The Role of Low-Coordinated Sites on the Adsorption of Glycerol on Defected Pt_n/Pt(111) Substrates: A Density Functional Investigation within the D3 van der Waals Correction

Several experimental studies have been reported for the conversion of glycerol on transition metal surfaces; however, only few studies have addressed the role of surface defects in the glycerol-substrate interactions. Here, we report ab initio calculations based on density functional theory within the D3 van der Waals (vdW) correction to investigate the adsorption properties of glycerol on flat and defected Pt(111) substrates, namely, (i) flat surface, (ii) dispersed adatoms, (iii) linear-type defect, (iv) island-type defect, and (v) vacancy-type defect. In the lowest and higher energy configurations, glycerol binds to the flat and defected Pt(111) substrates via one or two hydroxyl groups, in which the anionic O atom binds to cationic Pt site with the O-H bond nearly parallel to the Pt-Pt bonds in several cases, which indicates a contribution of the H^O-Pt interaction to the adsorption energy. The PBE adsorption energy is stronger on the low-coordinated sites of single Pt adatoms and six-adatom triangular defects, which can be explained by the shift of the center of gravity of the occupied d-states toward the Fermi level due to the reduction in the coordination adsorption site. The addition of the D3 vdW correction changes the preference of the adsorption sites, in particular, glycerol binds with a stronger adsorption energy on the six-adatom linear and triangle defects due the binding of multiple hydroxyls (the terminal and central one) to the substrate, which is expected due the attractive nature of the vdW correction. On the basis of Bader analysis, we obtained an effective charge transfer from glycerol to the Pt substrates, which helps to explain the work function reduction of the substrates upon glycerol adsorption along with the polarization of glycerol. These results indicate that permanent-induced dipole forces play an important role in the glycerol-substrate binding mechanism.