Morphology control and catalytic application of mesoporous structures prepared by sol-gel processing

A highly ordered mesoporous molecular sieve was synthesized in the acidic tetraethoxyorthosilane (TEOS) sol-gel solution containing an amphiphilic triblock copolymer of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (EP20PO70EO20, PEO 30 wt %) as structure directing agent. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurement showed that increasing the amount of EO20PO70EO20 with respect to TEOS resulted in a variety of morphology of the internal pore structure. At a molar ratio of TEOS to EO20PO70EO20 of about 40, the mesostructure with a long range hexagonal columnar ordering, denoted as M40, was synthesized. One synthesized with a molar ratio of TEOS to EO20PO70EO20 of 60 displayed a co-continuous morphology, similar to the gyroid structure observed in spherical block copolymers. Palladium was successfully immobilized on M40 to be applied as a catalyst with a high level of enantioselectivity in the asymmetric hydrogenation of alpha-keto acids to the corresponding amino acids.