杂多酸@介孔氮化碳高效催化无还原剂苯-O2羟基化制苯酚

One-step direct hydroxylation of benzene to phenol is a much desirable green process, but it has not been brought into practical utilization up to date. In this context, molecular oxygen O2 is a cheap oxidant with the highest atomic economy, however, the non-noble metal-catalyzed liquid-phase benzene hydroxylation with O2 in the absence of a sacrificial reductant remains a highly challenging issue. Based on the long-term experiences and the already obtained results on the hydroxylation reaction of benzene and heteropolyacid (HPA) catalysts, the applicant of this project designs and prepares the dual catalysis center-combined catalysts from the V-HPAs (Keggin-structured PMoV2 and Dawson-structured P2W15V3) and mesoporous g-C3N4 (mC3N4), i.e., the ionic bond-linked PMoV2@mC3N4 and covalent bond-linked P2W15V3@mC3N4. The two catalysts aim to highly efficiently catalyze the liquid-phase benzene hydroxylation with O2 in the absence of a sacrificial reductant with convenient catalyst recovery and reuse. Catalyst design and preparation, composition and structure, physical and chemical properties, and catalytic activities and stability, will be studied. Together with catalyst characterizations, the dual-catalysis mechanism where the benzene ring is activated by mC3N4 and the molecular oxygen by V-HPAs will be investigated and recognized. Further, influences of catalytic performances by key parameters will be elucidated, such as electronic effect, pore structure, distribution and synergy of the two active sites, and the organic linkers, based on which structure-activity relationship is discussed. This study will provide a new route and scientific foundation for establishing green and cheap heterogeneous catalytic process of highly effective hydroxylation of benzene with O2 to phenol.

苯直接一步羟基化制苯酚是至今未得到实际应用的绿色化工工艺，原子经济的无牺牲性还原剂非贵金属催化的液相苯-O2羟基化制苯酚更是极具挑战性的难题。基于申请人在液相苯羟基化及杂多酸催化剂研究中的长期积累和进展，本项目提出设计和制备由含V杂多酸(Keggin结构PMoV2及Dawson结构P2W15V3)和介孔类石墨烯结构的氮化碳(mC3N4)形成的"一体式"复合催化剂：即离子键链接的PMoV2@mC3N4和共价键链接的P2W15V3@mC3N4，旨在实现无还原剂苯-O2羟基化制苯酚的高效多相催化新工艺。重点研究催化剂的设计和制备，组成结构和物化性质，以及催化活性和稳定性；结合表征分析深入认识氮化碳活化苯环和杂多酸活化分子氧的双活性中心机理，揭示催化剂电子因素、孔结构、双活性中心分布与协同，以及有机链接体对催化性能的影响机制，为构建廉价高效苯-O2羟基化制苯酚绿色多相催化工艺提供新途径和科学基础。

面向苯的选择氧化过程，构建了多相有机催化新工艺，提高了反应活性和催化剂稳定性，深入认识了催化反应机理等关键科学问题，在Nat. Commun.、Appl. Catal. B: Environ.等期刊发表SCI论文22篇，申请中国发明专利3件。（1）针对氧气为氧源的无还原剂条件下的液相苯羟基化制苯酚，利用杂多酸、离子液体、碳材料等组分设计并制备了系列催化剂。发现贵金属Pd与离子液体的磷钼钒杂多酸盐组成的复合催化剂能够取得较高的苯酚收率，但催化剂稳定性不佳；在此基础上，制备了离子液体杂多酸盐纳米粒子与掺氮的介孔碳组成的纳米复合催化剂，获得了较高的苯酚收率，催化剂复用性能显著提高，提出了双中心协同催化作用机理。重点发展了含廉价金属铁的多孔碳材料催化的无还原剂条件下的液相苯羟基化制苯酚过程，苯酚收率和催化剂稳定性均得到显著提高，提出了+3价铁离子为活性中心的碳载体协同催化机制；进一步制备出表面富含羰基的掺氮碳材料，用来催化无还原剂条件下的液相苯羟基化制苯酚过程，获得了较高的苯酚收率和稳定的催化剂复用性能，阐明了碳材料表面羰基作为催化活性位的作用机制。（2）针对氧气为氧源的液相苯氧化偶联制联苯，开展了多孔聚合物负载贵金属的催化体系研究。设计制备了含有相邻双羧基和磺酸基的有机多孔聚合物，通过离子交换得到单原子分散Pd（II）的多孔有机聚合物，在带压的氧气气氛下实现了高效催化苯氧化偶联制备联苯，且催化剂可循环复用；进一步发展了担载Pd（II）的离子型多孔有机聚合物，实现了在常压氧气气氛下的苯氧化偶联制备联苯过程。（3）针对双氧水为氧源的苯羟基化制苯酚，发展了含钒的全硅TON拓扑结构的沸石分子筛催化剂。发现该催化剂成功实现了包括苯在内的10余种芳烃直接羟基化制备酚类化合物的瞬间反应，反应时间小于30秒，且催化剂能稳定复用，揭示了+4价钒过氧物种主导的非自由基快速催化循环新路径。所得结果为构建苯的选择氧化，特别是苯羟基化制苯酚的绿色多相催化工艺提供了新途径。