A DFT-D study on the reaction mechanism of selective catalytic reduction of NO by NH3 over the Fe2O3/Ni(111) surface

Abstract

The gas adsorption properties and NH₃-SCR reaction mechanism over the Fe₂O₃/Ni(111) surface were investigated by a DFT-D study. The results show that the Fe₂O₃ cluster has more excellent gas adsorption performance than the Ni carrier. Single gas adsorption products are coordinated ammonia, nitroso, and adsorption oxygen, respectively. The presence of O₂ promotes bimolecular adsorption. Three NH₃-SCR reaction routes are revealed and mainly follow the Eley–Rideal mechanism. The reaction of NH₃ and NO involves five steps: (1) NH₃* dehydrogenation, (2) NH₂NO* generation, (3) NHNO* generation, (4) NHNO* dissociation, and (5) H₂O generation. NHNO* dissociation into N₂ releases lots of energy. The reaction of O₂ and NO eventually forms NO₂, and is an energetically favorable process. Reaction of NO₂ with NH₃ involves three steps: (1) NH₂NO₂ generation, (2) NHNO₂ generation, and (3) NHNO₂ dissociation. NHNO₂* decomposition and H₂O* desorption as the rate-determining steps control the whole reaction rate. In addition, the reason for the high NO_x conversion of “fast-SCR” is that NO₂ reacts more easily with NH₂ to form a nitrogen intermediate compared to NO.