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| 2. |
- Bae, Juna, et al.
(författare)
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Phase Transformation Behavior of a Two-Dimensional Zeolite
- 2019
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 58:30, s. 10230-10235
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the molecular-level mechanisms of phase transformation in solids is of fundamental interest for functional materials such as zeolites. Two-dimensional (2D) zeolites, when used as shape-selective catalysts, can offer improved access to the catalytically active sites and a shortened diffusion length in comparison with their 3D analogues. However, few materials are known to maintain both their intralayer microporosity and structure during calcination for organic structure-directing agent (SDA) removal. Herein we report that PST-9, a new 2D zeolite which has been synthesized via the multiple inorganic cation approach and fulfills the requirements for true layered zeolites, can be transformed into the small-pore zeolite EU-12 under its crystallization conditions through the single-layer folding process, but not through the traditional dissolution/recrystallization route. We also show that zeolite crystal growth pathway can differ according to the type of organic SDAs employed.
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| 3. |
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| 4. |
- Cichocka, Magdalena O., et al.
(författare)
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High-throughput continuous rotation electron diffraction data acquisition via software automation
- 2018
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Ingår i: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 51:6, s. 1652-1661
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Tidskriftsartikel (refereegranskat)abstract
- Single-crystal electron diffraction (SCED) is emerging as an effective technique to determine and refine the structures of unknown nano-sized crystals. In this work, the implementation of the continuous rotation electron diffraction (cRED) method for high-throughput data collection is described. This is achieved through dedicated software that controls the transmission electron microscope and the camera. Crystal tracking can be performed by defocusing every nth diffraction pattern while the crystal rotates, which addresses the problem of the crystal moving out of view of the selected area aperture during rotation. This has greatly increased the number of successful experiments with larger rotation ranges and turned cRED data collection into a high-throughput method. The experimental parameters are logged, and input files for data processing software are written automatically. This reduces the risk of human error, and makes data collection more reproducible and accessible for novice and irregular users. In addition, it is demonstrated how data from the recently developed serial electron diffraction technique can be used to supplement the cRED data collection by automatic screening for suitable crystals using a deep convolutional neural network that can identify promising crystals through the corresponding diffraction data. The screening routine and cRED data collection are demonstrated using a sample of the zeolite mordenite, and the quality of the cRED data is assessed on the basis of the refined crystal structure.
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| 5. |
- Cichocka, Magdalena O., et al.
(författare)
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Multidimensional Disorder in Zeolite IM-18 Revealed by Combining Transmission Electron Microscopy and X-ray Powder Diffraction Analyses
- 2018
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 18:4, s. 2441-2451
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Tidskriftsartikel (refereegranskat)abstract
- A new medium-pore germanosilicate, denoted IM-18, with a three-dimensional 8 x 8 x 10-ring channel system, has been prepared hydrothermally using 4-dimethylaminopyridine as an organic structure-directing agent (OSDA). Due to the presence of stacking disorder, the structure elucidation of IM-18 was challenging, and a combination of different techniques, including electron diffraction, high-resolution transmission electron microscopy (HRTEM), and Rietveld refinement using synchrotron powder diffraction data, was necessary to elucidate the details of the structure and to understand the nature of the disorder. Rotation electron diffraction data were used to determine the average structure of IM-18, HRTEM images to characterize the stacking disorder, and Rietveld refinement to locate the Ge in the framework and the OSDA occluded in the channels.
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| 6. |
- Lin, Junzhong, et al.
(författare)
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Hierarchical Shell‐Like ZSM‐5 with Tunable Porosity Synthesized by using a Dissolution–Recrystallization Approach
- 2018
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 24:56, s. 14974-14981
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Tidskriftsartikel (refereegranskat)abstract
- Zeolites have been widely used in various fields in industry, such as catalysis, separation, and adsorption, etc. The small pore size of the micropores in the zeolite could lead to severe diffusion resistance in mass transfer. Numerous efforts have been dedicated to imposing hierarchical pore systems into zeolites by using templates or leaching methods. Here, we report the synthesis of single‐crystalline hierarchical shell‐like ZSM‐5 by utilizing a dissolution–recrystallization post‐treatment on mesoporous ZSM‐5. Tetrapropylammonium hydroxide solution was used in the post‐treatment. The hierarchical porosity in the crystalline shell can be controlled by adding sodium cations into the synthesis system. The hierarchical shell‐like ZSM‐5 reported here shows higher catalytic activity in acetalization reactions containing bulky molecules.
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| 7. |
- Wang, Xueting, 1991, et al.
(författare)
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Methanol Desorption From Cu-ZSM-5 Studied by In Situ Infrared Spectroscopy and First-Principles Calculations
- 2017
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:49, s. 27389-27398
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic interaction of methanol and its derivatives with Cu-exchanged ZSM- 5 during methanol temperature programmed desorption from 30 to 450 ◦C has been investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy and first-principles calculations. The results emphasize that defects in the framework structure of the zeolite and Brønsted acid sites constitute ion-exchange sites for Cu ions. The Cu sites introduced in ZSM-5 actively interact with methanol adsorbed at moderate temperature, i.e. below 250◦C, and take roles in further oxidation of the adsorbed species to formate and CO. Moreover, spectra recorded at higher temperatures, i.e. above 300◦C, after adsorption of methanol show strong interaction between methoxy groups and the zeolite framework, suggesting that under mild conditions proton extraction for methanol production during direct partial oxidation of methane to methanol over Cu-ZSM-5 is necessary.
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| 8. |
- Wang, Zhendong, et al.
(författare)
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Controllable direct-syntheses of delaminated MWW-type zeolites
- 2020
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Ingår i: Cuihuà xuébào. - 0253-9837 .- 1872-2067. ; 41:7, s. 1062-1066
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Tidskriftsartikel (refereegranskat)abstract
- A method for the direct syntheses of partially and fully delaminated MWW zeolites is reported herein. Two organic amines were introduced into the hydrothermal synthetic system: hexamethyleneimine (HMI), which acted as the structure-directing agent for the MWW layered structure; and dicyclohexylamine (DCHA), in the role of an in-situ delaminating agent. By varying the amount of DCHA, partially and fully delaminated MWW zeolites having two MWW structure layers and one single layer, respectively, were obtained. These were denoted as SCM-1 (Sinopec Composite Material) and SCM-6, respectively. The delaminated materials possess ultra-large external surface areas, and the transmission electron microscopy images illustrated their layered nature. In the reaction of liquid phase benzene alkylation with ethylene, SCM-1, the double-layered MWW zeolite, exhibited far superior catalytic performance compared to zeolite MCM-22.
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