Trends in atomic adsorption on Pt₃M(111) transition metal bimetallic surface overlayers

The general trends in adsorption behaviors of atomic H, N, O, and S on pure transition metal and bimetallic Pt-transition metal overlayers on Pt(111) are investigated from first principles. Consistent with d-band theory, the adsorbate binding energy on pure transition metal overlayers increases monotonically when the group number of the transition metal decreases. In contrast, bimetallic overlayers show a qualitatively different behavior for trends in adsorption. Using model Pt₃M(111) bimetallic surface overlayers, we find the binding of atomic N, O, and S to the Pt₃M overlayers increases first and then decreases when moving left in the periodic table. We correlate the different binding energy trends in terms of the change in adsorption geometry resulting from the competition between the adsorbate-metal interactions and formation of Pt₃M surface alloys. Charge transfer between the surface atoms and the adsorbates is much larger for early transition metals, leading to the different trends in adsorbate binding energies on Pt₃M overlayers with early transition metal M. We also find the surface segregation tendencies of solute metals M are influenced by the binding strength of the adsorbates to the alloy overlayers. O adsorbates qualitatively change the segregation tendency of early transition metals to segregate to the Pt(111) surface.