Steric Hindrance of NH(3) Diffusion on Pt(111) by Co-Adsorbed O-Atoms

[Image: see text] A detailed velocity-resolved kinetics study of NH(3) thermal desorption rates from p(2 × 2) O/Pt(111) is presented. We find a large reduction in the NH(3) desorption rate due to adsorption of O-atoms on Pt(111). A physical model describing the interactions between adsorbed NH(3) and O-atoms explains these observations. By fitting the model to the derived desorption rate constants, we find an NH(3) stabilization on p(2 × 2) O/Pt(111) of 0.147(–0.014)(+0.023) eV compared to Pt(111) and a rotational barrier of 0.084(–0.022)(+0.049) eV, which is not present on Pt(111). The model also quantitatively predicts the steric hindrance of NH(3) diffusion on Pt(111) due to co-adsorbed O-atoms. The derived diffusion barrier of NH(3) on p(2 × 2) O/Pt(111) is 1.10(–0.13)(+0.22) eV, which is 0.39(–0.14)(+0.22) eV higher than that on pristine Pt(111). We find that Perdew Burke Ernzerhof (PBE) and revised Perdew Burke Ernzerhof (RPBE) exchange–correlation functionals are unable to reproduce the experimentally observed NH(3)–O adsorbate–adsorbate interactions and NH(3) binding energies at Pt(111) and p(2 × 2) O/Pt(111), which indicates the importance of dispersion interactions for both systems.