Abstract
Polyoxometalates (POMs), renowned for their excellent catalytic activity, are widely used in oxidation reactions. Rational regulation of metal ion valence state of POMs is of great significance for the design and construction of highly active catalyst. In this work, we utilized mesoporous Y zeolite (meso-Y) as a host to load and disperse cesium phosphomolybdate (CsPMo) for selective oxidation of thioethers. The as-prepared CsPMo/meso-Y featured superior catalytic activity and recyclability. The electronic structures of the CsPMo/meso-Y were investigated by XPS and NMR spectra. The results indicated that embedding CsPMo into meso-Y caused electron transfer between CsPMo and meso-Y. Meanwhile, meso-Y could provide H+ due to its abundant Bronsted acid sites. The simultaneous appearance of electron and H+ facilitated the formation of MoV, resulting in a higher oxidation of thioethers activity for the CsPMo/meso-Y. Radical scavenger experiments and Raman analysis indicated that peroxo-metal species derived from CsPMo and oxidizing agent tert-butyl hydroperoxide (TBHP) were the real catalyst. MoV is more conducive to the formation of peroxo-metal species, causing the higher activity. This study provides a new insight into the role of meso-Y in CsPMo/meso-Y and a novel clue to regulate the valence states of metal ions of POMs to enhance catalytic performance of the polyoxometalate based catalysts.