Adsorbate Bond Number Dependency for σ- And π-bonds in Linear Scaling Relationships

Despite the exigent role of heterogeneous catalysts, designing them in a bottom-up fashion remains a challenge. Linear scaling relationships are, thus far, perhaps the most auspicious first-principles design methodology relating adsorbate strength to catalyst activity. Yet, the successful application of scaling relations as a general design strategy, or even rationally breaking them, is still often limited to simple reactions such as σ-bond cleavage for monodentate adsorbates, and the relationships are nearly always established on close-packed surfaces. Here, it is discussed that for σ- and π-bonds, the metal-adsorbate system has opposite energetic dependency in the offset, which is directly related to the corresponding two classes of structure sensitivity that have empirically been observed in the literature for decades. The discussed observations imply that some currently invoked theories explaining the physical and chemical principles that dominate linear scaling relationships in both inter-adsorbate and BEP linear scaling relationships perhaps do not sufficiently explain them. The discussion is aimed at broadening the applicability of this rational design principle.