THE DECOMPOSITION OF AMMONIA ON AN OXYGEN-PRECOVERED NI(110) SURFACE STUDIED BY SCANNING-TUNNELING-MICROSCOPY

The decomposition of ammonia on a Ni(110) surface with preadsorbed oxy gen has been investigated in ultra-high vacuum at room temperature usi ng scanning tunneling microscopy (STM). We propose a reaction model in which the high reactivity observed at low O coverage is ascribed to a direct interaction between the NH3 molecules and the terminating atom s of the short, mobile -Ni-O- added rows which are observed on the sur face under these conditions. This model is consistent with the observa tion that the surface becomes inert at high O coverage. We believe tha t the present reaction model can also explain results from some other experiments in which preadsorbed oxygen has been found to act as a pro moter for dissociation of H-containing species, such as for NH3 on Cu( 110) and H2O on Ni(110).