Direct Synthesis of Ordered Macroporous Silica Materials Functionalized with Polyoxometalate Clusters

Three-dimensionally ordered macroporous (3DOM) silica materials functionalized with highly dispersed polyoxometalate clusters have been prepared via direct synthesis. Lacunary g-decatungstosilicate clusters were incorporated into the wall structures of macroporous silica by reaction of the clusters in acidic solution with tetraethoxysilane, with or without addition of the polyfunctional linking group 1,2-bis(triethoxysilyl)ethane, followed by condensation around polystyrene colloidal crystals. Removal of the polystyrene template by extraction with a tetrahydrofuran/acetone solution produced the porous hybrid materials. The products were characterized by IR, solid-state ²⁹Si and ¹³C NMR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray energy dispersive spectroscopy (EDS), and chemical analysis. The polyoxometalate clusters remained intact in the hybrid structures and were nearly molecularly dispersed throughout the walls of the 3DOM materials. High incorporation levels of cluster were obtained, with no bulk particles on the external surfaces. The materials were demonstrated to exhibit catalytic activity for the epoxidation of cyclooctene with an anhydrous H₂O₂/t-BuOH solution at room temperature.