Exploration of Optical, Redox, and Catalytic Properties of Vanadia-Mayenite Nanocomposites

Shuvarakova, Ekaterina I.; Ilyina, Ekaterina V.; Stoyanovskii, Vladimir O.; Veselov, Grigory B.; Bedilo, Alexander F.; Vedyagin, Aleksey A.

doi:10.3390/jcs6100308

Cited by 3 publications

(1 citation statement)

References 68 publications

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“…In general, between these two samples, Pd/C12A7 exhibited better reproducibility in redox cycles, along with higher uptake values. At the same time, for both Pd-containing samples, these characteristics exceeded those of the C12A7 samples prepared from a hydroxide precursor via a non-aerogel approach [ 35 ]. All of this may be due to the advantages of the aerogel technique as expressed in the tailored surface area of the materials and the better accessibility of oxygen species for reagents.…”

Section: Resultsmentioning

confidence: 99%

Comparative Study of Pd-Mayenite Catalysts Prepared via Aerogel Approaches

Ilyina

Bedilo

Veselov

et al. 2022

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Pd-containing catalysts based on highly dispersed aerogel-derived mayenite were prepared via two approaches. The Pd@C12A7 sample was obtained through the addition of Pd nitrate solution to a fresh Ca(OH)2-Al(OH)3 gel. Pd/C12A7 was synthesized through conventional wet impregnation of the aerogel-derived mayenite. The evolution of the textural characteristics of the support (C12A7) depending on the calcination temperature was investigated. Pd-containing samples were explored using transmission electron microscopy and spin probe EPR spectroscopy. Using the latter method, the presence of active oxygen species capable of producing nitroxyl radicals from diphenylamine was observed. The activity of these species and the reproducibility of their redox behavior were studied in three cycles of temperature-programmed reduction in both hydrogen and CO atmospheres. A prompt thermal aging technique was used to access and compare the activity of the samples towards CO oxidation. The state of Pd species before and after the aging procedure was studied via UV–Vis spectroscopy. It was found that the dispersion of PdO was higher in the case of the Pd/C12A7 catalysts compared to the Pd@C12A7 sample. This is why the Pd/C12A7 catalyst demonstrated higher activity in CO oxidation and better reducibility in TPR cycles.

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Section: Resultsmentioning

confidence: 99%

Comparative Study of Pd-Mayenite Catalysts Prepared via Aerogel Approaches

Ilyina

Bedilo

Veselov

et al. 2022

Gels

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Aluminothermic Synthesis of Dispersed Electrides Based on Mayenite: XRD and EPR Study

et al. 2022

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The evolution of the structure and the phase composition of a dispersed mayenite at its interaction with metallic aluminum was studied in a temperature range from 900 to 1400 °C in both argon and air atmospheres. The aluminum loading was varied from 0 to 50 wt%. It was found that the addition of aluminum significantly affects the stability of the mayenite and other calcium aluminate phases within the studied temperature range. The formation of the electride state registered by the appearance of a characteristic electron paramagnetic resonance (EPR) signal from F+-like centers (g~1.994) in an argon atmosphere was shown to take place already at 1150 °C due to an aluminothermic reduction of this material. The super-narrow (Hp-p < 0.5 G) EPR spectra from F+-like centers, which were recently observed for the core–shell structures of the C12A7@C type only, were registered for mayenite for the first time. The results obtained in the present study testify firstly towards the possibility of significantly diminishing the temperatures required for the formation of the electride state in such systems and secondly towards the ability to stabilize the size of small electride nanoparticles within the synthesized calcium aluminate matrix.

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Solid-State Transformations of Mayenite and Core-Shell Structures of C12A7@C Type at High Pressure, High Temperature Conditions

et al. 2023

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Calcium aluminate of a mayenite structure, 12CaO∙7Al2O3 (C12A7), is widely applicable in many fields of modern science and technology. Therefore, its behavior under various experimental conditions is of special interest. The present research aimed to estimate the possible impact of the carbon shell in core-shell materials of C12A7@C type on the proceeding of solid-state reactions of mayenite with graphite and magnesium oxide under High Pressure, High Temperature (HPHT) conditions. The phase composition of the solid-state products formed at a pressure of 4 GPa and temperature of 1450 °C was studied. As is found, the interaction of mayenite with graphite under such conditions is accompanied by the formation of an aluminum-rich phase of the CaO∙6Al2O3 composition, while in the case of core-shell structure (C12A7@C), the same interaction does not lead to the formation of such a single phase. For this system, a number of hardly identified calcium aluminate phases along with the carbide-like phrases have appeared. The main product of the interaction of mayenite and C12A7@C with MgO under HPHT conditions is the spinel phase Al2MgO4. This indicates that, in the case of the C12A7@C structure, the carbon shell is not able to prevent the interaction of the oxide mayenite core with magnesium oxide located outside the carbon shell. Nevertheless, the other solid-state products accompanying the spinel formation are significantly different for the cases of pure C12A7 and C12A7@C core-shell structure. The obtained results clearly illustrate that the HPHT conditions used in these experiments lead to the complete destruction of the mayenite structure and the formation of new phases, which compositions differ noticeably depending on the precursor used—pure mayenite or C12A7@C core-shell structure.

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Exploration of Optical, Redox, and Catalytic Properties of Vanadia-Mayenite Nanocomposites

Cited by 3 publications

References 68 publications

Comparative Study of Pd-Mayenite Catalysts Prepared via Aerogel Approaches

Comparative Study of Pd-Mayenite Catalysts Prepared via Aerogel Approaches

Aluminothermic Synthesis of Dispersed Electrides Based on Mayenite: XRD and EPR Study

Solid-State Transformations of Mayenite and Core-Shell Structures of C12A7@C Type at High Pressure, High Temperature Conditions

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