基于同步辐射原位XAFS方法研究光催化醇选择性脱氢C-C偶联反应机理

Due to the diversity of chemical bonds in the alcohol molecules, the selective dehydrogenation of C-C coupling to ortho diols is difficult to synthesize using conventional chemical processes. The special environment of photocatalytic reactions provides an effective way for this process. The current research results show that the structure of the photocatalyst, the cocatalyst and the reaction medium play a key role in the selective dehydrogenation of alcohols. Limited by the utilization and development of in-situ photocatalytic characterization techniques, there is still considerable controversy over the understanding of the mechanism for the photocatalytic alcohol C-C coupling process. This project intends to focus on the reaction of photocatalytic alcohol selective dehydrogenation C-C coupling to ortho diol, based on in situ XAFS testing technology, we will design and develop in-situ photocatalytic reaction cell, systematically study the relationship between photocatalyst (TiO2 and CdS) structure, crystal type, surface group, cocatalysts (Pt, MoS2, etc.) and catalytic activity and selectivity of dehydrogenation coupling, reveal the mode of action of alcohol molecule on photocatalyst or cocatalyst, elucidate the essence of the promotion of the dehydrogenation coupling reaction by the presence of water molecules, in order to provide a more direct basis for the further optimization of the structure and performance of the catalyst and the understanding of the characteristics of the alcohol molecule C-C coupling reaction.

由于醇分子中化学键的多样性，选择性脱氢C-C偶联为邻位二醇很难利用常规化学过程完成，光催化反应的特殊环境为这一过程提供了有效途径。目前研究结果显示光催化剂的结构、助催化剂以及反应介质对醇选择性脱氢偶联起了关键作用。受限于光催化原位表征技术的开发和利用，对光催化醇C-C偶联过程机理的认识还存在较大争议。本项目拟聚焦于光催化醇选择性脱氢C-C偶联为邻位二醇这一反应，立足于原位XAFS测试技术，设计开发原位光催化反应池，系统研究光催化剂（TiO2和CdS）结构、晶型和表面基团及助催化剂种类（Pt和MoS2等）与催化活性和脱氢偶联选择性之间的关系及其内在实质，揭示醇分子与光催化剂或助剂的作用方式，阐明水分子的存在对脱氢偶联反应促进的实质，以期为进一步的催化剂结构和性能优化以及醇分子C-C偶联反应特征的认识提供更直接的基础信息。

光催化还原半反应包含光生电子从半导体往金属或金属性助催化剂（Pt、硫化物等）的转移及这些电子在助催化剂上发生电还原两个串联的过程。由于半导体-金属接触势垒高，使界面电子转移变慢而成为光催化反应的速率限制步骤。由于半导体-金属-溶液的串联关系，降低半导体-金属界面电子转移能耗，可赋予后续电还原更大的光生电势差。我们通过理论计算并经实验证明半导体与还原助催化剂Pt间形成的较高肖特基势垒严重阻碍了光生电子的转移，限制了Pt优异电催化析氢性能的发挥，并造成光能利用效率在一个太阳光强下出现极小值。为解决这一问题，本研究通过在半导体和Pt间引入同质超薄电子隧穿层、构筑功函数较低的金属电子转移桥梁和进行表面掺杂等，降低光生电子转移能耗，在较宽光强范围下整体提高光催化产氢性能，尤其是在一个太阳光强下，其光能利用效率提高了10倍以上，这为光催化剂的设计提供了新思路。