New size effect in the catalysis by interacting copper nanoparticles

Highly active catalysts consisting of copper nanoparticles deposited on surface-oxidized silicon were prepared by a new method of laser electrodispersion. This method allows fabricating the stable monodispersive nanoparticles comprised of amorphous copper core (the size is ≈3.5 nm) covered by the thin (<1 nm) Cu2O oxide shell. Taking chlorohydrocarbon conversions (dichlorobutene isomerization, carbon tetrachloride addition to 1-octene and carbon tetrachloride reaction with decane) as examples the unusually high activity (104-105 product mol/(metal mol h)) of closely packed ensembles of nanoparticles was observed. These catalysts are several orders of magnitude superior in activity than usual supported metal catalysts. In all the reactions studied, strong dependence of the catalytic activity on the particle surface density and on the polarity of the reactant solution was found. These results are in a good agreement with theoretical estimations indicating that nanoparticle charging, which occurs due to thermally activated electron tunneling between closely located particles is responsible for the formation of highly active catalytic system.