Lipophilicity of amphiphilic phosphotungstates matters in catalytic oxidative desulfurization of oil by H2O2

In order to develop an efficient amphiphilic catalyst for the oxidative desulfurization (ODS) of fuel oils by H2O2, seven surfactant-like heteropoly acid catalysts were prepared, and their ODS performance was studied at varying conditions for model oils. The results indicate that phosphotungstate (PWO) has higher catalysis than phosphomolybdate (PMoO), and cetyl-methyl-imidazolium phosphotungstate ([C16MIM](3)PWO) is one of the best catalysts for the oxidation of dibenzothiophene (DBT) with mere H2O2 without any other additives or extractants. The ideal amphiphilic catalysts should have at least one long alkyl group (C-12-C-18) in the monovalent cations so as to make them hydrophobic and oil dispersible, forming metastable W/O emulsion in oil even in the presence of excessive water. DBT can be oxidized completely within 40 min under optimal conditions (10 g model oil, 0.1 g catalyst, n(H2O2)/n(S) = 4, 313 K). [C16MIM](3)PWO shows excellent reusability with little activity decline after five recycled uses, and is effective for real diesel.