## 3 Results
### Catalytic Activity Measurements  
Figure 10 shows temperature dependences of NH\({}_{3}\) conversion (a) and concentrations of N\({}_{2}\) (b), N\({}_{2}\)O (c) and NO\({}_{\text{x}}\) (d) during the temperature- programmed reaction of NH\({}_{3}\) with O\({}_{2}\) (TPR-NH\({}_{3}\)+O\({}_{2}\)) up to 400 \({}^{\circ}\)C. The results obtained during two consecutive heating/cooling cycles are presented. As can be seen from the conversion curves in Figure 10a, during the first heating the catalyst based on the P25 support is the most active with the onset temperature \(\sim\)120 \({}^{\circ}\)C. However, during the second heating, the catalytic activity decreased and the profile becomes similar to ones of the Pt/Ti-PLA-400 catalyst. The Pt/Ti-PLA-400 sample exhibits high stability and little changes from the first to second cycle of TPR-NH\({}_{3}\)+O\({}_{2}\). The high activity of the Pt/Ti-P25-400 catalyst in the first cycle is accompanied by a higher selectivity to N\({}_{2}\) (Figure 10b), but, after heating of the catalyst to T \(\sim\) 200 \({}^{\circ}\)C, the N\({}_{2}\) concentration decreases and reaches a minimum level for all catalysts. During the second heating, N\({}_{2}\) concentrations over Pt/Ti-P25-400 and Pt/Ti-PLA-400 are similar up to 230 \({}^{\circ}\)C. The N\({}_{2}\) concentration for Pt/Ti-P25-400 catalyst drops above 230 \({}^{\circ}\)C, while it stays almost constant for Pt/Ti-PLA-400 catalyst. Figure 9: H\({}_{2}\) consumption and H\({}_{2}\)O evolution during temperature-programmed reduction (TPR-H\({}_{2}\)) for (**a**) Pt/Ti-PLA-400 and (**b**) Pt/Ti-P-25-400 catalysts. The difference between the catalysts is more pronounced if one analyzes temperature dependences of N\({}_{2}\)O concentration. For the Pt/Ti-P25-400 catalyst, the first cycle of TPR-NH\({}_{3}\)+O\({}_{2}\) is characterized by a three-stage growth of N\({}_{2}\)O concentration with a shift of the maximum N\({}_{2}\)O production towards higher temperatures. During the second heating the low-temperature (100-150 \({}^{\circ}\)C) activity disappears. Figure 11 shows the conversion curves as a function of temperature for the catalysts calcined at T = 400 \({}^{\circ}\)C and 600 \({}^{\circ}\)C (N\({}_{2}\) selectivity is presented in Table A3). For the Pt/Ti-P25 catalyst, an increase in the calcination temperature from 400 to 600 \({}^{\circ}\)C leads to a significant decrease of the low-temperature activity and T\({}_{50}\) increases to 185 \({}^{\circ}\)C. In contrast, for the Pt/Ti-PLA catalyst, calcination at 600 \({}^{\circ}\)C leads to an increase of the catalytic activity, and T\({}_{50}\) decreases to \(\sim\) 180 \({}^{\circ}\)C. The temperature of 100% conversion also significantly decreases. A comparison of the light-off curves for the catalysts calcined at 600 \({}^{\circ}\)C shows that the catalyst prepared with TiO\({}_{\text{x}}\)-PLA becomes more active compared to the catalyst based on the commercial P25 support. Figure A4 shows the N\({}_{2}\) and N\({}_{2}\)O selectivity depending on the temperature of the NH\({}_{3}\)+O\({}_{2}\) reaction. The profiles differ significantly for the Pt/Ti-PLA-400 (a, c) and Pt/Ti-P25-400 (b, d) catalysts. Thus, a characteristic feature for the Pt/Ti-PLA-400 catalyst is a sharp transition from a high N\({}_{2}\) selectivity level (70%) to a level of 50-55%, which is almost constant over a wide temperature range from 200 to 350 \({}^{\circ}\)C. The switch of the reaction mode is highlighted by blue color in the temperature range 180-210 \({}^{\circ}\)C. This transition is observed both during the first and second heating of the catalyst, which indicates the complete reversibility catalysts activity. Changes in the concentrations of the N\({}_{2}\) and N\({}_{2}\)O reaction products can reflect the surface reactions of adsorbed species occurring on active centers acting in the different temperature ranges.