Reaction mechanism of arsenic and nitrous oxides during coal combustion

The reaction mechanism between arsenic and nitrous oxides (N₂O, NO₂ and NO) was investigated by applying density functional theory in quantum chemistry. The geometries of reactants, intermediates, transition states and products for each reaction were optimized. Frequency analysis was applied to verify those geometries, and the authenticity of transition states were confirmed by intrinsic reaction coordinate analysis (IRC). The stationary points of the single point energy were calculated at B2PLYP level, and the kinetic analysis was conducted to further reveal the reaction mechanism. Results show that the energy barrier of the reactions between arsenic and nitrous oxides (N₂O, NO₂ and NO) is 78.45, 2.58 and 155.85 kJ/mol, respectively. The reaction rate increases in the range of 298-1800 K and keeps at a high level (>10¹² cm³/(mol·s)), although the temperature has a tiny impact on the reaction of arsenic with NO₂ as a result of a low energy barrier, indicating that the reaction is easy to take place. Furthermore, it is found that the rate of reaction between arsenic and N₂O or NO has a rapid increase at 298-900 K, and then the rate increment becomes less with the further increase of temperature.