I20-EDE-Energy Dispersive EXAFS (EDE)
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Xiaoqiang
Liang
,
Sen
Wang
,
Jingyu
Feng
,
Zhen
Xu
,
Zhenyu
Guo
,
Hui
Luo
,
Feng
Zhang
,
Wen
Chen
,
Lei
Feng
,
Chengan
Wan
,
Maria-Magdalena
Titirici
Diamond Proposal Number(s):
[28663]
Abstract: Electrocatalytic oxygen evolution reaction (OER) under neutral or near-neutral conditions has attracted research interest due to its environmental friendliness and economic sustainability in comparison with currently available acidic and alkaline conditions. However, it is challenging to identify electrocatalytically active species in the OER procedure under neutral environments due to non-crystalline forms of catalysts. Crystalline metal-organic framework (MOF) materials could provide novel insights into electrocatalytical active species because of their well-defined structures. In this study, we synthesized two isostructural two-dimensional (2D) MOFs [Co(HCi)2(H2O)2·2DMF]n (Co-Ci-2D) and [Ni(HCi)2(H2O)2·2DMF]n (Ni-Ci-2D) (H2Ci = 1H-indazole-5-carboxylic acid, DMF = N, N-Dimethyl-formamide) to investigate their OER performance in a neutral environment. Our results indicate that Co-Ci-2D holds a current density of 3.93 mA cm-2 at 1.8 V vs. RHE and a OER durability superior to the benchmark catalyst IrO2. Utilizing the advantages of structural transformation of MOF materials which are easier to characterize and analyze compared to ill-defined amorphous materials, we found out that a mononuclear coordination compound [Co(HCi)2(H2O)4] (Co-Ci-mono-A) and its isomer (Co-Ci-mono-B) were proven to be active species of Co-Ci-2D in the neutral OER process. For Ni-Ci-2D, mononuclear coordination compounds similar to structures of the cobalt material (Ni-Ci-mono-A and Ni-Ci-mono-B) together with NiHPO4 formed by the precipitation were confirmed as active species for the neutral OER catalysis. Additionally, the difference in OER activities between Co-Ci-2D and Ni-Ci-2D, approximately one order of magnitude, originates primarily from the opposite tendency of bond length changes in coordination octahedron after being treated by the PBS solution. These findings contribute to a better comprehension of the OER procedure in the neutral media.
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Apr 2023
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I20-EDE-Energy Dispersive EXAFS (EDE)
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Diamond Proposal Number(s):
[29667]
Abstract: Single-atoms on carbon-nitrogen supports are considered catalysts for a multitude of reactions. However, doubts remain whether really these species or subnanometer clusters formed under reaction conditions are the active species. In this work, we investigate the dynamics of palladium single-atoms on graphitic carbon nitride during ethylene hydrogenation and H2-D2 exchange. By employing aberration-corrected scanning transmission electron microscopy, x-ray photoelectron spectroscopy and x-ray absorption spectroscopy, we will show that palladium, originally present as single-atoms, agglomerates to clusters at 100 °C in a gas atmosphere that contains both ethylene and hydrogen. This agglomeration goes in hand with the emergence of catalytic activity in both ethylene hydrogenation and H2-D2 exchange, suggesting that clusters, rather than single-atoms, are the active species. The results presented herein highlight the potential of analytics over the course of reaction to identify the active species and provide new insights into the influence of gas atmosphere on metal speciation.
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Mar 2023
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E01-JEM ARM 200CF
I20-EDE-Energy Dispersive EXAFS (EDE)
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Hui
Luo
,
Victor Y.
Yukuhiro
,
Pablo S.
Fernández
,
Jingyu
Feng
,
Paul
Thompson
,
Reshma R.
Rao
,
Rongsheng
Cai
,
Silvia
Favero
,
Sarah J.
Haigh
,
James R.
Durrant
,
Ifan E. L.
Stephens
,
Maria-Magdalena
Titirici
Diamond Proposal Number(s):
[28663, 25476]
Open Access
Abstract: Pt-based bimetallic electrocatalysts are promising candidates to convert surplus glycerol from the biodiesel industry to value-added chemicals and coproduce hydrogen. It is expected that the nature and content of the elements in the bimetallic catalyst can not only affect the reaction kinetics but also influence the product selectivity, providing a way to increase the yield of the desired products. Hence, in this work, we investigate the electrochemical oxidation of glycerol on a series of PtNi nanoparticles with increasing Ni content using a combination of physicochemical structural analysis, electrochemical measurements, operando spectroscopic techniques, and advanced product characterizations. With a moderate Ni content and a homogenously alloyed bimetallic Pt–Ni structure, the PtNi2 catalyst displayed the highest reaction activity among all materials studied in this work. In situ FTIR data show that PtNi2 can activate the glycerol molecule at a more negative potential (0.4 VRHE) than the other PtNi catalysts. In addition, its surface can effectively catalyze the complete C–C bond cleavage, resulting in lower CO poisoning and higher stability. Operando X-ray absorption spectroscopy and UV–vis spectroscopy suggest that glycerol adsorbs strongly onto surface Ni(OH)x sites, preventing their oxidation and activation of oxygen or hydroxyl from water. As such, we propose that the role of Ni in PtNi toward glycerol oxidation is to tailor the electronic structure of the pure Pt sites rather than a bifunctional mechanism. Our experiments provide guidance for the development of bimetallic catalysts toward highly efficient, selective, and stable glycerol oxidation reactions.
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Nov 2022
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I20-EDE-Energy Dispersive EXAFS (EDE)
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Mengtian
Fan
,
Shaojun
Xu
,
Bing
An
,
Alena M.
Sheveleva
,
Alexander
Betts
,
Joseph
Hurd
,
Zhaodong
Zhu
,
Meng
He
,
Dinu
Iuga
,
Longfei
Lin
,
Xinchen
Kang
,
Christopher M. A.
Parlett
,
Floriana
Tuna
,
Eric J. L.
Mcinnes
,
Luke L.
Keenan
,
Daniel
Lee
,
Martin P.
Attfield
,
Sihai
Yang
Diamond Proposal Number(s):
[28575]
Abstract: The production of conjugated C4-C5 dienes from biomass can enable the sustainable synthesis of many important polymers and liquid fuels. Here, we report the first example of bimetallic (Nb, Al)-atomically doped mesoporous silica, denoted as AlNb-MCM-41, which affords quantitative conversion of 2-methyltetrahydrofuran (2-MTHF) to pentadienes with a high selectivity of 91%. The incorporation of Al(III) and Nb(V) sites into the framework of AlNb-MCM-41 has effectively tuned the nature and distribution of Lewis and Brønsted acid sites within the structure. Operando X-ray absorption, diffuse reflectance infrared and solid-state NMR spectroscopy collectively reveal the molecular mechanism of the conversion of adsorbed 2-MTHF over AlNb-MCM-41. Specifically, the atomically-dispersed Nb(V) sites play an important role in binding 2-MTHF to drive the conversion. Overall, this study highlights the potential of hetero-atomic mesoporous solids for the manufacture of renewable materials.
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Oct 2022
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I20-EDE-Energy Dispersive EXAFS (EDE)
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Diamond Proposal Number(s):
[23645]
Abstract: An integrated carbon capture and utilization (ICCU) process present an ideal solution to address anthropogenic carbon dioxide (CO2) emissions from fossil fuel-driven electricity production, allowing for capturing and subsequent utilization of CO2 instead of current release into the atmosphere. Effective dual-functional materials (DFMs), through the combination of CO2 sorbents and catalysts, can not only capture CO2 but also convert it into higher-value chemicals, such as CH4 or CO, under isothermal conditions within a single reactor are highly desirable for ICCU processes. In this study, we investigate the mechanism of ICCU over 10 %NiCaO by the time-resolved operando XAS/DRIFTS/MS and the influence of a reduction pretreatment on the process and the products formed. During the 1st stage of the ICCU process (carbon capture), CaO adsorbs CO2 resulting in bicarbonate, carbonate, and formate species formation. At the same time, the Ni catalytic active species are oxidized by CO2, leading to the formation of NiO and CO. However, pre-treating the same DFM under hydrogen, during heating to operating temperature, resulted in a switch to CH4 production, suggesting the presence of high levels of surface adsorbed H2. During the 2nd stage of ICCU (CO2 conversion), the NiO generated during capture is reduced by H2 to metallic Ni, which facilitates the reduction of bicarbonates, carbonates, and formats, via H2 dissociation, to produce and liberate gaseous CO. Thus, both adsorption and catalytic sites are regenerated for the subsequent ICCU cycle.
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Oct 2022
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E01-JEM ARM 200CF
I20-EDE-Energy Dispersive EXAFS (EDE)
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Diamond Proposal Number(s):
[28663, 28698]
Open Access
Abstract: Iron-based single-site catalysts hold immense potential for achieving highly selective chemical processes, with the added advantage of iron being an earth-abundant metal. They are widely explored in electrocatalysis for oxygen reduction and display promising catalytic activity for organic transformations. In particular, FeNx@C catalysts are active for the reduction of nitroarene into aromatic amines. Yet, they are difficult to mass-produce, and most preparation methods fail to avoid single site aggregation. Here we prepared FeNx@C catalysts from bio-derived compounds, xylose and haemoglobin, in a simple two-step process. Since haemoglobin naturally contains FeNx single-sites, we successfully repurposed them into hydrogenation catalytic centers and avoided their aggregation during the preparation of the material. Their single-site nature was demonstrated by aberration-corrected transmission electron microscopy and X-ray absorption techniques. They were shown to be active for transfer hydrogenation of nitroarenes into anilines, with excellent substrate selectivity and recyclability, as demonstrated by the preserved yield across seven catalytic cycles. We also showed that FeNx@C could be used to prepare 2-phenylbenzimidazole through a reduction/condensation tandem. Our work shows for the first time the viability of biomass precursors to prepare Fe single-site hydrogenation catalysts.
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Sep 2022
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B18-Core EXAFS
E01-JEM ARM 200CF
E02-JEM ARM 300CF
I20-EDE-Energy Dispersive EXAFS (EDE)
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Abstract: This thesis details the synthesis, characterisation and catalytic testing of a series of metal nanocluster (NC)-laden metal-organic frameworks (MOFs). The overall aim was to determine the effect of the functional group on the linker on the success of embedding palladium (Pd) NCs within the pores of the MOFs of the UiO-66 topology and to probe the impact on the catalytic activity and selectivity of the samples for some industrially important reactions. Firstly, the effect of the nature of the functional groups was investigated. It was found that the success of embedment of NCs in the pores was related to the ability of the functional group to interact with the Pd precursor, while also being able to accept electron density from the Pd NCs when formed. Subsequently, the effect of the number of functional groups per linker was explored. It was determined that, for functional groups which interact with the Pd guest species, the analogues with more functional groups per linker appeared to interact more strongly with the Pd precursor and required harsher synthetic conditions to form NCs. This changed the extent to which the Pd NCs could be contained within the pores. In analogues without host-guest interactions, increasing the number of functional groups per linker inhibited embedment within the pores entirely. Following these findings, two of the samples in which embedding of Pd NCs in the pores was successful, Pd⸦NH2-UiO-66 and Pd⸦I-UiO-66, underwent catalytic testing for some industrially important reactions. Pd⸦NH2-UiO-66 was found to be active for 1,3-butadiene hydrogenation, with a high selectivity for the desired product attributed to the small Pd NC size attained by embedment within the pores. It was also an active electrocatalyst for glycerol ii oxidation and for deNOx reactions, while Pd⸦I-UiO-66 was active for acetylene hydrogenation.
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Jul 2022
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E01-JEM ARM 200CF
I20-EDE-Energy Dispersive EXAFS (EDE)
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Jesus
Barrio
,
Angus
Pedersen
,
Jingyu
Feng
,
Saurav Ch.
Sarma
,
Mengnan
Wang
,
Alain Y.
Li
,
Hossein
Yadegari
,
Hui
Luo
,
Mary P.
Ryan
,
Maria-Magdalena
Titirici
,
Ifan E. L.
Stephens
Diamond Proposal Number(s):
[28663, 28698]
Open Access
Abstract: Single-atom catalysts, in particular the Fe–N–C family of materials, have emerged as a promising alternative to platinum group metals in fuel cells as catalysts for the oxygen reduction reaction. Numerous theoretical studies have suggested that dual atom catalysts can appreciably accelerate catalytic reactions; nevertheless, the synthesis of these materials is highly challenging owing to metal atom clustering and aggregation into nanoparticles during high temperature synthesis treatment. In this work, dual metal atom catalysts are prepared by controlled post synthetic metal-coordination in a C2N-like material. The configuration of the active sites was confirmed by means of X-ray adsorption spectroscopy and scanning transmission electron microscopy. During oxygen reduction, the catalyst exhibited an activity of 2.4 ± 0.3 A gcarbon−1 at 0.8 V versus a reversible hydrogen electrode in acidic media, comparable to the most active in the literature. This work provides a novel approach for the targeted synthesis of catalysts containing dual metal sites in electrocatalysis.
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Feb 2022
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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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I20-EDE-Energy Dispersive EXAFS (EDE)
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Abstract: Cu-BTC metal-organic framework (MOF) has been found to be a promising candidate for removing hazardous substances from air via adsorption1. To understand the role that the copper sites in Cu-BTC play in the adsorption process, we have performed a detailed X-ray absorption spectroscopy (XAS) study. Conventional XAS and high energy resolution fluorescence detection XAS (HERFD-XAS) were collected on degassed Cu-BTC, and after being exposed to CO2, water and benzene. The EXAFS analysis reveals that, although the local environment around the copper centers in all samples is similar, differences can be found in the first and second coordination shells. We have found that the Cu-O distance in the first coordination shell is slightly larger when the sample is immersed in water and benzene than in the degassed sample, while it does not change for the sample exposed to CO2. Small differences are also observed in the Cu-Cu distance, gradually increasing from 2.49 Å in the degassed sample, to 2.52 Å, 2.58 Å and 2.63 Å upon adsorption of CO2, benzene and water, respectively. HERFD-XAS has been used to obtain information about the electronic and geometric structure around the copper metal centers, as the use of high energy resolution enhances the features in the XANES spectrum enabling the detection of subtle changes2. We have observed differences in the intensity and the energy position of some of the XANES spectral features upon adsorption of different adsorbates that can be attributed to changes in the local environment around the copper centers, as detected in the EXAFS analysis.
In this study we show that XAS is a powerful and very sensitive tool for studying host-guest interactions in MOFs, providing atomic-level insights into adsorption mechanisms.
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Jul 2021
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