B18-Core EXAFS
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Antonis M.
Messinis
,
Stephen L. J.
Luckham
,
Peter P.
Wells
,
Diego
Gianolio
,
Emma K.
Gibson
,
Harry M.
O’brien
,
Hazel A.
Sparkes
,
Sean A.
Davis
,
June
Callison
,
David
Elorriaga
,
Oscar
Hernandez-fajardo
,
Robin B.
Bedford
Diamond Proposal Number(s):
[15151]
Abstract: Iron-catalysed cross-coupling is undergoing explosive development, but mechanistic understanding lags far behind synthetic methodology. Here, we find that the activity of iron–diphosphine pre-catalysts in the Negishi coupling of benzyl halides is strongly dependent on the diphosphine, but the ligand does not appear to be coordinated to the iron during turnover. This was determined using time-resolved in operando X-ray absorption fine structure spectroscopy employing a custom-made flow cell and confirmed by 31P NMR spectroscopy. While the diphosphine ligands tested are all able to coordinate to iron(ii), in the presence of excess zinc(ii)—as in the catalytic reaction—they coordinate predominantly to the zinc. Furthermore, combined synthetic and kinetic investigations implicate the formation of a putative mixed Fe–Zn(dpbz) species before the rate-limiting step of catalysis. These unexpected findings may not only impact the field of iron-catalysed Negishi cross-coupling, but potentially beyond to reactions catalysed by other transition metal/diphosphine complexes.
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Dec 2018
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B18-Core EXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[9621, 13559, 17243]
Abstract: Iron (oxyhydr)oxide nanoparticles are known to sorb metals, including radionuclides, from solution in various environmental and industrial systems. Effluent treatment processes including the Enhanced Actinide Removal Plant (EARP) (Sellafield, UK) use a neutralisation process to induce the precipitation of iron (oxyhydr)oxides to remove radionuclides from solution. There is a paucity of information on mechanism(s) of U(VI) removal under conditions relevant to such industrial processes. Here, we investigated removal of U(VI) from simulated effluents containing 7.16 mM Fe(III) with 4.2 × 10-4-1.05 mM U(VI), during the base induced hydrolysis of Fe(III). The solid product was ferrihydrite under all conditions. Acid dissolutions, Fourier Transform infrared spectroscopy and thermodynamic modelling indicated that U(VI) was removed from solution by adsorption to the ferrihydrite. The sorption mechanism was supported by X-ray Absorption Spectroscopy which showed U(VI) was adsorbed to ferrihydrite via a bidentate edge-sharing inner-sphere species with carbonate forming a ternary surface complex. At concentrations ≤0.42 mM U(VI) was removed entirely via adsorption, however at 1.05 mM U(VI) there was also evidence for precipitation of a discrete U(VI) phase. Overall these results confirm that U(VI) sequestered via adsorption to ferrihydrite over a concentration range from 4.2 × 10-4-0.42 mM confirming a remarkably consistent removal mechanism in this industrially relevant system.
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Nov 2018
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B18-Core EXAFS
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Chunzhen
Yang
,
Maria
Batuk
,
Quentin
Jacquet
,
Gwenaëlle
Rousse
,
Wei
Yin
,
Leiting
Zhang
,
Joke
Hadermann
,
Artem
Abakumov
,
Giannantonio
Cibin
,
Alan
Chadwick
,
Jean-marie
Tarascon
,
Alexis
Grimaud
Diamond Proposal Number(s):
[12559]
Abstract: Multiple electrochemical processes are involved at the catalyst/electrolyte interface during the oxygen evolution reaction (OER). With the purpose of elucidating the complexity of surface dynamics upon OER, we systematically studied two Ni-based crystalline oxides (LaNiO3-δ and La2Li0.5Ni0.5O4) and compared them with the state-of-the-art Ni-Fe (oxy)hydroxide amorphous catalyst. Electrochemical measurements such as rotating ring disk electrode (RRDE) and electrochemical quartz microbalance microscopy (EQCM), coupled with a series of physical characterizations including transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) are conducted to unravel the exact pH effect on both the OER activity and the catalyst stability. We demonstrate that for Ni-based crystalline catalysts the rate for surface degradation depends on the pH and is greater than the rate for surface reconstruction. This behavior is unlike for amorphous Ni oxyhydroxide catalyst which is found more stable and pH independent.
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Nov 2018
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Tugce
Ayvali
,
Lin
Ye
,
Simson
Wu
,
Benedict T. W.
Lo
,
Chen
Huang
,
Bin
Yu
,
Giannantonio
Cibin
,
Angus I.
Kirkland
,
Chiu
Tang
,
Abdulaziz A.
Bagabas
,
S. C. Edman
Tsang
Diamond Proposal Number(s):
[16358, 14647]
Abstract: Deposition of gold on supports can produce catalytically active forms of gold as well as spectators, but previous understanding of the nature of active immobilized precursors is poor. By using synchrotron X-ray powder diffraction (SXRD) and X-ray absorption spectroscopy (XAS) techniques, we report a novel synthesis and structural elucidation of atomically dispersed gold species anchored to the internal surface of TS-1 as K+Au(OH)2Na+(Of)3 (“f” signifies the framework atoms of TS-1 in the formula.). It is found that the choice of alkali ions plays a crucial role in nucleation and stabilization of the atomic precursor. These anchored single Au upon controlled reduction in H2 can form uniform gold clusters in direct contact with the TS-1 surface containing isolated Ti sites: their interface exhibits excellent specificity and stability towards epoxidation of propylene in H2/O2 due to synergetic effect.
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Nov 2018
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B18-Core EXAFS
I22-Small angle scattering & Diffraction
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Elizabeth
Raine
,
Adam
Clark
,
Glen
Smales
,
Andrew
Smith
,
Diego
Gianolio
,
Tong
Li
,
Jianwei
Zheng
,
Benjamin
Griffith
,
Timothy I.
Hyde
,
Mark
Feaviour
,
Paul
Collier
,
John V.
Hanna
,
Gopinathan
Sankar
,
Shik Chi Edman
Tsang
Diamond Proposal Number(s):
[16316, 16583]
Abstract: The strong directing effects and difficulties in the removal of organic based surfactants makes the templated synthesis of nanoparticles in solid porous structures of defined molecular sizes such as SBA-15, without the use of surfactants, considerably attractive. However, the effects of their internal surface structures, adsorption affinities and lattice mis-match on the particle morphology grown therein have not been fully appreciated. Here, we report the internal surface of the silica preferentially hosts isolated tetrahedrally coordinated oxidic Zn species on the molecular walls of the SBA-15 channels from wet impregnated Zn2+ and Pt2+ species. This leads to less thermodynamic stable but kinetic controlled configuration of atomic zinc deposition on core platinum nanoparticles with unique confined lattice changes and surface properties to both host and guest structures at the interface upon reduction of the composite. This method for the formation templated nanoparticles may generate interests to form new tunable materials as dehydrogenation catalysts.
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Nov 2018
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B18-Core EXAFS
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María
Retuerto
,
Federico
Calle-vallejo
,
Laura
Pascual
,
Pilar
Ferrer
,
Álvaro
García
,
Jorge
Torrero
,
Diego
Gianolio
,
José Luis G.
Fierro
,
Miguel A.
Peña
,
José Antonio
Alonso
,
Sergio
Rojas
Diamond Proposal Number(s):
[18119]
Abstract: The activity of oxides towards the oxygen evolution reaction (OER) is usually tuned by changing the transition metal components and/or the surface facets. An important yet less studied feature is the repercussion of the lattice oxygen content of the oxide in the active site's coordination and catalytic performance. This is illustrated here for the Ba-Ni-O system. We synthesized two oxides with Ni in different coordination and oxidation states, namely BaNiO2 with Ni2+ in square-planar positions, and BaNiO2.78(2) with Ni3+ and Ni4+ in octahedral positions. We show that the square-planar configuration of Ni endows BaNiO2 with high intrinsic OER activity, comparable to the best catalysts in the literature. DFT indicates that progressively lowering the lattice oxygen content from BaNiO3 to BaNiO2 increases the Ni sites' affinity for the reaction intermediates, thereby lowering the OER overpotential. Thus, oxygen content is an important parameter in oxide catalysts, as it modulates the coordination, orbital splitting, oxidation number, and catalytic activity of the active sites.
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Nov 2018
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B18-Core EXAFS
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Open Access
Abstract: In this work, we will report applications of the total external X-ray fluorescence (TXRF) station, a prototype assembled at the XLab Frascati laboratory (XlabF) at the INFN National Laboratories of Frascati (INFN LNF). XlabF has been established as a facility to study, design and develop X-ray optics, in particular, polycapillary lenses, as well as to perform X-ray experiments for both elemental analysis and tomography. The combination of low-power conventional sources and policapillary optics allows assembling a prototype that can provide a quasi-parallel intense beam for detailed X-ray spectroscopic analysis of extremely low concentrated samples, down to ng/g. We present elemental analysis results of elements contained in tree rings and of dust stored in deep ice cores. In addition to performing challenging environmental research studies, other experiments aim to characterize novel optics and to evaluate original experimental schemes for X-ray diffraction (XRD), X-ray fluorescence (XRF and TXRF) and X-ray imaging.
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Oct 2018
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B18-Core EXAFS
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Delphine
Malarde
,
Ian D.
Johnson
,
Ian J.
Godfrey
,
Michael J.
Powell
,
Giannantonio
Cibin
,
Raul
Quesada-cabrera
,
Jawwad A.
Darr
,
Claire J.
Carmalt
,
Gopinathan
Sankar
,
Ivan P.
Parkin
,
Robert G.
Palgrave
Diamond Proposal Number(s):
[17147]
Open Access
Abstract: Monoclinic vanadium(IV) oxide [VO2(M)] is a widely studied material due to its thermochromic properties and its potential use for energy-efficient glazing applications. VO2(M) nanoparticles can be a great advantage for energy-efficient glazing as below 50 nm the nanoparticles poorly interact with visible wavelengths – resulting in an increase in visible light transmittance whilst maintaining the thermochromic response of the material. The direct synthesis of VO2(M) nanoparticles with effective thermochromic properties will be a step forward towards industrial applications of this material. Unfortunately, many of the synthesis processes reported so far involve multiple steps, including post-treatment, and the synthesis is not always reproducible. In this study, we present the first direct synthesis of pure monoclinic VO2 nanoparticles by continuous hydrothermal flow synthesis (CHFS). TEM images showed that nanoparticles in the size range of 30-40 nm were produced. The VO2(M) nanoparticles also showed good thermochromic properties with a solar modulation (∆Tsol) of 3.8%, as established by UV/Vis spectroscopy. A range of analytical methods was used to characterise the materials, including X-ray absorption spectroscopy (XANES and EXAFS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The influence of niobium (Nb) doping on the physical and thermochromic properties of the VO2 nanoparticles was also explored. Previous work has shown a sharp metal-to-semiconductor transition of VO2 upon incorporation of Nb dopant. The results of the current work suggested these changes are likely due to changes on the local structure of the oxide.
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Oct 2018
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[18250]
Abstract: A series of surfactant-free nickel-core and silver-shell (Ni@Ag) nanoparticles encapsulated within the mesopores of SBA-15 were synthesized and tested as catalysts for direct propylene oxidation by molecular oxygen. The influences of temperature, Gas Hour Space Velocity (GHSV) and Ni/Ag ratio on catalytic activity were systematically investigated. Among the prepared samples, Ni1Ag0.4/SBA-15 exhibited the best catalytic performance with selectivity of 70.7% and PO production rate of 4.4 nmol/g/s under 1 bar at 220 °C with GHSV of 192 h-1. High selectivity was attributed to longer Ag-Ag interatomic distance obtained by careful engineering the thickness of Ag shell over preformed Ni nanoparticles. In addition, all prepared new Ni@Ag core-shell catalysts presented excellent stability, which could maintain the conversion and selectivity for at least 10 hours. These results suggest that new designs based on Ag surface atoms tailoring might pave the way to highly efficient and robust Ag catalysts for direct propylene oxidation using molecular oxygen as sole oxidant.
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Oct 2018
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B18-Core EXAFS
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Open Access
Abstract: Spin crossover (SCO) complexes are an example of potential molecular bistability. This effect describes the ability of a system to undergo a transition from a low spin (LS) to a high spin (HS) state by an external perturbation, e.g. temperature or pressure. The exact mechanisms underlying a spin transition are not completely understood yet, since complex processes take place both at the structural and the electronic level. With the known standard methods, these changes cannot be investigated simultaneously in one experiment (Structure change: XRD, XAS, spin state: Mößbauer, SQUID). Therefore, subject of this thesis is the in-depth analysis of existing methods and their improvement by development of new approaches for the analysis of temperature-dependent SCO processes with hard X-ray absorption and emission spectroscopic techniques. With these methods, it is possible to follow the structural and electronic changes in one experiment quasi-simultaneously without changing the experimental conditions. Temperature-dependent EXAFS, HERFD-XANES, CtC, and VtC XES experiments were performed on a mononuclear Fe (II) complex with a gradual SCO behaviour. All spectra showed interesting behaviour caused by the transition from the LS to the HS state. The spectral changes were quantified by several approaches and the results were compared to magnetization data obtained by SQUID magnetometry. It was shown that in principle all methods are well suited for the investigation of SCO processes.
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Oct 2018
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