Catalytic Properties

A majority of noble and transition metal nanoparticles are catalytically active in a number of reactions. Most of the articles dealing with catalytic properties of nanopar-ticle-containing nanostructured polymers present studies on catalytic hydrogenation of various substrates, as this is an easily available test of catalytic activity. For example, hydroxyl-terminated PAMAM dendrimers containing Pd nanoparticles showed high catalytic activity in alkene hydrogenation in water [93]. Moreover, the catalytic activity might be controlled by changing the dendrimer size (generation). In the author's opinion, the dendrimer works as a "nanofil-ter" with a controllable mesh size.

Block copolymer (PS-6-P4VP) micelles in organic solvents bearing mono- or bimetallic nanoparticles displayed a high selectivity and activity in hydrogenation of dehydroli-nalool to linalool (fragrant substance) [46]. The authors showed that modification of Pd nanoparticles with a second metal alters the electronic properties and surface geometry of the nanoparticles and, as a consequence, catalytic activity. Very high selectivity was provided due to modification of nanoparticle surface with pyridine units of the core-forming block.

Pd nanoparticles stabilized by the above block copolymers were also employed for Heck reaction: cross-coupling of alkylhalides and alkenes [94]. These systems showed reactivity similar to traditionally used Pd complexes but with much higher stability.

Pt nanoparticles formed in HPS [35] were successfully used for direct catalytic oxidation of L-sorbose to 2-keto-L-gulonic acid (vitamin C precursor). Here the catalytic activity and selectivity strongly depend on both the particle size and particle composition. The highest selectivity was obtained for the complex Pt0/Ptn/PtIV nanoparticles with a mean diameter of about 1.8 nm obtained in-situ during the induction period of catalytic reaction.

So, in general, catalytic properties of such systems depend on the particle size, particle composition, and the type of surrounding polymer system.

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