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On the High Structural Heterogeneity of Fe-Impregnated Graphitic-Carbon Catalysts from Fe Nitrate Precursor

1
School of Environment & Life Sciences, University of Salford, Cockcroft building, Greater Manchester M5 4WT, UK
2
Diamond Light Source Ltd., Harwell Science & Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK
3
Johnson Matthey Technology Centre, Blount’s Court Road, Sonning Common, Reading RG4 9NH, UK
*
Authors to whom correspondence should be addressed.
Catalysts 2019, 9(4), 303; https://doi.org/10.3390/catal9040303
Received: 7 March 2019 / Revised: 24 March 2019 / Accepted: 25 March 2019 / Published: 27 March 2019
(This article belongs to the Section Catalytic Materials)
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Abstract

Wet impregnation is broadly applied for the synthesis of carbon-supported metal/metal oxide nanostructures because of its high flexibility, simplicity and low cost. By contrast, impregnated catalysts are typified by a usually undesired nanostructural and morphological heterogeneity of the supported phase resulting from a poor stabilization at the support surface. This study on graphite-supported Fe-based materials from Fe nitrate precursor is concerned with the understanding of the chemistry that dictates during the multistep synthesis, which is key to designing structurally homogeneous catalysts. By means of core-level X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy and atomic resolution electron microscopy, we found not only a large variety of particles sizes and morphologies but also chemical phases. Herein, thermally stable single atoms and few atoms clusters are identified together with large agglomerates of an oxy-hydroxide ferrihydrite-like phase. Moreover, the thermally induced phase transformation of the initially poorly ordered oxy-hydroxide phase into several oxide phases is revealed, together with the existence of thermally stable N impurities retained in the structure as Fe–N–O bonds. The nature of the interactions with the support and the structural dynamics induced by the thermal treatment rationalize the high heterogeneity observed in these catalysts. View Full-Text
Keywords: ferrihydrite; Fe2p; O1s; N1s XPS; NEXAFS; HAADF-STEM ferrihydrite; Fe2p; O1s; N1s XPS; NEXAFS; HAADF-STEM
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Arrigo, R.; Schuster, M.E. On the High Structural Heterogeneity of Fe-Impregnated Graphitic-Carbon Catalysts from Fe Nitrate Precursor. Catalysts 2019, 9, 303.

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