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
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
B22-Multimode InfraRed imaging And Microspectroscopy
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Diamond Proposal Number(s):
[19850]
Abstract: Rational design of low-cost and active electrocatalysts is crucial for upgrading of biomass-derived chemicals into value-added products. Here, we report highly efficient catalysts of ternary NiCoMn-layered double hydroxides (NiCoMn-LDHs) nanosheets which are oxygen vacancy-rich, produced under controllable conditions for the electrocatalytic oxidation of both biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) and furfural to furoic acid (FurAc) in mild conditions, respectively. Electrochemical tests showed that the oxidation of HMF and furfural were preferential over the oxidation of water at the lower applied potentials with NiCoMn-LDHs catalysts. The high yields of FDCA (91.7%) and FurAc (92.4%) were achieved in 2.5 h using 1.15 nm thick NiCoMn-LDHs nanosheets with a NiCo:Mn ratio of 2:1 at 35 oC and atmospheric pressure. The mechanism for the superior performance, high durability, and good Faradaic efficiency of the catalysts has been elucidated by a comprehensive characterization, which confirmed the ultrathin nanosheets expose more Co-NiOOH active sites with oxygen vacancies, facilitating the synergistic effect between HMF as well as furfural oxidation reaction on Co-Ni and Mn2+ states. The oxygen vacancy-rich NiCoMn-LDHs nanosheets catalysts present a novel and energy-efficient solution to achieve a high yield of value-added chemicals from renewable sources.
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Apr 2021
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Open Access
Abstract: The utilization of operando spectroscopy has allowed us to watch the dynamic nature of supported metal nanoparticles. However, the realization that subtle changes to environmental conditions affect the form of the catalyst necessitates that we assess the structure of the catalyst across the reactant/product gradient that exists across a fixed bed reactor. In this study, we have performed spatial profiling of a Pd/Al2O3 catalyst during NH3 oxidation, simultaneously collecting mass spectrometry and X-ray absorption spectroscopy data at discrete axial positions along the length of the catalyst bed. The spatial analysis has provided unique insights into the structure–activity relationships that govern selective NH3 oxidation—(i) our data is consistent with the presence of PdNx after the spectroscopic signatures for bulk PdNx disappear and that there is a direct correlation to the presence of this structure and the selectivity toward N2; (ii) at high temperatures, ≥400 °C, we propose that there are two simultaneous reaction pathways—the oxidation of NH3 to NOx by PdO and the subsequent catalytic reduction of NOx by NH3 to produce N2. The results in this study confirm the structural and catalytic diversity that exists during catalysis and the need for such an understanding if improvements to important emission control technologies, such as the selective catalytic oxidation of NH3, are to be made.
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Feb 2021
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B18-Core EXAFS
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Phuoc Hoang
Ho
,
Giancosimo Sanghez
De Luna
,
Saverio
Angelucci
,
Andrea
Canciani
,
Wilm
Jones
,
Donato
Decarolis
,
Francesca
Ospitali
,
Elena Rodriguez
Aguado
,
Enrique
Rodríguez-Castellón
,
Giuseppe
Fornasari
,
Angelo
Vaccari
,
Andrew M.
Beale
,
Patricia
Benito
Abstract: Ni-based catalysts are selective in the hydrogenation of CO2 to CH4 but their activity and stability need improvement. Herein, we propose a hydrotalcite-derived high loaded Ni-Al2O3 catalyst promoted by La. The effect of La on the catalyst properties is investigated and compared with that of Y and Ce. The NiOx crystallite size and basic properties (rather than the nickel reducibility) as well as the catalytic activity depend on the rare-earth element. The La-catalyst achieves a more relevant activity enhancement at low temperature and high space velocity (480 L g-1 h-1, CO2/H2/N2 = 1/4/1 v/v), high CH4 productivity (101 LCH4 gNi-1 h-1) and stability, even under undiluted feeds. In situ DRIFTS and the characterization of spent catalysts confirm that this enhanced performance is related to the combination of dissociative and associative CO2 activation on more reduced, highly dispersed and stable Ni nanoparticles and basic sites in the La2O3-Al2O3 matrix, respectively.
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Jun 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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B18-Core EXAFS
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Diamond Proposal Number(s):
[18788]
Open Access
Abstract: Carbon monoxide (CO) purification from syngas impurities is a highly energy and cost intensive process. Adsorption separation using metal–organic frameworks (MOFs) is being explored as an alternative technology for CO/nitrogen (N2) and CO/carbon dioxide (CO2) separation. Currently, MOFs' uptake and selectivity levels do not justify displacement of the current commercially available technologies. Herein, we have impregnated a leading MOF candidate for CO purification, i.e. M-MOF-74 (M = Co or Ni), with Cu+ sites. Cu+ allows strong π-complexation from the 3d electrons with CO, potentially enhancing the separation performance. We have optimised the Cu loading procedure and confirmed the presence of the Cu+ sites using X-ray absorption fine structure analysis (XAFS). In situ XAFS and diffuse reflectance infrared Fourier Transform spectroscopy analyses have demonstrated Cu+–CO binding. The dynamic breakthrough measurements showed an improvement in CO/N2 and CO/CO2 separations upon Cu impregnation. This is because Cu sites do not block the MOF metal sites but rather increase the number of sites available for interactions with CO, and decrease the surface area/porosity available for adsorption of the lighter component.
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Jan 2020
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B18-Core EXAFS
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Open Access
Abstract: The self-assembly of gold nanoparticles (Au NPs) using polymer-encapsulated inverse micelles was studied using a set of advanced X-ray techniques (i.e. XAFS, SAXS) in addition to DLS, UV-vis spectroscopy and TEM. Importantly the combination of these techniques with the inverse micelle approach affords us detailed insight and to rationalize the evolving molecular chemistry and how this drives the formation of the Au NPs. We observe that the mechanism comprises three key steps: an initial fast reduction of molecular Au(III) species to molecular Au(I)Cl; the latter species are often very unstable during the self-assembly process. This is followed by a gradual reduction of these molecular Au(I) species and the formation of sub-nanometric Au clusters which coalesce into nanoparticles. It was also found that addition of small amounts of HCl can accelerate the formation of the Au clusters (the second phase) without affecting the final particle size or its particle size distribution. These findings would help us to understand the reaction mechanism of Au NP formation as well as providing insights into how NP properties could be further tailored for a wide range of practical applications.
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Aug 2019
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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George F.
Tierney
,
Donato
Decarolis
,
Norli
Abdullah
,
Scott M.
Rogers
,
Shusaku
Hayama
,
Martha
Briceno De Gutierrez
,
Alberto
Villa
,
C. Richard A.
Catlow
,
Paul
Collier
,
Nikolaos
Dimitratos
,
Peter
Wells
Diamond Proposal Number(s):
[17283]
Open Access
Abstract: Sol-immobilization is increasingly used to achieve supported metal nanoparticles (NPs) with controllable size and shape; it affords a high degree of control of the metal particle size and yields a narrow particle size distribution. Using state-of-the-art beamlines, we demonstrate how X-ray absorption fine structure (XAFS) techniques are now able to provide accurate structural information on nano-sized colloidal Au solutions at μM concentrations. This study demonstrates: (i) the size of Au colloids can be accurately tuned by adjusting the temperature of reduction, (ii) Au concentration, from 50 μM to 1000 μM, has little influence on the average size of colloidal Au NPs in solution and (iii) the immobilization step is responsible for significant growth in Au particle size, which is further exacerbated at increased Au concentrations. The work presented demonstrates that an increased understanding of the primary steps in sol-immobilization allows improved optimization of materials for catalytic applications.
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May 2019
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B18-Core EXAFS
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Open Access
Abstract: For supported nanoparticulate catalysts, the effect of their properties, such as size and interaction with support, on a catalytic process is still in debate. This is partially caused by the limited control that typical nanoparticle preparation methods offer which may lead to the presence of nanoparticles possessing a range of sizes and shapes, leading to a lack of clarity in the correlation between properties and catalysis. The work presented in this thesis focuses on producing size-selected monometallic supported nanoparticles and their detailed characterisation, both ex situ and in situ (under reaction conditions) mainly through the application of the technique of X-ray absorption spectroscopy (XAFS). Chapter 3 of this thesis focuses on understanding the mechanism of formation of Au nanoparticles produced by reverse micelle encapsulation, through a combination of various techniques (transmission electron microscopy, dynamic light scattering, UV-vis, combined small angle X-ray scattering/XAFS). From the combined data, it is possible to rationalise the synthesis process, which can be divided into three steps: fast reduction of Au (III) species to Au (I), slow reduction and agglomeration of Au atoms in sub-nanometric clusters and a final agglomeration to form the nanoparticles. Chapter 4 and 5 focus on the application of monometallic nanoparticles to the catalytic hydrogenation of 1,3-butadiene, used as a model reaction, using in situ XAFS to correlate size and support effect with their catalytic activities. For Au nanoparticles (chapter 4) it appears that a restructuring process takes places under reaction conditions. Depending on the sample, this process can be favourable (Au/SiO2) or detrimental (Au/Al2O3) and is highly dependent on particle size. For Pd nanoparticles (chapter 5) it was possible to identify the active species necessary (Pd0), and detrimental (PdH and PdC) for the selective hydrogenation of 1,3-butadiene in Pd as well as the role of support and size in promoting the presence of each phase.
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Mar 2019
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