Mixing Patterns and Redox Properties of Iron-Based Alloy Nanoparticles under Oxidation and Reduction Conditions

Papaefthimiou, Vasiliki; Tournus, Florent; Hillion, Arnaud; Khadra, Ghassan; Teschner, Detre; Knop‐Gericke, Axel; Dupuis, V.; Zafeiratos, Spyridon

doi:10.1021/cm403172a

Cited by 15 publications

(28 citation statements)

References 56 publications

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“…For bimetallic catalysts, redistribution of atoms within the nanoparticles owing to reaction conditions (elevated temperature, oxidative or reductive atmosphere) can in addition play an important role. For example, Fe segregates to the surface of Fe−Pt, Fe−Rh, and Fe−Au under O 2 atmosphere at 250 °C, and Cu moves to the surface of Co−Cu if it is exposed to H 2 and to the core if it is exposed to CO at 370 °C…”

Section: Introductionmentioning

confidence: 99%

Silica‐Supported Au–Ag Catalysts for the Selective Hydrogenation of Butadiene

et al. 2017

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Gold and silver are miscible over the entire composition range, and form an attractive combination for fundamental studies on bimetallic catalysts. Au–Ag catalysts have shown synergistic effects for different oxidation and liquid‐phase hydrogenation reactions, but have rarely been studied for gas‐phase hydrogenation. In this study 3 nm particles of Au, Ag and Au–Ag supported on silica (SBA‐15) were investigated as catalysts for selective hydrogenation of butadiene in an excess of propene. The Au catalyst was over an order of magnitude more active than the Ag catalyst at 120 °C. The initial activity of the Au–Ag catalysts scaled linearly with the Au‐content, suggesting a direct correlation between the surface and overall compositions of the nanoparticles and the absence of synergistic effects. All Au‐containing catalysts were highly selective to butenes (>99.9 %). The Au catalysts were stable, whereas the Au–Ag catalysts lost about half of their activity during 20 h run time at 200 °C, but the initial activity was restored by a consecutive oxidation‐reduction treatment. Near ambient pressure x‐ray photoelectron spectroscopy showed that exposure to H2 at elevated temperatures led to a gradual enrichment of the surface of the Au–Ag nanoparticles by Ag. These observations highlight the importance of considering progressive atomic rearrangements in bimetallic nanocatalysts under reaction conditions.

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Section: Introductionmentioning

confidence: 99%

Silica‐Supported Au–Ag Catalysts for the Selective Hydrogenation of Butadiene

et al. 2017

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“…The spectral shape of the NEXAFS V L3-edge is strongly correlated to the coordination environment and the number of 3d electrons of the metal center.51 Therefore, it may be used to provide interesting insights into the local geometry around the V 5+ cation, 92 as has been shown previously for other transition metal oxides. 95,96 Theoretical simulation of the V L3edge using the charge-transfer multiplet (CTM) approach can help to estimate the variations in the V−O interaction that are accountable for the differences in the lineshapes. 51,52 The two key parameters affecting the shape of the calculated XAS curves are 10Dq (crystal field splitting) and Δ (charge transfer energy).…”

Section: The Oxidation State and Surface Distribution Of Vanadiummentioning

confidence: 99%

Improving the Catalytic Performance of Cobalt for CO Preferential Oxidation by Stabilizing the Active Phase through Vanadium Promotion

et al. 2021

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Preferential oxidation of CO (COPrOx) is a catalytic reaction targeting the removal of trace amounts of CO from hydrogen-rich gas mixtures. Non-noble metal catalysts, such as Cu and Co, can be equally active to Pt for the reaction; however, their commercialization is limited by their poor stability. We have recently shown that CoO is the most active state of cobalt for COPrOx, but under certain reaction conditions, it is readily oxidized to Co3O4 and deactivates. Here, we report a simple method to stabilize the Co 2+ state by vanadium addition. The V promoted cobalt catalyst exhibits considerably higher activity and stability than pure cobalt. The nature of the catalytic active sites during COPrOx was established by operando NAP-XPS and NEXAFS, while the stability of the Co 2+ state on the surface was verified by in situ NEXAFS at 1 bar pressure. The active phase consists of an ultra-thin cobalt-vanadate surface layer, containing tetrahedral V 5+ and octahedral Co 2+ cations, with an electronic and geometric structure that is deviating from the standard mixed bulk oxides. In addition, V addition helps to maintain the population of Co 2+ species involved in the reaction, inhibiting carbonate species formation that are responsible for the deactivation. The promoting effect of V is discussed in terms of enhancement of CoO redox stability on the surface induced by electronic and structural modifications. These results demonstrate that V-promoted cobalt is a promising COPrOx catalyst and validate the application of in situ spectroscopy to provide the concept for designing better performing catalysts.

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“…Unfortunately, the Ag-Fe system at the nanoscale is not easy to stabilize. Iron (or iron oxide)-noble metal hybrid NPs have been the subject of many investigations, [34][35][36][37][38][39][40][41][42] and some studies focused on silver-iron [43][44][45] or silver-iron oxide with promising applications in the field of antimicrobial treatment and water decontamination. [46][47][48][49][50] It should be stressed here that both metals are immiscible in the bulk at all compositions.…”

Section: Introductionmentioning

confidence: 99%

Environmental Plasmonic Spectroscopy of Silver–Iron Nanoparticles: Chemical Ordering under Oxidizing and Reducing Conditions

et al. 2019

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The chemical structure and the localized surface plasmon resonance (LSPR) of sizeselected AgxFe1-x (x=0.5, 0.8) nanoparticles (NPs), produced by laser vaporization, were investigated experimentally and theoretically. Monte Carlo simulations employing a many-bodyembedded-atom model show that small isolated Ag-Fe NPs should preferentially adopt core@shell structures with an iron core that may be deformed or off-centered while keeping a silver shell around it. Experimentally, the optical response of silica-embedded NPs was measured with a new environmental spectrophotometer based on spatial modulation and is discussed in relation with the NP chemical structure independently studied by transmission electron microscopy (TEM). Measurements performed on as-prepared samples show that iron rapidly oxidizes when exposed to air to form a magnetite (Fe3O4) shell surrounding a purely metallic crystalline silver core. In situ optical measurements carried out successively under oxidizing and reducing atmospheres indicate that iron oxidation and reduction are reversible processes that are directly mirrored in the LSPR changes, in good agreement with optical simulations. The TEM observations, the environmental plasmonic spectroscopy measurements and the various simulations lead us to conclude that iron and silver initially adopt a segregated configuration with a silver-enriched surface and that, during oxidation, iron likely diffuses throughout the silver shell, leading to an Ag@Fe3O4 configuration, while an inverse process may occur during annealing under reducing atmosphere. Finally, we show that Ag-Fe NPs, co-deposited with alumina on a substrate kept at 400°C, offers an alternative to preserve the metallic character of iron.

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Mixing Patterns and Redox Properties of Iron-Based Alloy Nanoparticles under Oxidation and Reduction Conditions

Cited by 15 publications

References 56 publications

Silica‐Supported Au–Ag Catalysts for the Selective Hydrogenation of Butadiene

Silica‐Supported Au–Ag Catalysts for the Selective Hydrogenation of Butadiene

Improving the Catalytic Performance of Cobalt for CO Preferential Oxidation by Stabilizing the Active Phase through Vanadium Promotion

Environmental Plasmonic Spectroscopy of Silver–Iron Nanoparticles: Chemical Ordering under Oxidizing and Reducing Conditions

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