Effect of Electron Transfer at Metal Oxide Surfaces; NO2Adsorption on(CaO)n, n=2, 3, 4, 6, 8, 9, 12 Cluster ModelCalculations

ABSTRACT: In our previous article, the geometrical optimizations have been performed for the (CaO)n, n = 1-4, 6, 8, 9, and 12 cluster models, [WJERT, 2019, 5 (1), 328-341]. In this study,we have investigated theadsorption of performance NO2gas towards metal oxide clusters (CaO)n, n = 2, 3, 4, 6, 8, 9, 12) cluster models,and focus on electron transfer between the CaO and NO2 molecule by employing density functional theory(DFT), B3LYP method. Results show that the charge transferred goes from surface clusters to NO2 antibonding orbitals which makes more reactive, and becomes stronger. Moreover, NO2 adsorbs at the one, twoCa2+sites forming a nitrite (NO2−). Meanwhile, the interaction of NO2 with Lewis baseO2−,and consequently mayform a nitrate (NO32−) species, which is less adsorption favorable. The total adsorption energies revealed thatNO2 gas was strongly chemisorbed on the(CaO)n, n = 2, 4, 6 and 8cluster models, whereas (CaO)n, n=3, 9 and12 results in a weak interactions. Further, the results of optimized structure showed that the total adsorptionenergies and charge transfer contributions indicated that CaO is a better acid-base than MgO, due to theincreasing basicity and bigger cationic size of the CaO. The reason for these different basicities and reactivatescan be ascribed to the different electrostatic (Madelung) potentials at the two surfaces.

Keywords-Adsorption energy, CaO Cluster models, Density functional theory DFT, NO2 Adsorption