In Ukrainian

Abstract

The study of the thermochemical properties of caffeic acid and its surface complexes is important for the pharmaceutical and food industries, medicine and for development of technologies of heterogeneous catalytic pyrolysis of the renewable plant biomass components. In this work, the structure of the surface complexes of caffeic acid on the surface of nanosized cerium dioxide was investigated using FTIR spectroscopy, depending on the degree of the surface coverage (0.1–1.2 mmol/g). Thermal transformations of surface complexes were studied using temperature-programmed desorption mass spectrometry (TPD MS). The analysis of the magnitude of the difference between the assymmetric and symmetric carboxylate stretches СОО - (...) and in case of monodentate coordination, between the C=O and CO stretches (...) was carried out. Based on the obtained values of D, it can be assumed that bidentate chelating complexes ( ≈ 72 cm –1 ), bidentate bridging complexes ( ≈ 110 cm –1 ), and monodentate bound complexes ( ≈ 236 cm –1 ) of caffeic acid are present on the nanoceria surface. In addition, complexes bound through the phenolic hydroxyl groups are present on the surface. This is due to the ability of the nanoceria to generate basic hydroxyl groups that are able to deprotonate the phenolic groups to form phenolates on the surface. The analysis of mass spectrometric data allowed identification of products of thermal transformation and suggested possible ways of forming 3,4-dihydroxyphenylethylene, pyrocatechol, and phenol from surface complexes of caffeic acid, the structure of which was confirmed by data of IR spectroscopy. The kinetic parameters of the phenol formation reaction were calculated. It was established that on the surface of CeO 2 the decarboxylation, dehydration and decarbonylation reactions of caffeic acid occur effectively. These reactions are the desirable processes in biomass conversion technologies.