## 1 Introduction  
The containment of climate change requires developing a hydrogen economy, which needs sources of large amounts of hydrogen [1]. One of the possible methods for large-scale production of low-carbon hydrogen is the pyrolysis of methane (natural gas), also known as the thermal decomposition of methane, which has been actively studied in recent years [2; 3; 4; 5]. The decomposition of methane is a moderately endothermic process. If a catalyst is not used, a temperature of about 1100 \({}^{\circ}\)C or higher is required to achieve a reasonable yield [6]. The temperature of the process can be significantly reduced by using a catalyst [7]. Methane pyrolysis is described by the following equation:  
\[CH_{4}(\mathrm{g})\;\rightarrow\;2H_{2}(\mathrm{g})+C(s)\;\Delta H=75.6\;\mathrm{ kJ\;mol^{-1}}\]  
In [5], the following two equations were provided, showing the mass and energy on both sides of the equation:  
Mass: 1000 kg \(CH_{4}\)\(\rightarrow\) 250 kg \(H_{2}+750\) kg \(C\)  
Energy: \(50,000\;\mathrm{MJ}+\Delta H-\to 30,000\;\mathrm{MJ}+24,600\;\mathrm{MJ}\),  
where \(\Delta\)H = 4600 MJ. In terms of mass balance, the main product of this reaction is carbon, which accounts for 75% of the total mass. The process of methane pyrolysis is carried out in three different ways: non-catalytic thermal decomposition, catalytic decomposition, and plasma-chemical decomposition. All works in the literature can be divided into these three areas. For the thermal non-catalytic decomposition of methane, methods are used that involve passing it through molten metal elements or alloys. Metals (Ti, Sn, Ga, Pb), molten alloys (Ni-Bi, Cu-Bi), or molten salts (KBr, NaBr, NaCl, NaF, MnCl\({}_{2}\), KCl) are used as molten media [8; 9; 10; 11; 12; 13; 14]. The main advantage of such systems is the simple separation of the solid products and the gas stream, followed by the removal of solid products from the system. The disadvantages of this method include the difficulty of maintaining a high temperature in the melt's volume and clogging of the working volume with a carbon-containing product. Another way to decompose hydrocarbons is to use plasma processes, which have several advantages compared to thermal processes: high carbon and hydrogen yield, high degree of methane conversion, small reactor size, and relatively low energy costs [15; 16]. A wide range of hydrocarbon gases can be used in plasma processes. However, at present, the use of such a method in industry is too expensive [16]. A large number of research works are observed today in the direction of the catalytic decomposition of methane. Numerous metal catalysts have been studied in the process of thermal decomposition of methane. In recent decades, many experimental studies have been carried out using metallic, especially transition metals (Ni, Fe, Co, Cu, etc.) [17; 18; 19; 20; 21] and carbon catalysts [22; 23; 24; 25] to reduce the energy of activation. Such catalysts as Co/Mo/Al\({}_{2}\)O\({}_{3}\), Ni-Cu/SiO\({}_{2}\), Ni-Cu/Al\({}_{2}\)O\({}_{3}\), Mo-Fe/Al\({}_{2}\)O\({}_{3}\), Ni- and Fe/Al\({}_{2}\)O\({}_{3}\) are of great interest, as they exhibit high catalytic activity and stability [26; 27; 28; 29; 30]. Although some of these catalysts have good catalytic activity, they are often deactivated during the pyrolysis process. Some metals are quite expensive, and regeneration to the initial activity of the catalyst is practically impossible due to the deformation of the catalyst surface and the porous structure [31]. Although carbon-containing catalysts theoretically do not require regeneration, their catalytic activity also decreases after several hours of operation [32]. The use of catalysts allows the decomposition temperature to be decreased. However, such problems as carbon deposition on the surface of catalysts (both metal and carbon) and the need for catalyst regeneration do not allow us to comment on the large-scale use of this method. Instead of catalysts for the decomposition of methane, capillary tubes could be used.