System and method for treating an exhaust gas.

专利摘要:
A system for treating an exhaust gas is provided which comprises a first SCR catalyst zone comprising a large or medium pore iron loaded molecular sieve having a first ammonia storage capacity; and a second SCR catalyst zone comprising a small pore copper loaded molecular sieve having a second ammonia storage capacity, wherein the first SCR catalyst zone is disposed upstream of the second SCR catalyst zone with respect to the normal exhaust gas flow through the system and where the second ammonia storage capacity is greater than the first ammonia storage capacity. A method for using a system to treat exhaust gas is also provided.
公开号:BR112017002298B1
申请号:R112017002298-2
申请日:2015-07-30
公开日:2022-01-25
发明作者:Olivier Sonntag；Tim Genschow；Andrew Newman；Isabel Tingay；Gudmund Smedler
申请人:Johnson Matthey Public Limited Company；
IPC主号:

专利说明:

FUNDAMENTALSField of Invention
[0001] The present invention relates to a zoned catalyst system, and methods for treating combustion exhaust gas. Description of Related Technique
[0002] Combustion of hydrocarbon-based fuel in engines produces exhaust gas that largely contains relatively benign nitrogen (N2), water vapor (H2O) and carbon dioxide (CO2). But exhaust gases also contain, to a relatively small extent, harmful and/or toxic substances, such as carbon monoxide (CO) from incomplete combustion, hydrocarbons (HC) from unburned fuel, nitrogen oxides (NOx) from excessive combustion temperatures, and particulate matter (mostly soot). To lessen the environmental impact of fuel and exhaust gas released into the atmosphere, it is desirable to eliminate or reduce the amount of undesirable components, preferably by a process that, in turn, does not generate other harmful or toxic substances.
[0003] Typically, exhaust gases from lean combustion gas engines have a net oxidizing effect due to the high proportion of oxygen that is provided to ensure proper combustion of the hydrocarbon fuel. In such gases, one of the most problematic components to remove is NOx, which includes nitric oxide (NO), nitrogen dioxide (NO2) and nitrous oxide (N2O). The reduction of NOx to N2 is particularly problematic because the exhaust gas contains enough oxygen to favor oxidative reactions rather than reduction. Nevertheless, NOx can be reduced by a process commonly known as Selective Catalytic Reduction (SCR). An SCR process involves the conversion of NOx, in the presence of a catalyst and with the help of a reducing agent, such as ammonia, into elemental nitrogen (N2) and water. In an SCR process, a gaseous reductant, such as ammonia, is added to an exhaust gas stream before the exhaust gas contacts the SCR catalyst. The reductant is absorbed into the catalyst and the NOx reduction reaction takes place as the gases pass through or over the catalyzed substrate. The chemical equation for stoichiometric SCR reactions using ammonia is:

[0004] Zeolites having an exchanged transition metal are known to be useful as SCR catalysts. Conventional small pore copper exchanged zeolites are particularly useful for achieving high NOx conversion at low temperatures. However, the interaction of NH3 with NO absorbed in the transition metal of an exchanged zeolite can lead to an undesirable side reaction that produces N2O. This N2O is particularly troublesome to remove from the exhaust stream. Thus, there remains a need for improved methods that result in high NOx conversion with minimal N2O production. The present invention satisfies this need, among others. SUMMARY OF THE INVENTION
[0005] Applicants have found that the combination of at least two SCR catalytic zones, one of which contains an iron-loaded molecular sieve and the other contains a copper-loaded molecular sieve, can substantially reduce undesirable N2O production while maintaining At the same time the overall high N2 selectivity in an SCR reaction, since the iron loaded molecular sieve is upstream of the copper loaded molecular sieve and has a lower ammonia storage capacity compared to the copper loaded molecular sieve. For example, high N2 selectivity and low N2O by-product can be achieved when the iron-loaded molecular sieve has an ammonia storage capacity of not more than about 1.5 mmol NH3/g catalyst and the molecular sieve loaded with copper has an ammonia storage capacity of at least about 1.2 mmol NH3/g catalyst. Preferably, the upstream SCR catalyst zone is free or substantially free of copper and the downstream SCR catalyst zone is free or substantially free of iron.
[0006] In this way, in one aspect, there is provided a system for treating an exhaust gas comprising (a) a first SCR catalyst zone comprising an iron-loaded medium or large pore molecular sieve having a first storage capacity of iron. ammonia and (b) a second SCR catalyst zone comprising a copper loaded small pore molecular sieve having a second ammonia storage capacity; wherein the first SCR catalyst zone is arranged upstream of the second SCR catalyst zone with respect to the normal exhaust gas flow through the system and wherein the second ammonia storage capacity is greater than the first storage capacity of ammonia.
[0007] In another aspect of the invention, there is provided a method for treating an exhaust gas comprising the step of treating a mixture of ammonia and an exhaust gas derived from an internal combustion engine by bringing the mixture into contact, in series, with a first SCR catalyst zone comprising an iron-loaded molecular sieve having an ammonia storage capacity of not more than about 1.5 mmol NH3/g and a second SCR catalyst zone comprising a copper-loaded molecular sieve having an ammonia storage capacity of at least about 1.2 mmol NH3/g catalyst, provided that the iron-loaded molecular sieve has a lower ammonia storage capacity than the copper-loaded molecular sieve.BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a diagram showing an embodiment of the invention with a zoned array of SCR catalysts; Figure 2 is a diagram showing an embodiment of the invention with one or more another arrangement of zoned SCR catalysts; Figure 3 is a diagram showing an embodiment of the invention with another arrangement of zoned SCR catalysts; Figure 4 is a diagram showing an embodiment of the invention with another arrangement of SCR catalysts Figure 4A is a diagram showing an embodiment of the invention with another arrangement of zoned SCR catalysts; Figure 5 is a diagram showing an embodiment of the invention with an arrangement of zoned SCR catalysts and a ammonia; Figure 6 is a diagram showing an embodiment of the invention with another arrangement of SCR catalysts in zones comprising two substrates; Figure 6A is a diagram showing an embodiment of the invention with another arrangement of SCR catalysts in zones comprising two substrates and an ASC zone; Figure 7 is a diagram showing an embodiment of the invention with another zoned SCR catalyst arrangement, wherein one of the zones is in a body of extruded catalyst; Figure 7A is a diagram showing an embodiment of the invention with another zoned SCR catalyst arrangement, wherein one of the zones is in an extruded catalyst body; Figure 7B is a diagram showing an embodiment of the invention with another zoned SCR catalyst arrangement, wherein the zones are in an extruded catalyst body; Figure 8 is a diagram showing an embodiment of the invention with another arrangement of zoned SCR catalysts, wherein one of the zones is in an extruded catalyst body; Figure 9 is a diagram of a throughflow honeycomb substrate comprising zoned SCR catalysts; Figure 9A is a diagram of a cell of a flow-through honeycomb substrate; Figure 10 is a diagram of a system for treating exhaust gas in accordance with an embodiment of the invention; Figure 11A is a diagram of a system for treating exhaust gas in accordance with an embodiment of the invention; and Figure 11B is a diagram of another system for treating exhaust gas in accordance with an embodiment of the invention. DETAILED DESCRIPTION OF PREFERRED MODALITIES OF THE INVENTION
[0008] A system and method is provided for improving ambient air quality and, in particular, for treating exhaust gas emissions generated by power plants, gas turbines, lean combustion internal combustion engines and the like. Exhaust gas emissions are improved, at least in part, by reducing NOx concentrations over a wide operating temperature range. The NOx conversion is accomplished by bringing the exhaust gas into contact with two or more specific NH3-SCR catalysts arranged in zones.
[0009] In part, the system comprises two NH3-SCR catalyst zones: a first SCR catalyst zone comprising an iron loaded medium or large pore molecular sieve having a first ammonia storage capacity and a second ammonia storage zone. SCR catalyst comprising a copper-loaded small pore molecular sieve having a second ammonia storage capacity; wherein the first SCR catalyst zone is arranged upstream of the second SCR catalyst zone with respect to the normal exhaust gas flow through the system and wherein the second ammonia storage capacity is greater than the first storage capacity of ammonia. In one example, the iron-loaded medium or large pore molecular sieve is coated on and/or into the channel walls of the through monolith in a first zone and the copper-loaded small pore molecular sieve is coated on and/or in. of the channel walls of the overgrown monolith into a second zone, the first zone being upstream of the second zone. In certain embodiments, the first or second zone may be in the form of an extruded catalyst body and the other zone is a coating on the body. In another example, the iron loaded medium or large pore molecular sieve is coated on and/or inside a flow wall filter and the copper loaded small pore molecular sieve is coated on and/or inside the channel walls. of the passing monolith arranged downstream of the filter.
[0010] The iron-loaded molecular sieve may have, for example, an ammonia storage capacity of about 1.0 to about 1.5, about 1.0 to about 1.25, about 1, 25 to about 1.5 or about 1.35 to about 1.45 mmol Nlf/g catalyst.
[0011] The copper-loaded molecular sieve may have, for example, an ammonia storage capacity of about 1.2 to about 2.5, about 1.5 to about 2.5, about 1, 6 to about 2.0, or about 1.7 to about 1.9 mmol Nlf/g catalyst.
[0012] Here, the ammonia storage capacity is measured by Thermal Gravimetric Analysis (TGA). More particularly, ammonia storage capacity is measured by means of TGA, first purging water from the catalyst material at high temperatures (e.g. 550°C), then saturating the catalyst material with NH3 at 100°C, followed by purging with inert gas of the weakly bound NH3 from the catalyst material for about 10 minutes and then gradually increasing the temperature to at least 550°C at a rate of 5°C per minute. The total weight loss during the rise corresponds to the ammonia storage capacity of the material.
[0013] Returning to Figure 1, an embodiment of the invention is shown in which a flow-through honeycomb substrate (10) has a first catalyst zone (20) and a second catalyst zone (30), wherein the first and second catalyst zones are consecutive and in contact. The expressions "first zone" and "second zone" as used herein are indicative of the orientation of the zone on the substrate. More specifically, the zones are oriented in series such that, under normal operating conditions, the exhaust gas to be treated contacts the first zone before contacting the second zone.
[0014] The first and second SCR catalyst zones can be arranged consecutively such that one follows the other in unbroken succession (i.e. there is no catalyst or other exhaust gas treatment operation such as a filter between the first and second SCR catalyst zones). Therefore, in certain embodiments, the first SCR catalyst zone is upstream of the second SCR catalyst zone with respect to normal exhaust gas flow through or over a substrate or series of substrates.
[0015] Differences in catalyst materials of the first and second SCR catalyst zones result in different exhaust gas treatments. For example, the first SCR catalyst zone reduces NOx with lower selectivity to by-products (including low temperature N2O and high temperature NOx) and the second SCR catalyst zone efficiently reduces NOx to a greater selectivity over the first SCR catalyst zone. SCR catalyst. The synergistic effect of combining the two SCR catalyst zones improves overall catalyst performance compared to single catalyst systems or other zoned arrangements. Preferably, the first and second zones are in contact (i.e., there are no intervening catalytically active layers between the first and second SCR catalyst zones).
[0016] In Figure 9, a zoned catalytic substrate (2) is shown wherein the substrate is an alveolar throughflow monolith (100) having an inlet end (110) and an outlet end (120) with respect to to the normal direction of exhaust gas flow (1) through the substrate. The substrate has an axial length (190) that extends from the inlet end (110) to the outlet end (120). Figure 10 shows a single cell (200) of a honeycomb substrate having channel walls (110) that define open channels (120) through which exhaust gas can flow.
[0017] In general, the channel walls are preferably porous or semi-porous.
[0018] Typically, the catalyst for each zone can be a coating on the surface of the walls, a coating that partially or completely permeates the walls, incorporated directly into the wall as an extruded body, or some combination thereof.
[0019] In Figure 1, the first SCR catalyst zone (20) extends from the inlet end (110) to a first end point (29).
[0020] In general, the first end point is positioned about 10 to 90 percent, for example about 80 to 90 percent, about 10 to 25 percent, or about 20 to 30 percent, of the axial length (190).
[0021] The second SCR catalyst zone (120) typically extends from the outlet end (120) for some distance along the axial length (190), e.g. about 20 to 90 percent, e.g. about 60 to about 80 percent, or about 50 to about 75 percent, of the axial length (190). Preferably, the second SCR catalyst zone extends to at least the first end point such that the first and second SCR catalyst zones are in contact.
[0022] The axial length is preferably less than 24 inches, such as about 2.54 cm (1”) to about 60.96 cm (24 inches), about 7.62 cm (3”) to about 30.48 cm (12 inches), or about 7.62 cm (3”) to about 15.24 cm (6 inches).
[0023] In Figure 2, the first SCR catalyst zone (20) partially overlaps the second SCR catalyst zone (30). In Figure 3, the second SCR catalyst zone (30) partially overlaps the first SCR catalyst zone (20).
[0024] The overlap is preferably less than 90 percent of the axial length of the substrate, e.g. about 80 to about 90 percent, less than about 40, about 40 to about 60, about 10 to about 60 15 percent, or about 10 to about 25 percent. For embodiments in which the second SCR catalyst zone overlaps the first SCR catalyst zone, the overlap may be greater than 50 percent of the axial length, such as 80 to 90 percent. For embodiments in which the first SCR catalyst zone overlaps the second SCR catalyst zone, the overlap is preferably less than 50 percent of the axial length, for example, about 10 to 20 percent.
[0025] In Figure 4, the first SCR catalyst zone (20) completely overlaps the second SCR catalyst zone (30). For such embodiments, exhaust gas first contacts the first SCR catalyst zone, and is at least partially treated by it. At least a portion of the exhaust gas permeates through the first SCR catalyst zone, where it contacts the second SCR catalyst zone and is further treated. At least a portion of the treated exhaust gas permeates back through the first SCR catalyst zone, enters the open channel, and exits the substrate. Figure 4 shows an embodiment in which both the first and second SCR catalyst zones span the entire axial length of the substrate.
[0026] Figure 4A shows an embodiment in which the second SCR catalyst zone extends from the outlet end to less than the full axial length of the substrate and the first SCR catalyst zone extends the entire axial length of the substrate, thus completely overlapping the second SCR catalyst zone.
[0027] Figure 5 shows another embodiment of the invention. Here, a third catalyst zone is proximal to, and preferably extends from, the exit end of the substrate.
[0028] The third catalyst zone typically comprises an oxidation catalyst, preferably a catalyst effective to oxidize ammonia.
[0029] In general, the catalyst comprises one or more platinum group metals (PGMs), such as Pt, Pd, or a combination thereof, preferably on a metal oxide support, such as alumina.
[0030] The combination of the second and third catalyst zones in a layered arrangement serves as an unreacted ammonia catalyst, wherein at least a portion of the excess ammonia not consumed by the upstream SCR reaction passes through the second zone to the third catalyst zone, where it is oxidized to H2O and secondary NOx. The H2O and secondary NOx pass back through the second catalyst zone where at least a portion of the secondary NOx is reduced to N2 and H2O via an SCR-type reaction.
[0031] Preferably, the first and second SCR catalyst zones are arranged consecutively such that the first SCR catalyst zone contacts the second SCR catalyst zone.
[0032] Typically, the first and second SCR catalyst zones are coated or otherwise incorporated into separate substrates, which are arranged in an exhaust gas treatment system such that the first and second catalyst zones are SCRs are in series and are either in contact or a short distance apart with no intervening exhaust gas treatment catalyst.
[0033] Where two substrates are used, the substrates can be the same or different substrates. For example, the first substrate can be a flow-through wall filter and the second substrate can be a through-flow well, or the first and second substrates can be through-flow wells.
[0034] When two substrates are used, preferably when the first and second substrates are through-flow cells, the first substrate may have a higher porosity than the second substrate, the first and second substrates may be of different compositions or have a different cell density and/or the first and second substrates may have different lengths.
[0035] In Figure 6, the first and second SCR catalyst zones are arranged on separate substrates, which are arranged in an exhaust gas treatment system such that the first and second SCR catalyst zones are in contact with each other. series and are adjacent but not in direct contact.
[0036] The maximum distance between the first and second substrates is preferably less than 5.08 centimeters (2 inches), more preferably less than 2.54 centimeters (one inch) and preferably there are no intervening substrates, filters or catalyst materials between the first and second SCR catalyst zones and/or between the first and second substrates.
[0037] In Figure 6A, the second substrate additionally comprises an adjacent layer of ammonia oxidation catalyst (40) which extends from the exit end of the substrate to a length less than the total length of the substrate. The second SCR catalyst zone completely covers the oxidative catalyst and preferably extends the length of the substrate.
[0038] The first or second SCR catalyst zone may comprise an extruded catalyst material. The embodiment shown in Figure 7, for example, comprises a first SCR catalyst zone (26) in the form of a coating on and/or within a portion of an extruded catalyst substrate. The extruded catalyst substrate, in turn, comprises the second SCR catalyst zone (16). The first SCR catalyst zone is arranged on the substrate such that it is upstream of the second SCR catalyst zone with respect to the normal flow of exhaust gas (1). The catalytically active substrate in zone (16) comprises a catalytically active material similar to the other second SCR catalyst zones described herein.
[0039] In Figure 7, the first SCR catalyst zone extends from the inlet end to less than the full length of the substrate.
[0040] In Figure 7A, the first SCR catalyst zone (26) completely covers the catalytically active substrate comprising the second SCR catalyst zone.
[0041] In Figure 7B, a catalytically active substrate (300), for example a flow through honeycomb substrate formed from an extruded catalytic material, is coated with a first SCR catalyst zone (310) and a second catalyst zone of SCR (330).
[0042] Typically, the first SCR catalyst zone extends from the inlet end (312) to a first end point (314) that is positioned about 10 to 80 percent, e.g., about 50-80 percent. percent, about 10 to 25 percent, or about 20 to 30 percent of the axial length (390).
[0043] The second SCR catalyst zone typically extends from the outlet end (344) to a second end point (332) which is positioned about 20 to 80 percent, e.g., about 20 to 40 percent , about 60 to about 80 percent, or about 50 to about 75 percent of the axial length (390).
[0044] Overall, the first and second SCR catalyst zones are not in direct contact and thus there is a gap (320) between the upstream and downstream zone. Preferably, this gap does not contain a layer of catalyst, but is instead directly arranged for the exhaust gas to be treated. The exhaust gas contacts the catalytic body in the gap where the exhaust gas is treated, for example, to selectively reduce a portion of NOx in the exhaust gas.
[0045] The clearance, which is defined by the first end point (314) and the second end point (332), is preferably less than 75 percent of the axial length, for example, about 40 to about 60, about from 10 to about 15 percent, or about 10 to about 25 percent of the axial length (390).
[0046] An optional NH3 oxidation catalyst may be coated on and/or into the substrate (300) in a zone extending from the outlet end (344) to the inlet end (312) for a length that is equal to or less than the length of the downstream zone. The optional NH3 oxidation catalyst is preferably an adjacent layer, which is completely covered by the catalyst composition forming the downstream zone.
[0047] The compositions of catalysts in the upstream zone, the extruded body and the downstream zone are not particularly limited as long as at least two of the upstream zones, the extruded body and the downstream zone fit the first and second zones. , as defined herein, i.e. the iron loaded molecular sieve in the first zone has an ammonia storage capacity of not more than about 1.5 mmol NH3/g catalyst, the copper loaded molecular sieve in the second zone has an ammonia storage capacity of at least about 1.2 mmol NH3/g catalyst and the copper loaded molecular sieve has an ammonia storage capacity that is greater than the corresponding ammonia storage capacity of the loaded molecular sieve with iron.
[0048] In one example, the upstream zone corresponds to the first zone and the downstream zone corresponds to the second. The extruded catalyst body preferably comprises another type of SCR catalyst, such as vanadium, preferably supported on a metal oxide, such as TiOz, and optionally comprising one or more additional metals, such as tungsten.
[0049] In another example, the extruded catalyst body corresponds to the first zone and the downstream zone corresponds to the second zone. In this example, the upstream zone may comprise another type of catalyst. In another example, the upstream zone corresponds to the first zone and the extruded body corresponds to the second zone. In this example, this downstream zone may comprise another type of catalyst.
[0050] Figure 8 shows another embodiment in which a first catalytic zone (17) is part of an extruded catalytic body and the second SCR catalyst zone (37) is a coating on and/or within a portion of the SCR substrate. extruded catalyst. Again, the first zone is arranged upstream of the second zone with respect to the normal flow of exhaust gas (1) and the catalytically active substrate in zone (17) comprises a catalytically active material similar to the other first zones described herein.
[0051] The first catalytic zone comprises a first NH3-SCR catalyst composition. The first NH3-SCR catalyst comprises an iron-loaded molecular sieve as a catalytically active component, but may include other components, particularly catalytically inactive components, such as binders.
[0052] As used herein, a "catalytically active" component is one that directly participates in the catalytic reduction of NOx and/or oxidation of NH3 or other nitrogenous-based SCR reductants. By a corollary, a “catalytically inactive” component is one that does not directly participate in the catalytic reduction of NOx and/or oxidation of NH3 or other nitrogenous-based SCR reductants.
[0053] Useful molecular sieves are crystalline or quasi-crystalline materials which may be, for example, aluminosilicates (zeolites) or silicoaluminophosphates (SAPOs).
[0054] Such molecular sieves are constructed of tetrahedral repeating units of SiO4, AlO4 and, optionally, PO4 linked, for example, in rings, to form structures having regular intracrystalline cavities and molecular-sized channels. The specific arrangement of tetrahedral units (ring members) gives rise to the molecular sieve structure and, by convention, each unique structure is assigned a unique three-letter code (e.g. “CHA”) by the International Zeolite Association (IZA).
[0055] Examples of useful molecular sieve fours include large pore structures (i.e. having a minimum ring size of 12 members), medium pore structures (i.e. having a minimum ring size of 10 members) and small pore (i.e. having a minimum ring size of 8 members). Examples of structures include BEA, MFI, CHA, AEI, LEV, KFI, MER, RHO, ERI, OFF, FER, and AFX. Molecular sieve can also be an intergrowth of two or more structures, such as AEI and CHA. In certain embodiments, the first and/or second zones independently may comprise a combination of two or more molecular sieves. Preferred combinations have at least one molecular sieve having a CHA structure and, more preferably, a majority of the CHA structure.
[0056] Particularly useful molecular sieves are small pore zeolites. As used herein, the term "small pore zeolite" means a zeolite structure having a maximum ring size of eight tetrahedral atoms. Preferably, the primary crystalline phase of the molecular sieve is constructed of one or more small pore structures, although other crystalline phases of the molecular sieve may also be present. Preferably, the primary crystalline phase comprises at least about 90 weight percent, more preferably at least about 95 weight percent, and even more preferably at least about 98 or at least about 99 weight percent of the crystal structure. small pore molecular sieve, based on the total amount of molecular sieve material.
[0057] In some examples, the small pore zeolite for use in the present invention has a pore size in at least one dimension of less than 4.3 Å.
[0058] Small pore zeolite typically has a structure selected from the group consisting of: ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI , EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI , YUG and ZON. Preferred zeolite structures are selected from AEI, AFT, AFX, CHA, DDR, ERI, LEV, KFI, RHO and UEI.
[0059] For certain applications, preferred zeolite structures are selected from AEI, AFT and AFX, particularly AEI.
[0060] In certain application, a preferred zeolite structure is CHA. In certain applications, an ERI structure is preferred.
[0061] Particular zeolites that are useful for the present invention include SSZ-39, Mu-10, SSZ-16, SSZ-13, Sigma-1, ZSM-34, NU-3, ZK-5 and MU-18.
[0062] Other useful molecular sieves include SAPO-34 and SAPO-18.
[0063] Small pore zeolites are particularly useful in the second NH3-SCR catalyst.
[0064] In a preferred embodiment, the second NH3-SCR catalyst comprises an aluminosilicate having a copper-loaded CHA structure (e.g. SSZ-13) and the first NH3-SCR catalyst comprises an iron-loaded large pore zeolite , such as Beta iron or Beta isomorph.
[0065] Preferred aluminosilicates have a silica to alumina ratio (SAR) of about 10 to about 50, e.g. about 15 to about 30, about 10 to about 15, 15 to about 20, about from 20 to about 25, about 15 to about 18, or about 20 to about 30. Preferred SAPOs have a SAR of less than 2, for example, about 0.1 to about 1.5 or about 0.5 to about 1.0. The SAR of a molecular sieve can be determined by conventional analysis. This relationship should represent, as closely as possible, the relationship in the rigid atomic structure of the molecular sieve crystal and exclude silicon or aluminum in the binder or in the cationic form or otherwise in the channels. Since it can be difficult to directly measure the SAR of the molecular sieve after it has been combined with a binder material, particularly an alumina binder, the SAR value described here is expressed in terms of the SAR of the molecular sieve per se, i.e. before of the combination of the zeolite with the other components of the catalyst.
[0066] In another example, the second molecular sieve zone is a SAPO having a SAR less than 1.
[0067] The molecular sieve may include metals of the structure other than aluminum (ie, metal substituted zeolites). As used herein, the term "substituted metal" in connection with a molecular sieve means a molecular sieve structure in which one or more atoms of the aluminum or silicon structure have been replaced by the substituent metal. In contrast, the term “metal exchanged” means a molecular sieve in which one or more ionic species associated with the zeolite (e.g. H+, NH4+, Na+, etc.) have been replaced by a metal (e.g. a metal ion or free metal, such as metal oxide), where the metal is not incorporated as an atom of the molecular sieve structure (e.g., T atom), but is instead incorporated into the molecular pores or the outer surface of the molecular sieve. molecular sieve structure. Exchanged metal is a type of "extrastructure metal", which is a metal that resides in the molecular sieve and/or on at least a portion of the molecular sieve surface, preferably as an ionic species, does not include aluminum and does not include atoms that constitute the molecular sieve structure. The term "metal-loaded molecular sieve" means a molecular sieve that includes one or more extrastructure metals. As used herein, the terms "aluminosilicate" and "silicoaluminophosphate" are unique to metal substituted molecular sieves.
[0068] The iron-loaded or copper-loaded molecular sieves of the present invention comprise the metal disposed on and/or within the molecular sieve material as an extrastructure metal. Preferably, the presence and concentration of the iron or copper facilitates the treatment of exhaust gases, such as the exhaust gas of a diesel engine, including processes such as NOx reduction, NH3 oxidation and NOx storage, while also suppressing time the formation of N2O.
[0069] Unless otherwise specified, the amount of iron loaded onto a molecular sieve and the concentration of iron in the catalyst are referenced in terms of the iron per total weight of the corresponding molecular sieve and thus depend on the amount of loading of catalytic coating of the catalyst on the substrate or the presence of other materials in the catalytic coating of the catalyst. Likewise, the amount of copper loaded onto a molecular sieve and the concentration of copper on the catalyst are referenced in terms of copper per total weight of the corresponding molecular sieve and are thus independent of the amount of catalytic coating loading of the catalyst on the substrate or the presence of other materials in the catalytic coating of the catalyst.
[0070] Extrastructure copper may be present in the molecular sieve of the second zone at a concentration of from about 0.1 to about 10 weight percent (wt%) based on the total weight of the molecular sieve, for example from about 0.5% by weight to about 5% by weight, from about 0.5 to about 1% by weight, from about 1 to about 5% by weight, about 2.5% by weight at about 3.5% by weight and about 3% by weight to about 3.5% by weight.
[0071] Extrastructure iron may be present in the molecular sieve of the first zone at a concentration of from about 0.1 to about 10 weight percent (wt%) based on the total weight of the molecular sieve, for example from about 0.5% by weight to about 5% by weight, from about 1 to about 5% by weight, about 3% by weight to about 4% by weight, and about 4% by weight to about of 5% by weight.
[0072] Typically, the first zone has a higher metal charge concentration (based on zeolite weight) compared to the second zone.
[0073] In addition to the iron and copper, the molecular sieve may additionally comprise one or more additional extrastructure metals, provided that the additional extrastructure metal is present in a minor amount (i.e. < 50% by mol, such as about 1 to 30 mol %, about 1 to 10 mol % or about 1 to 5 mol %) with respect to iron or copper.
[0074] The additional extrastructure metal can be any of the recognized catalytically active metals that are used in the catalyst industry to form metal-exchanged molecular sieves, particularly those metals that are known to be catalytically active to treat exhaust gases derived from a combustion process. .
[0075] Particularly preferred are metals useful in NOx reduction and storage processes. Examples of such metals include nickel, zinc, iron, copper, tungsten, molybdenum, cobalt, titanium, zirconium, manganese, chromium, vanadium, niobium metals, as well as tin, bismuth and antimony; platinum group metals such as ruthenium, rhodium, palladium, indium, platinum, and precious metals such as gold and silver.
[0076] Preferred transition metals are base metals and preferred base metals include those selected from the group consisting of chromium, manganese, iron, copper, cobalt, nickel and mixtures thereof.
[0077] In certain examples of the invention, the iron-loaded or copper-loaded molecular sieves are free of platinum group metals.
[0078] In certain examples of the invention, the iron-loaded or copper-loaded molecular sieves are free of alkali metals and alkaline earth metals.
[0079] In certain examples of the invention, the iron-loaded molecular sieve is free of transition metals other than iron, and the copper-loaded molecular sieve is free of transition metals other than copper.
[0080] Preferably, the iron and copper are highly dispersed in the molecular sieve crystal, preferably without a high temperature treatment of the metal loaded molecular sieve.
[0081] The transition metal charge is preferably ion replacement completely and/or is preferably less than can be accommodated by the molecular sieve support replacement sites.
[0082] Preferably, the catalyst is free or substantially free of massive iron oxide or massive copper oxide, free or substantially free of iron or copper species on the outer molecular sieve crystal surfaces, and/or free or substantially free of metallic agglomerates of iron or copper, as measured by temperature programmed reduction (TPR) analysis and/or UV-vis analysis.
[0083] In one example, a metal-exchanged molecular sieve is created by mixing the molecular sieve, for example an H-shaped molecular sieve or an NH4 molecular sieve, into a solution containing soluble precursors of the catalytically active metal(s). (s). The pH of the solution can be adjusted to induce precipitation of catalytically active metal cations on or within the molecular sieve structure (but not including the molecular sieve structure. For example, in a preferred embodiment, a molecular sieve material is immersed in a solution containing a metal nitrate or metal acetate for a time sufficient to allow incorporation of the catalytically active metal cations into the molecular sieve structure by ion exchange. Unexchanged metal ions are precipitated. Depending on the application, a portion of the ions unexchanged can remain in the molecular sieve material as free metals. The metal exchanged molecular sieve can then be washed, dried and calcined. The calcined material can include a certain percentage of iron or copper as iron oxide or copper oxide, respectively , residing on the molecular sieve surface or within the molecular sieve cavities.
[0084] In general, ion exchange of the catalytic metal cation on or on the molecular sieve can be carried out at room temperature or at a temperature up to about 80°C over a period of about 1 to 24 hours at a pH of about of 7. The resulting catalytic molecular sieve material is preferably dried and then calcined at a temperature of at least about 500°C.
[0085] The catalyst composition may comprise the combination of iron or copper and at least one alkali metal or alkaline earth metal, wherein the iron or copper and alkali metal or alkaline earth(s) are disposed on or within the molecular sieve material. . The alkali metal or alkaline earth metal may be selected from sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium or some combination thereof. Preferred alkali or alkaline earth metals include calcium, potassium and combinations thereof.
[0086] Alternatively, the catalyst composition is essentially free of magnesium and/or barium. In certain embodiments, the catalyst is essentially free of any alkali metal or alkaline earth metal other than calcium and potassium. In certain embodiments, the catalyst is essentially free of any alkali metal or alkaline earth metal other than calcium. And, in certain other embodiments, the catalyst is essentially free of any alkali metal or alkaline earth metal, except potassium.
[0087] As used herein, the expression "essentially free" means that the material does not have a considerable amount of the particular metal. That is, the particular metal is not present in an amount that would affect the material's basic physical and/or chemical properties, particularly with respect to the material's ability to selectively reduce or store NOx. In certain embodiments, the molecular sieve material has an alkali content of less than 3 weight percent, more preferably less than 1 weight percent, and even more preferably less than 0.1 weight percent.
[0088] The alkali metal and/or alkaline earth metal (collectively AM) may be present in the molecular sieve material in an amount relative to the amount of iron or copper in the molecular sieve. Preferably, the Fe or Cu and AM are present, respectively, in a molar ratio of about 15:1 to about 1:1, for example, about 10:1 to about 2:1, about 10:1 to about 3:1, or about 6:1 to about 4:1, particularly where AM is calcium.
[0089] In certain embodiments that include an alkali metal and/or alkaline earth metal, such as calcium, the amount of iron or copper present is less than 2.5 percent by weight, for example, less than 2 percent by weight or less than 1 percent by weight, based on molecular sieve weight.
[0090] In certain embodiments, the copper loaded molecular sieve of the second zone contains an alkali metal or alkaline earth metal, particularly calcium, and the iron loaded molecular sieve of the first zone is essentially free of an alkali metal or alkaline earth metal. For such embodiments, the relative cumulative amount of iron or copper and alkali metal and/or alkaline earth (AM) present in the second zone molecular sieve material is relative to the amount of aluminum in the molecular sieve, namely the aluminum of the structure. As used herein, the ratio (TM+AM): Al is based on the relative molar amounts of transition metal (TM), (eg, both Cu and Fe) + AM to the molar structure Al in the corresponding molecular sieve. In certain embodiments, the second zone molecular sieve has a (TM+AM): Al ratio of no more than about 0.6, particularly where AM is calcium. In certain embodiments, the ratio (TM+AM): Al is at least 0.3, for example, about 0.3 to about 0.6. In such embodiments, the TM:Al ratio of the catalyst in the first zone is about 0.1 to about 0.375, provided that the TM:Al ratio in the catalyst in the first zone is less than the (TM+AM):Al ratio in the first zone. second zone catalyst.
[0091] In certain embodiments, the relative cumulative amount of iron or copper and alkali metal and/or alkaline earth (AM) is present in the second zone molecular sieve material in an amount with respect to the amount of aluminum in the molecular sieve, the namely, the aluminum of the structure. As used herein, the ratio (TM + AM): Al is based on the relative molar amounts of TM + AM to the Al of the structure on the corresponding molecular sieve. In certain embodiments, the catalyst material has a (TM+AM): Al ratio of no more than about 0.6. In certain embodiments, the ratio (TM+AM): Al is not more than 0.5, for example, about 0.05 to about 0.5, about 0.1 to about 0.4, or about from 0.1 to about 0.2.
[0092] The alkali metal/alkaline earth can be added to the molecular sieve by any known technique, such as ion exchange, impregnation, isomorph substitution, etc. The iron or copper and the alkali or alkaline earth metal can be added to the molecular sieve material in any order (e.g. the metal can be exchanged before, after or simultaneously with the alkali metal or alkaline earth metal), but preferably the alkali metal or alkaline earth is added before or simultaneously with iron or copper.
[0093] The catalytic articles of the present invention are applicable for heterogeneous catalytic reaction systems (ie, solid catalyst in contact with a gaseous reactant). To improve contact surface area, mechanical stability and/or liquid flow characteristics, SCR catalysts are arranged on and/or within a substrate, such as cellular cordierite brick.
[0094] In general, one or more of the catalyst compositions are applied to the substrate as a catalytic coating(s).
[0095] Alternatively, one or more of the catalyst compositions are combined together with other components, such as fillers, binders and reinforcing agents, into an extrudable paste which is then extruded through a die to form a honeycomb brick.
[0096] Certain aspects of the invention provide a catalytic coating. The catalytic coating comprising an iron-loaded or copper-loaded molecular sieve catalyst described herein is preferably a solution, suspension or slurry. Suitable coatings include surface coatings, coatings that penetrate a portion of the substrate, coatings that permeate the substrate, or some combination thereof.
[0097] A catalytic coating may also include non-catalytic components such as fillers, binders, stabilizers, rheology modifiers and other additives, including one or more of alumina, silica, silica alumina, titania, zirconia and non-molecular sieve ceria. In certain embodiments, the catalyst composition may comprise pore-forming agents such as graphite, cellulose, starch, polyacrylate and polyethylene and the like. These additional components do not necessarily catalyze the desired reaction, but, on the contrary, improve the effectiveness of the catalytic material, for example, increasing its operating temperature range, increasing the contact surface area of the catalyst, increasing the adhesion of the catalyst to a substrate. , etc. In preferred embodiments, the catalytic coating charge is > 0.3 g/in 3 , such as > 1.2 g/in 3 , > 1.5 g/in 3 , > 1.7 g/in 3 , or > 2.00 g/in 3 in3 and preferably < 3.5 g/in 3 , such as < 2.5 g/in 3 . In certain embodiments, the catalytic coating is applied to a substrate at a load of about 0.8 to 1.0 g/in 3 , 1.0 to 1.5 g/in 3 , 1.5 to 2.5 g/in 3 , or 2.5 to 3.5 g/in 3 .
[0098] Preferred substrates, particularly for mobile applications, include pass-through monoliths having a so-called honeycomb geometry that comprises multiple adjacent, parallel channels that are open at both ends and generally extend from the entrance face to the exit face. of the substrate and typically result in a high surface area-to-volume ratio.
[0099] For certain applications, the alveolar breakthrough monolith preferably has a high cell density, for example, about 600 to 1,000 cells per square inch and/or an average inner wall thickness of about 0.18 to 0, 35 mm, preferably about 0.20 to 0.25 mm. For certain other applications, the alveolar crossover flow monolith has a low cell density of about 150 to 600 cells per square inch, such as about 200 to 400 cells per square inch.
[00100] Preferably, the alveolar monoliths are porous. In addition to cordierite, silicon carbide, silicon nitride, ceramic and metal, other materials that can be used for the substrate include aluminum nitride, silicon nitride, aluminum titanate, α-alumina, mullite, e.g. acicular mullite, polucita, a thermet, such as AhOsZFe, AhOs/Ni or B4CZFe, or composites comprising segments of any two or more thereof. Preferred materials include cordierite, silicon carbide and alumina titanate.
[00101] Preferred filter substrates include diesel particulate filters and diesel particulate filters preferred for use in mobile applications include flow wall filters such as flow wall ceramic monoliths. Other filter substrates include flow-through filters, such as metal or ceramic foam or fibrous filters.
[00102] In addition to cordierite, silicon carbide, and ceramics, other materials that can be used for the porous substrate include, but are not limited to, alumina silica, aluminum nitride, silicon nitride, aluminum titanate, α-alumina , mullite, pollucite, zirconium, zirconia, spinel, borides, feldspar, titania, fused silica, borides, ceramic fiber composites, mixtures of any of the same, or composites comprising segments of any two or more of the same. Particularly preferred substrates include cordierite, silicon carbide and aluminum titanate (AT), where AT is the predominant crystalline phase.
[00103] The porous walls of a wall flow filter have an inlet side and an outlet side with respect to the typical direction of exhaust gas flow through the walls. The inlet side has an inlet surface which is exposed to channels open towards the front of the substrate and the outlet side has an outlet surface which is exposed to channels open towards the rear of the substrate.
[00104] Wall flow filter substrates for diesel engines typically contain about 100 to 800 cpsi (channels per square inch), e.g. about 100 to about 400 cpsi, about 200 to about 300 cpsi , or about 500 to about 600 cps.
[00105] The walls typically have an average wall thickness of about 0.1 to about 1.5 mm, for example, about 0.15 to about 0.25 mm, about 0.25 to about 0.25 to about 0.25 mm. 0.35 mm, or about 0.25 to about 0.50 mm.
[00106] Wall flow filters for use with the present invention preferably have an efficiency of at least 70%, at least about 75%, at least about 80%, or at least about 90%. In certain embodiments, the efficiency will preferably be from about 75 to about 99%, about 75 to about 90%, about 80 to about 90%, or about 85 to about 95%.
[00107] The filter utility range of porosity and average pore size is not particularly limited, but is correlated with, or is used to determine, the particle size and viscosity of the catalyst coating. As described herein, the porosity and average pore size of the filter substrate are determined based on an empty filter (eg without a catalyst coating).
[00108] In general, the porosity of the substrate is at least about 40%, more preferably at least about 50%, for example, about 50 to about 80%, about 50 to about 70 percent, or about from 55 to about 65 percent. Porosity can be measured by any suitable means, including mercury porosimetry.
[00109] Overall, the average pore size of the substrate is about 8 to about 40 μm, e.g. about 8 to about 12 μm, about 12 to about 20 μm, or about 15 to about 12 μm. of 25 μm. In certain embodiments, at least about 50% and more preferably at least about 75% of the pores are in these ranges, based on total pore volume and/or total number of pores. Average pore size can be determined by any acceptable means, including mercury porosimetry.
[00110] It may be preferable for the filter substrate to have an average pore size of about 12 to about 15 µm and a porosity of about 50 to about 55%.
[00111] It may be preferable for the filter substrate to have an average pore size of about 18 to about 20 µm and a porosity of about 55 to about 65%.
[00112] The catalytic coating of the catalyst of the first SCR catalyst zone can be loaded on the inlet side of the filter walls, the outlet side of the filter walls, partially or completely permeate the filter walls, or some combination thereof .
[00113] In certain embodiments, the filter is the substrate for the first or second SCR catalyst zone as described herein. For example, a flow wall filter can be used as a substrate for the first zone and a through flow cell can be used as the substrate for the second zone. In another example, a throughflow alveolus can be used as the substrate for the first zone and a wallflow filter can be used as the substrate for the second zone. In such embodiments, the wall flow substrate may additionally comprise an NH3 oxidation catalyst to form an ASC zone.
[00114] In certain embodiments, the invention is an article of catalyst made by a process described herein. In a particular embodiment, the catalyst article is produced by a process that includes the steps of applying the first SCR catalyst composition, preferably as a catalytic coating, to a substrate as a layer, both before and after the second SCR catalyst composition. SCR catalyst, preferably as a catalytic coating, has been applied to the substrate.
[00115] In certain embodiments, the second SCR catalyst composition is arranged on the substrate as a top layer and another composition, such as an oxidation catalyst, reduction catalyst, NOx removal component, or storage component, is arranged on the substrate as a base layer.
[00116] Overall, the production of an extruded solid body containing the first or second SCR catalyst composition involves combining the molecular sieve and iron (both separately and together as a metal-exchanged molecular sieve), a binder, a compound optional organic viscosity-enhancing slurry is then added to a binder/matrix component or a precursor thereof and, optionally, one or more of stabilized ceria and inorganic fibers. The combination is compacted in a mixing or kneading apparatus or an extruder. Blends have organic additives such as binders, pore formers, plasticizers, surfactants, lubricants, dispersants as processing aids to improve wetting and therefore produce a uniform batch. The resulting plastic material is then molded, in particular using an extrusion die or an extruder, including an extrusion mold, and the resulting molds are dried and calcined. Organic additives are “burned” during calcinations of the extruded solid. A metal promoted zeolite catalyst may also be coated with a catalytic coating or otherwise applied to the extruded solid as one or more sublayers that reside on the surface or fully or partially penetrate the extruded solid. Alternatively, a metal-promoted zeolite can be added to the slurry prior to extrusion. Preferably, the iron-loaded or copper-loaded molecular sieve is dispersed completely, and preferably uniformly completely throughout the extruded catalyst body.
[00117] Metal-promoted zeolite-containing extruded solid bodies in accordance with the present invention generally comprise a unitary structure in the form of an alveolus having parallel, uniformly sized channels extending from a first end to a second end thereof. . Channel walls that define the channels are porous. Typically, an outer "skin" surrounds a plurality of channels in the extruded solid body. The extruded solid body can be formed of any desired cross section, such as circular, square or oval. Individual channels in the plurality of channels can be square, triangular, hexagonal, circular, etc.
[00118] The catalytic article described here can promote the reaction of a nitrogenous reductant, preferably ammonia, with nitrogen oxides to selectively form elemental nitrogen (N2) and water (H2O). Examples of such nitrogen reductants include ammonia and ammonium hydrazine or any suitable ammonia precursor, such as urea ((NH2)2CO), ammonium carbonate, ammonium carbamate, ammonium hydrogencarbonate or ammonium formate. The SCR process of the present method can result in a NOx (NO and/or NO2) conversion of at least 75%, preferably at least 80%, and more preferably at least 90% over a wide temperature range (e.g., about from 150 to 700°C, about 200 to 350°C, about 350 to 550°C, or about 450 to 550°C).
[00119] Above all, the use of catalysts in zones according to the present invention generates low amounts of N2O by-product compared to conventional SCR catalysts. That is, the SCR process of the present method may result in low N2O generation, based on NO and/or NO2 at the SCR input.
[00120] For example, the relative ratio of NO concentration from the inlet to the SCR catalyst compared to the N2O concentration from the outlet after the SCR catalyst is greater than about 25, greater than about 30 (for example, about 30 to about 40), greater than about 50, greater than about 80, or greater than about 100 over a wide temperature range (e.g., about 150 to 700°C, about 200 to 350°C, about 350 to 550°C, or about 450 to 550°C). In another example, the relative ratio of inlet NO2 concentration to the SCR catalyst compared to the leaving N2O concentration after the SCR catalyst is greater than about 50, greater than about 80, or greater than about 100 over a wide temperature range (e.g., about 150 to 700°C, about 200 to 350°C, about 350 to 550°C, or about 450 to 550°C).
[00121] The metal catalyst loaded molecular sieve described herein may promote the storage or oxidation of ammonia or may be coupled with an oxidation catalyst such as platinum and/or palladium supported on alumina, may also promote the oxidation of ammonia and limiting the undesirable formation of NOx by the oxidation process (ie, an unreacted ammonia catalyst (ASC)).
[00122] It may be preferable that the catalytic article of the present invention contains an ASC zone at the exit end of the substrate.
[00123] Additionally or alternatively, an unreacted ammonia catalyst can be arranged in a separate brick downstream of the zoned SCR catalysts. These separate bricks may be adjacent and in contact with each other, or separated by a specific distance, provided they are in fluid communication with each other and provided that the SCR catalyst brick is disposed upstream of the SCR catalyst brick. unreacted ammonia.
[00124] Typically, the SCR and/or ASC process is carried out at a temperature of at least 100°C.
[00125] In general, the process(es) takes place at a temperature of about 150°C to about 750°C. In a particular embodiment, the temperature range is from about 175 to about 550°C. In another embodiment, the temperature range is 175 to 400°C. In yet another embodiment, the temperature range is 450 to 900°C, preferably 500 to 750°C, 500 to 650°C, 450 to 550°C, or 650 to 850°C.
[00126] According to another aspect of the invention there is provided a method for reducing NOX compounds and/or oxidizing NH3 in a gas, which comprises contacting the gas with a catalyst described herein for a time sufficient to reduce the level of NOx compounds in the gas. Methods of the present invention may comprise one or more of the following steps: (a) accumulating and/or burning soot that is in contact with a filter inlet; (b) introducing a nitrogenous reducing agent into the exhaust gas stream prior to contact with the SCR catalyst, preferably with no intervening catalytic step involving the NOx treatment and the reductant; (c) generating NH3 over a lean NOx scavenger or NOx separator catalyst and preferably using such NH3 as a reductant in a downstream SCR reaction; (d) contacting the exhaust gas stream with a DOC to oxidize the soluble organic fraction based on hydrocarbon (SOF) and/or carbon monoxide to CO2, and/or oxidize NO to NO2 which, in turn, can be used to oxidize particulate matter in particulate filter; and/or reduce particulate matter (PM) in the exhaust gas; (e) contacting the exhaust gas with one or more downstream SCR catalyst devices (through-flow filter or substrate) in the presence of a reducing agent to reduce the NOx concentration in the exhaust gas; and (f) bringing the exhaust gas into contact with an unreacted ammonia catalyst, preferably downstream of the SCR catalyst to oxidize most, if not all, of the ammonia before emitting the exhaust gas to the atmosphere or passing the gas exhaust through a recirculation loop before the exhaust gas enters/re-enters the engine.
[00127] It may be preferable that all or at least a portion of the nitrogen-based reductant, particularly NH3, for consumption in the SCR process, can be supplied by a NOX absorbent catalyst (NAC), a lean NOX separator ( LNT), or a NOX storage/reduction catalyst (NSRC), (collectively NAC) disposed upstream of the SCR catalyst. In certain embodiments, the NAC is coated on the same flow-through substrate as the zoned SCR catalyst. In such embodiments, the NAC and SCR catalysts are coated in series, with the NAC being upstream of the SCR zones.
[00128] NAC components used in the present invention include a combination of catalysts of a base material (such as alkali metal, alkaline earth metal or a rare earth metal, including alkali metal oxides, alkaline earth metal oxides and combinations thereof) and a precious metal (such as platinum) and, optionally, a component of the reduction catalyst, such as rhodium. Specific types of base material used in NAC include cesium oxide, potassium oxide, magnesium oxide, sodium oxide, calcium oxide, strontium oxide, barium oxide and combinations thereof. The precious metal is preferably present at about 10 to about 200 g/ft 3 , such as 20 to 60 g/ft 3 . Alternatively, the precious metal of the catalyst is characterized by the average concentration, which can be from about 40 to about 100 grams/ft3 .
[00129] Under certain conditions, during periodically rich regeneration events, NH3 can be generated on a catalyst of the NOx absorber. The SCR catalyst downstream of the NOx absorber catalyst can improve the overall NOx reduction efficiency of the system. In the combined system, the SCR catalyst is able to store the NH3 released by the NAC catalyst during rich regeneration events and utilize the stored NH3 to selectively reduce some or all of the NOx that escapes through the NAC catalyst during normal poor operating conditions.
[00130] In certain aspects, the invention is a system for treating exhaust gas generated by the combustion process, such as from an internal combustion engine (whether mobile or stationary), a gas turbine, coal-fired power plants or oil and the like. Such systems include a zoned SCR catalytic article described herein and at least one additional component for treating the exhaust gas, wherein the zoned SCR catalytic article and at least one additional component are designed to function as a coherent unit. The zoned SCR catalytic article and at least one additional component are in fluid communication, optionally by one or more conduit sections to channel exhaust gas through the system.
[00131] The exhaust gas treatment system may comprise an oxidation catalyst (e.g. a diesel oxidation catalyst (DOC)) to oxidize nitrogen monoxide in the exhaust gas to nitrogen dioxide may be located upstream of a measuring point of the nitrogen reducing agents in the exhaust gas.
[00132] The oxidation catalyst may be adapted to produce a gas stream entering the SCR zeolite catalyst having a ratio of NO to NO2 from about 4:1 to about 1:20 by volume, for example, the an exhaust gas temperature at the inlet of the oxidation catalyst of 200°C to 550°C. The oxidation catalyst may include at least one platinum group metal (or some combination thereof), such as platinum, palladium or rhodium, preferably coated on a monolith through-through substrate. Preferably, at least one metal of the platinum group is platinum, palladium or a combination of both platinum and palladium.
[00133] The platinum group metal can be supported on a large surface area catalytic coating component, such as alumina, a zeolite, such as an aluminosilicate zeolite, silica, non-zeolite silica alumina, ceria, zirconia, titania or a mixed oxide or composite containing both ceria and zirconia.
[00134] The exhaust gas treatment system may comprise an additional SCR catalyst in a second pass-through monolith or a wall flow filter, wherein the second pass through monolith or wall flow filter containing the additional SCR is positioned at upstream or downstream and in fluid communication with the first and second SCR catalyst zones described herein. The additional SCR catalyst is preferably a metal-exchanged zeolite, such as Fe-Beta, Fe-iron-Beta isomorph, Fe-ZSM5, Fe-CHA, Fe-ZSM-34, Fe-AEI, Cu-Beta, Cu- ZSM5, Cu-CHA, Cu-ZSM-34, or Cu-AEI.
[00135] The exhaust gas treatment system may comprise a NAC and/or an external source of nitrogen reductants (eg an ammonia or urea injector) disposed upstream of the catalytic article.
[00136] The system may include a controller for measuring external nitrogenous reductants in the exhaust gas flowing only when it is determined that the SCR catalyst zones are capable of catalyzing the reduction of NOx at or above the desired efficiency, such as above 100°C, above 150°C or above 175°C. The measurement of nitrogen reductants can be arranged such that 60% to 200% of the theoretical ammonia is present in the exhaust gas entering the SCR catalyst calculated at 1:1 NH3/NO and 4:3 NH3/NO2.
[00137] The exhaust gas treatment system may comprise a suitable particulate filter, such as a wall flow filter. Suitable filters include those useful in removing soot from an exhaust gas stream. The filter may be bare and passively regenerated or may contain a soot combustion catalyst or a hydrolysis catalyst. A filter can be positioned in the exhaust gas treatment system either upstream or downstream of the SCR catalysts. Preferably, the filter is positioned downstream of the DOC if a DOC is present. For embodiments comprising a simple filter (i.e. having no catalyst coating) and an ammonia injector upstream of the zoned SCR catalyst, the injector may be positioned upstream or downstream of the filter, provided it is positioned upstream of the SCR catalyst in zones. For embodiments having a filter containing a hydrolysis catalyst and SCR catalyst in downstream zones, an ammonia injector is preferably positioned upstream of the filter.
[00138] Returning to Figure 10 an exhaust gas treatment system is shown comprising an internal combustion engine (501), an exhaust gas treatment system (502), an exhaust gas flow direction through the system (1), an optional DOC 510 and/or an optional NAC (520), an optional particulate filter (570), an optional external ammonia source and injector 530, a zoned SCR catalyst (540), a Optional additional SCR (550) and an optional ASC (560).
[00139] Figure 11A shows an exhaust gas treatment system comprising a passive NOx absorber (PNA) (610) upstream of a wall flow filter (620) containing the first SCR catalyst zone, which is preferably coated on the outlet side of the filter. The PNA may contain an alkali metal and/or alkaline earth metal such as barium, strontium, potassium and a metal oxide such as BaO, TiO2, ZrO2, CeO2 and AhO3. Preferably, the PNA contains a PGM, such as rhodium, palladium, platinum, or a combination of metals, such as palladium and platinum and also contains a metal oxide, such as barium oxide, cerium oxide, or a metal oxide. mixture containing cerium or barium and at least one other transition metal. Suitable PGM loads may be, for example, 1 to 120 g/ft3 . The individual components of the PNA can be layered or combined into a single catalytic coating.
[00140] The system shown in Figure 11A further comprises a flow through substrate containing the second SCR catalyst zone, which is positioned downstream of the filter. The system preferably includes an unreacted ammonia catalyst as a separate brick downstream of the bypass substrate or at the rear of the bypass substrate, similar to the arrangement shown in Figure 6A. The system may optionally include a source of reducing SCR (620), such as an injector to introduce ammonia or an ammonia precursor into the system.
[00141] The flow wall filter in Figure 11A is preferably close to the flow through substrate, but the distance between the two is not particularly limited. Preferably, there are no intervening catalysts or filters between units (630) and (640) or between (610) and (630). Preferably, there are no intervening catalysts between the second SCR catalyst zone and the ASC. Preferably, there is no intervening exhaust gas treatment catalyst between the engine and the PNA or downstream of the second SCR or ASC catalyst zone.
[00142] Another configuration is shown in Figure 11B in which the PNA and first SCR catalyst zone are coated in a flow wall filter (635). Here, the PNA is coated on the inlet side of the filter as a catalytic coating on the wall surface and/or partially permeating the wall and the first SCR catalyst zone is coated on the outlet side of the filter as a catalytic coating on the surface of the filter. wall and/or partially permeating the wall. The system further comprises a flow through substrate containing the second SCR catalyst zone, which is positioned downstream of the filter. The system preferably includes an unreacted ammonia catalyst on a separate substrate downstream of the first and second SCR catalyst zones or at the back of the flow-through substrate containing the second SCR catalyst zone, similar to the arrangement shown in Figure 6A . A first reductant supplier (eg an injector) is positioned upstream of the filter and supplies reductant to the system under conditions that would not lead to reductant oxidation by the PNA (eg at temperatures below 400°C). An optional second reductant supplier (eg, an injector) is positioned between the first SCR catalyst zone and the second SCR catalyst zone and operates both independently and in conjunction with the first reductant supplier.
[00143] The flow wall filter in Figure 11B is preferably proximal to the flow through substrate, but the distance between the two is not particularly limited. Preferably, there are no intervening catalysts or filters between units (635) and (640). Preferably, there are no intervening catalysts between the second SCR catalyst zone and the ASC. Preferably, there is no intervening exhaust gas treatment catalyst between the engine and the PNA or downstream of the second SCR or ASC catalyst zone.
[00144] The method for treating exhaust gas as described herein can be carried out on an exhaust gas derived from a combustion process, such as an internal combustion engine (either mobile or stationary), a gas turbine and power plants. coal- or oil-fired power plants. The method can also be used to treat gas from industrial processes, such as refining, from refinery heaters and boilers, furnaces, the chemical processing industry, coke ovens, power plants and municipal waste incinerators, etc. In a particular embodiment, the method is used to treat exhaust gas from a vehicular lean-burning internal combustion engine, such as a diesel engine, a lean-burning gasoline engine, or an engine fueled by liquefied petroleum gas or gas. Natural.

权利要求:
Claims (14)
[0001]
1. System for treating an exhaust gas, characterized in that it comprises: a. a first SCR catalyst zone comprising a large or medium pore iron loaded molecular sieve having a first ammonia storage capacity; and b. a second SCR catalyst zone comprising a small pore copper loaded molecular sieve having a second ammonia storage capacity, wherein the first SCR catalyst zone is disposed upstream of the second SCR catalyst zone with respect to the flow of normal exhaust gas through the system, the second ammonia storage capacity is greater than the first ammonia storage capacity; and the first ammonia storage capacity is not more than 1.5 mmol/g catalyst and the second ammonia storage capacity is at least 1.2 mmol/g catalyst.
[0002]
2. System according to claim 1, characterized in that the system is free of any catalyst disposed between the first and second SCR catalyst zones.
[0003]
3. System according to any one of claims 1 or 2, characterized in that the first SCR catalyst zone is essentially copper-free and the second catalyst zone is essentially iron-free.
[0004]
A system according to any one of claims 1 to 3, characterized in that the first SCR catalyst zone comprises an iron-loaded molecular sieve having a BEA structure.
[0005]
A system according to any one of claims 1 to 4, characterized in that the second SCR catalyst zone comprises a copper-loaded molecular sieve having a structure selected from CHA, AEI, AFX and AFT.
[0006]
6. System according to any one of claims 1 to 5, characterized in that the molecular sieve of the first SCR catalyst zone and the molecular sieve of the second SCR catalyst zone independently have a silica-alumina ratio of 10 to 50.
[0007]
A system according to any one of claims 1 to 6, characterized in that the first and second SCR catalyst zones are coated on a flow through honeycomb substrate having an inlet end, an outlet end and a length. axial measured from the inlet end to the outlet end and the first and second SCR catalyst zones are adjacent or at least partially overlapping.
[0008]
8. System according to claim 1, characterized in that it additionally comprises an oxidation catalyst zone downstream of the second SCR catalyst zone.
[0009]
9. System according to claim 8, characterized in that the second SCR catalyst zone completely overlaps the oxidation catalyst zone.
[0010]
10. System according to claim 1, characterized in that the first SCR catalyst zone is in a flow wall filter having an inlet side and an outlet side, and the second SCR catalyst zone is in a through-flow honeycomb substrate provided so that there is no intervening catalyst between the first SCR catalyst zone and the second SCR catalyst zone.
[0011]
11. System according to claim 10, characterized in that it additionally comprises a passive NOx absorber disposed upstream of the first SCR catalyst zone.
[0012]
12. System according to claim 11, characterized in that it additionally comprises a first supply of reductant for introducing reductant based on nitrogen upstream of the filter and a second supply of reductant for introducing reductant based on nitrogen between the filter and the through-flow alveolar substrate.
[0013]
A system according to any one of claims 7, 10, 11 or 12, characterized in that it additionally comprises an ammonia slip catalyst coated on the through-flow substrate downstream of the second SCR catalyst zone.
[0014]
14. Method for treating an exhaust gas, characterized in that it comprises the step of bringing into contact, in series, a mixture of ammonia and exhaust gas derived from an internal combustion engine with (a) a first zone of SCR comprising a large or medium pore iron loaded molecular sieve having an ammonia storage capacity of not more than 1.5 mmol NH3/g and (b) a second SCR zone comprising a small pore copper loaded molecular sieve having an ammonia storage capacity of at least 1.2 mmol NH3/g of catalyst, provided that the iron loaded molecular sieve has a lower ammonia storage capacity relative to the copper loaded molecular sieve.

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法律状态:
2020-01-21| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|

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2021-12-07| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

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2022-01-25| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 30/07/2015, OBSERVADAS AS CONDICOES LEGAIS. |

优先权:

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申请号 | 申请日 | 专利标题

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US201462034458P| true| 2014-08-07|2014-08-07|

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US62/034458|2014-08-07|

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PCT/IB2015/055769|WO2016020806A1|2014-08-07|2015-07-30|Zoned catalyst for treating exhaust gas|

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