I14-Hard X-ray Nanoprobe
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Open Access
Abstract: The Hard X-ray Nanoprobe beamline, I14, at Diamond Light Source is a new facility for nanoscale microscopy. The beamline was designed with an emphasis on multi-modal analysis, providing elemental mapping, speciation mapping by XANES, structural phase mapping using nano-XRD and imaging through differential phase contrast and ptychography. The 185 m-long beamline operates over a 5 keV to 23 keV energy range providing a ≤50 nm beam size for routine user experiments and a flexible scanning system allowing fast acquisition. The beamline achieves robust and stable operation by imaging the source in the vertical direction and implementing horizontally deflecting primary optics and an overfilled secondary source in the horizontal direction. This paper describes the design considerations, optical layout, aspects of the hardware engineering and scanning system in operation as well as some examples illustrating the beamline performance.
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May 2021
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I20-EDE-Energy Dispersive EXAFS (EDE)
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Diamond Proposal Number(s):
[21869]
Abstract: Modelling the reservoirs and fluxes of Zn in Earth's crust and mantle requires data on the solubility of its mineral hosts and ores in coexisting fluids, as well as on the complexation of Zn in these fluids as a function of fluid composition, pressure, and temperature. However, due to experimental challenges, the availability of such data is limited to pressures below 1 GPa, which are only representative of upper crust conditions.
Here, we report the effects of salinity (0–4.5 m total Cl), pressure (0.5–6 GPa) and temperature (25–400 °C) on the solubility of smithsonite (ZnCO3) and speciation of Zn in aqueous fluids. Solubilities at mineral-fluid equilibria and Zn speciation in the coexisting aqueous fluids were determined in situ at high pressure-temperature conditions by synchrotron X-ray fluorescence (XRF) and X-ray absorption spectroscopy (XAS) using resistively heated diamond anvil cells (RH-DAC). The solubility of smithsonite increases with salinity, pressure, and temperature. In agreement with previous studies, conducted at lower pressures (below 1 GPa), we observed a gradual transition from octahedral hydrated [Zn(H2O)6]2+ to tetrahedral hydrated and chlorinated [Zn(H2O)4-nCln]2-n (n = 1–4) complexes with increasing salinity and temperature. Our results suggest that these tetrahedral complexes remain stable under the conditions relevant to cold slab dehydration. This change of coordination further enhances the solubility of smithsonite in Cl-rich fluids and provides a likely mechanism for the efficient uptake of Zn by slab-derived fluids.
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May 2021
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B18-Core EXAFS
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Diamond Proposal Number(s):
[13606]
Open Access
Abstract: Among all iron oxides, hematite (α-Fe2O3), goethite (α-FeOOH), and ferrihydrite (FeOOH⋅nH2O) are the most common mineral species. While immobilization of Mo6+ by surface adsorption on ferric oxides has been studied extensively, the mechanisms of incorporation in their structure have been researched little. The objective of this study was to investigate the relation between Mo content and its structural incorporation in hematite, goethite, and six-line ferrihydrite by a combination of X-ray absorption spectroscopy (XAS), powder X-ray diffraction (pXRD), and inductively-coupled plasma optical emission spectrometry (ICP-OES). Synthesized in the presence of Mo, the hematite, goethite, and six-line ferrihydrite phases incorporated up to 8.52, 0.03, and 17.49 wt. % Mo, respectively. For hematite and goethite, pXRD analyses did not indicate the presence of separate Mo phases. Refined unit-cell parameters correlated with increasing Mo concentration in hematite and goethite. The unit-cell parameters indicated an increase in structural disorder within both phases and, therefore, supported the structural incorporation of Mo in hematite and goethite. Analysis of pXRD measurements of Mo-bearing six-line ferrihydrites revealed small amounts of coprecipitated akaganéite. X-ray absorption near edge structure (XANES) measurements at the Mo L3-edge indicated a strong distortion of the MoO6 octahedra in all three phases. Fitting of extended X-ray absorption fine structure (EXAFS) spectra of the Mo K-edge supported the presence of such distorted octahedra in a coordination environment similar to the Fe position in the investigated specimen. Incorporation of Mo6+ at the Fe3+-position for both hematite and goethite resulted in the formation of one Fe vacancy in close proximity to the newly incorporated Mo6+ and, therefore, charge balance within the hematite and goethite structures.
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May 2021
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[19114]
Abstract: The preparation of MOFs including a metal with an easily exchangeable oxidation state, while maintaining the same crystal structure and stability, is of paramount importance for myriad applications. In this work, a new synthesis method is reported that can be used to prepare Ce/Zr‐MOFs (UiO‐66 structure) having only Ce(III), a mixed‐valence Ce(IV)/Ce(III), or only Ce(IV) cations, as desired. The materials are characterized using a large number of techniques, including X‐ray absorption and X‐ray photoelectron spectroscopies.
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May 2021
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B18-Core EXAFS
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Siyu
Zhao
,
Ruikuan
Xie
,
Liqun
Kang
,
Manni
Yang
,
Xingyu
He
,
Wenyao
Li
,
Ryan
Wang
,
Dan J. L.
Brett
,
Guanjie
He
,
Guoliang
Chai
,
Ivan P.
Parkin
Diamond Proposal Number(s):
[19850]
Open Access
Abstract: It remains a challenge to develop efficient electrocatalysts in neutral media for hydrogen evolution reaction (HER) due to the sluggish kinetics and switch of the rate determining step. Although metal phosphides are widely used HER catalysts, their structural stability is an issue due to oxidization, and the HER performance in neutral media requires improvement. Herein, a new material, i.e., grapevine‐shaped N‐doped iron phosphide on carbon nanotubes, as an efficient HER catalyst in neutral media is developed. The optimized catalyst shows an overpotential of 256 mV at a large current density of 65 mA cm−2, which is even 10 mV lower than that of the commercial 20% Pt/C catalyst. The excellent performance of the catalyst is further studied by combined computational and experimental techniques, which proves that the interaction between nitrogen and iron phosphides can provide more efficient active structures and stabilize the metal phosphide electrocatalysts for HER.
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May 2021
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I10-Beamline for Advanced Dichroism
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Xiaoqian
Zhang
,
Qiangsheng
Lu
,
Wenqing
Liu
,
Wei
Niu
,
Jiabao
Sun
,
Jacob
Cook
,
Mitchel
Vaninger
,
Paul F.
Miceli
,
David J.
Singh
,
Shang-Wei
Lian
,
Tay-Rong
Chang
,
Xiaoqing
He
,
Jun
Du
,
Liang
He
,
Rong
Zhang
,
Guang
Bian
,
Yongbing
Xu
Diamond Proposal Number(s):
[22532]
Open Access
Abstract: While the discovery of two-dimensional (2D) magnets opens the door for fundamental physics and next-generation spintronics, it is technically challenging to achieve the room-temperature ferromagnetic (FM) order in a way compatible with potential device applications. Here, we report the growth and properties of single- and few-layer CrTe2, a van der Waals (vdW) material, on bilayer graphene by molecular beam epitaxy (MBE). Intrinsic ferromagnetism with a Curie temperature (TC) up to 300 K, an atomic magnetic moment of ~0.21 𝜇B
μ
B
/Cr and perpendicular magnetic anisotropy (PMA) constant (Ku) of 4.89 × 105 erg/cm3 at room temperature in these few-monolayer films have been unambiguously evidenced by superconducting quantum interference device and X-ray magnetic circular dichroism. This intrinsic ferromagnetism has also been identified by the splitting of majority and minority band dispersions with ~0.2 eV at Г point using angle-resolved photoemission spectroscopy. The FM order is preserved with the film thickness down to a monolayer (TC ~ 200 K), benefiting from the strong PMA and weak interlayer coupling. The successful MBE growth of 2D FM CrTe2 films with room-temperature ferromagnetism opens a new avenue for developing large-scale 2D magnet-based spintronics devices.
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May 2021
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Open Access
Abstract: A scanning multi-crystal x-ray emission spectrometer to perform photon-in/photon-out spectroscopy at the I20-Scanning beamline at Diamond Light Source is described. The instrument, equipped with three analyzer crystals, is based on a 1m Rowland circle spectrometer operating in the vertical plane. The energy resolution of the spectrometer is of the order of 1 eV, having sufficient resolving power to overcome the core-hole lifetime broadening of most of the transition metals K-edges. Examples showing the capabilily of the beamline for performing high energy resolution fluorescence detection x-ray absorption spectroscopy (HERFD-XAS), non-resonant x-ray emission spectroscopy (XES) and resonant x-ray emission spectroscopy (RXES) are presented. The comparison of the Zn and Mn K-edge HERFD-XANES of ZnO and MnO with ab-initio calculations shows that the technique provides enhanced validation of the models by making subtle spectral features more visible.
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May 2021
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B18-Core EXAFS
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Monik
Panchal
,
June
Callison
,
Vainius
Skukauskas
,
Diego
Gianolio
,
Giannantonio
Cibin
,
Andrew P. E.
York
,
Manfred Erwin
Schuster
,
Timothy I.
Hyde
,
Paul
Collier
,
C. Richard A.
Catlow
,
Emma K.
Gibson
Diamond Proposal Number(s):
[24156]
Open Access
Abstract: Platinum group metals (PGM) such as palladium and rhodium based catalysts are currently being implemented in Gasoline Particulate Filter (GPF) autoexhaust aftertreatment systems. However, little is known about how the trapped particulate matter, such as the incombustible ash, interacts with the catalyst and so may affect its performance. This operando study follows the evolution of the Pd found in two different model GPF systems: one containing ash components extracted from a GPF and another from a catalyst washcoat prior to adhesion onto the GPF. We show that the catalytic activity of the two systems vary when compared with a 0 g ash containing GPF. Compared to the 0 g ash sample the 20 g ash containing sample had a higher CO light off temperature, in addition, an oscillation profile for CO, CO2 and O2 was observed, which is speculated to be a combination of CO oxidation, C deposition via a Boudouard Reaction and further partial oxidation of the deposited species to CO. During the ageing procedure the washcoat sample reduces NO at a lower temperature than the 0 g ash sample. However, post ageing the 0 g ash sample recovers and both samples reduce NO at 310 circleC. In comparison, the 20 g ash GPF sample maintains a higher NO reduction temperature of 410 circleC post ageing, implying that the combination of high temperature ageing and presence of ash has an irreversible negative effect on catalyst performance.
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May 2021
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B18-Core EXAFS
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Diamond Proposal Number(s):
[15151]
Abstract: Hydrothermal degreening and ageing procedures were applied to a tri-metal (Pt-Pd-Rh) fully formulated lean NOX Trap catalyst to evaluate the effects of thermal stress on the performances and structural properties. X-ray absorption fine structure (XAFS) analysis revealed that the average size of the platinum particles was the same after degreening and ageing treatments. The formation of a new phase of alloyed Pt-Pd was observed to increase with the thermal load. The size of the ceria particles also increased after the ageing treatment. NOX storage capacity experiments revealed a substantial decrease of the concentration of active NOX storage sites which correlated with both ageing and degreening protocols. The performances of the treated catalyst were evaluated through spatially resolved (SpaciMS) lean-rich cycles. During the lean phase, the impact of the decrease in storage sites was significant on the aged sample, where an enlargement of the area required to achieve full storage was observed. On the other hand, the regeneration functionalities did not appear to be particularly affected by ageing. Rather, the aged sample showed a decrease of oxygen storage capacity (OSC), which promoted a lower reductant consumption and therefore a quicker and more efficient reduction process. On the other hand, the different distributions of adsorbed species by the end of the lean phase produced greater spread presence of NH3 and NOX slip along the channels of the aged sample during the reduction.
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Apr 2021
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B18-Core EXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Abstract: Mixed metal oxides are important catalysts in industrial processes that transform bulk hydrocarbons into useful intermediates and products. The oxygen lattice is uniquely able to facilitate redox reactions by rapidly transporting reactive species between active sites. The bulk structure of the lattice governs the availability of electrons, the reactivity of oxygen, and hence the efficiency of catalytic processes. An in-depth understanding of catalyst structure and formation mechanisms is therefore key to the development of effective catalysts. The study of relatively simple oxides gives fundamental knowledge that cannot always be applied to the more complex mixed metal oxide systems that are patented and put into use industrially. The goal of this research is to apply fundamental techniques to complex, commercial catalysts, under industrially relevant conditions, and systematically make sense of the complexity. A range of characterisation techniques that probe different aspects of catalyst structure are used in this thesis during catalyst synthesis to follow (re)organisation pathways of mixed metal oxides and identify the different structures that form. Two mixed metal oxide systems were chosen for investigation: a Cu-spinel based hydrogenation catalyst and a Mo oxide selective oxidation catalyst. The structural transformations during different synthesis steps were analysed using X-ray Absorption Spectroscopy (XAS), X-ray Diffraction (XRD), Infrared (IR), and Raman spectroscopy. New insights into both catalyst systems are discussed and several approaches to catalyst characterisation on different length scales are demonstrated to deliver a holistic understanding of catalyst synthesis.
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Apr 2021
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