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Presentation Discussion

  • May 21, 2012 | 11:23 p.m.

    Nice poster and great presentation. Your work is very interesting even though this is really not my field.

    I understand that your nanoparticles were used because they served as a model geometry and material substrate for your study. I wonder if nanoparticles such as these can be utilized to improve design of catalytic converters based on the increased surface areas one may achieve with such an approach. Or is this what is being done?

    Also, how does your work translate into the design of novel solutions to the clean energy problem?

  • Icon for: Tyne Johns

    Tyne Johns

    May 22, 2012 | 11:31 a.m.

    Thank you for the nice compliment. Our method of deposition (electron beam evaporation) could not easily be scaled up for production of automotive catalysts. Physical vapor deposition techniques are not used for that reason. If we use what we learn about the fundamentals from these model catalyst studies, however, eventually we will be able to develop more stable catalysts to be used in catalytic converters.

    This work will help with the energy problems because some studies are showing that the addition of Pd to Pt actually increases catalytic activity. This is very promising because it means we could have more durable catalysts (longer lifetimes) with even better activity to reduce the emissions of pollutants.

  • Icon for: Carol Johnson

    Carol Johnson

    May 24, 2012 | 11:39 a.m.

    Neat experimental method! I like the way you deposited the nanoparticles directly onto the TEM grids. Did you follow specific particles before and after the experiment, or just look at the overall picture? It would be really interesting to see a specific particle get smaller while another gets bigger.

  • Icon for: Tyne Johns

    Tyne Johns

    May 24, 2012 | 01:01 p.m.

    Thank you. We’ve done both a statistical method where we looked at thousands of particles (the overall picture) and we found a way to track individual nanoparticles. The microscopic approach in the third column on my poster has images that were taken of the same group of particles. Take a look at the top 4 images. There are shapes around single particles and groups of particles showing that it is possible to track the same particles before and after aging using an ex-situ method, which has not been done before. Thanks for your question.

  • Further posting is closed as the competition has ended.

Icon for: Tyne Johns


University of New Mexico
Years in Grad School: 3

Adatom Emission from Nanoparticles: Implications for Ostwald Ripening

Catalysts are essential for the treatment of carbon monoxide, hydrocarbons, and nitrogen oxides in engine exhaust. Platinum (Pt) and palladium (Pd) are currently used in catalytic converters to transform these pollutants into less harmful molecules. The supply of precious metals is decreasing while demand for clean energy is increasing. Therefore, there is a need to develop more active catalysts with minimal use of precious metals such as Pt. A serious problem facing catalysts is the loss of activity during use. Several research groups have shown that Pt particles grow readily under oxidizing conditions, leading to poor durability, but it has been shown that addition of Pd to Pt leads to improved stability; however, it is unknown why.

It is suspected that volatile platinum oxides may be responsible for the rapid growth of Pt catalysts, but the relative importance of the surface and gas phase processes is not known. In automotive catalysts, this phenomenon can only be studied after aging. Therefore, we have developed a novel approach using model catalysts where it is possible to perform direct measurements of the emission of atoms from nanoparticles. Pt, Pd, and bimetallic Pt-Pd samples were created on TEM grids. The samples were reduced and aged under oxidizing conditions at different temperatures. We used a statistical approach and a microscopic approach to study the phenomena. Our results show that Pd impedes the emission of the volatile Pt oxides in the bimetallic samples; however, the vapor phase process does not fully explain the observed rates of Ostwald ripening.