基于多核3d-4f金属簇晶态分子催化剂的构筑及其光化学还原CO2性能研究

The realization of recycling energy and decreasing CO2 in atmosphere is the important goal for sustainable development. This project will choose earth-abundant metals (3d and 4f) and functionalized organic ligands to construct a series of stable multinuclear 3d/3d-4f clusters, and these materials will be uesd as heterogeneous molecular catalysts applied in photochemical reduction of CO2. The core concept is the synthesis of cluster with many/different kinds of metal active species by utilizing multiple redox 3d metal and specific organic ligand, and make the targeted cluster obtain good light-havsting capacity and structural stability. In addition, the introduction of 4f metal featuring high positive charge and coordination numbers will be expected to further improve the heterogenization of clusters. The photocatalytic active centers of cluster will primarily originate from the intra-cluster unsaturated coordination sites or leaving groups, while the corresponding structural robustness can efficiently enchance the long-term durability and recyclability of catalyst in artificial photosynthesis. The investigation content of this project will focus on the influences of altering the components, doped metal active centers ratio of stable 3d/3d-4f clusters and reaction conditions to photocatalytic CO2 reduction properties. On this foundation, we attempt to get the stable metal cluster including many active centers and excellent photocatalytic CO2 reduction property so as to provide the theoretical and experimental evidence for the construction and study of metal cluster-based heterogeneous molecular catalysts.

实现能源再利用和降低大气中CO2含量是可持续发展的重要目标。本课题拟选用地球储量丰富的过渡（3d）和稀土（4f）金属与功能化有机配体来构筑稳定的多核3d/3d-4f金属簇，该材料将作为异相分子催化剂被用于研究CO2光化学还原。核心思路是利用3d金属多重氧化还原价态的特性，结合特定结构修饰的有机配体，制备出包含多个/多种金属活性位点的簇合物，并使其具有良好的光富集能力和结构稳定性。此外，通过引入高正电荷与高配位数的4f金属以期进一步提高金属簇的异质化。金属簇内光催化活性中心主要通过金属不饱和配位点或易离去基团来实现，而其结构稳定性可以有效提高催化剂在反应中的再循环能力。本项目将探讨改变稳定3d/3d-4f金属簇的组成、金属活性中心掺杂比以及反应条件对光催化还原CO2性能的影响。总结规律，寻求包含多金属活性中心和光还原性能良好的稳定金属簇，为金属簇基异相光催化剂的制备和研究提供理论和实验依据。

随着人类社会发展进程的不断加快，日益枯竭的不可再生能源（煤炭、石油、天然气等）的急剧消耗及其燃烧带来的环境问题，已经濒临可持续发展的平衡底线。尤其是以CO2为主的温室气体排放，被认为是全球变暖的罪魁祸首。在众多二氧化碳利用的策略中，光催化CO2还原（也称“人工光合作用”）是一种利用太阳能将CO2转化为低碳燃料（如CO、CH4、HCOOH、HCHO、CH3OH、C2H5OH等）的绿色技术路径，它在解决上述问题方面具有非常大的前景。本项目围绕晶态金属簇合物，构筑了一系列具有高活性、高选择性的金属簇基CO2还原光催化剂：1. 构筑了首例“Keggin”型钛氧簇，该工作不仅将Ti引入传统Keggin家族中，而且首次利用钛氧簇合物为二氧化碳光催化剂并实现高选择还原二氧化碳为甲酸； 2. 3d异金属簇基人工光合成光催化剂。通过异金属团簇的调控与吸光有机配体结合，催化剂在不添加光敏剂和牺牲剂的条件下仅在纯水中完成二氧化碳还原与水氧化偶联的人工光合成全反应。产物为甲酸和氧气且选择性接近100%。这是晶态材料首次完成人工光合成全反应；3. 强还原性和强给电子能力的3d-4d多酸簇构筑的光催化剂，完成高选择性光催化二氧化碳还原到甲烷的转换；4. 卟啉配体与还原性多酸结合，完成自敏化。在不添加贵金属光敏剂的条件下完成二氧化碳到甲烷的高选择性转化。