Synthesis of nanoscale surfactant-encapsulated silica-supported polyoxometalate [Si/AlO2]@[PWZn]@CTAB and its catalytic application in the oxidation of alcohols†

Abstract

Silica-supported polyoxometalates [Si/AlO₂]@[PWM] (M = Zn, Cu, Ni, Co, Fe, Mn, and Cr) were produced by immobilizing transition metal substituted Keggin-type polyoxometalates on cationic silica nanoparticles. These silica-supported polyoxometalates were then encapsulated with hexadecyltrimethylammonium bromide to obtain [Si/AlO₂]@[PWM]@CTAB (M = Zn, Cu, Ni, Co, Fe, Mn, and Cr) to prevent polyoxometalate leaching. Characterization by FT-IR, TG-DTG, XRD, SEM, and TEM indicated that the polyoxometalate structure was retained after immobilization and encapsulation. These nanoscale compounds were used as heterogeneous catalysts in the oxidation of various alcohols, achieving very good to excellent yields with H₂O₂ as an oxidant, and demonstrating high reusability. These benefits introduce surfactant-encapsulated silica-supported polyoxometalates as highly efficient heterogeneous catalysts in different oxidation reactions.