Photochemical Water Oxidation by Manganese Oxides Supported on Zeolite Surfaces

Photocatalytic properties of disordered birnessite-like Mn oxides deposited on the zeolite Y surface is investigated. Synthesis was carried out by ion-exchanging Mn2+ along with M2+ = Ba2+, Sr2+, Ca2+, Mg2+ into zeolite, followed by precipitation of nanosized Mn oxides on the zeolite surface after reaction with KMnO4. These samples are labeled M2+ MnOx-Y, and they were treated with K+ to prepare KMnOx-Y(M2+). XRD, XPS, Raman, and electron microscopy provided information on the comparative structural features for M2+ MnOx-Y and KMnOx-Y(M2+). Photocatalytic water oxidation using these samples was evaluated using Ru(bpy)(3) (2+) - S2O8 (2+) system. The catalytic activity of KMnOx-Y(M2+) is higher than M2+ MnOx-Y, for comparable Mn loadings, and forms the interesting observation in this paper. For M2+ MnOx-Y, the catalytic activity normalized to the Mn content followed the order: Ba2+ > Sr2+ > Ca2+ > Mg2+ and is possibly reflection of the lower Mn loadings, which leads to smaller MnOx crystallites.