基于薄壁中空球分子筛的封装金属催化剂及其VOCs催化氧化性能研究

As a new type of catalysts to remove VOCs, zeolite-encapsulated noble metal catalysts have higher catalytic activity and thermal stability compared with the traditional zeolite-supported metal catalyst. However, the utilization of metal active sites is underutilized by an excessive thickness of the coating layer on the metal and unstable load position of the metal. Aiming at these problems, a notion was built for constructing an efficient catalyst for VOCs catalytic oxidation, which will be carried out by preparing metal nanoparticles encapsulated within thin-shelled hierarchical hollow zeolite spheres. To control the shell thickness of hollow zeolite spheres, based on electrostatic self-assembling, affinity interaction between anionic/cationic polyelectrolytes and silicate species is applied. To increase the utilization of active components, based on in-situ synthesis method, the hollow zeolite crystallization and the metal nanoparticles encapsulation are achieved at the same time under hydrothermal conditions, which contributes to encapsulate the metal nanoparticles within zeolite micropores. The shell thickness of hollow zeolite spheres and the size of metal particles will be adjusted to improve diffusion and adsorption of reactant as well as the diffusion and desorption of target product. This proposal will study the controllable synthesis method of metal nanoparticles encapsulated within thin-shelled hierarchical hollow zeolite spheres, explore the relationship between the catalyst preparation, structure property and catalytic performance, provide high efficiency catalytic materials for deep oxidation of VOCs, and make a foundation for the application of noble metal encapsulated with hierarchical zeolites for VOCs catalytic oxidation.

作为一类新型脱除VOCs的催化材料，分子筛封装金属相比传统的负载型催化剂具有更优异的低温反应活性和耐热稳定性，但同时存在活性组分包覆层过厚和分布位置不稳定的问题，降低了活性组分利用率。本项目提出制备薄壁中空球分子筛并对金属粒子进行封装，以构筑高效的脱除VOCs催化剂的设想。基于静电自组装技术，利用阴/阳离子聚电解质与分子筛前驱体的亲和作用，调控分子筛中空球壁厚。在此基础上，借助原位合成技术，在水热条件下，同步完成分子筛晶化和金属纳米颗粒封装，将金属颗粒限域在分子筛微孔孔道内，制备出薄壁中空球型级孔分子筛封装金属催化剂，以强化反应物/产物的扩散和吸附/脱附性能，减小金属颗粒尺寸，进而提高活性组分利用率。研究薄壁中空球分子筛封装金属的可控制备方法和催化剂制备-结构-性能关系，以期为VOCs深度氧化提供高效催化材料，也将为级孔分子筛封装金属材料在有机物氧化反应中的应用奠定基础。

在VOCs催化氧化治理中，催化剂制备及其使用过程的高温条件，常致使活性组分团聚烧结、多种结构共存，这种复杂显然不利于其构效关系的准确量化及高性能催化剂的设计。针对这一问题，本项目提出了制备单分散高能结构活性纳米粒子并对其进行稳定化封装，构筑高活性、高稳定性脱VOCs催化剂的设想。基于静电自组装技术，通过调变贵金属前驱体和分子筛晶化时间，实现中空分子筛封装贵金属的制备，最优催化剂可在187 oC下将VOCs 催化转化率提高到98%。在燃烧温度230 oC下，可以实现100 h内的VOCs的完全燃烧。此外，在本项目指引下，还发展了一系列不同贵金负载于各类分子筛催化剂，揭示了催化反应机理，丰富并深化了本项目的研究内涵，也为高性能VOCs燃烧催化剂的设计和开发提供科学依据和理论支持。