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

Nitrogen oxides (NO_x: NO, NO₂) are a concern due to their adverse health effects. Diesel engine transport sector is the major emitter of NO_x. The regulations have been strengthened and to comply with them, one of the two methods commonly used is the selective catalytic reduction of NO_x 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 NO_x 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 NO_x 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.