## 3 Results and Discussion
### XPS Analysis of CuO-CeO\({}_{2}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)  
Figure 6 shows the Cu 2p XPS spectra of CuO/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) and CuO-CeO\({}_{2}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\). CuO/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) shows signals of Cu\({}^{2+}\) at approximately 934.9 eV and Cu\({}^{+}\) and /or Cu\({}^{0}\) 932.6 eV, respectively [28; 29]. The XPS spectra of CuO-1% CuO/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) were similar to those of CuO/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\), indicating that the chemical states and electronic structures of the two catalysts were similar. When the CeO\({}_{2}\) content increased to 5% (CuO-5% CeO\({}_{2}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)) and 10% (CuO-10% CeO\({}_{2}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)), the XPS spectra revealed a significant change. This was a result of the doping of Cu into the CeO\({}_{2}\) lattice, which strengthened the interactions between Cu and Ce and promoted electron transfer between Cu and Ce. The reversible reactions Ce\({}^{3+}\) + Cu\({}^{2+}\leftrightarrow\) Ce\({}^{4+}\) + Cu\({}^{+}\) and 2 Ce\({}^{3+}\) + Cu\({}^{2+}\leftrightarrow\) 2 Ce\({}^{4+}\) + Cu\({}^{0}\) can occur on the surface of the CuO/CeO\({}_{2}\) catalyst [30; 31; 32]. As [PERSON] et al. reported [28], Cu\({}^{+}\) is bonded on oxygen vacancy (O\({}_{\rm v}\)) of CeO\({}_{2}\), forming a Cu\({}^{+}\)-O\({}_{\rm v}\)-Ce\({}^{3+}\) structure, which further enhanced the performance of the CuO/CeO\({}_{2}\) catalyst.  
Figure 7 shows the O1s XPS spectra of CuO/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) and CuO-CeO\({}_{2}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\). The oxygen species on the catalyst surface can be divided into two categories: (1) lattice oxygen (O\({}_{\rm lat}\)), which typically produces a binding energy peak at 529.0-531.0 eV; (2) surface adsorbed oxygen (O\({}_{\rm ads}\)), which includes chemically adsorbed oxygen, hydroxyl oxygen, and oxygen in adsorbed water, and produces a binding energy peak at 531.0-534.0 eV. Compared with lattice oxygen, surface-adsorbed oxygen has greater mobility and higher reactivity [14; 33].  
Figure 6: Cu 2p spectra of CuO/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\), CuO-1% CeO\({}_{2}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\), CuO-5% CeO\({}_{2}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\), and CuO-10% CeO\({}_{2}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\).  
The O1s XPS spectra of the catalyst are fitted, and the ratio of surface-adsorbed oxygen and lattice oxygen to total surface oxygen species (O\({}_{\text{ads}}\)/[O\({}_{\text{ads}}\) + O\({}_{\text{lat}}\)], O\({}_{\text{Lat}}\)/[O\({}_{\text{ads}}\) + O\({}_{\text{lat}}\)]) were calculated in Table 3. The results show that the ratio of surface-adsorbed oxygen on CuO-5% CeO\({}_{2}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) is the highest, at 0.50; CuO-1% CeO\({}_{2}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) has the second highest, at 0.39, and the surface adsorption oxygen ratios of CuO-10% CeO\({}_{2}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) and CuO/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) are both 0.35. Considering these results together with the protection time, the thermal catalytic decomposition performances of the catalysts were consistent with the amount of surface-adsorbed oxygen.