COLL 345 |
| Andrzej Wieckowski1, Panakkattu Babu1, Eric Oldfield1, Hee Soo Kim1, Eugene S. Smotkin2, Harry Rivera2, and Robert R. Diaz2. (1) Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL 61801, (2) Department of Chemistry, University of Puerto Rico at Rio Piedras, PO Box 23346, San Juan, PR 00931-3346 |
| We have carried out 195Pt NMR experiments on a series of Pt-Ru alloy nanoparticles and on pure Pt nanoparticles to explore the nanoparticle composition and the nature of the electronic alterations introduced by the addition of Ru to Pt. We have also studied the effect of heat-treatment on local composition of such Pt-Ru nanoparticles. The 195Pt NMR spectrum of the carbon-supported Pt catalyst consists of a broad, multi-Gaussian line shape that reflects the rapid variation in the Fermi level local density of states of the Pt atoms on the surface, subsurface and interior layers of the nanoparticle. For the Pt-Ru alloy nanoparticles (both supported and unsupported), the 195Pt NMR spectrum consists of a single Gaussian peak that is much narrower than the NMR spectrum of pure Pt nanoparticles. These 195Pt NMR results strongly suggest that there is a surface enrichment of Pt atoms in the Pt-Ru alloy nanoparticles. Additional measurements with 13C NMR spectrum indicate that isolated Ru islands do not exist on the surface. Combining our NMR results with electrochemical measurements, we find that the heat-treatment at 220 oC might help to optimize the surface composition of Pt and Ru whereas the heat-treatment at 600 oC considerably increases the particle sizes. Lattice parameter data of the as received, and heat treated to 220 oC and 600 oC Pt/Ru catalysts are consistent with a model that involves enrichment of Ru on the catalyst surface with heating. |
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Vibrational Analyses of Dry and Wet Surfaces
2:00 PM-5:30 PM, Tuesday, March 30, 2004 Marriott -- Grand Ballroom H, Oral
Division of Colloid and Surface Chemistry |