Adsorption of O 2, SO 2, and SO 3, on Nickel Oxide: Mechanism for Sulfate Formation

Calculations based on the atom superposition and electron delocalization molecular orbital (ASED‐MO) technique suggest that will adsorb preferentially end‐on at an angle 45° from normal on a nickel cation site on the (100) surface of . adsorption is also stronger on the nickel site; bonds through the sulfur atom in a plane perpendicular to the surface. Adsorption energies for on the nickel and oxygen sites are comparable in the preferred orientation in which the plane is parallel to the surface. The calculations suggest that the strength of adsorption varies as . On activation, adsorbed to an O 2− site forms a trigonal pyramidal species which yields, with a low barrier, a tetrahedral sulfate anion. Subsequently the anion reorients on the surface. Alternative mechanisms which require the formation of Ni 3+ or O − are discussed. thus formed may play a passivating role for the corrosion of Ni at low temperatures in the atmospheres and an active role at high temperatures, as discussed in the experimental literature.