Department of Environment Science and Engineering, Tsinghua University, Beijing 100084, China.
Environ Sci Technol. 2010 Mar 1;44(5):1799-805. doi: 10.1021/es903576d.
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.
在柴油机中，Fe-沸石在尿素-SCR 脱除 NO(x)的应用受到烃类导致催化剂失活的限制。在这项工作中，我们研究了丙烯对 Fe-ZSM-5 氨选择性催化还原（NH(3)-SCR）脱除 NO(x)活性的影响，并提出了丙烯残留物导致 Fe(3+)活性位堵塞失活的机理。在不同温度下，丙烯的存在会降低 NO 的转化率，而在进料中用 NO(2)替代 NO 时，这种影响并不显著，特别是在低温（<300°C）下。由于积碳，比表面积和孔体积减小。位阻主要发生在 Fe(3+)位上，NO 要在此被氧化为 NO(2)。在 400°C 以下，丙烯中毒的催化剂上，NO 氧化为 NO(2)的活性显著受到抑制。即使在丙烯中毒的催化剂上，NH(3)在 Brønsted 酸位上吸附形成 NH(4)(+)也不受阻碍，并且吸附的 NH(3)的量仍然丰富且足以与 NO(2)反应生成 N(2)。在催化剂表面上观察到了甲酸盐、乙酸盐和含氮有机化合物等烃类含氧物，但未形成石墨状碳质沉积物。
