The adsorption and reactions of NO₂ on the Ag(111) surface. I. XPS/UPS and annealing studies between 90 and 300 K

Abstract

The adsorption and reaction of NO2 on Ag(111) has been investigated at 90 and at 300 K. Reaction and desorption on annealing from 90 to 300 K have also been monitored. At 300 K the reaction is entirely dissociative, leading to a state characterized as NO(ads) + O(ads), where the species strongly interact, and where partial desorption of the NO(ads) products has occurred. At 90 K. the initial adsorption is also dissociative, leading to the same products, but without any desorption. This state saturates at low coverage (about one atomic monolayer). Further adsorption results in condensed multilayérs of N2O4. Annealing to 300 K causes N2O4 desorption, plus complex dissociation and association reactions in the 125-140 K range. The reaction product is NO3(ads). Further heating between 140 and 300 K results in a slow desorption of all species now present over the whole temperature range. By 300 K the only species not completely desorbed is NO3(ads). In comparison, heating a low coverage N2O4 initial situation results in simple desorption, leaving only the already formed NO(ads) + O(ads) state with no evidence for formation of NO3(ads). This different annealing behavior for the two coverages emphasizes the fact that in this system inter-molecular reactions are as important as reactions between adsorbate and substrate. © 1990.