SURFACE-STRUCTURE EFFECTS IN THE REACTIONS OF NITRIC-OXIDE WITH HYDROGEN AND CARBON-MONOXIDE ON RHODIUM - A COMPARISON WITH THE SURFACE-STRUCTURE EFFECTS OBSERVED FOR THE HYDROGEN OXYGEN AND CARBON-MONOXIDE OXYGEN REACTIONS

Using field electron microscopy (FEM) and thermal desorption and reaction spectroscopy (TDS) the behavior of various Rh single-crystal surfaces toward reactions involving NO has been studied. If, after NO adsorption up to saturation at 77 K, the temperature is slowly raised, the FEM results suggest that dissociation of NO starts at the (321), (331) and (533) surfaces. The reaction of NO//a//d//s with hydrogen also starts at these surfaces (at about 360 K), suggesting that NO bond scission initiates the reaction. After initiation, a surface explosion is observed. Depending on the heating rate, either a clean surface or a N//a//d//s covered surface is obtained after completion of the reaction. Apparently, the reduction of adsorbed N//a//d//s by hydrogen can occur at a significant rate at this temperature. At a higher heating rate the N adatoms formed do not react with hydrogen and are readily desorbed as N//2 at 600 K. The reaction of NO//a//d//s with CO also starts on the (321) and (331) surfaces. The rate of the reaction with CO is, however, much lower than that with hydrogen.