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

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.