B18-Core EXAFS
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Diamond Proposal Number(s):
[14673, 21040]
Open Access
Abstract: Time-resolved structural changes taking place during the reaction of Ca(OH)2 and CO2 forming different CaCO3 polymorphs, in aqueous and non-aqueous environments, were recorded operando using mid-infrared (mid-IR) and X-ray absorption near-edge structure (XANES) spectroscopy. Results show that Ca(OH)2 directly transforms into calcite in a pure water dispersion. In methanolic media with low water content, calcium di-methylcarbonate (Ca(OCOOCH3)2) is formed, which is hydrolysed to amorphous calcium carbonate (ACC) and vaterite in the presence of sufficient water. The addition of toluene shifts the equilibrium composition further from Ca(OH)2 to ACC and the crystalline forms of CaCO3, probably by affecting the activity of the methoxide intermediate. It can facilitate the formation of aragonite. No Ca(OH)2 conversion was detected in pure ethanol, isopropanol and toluene dispersions, except for nanoscale Ca(OH)2 in ethanolic dispersion, which formed calcium di-ethylcarbonate (Ca(OCOOCH2CH3)2). Our findings underline that vaterite formation is driven by the solution and solid state chemistry related to the reaction via alkoxides and carbonic acid esters of the alcohols, rather than the nucleation process in solution. The alcohol in these systems does not just act as a solvent but as a reactant.
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Apr 2025
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[31385]
Open Access
Abstract: A free-standing and compact reaction cell for combined in situ/operando x-ray spectroscopy, scattering, and imaging measurements at high pressures and high temperatures is described. The cell permits measurements under realistic operating conditions (up to 50 bar and 1000 °C), under static and flow conditions (up to 100 ml/min), over a wide range of hard x-ray energies, variable detection modes (transmission, fluorescence, and scattering), and at all angles of rotation. An operando XAS, x-ray fluorescence, x-ray computed tomography, and x-ray diffraction computed tomography case study on the reduction of a heterogeneous catalyst is presented to illustrate the performance of the reaction cell.
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Oct 2024
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B18-Core EXAFS
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Abstract: The MoS2 nanosheets are acquired via a facile hydrothermal strategy, and the M/MoS2 (M = Pt, Rh, Pd, Ru) samples are gained by impregnation. By comparing the catalytic behaviors of these catalysts for p-nitroacetophenone selective hydrogenation, it is found that the catalytic property and selectivity for one −NO2 group hydrogenation of Ru/MoS2 outperform those of other as-prepared catalysts. In addition, the Ru/MoS2 catalysts with various Ru contents (0.37, 0.88, or 2.45 wt %) are used for 3-nitrostyrene selective hydrogenation, and the results show that 0.88 wt % Ru/MoS2 displays the highest catalytic activity (turnover frequency) of TOF = 118.4 h–1 (TOF = 64.2 h–1 for 0.37 wt %Ru/MoS2 and TOF = 61.7 h–1 for 2.45 wt %Ru/MoS2) under the reaction conditions of 100 °C, 3.0 MPa H2, and 1 h. The nanostructure characterization of the as-prepared catalysts (XRD, XPS, TEM, HRTEM, H2-TPD, XAS, AC-STEM, AC-STEM-EDX elemental mapping, and line scanning) demonstrate that Ruδ+ single atoms and Ru clusters are well dispersed on the support. Moreover, 0.88 wt % Ru/MoS2 exhibits extremely high selectivity of one −NO2 group hydrogenation (∼100%) at high conversion for other selected nitroaromatics’ hydrogenation, such as nitrobenzene, 2-chloronitrobenzene, 1,3-dinitrobenzene, 3-nitrostyrene, p-nitroacetophenone, and p-nitrobenzonitrile. This is mainly due to the fact that Ru is present with single atoms and clusters, producing the synergism of Ruδ+ single atoms, Ru clusters, and MoS2 nanosheets. And the synergism mechanism is given below: hydrogen is preferentially adsorbed and activated at Ru clusters (forming activated H* species), the −NO2 group is easily adsorbed and activated at Ruδ+ single atoms (charge interaction between electrons from O in −NO2 and positive charge from Ruδ+ single atoms), and H* transfers to Ruδ+ single atoms by the hydrogen spillover effect of the MoS2 nanosheets, reacting with the −NO2 group, forming desired aromatic amines.
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Sep 2024
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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David C.
Grinter
,
Pilar
Ferrer
,
Federica
Venturini
,
Matthijs A.
Van Spronsen
,
Alexander I.
Large
,
Santosh
Kumar
,
Maximilian
Jaugstetter
,
Alex
Iordachescu
,
Andrew
Watts
,
Sven L. M.
Schroeder
,
Anna
Kroner
,
Federico
Grillo
,
Stephen M.
Francis
,
Paul B.
Webb
,
Matthew
Hand
,
Andrew
Walters
,
Michael
Hillman
,
Georg
Held
Open Access
Abstract: The beamline optics and endstations at branch B of the Versatile Soft X-ray (VerSoX) beamline B07 at Diamond Light Source are described. B07-B provides medium-flux X-rays in the range 45–2200 eV from a bending magnet source, giving access to local electronic structure for atoms of all elements from Li to Y. It has an endstation for high-throughput X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) measurements under ultrahigh-vacuum (UHV) conditions. B07-B has a second endstation dedicated to NEXAFS at pressures from UHV to ambient pressure (1 atm). The combination of these endstations permits studies of a wide range of interfaces and materials. The beamline and endstation designs are discussed in detail, as well as their performance and the commissioning process.
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May 2024
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B18-Core EXAFS
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Diamond Proposal Number(s):
[14673]
Open Access
Abstract: Process analytical technologies are widely used to inform process control by identifying relationships between reagents and products. Here, we present a novel process analytical technology system for operando XAS on multiphase multicomponent synthesis processes based on the combination of a conventional lab-scale agitated reactor with a liquid-jet cell. The preparation of sulfonate-stabilized CaCO3 particles from polyphasic Ca(OH)2 dispersions was monitored in real time by Ca K-edge XAS to identify changes in Ca speciation in the bulk solution/dispersion as a function of time and process conditions. Linear combination fitting of the spectra quantitatively resolved composition changes from the initial conversion of Ca(OH)2 to the Ca(R–SO3)2 surfactant to the ultimate formation of nCaCO3·mCa(R− SO3)2 particles. The system provides a novel tool with strong chemical specificity for probing multiphase synthesis processes at a molecular level, providing an avenue to establishing the relationships between critical quality attributes of a process and the quality and performance of the product.
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Oct 2023
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B18-Core EXAFS
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Diamond Proposal Number(s):
[22907]
Abstract: We report on intermediate (oxysulfides) and sulfided structures of NiMo supported on aluminium pillared clay (Al-PILC) during the catalyst activation process and the prefered guaiacol adsorption sites on the sulfided catalyst. In situ X-ray absorption fine structure (XAFS) together with density functional theory (DFT) calculations confirm the existence of ill- defined suboxides (MoOx, NiOx) and the well-known subsulfides (Mo2S9, Ni3S2) at the first stage which, at a later stage in the process, transform into MoS2 with two edges, oxygen-decorated Mo and Ni with zero sulfur coverage. The freshly sulfided NiMoS 2 catalyst under sulfiding agents is mainly terminated by Mo-edge surface with 50% sulfur coverage (Mo-S50) with a disordered Ni-edge surface that can be assigned as NiMoS ( [1 with combining overline]010) . When exposed to an inert atmosphere such as He gas, the Mo and Ni edges evolved partially into new structures of Mo and Ni edges with zero sulfur coverage, labelled as Mo-Bare and Ni-Bare. Guaiacol is often used as a model compound for lignin and a series of calculations of guaiacol on the structural edges of a sulfided NiMoS2 catalyst show relatively good agreement between the observed and calculated inelastic neutron scattering (INS) spectra for Mo-S50, Ni-Bare, and NiMoS ( [1 with combining overline]010) where guaiacol weakly chemisorbed via oxygen atom of OH group. The results also confirm that guaiacol is physisorbed on the basal plane of NiMoS2 in a horizontal (flat-lying) configuration via van der Waals interaction at a separation of about 3.25 Å.
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Dec 2022
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B18-Core EXAFS
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Abstract: Herein, we report a simple synthesis of PtNiCo trimetallic nanoparticles (NPs) loaded on carbon black (PtNiCo/C) via ambient-temperature chemical reduction and galvanic replacement reaction. The influence of thermal treatment temperature in 10%H2/N2 on PtNiCo NPs in PtNiCo/C-X nanostructures is revealed, where, X = 200 °C, 500 °C. XRD, XPS, TEM, HAADF-STEM, HRTEM, STEM-EDX elemental line-scanning (mapping), HS-LEIS, H2-TPR, atomic resolution aberration-corrected STEM (AC-STEM), XANES and EXAFS have been employed to characterize various nanostructures of PtNiCo NPs in PtNiCo/C-X. We established the relationship of nanostructure-reducing temperature thus catalytic behavior of PtNiCo/C-X: PtNiCo/C-200∼Pt island (single atom and cluster)-on-NiCo alloy NP, PtNiCo/C-500∼PtNiCo alloy NPs. PtNiCo/C-200 provides much improved catalytic activity and selectivity to target products (-NO2 group hydrogenation) as compared to PtNiCo/C-500 for nitroarenes selective hydrogenation under mild reaction conditions (1.0 MPa-H2 pressure, 18 °C or 40 °C-reaction temperature). That is considered to be closely correlated with the synergy effect of Pt islands and NiCo alloy nanoparticles in PtNiCo/C-200.
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Aug 2022
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B18-Core EXAFS
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Diamond Proposal Number(s):
[29684]
Abstract: A Pt–Ni–Co catalyst was synthesized with Pt single atoms and atomic clusters (SAACs) dispersed over (Ni,Co)(OH)2 nanoparticles on a carbon matrix, which leads to high catalytic activity, up to 100% conversion, and selectivity in the hydrogenation of nitroaromatics under moderate conditions (H2 ∼ 1.0 MPa and ≤40 °C). A synergistically coordinated ensemble effect of the Pt SAACs is identified with the strongly polarized Pt single atoms preferentially adsorbing the −NO2 and the Pt clusters adsorbing and homolytically dissociating H2 molecules, and the H species then readily move to the adsorbed −NO2 group, overcoming a much reduced energy barrier on the (Ni,Co)(OH)2, enhancing the reaction rate by ca. 50 times. The approach not only reveals the coordinated ensemble catalysis mechanism of SAACs but also provides a strategy of developing highly efficient and selective catalysts by fine tuning of the electronic microenvironment from single atoms to atomic clusters co-located over a multimetallic substrate. The demonstrated case for nitroarenes can be readily applied for other species containing −NO2 or other easily hydrogenated groups (such as C═C, C≡N, and C═O).
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Jun 2022
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B18-Core EXAFS
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Miren
Agote-Aran
,
Anna B.
Kroner
,
David S.
Wragg
,
Wojciech A.
Sławiński
,
Martha
Briceno
,
Husn U.
Islam
,
Igor V.
Sazanovich
,
María E.
Rivas
,
Andrew W. J.
Smith
,
Paul
Collier
,
Ines
Lezcano-Gonzalez
,
Andrew M.
Beale
Diamond Proposal Number(s):
[11623]
Open Access
Abstract: Small pore zeolites have shown great potential in a number of catalytic reactions. While Mo-containing medium pore zeolites have been widely studied for methane dehydroaromatisation (MDA), the use of small pore supports has drawn limited attention due to the fast deactivation of the catalyst. This work investigates the structure of the small pore Mo/H-SSZ-13 during catalyst preparation and reaction by operando X-ray absorption spectroscopy (XAS), in situ synchrotron powder diffraction (SPD), and electron microscopy; then, the results are compared with the medium pore Mo/H-ZSM-5. While SPD suggests that during catalyst preparation, part of the MoOx anchors inside the pores, Mo dispersion and subsequent ion exchange was less effective in the small pore catalyst, resulting in the formation of mesopores and Al2(MOO4)3 particles. Unlike Mo/H-ZSM-5, part of the Mo species in Mo/H-SSZ-13 undergoes full reduction to Mo0 during MDA, whereas characterisation of the spent catalyst indicates that differences also exist in the nature of the formed carbon deposits. Hence, the different Mo speciation and the low performance on small pore zeolites can be attributed to mesopores formation during calcination and the ineffective ion exchange into well dispersed Mo-oxo sites. The results open the scope for the optimisation of synthetic routes to explore the potential of small pore topologies.
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Nov 2020
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B18-Core EXAFS
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Andrew M.
Beale
,
Miren
Agote-Aran
,
Rachel E.
Fletcher
,
Martha
Briceno
,
Anna B.
Kroner
,
Igor V.
Sazanov
,
Ben
Slater
,
María E.
Rivas
,
Andrew W. J.
Smith
,
Paul
Collier
,
Ines
Lezcano-Gonzalez
Diamond Proposal Number(s):
[11623]
Abstract: The structure and activity of Mo/Silicalite‐1 (MFI, Si/Al = ∞) were compared to Mo/H‐ZSM‐5 (MFI, Si/Al = 15), a widely studied catalyst for methane dehydroaromatisation (MDA). The anchoring mode of Mo was evaluated by in situ X‐ray absorption spectroscopy (XAS) and density functional theory (DFT). The results showed that in Mo/Silicalite‐1, calcination leads to dispersion of MoO3 precursor into tetrahedral Mo‐oxo species in close proximity to the microporous framework. A weaker interaction of the Mo‐oxo species with the Silicalite‐1 was determined by XAS and DFT. While both catalysts are active for MDA, Mo/Silicalite‐1 undergoes rapid deactivation which was attributed to a faster sintering of Mo species leading to the accumulation of carbon deposits on the zeolite outer surface. The results shed light onto the nature of the Mo structure(s) while evidencing the importance of framework Al in stabilising active Mo species under MDA conditions.
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Sep 2019
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