Role of adsorbed surface oxygen in the adsorption of NO on alkaline earth oxides and Pt-promoted CaO surfaces

Adsorbed surface oxygens are formed on CaO, SrO, and BaO during exposure to N2O, and their presence is shown to affect the room-temperature NO adsorpt ion. Information about the adsorbed intermediates is contained in the desor ption products and in the desorption temperatures during the subsequent hea ting ramp in Ar. The presence of adsorbed oxygen species increases the tota l amount of adsorbed NO for CaO and BaO substrates, whereas for SrO the ads orbed intermediate is stabilized. Two NO desorption peaks are found for CaO and SrO, one at low and one at high temperature. The former is assigned to adsorbed NO, whereas the latter is assigned to adsorbed -NO2 and/or -NO3 s pecies. NO adsorption as -NO2 and/or -NO3 species finds evidence in the cor responding O-2 desorption. Only one NO desorption peak is found for BaO. Th is NO desorption peak disappears in the absence of preadsorbed surface oxyg ens. O-2 desorption is observed, even in the absence of any preadsorbed sur face oxygens, for CaO and SrO substrates. This suggests NO bond dissociatio n upon NO adsorption. The effect of the promotion of CaO by Pt has also bee n investigated. The respective desorption profiles are similar to those for the unpromoted CaO with preadsorbed surface oxygens, although the amounts are significantly increased.