NANOCARBON PRODUCTION TECHNOLOGY IN THE PRESENCE NiO/MgO CATALYST FROM METHANE

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 Ni_x Mg_1-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 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 Ni_x Mg_1-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.

Almost all developed countries have smaller industries based on the FT process. The main reactions in the FT process are [13]:

CO + 3H₂ → CH₄ + H₂O                      ΔH₂₉₈ = –247 kJ/mol                         (1)

nCO + nH₂ → C_nH_n + nH₂O                                                                          (2)

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 + H₂O ↔ CO₂ + H₂                        ΔH₂₉₈ = –41 kJ/mol                            (3)

2CO ↔ C + CO₂                                  ΔH₂₉₈ = –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 Ni_x Mg_1-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.

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 amorphization 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).

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 900-1800 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.

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 nanodiamond 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 Ni_x Mg_1-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.

References:

1. Xolmirzayeva H. N., Fayzullayev N. I. Obtaining Nanocarbon from Local Raw Materials and Studying Its Textural and Sorption Properties //arXiv preprint arXiv:2202.11751. – 2022.
2. Ibodullayevich F. N., Yunusovna B. S., Anvarovna X. D. Physico-chemical and texture characteristics of Zn-Zr/VKTS catalyst //Journal of Critical Reviews. – 2020. – Т. 7. – №. 7. – С. 917-920.
3. Mamadoliev I. I., Fayzullaev N. I. Optimization of the activation conditions of high silicon zeolite //International Journal of Advanced Science and Technology. – 2020. – Т. 29. – №. 3. – С. 6807-6813.
4. Fayzullaev N. I., Kholmirzaeva H. N., Normo’minov A. U. Synthesis And Study Of High-Silicon Zeolites From Natural Bentonite //Solid State Technology. – 2020. – Т. 63. – №. 6. – С. 3448-3459.
5. Lewicka K. Activated carbons prepared from hazelnut shells, walnut shells and peanut shells for high CO2 adsorption //Polish Journal of Chemical Technology. – 2017. – Т. 19. – №. 2.
6. Suhdi S., Wang S. C. The Production of Carbon Nanofiber on Rubber Fruit Shell-Derived Activated Carbon by Chemical Activation and Hydrothermal Process with Low Temperature //Nanomaterials. – 2021. – Т. 11. – №. 8. – С. 2038.
7. Xolmirzayeva H. N. Characteristics of the FE2 (MOO4) 3* MOO3 catalyst used in the synthesis of nanocarbons from methane //ACADEMICIA: An International Multidisciplinary Research Journal. – 2021. – Т. 11. – №. 9. – С. 598-605.
8. Tursunova N. S., Fayzullaev N. I. Kinetics of the reaction of oxidative dimerization of methane //International Journal of Control and Automation. – 2020. – Т. 13. – №. 2. – С. 440-446.
9. Kumar M., Ando Y. Chemical vapor deposition of carbon nanotubes: a review on growth mechanism and mass production //Journal of nanoscience and nanotechnology. – 2010. – Т. 10. – №. 6. – С. 3739-3758.
10. Shukrullah S. et al. Mass production of carbon nanotubes using fluidized bed reactor: A short review //Trends in Applied Sciences Research. – 2014. – Т. 9. – №. 3. – С. 121.
11. Moisala A. et al. Single-walled carbon nanotube synthesis using ferrocene and iron pentacarbonyl in a laminar flow reactor //Chemical Engineering Science. – 2006. – Т. 61. – №. 13. – С. 4393-4402.
12. Aida R. Karaeva, Sergey A. Urvanov, Nikita V. Kazennov, Eduard B. Mitberg and Vladimir Z. Mordkovich. Synthesis, Structure and Electrical Resistivity of Carbon Nanotubes Synthesized over Group VIII Metallocenes //Nanomaterials. – 2020. – Т. 10. – №. 11. – С. 2279.
13. Venkataraman A. et al. Carbon nanotube assembly and integration for applications //Nanoscale research letters. – 2019. – Т. 14. – №. 1. – С. 1-47.
14. Amara H., Bichara C. Modeling the growth of single-wall carbon nanotubes //Single-Walled Carbon Nanotubes. – 2019. – С. 1-23.
15. Li M. et al. Metallic catalysts for structure-controlled growth of single-walled carbon nanotubes //Single-Walled Carbon Nanotubes. – 2019. – С. 25-67.
16. Hirotani J., Ohno Y. Carbon nanotube thin films for high-performance flexible electronics applications //Single-Walled Carbon Nanotubes. – 2019. – С. 257-270.
17. Jeon I., Matsuo Y., Maruyama S. Single-walled carbon nanotubes in solar cells //Single-walled carbon nanotubes. – 2019. – С. 271-298.
18. Jia X., Wei F. Advances in production and applications of carbon nanotubes //Single-Walled Carbon Nanotubes. – 2019. – С. 299-333.
19. K. Srilatha, D.Bhagawan, S.Shiva Kumar, V.Himabindu. Sustainable fuel production by thermocatalytic decomposition of methane–A review //south african journal of chemical engineering. – 2017. – Т. 24. – С. 156-167.
20. Awad, I. Ahmed, D. Qadir, M. S. Khan, A. Idris. Catalytic Decomposition of 2% Methanol in Methane over Metallic Catalyst by Fixed-Bed Catalytic Reactor //Energies. – 2021. – Т. 14. – №. 8. – С. 2220.