Selective catalytic oxidation (SCO) of ammonia to nitrogen over Fe/ZSM-5 catalysts

In this paper, we report a Fe/ZSM-5 catalyst that has superior catalytic activities for the selective catalytic oxidation (SCO) of ammonia to nitrogen as compared to all previously known catalysts. This Fe/ZSM-5 catalyst was prepared by a simple impregnation method using NH4-ZSM-5 and FeCl2. The performance of the catalyst showed that the impregnation method based on NH4-ZSM-5 and FeCl2 is a surprisingly effective process for the preparation of Fe/ZSM-5 catalyst, which has superior catalytic activities for the SCO of ammonia in the presence of excess oxygen. This preparation process is in fact a combination of the conventional impregnation and solid-state ion-exchange processes. Two different procedures were used to prepare Fe/ZSM-5, which is referred to 1-step and 2-step method, respectively. The SCO activity results show that the Fe/ZSM-5 prepared by 2-step method using FeCl2 has the highest activity compared to other catalysts studied. For the Fe/ZSM-5 catalyst, there existed a good correlation between the N2 selectivity for the SCO reaction and the activity for the selective catalytic reduction (SCR) of NO with ammonia, i.e., the higher the SCR activity, the higher N2 selectivity for SCO reaction. The study of the effect on H2O and SO2 indicated that although SO2/H2O decreased the NH3 conversion, a high conversion was still obtained at 400 °C at a high space velocity, so the Fe/ZSM-5 prepared by NH4-ZSM-5 and FeCl2 should be a promising catalyst for the selective oxidation of NH3 to N2.