基于5-羟甲基糠醛氧化增值新型多相催化剂的构筑

The valorization of renewable lignocellulosic biomass for the sustainable production of fuels and chemicals has attracted much attention due to the depletion of fossil resources and environmental concerns. A very desirable approach is the (bio)chemical transformation of biomass to platform molecules followed by catalytic conversion into high-value-added chemicals, such as polymer precursors, pharmaceuticals and fine chemicals. 5-Hydroxymethylfurfural (HMF) has been identified as a key and versatile platform compound derived from cellulosic C6 carbohydrates, because HMF can be used for the integrated production of various building-block compounds. Particularly, 2,5-furandicarboxylic acid (FDCA), the symmetrical furanic diacid synthesized via oxidation of HMF, is a promising substitute for terephthalic acid that represents a petroleum-based monomer largely used for the manufacture of polyethylene terephthalate (PET) plastic. Heterogeneous selective oxidation of HMF to FDCA using molecular oxygen without addition of any homogeneous base is of great importance but remains significant challenging. Because soluble bases enable to facilitate alkoxide formation and C-H activation in the oxidation process, but further acidification and purification are required for subsequent use of FDCA in the polymer industrial, hampering the green footprint of the process. To the best of our knowledge, there is very few successful catalyst reported for the base-free HMF selective oxidation, which still suffers from instability and harsh reaction conditions. The objective of this project is to develop the formulation and preparation of novel functionalized materials such as supported nanoparticles of noble metals or mixed oxides of transition metals, being applied to direct FDCA production under base-free conditions in water solvent using O2 or air as oxidant. The breakthrough lies in finding new support materials that exhibit stable basic property and/or allow strong adsorption of HMF and its derived intermediates, as well as finding smart combination of active metal centers to activate O2 molecule and oxidize simultaneously hydroxyl and carbonyl groups in HMF compound. Moreover, the basicity of catalyst, the size and morphology of nanoparticles, the electronic configuration of metal centers, and the metal-support interactions will be systematically tuned and manipulated. The catalytic properties are fully characterized in depth by comprehensive chemico-physical techniques, and the catalytic processes upon different important parameters are optimized. Based on that, the relationship between catalyst formulation, properties and catalytic performances can be established, leading to proposition of active site modeling and reaction mechanism.

5-羟甲基糠醛（HMF）选择氧化制高附加值生物基聚合物单体2,5-呋喃二甲酸（FDCA）是具有重要应用前景的生物炼制过程。多相催化剂上以水为溶剂、氧气或空气为氧化剂，不添加可溶性碱的HMF选择氧化符合绿色化学要求，却极富挑战性。目前仅有少量研究报道且反应条件苛刻、催化剂循环使用率低。本项目旨在开发几种能够高效循环使用的新型多相催化剂以实现温和条件下HMF氧化制FDCA（收率>=95%），目标瞄准负载纳米贵金属（Au，Pt，Pd，Ru）和非贵金属（Cu，Ce，Mn，Zr，Fe, Co）复合氧化物。突破口在于合成对底物及中间体具有强吸附作用的碱性载体，以及构筑能够活化氧分子并同时转化HMF分子羟基和羰基的催化金属中心，调变催化剂碱性位，调控纳米材料粒径和形貌，调变金属中心电子构型，增强金属-载体协同作用。所得催化剂将进行综合物理化学表征，优化反应参数，探究催化剂活性相、构效关联和反应机理。

5-羟甲基糠醛（HMF）选择氧化制2,5-呋喃二甲酸（FDCA）是糠醛类平台分子转化增值的重要途径，对于生物基聚合物产业的可持续发展至关重要。研发以水为反应溶剂、以氧气为氧化剂、在无碱添加剂下工作的高效稳定的多相催化剂是核心问题。我们主要研发了Ru基、Pt基贵金属催化剂和Co-Mn复合氧化物非贵金属催化剂。其中，Ru和Pt催化剂主要为负载型高分散金属纳米粒子，包括Ru/HAP，Ru/MnxCeOy，RuxCoOy(OH)，RuPt-MgAlO，Pt/NiO，Pt/Mn(PO)xOy和Pt/Nbx@Co催化剂。上述多相催化剂均为首次报道，并表现出优异的催化性能和稳定的循环使用性，FDCA收率均在99%以上。与文献中公开报道的典型对照组催化剂相比，我们研发的催化剂在性能上和反应条件上均处于最佳或者领先的地位。我们系统地研究了催化剂的制备方法与形貌的关系，催化剂组成与载体酸碱性、氧化还原性的关系；载体中活性氧物种的种类和浓度与O2吸附活化的关系；主要反应参数与催化剂性能之间的关系。我们还深入探究了催化活性中心对HMF及反应中间体的OH基和C=O基的吸附活化。基于综合性物理化学表征技术和反应动力学实验，我们揭示了高分散金属态的Ru、Pt物种为催化活性中心；载体上的碱性位点可以促进OH基氧化为C=O基，而酸性位点则促进C=O基氧化为COOH基；载体中丰富的活性氧物种不仅作为氧化剂直接参与氧化反应，而且可以促进HMF和中间体的吸附活化，驱动无碱氧化反应；与此同时O2分子在催化剂表面的氧空穴上发生吸附解离，不断地生成活性氧物种；水作为溶剂参与了氧化反应并有助于FFCA转化为FDCA，即反应决速步；金属-载体强相互作用提升了催化活性中心的性能和稳定性。总之，针对HMF选择氧化制FDCA，我们清晰地揭示了催化剂活性相的本质，建立了催化剂结构与性能之前的关系，最终为讨论多相催化反应机理提供了实验和理论依据，并为设计高效稳定的生物质选择氧化多相催化剂积累了经验。