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 FeCl ₂. 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 N ₂.