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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E01-JEM ARM 200CF
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Lin
Ye
,
A. A. Hanif
Mahadi
,
Chalathan
Saengruengrit
,
Jin
Qu
,
Feng
Xu
,
Simon
Fairclough
,
Neil
Young
,
Ping-luen
Ho
,
Junjun
Shan
,
Luan
Nguyen
,
Franklin F.
Tao
,
Karaked
Tedsree
,
Shik Chi Edman
Tsang
Abstract: Ceria has been widely used as support in electrocatalysis for its high degree of oxygen storage, fast oxygen mobility and reduction and oxidation properties at mild conditions. However, it is unclear what are the underlying principles and the nature of surface involved. By controlling the growth of various morphologies of ceria nanoparticles, it is demonstrated that the cubic-form of ceria, predominantly covered with higher energy polar surface (100), as support for Pd gives much higher activity in the electrocatalytic oxidation of formic acid than ceria of other morphologies (rods and spheres) with low indexed facets ((110) and (111)). High resolution TEM confirms the alternating layer-to-layer of cations and anions in (100) surface, the electrostatic repulsion of oxygen anions within the same layers gives intrinsically higher oxygen vacancies on this redox active surface in order to reduce surface polarity. DFT calculations suggest that the properties of fast oxygen mobility to re-oxidize the CO-poisoned Pd may arise from the overdosed oxygens on these ceria surface layers during electro-oxidation hence sustaining higher activity.
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Apr 2019
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E01-JEM ARM 200CF
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Abstract: Doped-ZnO nanoparticles, capped with dioctylphosphinate ligands, are synthesised by the controlled hydrolysis of a mixture of organometallic precursors. Substitutional doping of the wurtzite ZnO nanoparticles with 5 mol% Mg(II), Al(III) and Cu(I) is achieved by the addition of sub-stoichiometric amounts of the appropriate dopant [(n-butyl)(sec-butyl)magnesium, triethylaluminium or mesitylcopper] to diethylzinc in the precursor mixture. After hydrolysis, the resulting colloidal nanoparticles (sizes of 2–3 nm) are characterised by powder X-ray crystallography, transmission electron microscopy, inductively-coupled plasma optical emission spectrometry and X-ray photoelectron spectroscopy. A solution of the doped-ZnO nanoparticles and colloidal Cu(0) nanoparticles [M:ZnO : Cu = 1 : 1] are applied as catalysts for the hydrogenation of CO2 to methanol in a liquid-phase continuous flow stirred tank reactor [210 °C, 50 bar, CO2[thin space (1/6-em)]:[thin space (1/6-em)]H2 = 1[thin space (1/6-em)]:[thin space (1/6-em)]3, 150 mL min−1, mesitylene, 20 h]. All the catalyst systems display higher rates of methanol production and better stability than a benchmark heterogeneous catalyst, Cu–ZnO–Al2O3 [480 μmol mmolmetal−1 h−1], with approximately twice the activity for the Al(III)-doped nanocatalyst. Despite outperforming the benchmark catalyst, Mg(II) doping is detrimental towards methanol production in comparison to undoped ZnO. X-Ray photoelectron spectroscopy and transmission electron microscopy analysis of the most active post-catalysis samples implicate the migration of Al(III) to the catalyst surface, and this surface enrichment is proposed to facilitate stabilisation of the catalytic ZnO/Cu interfaces.
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May 2020
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B18-Core EXAFS
E01-JEM ARM 200CF
E02-JEM ARM 300CF
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Liqun
Kang
,
Bolun
Wang
,
Adam
Thetford
,
Ke
Wu
,
Mohsen
Danaie
,
Qian
He
,
Emma
Gibson
,
Ling-dong
Sun
,
Hiroyuki
Asakura
,
Richard
Catlow
,
Feng Ryan
Wang
Diamond Proposal Number(s):
[16966, 17559, 18909, 19246, 19318, 20643, 20847, 17377, 15151, 14239]
Open Access
Abstract: Ru(II) compounds are widely used in catalysis, photocatalysis and medical applications. They are usually obtained in reductive environment as molecular O 2 can oxidize Ru(II) to Ru(III) and Ru(IV). Here we report the design, identification and evolution of an air‐stable surface ‐[bipy‐Ru(II)(CO) 2 Cl 2 ] site that is covalently mounted onto a polyphenylene framework. Such Ru(II) site was obtained by reduction of ‐[bipy‐Ru(III)Cl 4 ] ‐ with simultaneous ligand exchange from Cl ‐ to CO. This structural evolution was witnessed by a combination of in situ X‐ray and infrared spectroscopy studies. The ‐[bipy‐Ru(II)(CO) 2 Cl 2 ] site enables oxidation of CO with a turnover frequency of 0.73 × 10 ‐2 s ‐1 at 462 K, while the Ru(III) site is completely inert. This work contributes to the studies of structure‐activity relationship by demonstrating a practical control over both geometric and electronic structures of single‐site catalysts at molecular level, which can be further applied in other single site catalyst researches.
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Sep 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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E01-JEM ARM 200CF
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Yiding
Jiao
,
Liqun
Kang
,
Jasper
Berry-gair
,
Kit
Mccoll
,
Jianwei
Li
,
Haobo
Dong
,
Hao
Jiang
,
Ryan
Wang
,
Furio
Corà
,
Dan J. L.
Brett
,
Guanjie
He
,
Ivan
Parkin
Diamond Proposal Number(s):
[24450]
Open Access
Abstract: The primary issue faced by MnO2 cathode materials for aqueous Zn-ion batteries (AZIBs) is the occurrence of structural transformations during cycling, resulting in unstable capacity output. Pre-intercalating closely bonded ions into the MnO2 structures has been demonstrated as an effective approach to combat this. However, mechanisms of the pre-intercalation remain unclear. Herein, two distinct δ-MnO2 (K0.28MnO2·0.1H2O and K0.21MnO2·0.1H2O) are prepared with varying amounts of pre-intercalated K+ and applied as cathodes for AZIBs. The as-prepared K0.28MnO2·0.1H2O cathodes exhibit relatively high specific capacity (300 mA h g−1 at 100 mA g−1), satisfactory rate performance (35% capacity recovery at 5 A g−1) and competent cyclability (ca. 95% capacity retention after 1000 cycles at 2 A g−1), while inferior cyclability and rate performance are observed in K0.21MnO2·0.1H2O. A stable δ-MnO2 phase is observed upon cycling, with the reversible deposition of Zn4SO4(OH)6·5H2O (ZSH), ion migration between electrodes and synchronous transition of Mn valence states. This work firstly and systematically reveals the role of the pre-intercalated ions via density functional theory simulations and show that above a threshold K/Mn ratio of ca. 0.26, the K ions suppress structural transformations by stabilizing the δ phase. To demonstrate its commercial potential, AZIBs with high-loading active materials are fabricated, which deliver adequate energy and power densities compared with most commercial devices.
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Nov 2020
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E01-JEM ARM 200CF
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Diamond Proposal Number(s):
[21253]
Open Access
Abstract: The rejection of particles with different charges and sizes, ranging from a few Ångstroms to tens of nanometers, is key to a wide range of industrial applications, from wastewater treatment to product purification in biotech processes. Carbon nanotubes (CNTs) have long held the promise to revolutionize filtration, with orders of magnitude higher fluxes compared to commercial membranes. CNTs, however, can only reject particles and ions wider than their internal diameter. In this work, the fabrication of aligned boron nitride nanotube (BNNT) membranes capable of rejecting nanoparticles smaller than their internal diameter is reported for the first time. This is due to a mechanism of charge-based rejection in addition to the size-based one, enabled by the BNNTs surface structure and chemistry and elucidated here using high fidelity molecular dynamics and Brownian dynamics simulations. This results in ∼40% higher rejection of the same particles by BNNT membranes than CNT ones with comparable nanotube diameter. Furthermore, since permeance is proportional to the square of the nanotubes’ diameter, using BNNT membranes with ∼30% larger nanotube diameter than a CNT membrane with comparable rejection would result in up to 70% higher permeance. These results open the way to the design of more effective nanotube membranes, capable of high particle rejection and, at the same time, high water permeance.
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Jul 2020
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B18-Core EXAFS
E01-JEM ARM 200CF
I11-High Resolution Powder Diffraction
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Abstract: Industrial olefin metathesis catalysts generally suffer from low reaction rates and require harsh reaction conditions for moderate activities. This is due to their inability to prevent metathesis active sites (MAS) from aggregation and their intrinsic poor adsorption and activation of olefin molecules. Here, isolated tungstate species as single molecular MAS is immobilized inside zeolite pores by Brønsted acid sites (BAS) on the inner surface. It is demonstrated for the first time that unoccupied BAS in atomic proximity to MAS enhance olefin adsorption and greatly facilitate the formation of metallocycle intermediates in a stereospecific manner. Thus, effective cooperative catalysis takes place over the BAS-MAS pair. In consequence, for the cross-metathesis of ethene and trans-2-butene to propene, under the same mild reaction conditions, the propene production rate over WOx/USY is ca. 7,300 times that over the industrial WO3/SiO2 based catalyst. A propene yield up to 79% (80% selectivity) without observable deactivation was obtained over WOx/USY for a wide range of reaction conditions.
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Apr 2018
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E01-JEM ARM 200CF
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Diamond Proposal Number(s):
[20643]
Abstract: The magnesium–sulfur (Mg-S) battery may be a safer alternative for the lithium-sulfur battery because Mg plating usually proceeds without dendrite formation. Here, we correlate the thermal runaway of Mg-S battery with the associated change of electrolyte vapour pressure via battery testing calorimetery. Over-pressure builds up along with the programmed heating of the cell, and as a result, the thermal runaway is triggered at 20 to 45 K over the electrolyte boiling point, corresponding to 70 to 150 kPa pressure difference between the cell and the environment. The distinct performance-safety-cost behaviours of three ether type of electrolytes stems from the different CH2CH2O chain lengths. Such molecular insight will serve as a fundamental guideline in choosing and designing the desired electrolyte that simultaneously achieves a high explosion limit and good electrochemical performance.
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Jan 2021
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B18-Core EXAFS
E01-JEM ARM 200CF
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Xi
Sun
,
Simon R.
Dawson
,
Tanja E.
Parmentier
,
Grazia
Malta
,
Thomas E.
Davies
,
Qian
He
,
Li
Lu
,
David J.
Morgan
,
Nicholas
Carthey
,
Peter
Johnston
,
Simon A.
Kondrat
,
Simon J.
Freakley
,
Christopher J.
Kiely
,
Graham J.
Hutchings
Diamond Proposal Number(s):
[22766, 20643, 19580]
Abstract: Single-site catalysts can demonstrate high activity and selectivity in many catalytic reactions. The synthesis of these materials by impregnation from strongly oxidizing aqueous solutions or pH-controlled deposition often leads to low metal loadings or a range of metal species. Here, we demonstrate that simple impregnation of the metal precursors onto activated carbon from a low-boiling-point, low-polarity solvent, such as acetone, results in catalysts with an atomic dispersion of cationic metal species. We show the generality of this method by producing single-site Au, Pd, Ru and Pt catalysts supported on carbon in a facile manner. Single-site Au/C catalysts have previously been validated commercially to produce vinyl chloride, and here we show that this facile synthesis method can produce effective catalysts for acetylene hydrochlorination in the absence of the highly oxidizing acidic solvents previously used.
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Apr 2020
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