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Nanocatalysis in flow is catalysis by metallic nanoparticles (NPs; 1-50 nm) performed in microstructured reactors. These catalytic processes make use of the enhanced catalytic activity and selectivity of NPs and fulfill the requirements of green chemistry. Anchoring catalytically active metal NPs within a microfluidic reactor enhances the reagent/catalyst interaction, while avoiding diffusion limitations experienced in classical approaches. Different strategies for supporting NPs are reviewed herein, namely, packed-bed reactors, monolithic flow-through reactors, wall catalysts, and a selection of novel approaches (NPs embedded on nanotubes, nanowires, catalytic membranes, and magnetic NPs). Through a number of catalytic reactions, such as hydrogenations, oxidations, and cross-coupling reactions, the advantages and possible drawbacks of each approach are illustrated. [ABSTRACT FROM AUTHOR]

Generation three, four, and five (G3, G4, and G5) poly(amidoamine) dendrimers were used for the encapsulation of palladium nanoparticles (Pd NPs) and their covalent anchoring within glass microreactors. G3-encapsulated Pd NPs showed the highest activity for a model Suzuki-Miyaura cross-coupling (SMC) reaction of the three different encapsulated Pd NPs tested, as compared to G4 and G5. A kinetic study indicated a role of the nanoparticle as a procatalyst, from which molecular species are formed with an induction time of approximately 1 min. The dendrimer-nanoparticle catalytic platform exhibited excellent reactivity (high turnover frequencies and numbers) compared to other Pd NP flow reactors and dendrimer-encapsulated Pd NPs at batch scale. Moreover, the Pd microreactor exhibited good stability, as witnessed by running the SMC reaction for more than 7 days with a low Pd leaching of 1.2 ppm. The covalently attached dendrimers may play a crucial role in stabilizing the Pd NPs, a critical feature in flow SMC reactions. [ABSTRACT FROM AUTHOR]

The cover picture shows dendrimer‐encapsulated Pd nanoparticles (NPs), anchored within a continuous‐flow microreactor, that efficiently catalyze the Suzuki–Miyaura cross‐coupling (SMC) of iodobenzene and p‐tolylboronic acid. The different dendrimer generations employed in this study are represented by the size and the ramification of the trees. Pd NPs are entrapped within the trees along the shore, which is “washed” by the river, symbolizing the laminar flow within the microreactor. In their Full Paper, R. Ricciardi et al. show the influence of the dendrimer generation on the catalytic activity of the Pd NPs. The article highlighted by this cover can be found on p. 936 ff. of Issue 6, 2015. [ABSTRACT FROM AUTHOR]