Supported metal nanoparticles, M-NPs, are of great scientific and economic interest as they encompass application in chemical manufacturing, oil refining and environmental catalysis. Oxidation and hydrogenation reactions are among the major reactions catalyzed by supported M-NPs. Although supported M-NPs are preferable due to their easy recovery and reuse, there are still some practical issues regarding their catalytic activity and deactivation. This review highlights the general features of supported M-NPs as catalysts with particular attention to copper, gold, platinum, palladium, ruthenium, silver, cobalt and nickel and their catalytic evaluation in various reactions. The catalytic performance of noble M-NPs has been explored extensively in various selective oxidation and hydrogenation reactions. In general, noble metals are expensive and sensitive to poisons. Despite their significant merits and potential (easily available, comparatively inexpensive and less sensitive to poisons), catalysis by base M-NPs is relatively less explored. Therefore, activity of base M-NPs can be improved, and still, there is potential for such catalysts.

The synthesis of dendrimer-encapsulated palladium nanoparticles with ratios of 13 and 55 metal atoms to templating dendrimer, (Pd13- and Pd55-DENs) was successfully demonstrated with the use of hydroxyl-terminated generation 4 and 5 (G4 and G5) poly(amidoamine) (PAMAM) dendrimers as both templating and stabilizing agents. These Pd-DENs catalysts were fully characterized using spectroscopic techniques. High resolution transmission electron microscopy (HRTEM) was used for the determination of particle size. The average particle sizes were found to be 1.33 ± 0.15 and 1.66 ± 0.20 nm in diameters for Pd13 and Pd55-DENs, respectively. These catalysts were evaluated using the widely utilized model reaction, 4-nitrophenol (NP) reduction by sodium borohydride (NaBH4). The experimentally determined kinetic data was modeled using the Langmuir–Hinshelwood equation which relates the apparent rate k app, NP and BH4 – adsorption constants, K NP and K BH4 – respectively, the surface rate constant k, and the surface area, S. The behavior of the adsorption constants with increasing temperature was also investigated by varying the reaction temperature between 298 and 318 K. The Pd13-DENs showed greater adsorption of NP and BH4 – when compared to Pd55-DENs. The overall results showed that the Langmuir–Hinshelwood model can be successfully used for full kinetic analysis of NP reduction by BH4 – in the presence of Pd n -DENs catalysts.

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