Oxygen evolving reactions catalysed by manganese-oxo-complexes adsorbed on clays

A series of dinuclear manganese-oxo-complexes was prepared and adsorbed on kaolinite and montmorillonite clays. As indicated by UV-Vis spectroscopy, immobilization of the manganese compounds greatly altered the electronic properties due to strong interactions with the clay surfaces. When studied for their ability to catalyze oxygen formation upon reactions with the strong oxygen-transferring oxidants H2O2 and oxone, it was found that surface adsorption yielded catalysts of improved performance for oxygen formation in aqueous media. Both the rates of oxygen evolution and catalyst stabilities were significantly increased for the clay hybrids of most complexes in comparison to homogeneous solutions of the compounds. Additionally, four heterogeneous systems were also found to catalyze the evolution of O-2 in reactions with the non-oxygen transferring, single-electron oxidation agent Ce-IV-a reaction not observed for any dinuclear manganese complex in homogeneous reaction. Implications of these observations concerning the mechanism of oxygen formation and the development of manganese-based water oxidation catalysts are discussed.