Selective oxidation of benzyl alcohols with molecular oxygen as the oxidant using Ag-Cu catalysts supported on polyoxometalates

We report an efficient process for the oxidation of benzyl alcohols using molecular oxygen as the oxidant catalyzed by Ag-Cu catalysts supported on polyoxometalates (Ag-Cu/POM). The Ag-Cu/POM catalyst was prepared by galvanic displacement in the presence of polyvinyl pyrrolidone and polyethylene glycol. The catalysts were characterized using Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), powder X-ray diffraction (PXRD), X-ray fluorescence (XRF), Brunauer-Emmett-Teller (BET) surface analysis, transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and thermogravimetric analysis (TGA). The oxidation reaction was carried out using a Schlenk-line setup, under ambient atmospheric pressure. Reaction products were identified by GC-MS and quantified with GC using an internal standard method. The Ag-Cu/POM catalyst gave close to 100% benzyl alcohol conversion in 5 h with >99% selectivity to benzaldehyde. When tested on various benzyl alcohol derivatives the Ag-Cu catalysts showed good conversions and >99% selectivity to the corresponding aldehydes. The Ag-Cu catalysts supported on the POM are highly stable, and don't show tendency to leach or deactivate. The catalysts are heterogeneous in nature and easy to recover after reactions, and could be reused at least 5 times without significant loss in activity and selectivity.