Our latest work using multi-length scale chemical tomography to study fixed bed reactors during the oxidative coupling of methane reaction has just been published at the Journal of Catalysis. “Real-time multi-length scale chemical tomography of fixed bed reactors during the oxidative coupling of methane reaction” is a result of a collaboration between scientists at UCL, Finden, ESRF, Diamond Light Source, Research Complex at Harwell, ISIS Neutron and Muon Source, University of Manchester, Boreskov Institute of Catalysis SB RAS and VITO.
In this work, we present the results from multi-length-scale studies of a Mn-Na-W/SiO2 and a La-promoted Mn-Na-W/SiO2 catalyst during the oxidative coupling of methane reaction. The catalysts were investigated from the reactor level (mm scale) down to the single catalyst particle level (μm scale) with different synchrotron X-ray chemical computed tomography techniques (multi-modal chemical CT experiments). These operando spatially-resolved studies performed with XRD-CT (catalytic reactor) and multi-modal μ-XRF/XRD/absorption CT (single catalyst particle) revealed the multiple roles of the La promoter and how it provides the enhancement in catalyst performance. It is also shown that non-crystalline Mn species are part of the active catalyst component rather than crystalline Mn2O3/Mn7SiO12 or MnWO4.
Our scientists’ new work on the evolving solid-state chemistry in secondary LiMn2O4 (LMO) particles during lithiation and its impact on the performance of the electrode has been published in a new paper, “Spatial quantification of dynamic inter and intra particle crystallographic heterogeneities within lithium ion electrodes” in Nature Communications.
The work was performed with Donal Finegan from the National Renewable Energy Laboratory and in collaboration with a team from the Electrochemical Innovation Lab (EIL) from UCL Chemical Engineering using ESRF’s ID15A beamline.
The performance of lithium ion electrodes is hindered by unfavorable chemical heterogeneities that pre-exist or develop during operation. Time-resolved spatial descriptions are needed to understand the link between such heterogeneities and a cell’s performance. Here, operando high-resolution X-ray diffraction-computed tomography is used to spatially and temporally quantify crystallographic heterogeneities within and between particles throughout both fresh and degraded LixMn2O4 electrodes. This imaging technique facilitates identification of stoichiometric differences between particles and stoichiometric gradients and phase heterogeneities within particles. Through radial quantification of phase fractions, the response of distinct particles to lithiation is found to vary; most particles contain localized regions that transition to rock salt LiMnO2 within the first cycle. Other particles contain monoclinic Li2MnO3 near the surface and almost pure spinel LixMn2O4 near the core. Following 150 cycles, concentrations of LiMnO2and Li2MnO3 significantly increase and widely vary between particles.
Finegan, D.P., Vamvakeros, A., Tan, C. et al. Spatial quantification of dynamic inter and intra particle crystallographic heterogeneities within lithium ion electrodes. Nat Commun 11, 631 (2020).
Read the full article at https://doi.org/10.1038/s41467-020-14467-x
A new paper by our former PhD student Dorota Matras and partners from MEMERE project has been accepted in the Faraday Discussions.
In this study, we investigate the effect of thermal treatment/calcination on the stability and activity of a Na-Mn-W/SiO2 catalyst for the oxidative coupling of methane reaction. The catalyst performance and characterisation measurements suggest that the W species are directly involved in the catalyst active site responsible for CH4 conversion. Under operating conditions, the active components, present in the form of Na-W-O-Mn molten state, are highly mobile and volatile. By varying the parameters of the calcination protocol, it was shown that these molten components can be partially stabilised, resulting in a catalyst with lower activity (due to loss of surface area) but higher stability even for long duration OCM reaction experiments.
Read the full paper at https://doi.org/10.1039/C9FD00142E
Our scientists’ new work on Si-graphite electrodes used for Li-ion battery applications with high resolution in situ X-ray chemical imaging has been published in a new paper, “Spatially Resolving Lithiation in Silicon–Graphite Composite Electrodes via in Situ High-Energy X-ray Diffraction Computed Tomography” in Nano Letters. The work was performed with Donal Finegan from the National Renewable Energy Laboratory and in collaboration with a team from the Electrochemical Innovation Lab (EIL) from UCL Chemical Engineering using ESRF’s ID15A beamline.
Optimizing the chemical and morphological parameters of lithium-ion (Li-ion) electrodes is extremely challenging, due in part to the absence of techniques to construct spatial and temporal descriptions of chemical and morphological heterogeneities. In this work, we present the first demonstration of combined high-speed X-ray diffraction (XRD) and XRD computed tomography (XRD-CT) to probe, in 3D, crystallographic heterogeneities within Li-ion electrodes with a spatial resolution of 1 μm. The local charge-transfer mechanism within and between individual particles was investigated in a silicon(Si)−graphite composite electrode. High-speed XRD revealed charge balancing kinetics between the graphite and Si during the minutes following the transition from operation to open circuit. Subparticle lithiation heterogeneities in both Si and graphite were observed using XRD-CT, where the core and shell structures were segmented, and their respective diffraction patterns were characterized.
Read more about it at https://www.esrf.eu/home/news/spotlight/content-news/spotlight/spotlight346.html
Read the article at https://pubs.acs.org/doi/full/10.1021/acs.nanolett.9b00955
Finden scientists’ new work on the design and application of a new cell for proton-exchange membrane fuel cells has been published in a new paper, “X-ray transparent proton-exchange membrane fuel cell design for in situ wide and small angle scattering tomography” in the Journal of Power Sources. The cell design and experimental work was performed by Isaac Martens and Jakub Drnec using ESRF’s ID31 beamline.
We have constructed a 5 cm2 proton exchange membrane hydrogen fuel cell optimized for transparency of high energy X-rays. This cell allows for in situ elastic scattering measurements (WAXS, SAXS) during electrochemical operation with minimal trade-offs in cell performance vs benchtop designs, and is capable of reaching automotive current densities. A key feature is that the beam enters the cell at grazing incidence to the electrodes, massively increasing the effective pathlength and therefore the signal-to-background ratio. The transparency in the plane of the sample permits imaging coupled with advanced techniques, such as X-ray diffraction computed tomography.
The work was done at the The European Synchrotron (ESRF) and research partners included; University of British Columbia, Université Grenoble Alpes, University of Helsinki, Aalto University, Baltic Fuel Cells and University College London.
Read the article at https://www.sciencedirect.com/science/article/abs/pii/S0378775319308997
Finden scientists new work on the characterisation on 3D printed catalysts has been published in a new paper, “3D printed Ni/Al2O3 based catalysts for CO2 methanation – a comparative and operando XRD-CT study” in the Journal of CO2 Utilization. The X-ray chemical imaging work was performed with Vesna Middelkoop from the Flemish Institute for Technological Research (VITO) using ESRF’s ID15A beamline.
Ni-alumina-based catalysts were directly 3D printed into highly adaptable monolithic/multi-channel systems and evaluated for CO2 methanation. By employing emerging 3D printing technologies for catalytic reactor design such as 3D fibre deposition (also referred to as direct write or microextrusion), we developed optimised techniques for tailoring both the support’s macro- and microstructure, as well as its active particle precursor distribution. A comparison was made between 3D printed commercial catalysts, Ni-alumina based catalysts and their conventional counterpart, packed beds of beads and pellet. Excellent CO2 conversions and selectivity to methane were achieved for the 3D printed commercial catalyst (95.75% and 95.63% respectively) with stability of over 100 h. The structure-activity relationship of both the commercial and in-house 3D printed catalysts was explored under typical conditions for CO2 hydrogenation to CH4, using operando ‘chemical imaging’, namely X-Ray Diffraction Computed Tomography (XRD-CT). The 3D printed commercial catalyst showed a more homogenous distribution of the active Ni species compared to the in-house prepared catalyst. For the first time, the results from these comparative characterisation studies gave detailed insight into the fidelity of the direct printing method, revealing the spatial variation in physico-chemical properties (such as phase and size) under operating conditions.
Institute for Technological Research (VITO), Ghent University, University Colleges Leuven-Limburg, Grenoble Alpes University and University College London.
Read the article at https://www.sciencedirect.com/science/article/pii/S2212982019303063
Finden Ltd collaborated with Yoran De Vos (Ghent University) to look at the evolution of an Fe-based oxygen carrier under operando conditions. The project has resulted in a paper published in the International Journal of Greenhouse Gas Control titled, “Sustainable iron-based oxygen carriers for hydrogen production – Real-time operando investigation.“
In this work, a spray-dried Fe-based oxygen carrier with an in situ generated Mg1-xAl2-yFex+yO4-support was investigated during packed-bed chemical looping operation with methane at 900 °C. The evolution of the solid-state chemistry taking place in the oxygen carrier material was investigated in real-time with synchrotron X-ray diffraction while the spatial distribution of the phases was investigated using X-ray diffraction computed tomography (XRD-CT). These measurements revealed that some Fe-cations were systematically taken up and released from the spinel support. This take-up and release was shown to be strongly related with the oxidation state of the active phase. Although this take-up and release of Fe-cations decreased the amount of Fe-oxides active in the chemical looping process, the oxygen transfer capacity was still sufficiently high. The microstructure of the oxygen carriers along the length of the packed reactor bed was also investigated with scanning electron microscopy (SEM). The experiments indicate that the MgFeAlOx support with an extra Fe-based active phase is a promising material for oxygen carriers, as it forms a sustainable non-toxic, stable and green alternative to the typical Ni-based oxygen carriers, for hydrogen generation by chemical looping.
The work was done at the The European Synchrotron (ESRF) and research partners included; Flemish Institute for Technological Research (VITO), Ghent University and University College London.
Read the paper at https://www.sciencedirect.com/science/article/abs/pii/S175058361930146X.
Our new work on a state-of-the-art SOFC has been published in a paper “Design of next-generation ceramic fuel cells and real-time characterization with synchrotron X-ray diffraction computed tomography“ in Nature Communications.
Solid oxide fuel cells offer a clean and efficient means of producing electricity through a variety of fuels. However, miniaturization of cell dimensions for portable device applications remains a challenge, as volumetric power densities generated by readily-available planar/tubular ceramic cells are limited. In our work, we demonstrate a concept of ‘micro-monolithic’ ceramic cell design and evaluate the mechanical robustness and structural integrity of this design, for the first time, with synchrotron X-ray diffraction computed tomography. The successful miniaturization results in an exceptional power density of 1.27 W cm−2 at 800 °C, which is among the highest reported. This holistic design incorporates both mechanical integrity and electrochemical performance, leading to mechanical property enhancement and representing an important step toward commercial development of portable ceramic devices with high volumetric power (>10 W cm−3), fast thermal cycling and marked mechanical reliability. This is also the first time a real-life size solid oxide fuel cell has been investigated in situ demonstrating that such experiments are now possible, adding a very powerful characterisation tool for the SOFC community in general.
The synchrotron experiments were conceived, designed and performed by Dr Antony Vamvakeros and Dorota Matras in collaboration with a team from the Electrochemical Innovation Lab (EIL) from UCL Chemical Engineering using ESRF’s ID15A beamline using a state-of-the-art SOFC designed by Imperial College.
Read the full article at https://www.nature.com/articles/s41467-019-09427-z
Our paper on Operando and Postreaction Diffraction Imaging of the La–Sr/CaO Catalyst in the Oxidative Coupling of Methane Reaction has been published online by The Journal of Physical Chemistry.
A La–Sr/CaO catalyst was studied operando during the oxidative coupling of methane (OCM) reaction using the X-ray diffraction computed tomography technique. Full-pattern Rietveld analysis was performed in order to track the evolving solid-state chemistry during the temperature ramp, OCM reaction, as well as after cooling to room temperature. We observed a uniform distribution of the catalyst main components: La2O3, CaO–SrO mixed oxide, and the high-temperature rhombohedral polymorph of SrCO3. These were stable initially in the reaction; however, doubling the gas hourly space velocity resulted in the decomposition of SrCO3 to SrO, which subsequently led to the formation of a second CaO–SrO mixed oxide. These two mixed CaO–SrO oxides differed in terms of the extent of Sr incorporation into their unit cell. By applying Vegard’s law during the Rietveld refinement, it was possible to create maps showing the spatial variation of Sr occupancy in the mixed CaO–SrO oxides. The formation of the Sr-doped CaO species is expected to have an important role in this system through the enhancement of the lattice oxygen diffusion as well as increased catalyst basicity.
Read the full article at https://pubs.acs.org/doi/10.1021/acs.jpcc.8b09018
The nDTomo software is now publicly available for download. Developed by our research scientist Dr. Antony Vamvakeros and primarily designed for processing XRD-CT data, it can be used for other tomographic techniques as well. The software suite contains GUIs for the acquisition, pre-processing and analysis of X-ray chemical tomography data. Download it at https://github.com/antonyvam/ndtomo
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