THE INTERACTION OF NO, O-2 AND CO WITH CU(100) AND CU(110)

Exposure of NO or O2 to Cu(100) or Cu(110) (at temperatures between 370 and 670 K, pressures up to 0.1 Pa) leads to dissociative adsorption. Dissociation on Cu(110) is about an order of magnitude faster than on Cu(100). Saturation of the surface coverage (for both surfaces at about 0.42 monolayer) is followed by the structure-insensitive penetration of oxygen atoms into the crystal. Reduction proceeds via reaction of adsorbed CO and adsorbed oxygen, the effect of nitrogen can be explained by site-blocking. Again, the reaction is about an order of magnitude faster on Cu(110) than on Cu(100). In the case of Cu(100) a transition from a disordered to an ordered overlayer is observed at a fractional surface coverage of about 0.3. Nitrogen desorption is more difficult from Cu(100) than from Cu(110). The desorption temperature depends on the presence of oxygen (adsorbed as well as penetrated). At high CO pressures the formation of isocyanate facilitates the desorption of nitrogen.