## 5 Conclusions  
The precursor concentration in solvent and the catalyst room temperature aging on the growth morphology and surface characteristics of Ni-NiO nanopowders produced by dendrite combustion during SCS were studied. The TEM results highlighted that the nanocatalysts' microstructures were modified by changing the reactants' concentrations in water. Thus, the concentration of the initial mixture of Ni(NO\({}_{3}\))\({}_{2}\) and glycine in water played a significant role in the nanocatalysts. The dendrites' growth conditions appeared to be the main factor that was responsible for the observed changes in the crystallite size of the samples, as their structure depends on the concentration of nickel nitrate and glycine in the water. Various dendrite structures indicated that the combustion took place in different conditions during SCS, and the heat distribution during cooling was also affected. The IR high-speed camera demonstrated combustion in the dendrites. A new combustion type was discovered: combustion in dendrites. The more developed the structure of dendrites, the lower the combustion temperature, the higher the cooling velocity, and the smaller the crystallites. We studied the size dependence of the conventional exchange bias and anisotropic energy between the Ni-core and NiO-shell nanoparticles. The shell grew at the expense of the Ni-core, forming a passivating layer of NiO as confirmed and estimated by the XPS measurements. By comparing the XPS spectra intensities, it can clearly be seen that by increasingly adding water, the concentration of surface oxidized states increased considerably. The ratio of NiO/Ni\({}_{2}\)O\({}_{3}\) decreased from 4.3 (50 mL of water) to 1.35 (100 mL of water), justifying why nickel catalyst activity in the hydrogenation of maleic acid increased in this row. The reason for the changing activity was that the NiO structure resulted in the bridging of the oxygen structure. These bridging structures can cause problems in adsorption of hydrogen on the catalyst surface and, as a consequence, reduce its activity. Investigations of the reasons for the severe reduction in the catalysts' activity toward the liquid phase hydrogenation of maleic acid during room temperature aging was conducted by studying the hydrogen adsorption phenomena with reversed-flow inverse gas chromatography (RF-IGC). It indicated the existence of three different kinds of active sites corresponding to higher, intermediate, and lower energies of adsorption on the fresh catalyst. Aged catalyst appeared to have only one type of active site because of the change in the composition and structure, as indicated by the XPS and TEM analysis. Aging had an influence on the local monolayer capacities. In the case of fresh catalyst and aged catalyst, the local monolayer changed 2-3 times. Therefore, the monolayer capacity and the time of its maximum was a function of aging time. For the first time, room temperature aging of  
Figure 12: The local adsorption energy of the powdered catalyst samples at 80 \({}^{\circ}\)C and the role of aging on their local adsorption energy. oxide nanomaterials was investigated, as room temperature aging is new phenomenon for catalysts. Due to the increasing attention of researchers toward SCS and other approaches to synthesizing nano-catalysts as well as other nanomaterials, this research will play a significant role in nanomaterial studies.The importance of this work combined with our previous studies [19; 21; 40; 43; 44] is high, as it demonstrates that the severe control of the reaction conditions (such as the concentration of precursors in the solvent, the type of solvent, the solvent pretreatment conditions, preheating temperature, reagents concentration, etc.) provides the possibility of tuning the properties and characteristics of materials produced by SCS even at a large scale. This research will be of great interest for the larger community of scientists who are occupied with nanomaterial synthesis and processing.