Mechanism of Propene Poisoning on Fe-ZSM-5 for Selective Catalytic Reduction of NOX with Ammonia

Application of Fe-zeolites for urea-SCR of NOx in diesel engine is limited by catalyst deactivation with hydrocarbons. In this work, we investigated the effect of propene on the activity of Fe-ZSM-5 for selective catalytic reduction of NOx with ammonia (NH3-SCR), and proposed a deactivation mechanism of Fe3+ active site blockage by propene residue. The NO conversion decreased in the presence of propene at various temperatures, while the effect was not significant when NO was replaced by NO2 in the feed, especially at low temperatures (<300 degrees C). The surface area and pore volume were decreased due to carbonaceous deposition. The site blockage was mainly on Fe3+ sites on which NO was to be oxidized to NO2. The activity for NO oxidation to NO2 was significantly inhibited on a propene poisoned catalyst below 400 degrees C. The adsorption of NH3 on the Bronsted acid sites to form NH4+ was not hindered even on the propene poisoned catalyst, and the amount of absorbed NH3 was still abundant and enough to react with NO2 to generate N-2. The hydrocarbon oxygenates such as formate, acetate, and containing nitrogen organic compounds were observed on catalyst surface, however, no graphitic carbonaceous deposit was formed.