Yolk–shell smart Pickering nanoreactors for base-free one-pot cascade Knoevenagel-hydrogenation with high catalytic efficiency in water

Abstract

In the present work, Au@Pd nanoparticles, which serve as catalytic active centers, were first implanted in amphiphilic hollow vinyl-pyridyl group-doped periodic mesoporous organosilica (PMO) shells, and yolk–shell smart Pickering Au@Pd@Py-PMO nanoreactors were obtained. Herein, two smart aspects of the novel nanoreactor are demonstrated: one is the adsorption and the other is the catalytic process. Interestingly, it was found that the obtained vinyl-pyridyl group-doped nanoreactors can easily adsorb hydrophobic molecules containing nitro-groups or vinyl-groups into their interior rather than simply indiscriminately adsorb organic substances. Most importantly, although the so-called cascade reactions catalyzed by previously used catalysts whose two kinds of active centers are not spatially separated are actually carried out separately by the Knoevenagel reaction in air environment and the hydrogenation reaction in a hydrogen atmosphere, our novel yolk–shell Au@Pd@Py-PMO nanoreactor whose two kinds of spatially separated active sites are respectively located on a Au@Pd core and channel surfaces of the Py-PMO shell can catalyze the Knoevenagel-hydrogenation reaction via a real one-pot reaction only in a hydrogen atmosphere. In the one-pot reaction, reactants containing nitro-groups are first adsorbed easily into the channels in which intermediates being more conducive to the continuous adsorption are produced under the catalysis of weakly basic pyridine groups doped on the channel surfaces before entering the cavity to contact the Au@Pd core. Therefore, the Knoevenagel-hydrogenation reaction catalyzed by our smart Pickering nanoreactors can not only be carried out through a real one-pot cascade reaction but also show high catalytic efficiency in water.