四联吡啶类过渡金属配合物光催化二氧化碳还原反应机理与电子转移过程的理论研究

Global warming brought out by greenhouse gas emission has become one of the most serious environmental issues. And it has been a hot-spot to research how to build a cheap artificial photosynthesis system which can effectively promote the reduction of CO2. Recently, the CO2 reduction reaction in homogeneous system has shown great advantage in both reaction conditions and selectivity. However, most studies are limited to the experimental level and the catalytic mechanism is not clear enough. There is a lack of theoretical study on the photochemical reaction pathway and the corresponding electron transfer process. In this proposal, the multiconfiguration perturbation theory combined with the Marcus electron transfer method and the density functional method will be employed to investigate the interaction mechanisms for the photosensitizer, catalyst and substrate. The potential energy surface in the excited state will be computed, and the electron transfer rate associated with its influence factor between the photosensitizer and the catalyst will be revealed. In addition, the mechanism of the CO2 reduction induced by quaterpyridine transition metal catalyst will be elucidated. On the basis of these theoretical studies, it will offer an explanation for the experimental observation and help the design for the photosensitizer and catalyst in the artificial photosynthesis system.

温室气体的大量排放及由此造成的全球气候变暖已经成为一个严重的环境问题。如何构筑廉价的人工光合系统、实现高效光催化CO2还原是目前能源领域研究的热点和难点。近年来，均相体系中的光催化CO2还原反应无论在反应条件还是在产物选择性方面都呈现出较大优势，但这些研究大多局限于实验的表观层面上，反应机理不够明确，缺乏对其光化学反应途径及相应电子转移过程的理论研究。本项目拟采用多组态微扰理论结合Marcus电子转移速率计算方法和密度泛函方法，全面探索均相体系中光敏剂、催化剂以及反应底物的相互作用机制，计算相应的激发态势能面，揭示光敏剂与催化剂之间的激发态电子转移效率及其影响因素，阐明四联吡啶类过渡金属催化剂作用下的CO2还原机理，从理论角度为实验观测现象做出科学解释，为高效光敏剂、催化剂的设计与优化提供重要参考。

二氧化碳气体的过量排放可以破坏自然环境中的碳平衡，进而引发一系列环境问题。因此，构筑高效、廉价的人工光合系统将CO2转化成高附加值化学品成为能源领域的研究重点和难点，长期以来受到科学家们的广泛关注。本项目通过高精度的量子化学计算与实验测试相结合的方法，模拟了一系列过渡金属配合物、双组分异质结构以及二维材料等催化CO2还原反应路径，揭示了还原反应机理，探究了还原反应选择性。项目完成的部分结果概况如下：（1）四联吡啶类过渡金属配合物催化CO2还原至CO反应的决速步是第一步质子耦合的电子转移，此外，计算表明过渡金属配合物中金属中心的改变可以在很大程度上影响其CO2还原性能。（2）虽然单独的吡啶分子在水溶液中可以进行光催化CO2还原反应，但是其还原反应能垒相对于过渡金属配合物较高。（3）探究了多组分异质结构以及合金对CO2还原反应的调控机制，揭示了复合结构以及双原子效应可以大幅度提高CO2还原效率。（4）在上述研究结果基础上，采用第一性原理计算以及分子动力学模拟进一步扩展证实了双原子协同效应在氮还原反应中的重要调节作用。不仅成功解释了实验观测现象，同时为催化剂的改进与设计提供了技术支撑。