B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
B18-Core EXAFS
I20-EDE-Energy Dispersive EXAFS (EDE)
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Rachel H.
Blackmore
,
Maria Elena
Rivas
,
George F.
Tierney
,
Khaled M. H.
Mohammed
,
Donato
Decarolis
,
Shusaku
Hayama
,
Federica
Venturini
,
Georg
Held
,
Rosa
Arrigo
,
Monica
Amboage
,
Pip
Hellier
,
Evan
Lynch
,
Mahrez
Amri
,
Marianna
Casavola
,
Tugce
Eralp Erden
,
Paul
Collier
,
Peter P.
Wells
Diamond Proposal Number(s):
[20129, 20200, 22063, 15151]
Open Access
Abstract: The use of mechanochemistry to prepare catalytic materials is of significant interest; it offers an environmentally beneficial, solvent-free, route and produces highly complex structures of mixed amorphous and crystalline phases. This study reports on the effect of milling atmosphere, either air or argon, on mechanochemically prepared LaMnO3 and the catalytic performance towards N2O decomposition (deN2O). In this work, high energy resolution fluorescence detection (HERFD), X-ray absorption near edge structure (XANES), X-ray emission, and X-ray photoelectron spectroscopy (XPS) have been used to probe the electronic structural properties of the mechanochemically prepared materials. Moreover, in situ studies using near ambient pressure (NAP)-XPS, to follow the materials during catalysis, and high pressure energy dispersive EXAFS studies, to mimic the preparation conditions, have also been performed. The studies show that there are clear differences between the air and argon milled samples, with the most pronounced changes observed using NAP-XPS. The XPS results find increased levels of active adsorbed oxygen species, linked to the presence of surface oxide vacancies, for the sample prepared in argon. Furthermore, the argon milled LaMnO3 shows improved catalytic activity towards deN2O at lower temperatures compared to the air milled and sol–gel synthesised LaMnO3. Assessing this improved catalytic behaviour during deN2O of argon milled LaMnO3 by in situ NAP-XPS suggests increased interaction of N2O at room temperature within the O 1s region. This study further demonstrates the complexity of mechanochemically prepared materials and through careful choice of characterisation methods how their properties can be understood.
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Jun 2020
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B18-Core EXAFS
I20-EDE-Energy Dispersive EXAFS (EDE)
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Ellie K.
Dann
,
Emma K.
Gibson
,
C. Richard A.
Catlow
,
Veronica
Celorrio
,
Paul
Collier
,
Tugce
Eralp
,
Monica
Amboage
,
Christopher
Hardacre
,
Cristina
Stere
,
Anna
Kroner
,
Agnes
Raj
,
Scott
Rogers
,
Alexandre
Goguet
,
Peter P.
Wells
Diamond Proposal Number(s):
[17340, 17725]
Open Access
Abstract: Spatially resolved, combined energy dispersive EXAFS (EDE) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements have been performed over a fixed catalyst bed of Pd/γ-Al2O3 during kinetic oscillations of CO oxidation. The kinetic oscillations of CO oxidation over Pd (or for that matter Pt or Rh) catalysts are a complicated phenomenon that require characterisation techniques with high time resolution and spatial resolution in order to make links between catalyst structure and surface reactivity. By measuring the extent of Pd oxidation at the nanoparticle surface, from Pd K-edge EDE, and matching this with the CO coverage, from DRIFTS spectra, at multiple positions of the fixed bed reactor it is found that the majority of the catalyst undergoes a sharp transition from the CO poisoned catalyst to the highly active, oxidised Pd surface. This transition occurs initially at the end of the catalyst bed, nearest the outlet, and propagates upstream with increasing temperature of the reactor. The oscillations in Pd surface oxide formation and CO coverage are observed only in the first ∼1 mm of the bed, which gives rise to oscillations in CO2 and O2 concentrations observed by end-pipe mass spectrometry after the light-off temperature. The catalyst initially exists as less active, CO poisoned metallic Pd nanoparticles before light-off which transition to a highly active state after light-off when the Pd nanoparticle surface becomes dominated by chemisorbed oxygen. Kinetic oscillations only occur at the front of the catalyst bed where there is sufficient concentration of CO in the gas phase to compete with O2 for adsorption sites at the catalyst surface. We demonstrate the complex nature of the evolving catalyst structure and surface reactivity during catalytic operation and the need for spatially resolved operando methods for understanding and optimising catalyst technologies.
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May 2019
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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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I15-Extreme Conditions
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Diamond Proposal Number(s):
[7371, 7006]
Open Access
Abstract: The application of pressure to materials can reveal unexpected chemistry. Under compression, noble gases
form stoichiometric van der Waals (vdW) compounds with closed-shell molecules such as hydrogen, leading
to a variety of unusual structures. We have synthesised Kr(H2)4 for the first time in a diamond-anvil
high-pressure cell at pressures$5.3 GPa and characterised its structural and vibrational properties to above
50 GPa. The structure of Kr(H2)4, as solved by single-crystal synchrotron X-ray diffraction, is face-centred
cubic (fcc) with krypton atoms forming isolated octahedra at fcc sites. Rotationally disorderedH2 molecules
occupy four different, interstitial sites, consistent with the observation of four Raman activeH2 vibrons. The
discovery of Kr(H2)4 expands the range of pressure-stabilised, hydrogen-rich vdW solids, and, in
comparison with the two known rare-gas-H2 compounds, Xe(H2)8 and Ar(H2)2, reveals an increasing
change in hydrogen molecular packing with increasing rare gas atomic number.
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May 2014
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I15-Extreme Conditions
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Jose Luis
Jorda Moret
,
Fernando
Rey
,
German
Sastre
,
Susana
Valencia
,
Miguel
Palomino
,
Avelino
Corma
,
Alfredo
Segura
,
Daniel
Errandonea
,
Raul
Lacomba Perales
,
Francisco Javier
Manjon Herrera
,
Oscar
Gomis
,
Annette
Kleppe
,
Andrew
Jephcoat
,
Monica
Amboage
,
J. Alberto
Rodríguez-velamazán
Abstract: The first pressure-induced solid-phase synthesis of a zeolite has been found through compression of a common zeolite, ITQ-29 (see scheme, Si yellow, O red). The new microporous structure, ITQ-50, has a unique structure and improved performance for propene/propane separation with respect the parent material ITQ-29.
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Sep 2013
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I15-Extreme Conditions
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Jose L.
Jordá
,
Fernando
Rey
,
German
Sastre
,
Susana
Valencia
,
Miguel
Palomino
,
Avelino
Corma
,
Alfredo
Segura
,
Daniel
Errandonea
,
Raul
Lacomba
,
Francisco Javier
Manjon
,
Oscar
Gomis
,
Annette
Kleppe
,
Andrew
Jephcoat
,
Monica
Amboage
,
J. Alberto
Rodríguez-velamazán
Abstract: Durch Druckeinwirkung auf den herkömmlichen Zeolith ITQ-29 gelang erstmals die druckinduzierte Festphasensynthese eines Zeoliths (siehe Schema; Si gelb, O rot): Das Produkt, ITQ-50, hat eine einzigartige mikroporöse Struktur und ist leistungsfähiger in der Propen-Propan-Trennung als das Ausgangsmaterial ITQ-29.
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Aug 2013
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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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Abstract: We report X-ray diffraction measurements in CdIn2S4, MgIn2S4, and MnIn2S4 thiospinels at room temperature and high pressures. The pressure dependences of the structural parameters have been determined and compared to those from theoretical calculations. It is found that the three thiospinels have similar bulk moduli (B0) between 75 and 80 GPa (B0′ ∼ 3). The degree of inversion of these thiospinels has also been determined. The three thiospinels undergo a phase transition toward a defect LiTiO2-type structure above 9.5, 8.3, and 6.8 GPa in CdIn2S4, MgIn2S4, and MnIn2S4, respectively. Interestingly, the low- and high-pressure phases belong to the same symmetry group (Fd-3m), the transition mechanism being associated to the migration of the tetrahedrally coordinated cations to a Wyckoff position of higher multiplicity, where these cations present an octahedral environment. The new postspinel phase exhibits a larger compressibility than the spinel phase for the three compounds, likely due to the presence of stoichiometric vacancies in the unit cell as it occurs for defect chalcopyrites and stannites. The relation between the bulk and the polyhedral compressibilities is discussed as well.
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Jul 2012
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Abstract: The high pressure stability of the silicon type-III clathrate Ba24Si100 has been studied by x-ray diffraction (XRD) up to a maximum pressure of 37.4 GPa. The high pressure behavior of this Si type-III clathrate appears to be analogous to the structural type-I parent Ba8Si46. An isostructural volume collapse is observed at ~23 GPa, a value higher than for Ba8Si46 (13-15 GPa). The crystallinity of the structure is preserved up to the maximum attained pressure without amorphization, which appears to be in contradiction with the interpretation given in a Raman spectroscopy study [Shimizu et al., Phys. Rev. B 71, 094108 (2005)]. Nevertheless, the XRD analysis shows the appearance of a type-III disordered nanocaged-based crystalline structure after the volume collapse. Moreover, we find that the volume collapse transformation is (quasi)reversible after pressure release. Additionally, a low pressure transition first evidenced by Raman spectroscopy is also observed in our XRD study at 5 GPa: The variation of the isotropic thermal factors of Ba atoms shows a clear discontinuity at this pressure while the average positions of Ba atoms remain identical.
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Apr 2011
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