B18-Core EXAFS
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Diamond Proposal Number(s):
[19850]
Open Access
Abstract: Co3O4 nanoparticles were supported on different TiO2 polymorphs, namely, rutile, anatase, and a 15[thin space (1/6-em)]:[thin space (1/6-em)]85 mixture of rutile and anatase (also known as P25), via incipient wetness impregnation. The Co3O4/TiO2 catalysts were evaluated in the preferential oxidation of CO (CO-PrOx) in a H2-rich gas environment and characterised in situ using PXRD and magnetometry. Our results show that supporting Co3O4 on P25 resulted in better catalytic performance, that is, a higher maximum CO conversion to CO2 of 72.7% at 200 °C was achieved than on rutile (60.7%) and anatase (51.5%). However, the degree of reduction (DoR) of Co3O4 to Co0 was highest on P25 (91.9% at 450 °C), with no CoTiO3 detected in the spent catalyst. The DoR of Co3O4 was lowest on anatase (76.4%), with the presence of TixOy-encapsulated CoOx nanoparticles and bulk CoTiO3 (13.8%) also confirmed in the spent catalyst. Relatively low amounts of CoTiO3 (8.9%) were detected in the spent rutile-supported catalyst, while a higher DoR (85.9%) was reached under reaction conditions. The Co0 nanoparticles formed on P25 and rutile existed in the fcc and hcp crystal phases, while only fcc Co0 was detected on anatase. Furthermore, undesired CH4 formation took place over the Co0 present in the P25- and rutile-supported catalysts, while CH4 was not formed over the Co0 on anatase possibly due to encapsulation by TixOy species. For the first time, this study revealed the influence of different TiO2 polymorphs (used as catalyst supports) on the chemical and crystal phase transformations of Co3O4, which in turn affect its activity and selectivity during CO-PrOx.
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Feb 2023
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B18-Core EXAFS
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Ricardo
Navar
,
Giulia
Tarantino
,
Owain T.
Beynon
,
Daniele
Padovan
,
Luca
Botti
,
Emma K.
Gibson
,
Peter P.
Wells
,
Alun
Owens
,
Simon
Kondrat
,
Andrew J.
Logsdail
,
Ceri
Hammond
Diamond Proposal Number(s):
[12597]
Open Access
Abstract: Sn-Beta has emerged as a state-of-the-art catalyst for a range of sustainable chemical transformations. Conventionally prepared by bottom-up hydrothermal synthesis methods, recent research has demonstrated the efficiency of several top-down methods of preparation. One attractive top-down approach is Solid-State Incorporation, where a dealuminated Beta zeolite is physically mixed with a solid Sn precursor, in particular Sn (II) acetate, prior to heat treatment at 550 °C. This procedure is fast and benign, and metal incorporation requires no solvents and hence produces no aqueous Sn-containing waste streams. Although the performances of these catalysts have been well explored in recent years, the mechanism of heteroatom incorporation remains unknown, and hence, opportunities to improve the synthetic procedure via a molecular approach remain. Herein, we utilise a range of in situ spectroscopic techniques, alongside kinetic and computational methods, to elucidate the mechanisms that occur during preparation of the catalyst, and then improve the efficacy of the synthetic protocol. Specifically, we find that successful incorporation of Sn into the lattice occurs in several distinct steps, including i) preliminary coordination of the metal ion to the vacant lattice sites of the zeolite during physical grinding; ii) partial incorporation of the metal ion into the zeolite framework upon selective decomposition of the acetate ligands, which occurs upon heating the physical mixture in an inert gas flow from room temperature to 550 °C; and iii) full isomorphous substitution of Sn into the lattice alongside its simultaneous oxidation to Lewis acidic Sn(IV), when the physically mixed material is exposed to air during a short (<1 h) isotherm period. Long isotherm steps are shown to be unnecessary, and fully oxidised Sn(IV) precursors are shown to be unsuitable for successful incorporation into the lattice. We also find that the formation of extra-framework Sn oxides is primarily dependent on the quantity of Sn present in the initial physical mixture. Based on these findings, we demonstrate a faster synthetic protocol for the preparation of Sn-Beta materials via Solid-State Incorporation, and benchmark their performance of the catalyst for the Meerwein-Ponndorf-Verley transfer hydrogenation reaction and for the isomerisation of glucose to fructose.
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Sep 2022
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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
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
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Diamond Proposal Number(s):
[8071]
Open Access
Abstract: There is much about the action of bismuth within heterogeneous catalysis that still require a deeper understanding. We observed that, when Bi was added to AuPd bimetallic nanoparticles (NPs) supported on activated carbon, Bi affected the activity and significantly alters the selectivity in two model liquid phase reactions, namely the oxidation of cinnamyl alcohol and the hydrogenation of cinnamaldehyde. A combination of transmission electron microscopy and X-ray absorption spectroscopy provided a detailed characterization of trimetallic AuPdBi systems. We propose that the introduction of bismuth on AuPd NPs results in a partial blockage of most active sites, limiting the occurrence of consecutive reactions.
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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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Diamond Proposal Number(s):
[20129, 20200, 22063, 15151]
Abstract: The commercial catalysts currently used to remove polluting gases from vehicle exhausts rely on expensive precious metals, with demand continually growing. Preparing these catalysts often requires solvents, waste treatment and elevated temperatures, all with an environmental cost. One solution is to investigate the use of an alternative, more abundant material. LaMnO has shown promising catalytic behaviour and is made by physically mixing two solid reactants. The catalytic activity of materials is highly dependent on how they are produced. In this work, researchers synthesised LaMnO3 by a novel method, ball milling, to improve its catalytic properties. To replicate or optimise the final material structure, it is vital to investigate the chemical steps occurring within the ball mill. However, the ball mill setup makes it difficult to perform real-time analysis. Therefore, the research team replicated the conditions experienced within the ball mill by applying extreme pressures to the starting materials. Using Diamond Light Source’s Energy Dispersive EXAFS beamline (I20-EDE) meant they could monitor how the structure changes with increasing pressure, using X-ray Absorption Fine Structure (XAFS) measurements in real-time. This beamline setup also allowed them to use a specialised high-pressure cell. They used complementary measurements on Diamond’s Versatile Soft X-ray (VerSoX) beamline (B07) to study the surface properties of the materials during catalysis. Beamline I20-Scanning was used to look at electronic structure. For industrial companies researching ball milling as an alternative production route, i.e. for autocatalysis or battery materials, this research highlights that though the preparation route produces beneficial properties at a lower environmental cost, understanding its underlying chemistry is hugely challenging.
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Jul 2021
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B18-Core EXAFS
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Diamond Proposal Number(s):
[19850]
Abstract: We have studied the effect of different supports (CeO2, ZrO2, SiC, SiO2 and Al2O3) on the catalytic performance and phase stability of Co3O4 nanoparticles during the preferential oxidation of CO (CO-PrOx) under different H2-rich gas environments and temperatures. Our results show that Co3O4/ZrO2 has superior CO oxidation activity, but transforms to Co0 and consequently forms CH4 at relatively low temperatures. The least reduced and least methanation active catalyst (Co3O4/Al2O3) also exhibits the lowest CO oxidation activity. Co-feeding H2O and CO2 suppresses CO oxidation over Co3O4/ZrO2 and Co3O4/SiC, but also suppresses Co0 and CH4 formation. In conclusion, weak nanoparticle-support interactions (as in Co3O4/ZrO2) favour high CO oxidation activity possibly via the Mars-van Krevelen mechanism. However, stronger interactions (as in Co3O4/Al2O3) help minimise Co0 and CH4 formation. Therefore, this work reveals the bi-functional role required of supports used in CO-PrOx, i.e., to enhance catalytic performance and improve the phase stability of Co3O4.
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Jun 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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Arjun
Cherevotan
,
Jithu
Raj
,
Lakshay
Dheer
,
Soumyabrata
Roy
,
Shreya
Sarkar
,
Risov
Das
,
Chathakudath P.
Vinod
,
Shaojun
Xu
,
Peter
Wells
,
Umesh V.
Waghmare
,
Sebastian C.
Peter
Abstract: The discovery of new materials for efficient transformation of carbon dioxide (CO2) into desired fuel can revolutionize large-scale renewable energy storage and mitigate environmental damage due to carbon emissions. In this work, we discovered an operando generated stable Ni–In kinetic phase that selectively converts CO2 to methanol (CTM) at low pressure compared to the state-of-the-art materials. The catalytic nature of a well-known methanation catalyst, nickel, has been tuned with the introduction of inactive indium, which enhances the CTM process. The remarkable change in the mechanistic pathways toward methanol production has been mapped by operando diffuse reflectance infrared Fourier transform spectroscopy analysis, corroborated by first-principles calculations. The ordered arrangement and pronounced electronegativity difference between metals are attributed to the complete shift in mechanism. The approach and findings of this work provide a unique advance toward the next-generation catalyst discovery for going beyond the state-of-the-art in CO2 reduction technologies.
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Jan 2021
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B18-Core EXAFS
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Santhosh K.
Matam
,
Caitlin
Moffat
,
Pip
Hellier
,
Michael
Bowker
,
Ian P.
Silverwood
,
C. Richard A.
Catlow
,
S. David
Jackson
,
James
Craswell
,
Peter P.
Wells
,
Stewart F.
Parker
,
Emma K.
Gibson
Diamond Proposal Number(s):
[10306]
Open Access
Abstract: A MoOx/Al2O3 catalyst was synthesised and tested for oxidative (ODP) and non-oxidative (DP) dehydrogenation of propane in a reaction cycle of ODP followed by DP and a second ODP run. Characterisation results show that the fresh catalyst contains highly dispersed Mo oxide species in the +6 oxidation state with tetrahedral coordination as [MoVIO4]2− moieties. In situ X-ray Absorption Spectroscopy (XAS) shows that [MoVIO4]2− is present during the first ODP run of the reaction cycle and is reduced to MoIVO2 in the following DP run. The reduced species are partly re-oxidised in the subsequent second ODP run of the reaction cycle. The partly re-oxidised species exhibit oxidation and coordination states that are lower than 6 but higher than 4 and are referred to as MoxOy. These species significantly improved propene formation (relatively 27% higher) in the second ODP run at similar propane conversion activity. Accordingly, the initial tetrahedral [MoVIO4]2− present during the first ODP run of the reaction cycle is active for propane conversion; however, it is unselective for propene. The reduced MoIVO2 species are relatively less active and selective for DP. It is suggested that the MoxOy species generated by the reaction cycle are active and selective for ODP. The vibrational spectroscopic data indicate that the retained surface species are amorphous carbon deposits with a higher proportion of aromatic/olefinic like species.
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Nov 2020
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B18-Core EXAFS
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B.
Venezia
,
E.
Cao
,
Santhosh K.
Matam
,
C.
Waldron
,
G.
Cibin
,
E. K.
Gibson
,
S.
Golunski
,
P. P.
Wells
,
I.
Silverwood
,
C. R. A.
Catlow
,
G.
Sankar
,
A.
Gavriilidis
Diamond Proposal Number(s):
[19359]
Open Access
Abstract: Operando X-ray absorption spectroscopy (XAS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and mass spectrometry (MS) provide complementary information on the catalyst structure, surface reaction mechanisms and activity relationships. The powerful combination of the techniques has been the driving force to design and engineer suitable spectroscopic operando reactors that can mitigate limitations inherent to conventional reaction cells and facilitate experiments under kinetic regimes. Microreactors have recently emerged as effective spectroscopic operando cells due to their plug-flow type operation with no dead volume and negligible mass and heat transfer resistances. Here we present a novel microfabricated reactor that can be used for both operando XAS and DRIFTS studies. The reactor has a glass–silicon–glass sandwich-like structure with a reaction channel (3000 μm × 600 μm; width × depth) packed with a catalyst bed (ca. 25 mg) and placed sideways to the X-ray beam, while the infrared beam illuminates the catalyst bed from the top. The outlet of the reactor is connected to MS for continuous monitoring of the reactor effluent. The feasibility of the microreactor is demonstrated by conducting two reactions: i) combustion of methane over 2 wt% Pd/Al2O3 studied by operando XAS at the Pd K-edge and ii) CO oxidation over 1 wt% Pt/Al2O3 catalyst studied by operando DRIFTS. The former shows that palladium is in an oxidised state at all studied temperatures, 250, 300, 350, 400 °C and the latter shows the presence of linearly adsorbed CO on the platinum surface. Furthermore, temperature-resolved reduction of palladium catalyst with methane and CO oxidation over platinum catalyst are also studied. Based on these results, the catalyst structure and surface reaction dynamics are discussed, which demonstrate not only the applicability and versatility of the microreactor for combined operando XAS and DRIFTS studies, but also illustrate the unique advantages of the microreactor for high space velocity and transient response experiments.
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Oct 2020
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