System for treating exhaust gases from a nitrogen-containing fuel or hydrogen combustor

Abstract

A fuel combustion and exhaust gas system is provided that includes a fuel combustor and an exhaust gas treatment system, wherein the fuel combustor is a nitrogen-containing fuel or hydrogen combustor, and the exhaust gas treatment system includes a first catalyst article that includes an Fe-loaded small or medium pore molecular sieve, and the small or medium pore molecular sieve has a silica-to-alumina ratio (SAR) of 6 to 19.

Description

[Technical Field]

[0001] The present invention relates to a system for treating exhaust gases from nitrogen-containing fuel or hydrogen combustors, and in particular to a catalyst particularly suited for such purpose. [Background technology]

[0002] It is well known that in the automotive engine field, there is a general trend to move toward and investigate the suitability of engines that consume fuels other than fossil fuels, such as gasoline and diesel, in order to reach net-zero CO2 emissions targets. These alternative fuels include, for example, hydrogen (H2), ammonia (NH3), and methanol (CH3OH). However, of course, the use of such new fuels also means that the composition of the exhaust gases produced by burning such fuels will differ from the composition of the exhaust gases in fossil fuel-burning engines.

[0003] One major difference between the composition of exhaust gases produced by these alternative fuels and that produced by conventional fossil fuels is that these alternative fuels can produce much higher NO emissions. In other words, the concentration of NO in the exhaust gases produced by these alternative fuels can be much higher than in the exhaust gases produced by conventional fossil fuels.

[0004] Therefore, there is a need to develop exhaust gas catalysts for treating the exhaust gases produced by these alternative fuels that are effective against the unique profile of pollutants in the exhaust gases. Catalysts traditionally used in the exhaust systems of fossil fuel combustion engines cannot be guaranteed to be effective against the completely different composition of exhaust gases produced by burning these new alternative fuels. Summary of the Invention

[0005] 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.

[0006] The present invention provides, in accordance with the claims appended hereto, a fuel combustion and exhaust gas system, a method for treating exhaust gases, and the use of the catalysts described herein.

[0007] In particular, in a first aspect, the present invention provides a fuel combustion and exhaust gas system comprising a fuel combustor and an exhaust gas treatment system, wherein the fuel combustor is a nitrogen-containing fuel or hydrogen combustor, and the exhaust gas treatment system comprises a first catalyst article comprising an Fe-loaded small or medium pore molecular sieve, the small or medium pore molecular sieve having a silica-to-alumina ratio (SAR) of 6 to 19.

[0008] Each aspect or embodiment defined herein may be combined with any other aspect or embodiment unless expressly stated otherwise. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.

[0009] The present inventors have surprisingly found that catalysts comprising Fe-loaded small and medium pore molecular sieves can exhibit particularly high NO conversion when treating exhaust gases, and further, that reducing the SAR of the molecular sieves can further increase the NO conversion of the catalyst. This is unexpected. Accordingly, such catalysts can be particularly effective for use in exhaust systems for treating exhaust gases produced by combustors burning fuels that can generate relatively high concentrations of NO, including engines that burn alternative fuels such as ammonia and hydrogen.

[0010] "N2O conversion" is intended to refer to the typical chemical reaction 2N2O → 2N2 + O2 that is facilitated by such catalysts.

[0011] The present inventors have also surprisingly found that the Fe-loaded molecular sieves of the present invention exhibit increased NO conversion compared to Fe-loaded large pore molecular sieves and small or medium pore molecular sieves with higher SAR, which has not been previously studied.

[0012] These results are also particularly surprising because it is unusual to aim to reduce the SAR in molecular sieves for use in treating exhaust gases from combustors, such as from combustion engines. This is because it is generally known that reducing the SAR of such molecular sieves (or zeolites in particular) can reduce the hydrothermal stability of molecular sieve-based catalysts. Reduced hydrothermal stability is clearly undesirable for such applications, where typical operating environments can include temperatures of several hundred degrees Celsius. However, in the present invention, the benefits obtained in NO conversion can offset, at least to some extent, the drawbacks of reducing the SAR of molecular sieves.

[0013] NO may occur in high concentrations in nitrogen-containing fuel or hydrogen combustors, such as hydrogen and ammonia combustion engines (especially ammonia combustion engines), and therefore the catalysts described herein may be particularly advantageous when used in such applications, such as the present invention.

[0014] Furthermore, in an ammonia-burning engine, any ammonia fuel (and the NO produced thereby) that passes through the exhaust gases is particularly x exhaust) reacts in the first catalyst article to produce ammonia (and NO in a selective catalytic reduction (SCR) reaction). x) can be removed. However, the presence of ammonia may also enable the Fe-based molecular sieves of the present invention to convert NO at lower temperatures than in the absence of ammonia. Thus, ammonia slip through the engine may actually assist in reducing the large amounts of NO produced by ammonia-burning engines. This mechanism provides a further unexpected benefit associated with the use of the Fe-loaded molecular sieves of the present invention for the treatment of exhaust gases produced by the use of alternative fuels.

[0015] As used herein, the term "nitrogen-containing fuel or hydrogen combustor" may encompass a fuel combustor designed to burn a fuel containing molecules containing nitrogen gas or containing hydrogen, respectively. Preferably, more than 30 mol % of the molecules in the nitrogen-containing fuel contain nitrogen, more preferably more than 50 mol %, even more preferably more than 70 mol %, and even more preferably more than 90 mol %. Preferably, the nitrogen-containing fuel comprises one or more of ammonia, ammonia precursors (such as amines and / or urea), and organic waste. Preferably, the nitrogen-containing fuel comprises ammonia. Thus, the term "nitrogen-containing fuel or hydrogen combustor" may, of course, encompass a fuel combustor designed to burn a nitrogen-containing fuel (preferably ammonia) or a dual or mixed fuel containing hydrogen, such as a fuel blended with diesel, marine diesel, heavy fuel oil, and / or natural gas. In another embodiment, the fuel combustor is a methanol combustor.

[0016] Preferably, the fuel combustor comprises a combustion chamber. Preferably, the fuel combustor is a combustion engine, more preferably an internal combustion engine, even more preferably an automotive internal combustion engine. That is, the fuel combustor is preferably a nitrogen-containing fuel or hydrogen combustion engine. The term "engine" as used herein may encompass an engine in the conventional sense, such as an engine for use in an automobile or the like. In an alternative preferred embodiment, the fuel combustor is not an engine for use in an automobile or the like, but an industrial fuel combustor, for example, a fuel combustor that burns fuel in an industrial process, such as an ammonia cracking or (organic) waste incineration process.

[0017] The term "first" as used herein is intended as a label and does not limit the relative placement or location of a corresponding feature (here, a catalytic article) within an exhaust gas treatment system unless otherwise specified.

[0018] As used herein, the terms "article" or "catalyst article" may include an article on or in which a catalyst is supported. The article may take the form of, for example, a honeycomb monolith, such as a flow-through monolith, or a filter, e.g., a wall-flow filter. The catalyst article may also be in pellet form.

[0019] As used herein, the term "Fe-loaded" can include a molecular sieve that is metal-promoted with Fe, and the Fe can be loaded on the molecular sieve. In a metal-loaded molecular sieve, the loaded metal is of the "extraframework metal" type, i.e., a metal that is present within the molecular sieve and / or on at least a portion of the molecular sieve surface. This definition does not include atoms that make up the framework of the molecular sieve.

[0020] Metal-loaded molecular sieves in general and methods for producing such metal-loaded molecular sieves are known to those skilled in the art. For example, several methods for preparing metal-loaded molecular sieves, particularly metal-loaded zeolites, have been described in the literature. The direct synthesis of metal-loaded zeolites is a complex process and depends on the synthesis conditions (see M. Moliner, ISRN Materials Science, 2012, Article ID 789525). An alternative is to use commercially available zeolite supports and then add metals by post-synthesis treatment of the zeolite, such as wet impregnation, wet ion exchange, or solid-state ion exchange.

[0021] Known wet ion exchange methods for loading metals onto molecular sieves (e.g., zeolites) typically utilize soluble metal salts, such as metal acetates, sulfates, or chlorides, as active metal precursors, which react with the molecular sieves in aqueous solution. To accelerate the ion exchange, such processes typically require a heating step, where the mixture can be heated to temperatures in the range of 70-80°C for up to several hours.

[0022] The term "molecular sieve" as used herein is well known to those skilled in the art and can include crystalline or paracrystalline materials, which can be, for example, aluminosilicates (zeolites) or silicoaluminophosphates (SAPOs). Such molecular sieves are constructed, for example, from repeating SiO, AlO, and optionally PO tetrahedral units linked in rings to form a framework with regular intracrystalline cavities and channels of molecular dimensions. The specific arrangement of tetrahedral units (ring members) gives rise to the molecular sieve framework, and by convention, each unique framework has been assigned a unique three-letter code (e.g., "CHA") by the International Zeolite Association (IZA).

[0023] Molecular sieves are, for example, "H + Form" or "NH4 + In the context of molecular sieves, the term "H + The term "morphology" refers to the structure in which the backbone charge is a proton (i.e., H + It refers to a molecular sieve with an anionic framework balanced by cations. + The "morphology" refers to the structure in which the backbone charge is an ammonium cation (NH4 + When loaded with metals (e.g., Fe), these molecular sieves are no longer "H" + Form" or "NH4 +It cannot be considered a "form."

[0024] Molecular sieves (e.g., zeolites) can also be classified by pore size, e.g., the maximum number of tetrahedral atoms present in the molecular sieve framework. As defined herein, a "small pore" molecular sieve, such as CHA, contains a maximum ring size of 8 tetrahedral atoms, while a medium pore molecular sieve, e.g., MFI, contains a maximum ring size of 10 tetrahedral atoms, and a large pore molecular sieve, such as BEA, contains a maximum ring size of 12 tetrahedral atoms. In the present invention, small or medium pore molecular sieves are defined according to these commonly understood definitions.

[0025] This aspect requires that the first catalyst article comprises an Fe-supported small or medium pore molecular sieve. Accordingly, it should be appreciated that the present invention encompasses embodiments in which the first catalyst article comprises Fe supported on two or more different small or medium pore molecular sieves. The term "different" small or medium pore molecular sieves may encompass differences in the molecular sieve framework (i.e., framework type code) or other properties of the molecular sieves, such as SAR.

[0026] As used herein, the term "silica-to-alumina ratio" or "SAR" may include the molar ratio of silicon to aluminum present in the molecular sieve framework, calculated based on silica (SiO) and alumina (AlO), rather than silicon and aluminum atoms. Of course, in the chemical structure of the molecular sieve framework, silicon and aluminum are typically not present in the form of discrete silica and alumina. SAR is a term commonly used in the art and will be understood by those skilled in the art.

[0027] It should be appreciated that the fuel combustor is in fluid communication with the exhaust gas treatment system.

[0028] The first catalyst article may typically include a substrate and an Fe-loaded small or medium pore molecular sieve disposed on the substrate. The term "substrate" as used herein may include, for example, a ceramic or metal flow-through honeycomb, or a filter block, such as a wall-flow filter or a flow-through filter. The substrate may include a ceramic or metal monolithic substrate. The substrate may vary in terms of its material composition, size and configuration, cell shape and density, and wall thickness. Suitable substrate materials are known in the art.

[0029] As used herein, the term "disposed on" can include having the catalyst composition disposed directly on the substrate, i.e., without intervening materials, and / or indirectly on the substrate, i.e., with intervening materials. If the substrate is porous, the term "disposed on" can also include having the catalyst composition disposed therein, e.g., within the pores of the substrate, i.e., the catalyst composition is disposed on and / or within. The catalyst composition is typically disposed on the substrate in the form of a washcoat. The term "washcoat," as used herein, is well known in the art and generally refers to an adherent coating applied to a substrate during catalyst production. How the molecular sieve is disposed on the substrate is not particularly important for purposes of the present invention.

[0030] Alternatively, the first catalyst article may comprise a "fully active extrudate," where the substrate comprises an extrudate of Fe-loaded small or medium pore molecular sieve, ie, the substrate itself is catalytically active.

[0031] When the molecular sieve is a small pore molecular sieve, the small pore molecular sieve may have a framework represented by a framework type code selected from ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, KFI, LEV, LTA, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SFW, SIV, THO, TSC, UEI, UFI, VNI, YUG, and ZON, and mixtures and / or intergrowths thereof.

[0032] When the molecular sieve is a medium pore molecular sieve, the medium pore molecular sieve may have a framework represented by a framework type code selected from AEL, AFO, AHT, BOF, BOZ, CGF, CGS, CHI, DAC, EUO, FER, HEU, IMF, ITH, ITR, JRY, JSR, JST, LAU, LOV, MEL, MFI, MFS, MRE, MTT, MVY, MWW, NAB, NAT, NES, OBW, PAR, PCR, PON, PUN, RRO, RSN, SFF, SFG, STF, STI, STT, STW, SVR, SZR, TER, TON, TUN, UOS, VSV, WEI, and WEN, and mixtures and / or intergrowths thereof.

[0033] Preferably, the molecular sieve of the first catalyst article is a small pore molecular sieve. However, small or medium pore molecular sieves having a framework defined by a framework type code selected from CHA, FER, MFI, AEI, and AEI-CHA intergrowth, preferably CHA, FER, AEI, and AEI-CHA intergrowth, are also preferred. Most preferred are the small pore framework type codes CHA and AEI. That is, the molecular sieve preferably has a framework defined by a framework type code selected from CHA and AEI, and most preferably, the molecular sieve has a framework defined by the framework type code CHA.

[0034] Fe-loaded molecular sieves having frameworks defined by these preferred specific framework type codes have been shown to exhibit higher NO conversion than small pore molecular sieves with higher SAR (e.g., Fe / CHA with a SAR of 25) and Fe-loaded large pore molecular sieves (e.g., Fe / BEA).

[0035] Preferably, the small or medium pore molecular sieve of the first catalyst article is a small or medium pore zeolite.

[0036] The small or medium pore molecular sieve is preferably a powdered crystalline molecular sieve (i.e., in particulate form), where the particles comprise individual crystals, aggregates of crystals, or a combination thereof. The crystalline molecular sieve may have an average crystal size of 0.5 μm or more, preferably about 0.5 to about 15 μm, e.g., about 0.5 to 10 μm, about 0.5 to about 5 μm, about 1 to about 5 μm, or about 2 to about 5 μm, as measured by scanning electron microscopy (SEM).

[0037] Preferably, the small or medium pore molecular sieve of the first catalyst article has an SAR of 6 to 18, more preferably 6 to 17, more preferably 6 to 15, more preferably 6 to 13, more preferably 7 to 12, more preferably 9 to 11, and even more preferably about 10. As explained above, it has surprisingly been found that decreasing the SAR of the Fe-loaded small or medium pore molecular sieve can increase the NO conversion exhibited by the Fe-loaded molecular sieve catalyst. Therefore, the above ranges may be particularly preferred. Furthermore, the inventors unexpectedly found that decreasing the SAR of the molecular sieve appears to plateau NO conversion performance at an SAR of about 10. Therefore, although all of the preferred Fe-loaded molecular sieves provide significant improvements over higher SAR small and medium pore molecular sieves and large pore molecular sieves, an SAR of about 10 may be most preferred. This is because reducing the SAR below this value may return minimal benefits in NO conversion performance while risking reducing the hydrothermal stability of the molecular sieve. In other words, an SAR of about 10 provides an unexpected balance between molecular sieve stability and NO conversion performance of Fe-loaded molecular sieves as catalysts.

[0038] Accordingly, in some preferred embodiments, the present invention provides a fuel combustion and exhaust gas treatment system comprising a fuel combustor and an exhaust gas treatment system, wherein the fuel combustor is a nitrogen-containing fuel or hydrogen combustor, and the exhaust gas treatment system comprises a first catalyst article comprising an Fe-loaded small or medium pore molecular sieve, wherein the small or medium pore zeolite has a silica-to-alumina ratio (SAR) of 6 to 13, preferably the small or medium pore zeolite has a framework defined by framework type code CHA selected from CHA, FER, MFI, AEI, and the AEI-CHA bicrystal, more preferably CHA or AEI.

[0039] Preferably, the small or medium pore molecular sieve of the first catalyst article has a loading of at least 0.5 wt. % Fe, more preferably at least 1.5 wt. % Fe, preferably 1.5-4 wt. % Fe, and more preferably about 3 wt. % Fe, based on the total weight of the Fe-loaded small or medium pore molecular sieve. Catalysts having an Fe loading of about 3 wt. % have been shown to exhibit the advantageous NO conversion described herein.

[0040] Preferably, the first catalyst article is a flow-through monolith or a wall-flow filter. In other words, when the first catalyst article comprises a substrate and an Fe-loaded small or medium pore molecular sieve disposed on the substrate, the substrate preferably takes the form of a flow-through monolith or a wall-flow filter. Of course, the substrate may also comprise a "fully active extrudate," in which the substrate comprises an extrudate of the Fe-loaded small or medium pore molecular sieve.

[0041] Preferably, the exhaust gas treatment system further comprises a selective catalytic reduction (SCR) catalyst article upstream of the first catalyst article. As used herein, the term "SCR catalyst" refers to a catalyst that reduces nitrogen oxides (NO ) by, for example, ammonia. x The SCR catalyst article may include a catalyst that catalyzes the catalytic reduction of . Catalysts suitable for such function are well known to those skilled in the art, and the particular form of the SCR catalyst article is not particularly limited. However, for example, a Cu-SCR catalyst, such as a Cu / zeolite with Cu / CHA, or a V-based SCR catalyst may be used.

[0042] As used herein, the term "upstream" refers to a direction within a system toward the exhaust gas source. In contrast, as used herein, the term "downstream" refers to a direction within a system away from the exhaust gas source.

[0043] As mentioned above, the SCR catalyst reduces NOx present in the exhaust gases produced by the use of a fuel combustor. xHowever, the SCR catalyst may also generate additional NO during use, e.g., as a by-product. Thus, the presence of the first catalyst article of the present invention downstream of the SCR catalyst can also advantageously assist in removing this additional NO (i.e., where the concentration of NO in the exhaust gas is higher). In other words, when the SCR catalyst is upstream of the first catalyst article of the present invention, any NO by-product generated by the SCR catalyst is less problematic and less likely to be released into the atmosphere.

[0044] Preferably, the exhaust gas treatment system further comprises an ammonia slip catalyst (ASC) article upstream of the first catalyst article. The ASC has the function of converting residual ammonia present in the exhaust gas into N2 and HO. The ASC also converts NO x can be converted to N2 and HO. Catalysts suitable for such functions are well known to those skilled in the art, and the particular form of the ASC article is not particularly limited. Suitable ASC articles may include, for example, a PGM-supported support material, such as Pt-loaded zeolite or Pt-loaded alumina. Suitable ASC compositions are also described, for example, in WO 2012138405 (A1), WO 2017134454 (A1), WO 2018178627 (A1), WO 2019186121 (A1), and EP 2885514 (A1).

[0045] For the avoidance of doubt, the exhaust gas treatment system may independently further comprise either an SCR catalyst article or an ASC article upstream of the first catalyst article. The exhaust gas treatment system may also further comprise both an SCR catalyst article and an ASC article upstream of the first catalyst article. The catalyst articles may be present as different substrates, i.e., on one or more separate bricks, or on the same substrate, i.e., on a single brick.

[0046] Like an SCR catalyst article, an ASC article can also produce additional NO in the exhaust gas, and therefore the same advantages associated with having a first catalyst article of the present invention downstream from an SCR catalyst article apply to this embodiment of the ASC article.

[0047] Additionally, the use of an ASC article (only) upstream of the first catalyst article can be particularly advantageous for use with ammonia-burning engines, since ammonia concentrations in the exhaust gas can be particularly high when the fuel contains ammonia. Thus, such an exhaust gas treatment system can reduce both ammonia slip and NO slip.

[0048] When both an SCR catalyst article and an ASC article are present upstream of the first catalyst article, the SCR catalyst article is preferably upstream of the ASC article. In other words, the exhaust gas treatment system preferably includes, in downstream order, an SCR catalyst article, then an ASC article, and then the first catalyst article of the present invention. The advantages of providing an ASC article downstream of an SCR catalyst article are known. However, the advantage of further including the first catalyst article of the present invention downstream of these conventional catalysts provides the additional advantages discussed above.

[0049] Preferably, the exhaust gas treatment system further comprises means for injecting a nitrogen reducing agent upstream of the first catalyst article. The nitrogen reducing agent preferably includes ammonia and / or urea, more preferably is ammonia and / or urea. Other known ammonia precursors may also be suitable. The advantages conferred by the ability of the first catalyst article to convert NO due to the presence of ammonia in the exhaust gas to be treated are described above with respect to embodiments in which the fuel combustor is an ammonia combustion engine. However, in other embodiments, it may be beneficial to artificially introduce ammonia into the exhaust gas upstream of the first catalyst article. In embodiments in which the fuel combustor is an ammonia combustion engine, it may also be beneficial to further increase the concentration of ammonia in the exhaust gas for the same reasons.

[0050] If the exhaust gas treatment system further includes an SCR catalyst article upstream of the first catalyst article, the means for injecting a nitrogen reductant is preferably downstream of the SCR catalyst article. The advantages of having a means for injecting a nitrogen reductant upstream of the SCR catalyst are known to those skilled in the art. In embodiments where the fuel combustor is from an ammonia-burning engine, it may not be necessary to include a means for injecting a nitrogen reductant upstream of the SCR catalyst because the exhaust gas may already contain an acceptable concentration of ammonia. However, for reasons described herein, it may be advantageous to further increase the concentration of ammonia in the exhaust gas upstream of the SCR catalyst article, for example, to a level higher than that required for the SCR reaction, thereby intentionally allowing some ammonia to pass through the SCR catalyst unreacted. This means that some of the ammonia (or nitrogen reductant) introduced upstream of the SCR catalyst article may still reach the first catalyst article of the present invention.

[0051] Alternatively, if the concentration of ammonia in the SCR catalyst article is deemed acceptable for a particular use, means for injection of a nitrogenous reductant may be provided, for example, between the SCR catalyst article and the first catalyst article of the present invention to ensure that some ammonia reaches the first catalyst article to achieve the benefits described herein.

[0052] Furthermore, because the first catalyst article may preferably be at least the second or third catalyst article present in the exhaust gas treatment system in the upstream-to-downstream direction, the temperature of the exhaust gas at the location of the first catalyst article of the present invention may be relatively low. This means that the temperature of the first catalyst article itself may be relatively low. Therefore, ensuring the presence of ammonia in the exhaust gas contacting the first catalyst article provides a further advantage, as the presence of ammonia may enable the Fe-based molecular sieve of the present invention to convert NO at a lower temperature than in the absence of ammonia, as described herein.

[0053] When the exhaust gas treatment system further includes an SCR catalyst article upstream of the first catalyst article, the exhaust gas treatment system preferably further includes first means for injecting a nitrogenous reductant upstream of the SCR catalyst article and second means for injecting a nitrogenous reductant between the SCR catalyst and the first catalyst article. Having means for injecting a nitrogenous reductant at both of these locations may enable all of the associated advantages described above to be achieved. Furthermore, this configuration may enable the specific concentration of ammonia in the exhaust gas at different locations in the exhaust gas treatment system to be adjusted and / or varied, for example, depending on a particular use or specific conditions. For example, at low temperatures near the beginning of a fuel combustor or engine cycle, it may be beneficial to introduce a relatively high concentration of nitrogenous reductant immediately upstream of the first catalyst article of the present invention, i.e., while the catalyst may be cold, and then introduce a relatively low concentration of nitrogenous reductant as the fuel combustor or engine, and thus the first catalyst article of the present invention, begin to warm to higher operating temperatures. If the exhaust gas treatment system further includes an ASC article upstream of the first catalyst article, the second means for injection of nitrogenous reductant is preferably downstream of the ASC article. Preferably, the first catalyst article is the last catalytic component in the exhaust system before the treated exhaust gas is released to the atmosphere.

[0054] The first catalyst article may be configured to be electrically heated. In other words, the first catalyst article is preferably an electrically heated catalyst (EHC). As described above, the first catalyst article may preferably be at least the second or third catalyst article present in the exhaust gas treatment system in the upstream-to-downstream direction, so the temperature of the exhaust gas at the location of the first catalyst article of the present invention may be relatively low. This also means that the activity of the catalyst is lower than its potential. This problem can be solved by actively heating the first catalyst article with an electric heater. EHCs are generally known to those skilled in the art. This embodiment is not limited to a particular type of EHC. If an ASC is present, an EHC may not be needed (or may simply require less heating) because the ASC may generate heat during use that may heat the first catalyst article, especially if the ASC and the first catalyst article of the present invention are closely coupled.

[0055] Preferably, the small or medium pore molecular sieve of the first catalyst article is substantially free of base metals other than Fe supported thereon. As used herein, the term "substantially free" may encompass that the small or medium pore molecular sieve of the first catalyst article contains less than 0.1 wt. %, more preferably less than 0.05 wt. %, even more preferably less than 0.01 wt. %, and even more preferably less than 0.001 wt. % of components (here, base metals other than Fe) based on the total weight of the Fe-loaded small or medium pore molecular sieve. More preferably, the small or medium pore molecular sieve of the first catalyst article does not contain base metals other than Fe supported thereon. More preferably, the small or medium pore molecular sieve of the first catalyst article is substantially free of transition metals other than Fe supported thereon. Most preferably, the small or medium pore molecular sieve of the first catalyst article is free of transition metals other than Fe supported thereon.

[0056] In other words, Fe is preferably the only base metal supported on the small or medium pore molecular sieve, and more preferably the only transition metal supported on the small or medium pore molecular sieve. Of course, other metals may be present if the first catalyst article has other layers or zones disposed thereon, e.g., for different purposes and therefore may contain different components, which may contain metals other than Fe. That is, other metals may be transferred by physical contact. Such embodiments are not intended to be excluded.

[0057] In a further aspect, the present invention provides a method for treating exhaust gas from a nitrogen-containing fuel or hydrogen combustor, comprising passing the exhaust gas through a catalytic article comprising an Fe-loaded small or medium pore molecular sieve, the small or medium pore molecular sieve having an SAR of 6 to 19. Preferably, the method comprises passing the exhaust gas through an exhaust gas treatment system as defined in the first aspect. Preferably, the temperature of the exhaust gas and / or the catalytic article is 350 to 500°C.

[0058] All preferred embodiments and features described herein in relation to the first aspect apply equally to this aspect.

[0059] In a further aspect, the present invention also provides use of an Fe-loaded small or medium pore molecular sieve for reducing the concentration of NO in exhaust gas from a nitrogen-containing fuel or hydrogen combustor, wherein the small or medium pore molecular sieve has an SAR of 6 to 19.

[0060] All preferred embodiments and features described herein in relation to the first aspect apply equally to this aspect. As described herein, such uses have not been previously contemplated. The advantages of such uses are discussed herein. [Brief explanation of the drawings]

[0061] The invention will now be described with reference to the following non-limiting drawings. [Figure 1] 1 shows N2O conversion at 400° C. for five catalyst compositions corresponding to Fe-supported small or medium pore zeolites suitable for the first catalyst article of the present invention compared to four comparative catalyst compositions. [Figure 2] 1 shows N2O conversion at 150-500° C. for catalyst compositions corresponding to Fe-loaded small or medium pore zeolites suitable for the first catalyst article of the present invention compared to comparative catalyst compositions.

[0062] The invention will now be described with reference to the following non-limiting examples. [Example]

[0063] Example 1: Nine catalyst compositions were prepared by incipient wetness impregnation of FeCl salt into pre-prepared zeolites with specific frameworks and SARs. Each catalyst composition carried 3 wt.% Fe, based on the total weight of Fe / zeolite. Specifically, a metal salt solution was prepared using FeCl (Alfa Aesar iron(II) chloride, anhydrous, 99.5% (metal basis)) and double-distilled H2O and then added dropwise to the relevant zeolite sample. The mixture was homogeneously mixed until a wet, sandy appearance was observed. After preparation, the samples were dried in a static oven at 105 °C for 2 h. After drying, the powders were activated in a tube furnace at a heating rate of 10 °C / min to 500 °C in a N2 atmosphere for 2 h.

[0064] The zeolite composition of each catalyst composition and the N2O performance of each catalyst composition at each temperature are shown in Table 1 below.

[0065] Catalyst compositions 1 to 5 correspond to Fe-loaded small or medium pore zeolites suitable for the first catalyst article of the present invention. Catalyst compositions C1 to C4 are comparative examples that do not fall within the scope of the Fe-loaded small or medium pore molecular sieves of the present invention.

[0066] [Table 1]

[0067] Table 1 shows the results of NO performance tests at four different temperatures: 300, 350, 375, and 400 °C. Specifically, 0.2 g of pelletized sample was tested at a total flow rate of 100 mL / min, containing 58% He, 40% Ar, 1% NO, and 1% O. The temperatures investigated ranged from 300 to 400 °C. A ramp rate of 10 °C / min was set for each temperature, followed by a 45-minute dwell. Data were analyzed using a mass spectrometer. "NO performance" refers to the NO conversion at that particular temperature, i.e., the percentage of NO consumed from the sample gas after passing through the exemplary catalyst, on a ppm basis. For the avoidance of doubt, CHA and AEI are small-pore zeolites, FER and MFI are medium-pore zeolites, and BEA is a large-pore zeolite.

[0068] As described herein, the NO performance of the catalyst compositions that may be used in the fuel combustion and exhaust gas systems of the present invention is found to be significantly higher than comparative catalyst compositions in which the zeolite has a higher SAR and / or is a large pore zeolite. Furthermore, surprisingly, the NO performance of the catalyst compositions increases as the SAR decreases. The NO performance of a CHA zeolite with an SAR of 7 and a CHA zeolite with an SAR of 10 (Catalyst Compositions 1 and 2, respectively) is comparable.

[0069] Figure 1 shows the NO conversion at 400°C for five catalyst compositions corresponding to Fe-loaded small or medium pore zeolites suitable for the first catalyst article of the present invention, compared with four comparative catalyst compositions. In other words, Figure 1 is a visual representation of the right-most column of Table 1. The bars in Figure 1, from left to right, relate to Catalyst Composition 1, Catalyst Composition 2, Catalyst Composition 3, Catalyst Composition 4, Catalyst Composition 5, Catalyst Composition C1, Catalyst Composition C2, Catalyst Composition C3, and Catalyst Composition C4, in that order.

[0070] Example 2: Catalyst compositions 2 and C3 were tested at T = 150-500 °C in a complete gas mixture containing 100 ppm NO, 4500 ppm NH, 1000 ppm NO, 10% O, and 10% HO. 0.3 g of pelletized catalyst was tested in a gas flow of 2 L / min. The results are shown in Figure 2.

[0071] It can be seen that catalyst composition 2 exhibits significantly higher NO conversion at lower temperatures than catalyst composition C3, thus indicating that the catalysts of the present invention are advantageous over the comparative catalysts even when exposed to a complete gas mixture.

[0072] The foregoing detailed description has been provided for purposes of illustration and example, and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments set forth herein will be apparent to those skilled in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. 1. A fuel combustion and exhaust gas treatment system comprising: a fuel combustor; and an exhaust gas treatment system, wherein the fuel combustor is a nitrogen-containing fuel or hydrogen combustor; and the exhaust gas treatment system comprises a first catalyst article comprising an Fe-loaded small pore molecular sieve, the small pore molecular sieve having a silica-to-alumina ratio (SAR) of 6 to 19, and the small pore molecular sieve of the first catalyst article is a small pore zeolite having a framework defined by framework type code CHA.

2. 2. The fuel combustion and exhaust gas system of claim 1, wherein the small pore molecular sieve of the first catalyst article has an SAR of 6 to 13, preferably 7 to 12, more preferably 9 to 11, and even more preferably about 10.

3. 3. The fuel combustion and exhaust gas system of claim 1, wherein the small pore molecular sieve of the first catalyst article loads at least 0.5 wt. % Fe, preferably 1.5 to 4 wt. % Fe, and more preferably about 3 wt. % Fe, based on the total weight of the Fe-loaded small pore molecular sieve.

4. The fuel combustion and exhaust gas system of any one of claims 1 to 3, wherein the first catalytic article is a flow-through monolith or a wall-flow filter.

5. The fuel combustion and exhaust gas system of any one of claims 1 to 4, wherein the exhaust gas treatment system further comprises an SCR catalyst article upstream of the first catalyst article.

6. The fuel combustion and exhaust gas system of any one of claims 1 to 5, wherein the exhaust gas treatment system further comprises an ammonia slip catalyst (ASC) article upstream of the first catalyst article.

7. 7. The fuel combustion and exhaust gas system of claim 6 when dependent on claim 5, wherein the SCR catalyst article is upstream of the ASC article.

8. 8. A fuel combustion and exhaust gas system according to any one of claims 1 to 7, wherein the exhaust gas treatment system further comprises means for injection of a nitrogenous reductant upstream of the first catalyst article, preferably upstream of the SCR catalyst article when dependent on claim 5, preferably wherein the nitrogenous reductant comprises ammonia and / or urea.

9. 6. The fuel combustion and exhaust gas system of claim 5, wherein the exhaust gas treatment system further comprises: first means for injecting a nitrogenous reductant upstream of the SCR catalyst article; and second means for injecting a nitrogenous reductant between the SCR catalyst and the first catalyst article.

10. The fuel combustion and exhaust gas system of any one of claims 1 to 9, wherein the first catalytic article is configured to be electrically heated.

11. 11. The fuel combustion and exhaust gas system of claim 1, wherein the small pore molecular sieve of the first catalyst article is substantially free of base metals other than Fe supported thereon, and preferably is substantially free of transition metals other than Fe supported thereon.

12. 12. A method for treating exhaust gas from a nitrogen-containing fuel or hydrogen combustor, comprising passing the exhaust gas through a catalytic article comprising an Fe-loaded small pore molecular sieve, the small pore molecular sieve having an SAR of 6 to 19, the small pore molecular sieve of the first catalytic article being a small pore zeolite having a framework defined by framework type code CHA, and preferably the method comprising passing the exhaust gas through an exhaust gas treatment system as defined in any one of claims 1 to 11.

13. N in exhaust gas from nitrogen-containing fuel or hydrogen combustor ２ 1. Use of an Fe-loaded small pore molecular sieve to reduce the concentration of O, wherein the small pore molecular sieve has an SAR of 6 to 19, and the small pore molecular sieve of the first catalyst article is a small pore zeolite having a framework defined by framework type code CHA.

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