## 3 Results and Discussion
### Catalyst Intermediate Species and Oxidation Mechanisms  
Two typical kinetic models of the oxidation mechanisms of 1,2-DCE over noble metal catalysts as displayed in Scheme 1. In the low-temperature region, the oxidation mechanism of 1,2-DCE on noble metal catalysts obeys the Langmuir-Hinshelwood model: (1) 1,2-DCE and the oxygen species are simultaneously adsorbed onto the surficial active sites; (2) 1,2-DCE molecules react with the adsorbed oxygen and then produce Cl\({}_{2}\), H\({}_{2}\)O, HCl, and CO\({}_{2}\); (3) intermediates continuously react with the adsorbed oxygen and generate H\({}_{2}\)O, CO\({}_{2}\), HCl, and Cl\({}_{2}\). On the other hand, at high temperatures, the 1,2-DCE oxidation routes of the NM/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) catalysts follow the Eley-Rideal model [29]: (1) oxygen species are adsorbed; (2) the adsorbed oxygen species further react with the gas-phase 1,2-DCE to produce H\({}_{2}\)O, HCl, Cl\({}_{2}\), and CO\({}_{2}\). In summary, the surface-adsorbed oxygen species are the main source of 1,2-DCE oxidation. By combining other characterization methods and the by-product distribution, four reaction paths can be inferred, as displayed in Scheme 2 [40,59]. Path 1: 1,2-DCE induces the dehydrochlorination reaction to produce vinyl chloride; vinyl chloride reacts with H- to generate carbon dioxide positive ions; carbon dioxide positive ions react with O\({}^{2-}\) to create acetate. Path 2: vinyl chloride reacts with chlorine to produce trichloroethane; trichloroethylene can be generated by trichloroethane reacting with chlorine and the dehydrochlorination reaction. Path 3: 1,2-DCE induces C-C bond cleavage to create chloromethane; chloromethane reacts with H\({}^{+}\) and O\({}^{2-}\) to produce formate. Path 4: chloromethane reacts with chlorine in the dehydrochlorination reaction to generate dichloromethane; dichloromethane reacts with chlorine in the dehydrochlorination reaction to create trichloromethane; trichloroethane reacts with chlorine in the dehydrochlorination reaction to produce carbon tetrachloride. Finally, these intermediates are then deeply oxidized into H\({}_{2}\)O, HCl, Cl\({}_{2}\), and CO\({}_{2}\). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Samples**} & \multicolumn{3}{c}{**O 1s**} \\ \cline{2-4}  & **O\({}_{\alpha}\)1 ** & **O\({}_{\beta}\)2 ** & **O\({}_{\alpha}\)/(O\({}_{\alpha}\) + O\({}_{\beta}\))** \\ \hline Ru/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) & 53,918.9 & 7038.0 & 0.88 \\ Rh/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) & 48,460.7 & 11,390.2 & 0.81 \\ Pt/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) & 38,974.4 & 8706.5 & 0.82 \\ Pd/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) & 25,771.9 & 11,941.7 & 0.68 \\ Ir/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) & 41,634.6 & 7145.6 & 0.85 \\ Au/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) & 46,326.8 & 7463.6 & 0.86 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: XPS results of O 1s of prepared catalysts. To further explore the oxidation mechanisms of the 1,2-DCE catalyst over noble metals, _in situ_ DRIFTS measurements were applied to discover the reaction intermediates of all catalyst materials when 1,2-DCE degrades from 90 to 260 \({}^{\circ}\)C (Figure 10). All of the catalysts could be observed in the bands in the region of 3550-3060 cm\({}^{-1}\), which are determined by the -OH vibration with surficial adsorbed water. Of course, with the elevated operation temperature, the strength of these bands is reduced contrarily. Following the stretching vibration of the C-H band observed in the bands of 2930 and 2850 cm\({}^{-1}\), the vibration of the -CH\({}_{2}\) group can be distinguished. At the same time, the C-H vibration appeared at 2820 and 2720 cm\({}^{-1}\), indicating the emergence of the -CH\({}_{3}\) group. Moreover, the bands in the region of 1544-1371 cm\({}^{-1}\) are also associated with C-H vibration, which is attributed to the oscillation of -CH/-CH\({}_{2}\)/-CH\({}_{3}\) radicals.