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 N-2 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 N-2 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 degrees 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 N-2. (c) 2005 Elsevier B.V. All rights reserved.