Lewis acidic porous element organic frameworks for the selective catalytic transformation of monosaccharides

元素-有机骨架是一类比较年轻的纳米多孔无机-有机杂化材料，在多相催化中具有很大的潜力。尤其是锡基材料，基于锡掺杂沸石的众所周知的催化性能，是非常重要的。基于它们的活性路易斯酸性中心，特别是近年来对生物质平台化合物的转化，特别是糖的异构化，开辟了一个相对较新的多相化学催化领域。锡有机骨架(SnOF)显示出嵌入有机基质中的活性锡位，其内表面化学与沸石的内表面化学显著不同。初步工作表明，SnOF对糖的转化具有很高的活性。然而，在沸石的情况下，较佳的是催化醛糖的异构化，而不是催化醛糖异构化为酮糖。这种反向选择性可以用不同的反应机理来解释，这可能是由活性中心的类型和它们的化学环境所定义的。这种选择性的异构化使人们能够获得大量用于制药和食品工业的稀有醛类。在这个项目中，这一催化系统将由达姆施塔特理工大学和亚琛理工大学的两个技术化学小组在互补的合作下进一步研究和开发。在TUDA，将对合成的SnOF进行系统的修改，以便以缺陷的形式定制活性中心的类型和数量。将开发一种新材料的替代合成路线，具有更精确定义的活性中心，并对其进行全面表征。在连续操作的固定床反应器中进行了异构化催化，以确定最重要的反应参数并评价其技术可行性。在更高的温度下，将研究其他生物价值链的短链副产品的形成。在RWTH，重点是对异构化的机理研究和活性中心的表征，以便系统地推导出结构-活性关系，为进一步开发催化剂提供依据。最后，采用制备催化的方法，通过异构化反应优化了稀有醛的制备工艺。总体而言，该项目涉及一种基于新催化剂系统的创新方法，用于单糖的选择性转化。它结合了对新催化剂材料的基础研究和基于知识的新的非均相催化过程的开发，以便在新的价值链中利用可再生原材料。

Element-organic frameworks are a rather young class of nanoporous inorganic-organic hybrid materials and offer high potential in heterogeneous catalysis. Especially tin-based materials are important based on the well-known catalytic properties of Sn-doped zeolites. Based on their active Lewis-acidic sites especially the conversion of biomass-based platform chemicals has been investigated in recent years and particularly with the isomerization of saccharides, a relatively new area for heterogeneous chemocatalysis has been opened up. The Sn-organic frameworks (Sn-OF) exhibit active Sn sites embedded in an organic matrix with the internal surface chemistry differing significantly from that of the zeolites. In preliminary work it was shown that the Sn-OF show a high activity for the conversion of sugars. However, the epimerization of the aldoses is preferably catalyzed instead of the isomerization of aldoses to ketoses in case of the zeolites. This invers selectivity can be explained by a different reaction mechanism, which is probably defined by the type of active sites and their chemical environment. This selective epimerization enables access to a large number of rare aldoses for use in the pharmaceutical and food industries. In this project, this catalytic system will be further investigated and developed in a complementary collaboration by two groups in technical chemistry from TU Darmstadt and RWTH Aachen University. At TUDA the Sn-OF synthesis will be systematically modified in order to tailor the type and number of active sites in the form of defects. An alternative synthesis route towards new materials with more precisely defined active sites will be developed and comprehensively characterized. The epimerization catalysis is carried out in a continuously operated fixed-bed reactor in order to determine the most important reaction parameters and to evaluate the technical feasibility. At higher temperatures, the formation of shorter-chain by-products for other bio-based value chains will be investigated. At RWTH the focus is on mechanistic studies of the epimerization and the characterization of the active sites in order to systematically derive structure-activity relationships for a further development of the catalysts. Finally, the preparation of rare aldoses is optimized through epimerization using the approach of preparative catalysis. Overall, the project deals with an innovative approach based on a new catalyst system for the selective transformation of monosaccharides. It combines basic research for new catalyst materials with the knowledge-based development of a new heterogeneous catalytic process for the utilization of renewable raw materials in new value chains.