(154e) Synthesis and Characterization of Shape-Directed Pt Nanoparticles Toward Catalysis

Nanostructures with shape control are becoming increasingly more important as research heads toward more efficient, greener ideals. Growing nanoparticles with a particular shape is paramount to increasing catalytic efficiency as chemical reactions are more easily catalyzed by a particular facet(s) over another. Thus, it is important synthesize monodisperse well formed structures and to characterize their structure. Rigid control of the nanoparticle shape and size is paramount to increasing the efficiency of product yield by selectivity and enhanced conversion.

Platinum nanoparticles have been shown to quite effective in catalysis technology, especially in the realm of fuel cell development. The nanoparticle morphology at the single-digit to tens of nanometers length scale is changed at the atomistic level, where adatoms combine within micellar templates which in turn coalesce to nanocrystalline particles above a certain size domain. Tailoring the synthetic recipe of nanoparticles allows for strict size dispersions, that combined with tight morphologic control allow for very specific nanoparticles to be grown for use in catalysis where selectivity is important.

Platinum nanoparticles were synthesized via an inverse-micellar process, where metal salts are reduced in a polyol solvent. To achieve monodisperse or uniformly sized nanoparticles a surfactant (i.e. polyvinylpyrrolidone, myristyltrimethylammonium bromide) is added to the reaction mixture to achieve particles with good degree of monodispersity. The nanoparticles may grow in an octahedral form which is the corresponding Wulff shape for zero-valent Pt nanoparticles. However, the particles may be grown into other shapes such as nanocubes by introducing a shape controlling agent which binds to a particular facet, in this case (100) plane. Shape directing agents are added to the reaction mixture to elicit various morphological shapes. Addition of bromide ions via tetramethylammonium bromide allows for a high concentration of Br- ions to adhere to particular faces of the Pt nucleation seeds which kinetically stabilize the nanocube growth in only certain directions.

Therefore, a cubic shape is permitted to grow which can be much more active than other shapes of platinum nanoparticles in catalytic reactions. Particular nanoparticle morphologies have various facets in dominance, such as (100) and (111) for cubic and octahedral, respectively. The nanoparticle catalysts were characterized by transmission electron microscopy (TEM), high resolution TEM (HRTEM) techniques to analyze the shape and morphological distribution of as-synthesized nanoparticles. An intimate understanding how nanocatalysts’ shape morphologies are affected by synthesis, reaction, and support conditions is crucial to the success of coherent design of catalysts in the future.