The role of nano-sized manganese oxides in the oxygen-evolution reactions by manganese complexes: towards a complete picture.

Eighteen Mn complexes with N-donor and carboxylate ligands have been synthesized and characterized. Three Mn complexes among them are new and are reported for the first time. The reactions of oxygen evolution in the presence of oxone (2KHSO5·KHSO4·K2SO4) and cerium(iv) ammonium nitrate catalyzed by these complexes are studied and characterized by UV-visible spectroscopy, X-ray diffraction spectrometry, dynamic light scattering, Fourier transform infrared spectroscopy, electron paramagnetic resonance spectroscopy, transmission electron microscopy, scanning electron microscopy, membrane-inlet mass spectrometry and electrochemistry. Some of these complexes evolve oxygen in the presence of oxone as a primary oxidant. CO2 and MnO4(-) are other products of these reactions. Based on spectroscopic studies, the true catalysts for oxygen evolution in these reactions are different. We proposed that for the oxygen evolution reactions in the presence of oxone, the true catalysts are both high valent Mn complexes and Mn oxides, but for the reactions in the presence of cerium(iv) ammonium nitrate, the active catalyst is most probably a Mn oxide.

A simple mathematical model for manganese oxide-coated montmorillonite as a catalyst for water oxidation: from nano to macro sized manganese oxide.

Here, we propose a mathematical model that gives a good fit to the experimental data for water oxidation by Mn oxide-coated montmorillonite with different Mn content. Our data show that the water oxidation may progress by cooperation among only neighbor Mn ions on montmorillonite. It is a promising model for finding more about the mechanism of multi-electron reactions.