还原剂对La0.7Sr0.3Co0.8Fe0.2O3钙钛矿催化剂NOx储存性能的影响

采用溶胶-凝胶法制备了La0.7Sr0.3Co0.8Fe0.2O3钙钛矿催化剂,考察了还原剂种类(CO,C3H6,H2)对催化剂在氮氧化物储存还原(NSR)循环前后的氮氧化物储存量(NSC)和NO-to-NO2转化率的影响.O2程序升温脱附(O2-TPD)实验结果表明,CO还原后的钙钛矿催化剂上形成了较多的氧空位,而氧空位则是一种有效的NOx储存活性中心.活性测试和傅里叶红外变换(FTIR)光谱表征结果显示:在NSR循环中,以CO为还原剂时催化剂显示了最佳的氮氧化物(NOx)储存效果.进一步的研究结果显示,当采用CO作为还原剂时,经过三次NSR循环后,催化剂中出现了Sr3Fe2O7新物相,而该物相可能具有比La0.7Sr0.3Co0.8Fe0.2O3钙钛矿更佳的NOx储存性能.综上所述,CO作为还原剂时可能使钙钛矿催化剂产生更多的氧空位以及更易于储存NOx的Sr3Fe2O7物相,这些原因使其NOx储存性能得到了大幅度改善.

Influence of Reductants on the NOx Storage Performances of the La0.7Sr0.3Co0.8Fe0.2O3 Perovskite-Type Catalyst

A La_0.7Sr_0.3Co_0.8Fe_0.2O₃ perovskite-type catalyst was synthesized by a sol-gel method. The influence of different reductants (CO, C₃H₆, and H₂) on the NO_x storage capacity and NO-to-NO₂ conversion of the perovskite was evaluated before and after the NO_x storage-reduction (NSR) tests. Our O₂temperature programmed desorption findings showed that a large number of oxygen vacancies were generated in the COreduced perovskite. These oxygen vacancies are effective sites for NO_x storage. The catalytic tests and Fourier transform infrared (FTIR) spectroscopy results showed that during the NSRtests of catalysts that used CO as the reductant, the catalysts demonstrated excellent NO_x storage performance. Further investigations revealed the generation of a new Sr₃Fe₂O₇ phase in the catalyst. This new phase may possess better NO_x storage ability than the La_0.7Sr_0.3Co_0.8Fe_0.2O₃ perovskite. In conclusion, the NO_x storage ability of the catalyst was greatly improved after reduction by CO due to an increase in oxygen vacancies and the generation of a Sr₃Fe₂O₇ phase during NSR cycling.