(344d) Scaling Relationships on Transition Metals in Presence of Coadsorbates
An essential aspect of designing new heterogeneous catalysts is to understand how reactants interact with catalyst surfaces. One set of parameters that can quantify these interactions are the adsorption energies of key intermediates. These energies are, in turn, often related by classes of linear correlations known as scaling relationships [1,2]. These relationships are of interest not only because of their practical application to heterogeneous catalyst design, but also due to the fact that they provide fundamental insights into the nature of bonding of adsorbates with the catalytic surfaces. Indeed, they have proved to be surprisingly general and have been observed for metals, oxides, nitrides, and sulfides, among other types of materials . In spite of these exciting applications, however, very few studies have considered the effect of coverage on scaling relations [4,5]. In a real catalytic process, multiple intermediates are often present on the catalyst surface, and these coadsorbed species could non-intuitively change the functional form of the scaling correlations.
In the present study, the effect of common coadsorbates, including hydrogen and oxygen atoms, on several classes of scaling relationships is investigated. The coverage of the coadsorbate is varied on the close-packed surfaces of seven transition metals (Pt, Pd, Rh, Ru, Ni, Cu, Ag), and scaling relations between ten intermediates (CH3O, HCO, COH, CO, NOH, NH, OH, CH, C, O) are developed by systematically varying the coadsorbate coverage for each of these metals. In contrast to popular bond counting arguments for the slope of linear scaling relations , the slopes from our calculations are found to be metal dependent and do not always follow simple bond conservation theories. These results are discussed in the context of the well-known d-band theory  of surface adsorption, and the implications for catalst design principles are analyzed.
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