Selective catalytic oxidation of ammonia to nitrogen over Fe2O3-TiO2 prepared with a sol-gel method

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 N-2 than those prepared from nitrate. More than 92% of N-2 yields were obtained on the 10 wt% Fe2O3-TiO2 (SO42-) and 20 wt% Fe2O3-TiO2 (SO42-)at 400-450degreesC under the condition of GHSV = 2.0 x 105 h(-1). Also, after the Fe2O3-TiO2 prepared from nitrate was treated with SO2 + O-2 at 450degreesC, the N-2 selectivity and yield were enhanced significantly at 450-500degreesC, suggesting a promoting role by SO2. But H2O decreased the N-2 yield slightly. The N-2 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 N-2 by unreacted NH3 adsorbed species through a SCR reaction. The presence of sulfate species on Fe2O3-TiO2 (SO42-) increased surface acidity and 4, 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. (C) 2002 Elsevier Science (USA).