## 3 Results
### Catalytic Reaction  
The catalytic performances of different materials were studied and determined for the catalytic total CO oxidation and NO reduction with CO in oxidizing atmosphere (10% O\({}_{2}\)) and CO\({}_{2}\) rich stream under identical conditions. Light-off curve of support (Al\({}_{2}\)O\({}_{3}\)) and NO reduction or oxidation yield were determined and are reported in Figure 4.  
Figure 4: Light-off curves for Al\({}_{2}\)O\({}_{3}\) support and NO reduction or oxidation yield. It can thus be seen in Figure 4 that on the alumina it is possible to have a complete oxidation of the CO. For the conversion of NO, there is a slight oxidation of NO at very high temperature but no reduction. No activity was observed with an empty reactor. Figure 5 shows the activities of the catalysts for CO oxidation. They exhibit the activity for this reaction at the temperatures higher than 100 \({}^{\circ}\)C and the conversion increases with the reaction temperature. For all tests, catalytic performances were compared by considering T\({}_{50}\) and T\({}_{90}\) for CO oxidation (Table 4), which respectively corresponded to the temperatures at which 50% and 90% of CO were converted. The results obtained are illustrated in Figure 5. The conversion of CO to CO\({}_{2}\) reached 100% for all studied catalysts. Ir and Rh have similar activity values with T\({}_{50}\) at 236 \({}^{\circ}\)C. The general order of catalytic activity, based on the temperature required for 50% conversion (T\({}_{50}\)), is the following: Pt \(>\) Pd \(>\) Ir \(\sim\) Rh \(>\) Ru. Considering T\({}_{90}\), Pt shows the better performance (176 \({}^{\circ}\)C), Rh and Ru present similar activity values with 280 \({}^{\circ}\)C. The ranking for catalysts does not much change to that obtained at T\({}_{50}\): Pt \(>\) Pd \(>\) Ir \(>\) Rh \(\sim\) Ru. The oxidation of CO was investigated on noble metal catalysts supported on TiO\({}_{2}\) by [PERSON] et al. (2016) and they pointed out on metallic particles between 2-4 nm the same activity order: Pt \(>\) Pd \(>\) Ir \(>\) Rh. The oxidation of CO, reduction of NO and oxidation of NO over the impregnated Al\({}_{2}\)O\({}_{3}\) with Ir, Pd, Pt, Rh, Ru were evaluated, and the results obtained are reported in Figure 6. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Catalysts** & **T\({}_{\bf 50}\) (\({}^{\circ}\)C)** & **T\({}_{\bf 90}\) (\({}^{\circ}\)C)** \\ \hline Ir & 236 & 260 \\ \hline Pd & 194 & 212 \\ \hline Pt & 164 & 176 \\ \hline Rh & 236 & 280 \\ \hline Ru & 268 & 280 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: T\({}_{50}\) and T\({}_{90}\) of catalysts’ catalytic CO oxidation. Figure 5: Light-off curves of CO conversion for the different materials. Feedstream composition: 0.02% NO, 0.5% CO, 10% O\({}_{2}\) and 20% CO\({}_{2}\), and balance He. Space velocity: 2.24 10\({}^{4}\) h\({}^{-1}\). CO is completely oxidized at 260 \({}^{\circ}\)C with a 13% of NO reduction on Ir/Al\({}_{2}\)O\({}_{3}\) (Figure 6a). The oxidation of NO reached 72.3% at 340 \({}^{\circ}\)C.  
Pd activity in CO and NO reactions (Figure 6b) showed that the oxidation of CO is carried out at 220 \({}^{\circ}\)C. NO reduction reached a maximum with 11% at 200 \({}^{\circ}\)C.  
When using Pt catalyst, CO was totally oxidized at 180 \({}^{\circ}\)C (Figure 6c). NO reduction began from the start of CO oxidation. Pt/Al\({}_{2}\)O\({}_{3}\) reduced the NO from 140 \({}^{\circ}\)C to 300 \({}^{\circ}\)C with a maximum reduction (14.9%) at 220 \({}^{\circ}\)C, and the oxidation phase was also bell-shaped with an optimum (66.2%) at 340 \({}^{\circ}\)C.  
CO oxidation on supported Rh catalyst (Figure 6d) occurred at higher temperature than with Pt or Pd ones, and the total conversion of CO was only obtained at 300 \({}^{\circ}\)C. This was in full agreement with  
Figure 6: Catalytic activity for the (**a**) Ir, (**b**) Pd, (**c**) Pt, (**d**) Rh, (**e**) Ru, catalysts supported on alumina. Feedstream composition: 0.02% NO, 0.5% CO, 10% O\({}_{2}\) and 20% CO\({}_{2}\), and balance He.