炔醇加氢机理研究及高效催化剂的开发

Alkynol semi-hydrogenation is of great significance in the synthesis of Vitamins. Conventionally, semi-hydrogenation of alkynols was often carried out on Lindlar catalysts. Lindlar catalysts usually contains CaCO3 as support, palladium as active center and Pb(OAc)2 as modifier. Bi is an alternative metal to Pb. Pb and Bi are both harmful to the environment. Then some organic compounds, possessing nitrogen, phosphorous or sulfur heteroatoms, with a strong interaction to the surface is added to the reaction solution to improve alkenol selectivity. It will cost much to extract these compounds. This proposal mainly includes the following two aspects: (1) N-doped carbon (CN) material supported Pd catalysts (Pd/CN) would be prepared. The electronic property of Pd would be tuned by using several CN materials with different N-containing species distribution; (2) Some flexible polydentate ligands, which can improve alkenol selectivity, would be immobilized on the selected CN material, respectively. Some Pd-based catalysts would be obtained by using these functionalized CN materials as supports. The flexible polydentate ligands can also play a similar role as they are free and they would not leach into the solution. This proposal can pave the way to the exploration of structure-activity relationship in the semi-hydrogenation of alkynols and the design of new catalysts for this reaction.

炔醇选择性加氢是维生素产业链中的关键反应之一。工业上普遍采用的Lindlar催化剂不但含有Pb、Bi等有毒、有害的物质，在应用过程中还要加入含N、P、S的有机助剂来进一步提高烯醇的选择性，反应后分离能耗高。本项目从合作企业实际生产中所碰到的问题中提炼科学问题，通过基础研究解决问题后再服务于企业，以基础研究带动产业化应用。项目主要包含两个方面内容：（1）调控氮掺杂炭材料（CN）中不同种类N与Pd之间的相互作用，从研究CN负载的Pd基催化剂（Pd/CN）中Pd电子结构与炔醇加氢活性之间的构-效关系出发，从活性和选择性两个方面优选出最佳的Pd/CN催化剂；（2）在上述工作的基础上，将含N、P、S的“柔性”长链多齿有机助剂固载于CN载体表面，既可以提升目标产物烯醇的选择性，又可以防止有助剂流失于反应液中，简化后续的分离过程。该项目的开展能为炔醇加氢机理研究以及高效催化剂的开发提供新的思路。

炔半加氢反应是极其重要的一类催化反应，它是生产聚合级烯烃以及维生素、香料、原料药等高端精细化学品的关键过程，涉及下游产业近万亿元。在该反应中，如何实现串联加氢过程中烯烃这一亚稳中间产物的选择性生成一直是巨大的挑战。针对这一问题，商业Lindlar以Pd为活性组分，铅、喹啉、噻吩等为助剂的催化体系，该催化剂的设计思路是利用助剂组分阻塞大部分的活性位点，从而在低反应速率下很好地控制反应过程和选择性，但该催化剂长期面临着环境危害大、效率极低的突出问题。针对上述难题，本项目从柔性助剂修饰、活性位微环境调控、催化构效关系探究等三个方面开展研究。首先深入理解柔性多齿有机胺与Pd表面之间的相互作用及其对反应性能的影响机制，通过配位键在金属表面构建动态可逆的界面“呼吸模式”有效辨识反应物和中间体，选择性地抑制中间产物烯的吸附和加氢，所创制的Pd/NHPC-DETA催化剂在甲基丁炔醇半加氢反应的TOF值高达到14412 h-1，反应活性比商用的Lindlar催化剂高36倍，同时烯醇选择性也可以达到95%，也展现出良好的稳定性；其次通过氢溢流在催化剂表面构筑高密度羟基极性层，利用反应过程中催化剂表面极性的动态变化促进非极性产物烯的即时脱附，显著抑制其过加氢，反应选择性可提升至98.3%，同时溢流氢物种可以有效参与反应过程，提升催化活性；此外，项目还系统揭示了Pd颗粒尺寸对上述新催化机制的影响，发现减小颗粒尺寸可以最大程度强化表面极性对反应性能的影响，并进一步开发单原子催化剂，将贵金属利用率提升至100%，实现加氢催化剂的贵金属等效减量和生产成本的降低。