On the reversible deactivation of cobalt ferrite spinel nanoparticles applied in selective 2-propanol oxidation

Anke, Sven; Falk, Tobias; Bendt, Georg; Sinev, Ilya; Hävecker, Michael; Antoni, Hendrik; Zegkinoglou, Ioannis; Jeon, Hyosang; Knop‐Gericke, Axel; Schlögl, Robert; Cuenya, Beatriz Roldán; Schulz, Stephan; Mühler, Martin

doi:10.1016/j.jcat.2019.12.007

Cited by 36 publications

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“…The typical behavior of Co−Fe‐based spinel samples was observed with a low‐temperature maximum that is deactivated after the first run and can be regenerated by a temperature‐programmed oxidation (TPO) as observed in a previous study (Figure 8a) [21] . This deactivation is induced by the adsorption of strongly bound acetate species leading to a reduction of the catalyst surface and coke formation [20] . Approximately 60 % 2‐propanol conversion was detected at the low‐temperature maximum at 150 °C with acetone being the only product formed indicating an oxidative dehydrogenation pathway.…”

Section: Resultssupporting

confidence: 58%

“…The temperature corresponding to 50 % CO conversion (T 50 ) decreased from 273 to 188 K by substitution of 15 % Fe and remained similar up to 25 % Fe. Besides total oxidation, Co−Fe‐based spinel catalysts also showed excellent activity in selective oxidation, in particular of 2‐propanol in the gas phase [19–21] . For example, monocrystalline CoFe 2 O 4 synthesized by thermal decomposition of a layered double hydroxide was very active in dehydration yielding propene, while commercial CoFe 2 O 4 primarily catalyzed the oxidative dehydrogenation to acetone [19] .…”

Section: Introductionmentioning

confidence: 99%

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Identification of Active Sites in the Catalytic Oxidation of 2‐Propanol over Co_1+xFe_2–xO₄ Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces

et al. 2021

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A series of Co1+xFe2–xO4 (0≤x≤2) spinel nanowires was synthesized by nanocasting using SBA‐15 silica as hard template, which was characterized by X‐ray powder diffraction, X‐ray photoelectron spectroscopy, and transmission electron microscopy. The Co1+xFe2–xO4 spinels were applied in the aerobic oxidation of aqueous 2‐propanol solutions to systematically study the influence of exposed Co and Fe cations on the catalytic properties. The activity of the catalysts was found to depend strongly on the Co content, showing an exponential increase of the reaction rate with increasing Co content. Ensembles of Co3+cus (coordinatively unsaturated) sites were identified as the active sites for selective 2‐propanol oxidation, which are assumed to consist of more than six Co ions. In addition, gas‐phase oxidation with and without water vapor co‐feeding was performed to achieve a comparison with liquid‐phase oxidation kinetics. An apparent activation energy of 94 kJ mol−1 was determined for 2‐propanol oxidation over Co3O4 in the liquid phase, which is in good agreement with the gas‐phase oxidation in the presence of water vapor. In contrast to gas‐phase conditions, the catalysts showed high stability and reusability in the aqueous phase with constant conversion in three consecutive runs.

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Section: Resultssupporting

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Identification of Active Sites in the Catalytic Oxidation of 2‐Propanol over Co_1+xFe_2–xO₄ Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces

et al. 2021

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“…The 2-propanol oxidation is an established standard reaction for determining the performance of catalysts and CoxFe3-xO4 nanostructures have recently shown their suitability as an effective catalyst for the formation of acetone with high activity and selectivity. [27][28][29] We demonstrate that a blue emission is observable under UV irradiation with rising temperature in a 2-propanol/O2/N2 gas flow. By performing additional catalytic tests with gas chromatography under comparable thermo-catalytic conditions, we show that this blue PL signal follows the conversion of 2-propanol to acetone precisely.…”

Section: Main Textmentioning

confidence: 76%

Monitoring Catalytic 2-Propanol Oxidation over Co3O4 Nanowires via In Situ Photoluminescence Spectroscopy

Klein

Kampermann

Korte

et al. 2022

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Spectroscopic methods enabling real-time monitoring of dynamic surface processes are a prerequisite for identifying how a catalyst triggers a chemical reaction. We present an in situ photoluminescence spectroscopy approach for probing the thermo-catalytic 2-propanol oxidation over mesostructured Co3O4 nanowires. Under oxidative conditions, a distinct blue emission at ~420 nm is detected that increases with temperature up to 280 °C, with an intermediate maximum at 150 °C. Catalytic data gained under comparable conditions show that this course of photoluminescence intensity precisely follows the conversion of 2-propanol and the production of acetone. The blue emission is assigned to the radiative recombination of unbound acetone molecules, the n - π* transition of which is selectively excited by a wavelength of 270 nm. These findings open a pathway for studying thermo-catalytic processes via in situ photoluminescence spectroscopy thereby gaining information about the performance of the catalyst and the formation of intermediate products.

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“…Not solely Co-containing transition metal oxides are interesting for catalytic oxidation reactions, also mixed Co and Fe transition metal oxides are used either within perovskites or spinel structures [22][23][24][25][26][27][28][29][30][31][32]. With increasing Fe content in spinels, the reducibility decreased steadily until inversion of the spinel materials was found experimentally.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of Reactive Oxygen Species on Cobalt-Containing Spinel Oxides in Cyclic CO Oxidation

et al. 2021

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Reactive oxygen species (ROS) are considered to be responsible for the high catalytic activity of transition metal oxides like Co3-xFexO4 in oxidation reactions, but the detailed influences of catalyst composition and morphology on the formation of these reactive oxygen species are not fully understood. In the presented study, Co3O4 spinels of different mesostructures, i.e., particle size, crystallinity, and specific surface area, are characterized by powder X-ray diffraction, scanning electron microscopy, and physisorption. The materials were tested in CO oxidation performed in consecutive runs and compared to a Co3-xFexO4 composition series with a similar mesostructure to study the effects of catalyst morphology and composition on ROS formation. In the first run, the CO conversion was observed to be dominated by the exposed surface area for the pure Co-spinels, while a negative effect of Fe content in the spinels was seen. In the following oxidation run, a U-shaped conversion curve was observed for materials with high surface area, which indicated the in situ formation of ROS on those materials that were responsible for the new activity at low temperature. This activation was not stable at the higher reaction temperature but was confirmed after temperature-programmed oxidation (TPO). However, no activation after the first run was observed for low-surface-area and highly crystalline materials, and the lowest surface-area material was not even activated after TPO. Among the catalyst series studied here, a correlation of small particle size and large surface area with the ability for ROS formation is presented, and the benefit of a nanoscaled catalyst is discussed. Despite the generally negative effect of Fe, the highest relative activation was observed at intermediate Fe contents suggesting that Fe may be involved in ROS formation.

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On the reversible deactivation of cobalt ferrite spinel nanoparticles applied in selective 2-propanol oxidation

Cited by 36 publications

References 35 publications

Identification of Active Sites in the Catalytic Oxidation of 2‐Propanol over Co_1+xFe_2–xO₄ Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces

Identification of Active Sites in the Catalytic Oxidation of 2‐Propanol over Co_1+xFe_2–xO₄ Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces

Monitoring Catalytic 2-Propanol Oxidation over Co3O4 Nanowires via In Situ Photoluminescence Spectroscopy

Dynamics of Reactive Oxygen Species on Cobalt-Containing Spinel Oxides in Cyclic CO Oxidation

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On the reversible deactivation of cobalt ferrite spinel nanoparticles applied in selective 2-propanol oxidation

Cited by 36 publications

References 35 publications

Identification of Active Sites in the Catalytic Oxidation of 2‐Propanol over Co1+xFe2–xO4 Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces

Identification of Active Sites in the Catalytic Oxidation of 2‐Propanol over Co1+xFe2–xO4 Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces

Monitoring Catalytic 2-Propanol Oxidation over Co3O4 Nanowires via In Situ Photoluminescence Spectroscopy

Dynamics of Reactive Oxygen Species on Cobalt-Containing Spinel Oxides in Cyclic CO Oxidation

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Identification of Active Sites in the Catalytic Oxidation of 2‐Propanol over Co_1+xFe_2–xO₄ Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces

Identification of Active Sites in the Catalytic Oxidation of 2‐Propanol over Co_1+xFe_2–xO₄ Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces