Catalysis with Transition Metal Nanoparticles of Different Shapes

Abstract

ABSTRACTColloidal metal nanoparticles have a high surface-to-volume ratio which makes them potentially attractive catalysts. Furthermore, atoms located at different facets, edges, or corners could show different catalytic activity. For this reason, different shapes could have different catalytic activities. In addition, surface atoms are so active that there could be significant changes in their shape and size during the course of nanocatalysis. As a result, a thorough examination on the effect of the catalytic process on the shape and size of colloidal metal nanoparticles after catalysis is necessary to fully evaluate their use in catalytic processes.In this paper, we briefly review our recent work on examining the shape dependence of nanocatalysis as well as the stability of platinum and palladium nanoparticles during the course of two reactions: the electron transfer reaction and the Suzuki reaction. It is found that nanocatalysis is indeed shape-dependent during the early stages of the electron transfer reaction. During the full course of the reaction, there are changes in the nanoparticle shape as well as changes in the activation energy that takes place. In the case of a relatively harsh reaction such as the Suzuki reaction, spherical palladium nanoparticles grow in size due to Ostwald ripening processes. Tetrahedral platinum nanoparticles catalyzing the Suzuki reaction transform into spherical shape and grow larger in size. We also conducted studies on the effect of individual reactants on the nanoparticle size and shape. In addition, the surface catalytic mechanisms of the reactions have been confirmed using spectroscopic tools such as FTIR and Raman spectroscopy. These kinds of studies will be very useful in the process of designing better nanocatalysts in the future.