Study of the nitric oxide reduction of SCR-NH3 on γFe2O3 catalyst surface with quantum chemistry

The surface reaction process of gamma Fe2O3 catalyst for NOx removal with NH3 was studied by the first principles and density functional theory. The results show that the NH3 molecule is easily adsorbed on the surface of the catalyst, then dehydrogenated to produce NH2, NH and other products, yet most of the products are NH2 since the activation energy barrier from NH2 to NH is high under anaerobic condition. The next main step is that NH2 reacts with gaseous NO to generate NH2NO intermediate products, and then it decomposes to N-2 and H2O. The NH3 dehydrogenation is the rate determining step with the activation energy barrier of 88.040 kJ/mol. However, the NH fragment will be formed when oxygen exists since the activation energy barrier from NH2 to NH reduces under aerobic condition. After its formation, the NH fragment will combine with NO to yield NHNO and decomposes to N-2 and hydroxyl. In addition, NO2 can be produced on the surface by the absorbed NO reacting with an active O atom, and the NO2 can carry out fast SCR process. Otherwise, the N2O is not easily formed on the surface of gamma Fe2O3 catalyst which means that the catalyst has good selectivity.