Study of kinetical laws of process of the catalytic synthesis of nanocarbon from methane

Absract . In the study, the kinetic laws of the process of catalytic synthesis of nanoglyceum from methane were studied in the presence of a catalyst containing Fe 2 (MoO 4 ) 3 *MoO 3 /HSZ. The catalyst containing Fe 2 (MoO 4 ) 3 *MoO 3 /HSZ was prepared by hydrothermal processing. An Empyrean, Malvern Panalytical (Germany) X-ray Diffractometer (XRD) equipped with a modern computer was used to perform X-ray analysis of the samples. The phase composition of the nanocarbon was analyzed using a semi-quantitative method using X-ray diffractograms. The morphology and structure of the product using electron illumination microscopy (accelerating voltage of 40 to 120 kV, cathode-tungsten) in a microscope brand JEM-1400 (JEOL, Japan), were also examined using a scanning electron microscope brand JSM-7001F (JEOL). At a linear velocity of 20 cm/min of gas and a mass of 10 mg of catalyst, the effect of temperature on the synthesis of nanocarbons in the Fe 2 (MoO 4 ) 3 *MoO 3 catalyst was investigated. The work aims to study the kinetic laws of the process of catalytic synthesis of nanocarbon from methane and some characteristics of the resulting product and catalyst.


Introduction
To date, there has been a growing demand for effective, environmentally safe adsorbents in various sectors of the economy, including machinery and technology, including pharmaceuticals, petroleum, cosmetology, oil, and gas refining industries [1][2][3][4][5]. In addition, the properties of the obtained products and the nature of the surface centers of the catalysts have been studied in several studies [6][7][8]. Previous studies using a series of experiments [9,10] also performed the catalyst-based synthesis of nanocarbon from methane using Fe2(MoO4)3*MoO3/HSZ in previous studies using a series of experiments.
It is necessary to use some new methods for the catalytic synthesis of methane using catalysts consisting of Fe/Mo. Whichever of them shows the most effective, high effect, these methods are selected and applied in practice [11][12][13][14].The activity of catalysts was examined for a diluted 6% methane-nitrogen mixture in a tubular reactor at different temperatures between 600 °C and 800 °C under atmospheric pressure [15][16][17].
The catalytic methane decomposition to produce carbon oxides-free hydrogen and carbon nanomaterial is a promising method feasible for larger production at a moderately cheap price [18][19][20][21][22][23][24]. The produced hydrogen is refined and can be employed straight in fuel cells and in petrochemical industries to produce ammonia and methanol. Auto-thermal reforming of natural gas, partial oxidation, and steam reforming is the conventional techniques for hydrogen production in industry, though these processes incur excessive costs for the purification of hydrogen from producing carbon oxides [25]. Current research work on thermo-catalytic methane decomposition has concentrated on promoting the catalytic activity and stability for the simultaneous production of pure hydrogen and elemental carbon. The carbon is generated as nanotubes, which are important for the use of this material in numerous new technologies. In the present review, the thermodynamics of methane catalytic decomposition are elaborated, and extensive considerations are given to the development of catalyst components by emphasizing the role of active particles, the effect of catalyst promoters, and support [26,27].

Experimental part
The process of nanocarbon synthesis depends on many factors. The kinetic laws ofcatalytic and the process of nanocarbonsynthesis from methane were studied in the device shown in Fig. 1 below. The main element of the device has an inner diameter of 45 mm and a length of 600 mm and is filled with a nozzle of 100 mm to heat the delivered gas mixture evenly, while the bottom side is a nickel reactor (1) equipped with a nozzle (4) for gas injection. A catalyst (~ 15 mg) is placed in the central part of the reactor (3). During the process, the change in mass was checked against the parameters of the torsion balance (2) and attached to (3). The reactor was heated by an electric furnace, the temperature of which was controlled by an autotransformer (7). Temperature control in the reactor was performed using a chromelalumel alloy thermocouple (8) and a millivoltmeter (9) located inside the reactor. Gas and argon (17) from the natural gas network (16) were used to create a gaseous environment in the reactor. The delivery of gases to the reactor was done by taps (10,11). Gas consumption was determined using rotameters (12,13) and monitored with manometers (5,6). A reducer (15) was used to control the gas pressure in the cylinder.
Catalyst and nanometer particles obtained from methane are placed in the reactor operating in periodic modе. The hydrogen or nitrogen-hydrogen mixture was heated to a required temperature of 20 о С in a stream and kept at this temperature for various periods. After a certain time, the stopwatch and torsion balance readings were recorded. At the end of the process, the reactor was cooled in a methane stream. The resulting product was weighed on an analytical balance and washed from the catalyst with a 10% nitric acid solution at 60℃ for 4 hours. The product removed from the catalyst was washed with distilled water to remove nitric acid residues. The product quantity was determined by weighing the samples before and after the experiment. All samples were identified by the following relationship, characterized by the specific yield of nanocarbon: Where Xnanocarbon is the specific yield of nanocarbon, g/gcat; minitial -sample mass before the start of the experiment, g; minitialis the mass of the sample at the end of the experiment, g.
An Empyrean, Malvern Panalytical (Germany) X-ray Diffractometer (XRD) equipped with a modern computer was used to perform X-ray analysis of the samples. This method allows the detection of individual components from the composition of highly complex mixtures, when combined with diffractometer systems, phase analysis programs (e.g. High Score).
Quantitative and qualitative analysis of phases: CuKa-radiation (b-filter, Cu, the current made of 1.5406 A° and voltage applied to the tube at 30 mA and 30 kV, respectively) to study the phase composition of nanocarbon, 4°/ min with a step of 0.02° of the detector, at a constant speed of rotation (correlation ō / 2nd) was applied. The scan angle was changed from 0 ° to 90°. A rotating camera was used to record the experiments, with a rotational speed of 30 rpm. The phase composition of the nanocarbon was analyzed using a semi-quantitative method using X-ray diffractograms. The morphology and structure of the product were studied under a microscope brand JEM-1400 (JEOL, Japan) using electron illumination microscopy (accelerating voltage-40 to 120 kV, cathode-tungsten), as well as using a scanning electron microscope brand JSM-7001F (JEOL) [28][29].The specific surface area of the samples was determined by the thermal desorption method of nitrogen.

Results and discussion
The influence of gas flow rate, catalyst height, temperature, and other factors on the nanocarbon yield obtained from methane in the presence of Fe2(MoO4)3*MoO3catalyst was studied.
Experimental studies were performed at a temperature of 700 and a linear velocity of 90 cm/min with methane with a mass catalyst of 0.45 g. An increase in the processing time leads to an increase in the specific yield of the solid product and stops after 180-200 minutes (Table  1). The size of the resulting product is 15-60 nm and the degree of purity is 96%. The microimage of the synthesized product obtained using an electron microscope brand JEM-1400 (JEOL, Japan) is shown in Fig.2. According to the micro-images, the size of the nanoparticles is 15-60 nm and the degree of purity is 96%. This means that the product was detected using a very accurate and highquality electron microscope. The Fe2(MoO4)3*MoO3) catalyst with a mass of 0.45 g was obtained during the process at a high enough gas flow rate and temperature to produce a product with such a clear image.
Experimental data on the effect of catalyst height on product-specific yield is given in Table2. The experiments were performed at a temperature of 700℃ and a linear velocity of 90 cm/min for 80 min.  Table 2 above illustrates the effect of catalyst layer thickness on product-specific yield. With the increase in the mass of the catalyst Fe2(MoO4)3*MoO3in the reactor, we can see that the height of the catalyst and the product yield also increased significantly. This indicates that the product yield is directly proportional to the mass of the catalyst. As the mass decreases in the direction of methane flow in the reactor, we can see that the product yield changes randomly.
The effect of the linear velocity of methane delivery on the rate of nanoglycerate synthesis was evaluated at a height above 1 mm of the catalyst, in the range of 35-70 cm/min at process temperatures of 700 and 800℃. The results of the measurements are given in Table 3. The above data describe the time taken for the Fe2(MoO4)3*MoO3catalyst to achieve a specific yield of 15 g/g at different linear velocities through two different experiments. In experiment №1, we can see that the more time the methane in the gas stream increases, the less time is spent, that is, the velocity is inversely proportional to time. Experiment №2 shows the opposite.
At a linear velocity of 20 cm/min of gas and a mass of 10 mg of catalyst, the effect of temperature on the synthesis of nanocarbons in Fe2(MoO4)3*MoO3catalyst was investigated. The measured temperatures were 600, 650, and 700 ℃. The results of these measurements are presented in Table 4. In Table 4, we can see the formation of nanocarbon at different temperatures in the Fe2(MoO4)3*MoO3catalyst. These experiments, performed at the average gas flow rate, also show that the specific gravity of carbon at a given (stable) temperature increases over time. The experiments were performed at different temperatures, which did not differ much from each other. The relative mass of the obtained product also does not differ significantly from each other (Fig. 3). When the microphotographs of Fe2(MoO4)3 and Fe2 (MoO4)3*MoO3fired at 600 o C are compared, it is clear that the second microphotograph shows a small and dense catalytic active catalyst. This is because its surface area is much larger and more active than in the first microphotograph. The Fe2(MoO4)3*MoO3 catalyst helps to synthesize a product of industrial importance (Fig.4).   Fig. 4. TEM images of the nanocarbon produced and the corresponding diameter distribution, a) 600 °C and b) 550 °C. A total of 75 nanocarbons were produced. nano-carbon were considered to construct a diameter distribution histogram. ImageJ software was used to measure the diameter.
In the picture above, a TEM image of a nanocarbon synthesized using different temperatures is given. It shows two images of nanocarbon at 100 nm and compares histograms obtained using the ImageJ program to distribute the diameters (nm) of 75 nanocarbons. The diameters in both histograms increased first and then decreased. From this, we can understand that the process of realization of the process is similar, but we can see certain stability at high temperatures (Fig. 5). It is known that the formation of an active and stable catalyst affects its active surface morphology, phase, and chemical composition. Therefore, the element composition, phase composition, X-ray diffractometry (XRD), and scanning electron microscopy (SEM) of the synthesized catalysts were evaluated to study the effect of the carrier on the nature of the catalyst.

1.
A catalyst containing Fe2(MoO4)3*MoO3/HSZ was prepared by hydrothermal processing. The catalytic synthesis of nanocarbon from methane and the kinetic laws of the process were studied using an experimental device. 2. In the presence of the catalyst Fe2 (MoO4)3*MoO3the effects of gas flow rate, the height of the catalyst, temperature, and other factors on the nanocarbon yield obtained from methane were studied. 3. The size of the obtained product is 15-60 nm and the degree of purity is 96%. A microimage of the synthesized product, obtained using an electron microscope brand JEM-1400 (JEOL, Japan), was presented. 4. To study the effect of the carrier on the nature of the catalyst, the element composition, phase composition, X-ray diffractometry (XRD), and scanning electron microscopy (SEM) of the synthesized catalysts were evaluated.