Catalytic Ammonia Combustion over the Surface as well as Perimeter

Abstract

NH3 has been recognized as a carbon-free and renewable energy source. However, NH3 fuel has a high ignition temperature and its use results in the production of N₂O/NO_x. Therefore, these issues must be overcome. To overcome these issues, novel NH₃ combustion catalysts have been developed. Previously, combustion catalysts for hydrocarbon (HC)-based fuels were studied as a promising approach to decreasing NO_x emissions. On the other hand, it is considered that the catalytic NH₃ combustion system has advantages for decreasing not only NO_x but also N₂O emissions, and the low operating temperatures. In this articles, recent developments for NH₃ combustion catalysts are covered. Firstly, the catalytic activity for NH₃ combustion over metal oxides was investigated. According to the results, it is suggested that the NH₃ combustion activities of metal oxides are correlated with the metal–oxygen bond energy. In addition, in comparison with the other metal oxides, CuO (CuO_x) showed relatively high catalytic activity and low N₂O and NO_x product selectivity. Secondly, various CuO_x-based supported catalysts were prepared. Because, among the various supported CuO_x catalysts, CuO_x/3Al₂O₃·2SiO₂ (3A2S) catalysts exhibited the high performance for NH₃ combustion, the local structures, NH₃ combustion properties, and combustion mechanisms of CuO_x/3A2S after thermal ageing at 900 ℃ were studied in detail. Finally, monolithic honeycomb catalysts for NH₃ combustion were prepared, and the reaction properties were determined.