| 1. |
- 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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| 2. |
- Rzepka, Przemyslaw, et al.
(författare)
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CO2-Induced Displacement of Na+ and K+ in Zeolite INaKI-A
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:30, s. 17211-17220
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption technologies offer opportunities to remove CO2 from gas mixtures, and zeolite A has good properties that include a high capacity for the adsorption of CO2 . It has been argued that its abilities to separate CO2 from N-2 in flue gas and CO2 from CH4 in raw biogas can be further enhanced by replacing Na+ with K+ in the controlling pore window apertures. In this study, several compositions of I Na12-xKxI-A were prepared and studied with respect to the adsorption of CO2 N-2, and CH4, and the detailed structural changes were induced by the adsorption of CO2. The adsorption of CO2 gradually decreased on an increasing content of K+, whereas the adsorption of N-2 and CH4 was completely nulled already at relatively small contents of K. Of the studied samples, INa9K3I-A exhibited the highest CO2 over N-2/CH4 selectivities, with a(CO2/N-2 ) > 21 000 and a(CO2/CH4) > 8000. For samples with and without adsorbed CO2 analyses of powder X-ray diffraction (PXRD) data revealed that K+ preferred to substitute Na+ at the eight-ring sites. The Na(+ )ions at the six-ring sites were gradually replaced by K+ on an increasing content, and these sites split into two positions on both sides of the six-ring mirror plane. It was observed that both the eight-ring and six-ring sites tailored the maximum adsorption capacity for CO2 and possibly also the diffusion of CO2 into the alpha-cavities of INa12-xKxI-A. The adsorption of CH4 and N-2 on the other hand appeared to be controlled by the K+ ions blocking the eight-ring windows. The in situ PXRD study revealed that the positions of the extra-framework cations were displaced into the a-cavities of INa12(_)x,KxI-A on the adsorption of CO2 . For samples with a low content of K+, the repositioning of the cations was consistent with a mutual attraction with the adsorbed CO(2 )molecules.
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| 3. |
- Etman, Ahmed S., et al.
(författare)
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Insights into the Exfoliation Process of V2O5· nH2O Nanosheet Formation Using Real-Time 51V NMR
- 2019
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:6, s. 10899-10905
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Tidskriftsartikel (refereegranskat)abstract
- Copyright © 2019 American Chemical Society. Nanostructured hydrated vanadium oxides (V2O5·nH2O) are actively being researched for applications in energy storage, catalysis, and gas sensors. Recently, a one-step exfoliation technique for fabricating V2O5·nH2O nanosheets in aqueous media was reported; however, the underlying mechanism of exfoliation has been challenging to study. Herein, we followed the synthesis of V2O5·nH2O nanosheets from the V2O5 and VO2 precursors in real time using solution- and solid-state 51V NMR. Solution-state 51V NMR showed that the aqueous solution contained mostly the decavanadate anion [H2V10O28]4- and the hydrated dioxovanadate cation [VO2·4H2O]+, and during the exfoliation process, decavanadate was formed, while the amount of [VO2·4H2O]+ remained constant. The conversion of the solid precursor V2O5, which was monitored with solid-state 51V NMR, was initiated when VO2 was in its monoclinic forms. The dried V2O5·nH2O nanosheets were weakly paramagnetic because of a minor content of isolated V4+. Its solid-state 51V signal was less than 20% of V2O5 and arose from diamagnetic V4+ or V5+.This study demonstrates the use of real-time NMR techniques as a powerful analysis tool for the exfoliation of bulk materials into nanosheets. A deeper understanding of this process will pave the way to tailor these important materials. ©
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| 4. |
- Yuan, Ning, et al.
(författare)
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Insights into Functionalization of Metal-Organic Frameworks Using In Situ NMR Spectroscopy
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Postsynthetic reactions of metal-organic frameworks (MOFs) are versatile tools for producing functional materials, but the methods of evaluating these reactions are cumbersome and destructive. Here we demonstrate and validate the use of in situ NMR spectroscopy of species in the liquid state to examine solvent-assisted ligand exchange (SALE) and postsynthetic modification (PSM) reactions of metal-organic frameworks. This technique allows functionalization to be monitored over time without decomposing the product for analysis, which simplifies reaction screening. In the case of SALE, both the added ligand and the ligand leaving the framework can be observed. We demonstrate this in situ method by examining SALE and PSM reactions of the robust zirconium MOF UiO-67 as well as SALE with the aluminum MOF DUT-5. In situ NMR spectroscopy provided insights into the reactions studied, and we expect that future studies using this method will permit the examination of a variety of MOF–solute reactions.
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| 5. |
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| 6. |
- Taborda, Farlán, et al.
(författare)
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Synthesis and characterization of pure silica zeolite beta obtained by an aging-drying method
- 2011
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 143:1, s. 196-205
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Tidskriftsartikel (refereegranskat)abstract
- Pure silica zeolite beta materials were synthesized by an unconventional method of aging and drying the starting gels at room temperature followed by the conventional hydrothermal treatment. In addition, organic solvents were added to selected samples as complementary structure directing agents (SDA). The influence of the aging-drying method, complementary SDA addition and crystallization time upon the synthesis of pure silica zeolite beta were studied. Samples were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), thermogravimetric analyses (TGA) and nitrogen adsorption. Results revealed that the aging-drying process increased crystallization rate, produced crystals with unique morphology and scaled-surface and allowed polymorph A enrichments to about 68-70%. It was also found that addition of organic solvents during the thermal treatment tunes the crystal morphology but, does not affect the polymorphic enrichment.
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| 7. |
- Yuan, Ning, et al.
(författare)
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Investigation of the Deactivation and Reactivation Mechanism of a Heterogeneous Palladium(II) Catalyst in the Cycloisomerization of Acetylenic Acids by In Situ XAS
- 2021
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435 .- 2155-5435. ; 11:5, s. 2999-3008
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Tidskriftsartikel (refereegranskat)abstract
- A well-studied heterogeneous palladium(II) catalyst used for the cycloisomerization of acetylenic acids is known to be susceptible to deactivation through reduction. To gain a deeper understanding of this deactivation process and to enable the design of a reactivation strategy, in situ X-ray absorption spectroscopy (XAS) was used. With this technique, changes in the palladium oxidation state and coordination environment could be studied in close detail, which provided experimental evidence that the deactivation was primarily caused by triethylamine-promoted reduction of palladium(II) to metallic palladium nanoparticles. Furthermore, it was observed that the choice of the acetylenic acid substrate influenced the distribution between palladium(II) and palladium(0) species in the heterogeneous catalyst after the reaction. From the mechanistic insight gained through XAS, an improved catalytic protocol was developed that did not suffer from deactivation and allowed for more efficient recycling of the catalyst.
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| 8. |
- Lightowler, Molly, 1995-
(författare)
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Investigating polymorphism in small molecules using three-dimensional electron diffraction
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For scientific, regulatory and intellectual property reasons, the discovery and characterisation of polymorphic systems is an integral aspect of the development process of any solid-formulated drug product. Yet, these studies are often hindered by crystal quality and size, poor yields and the generation of mixtures of phases. Three-dimensional electron diffraction (3D ED) is a technique capable of structure determination from individually selected, nanometre-sized crystals. In this thesis, 3D ED is applied to investigate polymorphism in small molecules. The unique advantages of the method are highlighted across numerous studies to demonstrate how 3D ED can broaden the scope of polymorphism discovery and characterisation in the screening and selection of pharmaceutical crystal forms. 3D ED is first applied to reveal that two crystallisation methods believed for 47 years to produce Form δ of the pharmaceutical compound indomethacin result in two different polymorphs, highlighting the power of the method for polymorphism discovery. The polymorphic crystal structures of a small molecule are then determined directly from melt-grown compact spherulites for the first time to show how 3D ED can widen the application of melt crystallisation in polymorph screening, where polycrystalline spherulites are common products. Furthermore, 3D ED is combined with on-the-grid crystallisation and plunge freezing to follow the polymorph evolution of glycine during crystallisation from an aqueous solution to demonstrate the ability of the method to monitor crystallisation processes in situ. The final part of the thesis explores how a high-throughput method combining 3D ED data collection in batch mode with semi-automated data processing can be applied for the phase analysis of complex melt crystallisation products to improve the efficiency and accuracy of polymorph screening.
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| 9. |
- 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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| 10. |
- Bortolini, C., et al.
(författare)
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Atomic Structure of Amyloid Crystals
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A deep understanding of the self-assembly and crystallization of biomolecules as highly ordered biomaterials is crucial to enable the design and the generation of complex functional systems for cutting-edge applications in nanotechnology and biomedicine. In this work, we determined the atomic structure of Aβ16-20 crystals, a fragment of amyloid-β which aberrant folding is linked to the etiology of Alzheimer’s disease, the most common cause of dementia. We detailed the hierarchical aggregation mechanism of Aβ16-20 into highly ordered crystals and revealed that the self-assembly is reversible, leading to the formation of oligomers as an intermediate. Our structural investigation combined with molecular dynamics simulations highlights how a combination of favorable non-covalent interactions drives the efficient fast self-assembly and enhanced stability. We studied the chemical and surface properties of amyloid crystals, including their mechanical properties and their capability to transmit light; the long-rang order of Aβ16-20 crystals enables them to be used as optical waveguide materials for biologically based modulation and sensing. Our results shed new light on pathogenic amyloid assembly at the atomic level and reveal the potential of amyloid crystals for applications in nanotechnology.
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