Bimetallic heterostructures are used as industrial catalysts for many important transformations. However, conventional catalysts are primarily prepared in cost-effective manners without much appreciation in metal size control and metal-metal interaction. By employing recent nanotechnology, Pt nanocrystals with tailored sizes can be decorated with Co atoms in a controlled manner in colloid solution as preformed nanocatalysts before they are applied on support materials. Thus, we show that the terminal CO hydrogenation can be achieved in high activity, while the undesirable hydrogenation of the CC group can be totally suppressed in the selective hydrogenation of alpha,beta-unsaturated aldehydes to unsaturated alcohols, when Co decorated Pt nanocrystals within a critical size range are used. This is achieved through blockage of unselective low coordination sites and the optimization in electronic influence of the Pt nanoparticle of appropriate size by the Co decoration. This work clearly demonstrates the advantage in engineering preformed nanoparticles via a bottom-up construction and illustrates that this route of catalyst design may lead to improved catalytic processes.

A series of crystalline homometallic and heterometallic cobalt and nickel hydroxides and oxides were prepared using a continuous hydrothermal flow synthesis system. In all syntheses, the relevant metal salt solutions were pumped under high pressure to meet pH or other chemical modifiers (H 2 O 2 or PVP) before the mixture was brought into contact with a feed of superheated (or supercritical) water, whereupon precipitation and particle growth occurred. The resulting nanoparticle (typically less than 100 nm in diameter) suspensions were collected from the outlet of the back-pressure regulator of the hydrothermal system. The collected suspensions were centrifuged, and the washed solids were freeze-dried prior to analyses. The nanopowders were characterized by a number of analytical methods including X-ray powder diffraction, Brunauer-Emmett-Teller (BET) surface area measurements, and simultaneous thermogravimetric analysis/differential scanning calorimetry.

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