Direct synthesis of highly ordered large-pore functionalized mesoporous SBA-15 silica with methylaminopropyl groups and its catalytic reactivity in flavanone synthesis

Abstract

Functionalized SBA-15 mesoporous silica materials with a p6mm symmetry have been synthesized through a simple co-condensation approach of tetraethylorthosilicate (TEOS) and (3-(methylamino)propyl)trimethoxysilane (MAPTMS) using amphiphilic block co-polymers under acidic conditions. The influence of the amount of MAPTMS in the initial synthesis mixture on the mesostructural properties of the resultant materials was studied by varying the molar ratios of MAPTMS to TEOS. X-ray powder diffraction (XRD) and N 2 sortpion results indicated that the ordering of the mesoporous structure was dependent on the amount of MAPTMS added in the initial mixture. Solid-state nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA) and elemental analysis showed that the incorporation of the organic groups in the silica framework increased with the MAPTMS concentration in the synthesis mixture. TEOS pre-hydrolysis prior to the addition of MAPTES had great influence on the crystallographic ordering, pore size, surface area and pore volume of the resultant functionalized mesoporous silica materials. Moreover, the addition of inorganic salt in the initial mixture could greatly enhance the mesostructure ordering and stability of the mesoporous materials. With the aid of NaCl salt, the modified SBA-15 materials with the content of methylaminopropyl groups up to 2.37 mmol/g still possessed well-ordered mesoporous structure and had high specific area of 200 m 2g −1 and pore volume of 0.29 cm 3/g. The modified SBA-15 showed high catalytic activities and selectivities toward flavanones synthesis through the Claisen–Schmidt condensation of substituted acetophenones and benzaldehyde derivatives and subsequent intramolecular Michael addition in the absence of solvent.