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Nanocząstki metali przejściowych - synteza i aktywność katalityczna

Gniewek A., Trzeciak A. M.

Wiadomości Chemiczne

2009

[Z] 63, 11-12

953-984

Transition metal nanoparticles (also called metal colloids or nanoclusters) are ordered multi-atom sets characterized by a very small size, generally less than 20 nm. They are intermediate species between single atoms and crystals of macroscopic dimensions [1.8]. Nanoparticles have been synthesized by a variety of methods. The most common synthetic procedures involve chemical reduction of transition metal salts or complexes. By the choice of reduction conditions (kind of the reducing agent, type of the stabilizing agent and the elementary reaction parameters like temperature and concentration) it is possible to obtain colloids showing different particle sizes and morphologies. These two factors play a decisive role from the point of view of catalytic activity of nanoclusters. Palladium nanoparticles have been obtained by chemical reduction of PdCl2 aqueous solution using pyrogallol, hydrazine or chromium(II) acetate as the reducing agent. All these systems have demonstrated a very high catalytic activity in important carbon-carbon bond forming reactions (methoxycarbonylation, Heck and Suzuki processes) carried out under mild conditions [48, 49]. Some of the C.C coupling reactions have also been successfully catalyzed by nickel nanoparticles, however they require more harsh conditions [65, 66]. Cobalt and iron nanoparticles present magnetic properties attractive for application of these materials as removable electronic media of high capacity, as well as biosensors or magnetic probes for biological imaging and therapeutic use [9, 18]. The extreme reactivity of nanoparticles, specifically towards oxygen and water, complicates their synthesis, however it is also beneficial in catalytic applications [16, 17]. Conversion of CO/H2 mixture to hydrocarbons, known as Fischer-Tropsch synthesis, representing one of the most important routes to fuels production, is catalyzed very effectively by iron and cobalt nanoparticles. Monometallic and bimetallic cobalt nanoparticles are excellent catalysts of Pauson-Khand type couplings leading to cyclopentanones [17].