Synthesis and catalytic activity of amino-functionalized SBA-15 materials with controllable channel lengths and amino loadings

Abstract

Aminopropyl-functionalized SBA-15 mesoporous materials (NH₂-SBA-15) with different lengths of channeling pores and aminopropyl loadings up to 2.6 mmol g⁻¹ were synthesized by one-pot co-condensation of tetraethyl orthosilicate (TEOS) and aminopropyltrimethoxysilane (APTMS) with the aid of appropriate amounts of Zr(IV) ions and NaCl. The morphologies and pore lengths of the resultant materials were tuned by varying the Zr/TEOS and NaCl/TEOS molar ratios in the synthesis gels. The assembly processes were examined by in situsmall-angle X-ray scattering (SAXS) and conventional characterization techniques. Accordingly, TEOS prehydrolysis for around 2 h in the synthesis solution before the addition of APTMS was essential for preparing platelet NH₂-SBA-15 materials with well-ordered p6mmpore structure and narrowly distributed pore size distribution, due to the strong interference from APTMS. When applying these materials as solid base catalysts in solvent-free flavanone synthesis, the platelet material with short-channeling poresca. 200–300 nm was superior to the rod-like and fiber-like counterparts with lengthy channels in the micrometre scale due to better molecular diffusion and less possibility of pore blockage. Furthermore, the platelet materials with high surface areas (∼450 m² g⁻¹) and amino loadings around 1.4–1.8 mmol N g⁻¹ were the most efficient catalysts for flavanone synthesis, and the high activity was retained by a simple regeneration method.