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129Xe NMR Spectroscopy

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John A. Ripmeester – One of the best experts on this subject based on the ideXlab platform.

  • A New Approach to Characterizing Sorption in Materials with Flexible Micropores
    Chemistry of Materials, 2008
    Co-Authors: Roberto Anedda, Dmitriy V. Soldatov, Igor L. Moudrakovski, Mariano Casu, John A. Ripmeester
    Abstract:

    Microporous dipeptides, also known as organic zeolites or biozeolites, as examples of small-pore peptide nanotubes provide a convenient set of materials for developing a systematic approach based on 129Xe NMR Spectroscopy for the derivation of thermodynamic and molecular scale information on temperature dependent pore filling. The sorption of xenon in the isolated 1D chiral nanochannels of eight microporous dipeptides Ala-Val (AV), Val-Ala (VA), Leu-Ser (LS), Ala-Ile (AI), Val-Val (VV), Ile-Ala (IA), Ile-Val (IV), Val-Ile (VI) (all LL isomers) was monitored in situ with continuous-flow 129Xe NMR Spectroscopy over a temperature range of 173−343 K. The materials all showed strongly anisotropic signals, with isotropic chemical shift changing from 95 to 281 ppm depending on the dipeptide used and/or temperature. The isosteric heats of sorption (qst) and entropy factors were determined from two independent models. The sorption process was complicated by reversible phase transformations of some dipeptides and i…

  • Distribution of Gallium Nanocrystals in Ga/MCM-41 Mesocomposites by Continuous-Flow Hyperpolarized 129Xe NMR Spectroscopy
    Analytical chemistry, 2005
    Co-Authors: Weiping Zhang, Christopher I. Ratcliffe, Igor L. Moudrakovski, Chung-yuan Mou, John A. Ripmeester
    Abstract:

    The distribution of gallium nanocrystals in mesoporous MCM-41 host were analyzed by continuous-flow hyperpolarized 129Xe NMR Spectroscopy. In contrast to unclear TEM images for the high metal contents, laser-polarized 129Xe probe can detect the whole distribution of gallium in the MCM-41 host. It is found that gallium nanocrystals are included in the mesochannels of MCM-41; a part of them also remains in the interparticle voids. The distribution of gallium metal in MCM-41 is heterogeneous. Not all the mesochannels host metallic gallium even at a high gallium loading of 65.1 wt %. Variable temperature measurements can provide information on the xenon adsorption parameters. This approach opens a sensitive way to probe the distribution of high content species in porous host materials.

  • Probing the Alkyl Ligands on Silylated Mesoporous MCM-41 Using Hyperpolarized 129Xe NMR Spectroscopy
    The journal of physical chemistry. B, 2005
    Co-Authors: Shing-jong Huang, John A. Ripmeester, Chin-hui Huang, Wen-hua Chen, Xianping Sun, Xizhi Zeng, Huang-kuei Lee, Chuan-yuan Mou, Shang-bin Liu
    Abstract:

    Variable-temperature hyperpolarized (HP) Xe-129 NMR Spectroscopy has been employed to characterize surface properties of mesoporous MCM-41 modified by silylation treatment. The characteristic chemical shifts responsible for Xe-surface interactions exhibit strong correlations with both the surface coverage and chain length of the grafted alkylsilanes. Consequently, the deshielding medium contribution due to individual alkyl ligand can be deduced based on the group contribution analysis revealing the potential use of HP Xe-129 NMR for probing the surface properties of organic-functionalized porous materials.

Stefan Kaskel – One of the best experts on this subject based on the ideXlab platform.

  • The impact of defects and crystal size on negative gas adsorption in DUT-49 analyzed by in situ 129Xe NMR Spectroscopy.
    , 2020
    Co-Authors: Simon Krause, Stefan Kaskel, Irena Senkovska, Volodymyr Bon, Florian Reuter, Sebastian Ehrling, Eike Brunner
    Abstract:

    The origin of crystal size-dependent adsorption behavior of flexible metal-organic frameworks is increasingly studied. In this contribution, we probe the solid-fluid interactions of DUT-49 crystals of different size by in situ 129Xe NMR Spectroscopy at 200 K. With decreasing size of the crystals, the average solid-fluid interactions are found to decrease reflected by a decrease in chemical shift of adsorbed xenon from 230 to 200 ppm explaining the lack of adsorption-induced transitions for smaller crystals. However, recent studies propose that these results can also originate from the presence of lattice defects. To investigate the influence of defects on the adsorption behavior of DUT-49 we synthesized a series of samples with tailored defect concentrations and characterized them by in situ 129Xe NMR. In comparison to the results obtained for crystals with different size we find pronounced changes of the adsorption behavior and influence of the chemical shift only for very high concentrations of defects, which further emphasizes the important role of particle size phenomena.

  • In Situ Monitoring of Unique Switching Transitions in the Pressure-Amplifying Flexible Framework Material DUT-49 by High-Pressure 129Xe NMR Spectroscopy
    The Journal of Physical Chemistry C, 2017
    Co-Authors: Jana Schaber, Stefan Kaskel, Irena Senkovska, Silvia Paasch, Simon Krause, Volodymyr Bon, Daniel M. Többens, Dirk Wallacher, Eike Brunner
    Abstract:

    The pronounced flexibility of special metal–organic frameworks (MOFs), so-called soft porous crystals, is attracting increasing research interest. Studies of host–guest interactions in such materials are especially powerful if the measurements are performed in situ. 129Xe NMR Spectroscopy is favorable because it provides characteristic, structure-sensitive parameters such as chemical shifts. The combination of high-pressure xenon adsorption with 129Xe NMR Spectroscopy was used to elucidate the adsorption-induced phase transitions in the recently discovered pressure-amplifying framework material DUT-49, showing a unique negative gas adsorption (NGA) transition. In the open-pore state, DUT-49op exhibits a hierarchical pore system involving both micro- and mesopores. After reaching a critical relative pressure of ca. 0.15, adsorbed xenon induces mesopore contraction, resulting in a purely microporous contracted-pore phase. This contraction is accompanied by release of xenon from the mesopores. Further increa…

  • In Situ Monitoring of Unique Switching Transitions in the Pressure-Amplifying Flexible Framework Material DUT-49 by High-Pressure 129Xe NMR Spectroscopy
    , 2017
    Co-Authors: Jana Schaber, Stefan Kaskel, Irena Senkovska, Silvia Paasch, Simon Krause, Volodymyr Bon, Dirk Wallacher, Daniel M. Többens, Eike Brunner
    Abstract:

    The pronounced flexibility of special metal–organic frameworks (MOFs), so-called soft porous crystals, is attracting increasing research interest. Studies of host–guest interactions in such materials are especially powerful if the measurements are performed in situ. 129Xe NMR Spectroscopy is favorable because it provides characteristic, structure-sensitive parameters such as chemical shifts. The combination of high-pressure xenon adsorption with 129Xe NMR Spectroscopy was used to elucidate the adsorption-induced phase transitions in the recently discovered pressure-amplifying framework material DUT-49, showing a unique negative gas adsorption (NGA) transition. In the open-pore state, DUT-49op exhibits a hierarchical pore system involving both micro- and mesopores. After reaching a critical relative pressure of ca. 0.15, adsorbed xenon induces mesopore contraction, resulting in a purely microporous contracted-pore phase. This contraction is accompanied by release of xenon from the mesopores. Further increase of the pressure initiates the recovery of the mesopores without any indication of a structural intermediate in the NMR spectra. According to the NMR data, the structural transition induced by xenon is a collective, stepwise phenomenon rather than a continuous process. This is the first time that NGA has been studied by directly monitoring the guest and its interaction with the host framework

Victor Lara – One of the best experts on this subject based on the ideXlab platform.

  • Complementary Physicochemical Characterization by SAXS and 129Xe NMR Spectroscopy of Fe-ZSM-5: Influence of Morphology in the Selective Catalytic Reduction of NO
    Industrial & Engineering Chemistry Research, 2006
    Co-Authors: Ariel Guzmán-vargas, Enrique Lima, Gérard Delahay, Bernard Coq, Victor Lara
    Abstract:

    Fe-ZSM-5 catalysts were prepared by FeCl3 sublimation (CVD method) and impregnation in aqueous media. To describe the morphology of the iron species, the materials were characterized by XRD, SAXS, and 27Al and 129Xe NMR Spectroscopy. In the catalysts prepared by impregnation, XRD detected large hematite particles at the external surface of the zeolite. In contrast, the Fe2O3 phase was not detectable by XRD in the materials prepared by CVD, indicating much smaller species. The 129Xe NMR results show that, in the CVD-prepared materials, the amount of free space inside the zeolite cavities was decreased appreciably by the presence of the Fe oxo species. Furthermore, 129Xe NMR Spectroscopy reveals a sharp peak for the CVD-prepared material with Fe (3.8 wt %), indicating that this catalyst exhibits strong adsorption sites that are not detectable in the sample of similar Fe content that was prepared by impregnation. Morphology appears to be strongly affected by the method of preparation of the catalyst. The fra…

  • Complementary Physicochemical Characterization by SAXS and 129Xe NMR Spectroscopy of Fe-ZSM-5: Influence of Morphology in the Selective Catalytic Reduction of NO
    Industrial and engineering chemistry research, 2006
    Co-Authors: Ariel Guzmán-vargas, Enrique Lima, Gérard Delahay, Bernard Coq, Victor Lara
    Abstract:

    Fe-ZSM-5 catalysts were prepared by FeCl3 sublimation (CVD method) and impregnation in aqueous media. To describe the morphology of the iron species, the materials were characterized by XRD, SAXS, and 27Al and 129Xe NMR Spectroscopy. In the catalysts prepared by impregnation, XRD detected large hematite particles at the external surface of the zeolite. In contrast, the Fe2O3 phase was not detectable by XRD in the materials prepared by CVD, indicating much smaller species. The 129Xe NMR results show that, in the CVD-prepared materials, the amount of free space inside the zeolite cavities was decreased appreciably by the presence of the Fe oxo species. Furthermore, 129Xe NMR Spectroscopy reveals a sharp peak for the CVD-prepared material with Fe (3.8 wt %), indicating that this catalyst exhibits strong adsorption sites that are not detectable in the sample of similar Fe content that was prepared by impregnation. Morphology appears to be strongly affected by the method of preparation of the catalyst. The fractal dimension of the metal phase was associated with the catalytic activity in the selective catalytic reduction (SCR) of NO using ammonia and n-decane as reducing agents.