## 3 Results and Discussion  
### TG/FTIR Experiments  
Figure 3 shows the TG and DTG traces of the NNN and the NNN with the three catalysts, performed under inert atmosphere. Data below 100 \({}^{\circ}\)C are not shown because they correspond to the loss of water in the samples with the catalyst. Data under an inert atmosphere corresponding to sole NNN present a wide process with a peak at 190 \({}^{\circ}\)C and a shoulder at around 183 \({}^{\circ}\)C. Another shoulder, more marked, can be observed at 218 \({}^{\circ}\)C, as a result of NNN volatilization and decomposition. When using the two SBA-15 catalysts, the main peak is shifted to higher temperatures (267 \({}^{\circ}\)C), and another minor peak at 155 \({}^{\circ}\)C and a marked shoulder at 197 \({}^{\circ}\)C are observed. The first processes observed may correspond to the volatilization and decomposition of NNN that does not interact or interacts weakly with the catalyst (this peak is slightly more marked for the SBA-15f), whereas the main peak must be the result of the NNN adsorption in the catalyst pores and the further decomposition of the catalyst's pore structure. MCM-41 produces more marked changes, and up to four processes can be observed. At low temperatures, a shoulder at 155 \({}^{\circ}\)C and a peak at 176 \({}^{\circ}\)C, followed by other at 197 \({}^{\circ}\)C, can be observed. These two peaks are much more intense than those observed with the SBA-15 catalysts. The main peak appears at 247 \({}^{\circ}\)C, being lower than in the case of the other catalysts and presenting a tail at high temperatures. These changes, compared with the experiment without a catalyst, may be related to the interaction between the NNN and the different porous structures of these materials. The first peaks that appear in the presence of the catalyst below 200 \({}^{\circ}\)C are similar to those presented by NNN when it is alone, and could be due to the evaporation and partial decomposition of the nitrosamine that has not interacted with the catalyst. The rest of the NNN that decomposes at higher temperatures is probably retained in the pores of the catalysts or has been adsorbed on their external surface. According to the intensity of the main peaks of the DTG, the amount of NNN adsorbed would be higher for the SBA-15, which is consistent with its larger pore volume and external surface area. These peaks at a low temperature will be in good agreement with the results of the pyrolysis in the EGA equipment, where the decomposition of the NNN in the presence of catalysts is observed at lower temperatures, especially in the case of MCM-41. Under the air atmosphere (Figure 4), the results of sole-NNN are very similar to those under inert conditions, showing very little influence of the atmosphere on the thermal behavior of NNN. When using the catalyst, the first part of the thermogram is also very similar to that in N\({}_{2}\), but from temperatures around 290 \({}^{\circ}\)C a significant residue is obtained (i.e., around 15%) that decomposes at an almost constant rate up to 700 \({}^{\circ}\)C. Again, the traces corresponding to the two SBA-15s are very similar, and the greatest differences are produced by the MCM-41. In this case, a much more pronounced residue is obtained that oxidizes at temperatures between 500-700 \({}^{\circ}\)C.  
Figure 4: TG and DTG curves for experiments with NNN and NNN with three catalysts under oxidizing atmosphere. Figure 3: TG and DTG curves for experiments with NNN and NNN with three catalysts under inert atmosphere. The IR data under the inert atmosphere show a very poor resolution, and only the bands corresponding to NO at 1906 and 1842 cm\({}^{-1}\) and those corresponding to CN (triple bond) at 2229 cm\({}^{-1}\) can be hardly observed, being slightly more intense when using the catalyst. Nevertheless, the data show no conclusive differences.