Coadsorption of Oxygen and Carbon Monoxide upon a (110) Tungsten Surface

Abstract

A (110) surface of W that is covered by ½ a monolayer of O atoms will adsorb about ¼ monolayer of strongly held CO molecules and about half as many weakly held molecules. These are half the amounts that can be adsorbed on a clean (110) face. The CO is desorbed in its original form in two states at about 450° and 1100°K. No CO2 is formed. All the O is removable at 1950°K, apparently as oxides of W. The composite O–CO covered surface is a disordered structure if formed at room temperature, but if this is heated to about 1000°K a complex ordered surface is produced. This structure, having C (11×5) symmetry bears some resemblance to the C(9×5) structure produced in similar fashion without any oxygen. Experiments carried out in reverse order show that oxygen is not adsorbed at room temperature on a surface first saturated with CO, but if a CO saturated surface is held at 1000°K during exposure to O2, the same C(11×5) structure is formed as before. Exposure of a bare (110) surface to CO2 at a pressure below 10−7 torr results in negligible adsorption.