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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >p-Terphenyl-Sensitized Photoreduction of CO_2 with Cobalt and Iron Porphyrins. Interaction between CO and Reduced Metalloporphyrins
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p-Terphenyl-Sensitized Photoreduction of CO_2 with Cobalt and Iron Porphyrins. Interaction between CO and Reduced Metalloporphyrins

机译：钴和铁卟啉对对三苯敏化的CO_2光还原。 CO与还原金属卟啉之间的相互作用

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Iron and cobalt porphyrins (FeP and CoP) are utilized as electron-transfer mediators to effect photochemical reduction of CO_2 in homogeneous solutions. The species that activate and reduce CO_2 are the Fe~0P and CO~0P formed by reduction of the starting materials. Reduction of the metalloporphyrins (MP) is achieved by photolysis in dimethylformamide or acetonitrile solutions containing triethylamine (TEA) as a reductive quencher. The photoreduction is efficient for the M~(III)P -> M~(II)P stage and probably occurs by an intramolecular electron transfer from an axially bound TEA. However, TEA does not bind to the reduced metal complexes, and the quantum efficiency is much lower for the subsequent reduction steps. Considerably higher quantum yields are obtained by adding p-terphenyl (TP) as a sensitizer. TP is very effectively photoreduced by TEA to form the radical anion, TP~(centre dot -), which has a sufficiently negative reduction potential to reduce Co~IP and Fe~IP rapidly to their M~0P state. The rate constants for these reactions, determined by pulse radiolysis, are found to be nearly diffusion-controlled. THe quantum yield for the reduction of M~II)P to M~IP and for reduction of CO_2 to CO are increased by more than an order of magnitude in the presence of TP. Side reactions involve hydrogenation of the porphyrin ring and production of H_2. The hydrogenated porphyrins also catalyze reduction of CO_2, but the photochemical production of CO eventually stops. This limit on catalytic activity is due to destruction of the porphyrin macroscycle and accumulation of CO. CO can bind strongly to Fe~(II)P and to Fe~IP but not to Fe~0P, as demonstrated by electrochemical measurements and by optical spectra of the species produced by sodium reduction in tetrahydrofuran in the presence and absence of CO. Although binding of CO to Fe~(II)P and Fe~IP should not interfere with the formation of Fe~0P, the active catalyst, the potential for reduction of Fe~IP to Fe~0P becomes more negative. However, CO probably binds to the hydrogenated products thereby inhibiting the catalytic process.
机译：铁和钴卟啉（FeP和CoP）用作电子转移介质，以在均质溶液中实现CO_2的光化学还原。活化和还原CO_2的物种是通过还原原料形成的Fe〜0P和CO〜0P。金属卟啉（MP）的还原可通过在含有三乙胺（TEA）作为还原性淬灭剂的二甲基甲酰胺或乙腈溶液中进行光解来实现。对于M〜（III）P→M〜（II）P阶段，光还原是有效的，并且可能通过从轴向结合的TEA的分子内电子转移而发生。但是，TEA不能与还原的金属络合物结合，并且对于随后的还原步骤，其量子效率要低得多。通过添加对-三联苯（TP）作为敏化剂，可以获得相当高的量子产率。 TP被TEA非常有效地光还原形成自由基阴离子TP〜（中心点-），该负离子具有足够的负还原电位，可将Co〜IP和Fe〜IP快速还原为M〜0P状态。通过脉冲辐射分解确定的这些反应的速率常数几乎是受扩散控制的。在TP存在下，用于将M〜II）P还原为M〜IP以及将CO_2还原为CO的量子产率提高了一个数量级以上。副反应涉及卟啉环的氢化和H_2的产生。氢化卟啉也催化CO_2的还原，但最终CO的光化学生成停止了。这种对催化活性的限制是由于卟啉大环的破坏和CO的积累。CO可以牢固地与Fe〜（II）P和Fe〜IP结合，而不与Fe〜0P结合，如电化学测量和光谱所证明的那样。在存在和不存在CO的情况下，通过四氢呋喃中的钠还原产生的物种。尽管CO与Fe〜（II）P和Fe〜IP的结合不应干扰活性催化剂Fe〜0P的形成， Fe〜IP还原为Fe〜0P变得更加不利。然而，CO可能与氢化产物结合，从而抑制了催化过程。

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