E01-JEM ARM 200CF
I20-EDE-Energy Dispersive EXAFS (EDE)
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Hui
Luo
,
Victor Y.
Yukuhiro
,
Pablo S.
Fernández
,
Jingyu
Feng
,
Paul
Thompson
,
Reshma R.
Rao
,
Rongsheng
Cai
,
Silvia
Favero
,
Sarah J.
Haigh
,
James R.
Durrant
,
Ifan E. L.
Stephens
,
Maria-Magdalena
Titirici
Diamond Proposal Number(s):
[28663, 25476]
Open Access
Abstract: Pt-based bimetallic electrocatalysts are promising candidates to convert surplus glycerol from the biodiesel industry to value-added chemicals and coproduce hydrogen. It is expected that the nature and content of the elements in the bimetallic catalyst can not only affect the reaction kinetics but also influence the product selectivity, providing a way to increase the yield of the desired products. Hence, in this work, we investigate the electrochemical oxidation of glycerol on a series of PtNi nanoparticles with increasing Ni content using a combination of physicochemical structural analysis, electrochemical measurements, operando spectroscopic techniques, and advanced product characterizations. With a moderate Ni content and a homogenously alloyed bimetallic Pt–Ni structure, the PtNi2 catalyst displayed the highest reaction activity among all materials studied in this work. In situ FTIR data show that PtNi2 can activate the glycerol molecule at a more negative potential (0.4 VRHE) than the other PtNi catalysts. In addition, its surface can effectively catalyze the complete C–C bond cleavage, resulting in lower CO poisoning and higher stability. Operando X-ray absorption spectroscopy and UV–vis spectroscopy suggest that glycerol adsorbs strongly onto surface Ni(OH)x sites, preventing their oxidation and activation of oxygen or hydroxyl from water. As such, we propose that the role of Ni in PtNi toward glycerol oxidation is to tailor the electronic structure of the pure Pt sites rather than a bifunctional mechanism. Our experiments provide guidance for the development of bimetallic catalysts toward highly efficient, selective, and stable glycerol oxidation reactions.
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Nov 2022
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I16-Materials and Magnetism
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Peter
Finkel
,
Markys G.
Cain
,
Thomas
Mion
,
Margo
Staruch
,
Jakub
Kolacz
,
Sukriti
Mantri
,
Chad
Newkirk
,
Kyril
Kavetsky
,
John
Thornton
,
Junhai
Xia
,
Marc
Currie
,
Thomas
Hase
,
Alex
Moser
,
Paul
Thompson
,
Christopher
Lucas
,
Andy
Fitch
,
Julie M.
Cairney
,
Scott D.
Moss
,
A. Gareth A.
Nisbet
,
John E.
Daniels
,
Samuel E.
Lofland
Diamond Proposal Number(s):
[18924]
Open Access
Abstract: Electrical switching of ferroelectric domains and subsequent domain wall motion promotes strong piezoelectric activity; however, light scatters at refractive index discontinuities such as those found at domain wall boundaries. Thus, simultaneously achieving large piezoelectric effect and high optical transmissivity is generally deemed infeasible. Here, it is demonstrated that the ferroelectric domains in perovskite Pb(In1/2Nb1/2)O3 Pb(Mg1/3Nb2/3)O3-PbTiO3 domain-engineered crystals can be manipulated by electrical field and mechanical stress to reversibly and repeatably, with small hysteresis, transform the opaque poly-domain structure into a highly transparent mono-domain state. This control of optical properties can be achieved at very low electric fields (less than 1.5 kV cm−1) and is accompanied by a large (>10000 pm V−1) piezoelectric coefficient that is superior to that of linear state-of-the-art materials by a factor of three or more. The coexistence of tunable optical transmissivity and high piezoelectricity paves the way for a new class of photonic devices.
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Nov 2021
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B18-Core EXAFS
E01-JEM ARM 200CF
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George F.
Tierney
,
Shahram
Alijani
,
Monik
Panchal
,
Donato
Decarolis
,
Martha
Briceno De Gutierrez
,
Khaled
Mohammed
,
June
Callison
,
Emma
Gibson
,
Paul
Thompson
,
Paul
Collier
,
Nikolaos
Dimitratos
,
E. Crina
Corbos
,
Frederic
Pelletier
,
Alberto
Villa
,
Peter
Wells
Open Access
Abstract: We demonstrate a modified sol-immobilization procedure using (MeOH) x /(H 2 O) 1-x solvent mixtures to prepare Pd/TiO 2 catalysts that are able to reduce the formation of acid catalyzed products, e.g. ethers, for the hydrogenation of furfural. Transmission electron microscopy found a significant increase in polyvinyl alcohol (PVA) deposition at the metal-support interface and temperature programmed reduction found a reduced uptake of hydrogen, compared to an established Pd/TiO 2 preparation. We propose that the additional PVA hinders hydrogen spillover onto the TiO 2 support and limits the formation of Brønsted acid sites, required to produce ethers. Elsewhere, the new preparation route was able to successfully anchor colloidal Pd to the TiO 2 surface, without the need for acidification. This work demonstrates the potential for minimizing process steps as well as optimizing catalyst selectivity – both important objectives for sustainable chemistry.
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Oct 2021
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I16-Materials and Magnetism
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Stephan
Geprags
,
Bjorn Erik
Skovdal
,
Monika
Scheufele
,
Matthias
Opel
,
Didier
Wermeille
,
Paul
Thompson
,
Alessandro
Bombardi
,
Virginie
Simonet
,
Stephane
Grenier
,
Pascal
Lejay
,
Gilbert Andre
Chahine
,
Diana Lucia
Quintero-Castro
,
Rudolf
Gross
,
Danny
Mannix
Diamond Proposal Number(s):
[12770]
Abstract: We report on a comprehensive investigation of the effects of strain and film thickness on the structural and magnetic properties of epitaxial thin films of the prototypal
J
eff
=
1
/
2
compound
Sr
2
IrO
4
by advanced x-ray scattering. We find that the
Sr
2
IrO
4
thin films can be grown fully strained up to a thickness of 108 nm. By using x-ray resonant scattering, we show that the out-of-plane magnetic correlation length is strongly dependent on the thin film thickness, but independent of the strain state of the thin films. This can be used as a finely tuned dial to adjust the out-of-plane magnetic correlation length and transform the magnetic anisotropy from two-dimensional to three-dimensional behavior by incrementing film thickness. These results provide a clearer picture for the systematic control of the magnetic degrees of freedom in epitaxial thin films of
Sr
2
IrO
4
and bring to light the potential for a rich playground to explore the physics of
5
d
transition-metal compounds.
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Dec 2020
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B18-Core EXAFS
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Diamond Proposal Number(s):
[19850]
Open Access
Abstract: The chemical and structural nature of potassium compounds involved in catalytic soot oxidation have been studied by a combination of temperature programmed oxidation and operando potassium K-edge X-ray absorption spectroscopy experiments. These experiments are the first known operando studies using tender X-rays (∼3.6 keV) under high temperature oxidation reaction conditions. X-ray absorption near edge structure analysis of K2CO3/Al2O3 catalysts during heating shows that, at temperatures between 100 and 200 °C, potassium species undergo a structural change from an initial hydrated K2CO3·xH2O and KHCO3 mixture to well-defined K2CO3. As the catalyst is heated from 200 °C to 600 °C, a feature associated with multiple scattering shifts to lower energy, indicating increased K2CO3 dispersion, due to its mobility at high reaction temperature. This shift was noted to be greater in samples containing soot than in control experiments without soot and can be attributed to enhanced mobility of the K2CO3, due to the interaction between soot and potassium species. No potassium species except K2CO3 could be defined during reactions, which excludes a potential reaction mechanism in which carbonate ions are the active soot-oxidising species. Simulations of K-edge absorption near edge structures were performed to rationalise the observed changes seen. Findings showed that cluster size, unit cell distortions and variation in the distribution of potassium crystallographic sites influenced the simulated spectra of K2CO3. While further simulation studies are required for a more complete understanding, the current results support the hypothesis that changes in the local structure on dispersion can influence the observed spectra. Ex situ characterisation was carried out on the fresh and used catalyst, by X-ray diffraction and X-ray photoelectron spectroscopy, which indicated changes to the carbonate species, in line with the X-ray absorption spectroscopy experiments.
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Jul 2020
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B18-Core EXAFS
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Grazia
Malta
,
Simon A.
Kondrat
,
Simon J.
Freakley
,
David J.
Morgan
,
Emma K.
Gibson
,
Peter P.
Wells
,
Matteo
Aramini
,
Diego
Gianolio
,
Paul B. J.
Thompson
,
Peter
Johnston
,
Graham J.
Hutchings
Diamond Proposal Number(s):
[15214]
Open Access
Abstract: The replacement of HgCl2/C with Au/C as a catalyst for acetylene hydrochlorination represents a significant reduction in the environmental impact of this industrial process. Under reaction conditions atomically dispersed cationic Au species are the catalytic active site, representing a large-scale application of heterogeneous single-site catalysts. While the metal nuclearity and oxidation state under operating conditions has been investigated in catalysts prepared from aqua regia and thiosulphate, limited studies have focused on the ligand environment surrounding the metal centre. We now report K-edge soft X-ray absorption spectroscopy of the Cl and S ligand species used to stabilise these isolated cationic Au centres in the harsh reaction conditions. We demonstrate the presence of three distinct Cl species in the materials; inorganic Cl−, Au–Cl, and C–Cl and how these species evolve during reaction. Direct evidence of Au–S interactions is confirmed in catalysts prepared using thiosulfate precursors which show high stability towards reduction to inactive metal nanoparticles. This stability was clear during gas switching experiments, where exposure to C2H2 alone did not dramatically alter the Au electronic structure and consequently did not deactivate the thiosulfate catalyst.
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Jun 2020
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[9850]
Abstract: In situ electrochemical surface X-ray diffraction was employed to investigate the atomic scale structure of the electrochemical double layer and the relaxation at the Pt(111) electrode surface in non-aqueous and aqueous acetonitrile electrolytes under potential control. The X-ray measurements provide insight into the potential-dependence of the interface structure by combining potentiodynamic measurements (X-ray voltammetry) with potentiostatic measurements (crystal truncation rod data) to probe both the metal and electrolyte sides of the interface. The crystal truncation rod measurements are consistent with the potential dependent reorientation of acetonitrile in the absence of water and a parallel arrangement in the presence of water. As acetonitrile concentration increases, the electron density closest to the electrode surface also increases. Finally, Pt surface relaxation in a range of aqueous and non-aqueous solvents is discussed in general with regards to the structure of the electrochemical double layer.
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Feb 2019
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I09-Surface and Interface Structural Analysis
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Richard M.
Fogarty
,
Richard P.
Matthews
,
Matthew T.
Clough
,
Claire R.
Ashworth
,
Agnieszka
Brandt-Talbot
,
Paul J.
Corbett
,
Robert G.
Palgrave
,
Richard A.
Bourne
,
Thomas W.
Chamberlain
,
Tom
Vander Hoogerstraete
,
Paul B. J.
Thompson
,
Patricia A.
Hunt
,
Nicholas A.
Besley
,
Kevin R. J.
Lovelock
Diamond Proposal Number(s):
[10195, 12754]
Abstract: Experimental near edge X-ray absorption fine structure (NEXAFS) spectra are reported for 12 ionic liquids (ILs) encompassing a range of chemical structures for both the sulfur 1s and nitrogen 1s edges and compared with time-dependent density functional theory (TD-DFT) calculations. The energy scales for the experimental data were carefully calibrated against literature data. Gas phase calculations were performed on lone ions, ion pairs and ion pair dimers, with a wide range of ion pair conformers considered. For the first time, it is demonstrated that TD-DFT is a suitable method for simulating NEXAFS spectra of ILs, although the number of ions included in the calculations and their conformations are important considerations. For most of the ILs studied, calculations on lone ions in the gas phase were sufficient to successfully reproduce the experimental NEXAFS spectra. However, for certain ILs – for example, those containing a protic ammonium cation – calculations on ion pairs were required to obtain a good agreement with experimental spectra. Furthermore, significant conformational dependence was observed for the protic ammonium ILs, providing insight into the predominant liquid phase cation–anion interactions. Among the 12 investigated ILs, we find that four have an excited state that is delocalised across both the cation and the anion, which has implications for any process that depends on the excited state, for example, radiolysis. Considering the collective experimental and theoretical data, we recommend that ion pairs should be the minimum number of ions used for the calculation of NEXAFS spectra of ILs.
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Nov 2017
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B18-Core EXAFS
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John B.
Brazier
,
Mark A.
Newton
,
Elena M.
Barreiro
,
Stephen
Parry
,
Luis A.
Adrio
,
Christopher J.
Mulligan
,
Klaus
Hellgardt
,
King Kuok (mimi)
Hii
,
Paul B. J.
Thompson
,
Rachel
Nichols
,
Bao N.
Nguyen
Diamond Proposal Number(s):
[9584]
Open Access
Abstract: The reduction of γ-Al2O3-supported PdO in flowing aqueous ethanol was investigated. Quick EXAFS (QEXAFS) performed at the Pd K-edge reveals that the presence of Cl can have a profound
effect on the reduction process. At low loadings of Pd (1 wt-%), the size dependency of the process is inverted, compared to Cl-free samples. The extent of reduction was found to be dependent
on loading/particles size. It is shown, using in situ QEXAFS at the Cl K- and Pd L3-edges, that residual Cl is not removed by the flowing solvent mixture, even at an elevated temperature of 350 K. The origins of these behaviours are discussed in terms of the differing effects that Cl may have when bonded to oxidic or reduced metal centres and the results were compared to earlier
observations made on the effects of Cl on commercial polyurea encapsulated Pd ENCAT™ NP 30 catalysts.
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Feb 2017
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[7260]
Abstract: The growth and atomic structure of thin Co films electrodeposited onto Au(111) have been studied using in situ surface X-ray diffraction (SXRD) and scanning tunneling microscopy (STM). SXRD is used to monitor the growth in real-time and, following Co deposition, the strain of the Co film is characterized as a function of the Co thickness. In-plane SXRD measurements show that Co deposition leads to the formation of a reconstructed Au layer at the Au-Co interface which is composed of an unfaulted, single Au monolayer uniformly compressed with respect to the underlying bulk Au lattice. The surface normal structure of the Au-Co interface and Co films are examined by measurement of the extended X-ray reflectivity (or specular crystal truncation rod (CTR)) for a nominally two monolayer thick (2 ML) Co deposit. In situ STM has also been used to obtain the morphology of the Co films and the Au(111) reconstruction pattern both before and after Co dissolution. The STM data give complementary information to the SXRD results. The influence on the Co structure of the adsorption of carbon monoxide is also investigated in detail for a 2-3 ML thick Co film. It is shown that CO adsorption induces small vertical relaxations in the Co layers. In contrast, varying the electrochemical potential has negligible influence on the Co structure and affects only the electrolyte layering in the electrochemical double layer. The results are discussed in relation to the magnetic properties, in particular the change in the spin reorientation transition caused by CO adsorption.
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Jan 2016
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