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
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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
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C.
Waldron
,
G.
Cibin
,
E. K.
Gibson
,
S.
Golunski
,
P. P.
Wells
,
I.
Silverwood
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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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Aug 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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