## 1 Introduction
The yield of propyl-cyclohexane was 83%, and propyl-cyclohexanol was \(<\) 1%. In this case, the catalyst worked effectively both in the presence of water and in anhydrous conditions [37]. Catalytic systems composed of both CeO\({}_{2}\) and ZrO\({}_{2}\) have proven their effectiveness [16; 35; 38; 43]. They have many advantages over the individual oxides [35]. In particular, the combination of CeO\({}_{2}\) and ZrO\({}_{2}\) promotes a decrease in the required surface temperature and reduction volume as well as an increase in the number of oxygen vacancies. Such catalytic systems dissociate hydrogen and create oxygen vacancies under mild conditions. The inclusion of zirconium ions in the cerium lattice leads to structural compression and promotes the formation of oxygen vacancies. In addition, the presence of zirconium partially suppresses crystallization during the synthesis of catalysts and leads to the formation of small and active crystallites [35]. Using a CeO\({}_{2}\)/ZrO\({}_{2}\) catalyst for the hydrodeoxygation of guaiacol [35], valuable products such as phenol, catechol, and benzene were obtained. In addition, the use of this catalytic system increased the conversion efficiency of guaiacol and eliminated the formation of the undesirable oligomeric products containing hydrogenated rings. Moreover, these catalysts showed no signs of deactivation after 72 h of flow [35]. The efficiency of CeO\({}_{2}\), CeO\({}_{2}\)-ZrO\({}_{2}\), Ni/CeO\({}_{2}\), and Ni/CeO\({}_{2}\)-ZrO\({}_{2}\) catalysts for hydrodeoxygation of phenol at intermediate temperature and pressure (275 \({}^{\circ}\)C and 100 bar) in a batch reactor was tested in [43]. Oxide catalysts (CeO\({}_{2}\), CeO\({}_{2}\)/ZrO\({}_{2}\)) showed low activity on the hydrodeoxygation of phenol under these conditions due to their inability to hydrogenate the phenolic ring [43]. Reduced metal catalysts for both noble and base metals were significantly more active. Hydrodeoxygation of phenol proceeded through initial hydrogenation to cyclohexanone, which rapidly hydrogenates to cyclohexanol [43]. Ni/CeO\({}_{2}\) and Ni/CeO\({}_{2}\)-ZrO\({}_{2}\) were the most active catalysts for the initial hydrogenation of phenol to cyclohexanol but were insufficiently active in the next stage of deoxygenation [43]. Catalysts CeO\({}_{2}\), ZrO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), CeO\({}_{2}\)-SiO\({}_{2}\), and CeO\({}_{2}\)-ZrO\({}_{2}\) were used in the ketonization of valeric acid into 5-nonanone, [44; 45; 46] and various fatty acids (C\({}_{2}\)-C\({}_{10}\), D\({}_{6}\)CCOOH, and CH\({}_{3}\)COOH) into symmetric ketones [46]. The majority of the studied acids [46], especially valeric, acetic, levulinic, furandicarboxylic, and other acids, can be obtained by converting lignocellulosic biomass [47]. Conversely, lignin is a source for a number of natural cinnamic acids [1; 48]. In [38], the activity and surface properties based on oxides of CeO\({}_{2}\) and ZrO\({}_{2}\) coated with nickel (Ni/CeO\({}_{2}\)-ZrO\({}_{2}\)) were used in the thermochemical conversion of cellulose. The catalyst Ni/CeO\({}_{2}\)-ZrO\({}_{2}\) was effective in producing hydrogen during the conversion of cellulose raw materials. The presence of cerium oxide in such catalytic systems contributed to a slower decrease in their activity versus Ni/ZrO\({}_{2}\). It has been shown [38] that the tested catalysts allow the efficient formation of a gaseous fraction [38]. At the same time, in studies [16], Ni/CeO\({}_{2}\)-ZrO\({}_{2}\) catalytic systems were used for lignin conversion. The main phenolic compounds in the obtained lignin oil were: guaiaicol, methylguaiaicol, ethylguaiaicol, vanillin, and homovanillic acid [16]. However, the exact mechanisms of the transformations that occurred remain unclear. In this work, we examined thermal transformations of several aromatic model compounds of lignin (guaiacol, pyrocatechol, vanillic acid, and ferulic acid) over the nanoceria catalyst.