Cobalt and manganese oxides and their complex oxide compositions were obtained by the sol-gel method using various precipitators(ammonia solution and HMTA). It was determined by X-ray diffraction method that both individual and co-precipitated hydroxo compounds after calcination at 400 °С form oxide phases of Co3O4 and Mn3O4 composition. Samples obtained by sedimentation with ammonia solution have a larger specific surface area than synthesized in HMTA solution. When calcined at 400 °C, the specific surface area for cobalt-containing samples sedimentated with ammonia solution decreases, and for samples sedimentated from HMTA solution - increases. The pore volume depends on the precipitator and changes little during calcination. For co-sedimentated and calcined at 400 °C samples, the specific surface area plays a significant role: the higher it is, the greater the catalytic ability of the sample to decompose hydrogen peroxide. On the SEM image of samples driedat 100 °C, sedimentated with ammonia solution, agglomeration of flat particles of gitrated oxides of cobalt and/or manganese of globular form is observed. For samples deposited in HMTA solution, SEM images are represented by agglomeration of particles in the form of planar layers. Calcination at 400 °C partially destroys the structure. Kinetic studies of the decomposition of hydrogen peroxide with theparticipation of the obtained samples indicate the first order of the reaction. Samples of cobalt hydroxide and co-sedimentated cobalt and manganese hydroxy compounds synthesized in HMTA solution showed the best ability to catalyze. The highest productivity (dm3 H2O2 of decomposed 1 g of catalyst) is inherent in samples of cobalt hydroxy compounds and its composition with manganese compounds synthesized by HMTA, after heat treatment at 100 °C. The ability of such samples to catalytic decomposition of hydrogen peroxide is estimated to be not less than 2.4 dm3 H2O2 (14 days). Compared to compounds synthesizedwith ammonia solution, they retain their activity for a longer time.
The results of studies of the interaction of titanium dioxide with the eutectic melt of (0.48) NaCl–(0.52) CaCl2 (mol.) in the temperature range of 823–1073 K are shown. It is established that the interaction of titanium dioxide with the melt of sodium chlorides and calcium is accompanied by the formation in the salt phase of titanium compounds soluble in 1.0% solution of hydrochloric acid, and in the solid residue is recorded calcium titanate, and the number of products formed in both phases substantially. At temperatures above 923 K is formed calcium titanate, the relative amount of which increases with increasing temperature by reducing the equilibrium content of titanium compounds in the salt phase. At temperatures below 923 K, calcium titanate was not detected in the interaction products, and the content of titanium compounds in the salt phase was higher than at higher temperatures. The absence of calcium titanate in the solid residue after prolonged isothermal contact of TiO2 with the NaCl-CaCl2 melt in the temperature range 823–923 K may be due to the fact that at such temperatures, the dissolution of titanium dioxide occurs by physical mechanism or by a mixed physicochemical mechanism. The results of the calculations by the Schroeder-Le Chatelier equation support this. In the specified temperature range, the concentration of titanium compounds increases with temperature. Starting from 923 K the nature of the interaction between titanium dioxide and the melt changes. Apparently at such temperatures (923–1073 K), the contribution of the chemical interaction between the components accompanied by the formation of calcium metatanate and volatile titanium compounds is dominant. The quantitative content of the phase, which in composition in the solid residue is identified as CaTiO3, increases, and the number of titanium compounds in the salt phase (based on TiO2) decreases. The change of isobaric isothermal potential (∆G) in the temperature range of 300–1300 K of the exchange reactions between sodium chloride and calcium and titanium oxide is positive, so self-directed course is unlikely. The lowest Gibbs free energy values correspond to the reaction of the interaction of calcium chloride with titanium dioxide to form titanate or calcium oxide and tetrachloride or titanium oxochloride.
Cobalt oxides and/or manganese and their com-position based on cerium and zirconium oxides (CeO2 : ZrO2 = 1:1 mol.%) with a content of up to 20 wt. % are synthesized. Samples of both individual oxides and complex oxide compositions were prepared by precipitation from solutions of am-monia (room temperature) or hexamethylenetet-ramine (80–90 °C) followed by heat treatment. Results of DTA show, that due to the calcination at 400 ° C (2 h), the obtained samples lose 17–22 wt. % corresponding to 2–3.8 molecules of water. According to the X-ray powder analysis, initially are formed hydroxide compounds of cobalt (CoO· xH2O) and manganese (MnO2·yН2О), which, after being heated at 400 °C for 2 hours, are converted into mixed oxides from the composition of Co3O4 and Mn3O4. The average particle size calculated by the Sherer equation is 18–30 nm. In the study of catalytic activity on the example of the reaction of the hydrogen peroxide decomposition, it was found that the obtained samples from the solution of GMTA show a greater ability to catalytically decompose hydrogen peroxide compared to samples obtained from the ammonia solution. In this case, the catalytic activity of dried samples is twice as high as roasted, regardless of the method of obtaining. Samples of oxide compo-sitions with deposited 5–10 wt. % of Ce–Zr oxides (1:1) exhibit the highest ability to decompose H2O2. In this case, samples of compositions obtained from the solution of GMTA, have a prolonged catalytic action, and when precipitation in the solution of ammonia, the reaction takes place quite actively during 4–5 days. Compositions formed from co-deposited or mechanically mixed hydroxocompounds of cobalt and manganese with 5 wt. % of CeO2–ZrO2 (1:1) deposited on them have different catalytic activity. In the case of mechanically mixed, it is 30% lower and with subsequent calcination at 400 °C, it is reduced by almost half, and with co-precipitation, the activity is quite high and does not change with heat treatment. In the case of obtaining samples of Co–Mn with Ce–Zr (1:1) deposited on them in excess of 10 wt. % the catalytic activity of the samples dried at 80 °C is equal to the activity of the co-deposited hydroxocompounds of cobalt and manganese and the calcination at 400 °C it reduces it by 30 %. The best ability for catalysis was found in samples CoO·xH2O + 5 wt. % MnO2·yН2О, СоO×хН2О + 10 wt. % CeO2:ZrO2 and СоO×хН2О–MnO2×yН2О, precipitated with the GMTA solution and dried at 80 °C. The besser catalytic properties revealed a sample of СоО×хН2О + 10 wt. % CeO2:ZrO2, which with-out stirring is capable of decomposing 1.2–1.4 dm3/g of hydrogen peroxide with a rapid reaction and in the experiment the volume of H2O2 reacted was 3.4 dm3/g.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.