## 3 Results and Discussion
### Effects of SO\({}_{2}\) and H\({}_{2}\)O on NO Removal Activity
#### 3.3.2 Xps  
XPS experiments were performed to investigate the surface component and chemical state change of elements over the fresh and sulfated catalysts. The surface atomic concentrations of Mn, Ce, O, and S are summarized in Table 1, and the photoelectron spectra of the Mn 2p, Ce 3d, O 1s, and S 2p levels are displayed in Figure 7.  
Figure 5: N2 adsorption–desorption isotherms and Barrett-Joyner-Halenda (BJH) pore size distribution of Mn–Ce/Al2O3 before (F) and after (S) poisoning by SO2. Figure 6: X-ray diffraction (XRD) patterns of Mn–Ce/Al2O3 before (F) and after (S) poisoning by SO2. The Mn 2p XPS spectra of the fresh and sulphated Mn-Ce/Al2O3 samples are shown in Figure 7a. Two peaks, due to Mn 2p\({}_{1/2}\) and Mn 2p\({}_{3/2}\), were observed from 637.0 eV to 662.5 eV, which are characteristic of a mixed-manganese system (Mn\({}^{2+}\), Mn\({}^{3+}\), and Mn\({}^{4+}\)) [28]. The Mn 2p XPS spectra of the F-Mn-Ce/Al2O3 could be classified into six subpeaks: Mn\({}^{2+}\) (641.6 and 652.1 eV), Mn\({}^{3+}\) (643.1 and 653.9 eV), and Mn\({}^{4+}\) (644.2 and 655.1 eV) [29], indicating that Mn\({}^{2+}\), Mn\({}^{3+}\), and Mn\({}^{4+}\) co-exist on the surface of the catalysts. Compared with F-Mn-Ce/Al2O3, the Mn 2p peak for the poisoned S-Mn-Ce/Al2O3 slightly shifted to a higher binding energy (0.2-0.5 eV higher), which may be attributed to the formation of species other than manganese oxides for Mn-Ce/Al2O3, which could occur when catalysts are sulfated, shifting them to a higher binding energy [30]. Here, the binding energies were shifted higher during the SCR reaction in the presence of SO2, which means that the Mn species on the surface of the Mn-Ce/Al2O3 catalyst were less active, thus resulting in performance degradation. In addition, [PERSON] et al. [31] demonstrated that Mn\({}^{4+}\) has a better redox ability than Mn\({}^{2+}\)and Mn\({}^{3+}\) over the spectrum of manganese-based catalysts. For the two samples, the ratio Mn\({}^{4+}\)/(Mn\({}^{2+}\)+Mn\({}^{3+}\)+Mn\({}^{4+}\)) can be calculated from the characteristic peaks intensities of Mn\({}^{2+}\), Mn\({}^{3+}\), and Mn\({}^{4+}\). The ratio of Mn\({}^{4+}\)/(Mn\({}^{2+}\)+Mn\({}^{3+}\)+Mn\({}^{4+}\)) decreased by 8.86% for F-Mn-Ce/Al2O3 and S-Mn-Ce/Al2O3. Therefore, the decreased concentration of Mn\({}^{4+}\) can also reflect the reason for the activity decrease. The complicated Ce 3d XPS spectra of the fresh and sulphated Mn-Ce/Al2O3 catalyst are presented in Figure 7b. The bands labelled u and v are representative of the 3d\({}_{3/2}\) spin-orbit states \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & \multicolumn{4}{c}{**Atomic Concentration (at \%)**} & \multicolumn{4}{c}{**Surface Atomic Ratio (\%)**} \\ \cline{2-9}  & **Mn** & **Ce** & **O** & **S** & **Ce\({}^{3+}\)/(Ce\({}^{3+}\) + Ce\({}^{4+}\))** & **Mn\({}^{4+}\)/(Mn\({}^{2+}\) + Mn\({}^{3+}\) + Mn\({}^{4+}\))** & **O\({}^{\prime}\)/O\({}^{\prime}\) + O\({}^{\prime\prime}\)** \\ \hline F-Mn-Ce/Al2O3 & 7.31 & 2.49 & 55.21 & 0 & 11.6 & 35.6 & 15.8 \\ S-Mn-Ce/Al2O3 & 4.05 & 1.99 & 66.75 & 3.01 & 12.7 & 26.74 & 30.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Surface atomic distributions of the catalysts by X-ray photoelectron spectroscopy (XPS). Figure 7: X-ray photoelectron spectroscopy (XPS) spectra of the catalysts before and after 24 h of an SO2-containing reaction at 100 \({}^{\circ}\)C. (**a**) Mn 2p; (**b**) Ce 3d; (**c**) O 1s; and (**d**) S 2p. and 3d\({}_{5/2}\) states, respectively. The peaks assigned u\({}^{\prime}\) and v\({}^{\prime}\) are representative of the 3d\({}^{10}\)4f\({}^{1}\) electronic state of Ce\({}^{3+}\) ions, while u, u\({}^{\prime\prime}\), u\({}^{\prime\prime\prime}\) and v, v\({}^{\prime\prime}\), v\({}^{\prime\prime\prime}\) are attributed to the 3d\({}^{10}\)4f\({}^{0}\) state of the Ce\({}^{4+}\) species [32; 33]. The intensities of the Ce\({}^{3+}\) peaks slightly increased after the SCR reaction in the presence of SO\({}_{2}\).