Mesoporous silica-based nanotubes loaded Pd nanoparticles: Effect of framework compositions on the performance in heterogeneous catalysis

Abstract

Well-shaped mesoporous silica-based nanotubes with different framework compositions, such as organic groups (ethylene, phenylene), carbon/silica hybrids, could be controllably synthesized with the inner diameter of less than 10 nm and the surface areas of about 400–900 m2 g−1. Through an impregnation-reduction process, palladium (Pd) nanoparticles have been uniformly dispersed in the channels of these different nanotubes, which were confirmed by electron microscopy analysis. The catalytic performance of these silica-based nanotubes loaded Pd nanoparticles was evaluated by the aerobic oxidation of benzyl alcohol and enantioselective hydrogenation of α,β-unsaturated carboxylic acid, respectively. Due to one-dimensional nanotube structures and tunable hydrophilic/hydrophobic properties, the organosilica nanotubes supported Pd nanoparticles could afford >99% conversion of benzyl alcohol and 89% selectivity of benzaldehyde within 2 h. Importantly, carbon/silica hybrid nanotubes may have a positive effect on the reaction, which gave about 95% selectivity of benzaldehyde. The catalysts could be reused without an obvious decrease in both conversion and selectivity. Furthermore, the silica-based nanotubes supported Pd nanoparticles were also efficient for asymmetric hydrogenation of α,β-unsaturated carboxylic acids, which showed a highest conversion of 99% with 48% enantioselectivity.