A recoverable sandwich phosphorotungstate stabilized palladium (0) catalyst for aerobic oxidation of alcohols in water

The preparation, characterization and catalytic properties of tetra metal substituted sandwich phosphorotungstate [M-4(H2O)(2)(PW9O34)(2)](10-)(M4P2W18, M2+ = Fe2+, Co2+, Mn2+, Cu2+, VO2+) stabilized Pd nanoparticles, which were in-situ encapsulated in mesoporous aluminum phosphate (mAPO) by a one-pot method, were demonstrated for aerobic oxidation of alcohol in water. The synthesized catalysts were characterized with N-2 adsorption, XRD, TEM, FT-IR and UV-vis. TEM analysis revealed that Pd-M4P2W18/mAPO thus obtained has a mean palladium particle size of less than 5 nm. The solid PdM4P2W18/mAPO catalysts exhibit excellent activity for aerobic oxidation of benzyl alcohols in water without any base additives. It was found the introduced M4P2W18 polyoxanions encapsulated palladium nanoparticles as both stabilizing agent and promoters, leading to enhanced activity and recyclability of palladium catalyst. The recycling test of representative Pd-(VO)(4)P2W18/mAPO for oxidation of benzyl alcohol suggested no significant decrease in activity and selectivity even after twelve times of successive reactions. This novel heterogeneous catalyst composed of polypxometalates stabilized palladium nanocatalysts and mesoporous aluminophosphate can also be extended to the selective oxidation of various alcohols. (C) 2016 Elsevier B.V. All rights reserved.