Coupled NO_x storage and reduction and selective catalytic reduction using dual-layer monolithic catalysts

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• 作者：Yi Liu ; Michael P. Harold ; ^{mharold@uh.edu} ; Dan Luss ; ^dluss@uh.edu
• 关键词：Dual-layer catalyst ; Monolith ; Lean NOx Trap ; NOx storage and reduction ; Selective catalytic reduction ; Ceria ; Cu ; Fe ; ZSM-5 ; NH3 ; Lean NOx reduction ; Pt
• 刊名：Applied Catalysis B ; Environmental
• 出版年：2012
• 期刊代码：4_09263373
• 类别：ce
• 出版时间：13 June, 2012
• 卷：121-122
• 期：Complete
• 页码：239-251
• 文件大小：2494 K

摘要

Lean reduction of NO_x (NO and NO₂) was studied using monolith-supported catalysts consisting of a layer of a metal-exchanged (Fe, Cu) zeolite (ZSM-5) selective catalytic reduction (SCR) catalyst deposited on top of a Pt/Rh/BaO/CeO₂ lean NO_x trap (LNT) catalyst. During periodic switching between lean and rich feeds, the LNT layer reduces NO_x to N₂ and NH₃. The SCR layer traps the latter, resulting in additional NO_x reduction. The dual-layer catalysts exhibited high N₂ selectivity and low NH₃ selectivity over the temperature range of 150-300 掳C. The NO_x conversion was incomplete due to undesired side reactions in the LNT layer, such as NH₃ oxidation to N₂O at low temperature and NO_x at high temperature. The NO_x conversion and N₂ selectivity of the Cu-exchanged ZSM-5 was higher than that of the Fe-exchanged ZSM-5. This was due to a higher low temperature SCR activity and a higher NH₃ storage capacity on the Cu-zeolite. The dual-layer catalyst had a higher NO_x conversion than the LNT catalyst below 300 掳C and a higher N₂ selectivity over the entire temperature range when H₂O and CO₂ were present in the feed. The NO_x storage capacity and NH₃ generation increased upon addition of CeO₂ to the LNT layer below 250 掳C. It also led to increased NH₃ oxidation at high temperatures. The addition of ceria mitigated the undesirable migration of Pt between the LNT and SCR layers. Hydrothermal aging had a smaller effect on dual-layer catalysts containing ceria.