Preparation of carboxyethyltin group-functionalized highly ordered mesoporous organosilica composite material with double acid sites

A series of highly ordered mesoporous ethane-bridged organosilica composite materials functionalized by carboxyethyltin group, SnR-Si(Et)Si-X (SnR and Si(Et)Si denote [Sn(CH2)(2)COOH](3+) and ethane-bridged organosilica groups, respectively), were successfully designed through one-step co-condensation-hydrothermal method. The pore morphology and textural properties, Sn(IV) coordination environment, the type of acid site, Bronsted and Lewis acid strength were systematically characterized by LXRD, TEM observation, N-2 porosimetry measurements, MAS NMR (Si-29, C-13, Sn-119), UV-Vis diffuse reflectance spectrum, as well as H-1 and P-31 MAS NMR, FT-IR analysis of adsorbed pyridine, acid-base titration. Composite materials SnR-Si(Et)Si-X possess Bronsted and Lewis acid sites, which originates from -COOH in [Sn(CH2)(2)COOH](3+) group and bridging OH in [Si(OH)SnR] group as well as tetrahedral coordination framework Sn(IV) in the open configuration [SnR(SiO)(3)(OH)], respectively. The above 2D hexagonal mesoporous structure with unique textural properties, double acid sites (Bronsted and Lewis acid sites) and hydrophobic surface make SnR-Si(Et)Si-X exhibit excellent acid catalytic activity, reusability and water tolerance toward ketalization of cyclohexanone with glycol in absence of azeotrope agent at low temperature.