NCO adsorption over SiO2 and Cu/SiO2 cluster models from density functional theory

Abstract

The adsorption of NCO over two types of surface defects on silica surface, Si• and Si-O•, were studied using the density functional theory formalism. The adsorption is preferred on Si• site in agreement with experimental results. The NCO adsorption is also studied over atomic and dimer copper deposited on silica defects and, for comparison reasons, on free Cu and Cu2. While in the first case the support does not affect the Cu-NCO bonding, it enhances that interaction in the second case. This behaviour is related to the higher charge transfer from the dimer to NCO, which produces a strong Cu-NCO bonding which has an important ionic character. Besides, the adsorbate modifies the metal-support interaction due to an electrostatic bond enhancement between the terminal Cu atom and a regular bridging O atom of the silica surface. The NCO asymmetric stretching frequencies were also calculated and analysed.