SITE POISONING DURING DECOMPOSITION OF NITRIC-OXIDE ON NI(110)

The adsorption and decomposition of NO on Ni(110) at 110 K and during subsequent heating has been studied by using low-dose, pulsed Ar+ sput tering followed by photoionization and time-of-flight mass spectrometr y to monitor the surface concentration of molecularly adsorbed NO. Par tial decomposition of NO occurs after adsorption at 110 K. The extent of the decomposition at 110 K is approximately described by assuming t hat (1) site occupation during adsorption is random, (2) decomposition of one NO poisons decomposition at three or four surrounding sites, a nd (3) diffusion of adsorbed NO does not occur. Approximately 20-25% o f a saturation coverage decomposes at 110 K. Decomposition of the frac tion of NO molecularly adsorbed at 110 K occurs during subsequent heat ing. These decomposition kinetics display a strong dependence on cover age. For low coverages, decomposition begins at approximately 115 K an d is complete by 200 K. For a saturation coverage, decomposition is no t complete until 400 K. The decomposition kinetics during heating are discussed in terms of several kinetic models including decomposition a t sites exhibiting a range of activation energies.