Selective Catalytic Oxidation of Ammonia to Nitrogen over Fe2O3–TiO2 Prepared with a Sol–Gel Method

Abstract

Fe2O3–Al2O3, Fe2O3–TiO2, Fe2O3–ZrO2, and Fe2O3–SiO2 were prepared with a sol–gel method and they showed high activities for selective catalytic oxidation (SCO) of ammonia to nitrogen in the presence of excess oxygen. The Fe2O3–TiO2 catalysts prepared from iron sulfate yielded a higher selectivity for N2 than those prepared from nitrate. More than 92% of N2 yields were obtained on the 10 wt% Fe2O3–TiO2 (SO42−) and 20 wt% Fe2O3–TiO2 (SO42−) at 400–450°C under the condition of GHSV=2.0×105 h−1. Also, after the Fe2O3–TiO2 prepared from nitrate was treated with SO2+O2 at 450°C, the N2 selectivity and yield were enhanced significantly at 450–500°C, suggesting a promoting role by SO2. But H2O decreased the N2 yield slightly. The N2 selectivity for the SCO reaction is in good agreement with their surface acidity and the activity for selective catalytic reduction (SCR) of NO with ammonia. This further supports the two-step SCO mechanism in which NH3 is first oxidized to NO and then NO is reduced to N2 by unreacted NH3 adsorbed species through a SCR reaction. The presence of sulfate species on Fe2O3–TiO2 (SO42−) increased surface acidity and thus improved SCO performance. Temperature-programmed desorption and temperature-programmed surface reaction of ammonia showed that gaseous, adsorbed, and lattice oxygen may participate in the SCO reaction.