| 1. |
- Andersen, Casper Welzel, et al.
(författare)
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Redox-Driven Migration of Copper Ions in the Cu-CHA Zeolite as Shown by the InSitu PXRD/XANES Technique
- 2017
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Ingår i: Angewandte Chemie - International Edition. - : Wiley. - 1433-7851. ; 56:35, s. 10367-10372
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Tidskriftsartikel (refereegranskat)abstract
- Using quasi-simultaneous insitu PXRD and XANES, the direct correlation between the oxidation state of Cu ions in the commercially relevant deNOx NH3-SCR zeolite catalyst Cu-CHA and the Cu ion migration in the zeolitic pores was revealed during catalytic activation experiments. A comparison with recent reports further reveals the high sensitivity of the redox-active centers concerning heating rates, temperature, and gas environment during catalytic activation. Previously, Cu+ was confirmed present only in the 6R. Results verify a novel 8R monovalent Cu site, an eventually large Cu+ presence upon heating to high temperatures in oxidative conditions, and demonstrate the unique potential in combining insitu PXRD and XANES techniques, with which both oxidation state and structural location of the redox-active centers in the zeolite framework could be tracked.
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| 2. |
- Borup, Anders Bæk, et al.
(författare)
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Unveiling the formation mechanism of PbxPdy intermetallic phases in solvothermal synthesis using in situ X-ray total scattering
- 2023
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Ingår i: Nanoscale. - 2040-3364. ; 15:45, s. 18481-18488
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Tidskriftsartikel (refereegranskat)abstract
- Pd possesses attractive catalytic properties and nano-structuring is an obvious way to enhance catalytic activity. Alloying Pd with Pb has been shown to enhance the catalytic effect of alcohol oxidation. Further optimization of the catalytic effect can be accomplished by controlling the particle size and key to this is understanding the formation mechanism. By monitoring solvothermal syntheses using in situ X-ray total scattering, this study unveils the formation mechanism of PbxPdy intermetallic nanoparticles. The formation occurs through a multi-step mechanism. Initially, Pd nanoparticles are formed, followed by incorporation of Pb into the Pd-structure, thus forming PbxPdy intermetallic nanoparticles. By varying the reaction time and temperature, the incorporation of Pb can be controlled, thereby tailoring the phase outcome. Based on the in situ solvothermal syntheses, ex situ autoclave syntheses were performed, resulting in the synthesis of Pb3Pd5 and Pb9Pd13 with a purity above 93%. The catalytic effect of these intermetallic phases towards the hydrogen evolution reaction (HER) is assessed. It is found that Pd, Pb3Pd5, and Pb9Pd13 have comparable stabilities, however, the overpotential increases with increasing amounts of Pb.
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| 3. |
- Broge, Nils Lau Nyborg, et al.
(författare)
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Exploration of anion effects in solvothermal synthesis using in situ X-ray diffraction
- 2024
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Ingår i: Physical Chemistry Chemical Physics. - 1463-9076. ; 26:15, s. 12121-12132
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Tidskriftsartikel (refereegranskat)abstract
- Solvothermal synthesis presents a facile and highly flexible approach to chemical processing and it is widely used for preparation of micro- and nanosized inorganic materials. The large number of synthesis parameters in combination with the richness of inorganic chemistry means that it is difficult to predict or design synthesis outcomes, and it is demanding to uncover the effect of different parameters due to the sealed and complex nature of solvothermal reactors along with the time demands related to reactor cleaning, sample purification, and characterization. This study explores the effect on formation of crystalline products of six common anions in solvothermal treatment of aqueous and ethanolic precursors. Three different cations are included in the study (Mn2+, Co2+, Cu2+) representing chemical affinities towards different regions of the periodic table with respect to the hard soft acid base (HSAB) classification and the Goldschmidt classification. They additionally belong to the commonly used 3d transition metals and display a suitable variety in solvothermal chemistry to highlight anion effects. The results of the solvothermal in situ experiments demonstrate a clear effect of the precursor anions, with respect to whether crystallization occurs or not and the characteristics of the formed phases. Additionally, some of the anions are shown to be redox active and to influence the formation temperature of certain phases which in turn relates to the observed average crystallite sizes.
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| 4. |
- Kløve, Magnus, et al.
(författare)
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Zr4+ solution structures from pair distribution function analysis
- 2022
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- The structures of metal ions in solution constitute essential information for obtaining chemical insight spanning from catalytic reaction mechanisms to formation of functional nanomaterials. Here, we explore Zr4+ solution structures using X-ray pair distribution function (PDF) analysis across pH (0-14), concentrations (0.1-1.5 M), solvents (water, methanol, ethanol, acetonitrile) and metal sources (ZrCl4, ZrOCl2·8H2O, ZrO(NO3)2·xH2O). In water, [Zr4(OH)8(OH2)16]8+-tetramers are predominant, while non-aqueous solvents contain monomeric complexes. The PDF analysis also reveals second sphere coordination of chloride counter ions to the aqueous tetramers. The results are reproducible across data measured at three different beamlines at the PETRA-III and MAX IV synchrotron light sources.
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| 5. |
- Ma, Yi, 1982, et al.
(författare)
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Thermoelectric characteristics of electrochemically deposited Bi2Te3 and Sb2Te3 thin films of relevance to multilayer preparation.
- 2012
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Ingår i: Journal of Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 159:2
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Tidskriftsartikel (refereegranskat)abstract
- Thermoelectric thin films of Bi2Te3 and Sb2Te3 were synthesized on a gold-coated silicon substrate from an aqueous acid bath at room temperature by electrochemical deposition. Both constant potential deposition and pulsed potential deposition were employed and the influence of the deposition conditions on the elemental composition, crystal structure and surface morphology of the films was investigated. After transfer of the films to an insulating substrate, the thermoelectric and transport properties of the as-deposited and annealed films were measured. The results show that the as-deposited Bi2Te3 thin films are polycrystalline with n-type semiconducting properties, while the as-deposited Sb2Te3 films displayed an amorphous structure. Annealing the as-deposited Sb2Te3 films caused them to crystallize as Sb2Te3 and in addition, resulted in a separate Te phase. The annealed films showed p-type semiconducting properties. For both systems, the thermoelectric properties of the films are consistently lower than their bulk counterparts. The reasons for the inferior thermoelectric properties are different for the two material types. Based on the studies of electrodeposition of the two compounds, an electrochemical method for preparation of multilayers composed of alternating Bi2Te3 and Sb2Te3 layers was explored.
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| 6. |
- Ma, Yi, 1982, et al.
(författare)
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Thermoelectric properties of thin films of bismuth telluride electrochemically deposited on stainless steel substrates
- 2011
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 56:11, s. 4216-4223
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Tidskriftsartikel (refereegranskat)abstract
- Bismuth telluride thin films have been synthesized by electrochemical deposition onto stainless steel substrates from acidic solutions. The influence of deposition variables on film composition, morphology and crystal orientation associated with the growth of the film was investigated by means of constant potential deposition and pulsed potential deposition. In-plane thermoelectric and transport properties of the electrodeposited films were measured. The carrier concentration of the electrodeposited films was found to be one order of magnitude larger than typically reported for optimized bulk bismuth telluride, which explains the unusually low Hall mobility and Seebeck coefficient values found for the electrodeposited films. Pulse deposited films showed slightly lower electrical resistivity and higher Seebeck coefficient due to the lower porosity and less preferred crystal orientation of the films compared to the continuously deposited films. Improvements of the film properties are necessary to make them viable for applications.
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| 7. |
- Nylen, Johanna, et al.
(författare)
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Low-temperature structural transitions in the phonon-glass thermoelectric material beta-Zn4Sb3 : Ordering of Zn interstitials and defects
- 2007
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 19:4, s. 834-838
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Tidskriftsartikel (refereegranskat)abstract
- The low-temperature phase transitions of thermoelectric Zn4Sb3 have been characterized using single-crystal X-ray diffraction, electrical resistance, and thermal conductivity measurements. Room-temperature stable, disordered beta-Zn4Sb3 undergoes a phase transition at 254 K to ordered alpha-Zn4Sb3, which has an ideal composition Zn13Sb10. Below 235 K, a second low-temperature phase (alpha'-Zn4Sb3) can be detected. The sequence of phase transitions beta-alpha-alpha' is reversible. The alpha-alpha' transformation originates from a slight Zn deficiency with respect to Zn13Sb10. The actual composition of Zn4Sb3 is Zn13-delta Sb10.
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| 8. |
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| 9. |
- Sangeetha, N. S., et al.
(författare)
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First-order antiferromagnetic transitions of SrMn2P2 and CaMn2P2 single crystals containing corrugated-honeycomb Mn sublattices
- 2021
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 118:44
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Tidskriftsartikel (refereegranskat)abstract
- SrMn2P2 and CaMn2P2 are insulators that adopt the trigonal CaAl2Si2-type structure containing corrugated Mn honeycomb layers. Magnetic susceptibility χ and heat capacity versus temperature T data reveal a weak first-order antiferromagnetic (AFM) transition at the Néel temperature TN=53(1) K for SrMn2P2 and a strong first-order AFM transition at TN=69.8(3) K for CaMn2P2. Both compounds exhibit isotropic and nearly T-independent χ(T≤TN), suggesting magnetic structures in which nearest-neighbor moments are aligned at ≈120° to each other. The 31P NMR measurements confirm the strong first-order transition in CaMn2P2 but show critical slowing down above TN for SrMn2P2, thus also evidencing second-order character. The 31P NMR measurements indicate that the AFM structure of CaMn2P2 is commensurate with the lattice whereas that of SrMn2P2 is incommensurate. These first-order AFM transitions are unique among the class of (Ca, Sr, Ba)Mn2 (P, As, Sb, Bi)2 compounds that otherwise exhibit second-order AFM transitions. This result challenges our understanding of the circumstances under which first-order AFM transitions occur.
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| 10. |
- Svane, Bjarke, et al.
(författare)
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Multipole electron densities and atomic displacement parameters in urea from accurate powder X-ray diffraction
- 2019
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Ingår i: Acta Crystallographica Section A: Foundations and Advances. - 2053-2733. ; 75, s. 600-609
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Tidskriftsartikel (refereegranskat)abstract
- Electron density determination based on structure factors obtained through powder X-ray diffraction has so far been limited to high-symmetry inorganic solids. This limit is challenged by determining high-quality structure factors for crystalline urea using a bespoke vacuum diffractometer with imaging plates. This allows the collection of data of sufficient quality to model the electron density of a molecular system using the multipole method. The structure factors, refined parameters as well as chemical bonding features are compared with results from the high-quality synchrotron single-crystal study by Birkedal et al. [Acta Cryst. (2004), A60, 371-381] demonstrating that powder X-ray diffraction potentially provides a viable alternative for electron density determination in simple molecular crystals where high-quality single crystals are not available.
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