铈基催化剂/ZSM-5膜双层多效催化剂协同净化HCN、N2O和NH3研究

Nowadays, the pollutants with high concentration of CxHy, CO , NOx and PM in automobile exhaust have attracted much attention. However, the pollutants of HCN, N2O and NH3 are almost neglected. This study prepares a multi-way dual layer catalyst of cerium-based catalyst (lower layer)/metal ion modified ZSM-5 membrane (upper layer) over cordierite, then the preparation conditions and influencing factors are investigated. This dual layer catalyst consists of an upper layer of ZSM-5 membrane and a lower layer of cerium-based catalyst. The HCN catalytic hydrolysis coupling of N2O catalytic decomposition are first carried out on the upper layer catalyst, then the catalytic oxidation of CO and NH3 are proceeded over the lower layer catalyst. This study will investigate the mechanism of HCN catalytic hydrolysis, N2O catalytic decomposition as well as catalytic oxidation of NH3 and CO, respectively. Then we will study the catalytic principle and the interaction mechanism of synergistic purification of HCN, N2O and NH3, furthermore, the reaction mechanism and the co-relationship between physicochemical properties of dual layer catalyst and synergistic reaction are also investigated. This study aims to reveal some key mechanisms of the process of synergistic purification, and the results can provide enough technical supports for the principles of synergistic purification of HCN, N2O and NH3.

高浓度CxHy、CO、NOx和PM一直是汽车尾气中倍受关注的污染物，而汽车尾气中HCN、N2O和NH3却未引起足够重视。本课题在堇青石上构建铈基催化剂(底层)/金属离子改性ZSM-5膜（上层）双层多效催化剂，并考察催化剂的制备条件及影响因素。通过在上层ZSM-5膜上先实现HCN催化水解和N2O催化分解反应的耦合，然后HCN水解产物（NH3和CO）和NH3在底层铈基催化剂层被高效催化氧化，从而实现HCN、N2O和NH3的协同净化。本研究在明晰HCN催化水解、N2O催化分解和NH3及CO催化氧化反应机理的基础上，进一步揭示双层催化剂协同净化HCN、N2O和NH3的催化原理和各反应间的相互作用机制，阐明双层催化剂的物化性质与协同反应的内在联系规律，并解析协同反应的机理。本研究旨在揭示双层催化剂协同净化HCN、N2O和NH3过程中的若干关键机理问题，将为HCN、N2O和NH3协同净化建立技术基础。

高浓度 CxHy、CO、NOx和PM一直是汽车尾气中倍受关注的污染物，而汽车尾气中 HCN、N2O和NH3却未引起足够重视，本课题研发的分子筛及铈基催化剂对其有良好的去除效果，并考察催化剂的制备条件及影响因素，分析了催化剂的制备工艺、微观结构、表面物种与催化活性之间的联系，明确其反应途径，该项目主要从四个方面展开研究：（1）Fe-Nb/ZSM-5催化剂催化水解HCN的研究，研究表明Fe和Nb物种的相互作用可提高催化剂的氧化还原性能、表面酸性以及孔结构，进而促进HCN的水解。HCN和水反应生成甲酰胺，甲酰胺进一步与水反应生成甲酸铵并分解甲酸和氨，甲酸通过热解进一步转化为CO和H2O。（2）Ce基催化剂催化氧化CO，模板剂和沉淀剂对CeO2的形貌有重要影响。氨水作沉淀剂有利于形成八面体CeO2；浸渍过程有利于增加表面高分散PdO，活性增高。尿素、草酸和碳酸铵沉淀有利于形成无定形Pd/CeO2颗粒，活性降低。 Zr和Al的加入Pd/CeO2入会造成比表面积的提升、表面PdO增多和催化活性的提高。（3）高分散的CuO是Cu/Ce-SAPO-34催化剂的活性组分，团聚态的CuO会降低催化剂的氮气选择性，Ce物种的加入可提高CuO物种的分散性，增强催化剂的水热稳定性能；双层涂覆式Fe/Cu负载分子筛催化剂具备良好的活性和N2选择性，且Fe物种的加入有利于N2选择性的提高；针对Cu-Fe氧化物催化剂，NH3-SCO反应遵循i-SCR机理：吸附的NH3被活化并与氧原子反应生成亚硝酰基（-HNO），-HNO被来自O2中的氧原子氧化生成NO物种，NO与-NH2反应生成N2。（4）Co3O4¬催化剂显示出了良好的催化分解N2O的活性，且向Co3O4催化剂中引入Ca和Sr物种可增强其催化活性。