Quantum Chemical and Kinetic Studies of N2O Formation during Interaction between Char(N) and NO: Influence of Oxygen, Active Sites, and Nitrogen Status.

Abstract

In order to obtain a deep insight into the N2O formation mechanism in a fluidized bed, density functional theory was used to investigate the interaction between char(N) and NO at a molecular level. Three key influencing factors for the formation of N2O, namely, active sites, nitrogen status, and oxygen molecules, were taken into study. The geometric structures, electron distribution characteristics, and reaction paths were optimized and calculated. The outer orbital electron properties of char(N) and NO indicate that NO acts as an oxidizer, which tends to abstract electrons from char(N) during the char(N)-NO interaction. A stable N2O molecule has a singlet state and presents as a linear molecular structure. The chemisorption on the char surface will weaken the bond energy of NO from 620 to 94.1 kJ/mole, which promotes the catalytic reduction of NO. Active sites on the char surface benefit the reduction of NO to N2, rather than N2O, which indicates that excessive high temperatures will inhibit the production of N2O. The combination of pyridine nitrogen and NO to form N2O needs to overcome a much higher energy barrier of 357.4 kJ/mole. The initial chemisorption of oxygen molecules on the char surface will promote the formation of N2O by lowering the dissociation energy of N2O from the char surface as well as exposing nitrogen to the char surface.