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Open AccessArticle

Microstructure, Thermal Stability, and Catalytic Activity of Compounds Formed in CaO-SiO2-Cr(NO3)3-H2O System

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Department of Silicate Technology, Kaunas University of Technology, Radvilenu 19, LT-50270 Kaunas, Lithuania
2
Department of Physical and Inorganic Chemistry, Kaunas University of Technology, Radvilenu 19, LT-50270 Kaunas, Lithuania
*
Author to whom correspondence should be addressed.
Nanomaterials 2020, 10(7), 1299; https://doi.org/10.3390/nano10071299
Received: 28 May 2020 / Revised: 19 June 2020 / Accepted: 29 June 2020 / Published: 2 July 2020
In this work, the thermal stability, microstructure, and catalytic activity in oxidation reactions of calcium silicate hydrates formed in the CaO-SiO2-Cr(NO3)3-H2O system under hydrothermal conditions were examined in detail. Dry primary mixture with a molar ratio of CaO/SiO2 = 1.5 was mixed with Cr(NO3)3 solution (c = 10 g Cr3+/dm3) to reach a solution/solid ratio of the suspension of 10.0:1. Hydrothermal synthesis was carried out in unstirred suspensions at 175 °C for 16 h. It was determined that, after treatment, semicrystalline calcium silicate hydrates C-S-H(I) and/or C-S-H(II) with incorporated Cr3+ ions (100 mg/g) were formed. The results of in situ X-ray diffraction and simultaneous thermal analyses showed that the products were stable until 500 °C, while, at higher temperatures, they recrystallized to calcium chromate (CaCrO4, 550 °C) and wollastonite (800–850 °C). It was determined that both the surface area and the shape of the dominant pore changed during calcination. Propanol oxidation experiments showed that synthetic semicrystalline calcium silicate hydrates with intercalated chromium ions are able to exchange oxygen during the heterogeneous oxidation process. The obtained results were confirmed by XRD, STA, FT-IR, TEM, SEM, and BET methods, and by propanol oxidation experiments. View Full-Text
Keywords: calcium chromate; calcium silicate; BET analysis; thermal stability; microstructure; calcium silicate hydrate; mesoporous; catalytic activity calcium chromate; calcium silicate; BET analysis; thermal stability; microstructure; calcium silicate hydrate; mesoporous; catalytic activity
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Niuniavaite, D.; Baltakys, K.; Dambrauskas, T.; Eisinas, A.; Rubinaite, D.; Jaskunas, A. Microstructure, Thermal Stability, and Catalytic Activity of Compounds Formed in CaO-SiO2-Cr(NO3)3-H2O System. Nanomaterials 2020, 10, 1299.

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