Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Environ Sci Technol. 2013 Apr 2;47(7):3293-8. doi: 10.1021/es304421v. Epub 2013 Mar 21.
Hydrothermal stability is one of the challenges for the practical application of Fe-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with NH3 (NH(3)-SCR) for diesel engines. The presence of NO(3) in the exhaust gases can enhance the deNOx activity because of the fast SCR reaction. In this work, a Fe-ZSM-5 catalyst was prepared by a solid-state ion-exchange method and was hydrothermally deactivated at 800 °C in the presence of 10% H(2)O. The activity of fresh and hydrothermal aged Fe-ZSM-5 catalysts was investigated in standard SCR (NO(2)/NOx = 0) and in fast SCR with NO(2)/NOx = 0.3 and 0.5. In standard SCR, hydrothermal aging of Fe-ZSM-5 resulted in a significant decrease of low-temperature activity and a slight increase in high-temperature activity. In fast SCR, NOx conversion over aged Fe-ZSM-5 was significantly increased but was still lower than that over fresh catalyst. Additionally, production of N(2)O in fast SCR was much more apparent over aged Fe-ZSM-5 than over fresh catalyst. We propose that, in fast SCR, the rate of key reactions related to NO is slower over aged Fe-ZSM-5 than over fresh catalyst, thus increasing the probabilities of side reactions involving the formation of N(2)O.
水热稳定性是 Fe-ZSM-5 催化剂在柴油机 NH3 选择性催化还原（NH3-SCR）中实际应用的挑战之一。由于快速 SCR 反应，废气中存在的 NO3-可以提高脱氮活性。在这项工作中，通过固态离子交换法制备了 Fe-ZSM-5 催化剂，并在存在 10% H2O 的情况下在 800°C 下水热处理失活。在标准 SCR（NO2/NOx=0）和快速 SCR（NO2/NOx=0.3 和 0.5）中研究了新鲜和水热老化的 Fe-ZSM-5 催化剂的活性。在标准 SCR 中，Fe-ZSM-5 的水热处理导致低温活性显著降低，高温活性略有增加。在快速 SCR 中，老化的 Fe-ZSM-5 上的 NOx 转化率显著增加，但仍低于新鲜催化剂。此外，老化的 Fe-ZSM-5 上快速 SCR 中 N2O 的生成量明显高于新鲜催化剂。我们提出，在快速 SCR 中，老化的 Fe-ZSM-5 上与 NO 相关的关键反应的速率比新鲜催化剂慢，从而增加了涉及 N2O 形成的副反应的可能性。
