Synthesis of Convertible {PO4[WO3$$\rightleftharpoons$$ W(O)2(O2)]4}-DMA16 in SBA-15 Nanochannels and Its Catalytic Oxidation Activity

Abstract

A phase transfer catalyst ({PO4[WO3]4}-DMA16) had been first synthesized and stabilized in mesochannels of (3-chloropropyl)trimethoxysilane-functionalized mesoporous silica SBA-15 to build an active nano-environment for triphase cyclohexene oxidation. Tungsten precursor ({PO4[WO3]4}3−) and organic amino N,N-dimethylhexadecan-1-amine (DMA16) self-assembled in channels of SBA-15 to form a hybrid catalyst {PO4[WO3]4}-DMA16-SBA-15, which combined advantages of homogeneous and heterogeneous catalysts. Insoluble {PO4[WO3]4}-DMA16 formed soluble {PO4[W(O)2(O2)]4}-DMA16 active species with the aid of H2O2, and when H2O2 was consumed out, {PO4[WO3]4}-DMA16 was recombined. In addition, free remaining organic moieties (–Cl and -DMA16) on the surface of SBA-15 allowed {PO4[WO3]4}-DMA16-SBA-15 catalyst possessed more hydrophobic surface property, which further facilitated the compatibility between organic reactant cyclohexene and inorganic H2O2 molecules. The easy reusability of {PO4[WO3]4}-DMA16-SBA-15 catalyst for five catalytic runs without distinct change in catalytic activity was a significant “green” attribute of this catalyst.