Spectroscopic study of NO adsorption on magnesium oxide, nickel oxide and their solid solutions

Abstract

The adsorption of NO on pure MgO at 77 K gives N₂O₂(cis) dimers on {100} faces and NO^–₂(nitrite), N₂O^2–₂(hyponitrite) and N₂O₂(cis) dimers on edges and steps. The hyponitrite anions (which are the precursors of N₂O gas formation) and the dimeric N₂O₂(cis) species are absent at room temperature, while the NO^–₂ species are formed in larger proportions. NO adsorption on dilute NiO–MgO solid solutions not only gives the species found on pure MgO but also surface Ni²⁺—NO nitrosyls; moreover, the presence of Ni²⁺ ions on the surface depresses the formation of N₂O^2–₂(hyponitrite) anions and favours the formation of N₂O in the gas phase. On pure NiO, surface Ni²⁺—NO nitrosyls are the main product of NO adsorption at both room temperature and 77 K. The measured coverage is, however, only half the theoretical one, because repulsive forces prevent the occupation of all surface Ni²⁺ sites. The stability of the Ni²⁺—NO adducts prevents the extensive formation of N₂O₂ dimers.