qL+M > 1.2 mol/L) and moderately high selectivity (SL+M ≈ 10). Finally, we examined the role of pore shape in hexane isomer separations, especially of triangular-shaped pores. We show through the potential energy surface and three-dimensional siting analyses that linear alkanes do not populate the corners of narrow triangular channels and that structures with nontriangular pores can efficiently separate hexane isomers. Detailed thermodynamic analysis illustrates how differences in the free energy of adsorption contribute to shape-selective separation in nanoporous materials. [ABSTRACT FROM AUTHOR]

Efforts to computationally characterize large numbers of nanoporous materials often rely on databases of experimentally resolved crystal structures. The accuracy of experimental crystal structures used in such calculations has a significant impact on the reliability of the results. In this work, we report structures optimized using periodic density functional theory (DFT) for more than 800 experimentally synthesized metal-organic frameworks (MOFs). Many MOFs changed significantly upon structural optimization, particularly materials that were crystallographically resolved in their solvated form. For each MOF, we simulated the adsorption of CH4 and CO2 using grand canonical Monte Carlo both before and after DFT optimization. The DFT optimization has a large impact on simulated gas adsorption in some cases. For example, CO2 loading at 1 bar changed by more than 25% in over 25% of the MOFs we considered. [ABSTRACT FROM AUTHOR]

Experimentally refinedcrystal structures for metal–organicframeworks (MOFs) often include solvent molecules and partially occupiedor disordered atoms. This creates a major impediment to applying high-throughputcomputational screening to MOFs. To address this problem, we haveconstructed a database of MOF structures that are derived from experimentaldata but are immediately suitable for molecular simulations. The computation-ready,experimental (CoRE) MOF database contains over 4700 porous structureswith publically available atomic coordinates. Important physical andchemical properties including the surface area and pore dimensionsare reported for these structures. To demonstrate the utility of thedatabase, we performed grand canonical Monte Carlo simulations ofmethane adsorption on all structures in the CoRE MOF database. Weinvestigated the structural properties of the CoRE MOFs that governmethane storage capacity and found that these relationships agreewell with those derived recently from a large database of hypotheticalMOFs. [ABSTRACT FROM AUTHOR]

A metal–organic framework(MOF) with high volumetric deliverablecapacity for methane was synthesized after being identified by computationalscreening of 204 hypothetical MOF structures featuring (Zr6O4)(OH)4(CO2)ninorganicbuilding blocks. The predicted MOF (NU-800) has an fcutopology in which zirconium nodes are connected via ditopic1,4-benzenedipropynoic acid linkers. Based on our computer simulations,alkyne groups adjacent to the inorganic zirconium nodes provide moreefficient methane packing around the nodes at high pressures. Thehigh predicted gas uptake properties of this new MOF were confirmedby high-pressure isotherm measurements over a large temperature andpressure range. The measured methane deliverable capacity of NU-800between 65 and 5.8 bar is 167 cc(STP)/cc (0.215 g/g),the highest among zirconium-based MOFs. High-pressure uptake valuesof H2and CO2are also among the highest reported.These high gas uptake characteristics, along with the expected highlystable structure of NU-800, make it a promising materialfor gas storage applications. [ABSTRACT FROM AUTHOR]