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Reports: DNI6 49191-DNI6: Fundamental Surface Reactions of Lactic Acid with MgO
The overall goal of this research is to examine the adsorption and reaction mechanisms of lactic acid, a biorenewable molecule, with magnesium oxide using theoretical methods such as density functional theory (DFT) and second-order perturbation theory (MP2). In the first stage of this research, the adsorption modes of lactic acid (LA) on model (MgO)2 and (MgO)12 clusters are examined. The structures and relative energies for the LA-(MgO)2 complex calculated at the PBE/6-31G** level of theory using GAMESS are shown in the Nugget. Examination of other basis sets including cc-pVDZ and TZV showed that the relative ordering of these structures is mostly insensitive to basis set.
As originally hypothesized, dissociative adsorption of the carboxylic acid group leads to the most stable LA-(MgO)2 complexes, followed by dissociative adsorption of the hydroxy group. Molecular adsorption of the carboxy or hydroxy groups lies about 50-70 kcal/mol higher in energy. In the lowest energy complexes, two oxygen atoms from LA commonly interact with the (MgO)2 cluster. These two oxygen atoms are not necessarily the two from the carboxylic acid group.
Current studies are extending the LA-(MgO)2 complexes to studies with the (MgO)12 and larger clusters. The effect of freezing the lowest layer of the cluster as opposed to a full optimization is under consideration. Full optimization of the (MgO)12 system leads to hexagonal "nanotube" structures such as those observed previously for formaldehyde on (MgO)12.
