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Charles E. Lyman Research

Dr. Lyman's research interests include electron microscopy and microanalysis of metals, ceramics, and heterogeneous catalysts. He and his students have found structure-property relationships of supported alloy catalysts, particularly the microstructure of Pt-Rh catalysts that optimize the activity of reactions for the low-temperature reduction of nitric oxide. Other research has included work on aluminum alloys, stainless steels, transition metal oxides, and carbon fibers.

Bimetallic nanoparticles have been used as catalysts for many years without knowing the details of the composition or the structure of individual particles within a particular particle population. Important improvements in catalytic properties have been made by directly analyzing individual particles, rather than by assuming that all the particles in a population are identical. Professor Lyman and his students have used scanning transmission electron microscopy and in-situ FTIR to determine the microstructure of the ideal bimetallic nanoparticle that is most favorable for high activity and selectivity in the reduction of NO with H2. A typical catalyst for this reaction is Pt-Rh/γ-Al2O3, and this catalyst may be used for control of emissions from fossil fuel electric power plants. The findings from this research include the discovery that certain nanoparticle populations can form into separate phases [1], the demonstration that single-phase bimetallic nanoparticles with minute amounts of the second element have the highest selectivity [1, 2], and that a Pt-Ni catalyst reduces NO with higher selectivity to N2 than the more expensive Pt-Rh catalyst [3]. The structure of the active Pt-Ni nanoparticle is expected to be a decoration of a 2-nm Pt particle with a few Ni surface atoms.

Composition-size diagram showing two bimetallic alloy catalysts after similar heat treatments. This type of diagram provides a fingerprint for a catalyst population. The Pt-Rh nanoparticles have separated into a Pt-rich phase and a Rh-rich phase [1]. The Pt-Re nanoparticles are about 1 nm in size and exhibit a range of Pt-rich alloy compositions [4].

[1] R. E. Lakis et al., J. Catal., 154 (19 95) 261-275.

[2] P. S. Dimick et al., Applied Catalysis B: Environmental 89 (2009) 1-11.

[3] P. S. Dimick et al., Catalysis Letters 138 (2010) 148-154.

[4] R. Prestvik et al., J. Catal. 176 (1998) 246-252.

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