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15 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2 [Next/Last]

Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS I20-EDE-Energy Dispersive EXAFS (EDE)	Combined spatially resolved operando spectroscopy: New insights into kinetic oscillations of CO oxidation on Pd/γ-Al2O3 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 Journal Of Catalysis 373, 201 - 208 DOI: 10.1016/j.jcat.2019.03.037 Diamond Proposal Number(s): [17340, 17725] Open Access Show Abstract ▼ 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.	May 2019
I20-Scanning-X-ray spectroscopy (XAS/XES) Optics	The scanning four-bounce monochromator for beamline I20 at the Diamond Light Source 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 Journal Of Synchrotron Radiation 25 DOI: 10.1107/S1600577518008974 Open Access Show Abstract ▼ 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.	Sep 2018
B18-Core EXAFS I18-Microfocus Spectroscopy I20-EDE-Energy Dispersive EXAFS (EDE) I20-Scanning-X-ray spectroscopy (XAS/XES) Controls Detectors Optics	The Spectroscopy Village at Diamond Light Source 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 Journal Of Synchrotron Radiation 25 DOI: 10.1107/S1600577518006173 Open Access Show Abstract ▼ 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.	Jul 2018
I15-Extreme Conditions	New high-pressure van der Waals compound Kr(H2)4 discovered in the krypton-hydrogen binary system Annette Kleppe , Monica Amboage , Andrew Jephcoat Scientific Reports 4 DOI: 10.1038/srep04989 Diamond Proposal Number(s): [7371, 7006] Open Access Show Abstract ▼ 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.	May 2014
I15-Extreme Conditions	Synthesis of a Novel Zeolite through a Pressure-Induced Reconstructive Phase Transition Process 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 Angewandte Chemie International Edition 52 (40), 10458 - 10462 DOI: 10.1002/anie.201305230 Show Abstract ▼ 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.	Sep 2013
I15-Extreme Conditions	Synthesis of a Novel Zeolite through a Pressure-Induced Reconstructive Phase Transition Process 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 Angewandte Chemie DOI: 10.1002/ange.201305230 Show Abstract ▼ 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.	Aug 2013
I20-Scanning-X-ray spectroscopy (XAS/XES)	The hydration structure of Cu2+: More tetrahedral than octahedral? Daniel Bowron , Monica Amboage , Roberto Boada Romero , Adam Freeman , Shusaku Hayama , Sofia Diaz-moreno Rsc Advances DOI: 10.1039/c3ra42400f Show Abstract ▼ 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.	Jul 2013
	Crystal Chemistry of CdIn2S4, MgIn2S4, and MnIn2S4 Thiospinels under High Pressure D. Santamaria-perez , Monica Amboage , F. J. Manjon , Daniel Errandonea , A. Munoz , P. Rodriguez-hernandez , A. Mujica , S. Radescu , V. V. Ursaki , I. M. Tiginyanu Journal Of Physical Chemistry C 116 (26), 14078-14087 DOI: 10.1021/jp303164k Show Abstract ▼ 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.	Jul 2012
	High pressure x-ray diffraction study of the volume collapse in Ba24Si100 clathrate P. Toulemonde , D. Machon , A. San Miguel , Monica Amboage Physical Review B 83 (13), 134110 DOI: 10.1103/PhysRevB.83.134110 Show Abstract ▼ 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.	Apr 2011
I20-EDE-Energy Dispersive EXAFS (EDE) Optics	Geometrical and wave-optical effects on the performance of a bent-crystal dispersive X-ray spectrometer John Sutter , Monica Amboage , Shusaku Hayama , Sofia Diaz-moreno Nuclear Instruments And Methods In Physics Research Section A DOI: 10.1016/j.nima.2010.03.139 Show Abstract ▼ 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.	Apr 2010

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