| 1. |
|
|
| 2. |
- Bae, Juna, et al.
(författare)
-
Phase Transformation Behavior of a Two-Dimensional Zeolite
- 2019
-
Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 58:30, s. 10230-10235
-
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.
|
|
| 3. |
- Bello, Estefania, et al.
(författare)
-
NH3-SCR catalysts for heavy-duty diesel vehicles : Preparation of CHA-type zeolites with low-cost templates
- 2022
-
Ingår i: Applied Catalysis B. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 303
-
Tidskriftsartikel (refereegranskat)abstract
- Computer-assistance allows selecting the most adequate low-cost organic structure directing agents (OSDAs) for the crystallization of Al-rich CHA-type zeolites. The host-guest stabilization energies of tetraethylammonium (TEA), methyltriethylammonium (MTEA) and dimethyldiethylammonium (DMDEA), in combination with Na, were first theoretically evaluated. This ab-initio analysis reveals that two TEA show a serious steric hindrance in a cha cavity, whereas two MTEA would present excellent host-guest confinements. The synthesis of Al-rich CHA-type zeolites has been accomplished using TEA and MTEA. Electron diffraction and high-resolution transmission electron microscopy reveal large CHA-domains with narrow faulted GME-domains in the CHAtype material synthesized with TEA, confirming the better OSDA-directing roles of MTEA cations towards the cha cavity, in good agreement with DFT calculations. Cu-exchanged Al-rich CHA-type samples achieved with MTEA and TEA show excellent catalytic activity and hydrothermal stability for the selective catalytic reduction (SCR) of NOx with ammonia under conditions relevant for future heavy duty diesel conditions.
|
|
| 4. |
- Bello-Jurado, Estefanía, et al.
(författare)
-
Tunable CHA/AEI Zeolite Intergrowths with A Priori Biselective Organic Structure-Directing Agents : Controlling Enrichment and Implications for Selective Catalytic Reduction of NOx
- 2022
-
Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 61:28
-
Tidskriftsartikel (refereegranskat)abstract
- A novel ab initio methodology based on high-throughput simulations has permitted designing unique biselective organic structure-directing agents (OSDAs) that allow the efficient synthesis of CHA/AEI zeolite intergrowth materials with controlled phase compositions. Distinctive local crystallographic ordering of the CHA/AEI intergrowths was revealed at the nanoscale level using integrated differential phase contrast scanning transmission electron microscopy (iDPC STEM). These novel CHA/AEI materials have been tested for the selective catalytic reduction (SCR) of NOx, presenting an outstanding catalytic performance and hydrothermal stability, even surpassing the performance of the well-established commercial CHA-type catalyst. This methodology opens the possibility for synthetizing new zeolite intergrowths with more complex structures and unique catalytic properties.
|
|
| 5. |
- Bueken, Bart, et al.
(författare)
-
Gel-based morphological design of zirconium metal-organic frameworks
- 2017
-
Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 8:5, s. 3939-3948
-
Tidskriftsartikel (refereegranskat)abstract
- The ability of metal-organic frameworks (MOFs) to gelate under specific synthetic conditions opens up new opportunities in the preparation and shaping of hierarchically porous MOF monoliths, which could be directly implemented for catalytic and adsorptive applications. In this work, we present the first examples of xero-or aerogel monoliths consisting solely of nanoparticles of several prototypical Zr4+-based MOFs: UiO-66-X (X - H, NH2, NO2, (OH)(2)), UiO-67, MOF-801, MOF-808 and NU-1000. High reactant and water concentrations during synthesis were observed to induce the formation of gels, which were converted to monolithic materials by drying in air or supercritical CO2. Electron microscopy, combined with N-2 physisorption experiments, was used to show that irregular nanoparticle packing leads to pure MOF monoliths with hierarchical pore systems, featuring both intraparticle micropores and interparticle mesopores. Finally, UiO-66 gels were shaped into monolithic spheres of 600 mm diameter using an oil-drop method, creating promising candidates for packed-bed catalytic or adsorptive applications, where hierarchical pore systems can greatly mitigate mass transfer limitations.
|
|
| 6. |
- Cho, Jungyoun, 1991-
(författare)
-
Detailed structure features from 3D electron diffraction : Heteroatoms, framework disorders, and guest species in zeolites
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 3D electron diffraction (3D ED) has evolved as a powerful method for ab initio structure determination from sub micrometer-sized crystals. It can be used to elucidate the arrangement of atoms in crystalline materials and to provide insights into the laws of nature that govern the properties of matter. This thesis explores the advantages, challenges, and applications of 3D ED in structure determination of zeolites. It demonstrates that 3D ED can be used to reveal not only the framework structures but also structure details, which facilitates the study of zeolite chemistry.Zeolites are porous silicate materials used in a wide range of applications as shape-selective ion-exchangers, catalysts, and adsorbents. They feature regularly arranged pores of molecular dimensions that can discriminate between molecules with sub-Ångström precision. However, zeolites often crystallize as polycrystalline powders, and their structures are complex and difficult to determine.In this thesis, eight zeolites have been investigated by 3D ED. The structures of three novel materials, PST-24, EMM-59, and EMM-25 are determined. The silicate PST-24 exhibits columnal disorder that yields varying intracrystalline channel dimensionality, which is unprecedented in zeolites. The borosilicate EMM-59 consists of intersecting 3D 12 × 10 × 10-ring channels and is one of the most complex zeolites. The boron sites in the framework can be located by both 3D ED and integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM). Structure refinement reveals structural changes upon calcination associated to the change of boron coordination. EMM-25 is also a borosilicate with 2D 11 × 10-ring channels. 3D ED reveals that the EMM-25 structure contains zigzag chains that are disordered with two configurations. Further investigations show that similar disorders also exist in other zeolites containing zigzag chains, i.e., EU-1, ITQ-27, and nonasil. We show that disordered atomic sites that are beyond the data resolution can also be identified and refined using 3D ED data.Furthermore, factors that impact the location of organic guest species in zeolites using 3D ED are investigated. Because of the disorder and flexibility of the organic species in EMM-25 and EMM-59, only their average locations can be found using 3D ED. Therefore, we selected a STW-type zeolite HPM-1 with chiral channels for further study. HPM-1 was synthesized using 2-ethyl-1,3,4-trimethylimidazolium cations, and the guest species are intact and ordered in the channels of HPM-1, as previously determined by single crystal X-ray diffraction. We demonstrate that is possible to locate guest species using continuous rotation 3D ED data. Their atomic positions are refined against 3D ED data through both kinematical and dynamical refinements. Finally, the effect of electron fluence on the location of the organic guest species in the zeolite is investigated.
|
|
| 7. |
- Cho, Jung, et al.
(författare)
-
EMM-25 : The Structure of Two-Dimensional 11 x 10 Medium-Pore Borosilicate Zeolite Unraveled Using 3D Electron Diffraction
- 2021
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 33:11, s. 4146-4153
-
Tidskriftsartikel (refereegranskat)abstract
- The structure of the novel medium-pore borosilicate zeolite EMM-25 has been determined by continuous rotation electron diffraction (cRED). EMM-25 crystallizes in the space group Cmcm with unit cell parameters a = 11.055, b = 22.912, and c = 24.914 angstrom and a composition of IC4H8(C11H25N)(2)I (2)[Si112.5B3.5O232]. The EMM-25 framework possesses a two-dimensional channel system composed of 10-ring channels connected via 11-ring windows. Its channel system is analogous to that of the medium-pore zeolite NU-87 framework but with 11- rather than 12-ring windows, suggesting a different shape selectivity. EMM-25 was first obtained using 1,4-bis(N-methyl-N,N-dihexylammonium)butane as an organic structure directing agent (OSDA). Based on a molecular docking study of the OSDA within the pores of the determined framework structure, a new ammonium dication OSDA with an improved fit was devised. By using this new OSDA, the synthesis time was reduced 80%, from 52 to just 10 days. Furthermore, cRED data revealed a structural disorder of the EMM-25 framework present as swinging zigzag chains. The introduction of the disorder, which is a consequence of geometry relaxation, was crucial for an accurate structure refinement. Lastly, the cRED data from as-made EMM-25 showed residual potential consistent with the location of the OSDA position determined from the Rietveld refinement, concluding a complete refinement of the as-made structure based on the cRED data.
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
- Cho, Jung, 1991-, et al.
(författare)
-
The synergistic development of electron crystallography and zeolite discovery
- 2023
-
Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 358
-
Tidskriftsartikel (refereegranskat)abstract
- During the past decades, the advancement of new electron crystallographic techniques has made important impacts for the discovery of novel zeolites. High-resolution transmission electron microscopy (HRTEM) imaging directly reveals detailed structural features in zeolites, which is especially useful for studying disordered materials. 3D atomic structures of new zeolites are determined by combining HRTEM images along several projections. Electron diffraction techniques have evolved from 2D zonal-axis electron diffraction to 3D electron diffraction (3D ED), which has transformed a TEM into a single nanocrystal diffractometer for structural elucidation. The development of electron crystallography parallels the discovery of novel zeolites, where Corma's research group has played the key role and contributed to at least 30 zeolite frameworks in the Database of Zeolite Structures. Herein, we present how the ITQ zeolite materials developed by Corma's group pushed the development of electron crystallographic techniques, and how the new 3D ED techniques accelerated the discovery of novel zeolites. During the past 7 years, nearly 80% of new zeolite structures have been determined by electron crystallography. Detailed atomic structural information has been revealed from nano- and micrometer-sized crystals of extra-large pore zeolites, disordered zeolites, and low-dimensional zeolites such as nanotubes and nanosheets.
|
|
