Spherical superstructures of oxide nanoparticles for catalytic reactions in microchemical reactors

We report the fabrication of spherical superstructures composed of SiO2 and TiO2 nanoparticles and their applications in catalyzing organic reactions. Assembling of the nanoparticles into superstructures is done by heating a water-in-oil micro-emulsion, which contains chemically activated oxide nanoparticles in the aqueous microdroplet phase. Water vapour-induced convective flow leads to microdroplet fusion and subsequent concentrical arrangement of all nanoparticles of the emulsion into a larger superstructure, mimicking a pearl-like, layer-over-layer, growth mechanism. These superstructures are subsequently employed for catalyzing the anti-Markovnikov addition reaction of thiol to olefin, and in an aromatic azo-compound synthesis in microchemical reactors under static and dynamic flow conditions. The superstructure format presents the advantage of an easier recovery of the catalysts from the reactor, compared to the use of the native individual nanoparticles.