## 3 Results and Discussion  
### Textural and Structural Characterization  
The determination of the textural properties (surface area, pore volume, pore size) of CeO\({}_{2}\)/ZnO samples was carried out by means of nitrogen adsorption-desorption (BET) analysis. The results obtained are summarized in Table 1. The lowest value in BET surface area is demonstrated by ZnO (7.05 m\({}^{2}\)/g). CeO\({}_{2}\) nanorods exhibit the highest surface area (79.31 m\({}^{2}\)/g) followed by CeO\({}_{2}\)/ZnO-0.2 (76.22 m\({}^{2}\)/g), CeO\({}_{2}\)/ZnO-0.4 (62.21 m\({}^{2}\)/g), CeO\({}_{2}\)/ZnO-0.6 (56.12 m\({}^{2}\)/g) and ZnO (7.05 m\({}^{2}\)/g). In general, ZnO addition progressively decreases the BET surface area. This is also in agreement with the gradual increase of pore size with the increase of ZnO content, as discussed below. The adsorption-desorption isotherms and the Barrett-Joyner-Halenda (BJH) desorption pore size distribution (PSD) of as-prepared samples are shown in Figure 1a,b, respectively. The pore size distribution in all samples is well within the mesopores region, which is further corroborated by the existence of type IV isotherms (Figure 1a). As presented in Table 1 and Figure 1b, the addition of ZnO leads to an increase in pore volume and average pore size, with the CeO\({}_{2}\)/ZnO-0.6 sample exhibiting the highest pore size (55.9 nm) followed by CeO\({}_{2}\)/ZnO-0.4 (40.6 nm), CeO\({}_{2}\)/ZnO-0.2 (34.4 nm), CeO\({}_{2}\) (24.2 nm) and ZnO (23.0 nm). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**BET Analysis**} \\ \cline{2-4}  & **Surface Area (m\({}^{2}\)/g)** & **Pore Volume (cm\({}^{3}\)/g)** & **Average Pore Size (nm)** \\ \hline CeO\({}_{2}\) & 79.31 \(\pm\) 0.15 & 0.48 & 24.2 \\ CeO\({}_{2}\)/ZnO–0.2 & 76.22 \(\pm\) 0.12 & 0.67 & 34.4 \\ CeO\({}_{2}\)/ZnO–0.4 & 62.21 \(\pm\) 0.11 & 0.65 & 40.6 \\ CeO\({}_{2}\)/ZnO–0.6 & 56.12 \(\pm\) 0.09 & 0.91 & 55.9 \\ ZnO & 7.05 \(\pm\) 0.01 & 0.06 & 23.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Textural characteristics of bare CeO\({}_{2}\), ZnO and the CeO\({}_{2}\)/ZnO samples. Figure 1: (**a**) N\({}_{2}\) adsorption-desorption isotherms and (**b**) pore size distribution of bare CeO\({}_{2}\), ZnO and the CeO\({}_{2}\)/ZnO samples. Figure 2 depicts the XRD patterns of CeO\({}_{2}\), ZnO and CeO\({}_{2}\)/ZnO (Zn:Ce = 0.2, 0.4, 0.6) mixed oxide phases. The main diffraction peaks for bare ceria at 20 = 28.5\({}^{\circ}\), 33.1\({}^{\circ}\), 47.5\({}^{\circ}\) and 56.3\({}^{\circ}\) correspond to (111), (200), (220) and (311) planes, respectively. The diffraction peaks are attributed to ceria face-centered cubic fluorite structure (Fm3m symmetry, no. 225) (JCPDS card: 01-081-0792). Similarly, the XRD patterns of pure ZnO exhibit the typical hexagonal wurtzite structures (P63 mc symmetry, no. 186) (JCPDS card: 01-079-0208). The strong peaks at 20 = 31.7\({}^{\circ}\), 34.4\({}^{\circ}\) and 36.2\({}^{\circ}\) can be attributed to (100), (002), (101) lattice planes, respectively. For the CeO\({}_{2}\)/ZnO samples, reflection planes perfectly matched to both indexed CeO\({}_{2}\) cubic and ZnO hexagonal structures. The XRD patterns indicate the formation of mixed oxides with finely dispersed phases of parent oxides. When ZnO content is increased, the intensity of ZnO reflections at (100), (002) and (101) is also increased, while the XRD profile of CeO\({}_{2}\) remains unaffected. The sharp diffraction peaks in the XRD patterns indicate that the synthesized catalysts are well crystallized. By applying the Scherrer equation, the average crystallite size of the as-prepared samples was calculated and the results are presented in Table 2. The lattice parameters are also included in Table 2. Bare CeO\({}_{2}\) exhibits a crystallite size of 13.0 nm, while pure ZnO exhibits a much larger crystallite size (34.5 nm). For the CeO\({}_{2}\)/ZnO samples, ceria crystallite size displays a small decrease with the addition of ZnO, while the crystallite size of ZnO is increased.