Sorbonne Paris Cité, Laboratoire d'Electrochimie Moléculaire, Unité Mixte de Recherche Université - CNRS No. 7591, Université Paris Diderot , Bâtiment Lavoisier, 15 rue Jean de Baïf, 75205 Cedex 13 Paris, France.
J Am Chem Soc. 2015 Oct 28;137(42):13535-44. doi: 10.1021/jacs.5b06834. Epub 2015 Oct 16.
Despite decades of active attention, important problems remain pending in the catalysis of dioxygen reduction by iron porphyrins in water in terms of selectivity and mechanisms. This is what happens, for example, for the distinction between heterogeneous and homogeneous catalysis for soluble porphyrins, for the estimation of H2O2/H2O product selectivity, and for the determination of the reaction mechanism in the two situations. With water-soluble iron tetrakis(N-methyl-4-pyridyl)porphyrin as an example, procedures are described that allow one to operate this distinction and determine the H2O2/H2O product ratio in each case separately. It is noteworthy that, despite the weak adsorption of the iron(II) porphyrin on the glassy carbon electrode, the contribution of the adsorbed complex to catalysis rivals that of its solution counterpart. Depending on the electrode potential, two successive catalytic pathways have been identified and characterized in terms of current-potential responses and H2O2/H2O selectivity. These observations are interpreted in the framework of the commonly accepted mechanism for catalytic reduction of dioxygen by iron porphyrins, after checking its compatibility with a change of oxygen concentration and pH. The difference in intrinsic catalytic reactivity between the catalyst in the adsorbed state and in solution is also discussed. The role of heterogeneous catalysis with iron tetrakis(N-methyl-4-pyridyl)porphyrin has been overlooked in previous studies because of its water solubility. The main objective of the present contribution is therefore to call attention, by means of this emblematic example, to such possibilities to reach a correct identification of the catalyst, its performances, and reaction mechanism. This is a question of general interest, so that reduction of dioxygen remains a topic of high importance in the context of contemporary energy challenges.
尽管几十年来一直受到关注，但在水中铁卟啉催化氧气还原的选择性和机制方面仍存在重要问题悬而未决。例如，对于可溶性卟啉的多相和均相催化的区分、H2O2/H2O 产物选择性的估计以及两种情况下反应机制的确定，都存在这种情况。以水溶性铁四( N-甲基-4-吡啶基)卟啉为例，介绍了允许进行这种区分并分别确定每种情况下 H2O2/H2O 产物比的程序。值得注意的是，尽管铁(II)卟啉在玻璃碳电极上的吸附较弱，但吸附配合物对催化的贡献可与其溶液对应物相媲美。根据电极电位，已经确定并从电流-电位响应和 H2O2/H2O 选择性方面对两种连续的催化途径进行了表征。这些观察结果在普遍接受的铁卟啉催化氧气还原机制的框架内进行了解释，同时检查了其与氧气浓度和 pH 值变化的兼容性。还讨论了吸附状态下的催化剂与溶液中催化剂之间固有催化反应性的差异。由于铁四( N-甲基-4-吡啶基)卟啉的水溶性，在以前的研究中忽视了其多相催化作用。因此，本研究的主要目的是通过这个有代表性的例子引起人们对这些可能性的关注，以便正确识别催化剂、其性能和反应机制。这是一个普遍关注的问题，因此氧气还原仍然是当代能源挑战背景下的一个重要话题。
