Adsorption mechanism of NH3, NO, and O2 molecules over the FexOy/AC catalyst surface: a DFT-D3 study

Abstract

Activated carbon-supported iron-based catalysts (Fe_xO_y/AC) show excellent deNO_x efficiency. However, the specific adsorption mechanism of NH₃, NO, and O₂ molecules on their surfaces is still unknown. In this study, models of Fe_xO_y/AC were built and the adsorption mechanism of NH₃, NO, and O₂ molecules on their surfaces was investigated by a DFT-D3 study. FeO, Fe₂O₃, and Fe₃O₄ clusters can be stably adsorbed on the vacancy sites of the AC surface with charge redistribution. An NH₃ molecule undergoes chemisorption to bind with the active Fe atoms of the Fe_xO_y/AC surface, which can form a coordinated NH₃. The Fe₂O₃ cluster is the most beneficial to NH₃ adsorption and results in the NH₃–SCR deNO_x reaction. When NO is adsorbed on the Fe_xO_y/AC surface, three kinds of adsorption products are obtained: nitrosyl (–NO), nitro (–NO₂), and nitrite (–ONO) species. O₂ can be adsorbed on the Fe_xO_y/AC surface to form adsorbed oxygen. The Fe₃O₄/AC surface has the most excellent adsorption property for NO and O₂. NO can react with the adsorbed oxygen to form nitro, nitrite, and nitrate (–NO₃) species. Moreover, the reaction paths and transition states of NH₂ and NO₂ formation were also investigated.