State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China.
Environ Sci Technol. 2012 Feb 7;46(3):1747-54. doi: 10.1021/es203070g. Epub 2012 Jan 20.
Application of Fe-zeolites for urea-SCR of NO(x) in diesel engine is limited by catalyst deactivation with hydrocarbons (HCs). In this work, a series of Fe-zeolite catalysts (Fe-MOR, Fe-ZSM-5, and Fe-BEA) was prepared by ion exchange method, and their catalytic activity with or without propene for selective catalytic reduction of NO(x) with ammonia (NH(3)-SCR) was investigated. Results showed that these Fe-zeolites were relatively active without propene in the test temperature range (150-550 °C); however, all of the catalytic activity was suppressed in the presence of propene. Fe-MOR kept relatively higher activity with almost 80% NO(x) conversion even after propene coking at 350 °C, and 38% for Fe-BEA and 24% for Fe-ZSM-5 at 350 °C, respectively. It was found that the pore structures of Fe-zeolite catalysts were one of the main factors for coke formation. As compared to ZSM-5 and HBEA, MOR zeolite has a one-dimensional structure for propene diffusion, relatively lower acidity, and is not susceptible to deactivation. Nitrogenated organic compounds (e.g., isocyanate) were observed on the Fe-zeolite catalyst surface. The site blockage was mainly on Fe(3+) sites, on which NO was activated and oxidized. Furthermore, a novel fully formulated Fe-BEA monolith catalyst coating modified with MOR was designed and tested, the deactivation due to propene poisoning was clearly reduced, and the NO(x) conversion reached 90% after 700 ppm C(3)H(6) exposure at 500 °C.
用于柴油机尿素 SCR 的 Fe-沸石受烃（HC）影响催化剂失活的限制。在这项工作中，通过离子交换法制备了一系列 Fe-沸石催化剂（Fe-MOR、Fe-ZSM-5 和 Fe-BEA），并研究了它们在有或没有丙烯存在时用于氨选择性催化还原（NH3-SCR）的催化活性。结果表明，在测试温度范围内（150-550°C），这些 Fe-沸石在没有丙烯的情况下具有相对较高的活性；然而，在丙烯存在下，所有的催化活性都受到抑制。在 350°C 下丙烯结焦后，Fe-MOR 仍保持相对较高的活性，NOx 转化率接近 80%，而 Fe-BEA 为 38%，Fe-ZSM-5 为 24%。研究发现，Fe-沸石催化剂的孔结构是形成积碳的主要因素之一。与 ZSM-5 和 HBEA 相比，MOR 沸石具有丙烯扩散的一维结构，相对较低的酸度，不易失活。在 Fe-沸石催化剂表面观察到含氮有机化合物（如异氰酸酯）。位阻主要发生在 Fe(3+)位上，NO 在这些位上被活化和氧化。此外，设计并测试了一种新型的全配方 Fe-BEA 整体式催化剂涂层，对其进行了 MOR 改性，明显减少了丙烯中毒失活的现象，在 500°C 下暴露于 700ppm C(3)H(6)时，NO(x)转化率达到 90%。
