METHOD FOR TREATING EXHAUST GAS AND SYSTEM FOR TREATING EXHAUST GAS - Patent application

Abstract

A method for treating exhaust gas from a lean-burn internal combustion engine is disclosed. The method includes introducing ammonia or an ammonia precursor into the exhaust gas upstream of an Fe-SCR catalyst comprising iron and a zeolite, and contacting the exhaust gas with the Fe-SCR catalyst, wherein the amount of ammonia or an ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is controlled such that the ammonia to NOx molar ratio (ANR) in the exhaust gas contacting the Fe-SCR catalyst is greater than 2 and less than 6.

Description

[Technical field]

[0001] The present invention relates to a method for treating exhaust gases, a system for treating exhaust gases, the use of the system, and the use of an Fe-SCR catalyst. [Background technology]

[0002] Nitrogen oxides (NO) produced by ammonia or nitrogen compounds such as urea, which is an ammonia precursor x Selective catalytic reduction (SCR) of NOx was first developed to handle industrial stationary applications. SCR technology was first used in thermal power plants in Japan in the late 1970s and has been widely applied in Europe since the mid-1980s. In the United States, SCR systems were introduced in gas turbines in the 1990s and more recently in coal-fired power plants. In addition to coal-fired cogeneration plants and gas turbines, SCR applications include heaters and boilers in plants and refineries in the chemical processing industry, furnaces, coke ovens, municipal waste plants and incinerators. More recently, NOx reduction systems based on SCR technology have been developed. x Reduction systems have been developed in Europe, Japan, and the United States for many vehicle applications, for example to treat diesel exhaust gases.

[0003] Several chemical reactions occur in the NH3SCR system, all of which result in the production of NO x The preferred reaction is the reduction of nitrous oxide to nitrogen. The dominant reaction is represented by reaction (1). 4NO+4NH3+O2→4N2+6H2O(1)

[0004] Competing, non-selective reactions with oxygen can produce secondary emissions or waste ammonia. One such non-selective reaction is the complete oxidation of ammonia, shown in reaction (2). 4NH3+5O2→4NO+6H2O(2)

[0005] Side reactions can also lead to undesirable products such as NO, as shown by reaction (3). 4NH3+5NO+3O2→4N2O+6H2O(3)

[0006] In reaction (1), there is a 1:1 (i.e., stoichiometric) molar relationship between NO and NH3, so in a practical system, the ratio of alumina to NO x Molar ratio (alumina-to-NO x The NO molar ratio (ANR) of the SCR catalyst is controlled to about 1 to 1.5. x A desirable balance is achieved between conversion performance and the potential for excess ammonia to "slip" through the exhaust system and into the atmosphere.

[0007] Aluminosilicate zeolites are x One application is the reduction of NO from vehicle diesel engines by a reductant obtainable from ammonia precursors such as urea, or by injecting ammonia itself. x The primary objective of the study is to control NO emissions. Transition metals are incorporated into aluminosilicate zeolites to promote catalytic activity. The most commonly tested transition metal zeolites are Cu / ZSM-5, Cu / Beta, Fe / ZSM-5, and Fe / Beta because they have relatively wide temperature activity windows. In general, Cu-based zeolite catalysts have better low temperature NO emissions than iron-based zeolite catalysts. x It exhibits reducing activity.

[0008] WO 2008 / 106519(A1) relates to a known Cu-CHA zeolite SCR catalyst, particularly its performance at low temperatures. For example, Comparative Example 11 relates to a Cu / Beta catalyst, and Example 10 relates to a Cu / Y zeolite catalyst. As expected, in the test examples, the ANR is controlled to about 1.

[0009] Joseph R. Theis, Ford Motor Company, SAE Int. J. Fuel Lubr., Vol. 1, Issue 1, 364-375, 2008, relates to a series of performance evaluation tests for SCR catalysts for lean-burn gasoline engines. Several different parameters were tested under laboratory conditions.

[0010] SCR catalytic activity, especially at low temperatures, especially NO x There is a continuing need to improve conversion performance. Summary of the Invention

[0011] One aspect of the disclosure is a method for treating exhaust gas from a lean-burn internal combustion engine, comprising: introducing ammonia or an ammonia precursor into the exhaust gas upstream of an Fe-SCR catalyst comprising iron and a zeolite; and contacting the exhaust gas with the Fe-SCR catalyst, wherein the amount of ammonia or an ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is adjusted to a ratio of ammonia to NO in the exhaust gas contacting the Fe-SCR catalyst. x The molar ratio (ANR) is controlled to be greater than 2 and less than 6.

[0012] Another aspect of the disclosure is a system for treating exhaust gas from a lean-burn internal combustion engine, the system including: a reductant injector for introducing ammonia or an ammonia precursor into the exhaust gas; a substrate; an Fe-SCR catalyst contained within or disposed on the substrate, the Fe-SCR catalyst including iron and a zeolite; and an engine control unit, wherein the reductant injector is located upstream of the Fe-SCR catalyst, and the engine control unit is configured to determine the ratio of ammonia to NO in the exhaust gas contacting the Fe-SCR catalyst. x The system is configured to control the amount of ammonia or ammonia precursor introduced into the exhaust gas by the reductant injector during use so that the molar ratio (ANR) is greater than 2 and is between 6.

[0013] Another aspect of the present disclosure relates to the use of the system of the above aspect in a method according to the first aspect.

[0014] Another aspect of the present disclosure is a method for producing a 100 ppm NO x The present invention relates to a use of an Fe-SCR catalyst for treating exhaust gas from a lean-burn internal combustion engine containing iron and a zeolite, the Fe-SCR catalyst comprising iron and a zeolite, and an ANR of greater than 2 to 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention aims to address at least some of the problems associated with the prior art, or at least to provide a commercially acceptable alternative solution.

[0016] In a first aspect, the present invention provides a method for treating exhaust gas from a lean-burn internal combustion engine, comprising: introducing ammonia or an ammonia precursor into the exhaust gas upstream of an Fe-SCR catalyst comprising iron and a zeolite; contacting the exhaust gas with an Fe-SCR catalyst; The amount of ammonia or ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is adjusted to reduce the ratio of ammonia to NO in the exhaust gas contacting the Fe-SCR catalyst. x The molar ratio (ANR) is controlled to be greater than 2 and less than 6.

[0017] Each aspect or embodiment defined in this specification may be combined with any other aspect or embodiment unless expressly indicated otherwise. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.

[0018] Surprisingly, when the method of this embodiment is practiced, particularly with the combination of the Fe-SCR catalyst and the particular high ANR, (without wishing to be bound by theory) unexpectedly high NO xConversion performance has been observed to be improved, especially when compared to similar Cu-SCR catalysts. This is contrary to current "standard" practice where the ANR is typically kept below 2, and preferably around 1-1.5.

[0019] In the SCR response, the ANR is increased by NO x Some increase in NO conversion is to be expected, due to the increased concentration of ammonia, a reductant, in the exhaust gas. However, it is surprising that for the Fe-SCR catalyst described herein, there is no significant increase in NO conversion, particularly as the ANR increases above 2. x It has been observed that the NO conversion performance is increased by a much greater amount than would be expected, and importantly, to a greater extent than a comparative SCR catalyst, such as a Cu-SCR catalyst. For example, the NO conversion performance of both the Fe-SCR catalyst and the Cu-SCR catalyst x Conversion performance would be expected to increase at the same or similar rate as the ANR increases. The Cu-SCR catalyst may also be preferred at low temperatures, and therefore it would be expected that the Cu-SCR catalyst would perform better at low temperatures. However, a substantial increase in performance was observed for the Fe-SCR catalyst compared to the corresponding Cu-SCR catalyst as the ANR increases above 2, especially at low temperatures.

[0020] Increased ANR and NO x There is also a "trade-off" between the level of performance, because the higher the ANR, the greater the chance of "ammonia slip" in the exhaust system, the undesirable result of unreacted ammonia reductant passing through the exhaust system and being released into the atmosphere. However, the NOx reduction that can be exhibited by such an ANR in the method of the present invention is x Due to the increased conversion, this benefit is especially prevalent at low temperatures and / or low NO x In some conditions, the increased ANR may outweigh the risk of increased ammonia slip in the system. Thus, contrary to teachings in the art, a higher ANR may be beneficial in certain circumstances in combination with the Fe-SCR catalysts described herein.

[0021] These advantages could not have been anticipated from WO 2008 / 106519(A1), which may be considered to represent some standard SCR practice in the art. Following this publication, one may expect to use Cu-SCR catalysts to achieve improved SCR catalysis at low temperatures. Furthermore, no consideration is given of modifying the ANR. Theis paper also does not consider the effect of increased ANR in the context of Fe-SCR catalysts.

[0022] As used herein, the term "lean burn internal combustion engine" has its ordinary meaning in the art, such as an internal combustion engine that combusts fuel in an excess of air.

[0023] The term "ammonia precursor" as used herein includes any compound that can decompose into ammonia when released, for example, into an exhaust system. Typical ammonia precursors used in the field of the present invention include urea, hydrazine, ammonium carbonate, ammonium carbamate, ammonium bicarbonate, and ammonium formate.

[0024] The term "upstream" as used herein refers to the relative location of a feature in an exhaust system. In particular, the term "upstream" as used herein refers to a feature closer to the exhaust gas source along the path of the exhaust gas in the exhaust system. Thus, the term "downstream" as used herein refers to a feature further away from the exhaust gas source along the path of the exhaust gas in the exhaust system. It will also be recognized that an exhaust system including means, such as injectors, for introducing a reductant or reductant precursor and an SCR catalyst is necessarily oriented from upstream to downstream, such that the introduction of the reductant (or its precursor) occurs upstream from the SCR catalyst. If the orientation were reversed, and the reductant (or its precursor) was introduced only downstream of the SCR catalyst, the SCR catalyst would not have a source of reductant to perform its required function of reducing nitrogen oxides. Thus, in this context, the terms "upstream" and "downstream" as used in relation to an exhaust system provide a clear orientation, such that the exhaust system is not merely suitable to be oriented in either direction.

[0025] The term "SCR" as used herein means "selective catalytic reduction" as known in the art. As used herein, the term "SCR" refers to the reduction of NOx present in exhaust gas in the presence of a reducing agent, such as ammonia or an ammonia precursor. x This includes catalytic reduction (i.e., catalyst removal) of

[0026] An Fe-SCR catalyst comprises iron and a zeolite. Typically, the iron is disposed on the zeolite. For example, in the context of the present invention, the term "disposed on" in the context of a metal being "disposed on a zeolite" can include having the metal supported on the surface or within the pores of the zeolite, but the zeolite is preferably "ion-exchanged" with Fe.

[0027] The term "zeolite" as used herein has its ordinary meaning in the art. The term "zeolite" encompasses aluminosilicate molecular sieves, which are further defined and classified by the International Zeolite Association, as known to those skilled in the art.

[0028] Preferably, the amount of ammonia or ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is controlled to provide an ANR in the exhaust gas contacting the Fe-SCR catalyst of between 3 and 5, more preferably between 4 and 5. In some preferred embodiments, the amount of ammonia or ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is controlled to provide an ANR in the exhaust gas contacting the Fe-SCR catalyst of greater than 2.5. Surprisingly, the increased NO x It has been found that the above-described effects on conversion performance can be observed even more strongly in such ANR. For example, it is surprising that the NO x The difference in conversion performance between a comparable SCR catalyst, such as a Cu-SCR catalyst, can be even greater at such ratios, which is contrary to current "standard" practice where the ANR is generally kept below 2, preferably around 1-1.5.

[0029] NO in exhaust gas that comes into contact with the Fe-SCR catalyst x The concentration may not be particularly limited, and the effects described above may be more pronounced at high NO concentrations, such as above 100 ppm, e.g., 150 ppm to 1100 ppm. x However, preferably, the NO concentration in the exhaust gas contacting the Fe-SCR catalyst is x The concentration is 100 ppm or less. More preferably, the NO concentration in the exhaust gas contacting the Fe-SCR catalyst is 100 ppm or less. x The concentration is preferably 50 ppm or less, and even more preferably 10 ppm or less. xIn other words, the advantage of the Fe-SCR catalyst described herein compared to other SCR catalysts, such as Cu-SCR catalysts, is that such low NO x This may be particularly evident in the NO concentration. Moreover, the method of the present invention may be particularly suitable for such exhaust gas conditions. This is because such low NO x Even if the ANR is high, the absolute ammonia concentration in the exhaust gas may still remain relatively low, and therefore the risk associated with (absolute) ammonia slip may also remain low.

[0030] Preferably, the concentration of NO in the exhaust gas contacting the Fe-SCR catalyst vs. NO x is greater than or equal to 0.8, more preferably greater than or equal to 0.9. The method of the present invention may be particularly suitable for such exhaust gas conditions.

[0031] Preferably, the method further comprises the step of: introducing ammonia or an ammonia precursor into the exhaust gas; x For example, preferably, the method further comprises reducing the concentration of NO in exhaust gases exiting a lean-burn internal combustion engine. x The concentration of NO in the exhaust gas is greater than 100 ppm prior to the step of introducing ammonia or an ammonia precursor into the exhaust gas. x Reducing the concentration of NO in the exhaust gas x The concentration of NO in the exhaust gas is reduced to 100 ppm or less, preferably 50 ppm or less, and more preferably 10 ppm or less. x Reducing the concentration of NO preferably involves diverting the exhaust gas to a further SCR catalyst, an oxidation catalyst and / or a passive NO x Adsorbent (passive NO xThe oxidation catalyst may be achieved by contacting the catalytic converter with a PNA (Pol-adsorber) catalyst. Preferably, the further SCR catalyst comprises a Cu-SCR catalyst, which comprises copper and a zeolite. The copper is typically disposed on a zeolite. Preferably, the Cu-SCR catalyst comprises copper disposed on a small pore zeolite, such as an AEI or CHA zeolite. Preferably, the oxidation catalyst comprises a diesel oxidation catalyst (DOC). Preferably, the DOC comprises a platinum group metal, such as platinum, disposed on a support material, such as alumina. Preferably, the PNA catalyst comprises a platinum group metal (PGM), preferably palladium, disposed on a small pore zeolite, preferably having a framework type comprising CHA and / or AEI. As used herein, the term "platinum group metal" may include one or more of iridium, osmium, palladium, platinum, rhodium, and ruthenium. As used herein, "passive NO oxidation catalyst" may include one or more of iridium, osmium, palladium, platinum, rhodium, and ruthenium. x The term "adsorbent" or "PNA" refers to a material that, for example, is capable of dissolving NO at or below low temperatures. x At higher temperatures than low temperatures, the adsorbed NO x Suitable PNAs are discussed, for example, in WO 2015 / 085303(A1). Such methods may enable the advantages described above of low NO x This may help achieve exhaust gas conditions.

[0032] The method of the present invention may be particularly applicable to the type of exhaust gas produced by lean-burn engines, especially vehicular lean-burn engines. For example, the lean-burn internal combustion engine may preferably be a diesel engine, a hydrogen engine, or an engine powered by liquefied petroleum gas or natural gas. The lean-burn internal combustion engine preferably includes a diesel engine. Preferably, the lean-burn internal combustion engine is not a gasoline engine.

[0033] Preferably, the temperature of the exhaust gas contacting the Fe-SCR catalyst is 500° C. or less. More preferably, the temperature of the exhaust gas contacting the Fe-SCR catalyst is 350° C. or less, even more preferably 300° C. or less, and even more preferably 200° C. or less. The surprising beneficial effects described herein may be observed at higher temperatures, but the improved NOx of the Fe-SCR catalyst at higher ANRs is not evident. x The conversion performance is particularly evident at lower exhaust gas temperatures, especially compared to comparative SCR catalysts. Thus, the method of the present invention may be particularly applicable during the cold start period of an engine when the engine temperature remains relatively low. For example, the NO conversion of an SCR catalyst during a cold start (low temperature SCR) period may be x Improved conversion performance is highly desirable in the art and therefore such benefits can be very significant.

[0034] At such low temperatures, hydrolysis of urea (i.e., the ammonia precursor) may be unlikely, however, a heated urea injector may be used.

[0035] Therefore, preferably, in the method of the present invention, when the temperature of the exhaust gas contacting the Fe-SCR catalyst is equal to or lower than a predetermined threshold temperature, the amount of ammonia or ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is controlled so that the ANR in the exhaust gas contacting the Fe-SCR catalyst is greater than 2 and equal to 6, and when the temperature of the exhaust gas contacting the Fe-SCR catalyst is higher than the threshold temperature, the amount of ammonia or ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is controlled so that the ANR in the exhaust gas contacting the Fe-SCR catalyst is equal to or lower than 2. More preferably, when the temperature of the exhaust gas contacting the Fe-SCR catalyst is equal to or lower than a predetermined threshold temperature, the amount of ammonia or ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is controlled so that the ANR in the exhaust gas contacting the Fe-SCR catalyst is equal to or lower than 3 and equal to 5. In other words, in some preferred embodiments, the method of the present invention is used only while the engine is in a cold start period, and then, when the engine is warmed up so that the temperature of the exhaust gas is above the threshold temperature, standard methods known in the art are used to maintain the ANR within a typical range. Thus, when the engine is warmed up and the benefits of a high ANR are less significant, the amount of ANR can be reduced so that the risk of ammonia slip can be reduced.

[0036] Preferably, the threshold temperature is 500° C., more preferably 350° C., even more preferably 300° C., and even more preferably 200° C., for the reasons discussed above.

[0037] Preferably, the zeolite of the Fe-SCR catalyst comprises a zeolite having a framework type selected from one or more of AFX, AEI, BEA, FER, MFI, FAU, LTA, LTL, CHA, or mixtures or intergrowths thereof, more preferably AEI, AFX, BEA, FER, MFI, FAU, or mixtures or intergrowths thereof. BEA zeolites include beta zeolites. The framework topology of zeolite beta is discussed in JB Higgins et al., Zeolite 8, 446-452 (1988); and JM Newsam et al., Proc. R. Soc. Lond. A 420, 375-405 (1988). FER zeolites include ferrierite. MFI zeolites include, for example, ZSM-5. FAU zeolites include zeolite X and zeolite Y. AEI zeolites include SSZ-39. AFX zeolites include SSZ-16. Such framework types are known to those skilled in the art and are defined by the International Zeolite Association. Preferably, the zeolite of the Fe-SCR catalyst comprises a medium pore zeolite and / or a large pore zeolite. Such zeolites are preferred because they allow the Fe-SCR catalyst to achieve the advantageous high NO2 emission at high ANRs described above. x This can be particularly useful in enabling the conversion rate to be indicated.

[0038] As used herein, the term "small pore zeolites" may include zeolites having a maximum ring size of 8 tetrahedral atoms. As used herein, the term "medium pore zeolites" may include zeolites having a maximum ring size of 10 tetrahedral atoms. As used herein, the term "large pore zeolites" may include zeolites having a maximum ring size of 12 tetrahedral atoms.

[0039] Preferably, the zeolite of the Fe-SCR catalyst comprises a zeolite having a framework type including AEI, AFX, BEA and / or FER, preferably BEA. Preferably, the zeolite of the Fe-SCR catalyst is a beta zeolite. BEA zeolites, such as beta zeolites, have been shown to be particularly applicable to the process of the present invention to achieve the advantages described herein. Unfortunately, however, BEA zeolites may not be particularly thermally durable, especially in the hostile temperature environments experienced by exhaust gas catalysts. The Fe-FER catalyst has similar levels of NO2 as the Fe-BEA catalyst. x FER zeolites may also be preferred since they may achieve higher conversion and exhibit better thermal durability.

[0040] Preferably, the zeolite of the Fe-SCR catalyst has a silica-to-alumina molar ratio (SAR) of from about 7 to about 50, more preferably from about 10 to about 35, even more preferably from about 20 to about 30, and still more preferably from about 22 to about 28. Such zeolites enable the Fe-SCR catalyst to achieve the advantageous high NO2 production described above at high ANR. x For example, when the zeolite of the Fe-SCR catalyst comprises a zeolite having a framework type including BEA and / or FER, the zeolite of the Fe-SCR catalyst preferably has an SAR of about 25 and the AEI preferably has an SAR of 20.

[0041] Preferably, the zeolite of the Fe-SCR catalyst comprises iron disposed on the zeolite at a loading of from about 1 to about 7 weight percent, preferably from about 2 to about 5 weight percent, and most preferably about 3 weight percent, based on the weight of the zeolite.

[0042] In some preferred embodiments, the Fe-SCR catalyst further comprises copper disposed on the zeolite. Thus, the advantages associated with the presence of each of copper and iron can be utilized. In this regard, the results of the examples generally show that in lean-burn internal combustion engines that emit relatively low temperature exhaust gases or are located where the exhaust gases are relatively low temperature, e.g., less than 300° C., improved NOx reduction can be achieved by using an Fe-SCR catalyst and contacting the catalyst with an ANR of greater than 2 to 6. x This suggests that conversion can be achieved.

[0043] However, further, when the exhaust gases of a lean burn internal combustion engine in dynamic operation span a temperature range below and above 300°C, the exhaust system preferably combines an Fe-SCR zeolite catalyst and a Cu-SCR zeolite catalyst with appropriate control of the ANR to include an ANR of greater than 2 to 6 at lower temperatures where the Fe-SCR zeolite catalyst is more active, and a lower ANR at higher temperatures where the Cu-SCR zeolite catalyst may be more active, thereby providing NO over a wider temperature window. x Configurations combining Fe-SCR and Cu-SCR zeolite catalysts include layered arrangements, mixtures of both catalysts, and zone-coated (side-by-side) monolith substrates.

[0044] Preferably, the Fe-SCR catalyst is contained within or disposed on a substrate, the substrate including two or more catalytic zones, and the Fe-SCR catalyst is contained within the first catalytic zone.

[0045] The term "substrate" as used herein may include, for example, ceramic or metal honeycombs, or filter blocks, such as wall-flow filters or flow-through substrates. Substrates may include monolithic (or monolith) substrates. Substrates may include ceramic monolith substrates. Substrates may vary in their material composition, size and configuration, cell shape and density, and wall thickness. Suitable substrates are known in the art.

[0046] The term "contained within" in the context of this feature can include embodiments where the substrate is an extruded substrate, for example, where the Fe-SCR catalyst is incorporated into the extrudate when forming the extruded substrate.

[0047] The term "disposed on" in the context of this feature can include both having the Fe-SCR catalyst disposed directly on the substrate (i.e., without an intervening material) and / or having the Fe-SCR catalyst disposed indirectly on the substrate (i.e., with an intervening material). If the substrate is porous, the term "disposed on" can also include the Fe-SCR catalyst being disposed within the substrate, e.g., within the pores of the substrate, i.e., the Fe-SCR catalyst being disposed on and / or within the substrate. The Fe-SCR catalyst may be disposed on the substrate, typically in the form of a washcoat.

[0048] The term "catalytic zone" as used herein includes a defined region of a substrate that is distinguishable from another region of the substrate, for example, by having a different catalytic composition contained in or disposed on the substrate. A "zone" typically has a distinct boundary or edge (i.e., it is possible to distinguish one zone from another using conventional analytical techniques). Furthermore, the term "zone" as used herein refers to a region having an axial length that is less than the entire axial length of the substrate, such as 75% or less of the entire length of the substrate. A "zone" typically has a length (i.e., a substantially uniform length) of at least 5% (e.g., 5% or more), for example, preferably 30% or more, more preferably 40% or more of the entire length of the substrate.

[0049] The substrate may comprise a wall-flow filter substrate, but in a preferred embodiment, the substrate comprises a flow-through substrate. The substrate may be a "blank" (i.e., unwashcoated) substrate prior to application of the Fe-SCR catalyst. Alternatively, the substrate may have one or more washcoats already supported thereon. In such a situation, the final catalyst article may comprise multiple layers of different washcoats. The substrate preferably comprises cordierite. However, the composition of the substrate is not particularly limited. The term "washcoat" as used herein is known in the art and typically refers to an adherent coating applied to a substrate during production of the catalyst.

[0050] Preferably, the Cu-SCR catalyst is contained in a second catalytic zone distinct from the first catalytic zone, the Cu-SCR catalyst comprising copper and a zeolite. The second catalytic zone is typically supported on the surface of the substrate and abuts the Fe-SCR catalytic zone or minimally overlaps with the Fe-SCR catalyst (or depending on the application sequence of the Fe-SCR catalyst and Cu-SCR catalyst washcoats, the Fe-SCR catalyst may minimally overlap with the Cu-SCR catalyst, with "minimal overlap" defining unintended overlap to allow for "real world" depth of coating tolerances obtained during manufacturing). The copper is typically disposed on the zeolite. The zeolite may comprise, for example, a small pore zeolite such as AEI or CHA.

[0051] Preferably, the second catalytic zone is located upstream of the first catalytic zone, which may be a particularly preferred arrangement of the catalytic zones.

[0052] If copper is not necessarily present in the Fe-SCR catalyst, the method preferably further comprises contacting the exhaust gas with a Cu-SCR catalyst comprising copper and a zeolite prior to contacting the exhaust gas with the Fe-SCR catalyst, the Cu-SCR catalyst being located in a close-coupled position upstream of the Fe-SCR catalyst. The preferred Cu-SCR catalysts described elsewhere herein apply equally to this embodiment.

[0053] The method preferably further comprises contacting the exhaust gas with a Cu-SCR catalyst comprising copper and a zeolite downstream of the Fe-SCR catalyst, the Cu-SCR catalyst being located downstream of the Fe-SCR catalyst in an underfloor position. The preferred Cu-SCR catalysts described elsewhere herein apply equally to this embodiment.

[0054] Preferably, the ammonia precursor comprises urea. Other suitable ammonia precursors may include hydrazine, ammonium carbonate, ammonium carbamate, ammonium bicarbonate or ammonium formate.

[0055] In a further aspect, the present invention provides a system for treating exhaust gas from a lean-burn internal combustion engine, comprising: a reductant injector for introducing ammonia or an ammonia precursor into the exhaust gas; A substrate; an Fe-SCR catalyst contained within or disposed on a substrate, the Fe-SCR catalyst comprising iron and a zeolite; an engine control unit; A reductant injector is located upstream of the Fe-SCR catalyst; The engine control unit detects ammonia versus NO in the exhaust gas that comes into contact with the Fe-SCR catalyst. x The system is configured to control the amount of ammonia or ammonia precursor introduced into the exhaust gas by the reductant injector during use such that the molar ratio (ANR) is greater than 2 and less than 6.

[0056] The term "reductant injector" may include any device suitable for releasing or injecting ammonia or an ammonia precursor into an exhaust gas stream. Suitable reductant injectors are known in the art and may include a heated injector nozzle to promote the thermal decomposition of an ammonia precursor, such as urea.

[0057] Configuring the engine control unit to control the amount of ammonia or ammonia precursor introduced into the exhaust gas by the reductant injector during use may include the engine control unit being pre-programmed to provide such functionality. For example, the engine control unit may be configured to control the amount of ammonia or ammonia precursor introduced into the exhaust gas by the reductant injector upstream of the reductant injector. x Responds to the signal received from the sensor (i.e., NO in the exhaust gas) x The amount of reductant released by the reductant injector can be controlled accordingly, thereby maintaining the desired ANR using such a feedback loop. x Directly measure NO concentration x As an alternative to sensors, NO x The concentration may be, for example, a predicted NO concentration in the exhaust gas relative to any other suitable parameters of the engine condition. x It may be determined indirectly using a pre-correlated look-up table or map (stored within the control unit) that correlates with concentration.

[0058] The surprising advantages associated with the method of the first aspect apply equally to this aspect.

[0059] Preferably, the system further includes a lean burn internal combustion engine.

[0060] Preferably, the engine control unit is configured to control the amount of ammonia or ammonia precursor introduced into the exhaust gas by the reductant injector, in use, so that the ANR in the exhaust gas contacting the Fe-SCR catalyst is between 3 and 6.

[0061] Preferably, the system includes a further SCR catalyst, an oxidation catalyst and / or a PNA catalyst upstream of the Fe-SCR catalyst. x The concentration may be reduced prior to contact with the Fe-SCR catalyst.

[0062] Preferably, the lean-burn internal combustion engine is not a gasoline engine. The use of the system of the present invention may be particularly applicable to the type of exhaust gas produced by such engines. For example, preferably, the lean-burn internal combustion engine may be a diesel engine, a hydrogen engine, or an engine powered by liquefied petroleum gas or natural gas. The lean-burn internal combustion engine is most preferably a diesel engine.

[0063] Preferably, the zeolite of the Fe-SCR catalyst comprises a zeolite having a framework type selected from one or more of AEI, AFX, BEA, FER, MFI, FAU, LTA, LTL, CHA, or mixtures or intergrowths thereof, more preferably AEI, AFX, BEA, FER, MFI, FAU, or mixtures or intergrowths thereof. BEA zeolites include beta zeolites. FER zeolites include ferrierite. MFI zeolites include, for example, ZSM-5. FAU zeolites include zeolite X and zeolite Y. AEI zeolites include SSZ-39. AFX zeolites include SSZ-16. Such framework types are known to those skilled in the art and are defined by the International Zeolite Association. Preferably, the zeolite of the Fe-SCR catalyst comprises a medium pore zeolite and / or a large pore zeolite. Such zeolites provide the advantageous high NO2 and high ANR properties of Fe-SCR catalysts described above. x This can be particularly useful in enabling the conversion rate to be indicated.

[0064] Preferably, the zeolite of the Fe-SCR catalyst comprises a zeolite having a framework type including AEI, AFX, BEA and / or FER, preferably BEA. Preferably, the zeolite of the Fe-SCR catalyst is a beta zeolite. BEA zeolites, such as beta zeolites, have been shown to be particularly applicable for use in the systems of the present invention to achieve the advantages described herein. Unfortunately, however, BEA zeolites may not be particularly thermally durable, especially in the hostile temperature environments experienced by exhaust gas catalysts. The Fe-FER catalyst has similar levels of NO2 as the Fe-BEA catalyst. x FER zeolites may also be preferred since they may achieve higher conversion and exhibit better thermal durability.

[0065] Preferably, the zeolite of the Fe-SCR catalyst has a silica-to-alumina molar ratio (SAR) of from about 15 to about 50, more preferably from about 15 to about 35, even more preferably from about 20 to about 30, and still more preferably from about 22 to about 28. Such zeolites are preferred because they allow the Fe-SCR catalyst to achieve the advantageous high NO2 production described above at high ANR. x For example, when the zeolite of the Fe-SCR catalyst comprises a zeolite having a framework type including BEA and / or FER, the zeolite of the Fe-SCR catalyst preferably has an SAR of about 25.

[0066] Preferably, the zeolite of the Fe-SCR catalyst comprises iron disposed on the zeolite at a loading of from about 1 to about 7 weight percent, preferably from about 2 to about 5 weight percent, and most preferably about 3 weight percent, based on the weight of the zeolite.

[0067] In some preferred embodiments, the Fe-SCR catalyst further comprises copper disposed on the zeolite, so that the advantages associated with the presence of copper and iron, respectively, can be utilized.

[0068] Preferably, the substrate comprises two or more catalytic zones, with the Fe-SCR catalyst being contained within the first catalytic zone.

[0069] Preferably, the substrate comprises a wall-flow filter substrate. In an alternative preferred embodiment, the substrate comprises a flow-through substrate. The substrate may be a "blank", i.e., unwashcoated substrate. Alternatively, the substrate may have one or more washcoats already deposited thereon. In such a situation, the final catalyst article may include multiple layers of different washcoats. The substrate preferably comprises cordierite. However, the composition of the substrate is not particularly limited.

[0070] Preferably, the Cu-SCR catalyst is contained in a second catalytic zone distinct from the first catalytic zone, and the Cu-SCR catalyst comprises copper and a zeolite. The copper is typically disposed on the zeolite. The zeolite may comprise, for example, a small pore zeolite such as AEI or CHA.

[0071] Preferably, the second catalytic zone is located upstream of the first catalytic zone, which may be a particularly preferred arrangement of the catalytic zones.

[0072] If copper is not necessarily present in the Fe-SCR catalyst, the system preferably further comprises a Cu-SCR catalyst located in a close coupled position upstream of the Fe-SCR catalyst, the Cu-SCR catalyst comprising copper and a zeolite. The preferred Cu-SCR catalysts described elsewhere herein apply equally to this embodiment.

[0073] The system preferably further includes a Cu-SCR catalyst located downstream of the Fe-SCR catalyst in an underbed location, the Cu-SCR catalyst including copper and a zeolite. The preferred Cu-SCR catalysts described elsewhere herein apply equally to this embodiment.

[0074] Preferably, the ammonia precursor comprises urea.

[0075] In a further aspect, the present invention provides the use of the system of the above aspect in a method according to the first aspect. Accordingly, all preferred features and embodiments applicable to the first aspect apply equally to the system of the present invention and vice versa.

[0076] In a further embodiment, the present invention provides a method for producing a 100 ppm NO x The present invention provides a use of an Fe-SCR catalyst for treating exhaust gas from a lean-burn internal combustion engine containing NO, wherein the Fe-SCR catalyst comprises iron and a zeolite and has an ANR of more than 2 to 6. x are not particularly limited. Each of the preferred features and embodiments that apply to other aspects apply equally to this aspect of the invention.

[0077] The invention may also be defined according to one or more of the following statements. 1. A method for treating exhaust gas from a lean-burn internal combustion engine, the method comprising: introducing ammonia or an ammonia precursor into the exhaust gas upstream of an Fe-SCR catalyst comprising iron and a zeolite; and contacting the exhaust gas with the Fe-SCR catalyst, wherein the amount of ammonia or an ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is adjusted to a ratio of ammonia to NO in the exhaust gas contacting the Fe-SCR catalyst. x The method wherein the molar ratio (ANR) is controlled to be greater than 2 and less than 6. 2. The method according to claim 1, wherein the amount of ammonia or ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is controlled such that the ANR in the exhaust gas contacting the Fe-SCR catalyst is 3-5. 3. NO in exhaust gas that comes into contact with the Fe-SCR catalyst x 3. The method according to claim 1 or 2, wherein the concentration is 100 ppm or less. 4. NO in exhaust gas that comes into contact with the Fe-SCR catalyst x 4. The method according to claim 3, wherein the concentration is 50 ppm or less, preferably 10 ppm or less. 5. Concentration of NO in exhaust gas contacting Fe-SCR catalyst vs. NO x5. The method according to any one of 1 to 4, wherein the concentration ratio of is 0.8 or more. 6. Concentration of NO in exhaust gas contacting Fe-SCR catalyst vs. NO x 6. The method of claim 5, wherein the ratio of concentrations is 0.9 or more. 7. The method further comprises: prior to the step of introducing ammonia or an ammonia precursor into the exhaust gas, x 7. The method of any one of 1 to 6, further comprising reducing the concentration of. 8. NO in exhaust gases leaving lean-burn internal combustion engines x The concentration of NO in the exhaust gas is greater than 100 ppm prior to the step of introducing ammonia or an ammonia precursor into the exhaust gas. x Reducing the concentration of NO in the exhaust gas x 8. The method according to claim 7, wherein the concentration of is reduced to 100 ppm or less, preferably 50 ppm or less, more preferably 10 ppm or less. 9. Removing NO from the exhaust gas prior to the step of introducing ammonia or an ammonia precursor into the exhaust gas. x The concentration of NO can be reduced by diverting the exhaust gas to a further SCR catalyst, oxidation catalyst and / or passive NO x 9. The method of claim 7 or 8, comprising contacting with an adsorbent (PNA) catalyst. 10. The method of claim 9, wherein the PNA catalyst comprises a platinum group metal (PGM), preferably Pd, disposed on a small pore zeolite, preferably having a framework type comprising CHA and / or AEI. 11. The method according to any one of 1 to 10, wherein the lean-burn internal combustion engine is not a gasoline engine. 12. The method according to any one of 1 to 11, wherein the lean-burn internal combustion engine is a diesel engine, a hydrogen engine, or an engine powered by liquefied petroleum gas or natural gas. 13. The method according to any one of 1 to 12, wherein the temperature of the exhaust gas contacting the Fe-SCR catalyst is 500°C or lower. 14. The method according to claim 13, wherein the temperature of the exhaust gas contacting the Fe-SCR catalyst is 350°C or less, preferably 300°C or less, more preferably 200°C or less. 15. A method according to any one of 1 to 12, wherein when the temperature of the exhaust gas in contact with the Fe-SCR catalyst is below a predetermined threshold temperature, the amount of ammonia or ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is controlled so that the ANR in the exhaust gas in contact with the Fe-SCR catalyst is greater than 2 and is 6, and when the temperature of the exhaust gas in contact with the Fe-SCR catalyst is higher than the threshold temperature, the amount of ammonia or ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is controlled so that the ANR in the exhaust gas in contact with the Fe-SCR catalyst is 2 or less. 16. The method according to claim 15, wherein when the temperature of the exhaust gas contacting the Fe-SCR catalyst is equal to or lower than a predetermined threshold temperature, the amount of ammonia or ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is controlled so that the ANR in the exhaust gas contacting the Fe-SCR catalyst is between 3 and 5. 17. The method according to claim 15 or 16, wherein the threshold temperature is 500°C. 18. The method according to claim 17, wherein the threshold temperature is 350°C, preferably 300°C, more preferably 200°C. 19. The method of any one of 1 to 18, wherein the zeolite of the Fe-SCR catalyst comprises a zeolite having a framework type selected from one or more of AEI, AFX, BEA, FER, MFI, FAU, LTA, LTL, CHA, or mixtures or intergrowths thereof. 20. The method according to any one of 1 to 19, wherein the zeolite of the Fe-SCR catalyst comprises a medium pore zeolite and / or a large pore zeolite. 21. The method of claim 19 or 20, wherein the zeolite of the Fe-SCR catalyst comprises a zeolite having a framework type comprising AEI, AFX, BEA and / or FER, preferably BEA. 22. The method according to claim 21, wherein the zeolite of the Fe-SCR catalyst is beta zeolite. 23. The method of any one of 1 to 22, wherein the zeolite of the Fe-SCR catalyst has a silica-to-alumina molar ratio (SAR) of about 7 to about 50. 24. The method according to claim 23, wherein the zeolite of the Fe-SCR catalyst has an SAR of about 10 to about 35, preferably about 20 to about 30, and more preferably about 22 to about 28. 25. The method of claim 21, wherein the zeolite of the Fe-SCR catalyst has an SAR of about 25. 26. The method of any one of 1 to 25, wherein the zeolite of the Fe-SCR catalyst comprises iron disposed on the zeolite at a loading of about 1 to about 7 wt.%, preferably about 2 to about 5 wt.%, based on the weight of the zeolite. 27. The method of any one of 1 to 26, wherein the Fe-SCR catalyst further comprises copper disposed on a zeolite. 28. The method of any one of 1 to 27, wherein the Fe-SCR catalyst is contained within or disposed on a substrate, the substrate comprising two or more catalytic zones, and the Fe-SCR catalyst is contained within a first catalytic zone. 29. The method of claim 28, wherein the Cu-SCR catalyst is contained in a second catalytic zone different from the first catalytic zone, the Cu-SCR catalyst comprising copper and a zeolite. 30. The method of claim 29, wherein the second catalytic zone is located upstream of the first catalytic zone. 31. The method of any one of 1 to 26, further comprising contacting the exhaust gas with a Cu-SCR catalyst comprising copper and a zeolite prior to contacting the exhaust gas with the Fe-SCR catalyst, wherein the Cu-SCR catalyst is located in a close-coupled position upstream of the Fe-SCR catalyst. 32. The method of any one of 1 to 31, further comprising contacting the exhaust gas with a Cu-SCR catalyst comprising copper and a zeolite downstream of the Fe-SCR catalyst, the Cu-SCR catalyst being located downstream of the Fe-SCR catalyst in an underfloor position. 33. The method of any one of 1 to 32, wherein the ammonia precursor comprises urea. 34. A system for treating exhaust gas from a lean-burn internal combustion engine, comprising: a reductant injector for introducing ammonia or an ammonia precursor into the exhaust gas; a substrate; an Fe-SCR catalyst contained within or disposed on the substrate, the Fe-SCR catalyst comprising iron and a zeolite; and an engine control unit, wherein the reductant injector is located upstream of the Fe-SCR catalyst, and the engine control unit controls a ratio of ammonia to NO in the exhaust gas contacting the Fe-SCR catalyst. x The system is configured to control the amount of ammonia or ammonia precursor introduced into the exhaust gas by the reductant injector during use such that the molar ratio (ANR) is greater than 2 and is between 6. 35. The system of claim 34, wherein the system further comprises a lean-burn internal combustion engine. 36. A system as described in 34 or 35, wherein the engine control unit is configured to control the amount of ammonia or ammonia precursor introduced into the exhaust gas by the reductant injector during use so that the ANR in the exhaust gas contacting the Fe-SCR catalyst is between 3 and 6. 37. A system according to any one of 34 to 36, wherein the system comprises a further SCR catalyst, an oxidation catalyst and / or a PNA catalyst upstream of the Fe-SCR catalyst. 38. A system according to any one of claims 34 to 37, wherein the lean-burn internal combustion engine is not a gasoline engine. 39. A system according to any one of 34 to 38, wherein the lean-burn internal combustion engine is a diesel engine, a hydrogen engine, or an engine powered by liquefied petroleum gas or natural gas. 40. The system described in any one of 34 to 39, wherein the zeolite of the Fe-SCR catalyst comprises a zeolite having a framework type selected from one or more of AEI, AFX, BEA, FER, MFI, FAU, LTA, LTL, CHA, or mixtures or intergrowths thereof. 41. The system according to any one of 34 to 40, wherein the zeolite of the Fe-SCR catalyst comprises a medium pore zeolite and / or a large pore zeolite. 42. The system of 40 or 41, wherein the zeolite of the Fe-SCR catalyst comprises a zeolite having a framework type comprising AEI, AFX, BEA and / or FER, preferably BEA. 43. The system described in 42, wherein the zeolite of the Fe-SCR catalyst is beta zeolite. 44. The system of any one of 34 to 43, wherein the zeolite of the Fe-SCR catalyst has a silica-to-alumina molar ratio (SAR) of about 15 to about 50. 45. The system according to 44, wherein the zeolite of the Fe-SCR catalyst has an SAR of about 15 to about 35, preferably about 20 to about 30, and more preferably about 22 to about 28. 46. ​​The system described in 42, wherein the zeolite of the Fe-SCR catalyst has an SAR of about 25. 47. The system of any one of 34 to 46, wherein the zeolite of the Fe-SCR catalyst comprises iron disposed on the zeolite at a loading of about 1 to about 7 weight percent, preferably about 2 to about 5 weight percent, based on the weight of the zeolite. 48. The system of any one of 34 to 47, wherein the Fe-SCR catalyst further comprises copper disposed on a zeolite. 49. The system of any one of 34-48, wherein the substrate comprises two or more catalytic zones and the Fe-SCR catalyst is contained within the first catalytic zone. 50. The system of claim 49, wherein the Cu-SCR catalyst is contained in a second catalytic zone distinct from the first catalytic zone, the Cu-SCR catalyst comprising copper and a zeolite. 51. The system of claim 50, wherein the second catalytic zone is located upstream of the first catalytic zone. 52. The system of any one of 34 to 47, further comprising a Cu-SCR catalyst located in a close-coupled position upstream of the Fe-SCR catalyst, the Cu-SCR catalyst comprising copper and a zeolite. 53. The system of any one of 34 to 53, further comprising a Cu-SCR catalyst located downstream of the Fe-SCR catalyst at an underbed position, the Cu-SCR catalyst comprising copper and a zeolite. 54. The system of any one of 34 to 53, wherein the ammonia precursor comprises urea. 55. Use of a system according to any one of claims 34 to 54 in a method according to any one of claims 1 to 33. 56. NO below 100ppm x Use of an Fe-SCR catalyst for treating exhaust gas from a lean-burn internal combustion engine containing, wherein the Fe-SCR catalyst comprises iron and a zeolite, and has an ANR of greater than 2 to 6.

[0078] The invention will now be described with reference to the following non-limiting examples. EXAMPLES

[0079] Example 1 - Method for preparing fresh 3.0 wt% Fe / Beta zeolite catalyst and coated honeycomb monolith substrate Commercially available H-type aluminosilicate beta zeolite was dissolved in a solution of NH4NO3 and NH4 + The slurry was filtered, washed and dried. This procedure can be repeated to achieve the desired metal loading. The final product was calcined.

[0080] Cordierite honeycomb (i.e., flow-through) cylindrical monolith substrates measuring 4.66 inches in diameter and 3 inches in length, with a wall thickness of 0.004 inches (4 mils) and a cell density of 400 cpsi (cells per square inch), were coated with Fe / Beta zeolite (silica-to-alumina ratio (SAR) of 25) catalyst by adding the catalyst to deionized water to make a catalyst slurry that also contained 10% by weight of water-dispersible boehmite based on the weight of the zeolite (as a binder). The solids content of the slurry used to coat each substrate was 30%. The substrates were coated with the substrate using the process disclosed in EP 1064094 B1. The resulting catalyst cores each had a mass of 2.4 g / in 3The entire substrate was first dried in flowing air at 105° C. and then calcined in a muffle furnace at 500° C. for 4 hours. The resulting catalyst is referred to as the “fresh” catalyst.

[0081] The "fresh" catalyst coated substrates were hydrothermally aged in the oven box in a furnace at 700°C for a total of 10 hours, with the furnace temperature increasing at a "ramp rate" of 10°C / min starting at room temperature and pressure until a temperature of 700°C was reached. The 10 hour residence time did not begin until 700°C was reached. A constantly replenished gas mixture of 10% by volume O2 / 10% H2O / N2, balanced by mass and liquid flow controllers, respectively, was pumped into the oven box at a flow rate of 6 liters per minute. The honeycomb substrate cores were placed in the oven box with the channels extending vertically, and the flowing gas mixture was forced into the channels of each core disposed in the oven box at its lower end.

[0082] A sample core 1 inch in diameter and 3 inches in length was cut from the aged catalyst coated flow-through substrate. The resulting core is labeled as "Catalyst A."

[0083] Comparative Example 2 - Preparation of fresh Cu / zeolite catalyst and honeycomb monolith substrate coated therewith Commercially available H-type aluminosilicate AEI (SSZ-39) zeolite (SAR of 20) was dissolved in NH4NO3 and NH4 + The resulting material was added to an aqueous solution of copper acetate with stirring. The slurry was filtered, then washed and dried. This procedure can be repeated to achieve the desired copper metal loading of 3.0 wt.%. The final product was calcined.

[0084] Similarly, a commercially available H-type aluminosilicate CHA zeolite (SAR of 23) was dissolved in NH4NO3 and NH4 +The resulting material was added to an aqueous solution of copper acetate with stirring. The slurry was filtered, then washed and dried. This procedure can be repeated to achieve the desired copper metal loading of 2.0 wt.%. The final product was calcined.

[0085] The Cu / AEI and Cu / CHA zeolite catalysts thus prepared were each coated onto separate bare cordierite honeycomb (i.e., flow-through) cylindrical monolith substrates identical to those used for the Fe / BEA zeolite catalyst in Example 1, and both coated substrates were aged in the same manner as the Fe / BEA zeolite-coated substrate, and identically sized cores were cut from each aged substrate for testing. The comparative Cu / AEI zeolite catalyst was labeled as "Catalyst B" and the comparative Cu / CHA zeolite catalyst was labeled as "Catalyst C."

[0086] Example 3-NO x Evaluation of conversion rate The catalyst cores prepared in Example 1 and Comparative Example 2 were treated with NO x Conversion activity was evaluated. All aged cores were tested in a laboratory selective catalytic activity test (SCAT) apparatus using the following gas mixture containing ammonia reductant: 75 ppm NO, "X" ppm NH3 (ammonia vs. NO used). x Depending on the ratio (ANR) (see Tables 1 and 2 below), 10% O2, 8% CO2, 5% H2O, balance N2.

[0087] NO at various ANRs at 175℃ and 300℃ x The conversion results are shown in Tables 1 and 2 below.

[0088] [Table 1]

[0089] [Table 2]

[0090] From the results shown in Tables 1 and 2, it is quite surprising that at a low temperature of 175° C., the NO x It can be seen that the conversion is significantly improved over the two comparative Cu / zeolite samples. At the higher reaction temperature point of 300 °C, the NO conversion of the Fe / BEA aluminosilicate zeolite catalyst is significantly improved. x Conversion also improves with higher ANR. ****************************

[0091] The foregoing detailed description has been provided for purposes of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments described herein will be apparent to those of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.

[0092] For the avoidance of any doubt, all documents and the entire contents of all documents cited herein are hereby incorporated by reference into this application.

Claims

1. A method for treating exhaust gases from a lean-burn internal combustion engine, Introducing ammonia or an ammonia precursor into the exhaust gas upstream of an Fe-SCR catalyst containing iron and zeolite, This includes contacting the exhaust gas with the Fe-SCR catalyst, The amount of ammonia or ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is such that the ammonia in the exhaust gas that comes into contact with the Fe-SCR catalyst is equal to the amount of NO in the exhaust gas. ｘ A method for treating exhaust gases from a lean-burn internal combustion engine, where the molar ratio (ANR) is controlled to be greater than 2 and between 2 and 6.

2. NO in the exhaust gas that comes into contact with the Fe-SCR catalyst ｘ The method according to claim 1, wherein the concentration of is 100 ppm or less.

3. Concentration of NO in the exhaust gas in contact with the Fe-SCR catalyst vs. NO ｘ The method according to claim 1 or 2, wherein the ratio of the concentrations is 0.8 or greater.

4. The method according to claim 1 or 2, wherein the lean-burn internal combustion engine is a diesel engine, a hydrogen engine, or an engine powered by liquefied petroleum gas or natural gas.

5. The method according to claim 1 or 2, wherein the temperature of the exhaust gas in contact with the Fe-SCR catalyst is 500°C or less.

6. When the temperature of the exhaust gas in contact with the Fe-SCR catalyst is below a predetermined threshold temperature, the amount of ammonia or ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is controlled so that the ANR in the exhaust gas in contact with the Fe-SCR catalyst is greater than 2 to 6. The method according to claim 1 or 2, wherein, when the temperature of the exhaust gas in contact with the Fe-SCR catalyst exceeds the threshold temperature, the amount of ammonia or ammonia precursor introduced into the exhaust gas upstream of the Fe-SCR catalyst is controlled so that the ANR in the exhaust gas in contact with the Fe-SCR catalyst is 2 or less.

7. The method according to claim 1 or 2, wherein the zeolite of the Fe-SCR catalyst comprises one or more of AEI, AFX, BEA, FER, MFI, FAU, LTA, LTL, CHA, or mixtures thereof or intercrystals, preferably a zeolite having a framework type selected from AEI, AFX, BEA and / or FER, most preferably BEA.

8. The method according to claim 1 or 2, wherein the zeolite of the Fe-SCR catalyst has a silica-to-alumina molar ratio (SAR) of about 7 to about 50.

9. The method according to claim 1 or 2, wherein the zeolite of the Fe-SCR catalyst contains iron arranged on the zeolite in a supported amount of about 1 to about 7% by weight, preferably about 2 to about 5% by weight, based on the weight of the zeolite.

10. The method according to claim 1 or 2, wherein the Fe-SCR catalyst further comprises copper disposed on the zeolite.

11. The method according to claim 1 or 2, wherein the Fe-SCR catalyst is contained in or arranged on a substrate, the substrate comprises two or more catalyst zones, and the Fe-SCR catalyst is contained in a first catalyst zone.

12. The method according to claim 11, wherein the Cu-SCR catalyst is contained in a second catalyst zone different from the first catalyst zone, and the Cu-SCR catalyst comprises copper and zeolite.

13. The method according to claim 12, wherein the second catalyst zone is located upstream of the first catalyst zone.

14. A system for processing exhaust gases from a lean-burn internal combustion engine, A reducing agent injector for introducing ammonia or an ammonia precursor into the exhaust gas, Substrate and An Fe-SCR catalyst contained in or disposed on the substrate, comprising iron and zeolite, Equipped with an engine control unit, The reducing agent injector is located upstream of the Fe-SCR catalyst, The engine control unit contacts the Fe-SCR catalyst with ammonia versus NO in the exhaust gas. ｘ A system configured to control the amount of ammonia or ammonia precursor introduced into the exhaust gas by the reducing agent injector during use, such that the molar ratio (ANR) is greater than 2 to 6.

15. Use of the system according to claim 14 in the method according to claim 1.

16. NO below 100 ppm ｘ Use of an Fe-SCR catalyst for treating exhaust gas from a lean-burn internal combustion engine containing iron and zeolite, wherein the Fe-SCR catalyst comprises iron and zeolite and has an ANR of greater than 2 and less than or equal to 6.