US20200332691A1 - Combination of a Zeolite-Based SCR Catalyst with a Manganese-Based SCR Catalyst in the Bypass - Google Patents

Combination of a Zeolite-Based SCR Catalyst with a Manganese-Based SCR Catalyst in the Bypass Download PDF

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US20200332691A1
US20200332691A1 US16/770,876 US201816770876A US2020332691A1 US 20200332691 A1 US20200332691 A1 US 20200332691A1 US 201816770876 A US201816770876 A US 201816770876A US 2020332691 A1 US2020332691 A1 US 2020332691A1
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scr
exhaust gas
temperature
low
catalyst
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Nicola Soeger
Andrea De Toni
Fei Wen
Stephan Malmberg
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Umicore AG and Co KG
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Umicore AG and Co KG
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Assigned to UMICORE AG & CO. KG reassignment UMICORE AG & CO. KG ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: DE TONI, Andrea, MALMBERG, STEPHAN, SOEGER, NICOLA, WEN, Fei
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/08—Other arrangements or adaptations of exhaust conduits
    • F01N13/087—Other arrangements or adaptations of exhaust conduits having valves upstream of silencing apparatus for by-passing at least part of exhaust directly to atmosphere
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
    • F01N3/033—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices
    • F01N3/035—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices with catalytic reactors, e.g. catalysed diesel particulate filters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2053—By-passing catalytic reactors, e.g. to prevent overheating
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F01N3/208—Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2370/00—Selection of materials for exhaust purification
    • F01N2370/02—Selection of materials for exhaust purification used in catalytic reactors
    • F01N2370/04—Zeolitic material
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
    • F01N2560/06—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being a temperature sensor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/10—Adding substances to exhaust gases the substance being heated, e.g. by heating tank or supply line of the added substance
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
    • F01N2900/06—Parameters used for exhaust control or diagnosing
    • F01N2900/14—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust gas
    • F01N2900/1404—Exhaust gas temperature
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the present invention relates to an exhaust gas aftertreatment system for selective catalytic reduction with a plurality of SCR catalysts, which system can both reduce NO x in a large temperature range and store SO x .
  • the present invention also relates to a method for treating an exhaust gas flow, in which method the exhaust gas aftertreatment system according to the invention is used.
  • SCR systems known in the prior art comprise SCR catalysts which effectively reduce nitrogen oxides NO x from exhaust gas flows of internal combustion engines during operation in normal to high temperature ranges, for example in temperature ranges between approximately 250° C. and 450° C. SCR in this case stands for “selective catalytic reduction.” However, during the cold start of an engine but also in low-load operation, the exhaust gas temperatures may fall to low temperature ranges between approximately 60° C. and approximately 250° C. In such temperature ranges, conventional SCR catalysts do not succeed in effectively reducing NO x from exhaust gas flows.
  • TT-SCRs low-temperature SCR catalysts
  • These are combinations of individual or a mixture of transition metals or transition metal oxides, which are applied to oxides, mixed oxides or a combination of a plurality of oxides or mixed oxides.
  • Particular TT-SCRs which contain manganese-containing mixed oxides or manganese or manganese oxide supported on metal oxides exhibit very high NO conversions even at low temperatures, sometimes even below 100° C.
  • WO 2016/028290 A1 proposes avoiding sulfurization of the SCR catalyst by connecting a selective alkali metal- or alkaline earth metal-containing SO 3 trap upstream.
  • This SO 3 trap can be combined with a second SCR catalyst in a suitable manner, for example through a layer or zone structure. If the capacity of the SO 3 trap is exhausted, replacement of the component or thermal regeneration takes place.
  • the solution proposed in WO 2016/028290 A1 for avoiding sulfur contamination on an SCR catalyst is particularly unsuitable for manganese-containing catalysts. For this purpose, it is necessary to remove SO 2 from the exhaust gas in addition to SO 3 . Thus, a routine replacement of the SO 3 trap would not be possible because of operating times that are too short.
  • thermal regeneration would have the disadvantage that the SO 3 emitted from the SO 3 trap migrates to the downstream TT-SCR and the protection of such manganese-containing TT-SCR catalyst thus does not function permanently.
  • WO 2016/018778 A1 discloses exhaust gas aftertreatment systems comprising a TT-SCR and an HT-SCR.
  • the exhaust gas aftertreatment system furthermore comprises a bypass:
  • the exhaust gas is conducted over the TT-SCR at low temperatures, over the HT-SCR at higher temperatures.
  • the TT-SCR contains a mixture of catalytically active metals, which are preferably applied to a beta zeolite.
  • the mixture of catalytically active metals contains at least one mixture selected from Cu and Ce, Mn and Ce, Mn and Fe, Cu and W, and Ce and W, and at least one alkali metal and/or one metal from the group of lanthanides.
  • Low-temperature SCR catalysts are described, for example, in Junhua Li, Huazhen Chang, Lei Ma, Jinming Hao and Ralph T. Yang: “Low-temperature selective catalytic reduction of NO x with NH 3 over metal oxide and zeolite catalysts—A review,” Catal Today 2011, 175, 147-156.
  • SO x in the exhaust gas can lead to deactivation because of the occupation of the active centers of the catalyst by manganese or ammonium sulfates.
  • Zeolites containing Fe and Cu are essentially more stable to SO 2 and exhibit good thermal stability, but have significantly lower NO x conversion rates at low temperatures than manganese-containing catalysts.
  • the reactivity of Fe-containing zeolites in the NO x conversion is lower than that of Cu zeolites.
  • the activity of Cu zeolites with respect to NO x decreases markedly more in the presence of H 2 O.
  • Fe beta zeolites have a fairly good NO x conversion rate at low temperatures. On the other hand, they react particularly sensitively to hydrocarbon sooting with incomplete combustion of the fuel in diesel engines.
  • an exhaust gas aftertreatment system which can be coupled to an internal combustion engine in such a way that it receives the exhaust gas flow, comprising
  • novel SCR system and the method for treating an exhaust gas flow comprising the novel SCR system are explained below.
  • the invention encompasses all the embodiments listed both individually and in combination with one another.
  • exhaust gas flow within the meaning of the present invention relates to an exhaust gas flow from an internal combustion engine, irrespective of the burned fuel.
  • the internal combustion engines can be gasoline engines or lean burn engines, for example.
  • lean burn engines are diesel engines.
  • diesel engines encompasses both light-duty diesel engines (LDD) as well as heavy-duty diesel engines (HDD).
  • HT-SCR catalysts which are described below and which contain Cu- or Fe-based zeolites as catalytically active component, not only efficiently reduce nitrogen oxides in normal to high temperature ranges to nitrogen, but also quantitatively store sulfur oxides SO x in low to medium temperature ranges, and thus can effectively protect a downstream TT-SCR from contamination by SO x .
  • the present invention makes use of this effect in that the exhaust gas flow is basically first conducted through the HT-SCR. It also stores SO x in low temperature ranges and thus removes this component from the exhaust gas flow. This prevents contamination of the downstream TT-SCR by SOx.
  • the HT-SCR thus serves as an SO x trap, while the nitrogen oxides NO x are reduced completely or at least largely in the TT-SCR, since the HT-SCR has no or only very low NO x conversion rates in low temperature ranges.
  • the HT-SCR in the normal to high temperature range, not only continues to act as an SO x trap, but additionally also assumes the NO x conversion.
  • a temperature threshold value is exceeded, the exhaust gas flow is conducted past the TT-SCR via a bypass. This operating strategy offers several advantages. On the one hand, the TT-SCR is prevented from being damaged by the hot exhaust gas flow.
  • the TT-SCR is protected by such measure from SO x emissions, which are released from the HT-SCR in high temperature ranges or can no longer be stored completely due to the elevated temperatures.
  • the selection of the temperature threshold value for a particular embodiment of the present invention results from the actual exhaust gas temperature; the exhaust gas mass flow, the sulfur concentration in the exhaust gas, the size of the HT-SCR, and the temperature sensitivity of the TT-SCR. These factors are essentially determined by the final application. Therefore, the temperature threshold value is also a variable which depends on the respective application and is determined by the end user. The person skilled in the art is aware of the described phenomenon and can determine the temperature threshold value, without departing from the scope of protection of the present invention.
  • the temperature threshold value is advantageously at a temperature above 250° C. or greater than or equal to the light-off temperature of the HT-SCR.
  • a “low” temperature range means temperatures of 60° C. to less than 250° C.
  • a “medium” temperature range means temperatures of 250° C. to less than 450° C.
  • a “high” temperature range means temperatures of 450° C. to 700° C.
  • the SCR system according to the invention effectively reduces nitrogen oxides from exhaust gases from internal combustion engines in low, medium and high temperature ranges.
  • “effective” means that the nitrogen oxides are effectively and efficiently reduced.
  • the SCR system according to the invention has high activity, selectivity and temperature stability.
  • the SCR system according to the invention comprises an HT-SCR and a TT-SCR, i.e., two catalysts.
  • Catalyst activity the extent to which it increases the speed of a chemical reaction
  • Catalyst selectivity influences its course
  • Catalyst life the course of the effectiveness lasts
  • Catalyst activity is thus a measure for how quickly the catalyst converts reactants to products.
  • the reactants are nitrogen oxides (NO x ) and reductants
  • the products are nitrogen (N 2 ) and water.
  • catalyst selectivity describes the phenomenon that one of a plurality of possible reaction products is preferably formed during a reaction.
  • N 2 and N 2 O can be formed during the reaction of NO x with reductants, wherein N 2 is desirable and N 2 O is undesirable. SCR catalysts with high selectivity for the formation of N 2 are therefore advantageous.
  • a “temperature-stable” catalyst is heat-resistant even at relatively high temperatures.
  • the resistance here relates primarily to the structure of the catalytically active coating and of the carrier substrate, both of which are explained in more detail below.
  • “temperature stability” is also defined specifically to the application as the ability to carry out a certain function.
  • “temperature-stable” SCR systems are arrangements comprising an HT-SCR and a TT-SCR, wherein the SCR systems are designed such that they are heat-resistant. on the one hand, and reduce nitrogen oxides to nitrogen for the mentioned low, medium and high temperature ranges, on the other hand. This is achieved by conducting the exhaust gas, depending on the temperature threshold value and the current exhaust gas temperature, either only through the upstream HT-SCR or first through the HT-SCR and then through the downstream TT-SCR.
  • both the HT-SCR and the TT-SCR are advantageously present in the form of a catalytically active coating on a carrier substrate.
  • Carrier substrates can be so-called flow-through substrates or wall-flow filters. Both can consist of inert materials, for example ceramic materials, such as silicon carbide, aluminum titanate or cordierite. Alternatively, in the case of a flow-through substrate, the inert material may be metal substrates.
  • the carrier substrates of both SCRs can consist of inert materials, or both consist of metal substrates, or one of the two SCRs has a carrier substrate made of an inert ceramic material and the other has a carrier substrate made of metal.
  • the mentioned carrier substrates are known to the person skilled in the art and are commercially available.
  • the carrier substrates themselves can also be catalytically active and contain catalytically active material, for example SCR catalytically active material.
  • SCR catalytically active materials for the TT-SCR mixed oxide-based materials known to the person skilled in the art and containing manganese compounds are used.
  • carrier substrates contain a matrix component in addition to the catalytically active material.
  • All inert materials that are also otherwise used to produce catalyst substrates can be used as matrix components. These are, for example, silicates, oxides, nitrides or carbides, wherein in particular magnesium aluminum silicates are preferred.
  • the catalyst according to the invention it is itself present as part of a carrier substrate, i.e., for example, of a flow-through substrate or wall-flow filter.
  • a carrier substrate i.e., for example, of a flow-through substrate or wall-flow filter.
  • Such carrier substrates additionally contain the matrix components already described above.
  • Carrier substrates containing catalysts according to the invention can be used as such in exhaust gas purification. However, they can also in turn be coated with catalytically active materials, for example SCR catalytically active materials. If such materials are to be SCR catalytically active, the aforementioned SCR catalysts come into consideration.
  • catalytically active materials for example SCR catalytically active materials. If such materials are to be SCR catalytically active, the aforementioned SCR catalysts come into consideration.
  • catalytically active carrier substrates In order to produce catalytically active carrier substrates, a mixture consisting of, for example, 10 to 95% by weight of an inert matrix component and 5 to 90% by weight of catalytically active material is, for example, extruded according to methods known per se.
  • inert materials that are also otherwise used to produce catalyst substrates can be used as matrix components. These are, for example, silicates, oxides, nitrides or carbides, wherein in particular magnesium aluminum silicates are preferred.
  • Applying the catalyst according to the invention to the inert or itself catalytically active carrier substrate and applying a catalytically active coating to a carrier substrate comprising a catalyst according to the invention may be carried out by methods known to the person skilled in the art, thus, for instance, according to the usual dip coating methods or pump and vacuum coating methods with subsequent thermal aftertreatment (calcination).
  • the latter's average pore size and the average particle size of the catalyst according to the invention can be adapted to each other such that the resulting coating lies on the porous walls that form the channels of the wall-flow filter (on-wall coating).
  • average pore size and average particle size are preferably adapted to one another such that the catalyst according to the invention is located in the porous walls that form the channels of the wall-flow filter, that a coating of the inner pore surfaces thus takes place (in-wall coating).
  • the average particle size of the catalyst according to the invention must be small enough to penetrate into the pores of the wall-flow filter.
  • catalytically active coating and “catalytically active layer” are used synonymously.
  • SAR in this case stands for “silica-to-alumina ratio”, i.e., for the molar ratio of SiO 2 to Al 2 O 3 of an aluminosilicate zeolite.
  • silicon aluminum phosphates also referred to as “SAPOs,” indicate the (Al+P)/Si value. This is the sum of the amounts of aluminum and phosphorus divided by the amount of silicon.
  • the SAR is 5 to 50, preferably 10 to 35, particularly preferably 12 to 30, and most preferably 30.
  • the molecular sieve contains 1 to 10% by weight, preferably 1 to 9% by weight, particularly preferably 2.5 to 7% by weight, and most preferably 3.5 to 4.5% by weight of a transition metal selected from iron, copper, and mixtures thereof, calculated as Fe 2 O 3 and CuO respectively, and based on the total weight of the molecular sieve.
  • the molecular sieve contains 1 to 10% by weight Fe, preferably 3 to 9% by weight Fe, particularly preferably 4 to 7% by weight Fe, and most preferably 3.5% by weight Fe, in each case calculated as Fe 2 O 3 and based on the total weight of the molecular sieve.
  • the molecular sieve contains 1 to 10% by weight Cu, preferably 1 to 7% by weight Cu, particularly preferably 2.5 to 4% by weight Cu, and most preferably 4.5% by weight Cu, in each case calculated as CuO and based on the total weight of the molecular sieve.
  • the molecular sieve constituting the catalytically active layer of the HT-SCR is SAPO-34.
  • the (Al+P)/Si value and the contents of CuO and/or Fe 2 O 3 , the alkali metal and alkaline earth metal content, and the content of the metals Co, Mn, Cr, Zr and Ni correspond to the above specifications.
  • zeolites are classified by their pore size.
  • the pore size is defined by the ring size of the largest pore opening. Large-pore zeolites have a maximum ring size of 12 tetrahedral atoms, medium-pore zeolites have a maximum ring size of 10 and small-pore zeolites have a maximum ring size of 8 tetrahedral atoms.
  • Small-pore zeolites are, for example, 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.
  • Zeolites having a medium pore size are, for example, FER, MFI, ZSM-57 and SUZ-4.
  • the HT-SCR is a Cu-CHA having a SAR of 10 to 35, an alkali metal content of 0 to 07% by weight, particularly preferably 0 to 0.5% by weight, calculated as pure metals, and a Cu content of 1 to 7% by weight, particularly preferably 3.5% by weight, calculated as CuO, wherein the alkali metal and Cu contents are each based on the total weight of the zeolite.
  • the manganese-containing coating is a manganese-containing mixed oxide selected from
  • the manganese-containing coating is a mixed oxide of the general formula Mn w Ce x Me 1-w-x O y
  • Me is selected from the group Fe, Co, Ni, Cu, Zr, Nb, Mo, W, Ag, Sn, Ce, Pr, La, Nd, Ti and Y.
  • w 0.02-0.98
  • x 0.02-0.98
  • y 1.0-2.5.
  • Me is particularly advantageously selected from Fe, Cu, Nb, Mo, W, Sn and Ti.
  • the reductant source is advantageously selected from aqueous solutions of ammonia, urea, ammonium carbamate, ammonium formate, ammonium acetate, ammonium propionate, guanidinium formate, methanamide and mixtures of the specified aqueous solutions.
  • the reductant source is connected to the pump in such a way that is delivers reductant, wherein the pump is designed to pump reductant from the reductant source to the dispenser.
  • the dispenser can comprise a reductant injector or a reductant metering device arranged upstream of the bypass valve 150 and the HT-SCR catalyst 120 .
  • the reductant injector may be located at other locations of the aftertreatment system, such as upstream of the DOC in FIGS. 4 a and 4 b .
  • the injector may be selectively controlled to inject reductant directly into the exhaust gas flow prior to the exhaust gas flow passing through the bypass valve 150 .
  • the reductant supply system may comprise more than one reductant injector, whereby HT-SCR 220 and TT-SCR 230 may be supplied with reductant independently of each other.
  • This operating mode is particularly advantageous in order to allow the TT-SCR a very short light-off time, since the reductant does not have to flow through the HT-SCR beforehand and is possibly adsorbed there.
  • the reductant in the SCR catalysts reacts with NO x to reduce it to harmless emissions N 2 and H 2 O.
  • the exhaust gas bypass and/or flow control valve is designed to conduct the entire exhaust gas flow through the low-temperature SCR catalyst, if a temperature of the exhaust gas flow is below the minimum operating temperature of the HT-SCR catalyst and the HT-SCR still has no high conversion rates.
  • the minimum operating temperature may be lower than the temperature threshold value.
  • the exhaust gas bypass and/or flow control valve may gradually decrease the amount of the exhaust gas flow that flows through the low-temperature SCR catalyst from 100% to 0% of the exhaust gas flow, if the temperature of the exhaust gas flow rises accordingly from the minimum operating temperature to the temperature threshold value.
  • the bypass valve may gradually increase the amount of exhaust gas flow that flows through the low-temperature SCR catalyst from 0% to 100% of the exhaust gas flow, if the temperature of the exhaust gas flow decreases accordingly from the temperature threshold value to the minimum operating temperature.
  • the exhaust gas bypass and/or flow control valve in the closed position results in the TT-SCR being bypassed.
  • the exhaust gas bypass and/or flow control valve may be adjusted to any positions between the open and the closed position to selectively regulate the flow rate to the TT-SCR.
  • the exhaust gas bypass and/or flow control valve may be controlled such that any partial amounts of exhaust gas from the HT-SCR flow into the TT-SCR catalyst.
  • the gas path i.e., the flow direction of the exhaust gas, is illustrated schematically in FIGS. 6 a and 6 b.
  • the minimum operating temperature here is the temperature that is at least required in order to initiate the provision of the reductant and the actual catalytic reaction.
  • a further reductant supply system is arranged directly upstream of the TT-SCR.
  • the reductant supply system contains a) a reductant source, b) a reductant pump, and c) a reductant dispenser or a reductant injector.
  • a pump is dispensed with when metering the liquid reductant.
  • the container or tank containing the reductant is attached such that the delivery to the reductant dispenser or the reductant injector is brought about by gravity.
  • further reductant supply systems may also be present.
  • Such further reductant supply systems are advantageously arranged directly upstream of the TT-SCR, as shown in FIGS. 2 a , 2 b , 3 a , 3 b and 5 .
  • an oxidation catalyst is located directly upstream of the reductant supply system located directly upstream of the HT-SCR.
  • inert carrier substrates known to the person skilled in the art are in particular used according to the present invention as carrier substrates.
  • these are honeycomb bodies made of metal or preferably of ceramic, which can be designed as flow-through honeycomb bodies or else as wall-flow filter bodies. Ceramic honeycomb bodies made of cordierite are preferred.
  • a further HT-SCR is located between the HT-SCR, upstream of which a reductant supply system is located, and the temperature sensor.
  • the different HT-SCR units can represent a combination of various technologies. For example, combinations of Fe zeolite, for example Fe-BEA, and Cu zeolite, for example Cu-SSZ-13, as well as combinations of vanadium-based systems and Cu zeolite, on the one hand, and also the combination of various Cu zeolite technologies, on the other hand, can be used.
  • the already mentioned flow-through substrates are used.
  • the HT-SCR can also be an SDPF, i.e., an SCR which is integrated on a DPF. All combinations mentioned here are known to the person skilled in the art and can be used, without departing from the scope of protection of the claims.
  • particulate filters In order to remove particulate emissions from the exhaust gas of diesel vehicles, special particulate filters are used, which can be provided with an oxidation-catalytically active coating to improve their properties. Such a coating serves to reduce the activation energy for the oxygen-based particle combustion (soot combustion) and hence to reduce the soot ignition temperature on the filter, to improve the passive regeneration behavior by oxidation of nitrogen monoxide contained in the exhaust gas into nitrogen dioxide, and to suppress breakthroughs of hydrocarbon and carbon monoxide emissions.
  • Suitable carrier substrates for such CDPFs are, for example, wall-flow filters of silicon carbide, aluminum titanate and cordierite.
  • one or more HT-SCRs are arranged upstream of the oxidation catalyst.
  • a reductant supply system is located directly upstream of the HT-SCR closest to the internal combustion engine.
  • one or more HT-SCRs and an ASC are arranged upstream of the oxidation catalyst.
  • a reductant supply system is located directly upstream of the HT-SCR closest to the internal combustion engine.
  • the ASC is located in the most downstream position.
  • the ASC is then located directly upstream of the oxidation catalyst.
  • ammonia barrier catalysts are known, which are arranged downstream of an SCR catalyst in the flow direction of the exhaust gas in order to oxidize ammonia breaking through. Ammonia barrier catalysts in various embodiments are described, for example, in U.S. Pat. No. 5,120,695, WO 02/100520 A1 and EP 0 559 021 A2.
  • the catalyst arrangement according to the invention therefore comprises an ammonia barrier catalyst that follows the second SCR catalyst.
  • Dashed arrows, for example between the two components engine 110 and SCR 120 in FIG. 1 a and FIG. 1 b mean that further components can optionally be located between such components.
  • Dotted arrows represent the conducting of the entire exhaust gas flow past the low-temperature SCR, if such exhaust gas flow has a temperature above a temperature threshold value, see 180 , 280 , 380 , 480 and 580 in FIGS. 1 to 5 .
  • the catalytic systems i.e., the HT-SCR, the TT-SCR, the OX, the DPF, the SDPF and the ASC, can each be composed independently of each other of one or any number of bricks of different dimensions and shape.
  • FIG. 1 a shows the core of the present invention.
  • An HT-SCR catalyst 120 for medium to high temperatures is located downstream of the engine 110 .
  • a reductant supply system 160 which comprises a reductant source, a reductant pump, and a reductant dispenser or a reductant injector (not shown), is located directly upstream of such SCR catalyst 120 .
  • An exhaust gas temperature sensor 140 is located downstream of the SCR 120 .
  • An exhaust gas bypass and/or flow control valve 150 which communicates with the SCR 120 in such a way that it receives exhaust gas, is located downstream of the exhaust gas temperature sensor 140 .
  • the exhaust gas bypass and/or flow control valve 150 conducts the exhaust gas flow past the low-temperature SCR 130 via the bypass 180 , if the exhaust gas flow has a temperature greater than or equal to a temperature threshold value. However, if the temperature of the exhaust gas flow is below such temperature threshold value, the exhaust gas flow is conducted, completely or partially, through the low-temperature SCR 130 , see arrow 170 .
  • a further reductant supply system 190 is also located between exhaust gas bypass and/or the flow control valve 150 and the low-temperature SCR 130 .
  • the exhaust gas flow is conducted through the low-temperature SCR and, immediately before this introduction, the low-temperature SCR is supplied with reductant.
  • FIG. 2 shows a preferred embodiment of an exhaust gas purification system comprising the combination according to the invention of an SCR for normal to high temperatures and a low-temperature SCR.
  • This system comprises an oxidation catalyst 215 .
  • a reductant supply system 260 which is constructed like the corresponding system 160 in FIG. 1 a and FIG. 1 b and supplies reductant to the SDPF 225 is located directly downstream of such oxidation catalyst 215 .
  • An SCR 220 is located directly downstream of the SDPF 225 .
  • An exhaust gas temperature sensor 240 is arranged downstream of the SCR 220 .
  • An exhaust gas bypass and/or flow control valve 250 which communicates with the SCR 220 in such a way that it receives exhaust gas, is located downstream of exhaust gas temperature sensor 240 .
  • the exhaust gas bypass and/or flow control valve 250 conducts the exhaust gas flow past the low-temperature SCR 230 via the bypass 280 , if the exhaust gas flow has a temperature greater than or equal to a temperature threshold value. However, if the temperature of the exhaust gas flow is below such temperature threshold value, the exhaust gas flow is conducted, partially or completely, through the low-temperature SCR 230 , see arrow 270 .
  • a further reductant supply system 290 may also be provided between the exhaust the gas bypass and/or the flow control valve 250 and the low-temperature SCR 230 as described in FIG. 1 b. In the event that the temperature of the exhaust gas flow is below the temperature threshold value, the exhaust gas flow is conducted through the low-temperature SCR and, immediately before this introduction, the low-temperature SCR is supplied with reductant.
  • FIG. 3 a shows another advantageous embodiment of an exhaust gas purification system containing the combination according to the invention of an SCR for normal to high temperatures and a low-temperature SCR.
  • This system comprises an oxidation catalyst 315 and a CDPF 316 located directly downstream thereof.
  • a reductant supply system 360 which is constructed like the corresponding system 160 in FIG. 1 a and FIG. 1 b and supplies reductant to the SCR 225 , is located downstream of the CDPF.
  • An exhaust gas temperature sensor 340 is arranged downstream of the SCR 320 .
  • An exhaust gas bypass and/or flow control valve 350 which communicates with the SCR 320 in such a way that it receives exhaust gas, is located downstream of the exhaust gas temperature sensor 340 .
  • the exhaust gas bypass and/or flow control valve 350 conducts the exhaust gas flow past the low-temperature SCR 330 via the bypass 380 , if the exhaust gas flow has a temperature greater than or equal to a temperature threshold value. However, if the temperature of the exhaust gas flow is below such temperature threshold value, the exhaust gas flow is conducted through the low-temperature SCR 330 , see arrow 370 .
  • a further reductant supply system 390 may also be provided between the exhaust gas bypass and/or the flow control valve 350 and the low-temperature SCR 330 as described in FIG. 1 b . In the event that the temperature of the exhaust gas flow is below the temperature threshold value, the exhaust gas flow is conducted through the low-temperature SCR and, immediately before this introduction, the low-temperature SCR is supplied with reductant.
  • FIG. 3 b shows another advantageous embodiment of the present invention.
  • the system comprises an oxidation catalyst 315 , followed by a reductant supply system 360 , which is constructed like the corresponding system 160 in FIG. 1 a and FIG. 1 b and supplies reductant to the SDPF 325 .
  • An exhaust gas temperature sensor 340 is arranged downstream of the SDPF 325 .
  • An exhaust gas bypass and/or flow control valve 350 which communicates with the SDPF 325 in such a way that it receives exhaust gas, is located downstream of the exhaust gas temperature 340 .
  • the exhaust gas bypass and/or flow control valve 350 conducts the exhaust gas flow past the low-temperature SCR 330 via the bypass 380 , if the exhaust gas flow has a temperature greater than or equal to a temperature threshold value.
  • the exhaust gas flow is conducted through the low-temperature SCR 330 , see arrow 370 .
  • a further reductant supply system 390 may also be provided between the exhaust gas bypass and/or the flow control valve 350 and the low-temperature SCR 330 as described in FIG. 1 b .
  • the exhaust gas flow is conducted through the low-temperature SCR and, immediately before this introduction, the low-temperature SCR is supplied with reductant.
  • FIG. 4 a relates to a further embodiment based on the system described in FIG. 3 a .
  • a reductant supply system 465 which is constructed like the corresponding system 160 in FIG. 1 a and FIG. 1 b and supplies reductant to the SCR 425 , is located upstream of the oxidation catalyst 415 and a CDPF 416 located directly downstream thereof.
  • a further reductant supply system 460 which is constructed like the corresponding system 160 in FIG. 1 a and FIG. 1 b and supplies reductant to the SCR 420 , is arranged downstream of the oxidation catalyst 415 and the CDPF 416 .
  • An exhaust gas temperature sensor 440 is arranged downstream of the SCR 420 .
  • FIG. 4 b relates to a further embodiment based on the system described in FIG. 4 a .
  • a reductant supply system 465 which is constructed like the corresponding system 160 in FIG. 1 a and FIG. 1 b and supplies reductant to the two SCR 425 located one after the other, is located upstream of the oxidation catalyst 415 .
  • a reductant supply system 465 which is constructed like the corresponding system 160 in FIG. 1 a and FIG. 1 b and supplies reductant to the SDPF 420 , is downstream of the oxidation catalyst 415 .
  • An exhaust gas temperature sensor 440 is arranged downstream of the SDPF 420 .
  • An exhaust gas bypass and/or flow control valve 450 which communicates with the SDPF 420 in such a way that it receives exhaust gas, is located downstream of the exhaust gas temperature sensor 440 .
  • the exhaust gas bypass and/or flow control valve 450 conducts the exhaust gas flow past the low-temperature SCR 430 via the bypass 480 .
  • the exhaust gas flow has a temperature greater than or equal to a temperature threshold value.
  • the temperature of the exhaust gas flow is below such temperature threshold value, the exhaust gas flow is conducted through the low-temperature SCR 430 , see arrow 470 .
  • a further reductant supply system 390 may also be provided between the exhaust gas bypass and/or the flow control valve 450 and the low-temperature SCR 430 as described in FIG. 1 b. In the event that the temperature of the exhaust gas flow is below the temperature threshold value, the exhaust gas flow is conducted through the low-temperature SCR and, immediately before this introduction, the low-temperature SCR is supplied with reductant.
  • FIG. 5 schematically shows a further advantageous embodiment of the present invention, which is illustrated by way of example as a supplement to FIG. 1 a.
  • An SCR catalyst 520 for normal to high temperatures is located downstream of the engine (not shown) in FIG. 5 .
  • a reductant supply system 560 which comprises a reductant source, a reductant pump, and reductant dispenser or a reductant injector (not shown), is located directly upstream of such SCR catalyst 520 .
  • An exhaust gas temperature sensor 540 is arranged downstream of the SCR 520 .
  • An exhaust gas bypass and/or flow control valve 550 which communicates with the SCR 520 in such a way that it receives exhaust gas, is located downstream of the exhaust gas temperature sensor 540 .
  • FIG. 6 a shows an exhaust gas bypass or flow valve, hereinafter referred to as a “bypass valve,” which is 100% open.
  • “100% open” means that the exhaust gas paths 1 and 2 are connected so that exhaust gas from the HT-SCR flows into the TT-SCR.
  • the arrow 1 shows the gas discharge from the HT-SCR and the entry into the bypass valve.
  • Arrow 2 shows the discharge of the exhaust gas from the bypass valve toward the TT-SCR.
  • Arrow 3 shows the discharge of the exhaust gas from the bypass valve toward the bypass. In FIG. 6 a , the outlet 3 is completely closed.
  • the exhaust gas is conducted through the TT-SCR after exiting the HT-SCR, regardless of whether or not the minimum operating temperature of the HT-SCR has already been reached.
  • FIG. 6 b shows a bypass valve, which is 100% closed. “100% closed” is equivalent to “0% open.”
  • the exhaust gas paths 1 and 3 are connected so that exhaust gas coming from the HT-SCR flows into the bypass and not through the TT-SCR. In this case, the following applies:
  • the bypass valve is closed. After exiting the HT-SCR, the exhaust gas flow is then conducted past the TT-SCR.
  • the actual temperature of the HT-SCR is greater than its minimum operating temperature but less than the temperature threshold value.
  • a proportionality factor which indicates the degree of opening of the flow valve can be determined from (T Thd ⁇ T actual ). In this case, the following boundary condition applies:
  • bypass valve is 0% open, which is equivalent to 100% closed.
  • FIG. 7 shows the nitrogen oxide conversion values U Nox [%] of three HT-SCR catalysts in the temperature range between 200 and 550° C.
  • HT-SCR1 is a vanadium-containing SCR
  • HT-SCR2 is an iron-containing SCR
  • HT-SCR3 is a copper-containing SCR.
  • the experimental conditions for the measurement of the nitrogen oxide conversion values are given in Exemplary Embodiment 4.
  • FIG. 8 shows the SO 2 curve after flowing through the DPF for three stationary sulfurization experiments on an engine test bench for a Cu zeolite HT-SCR. Such sulfurization experiments are described in Exemplary Embodiment 5. In this case, the SCR inlet temperature and space velocity in the SCR were varied for the three experiments.
  • FIG. 9 shows the SO 2 curve after flowing through the Cu zeolite HT-SCR for three stationary sulfurization experiments on an engine test bench. Such sulfurization experiments are described in Exemplary Embodiment 5. In this case, the SCR inlet temperature and space velocity in the SCR were varied for the three experiments. Together with FIG. 8 . This shows the ability of the Cu zeolite to store SO x at different temperatures and space velocities.
  • the SO x trap efficiency decreases somewhat. However, since in this case the NO x conversion can be ⁇ 100% (see FIGS. 7 and 10 ), the TT-SCR can already be switched into the bypass in these cases.
  • FIG. 10 shows the NO x conversion of the Cu zeolite for the three sulfurization experiments.
  • the HT-SCR shows no full conversion at 190° C. since such temperature is below its minimum temperature. Nevertheless, the conversion of 80% is maintained for a long time despite sulfur exposure. It can also be derived from FIG. 7 that at the beginning of the sulfurization, ⁇ 100% NO x conversion arises at EOP_02 and EOP_03.
  • FIG. 11 shows the sulfur breakdown curve from dynamic engine test bench experiments for a V HT-SCR and a Cu HT-SCR.
  • the V HT-SCR shows hardly any sulfur storage functionality for the test time.
  • the Cu HT-SCR exhibits the property as sulfur trap even under dynamic conditions.
  • the nitrogen oxide conversion values U NOx [%] obtained were applied as a function of the pre-catalyst temperature measured to evaluate the SCR activity of the materials investigated. This is shown in FIG. 7 .
  • the SO x input and output concentrations were measured as SO 2 by a mass spectrometer each at the DPF output and SCR output.
  • the experiments were carried out in stationary operating mode. For this purpose, three different operating points were selected which differ with regard to their SCR inlet temperature and the exhaust gas mass flow or the SCR space velocity (GHSV or SV).
  • GHS gas hourly space velocity
  • SV space velocity
  • EOP_01 represents an operating point at which the exhaust gas temperature is below the threshold value and at the same time below the minimum temperature of the HT-SCR.
  • EOP_02 and EOP_03 are above the minimum temperature.
  • B10 diesel fuel was used, which was additionally mixed with sulfur. Fuels of this type are commercially available. For all three operating points, the experiment was carried out until ⁇ 2 g of sulfur (not SOx but S) per liter of SCR volume was emitted.
  • the SO2 curve after passage through the DPF is shown in FIG. 8 and the SO2 curve after passage through the SCR is shown in FIG. 9 .
  • the SO x input and output concentrations were measured as SO 2 by a mass spectrometer each at the DPF output and SCR output.
  • the experiments were carried out in dynamic operating mode. To this end, a sequence of WHTC cycles (world harmonized transient cycles) was performed. WHTCs are legally predefined test cycles used for testing, qualifying and releasing heavy-duty/payload engines. The performance and design of a WHTC and the implementation of the test procedure are known to the person skilled in the art.
  • B10 diesel fuel was used, which was additionally mixed with sulfur. Fuels of this type are commercially available.
  • the sulfur emission per WHTC was ⁇ 1375 mg.
  • the NO x conversion of the Cu HT-SCR is shown in FIG. 10 .
  • the sulfur breakdown curve from the dynamic engine test bench experiments for a V HT-SCR and the Cu HT-SCR is shown in FIG. 11 .
  • FIG. 12 shows the NO x conversion curves from the dynamic engine test bench tests for a V HT-SCR and a Cu HT-SCR.
  • the cumulative mass of SO 2 per cycle, measured at the output of the SCR is plotted against the number of sulfation cycles.

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