The adsorption of oleic acid on CaO(100): A DFT study

Abstract

The adsorption behavior of oleic acid on the CaO(100) surface was investigated using density functional theory (DFT) with van der Waals corrections. Two main adsorption configurations were explored: interaction through the carboxylic group (upright orientation) and through the C=C double bond (flat orientation). The most stable adsorption corresponds to the upright configuration, in which the carboxylic acid group dissociates spontaneously upon contact with the surface, forming a bidentate oleate species with a calculated adsorption energy of –1.94 eV. In contrast, adsorption via the double bond resulted in weaker interactions, with energies ranging from –0.59 to –0.76 eV. Charge distribution, density of states (DOS), and bond order analyses confirm significant electronic rearrangement upon adsorption, particularly in the carboxylic group and adjacent surface sites. These findings provide molecular-level insight into the interaction mechanisms between fatty acids and basic oxide catalysts, contributing to the understanding of CaO's role in several important phenomena, including metal leaching in biodiesel reactions and initial steps in decarboxylation of oleic acid into lighter organic compounds and separation of calcium minerals by flotation.