Density functional theory study of lactic acid adsorption and dehydration reaction on monoclinic 0 1 1, 1¯01, and 1¯11 zirconia surfaces

Lactic acid adsorption and dehydration toward acrylic acid processes have been studied by means of density functional theory (DFT) calculations on 0 1 1, 1¯01, and 1¯11 monoclinic zirconia surfaces. Lactic acid presents two function types (carboxylic acid and alcohol). Therefore, seven modes of monodentate or bidentate adsorption have been characterized on the potential energy surfaces. Lactic acid is preferentially stabilized in a bidentate bridging mode with O–H bond dissociation whatever the studied surface. For the lactic acid dehydration reaction, two mechanisms have been studied. The carbocation formation by direct C–OH breaking proceeds with a very high activation energy ranging from 2.54 to 3.10 eV depending on the surface. On the contrary, lattice oxygen atoms can easily abstract a hydrogen atom from the methyl group of the lactic acid, and this reaction leads to carbanion formation with a lower activation energy ranging from 1.09 to 1.29 eV. Therefore, this mechanism could be a part of acrylic acid formation.

Graphical abstractPossible reaction pathways for lactic acid dehydration on ZrO2 surfaces. The formation of carbanion is favored. Figure optionsDownload full-size imageDownload high-quality image (67 K)Download as PowerPoint slideHighlights► DFT study of lactic acid dehydration on ZrO2 has been performed. ► Acidic mechanism leading to a carbocation is unlikely. ► Basic mechanisms, involving surface oxygen atom, present low activation energies.