| 1. |
- Bonneau, Charlotte, et al.
(författare)
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Open-Framework Germanate Built from the Hexagonal Packing of Rigid Cylinders
- 2009
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 48:21, s. 9962-9964
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel open-framework oxide material constructed from Ge10(O,OH)28 (Ge10) oxide clusters prepared via a nonsurfactant route. The material shows two distinct pore windows of 9.43 and 4.65 Å and a low framework density structure of 12.7 Ge atoms per 1000 Å3. The topological study leads to the recognition of a newly observed trinodal 6,7-heterocoordinated net related to the 7-coordinated swh net. The structure displays large rigid cylinders showing features indicating a growth mechanism by hard-sphere packing of the inorganic moiety similar to that observed in mesoporous materials.
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| 2. |
- Corma, Averlino, et al.
(författare)
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Synthesis and structure of polymorph B of zeolite Beta
- 2008
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 20:9, s. 3218-3223
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Tidskriftsartikel (refereegranskat)abstract
- It was found that either polymorph B or polymorph C of zeolite beta can be obtained from the same structure directing agent: 4,4-dimethyl-4-azonia-tricyclo[5.2.2.02,6]undec-8-ene hydroxide. The synthesis occurs through a consecutive process where polymorph B is first formed and then transformed into polymorph C. It is possible to produce a zeolite highly enriched in polymorph B, provided that the transformation of this phase into polymorph C is slowed down up to the point where polymorph C is only detected at trace levels. The structure of polymorph B was determined for the first time by electron crystallography with SAED and HRTEM from areas of unfaulted polymorph B crystals.
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| 3. |
- Han, Yu, et al.
(författare)
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A tri-continuous mesoporous material IBN-9 with the silica pore wall following a hexagonal minimal surface
- 2009
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Ingår i: Nature Chemistry. - : Springer Science and Business Media LLC. - 1755-4349 .- 1755-4330. ; 1, s. 123-127
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Tidskriftsartikel (refereegranskat)abstract
- Ordered porous materials with unique pore structures and pore sizes in the mesoporous range (2–50 nm) have many applications in catalysis, separation and drug delivery. Extensive research has resulted in mesoporous materials with onedimensional, cage-like and bi-continuous pore structures. Three families of bi-continuous mesoporous materials have been made, with two interwoven but unconnected channels, corresponding to the liquid crystal phases used as templates. Here we report a three-dimensional hexagonal mesoporous silica, IBN-9, with a tri-continuous pore structure that is synthesized using a specially designed cationic surfactant template. IBN-9 consists of three identical continuous interpenetrating channels, which are separated by a silica wall that follows a hexagonal minimal surface. Such a tri-continuous mesostructure was predicted mathematically, but until now has not been observed in real materials. Keywords: mesoporous structure, electron microscopy, self-assembly
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| 4. |
- Lindmark, Jonas, et al.
(författare)
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Impregnation of zeolite membranes for enhanced selectivity
- 2010
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 365:1-2, s. 188-197
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Tidskriftsartikel (refereegranskat)abstract
- A new method to enhance the selectivity of zeolite membranes for alternative separation tasks has been developed. Calcined MFI membranes were impregnated with a solution of Ca(NO3)2 in methanol and calcined at 600 °C to thermally decompose the nitrate. SEM and EDS data indicated that calcium compounds were evenly distributed in the entire MFI film and in addition, a few crystals of a calcium compound were observed on top of the film in some locations. A HR-TEM investigation showed that calcium compounds were present in low concentration in the sample and that the interiors of the MFI crystals remained fully crystalline after impregnation and calcination. However, the HR-TEM investigation could neither confirm nor rule out the occurrence of calcium compounds in the pores in the interiors of the crystals. In accordance with the SEM and TEM observations, XRD data showed that calcium compounds on top of the film were relatively large CaCO3 crystals and that the zeolite film remained crystalline after impregnation. However, eventual calcium compounds in the pores of the zeolite could not be studied by XRD since these would probably generate a very weak signal of amorphous material. FTIR data indicated that impregnation increased the amount of both physisorbed and chemisorbed CO2, the latter resulting in carbonate species in the film. n-Hexane/helium adsorption branch permporometry showed that the high quality of the membranes remained after modification. The single component permeance ratio CO2/H2 increased from 0.6 to 1.5 after impregnation. Calculations indicated that the increased CO2/H2 single component permeance ratios were both an effect of increased adsorption of CO2 in the film and reduced pressure drop in the support. The dual component separation factor α CO2/H2 at room temperature increased drastically from 0.7 (H2 selective) to 3.4 (CO2 selective) after impregnation. This work shows for the first time that impregnation procedures can be used to tailor the diffusion properties of zeolite membranes in a similar way as impregnation procedures are used to tailor the catalytic performance of catalysts.
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| 5. |
- Oleynikov, Peter, et al.
(författare)
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Quantitative electron diffraction for crystal structure determination
- 2009
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Ingår i: Electron crystallography for materials research and quantitative characterization of nanostructured materials. ; , s. GG01-04
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Konferensbidrag (refereegranskat)abstract
- We present a quantitative investigation of data quality using electron precession, compared to standard selected-area electron diffraction (SAED). Data can be collected on a CCD camera and automatically extracted by computer. The critical question of data quality is addressed – can electron diffraction data compete with X-ray diffraction data in terms of resolution, completeness and quality of intensities?
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| 6. |
- Sun, Junliang, et al.
(författare)
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Extensive inspection of an unconventional mesoporous material at all length scales
- 2010
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 23:2, s. 229-238
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Tidskriftsartikel (refereegranskat)abstract
- The structure of an unconventional mesoporous material, formed by the packing of silica coated spherical micelles as hard spheres, has been uniquely determined through a series of advanced characterization techniques. The synchrotron-based small-angle X-ray scattering (SAXS) analysis confirms that the bulk material assembled via the hard sphere packing (HSP) route exhibits a strong 200 reflection and a relatively weaker 111 reflection, which is the first example in all reported mesostructured materials with the same symmetry. At the morphological macroscale, high-resolution scanning electron microscopy (SEM) images directly show that the hexagonal platelike micrometer-sized particles consist of nanospheres (20 nm in diameters) in a close packing mode. The intrinsic pore structure of calcined HSP material has been reconstructed using both electron crystallography (EC) and electron tomography (ET) techniques, which can be simply viewed as a face-centered cubic (fcc) packing of monodispersed hollow silica nanospheres. The EC technique provides a three-dimensional visualization of the pore organization and demonstrates the existence and crystallographic positions of the cagelike mesopores, octahedral and tetrahedral cavities. The ET method directly and accurately determines the sizes of the mesopores and octahedral cavity and offers nanometer-scale structural information at any given local area, which cannot be obtained by conventional transmission electron microscopy (TEM). To our knowledge, this is the first time that the EC and ET techniques are simultaneously employed and provide complementary information for the mesostructure determination. More importantly, the structural details collected from the synchrotron SAXS, high resolution SEM, EC and ET techniques are consistent and support the HSP mechanism, different from the well-understood liquid crystal templating or cooperative self-assembly pathways. The complex pore structure and the existence of octahedral and tetrahedral cavities are responsible for the unusual indexation of the SAXS, which is further validated by the structural simulation. Our work provides both a comparative and comprehensive case study to show the strength and limitation of individual techniques and demonstrates the need for the careful characterization of novel structures by a selection of complementary, state-of-the-art methods which provide selective structural information at different length scales.
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| 7. |
- Sun, Junliang, et al.
(författare)
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Structure determination of zeolites by electron crystallography
- 2008
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Ingår i: EMC 2008 14th European Microscopy Congress 1–5 September 2008, Aachen, Germany: 1, Instrumentation and methods. - Berlin Heidelberg : Springer. - 9783540851547 ; , s. 757-758
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Konferensbidrag (refereegranskat)abstract
- Many zeolite structures have remained unsolved for a long time because of their structural complexity, the size of the crystallites or the presence of defects or impurities. By combining electron microscopy and X-ray powder diffraction data, some of them have been solved (e.g. the high-silica zeolite IM-5, which was first reported in 1998 [1] and recently solved using a charge-flipping structure solution algorithm [2] ), while for other zeolites, good X-ray powder diffraction data are hard to obtain (e.g. polymorph A or B of zeolite Beta). Here we demonstrate a complete structure determination of IM-5 (one of the most complicated zeolited) and polymorph B of zeolite Beta [3] using electron crystallography alone. This shows the power and advantage of structure determination by electron microscopy compared with the X-ray diffraction techniques. The method is general and can be applied to both zeolites and other materials, where the crystals are too small or the structure too complicated to be solved from X-ray powder diffraction data alone [4] . It is particularly useful for structures containing defects.
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| 8. |
- Sun, Junliang, et al.
(författare)
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The ITQ-37 mesoporous chiral zeolite
- 2009
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 458, s. 1154-1157
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of crystalline molecular sieves with pore dimensions that fill the gap between microporous and mesoporous materials is a matter of fundamental and industrial interest. The preparation of zeolitic materials with extralarge pores and chiral frameworks would permit many new applications. Two important steps in this direction include the synthesis of ITQ-33, a stable zeolite with 18 × 10 × 10 ring windows, and the synthesis of SU-32, which has an intrinsically chiral zeolite structure and where each crystal exhibits only one handedness. Here we present a germanosilicate zeolite (ITQ-37) with extralarge 30-ring windows. Its structure was determined by combining selected area electron diffraction (SAED) and powder X-ray diffraction (PXRD) in a charge-flipping algorithm. The framework follows the SrSi2 (srs) minimal net and forms two unique cavities, each of which is connected to three other cavities to form a gyroidal channel system. These cavities comprise the enantiomorphous srs net of the framework. ITQ-37 is the first chiral zeolite with one single gyroidal channel. It has the lowest framework density (10.3 T atoms per 1,000 Å3) of all existing 4-coordinated crystalline oxide frameworks, and the pore volume of the corresponding silica polymorph would be 0.38 cm3 g-1. Keywords: srs-net, powder X-ray, charge flipping, electron microscopy
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| 9. |
- Willhammar, Tom, et al.
(författare)
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Structure and catalytic properties of the most complex intergrown zeolite ITQ-39 determined by electron crystallography
- 2012
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Ingår i: Nature Chemistry. - : Springer Science and Business Media LLC. - 1755-4330 .- 1755-4349. ; 4, s. 188-194
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Tidskriftsartikel (refereegranskat)abstract
- Porous materials such as zeolites contain well-defined pores in molecular dimensions and have important industrial applications in catalysis, sorption and separation. Aluminosilicates with intersecting 10- and 12-ring channels are particularly interesting as selective catalysts. Many porous materials, especially zeolites, form only nanosized powders and some are intergrowths of different structures, making structure determination very challenging. Here, we report the atomic structures of an aluminosilicate zeolite family, ITQ-39, solved from nanocrystals only a few unit cells in size by electron crystallography. ITQ-39 is an intergrowth of three different polymorphs, built from the same layer but with different stacking sequences. ITQ-39 contains stacking faults and twinning with nano-sized domains, being the most complex zeolite ever solved. The unique structure of ITQ-39, with a three-dimensional intersecting pairwise 12-ring and 10-ring pore system, makes it a promising catalyst for converting naphtha into diesel fuel, a process of emerging interest for the petrochemical industry.
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| 10. |
- Zhang, Daliang, 1980-
(författare)
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3D Electron crystallography : Real space reconstruction and reciprocal space tomography
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electron crystallography is an important technique for studying micro- and nano-sized materials. It has two important advantages over X-ray crystallography for structural studies: 1) crystals millions of times smaller than those needed for X-ray diffraction can be studied; 2) it is possible to; focus the electrons to form an image. The local atomic arrangement can be seen directly by high-resolution transmission electron microscopy (HRTEM). The crystallographic structure factor phases, which are lost in recording diffraction patterns, are present in HRTEM images and can be determined experimentally. The main disadvantages of electron crystallography compared to X-ray diffraction are that the data are difficult to collect, often incomplete and suffer from dynamic scattering. New methods need to be developed to overcome these problems. In this work, structure determination of several unique and complex porous materials including zeolites and mesoporous silica is demonstrated. None of the structures of these materials could be solved by X-ray crystallography. New techniques are also developed in order to overcome the disadvantages of electron crystallography. The new techniques include a digital sampling method for collecting precession electron diffraction data and a rotation method for automatic collection of complete 3D electron diffraction data. A number of practical issues concerning data collection and data processing are described and the data quality is analysed.
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