Structure, stability, electrochemical and catalytic properties of polyoxometalates immobilized on choline-based hybrid mesoporous silica

Abstract

Polyoxometalate-based heterogeneous catalysts have been prepared by immobilization of Keggin-type heteropolyacid on hybrid mesoporous silica nanoparticles with choline hydroxide based ionic liquid. The immobilization process has been accomplished by a simple acid-base reaction with phosphomolybdic acid. For comparison purposes, additional supports (hybrid-SBA-15 and TiO2) have been also used in order to establish the nature of the interactions between the heteropolyacid and the surface's groups of the support. To do this, electrochemical and 31P MAS-NMR studies have been carried out finding the formation of moieties like (Chol)2[HPMo12O40] and/or (Chol)3[PMo12O40] on the silica materials. Polyoxometalate-based heterogeneous catalysts have been effectively tested for the oxidative desulfurization of DBT in model oil. Thus, complete removal of sulfur (99.7%) was achieved with polyoxometalate supported on the silica after 2 h and using H2O2 as a green oxidant. Additionally, reusability and stability studies of the most active catalyst have been performed.