Keggin-type polyoxometalates (POM) immobilized on alkylaminophosphazene (RPN)-functionalized silica (POM/RPN-SiO2) are new effective single-site solid catalysts for oxidative desulfurization (ODS) of diesel fuel under mild conditions in a biphasic system composed of a benzothiophene-containing model diesel fuel (heptane) and aqueous 30% H2O2 . The catalytic activity of POM/RPN-SiO2 was found to be influenced by the choice of POM and the amine R group in RPN, decreasing in the order PMo > PW > SiW and Bz > iBu > iPr, respectively. The most effective catalyst, PMo/BzPN-SiO2 (PMo = PMo12O403-), exhibited 100% removal of dibenzothiophene from model diesel fuel at 60 degrees C and ambient pressure and could be reused without loss of activity. This catalyst outperforms other recently reported heterogeneous catalysts for ODS in similar systems. C-13, Si-29 and P-31 MAS NMR, FUR, SEM, BET and elemental analysis were used to characterize the structure of surface phosphazene and POM species in the new catalysts.