预硫化处理对Ce-TiO2催化剂NH3-SCR反应活性影响及其反应机理研究

通过对Ce-TiO2催化剂进行SO2+O2气氛下的不同时间的预硫化处理并用于NH3-SCR反应，研究了Ce-TiO2催化剂物化特性随预硫化时间的演变规律，以及预硫化对中低温活性及NH3-SCR反应路径的影响。结果表明Ce-TiO2催化剂表面氧化铈的硫酸化相当迅速，在预硫化处理0.5h后，几乎所有的表面氧化铈都被硫酸盐化形成硫酸铈，随着硫酸化时间的增加到1h和1.5h，Ce-TiO2催化剂上沉积的硫缓慢增加。活性测试表明预硫化后的催化剂对SCR活性的抑制作用随着反应温度的提高而减弱，结合NO-DRIFT、NH3-DRIFT等多种原位表征，结果表明预硫化后低温NH3-SCR活性大幅降低是由于生成硫酸铈后催化剂氧化还原能力大幅削弱，E-R反应路径严重受阻。随着反应温度的升高，SCR活性逐渐不受硫酸铈沉积的影响，一方面，氧化还原性能的提高导致E-R反应路径逐渐恢复；另一方面，硫酸铈的生成促进了NO的活化，增强了L-H反应路径，两者共同导致了预硫化后较高的中温NH3-SCR活性。

Effect of Pre-sulfation Treatment on NH3-SCR Performance over Ce-TiO2 Catalyst and Its Reaction Mechanism

A series of sulfated Ce-TiO2 catalysts for selective catalytic reduction (SCR) were obtained by sulfation treatment in SO2+O2 atmosphere. The revolution of the physical and chemical properties over Ce-TiO2 catalyst has been investigated with the increase of sulfated time, as well as the sulfation effect on SCR activity and reaction mechanism. The sulfation of surface ceria over Ce-TiO2 catalyst is rather rapid and almost all the surface ceria is sulfated to form cerium sulfates in the first 0.5h of sulfation treatment. With the increase of sulfated time to 1h and 1.5h, the sulfation of surface ceria is inhibited as no ceria is existed on the surface, and the content of sulfur increased slowly. According to the activity result, the inhibition effect of sulfation on SCR activity is moderated with increase of reaction temperature. Combined with comprehension characterizations such as NH3-DRIFT and NO-DRIFT, the results indicated that the significant decrease of low temperature NH3-SCR activity after pre-sulfation was due to the significant weakening of catalyst redox ability after the generation of cerium sulfate, inhibiting E-R reaction path severely. With the increase of reaction temperature, the SCR activity was gradually unaffected by the deposition of cerium sulfate. On the one hand, the improvement of redox performance led to the gradual recovery of the E-R reaction path; on the other hand, the generation of cerium sulfate promoted the activation of NO and enhanced the L-H reaction path, which together contributed to the higher medium-temperature NH3-SCR activity after pre-sulfation.