Adsorption of nitrogen and ammonia at zirconia surfaces

Incorporation of nitrogen into the bulk material is the key step in the preparation of N-doped transition metal oxides. As a first attempt to understand the basic reaction mechanisms involved in the surface process, molecular and dissociative adsorption of nitrogen (N-2) and ammonia (NH3) at the perfect and oxygen-deficient (111) surface of cubic zirconia has been studied theoretically at hybrid density functional level. Coverages 0 = 1/2 and 0 = 1/4 were considered. In agreement with experimental observation nitrogen does not interact with the nondefective surface. Anionic adsorbed species, mainly N-2(-), are observed in the presence of oxygen vacancies in the topmost layer independent of coverage. NH3 adsorbs molecularly also on the defect-free surface whereas at the defective surface both molecular and dissociative adsorption is found. After dissociation the anions NH2- and NH-, accompanied by surface bound OH- and H-, are formed. (C) 2009 Elsevier B.V. All rights reserved.