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Herein the defect engineering is reported in zirconium 1,4‐dicarboxybenzene metal‐organic frameworks (UiO‐66) both inducing new adsorption sites and enhancing the adsorption affinity of indole adsorbates. The result shows that high adsorption energies for indole are obtained at the deprotonated μ3‐O, followed by unsaturated Zr‐cation sites in defective UiO‐66 structures. The key interactions are the hydrogen bonding between the hydrogen donor NH group of indole with the negative charge oxygen atom of the induced μ3‐O site and the dative covalent bond between the nitrogen atom of indole with the unsaturated Zr‐cation. For hydrogen bonding, the binding energies tend to increase with the increasing of defect concentrations and spread a broad range up to ≈−2.00 eV. It is also shown that the vibrational modes of indole molecules are influenced by their adsorption sites. Accordingly, the NH stretching modes of the adsorbed indole are redshifted ≈100–300 cm−1 compared to its counterpart in the isolated indole. The strongest redshift is obtained for indole adsorbed at the μ3‐O site with three missing linkers. The occupation of water at the active sites may enhance or diminish the adsorption affinity of indole relying on the hydrogen bonding mechanism. [ABSTRACT FROM AUTHOR]

In this work, we investigate the effects of water on the structural stability of Mn2(DSBDC) metal–organic framework (MOF) using DFT-based calculations. It has been found that the adsorption of multiple water molecules forming a hydrogen bond network around the Mn centers plays an important role in the decomposition process. Different effects contribute to the destabilization of the MOF: water molecules that directly coordinate to the open sites displayed by a part of the Mn centers can induce a significant shift in the charge distribution as indicated by the analysis of charge density differences and the Bader charges. This adsorption process leads to a slight elongation of the metal-linker bonds. The direct interaction with the Mn center is the most stable adsorption mode for water in Mn2(DSBDC). Once these adsorption sites at the Mn centers are fully occupied, additional water molecules start to bind via hydrogen bonds to the already present water molecules or, more importantly, to the linker molecules. This, in return, leads to a significant weakening of the Mn-linker bonds, thus allowing water insertion into the Mn-linker bonds with a barrier of only 0.16 eV, which is believed to initiate the decomposition of the Mn2(DSBDC) framework. Based on a kinetic Monte Carlo model, it can be shown that high temperatures can prevent the adsorption of water molecules around the Mn sites and thus slow down the MOF decomposition. [ABSTRACT FROM AUTHOR]

In this study, we have examined the adsorption properties of hydrogen on pristine Sc2C monolayers by DFT calculations. Based on these calculations, we have proposed a thermodynamic model to estimate the hydrogen storage capability within the typical ranges for the operating temperature and pressure. Our thermodynamic modeling has shown that the maximum uptake of usable hydrogen could reach up to 7.2 wt% under cryogenic conditions. When calculating the usable hydrogen uptake, we have taken into consideration that, under realistic operating conditions, not all hydrogen adsorbed on pristine Sc2C can be desorbed from the surface, as some surface–adsorbate interactions are too strong. On the other hand, the interaction between the usable hydrogen and Sc2C appears to be too weak to reach the targets for the year 2025 set by the US Department of Energy (5.5 wt% at operating temperatures between 233 K and 358 K and delivery pressures of up to 12 bar). According to the modeling results, one needs to decrease the temperature to 120 K to reach 5.5 wt% hydrogen uptake at 12 bar. The results obtained with the thermodynamic model have been confirmed with a kinetic Monte Carlo simulation, which has also been used to estimate the time scale of the hydrogen adsorption and desorption processes. In addition, we have also evaluated the changes in the electronic structure of the Sc2C monolayer upon adsorbing hydrogen. As the band gap of Sc2C changes significantly upon adsorbing H2, Sc2C may have more potential as a hydrogen detector instead of as a hydrogen storage material. [ABSTRACT FROM AUTHOR]

In this article, we describe a C/C++ program called SurfKin (Surface Kinetics) to construct microkinetic mechanisms for modeling gas-surface reactions. Thermodynamic properties of reaction species are estimated based on density functional theory calculations and statistical mechanics. Rate constants for elementary steps (including adsorption, desorption, and chemical reactions on surfaces) are calculated using the classical collision theory and transition state theory. Methane decomposition and water-gas shift reaction on Ni(111) surface were chosen as test cases to validate the code implementations. The good agreement with literature data suggests this is a powerful tool to facilitate the analysis of complex reactions on surfaces, and thus it helps to effectively construct detailed microkinetic mechanisms for such surface reactions. SurfKin also opens a possibility for designing nanoscale model catalysts. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

In this work, we investigate the effects of water on the structural stability of Mn 2 (DSBDC) metal-organic framework (MOF) using DFT-based calculations. It has been found that the adsorption of multiple water molecules forming a hydrogen bond network around the Mn centers plays an important role in the decomposition process. Different effects contribute to the destabilization of the MOF: water molecules that directly coordinate to the open sites displayed by a part of the Mn centers can induce a significant shift in the charge distribution as indicated by the analysis of charge density differences and the Bader charges. This adsorption process leads to a slight elongation of the metal-linker bonds. The direct interaction with the Mn center is the most stable adsorption mode for water in Mn 2 (DSBDC). Once these adsorption sites at the Mn centers are fully occupied, additional water molecules start to bind via hydrogen bonds to the already present water molecules or, more importantly, to the linker molecules. This, in return, leads to a significant weakening of the Mn-linker bonds, thus allowing water insertion into the Mn-linker bonds with a barrier of only 0.16 eV, which is believed to initiate the decomposition of the Mn 2 (DSBDC) framework. Based on a kinetic Monte Carlo model, it can be shown that high temperatures can prevent the adsorption of water molecules around the Mn sites and thus slow down the MOF decomposition.

In this study, we have examined the adsorption properties of hydrogen on pristine Sc 2 C monolayers by DFT calculations. Based on these calculations, we have proposed a thermodynamic model to estimate the hydrogen storage capability within the typical ranges for the operating temperature and pressure. Our thermodynamic modeling has shown that the maximum uptake of usable hydrogen could reach up to 7.2 wt% under cryogenic conditions. When calculating the usable hydrogen uptake, we have taken into consideration that, under realistic operating conditions, not all hydrogen adsorbed on pristine Sc 2 C can be desorbed from the surface, as some surface-adsorbate interactions are too strong. On the other hand, the interaction between the usable hydrogen and Sc 2 C appears to be too weak to reach the targets for the year 2025 set by the US Department of Energy (5.5 wt% at operating temperatures between 233 K and 358 K and delivery pressures of up to 12 bar). According to the modeling results, one needs to decrease the temperature to 120 K to reach 5.5 wt% hydrogen uptake at 12 bar. The results obtained with the thermodynamic model have been confirmed with a kinetic Monte Carlo simulation, which has also been used to estimate the time scale of the hydrogen adsorption and desorption processes. In addition, we have also evaluated the changes in the electronic structure of the Sc 2 C monolayer upon adsorbing hydrogen. As the band gap of Sc 2 C changes significantly upon adsorbing H 2 , Sc 2 C may have more potential as a hydrogen detector instead of as a hydrogen storage material.