(VO)²⁺ ions immobilized on functionalized surface of mesoporous silica and their activity toward the hydroxylation of benzene

Mesoporous silica MCM-41 was organofunctionalized by 3-aminopropyltrimethoxysilane (APTS) on the surface of its nanochannels. The amino groups of the mesoporous MCM-41 solids were then used to immobilize (VO)²⁺ ions which were employed to study the catalytic oxidation of benzene. We found the vanadium peroxo complex of V⁵⁺-O-O^• radicals play an important role in the hydroxylation of aromatic hydrocarbons, such as from benzene to phenol. In a series of spectroscopic studies, we found the binding of ligands in these complexes depends on the surface density of APTS, which affects crucially its catalytic activity. The anchored vanadium complexes have better catalytic activities with higher stability than the framework-substituted V-MCM-41 materials. We further demonstrate that immobilization of catalytic metal ion on functionalized surface has the advantages of better control of available reactive sites and site isolation.