Reaction of Nanoparticles with Gases

It is known that the activation energies for some processes taking place in nanoscale particles are different from ones for bulk substance. For example, the activation energy for diffusion of atoms in nanoparticles decreases with the particle size [1], In turn it can affect other processes related to mobility of atoms (molecules) in nanoparticles (e.g. absorption of foreign gases by nanoparticles, nanoparticle coalescence, chemical reactions in nanoparticles). 

Catalytic activity of MCM-41 with rhodium oxide nanoparticles prepared by addition of RhClj 3H2O in sol-gel mixture were studied in the high-tempera-ture NO-CO catalytic reaction [22]. Catalyst containing RhO nanoparticles with diameters less than 3 run exhibited a novel promotional effect in the amount of N2 and N2O formation with excess O2, while most of Rh catalysts become poisoned with the O2 excess. The authors also claim that catalysts with 6-8 nm RhO nanoparticles in the MCM-41 had drastically retarded the formation of target molecules. Since the Rh precursor is added to the sol-gel mixture and particles can be located in the siHca body, the comparison of solely particle size in determination of catalytic properties can be misleading, as particle location (accessible for gases or not) may be a crucial feature. 

On the other hand, if 02 existed in the reaction system, the reaction mechanism would be affected by the reactions with 02 the reaction mechanism is dependent on the types of dissolved gases in the sample solution. The details for the effects of various parameters on the reduction of metal ions and formation of metal nanoparticles are described in the following sections. 

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