The selective catalytic oxidation of ammonia (NH₃-SCO) is the last mitigation step in exhaust treatment using a 4-way catalytic converter to convert any excess and unreacted NH₃ (that was used as a reductant of NO_x) into environmentally benign N₂ and H₂O. Here, we report a series of highly reactive and selective nano Cu/zeolites for the NH₃-SCO reaction. The NH₃-SCO activity was found in the order nano Cu/ZSM-5 (MFI topology) > Cu/Beta (BEA) > Cu/MCM-49 (MWW) > Cu/Y (FAU) > Cu/Mordenite (MOR) > Cu/Ferrierite (FER). The best catalyst, i.e., nano Cu/ZSM-5, achieves 98% NH₃ conversion at 250 °C with the N₂ yield maintained at >98% even at up to 500 °C. When assessed under practical exhaust conditions in the presence of moisture (5% H₂O) as well as that after hydrothermal aging (5% H₂O, 850 °C, 8 h), the nano Cu/ZSM-5 exhibited only minor deactivation as a result of its good retention of Cu dispersion, pore structure and specific surface area. Furthermore, small micropore (10-membered ring, 10-MR) topologies were found to be crucial in maintaining high N₂ yields. For Cu/Y and Cu/Mordenite, composed of 12-MR pores that are non-interconnected with smaller pores, their N₂ yields were compromised by forming NO_x at temperatures above 400 °C. Based on the in situ DRIFTS study, the iSCR mechanism appears to be applicable for all fresh and aged Cu/zeolites with the exception of fresh Cu/MCM-49 that follows the imide mechanism.

中文翻译：

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具有不同拓扑结构的纳米Cu /沸石上氨的选择性催化氧化

氨的选择性催化氧化（NH ₃ -SCO）是排气处理中的最后一个缓解步骤，使用四效催化转化器将任何过量且未反应的NH ₃（用作NO _x的还原剂）转化为对环境无害的N ₂和H ₂ O.在此，我们报道了一系列的高反应性和选择性的纳米铜/沸石的NH ₃ - SCO反应。NH ₃ -SCO活性的发现顺序为：纳米Cu / ZSM-5（MFI拓扑）> Cu /β（BEA）> Cu / MCM-49（MWW）> Cu / Y（FAU）> Cu /丝光沸石（MOR ）>铜/镁碱沸石（FER）。最好的催化剂，即纳米Cu / ZSM-5，在250°C的温度下使用N可以达到98％的NH ₃转化率。即使在高达500°C的温度下， ₂收率仍保持> 98％。当在有水分（5％H ₂ O）的情况下以及在水热老化（5％H ₂ O，850°C，8小时）的实际排气条件下进行评估时，纳米Cu / ZSM-5仅表现出微量由于其良好的保留铜分散，孔结构和比表面积的结果而失活。此外，发现小的微孔（10元环，10-MR）拓扑对于维持高N ₂产量至关重要。对于由不相互连接的12-MR孔和较小孔组成的Cu / Y和Cu / Mordenite，其N ₂产率因在高于400°C的温度下形成NO _x而受到损害。基于原位 在DRIFTS研究中，iSCR机制似乎适用于所有新鲜和老化的Cu /沸石，但遵循酰亚胺机制的新鲜Cu / MCM-49除外。