The adsorption and the thermal desorption of hydrogen in as-made and surface-modified silicalite-1 (MFI) loose crystals has been studied to shed light on the relation between the outer surface ...barrier and the transport of mass through it. The four different surface modifications can be probed by the change in the contact angle of water, but do not produce any apparent change in the morphology and the structure of the crystals. The H2 adsorption isotherms in a Sievert's-type apparatus at 77 K and up to 8 MPa on the pristine and the modified silicalite-1 samples are almost overlapping, showing that the modifications involve the external surface of the samples. However the diffusion coefficients of H2, as derived from the sorption kinetics, evidence different sorption rates of H2 into the different silicalite-1 samples. In particular the unmodified silicalite-1 sample presents the lowest diffusion coefficient and yields the highest H2 desorption temperature in Thermal Desorption Spectra acquired at 0.03 K/s. The observed phenomena have been attributed to the surface silanols on the outer surface of the as-made silicalite-1 crystals, which are either eliminated or greatly reduced in number by the modifying agents. Polar and hydrophilic silanol groups bind frozen water molecules on the outer surface of as-made crystals which hinder the diffusion of hydrogen, and interact more strongly with the H2 molecules. This provides sorption sites with higher potential energy barriers, and at the same time physically obstructs the pore entrances of the molecular sieve. The surface modification of porous fillers is of interest for the manufacture of mixed matrix membranes, for the improvement of the performance of pressure swing adsorption processes, and for gas storage applications.
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•A surface barrier for the transport of H2 at 77 K is evidenced on silicalite-1.•Surface modification of MFI crystals speeds up H2 sorption and desorption.•Surface silanols trap moisture and enhance the surface barrier.•Pore obstruction and stronger sorption may explain the enhancement of the barrier.•Surface modification can tailor the transport properties of fillers and adsorbents.
The present work aims at providing additional insight into the crucial effect of pore size and pressure on the adsorption of H
2
and D
2
in porous carbons by means of Grand Canonical Monte Carlo ...simulations in model slit micropores at 77 K. In order to address the quantum behavior of the molecules the Feynman–Hibbs corrected LJ interaction potential is used for fluid–solid and fluid–fluid interactions. Based on the GCMC isotherms for the two isotopes, D
2
selectivity over H
2
is deduced for pores with different sizes as a function of pressure. Furthermore, GCMC results are coupled with experimental high pressure H
2
and D
2
adsorption data at 77 K for a commercial carbon molecular sieve (Takeda 3A).
The purpose of this research was to obtain porous, high‐quality cathodes for solid oxide fuel cells in both planar and tubular shapes. To accomplish this, cathodic electrophoretic deposition of the ...LaMnO3 powder (synthesized by the modified sol–gel method proposed by Pechini) was performed. The optimal sintering temperatures were 1200°C and 1300°C for the tubular and planar configurations, respectively. Single‐phase deposits with about 40% porosity were obtained in both configurations. The cathode quality was confirmed by depositing an electrolyte layer of YSZ. After the cosintering of both layers, an extremely dense electrolyte layer was obtained, and the cathode layer retained its high porosity.
A highly porous member of isoreticular MFU‐4‐type frameworks, Zn5Cl4(BTDD)3 (MFU‐4l(arge)) (H2‐BTDD=bis(1H‐1,2,3‐triazolo4,5‐b,4′,5′‐i)dibenzo1,4dioxin), has been synthesized using ZnCl2 and H2‐BTDD ...in N,N‐dimethylformamide as a solvent. MFU‐4l represents the first example of MFU‐4‐type frameworks featuring large pore apertures of 9.1 Å. Here, MFU‐4l serves as a reference compound to evaluate the origin of unique and specific gas‐sorption properties of MFU‐4, reported previously. The latter framework features narrow‐sized pores of 2.5 Å that allow passage of sufficiently small molecules only (such as hydrogen or water), whereas molecules with larger kinetic diameters (e.g., argon or nitrogen) are excluded from uptake. The crystal structure of MFU‐4l has been solved ab initio by direct methods from 3D electron‐diffraction data acquired from a single nanosized crystal through automated electron diffraction tomography (ADT) in combination with electron‐beam precession. Independently, it has been solved using powder X‐ray diffraction. Thermogravimetric analysis (TGA) and variable‐temperature X‐ray powder diffraction (XRPD) experiments carried out on MFU‐4l indicate that it is stable up to 500 °C (N2 atmosphere) and up to 350 °C in air. The framework adsorbs 4 wt % hydrogen at 20 bar and 77 K, which is twice the amount compared to MFU‐4. The isosteric heat of adsorption starts for low surface coverage at 5 kJ mol−1 and decreases to 3.5 kJ mol−1 at higher H2 uptake. In contrast, MFU‐4 possesses a nearly constant isosteric heat of adsorption of ca. 7 kJ mol−1 over a wide range of surface coverage. Moreover, MFU‐4 exhibits a H2 desorption maximum at 71 K, which is the highest temperature ever measured for hydrogen physisorbed on metal–organic frameworks (MOFs).
Future framework: An MFU‐4‐type framework, MFU‐4l, which possesses large pores, has been synthesized and characterized (see scheme). Hydrogen adsorption/desorption experiments show that MFU‐4 can be used for the development of materials for hydrogen storage, whereas MFU‐4l is a promising framework for future catalytic applications.
Successive filling of different adsorption sites in Cu-BTC by partical loading with deuterium.
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► For the first time D
2 desorption from Cu–BTC is investigated by TDS. ► The desorption ...maxima are assigned to three different sites in the Cu–BTC structure. ► Different maxima are separated by partial loading or interrupted desorption. ► By calibration the amount of deuterium adsorbed in Cu–BTC is determined.
Hydrogen and deuterium adsorption sites in the crystalline MOF copper(II) benzene-1,3,5-tricarboxylate, Cu–BTC were studied by low-temperature thermal desorption spectroscopy. For a maximum loading of 218 D
2 molecules per unit cell of Cu–BTC three desorption maxima were observed. The maxima could be separated by either interrupted desorption or partial loading. By comparing to neutron diffraction studies from the literature the maxima could be assigned to three different adsorption sites, i.e. coordinatively-unsaturated Cu
2+ sites, tetrahedral side pockets and the large pores.
The critical effect of confinement on the interaction of hydrogen isotopes (H2 and D2) with carbon surfaces was investigated through a combined low temperature adsorption/thermal desorption ...spectroscopy (TDS) study on three carbon molecular sieves (CMS) possessing nanopores with nominal sizes between 0.3 and 0.5nm. The porous structure and the sorption properties of all three adsorbents were characterized by N2 (77K) and CO2 (273K), as well as H2 and D2 (77K) low pressure (up to 1bar) adsorption measurements. The interaction of the carbons with hydrogen, deuterium, and an isotopic H2/D2 gas mixture was further studied by means of TDS measurements, extended to temperatures down to 20K. The differences in the H2/D2 adsorption/desorption profiles of the three CMS samples are correlated with the respective micropore size distributions. The presence of very narrow micropores, with size close to the kinetic diameter of the hydrogen molecule, resulted in enhanced hydrogen (both for H2 and D2) interactions, giving rise to a TDS maximum centered on 122K, the highest desorption temperature ever measured for the desorption of physisorbed hydrogen. Furthermore, the quantum effects on hydrogen/deuterium adsorption on CMS adsorbents have been addressed for the first time using the TDS technique.
Hence economic growth requires more and more investments in the harbor area, especially nearby waterfront structures, a special attention must be taken into account regarding proper infrastructure ...design for structures with high vertical loads. At the same time, we have to consider the good behavior of the new design structures and also their impact on the existing nearby waterfront infrastructure. Being adjacent to waterfront structures and due to the limited available space, these structures are typically tall and narrow, and exert average soil pressures on the order of 300KPa. These loads can only be accommodated by ground with an adequate bearing capacity. This publication presents case studies of waterfront projects like grain silos storage facility. Available results for the certification and monitoring of the works are also presented, as well as other considerations based on the author’s experience.
The use of composite systems in protecting, preserving and maintaining historical monuments has become more and more used. There are several consolidation procedures with fiber-reinforced polymeric ...polymers that can be applied as required or on the basis of the basic material (concrete, masonry, wood, etc.). Besides the many advantages it provides, the application of composite systems in the rehabilitation of heritage buildings and historical monuments requires minimal workmanship. More and more cities are actively involved in the rehabilitation and preservation of heritage buildings and historical monuments by launching good practice guides to preserve local cultural heritage by applying composite elements as robust as possible without the need to modify the overall dimensions of the buildings through a classic covering.
The hydrogen adsorption and desorption properties of a microporous metal–organic framework, magnesium formate, are investigated. The material has channel‐like pores of approximately 3.4 Å diameter. ...The pore size is below the kinetic diameter of nitrogen and causes a breakdown of the linear relationship between maximum hydrogen uptake and specific surface area measured by nitrogen adsorption. From the experimental isotherms the isosteric heat of adsorption for hydrogen is calculated with very high accuracy over a wide range of surface coverage, up to 80 %. The isosteric heat of adsorption is 6.5–7 kJ mol−1 which is one of the highest values ever observed over the whole range of surface coverage.
Hot MOF′ins: Hydrogen adsorption in a newly developed metal–organic framework, magnesium formate, with very small channel‐like pores is investigated. From the experimental isotherms the isosteric heat of adsorption is calculated, which is one of the highest observed so far for metal–organic frameworks. This makes the material suitable for hydrogen storage applications.
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