用于化学固定CO2的介孔金属膦酸盐高效固体催化剂的设计和合成

Considering the greenhouse effect and the depletion of fossil fuels, development of highly efficient methods for chemical fixation of carbon dioxide (CO2) is one of the urgent and attractive subjects for investigation. A feasible route is by utilization of small-membered ring compounds such as epoxides and aziridines to react with CO2 as a C1 building block. Therefore many homogeneous catalysts and heterogeneous catalysts have been investigated for the catalytic reaction of aziridine with CO2, showing rather good activity. However, organic solvents, co-catalysts, stringent synthetic conditions or halogen-containing in catalysts are required. It is thus still a challenge to develop efficient and environmentally friendly solid catalysts for chemical CO2 fixation. This project is thus developing a new solid catalyst, mesoporous metal organophosphonates, for efficient chemica CO2 fixation based on our previous works. By surfactant assisted method, a series of mesoporous metal organophosphonates （Ti-, Al-, Zr- and Sn-based） bridging specific organic groups in the framework are going to be synthesized. The final hybrid materials will have uniform mesopores and high specific surface areas, and their hybrid framework will be uniformly dispersed functional organic groups and inorganic species, which is used to activate CO2 and epoxides / aziridines. Then the newly synthesized mesoporous metal organophosphonates are utilized to catalyze the reaction of CO2 and small-ring compounds. By systematically analyzing the reaction results, high-efficient mesoporous metal organophosphonate solid catalysts will be screened out. And this result will be helpful to understand the surface property and structure feature of a high-efficient mesoporous metal organophosphonate solid catalyst required. The findings provide a new perspective for the investigation of catalytic mechanism of mesoporous metal phosphonates for chemical CO2 fixation, as well as for development of other high-performance catalysts.

本课题针对CO2与小环化合物反应所使用的现有催化剂在催化过程中往往需要添加有机溶剂、共催化剂以及苛刻的反应条件等问题，拟开发一类新型的固体催化剂-介孔金属膦酸盐。采用表面活性剂辅助的方法合成有特定有机基团桥连的一系列介孔金属膦酸盐，包括钛基、铝基、锆基、锡基，使得这一材料在织构上具有均一可调的介孔孔径和高的比表面积；同时在骨架上均匀分布着活化CO2和有机小分子的功能性基团。通过系统研究介孔金属膦酸盐作为固体催化剂催化CO2与小环化合物（环氧化物和氮杂丙叮衍生物）的反应结果，筛选出介孔金属膦酸盐高效固体催化剂；通过分析催化结果，进一步认识用于化学固定CO2介孔金属膦酸盐高效固体催化剂所需要的表面特性和结构特征，并进一步的对合成介孔金属膦酸盐高效固体催化剂提供实验指导。本课题的研究对揭示金属膦酸盐对CO2与有机小分子的催化机理有重要指导意义；也为设计催化CO2化学反应的其他固体催化剂提供思路。

CO2是温室气体的主要成员之一，如何减少CO2的排放并改善环境中已存在的过量CO2，引起了研究者们广泛的兴趣。本课题拟采用化学转化的方法，设计合成一类新的高效固体催化剂¬—金属膦酸盐双功能型固体催化剂用于催化转化CO2为有用的化学物质。该类催化剂的合成，所选磷源包括羟基乙叉二膦酸(HEDP)，乙二胺四甲叉膦酸(EDTMP)，二乙烯三胺五亚甲基叉膦酸(DTPMP)，金属盐主要包括锡基（SnCl4•5H2O）和铝基(AlCl3•8H2O，Al(NO3)3•9H2O，Al2(SO4)3•18H2O，Al(OC4H9)3)。其中所合成得到的碳掺杂介孔磷酸铝具有可调的介孔孔径（1.5～3.0 nm），和可控制的比表面积（200～600 m2/g）；介孔膦酸锡的比表面积在100～450 m2/g，而且该材料可以通过在合成过程中是否加入CTAB来改变膦酸锡催化剂骨架表面性质和活性基团分布，同时通过调变氢氧化钠加入量来改变催化剂骨架上活性基团的量。通过大量的催化实验，我们发现碳掺杂介孔磷酸铝在催化CO2和1-乙基-2-苯基氮杂丙叮表现出非常好的催化活性，重复循环四次，催化效果未见明显下降。另外，在无表面活性剂辅助条件下合成的有机膦酸锡对CO2和苯基环氧乙烯环加成反应表现出一定的催化活性。本课题的研究揭示选择金属膦酸盐酸碱双功能型催化剂用于催化CO2与有机小分子的环加成反应是一条可行的途径。