## 1 Introduction  
The synthesis of nanosized metals, as well as their oxides and hydroxides, in different highly porous matrices and the study of their physicochemical properties are important issues in modern nanomaterials science. Since these nanostructured composites (NC) possess unique catalytic, magnetic and electrode features, they outperform macroscopic metal powders and their compounds in many aspects. The use of highly porous matrices for the synthesis of such NC allows one to overcome two important problems in the use of metal nanoparticles. Firstly, a highly developed surface of these particles makes them more chemically active in comparison to macroscopic materials, which leads to their complete or partial oxidation. Secondly, metal nano-powders undergo processes of spontaneous agglomeration, which leads to the loss of some unique physicochemical properties and complicates their further application. The composites which use transition metals, their oxides or hydroxides as the active substances, are widely used as catalysts, devices for recording and storing information, active materials for supercapacitor electrodes and magnetically sensitive adsorbents [1, 2, 3, 4, 5, 6, 7, 8]. A relatively simple approach to obtain highly porous metal/carbon composites is the method based on metal ions reduction from solutions of their salts in a carbon matrix. The first important factor to take into account is the accessibility of the carbon material surface for ions, as well as the chemical composition of the surface groups. For example, it was shown in [9] that different surface groups had different effects on the reduction of palladium. Therefore, by modifying the surface of the carbon matrix, for example, by treating it with acids, it is possible to increase the reducing properties of the matrix for the synthesis of NC metals [10; 11]. However, this method is suitable mainly for noble metals. For transition metals, more complex conditions are required: high temperatures, complex solvents, the presence of excipients, for example, sodium acetate [12]. Another method traditionally used to produce carbon materials is pyrolysis. Encapsulated nanoparticles of metals and their alloys can be obtained using pyrolysis. In [13], nanoparticles of NiFe solid solution, 10-20 nm in diameter, covered with a thin carbon shell approximately 6 nm thick, were obtained by Na\({}_{2}\)Fe(CN)\({}_{5}\)NO and Ni(NO\({}_{3}\))\({}_{2}\) pyrolysis on the surface of gamma-aluminum. The pyrolysis can be combined with detonation technology, as demonstrated in [14]. To that end, the authors used a mixture of picric acid (2,4,6-trintirophenol) and ferrocene, which was placed in a closed vessel and heated to 290 \({}^{\circ}\)C. At this temperature, the acid explosion occurred, which led to an increase in pressure up to 40 MPa and temperature up to 1000 \({}^{\circ}\)C. Such conditions caused the decomposition of ferrocene and formation of encapsulated 5-20 nm iron nanoparticles. The carbon nanotubes with a diameter of 40-100 nm also formed in the process of detonation. Their amount depended on the acid/ferrocene ratio. Notwithstanding the significant advances in the synthesis of transition metals NC, many scientists are looking for technologically simpler, cheaper and, most importantly, environmentally friendly ways to obtain NC with high performance characteristics. To achieve this goal, various natural materials [15; 16], ready-made porous carbon materials [17], metal foams [18] or polymer matrices [19] are used as substrates. It has been established that the properties of the obtained NC largely depend on the properties of the matrix used and the synthesis method; therefore, it is extremely important to study the structure and properties of NC according to the conditions for their preparation.