Adsorption of NO₂ and NO₃ on Cobalt Spinel Nanocubes and Interfacial Dynamics of the Resultant NO_<i>x</i> Adspecies (<i>x</i> = 1, 2, and 3): DFT, Atomistic Thermodynamic, IR, and Isotopic Exchange Study

Abstract

Periodic GGA+U and atomistic thermodynamic modeling, combined with IR and isotopic exchange investigations, were employed for comprehensive description of NO2 and NO3 adsorption on the (100) surface of Co3O4 nanocubes. A wide range of identified NO2 and NO3 adspecies includes N- and O-bound monodentate (η1), bidentate (η2), bridging bidentate (μ-η2), and bridging monodentate (μ-η1:η1) surface complexes. The most stable were the bridging μ-η1(O):η1(O)-CoT–ONO–CoO (−1.91 eV) and chelating η2(O,O)-NO2–CoT (Eads = −1.87 eV) adducts over dual tetrahedral (CoT2c) and ocatehedral (CoO5c) sites, whereas the μ-η1(O):η1(O)-CoO–ONO–CoO (−1.25 eV) and η2(O,O)-NO2–CoO (−1.57 eV) adducts of the CoO centers only were less strongly bound. The DOS structure, spin density repartition, and atomic partial charge analysis were used for detailed interpretation of the electronic structure of the most stable NO2 and NO3 adducts. Thermodynamic ΘNO2 = f(pNO2, T) diagrams were constructed for quantitative interpretation of the NO2 and NO3 adsorption on the (100) surface. A complex set of intermolecular surface O ↔NO ↔ NO2↔ NO3 dynamics was thoroughly examined and applied for elucidation of an intricate mechanism of the NO2 and NO3 desorption, NO oxidation, and N16O/N18O isotopic exchange, providing a scientific background for SCR, deNOx, or NOx-sensing reactions as well.