# Effect of Zr Modification on NH\({}_{3}\)-SCR Reaction Performance of Cu-Ce/SAPO-34 Catalysts
## 3 Results and Discussion
### XPS  
Figures 10-12 show the XPS spectra of Cu 2p, Ce 3d, and Zr 3d of 4 Cu-4 Ce/SAPO-34 and 4 Cu-4 Ce-4 Zr/SAPO-34 catalysts, respectively, in which the surface valence structure of the catalyst and the influence of Zr doping on the catalyst were analyzed. Figure 10: Cu 2p XPS spectra of 4 Cu-4 Ce/SAPO-34 and 4 Cu-4 Ce-4 Zr/SAPO-34. Figure 9: In situ DRIFTS of NH\({}_{3}\) reacting with pre-adsorbed NO+O\({}_{2}\) over the 4 Cu-4 Ce-4 Zr/SAPO-34 catalyst. There were two characteristic peaks of Cu 2p\({}_{3/2}\) and Cu 2p\({}_{1/2}\) orbits in the Cu 2p spectrum of 4 Cu-4 Ce/SAPO-34, as shown in Figure 10. According to the reference [38,39], Cu 2p\({}_{3/2}\) can be resolved into two characteristic peaks. The characteristic peak with a binding energy of 933.3 eV was due to Cu\({}^{+}\), and the characteristic peak with a binding energy of 935.7 eV was due to Cu\({}^{2+}\). Similarly, the characteristic peak with a binding energy of 953.6 eV at Cu 2p\({}_{1/2}\) was classified as Cu\({}^{+}\), and the satellite peak with a binding energy of 943.1 eV was classified as Cu\({}^{2+}\). After doping with Zr, the binding energies of the Cu\({}^{+}\) characteristic peak were 933.2 eV and 953 eV, and the binding energies of the Cu\({}^{2+}\) characteristic peak were 936 eV were 943.9 eV, which was similar with the characteristic peak of the binding energy of 4 Cu-4 Ce/SAPO-34 copper ions. As for the area of the characteristic peak, after doping with Zr, the area of the characteristic peak of Cu\({}^{+}\) increased by about 15%. Cu\({}^{+}\) can promote the catalytic performance of a catalyst in the low-temperature range [40,41], so the doping with Zr improved the low-temperature performance of the catalyst. The characteristic peak area of Cu\({}^{2+}\) decreased by about 40%, and the total  
Figure 11: Ce 3d XPS spectra of 4 Cu-4 Ce-4 Zr/SAPO-34 and 4 Cu-4 Ce/SAPO-34. Figure 12: Zr 3d XPS spectrum of 4 Cu-4 Ce-4 Zr/SAPO-34. characteristic peak area of Cu\({}^{+}\)+Cu\({}^{2+}\) decreased by about 8.3%. Cu\({}^{+}\)+Cu\({}^{2+}\) played a key role in the performance of the catalyst, which might be the reason for the decline in the catalyst performance after Zr doping. In the Ce 3d spectrum of 4 Cu-4 Ce/SAPO-34, as shown in Figure 11, there were characteristic peaks of Ce 3d\({}_{5/2}\) and Ce 3d\({}_{3/2}\) orbits. According to reference [42; 43], both Ce 3d\({}_{5/2}\) and Ce 3d\({}_{3/2}\) can be resolved into two characteristic peaks. The characteristic peaks with binding energies of 886.1 eV and 904.5 eV were classified as Ce\({}^{3+}\), which were caused by its photoelectron emission, while the characteristic peaks with binding energies of 882.4 eV and 900.6 eV were caused by photoelectron emission of Ce\({}^{4+}\). After doping with Zr, the binding energies of the characteristic peaks of Ce\({}^{3+}\) were 886.2 eV and 904.9 eV, and those of the characteristic peaks of Ce\({}^{4+}\) were 882.5 eV and 900.9 eV. The binding energies of the four characteristic peaks were slightly increased, which confirmed that Zr could increase the stability of the catalyst. The area of the characteristic peak of Ce\({}^{3+}\) decreased by 90.6%, the area of the characteristic peak of Ce\({}^{4+}\) decreased by about 92.3%, and the total area of the characteristic peak of Ce\({}^{3+}\)+Ce\({}^{4+}\) decreased by about 91.1%. The transition from Ce\({}^{4+}\) to Ce\({}^{3+}\) enabled the Ce to have a strong redox performance and oxygen storage performance [43; 44]. The addition of Zr caused a significant decrease in the total amount of Ce\({}^{3+}\)+Ce\({}^{4+}\), which was one of the reasons for the decline in the performance of the catalyst after Zr doping. The Zr 3d spectrum of 4 Cu-4 Ce-4 Zr/SAPO-34 shown in Figure 12 contains the characteristic peaks of Zr 3d\({}_{5/2}\) and Zr 3d\({}_{3/2}\) orbits. According to the reference [45; 46], the characteristic peak binding energy of the Zr 3d\({}_{3/2}\) orbit was 185.18 eV, and that of the Zr 3d\({}_{5/2}\) orbit was 182.78 eV. Both characteristic peaks belonged to Zr\({}^{4+}\).