I11-High Resolution Powder Diffraction
I15-1-X-ray Pair Distribution Function (XPDF)
I15-Extreme Conditions
I20-EDE-Energy Dispersive EXAFS (EDE)
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Diamond Proposal Number(s):
[31314, 31898, 20038, 29957, 30178]
Abstract: Metal-organic frameworks (MOFs) are a versatile class of hybrid inorganic-organic materials known for their adjustable chemical and physical properties, as well as their exceptional porosity. These characteristics render MOFs particularly valuable for applications requiring extensive surface areas, such as gas storage and catalysis. Despite being advantageous in many applications, the high porosity and specific bonding characteristics of crystalline MOFs can, however, make them susceptible to pore collapse and amorphisation under pressure. This limits the practical effectiveness of MOFs in their most commonly synthesised form of crystalline powders, as large-scale production and shaping of powders for industrial use often involves pressure and heating.
This thesis examines how a range of MOFs behave under various high pressure and high pressure-temperature conditions to examine both their amorphisation mechanisms and amorphous phases formed. The MOFs were selected to fall within two groups: zirconium-based (UiO-66, MOF-808 and NU-1000) and zinc-based (ZIF-8, ZIF-4 and ZIF-62). The methods chosen for investigations were hydrostatic compression, non-hydrostatic compression, and ball-milling, as they are all used for industrial processing of powders: The former two are methods for shaping, and the latter for mixing. Hydrostatic compression of these MOFs is investigated in depth through in situ high pressure-temperature crystallographic and spectroscopic measurements, allowing real-time analysis on the MOFs’ collapse mechanisms. Both groups display partially reversible amorphisation under hydrostatic compression to certain pressures, indicating a displacive amorphisation transition into an amorphous phase topologically similar to the crystalline. Penetration of the pressure-transmitting media into the framework’s pores was also indicated in each MOF, with clear negative volume compressibility shown in the zinc-based MOFs.
Ex situ investigations into non-hydrostatic compression then introduce the effect of shear stress so its effect on the MOFs can be highlighted, where the two groups demonstrate quite different behaviour attributed to differences in the connectivity of their inorganic components. Ball-milling is finally examined as a non-compression form of amorphisation with a high shear component. In both shear-based pressure states, decoordination of the organic components from the inorganic is seen as a driving factor of amorphisation. Understanding the collapse mechanisms and resultant amorphous phases from various amorphisation methods in these MOFs gives insight into trends in mechanical properties and stability within this class of materials, and is essential for the future industrialisation of MOFs.
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Jan 2025
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
E01-JEM ARM 200CF
E02-JEM ARM 300CF
I20-EDE-Energy Dispersive EXAFS (EDE)
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Lu
Chen
,
Xuze
Guan
,
Zhaofu
Fei
,
Hiroyuki
Asakura
,
Lun
Zhang
,
Zhipeng
Wang
,
Xinlian
Su
,
Zhangyi
Yao
,
Luke L.
Keenan
,
Shusaku
Hayama
,
Matthijs A.
Van Spronsen
,
Burcu
Karagoz
,
Georg
Held
,
Christopher S.
Allen
,
David G.
Hopkinson
,
Donato
Decarolis
,
June
Callison
,
Paul J.
Dyson
,
Feng Ryan
Wang
Diamond Proposal Number(s):
[30622, 33257, 31922]
Open Access
Abstract: Selective catalytic oxidation (SCO) of NH3 to N2 is one of the most effective methods used to eliminate NH3 emissions. However, achieving high conversion over a wide operating temperature range while avoiding over-oxidation to NOx remains a significant challenge. Here, we report a bi-metallic surficial catalyst (PtSCuO/Al2O3) with improved Pt atom efficiency that overcomes the limitations of current catalysts. It achieves full NH3 conversion at 250 °C with a weight hourly space velocity of 600 ml NH3·h−1·g−1, which is 50 °C lower than commercial Pt/Al2O3, and maintains high N2 selectivity through a wide temperature window. Operando XAFS studies reveal that the surface Pt atoms in PtSCuO/Al2O3 enhance the redox properties of the Cu species, thus accelerating the Cu2+ reduction rate and improving the rate of the NH3-SCO reaction. Moreover, a synergistic effect between Pt and Cu sites in PtSCuO/Al2O3 contributes to the high selectivity by facilitating internal selective catalytic reduction.
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Jan 2025
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I20-EDE-Energy Dispersive EXAFS (EDE)
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Abstract: Metal hexacyanoferrate (MHCF) compounds are candidate electrode materials for aqueous sodium and potassium ion batteries and supercapacitors. This is due to their large open structure, long cycling stability and high current density. In this work we have investigated the electron transfer kinetics during the (de)intercalation of cations into/from the MHCF lattice using energy dispersive EXAFS for the cases where M = Fe, Cu, Ni, Co, and Mn. Energy dispersive EXAFS enables the oxidation state (XANES, edge position) to be determined in real time during cycling or following a potential step applied electrochemically. By comparison of the EDE and electrochemical data we were able to explore the differences in the rates of ion and electron transfer in some cases. These differences were most apparent when the oxidation/reduction of the metal ions resulted in a change in the conductivity of the MHCF. For FeHCF we observed that the change from insulator to conductor when the high-spin, carbon bound Fe atom, is reduced, the rate of the process was limited by the electron transfer reaction, whilst the reoxidation (conductor to insulator) was limited by the rate of diffusion of the cations in the FeHCF lattice. In the case of CuHCF and NiHCF, only the low spin, nitrogen bound Fe, atom is electrochemically active and, as there was little change in the conductivity of the material upon oxidation from Fe2+ to Fe3+, we were unable to separate the rates of the ion and electron transfer. For CoHCF and MnHCF, both the Co or Mn and Fe atoms are electrochemically active and by using EDE we were able to monitor the rates of change of the oxidation states of both species in a truly simultaneous manner by collecting the data over an energy range that covered both absorption edges. As in the case of FeHCF, the rate determining process (ion or electron transfer) was found to be dependent on the oxidation state of the carbon bound metal atom, but not on the oxidation state of the nitrogen bound metal atom.
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Jan 2025
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I20-EDE-Energy Dispersive EXAFS (EDE)
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Abstract: The development and growth of heterogeneous catalysis are directly connected to the knowledge of the structure and associated changes that arise from reactions it has, under specific environmental conditions. In liquid phase catalysed reactions, which was the focus of this thesis, information associated with the reaction, e.g. the active site, is often difficult to obtain due to the solvent being present at higher quantities in comparison to the much smaller quantity of active species. Additionally, difficulties associated with the characterisation of such systems arise from the frequently short lifetime of active species, and the tendency of catalytic events to occur on the surface of the catalyst, with the bulk structure barely participating in any reactions. The purpose of this thesis was to conduct a research study, integrating modulation excitation (ME) approach with total neutron scattering (TNS) and X-ray absorption spectroscopy (XAS) techniques. The combination of periodic modulation excitation with phase-sensitive detection (PSD) analysis, and their integration within TNS and XAS, allowed us to probe surface structural changes. This approach demonstrated an enhanced signal-to-noise ratio of the experimental data and significantly improved the sensitivity of the respective instruments to weak component contributions. Periodic electrical potential switches were employed as external stimulations to perturb the investigated systems reversibly and measure the active species contributions. In contrast to XAS, where ME methodology has been extensively implemented to the study of gas-phase catalytic reactions and most recently to liquid-phase catalytic reactions; combined ME-TNS studies is a novel approach that was successfully developed and demonstrated for the first time in this thesis. Ultimately, the essential instrumentation and innovative analysis procedures to extract useful structural information from the newly acquired ME-TNS data are demonstrated in the results chapters of this thesis. Finally, the ME technique was implemented at the Energy Dispersive EXAFS (EDE) branch of the I20 X-ray absorption spectroscopy beamline at Diamond Light Source, while the NIMROD instrument at ISIS neutron and muon source was developed to enable it to obtain ME-neutron scattering data.
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Dec 2024
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I20-EDE-Energy Dispersive EXAFS (EDE)
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Diamond Proposal Number(s):
[28203]
Abstract: Understanding nature of intermediates/active species in reactions is a major challenge in chemistry. This is because spectator species typically dominate the experimentally derived data and consequently active phase contributions are masked. Transient methods offer a means to bypass this difficulty. In particular, modulation excitation with phase-sensitive detection (ME-PSD) provides a mechanism to distinguish between spectator and reacting species. Herein, modulation excitation (ME) time-resolved (energy dispersive) X-ray absorption spectroscopy, assisted by phase sensitive detection (PSD) analysis, has been applied to the study of a liquid phase process; in this case the classic ferrocyanide/ferricyanide redox couple. Periodic switches of the electrical potential (anodic/cathodic) enabled the use of the ME approach. Structural changes at fractions as low as 2% of the total number of electroactive species were detected within the X-ray beam probe volume containing ~30 pmol of Fe(II)/Fe(III).
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Aug 2024
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
E01-JEM ARM 200CF
I09-Surface and Interface Structural Analysis
I20-EDE-Energy Dispersive EXAFS (EDE)
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Xuze
Guan
,
Rong
Han
,
Hiroyuki
Asakura
,
Bolun
Wang
,
Lu
Chen
,
Jay Hon Cheung
Yan
,
Shaoliang
Guan
,
Luke
Keenan
,
Shusaku
Hayama
,
Matthijs A.
Van Spronsen
,
Georg
Held
,
Jie
Zhang
,
Hao
Gu
,
Yifei
Ren
,
Lun
Zhang
,
Zhangyi
Yao
,
Yujiang
Zhu
,
Anna
Regoutz
,
Tsunehiro
Tanaka
,
Yuzheng
Guo
,
Feng Ryan
Wang
Diamond Proposal Number(s):
[23759, 24450, 29092, 31852]
Open Access
Abstract: Single-atom catalysts have garnered significant attention due to their exceptional atom utilization and unique properties. However, the practical application of these catalysts is often impeded by challenges such as sintering-induced instability and poisoning of isolated atoms due to strong gas adsorption. In this study, we employed the mechanochemical method to insert single Cu atoms into the subsurface of Fe2O3 support. By manipulating the location of single atoms at the surface or subsurface, catalysts with distinct adsorption properties and reaction mechanisms can be achieved. It was observed that the subsurface Cu single atoms in Fe2O3 remained isolated under both oxidation and reduction environments, whereas surface Cu single atoms on Fe2O3 experienced sintering under reduction conditions. The unique properties of these subsurface single-atom catalysts call for innovations and new understandings in catalyst design.
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Jul 2024
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I20-EDE-Energy Dispersive EXAFS (EDE)
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Donato
Decarolis
,
Monik
Panchal
,
Matthew
Quesne
,
Khaled
Mohammed
,
Shaojun
Xu
,
Mark
Isaacs
,
Adam H.
Clark
,
Luke L.
Keenan
,
Takuo
Wakisaka
,
Kohei
Kusada
,
Hiroshi
Kitagawa
,
C. Richard A.
Catlow
,
Emma K.
Gibson
,
Alexandre
Goguet
,
Peter
Wells
Diamond Proposal Number(s):
[21593]
Open Access
Abstract: Unravelling kinetic oscillations, which arise spontaneously during catalysis, has been a challenge for decades but is important not only to understand these complex phenomena but also to achieve increased activity. Here we show, through temporally and spatially resolved operando analysis, that CO oxidation over Rh/Al2O3 involves a series of thermal levering events—CO oxidation, Boudouard reaction and carbon combustion—that drive oscillatory CO2 formation. This catalytic sequence relies on harnessing localized temperature episodes at the nanoparticle level as an efficient means to drive reactions in situations in which the macroscopic conditions are unfavourable for catalysis. This insight provides a new basis for coupling thermal events at the nanoscale for efficient harvesting of energy and enhanced catalyst technologies.
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Jul 2024
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B18-Core EXAFS
I20-EDE-Energy Dispersive EXAFS (EDE)
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Khaled
Mohammed
,
Reza
Vakili
,
Donato
Decarolis
,
Shaojun
Xu
,
Luke L.
Keenan
,
Apostolos
Kordatos
,
Nikolay
Zhelev
,
Chris K.
Skylaris
,
Marina
Carravetta
,
Emma K.
Gibson
,
Haresh
Manyar
,
Alexandre
Goguet
,
Peter P.
Wells
Diamond Proposal Number(s):
[28666, 34632]
Open Access
Abstract: The need to achieve net zero requires decarbonisation across all areas of our industrialised society, including the production of chemicals. One example is the production of acetonitrile, which currently relies on fossil carbon. Recently, supported Pd nanoparticles have been shown to promote the selective transformation of bio-derived ethanol to acetonitrile. Elsewhere, current research has demonstrated the importance of interstitial structures of Pd in promoting specific transformations. In this study, we demonstrate through a spatially resolved operando energy-dispersive-EXAFS (EDE) technique that the selectivity to acetonitrile (up to 99%) is concurrent with the formation of a PdNx phase. This was evidenced from the features observed in the X-ray Absorption near edge structure validated against PdNx samples made via known synthesis methods. . Above 240 ℃, the Pd nanoparticles became progressively oxidised which led to the production of unwanted byproducts, primarily CO2. The spatially resolved analysis indicated that the Pd speciation was homogeneous across the catalyst profile throughout the series of studies performed. This work resolved the structural selectivity of Pd nanoparticles that directs ethanol ammoxidation towards acetonitrile, and provides important information on the performance descriptors required to advance this technology.
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Apr 2024
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I20-EDE-Energy Dispersive EXAFS (EDE)
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Diamond Proposal Number(s):
[29667]
Abstract: Heterogeneous catalysis - where the catalyst is in a different phase to the reactants - is a stalwart of the chemicals and energy industries. The development of active, selective, and energy-efficient heterogeneous catalysts is, therefore, a crucial pillar of our transition to more sustainable technologies. There has been a recent focus on single-atom heterogeneous catalysts (SAHCs), due to their maximum metal utilisation and unique reactivity. However, while carbon-nitrogen supports are widely used for SAHCs, most studies of their dynamics through a reaction have used oxide supports.
It is not yet clear whether single atoms or sub nanometre clusters that form under reaction conditions are active species. In work recently published in the Journal of Catalysis, a team of researchers used aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) to investigate the dynamics of palladium SAHCs on graphitic carbon nitride supports during two reactions - ethylene hydrogenation and H2-D2 exchange. Their results show that, at 100°C in a gas containing ethylene and hydrogen, the palladium single atoms form clusters, and suggest that these clusters are the active species. Their work offers new insights into the effect of gas atmosphere on speciation.
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Apr 2024
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I20-EDE-Energy Dispersive EXAFS (EDE)
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Diamond Proposal Number(s):
[28536]
Open Access
Abstract: Amorphous metal–organic frameworks are rarely formed via direct synthesis. Our limited understanding of their atomic assembly in solution prevents full exploitation of their unique structural complexity. Here, we use in situ synchrotron X-ray absorption spectroscopy with sub-second time resolution to probe the formation of the amorphous Fe-BTC framework. Using a combination of spectral fingerprinting, linear combination analysis, and principal component analysis coupled with kinetic analyses, we reveal a multi-stage formation mechanism that, crucially, proceeds via the generation of a transient intermediate species.
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Feb 2024
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