The ability to design highly active, selective, and stable catalysts would greatly reduce energy consumption and minimize pollutant formation. For monometallic catalysts, surface structure, oxidation state, and nature of the metal-oxide interface are key catalyst features that dictate the catalytic properties. In the present work, monodisperse Pt and Rh nanoparticles with size and shape control were used to probe the influences of surface structure and oxidation state upon the catalytic properties.
Ultrasmall (as small as ~ 1 nm) monometallic and bimetallic Pt and Rh nanoparticles were synthesized by using fourth generation PAMAM dendrimers as the templating and capping agent. Spherical (1.5 nm and larger) and cubic Pt nanoparticles (5 nm and larger) were synthesized using various colloid chemistry routes. Nanoparticles were loaded onto mesoporous silica (SBA-15 or MCF-17) by sonication. Characterization of the unsupported and silica supported nanoparticles was performed by techniques such as electron microscopy (TEM), elemental analyses (ICP-MS), X-ray photoelectron spectroscopy (XPS), chemisorption, and vibrational spectroscopy.
Using ethylene hydrogenation as a test reaction, treatments were optimized to maximize catalytic activity and the capping and shaping agents were determined not to influence the catalytic behavior. Then, influences of surface structure and oxidation state were examined for pyrrole hydrogenation, a model reaction for the study of hydrodenitrogenation. Hydrogenation of the ring occurred more rapidly, regardless of size, over Rh catalysts than Pt ones. However, the scission of C-N bonds occurred more readily over Pt catalysts. Moreover, C-N bond breaking was more rapid when the Pt particles were larger than 2 nm, and consequently n-butylamine and butane were more likely to form over larger nanoparticles. Formation of n-butylamine and butane were also enhanced over cubic Pt nanoparticles compared to spherical particles. These results indicated that the surface structure was responsible for the differences in selectivity.
John earned his Bachelor's degree in Chemical Engineering at the University of Dayton in 2002. During that time, he also performed research at the Air Force Research Laboratory at Wright-Patterson Air Force Base. John completed his doctorate in Chemical Engineering at the Ohio State University in 2007 with Professor Umit Ozkan as his advisor. Currently, he is working with Professor Gabor Somorjai as a postdoctoral fellow in the Chemistry Department at the University of California, Berkeley and also holds a joint appointment in the Chemical and Materials Sciences Divisions of Lawrence Berkeley National Laboratory.
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