ADSORPTION AND REACTIONS OF NO ON NIAL(111) AT 75 K

The adsorption and reactions of NO on NiAl(111) at 75 K were studied b y high resolution electron energy loss spectroscopy, temperature progr ammed desorption, Auger electron spectroscopy, and low energy electron diffraction. At low exposure (less than or equal to 1 L), NO mainly a dsorbs molecularly on top in an upright geometry on Ni atoms. Simultan eously, a small amount of NO dissociates. Higher exposures (greater th an or equal to 2 L up to saturation) lead to the formation of a thin a morphous Al-oxynitride (am-ALON) film. In the presence of am-ALON, a m olecular adsorption of NO on am-ALON sites and/or in the neighborhood of ALON islands is observed. Besides the upright geometry, NO molecule s are adsorbed in disarranged (bent or tilted) configurations. The gro wing am-ALON film acts as a catalyst for the reduction of NO to N2O. S ubstantial amounts of N2O are formed for NO exposures higher than 5 L, and are coadsorbed molecularly. The main thermal desorption products are N2O, N-2 and NO. For an exposure of 20 L NO, the ratios of the amo unts of desorbing molecules are: N2O:N-2:NO=1:0.43:0.36. It could be s hown that the N-2 Signal is due to a recombinative desorption of adsor bed nitrogen atoms. (C) 1997 American Institute of Physics.