SUMMARY

NOx emissions to the atmosphere are one of the main environmental problems. It is well known that NOx contribute to the formation of the acid rain and the photochemical smog. In addition some diseases as bronquitis or pneumonia, or some alterations of the immunologic system are related with the presence of NOx in the atmosphere. For this reason the development of new techniques for the control of the NOx emissions is a subject of actuality.
Approximately, half of the NOx emissions come from the traffic. The technology used, as the three way catalysts (TWC), is not very effective for the control of this pollutant in diesel vehicles or in lean-burn motors. This is due to the fact that these motors work mainly with an excess of oxygen over the stoichiometric conditions. Then, it is necessary to design a new catalytic system that will be able to reduce specifically the NOx emissions in these motors.
Another source of NOx emissions is the fluid catalytic cracking regenerator. The increasing legislative restrictions forces to develop new techniques in order to control them. An interesting possibility to achieve this goal is the development of new catalytic additives that reduce the NOx formed.
This thesis belongs to the area of Environmental Catalysis and its first objective is to develop a NOx storage-reduction catalyst (NSR), also known as lean NOx-traps (LNT). In order to achieve this objective, the activity of new catalysts based in mixed oxides derived from hydrotalcites and doped with transition metals is studied at different temperatures and in presence of possible poisons as water and SO2.
The results obtained show that the catalysts derived from Mg/Al hydrotalcite containing copper or cobalt are active at low temperatures, mainly in the samples containing 10 or 15 % of cobalt. The addition of 1% weight of some transition metals, with redox properties, as Pt, Pd, V or Ru, increases the catalysts activity because an adequate combination of the redox properties of these metals and the acid-base properties of the hydrotalcite. The best results were obtained with the catalyst with a molar ratio Co/Mg/Al = 15/60/25 containing sodium and 1 % of V or Ru. This is due to the fact that this material has a high bascity increased by the presence of sodium. This allows the adsorption of the NOx as nitrates in the oxidative cycle of the motor (lean cycle). At the same time, the redox properties of cobalt and V or Ru facilitate the reduction of the adsorbed nitrates during the reductive cycle of the motor (rich cycle). These materials show a high activity at low temperature and in presence of water and SO2. Finally the absence of noble metals, as Pt or Pd, makes these materials very interesting from the economic point of view.
The second objective of this thesis is the development of a new catalytic system to reduce the NOx formed in the fluid catalytic cracking (FCC) regenerator. In order to get this objective, some catalysts based on Ce-Al-O/?-Al2O3, containing other mixed metals were prepared and its activity studied in the working conditions of the FCC regenerator.
The best results were obtained with Sn–Al-O/Cu–Al–O clusters interacting with Ce-Al-O mixed oxides supported on ?-Al2O3. The strong interaction between both complex oxides results in a stable and active catalyst at high temperature. This additive will be active in the dense phase of the FCC regenerator.





	
Reducción catalítica de Óxidos de Nitrógeno (NOx) en corrientes  gaseosas                                                      Resumen
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