B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
B18-Core EXAFS
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Diamond Proposal Number(s):
[26554]
Open Access
Abstract: The nature and evolution of FeNxCy moieties in Fe/C/N catalysts has been studied by analysing Fe and N environments. TEM and Fe-XAS reveal the presence of FeNx moieties and Fe3C particles in the fresh catalyst. NEXAFS reveals the presence of two groups of (Fe)NxCy ensembles, namely (Fe)Nx-pyridinic and (Fe)Nx-pyrrolic. The architecture of the FeNxCy ensembles and their evolution during the ORR has been analysed by XAS, NEXAFS, and identical locations TEM. NxCy, FeNxCy and Fe3C species are partially removed during the ORR, resulting in the formation of Fe2O3 and Fe3O4 particles with different morphologies. The process is more severe in acid electrolyte than in alkaline one. (Fe)Nx-pyrrolic moieties are the main ones in the fresh catalysts, but (Fe)Nx-pyridinic groups are more stable after the ORR. The correlation between the evolution of the ORR activity and that of the FeNxCy ensembles indicates that FeNx-pyridinic ensembles are responsible for the ORR activity.
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Apr 2021
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Alexander
Large
,
Jake
Seymour
,
Wilson
Quevedo Garzon
,
Kanak
Roy
,
Federica
Venturini
,
David C.
Grinter
,
Luca
Artiglia
,
Emily
Brooke
,
Martha
Briceno De Gutierrez
,
Agnes
Raj
,
Kevin
Lovelock
,
Roger A.
Bennett
,
Tugce
Eralp-erden
,
Georg
Held
Diamond Proposal Number(s):
[19464, 20952, 22702, 24584]
Open Access
Abstract: Near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) was used to study the chemical states of a range of alumina-supported monometallic Pd and bimetallic Pd-Pt nanocatalysts, under methane oxidation conditions. It has been suggested before that for optimal complete methane oxidation, palladium needs to be in an oxidised state. These experiments, combining NAP-XPS with a broad range of characterisation techniques, demonstrate a clear link between Pt presence, Pd oxidation, and catalyst activity under stoichiometric reaction conditions. Under oxygen-rich conditions this behaviour is less clear, as all of the palladium tends to be oxidised, but there are still benefits to the addition of Pt in place of Pd for complete oxidation of methane.
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Jan 2021
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Diamond Proposal Number(s):
[23855]
Open Access
Abstract: In-situ analysis of the TiO2 / water interface via NAP-XPS is demonstrated in both a lab based system (NAP-cell configuration) and synchrotron endstation (backfill configuration). Ultra-thin wetting layers (UTWL) of liquid water (~10 nm) are formed on a rutile TiO2 surface with minimal contamination present in addition to unique insight during the growth of the liquid films as indicated via NAP-XPS, in-situ sample temperature and background vapour pressure monitoring. Chemical changes at the solid / liquid interface are also demonstrated via healing of Ti3+ surface defect states. Photon depth profiling of the as grown liquid layers indicate that the formed films are ultra-thin (~10 nm) and likely to be continuous in nature. This work demonstrates a novel and flexible approach for studying the solid / liquid interface via NAP-XPS which is readily integrated with any form of NAP-XPS system, thereby making a critical interface of study available to a wide audience of researchers for use in operando electrochemical and photocatalytic research.
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Jan 2021
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Ye
Fan
,
Kenichi
Nakanishi
,
Vlad P.
Veigang-radulescu
,
Ryo
Mizuta
,
J. Callum
Stewart
,
Jack E. N.
Swallow
,
Alice E.
Dearle
,
Oliver J.
Burton
,
Jack A.
Alexander-webber
,
Pilar
Ferrer
,
Georg
Held
,
Barry
Brennan
,
Andrew J.
Pollard
,
Robert S
Weatherup
,
Stephan
Hofmann
Diamond Proposal Number(s):
[22123]
Open Access
Abstract: We find that the use of Au substrate allows fast, self-limited WS2 monolayer growth using a simple sequential exposure pattern of low cost, low toxicity precursors, namely tungsten hexacarbonyl and dimethylsulfide (DMS). We use this model reaction system to fingerprint the technologically important metal organic chemical vapour deposition process by operando X-ray photoelectron spectroscopy (XPS) to address the current lack of understanding of the underlying fundamental growth mechanisms for WS2 and related transition metal dichalcogenides. Au effectively promotes the sulfidation of W with simple organosulfides, enabling WS2 growth with low DMS pressure (<1 mbar) and a suppression of carbon contamination of as-grown WS2, which to date has been a major challenge with this precursor chemistry. Full WS2 coverage can be achieved by one exposure cycle of 10 minutes at 700 °C. We discuss our findings in the wider context of previous literature on heterogeneous catalysis, 2D crystal growth, and overlapping process technologies such as atomic layer deposition (ALD) and direct metal conversion, linking to future integrated manufacturing processes for transition metal dichalcogenide layers.
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Oct 2020
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Georg
Held
,
Federica
Venturini
,
David C.
Grinter
,
Pilar
Ferrer
,
Rosa
Arrigo
,
Liam
Deacon
,
Wilson
Quevedo Garzon
,
Kanak
Roy
,
Alex
Large
,
Christopher
Stephens
,
Andrew
Watts
,
Paul
Larkin
,
Matthew
Hand
,
Hongchang
Wang
,
Linda
Pratt
,
James J.
Mudd
,
Thomas
Richardson
,
Suren
Patel
,
Michael
Hillman
,
Stewart
Scott
Open Access
Abstract: The ambient-pressure endstation and branchline of the Versatile Soft X-ray (VerSoX) beamline B07 at Diamond Light Source serves a very diverse user community studying heterogeneous catalysts, pharmaceuticals and biomaterials under realistic conditions, liquids and ices, and novel electronic, photonic and battery materials. The instrument facilitates studies of the near-surface chemical composition, electronic and geometric structure of a variety of samples using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy in the photon energy range from 170 eV to 2800 eV. The beamline provides a resolving power hν/Δ(hν) > 5000 at a photon flux > 1010 photons s−1 over most of its energy range. By operating the optical elements in a low-pressure oxygen atmosphere, carbon contamination can be almost completely eliminated, which makes the beamline particularly suitable for carbon K-edge NEXAFS. The endstation can be operated at pressures up to 100 mbar, whereby XPS can be routinely performed up to 30 mbar. A selection of typical data demonstrates the capability of the instrument to analyse details of the surface composition of solid samples under ambient-pressure conditions using XPS and NEXAFS. In addition, it offers a convenient way of analysing the gas phase through X-ray absorption spectroscopy. Short XPS spectra can be measured at a time scale of tens of seconds. The shortest data acquisition times for NEXAFS are around 0.5 s per data point.
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Sep 2020
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Andrea
Resta
,
Uta
Hejral
,
Sara
Blomberg
,
Stefano
Albertin
,
Alina
Vlad
,
Yves
Garreau
,
Corentin
Chatelier
,
Federica
Venturini
,
Pilar
Ferrer
,
Georg
Held
,
Dave
Grinter
,
Edvin
Lundgren
,
Alessandro
Coati
Diamond Proposal Number(s):
[21936]
Abstract: The reaction of ammonia oxidation over PtRh binary alloy has been studied with a surface science approach by operando techniques such as Near Ambient Pressure X-Ray Photoemission Spectroscopy (NAP-XPS) and Surface X-Ray Diffraction (SXRD) combined with mass spectrometry. The article will explore the surface evolution across five different oxygen to ammonia ratios in the millibar regime for two different temperatures. The presented data-set allows to link variations in the atomic structures measured by diffraction methods and surface species information from NAP-XPS to reaction products in the gas phase. We will show that NO production coincides with significant changes of the surface structure and the formation of a RhO2 surface oxide. It was also observed that the RhO2 surface oxide only fully forms when the nitrogen signal in the N1s has disappeared.
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Sep 2020
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
B18-Core EXAFS
I20-EDE-Energy Dispersive EXAFS (EDE)
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Rachel H.
Blackmore
,
Maria Elena
Rivas
,
George F.
Tierney
,
Khaled M. H.
Mohammed
,
Donato
Decarolis
,
Shusaku
Hayama
,
Federica
Venturini
,
Georg
Held
,
Rosa
Arrigo
,
Monica
Amboage
,
Pip
Hellier
,
Evan
Lynch
,
Mahrez
Amri
,
Marianna
Casavola
,
Tugce
Eralp Erden
,
Paul
Collier
,
Peter P.
Wells
Diamond Proposal Number(s):
[20129, 20200, 22063, 15151]
Open Access
Abstract: The use of mechanochemistry to prepare catalytic materials is of significant interest; it offers an environmentally beneficial, solvent-free, route and produces highly complex structures of mixed amorphous and crystalline phases. This study reports on the effect of milling atmosphere, either air or argon, on mechanochemically prepared LaMnO3 and the catalytic performance towards N2O decomposition (deN2O). In this work, high energy resolution fluorescence detection (HERFD), X-ray absorption near edge structure (XANES), X-ray emission, and X-ray photoelectron spectroscopy (XPS) have been used to probe the electronic structural properties of the mechanochemically prepared materials. Moreover, in situ studies using near ambient pressure (NAP)-XPS, to follow the materials during catalysis, and high pressure energy dispersive EXAFS studies, to mimic the preparation conditions, have also been performed. The studies show that there are clear differences between the air and argon milled samples, with the most pronounced changes observed using NAP-XPS. The XPS results find increased levels of active adsorbed oxygen species, linked to the presence of surface oxide vacancies, for the sample prepared in argon. Furthermore, the argon milled LaMnO3 shows improved catalytic activity towards deN2O at lower temperatures compared to the air milled and sol–gel synthesised LaMnO3. Assessing this improved catalytic behaviour during deN2O of argon milled LaMnO3 by in situ NAP-XPS suggests increased interaction of N2O at room temperature within the O 1s region. This study further demonstrates the complexity of mechanochemically prepared materials and through careful choice of characterisation methods how their properties can be understood.
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Jun 2020
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Molly Meng-jung
Li
,
Hanbo
Zou
,
Jianwei
Zheng
,
Tai-sing
Wu
,
Ting-shan
Chan
,
Yun-liang
Soo
,
Xin-ping
Wu
,
Xueqing
Gong
,
Tianyi
Chen
,
Kanak
Roy
,
Georg
Held
,
Edman Shik Chi
Tsang
Abstract: Recent years have seen an increasing interest in capturing hydrogen generated from renewables with CO 2 to produce methanol. However, renewable hydrogen production is currently expensive and in limited quantity as compared to CO 2 . Excess CO 2 and limited H 2 in the feedstock gas mixture is not favourable for the CO 2 hydrogenation to methanol reaction, which causes low activity and poor methanol selectivity. Here we report a new class of Rh‐In catalysts with optimal adsorption property to the intermediates of methanol production. The Rh‐In catalyst can effectively catalyse methanol synthesis but inhibit reverse water‐gas shift reaction under H 2 ‐deficient gas flow and shows the best competitive methanol productivity under industrially applicable conditions in comparison with the literature reported values. This work demonstrates a strong potential of Rh‐In bimetallic composition, from which a convenient methanol synthesis based on flexible feedstock compositions (e.g. H 2 /CO 2 from biomass derivatives) with lower energy cost can be established.
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May 2020
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
E01-JEM ARM 200CF
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Gianfranco
Giorgianni
,
Chalachew
Mebrahtu
,
Manfred E.
Schuster
,
Alexander I.
Large
,
Georg
Held
,
Pilar
Ferrer
,
Federica
Venturini
,
David
Grinter
,
Regina
Palkovits
,
Siglinda
Perathoner
,
Gabriele
Centi
,
Salvatore
Abate
,
Rosa
Arrigo
Diamond Proposal Number(s):
[19472]
Abstract: Hydrotalcite-derived Ni and Fe-promoted hydrotalcite-derived Ni catalysts were found to outperform industrial catalysts in the CO2 methanation reaction, however the origin of the improved activity and selectivity of these catalysts is not clear. Here, we report a study of these systems by means of in situ X-ray photoelectron spectroscopy and near-edge X-ray absorption spectroscopy elucidating the chemical nature of the catalysts` surface under reaction conditions and revealing the mechanism by which Fe promotes activity and selectivity towards methane. We show that the increase of the conversion leads to hydroxylation of the Ni surface following the formation of water during the reaction. This excessive Ni surface hydroxylation has however a detrimental effect as shown by a controlled study. A dominant metallic Ni surface exists in conditions of higher selectivity towards methane whereas if an increase of the Ni surface hydroxylation occurs, a higher selectivity towards carbon monoxide is observed. The electronic structure analysis of the Fe species under reaction conditions reveals the existence of predominantly Fe(III) species at the surface, whereas a mixture of Fe(II)/Fe(III) species is present underneath the surface. Our results highlight that Fe(II) exerts a beneficial effect on maintaining Ni in a metallic state, whereas the extension of the Fe oxidation front from the surface towards the bulk is accompanied by a more extended Ni surface hydroxylation with a negative impact on the selectivity towards methane.
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Apr 2020
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Simson
Wu
,
Yung-kang
Peng
,
Tianyi
Chen
,
Jiaying
Mo
,
Alex
Large
,
Ian
Mcpherson
,
Hung-lung
Chou
,
Ian
Wilkinson
,
Federica
Venturini
,
David
Grinter
,
Pilar
Ferrer Escorihuela
,
Georg
Held
,
Shik Chi Edman
Tsang
Abstract: The increasing availability of low-cost and low pressure, renewable H2 from wind and solar means has triggered tremendous interest in developing low pressure ammonia synthesis with N2 as energy carrier as well as green fertilizer. As such Cs-promoted Ru/MgO catalysts used in Kellogg process show superiority to Fe-based catalysts at milder conditions, however, as known, the surface poisoning of Ru sites by competitive strong H2 dissociative adsorption limits the overall rate. It is demonstrated for the first time that the use of simple polar MgO(111) to replace non-polar MgO as support can significantly alleviate the hydrogen poisoning and facilitate an unprecedented ammonia production rate by its high intrinsic proton capture ability.
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Apr 2020
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