The synthesis of silver nanoparticles with small average size and narrow size distribution is a requirement for applications in different fields such as antibacterial or catalysis. Previous studies of nanoparticles synthesis confirm the advantages of combining continuous flow and microwave dielectric heating, given the possibilities that arise regarding control of residence time and localized volumetric heating. In this paper, we present two experimental set-ups to perform the continuous synthesis of silver nanoparticles using microwave heating (MWH) and conventional heating (CH). Experimental and simulated data confirm a different temperature profile along the reactor, being more favorable in the case of MWH. As a result, the nanoparticles synthesized under MWH presented a synthesis yield of 54% and a narrow particle size distribution (19±4.3nm). Furthermore, MWH led to reduced wall fouling by deposition of product material and allowed fast cooling of the product stream, preventing further growth of the nanoparticles.
Metal nanoclusters are becoming exciting candidates as highly efficient catalysts for heterogeneous processes in view of their extraordinary surface to volume ratio and the high concentration of uncoordinated atoms that contribute to enhanced catalytic activity. For this reason, the development of accurate and reliable procedures for the synthesis of stable and supported metal nanoclusters is highly desirable. Although Ag nanoclusters (Ag NCs) stabilized by anion templates with a structure like Ag m+n m+ and a long lifetime have been widely investigated, supported clusters present significant advantages regarding their recovery and recyclability. In spite of their potential, the stabilization of clusters of precious metals on porous substrates is scarcely investigated. Herein, we present an innovative approach for the synthesis of stable Ag nanoclusters designed with the aim of achieving a strict control of key phases such as mixing, microwave heating, and quenching. The catalyst was used for the activation of alkynes showing excellent activity for the formation of C−O, C−N, and C−C bonds. When compared with commonly used homogeneous Ag salts, Ag NCs enhanced the catalytic activity toward the cyclization of a wide range of substrates, thereby minimizing the metal loading and allowing the separation as well as the reuse of the catalyst for multiple cycles.
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