光催化CO2还原的反应动力学高度取决于电子和质子向吸附在催化中心上的CO2分子的转移速率。关于揭示催化剂中质子对CO2还原光催化活性的影响的研究是重要的,但很少报道。在本文中,我们,从分子水平,结果表明,CO2还原的光催化活性与催化剂中的质子利用率密切相关。具体来说,设计并合成了四个基于具有不同羧基数的Robson型配体(-nCOOH;n=0,2,4,6)的双核Co(II)配合物。在可见光照射下,所有这些络合物都显示出在含水系统中将CO2还原为CO的光催化活性。有趣的是,随着双核Co(II)配合物中羧基数的增加,CO产率正增加。含有-6COOH的物质对CO2还原为CO表现出最佳的光催化活性,TON值高达10294。该值比含有-4COOH的值高1.8、3.4和7.8倍,-2COOH,和-0COOH,分别。高TON值还使具有-6COOH的双核Co(II)络合物在已报道的用于光催化CO2还原的均相分子催化剂中表现突出。控制实验和密度泛函理论计算表明,催化剂中更多的羧基赋予催化剂更多的质子继电器。从而加速质子转移和促进光催化CO2还原。这项研究,在分子水平上,阐明了催化剂中更多的羧基有利于提高光催化CO2还原的反应动力学。
The reaction kinetics of photocatalytic CO2 reduction is highly dependent on the transfer rate of electrons and protons to the CO2 molecules adsorbed on catalytic centers. Studies on uncovering the proton effect in catalysts on photocatalytic activity of CO2 reduction are significant but rarely reported. In this paper, we, from the molecular level, revealed that the photocatalytic activity of CO2 reduction is closely related to the proton availability in catalysts. Specifically, four dinuclear Co(II) complexes based on Robson-type ligands with different number of carboxylic groups (-nCOOH; n = 0, 2, 4, 6) were designed and synthesized. All these complexes show photocatalytic activity for CO2 reduction to CO in a water-containing system upon visible-light illumination. Interestingly, the CO yields increase positively with the increase of the carboxylic-group number in dinuclear Co(II) complexes. The one containing -6COOH shows the best photocatalytic activity for CO2 reduction to CO, with the TON value reaching as high as 10,294. The value is 1.8, 3.4, and 7.8 times higher than those containing -4COOH, -2COOH, and -0COOH, respectively. The high TON value also makes the dinuclear Co(II) complex with -6COOH outstanding among reported homogeneous molecular catalysts for photocatalytic CO2 reduction. Control experiments and density functional theory calculation indicated that more carboxylic groups in the catalyst endow the catalyst with more proton relays, thus accelerating the proton transfer and boosting the photocatalytic CO2 reduction. This study, at a molecular level, elucidates that more carboxylic groups in catalysts are beneficial for boosting the reaction kinetics of photocatalytic CO2 reduction.