INFLUENCE OF HYDROTHERMAL AGING ON THE ACTIVITY OF SELECTIVE CATALYTIC REDUCTION OF NITROGEN-OXIDE WITH AMMONIA OVER COPPER-BETA ZEOLITE CATALYST

Vehicle emissions containing NOx which have bad effects to human health and environment ha e led to great efforts in NOx reduction. Selective catalytic reduction (SCR) with ammonia is one of the effective ways to reduce NOx for diesel application. Metal ion exchanged zeolite catalysts have been proven to be the promising catalyst for NH3 SCR. Unfortunately this type of catalyst, including Cu-zeolite, is indicated a decreasing activity due to hydrothermal aging. The aim of this study is to investigate influence of hydrothermal aging towards conversion of reactions in the SCR of NOx with ammonia over Cu-beta catalyst. Effect of NO2/NOx ratio to the conversion and selectivity of the NOx reduction as well as the NH3 and NO oxidation behaviour were examined. Cu-beta catalyst was synthesized from beta zeolite with ion exchanged method and was then washcoated on a monolith substrate. After the catalyst was hydrothermally aged at 500 up to 900 °C, the activities on NH3 temperature programmed desorption, NH3 oxidation, NO oxidation and NH3 SCR reactions were studied using a flow reactor. Each reaction was performed from 150 up to 500 °C. Influence of NO2 to NOx ratio was studied by varying the NO2/NOx ratio to 0, 0.5 and 0.75. Results of the experiments showed ammonia storage of the catalyst decreased with increasing aging temperature. The hydrothermal aging suppressed catalyst activity on ammonia and NO oxidation as well as the SCR reactions. Equimolar NO to NO2 ratio showed the maximum NOx reduction and also minimum decreasing activity due to hydrothermal aging. Furthermore, nitrous oxide was observed during SCR reactions over Cu-beta catalyst despite the absence of NO2 in the feed. A higher NO2/NOx ratio led to the higher N2O produced. Since the ammonia oxidation only produced small amount N2O, it is possible that most of the N2O observed during SCR reactions came from the side reactions