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Instruments / Technical Area	Publication Details	Published	Actions
B18-Core EXAFS I20-EDE-Energy Dispersive EXAFS (EDE)	Improving synchrotron methods for advanced characterisation of heterogeneous catalysts Eleanor Dann Open Access Show Abstract ▼ Abstract: Heterogeneous catalyst materials, in particular supported metal nanoparticles, are hugely important in industrial processes such as emissions control technology. In order to design new catalyst materials with improved catalytic performance, the catalytic properties and mechanistic pathways must be well understood. The work presented in this thesis makes advances to operando spectroscopy methods for the characterisation of industrial heterogeneous catalyst materials operating in realistic reaction conditions. A multi-technique approach, employing XAFS and DRIFTS simultaneously, has been used to probe the electronic and structural properties of metal nanoparticles as well as the molecular vibrations of reactants and intermediates at the catalyst surface. In this work, the preparation of supported metal nanoparticle catalysts have been investigated using time-resolved XAFS and DRIFTS spectroscopy approach. Structure-activity relationships of the supported Pd nanoparticle catalysts have been identified during their operation for an important reaction used in diesel after-treatment technology; the selective catalytic oxidation of NH3. The selectivity of the reaction towards the different reaction products (N2, N2O and NO), within the relevant temperature window for industrial application, has been linked to the different structural phases of Pd, including a previously unidentified PdNx species. The major challenges for operando measurements, concerning improved time resolution and spatial resolution, have been addressed with the development of a new reactor for combined XAFS and DRIFTS of a catalyst bed operating in plug-flow reaction conditions. The advantage of this reactor design for operando characterisation has been demonstrated in the investigation of a supported Pd nanoparticle catalyst (Pd/γ-Al2O3) during oscillating CO oxidation. This reactor improves on previous designs by allowing spectroscopic measurements to be performed with spatial resolution along the axial length of a catalyst bed. In this way, there is scope for elucidating the structure-function relationships of many other heterogeneous catalysts.	Apr 2019
B18-Core EXAFS	Oxygen reduction reaction at LaxCa1−xMnO3 nanostructures: interplay between A-site segregation and B-site valency Veronica Celorrio , Laura Calvillo Lamana , Eleanor Dann , Gaetano Granozzi , Ainara Aguadero , Denis Kramer , Andrea Russell , David J. Fermín Catalysis Science & Technology DOI: 10.1039/C6CY01105E Diamond Proposal Number(s): [10306] Open Access Show Abstract ▼ Abstract: The mean activity of surface Mn sites at LaxCa1−xMnO3 nanostructures towards the oxygen reduction reaction (ORR) in alkaline solution is assessed as a function of the oxide composition. Highly active oxide nanoparticles were synthesised by an ionic liquid-based route, yielding phase-pure nanoparticles, across the entire range of compositions, with sizes between 20 and 35 nm. The bulk vs. surface composition and structure are investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). These techniques allow quantification of not only changes in the mean oxidation state of Mn as a function of x, but also the extent of A-site surface segregation. Both trends manifest themselves in the electrochemical responses associated with surface Mn sites in 0.1 M KOH solution. The characteristic redox signatures of Mn sites are used to estimate their effective surface number density. This parameter allows comparing, for the first time, the mean electrocatalytic activity of surface Mn sites as a function of the LaxCa1−xMnO3 composition. The ensemble of experimental data provides a consistent picture in which increasing electron density at the Mn sites leads to an increase in the ORR activity. We also demonstrate that normalisation of electrochemical activity by mass or specific surface area may result in inaccurate structure–activity correlations.	Jul 2016

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