COMPARATIVE STUDY ON THE NO₂ BINDINGS TO (MGO)N AND (CAO)N CLUSTERS, N = 4, 6, AND 9: FORMATION OF NITRITE AND NITRATE

Abstract

A comparative study on MgO and CaO clusters toward NO2 adsorption have been investigated theoretically by the density functional theory, approach Beck3LYP. Bond lengths, bond angles as well as adsorption energies of the MgO−NO₂ and CaO−NO₂ modes are calculated for varieties of sites on the three model clusters. The results indicated that there is a weak bound involving the (MgO)₉ cluster to the magnesium cations at face site (0.32 eV) and edge site (0.36 eV), and found sensitive to the size of the cluster that (0.87 eV) and (1.23 eV) are obtained for (MgO)₆ and (MgO)₄, respectively. In contrast, the binding stabilities for NO₂ towards surface nitrite formation reveal significantly different (1.37 eV) and (1.66 eV) are obtained for (CaO)₄, and (CaO)₉ clusters respectively. The NO₂ adsorption was found also reactive on (CaO)₉ forming nitrate species, and present slightly large binding energy compared to (MgO)₉ clusters. The reason for the difference in binding energies is discussed in terms of cluster electro-positivity, and the nature of the highest occupied molecular orbital. NO₃²⁻surface species is also characterized.