(628e) Correlating Electronic Properties of Bimetallic Surfaces with Reaction Pathways of C2 Hydrocarbons

The activity and selectivity of reactions on transition metal surfaces can be increased by creation of bimetallic combinations. The interaction of bimetallic components leads to a change in the electronic properties of the surface, which in turn results in changes in chemical reactivity [1-5]. In this work we illustrate the correlation of the electronic properties of bimetallic surfaces with the reaction pathways of C2 hydrocarbons and fragments. Density Functional Theory (DFT) was used to study the binding of hydrogen, ethylene, acetylene, ethyl and vinyl on monometallic and bimetallic transition metal surfaces [6,7]. The binding energies of these species were found to correlate with the d-band centers of the monometallic and the bimetallic surfaces. The binding strength increases as d-band center moves closer to the Fermi level. The binding energies for the adsorption of hydrogen on bimetallic surfaces were found to be lower than on the corresponding parent metal surfaces. A similar trend was found for ethylene and acetylene binding. Bond order conservation (BOC) theory was used to determine the trend in the activation barriers for ethyl dehydrogenation to ethylene and vinyl dehydrogenation to acetylene. The activation barriers for these reactions were correlated to the d-band center of the substrates.

DFT-calculated binding energy and BOC-calculated activation barrier values were used to calculate the selectivity for acetylene hydrogenation vs. ethylene hydrogenation. The results showed that for monometallic fcc(111) surfaces, the selectivity for acetylene hydrogenation followed the trend Ni > Pt > Pd. The selectivity for thermodynamically stable bimetallic surfaces was found to be lower than the corresponding parent metals. Parallel reactor studies of selective hydrogenation of acetylene are underway to verify the DFT/BOC predictions.

References

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