Correlating electronic properties of bimetallic surfaces with reaction pathways of dicarbon hydrocarbons
Date
2005
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Publisher
University of Delaware
Abstract
The rate and selectivity of chemical reactions on transition metal surfaces can be controlled by using different bimetallic combinations. The interaction of bimetallic components leads to a change in the electronic properties of the surface, which in turn produces a change in chemical reactivity. In the current paper, we illustrate the correlation of the electronic properties of bimetallic surfaces with the reaction pathways of C<sub>2</sub> hydrocarbons. Density Functional Theory (DFT) was used to study the binding of hydrogen, ethylene, acetylene, ethyl and vinyl on monometallic and bimetallic transition metal surfaces. The binding energies of these species were found to correlate with the d-band centers of these surfaces. The binding energies for hydrogen atoms on bimetallic surfaces were lower than on the corresponding parent metal surfaces. This trend was consistent for ethylene and acetylene binding. Comparative studies between acetylene and ethylene revealed that acetylene was more strongly bonded to the monometallic surfaces than was ethylene, but this trend reversed for the bimetallic surfaces. Bond order conservation (BOC) theory was used to calculate the activation barriers for ethyl dehydrogenation to ethylene and vinyl dehydrogenation to acetylene. The activation barriers for these reactions were correlated to the surface d-band center of the substrates. The activation barriers for dehydrogenation reactions were found to vary linearly with the heats of surface reactions, consistent with the Evans-Polanyi postulate.