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

• Pd NPs were stabilized by POMs and in situ encapsulated in mesoporous support.
• Pd NPs remained high dispersion on mesoporous aluminophosphate without aggregation.
• The catalyst is highly efficient for aerobic oxidation of alcohols in water.
• The catalyst could be used for twelve times without obvious loss in activity.

The preparation, characterization and catalytic properties of tetra metal substituted sandwich phosphorotungstate [M4(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 N2 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 Pd-M4P2W18/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)4P2W18/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 polyoxometalates stabilized palladium nanocatalysts and mesoporous aluminophosphate can also be extended to the selective oxidation of various alcohols.

Figure optionsDownload high-quality image (247 K)Download as PowerPoint slideThe titled catalyst was synthesized by first generation of polyoxometalates stabilized Pd nanoparticles and then in situ encapsulation of polyoxometalates stabilized Pd nanoparticles in mesoporous aluminophosphate by sol-gel method, the template was removed by extraction and calcination procedures. The resulting catalyst is high efficient and recyclable for aerobic oxidation of alcohols in water.