基于氧空位调变的稀土烧绿石型催化剂及其碳烟微粒催化燃烧性能研究

This proposal is based on the prevention of diesel engine emission which is an important source of particulate matters in the air. Soot particulate is one of the main pollutants in diesel engine emissions causing serious problems to global environment and human health.Filtration and controllable regeneration within the exhaust stream are among the most promising methods for diesel soot removal, while the key technology of controllable regeneration is oxidation catalysis. Thus the goal of this study is to develop a new kind of lowcost and highly efficient rear-earth pyrocholres(A2B2O7) composite oxides for catalytic combustion of diesel soot particulate and to interpret the catalytic mechanisms.Due to the controllability of compositions and performances of pyrochlores, oxygen vacancies in A2B2O7 can be modulated through different preparation methods, isomorphous replacements of A site(by La, Ce, Nd) and/or B sites (by Sn, Mn and Fe, Co, Cu), and doping with trace amount of noble metal as well. Thereby, both the concentration and mobility of reactive oxygen species can be changed; redox and acid/basic synergistic effects can be also formed. The catalyst activity will be improved from the internal (active elements) side and extrinsic (catalyst and soot contact) side. In this study, the oxygen vacancy is characterized by Raman technique, the active oxygen is quantified using isothermal anaerobic titrations with soot as a probe molecule, and the intermediates and mechanism for soot combustion can be determined by In situ IR. As a result, the relationship among oxygen vacancy, active oxygen species, redox property and catalytic performance will be established. After this study, we hope to provide the scientific basis for the design of a new generation of diesel soot combustion catalyst.

本项目基于柴油车尾气污染尚未根本解决这一问题而申请，利用我国丰富的稀土资源，开发低成本、高功效的稀土烧绿石A2B2O7型复合氧化物催化剂，使碳烟在排气温度下催化氧化去除，实现颗粒过滤器的原位再生。利用A2B2O7组成及性能的可控性，通过制备方法的选择，实现A位(La,Ce,Nd)和B位(Sn,Mn,Fe,Co,Cu)元素的同晶取代及微量贵金属的掺杂，以调变氧空位的类型和浓度，进而改变活性氧的浓度和移动性，形成氧化还原协同和酸碱协同作用，从内因(活性组元)和外因(催化剂与碳烟接触)两方面提高催化剂活性。采用拉曼技术表征氧空位浓度变化，结合碳烟厌氧滴定研究活性氧物种浓度及迁移规律，借助原位技术研究反映中间物种的转化规律，明确氧空位浓度、活性中心结构、氧化还原性与催化活性之间的关系；揭示碳烟在A2B2O7上催化燃烧的反应机制，为设计新一代柴油车碳烟燃烧催化剂提供科学依据。

机动车尾气特别是柴油车排放的尾气是造成城市灰霾天气和光化学烟雾污染的重要来源，尾气催化后处理技术是源头消除机动车污染物的关键。随着排放法规的日益严格，普遍认为在排气管安装碳烟催化燃烧过滤器是最有前途的碳烟消除技术之一，高活性的碳烟燃烧催化剂是该技术的核心。本项目基于稀土烧绿石（A2B2O7）复合氧化物的新型柴油车碳烟氧化催化剂的优化合成和微观机制研究，建立了简单方便的烧绿石复合材料的制备技术，合理优化了催化剂组成，制备出较大比表面、晶型结构完整的烧绿石型复合氧化物；提高了催化消除碳烟的性能，使碳烟燃烧温度降至300°C左右，同时兼顾了NOx消除。通过多种现代表征手段，获得了稀土烧绿石复合氧化物催化剂的氧空位浓度、活性氧量、活性组分、粒度及孔结构性质等内部和外在因素等与碳烟催化去除活性之间的规律性认识。. 采用了共沉淀法、水热法和溶胶凝胶法等多种制备方法，调控多元复合氧化物催化剂的组成和形貌，制备出活性组分高分散的、具有较大比表面积的烧绿石复合氧化物多孔材料，以改善催化剂孔结构性质和氧物种的可移动性，这是实现碳烟氧化催化剂高活性的必要外界条件；同时，利用烧绿石型复合氧化物结构开放的特点，通过A位和B位阳离子同晶取代将活性金属元素成功引入到其结构中，进而调变催化剂的氧化还原性质、表面酸碱性能和氧空位浓度等，这是提高碳烟燃烧去除活性的内在因素。利用碳烟厌氧滴定技术研究了活性氧物种浓度及催化反应的转化频率（TOF），结合原位技术研究了反映中间物种的转化规律，明确了氧空位浓度、活性氧量、氧化还原性与催化活性之间的关系；碳烟在A2B2O7上催化燃烧的反应机制研究表明，碳烟催化氧化去除过程中氧溢流机理和氧化还原机理同时存在。本研究为设计新一代高效催化剂提供了有效的科学依据。