## 3 Results and Discussion
### Thermal Transformations of Model Lignin Compounds on the Surface of CeO\({}_{2}\)
#### 3.2.4 Ferulic Acid  
The results of the TPD MS study of the FA/CeO\({}_{2}\) sample are presented in Figures 11 and 12. According to Figure 11, the main decomposition products were the 3-methoxy-4-vinyl phenol (MVPh) (M.r. = 150 Da, \(m/z\) 150, T\({}_{\rm max}\)\(\approx\)110 and 220 \({}^{\circ}\)C), guaicaol (Mr = 124 Da, \(m/z\) 124, T\({}_{\rm max}\)\(\approx\) 261 \({}^{\circ}\)C), 4-Vinylmethylguaiacol (Mr = 164 Da, \(m/z\) 164, T\({}_{\rm max}\)\(\approx\) 334 \({}^{\circ}\)C) and hydroxybenzene (Mr = 94 Da, \(m/z\) 94, T\({}_{\rm max}\)\(\approx\) 407 \({}^{\circ}\)C). The decomposition of the sample occurred from 55 to 700 \({}^{\circ}\)C (Figure 12A,B). The MVPh was formed as a result of the decarboxylation of FA. The TPD curve of the MVPh molecular ion had two peaks at 110 and 220 \({}^{\circ}\)C (Figure 12C). During the decomposition of FA in the pristine state in the air atmosphere, the release of MVPh was registered at 280 \({}^{\circ}\)C [22]. Conversely, during the TPD MS study, its formation was observed at T\({}_{\rm max}\) 480 \({}^{\circ}\)C [23]. The temperature maximum rate of the MVF formation on the SiO\({}_{2}\) surface corresponded to 400 \({}^{\circ}\)C [50]. Thus, the interaction of FA with the CeO\({}_{2}\) surface led to a significant decrease in the temperature of the MVPh formation. The release of the MVPh at T\({}_{\rm max}\) = 110 \({}^{\circ}\)C may be associated with the decomposition of monodentate carboxylate complexes (Scheme 3) and the destruction of FA associates (Scheme 4), the presence of which was evidenced by the FT-IR spectra of FA/CeO\({}_{2}\). The presence of \begin{table}
\begin{tabular}{c c c c c} \hline
**Sample** & **Stage** & **T\({}_{\rm max}\) (\({}^{\circ}\)C)** & **Volatiles (\%)** & **Char (\%)** \\ \hline VA/CeO\({}_{2}\) & I & 115 & 4.3 & \\ VA/CeO\({}_{2}\) & II & 175 & 10.9 & \\ VA/CeO\({}_{2}\) & III & 265 & 63.0 & \\ VA/CeO\({}_{2}\) & \(\Sigma\)(I + II + III) & & 78.2 & \\ \hline \end{tabular}
\end{table} 
Table 7: Pyrolysis yields for TGA pyrolysis of VA/CeO\({}_{2}\) (0.6 mmol/g). Figure 11: Mass spectra obtained by decomposition of FA/CeO\({}_{2}\) at a temperature of 250 \({}^{\circ}\)C (**A**), 330 \({}^{\circ}\)C (**B**), and 400 \({}^{\circ}\)C (**C**). Figure 12: Thermal decomposition of FA/CeO\({}_{2}\) (0.6 mmol/g); vapor pressure measured as a function of temperature for the FA/CeO\({}_{2}\) sample (**A**); TPD curves for ions with \(m/z\) 18, 24, and 44 (**B**), for ions with \(m/z\) 77, 107, 135, and 150 (**C**) and for ions with \(m/z\) 94, 108, 124, 128, and 164 (**D**). associates was indicated by bands at 1666, 1691 (C = O), 1325 \(\beta\)(COH), and at 949 cm\({}^{-1}\) 8(COH), which were revealed in the IR-spectra of the samples FA/CeO\({}_{2}\) (0.6-1.2 mmol/g) (Figure 4). **Scheme 3. The decomposition of the monodentate carboxylate complexes of FA. **  
The second peak (\(\sim\) 220 \({}^{\circ}\)C) was formed due to the transformation of the bidentate carboxylate complexes (Scheme 5). The second peak (\(\sim\) 220 \({}^{\circ}\)C) was formed due to the transformation of the bidentate carboxylate complexes (Scheme 5), which were detected in the IR spectroscopic study of FA/CeO\({}_{2}\) by the appearance of bands \(\
u\)(COO\({}^{-}\)) at 1405, 1450, and 1502 cm\({}^{-1}\). **Scheme 5. The decomposition of the bidentate carboxylate complexes of FA. **  
Increasing the amount of FA on the oxide surface, the first TPD peak of the MVPh desorption increased compared to the second (Figure 13). In this case, the relative intensity of the absorption band (1608 cm\({}^{-1}\)) corresponding to C = O vibrations of VA molecules, which form monodentate carboxylate complexes, also increased in the IR spectra of FA/CeO\({}_{2}\) (Figure 4). This indicated an increase in the relative amount of these complexes at higher acid concentrations. The destruction of FA complexes formed on the surface of CeO\({}_{2}\) with the participation of aromatic ligands was accompanied by the release of guaiacol (M.r.