Application of metal–organic frameworks with coordinatively unsaturated metal sites in storage and separation of methane and carbon dioxide

Dıetzel, Pascal D. C.; Besikiotis, Vasileios; Blom, Richard

doi:10.1039/b911242a

Cited by 652 publications

(585 citation statements)

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“…In our simulation we assumed a perfect crystalline material in which every Mg atom was activated-as all Mg atoms are equivalent, one would expect this inflection to occur at exactly one CO 2 molecule per Mg. These observations support the conclusion of Dietzel et al 10 , according to which, not all Mg sites are accessible in the real system. Our simulations, in agreement with the experimental data of both Dietzel et al 10 and Simmons et al 25 , showed an increase in the heat of adsorption as a function of the loading.…”

Section: Resultssupporting

confidence: 82%

“…The separation of flue gas, however, requires thermodynamic information (for example, adsorption isotherms) at flue-gas conditions (40 8C and 1 atm). This type of information can be obtained from molecular simulation using classical force fields.For some classes of MOFs these predictions still pose significant difficulties, namely for MOFs with unsaturated-referred to as 'open'-metal sites [8][9][10][11][12][13][14][15] . These materials crystallize in such a way that both linkers and solvent molecules coordinate to the metal centres.…”

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confidence: 99%

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Ab initio carbon capture in open-site metal–organic frameworks

et al. 2012

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During the formation of metal-organic frameworks (MOFs), metal centres can coordinate with the intended organic linkers, but also with solvent molecules. In this case, subsequent activation by removal of the solvent molecules creates unsaturated 'open' metal sites known to have a strong affinity for CO 2 molecules, but their interactions are still poorly understood. Common force fields typically underestimate by as much as two orders of magnitude the adsorption of CO 2 in open-site Mg-MOF-74, which has emerged as a promising MOF for CO 2 capture. Here we present a systematic procedure to generate force fields using high-level quantum chemical calculations. Monte Carlo simulations based on an ab initio force field generated for CO 2 in Mg-MOF-74 shed some light on the interpretation of thermodynamic data from flue gas in this material. The force field describes accurately the chemistry of the open metal sites, and is transferable to other structures. This approach may serve in molecular simulations in general and in the study of fluid-solid interactions. Most energy scenarios project a significant increase in the role of renewable energy sources 1 . These scenarios also predict an even higher increase in our energy needs. As a consequence, although the relative consumption of fossil fuels will be decreasing, in absolute terms we will continue to burn more coal. In such a scenario, carbon capture and sequestration will be one of the only viable technologies to mitigate CO 2 emissions 1,2 . At present the cost associated with the capture of CO 2 from flue gas is one of the bottlenecks in the large-scale deployment of this technology. Of particular concern is that the efficiency of a coal-fired power plant decreases by as much as 30-40% (ref. 3) because of the energy required to separate and compress CO 2 . The aim of decreasing this parasitic load has motivated the search for novel materials 4,5 .A promising class of materials is metal-organic frameworks (MOFs) 4,6 . MOFs are crystalline materials that consist of metal centres connected by organic linkers. These materials have an extremely large internal surface area and, compared to other common adsorbents, promise very specific customization of their chemistry. By changing the metal and the linker, one can in principle generate many millions of possible materials. In practice, however, we can synthesize only a very small fraction of these materials, and it is important to develop a theoretical method that supports the experimental efforts to identify an ideal MOF for carbon capture. A key aspect is the ability to predict the properties of a MOF before the material is synthesized. At present it is possible to carry out accurate quantum chemical calculations on these types of systems 7 . State-of-the-art density functional theory (DFT) calculations provide important insights into the energetics and siting of CO 2 at zero Kelvin 7 . The separation of flue gas, however, requires thermodynamic information (for example, adsorption isotherms) at flue-gas conditions (40...

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Section: Resultssupporting

confidence: 82%

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Ab initio carbon capture in open-site metal–organic frameworks

et al. 2012

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“…2,49−52 Among these, Dietzel et al 49 and Britt et al 50 employ the most "direct" method to obtain the heat of adsorption from measured CO 2 adsorption isotherms, without making assumption on the functional form of the isotherm. They report 42 kJ/mol, 49 for a nearly fully loaded MOF (around 1CO 2 :1Mg), and 39 kJ/mol 50 for the infinite dilution limit, respectively. However, at low CO 2 loading (around Table 2 reports the computed enthalpy of adsorption obtained by applying the PBE ZPE+TE for both Mg-MO74 and Ca-BTT.…”

Section: Mg-mof74mentioning

confidence: 99%

CO₂ Capture by Metal–Organic Frameworks with van der Waals Density Functionals

2012

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We use density functional theory calculations with van der Waals corrections to study the role of dispersive interactions on the structure and binding of CO 2 within two distinct metal−organic frameworks (MOFs): Mg-MOF74 and Ca-BTT. For both classes of MOFs, we report calculations with standard gradient-corrected (PBE) and five van der Waals density functionals (vdW-DFs), also comparing with semiempirical pairwise corrections. The vdW-DFs explored here yield a large spread in CO 2 −MOF binding energies, about 50% (around 20 kJ/ mol), depending on the choice of exchange functional, which is significantly larger than our computed zero-point energies and thermal contributions (around 5 kJ/mol). However, two specific vdW-DFs result in excellent agreement with experiments within a few kilojoules per mole, at a reduced computational cost compared to quantum chemistry or many-body approaches. For Mg-MOF74, PBE underestimates adsorption enthalpies by about 50%, but enthalpies computed with vdW-DF, PBE+D2, and vdW-DF2 (40.5, 38.5, and 37.4 kJ/mol, respectively) compare extremely well with the experimental value of 40 kJ/mol. vdW-DF and vdW-DF2 CO 2 −MOF bond lengths are in the best agreement with experiments, while vdW-C09 x results in the best agreement with lattice parameters. On the basis of the similar behavior of the reduced density gradients around CO 2 for the two MOFs studied, comparable results can be expected for CO 2 adsorption in BTT-type MOFs. Our work demonstrates for this broad class of molecular adsorbate-periodic MOF systems that parameter-free and computationally efficient vdW-DF and vdW-DF2 approaches can predict adsorption enthalpies with chemical accuracy. ■ INTRODUCTIONMetal−organic frameworks (MOFs) are a broad class of threedimensional nanoporous materials that have attracted much attention during the past decade for CO 2 capture from flue gas. 1−6 MOFs consist of metal centers joined by organic molecular "linkers"; there are many possibilities for cation/ linker combinations, and thousands of different MOFs have already been synthesized. 3,5 Understanding mechanisms for CO 2 binding within these frameworks is a fundamental step toward the design of new materials for carbon capture.In order to explore and predict new materials that efficiently capture CO 2 , an accurate quantitative description of both its adsorption energy and geometry is needed. Whereas quantum chemistry methods, such as HF/MP2 or CCSD(T), scale unfavorably with the number of basis functions (N 5 and N 7 ) and are primarily restricted to cluster calculations, density functional theory (DFT) is a very promising framework for studying the mechanism of interaction between CO 2 and extended MOFs. Although DFT is a many-particle framework that includes, in principle, fully nonlocal interactions, its common approximations, such as the local density approximation (LDA) and the generalized gradient approximation (GGA), neglect attractive long-range contributions to van der Waals interactions, so-called London dispersion intera...

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“…The regeneration energy cost to utilize these porous materials for CO 2 capture by the implementation of temperature swing adsorption, pressure swing adsorption (PSA) and vacuum swing adsorption is significantly lower than the abovementioned alkanolamine technology. More importantly, the rapid development over the past decade in this research field to target some porous MOFs for their extremely high uptake of CO 2 at high pressure 11,12 and to immobilize functional sites, such as open metal sites [13][14][15][16][17][18][19][20][21][22][23] , -NH 2 and -OH organic sites into the pore surfaces to enhance their interactions and thus enforce their efficient CO 2 separation selectivity have principally ensured the feasibility of porous MOFs for CO 2 capture [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] .…”

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confidence: 99%