Ethanol adsorption on MgO surface with and without defects from a theoretical point of view

In this work, the ethanol adsorption on a perfect MgO(1 0 0) surface, and also on topologic surface defects of MgO, is studied. Terrace, edge and corner sites were analyzed, whose O and Mg ions are five, four and three fold coordinated, respectively. All the calculations were performed using a cluster approach and the DFT based method. The ethanol molecule chemisorbs non-dissociatively on terrace sites of MgO by means of a two fold interaction while strong dissociative chemisorptions are produced on edge and corner sites. The weakened alcohol OH group is always oriented so that its oxygen (Oa) atom is linked to a Mg cation and the H atom to a surface O anion. The MgOa distance for edge and corner sites is smaller than that for the terrace site. This indicates that lowering the coordination number of ions in the adsorption site yields an increase of molecule-surface bond strength in agreement with a greater basicity of low coordinate sites. The behavior of the adsorption energy and the charge transfers are in accord with the idea of a strong basic character for the MgO substrate, which is more pronounced as the coordination number of ions decrease.