Model catalyst studies with single crystals and epitaxial thin oxide films

The paper describes recent results from our relatively new program to perfo rm detailed studies of the catalytic properties of metal-oxide materials; i n particular, to effect a determination of the active catalytic site(s) and the mechanism for reactions over this especially important class of hetero geneous catalysts. Issues of structure-sensitivity, poisoning and promotion , and competing reaction mechanisms are critical questions that need to be addressed in a detailed manner for catalysis by oxides. As just one importa nt example, both surface (Langmui-Hinshelwood) and direct (Eley-Rideal) rea ction mechanisms have been proposed for the selective catalytic reduction ( SCR) reaction of nitrogen oxides (NOx) over vanadia/titania catalysts. For this program, we are using a number of unique, state-of-the-art capabilitie s available in the Environmental Molecular Sciences Laboratory (EMSL) at Pa cific Northwest National Laboratory; for example, the first molecular beam epitaxy (MBE) system dedicated to the growth of model metal-oxide films, an d a unique moderate-pressure catalytic reactor/surface science apparatus. W e describe the growth, characterization, and water adsorption properties of a thin Fe3O4(0 0 1) him grown on a lattice-matched MgO(0 0 1) substrate. B ecause our moderate pressure catalysis studies are preliminary at this poin t, we instead describe our previous results on the CO oxidation reaction ov er a Ru(0 0 0 1) model catalyst to demonstrate the utility of the experimen tal approach. We specifically discuss the possibility that this reaction oc curs by an Eley-Rideal mechanism. (C) 1999 Elsevier Science B.V. All rights reserved.