## 3 Results
### Testing of Synthesized CoFe\({}_{2}\)O\({}_{4}\)/PVP Nanocomtite during Phenol Oxidation
When studying the effect of hydrogen peroxide concentration on the rate of phenol oxidation (Table 5), it was found that, with an increase in the concentration of \(\text{H}_{2}\text{O}_{2}\) from 362 mg/L to 1448 mg/L, the reaction rate increases. A further increase leads to a slight increase in the reaction rate, which is explained by an increase in the rate of decomposition of \(\text{H}_{2}\text{O}_{2}\) as a result of side reactions. Carrying out the reaction at a concentration of \(\text{H}_{2}\text{O}_{2}\)  
Figure 6: Typical chromatograms of phenol (**a**), hydroquinone (**b**), and benzoquinone (**c**). Red color indicates peak numbering, green triangles indicate the beginning and end of peaks (for calculating peak area). of 362 mg/L leads to the incomplete conversion of phenol (56-57%) due to an insufficient amount of hydrogen peroxide. Figure 8a shows the conversion curves of phenol oxidation on various catalyst suspensions from 0.01 to 0.1 g. The reaction rate increases in direct proportion with an increase in the amount of catalyst. The directly proportional dependence of the initial oxidation rate on the amount of catalyst (Figure 8b) indicates the course of the reaction in the external kinetic region. With an increase in the amount of catalyst from 0.01 to 0.1 g, the volume of absorbed oxygen increases from the calculated amount. At low catalyst concentrations (0.01 g), there is insufficient oxygen absorption (i.e., below the calculated amount). The analysis of the final sample after the reaction showed that the selective oxidation of phenol occurs, and undesirable by-products are formed at high concentrations (0.08-0.1 g). The overall selectivity and yield of the products are maximal, with a catalyst content of 0.02 g.  
With the increase in the catalyst content, the proportion of hydroquinone in the reaction mass decreases, and the proportion of 1,4 benzoquinone increases. The observed dependence is associated with an increase in the number of active sites on which hydroquinone is reoxidized as it accumulates in the reaction mass. Figure 7: The proposed mechanism of the phenol oxidation process. The effect of phenol concentration on the rate and selectivity of the process was studied at a temperature of 70 \({}^{\circ}\)C and an oxygen pressure of 1.0 MPa. Figure 9 shows the experimental results demonstrating the effect of the initial phenol concentration on the rate of its oxidation with oxygen in the presence of H\({}_{2}\)O\({}_{2}\) on CoFe\({}_{2}\)O\({}_{4}\)/PVP. An increase in the phenol concentration from 0.05 mol/L to 0.3 mol/L increases the initial reaction rate; the optimal phenol concentration was 0.1 mol/L, since the maximum yield of the product (benzoquinone) is achieved at this concentration. This may be due to the fact that the catalytic reaction can be inhibited by a high concentration of the substrate (phenol). With the increase in the concentration of phenol, the oxidation rate increases and the amount of absorbed oxygen increases proportionally in accordance with the stoichiometry of reaction (2):  
\[\mathrm{C_{6}H_{5}OH+O_{2}\to O=C_{6}H_{4}=O+H_{2}O} \tag{2}\]  
The effect of temperature on the rate and selectivity of phenol oxidation was studied at 1.0 MPa in the range of 40-80 \({}^{\circ}\)C. The experiments were carried out with an initial reaction volume of 10 mL, a catalyst sample of 0.02 g, a phenol concentration of 0.01 mol/L, pH 3.5, and H\({}_{2}\)O\({}_{2}\) of 120 \(\mu\)L. The conversion curves of phenol oxidation at different temperatures are shown in Figure 10. With the increase in the reaction temperature from 40 \({}^{\circ}\)C to 70 \({}^{\circ}\)C, the initial rate of formation of products increases, and the growth of the initial rate of formation of 1,4-benzoquinone exceeds the growth of the initial rate of formation of hydroquinone, which indicates a greater acceleration of the secondary oxidation reaction with an increase in temperature, as well as the acceleration of side condensation reactions.