Enhancement of catalytic performance by creating shell layers on sulfonic acid-functionalized monodispersed mesoporous silica spheres

New types of organically functionalized core/shell monodispersed mesoporous silica spheres (MMSS) containing catalytic sites (sulfonic acid groups) in the core portion and adsorption sites (hydrophobic organic functional groups) in the shell portion were successfully synthesized by the co-condensation/expansion method. These SO3H-core/hydrophobic-shell MMSS have radially aligned hexagonal mesopores and display different chemical properties in the core and shell portions. The acid catalytic activities of the SO3H-core/hydrophobic-shell MMSS were studied in condensation reactions between 2-methylfuran and acetone. It was found that the catalytic activities were most enhanced by incorporating ethyl or propyl groups into the shell portion. These groups have molecular sizes and affinity that are particularly suitable for entry of two reactants with completely different polarity at a proper balance and discharge of products. In addition, the SO3H-core/hydrophobic-shell MMSS had higher catalytic activities than MMSS having randomly distributed SO3H and hydrophobic groups.