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O: Fachverband Oberflächenphysik

O 101: Particles and clusters II

O 101.6: Vortrag

Freitag, 18. März 2011, 12:30–12:45, WIL C107

Adsorbate-induced smoothing of Re particles on the atomic scale — •Payam Kaghazchi and Timo Jacob — Universität Ulm, Albert-Einstein-Allee 47, D-89069 Ulm, Germany

Using density functional theory in combination with the ab initio atomistic thermodynamics approach we studied the equilibrium shape of Re particles in the presence of strongly interacting O and N adsorbates. At low and intermediate coverages, oxygen adsorption has minor influence on the equilibrium shape of the corresponding clean particles, i.e., truncated polyhedra, while nitrogen adsorption leads to stabilization of spherical-like polyhedra with a large contribution from atomically-rough (1342) faces[1]. At very high coverages of O and N, particles are perfect prisms consisting of the (0001) and (1010) faces. Since the close-packed surfaces are often less active in O and N-involved reactions than atomically-rough ones, these results offer a possible explanation for the experimentally-observed reduction in the activity of Re particles for ammonia synthesis and also predict a decrease in the activity of this system in oxidation reactions at high coverages. This study suggests that, besides the site-blocking effect, adsorbate-induced smoothing of particles on the atomic scale can reduce catalytic activity of transition metals[2]. [1] P. Kaghazchi and T. Jacob, Phys. Rev. B, 82, 165448 (2010). [2] P. Kaghazchi and T. Jacob, in preparation.