Effect of Ca and Sr in MgO(100) on the activation of methanol and methyl acetate

Abstract

The activation of methanol (CH3OH) via HO and of methyl acetate (CH3COOCH3) via CO and CH bond dissociations, has been studied using periodic density functional theory to probe the effect of small amount of higher basic alkaline earth metals in MgO(100) surface. The interaction of methyl acetate, methanol and ionic dissociation products including methoxide, acetyl, acetate, proton, enolate, methylene acetate, methylene are studied on MgO(100)-1Ca/1Sr/2Sr/2Ca surfaces in terms of adsorption, activation, dissociation and association energies. The strength of methanol interaction increases progressively with the basicity and concentration of alkaline earth oxides in the surface: MgO(100)<MgO-1Ca<MgO-1Sr<MgO-2Ca<MgO-2Sr. This increase of basicity and concentration do not affect in the same manner the activation of methyl acetate. The adsorption energies of methyl acetate and the activation energies of CO and CH bond dissociations are only slightly reduced compared to pure MgO surface. Only the stability of fragments that bind with the oxygen on these surfaces is increased when increasing the basicity and concentration, fact reflected in the dissociation energy and the activation energy of the reverse bond formation. These results were discussed in the context of transesterification and intersetrification reactions with application in biodiesel production.