Ab initio study of the isocyanate surface complex over silica and alumina

Ab initio calculations have been performed to study the stability of isocya nate complex (NCO) over silica and alumina surfaces. Mulliken and natural b ond population analysis methods have been used in order to analyze charge d istributions and the direction of charge transfer processes. The results in dicate that the NCO group adsorbs linearly and perpendicularly to both surf aces; namely, on top site over silica and on bridge site over alumina. It w as observed that the charge transfer from the oxygen lone pairs of NCO to t he N-C antibonds produces a weakening of N-C link. This phenomenon is more important over alumina, yielding to an easier NCO decomposition over the su rface of this oxide. (C) 2001 Elsevier Science B.V. All rights reserved.