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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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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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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Open Access
Abstract: We have made high surface area catalysts for the selective oxidation of methanol to formaldehyde. This is done in two ways – (i) by doping haematite with Al ions, to increase the surface area of the material, but which itself is unselective and (ii) by surface coating with Mo which induces high selectivity. Temperature programmed desorption (TPD) of methanol shows little difference in surface chemistry of the doped haematite from the undoped material, with the main products being CO2 and CO, but shifted to somewhat higher desorption temperature. However, when Mo is dosed onto the haematite surface, the chemistry changes completely to show mainly the selective product, formaldehyde, with no CO2 production, and this is little changed up to 10% Al loading. But at 15 wt% Al, the chemistry changes to indicate the presence of a strongly acidic function at the surface, with additional dimethyl ether and CO/CO2 production characteristic of the presence of alumina. Structurally, X-ray diffraction (XRD) shows little change over the range 0–20% Al doping, except for some small lattice contraction, while the surface area increases from around 20 to 100 m2 g−1. Using X-ray absorption spectroscopy (XAS) it is clear that, at 5% loading, the Al is incorporated into the Fe2O3 corundum lattice, which has the same structure as α-alumina. By 10% loading then it appears that the alumina starts to nano-crystallise within the haematite lattice into the γ form. At higher loadings, there is evidence of phase separation into separate Al-doped haematite and γ-alumina. If we add 1 monolayer equivalent of Mo to the surface there is already high selectivity to formaldehyde, but little change in structure, because that monolayer is isolated at the surface. However, when three monolayers equivalent of Mo is added, we then see aluminium molybdate type signatures in the XANES spectra at 5% Al loading and above. These appear to be in a sub-surface layer with Fe molybdate, which we interpret as due to Al substitution into ferric molybdate layers immediately beneath the topmost surface layer of molybdena. It seems like the separate γ-alumina phase is not covered by molybdena and is responsible for the appearance of the acid function products in the TPD.
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May 2020
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B18-Core EXAFS
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Diamond Proposal Number(s):
[10306]
Open Access
Abstract: Creating a new chemical ecosystem based on platform chemicals derived from waste biomass has significant challenges; catalysts need to be able to convert these highly functionalised molecules to specific target chemicals, economical – not relying on large quantities of precious metals - and maintain activity over many cycles. Herein, we demonstrate how Pd/NiO is able to direct the selectivity of furfural hydrogenation and maintain performance at low Pd loading by a unique dual-site mechanism. Sol-immobilization was used to prepare 1 wt% Pd nanoparticles supported on NiO and TiO2, with the Pd/NiO catalyst showing enhanced activity with a significantly different selectivity profile; Pd/NiO favours tetrahydrofurfuryl alcohol (72%), whereas Pd/TiO2 produces furfuryl alcohol as the major product (68%). Density functional theory studies evidenced significant differences on the adsorption of furfural on both NiO and Pd surfaces. Based on this observation we hypothesised that the role of Pd was to dissociate hydrogen, with the NiO surface adsorbing furfural. This dual-site hydrogenation mechanism was supported by comparing the performance of 0.1 wt% Pd/NiO and 0.1 wt% Pd/TiO2. In this study, the 0.1 and 1 wt% Pd/NiO catalysts had a comparable activity, whereas there was a 10 fold reduction in performance for 0.1 wt.% Pd/TiO2. When using TiO2 as the support the Pd nanoparticles are responsible for both hydrogen dissociation and furfural adsorption, and the activity is strongly correlated with the effective metal surface area. This work has significant implications for the upgrading of bio-derived feedstocks, suggesting alternative ways for promoting selective transformations and reducing the reliance on precious metals.
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Apr 2020
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Open Access
Abstract: The catalytic performance of a series of 1 wt % Pd/C catalysts prepared by the sol-immobilization method has been studied in the liquid-phase hydrogenation of furfural. The temperature range studied was 25–75 °C, keeping the H2 pressure constant at 5 bar. The effect of the catalyst preparation using different capping agents containing oxygen or nitrogen groups was assessed. Polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and poly (diallyldimethylammonium chloride) (PDDA) were chosen. The catalysts were characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The characterization data suggest that the different capping agents affected the initial activity of the catalysts by adjusting the available Pd surface sites, without producing a significant change in the Pd particle size. The different activity of the three catalysts followed the trend: PdPVA/C > PdPDDA/C > PdPVP/C. In terms of selectivity to furfuryl alcohol, the opposite trend has been observed: PdPVP/C > PdPDDA/C > PdPVA/C. The different reactivity has been ascribed to the different shielding effect of the three ligands used; they influence the adsorption of the reactant on Pd active sites.
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Dec 2019
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B18-Core EXAFS
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Ewa
Nowicka
,
Christian
Reece
,
Sultan M.
Althahban
,
Khaled M. H.
Mohammed
,
Simon A.
Kondrat
,
David John
Morgan
,
Qian
He
,
David J.
Willock
,
Stanislaw
Golunski
,
Christopher J.
Kiely
,
Graham J.
Hutchings
Diamond Proposal Number(s):
[8071]
Abstract: A mixed oxide support containing Ce, Zr and Al was synthesized using a physical grinding method and applied in the oxidative dehydrogenation of propane using CO2 as the oxidant. The activity of the support was compared with that of fully-formulated catalysts containing palladium. The Pd/CeZrAlOx material exhibited long-term stability and selectivity to propene (during continuous operation for 140 h) which is not normally associated with dehydrogenation catalysts. From temperature-programmed desorption of NH3 and CO2 it was found that the catalyst possessed both acidic and basic sites. In addition, temperature programmed reduction showed that palladium promoted both the reduction and re-oxidation of the support. When the role of CO2 was investigated in the absence of gas-phase oxidant, using a Temporal Analysis of Products (TAP) reactor, it was found that CO2 dissociates over the reduced catalyst leading to formation of CO and selective oxygen species. It is proposed that CO2 has the dual role of regenerating selective oxygen species, and shifting the equilibrium for alkane dehydrogenation by consuming H2 through the reverse water-gas-shift reaction. These two mechanistic functions have previously been considered to be mutually exclusive.
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Mar 2018
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B18-Core EXAFS
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Diamond Proposal Number(s):
[7546, 7638]
Abstract: A capillary-based sample environment with hot air blower and integrated gas system was developed at Diamond to conduct X-ray absorption spectroscopy (XAS) studies of materials under time-resolved, in situ conditions. The use of a hot air blower, operating in the temperature range of 298-1173 K, allows introduction of other techniques e.g. X-ray diffraction (XRD), Raman spectroscopy for combined techniques studies. The flexibility to use either quartz or Kapton capillaries allows users to perform XAS measurement at energies as low as 5600 eV. To demonstrate performance, time-resolved, in situ XAS results of Rh catalysts during the process of activation (Rh K-edge, Ce L3-edge and Cr K-edge) and the study of mixed oxide membrane (La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-G) under various partial oxygen pressure conditions are described.
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Jul 2016
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B18-Core EXAFS
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Diamond Proposal Number(s):
[8071]
Open Access
Abstract: Multicomponent oxide shell@core catalysts have been prepared, affording overlayers of MoOx on Fe2O3. This design approach allows bulk characterization techniques, such as X-ray Absorption Fine Structure (XAFS), to provide surface sensitive information. Coupling this approach with in situ methodologies provides insights during crucial catalytic processes. Calcination studies were followed by a combination of XAFS and Raman, and demonstrate that amorphous multi-layers of MoOx are first converted to MoO3 before formation of Fe2(MoO4)3. However, a single overlayer of Oh Mo units remains at the surface at all times. In situ catalysis studies during formaldehyde production identified that Mo6+ was present throughout, confirming that gas phase oxygen transfer to molybdenum is rapid under reaction conditions. Reduction studies in the presence of MeOH resulted in the formation of reduced Mo-Mo clusters with a bonding distance of 2.6 Å. It is proposed that the presence of the clusters indicates that the selective conversion of MeOH to formaldehyde requires multiple Mo sites.
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Aug 2015
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