E01-JEM ARM 200CF
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Diamond Proposal Number(s):
[33314]
Open Access
Abstract: Rigorous comparisons between single site- and nanoparticle (NP)-dispersed catalysts featuring the same composition, in terms of activity, selectivity, and reaction mechanism, are limited. This limitation is partly due to the tendency of single metal atoms to sinter into aggregated NPs at high loadings and elevated temperatures, driven by a decrease in metal surface free energy. Here, we have developed a unique two-step method for the synthesis of single Cu sites on ZSM-5 (termed CuS/ZSM-5) with high thermal stability. The atomic-level dispersion of single Cu sites was confirmed through scanning transmission electron microscopy, X-ray absorption fine structure (XAFS), and electron paramagnetic resonance spectroscopy. The CuS/ZSM-5 catalyst was compared to a CuO NP-based catalyst (termed CuN/ZSM-5) in the oxidation of NH3 to N2, with the former exhibiting superior activity and selectivity. Furthermore, operando XAFS and diffuse reflectance infrared Fourier transform spectroscopy studies were conducted to simultaneously assess the fate of the Cu and the surface adsorbates, providing a comprehensive understanding of the mechanism of the two catalysts. The study shows that the facile redox behavior exhibited by single Cu sites correlates with the enhanced activity observed for the CuS/ZSM-5 catalyst.
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Jul 2024
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
B18-Core EXAFS
E02-JEM ARM 300CF
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Longxiang
Liu
,
Liqun
Kang
,
Jianrui
Feng
,
David G.
Hopkinson
,
Christopher S.
Allen
,
Yeshu
Tan
,
Hao
Gu
,
Iuliia
Mikulska
,
Veronica
Celorrio
,
Diego
Gianolio
,
Tianlei
Wang
,
Liquan
Zhang
,
Kaiqi
Li
,
Jichao
Zhang
,
Jiexin
Zhu
,
Georg
Held
,
Pilar
Ferrer
,
David
Grinter
,
June
Callison
,
Martin
Wilding
,
Sining
Chen
,
Ivan
Parkin
,
Guanjie
He
Diamond Proposal Number(s):
[30614, 32058, 32035, 32117, 33466, 29271]
Open Access
Abstract: Electrochemical hydrogen peroxide (H2O2) production (EHPP) via a two-electron oxygen reduction reaction (2e- ORR) provides a promising alternative to replace the energy-intensive anthraquinone process. M-N-C electrocatalysts, which consist of atomically dispersed transition metals and nitrogen-doped carbon, have demonstrated considerable EHPP efficiency. However, their full potential, particularly regarding the correlation between structural configurations and performances in neutral media, remains underexplored. Herein, a series of ultralow metal-loading M-N-C electrocatalysts are synthesized and investigated for the EHPP process in the neutral electrolyte. CoNCB material with the asymmetric Co-C/N/O configuration exhibits the highest EHPP activity and selectivity among various as-prepared M-N-C electrocatalyst, with an outstanding mass activity (6.1 × 105 A gCo−1 at 0.5 V vs. RHE), and a high practical H2O2 production rate (4.72 mol gcatalyst−1 h−1 cm−2). Compared with the popularly recognized square-planar symmetric Co-N4 configuration, the superiority of asymmetric Co-C/N/O configurations is elucidated by X-ray absorption fine structure spectroscopy analysis and computational studies.
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May 2024
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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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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):
[17031]
Open Access
Abstract: In this study, we aim to contribute an understanding of the pathway of formation of Fe species during top-down synthesis of dispersed Fe on N-functionalized few layer graphene. We use X-ray absorption spectroscopy to determine the electronic structure and coordination geometry of the Fe species and in situ high angle annular dark field scanning transmission electron microscopy combined with atomic resolved electron energy loss spectroscopy to localize these, identify their chemical configuration and monitor their dynamics during thermal annealing. We show the high mobility of peripheral Fe atoms, first diffusing rapidly at the trims of the graphene layers and at temperatures as high as 573 K, diffusing from the edge planes towards in-plane locations of the graphene layers forming three-, four-coordinated metal sites and more complexes polynuclear Fe species. This process occurs via bond breaking which partially reduces the extension of the graphene domains. However, the vast majority of Fe is segregated as a metal phase. This dynamic interconversion depends on the structural details of the surrounding graphitic environment in which these are formed as well as the Fe loading. N species appear stabilizing isolated and polynuclear Fe species even at temperatures as high as 873 K. The significance of our results lies on the fact that single Fe atoms in graphene are highly mobile and therefore a structural description of the active sites as such is insufficient and more complex species might be more relevant, especially in the case of multielectron transfer reaction. Here we provide the experimental evidence on the formation of these polynuclear Fe-N sites and their structural characteristics.
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May 2021
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B18-Core EXAFS
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Diamond Proposal Number(s):
[198590]
Open Access
Abstract: The aqueous phase reforming of glycerol, to hydrogen, alkanes and liquid phase dehydration/dehydrogenation products, was studied over a series of 1 wt% Pt/LaMO3 (where M = Al, Cr, Mn, Fe, Co, Ni) catalysts and compared to a standard 1 wt% Pt/γ-Al2O3 catalyst. The sol–gel combustion synthesis of lanthanum-based perovskites LaMO3 produced pure phase perovskites with surface areas of 8–18 m2g−1. Glycerol conversions were higher than the Pt/γ-Al2O3 (10%) for several perovskite supported catalysts, with the highest being for Pt/LaNiO3 (19%). Perovskite-based catalysts showed reduced alkane formation and significantly increased lactic acid formation compared to the standard catalyst. However, most of the perovskite materials undergo phase separation to LaCO3OH and respective M site oxides with Pt particle migration. The exception being the LaCrO3 support which was found to remain structurally stable. Catalytic performance remained stable over several cycles, for catalysts M = Al, Cr and Ni, despite phase separation of some of these materials. Materials where M site leaching into solution was observed (M = Mn and Co), were found to be catalytically unstable, which was hypothesised to be due to significant loss in support surface area and uncontrolled migration of Pt to the remaining support surface. In the case of Pt/LaNiO3 alloying between the exsoluted Ni and Pt was observed post reaction.
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May 2021
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B18-Core EXAFS
E01-JEM ARM 200CF
E02-JEM ARM 300CF
I11-High Resolution Powder Diffraction
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Liqun
Kang
,
Bolun
Wang
,
Qiming
Bing
,
Michal
Zalibera
,
Robert
Büchel
,
Ruoyu
Xu
,
Qiming
Wang
,
Yiyun
Liu
,
Diego
Gianolio
,
Chiu C.
Tang
,
Emma K.
Gibson
,
Mohsen
Danaie
,
Christopher
Allen
,
Ke
Wu
,
Sushila
Marlow
,
Ling-Dong
Sun
,
Qian
He
,
Shaoliang
Guan
,
Anton
Savitsky
,
Juan J.
Velasco-Vélez
,
June
Callison
,
Christopher W. M.
Kay
,
Sotiris E.
Pratsinis
,
Wolfgang
Lubitz
,
Jing-Yao
Liu
,
Feng Ryan
Wang
Diamond Proposal Number(s):
[15151, 15763, 16966, 17377, 19072, 19246, 20939, 17559, 24285, 19318, 19850]
Open Access
Abstract: Supported atomic metal sites have discrete molecular orbitals. Precise control over the energies of these sites is key to achieving novel reaction pathways with superior selectivity. Here, we achieve selective oxygen (O2) activation by utilising a framework of cerium (Ce) cations to reduce the energy of 3d orbitals of isolated copper (Cu) sites. Operando X-ray absorption spectroscopy, electron paramagnetic resonance and density-functional theory simulations are used to demonstrate that a [Cu(I)O2]3− site selectively adsorbs molecular O2, forming a rarely reported electrophilic η2-O2 species at 298 K. Assisted by neighbouring Ce(III) cations, η2-O2 is finally reduced to two O2−, that create two Cu–O–Ce oxo-bridges at 453 K. The isolated Cu(I)/(II) sites are ten times more active in CO oxidation than CuO clusters, showing a turnover frequency of 0.028 ± 0.003 s−1 at 373 K and 0.01 bar PCO. The unique electronic structure of [Cu(I)O2]3− site suggests its potential in selective oxidation.
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Aug 2020
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B18-Core EXAFS
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Bingqiao
Xie
,
Roong Jien
Wong
,
Tze Hao
Tan
,
Michael
Higham
,
Emma K.
Gibson
,
Donato
Decarolis
,
June
Callison
,
Kondo-Francois
Aguey-Zinsou
,
Michael
Bowker
,
C. Richard A.
Catlow
,
Jason
Scott
,
Rose
Amal
Diamond Proposal Number(s):
[19850]
Open Access
Abstract: Although photoexcitation has been employed to unlock the low-temperature equilibrium regimes of thermal catalysis, mechanism underlining potential interplay between electron excitations and surface chemical processes remains elusive. Here, we report an associative zinc oxide band-gap excitation and copper plasmonic excitation that can cooperatively promote methanol-production at the copper-zinc oxide interfacial perimeter of copper/zinc oxide/alumina (CZA) catalyst. Conversely, selective excitation of individual components only leads to the promotion of carbon monoxide production. Accompanied by the variation in surface copper oxidation state and local electronic structure of zinc, electrons originating from the zinc oxide excitation and copper plasmonic excitation serve to activate surface adsorbates, catalysing key elementary processes (namely formate conversion and hydrogen molecule activation), thus providing one explanation for the observed photothermal activity. These observations give valuable insights into the key elementary processes occurring on the surface of the CZA catalyst under light-heat dual activation.
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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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B18-Core EXAFS
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Diamond Proposal Number(s):
[10306]
Open Access
Abstract: Sustainable technologies require both renewable feedstocks and catalysts that are able to direct their conversion to specific products. We establish a structure-activity relationship for the aqueous phase reforming of glycerol over 2% Pt/Al2O3 catalysts, whereby the reaction pathway can be controlled to produce either hydrogen or 1,2-propanediol as the main product. Using the colloidal synthesis method, the reduction temperature was altered to produce Pt nanoparticle catalysts supported on Al2O3 with varying Pt particle size. The catalytic activity of the samples for the APR of glycerol resulted in a higher conversion of glycerol (34%) for the larger Pt particle size of ∼3.5 nm, producing the liquid 1,2-propanediol as the major product with a yield of 12.5%, whereas smaller particles of ∼2.2 nm gave hydrogen as the main product (5.5% yield). This work demonstrates how the APR of glycerol can be tuned to yield both valuable liquid and gas products using tailored Pt nanoparticles.
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Dec 2018
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