Striking Improvement of N₂ Selectivity in NH₃ Oxidation Reaction on Fe₂O₃-Based Catalysts via SiO₂ Doping

The emission of NH₃ has been reported to pose a serious threat to both human health and the environment. To efficiently eliminate NH₃, catalysts for the selective catalytic oxidation of NH₃ (NH₃-SCO) have been intensively studied. Fe₂O₃-based catalysts were found to exhibit superior NH₃ oxidation activity; however, the low N₂ selectivity made it less attractive in practical applications. In this work, aimed at improving the N₂ selectivity on Fe₂O₃-based catalysts, a simple SiO₂ doping strategy was proposed. Although the NH₃ oxidation activity showed almost no change on Fe₂O₃ after SiO₂ doping, the N₂ selectivity was significantly improved. Systematic characterizations revealed that SiO₂ doping could increase the specific surface area of Fe₂O₃, and a strong interaction of Fe-O-Si was formed in Fe₂O₃-SiO₂ mixed oxide catalysts. Furthermore, abundant Brønsted acid sites were formed on Fe₂O₃-SiO₂ catalysts due to the facile hydrolysis of the Fe-O-Si structure into Si-OH and Fe-OH. Although SiO₂ doping was found to weaken the redox ability of Fe₂O₃, the abundant Brønsted acid sites on Fe₂O₃-SiO₂ catalysts could facilitate NH₃ oxidation reaction through an internal SCR (i-SCR) pathway, thus achieving superior N₂ selectivity. This work can provide new insights into constructing efficient NH₃-SCO catalysts with high N₂ selectivity.