Adsorption-Induced Surface Electronic Reconstruction of Pt and Pt-Sn Alloys during CO Adsorption

CO adsorption on Pt(111) and Pt3Sn(111) at coverages ranging from 0.11 to 0.5 ML has been studied using theoretical ab initio methods. DFT-AER has been proven to give the correct site preference of CO adsorption, in parallel to experimental surface science studies, on both pure Pt and Pt-Sn alloy surfaces. According to the results, the linear adsorption of CO is the most stable structure on these surfaces. The difference in the adsorption strength between linear adsorption and multifold adsorption is very small on Pt3Sn(111), which results in the presence of multifold-adsorbed CO along with linearly adsorbed CO. On the Pt(111) surface, the difference in the adsorption strength is larger. CO binding on the surface causes a reconstruction of the electronic structure of the neighboring sites on Pt(111). For CO concentrations up to 0.33 ML, a shift of the d-band of neighboring bare Pt atoms to lower values favors linear CO adsorption on these sites. This leads to the formation of a (root 3 x root 3)R30 degrees pattern with all the CO linearly adsorbed at low surface coverages. Further increase in CO coverage forces bridge-type CO adsorption.