Mechanism of molecular oxygen adsorption and desorption on the defective YCrO₃ (100) surface: a DFT study

Density functional theory calculations were performed to investigate the adsorption and desorption of molecular oxygen on the defective YCrO₃(100) surface. The formation energy of a surface oxygen vacancy was calculated to be 2.23 eV, substantially lower than the corresponding value in the bulk crystal. Adsorption of an oxygen molecule at the vacancy results in the formation of an asymmetric bridge configuration involving covalent bonding to a surface chromium atom. Desorption proceeds through a transition to a terminal adsorption geometry accompanied by electron-density redistribution and the formation of a reactive oxygen intermediate exhibiting strong molecular polarization and pronounced localization of the unpaired electron. The final stage of desorption corresponds to the complete loss of covalent interaction with the surface and the release of the oxygen molecule. The electronic structure of the identified intermediate suggests that its formation may represent the rate-limiting step in the catalytic oxidation of organic compounds. Based on quantum-mechanical calculations, a mechanism reflecting the kinetic hierarchy of the interaction between an adsorbed oxygen molecule and organic substrates is proposed. An experiment on carbon oxidation catalyzed by yttrium orthochromite was performed to test the proposed kinetic description. The experimentally determined activation energy is in good agreement with the calculated formation energy of the O˙ radical centre. These results provide a basis for the development of phenomenological models describing the kinetics of surface oxidation.