Novel iron titanate catalyst for the selective catalytic reduction of NO with NH3 in the medium temperature range

Abstract

An iron titanate catalyst with a crystallite phase, prepared by a co-precipitation method, showed excellent activity, stability, selectivity and SO 2 /H 2 O durability in the selective catalytic reduction of NO with NH 3 in the medium temperature range.Nitrogen oxides (NO x ) have become a major source of air pollution which can result in photochemical smog, acid rain and ozone depletion and have strong respiratory toxicity endangering human health.1 Stringent environmental legislation has been made worldwide to reduce NO x emitted from mobile and stationary resources including vehicles and coal-fired power plants. Selective catalytic reduction of NO with NH 3 (NH 3 -SCR) is an effective and economical method to remove NO and nowadays the most widely used catalyst system is V 2 O 5 -WO 3 /TiO 2 or V 2 O 5 -MoO 3 /TiO 2 with a relatively narrow temperature window of 350-400 1C.2 The problems of this system are as follows: the low N 2 selectivity in the high temperature range because of N 2 O formation and NH 3 overoxidation; the toxicity of vanadium pentoxide to the environment; and high conversion of SO 2 to SO 3 with increasing vanadium amounts, which can result in catalyst deactivation. 13 with excellent SCR activity and H 2 O/SO 2 durability in the medium temperature range. Based on the idea of combining the predominant SCR activity, thermal stability and N 2 selectivity of Fe-based catalysts and the excellent SO 2 durability of TiO 2 , here we present a novel non-toxic catalyst using an iron titanate crystallite as the active component with a broad operation window in the medium temperature range (200-400 1C) under relatively high space velocities. NO conversion at 300 1C remaining at 100% in the presence of 10% H 2 O and (or) 100 ppm SO 2 makes this catalyst a potential candidate for industrial applications.The iron titanate catalysts were prepared by the conventional co-precipitation method using Fe(NO 3 ) 3 Á9H 2 O and Ti(SO 4 ) 2 as precursors (Fe : Ti ¼ 1 : 1 in molar ratio) and 25 wt% NH 3 ÁH 2 O as precipitator with subsequent filtration, washing, and drying at 100 1C overnight and calcination at 400, 500, 600, 700 1C for 6 h, respectively (signified by Fe x TiO y -400, 500, 600, 700 1C). Catalysts sieved with 20-40 mesh were used in the activity test experiments and the reaction conditions were as follows: 0.6 ml sample, 500 ppm NO, 500 ppm NH 3 , 5% O 2 , 100 ppm SO 2 (when used), 10% H 2 O (when used), balance N 2 , 500 ml min À1 total flow rate and gas hourly space velocity (GHSV) ¼ 50 000 h À1. The water vapor was injected with an accurate syringe pump equipped with an evaporator which was heated to 300 1C. The tubing of the activity test system was heated to 120 1C to avoid deposition of ammonium salts and water droplets. The effluent gas, including NO, NH 3 , N 2 O and NO 2 dried using CaSO 4 was continuously analyzed by an FTIR spectrometer (Thermo Nicolet Corporation Nexus 670, OMNIC Quantpad software) equipped with a heated, low volume multiple-path gas cell (2 m). The spectra were collected...

Nanosized Cation-Deficient Fe−Ti Spinel: A Novel Magnetic Sorbent for Elemental Mercury Capture from Flue Gas

“…Previous research reported that Fe-Ti mixed oxide was a novel catalyst for the selective catalytic reduction of NO with NH 3 in the medium temperature range (200-400°C) which was placed after the flue gas desulfurization (FGD). 58 In our future work, (Fe 2 Ti) 0.8 O 4 will be investigated to control the emission of NO x . If (Fe 2 Ti) 0.8 O 4 is an excellent catalyst for the control of NO x emission, it will be mainly used to control the emission of NO x , and elemental mercury will be captured as a cobenefit.…”

Effect of manganese substitution on the structure and activity of iron titanate catalyst for the selective catalytic reduction of NO with NH3

“…The interaction between iron, manganese and titanium species led to a highly dispersive state of active phases, without forming iron oxides, manganese oxides or titanium oxide particles. In our previous study [5,6], we have concluded that the FeTiO x catalyst was mainly in the form of crystallite phases of Fe 2 TiO 5 and FeTiO 3 with specific Fe-O-Ti structure which showed high SCR activity. The substitution of Fe by Mn did not destroy the crystallite structures; furthermore, some crystallites with Mn-O-Ti and Fe-O-Mn structures might also be formed, because either FeMnTiO 4 or MnTiO 3 also has some diffraction peaks in the positions of the broad bumps.…”

“…Because of some inevitable disadvantages in practical application, such as the narrow operation temperature window [2], high conversion of SO 2 to SO 3 at high temperatures [3] and the toxicity of vanadium pentoxide to environment and human health [4], more and more researchers are focusing on the development of new SCR catalysts. In our previous study [5,6], we have developed an environmentally friendly novel iron titanate catalyst in crystallite phase with specific Fe-O-Ti structure, which showed excellent SCR activity, N 2 selectivity and H 2 O/SO 2 durability in the medium temperature range. However, the catalytic activity was not high enough for the application in denitrogenation of exhaust gas with low temperature, such as the flue gas after dust removal and desulfurization from coal-fired power plants and the exhaust gas from diesel engines in cold-start process.…”

Selective catalytic reduction of NOx by NH3 for heavy-duty diesel vehicles

“…Therefore, efforts should be made for the development and industrial application of environmentally benign NH3-SCR catalysts for controlling NOx emissions from diesel engines. In our previous studies, we developed several easily prepared Ce-based [17,18] and Fe-based [25] oxide catalysts and a Cu-SSZ-13 [13] small pore zeolite catalyst with excellent NH3-SCR performance. The CeWOx catalyst has already been studied for industrial application.…”

“…However, the toxicity of vanadium species together with the narrow operation temperature window has limited the practical application of vanadium-based catalysts. Accordingly, some transition metal exchanged zeolites, e.g., Fe-ZSM-5 [7][8][9], Cu-SSZ-13 [10][11][12][13], and Cu-SAPO-34 [14][15][16], and vanadium-free oxide catalysts, e.g., Ce-based [17][18][19][20][21][22][23][24], Fe-based [25][26][27], and Cu-based [28] oxides, have been studied as potential substitutes of vanadium-based catalysts for diesel vehicles. However, the quality of the diesel fuel in China is still relatively low, and the sulfur content in the diesel fuel is often rather high.…”