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июнь, 2022 г.
CHEMISTRY OF SOLIDS
NANOCARBON PRODUCTION TECHNOLOGY IN THE PRESENCE NiO/MgO CATALYST
FROM METHANE
Islombek F. Usmonov
Student, Faculty of Chemistry, Samarkand State University, Uzbekistan, Samarkand Е-mail: islombek [email protected]
Khilola N. Kholmirzayeva
Doctoral student, Department of Physical and Colloid Chemistry,
Samarkand State University, Uzbekistan, Samarkand E-mail: [email protected]
Normurot I. Fayzullayev
DSc, Professor,
Department of Polymer Chemistry and Chemical Technology,
Samarkand State University, Uzbekistan, Samarkand E-mail: _ f-normurot@samdu. uz
ТЕХНОЛОГИЯ ПОЛУЧЕНИЯ НАНОУГЛЕРОДА В ПРИСУТСТВИИ КАТАЛИЗАТОРА NiO/MgO ИЗ МЕТАНА
Усманов Исломбек Фозил угли
студент, химический факультет, Самаркандский государственный университет, Республика Узбекистан, г. Самарканд Е-mail: islombek_usmonov@inbox. ru
Холмирзаева Хилола Норбой кизи
докторант, кафедры физической и коллоидной химии, Самаркандский государственный университет, Республика Узбекистан, г. Самарканд E-mail: [email protected]
Файзуллаев Нормурот Ибодуллаевич
д-р тех. наук, профессор, кафедра химии полимеров и химической технологии,
Самаркандский государственный университет, Республика Узбекистан, г. Самарканд E-mail: f-normurot@samdu. uz
ABSTRACT
Physicochemical and operational properties of two industrial catalysts for nanocarbon synthesis were analyzed. Different methods: X-ray phase, chemical, and IR spectroscopy studied the composition of catalysts. The catalyst was obtained by reduction in a hydrogen atmosphere at 873 K of a NiO/MgO precursor prepared by co-precipitation in an acid medium of nickel and magnesium salts. Approximate equality of ionic radius Mg2+ and Ni2+ promotes the fact that NiO and MgO have good mutual solubility and in the binary system, NiO /MgO forms a solid solution Nix Mg1-xO. Thus, nanocarbon synthesis catalysts in the industry are of high quality, which ensures high activity throughout the entire service life.
АННОТАЦИЯ
Проанализированы физико-химические и эксплуатационные свойства двух промышленных катализаторов синтеза наноуглеродов. Различные методы: рентгенофазовый, химический и ИК-спектроскопия изучали состав
Библиографическое описание: Usmonov I., Kholmirzayeva K., Fayzullayev N. NANOCARBON PRODUCTION TECHNOLOGY IN THE PRESENCE NiO/MgO CATALYST FROM METHANE // Universum: химия и биология : электрон. научн. журн. 2022. 6(96). URL: https://7universum.com/ru/nature/archive/item/13825
№ 6 (96)
июнь, 2022 г.
катализаторов. Катализатор получен восстановлением в атмосфере водорода при 873 К прекурсора NiO/MgO, полученного соосаждением в кислой среде солей никеля и магния. Примерное равенство ионного радиуса Mg2+ и Ni2+ способствует тому, что NiO и MgO обладают хорошей взаимной растворимостью и в бинарной системе NiO/MgO образуют твердый раствор Nix Mg1-xO. Таким образом, катализаторы синтеза наноуглеродов в промышленности отличаются высоким качеством, что обеспечивает высокую активность на протяжении всего срока службы.
Keywords: Fisher -Tropish, nickel, magnesium, catalyst, electron microscope, Raman spectroscopy
Ключевые слова: Фишер-Тропиш, никель, магний, катализатор, электронный микроскоп, рамановская спектроскопия.
Introduction. The influence of various factors on the synthesis of nanocarbon from the walnut peel, apricot kernel, methane, natural gas, and propane-butane fractions was studied and the texture and sorption characteristics of the obtained nanocarbon were examined. At the same time, the influence of various factors on the rate of formation of nanocarbon obtained from methane, natural gas, and propane-butane fractions was studied and optimal process conditions were proposed [1-6].
Chemical evaporation of carbon nanotubes (CVD) from a mixture of gas consisting of methane (carbon precursor) and hydrogen (carrier gas) in the presence of catalytic particles on the scale of reactor length modelled by solving problems [7-14].
Thermocatalytic decomposition (TCD) of methane is studied as a method of converting natural gas to hydrogen and functional carbon. In these processes, carbon is usually formed over the catalyst phase, leading to the growth of particles. Therefore, the development of
a particle growth model is necessary to understand the thermocatalytic decomposition limitations of methane and to evaluate the optimal parameters and process conditions. The Multi-Grain Model (MGM) has been used to combine the effects of particle growth, kinetics, and internal heat and mass transfer [15 - 17].
Methane conversion in the reactor is calculated as a function of the longitudinal coordinate, temperature, and specific gas and catalyst flow rate of the specific carbon content and relative catalyst activity. At the specified specific methane flow rate, it is shown that there is an optimal specific catalyst flow with a maximum specific yield of carbon nanotubes, in which case the efficiency in the combined reactor is higher than in the countercurrent reactor [18-20].
Experimental part. The FT process involves the processing of natural gas, coal, and biomass into gas-to-liquid (GTL), coal-to-liquid (CTL), and biomass-to-liquid (BTL) technologies, respectively. started.
Figure 1. Comparison of Fisher-Tropsch process and dieselfraction obtained using conventional dieselfuel
Figure 2. The two main mechanisms proposed for the FT process
Almost all developed countries have smaller industries based on the FT process. The main reactions in the FT process are [13]:
In this case, side reactions of water gas displacement (WG) (3) and CO (DP) asymmetry with carbonization of the catalyst surface (4) are possible:
CO + 3H2 ^ CH4 + H2O AH298 = -247 kJ/mol (1) nCO + nH2 ^ CnHn + nH2O (2)
CO + H2O ~ CO2 + H2 AH298 = -41 kJ/mol (3) 2CO ~ C + CO2 AH298 = -172 kJ/mol (4)
In the literature, many different mechanisms of the hydrocarbon formation process have been proposed, the two main of which are currently carbide (direct) and indirect (Fig. 2).
In the first case, the initial stage of the process is the dissociation of the CO molecule on the catalyst surface, its hydrogenation, and the growth of the chain on the carbon atom formed. The indirect mechanism involves
the adsorption of a CO molecule and its hydrogenation with dissociated hydrogen, followed by the destruction of an oxygen atom in the form of water or CO2, and the growth of the chain. Studies are proving the mechanisms of the first and second types. Recent data suggest that the reaction can occur through both carbide and indirect mechanisms.
Figure 3. Schematic diagram of a CVD process for CNT synthesis
Carbon Nanotubes (CNT), chemical vapor deposition (CVD). The catalyst was obtained by reduction in a hydrogen atmosphere at 873 K of a NiO/MgO precursor prepared by co-precipitation in an acid medium of nickel and magnesium salts. Approximate equality of ionic radius Mg2+ and Ni2+ promotes the fact that NiO and MgO have good mutual solubility and in the binary system, NiO /MgO forms a solid solution Nix Mg1-xO. Because
of this, nickel ions are distributed sparsely and uniformly over the volume of the MgO lattice, and when the precursor interacts with hydrogen, only a small part of nickel ions is reduced to metallic Ni, and the complete reduction of all nickel is also prevented by valence stabilization by the crystal field of MgO. As a result, metallic nickel clusters are rarely and evenly distributed on the support surface and are small in size (Table 1).
Table 1.
To obtain the result, the experimenters also increased the temperature of the process in steps
Ni/Mg 2:1 1:3 1:5 1:10 1:20
T, oC 510 580 620 630 650
Dgmcns, nm 35 - 21 17 13
GMCVS- Growth Mechanism of Carbon Nanostructures
Figure 4. Transmission electron microscopy images (a) single-walled carbon nanotubes; (b) double-walled carbon nanotubes.
Hydrothermal synthesis of nickel and magnesium oxide. Hydrothermal synthesis has long proven itself as one of the most common methods of obtaining various functional nanomaterials with the desired micro-and nanostructure. That demonstrated the advantages of processing nanostructured materials for various fields, such as electronics, optoelectronics, catalysis, ceramics, magnetic data storage, biomedicine, and biophotonics. In the process of hydrothermal synthesis, nucleation and growth of nanocrystals begin. In particular, the formation of crystalline products through a hydrothermal process can take place at significantly lower temperatures than those required in solid-phase synthesis. Due to such advantages, hydrothermal synthesis is one of the
most promising methods at relatively low reaction temperatures and as a chemical homogeneity. Hydrothermal synthesis allows the production of nanocrystalline powders in one step with the ability to control the morphology, particle size, and phase composition of products under relatively mild conditions. X-ray phase analysis data show that not only temperature but also the duration of synthesis has a significant effect on the formation of the crystalline precipitate. Hydrothermal treatment (HTT) for 4 hours at a temperature of 100 °C results in the formation of well-crystallized phases (Fig. 5). Increasing the TRP time to 8 hours results in strong amor-phization of the product. The formation of this phase indicates that nickel and magnesium oxide cannot be injected as one of the known crystalline phases (Fig. 5).
RS-shlft. snr1
Figure 5. Raman spectra of CNTs
The traditionally used indicator of the change in the structural properties of carbon materials is the ID / IG ratio. However, there are also lines defined as D8 (~1100-1250 cm-1), D3 (~1500 cm-1) and D2 (D') (~ 1600-1620 cm-1) for mathematical analysis of 9001800 cm (Fig. 6). The intensity of the D2 or (D ') line is usually directly related to the intensity of D1 and corresponds to the graphene layers that are not part of the graphite "sandwich" structure, that is, in fact, it may be an indicator of the ratio. the number of surface layers
from the inner or surface to the volume. The surface of line D2 is explained by the elongated oscillations of an aromatic ring in fine graphite crystallites coated with oxygen-containing functional groups. This line also applies to peripheral carbon atoms, and it has been found that the intensity of a crystallite increases with decreasing volume. A decrease in the diameter of the CNT and a fracture of the graphite simultaneously lead to an increase in the intensity of D and D2.
RS-shlft,
Figure 6. Decomposition of the first-order Raman spectrum region into components
The origin of the D3 (D '') line in the 1450-1550 cm-1 range in the spectra of carbon materials is still a matter of controversy, with some authors linking the "artefacts" of the calculation of this component to the actual line. However, in many studies that emphasize this line, its appearance is associated with the formation of stratification defects, turbo stratification of the graphite structure, and changes in the interlayer distance. This component has also appeared in the Raman spectra of various polyene structures (e.g., polyacetylene, phenyl polyenes, polyenecarboxylic acids).
As the number of layers in the graphite decreases, the intensity of the line increases by ~1500 cm-1, which is explained by the authors by the deterioration of the resistance of several layered fragments to changes in the interlayer distance. Finally, a broad component with a wavelength of ~1100-1250 cm-1 is sometimes associated with an amorphous portion of a carbon material or a mixture of graphite. It should be noted that a line with this wavelength, similar to the 1500 cm- 1 line, appears in the Raman spectra of many polyene structures, as well as compounds and polymers containing aromatic rings (biphenyl, triphenyl, poly-para phenylene). Ferrari and Robertson studied the Raman spectra of the nanodia-mond and concluded that this component did not belong
to the sp3-hybridized carbon but to the polyacetylene surface parts visible along the ~ 1450 cm-1 line. C=C was explained by a combination of elongation oscillations and C-H fan oscillations.
Conclusion. Physicochemical and operational properties of two industrial catalysts for nanocarbon synthesis were analyzed. The catalyst was obtained by reduction in a hydrogen atmosphere at 873 K of a NiO/MgO precursor prepared by co-precipitation in an acid medium of nickel and magnesium salts. Approximate equality of ionic radius Mg2+ and Ni2+ promotes the fact that NiO and MgO have good mutual solubility and in the binary system, NiO /MgO forms a solid solution Nix Mg1-xO. As the number of layers in the graphite decreases, the intensity of the line increases by ~ 1500 cm-1, which is explained by the authors by the deterioration of the resistance of several layered fragments to changes in the interlayer distance. Examining the Raman spectra, it was concluded that this component did not belong to the sp3-hybridized carbon but to the polyacetylene surface parts visible along the ~ 450 cm-1 line. Thus, nanocarbon synthesis catalysts in the industry are of high quality, which ensures high activity throughout the entire service life.
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