Nanostructured carbon-metal oxide hybrids as amphiphilic emulsion catalysts

Nanohybrids composed of "onion-like" carbon, single-walled (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) fused to silica or alumina particles have been compared as stabilizers of water/oil emulsions and interfacial catalysts. The amphiphilic character of these nanohybrids makes them effective in stabilizing emulsions (up to 85 % of total volume) comprising of small droplets (less than 40 μm). Furthermore, these nanohybrids have been used as supports for transition metal particles (palladium and copper) to catalyze reactions at the water/oil interface. Three different reaction systems have been conducted in the emulsions to demonstrate the principle: 1) hydrogenation of phenanthrene; 2) hydrogenation of glutaraldehyde and benzaldehyde; 3) oxidation of tetralin. Comparison of the maximum conversions achieved in emulsions as opposed to the single phase, together with much better control of selectivity in the two-phase system shows the benefits of using these nanohybrid catalysts.