SAPO-5分子筛表面过渡金属-氧孤立结构激元的构建及其对CO2活化与光催化转化机制

The poor activity of CO2 molecules, the easy recombination of the delocalized photongenerated carriers on the semiconductor photocatalysts and the unclear photocatalytic mechanism are the open questions in the photocatalytic reduction of CO2. It was found that the electrons from the locally excited isolated meta-oxo species on the surface of molecular sieve could directly reduce CO2 without the separation process. Thus, this proposal proposes a new idea to develop well-defined isolated metal-oxo species on the surface of SAPO-5 molecular sieves through a surface organometallic chemistry method. These isolated species activated under UV and visible light irradiation to form the located excited electron-hole pairs which could activate and transform CO2 molecules efficiently. We will prepare these isolated species on the surface of SAPO-5 by a grafting reaction of transition metal complex. The adsorption and activation states of the reactant molecules, such as CO2, on the photocatalysts, will be investigated in detail. The interaction relationship between CO2 and the surface microstructures of molecular sieve will be uncovered. Furthermore, we will also study the reaction efficiency and product distribution toward the photocatalytic reduction of CO2 with H2O. The main influence factors on the reduction efficiency and reaction direction of CO2 will also be analyzed. The effects of the component, structure, and surface state of the catalysts on the photocatalytic activity and stability will be clarified. Also, the transformation of CO2 molecules on the interface of the catalysts will be elucidated. Finally, probable photocatalytic mechanisms will be proposed. These studies may establish a foundation to design and develop the new photocatalysts for the efficient reduction of CO2.

针对CO2分子难活化、半导体催化剂离域的光生载流子易复合和光催化还原分子机制不清楚等问题，基于分子筛表面局域化激发态的电子无需分离可直接还原CO2分子的发现，本项目提出用表面金属有机化学的思路和方法在SAPO-5分子筛上构筑含孤立过渡金属-氧物种的新思路；其可在紫外和可见光下产生局域的电子-空穴对激发态，且能有效地活化转化CO2分子。项目将采用过渡金属有机配合物的接枝反应在SAPO-5分子筛表面制备该物种，系统研究CO2等反应物分子在其上的吸附、活化状态，揭示CO2分子与分子筛表面微观结构的相互作用；详细评价CO2用H2O还原的光催化反应效率和产物分布，分析影响CO2还原效率和反应方向的主要因素，指出系列材料的组成-结构-表面态等对其光催化活性和活性稳定性的影响；阐明CO2分子在催化剂界面的转化过程，提出光催化反应机制模型。该研究可为设计开发具有高效还原CO2性能的新型光催化剂奠定基础。

本项目发展了系列SAPO-5基、钛基、铌基、氮化碳复合材料等二维纳米片光催化剂。这些二维纳米片材料在CO2还原和光解水方面表现出了优异的性能和催化活性稳定性。同时为了提升其光催化活性，进一步利用过渡金属修饰等方法来构建复合材料。研究了二维纳米片制备条件对于材料质量的影响，探讨了这一系列材料的组成、结构、表面态等对光催化性能的影响。利用分子光谱和原位表征手段，揭示了这些材料光催化反应过程本质。通过原位红外实验揭示了光催化还原CO2为CO的反应体系中，起主要作用的活性物种为表面吸附活化的CO2-，吸附的H2O起到提供质子的作用。这些研究成果将对超薄二维纳米片光催化剂的制备、结构调控以及分子水平上认识光催化作用提供重要的学术性指导作用，有效推动了光催化领域的发展。

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