A Predictive Model of Hydrogen Sorption for Metal−Organic Materials

Belof, Jonathan L.; Stern, Abraham C.; Space, Brian

doi:10.1021/jp901988e

Cited by 43 publications

(84 citation statements)

References 34 publications

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“…[52] Very recently, a more sophisticated hydrogen potential model was employed in GCMC simulations, together with UFF parameters and partial charges. [53] The resulting isotherms were in excellent agreement with experimental data, eliminating the slight underestimation of the loading at low pressures that is observed in the present study. In con-trast to this, the employment of a complete set of ab-initio derived FF parameters led to a significant underestimation of the hydrogen uptake at high pressures.…”

Section: Irmof-1supporting

confidence: 88%

Preferred Hydrogen Adsorption Sites in Various MOFs—A Comparative Computational Study

2009

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Force-field based grand-canonical Monte Carlo simulations are employed to predict the hydrogen adsorption properties of seven structurally different MOFs. The performance of different parameter sets is assessed by comparison with experimental data, and the capabilities and limitations of the methodology are critically discussed, with a particular emphasis on systems with unsaturated metal sites. In addition to adsorption isotherms and isosteric heats of adsorption, the preferred adsorption sites are obtained from a detailed analysis of the calculated hydrogen density fields. Where possible, these positions are compared to the results of neutron diffraction experiments. This study highlights the capabilities of computational methods to identify the structural features which are most favourable for hydrogen adsorption, providing valuable implications for the synthesis of novel MOFs.

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Section: Irmof-1supporting

confidence: 88%

Preferred Hydrogen Adsorption Sites in Various MOFs—A Comparative Computational Study

2009

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“…The development of the force field for In-soc-MOF was performed according to the procedure described in previous work. 12,24,25,[29][30][31][32][33][34][35][36][37][38][39][40][41] Nevertheless, a brief outline is given here. For all C, H, and N atoms on the organic linker in In-soc-MOF, the Lennard-Jones 12-6 parameters, representing van der Waals interactions between the sorbate molecules and the MOF atoms, were acquired from the Optimized Potentials for Liquid Simulations -All Atom (OPLS-AA) force field.…”

Section: A Mof Parametersmentioning

confidence: 99%

Understanding Hydrogen Sorption in In-soc-MOF: A Charged Metal-Organic Framework with Open-Metal Sites, Narrow Channels, and Counterions

Pham

Forrest

Hogan

et al. 2015

Crystal Growth & Design

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Grand canonical Monte Carlo (GCMC) simulations of hydrogen sorption were performed in In-soc-MOF, a charged metal-organic framework (MOF) that contains In3O trimers coordinated to 5,5 -azobis-1,3-benzenedicarboxylate linkers. The MOF contains nitrate counterions that are located in carcerand-like capsules of the framework. This MOF was shown to have a high hydrogen uptake at 77 K and 1.0 atm. The simulations were performed with a potential that includes explicit many-body polarization interactions, which were important for modeling gas sorption in a charged/polar MOF such as In-soc-MOF. The simulated hydrogen sorption isotherms were in good agreement with experiment in this challenging platform for modeling. The simulations predict a high initial isosteric heat of adsorption, Qst, value of about 8.5 kJ mol −1 , which is in contrast to the experimental value of 6.5 kJ mol −1 for all loadings. The difference in the Qst behavior between experiment and simulation is attributed to the fact that, in experimental measurements, the sorbate molecules cannot access the isolated cages containing the nitrate ions, the most energetically favorable site in the MOF, at low pressures due to an observed diffusional barrier. In contrast, the simulations were able to capture the sorption of hydrogen onto the nitrate ions at low loading due to the equilibrium nature of GCMC simulations. The experimental Qst values were reproduced in simulation by blocking access to all of the nitrate ions in the MOF. Furthermore, at 77 K, the sorbed hydrogen molecules were reminiscent of a dense fluid in In-soc-MOF starting at approximately 5.0 atm, and this was verified by monitoring the isothermal compressibility, βT , values. The favorable sites for hydrogen sorption were identified from the polarization distribution as the nitrate ions, the In3O trimers, and the azobenzene nitrogen atoms. Lastly, the two-dimensional quantum rotational levels for a hydrogen molecule sorbed about the aforementioned sites were calculated and the transitions were in good agreement to those that were observed in the experimental inelastic neutron scattering (INS) spectra.

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“…These results were found to be consistent with theoretical calculations. 34,35 Liquid densities were also recently observed for supercritical methane and carbon dioxide sorbed in HKUST-1 using the same approach. 36 In this context, it can be assumed that the onset of a regime where constant r a and v a values are observed (in the linearly decreasing regime of n ex vs. r g ) effectively indicates P s .…”

Section: Saturation With a Supercritical Adsorbed Phasementioning

confidence: 74%

Saturation properties of a supercritical gas sorbed in nanoporous materials

Poirier¹,

Dailly

2012

Phys. Chem. Chem. Phys.

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The description of experimental gas adsorption data in terms of an accurate model is key to understand the adsorption mechanism and its limits. As a basic feature such a model should predict correctly the conditions under which saturation occurs. However, in the absence of bulk condensation properties for a supercritical adsorbate this matter remains open to discussions. In this study, the decreasing region of excess hydrogen adsorption isotherms measured down to 50 K is used to determine the adsorbed phase volume, density and pressure corresponding to saturation. The experimental method developed for these key measurements addresses the challenges of very low temperature adsorption measurements at high pressure. Therefore, the modifications specially made to a cryostat used in conjunction with a Sievert apparatus to reach high temperature stability (±10 mK) down to 40 K are presented. The approach is implemented on the novel nanoporous materials UMCM-1 and NOTT-112 over 50-77 K and 0-40 bar. The derived hydrogen saturation properties are found to be consistent with a Dubinin-Astakhov model. Importantly, the measured adsorbed hydrogen phase volume also compares well with the pore volume obtained from Ar porosimetry. The found saturation properties provide a physical basis to calculate consistent absolute adsorption isotherms and enthalpies, and to project the ultimate adsorption capacity of a conceptual material with a maximized specific surface area. The present findings provide additional evidence that the common view on supercritical adsorption, in which it is assumed that no liquid is formed and that the only possible mechanism involves monolayer coverage, does not hold in many nanoporous materials.

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A Predictive Model of Hydrogen Sorption for Metal−Organic Materials

Cited by 43 publications

References 34 publications

Preferred Hydrogen Adsorption Sites in Various MOFs—A Comparative Computational Study

Preferred Hydrogen Adsorption Sites in Various MOFs—A Comparative Computational Study

Understanding Hydrogen Sorption in In-soc-MOF: A Charged Metal-Organic Framework with Open-Metal Sites, Narrow Channels, and Counterions

Saturation properties of a supercritical gas sorbed in nanoporous materials

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