Alkali metal effect on catalytic CO oxidation on a transition metal surface: a lattice-gas model

We present a lattice-gas-type model which accounts for short-range correlations between coadsorbates to describe analytically the alkali-modified CO oxidation reaction on a transition metal surface. The effect of the adsorbed alkali near the surface is described in terms of long-range fields which change the binding energies of adsorbed CO and oxygen, and of the coadsorption-modified sticking coefficients. An decrease of the binding energy of CO in chemisorbed state which provides an increase of oxygen coverage on the surface and an alkali-induced delocalization of adsorbed CO accompanied by a lowering of the CO coverage is predicted. As net result the reactive state (oxygen covered surface) is enlarged towards higher pCO pressures in agreement with the experimentally obtained phase diagrams (pCO, 1/T).