## 3 Results and Discussion
### FT-IR Spectroscopic Studies
#### 3.1.1 Pyrocatech
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Frequency (cm\({}^{-1}\))**} \\
**Assignments** & **P** & **P/CeO\({}_{2}\)** & **Ref.** \\ \hline \(\beta\)(CH) & 721 & – & [53] \\ \(\beta\)(CH) & 937 & – & [53] \\ \(\delta\)(OH) + \(\delta\)(CH)) & 756 & – & [53] \\ \(\
u\)(CC) + \(\
u\)(CO) + \(\
u\)(CC) + \(\beta\)(CCH) & 1167 & – & [53] \\ \(\beta\)(CCH) + \(\
u\)(CC) + \(\beta\)(COH) & 1188 & 1188 & [51; 53] \\ \(\beta\)(CCH) + \(\beta\)(COH) + \(\
u\)(CC) & 1242 & – & [53] \\ \(\beta\)(CCH) + \(\beta\)(COH) + \(\
u\)(CC) & 1255 & 1261 & [51; 53] \\ \(\
u\)(CC) + \(\
u\)(CO) + \(\beta\)(CCC) & 1281 & – & [51; 53] \\ \(\beta\)(CCH) + \(\beta\)(COH) + \(\
u\)(CC) & 1363 & 1361 & [53] \\ \(\beta\)(COH) + \(\
u\)(CO) & – & 1273 * & \\ \(\
u\)(CO) & – & 1297 & \\ \(\beta\)(CCH) + \(\
u\)(CC) + \(\beta\)(COH) + \(\beta\)(CCO) & 1440 & 1446 & [53] \\ \(\
u\)(CC) + \(\beta\)(CH) & 1471 & – & [53] \\ \(\
u\)(CC) + \(\beta\)(CH) & – & 1483 & \\ \(\
u\)(CC) + \(\beta\)(CH) & 1514 & 1514 * & [53] \\ \(\
u\)(CC) + \(\beta\)(CH) & – & 1576 & \\ \(\
u\)(CC) + \(\beta\)(CH) & 1603 & 1603 * & [53] \\ \(\
u\)(CC) + \(\beta\)(CH) & 1620 & – & [53] \\ \hline \hline \end{tabular}
* band appears for P concentrations \(>\) 0.6 mmol/g.  
\end{table} 
Table 1: Assignments of infrared bands of pure P and of P/CeO\({}_{2}\) (0.6 mmol/g). At the same time, all P/CeO\({}_{2}\) spectra contained a new band at 1297 cm\({}^{-1}\), which may indicate the formation of a bond between pyrocatechol and CeO\({}_{2}\). It is known that the new bands found in this area by the interaction of phenol and phenolic compounds with metal surfaces, as well as surfaces of oxides and hydroxides of metals [54; 55; 56; 57; 58], were signs of the formation of new bonds. The binding of P to the oxide surface significantly affected the absorption of its aromatic ring, which manifested in the displacement of the absorption bands of P and changes in their intensity. In particular, for pure P, the vibration band \(\
u\) (CC) was registered at 1471, 1514, 1603, and 1620 cm\({}^{-1}\)[53], while in the P/CeO\({}_{2}\) spectrum, the corresponding absorptions were registered at 1446, 1483, and 1576 cm\({}^{-1}\). Bands characteristic of pure P (1471, 1514, 1603, and 1620 cm\({}^{-1}\)) also appeared in the spectra of P/CeO\({}_{2}\) samples with a P concentration above 0.6 mmol/g (Figure 1). This is probably because the amount of P exceeds the number of active centers of the CeO\({}_{2}\) surface. The obtained results indicate the formation of chemisorbed pyrocatechol complexes on the CeO\({}_{2}\) surface. The P/CeO\({}_{2}\) spectrum (Figure 1) is similar to the IR spectra of pyrocatechol adsorbed on the nanosized TiO\({}_{2}\) surface [59; 60; 51; 61]. According to the results of quantum chemical calculations [61] and experimental data [51; 56; 60; 61], this type of spectra of P adsorbed on TiO\({}_{2}\), in which the bands 1250 cm\({}^{-1}\) and 1475 cm\({}^{-1}\) are the most intense, is more characteristic of complexes with a bidentate bridge structure. Since the most intense absorptions in the P/CeO\({}_{2}\) spectrum correspond to the bands 1263 and 1483 cm\({}^{-1}\) (Figure 1), it is probable that the P complexes on the CeO\({}_{2}\) surface also have a bidentate bridge structure (two oxide atoms of phenolic groups of P interact with two metal atoms).