Selective catalytic oxidation (SCO) of ammonia to nitrogen over Fe/ZSM-5 catalysts Gongshin Qi, Ralph T. Yang * Department of Chemical Engineering, University of Michigan, 3074F H.H. Dow Building, 2300 Hayward, Ann Arbor, MI 48109-2136, USA Received 15 November 2004; received in revised form 3 March 2005; accepted 6 March 2005 Abstract 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 NH 4 - ZSM-5 and FeCl 2 . The performance of the catalyst showed that the impregnation method based on NH 4 -ZSM-5 and FeCl 2 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 FeCl 2 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 H 2 O and SO 2 indicated that although SO 2 /H 2 O decreased the NH 3 conversion, a high conversion was still obtained at 400 8C at a high space velocity, so the Fe/ZSM-5 prepared by NH 4 -ZSM-5 and FeCl 2 should be a promising catalyst for the selective oxidation of NH 3 to N 2 . # 2005 Elsevier B.V. All rights reserved. Keywords: Selective catalytic oxidation (SCO); Selective catalytic reduction (SCR); SCO of ammonia; SCR of NO with ammonia; Fe/ZSM-5 1. Introduction The removal of ammonia from waste streams is becoming an important problem. Many chemical processes use reactants containing ammonia or produce ammonia as a by-product. They are all plagued with the ammonia emission problem. Selective catalytic oxidation (SCO) of ammonia to nitrogen is potentially an ideal technology for removing ammonia from oxygen-containing waste gases and conse- quently it has become of increasing interesting in recent years [1–11]. Moreover, ammonia is used effectively in power plants for NO x (x = 1, 2) abatement by selective catalytic reduction (SCR). In order to control the ammonia slip, most processes are carried out under conditions such that NH 3 /NO < 1, at the expense of decreased NO reduction efficiencies. For improving the NO reduction efficiency, the use of stoichiometric or an excess amount of ammonia is desirable. The SCO of ammonia can be applied to the SCR of NO with ammonia in a secondary bed to oxidize the residual ammonia to N 2 , without introducing other reactants into the gas mixture. The SCO process can also be applied to biomass-derived fuels for removing the large amounts of NH 3 impurity [3,4]. Further applications of SCO are the treatment of reformates for fuel cell systems and the deodorization of ammonia-containing gases [13]. Several types of materials have been reported to be active for SCO of ammonia to N 2 , such as Pt, Rh, and Pd exchanged to ZSM-5 [2]; Ni, Fe, and Mn oxides supported on g-Al 2 O 3 [3,4],V 2 O 5 /TiO 2 , CuO/TiO 2 and Cu-ZSM-5 [5]; CuO/ Al 2 O 3 [6,7]; Cu-Mn/TiO 2 [8]; Fe-exchanged TiO 2 -PILC [9]; Fe-exchanged ZSM-5 and other zeolites [10,11]; Fe 2 O 3 - TiO 2 [12] and manganese oxide-silica aerogels [13]. These catalysts exhibited activities for N 2 formation under various www.elsevier.com/locate/apcata Applied Catalysis A: General 287 (2005) 25–33 * Corresponding author. Tel.: +1 734 936 0771; fax: +1 734 764 7453. E-mail address: yang@umich.edu (R.T. Yang). 0926-860X/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2005.03.006