Selective catalytic reduction of nitrogen oxides over a modified silicoaluminophosphate commercial zeolite.

Nitrogen oxides (NOx: NO, NO2) are a concern due to their adverse health effects. Diesel engine transport sector is the major emitter of NOx. The regulations have been strengthened and to comply with them, one of the two methods commonly used is the selective catalytic reduction of NOx by NH3 (NH3-SCR), NH3 being supplied by the in-situ hydrolysis of urea. Efficiency and durability of the catalyst for this process are highly required. Durability is evaluated by hydrothermal treatment of the catalysts at temperature above 800°C. In this study, very active catalysts for the NH3-SCR of NOx were prepared by using a silicoaluminophosphate commercial zeolite as copper host structure. Characterizations by X-ray diffraction (XRD), scanning electron microscopy (SEM) and temperature programmed desorption of ammonia (NH3-TPD) showed that this commercial zeolite was hydrothermally stable up to 850°C and, was able to retain some structural properties up to 950°C. After hydrothermal treatment at 850°C, the NOx reduction efficiency into NH3-SCR depends on the copper content. The catalyst with a copper content of 1.25wt.% was the most active. The difference in activity was much more important when using NO than the fast NO/NO2 reaction mixture.