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.

This study discusses the preparation of various sized dendrimer encapsulated ruthenium nanoparticles (RuDEN) with the use of the generation 4 (G4), generation 5 (G5), and generation 6 (G6) hydroxyl-terminated poly(amidoamine) (PAMAM-OH) dendrimers as templating agents. The size of the nanoparticles ranges from 1.1 to 2.2 nm. These catalysts were fully characterized using UV/vis spectrophotometry, infrared (IR) spectroscopy, and transmission electron microscopy (TEM). The RuDEN catalysts were evaluated in the reduction of 4-nitrophenol (4NP) in the presence of sodium borohydride (BH4(-)) for various concentrations of either. The kinetic data obtained were modeled to the Langmuir-Hinshelwood equation. The model allows the relation of the apparent rate constant to the total surface area S of the nanoparticle, the kinetic constant k which is related to the rate-determining step, and the adsorption constants K(4NP) and K(BH4) for 4NP and borohydride, respectively. These parameters were calculated for each of the RuDENs, proving the Langmuir-Hinshelwood model to be suitable for the kinetic evaluation of RuDENs in the catalytic reduction of 4NP.

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