Exhaust system including scrf catalyst with oxidation zone

Abstract

The system and method of the present invention relates to an exhaust gas purification system comprising: (a) a first injector for injecting ammonia or a compound capable of decomposing to ammonia into the exhaust gas; (b) a diesel particulate filter comprising an inlet and an outlet, wherein the filter comprises a selective catalytic reduction (SCR) catalyst and an oxidation catalyst; (c) a second injector for injecting ammonia or a compound capable of decomposing to ammonia into the exhaust gas and located downstream of the filter; and (d) a downstream catalyst comprising a selective catalytic reduction catalyst and located downstream of the second injector.

Description

[0001] This application is a divisional application of Chinese patent application No. 201980023410.9, filed on March 29, 2019, entitled "Exhaust System Including SCRF Catalyst with Oxidation Zone". Background Technology

[0002] Reducing emissions of harmful byproducts and increasing pressure to improve fuel economy are challenges facing internal combustion engines. Diesel engines generally produce exhaust emissions of at least four types of pollutants regulated by legislation from intergovernmental organizations worldwide: carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (NOx). x Pollutants include particulate matter (PM) and particulate matter. Various emission control devices exist to treat one or more of these pollutants. These emission control devices are typically integrated as part of an exhaust system to ensure that all four types of pollutants are treated before exhaust gases are released into the environment. Summary of the Invention

[0003] According to some embodiments of the present invention, an exhaust gas purification system includes: (a) a first injector for injecting ammonia or a compound capable of decomposing into the exhaust gas; (b) a diesel particulate filter including an inlet and an outlet, wherein the filter includes a selective catalytic reduction (SCR) catalyst and an oxidation catalyst; (c) a second injector for injecting ammonia or a compound capable of decomposing into the exhaust gas and located downstream of the filter; and (d) a downstream catalyst including a selective catalytic reduction catalyst and located downstream of the second injector.

[0004] In some embodiments, the oxidation catalyst is coated on the outlet of the filter. The oxidation catalyst may include one or more platinum group metals, such as platinum, palladium, or combinations thereof. Suitable selective catalytic reduction catalysts may include metal oxide-based SCR catalyst formulations, molecular sieve-based SCR catalyst formulations, or mixtures thereof.

[0005] In some embodiments, the downstream catalyst further includes an ammonia oxidation catalyst. In some embodiments, the system also includes an upstream catalyst located upstream of the filter, the upstream catalyst including a diesel oxidation catalyst and NO. x Store catalysts or combinations thereof.

[0006] In some embodiments, the exhaust gas entering the downstream catalyst has a NO2:NO content greater than 10%. x ratio.

[0007] According to some embodiments of the present invention, a method for purifying exhaust gas includes: (a) adding ammonia or a compound capable of decomposing into ammonia to the exhaust gas through a first injector; (b) passing the exhaust gas through a diesel particulate filter including an inlet and an outlet, wherein the filter includes a selective catalytic reduction (SCR) catalyst and an oxidation catalyst; (c) adding ammonia or a compound capable of decomposing into ammonia to the exhaust gas through a second injector located downstream of the filter; and (d) passing the exhaust gas through a downstream catalyst including a selective reduction catalyst located downstream of the second injector. Attached Figure Description

[0008] Figure 1 The post-SCRF test results are shown in comparison system 1 and system 2. ™ Catalyst NO2 ratio. Detailed Implementation

[0009] The systems and methods of this invention relate to the purification of exhaust gases from internal combustion engines. More particularly, this invention relates to the cleaning of exhaust gases from diesel engines.

[0010] The system and method of the present invention may include: (1) a first injector for injecting ammonia or a compound capable of decomposing into exhaust gas; (2) a diesel particulate filter including a selective catalytic reduction (SCR) catalyst and an oxidation catalyst; (3) a second injector for injecting ammonia or a compound capable of decomposing into exhaust gas; and (4) a downstream catalyst including a selective catalytic reduction catalyst and located downstream of the second injector. The oxidation catalyst may be located, for example, on the outlet side of the diesel particulate filter. In some embodiments, such a system may include an upstream catalyst located upstream of the diesel particulate filter, the upstream catalyst including a diesel oxidation catalyst and NO. x Store catalysts or combinations thereof.

[0011] It has been found that the system configuration of the present invention provides lower total exhaust emissions. In addition to the SCR catalyst, an oxidation catalyst is also included on the diesel particulate filter to remove secondary emissions such as NH3, CO, and hydrocarbons during filter regeneration. However, in embodiments of the present invention, the oxidation catalyst on the diesel particulate filter can also provide beneficial effects by producing NO2 to optimize the performance of the downstream SCR catalyst. It has also been found that a second reducing agent injector is needed to achieve these beneficial effects in order to supply the reducing agent required for the SCR reaction on the downstream SCR catalyst.

[0012] The system components, configuration, and beneficial effects are described in more detail in this paper.

[0013] Filter

[0014] The system of the present invention includes a filter comprising an SCR catalyst and an oxidation catalyst. Such a filter may also be referred to herein as an SCRF with an oxidation catalyst. ™ Catalyst. In some embodiments, filters including SCR catalysts and oxidation catalysts can be formulated and configured to provide the desired NO2 / NO2 ratio. x The ratio is adjusted to optimize the SCR reaction on the downstream SCR catalyst.

[0015] SCR catalyst

[0016] The system of the present invention may include one or more SCR catalysts. The system includes an SCR catalyst on a diesel particulate filter as described above, and an SCR catalyst positioned downstream of the diesel particulate filter. The system of the present invention may also include one or more additional SCR catalysts.

[0017] The exhaust system of the present invention may include an SCR catalyst positioned downstream of an injector for introducing ammonia or a compound decomposed into ammonia into the exhaust gas. The SCR catalyst may be positioned directly downstream of the injector for injecting ammonia or a compound decomposed into ammonia (e.g., there is no intermediary catalyst between the injector and the SCR catalyst).

[0018] SCR catalysts include a substrate and a catalyst composition. The substrate can be a flow-through substrate or a filter substrate. When the SCR catalyst has a flow-through substrate, the substrate may contain the SCR catalyst composition (i.e., the SCR catalyst is obtained by extrusion), or the SCR catalyst composition may be disposed on or supported on the substrate (i.e., the SCR catalyst composition is applied to the substrate by a wash-coating method).

[0019] When an SCR catalyst has a filter substrate, it is a selective catalytic reduction filter catalyst, which is abbreviated as "SCRF" in this paper. ™ "Catalyst". SCRF ™ The catalyst comprises a filter substrate and a selective catalytic reduction (SCR) composition. Throughout this application, references to the use of SCR catalysts should be understood to also include, where applicable, the use of SCRF. ™ catalyst.

[0020] Selective catalytic reduction compositions may comprise or consist substantially of metal oxide-based SCR catalyst formulations, molecular sieve-based SCR catalyst formulations, or mixtures thereof. Such SCR catalyst formulations are known in the art.

[0021] Selective catalytic reduction compositions may comprise or consist substantially of metal oxide-based SCR catalyst formulations. Metal oxide-based SCR catalyst formulations comprise vanadium or tungsten, or mixtures thereof, supported on a refractory oxide. The refractory oxide may be selected from alumina, silica, titanium dioxide, zirconium oxide, cerium dioxide, and combinations thereof.

[0022] SCR catalyst formulations based on metal oxides may comprise or consist substantially of vanadium oxides (e.g., V₂O₅) and / or tungsten oxides (e.g., WO₃) supported on refractory oxides selected from titanium dioxide (e.g., TiO₂), cerium dioxide (e.g., CeO₂), and mixed or composite oxides of cerium and zirconium (e.g., CeO₂). x Zr (1-x) O2, where x = 0.1 to 0.9, preferably x = 0.2 to 0.5).

[0023] When the refractory oxide is titanium dioxide (e.g., TiO2), the concentration of vanadium oxide is preferably 0.5% to 6% by weight (e.g., in metal oxide-based SCR formulations), and / or the concentration of tungsten oxide (e.g., WO3) is 5% to 20% by weight. More preferably, vanadium oxide (e.g., V2O5) and tungsten oxide (e.g., WO3) are supported on titanium dioxide (e.g., TiO2).

[0024] When the refractory oxide is cerium dioxide (e.g., CeO2), the concentration of vanadium oxide is preferably from 0.1% to 9% by weight (e.g., in metal oxide-based SCR formulations), and / or the concentration of tungsten oxide (e.g., WO3) is from 0.1% to 9% by weight.

[0025] Metal oxide-based SCR catalyst formulations may comprise or consist essentially of vanadium oxides (e.g., V2O5) supported on titanium dioxide (e.g., TiO2) and optionally tungsten oxides (e.g., WO3).

[0026] Selective catalytic reduction compositions may comprise or consist substantially of sieve-based SCR catalyst formulations. Sieve-based SCR catalyst formulations comprise sieves, optionally transition metal-exchanged sieves. Preferably, the SCR catalyst formulation comprises transition metal-exchanged sieves.

[0027] Generally, SCR catalyst formulations based on molecular sieves may comprise molecular sieves having an aluminosilicate framework (e.g., zeolite), an aluminum phosphate framework (e.g., AlPO), a silica-aluminophosphate framework (e.g., SAPO), a heteroatom-containing aluminosilicate framework, a heteroatom-containing aluminum phosphate framework (e.g., MeAlPO, where Me is a metal), or a heteroatom-containing silica-aluminophosphate framework (e.g., MeAPSO, where Me is a metal). The heteroatoms (i.e., in the heteroatom-containing framework) may be selected from: boron (B), gallium (Ga), titanium (Ti), zirconium (Zr), zinc (Zn), iron (Fe), vanadium (V), and any two or more combinations thereof. Preferably, the heteroatoms are metals (e.g., each of the above heteroatom-containing frameworks may be a metal-containing framework).

[0028] Preferably, the molecular sieve-based SCR catalyst formulation comprises or is substantially composed of a molecular sieve having an aluminosilicate framework (e.g., zeolite) or a silica-aluminophosphate framework (e.g., SAPO).

[0029] When the molecular sieve has an aluminosilicate framework (e.g., the molecular sieve is zeolite), the molecular sieve typically has a silica to alumina molar ratio (SAR) of 5 to 200 (e.g., 10 to 200), preferably 10 to 100 (e.g., 10 to 30 or 20 to 80), such as 12 to 40, more preferably 15 to 30.

[0030] Typically, molecular sieves are microporous. Microporous molecular sieves have pores with a diameter of less than 2 nm (e.g., according to the IUPAC definition of "microporous" [see, Pure & Appl. Chem ., 66(8), (1994), 1739-1758)]).

[0031] SCR catalyst formulations based on molecular sieves may comprise small-pore molecular sieves (e.g., molecular sieves with a maximum ring size of eight tetrahedral atoms), mesopore molecular sieves (e.g., molecular sieves with a maximum ring size of ten tetrahedral atoms), or macropore molecular sieves (e.g., molecular sieves with a maximum ring size of twelve tetrahedral atoms), or combinations of two or more of these.

[0032] When the molecular sieve is a small-pore molecular sieve, it may have a framework structure represented by a framework type code (FTC) selected from the following: ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, LTA, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SFW, SIV, THO, TSC, UEI, UFI, VNI, YUG, and ZON, or a mixture of two or more of these and / or commensal forms. Preferably, the small-pore molecular sieve has a framework structure represented by an FTC selected from the following: CHA, LEV, AEI, AFX, ERI, LTA, SFW, KFI, DDR, and ITE. More preferably, the small-pore molecular sieve has a framework structure represented by FTC selected from the following: CHA and AEI. The small-pore molecular sieve may have a framework structure represented by FTC CHA. The small-pore molecular sieve may have a framework structure represented by FTC EI. When the small-pore molecular sieve is a zeolite and has a framework represented by FTC CHA, the zeolite may be chalcogenide.

[0033] When the molecular sieve is a mesoporous molecular sieve, it may have a framework structure represented by a framework type code (FTC) selected from the following: AEL, AFO, AHT, BOF, BOZ, CGF, CGS, CHI, DAC, EUO, FER, HEU, IMF, ITH, ITR, JRY, JSR, JST, LAU, LOV, MEL, MFI, MFS, MRE, MTT, MVY, MWW, NAB, NAT, NES, OBW, -PAR, PCR, PON, PUN, RRO, RSN, SFF, SFG, STF, STI, STT, STW, -SVR, SZR, TER, TON, TUN, UOS, VSV, WEI, and WEN, or a mixture of two or more of these and / or commensal forms. Preferably, the mesoporous molecular sieve has a framework structure represented by an FTC selected from the following: FER, MEL, MFI, and STT. More preferably, the mesoporous molecular sieve has a framework structure represented by FTC selected from the following: FER and MFI, specifically MFI. When the mesoporous molecular sieve is a zeolite and has a framework represented by FTC FER or MFI, the zeolite may be magnesium alkali zeolite, siliceous rock, or ZSM-5.

[0034] When the molecular sieve is a macroporous molecular sieve, the macroporous molecular sieve may have a framework structure represented by a framework type code (FTC) selected from the following: AFI, AFR, AFS, AFY, ASV, ATO, ATS, BEA, BEC, BOG, BPH, BSV, CAN, CON, CZP, DFO, EMT, EON, EZT, FAU, GME, GON, IFR, ISV, ITG, IWR, IWS, IWV, IWW, JSR, LTF, LTL, MAZ, MEI, MOR, MOZ, MSE, MTW, NPO, OFF, OKO, OSI, -RON, RWY, SAF, SAO, SBE, SBS, SBT, SEW, SFE, SFO, SFS, SFV, SOF, SOS, STO, SSF, SSY, USI, UWY, and VET, or a mixture of two or more of them and / or commensal organisms. Preferably, the macroporous molecular sieve has a framework structure represented by an FTC selected from the following: AFI, BEA, MAZ, MOR, and OFF. More preferably, the macroporous molecular sieve has a framework structure represented by an FTC selected from the following: BEA, MOR, and MFI. When the macroporous molecular sieve is a zeolite and has a framework represented by an FTC BEA, FAU, or MOR, the zeolite may be β-zeolite, octahedral zeolite, zeolite Y, zeolite X, or mordenite.

[0035] Generally speaking, small-pore molecular sieves are preferred.

[0036] SCR catalyst formulations based on molecular sieves preferably contain transition metal exchanged molecular sieves. The transition metals may be selected from cobalt, copper, iron, manganese, nickel, palladium, platinum, ruthenium, and rhenium.

[0037] The transition metal can be copper. The advantage of SCR catalyst formulations containing copper-exchanged molecular sieves is that these formulations exhibit excellent low-temperature NO₂ content. x Reduction activity (e.g., its superior low-temperature NO reduction activity compared to iron-exchanged molecular sieves) x (Reduction activity). The systems and methods of the present invention may include any type of SCR catalyst; however, systems according to the present invention comprising copper-containing SCR catalysts (“Cu-SCR catalysts”) may experience more significant beneficial effects because they are particularly susceptible to sulfation effects. Cu-SCR catalyst formulations may comprise, for example, Cu-exchanged SAPO-34, Cu-exchanged CHA zeolite, Cu-exchanged AEI zeolite, or combinations thereof.

[0038] Transition metals can be present on the extra-skeletal sites on the outer surface of the molecular sieve, or within the channels, cavities, or cages of the molecular sieve.

[0039] Typically, transition metal exchanged molecular sieves contain 0.10% to 10% by weight, preferably 0.2% to 5% by weight, of transition metal exchanged molecules.

[0040] Generally speaking, selective catalytic reduction catalysts contain a total concentration of 0.5 g·in⁻¹. -3 Up to 4.0g·in -3 Preferably 1.0 g·in -3 Up to 3.0g·in -3 Selective catalytic reduction composition.

[0041] SCR catalyst compositions may comprise a mixture of metal oxide-based SCR catalyst formulations and sieve-based SCR catalyst formulations. (a) The metal oxide-based SCR catalyst formulation may comprise or consist substantially of vanadium oxides (e.g., V2O5) and optionally tungsten oxides (e.g., WO3) supported on titanium dioxide (e.g., TiO2), and (b) the sieve-based SCR catalyst formulation may comprise transition metal-exchanged sieves.

[0042] When the SCR catalyst is SCRF ™ When using a catalyst, the filter substrate is preferably a wall-flow filter substrate, such as that described herein with respect to catalytic dust filters. Wall-flow filter substrates (e.g., wall-flow filter substrates for SCR-DPFs) typically have a pore density of 60 to 400 pores per square inch (cpsi). Preferably, the wall-flow filter substrate has a pore density of 100 to 350 cpsi, more preferably 200 to 300 cpsi.

[0043] The substrate of the wall flow filter may have a wall thickness (e.g., average inner wall thickness) of 0.20 mm to 0.50 mm, preferably 0.25 mm to 0.35 mm (e.g., about 0.30 mm).

[0044] Generally speaking, the uncoated wall-flow filter substrate has a porosity of 50% to 80%, preferably 55% to 75%, and more preferably 60% to 70%.

[0045] Uncoated wall-flow filter substrate typically has an average pore size of at least 5 μm. Preferably, the average pore size is 10 µm to 40 µm, such as 15 µm to 35 µm, more preferably 20 µm to 30 µm.

[0046] Wall-flow filter substrates can have symmetrical or asymmetrical pore designs.

[0047] Generally speaking, for SCRF ™The catalyst, a selective catalytic reduction composition, is disposed within the wall of the wall-flow filter substrate. Alternatively, the selective catalytic reduction composition may be disposed on the wall of the inlet channel and / or the wall of the outlet channel.

[0048] Oxidation catalyst

[0049] The system of the present invention may include a filter comprising an SCR catalyst and an oxidation catalyst. In some embodiments, the oxidation catalyst is coated on the outlet of the filter. In some embodiments, the filter comprising the SCR catalyst and the oxidation catalyst may be formulated and configured to provide a desired NO2 / NO2 ratio. x The ratio is adjusted to optimize the SCR reaction on the downstream SCR catalyst. The oxidation catalyst can be: 1) coated on the filter such that it is positioned on the surface of the wall (inlet or outlet); 2) coated on the porous wall such that it permeates the filter, i.e., it is positioned inside the filter; or 3) coated such that it is both inside the porous filter wall and on the surface of the wall.

[0050] In some embodiments, the oxidation comprises one or more platinum group metals. In some embodiments, the oxidation catalyst is formulated to oxidize NO to NO2; this addresses the problem of NO2 causing leakage of SCR catalyst on the filter and yields a more favorable NO2:NO ratio. x The ratio is used to carry out downstream SCR reactions.

[0051] ammonia oxidation catalyst

[0052] The system of the present invention may include one or more ammonia oxidation catalysts, also known as ammonia leakage catalysts (“ASCs”). One or more ASCs may be included downstream of an SCR catalyst to oxidize excess ammonia and prevent its release into the atmosphere. In some embodiments, the ASCs may be included on the same substrate as the SCR catalyst. In some embodiments, the ammonia oxidation catalyst material may be selected to favor the oxidation of ammonia rather than NO. x Or the formation of N2O. Preferred catalyst materials include platinum, palladium, or combinations thereof, with platinum or a platinum / palladium combination being preferred. Preferably, the ammonia oxidation catalyst comprises platinum and / or palladium supported on a metal oxide. Preferably, the catalyst is disposed on a high surface area support, which includes, but is not limited to, alumina.

[0053] In some embodiments, the ammonia oxidation catalyst comprises a platinum group metal on a silica support. The silica material may include materials such as: (1) silica; (2) zeolite with a silica-to-alumina ratio of at least 200; and (3) amorphous silica-doped alumina with a SiO2 content ≥40%. In some embodiments, the silica material may include zeolite with a silica-to-alumina ratio of at least 200; at least 250; at least 300; at least 400; at least 500; at least 600; at least 750; at least 800; or at least 1000. In some embodiments, the platinum group metals are present on the support in the following amounts: from about 0.5 wt% to about 10 wt% of the total weight of the platinum group metals and the support; from about 1 wt% to about 6 wt% of the total weight of the platinum group metals and the support; from about 1.5 wt% to about 4 wt% of the total weight of the platinum group metals and the support; from about 10 wt% of the total weight of the platinum group metals and the support; from about 0.5 wt% of the total weight of the platinum group metals and the support; from about 1 wt% of the total weight of the platinum group metals and the support; from about 2 wt% of the total weight of the platinum group metals and the support; from about 3 wt% of the total weight of the platinum group metals and the support; from about 4 wt% of the total weight of the platinum group metals and the support; from about 5 wt% of the total weight of the platinum group metals and the support; from about 6 wt% of the total weight of the platinum group metals and the support; from about 7 wt% of the total weight of the platinum group metals and the support; from about 8 wt% of the total weight of the platinum group metals and the support; from about 9 wt% of the total weight of the platinum group metals and the support; or from about 10 wt% of the total weight of the platinum group metals and the support.

[0054] In some embodiments, the silica support may include molecular sieves having a BEA, CDO, CON, FAU, MEL, MFI, or MWW framework type.

[0055] Reducing agent / urea injector

[0056] As described herein, the system of the present invention may include at least two reducing agent injectors. The system may include methods for introducing a nitrogen-containing reducing agent into the SCR and / or SCRF. ™ A device in the exhaust system upstream of the catalyst. Preferably, the device for introducing the nitrogen-containing reducing agent into the exhaust system is located directly in the SCR or SCRF. ™ Upstream of the catalyst (e.g., in a device for introducing a nitrogen-containing reducing agent with SCR or SCRF) ™ There is no intermediary catalyst between the catalysts.

[0057] The reducing agent is added to the flowing exhaust gas using any suitable means for introducing the reducing agent into the exhaust gas. Suitable means include injectors, sprayers, or feeders. Such means are well known in the art.

[0058] The nitrogen-containing reducing agent used in the system can be ammonia itself, hydrazine, or an ammonia precursor, wherein the ammonia precursor is selected from urea, ammonium carbonate, ammonium carbamate, ammonium bicarbonate, and ammonium formate. Urea is particularly preferred.

[0059] The exhaust system may also include a means of controlling the introduction of a reducing agent into the exhaust gas in order to reduce NO therein. x The device. Preferred control devices may include an electronic control unit, an optional engine control unit, and may additionally include NO located downstream of the NO reduction catalyst. x sensor.

[0060] base

[0061] The catalyst and adsorbent of the present invention may each comprise a flow-through substrate or a filter substrate. In one embodiment, the catalyst / adsorbent may be coated onto a flow-through substrate or filter substrate, and preferably deposited onto the flow-through substrate or filter substrate using a wash-coating process.

[0062] The combination of SCR catalyst and filter is called a selective catalytic reduction filter (SCRF). ™ Catalyst). SCRF ™ The catalyst is a single-base device combining the functions of SCR and particulate filter, and is suitable for embodiments of the present invention as needed. Throughout this application, descriptions and references to SCR catalysts should be understood to also include, where applicable, SCRF. ™ catalyst.

[0063] A flow-through substrate or filter substrate is a substrate capable of containing catalyst / adsorbent components. The substrate is preferably a ceramic or metallic substrate. The ceramic substrate can be made of any suitable refractory material, such as alumina, silica, titanium dioxide, cerium dioxide, zirconium oxide, magnesium oxide, zeolite, silicon nitride, silicon carbide, zirconium silicate, magnesium silicate, aluminosilicates, metallic aluminosilicates (such as cordierite and spodumene), or mixtures or mixed oxides of any two or more of these. Cordierite, magnesium aluminosilicate, and silicon carbide are particularly preferred.

[0064] The metal substrate can be made of any suitable metal, and specifically of heat-resistant metals and metal alloys, such as titanium and stainless steel, as well as ferritic alloys containing iron, nickel, chromium and / or aluminum in addition to other trace metals.

[0065] The flow-through substrate is preferably a monolithic flow-through substrate with a honeycomb structure having a number of small, parallel, thin-walled channels that extend axially through the substrate and from either an inlet or outlet. The channel cross-sections of the substrate can be of any shape, but are preferably square, sinusoidal, triangular, rectangular, hexagonal, trapezoidal, circular, or elliptical. The flow-through substrate can also have a high porosity that allows the catalyst to permeate into the substrate walls.

[0066] The filter substrate is preferably a wall-flow filter. In a wall-flow filter, the channels are alternately blocked, causing the exhaust gas to enter the channel from the inlet, then flow over the channel wall, and exit the filter through different channels leading to the outlet. Therefore, particles in the exhaust gas are captured in the filter.

[0067] Catalysts / adsorbents can be added to flow-through substrates or filter substrates in any known manner (such as wash-coating processes).

[0068] Upstream catalysts

[0069] The system of the present invention may include an upstream catalyst located upstream of a filter comprising an SCR catalyst and an oxidation catalyst. In some embodiments, the upstream catalyst may include a diesel oxidation catalyst, NO... x Store catalysts or combinations thereof.

[0070] Diesel oxidation catalyst

[0071] The system of the present invention may comprise one or more diesel oxidation catalysts. Oxidation catalysts, and specifically diesel oxidation catalysts (DOC), are well known in the art. Oxidation catalysts are designed to oxidize CO to CO2 and to oxidize gaseous hydrocarbons (HC) and the organic fraction (soluble organic fraction) of diesel particulates to CO2 and H2O. Typical oxidation catalysts include platinum on high surface area inorganic oxide supports such as alumina, silica-alumina, and zeolites, and optionally also include palladium.

[0072] NO x Storage catalyst

[0073] The system of the present invention may contain one or more NOs x Catalyst storage. NO x Catalyst storage may include the adsorption, release, and / or reduction of NO under certain conditions (typically depending on temperature and / or rich / lean exhaust gas conditions). x The equipment. NO. x Storage catalysts may include, for example, passive NO. x Adsorbent, cold start catalyst, NO x Trapping devices, etc.

[0074] Passive NO x Adsorbent

[0075] The system of the present invention may contain one or more passive NO. x Adsorbent. Passive NO x The adsorbent is effective at adsorbing NO at or below low temperatures. x And release the adsorbed NO at temperatures above low temperature. x The equipment. Passive NO x The adsorbent may include noble metals and small-pore molecular sieves. The noble metals are preferably palladium, platinum, rhodium, gold, silver, iridium, ruthenium, osmium, or mixtures thereof. Preferably, the low temperature is about 200°C, about 250°C, or between about 200°C and about 250°C. Suitable passive NO x Examples of adsorbents are described in U.S. Patent Publication 20150158019, the entire contents of which are incorporated herein by reference.

[0076] Small-pore molecular sieves can be any natural or synthetic molecular sieve, including zeolites, and are preferably composed of aluminum, silicon, and / or phosphorus. Molecular sieves typically have a three-dimensional arrangement of SiO4, AlO4, and / or PO4 linked by shared oxygen atoms, but can also have a two-dimensional structure. The molecular sieve framework is typically anionic, with charge-compensated cations typically being alkali and alkaline earth metals (e.g., Na, K, Mg, Ca, Sr, and Ba), ammonium ions, and proton balance. Other metals (e.g., Fe, Ti, and Ga) can be incorporated into the framework of the small-pore molecular sieve to prepare metal-doped molecular sieves.

[0077] Preferably, the small-pore molecular sieve is selected from aluminosilicate molecular sieves, metal-substituted aluminosilicate molecular sieves, aluminum phosphate molecular sieves, or metal-substituted aluminum phosphate molecular sieves. More preferably, the small-pore molecular sieve is a molecular sieve having the following framework types: 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, as well as mixtures or composites of any two or more. Particularly preferred small-pore molecular sieve composites include KFI-SIV, ITE-RTH, AEW-UEI, AEI-CHA, and AEI-SAV. Most preferably, the small-pore molecular sieve is AEI or CHA, or an AEI-CHA symbiotic.

[0078] Appropriate passive NO xAdsorbents can be prepared by any known method. For example, noble metals can be added to small-pore molecular sieves to form passive NO by any known method. x Adsorbents. For example, noble metal compounds (such as palladium nitrate) can be supported on molecular sieves through impregnation, adsorption, ion exchange, initial impregnation, precipitation, etc. Other metals can also be added to passive NO. x In the adsorbent. Preferably, passive NO x Some of the precious metals in the adsorbent (greater than 1% of the total added precious metals) are located within the pores of the small-pore molecular sieve. More preferably, more than 5% of the total precious metals are located within the pores of the small-pore molecular sieve; and even more preferably, more than 10%, more than 25%, or more than 50% of the total precious metals are located within the pores of the small-pore molecular sieve.

[0079] Preferably, passive NO x Adsorbents also include flow-through substrates or filter substrates. These can absorb passive NO. x The adsorbent is coated onto a flow-through substrate or filter substrate, and preferably deposited onto the flow-through substrate or filter substrate using a wash-coating process to generate passive NO. x Adsorbent system.

[0080] Cold start catalyst

[0081] The system of this invention may include one or more cold-start catalysts. Cold-start catalysts are effective at adsorbing NO at or below low temperatures. x And hydrocarbons (HC) and convert and release the adsorbed NO at temperatures above low temperatures. x The equipment and HC. Preferably, the low temperature is about 200°C, about 250°C, or between about 200°C and about 250°C. Examples of suitable cold-start catalysts are described in WO 2015085300, the entire contents of which are incorporated herein by reference.

[0082] Cold-start catalysts can include molecular sieve catalysts and supported platinum group metal catalysts. Molecular sieve catalysts may consist of or be substantially composed of noble metals and molecular sieves. Supported platinum group metal catalysts comprise one or more platinum group metals and one or more inorganic oxide supports. The noble metals are preferably palladium, platinum, rhodium, gold, silver, iridium, ruthenium, osmium, or mixtures thereof.

[0083] Molecular sieves can be any natural or synthetic material, including zeolites, and are preferably composed of aluminum, silicon, and / or phosphorus. Molecular sieves typically have a three-dimensional arrangement of SiO4, AlO4, and / or PO4 linked by shared oxygen atoms, but can also be two-dimensional structures. The molecular sieve framework is typically anionic, with charge-compensated cations typically being alkali and alkaline earth metals (e.g., Na, K, Mg, Ca, Sr, and Ba), ammonium ions, and proton balance.

[0084] The molecular sieve is preferably a small-pore molecular sieve (with a maximum ring size of eight tetrahedral atoms), a mesopore molecular sieve (with a maximum ring size of ten tetrahedral atoms), or a macropore molecular sieve (with a maximum ring size of twelve tetrahedral atoms). More preferably, the molecular sieve has a framework structure of AEI, MFI, EMT, ERI, MOR, FER, BEA, FAU, CHA, LEV, MWW, CON, EUO, or a mixture thereof.

[0085] Supported platinum group metal catalysts comprise one or more platinum group metals (“PGMs”) and one or more inorganic oxide supports. The PGM can be platinum, palladium, rhodium, iridium, or combinations thereof, and is most preferably platinum and / or palladium. Inorganic oxide supports most commonly include oxides of elements from Groups 2, 3, 4, 5, 13, and 14. Available inorganic oxide supports preferably have a [missing information - likely a specific structure or feature] at 10 m [missing information - likely a specific structure or feature]. 2 / g to 700m 2 The surface area is in the range of / g, the pore volume is in the range of 0.1 mL / g to 4 mL / g, and the pore size is about 10 angstroms to 1000 angstroms. The inorganic oxide support is preferably alumina, silica, titanium dioxide, zirconium oxide, cerium dioxide, niobium oxide, tantalum oxide, molybdenum oxide, tungsten oxide, or any two or more of these mixed oxides or composite oxides, for example, silica-alumina, cerium dioxide-zirconia, or alumina-cerium dioxide-zirconia. Alumina and cerium dioxide are particularly preferred.

[0086] Supported platinum group metal catalysts can be prepared by any known method. Preferably, the platinum group metal or metal is loaded onto one or more inorganic oxides in any known manner to form a supported PGM catalyst; the method of addition is not considered particularly critical. For example, platinum compounds (such as platinum nitrate) can be supported on inorganic oxides by impregnation, adsorption, ion exchange, initial impregnation, precipitation, etc. Other metals such as iron, manganese, cobalt, and barium can also be added to the supported PGM catalyst.

[0087] The cold-start catalyst of the present invention can be prepared by methods well known in the art. Molecular sieve catalysts and supported platinum group metal catalysts can be physically mixed to produce a cold-start catalyst. Preferably, the cold-start catalyst further includes a flow-through substrate or a filter substrate. In one embodiment, the molecular sieve catalyst and the supported platinum group metal catalyst are coated onto a flow-through substrate or a filter substrate, and preferably deposited onto the flow-through substrate or filter substrate using a wash-coating process to produce a cold-start catalyst system.

[0088] NO x trap

[0089] The system of the present invention may contain one or more NOs x Trapper. NO. x The filter adsorbs NO under lean-burn exhaust gas conditions. x Under fuel-rich conditions, the adsorbed NO is released. x And the device that reduces the released NOx to form N2.

[0090] NO. of the embodiment of the present invention x The trap may include a device for storing NO x NO x Adsorbents and oxidation / reduction catalysts. Typically, in the presence of an oxidation catalyst, nitric oxide reacts with oxygen to produce NO2. Secondly, NO2 is converted to inorganic nitrates by NO... x Adsorbent adsorption (e.g., in NO) x BaO or BaCO3 is converted to Ba(NO3) on the adsorbent. 3)2 Finally, when the engine is running under rich combustion conditions, the stored inorganic nitrates decompose to form NO or NO2, which then reacts with carbon monoxide, hydrogen, and / or hydrocarbons (or via NH4+) in the presence of a reduction catalyst. X Nitrogen oxides are reduced to N2 through a reaction with NCO intermediates. Typically, nitrogen oxides are converted into nitrogen, carbon dioxide, and water in the presence of heat, carbon monoxide, and hydrocarbons in the exhaust stream.

[0091] NO x The adsorbent component is preferably an alkaline earth metal (e.g., Ba, Ca, Sr, and Mg), an alkali metal (e.g., K, Na, Li, and Cs), a rare earth metal (e.g., La, Y, Pr, and Nd), or a combination thereof. These metals are typically present in the form of oxides. The oxidation / reduction catalyst may contain one or more noble metals. Suitable noble metals may include platinum, palladium, and / or rhodium. Preferably, platinum is included to perform the oxidation function, and rhodium is included to perform the reduction function. The oxidation / reduction catalyst and NO... x Adsorbents can be loaded onto carrier materials, such as inorganic oxides used in exhaust systems.

[0092] Filter

[0093] In addition to filters including the SCR catalyst and oxidation catalyst as described above, the system of the present invention may also include one or more particulate filters. Particulate filters are devices for reducing particulate matter from internal combustion engine exhaust. Particulate filters include catalytic particulate filters and bare (non-catalytic) particulate filters. Catalytic particulate filters, also known as catalytic soot filters (for diesel and gasoline applications), include metal and metal oxide components (such as Pt, Pd, Fe, Mn, Cu, and cerium dioxide) to oxidize hydrocarbons and carbon monoxide, and to break down soot captured by the filter.

[0094] fuel injectors

[0095] The system of the present invention may include one or more fuel injectors. For example, the system may include a secondary fuel injector upstream of a diesel oxidation catalyst. Any suitable type of fuel injector can be used in the system of the present invention.

[0096] Implementation Plan / System

[0097] The system of the present invention may include: (1) a first injector for injecting ammonia or a compound capable of decomposing into the exhaust gas; (2) a diesel particulate filter including an inlet and an outlet, wherein the filter includes a selective catalytic reduction (SCR) catalyst and an oxidation catalyst; (3) a second injector for injecting ammonia or a compound capable of decomposing into the exhaust gas and located downstream of the filter; and (4) a downstream catalyst including a selective catalytic reduction catalyst and located downstream of the second injector.

[0098] In some implementations, the system includes an upstream catalyst, which includes a diesel oxidation catalyst and NO. x Store catalysts or combinations thereof.

[0099] In some embodiments, the SCR catalyst and the oxidation catalyst are configured on the filter such that the exhaust gas comes into contact with the SCR catalyst before contacting the oxidation catalyst. In some embodiments, the oxidation catalyst is coated on the outlet of the filter. In some embodiments, the SCR catalyst is located at the inlet of the filter.

[0100] In some embodiments, the SCR catalyst is contained in a layer extending from the inlet end of the filter toward the outlet end but not overlapping with the oxidation catalyst. In some embodiments, the SCR catalyst is contained in a layer extending from the inlet end of the filter and at least partially covering the oxidation catalyst. In some embodiments, the layer containing the SCR catalyst completely covers the oxidation catalyst. In some embodiments, the layer containing the SCR catalyst partially covers the oxidation catalyst. In some embodiments, the layer containing the SCR catalyst covers approximately 0%; 5%; 7%; 10%; 15%; 20%; 25%; 30%; 35%; 40%; 45%; 50%; 55%; 60%; 65%; 70%; 75%; 80%; 85%; 90%; 95%; 100% of the length of the oxidation catalyst; up to approximately 10%; approximately 5% to approximately 50%; approximately 20% to approximately 50%; approximately 25% to approximately 75%; or approximately 30% to approximately 70%.

[0101] In some embodiments, the oxidation catalyst is contained in a bottom layer extending the entire length of the filter substrate; and the SCR catalyst is contained in a top layer extending from the inlet end of the substrate, covering all or part of the oxidation catalyst layer.

[0102] method

[0103] A method for purifying exhaust gas may include: (1) adding ammonia or a compound capable of decomposing into ammonia to the exhaust gas via a first injector; (2) passing the exhaust gas through a diesel particulate filter including an inlet and an outlet, wherein the filter includes an SCR catalyst and an oxidation catalyst; (3) adding ammonia or a compound capable of decomposing into ammonia to the exhaust gas via a second injector located downstream of the diesel particulate filter; and (4) passing the exhaust gas through a downstream catalyst including a selective reduction catalyst located downstream of the second injector.

[0104] In some implementations, the SCR catalyst and oxidation catalyst on the filter can be formulated and configured to provide the desired NO2 / NO2 ratio. x The ratio is adjusted to optimize the SCR reaction on the downstream SCR catalyst. In some embodiments, the exhaust gas from the filter containing both the SCR catalyst and the oxidation catalyst has a NO2 / NO2 ratio greater than 10%; preferably at least 15%; more preferably at least 20%. x Ratio. In some embodiments, the exhaust gas discharged from the filter containing both the SCR catalyst and the oxidation catalyst has a NO2 / NO2 ratio of 10% to 70%; preferably 15% to 65%; more preferably 20% to 60%. x Ratio. In some embodiments, the exhaust gas emanating from a filter containing both an SCR catalyst and an oxidation catalyst has a NO2 / NO2 ratio of 15% to 40% or 25% to 35%.x The ratio. In some embodiments, the exhaust gas emitting from filters containing both an SCR catalyst and an oxidation catalyst has a NO2 / NO2 ratio of 40% to 70% or 40% to 60%. x ratio.

[0105] Beneficial effects

[0106] It has been found that the system configuration of the present invention provides lower total exhaust emissions. Including an oxidation catalyst on the filter, along with an SCR catalyst, can be used to remove secondary emissions such as NH3, CO, and hydrocarbons during filter regeneration. However, in embodiments of the present invention, the oxidation catalyst on the diesel particulate filter can also provide beneficial effects by producing NO2 to optimize the performance of the downstream SCR catalyst. Generally, emissions with an SCR catalyst (i.e., SCRF) ™ NO2 / NO2 in exhaust gas from diesel particulate filters (catalysts) x The ratio can be very low, while the SCR reaction is best performed at approximately 50% NO2 / NO2. x The ratio is used. In the system of the present invention, the oxidation catalyst on the diesel particulate filter can oxidize NO that leaks from the SCR catalyst on the filter to NO2, in order to obtain a more favorable NO2 / NO ratio. x This ratio enhances the performance of downstream SCR catalysts.

[0107] It has also been found that a second reducing agent injector is needed to achieve these beneficial effects in order to supply the reducing agent required for the SCR reaction on the downstream SCR catalyst.

[0108] Example

[0109] Comparison System 1 : DOC + SCRF ™ catalyst

[0110] One type is DOC followed by SCRF ™ The system composed of catalysts, this SCRF ™ The catalyst comprises a Cu-zeolite-based catalyst coated onto a silicon carbide wall-flow filter (DPF) having approximately 300 pores per square inch (CPSI) and a wall thickness of approximately 12 mils (WT).

[0111] system 2 :Include DOC Components DOC+SCRF ™ catalyst

[0112] A type of SCRF consisting of DOC followed by an oxide layer ™ The system composed of catalysts, this SCRF ™ The catalyst consists of a Cu-zeolite-based catalyst similar to that in Comparative System 1 and a base composition with added oxidizing components, as described in the specification.

[0113] V6-3L Engine bench test

[0114] As shown in Table 1, the target temperatures for the engine evaluation setpoints are 200°C, 250°C, and 300°C. To achieve these temperatures, the engine generates different airflows and NO₂ levels. x HC and CO. In SCRF ™ The amount of urea added to the catalyst is α1.1.

[0115] Table 1 Steady-state test conditions

[0116]

[0117] like Figure 1 As shown, in comparison system 1, under the steady-state test conditions in Table 1, the post-SCRF ™ The catalyst (non-oxidizing zone) NO2 ratio is <10% (solid line). In contrast, under the same test conditions as System 2, starting at 250°C, the post-SCRF with the oxidizing zone... ™ The catalyst has a NO2 ratio >10% (dashed line). This high NO2 ratio leads to increased NO content. x Improved conversion rate (after a rapid SCR reaction) will reduce NO on downstream SCR. x Conversion rate improved.

[0118] As used in this specification and the appended claims, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” include plural references. Thus, for example, the term “catalyst” refers to a mixture comprising two or more catalysts, etc.

[0119] The term "ammonia leakage" refers to the amount of unreacted ammonia that passes through the SCR catalyst.

[0120] The term "carrier" refers to the material on which the catalyst is fixed.

[0121] The term "calcination" refers to heating a material in air or oxygen. This definition conforms to the IUPAC definition of calcination (IUPAC. Compendium of Chemical Terminology, 2nd Edition (“Gold Book”), compiled by AD McNaught and A. Wilkinson, Blackwell Scientific Publications, Oxford (1997). XML online corrected version: http: / / goldbook.iupac.org (2006-), created by M. Nic, J. Jirat, B. Kosata; updated and compiled by A. Jenkins, ISBN 0-9678550-9-8. doi:10.1351 / goldbook.). Calcination is performed to decompose metal salts and promote the exchange of metal ions within the catalyst, and also to adhere the catalyst to the substrate. The temperature used for calcination depends on the composition of the material to be calcined and is typically between about 400°C and about 900°C for about 1 to 8 hours. In some cases, calcination can be carried out at temperatures up to about 1200°C. In applications involving the methods described herein, calcination is generally carried out at a temperature of about 400°C to about 700°C for about 1 hour to 8 hours, preferably at a temperature of about 400°C to about 650°C for about 1 hour to 4 hours.

[0122] Unless otherwise specified, when one or more ranges of various numerical elements are provided, the ranges may include the value.

[0123] The term "N2 selectivity" refers to the percentage of ammonia converted into nitrogen gas.

[0124] The terms "diesel oxidation catalyst" (DOC), "diesel exothermic catalyst" (DEC), and "NO" are also mentioned. x "Adsorbent", "SCR / PNA" (Selective Catalytic Reduction / Passive NOx Adsorbent), "Cold Start Catalyst" (CSC), and "Three-Way Catalyst" (TWC) are well-known terms in the art, used to describe various types of catalysts used to treat exhaust gases from combustion processes.

[0125] The term "platinum group metals" or "PGM" refers to platinum, palladium, ruthenium, rhodium, osmium, and iridium. Platinum group metals are preferably platinum, palladium, ruthenium, or rhodium.

[0126] The terms “downstream” and “upstream” describe the orientation of the catalyst or substrate, where the flow of exhaust gas is from the inlet end of the substrate or product to the outlet end.

Claims

1. A waste gas purification system, the waste gas purification system comprising: a. A first injector, the first injector being used to inject ammonia or a compound capable of decomposing into the exhaust gas; b. A diesel particulate filter, the diesel particulate filter comprising an inlet and an outlet, wherein the filter comprises a selective catalytic reduction (SCR) catalyst and an oxidation catalyst; c. A second injector, the second injector being used to inject ammonia or a compound capable of decomposing into the exhaust gas and being located downstream of the filter; as well as d. A downstream catalyst, the downstream catalyst comprising a selective catalytic reduction catalyst and located downstream of the second injector.

2. The waste gas purification system according to claim 1, wherein the oxidation catalyst is coated on the outlet of the filter.

3. The waste gas purification system according to claim 1, wherein the oxidation catalyst comprises one or more platinum group metals.

4. The waste gas purification system according to claim 1, wherein the oxidation catalyst comprises platinum, palladium, or a combination thereof.

5. The waste gas purification system according to claim 1, wherein the selective catalytic reduction catalyst comprises a metal oxide-based SCR catalyst formulation, a molecular sieve-based SCR catalyst formulation, or a mixture thereof.

6. The waste gas purification system according to claim 1, wherein the downstream catalyst further includes an ammonia oxidation catalyst.

7. The waste gas purification system according to claim 1, wherein the waste gas entering the downstream catalyst has a NO2:NO content greater than 10%. x ratio.

8. The waste gas purification system according to claim 1 further includes an upstream catalyst located upstream of the filter, the upstream catalyst comprising a diesel oxidation catalyst and NO... x Store catalysts or combinations thereof.

9. A method for purifying waste gas, the method comprising: a. Ammonia or a compound capable of decomposing into ammonia is added to the exhaust gas via a first injector; b. Pass the exhaust gas through a diesel particulate filter including an inlet and an outlet, wherein the filter includes a selective catalytic reduction (SCR) catalyst and an oxidation catalyst; c. Ammonia or a compound capable of decomposing into ammonia is added to the exhaust gas via a second injector located downstream of the filter; as well as d. Pass the exhaust gas through a downstream catalyst, which includes a selective reduction catalyst, located downstream of the second injector.

10. The method of claim 9, wherein the oxidation catalyst is coated on the outlet of the filter.

11. The method of claim 9, wherein the oxidation catalyst comprises one or more platinum group metals.

12. The method of claim 9, wherein the oxidation catalyst comprises platinum, palladium, or a combination thereof.

13. The method of claim 9, wherein the selective catalytic reduction catalyst comprises a metal oxide-based SCR catalyst formulation, a molecular sieve-based SCR catalyst formulation, or a mixture thereof.

14. The method of claim 9, wherein the downstream catalyst further comprises an ammonia oxidation catalyst.

15. The method of claim 9, wherein the exhaust gas entering the downstream catalyst has a NO2:NO content greater than 10%. x ratio.

16. The method of claim 9, further comprising an upstream catalyst located upstream of the filter, the upstream catalyst comprising a diesel oxidation catalyst, NO... x Store catalysts or combinations thereof.

Images