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
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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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Open Access
Abstract: Understanding the interaction of amino acids with metal surfaces is essential for the rational design of chiral modifiers able to confer enantioselectivity to metal catalysts. We present here an investigation of the adsorption of aspartic acid (Asp) on the Ni{100} surface, using a combination of synchrotron X-Ray Photoelectron Spectroscopy (XPS) and Near-Edge X-ray Absorption Fine Structure (NEXAFS), and Density Functional Theory (DFT) simulations. Based on the combined analysis of the experimental and simulated data, we can identify the dominant mode of adsorption as a pentadentate configuration with three O atoms at the bridge sites of the surfaces, and the remaining oxygen atom and the amino nitrogen are located on atop sites. From temperature-programmed XPS measurements it was found that Asp starts decomposing above 400 K, which is significantly higher than typical decomposition temperatures of smaller organic molecules on Ni surfaces. Our results offer valuable insights for understanding the role of Asp as a chiral modifier of nickel catalyst surfaces for enantioselective hydrogenation reactions.
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Jul 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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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Diamond Proposal Number(s):
[19299]
Abstract: Methanol is a promising chemical for the safe and efficient storage of hydrogen, where methanol conversion reactions can generate a hydrogen-containing gas mixture. Understanding the chemical state of the catalyst over which these reactions occur and the interplay with the adsorbed species present is key to the design of improved catalysts and process conditions. Here we study polycrystalline Cu foils using ambient pressure X-ray spectroscopies to reveal the Cu oxidation state and identify the adsorbed species during partial oxidation (CH3OH + O2), steam reforming (CH3OH + H2O), and autothermal reforming (CH3OH + O2 + H2O) of methanol at 200 °C surface temperature and in the mbar pressure range. We find that the Cu surface remains highly metallic throughout partial oxidation and steam reforming reactions, even for oxygen-rich conditions. However, for autothermal reforming the Cu surface shows significant oxidation towards Cu2O. We rationalise this behaviour on the basis of the shift in equilibrium of the CH3OH* + O* ⇌ CH3O* + OH* caused by the addition of H2O.
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Mar 2020
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
B18-Core EXAFS
E01-JEM ARM 200CF
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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
Open Access
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.
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Dec 2019
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[12800]
Abstract: The adsorption of organic molecules on solid substrates is important to applications in fields such as catalysis, photovoltaics, corrosion inhibition, adhesion, and sensors. The molecular level description of the surface-molecule interaction and of the adsorption structures in these complex systems is crucial to understand their properties and function. Here we present the investigation of one such system, benzotriazole (BTAH) on single crystal Cu(111) in vacuum conditions. BTAH is the most widely used corrosion inhibitor for copper and thus a molecule of great industrial relevance. We show that the co-application of a wide range of spectroscopic techniques with theoretical methods provides unique insight in the description of the atomistic details of the adsorbed structures. Specifically, spectroscopic photoemission, absorption and standing wave experiments combined with ab initio computational modeling allowed us to identify that benzotriazole forms overlayers of intact BTAH when deposited at low temperature and it dissociates into BTA and H at room temperature and above. The dissociated molecule then forms complex structures of mixed chains and dimers of BTA bound to copper adatoms. Our work also reveals that copper adatoms at low concentrations, such as the theoretically predicted superstructures cannot be be resolved by means of current X-ray photoelectron spectroscopy (XPS) as the modelled Cu 2p spectra are practically indistinguishable from those for a Cu surface without adatoms. Overall this study significantly deepens understanding of BTAH on Cu – a system studied for more than 50 years – and it highlights the benefits of combining spectroscopic and computational methods in order to obtain a complete picture of a complex adsorption system.
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Jan 2019
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