介孔氧化铝-碳复合材料的设计、制备及其在不对称催化加氢的应用

The alpha-hydroxy acid ester obtained by the hydrogenation of Pt/Cinchona system is a common structure unit of a large class of drugs. So much attention has been paid to this catalytic system and its support has become the research hotspot. Compared with other inorganic supports，the traditional platinum catalyst supported on alumina exhibit good enantioselectivity. The reason of this performance is that the alumina can provide the acidic potential and can form a kind of electrophilic alumina compound, O+(Al(OAC)2)3 (oxonium ions). However the reusability of Pt/Al2O3 is poor. The performance of platinum catalysts supported by mesoporous carbon or resin materials is opposite. Pt/mesoporous-carbon show excellent reusability but unsatisfied enantioselectivity. Based on two key issues of enantioselectivity and reusability in the asymmetric hydrogenation of α-ketoesters on Pt supported catalysts, a new kind of mesoporous alumina-carbon composites, synthesized by chelate-assisted co-assembly method, are being used as the supports of Pt nanoparticles. In this work, phenol/formaldehyde, resorcinol/formaldehyde and phloroglucinol/formaldehyde are being selected as carbon sources. The template agent, the proportion of carbon source and aluminum source, the proportion of aluminum source and chelating agent and carbonization temperature will also be changed to adjust the properties of composite materials, including porous structure, surface groups and alumina distribution; Combined with composite material and catalyst structure characterization, surface catalytic reaction mechanism research and asymmetric hydrogenation performance evaluation, catalyst structure-activity regulatory mechanism will be clarified. Besides, highly effective and reusable catalysts can be offered for the asymmetric hydrogenation of α-ketoesters. This study also can offer some references to the preparation of inorganic-organic composites and the application in asymmetric catalysis.

铂/金鸡纳碱催化体系因其手性产物α-羟基酸酯是多种药物共同的结构单元而备受关注，其载体材料的选择和设计是研究的热点。相较于其他无机材料，氧化铝能提供酸性位并生成关键的铝中间物，其负载的铂催化剂可实现突出的光学活性，但重复利用性能差；介孔碳材料负载的铂催化剂重复利用性能优异，但光学选择性欠佳。本项目创新性地提出螯合辅助共组装法制备氧化铝均匀嵌入介孔碳结构的复合材料，旨在发挥氧化铝和碳在该催化体系中的双重优势。选取苯酚/甲醛、间苯二酚/甲醛和间苯三酚/甲醛作为碳源，改变模板剂类型、碳源和铝源及螯合剂配比以及碳化温度，调变复合材料的孔道结构、表面基团以及氧化铝分布；结合复合材料和催化剂结构表征、表面催化机理探索和不对称加氢性能评价，寻求构效调控机制和规律，最终得到兼有突出光学选择性和优异重复利用性能的负载铂催化剂。本项目的完成，可为无机-有机介孔复合材料的制备及在不对称催化的应用提供理论依据。

铂/金鸡纳碱催化体系因其手性产物α-羟基酸酯是多种药物共同的结构单元而备受关注。本项目创新性地提出螯合辅助共组装法制备氧化铝均匀嵌入介孔碳结构的复合材料，作为该体系的催化剂载体，旨在结合并发挥氧化铝和碳在该催化体系中对映选择性和重复使用性能的双重优势。选取苯酚/甲醛、间苯二酚/甲醛和间苯三酚/甲醛三个典型体系作为碳源，改变模板剂类型、碳源和铝源及螯合剂配比以及碳化温度，调变复合材料的孔道结构、表面基团以及氧化铝分布；结合复合材料和催化剂结构表征、表面催化机理探索和不对称加氢性能评价，寻求构效调控机制和规律，最终得到兼有突出光学选择性和优异重复利用性能的负载铂催化剂。研究表明碳源体系、介孔碳复合材料中的氧化铝含量、铂前体的浸渍溶剂和催化剂的还原方法对催化剂结构性质、表面元素及含量等有很大影响，并最终决定了催化剂性能。以苯酚/甲醛为碳源，在最优条件下（氧化铝含量为15 wt%的复合载体、氯铂酸水溶液浸渍以及600 ℃一步氢气还原）制备催化剂Pt/15AM，不对称加氢反应中催化性能最好，在2-氧-4-苯基丁酸乙酯不对称加氢中取得最高84.8%的光学收率，在丙酮酸乙酯不对称加氢中也能取得最高87.5%的光学选择性，并且该催化剂具有优异的重复利用性能，可重复21次以上而活性没有明显下降。以间苯二酚/甲醛为碳源，获得的复合材料通过浸渍法制备的Pt/Al@RFC催化剂在EOPB的不对称加氢制备(R)-EHPB的反应中得到98.9%的转化率和82.3%的光学选择性；该催化剂在酸性反应条件下能重复使用15次以上；并且表现出卓越的反应活性，其初始TOF值高达70000 h-1，优于现有的EOPB不对称加氢催化剂。本项目的完成，设计制备出多个不对称氢化性能优异的催化剂，相关研究为无机-有机介孔复合材料的制备及在不对称催化的应用提供理论依据。