I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[16508]
Abstract: The reaction between ceria and hydrogen has been subject to numerous theoretical and experimental studies due to its importance as a catalytic material. Here we present dynamic and reversible evolution of the cerium oxidation states observed through X-ray Absorption Spectroscopy experiments in addition to the investigation of associated lattice expansion and contraction through X-ray diffraction and PDF methods. Employing a novel calculation of the temperature dependence of the Gibbs free energy through consideration of the relationship between the instantaneous thermal lattice expansion and the rate of change of the cerium oxidation state, the unusual redox chemistry is reported here. This unusual behaviour is interpreted as due to the formation of a metastable cerium oxyhydride as suggested.
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Aug 2019
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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George F.
Tierney
,
Donato
Decarolis
,
Norli
Abdullah
,
Scott M.
Rogers
,
Shusaku
Hayama
,
Martha
Briceno De Gutierrez
,
Alberto
Villa
,
C. Richard A.
Catlow
,
Paul
Collier
,
Nikolaos
Dimitratos
,
Peter
Wells
Diamond Proposal Number(s):
[17283]
Open Access
Abstract: Sol-immobilization is increasingly used to achieve supported metal nanoparticles (NPs) with controllable size and shape; it affords a high degree of control of the metal particle size and yields a narrow particle size distribution. Using state-of-the-art beamlines, we demonstrate how X-ray absorption fine structure (XAFS) techniques are now able to provide accurate structural information on nano-sized colloidal Au solutions at μM concentrations. This study demonstrates: (i) the size of Au colloids can be accurately tuned by adjusting the temperature of reduction, (ii) Au concentration, from 50 μM to 1000 μM, has little influence on the average size of colloidal Au NPs in solution and (iii) the immobilization step is responsible for significant growth in Au particle size, which is further exacerbated at increased Au concentrations. The work presented demonstrates that an increased understanding of the primary steps in sol-immobilization allows improved optimization of materials for catalytic applications.
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May 2019
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Open Access
Abstract: Diamond Light Source (DLS) I20-Scanning is a high flux X-ray Absorption Spectroscopy (XAS) beamline optimized for challenging samples, operating between 4keV and 20keV. The principal detector used for collecting XAS in fluorescence mode is a Canberra 64-pixel Monolithic Segmented Hyper Pure Germanium Detector (HPGe) historically partnered with the STFC Xspress2 Digital Pulse Processor (DPP). Prior signal analysis had shown that key parameters such as Energy Resolution and Peak-to-Background ratio are compromised by pixel-to-pixel crosstalk within the detector, especially at higher count rates (>250kcps per pixel). The DLS Detector Group have developed the new Xspress4 DPP to address such issues. This results in typically a factor 3-7 increase in detector system count rate for the same Energy Resolution and Peak-to-Background ratio compared to the previous state-of-the-art DPP. An overview of the complete detector system is given and recent results obtained during the commissioning on the beamline are shown. Further, comparative results from challenging experiments are also shown, demonstrating the improved performance attainable at the previous high count rate by partnering legacy HPGe Detectors with the latest DPP technology.
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Jan 2019
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[9925]
Abstract: Fe-containing zeolites were studied as catalysts for the standard NH3-SCR reaction with the primary aim of gaining insight into the structure-function relationship of these materials. Catalysts with different Fe nuclearity (i.e. isolated species, clusters, large particles) were synthesised by incipient wetness impregnation, using H-ZSM-5, H-SSZ-13 and Silicalite-1 as supports, and characterised by in situ and operando X-ray emission spectroscopy (XES) and high energy resolution fluorescence detected X-ray absorption near-edge spectroscopy (HERFD-XANES) under NH3-SCR conditions. The combination of these techniques allowed us to obtain a detailed understanding of the changes in Fe coordination, oxidation state and geometry occurring during reaction. The results obtained suggested that isolated octahedral Fe3+ species on H-ZSM-5 are highly active under the conditions studied, undergoing reduction when exposed to NH3 or under SCR conditions. In contrast, isolated tetrahedral Fe3+ sites present in Silicalite-1 exhibited lower redox properties, leading to a reduced NO conversion. Clusters and FexOy particles on H-SSZ-13 exhibited low SCR activity.
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Nov 2018
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I20-Scanning-X-ray spectroscopy (XAS/XES)
Optics
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Shusaku
Hayama
,
Graham
Duller
,
John
Sutter
,
Monica
Amboage
,
Roberto
Boada
,
Adam
Freeman
,
Luke
Keenan
,
Brian
Nutter
,
Leo
Cahill
,
Pete
Leicester
,
Ben
Kemp
,
Nicholas
Rubies
,
Sofia
Diaz-moreno
Open Access
Abstract: A description of the technical and design details of a scanning four-bounce crystal monochromator that has recently been commissioned for the Versatile X-ray Absorption Spectroscopy (XAS) beamline at Diamond Light Source is presented. This device consists of two independent rotary axes of unique design which are synchronized using a multiple read-head encoder system. This monochromator is shown to be capable of maintaining the flux throughput of the Bragg axes without the need of any external feedback mechanism from 4 to 20 keV. The monochromator is currently equipped with cryogenically cooled crystals with the upstream axis consisting of two independent Si(111) crystals and a pair of channel-cut crystals in the downstream axis. The possibility of installing an additional Si(311) crystal-set to extend the energy range to 34 keV is incorporated into the preliminary design of the device. Experimental data are presented showing the exceptional mechanical stability and repeatability of the monochromator axes.
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Sep 2018
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B18-Core EXAFS
I18-Microfocus Spectroscopy
I20-EDE-Energy Dispersive EXAFS (EDE)
I20-Scanning-X-ray spectroscopy (XAS/XES)
Controls
Detectors
Optics
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Sofia
Diaz-moreno
,
Monica
Amboage
,
Mark
Basham
,
Roberto
Boada
,
Nicholas E.
Bricknell
,
Giannantonio
Cibin
,
Thomas
Cobb
,
Jacob
Filik
,
Adam
Freeman
,
Kalotina
Geraki
,
Diego
Gianolio
,
Shusaku
Hayama
,
Konstantin
Ignatyev
,
Luke
Keenan
,
Iuliia
Mikulska
,
J. Frederick W.
Mosselmans
,
James J.
Mudd
,
Stephen A.
Parry
Open Access
Abstract: This manuscript presents the current status and technical details of the Spectroscopy Village at Diamond Light Source. The Village is formed of four beamlines: I18, B18, I20-Scanning and I20-EDE. The village provides the UK community with local access to a hard X-ray microprobe, a quick-scanning multi-purpose XAS beamline, a high-intensity beamline for X-ray absorption spectroscopy of dilute samples and X-ray emission spectroscopy, and an energy-dispersive extended X-ray absorption fine-structure beamline. The optics of B18, I20-scanning and I20-EDE are detailed; moreover, recent developments on the four beamlines, including new detector hardware and changes in acquisition software, are described.
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Jul 2018
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B18-Core EXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Roberto
Boada
,
Giannantonio
Cibin
,
Fergal
Coleman
,
Sofia
Diaz-moreno
,
Diego
Gianolio
,
Christopher
Hardacre
,
Shusaku
Hayama
,
John D.
Holbrey
,
Rafin
Ramli
,
Keneth R.
Seddon
,
Geetha
Srinivasan
,
Gosia
Swadzba-kwasny
Diamond Proposal Number(s):
[2452, 11881]
Abstract: Mercury scrubbing from gas streams using a supported 1-butyl-3-methylimidazolium chlorocuprate(II)ionic liquid ([C4mim]2[Cu2Cl6]) has been studied using operandoEXAFS. Initial oxidative capture as [HgCl3]− anions was confirmed, this was then followed by the unanticipated generation of mercury(I) chloride through comproportionation with additional mercury from the gas stream. Combining these two mechanisms leads to net one electron oxidative extraction of mercury from the gas with increased potential capacity and efficiency for supported ionic liquid mercury scrubbers.
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Oct 2016
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Abstract: A comprehensive multi-technique approach has been used to address the controversial question of the preferred geometric form of the Cu2+ aqua-ion hydration shell. A combination of H/D isotopic substitution neutron scattering and X-ray scattering has been used to refine atomistic models of 0.5 m and 2.0 m solutions of Cu(ClO4)2, that have also been constrained to simultaneously reproduce detailed local structure information about the cation environment obtained by X-ray Absorption spectroscopy. The adoption of the Empirical Potential Structure Refinement (EPSR) technique as a single unified analytical framework minimises the chances for biasing the result in favour of a specific pre-conceived outcome. The results are consistent with an average coordination for each Cu2+ ion of 4.5 ± 0.6 water molecules that matches the more recent picture of five-fold coordination in a 2.0 m solution, but interestingly this combined study highlights that the preferred local geometry of the ion sites is found to have a mixed character of tetrahedral, trigonal bipyramidal and octahedral components. A further point to note is that this new model adds support to a largely ignored result in the literature relating to the linear electric field effect induced g-shifts observed in the electron paramagnetic resonance spectra of glassy Cu2+ complexes (Peisach and Mims, Chem. Phys. Lett., 1976, 37, 307–310) that first highlighted the importance of tetrahedral distortions in the cation's hydration shell structure.
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Jul 2013
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I20-EDE-Energy Dispersive EXAFS (EDE)
Optics
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Abstract: The X-ray focusing properties of a bent single crystal diffracting in Bragg geometry are discussed. First, it is assumed that a polychromatic point source is focused to a point image. The elliptical arc that the crystal must trace and the aberrations caused by bending the crystal cylindrically are derived from the ray paths. For a source of finite size, the magnification is found to vary over the crystal's length, so that rays of different wavelength produce images of different size. More realistic treatments of penetration and diffraction are performed with spherical monochromatic incident waves, using Takagi–Taupin calculations to create the diffracted wave and the Fresnel integral to trace the diffracted wave's evolution. Such “wave-optical” calculations on a symmetric Si (1 1 1) crystal with 7 keV X-rays predict beam sizes different from those found in ray traces. Optimal sample and detector placement therefore requires wave effects to be considered.
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Apr 2010
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I20-EDE-Energy Dispersive EXAFS (EDE)
I20-Scanning-X-ray spectroscopy (XAS/XES)
Optics
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Abstract: The Versatile Spectroscopy beamline at Diamond Light Source, I20, is currently under construction and aims to begin operation in late 2009 and early 2010. The beamline aims to cover applications from physics, chemistry and biology through materials, environmental and geological science. Three very distinctive modes of operation will be offered at the beamline: scanning X-ray Absorption spectroscopy (XAS), XAS in dispersive mode, and X-ray emission spectroscopy (XES). To achieve this, the beamline has been designed around two independent experimental end-stations operating from a pair of canted wigglers located in a 5m diamond straight section. One branch of the beamline will deliver monochromatic x-ray radiation of high spectral purity to one of the experimental hutches, whilst the other branch will constitute an energy dispersive spectrometer. The novel design of the beamline allows both branches to operate simultaneously.
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Jul 2009
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