Using nanocrystals with specific crystal facets is an effective way to enhance activity and selectivity for numerous catalytic reactions . However, the intrinsic facet effect is not fully understood. Herein, using Pt catalyzed glycerol oxidation reaction as the model system, the intrinsic facet effect on catalytic property is evaluated by three kinds of Pt nanocrystal catalysts with cubic, spherical and tetrahedral shapes. Size effect, support effect, surfactant effect as well as the metal-support interaction of the catalysts are avoided to the maximum extent. The supported Pt nanocubes enclosed by Pt(1 0 0) facets are found to exhibit much higher catalytic activity and stability for the aerobic oxidation of glycerol than catalysts with Pt nanotetrahedrons enclosed by Pt(1 1 1) facets. DFT calculations indicate that the adsorption of oxygen and glycerol would materialize easier on Pt(1 0 0) than on Pt(1 1 1). Furthermore, Pt(1 0 0) may prevent deactivation caused by product adsorption as well.
A variety of spherical and structured activated charcoal supported Pt/Fe 3 O 4 composites with an average particle size of ∼100 nm have been synthesized by a self-assembly method using the difference of reduction potential between Pt (IV) and Fe (II) precursors as driving force. The formed Fe 3 O 4 nanoparticles (NPs) effectively prevent the aggregation of Pt nanocrystallites and promote the dispersion of Pt NPs on the surface of catalyst, which will be favorable for the exposure of Pt active sites for high-efficient adsorption and contact of substrate and hydrogen donor. The electron-enrichment state of Pt NPs donated by Fe 3 O 4 nanocrystallites is corroborated by XPS measurement, which is responsible for promoting and activating the terminal C=O bond of adsorbed substrate via a vertical configuration. The experimental results show that the activated charcoal supported Pt/Fe 3 O 4 catalyst exhibits 94.8% selectivity towards cinnamyl alcohol by the transfer hydrogenation of cinnamaldehyde with Pt loading of 2.46% under the optimum conditions of 120 °C for 6 h, and 2-propanol as a hydrogen donor. Additionally, the present study demonstrates that a high-efficient and recyclable catalyst can be rapidly separated from the mixture due to its natural magnetism upon the application of magnetic field.
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