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

Instruments / Technical Area	Publication Details	Published
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS B18-Core EXAFS E01-JEM ARM 200CF	Influence of synthesis conditions on the structure of nickel nanoparticles and their reactivity in selective asymmetric hydrogenation Rosa Arrigo , Simone Gallarati , Manfred E. Schuster , Jake Seymour , Diego Gianolio , Ivan Da Silva , June Callison , Haosheng Feng , John E. Proctor , Pilar Ferrer , Federica Venturini , Dave Grinter , Georg Held Chemcatchem DOI: 10.1002/cctc.201901955 Open Access Show Abstract ▼ Abstract: Unsupported and SiO 2 ‐supported Ni nanoparticles (NPs), were synthesised via hot‐injection colloidal route using oleylamine (OAm) and trioctylphosphine (TOP) as reducing and protective agents, respectively. By adopting a multi‐length scale structural characterization, it was found that by changing equivalents of OAM and TOP not only the size of the nanoparticles is affected but also the Ni electronic structure. The synthetized NPs were modified with ( R , R )‐tartaric acid (TA) and investigated in the asymmetric hydrogenation of methyl acetoacetate to chiral methyl‐3‐hydroxy butyrate. The comparative analysis of structure and catalytic performance for the synthetized catalysts has enabled us to identify a Ni metallic active surface, whereby the activity increases with the size of the metallic domains. Conversely, at the high conversion obtained for the unsupported NPs there was no impact of particle size on the selectivity. ( R )‐selectivity was very high only on catalysts containing positively charged Ni species such as over the SiO 2 ‐supported NiO NPs. This work shows that the chiral modification of metallic Ni NPs with TA is insufficient to maintain high selectivity towards the ( R )‐enantiomer at long reaction time and provide guidance for the engineering of long‐term stable enantioselective catalysts.	Dec 2019
E01-JEM ARM 200CF	On the high structural heterogeneity of Fe-impregnated graphitic-carbon catalysts from Fe nitrate precursor Rosa Arrigo , Manfred Erwin Schuster Catalysts 9 DOI: 10.3390/catal9040303 Open Access Show Abstract ▼ Abstract: Wet impregnation is broadly applied for the synthesis of carbon-supported metal/metal oxide nanostructures because of its high flexibility, simplicity and low cost. By contrast, impregnated catalysts are typified by a usually undesired nanostructural and morphological heterogeneity of the supported phase resulting from a poor stabilization at the support surface. This study on graphite-supported Fe-based materials from Fe nitrate precursor is concerned with the understanding of the chemistry that dictates during the multistep synthesis, which is key to designing structurally homogeneous catalysts. By means of core-level X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy and atomic resolution electron microscopy, we found not only a large variety of particles sizes and morphologies but also chemical phases. Herein, thermally stable single atoms and few atoms clusters are identified together with large agglomerates of an oxy-hydroxide ferrihydrite-like phase. Moreover, the thermally induced phase transformation of the initially poorly ordered oxy-hydroxide phase into several oxide phases is revealed, together with the existence of thermally stable N impurities retained in the structure as Fe–N–O bonds. The nature of the interactions with the support and the structural dynamics induced by the thermal treatment rationalize the high heterogeneity observed in these catalysts.	Mar 2019
Optics	Compensation of x-ray mirror distortion by cooling temperature control Matthew Hand , Hongchang Wang , Maria Harkiolaki , Federica Venturini , Rosa Arrigo , Pilar Ferrer Escorihuela , Simon Alcock , Ioana Nistea , Andy Marshall , Stewart Scott , Liz Duke , Georg Held , Kawal Sawhney Proceedings of the 13th International Conference on Synchrotron Radiation Instrumentation – SRI2018 DOI: 10.1063/1.5084675 Open Access Show Abstract ▼ Abstract: Synchrotron radiation is emitted from a bending magnet source in a wide ray fan which is collected by the first optical element in a beamline. In order to maximize angular acceptance, and hence flux, it is beneficial to increase the length of this mirror and optical design requirements may necessitate that the optical surface be over 1 m in length. Such mirrors also require cooling as they may be subject to high heat loads from the incident radiation. Two beamlines, B07 and B24, at Diamond Light Source, UK, use 1.4 m long toroidal mirrors which utilize a similar side-clamped cooling manifold design. While this scheme has been successful in providing effective cooling of the mirror, it has also been discovered that it introduces deformation of the radius of curvature which is sufficient to alter the focusing characteristics of the mirror. At both beamlines, the horizontal focus of the beam was found to differ by up to several meter from the design position at the exit slit which resulted in poor flux throughput, reduced energy resolution and other side effects. A pencil beam scan method has been used to diagnose this issue and infer the position of the focus and mirror shape. Through the use of a standalone chiller to alter the temperature of the water within the cooling loop, it has been possible to correct the distortion of the radius and restore the focus to its nominal position.	Jan 2019
	The role of the copper oxidation state in the electrocatalytic reduction of CO2 into valuable hydrocarbons Juan-jesús Velasco-vélez , Travis E. Jones , Dunfeng Gao , Emilia Carbonio , Rosa Arrigo , Cheng-jhih Hsu , Yu-cheng Huang , Chung Li Dong , Jin-ming Chen , Jyh-fu Lee , Peter Strasser , Beatriz Roldan-cuenya , Robert Schloegl , Axel Knop-gericke , Cheng-hao Chuang Acs Sustainable Chemistry & Engineering DOI: 10.1021/acssuschemeng.8b05106 Show Abstract ▼ Abstract: Redox-active copper catalysts with accurately prepared oxidation states (Cu0, Cu+ and Cu2+) and high selectivity to C2 hydrocarbon formation, from electrocatalytic cathodic reduction of CO2, were fabricated and characterized. The electrochemically prepared copper-redox electro-cathodes yield higher activity for the production of hydrocarbons at lower oxidation state. By combining advanced X-ray spectroscopy and in situ micro-reactors it was possible to unambiguously reveal the variation in the complex electronic structure that the catalysts undergo at different stages (i.e. during fabrication and electrocatalytic reactions). It was found that the surface, sub-surface and bulk properties of the electrochemically prepared catalysts are dominated by the formation of copper carbonates on the surface of cupric-like oxides, which prompts catalyst deactivation by restraining effective charge transport. Furthermore, the formation of reduced or partially-reduced copper catalysts yields the key dissociative proton-consuming reactive adsorption of CO2 to produce CO; allowing the subsequent hydrogenation into C2 and C1 products by dimerization and protonation. These results yield valuable information on the variations in the electronic structure that redox-active copper catalysts undergo in the course of the electrochemical reaction, which, under extreme conditions are mediated by thermodynamics but, critically, kinetics dominate near the oxide/metal phase transitions.	Nov 2018
	Electrochemically active Ir NPs on graphene for OER in acidic aqueous electrolyte investigated by in situ and ex situ spectroscopies J. J. Velasco-vélez , T. E. Jones , V. Streibel , M. Hävecker , C.-h. Chuang , L. Frevel , M. Plodinec , A. Centeno , A. Zurutuza , R. Wang , R. Arrigo , R. Mom , S. Hofmann , R. Schlögl , A. Knop-gericke Surface Science 681, 1 - 8 DOI: 10.1016/j.susc.2018.10.021 Show Abstract ▼ Abstract: An electrode for the oxygen evolution reaction based on a conductive bi-layered free standing graphene support functionalized with iridium nanoparticles was fabricated and characterized by means of potentiometric and advanced X-ray spectroscopic techniques. It was found that the electrocatalytic activity of iridium nanoparticles is associated to the formation of Ir 5d electron holes. Strong Ir 5d and O 2p hybridization, however, leads to a concomitant increase O 2p hole character, making oxygen electron deficient and susceptible to nucleophilic attack by water. Consequently, more efficient electrocatalysts can be synthesized by increasing the number of electron-holes shared between the metal d and oxygen 2p.	Oct 2018
	In situ electrochemical cells to study the oxygen evolution reaction by near ambient pressure x-ray photoelectron spectroscopy Verena Streibel , Michael Hävecker , Youngmi Yi , Juan J. Velasco Vélez , Katarzyna Skorupska , Eugen Stotz , Axel Knop-gericke , Robert Schlögl , Rosa Arrigo Topics In Catalysis 19 DOI: 10.1007/s11244-018-1061-8 Open Access Show Abstract ▼ Abstract: In this contribution, we report the development of in situ electrochemical cells based on proton exchange membranes suitable for studying interfacial structural dynamics of energy materials under operation by near ambient pressure X-ray photoelectron spectroscopy. We will present both the first design of a batch-type two-electrode cell prototype and the improvements attained with a continuous flow three-electrode cell. Examples of both sputtered metal films and carbon-supported metal nanostructures are included demonstrating the high flexibility of the cells to study energy materials. Our immediate focus was on the study of the oxygen evolution reaction, however, the methods described herein can be broadly applied to reactions relevant in energy conversion and storage devices.	Oct 2018
B18-Core EXAFS E01-JEM ARM 200CF	Operando spectroscopy study of the carbon dioxide electro-reduction by iron species on nitrogen-doped carbon Chiara Genovese , Manfred E. Schuster , Emma K. Gibson , Diego Gianolio , Victor Posligua , Ricardo Grau-crespo , Giannantonio Cibin , Peter Wells , Debi Garai , Vladyslav Solokha , Sandra Krick Calderon , Juan J. Velasco-velez , Claudio Ampelli , Siglinda Perathoner , Georg Held , Gabriele Centi , Rosa Arrigo Nature Communications 9 DOI: 10.1038/s41467-018-03138-7 Diamond Proposal Number(s): [17031, 10306] Open Access Show Abstract ▼ Abstract: The carbon–carbon coupling via electrochemical reduction of carbon dioxide represents the biggest challenge for using this route as platform for chemicals synthesis. Here we show that nanostructured iron (III) oxyhydroxide on nitrogen-doped carbon enables high Faraday efficiency (97.4%) and selectivity to acetic acid (61%) at very-low potential (−0.5 V vs silver/silver chloride). Using a combination of electron microscopy, operando X-ray spectroscopy techniques and density functional theory simulations, we correlate the activity to acetic acid at this potential to the formation of nitrogen-coordinated iron (II) sites as single atoms or polyatomic species at the interface between iron oxyhydroxide and the nitrogen-doped carbon. The evolution of hydrogen is correlated to the formation of metallic iron and observed as dominant reaction path over iron oxyhydroxide on oxygen-doped carbon in the overall range of negative potential investigated, whereas over iron oxyhydroxide on nitrogen-doped carbon it becomes important only at more negative potentials.	Mar 2018
	In situ X-ray Photoelectron Spectroscopy of Electrochemically Active Solid-Gas and Solid-Liquid Interfaces Axel Knop-gericke , Verena Pfeifer , Juan-jesus Velasco-velez , Travis Jones , Rosa Arrigo , Michael Hävecker , R. Schlögl Journal Of Electron Spectroscopy And Related Phenomena DOI: 10.1016/j.elspec.2017.03.010 Show Abstract ▼ Abstract: In this account the application of synchrotron radiation based X-ray photoelectron spectroscopy (XPS) for the investigation of electrochemically active gas-solid and liquid-solid interfaces will be discussed. The potential of Near Ambient Pressure XPS (NAP-XPS) for the estimation of the electronic surface structure of electrochemically active interfaces will be described by two examples. Thereto the oxygen evolution reaction (OER) over Pt and IrOx anodes will be introduced. In particular the analysis of XP core level spectra of IrOx requires the development of an appropriate fit model. Furthermore the design of reaction cells based on proton exchange membranes (PEM) and on electron transparent graphene membranes, which enables the investigation of liquid-gas and liquid-solid interfaces under electrochemical relevant conditions will be discussed. In the last part of this article a perspective to the EMIL project at the synchrotron radiation facility BESSY will be given. The purpose of this project is the implementation of two new beamlines enabling X-ray photoelectron spectroscopy in the X-ray regime from 80 eV − 8 keV under reaction conditions. The extension to the so called tender X-ray regime will allow the release of higher kinetic energy photoelectrons which have a higher inelastic mean free path compared to photoelectrons excited by soft X-ray radiation and therefore will enable the investigation of solid-liquid interfaces under electrochemical reaction conditions.	Mar 2017
	In situ observation of reactive oxygen species forming on oxygen-evolving iridium surfaces Verena Pfeifer , Travis E. Jones , Juan J. Velasco Vélez , Rosa Arrigo , Simone Piccinin , Michael Hävecker , Axel Knop-gericke , Robert Schlögl Chem. Sci. DOI: 10.1039/C6SC04622C Open Access Show Abstract ▼ Abstract: Water splitting performed in acidic media relies on the exceptional performance of iridium-based materials to catalyze the oxygen evolution reaction (OER). In the present work, we use in situ X-ray photoemission and absorption spectroscopy to resolve the long-standing debate about surface species present in iridium-based catalysts during the OER. We find that the surface of an initially metallic iridium model electrode converts into a mixed-valent, conductive iridium oxide matrix during the OER, which contains OII− and electrophilic OI− species. We observe a positive correlation between the OI− concentration and the evolved oxygen, suggesting that these electrophilic oxygen sites may be involved in catalyzing the OER. We can understand this observation by analogy with photosystem II; their electrophilicity renders the OI− species active in O–O bond formation, i.e. the likely potential- and rate-determining step of the OER. The ability of amorphous iridium oxyhydroxides to easily host such reactive, electrophilic species can explain their superior performance when compared to plain iridium metal or crystalline rutile-type IrO2.	Dec 2016
	Reactive oxygen species in iridium-based OER catalysts Verena Pfeifer , Travis E. Jones , Sabine Wrabetz , Cyriac Massué , Juan J. Velasco Vélez , Rosa Arrigo , Michael Scherzer , Simone Piccinin , Michael Hävecker , Axel Knop-gericke , Robert Schlögl Chem. Sci. 7, 6791 - 6795 DOI: 10.1039/C6SC01860B Open Access Show Abstract ▼ Abstract: Tremendous effort has been devoted towards elucidating the fundamental reasons for the higher activity of hydrated amorphous IrIII/IV oxyhydroxides (IrOx) in the oxygen evolution reaction (OER) in comparison with their crystalline counterpart, rutile-type IrO2, by focusing on the metal oxidation state. Here we demonstrate that, through an analogy to photosystem II, the nature of this reactive species is not solely a property of the metal but is intimately tied to the electronic structure of oxygen. We use a combination of synchrotron-based X-ray photoemission and absorption spectroscopies, ab initio calculations, and microcalorimetry to show that holes in the O 2p states in amorphous IrOx give rise to a weakly bound oxygen that is extremely susceptible to nucleophilic attack, reacting stoichiometrically with CO already at room temperature. As such, we expect this species to play the critical role of the electrophilic oxygen involved in O–O bond formation in the electrocatalytic OER on IrOx. We propose that the dynamic nature of the Ir framework in amorphous IrOx imparts the flexibility in Ir oxidation state required for the formation of this active electrophilic oxygen.	Jul 2016

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