Coupled NOx storage and reduction and selective catalytic reduction using dual-layer monolithic catalysts
Coupled NOx storage and reduction and selective catalytic reduction using dual-layer monolithic catalysts
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DOI：
10.1016/j.apcatb.2012.04.013
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发表时间：
2012-06
影响因子：
22.1
通讯作者：
Yi Liu;M. Harold;D. Luss
中科院分区：
文献类型：
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作者：
Yi Liu;M. Harold;D. Luss
在铂/Rh/BaO/CeO2稀有NOxTrap(LNT)催化剂上沉积了一层金属交换(Fe，Cu)沸石(ZSM-5)选择性催化还原(SCR)催化剂，用整体负载型催化剂研究了NOx(NO和NO2)的贫化还原。在精料和富含饲料之间的周期性转换过程中，LNT层将NOx还原为N2和NH3。SCR层捕获后者，导致额外的NOx减少。双层催化剂在150~300℃温度范围内表现出较高的N2选择性和较低的NH3选择性。由于LNT层的副反应，如低温NH3氧化成N2O和高温NOx，NOx转化不完全。铜离子交换的ZSM-5催化剂的NOx转化率和氮气选择性高于铁离子交换的ZSM-5分子筛。这是由于铜分子筛具有较高的低温SCR活性和较高的NH3储存容量。当进料中存在H2O和CO2时，双层催化剂在300℃以下的NOx转化率高于LNT催化剂，并且在整个温度范围内具有更高的氮气选择性。在250°C以下的LNT层中添加CeO2后，NOx的存储容量和NH3生成量增加，这也导致了NH3在高温下的氧化增加。CeO_2的加入缓解了铂在LNT和SCR层之间的不希望的迁移。水热老化对含CeO_2双层催化剂的影响较小。
Lean reduction of NOx(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/CeO2lean NOxtrap (LNT) catalyst. During periodic switching between lean and rich feeds, the LNT layer reduces NOxto N2and NH3. The SCR layer traps the latter, resulting in additional NOxreduction. The dual-layer catalysts exhibited high N2selectivity and low NH3selectivity over the temperature range of 150–300°C. The NOxconversion was incomplete due to undesired side reactions in the LNT layer, such as NH3oxidation to N2O at low temperature and NOxat high temperature. The NOxconversion and N2selectivity 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 NH3storage capacity on the Cu-zeolite. The dual-layer catalyst had a higher NOxconversion than the LNT catalyst below 300°C and a higher N2selectivity over the entire temperature range when H2O and CO2were present in the feed. The NOxstorage capacity and NH3generation increased upon addition of CeO2to the LNT layer below 250°C. It also led to increased NH3oxidation 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.