柴油机选择性催化还原捕集技术(SDPF)的研究现状与发展趋势

日益严格的柴油机排放法规使得其主要排放污染物氮氧化物（NO_x）和颗粒物（PM）限值进一步降低.目前去除NO_x的主要机外手段是选择性催化还原（SCR）技术，该技术通常在200℃以上才有良好的NO_x转化率，而在柴油机冷起动阶段，SCR入口的排气温度无法达到200℃，NO_x排放控制困难.尽管冷起动时间较短，但该阶段的NO_x排放量占比很高.在严格的排放法规要求下，冷起动阶段的NO_x排放控制日益受到关注.选择性催化还原捕集技术（SDPF）将SCR催化剂涂覆在壁流式颗粒捕集器（DPF）载体上，能够同时去除NO_x和PM.与SCR技术相比，SDPF更加靠近柴油机排气门，NO_x催化还原反应的温度得到有效提高.因此，SDPF成为了提高低温NO_x转化率的关键技术.本文从SDPF结构与原理、载体与催化剂、性能及影响因素、SDPF技术路线等四个方面展开综述.SDPF结构与原理方面，介绍了SDPF的基本结构和化学反应原理，并指出了该技术面临的主要挑战；SDPF载体与催化剂方面，阐述了常见的载体材料、SCR催化剂涂覆、载体结构参数设计和提高载体性能的膜技术，以及钒基、沸石基SCR催化剂的研究进展；SDPF性能及影响因素方面，对SDPF的碳烟氧化性能、NO_x还原性能、尿素混合性能和耐久性能进行了分析，需要重点优化碳烟氧化与NO_x还原之间的竞争性反应；SDPF技术路线方面，介绍了带有SDPF的后处理系统优化，尿素双喷技术、低温NO_x吸附、热管理等技术耦合SDPF能够进一步拓宽后处理系统的温度窗口，是满足未来超低排放法规的后处理技术发展趋势.

Research status and development trend of selective catalytic reduction filter (SDPF) technology of diesel engines

The limits of NO_x and PM of diesel engines are further reduced with the more stringent emission regulations. At present, the fundamental method of external purification to remove NO_x is selective catalytic reduction (SCR) technology, which usually has good NO_x conversion efficiency above 200℃. However, in the cold start phase of diesel engines, the exhaust gas temperature of SCR inlet can not reach 200℃, so it is difficult to control NO_x emission. Although the duration of the cold start is short, the NO_x emission in this phase accounts for a high proportion. Under strict emission regulations, the control of NO_x emission in the cold start phase has been paid more and more attention. Selective catalytic reduction filter (SDPF) technology can remove NO_x and PM simultaneously by coating SCR catalyst in the substrate of wall-flow diesel particulate filter (DPF). Compared with the SCR technology, SDPF is closer to the engine exhaust valve, and the temperature of catalytic reduction reaction of NO_x is effectively improved. Therefore, SDPF has become the key technology to enhance the low-temperature NO_x conversion efficiency. In this paper, the structure and principle, substrate and catalysts, performance and its influencing factors, and the technical route with SDPF were reviewed. In terms of the structure and principle of SDPF, the basic structure and chemical reaction principle of SDPF were introduced, and the main challenges faced by the technology were pointed out; in terms of SDPF substrate and catalyst, the common materials of the substrate, SCR catalyst coating, the design of substrate structure parameters and membrane technology to improve the performance of substrate were described, as well as the research progress of vanadium based and zeolite based SCR catalysts; in terms of SDPF performance and its influencing factors, the performance of soot oxidation, NOx reduction, urea mixing performance and durability of SDPF were analyzed, and the competitive reaction between soot oxidation and NO_x reduction needs to be optimized; in the aspect of the technical route of SDPF, the optimization of aftertreatment system with SDPF was introduced, and the double urea injection technology, low-temperature NO_x adsorption and thermal management technology coupling with SDPF can further broaden the temperature window of the aftertreatment system, which is the development trend of aftertreatment technology to meet the future ultra-low emission regulations.