单原子位点催化剂高效电催化木质素Cα-Cβ键选择氧化断裂研究

Electrocatalytic oxidation is a green technique for lignin degradation to harvest value-added aromatic compounds. Traditional bulk metal or metal oxide catalysts suffer from low lignin conversion and low target product yield. Therefore, there is an urgent need to develop high-efficiency new catalysts. In this project, utilizing bi-heteroatom doped hierarchically porous carbon nanotubes (X-N-HPCNTs) as supports to construct a series of single-atom catalysts with bi-heteroatom coordination structures (M1-X-N-HPCNTs) for electrocatalytic oxidative cleavage of Cα-Cβ bond in lignin is proposed. Due to the π-electron conjugated system and hierarchical micro-mesoporous structure of HPCNTs, π-π stacking interactions can be enhanced between catalyst surfaces and lignin molecules, and the mass and charge transfer can be facilitated. By adjusting the coordination structure of single atom site to promote anisotropic distribution of d electrons and active oxygen species generation, in combination with regulating the uniform single atom site to achieve single reaction path, highly efficient selective catalytic oxidation degradation of lignin can be achieved. By means of physical and chemical characterization and DFT calculation, the relationship of catalyst’s microstructure, physical and chemical properties and its electrocatalytic performance will be established. We will try to reveal the mechanism of electrocatalytic oxidative cleavage of Cα-Cβ bond of lignin on M1-X-N-HPCNTs. Overall, this project will provide new ideas and scientific basis for the highly efficient conversion of lignin into high value-added chemicals.

电催化氧化是降解木质素制备高附加值芳香化学品的绿色途径。传统体相金属或金属氧化物催化剂存在木质素降解效率低、目标产物选择性差等问题，因此迫切需要发展新型高效催化剂。本项目提出以双杂原子掺杂的层状多孔碳纳米管为载体，构筑双杂原子配位单原子催化剂，用于选择性氧化断裂Cα-Cβ键的新思路。利用碳纳米管共轭π电子体系和管壁的微介孔层级结构，增强催化剂与底物分子之间的π-π相互作用，促进传质和电荷转移；通过调节双杂原子配位单原子位点配位结构，使其d轨道电子云各向异性分布而促进活性氧物种生成，进一步利用单原子位点结构均一的特点，调控为单一反应路径，实现高效高选择性氧化裂解木质素。借助物理化学表征和DFT计算分析催化反应历程，建立催化剂微观结构与物化性质同其基元电极过程与电催化性能之间的内在关联，揭示单原子位点催化剂催化木质素Cα-Cβ键氧化断裂机理。本项目将为木质素资源化利用提供新思路和科学基础。

木质素结构中C-C键约占化学键总量的三分之一，键能高达69-123kcal/mol，选择性断裂C-C键是降解木质素制备芳香单体化合物的关键。项目针对木质素Cα-Cβ连接键的电化学选择氧化断裂，开展了碳基杂原子配位单原子位点催化剂的精准构筑与性能调控研究。首先，发展建立了聚合-碳化、自组装-热解、熔融盐辅助热解三种策略分别实现了N、B、O、Cl杂原子在碳载体中的精准可控掺杂，并进一步精准构筑了杂原子配位单原子位点催化剂，包括Pt-N3C1、Pt-N3Cl1、Pt-N2Cl2、Pt-N4、Ir-N2B2、Ir-O2B2等。其次，电催化性能测试表明，Pt-N3C1单原子位点催化剂具有最优的Cα-Cβ键断裂活性和选择性，目标产物苯甲醛收率高达81%，明显超过了之前报道的电催化剂。此外，与体相Pt电极和Pt/C基准催化剂的性能相比，Pt-N3C1也具有显著优势。最后，通过实验结合DFT理论计算进行机理研究，发现反应涉及Cβ自由基中间体，该中间体能够与tBuO•自由基发生偶联反应从而选择性断裂Cα-Cβ键。这项工作是首次发现碳、氮共配位单原子Pt催化剂能够有效电催化氧化裂解木质素Cα-Cβ键，为木质素通过绿色可持续的电化学路径的转化利用提供了新思路。