Combining nonthermal plasma with perovskite-like catalyst for NOx storage and reduction

Effects of substituting iron for aluminum on the low-temperature catalytic activity and sulfur resistance of hydrotalcite-derived LNT catalysts

The storage and reduction of NOx on a series of Fe-modified hydrotalcite-based lean NOx trap catalysts were assessed, together with the product selectivity. The crystal structures and micromorphologies of these materials were characterized using X-ray diffraction and scanning electron microscopy, while in situ diffuse reflectance Fourier transform infrared spectroscopy was used to evaluate the evolution of transition state species. The introduction of Fe was found to improve the synergistic interaction between the Mg and Fe in the hydrotalcite structure, allowing these catalysts to work efficiently at low temperatures. In addition, both Pt/BaO/MgAlO and Pt/BaO/MgFeO catalysts exhibited better NOx adsorption and reduction performance compared with Pt/BaO/Al₂O₃. The superior performance of the former two materials was attributed to the enhanced adsorption of NOx in the form of nitrates and nitrites by Fe and Mg and to the ready decomposition of these nitrates at low temperatures. A Pt/BaO/MgFeO catalyst showed excellent low temperature activity and high selectivity for N₂ together with superior sulfur resistance compared with Pt/BaO/Al₂O₃.

Storage and reduction of NOx by combining Sr-based perovskite catalyst with nonthermal plasma

A novel NO_x storage and reduction (NSR) system is developed for NO_x removal by integrating Sr-based perovskite catalyst with nonthermal plasma (NTP)-assisted process. In this hybrid system, Sr-based perovskite catalyst is applied for NO_x adsorption in the lean-burn condition while NTP is used as a desorption-reduction step to convert NO_x into N₂ under rich-burn condition. Innovative Sr-based perovskites including SrKMnCoO₄/BaO/Al₂O₃ (SKMCBA), SrKMnCeO₄/BaO/Al₂O₃ (SKMCeBA), and SrKCoNiO₄/BaO/Al₂O₃ (SKCNBA) are successfully prepared by impregnation method. Results indicate that SKMCBA possesses the highest NO_x trapped (214 μmole NO_x/g_catalyst) at 400 °C among 3 Sr-based perovskites investigated. High performance of SKMCBA for NO_x adsorption is mainly attributed to the addition of Mn and Co which own good oxidation ability. Further, SKMCBA is combined with NTP-assisted process for NO_x reduction. Result indicates that NO_x conversion achieved with NTP-assisted process reaches 83% with the applied voltage of 18 kV and frequency of 10 kHz in the absence of reducing agent. Additionally, various reducing agents including hydrogen (H₂), carbon monoxide (CO), and propene (C₃H₆) are introduced, individually, into the NTP reduction process, and the results indicate that performance of NSR with NTP can be effectively enhanced. Especially, 100% NO_x conversion is achieved with H₂-NTP. This study demonstrates that reduction of NO_x via NTP-assisted process is promising.