| 1. |
- Bleken, Bjørn Tore L., et al.
(författare)
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Unit cell thick nanosheets of zeolite H-ZSM-5 : Structure and activity
- 2013
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Ingår i: Topics in catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 56:9-10, s. 558-566
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Tidskriftsartikel (refereegranskat)abstract
- nosheets of zeolite H-ZSM-5 were synthesized and characterized by X-ray diffraction, transmission electron microscopy (TEM), N2- physisorption, FT-IR spectroscopy, 27Al and 29Si MAS NMR spectroscopy in addition to catalytic testing in conversion of methanol to hydrocarbons (MTH). It was found that Rietveld analysis, involving anisotropic broadening parameters, gave average crystallite dimensions in good agreement with TEM images. The selectivities in MTH is intact in the mesoporous nanosheet H-ZSM-5 with the largest difference being a higher C3/C2 ratio compared to regular H-ZSM-5.
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| 2. |
- Boström, Zebastian, 1983, et al.
(författare)
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Preparation of high silica chabazite with controllable particle size
- 2014
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811. ; 195, s. 294-302
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Tidskriftsartikel (refereegranskat)abstract
- In this work synthesis procedures for controlling particle size distributions of high silica chabazite (Si/Al=100) zeolites between 0.3-4.5 μm is described. The chabzite zeolite crystallization and crystal growth have been monitored using XRD, SEM and DLS. Hydrothermal treatment parameters such as time, temperature and agitation and gel composition parameters such as amounts of water and structure directing agent (SDA) have been correlated with chabazite zeolite crystal size, crystal shape, synthesis yield and crystallinity. From this data a chabazite zeolite formation and crystal growth mechanism based on experimental studies and previous studies has been proposed. It was also found that large aggregates formed in the chabazite zeolite gel before any hydrothermal treatment (1 μm large when using zeolite gel with composition 1Al2O3:100SiO2: 60TMAdaOH:3100H2O). The size controlling parameter and size controlling synthesis step of the chabazite zeolite (below 1 μm) has been identified as the primary fractal aggregation of the silicium/aluminium/SDA species.
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| 3. |
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| 4. |
- Samperisi, Laura, et al.
(författare)
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Probing Molecular Motions in Metal-Organic Frameworks by Three-Dimensional Electron Diffraction
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:43, s. 17947-17952
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Tidskriftsartikel (refereegranskat)abstract
- Flexible metal-organic frameworks (MOFs) are known for their vast functional diversities and variable pore architectures. Dynamic motions or perturbations are among the highly desired flexibilities, which are key to guest diffusion processes. Therefore, probing such motions, especially at an atomic level, is crucial for revealing the unique properties and identifying the applications of MOFs. Nuclear magnetic resonance (NMR) and single-crystal X-ray diffraction (SCXRD) are the most important techniques to characterize molecular motions but require pure samples or large single crystals (>5 x 5 x 5 mu m(3)), which are often inaccessible for MOF synthesis. Recent developments of three-dimensional electron diffraction (3D ED) have pushed the limits of single-crystal structural analysis. Accurate atomic information can be obtained by 3D ED from nanometer- and submicrometer-sized crystals and samples containing multiple phases. Here, we report the study of molecular motions by using the 3D ED method in MIL-140C and UiO-67, which are obtained as nanosized crystals coexisting in a mixture. In addition to an ab initio determination of their framework structures, we discovered that motions of the linker molecules could be revealed by observing the thermal ellipsoid models and analyzing the atomic anisotropic displacement parameters (ADPs) at room temperature (298 K) and cryogenic temperature (98 K). Interestingly, despite the same type of linker molecule occupying two symmetry-independent positions in MIL140C, we observed significantly larger motions for the isolated linkers in comparison to those reinforced by p-p stacking. With an accuracy comparable to that of SCXRD, we show for the first time that 3D ED can be a powerful tool to investigate dynamics at an atomic level, which is particularly beneficial for nanocrystalline materials and/or phase mixtures.
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