Mechanism of propene poisoning on Fe-ZSM-5 for selective catalytic reduction of NO(x) with ammonia.

Application of Fe-zeolites for urea-SCR of NO(x) 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 NO(x) with ammonia (NH(3)-SCR), and proposed a deactivation mechanism of Fe(3+) 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 NO(2) 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 Fe(3+) sites on which NO was to be oxidized to NO(2). The activity for NO oxidation to NO(2) was significantly inhibited on a propene poisoned catalyst below 400 degrees C. The adsorption of NH(3) on the Bronsted acid sites to form NH(4)(+) was not hindered even on the propene poisoned catalyst, and the amount of absorbed NH(3) was still abundant and enough to react with NO(2) 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.