Applied Catalysis B: Environmental 103 (2011) 369–377 Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb Inﬂuence of sulfation on iron titanate catalyst for the selective catalytic reduction of NO x with NH 3 Fudong Liu a , Kiyotaka Asakura b , Hong He a,∗ , Wenpo Shan a , Xiaoyan Shi a , Changbin Zhang a a State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, PR China b Catalysis Research Center, Hokkaido University, Sapporo 001-0021, Japan article info Article history: Received 30 September 2010 Received in revised form 25 January 2011 Accepted 31 January 2011 Available online 1 March 2011 Keywords: Selective catalytic reduction Iron titanate catalyst Sulfation Sulfate species Langmuir–Hinshelwood reaction pathway Eley–Rideal reaction pathway abstract Iron titanate catalyst (FeTiO x ) is a potential candidate for the substitution of conventional V 2 O 5 –WO 3 (MoO 3 )/TiO 2 and Fe/Cu-zeolite catalysts for the selective catalytic reduction (SCR) of NO x with NH 3 because of its high SCR activity and N 2 selectivity in the medium temperature range. Due to the presence of small amount of SO 2 in typical diesel exhaust derived from combustion of sulfur-containing fuels, it is very important to investigate the inﬂuence of sulfation on SCR activity, catalyst structure and reac- tion mechanism. After sulfation under the SCR condition, the surface area and pore volume of FeTiO x catalyst decreased to a certain extent due to the formation of sulfate species. According to the char- acterizations of FeTiO x catalyst using X-ray diffraction, X-ray absorption ﬁne structure spectroscopy, and in situ diffuse reﬂectance infrared Fourier transform spectroscopy of SO 2 +O 2 treatment, the sulfate species mainly formed on iron sites in a chelating bidentate conformation, resulting in the enhancement of Brønsted acidity and Lewis acid strength simultaneously. NH 3 adsorption was greatly enhanced in the high temperature range, while NO x adsorption was severely inhibited due to the stronger acidity of sulfate species. The operation temperature window of the sulfated catalyst shifted ca. 50 ◦ C towards high temperature range accordingly. The reaction mechanism study shows that the Langmuir–Hinshelwood reaction pathway was cut off by the sulfation process, resulting in the activity loss at low temperatures; only Eley–Rideal reaction pathway between adsorbed NH 3 species and gaseous or weakly adsorbed NO dominated in the SCR reaction, which made this catalyst resistant to SO 2 poisoning at relatively high temperatures. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Selective catalytic reduction (SCR) of NO x with NH 3 over V 2 O 5 –WO 3 (MoO 3 )/TiO 2 catalyst is a well proven technique for the removal of NO x from stationary and mobile sources [1]. Due to some inevitable disadvantages of the present vanadium-based catalyst including the narrow operation temperature window and the tox- icity of vanadium pentoxide etc. [2,3], more and more researchers are focusing on the development of new vanadium-free SCR cata- lysts, such as Fe-, Cu-, Mn-, Ce-based exchanged zeolites, supported type or mixed oxide catalysts [3–14]. In our previous study, we also reported a novel and environmental-friendly iron titanate cat- alyst (FeTiO x ) prepared by facile co-precipitation method showing excellent SCR activity and N 2 selectivity in medium temperature range, which is possibly suitable for the DeNO x process for diesel engines [15–17]. It is well known that nowadays the typical diesel ∗ Corresponding author at: P.O. Box 2871, 18 Shuangqing Road, Haidian District, Beijing 100085, PR China. Tel.: +86 10 62849123; fax: +86 10 62849123. E-mail address: honghe@rcees.ac.cn (H. He). exhaust usually contains a small amount of SO 2 below 50 ppm from the combustion of sulfur-containing fuels. Even when using fuels and engine oils with “ultra low” sulfur content (<15 ppm) in the near future, the exhaust after combustion in lean burn conditions still contains some fractions of SO 2 [18]. After long time SCR reac- tion, even this small amount of SO 2 can deactivate the SCR catalysts due to the formation of metal sulfate species, the blockage of cata- lyst pore channels or the cutting off of redox cycle of active phases [14,19,20]. So far as known, no vanadium-free catalyst can exhibit both high SCR activity and high SO 2 durability at the same time below 200 ◦ C. Additionally, the SCR reaction mechanism over sul- fated catalyst may also differ from that over the fresh one. It is important, therefore, to investigate the inﬂuence of sulfation on the activity and structure of our FeTiO x catalyst, which will help understand the deactivation mechanism and further improve of its SO 2 durability in future studies. In our previous study, we have already investigated the SO 2 durability (100 ppm) of FeTiO x catalyst in the SCR reaction at a ﬁxed temperature (300 ◦ C), with no obvious decrease of NO conversion observed in a 48 h test [15]. In this study, the inﬂuence of sulfation on this catalyst in a wider temperature range (150–400 ◦ C) will be 0926-3373/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2011.01.044