高效稳定的铜分子筛用于柴油车尾气NOx去除研究

The selective catalytic reduction of NOx by NH3 (NH3-SCR) is one of the most promising technologies for NOx emission control for diesel vehicles. Recently, Cu-chabazite (CHA) catalysts have received much attention due to their high hydrothermal stability and activity in SCR reaction, and have been commercialized on diesel vehicles. This program focuses on Cu-CHA catalysts prepared by one-pot synthesis and solvent-free synthesis methods, which are considered as economical and “green” ways compared with conventional synthesis methods. In this project, the hydrothermal deactivation mechanisms of Cu-CHA catalysts will be investigated and the crucial parameters of hydrothermal stability will be clarified. The role of the various aging factors, including poisons like sulfur, hydrocarbon, H2O and phosphorous, on the performance of Cu-CHA catalysts will be studied and the poison mechanism will be revealed. Based on comprehensively results, the strategies to regeneration of poisoned catalysts can be proposed. The reaction mechanism of SCR reaction over Cu-CHA catalysts will be studied, specifically the key factors for controlling the reactivity of Cu-CHA in the low temperature range. In addition the effectiveness of a SCR catalytic system comprising Fe-zeolite and Cu-CHA catalysts monoliths will be examined by the experimental and modeling study. These results will provide new ideas and theoretical basis for optimizing and designing highly efficient NH3-SCR zeolites catalysts for the reduction of NOx from diesel exhaust.

氨选择性催化还原技术(NH3-SCR)是柴油车NOx净化的主流技术之一。近年来, Cu基菱沸石小孔分子筛(Cu-CHA)由于其在NH3-SCR反应中的高活性和高水热稳定性而受到关注，并开始商业化应用。本项目以比传统合成方法更为经济、绿色的一步合成法和固相合成法制备的Cu-CHA分子筛为研究对象，深入研究Cu-CHA分子筛的水热稳老化机制，明确决定其水热稳定性的关键因素；深入研究硫、碳氢、水、磷等劣化因素对Cu-CHA分子筛催化剂的SCR性能的影响，揭示中毒机理，提出中毒催化剂再生策略；研究Cu-CHA分子筛催化剂的SCR反应机理，尤其是确定影响催化剂低温活性的决定因素；研究整体成型的Fe分子筛与Cu-CHA分子筛组成的SCR催化剂系统的协同效应。所得研究结果将对优化和设计合成高效的NH3-SCR分子筛催化剂提供新的思路和理论依据。

氨选择性催化还原(NH3-SCR)技术是柴油车NOx净化的主流技术之一。Cu基菱沸石小孔分子筛Cu-SSZ-13和Cu-SAPO-34 是具有高活性和优良高温水热稳定性的SCR催化剂。本项目主要聚焦在提高一步合成法制备的Cu-SAPO-34的低温水热稳定性和抗硫性能；一步合成法制备的富铝Cu-SSZ-13(Si/Al~4)催化剂的劣化因素和NH3-SCR反应机理研究。 .Cu-SAPO-34催化剂具有优异的高温水热稳定性，但暴露于低温（<100oC)含水气氛会发生一定程度的失活。柴油机尾气不可避免含水，因此，提高Cu-SAPO-34的低温水热稳定性对其应用至关重要。通过直接在初始凝胶中添加硝酸铈为铈源，采用一步合成法制备了新型的CuCe-SAPO-34分子筛催化剂。研究表明Ce的存在提高了Cu-SAPO-34的低温水热稳定性。主要是由于Ce的添加提高了Cu-SAPO-34的分子筛骨架和铜物种的稳定性，阻止了含水气氛中活性铜物种向非活性铜物种的转变。Cu-SAPO-34在中低温(<400oC)的硫中毒主要是由于催化剂表面吸附的SO2与NH3形成硫酸铵盐堵塞孔道。通过在初始凝胶中添加Nb一步合成法制备的CuNb-SAPO-34催化剂，具有更优的硫中毒再生恢复能力。.Cu-SSZ-13的高温水热稳定性研究通常只考虑含水情况。我们研究了Cu-SSZ-13在SO2共存时的高温水热老化机制，发现高温水热老化时SO2共存会加剧Cu-SSZ-13催化剂失活，揭示了主要是由于SO2共存加剧了Cu-SSZ-13高温水热老化过程中骨架脱铝，使得分子筛骨架彻底崩塌；骨架坍塌促进酸性位丧失和活性物种Cu2+向非活性CuOx的迁移。.研究了Cu-SSZ-13在NO2/NO-NH3-SCR反应中的机理。在标准SCR中，孤立的铜物种是NO还原的活性位；在快速SCR中 (>250oC）， NO2与NO可直接与吸附在H-SSZ-13酸性位上的氨反应。 发现NO2对Cu-SSZ-13的低温NOx转化率的抑制程度受Cu含量影响，Cu含量较高的样品，抑制效应更明显。.Cu-SSZ-13和Cu-SAPO-34研究成果对未来研究用于NH3-SCR反应的新型铜基小孔分子筛具有重要指导意义。