## 3 Results and Discussion
### Thermal Transformations of Model Lignin Compounds on the Surface of CeO\({}_{2}\)
#### 3.2.4 Ferulic Acid
= 124 Da, \(m/z\) 124) (Scheme 6) and hydroxybenzene (M.r. = 94 Da, \(m/z\) 94) (Figure 12D). The participation in the interaction with the oxide of both active groups of the aromatic ring was confirmed by the obtained data of FTIR spectroscopy, presented in Figure 4. The thermal transformation of FA molecules bound to the oxide surface through the OCH\({}_{3}\) group occurred with the formation of guaiacol (M.r. = 124 Da, \(m/z\) 124, T\({}_{\rm max}\)\(\approx\)265 \({}^{\circ}\)C). FA complexes formed due to the simultaneous interaction of OH and OCH\({}_{3}\) groups of the aromatic ring with the CeO\({}_{2}\) surface being destroyed at about 400 \({}^{\circ}\)C (Scheme 7). As a result, hydroxybenzene was formed (M.r. = 94 Da, \(m/z\) 94, T\({}_{\rm max}\)\(\approx\)407 \({}^{\circ}\)C) (Figure 12D). In the same way, similar complexes of caffeic acid decomposed on the CeO\({}_{2}\) surface [79]. Figure 13: TPD-curves for the ion with \(m/z\) 150 (3-methoxy-4-vinilphenol), obtained by thermal decomposition of samples of FA/CeO\({}_{2}\) (a: 0.6 mmol/g, b: 0.9 mmol/g, c: 1.2 mmol/g). At higher temperatures, desorption of aromatic products such as naphthalene (\(m/z\) 128, T\({}_{\text{max}}\approx\) 430 \({}^{\circ}\)C) was detected (Figure 12D). However, the intensity of their release was low. The formation of polyaromatic products was also detected during the pyrolysis of caffe and fertile acids and a number of coumarins on the surfaces of nanoscale oxides ([PERSON] _et al._, 2016; [PERSON] _et al._, 2016; [PERSON] _et al._, 2016). However, the decomposition of cinnamic acid on the SiO\({}_{2}\) surface did not reveal such products ([PERSON] _et al._, 2016). Therefore, their formation was seemingly due to the transformation of complexes bound to the oxide through the active groups of the aromatic ring. In accordance with DTG/DTA/TG data obtained by pyrolysis of the FA/CeO\({}_{2}\) sample (Figure 15), the decomposition of FA occurred in the temperature range of 100 to 500 \({}^{\circ}\)C in four stages. All stages were exothermic. The maximum weight loss corresponded to the third stage (\(\sim\)259 \({}^{\circ}\)C) (Table 8). 2.5 Kinetic Parameters of the Catalytic Reactions of Vanillic and Ferulic Acids during Pyrolysis over Nanoceria Catalyst  
The kinetic parameters of the formation of the main products during VA and FA catalytic pyrolysis were calculated in this study (Table 9). Based on calculated negative values of activation entropy, the formation processes of phenol, guaiacol, cresol, and methylated 4-vinylguaiacols run through highly ordered cyclic transition states on the nanoceria surface. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **Stage** & **T\({}_{\text{max}}\) (\({}^{\circ}\)C)** & **Volatiles (\%)** & **Char (\%)** \\ \hline \multirow{6}{*}{FA/CeO\({}_{2}\)} & I & 120 & 7.7 & \\  & II & 158 & 11.5 & \\ \cline{1-1}  & III & 219 & 23.0 & 12.6 \\ \cline{1-1}  & IV & 259 & 45.2 & \\ \cline{1-1}  & \(\Sigma\)(I–IV) & & 87.4 & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Pyrolysis yields for TGA pyrolysis of FA/CeO\({}_{2}\) (0.6 mmol/g). Figure 15: Differential thermal analysis (DTA), differential thermogravimetric analysis (DTG), and thermogravimetric (TG) curves for FA/CeO\({}_{2}\).