Simon Klacar

Low Temperature CO Oxidation over Supported Ultrathin MgO Films

Density functional theory is used to investigate CO oxidation over an ultrathin MgO film supported on Ag(100). O(2) is found to be activated on MgO/Ag(100) whereas CO is only weakly bonded to the surface. These adsorption properties together with a low activation barrier render the MgO/Ag system an efficient catalyst for CO oxidation at low temperatures. As the predicted mechanism is general in nature, the result is suggested to have implications for a wide range of oxidation reactions.

H2 dissociation over Ag/Al2O3: the first step in hydrogen assisted selective catalytic reduction of NOx

Hydrogen assisted selective catalytic reduction of NOx over Ag/Al2O3 with either hydrocarbons or ammonia as reducing agents is an emerging technology for lean NOx reduction. Herein, we present a density functional theory study of H2 dissociation over a representative set of sites present on the Ag/Al2O3 catalyst. Whereas H2 dissociation over supported Ag ions and oxidized Ag surfaces is found to be facile, dissociation over metallic Ag, defect free Al2O3 and alumina-supported Ag is associated with high barriers. The results are rationalized by analysis of the electronic structure.

Influence of surface pinning points on diffusion of adsorbed lipid vesicles

Using a simple model of a vesicle and a substrate, we have studied the surface diffusion of an adsorbed vesicle. We show that the experimentally observed but unexplained fact, that a neutral (POPC) vesicle adsorbed to a SiO(2) or mica surface does not diffuse but can be moved laterally by an atomic force microscope (AFM) tip, without rupture, can be explained by transient (i.e., temporary) pinning of lipid head groups to surface charges. We studied the surface diffusion for different vesicle adsorption strengths (without any pinning taking place), with the observation that a stronger vesicle-surface attraction leads to slower surface diffusion. However, the surface diffusion was still significant and too high to explain the experimentally observed immobility. When allowing transient lipid pinning between the vesicle and the surface, a 1-2 orders of magnitude decrease in the surface diffusion coefficient was observed. For a lipid adsorption potential of around 20 k(B)T and a lipid pinning potential of about 25 k(B)T, the vesicle is found to be practically immobile on the surface.