The impact of Fe speciation on low-temperature NH3-SCR activity of Fe-CHA and Fe-BEA catalysts probed by operando HERFD-XANES

The development of after-treatment catalysts for internal combustion engines remains of great importance. This is because, despite the shifting focus to more carbon-neutral technologies, there is a growing demand for diesel cars in developing countries as well as a high demand for heavy-duty trucks. Over the last 20 yeasr, Cu-CHA catalysts have dominated the aftertreatment technology market for diesel exhaust systems. With upcoming legislation putting restriction on levels of N2O - a greenhouse gas - for the first time, the low N2O formation on Fe-modified zeolites make them particularly desirable for new technologies. There is, however, some way to go before Fe-modified zeolites can measure up to Cu-CHA, particularly in the low temperature window. Understanding the active Fe species required for low temperature SCR reactivity is paramount to developing the new technologies. The speciation information obtained by HERFD-XANES measurements will provide this much needed insight.

内燃机尾气后处理催化剂的研发依旧具有重要意义。这是因为，尽管行业重心正转向更具碳中和属性的技术，但发展中国家对柴油乘用车的需求持续增长，同时重型卡车的需求也居高不下。过去二十年间，Cu-CHA催化剂（Cu-CHA）一直主导着柴油排气系统的后处理技术市场。随着全球首部针对一氧化二氮（N₂O，一种温室气体）排放水平设置限制的法规即将正式施行，铁改性沸石极低的N₂O生成特性使其成为新兴技术的理想候选材料。不过，铁改性沸石要达到Cu-CHA催化剂的性能水平仍有一段路要走，尤其是在低温工况窗口下。明确低温选择性催化还原（Selective Catalytic Reduction, SCR）反应活性所需的活性铁物种，是推动该项新兴技术研发的核心关键。通过高分辨荧光检测X射线吸收近边结构光谱（High Energy Resolution Fluorescence Detected X-ray Absorption Near Edge Structure, HERFD-XANES）测试获取的物种形态信息，将为解决这一研究痛点提供亟需的认知支撑。