WO2023028928A1 - 氨吸附催化剂及其制备方法和应用 - Google Patents

氨吸附催化剂及其制备方法和应用 Download PDF

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WO2023028928A1
WO2023028928A1 PCT/CN2021/116066 CN2021116066W WO2023028928A1 WO 2023028928 A1 WO2023028928 A1 WO 2023028928A1 CN 2021116066 W CN2021116066 W CN 2021116066W WO 2023028928 A1 WO2023028928 A1 WO 2023028928A1
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Prior art keywords
ammonia
adsorption
catalyst
molecular sieve
ammonia adsorption
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PCT/CN2021/116066
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English (en)
French (fr)
Inventor
徐立峰
沈源
韦虹
王瑞平
肖逸阁
Original Assignee
宁波吉利罗佑发动机零部件有限公司
极光湾科技有限公司
浙江吉利控股集团有限公司
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Application filed by 宁波吉利罗佑发动机零部件有限公司, 极光湾科技有限公司, 浙江吉利控股集团有限公司 filed Critical 宁波吉利罗佑发动机零部件有限公司
Priority to CN202180039636.5A priority Critical patent/CN115843275B/zh
Priority to JP2023513253A priority patent/JP2023543668A/ja
Priority to EP21953607.5A priority patent/EP4183485A4/en
Priority to PCT/CN2021/116066 priority patent/WO2023028928A1/zh
Priority to US18/173,184 priority patent/US20230201812A1/en
Publication of WO2023028928A1 publication Critical patent/WO2023028928A1/zh

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    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/50—Zeolites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/50—Zeolites
    • B01D2255/502—Beta zeolites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/902—Multilayered catalyst
    • B01D2255/9022—Two layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/904—Multiple catalysts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/911—NH3-storage component incorporated in the catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/40—Nitrogen compounds
    • B01D2257/406—Ammonia
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases
    • B01D2258/014—Stoichiometric gasoline engines
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9459—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts
    • B01D53/9477—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts with catalysts positioned on separate bricks, e.g. exhaust systems
    • 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
    • F01N2510/00—Surface coverings
    • F01N2510/06—Surface coverings for exhaust purification, e.g. catalytic reaction
    • F01N2510/068—Surface coverings for exhaust purification, e.g. catalytic reaction characterised by the distribution of the catalytic coatings
    • F01N2510/0684—Surface coverings for exhaust purification, e.g. catalytic reaction characterised by the distribution of the catalytic coatings having more than one coating layer, e.g. multi-layered coatings
    • 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
    • F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
    • F01N2570/18—Ammonia
    • 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
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • 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 invention relates to the field of engine tail gas treatment catalysts, in particular to an ammonia adsorption catalyst and its preparation method and application.
  • Ammonia (NH 3 ) in the aftertreatment exhaust system of automobile engines has two sources: (1) under rich operating conditions, in catalysts (such as three-way catalysts (TWC) and lean NOx trap catalysts ( (2) Actively added to the aftertreatment system from outside as the reductant of the lean-burn selective reduction of nitrogen oxides catalyst (SCR).
  • the basic function of the ammonia oxidation catalyst (ASC) is to absorb and eliminate (including conversion or oxidation) excess ammonia (NH 3 ) in the exhaust gas, so as to reduce the leakage of ammonia along with the exhaust gas.
  • the ASC catalyst is arranged at the rear end of the aftertreatment system.
  • ASC products currently on the market generally have two independent coatings, one is an ammonia oxidation coating (such as the ammonia oxidation layer 2 of Figure 1) positioned on the surface of the carrier 3, and the other is an ammonia adsorption material layer positioned on the surface of the ammonia oxidation coating ( Adsorption layer 1) in Figure 1, as shown in Figure 1, the ammonia-containing airflow f passes through the ASC, and is first adsorbed by the adsorption layer 1 at the front end, and the adsorbed ammonia is gradually desorbed along with the flow of engine exhaust, and after desorption The ammonia quickly passes through the ammonia oxidation layer 2 and is at least partially oxidized (during this process, the unadsorbed and unoxidized ammonia continues to be adsorbed, desorbed and oxidized by the downstream adsorption layer and ammonia oxidation layer).
  • an ammonia oxidation coating such as the ammonia oxidation layer 2 of Figure 1
  • Adsorption layer 1
  • the typical ammonia adsorption material used to form the ammonia adsorption material layer is a molecular sieve material (such as Cu- ⁇ , Fe- ⁇ , Cu-SSZ-13, etc.) replaced by metal atoms.
  • this type of molecular sieve material also Ammonia can be gradually consumed as a reducing agent for converting NOx under the condition of lean combustion (air-fuel ratio ⁇ >1.0), which mainly adsorbs the ammonia in the exhaust gas through chemical and physical adsorption.
  • Chemisorbed ammonia is relatively stable and not easy to desorb, but the amount of chemisorption is very limited (chemisorption mainly occurs at the Bronsted acid sites (BAS) in molecular sieves, and usually the amount of chemisorbed ammonia is less than the total amount of ammonia adsorbed 15%.
  • BAS Bronsted acid sites
  • the BAS acid sites will be greatly reduced, thereby significantly reducing the amount of chemical adsorption of ammonia by the adsorbent) .
  • a large amount of ammonia in the exhaust is temporarily physically adsorbed in the molecular sieve through the van der Waals force in the molecular sieve.
  • the ammonia adsorbed in the molecular sieve will gradually desorb with the flow of engine exhaust, and the ammonia desorbed from the front-end molecular sieve will be released again. It is re-adsorbed and desorbed by the downstream molecular sieve, and the cycle repeats.
  • the ammonia oxidation material in the ammonia oxidation layer usually includes a matrix material such as alumina and a noble metal (such as platinum (Pt) etc.) loaded on the matrix material. After ammonia is desorbed from the molecular sieve material of the adsorption layer, it quickly passes through the ammonia oxidation layer. And be at least partially oxidized, the unoxidized ammonia continues to be adsorbed, desorbed and oxidized by the downstream adsorption layer and ammonia oxidation layer.
  • LNG Compressed Natural Gas
  • TWC three-way catalyst
  • NOx in the exhaust gas can generally be removed by SCR, specifically injecting urea, which is hydrolyzed into ammonia, ammonia selectively reduces NOx to nitrogen and water, and the SCR rear end Excess, would-be-spill ammonia can be removed by ASC.
  • ammonia is mainly removed by ASC in three ways: (1) it is catalyzed and oxidized by the ammonia oxide layer; (2) it is partially consumed as a reducing agent for converting NOx in the molecular sieve material; (3) ) A small part of ammonia is oxidized into nitrogen in the molecular sieve material at high temperature.
  • the working principle of ASC in the TWC aftertreatment system of the equivalent running engine is as follows: Unlike the active input of ammonia (urea injection) in the SCR aftertreatment system of the lean burn running engine, the ammonia generated on the TWC is only under the condition of partial richness ( ⁇ 1.0) Generated and adsorbed by downstream ASC (the adsorbed ammonia cannot be oxidized or eliminated under rich conditions), when the exhaust gas is switched to a lean state ( ⁇ >1.0) (including engine operating modes such as deceleration and fuel cut-off) , Ammonia is mainly oxidized in the oxide layer under oxygen-enriched conditions. The greater the adsorption amount of ASC to ammonia, the higher the oxidation efficiency, and the stronger the leakage ability of ammonia in the exhaust gas of the reduced equivalent operation engine.
  • the current typical ASC catalyst consists of the surface adsorption layer and the bottom ammonia oxidation layer (as shown in Figure 1).
  • the amount of ammonia adsorption materials must be increased as much as possible.
  • the amount of layer usually reaches more than 150 g/L catalyst carrier, and the amount of ammonia oxidation layer is below 50 g/L carrier.
  • the current ASC generally has the following defects: (1) Even if the total coating amount is above 200 g/L carrier, The ammonia adsorption capacity of ASC is still insufficient, and the adsorption efficiency is low; (2) The oxidation of ammonia is mainly completed through the ammonia oxidation layer in the short time between the desorption of ammonia from the molecular sieve material and the adsorption by the molecular sieve material, and the reaction time is short.
  • the conversion efficiency is limited; (3) The specific combination of the adsorption layer and the ammonia oxidation layer determines that ASC must be applied independently (different carriers or partition coatings are used with other catalysts), which will increase the cost of the carrier and packaging of the post-treatment system At the same time, it may bring difficulties to the reasonable layout of the limited chassis space.
  • the invention provides an ammonia adsorption catalyst, which has the advantages of high ammonia adsorption/conversion efficiency, low cost, flexible application, etc., and can effectively improve the defects existing in the prior art.
  • One aspect of the present invention provides an ammonia adsorption catalyst, which includes a carrier and an adsorption layer located on the surface of the carrier, the adsorption layer contains molecular sieve adsorption materials containing noble metals.
  • the noble metal includes platinum and/or palladium.
  • the content of the noble metal in the molecular sieve adsorption material containing noble metal is 1-20 g/cubic foot.
  • the molecular sieve adsorption material containing precious metals is obtained by exchanging precious metals into molecular sieves by ion exchange, and the molecular sieves include at least one of ⁇ molecular sieves, Y molecular sieves, and ZSM-5 molecular sieves.
  • the mass content of the molecular sieve adsorption material containing precious metals in the adsorption layer is 90-100%.
  • the mass-to-volume ratio of the molecular sieve adsorption material containing precious metals to the carrier is 30-200 g: 1 L.
  • the carrier includes at least one of cordierite, silicon carbide, and metal carriers.
  • Another aspect of the present invention provides a method for preparing the above-mentioned ammonia adsorption catalyst, comprising: using a noble metal precursor to carry out ion exchange treatment on molecular sieves to obtain molecular sieve adsorption materials containing noble metals; combining the molecular sieve adsorption materials containing noble metals with a binder and solvents are mixed to prepare a slurry; the slurry is coated on a carrier, dried and calcined to form an adsorption layer to obtain the ammonia adsorption catalyst.
  • Another aspect of the present invention provides an application of the above-mentioned ammonia adsorption catalyst in an engine aftertreatment system.
  • the engine aftertreatment system includes an engine aftertreatment system in normal operation.
  • the engine aftertreatment system includes a three-way catalyst, and the gas to be treated in the engine aftertreatment system is first treated by the three-way catalyst and then treated by the ammonia adsorption catalyst; or, the The engine aftertreatment system includes a selective redox catalyst, and the gas to be treated in the engine aftertreatment system is first treated by the selective redox catalyst and then treated by the ammonia adsorption catalyst.
  • the ammonia adsorption catalyst is used in combination with the three-way catalyst, and the compounding method includes at least one of the following methods A and B: method A: the adsorption layer of the ammonia adsorption catalyst A three-way catalyst layer formed of a three-way catalyst is arranged between the carrier and the carrier; mode B: the adsorption layer of the ammonia adsorption catalyst also contains the three-way catalyst.
  • noble metals are introduced into the molecular sieve adsorption material, and there is no need to coat the ammonia oxide layer on the carrier, which simplifies the production process of the catalyst, reduces the difficulty of production, reduces the cost, and saves space at the same time, and can load more catalysts on the carrier.
  • the molecular sieve adsorption material increases the adsorption capacity of ammonia, and the ammonia adsorbed in the molecular sieve adsorption material can be directly catalyzed and oxidized in the molecular sieve adsorption material, which increases the oxidation reaction time of ammonia, thereby improving the conversion rate of ammonia; in addition, the present invention
  • the ammonia adsorption catalyst can also be used in combination with other catalysts (for example, it can be used in combination with a three-way catalyst (TWC) coating to absorb ammonia when the exhaust gas is relatively rich ( ⁇ 1.0), and to oxidize ammonia when the exhaust gas is relatively lean ( ⁇ >1.0).
  • TWC three-way catalyst
  • the application is more flexible; in addition, studies have shown that, compared to conventional molecular sieves (such as Cu-molecular sieves) and hydrogen-type molecular sieves (H-molecular sieves), the present invention introduces molecular sieve adsorption materials of precious metals (replacement in molecular sieves)
  • molecular sieve adsorption materials of precious metals replacement in molecular sieves
  • noble metals in molecular sieves for Bronsted acid sites H + can not only increase the amount of ammonia adsorption, but also show better thermal stability, and can also show relatively better
  • the ammonia adsorption performance, the thermal aging temperature is generally higher than the actual application temperature, and the temperature during the application of the catalyst is generally 200-500°C.
  • the ammonia adsorption catalyst of the present invention can be used at a temperature of 200-500°C or even higher. Therefore, the ammonia adsorption catalyst of the present invention has the advantages of high ammonia adsorption/conversion efficiency, low cost, flexible application, good thermal stability, etc., and is of great significance for practical industrial application.
  • FIG. 1 is a schematic diagram of the structure and application process of an existing ASC.
  • Fig. 2 is a curve diagram of the ammonia adsorption capacity of different ammonia adsorption catalysts ASC with the same molecular sieve loading after freshness and aging in an embodiment of the present invention
  • Fig. 3 ( ⁇ >1) is a graph showing the ammonia conversion efficiency of the ammonia adsorption catalyst in an embodiment of the present invention and the ASC in a comparative example as a function of temperature under lean burn conditions.
  • the ammonia adsorption catalyst of the present invention comprises a carrier and an adsorption layer on the surface of the carrier, the adsorption layer contains molecular sieve adsorption materials containing precious metals.
  • the molecular sieve adsorption material has good adsorption and catalytic oxidation ability to ammonia
  • the noble metal introduced into the molecular sieve adsorption material mainly plays the function of catalytic oxidation of ammonia
  • the noble metal can include platinum (Pt), palladium (Pd ), rhodium (Rh), but not limited thereto, in some preferred embodiments, the noble metal includes platinum and/or palladium, which is beneficial to further improving the efficiency of ammonia adsorption catalytic oxidation while saving costs.
  • the content of precious metals in molecular sieve adsorption materials is 1-20 g/cubic feet, such as 1 g/cubic feet, 3 g/cubic feet, 5 g/cubic feet, 7 g/cubic feet, 10 g/cubic feet, 12 g/cubic feet Cubic feet, 15 g/cubic feet, 18 g/cubic feet, 20 g/cubic feet or any combination thereof, generally preferably 3 to 5 g/cubic feet.
  • the above-mentioned molecular sieve adsorption material containing precious metals can be obtained by exchanging precious metals into molecular sieves by ion exchange.
  • the molecular sieves used can include at least one of ⁇ molecular sieves, Y molecular sieves, and ZSM-5.
  • the volume of the molecular sieve adsorption material is basically equal to the volume of the molecular sieve used.
  • the amount of precious metal and molecular sieve can be controlled to meet 3-5 grams: 1 cubic foot, so as to obtain a precious metal content of 3-5 grams. / cubic foot of molecular sieve adsorbent material.
  • the present invention is not limited to the ion exchange method, and the noble metal can also be exchanged on the molecular sieve by means of spraying or the like.
  • the process of the ion exchange method may generally include: dissolving the noble metal precursor in a solvent to form an impregnating solution, using the impregnating solution to impregnate the molecular sieve, such as equal-volume impregnation, etc., followed by drying and calcining to obtain a molecular sieve containing noble metal Adsorption material;
  • noble metal precursor generally can comprise the compound containing noble metal such as the salt of noble metal, specifically can comprise the soluble salt of noble metal, for example nitrate, as platinum nitrate and/or palladium nitrate etc., usually can be in drying, calcining process It decomposes anions such as nitrate, so as to be separated from the molecular sieve material.
  • the above-mentioned adsorption layer may also contain binders and/or auxiliary materials (auxiliary materials), which are beneficial to bonding the above-mentioned molecular sieve adsorption materials containing precious metals to form a coating (ie, an adsorption layer), and optimize the strength and stability of the adsorption layer.
  • auxiliary materials auxiliary materials
  • the mass content of the molecular sieve adsorption material containing precious metals in the adsorption layer is 90-100%, and the balance can be binder and auxiliary materials.
  • the binder may include aluminum glue and/or silica gel, etc.
  • the auxiliary material may include cerium material and/or zirconium material, etc.
  • the above-mentioned molecular sieve adsorption material containing precious metals can be coated on the surface of the carrier to form an adsorption layer.
  • the molecular sieve adsorption material can be mixed with a binder and a solvent to form a slurry, and the slurry can be coated On the surface of the carrier, an adsorption layer is formed after drying.
  • the mass volume ratio of the above-mentioned molecular sieve adsorption material containing precious metals to the carrier can be 30-280g:1L, for example, 30g:1L, 50g:1L, 80g:1L, 100g:1L, 120g:1L, 150g:1L, 180g: 1L, 200g: 1L, 230g: 1L, 250g: 1L, 280g: 1L or any two of them.
  • the thickness of the adsorption layer (coating amount of the molecular sieve adsorption material on the carrier) can be regulated according to the chassis space of the automobile, and as much molecular sieve adsorption material as possible can be coated to increase the ammonia adsorption amount.
  • the ratio of the mass of the adsorption layer to the volume of the carrier is preferably 150g-230g:1L.
  • the present invention can use conventional supports in the field.
  • the supports include at least one of cordierite (generally ceramic honeycomb), silicon carbide and metal supports.
  • the structure of the carrier is, for example, a particle filter (GPF), etc., which is not particularly limited in the present invention.
  • the preparation method of the ammonia adsorption catalyst comprises: using a noble metal precursor to carry out ion exchange treatment on molecular sieves (that is, exchanging noble metals into molecular sieves by ion exchange) to obtain molecular sieve adsorption materials containing noble metals; adsorbing molecular sieves containing noble metals
  • the material is mixed with a binder and a solvent to make a slurry; the slurry is coated on the surface of the carrier, dried at 80-90°C to remove a large amount of solvent, then dried at 100-200°C to remove the residual solvent, and then dried at 500 Roast at -650°C to form an adsorption layer on the surface of the carrier to obtain an ammonia adsorption catalyst; the calcination time can be 1 to 2 hours, but not limited thereto.
  • the above-mentioned ammonia adsorption catalyst can be used directly, and can also be compounded with other catalysts or their functional components.
  • the above-mentioned ammonia adsorption catalyst can be combined with TWC to form a multifunctional catalyst.
  • TWC can be introduced into the adsorption layer , that is, the molecular sieve adsorption material containing precious metals is mixed with TWC to form an adsorption layer, that is, the above-mentioned adsorption layer also contains a TWC catalyst; or, in addition to the adsorption layer, the surface of the carrier can also be provided with a TWC coating formed by TWC.
  • the adsorption layer and TWC The coating is located in different areas of the carrier surface (that is, it is arranged in partitions on the carrier surface), and the two can be connected or not (that is, separated by a distance); or, the TWC coating and the adsorption layer are layered on the carrier surface, and the TWC coating
  • the layer is located between the carrier surface and the adsorption layer, or the adsorption layer is located between the TWC coating and the carrier surface, preferably the adsorption layer is located between the TWC coating and the carrier surface.
  • the present invention also provides the application of the above-mentioned ammonia adsorption catalyst in an engine aftertreatment system
  • the engine aftertreatment system may include an equivalent operation engine aftertreatment system, that is, the above-mentioned ammonia adsorption catalyst can be used in an equivalent operation engine aftertreatment system, for example, it can be used in Equivalent operation of the TWC rear end in the engine aftertreatment system (that is, the engine exhaust is first treated by TWC and then treated by the above-mentioned ammonia adsorption catalytic gas) can efficiently adsorb and convert ammonia.
  • ammonia is generated on the TWC under the condition of partial richness ( ⁇ 1.0).
  • the ammonia adsorption catalyst basically cannot oxidize ammonia, but mainly by adsorption Ammonia is the main component. Under the condition of partial dilution ( ⁇ >1.0), ammonia will no longer be generated on the TWC.
  • the ammonia adsorption catalyst can oxidize ammonia, so it is mainly used to oxidize ammonia.
  • the ammonia adsorption catalyst of the present invention can be used in an aftertreatment system of an engine with equivalent operation, can significantly increase the amount of ammonia adsorption, and also exhibits good ammonia conversion (catalytic oxidation) performance.
  • the above-mentioned engine aftertreatment system may also include an aftertreatment system for a lean-burn ( ⁇ >1.0) engine, that is, the above-mentioned ammonia adsorption catalyst can be used in an engine aftertreatment system for a lean-burn engine, such as SCR rear end used in lean burn engine aftertreatment systems.
  • the ammonia adsorption catalyst can be used alone.
  • the engine aftertreatment system includes a three-way catalyst (TWC).
  • Ammonia adsorption catalyst treatment that is, ammonia adsorption catalyst is used in TWC backend.
  • the engine aftertreatment system includes a selective redox catalyst (SCR).
  • SCR selective redox catalyst
  • Adsorption catalysts are used in the SCR catalyst backend.
  • the ammonia adsorption catalyst can also be combined with other catalysts (such as TWC, etc.) or its functional components.
  • the ammonia adsorption catalyst is used in combination with the three-way catalyst, so
  • the compounding mode includes at least one of the following mode A and mode B: mode A: a three-way catalyst layer formed by a three-way catalyst is arranged between the adsorption layer of the ammonia adsorption catalyst and the carrier; mode B: The adsorption layer of the ammonia adsorption catalyst also contains the three-way catalyst.
  • it can be specifically used in the TWC system in the engine aftertreatment system.
  • the ammonia adsorption catalyst of this embodiment (referred to as fresh (Pt-molecular sieve)) consists of a carrier, an alumina coating on the surface of the carrier, and an adsorption layer on the surface of the alumina coating, wherein the alumina coating is made of alumina material Formed with binder coating, the adsorption layer is formed by platinum-containing molecular sieve adsorption material (Pt-molecular sieve) and binder coating;
  • the components of the adsorption layer are binder and platinum-containing molecular sieve adsorption material (Pt-molecular sieve), the mass content of Pt-molecular sieve in the adsorption layer is 97%, and the balance is binder;
  • the content of platinum in the Pt-molecular sieve is 5 grams per cubic foot;
  • Pt-molecular sieve is obtained by exchanging platinum into molecular sieve by ion exchange method, and the molecular sieve used is ⁇ molecular sieve;
  • the mass volume ratio of Pt-molecular sieve to carrier is 150g: 1L (that is, the loading capacity of Pt-molecular sieve is 150g/L);
  • the mass volume ratio of alumina coating to carrier is 50g:1L (that is, the loading capacity of alumina is 50g/L);
  • the carrier is cordierite
  • Example 2 The difference between Example 2 and Example 1 is that the ammonia adsorption catalyst consists of a carrier and an adsorption layer positioned on the carrier surface (that is, there is no alumina coating), and the mass-to-volume ratio of the Pt-molecular sieve to the carrier is 200g: 1L (that is, the Pt- The loading capacity of molecular sieve is 200g/L);
  • the catalyst of this comparative example 1 (recorded as fresh (Cu-molecular sieve)) is a conventional ASC, which is composed of a carrier, an ammonia oxidation layer on the surface of the carrier, and an ammonia adsorption layer on the surface of the ammonia adsorption layer.
  • the ammonia adsorption layer is made of Cu-molecular sieve.
  • the coating formed by coating with binder, the ammonia oxide layer is a coating (50g/L) formed by coating alumina material loaded with platinum and binder; wherein:
  • the carrier in Comparative Example 1 is identical to the carrier in Example 1;
  • the platinum content in the total coating consisting of the ammonia adsorption layer and the ammonia oxidation layer in comparative example 1 is the same as the platinum content in the adsorption layer in Example 1;
  • the loading amount of Cu-molecular sieve in Comparative Example 1 is the same as that of Pd-molecular sieve in Example 1 (150 g/L).
  • Example 1 The ammonia adsorption catalyst in Example 1 was reacted for 40 hours in a tubular reactor at 720° C. under the condition of maintaining a space velocity of 30,000 hr ⁇ 1 to obtain an aged ammonia adsorption catalyst (referred to as aging (Pt-molecular sieve));
  • aging Pt-molecular sieve
  • the catalyst in Comparative Example 1 is aged to obtain the aged catalyst (referred to as aging (Cu-molecular sieve));
  • the catalyst in Comparative Example 2 is aged to obtain an aged catalyst (referred to as aging (H-molecular sieve));
  • Test 1 Simulate the composition of the exhaust gas after TWC in the aftertreatment system of the equivalent running engine (see synthesis gas in the ammonia adsorption experiment in Table 1), the space velocity is 170000hr -1 , and the ammonia adsorption capacity (storage capacity) of the catalyst is tested under this condition Variation curve with temperature;
  • Test 2 Simulate the composition of the exhaust gas after SCR in the aftertreatment system of the lean-burn engine (see synthetic gas in the ammonia oxidation experiment in Table 1), the space velocity is 170000hr -1 , and the efficiency of the catalyst to convert ammonia (ammonia Conversion rate) as a function of temperature.
  • the ammonia adsorption capacity of aging (Pd-molecular sieve) at 200 ° C is about 1.36 g/L; in addition, no matter it is fresh or after aging, the ammonia adsorption of the ammonia adsorption catalyst in Example 1 The amount is higher than the catalyst in Comparative Example 1 and Comparative Example 2, showing better ammonia adsorption performance and thermal stability, fresh (Pt-molecular sieve), fresh (Cu-molecular sieve), fresh (H-molecular sieve) at 200
  • the ammonia adsorption at °C is 2.79g/L, 2.4g/L, and 2.3g/L in turn, and the ammonia adsorption of aging (Pt-molecular sieve), aging (Cu-molecular sieve), and aging fresh (H-molecular sieve) is at 200
  • the ammonia adsorption amounts at °C were 1.36 g/L, 0.9 g/L, and 0.67 g
  • the ammonia adsorption catalyst of Example 1 also has good ammonia conversion performance while increasing the amount of ammonia adsorption, which is close to the ammonia conversion rate of the catalyst in Comparative Example 1 and Comparative Example 2;
  • the conversion rate tends to increase with the increase of temperature, and the ammonia conversion performance of the aged catalyst decreases, but the aging (Pt-molecular sieve) can still maintain a high ammonia conversion rate.
  • ammonia is produced when the fuel is relatively rich and is absorbed by catalysts such as ASC, and ammonia is oxidized when the fuel is lean.
  • the catalytic oxidation efficiency of the ammonia adsorption catalyst to ammonia is basically equivalent to that of the catalysts in Comparative Examples 1 and 2, and the ammonia adsorption amount of the ammonia adsorption catalyst in Example 1 is significantly better than that of the catalysts in Comparative Examples 1 and 2, and the ammonia adsorption catalyst in Example 1
  • the adsorption catalyst can be coated with up to 30% more ammonia adsorption (molecular sieve) materials than in comparative examples 1 and 2 under the same size carrier situation, and under the situation that the catalytic oxidation efficiency to ammonia is basically equal, the larger the ammonia adsorption capacity is, the greater the The better the removal effect of ammonia in the exhaust gas.
  • the above-mentioned embodiment 1 is designed, and the relevant experimental process of embodiment 1 and comparative example 1 is listed, which proves that the ammonia adsorption catalyst of the present invention has more excellent performance than conventional ASC Ammonia reduction effect, the present invention has further designed embodiment 2, and carried out above-mentioned experimental test to the catalyst of embodiment 2, the results show that the performances such as ammonia adsorption performance, ammonia oxidation performance and thermal stability of embodiment 2 are all better than embodiment 1 ammonia adsorption catalyst.

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Abstract

本发明提供一种氨吸附催化剂及其制备方法和应用，所述氨吸附催化剂包括载体、以及位于所述载体表面的吸附层，所述吸附层包含含有贵金属的分子筛吸附材料。本发明的催化剂兼具氨吸附/转化效率高、成本低、应用灵活等优点。

Description

氨吸附催化剂及其制备方法和应用 技术领域
本发明涉及发动机尾气处理催化剂领域，具体涉及一种氨吸附催化剂及其制备方法和应用。
背景技术
汽车发动机后处理排放系统中的氨(NH 3)有两个来源：(1)在偏富的运行条件下，在催化剂(例如，三效催化剂(TWC)和稀燃氮氧化物捕集催化剂(LNT))上产生；(2)作为稀燃选择性还原氮氧化物催化剂(SCR)的还原剂从外部主动加入到后处理系统中。氨氧化催化剂(ASC)的基本功能是吸附和消除(包括转化或氧化)排放气体中多余的氨(NH 3)，以减少氨随着尾气泄露。通常ASC催化剂布置在后处理系统的后端。目前市场上的ASC产品一般具有两个独立涂层，一个是位于载体3表面的氨氧化涂层(如图1的氨氧化层2)，一个是位于氨氧化涂层表面的氨吸附材料层(如图1的吸附层1)，如图1所示，含氨的气流f通过ASC，首先被前端的吸附层1吸附，被吸附的氨随着发动机排气的流动逐渐脱附，脱附后的氨快速通过氨氧化层2并被至少部分氧化(该过程中，未被吸附、未被氧化的氨继续被下游的吸附层和氨氧化层进行吸附、脱附和氧化过程)。
其中，用于形成氨吸附材料层的典型氨吸附材料是由金属原子置换的分子筛材料(如Cu-β、Fe-β、Cu-SSZ-13等)，这类分子筛材料除了吸附氨外，还能在稀燃(空燃比λ>1.0)条件下把氨作为转化NOx的还原剂逐渐消耗掉，其主要是通过化学和物理吸附两类方式吸附排气中的氨。化学吸附的氨比较稳定，不容易脱附出来，但是化学吸附的量很有限(化学吸附主要发生在分子筛中的布朗斯特酸位点(BAS)，通常化学吸附氨量小于总氨吸附量的15％。当催化剂暴露在正常的热老化温度下(一般在650-700℃左右，尤其是>700℃)，BAS酸位点会极巨减少，从而显著减少吸附材料对氨的化学吸附量)。排气中的大量氨是通过分子筛中的范德 华尔斯力短暂地物理吸附在分子筛中，被吸附在分子筛中的氨会随着发动机排气的流动逐渐脱附，从前端分子筛脱附的氨又被下游的分子筛再吸附、脱附，周而复始。氨氧化层中的氨氧化材料通常包括氧化铝等基体材料以及负载在该基体材料上的贵金属(例如铂(Pt)等)，氨从吸附层的分子筛材料中脱附后快速通过氨氧化层，并被至少部分氧化，未被氧化的氨继续被下游的吸附层和氨氧化层进行吸附、脱附和氧化过程。
目前，ASC已被广泛用于稀燃运行状态下选择性氧化还原(SCR)系统和当量(λ＝0.98～1.02)运行状态下天然气(包括压缩天然气Compressed Natural Gas(CNG)和液化天然气Liquified Natural Gas(LNG))发动机运行系统三效催化剂(TWC)后端，以减少后处理系统的氨泄漏。具体来说，在稀燃(富氧)运行状态下，排气中的NOx一般可以通过SCR去除，具体是喷射尿素，尿素水解为氨，氨将NOx选择性还原为氮气和水，SCR后端可以通过ASC去除过量、将要泄漏的氨。在该稀燃状态下，氨主要通过三种途径被ASC去除：(1)被氨氧化层催化氧化掉；(2)在分子筛材料中作为转化NOx的还原剂，从而被部分消耗掉；(3)高温下小部分氨在分子筛材料中被氧化成氮气等。ASC在当量运行发动机TWC后处理系统中的工作原理如下：不同于稀燃运行发动机SCR后处理系统中主动输入氨(尿素喷射)，TWC上生成的氨只在偏富(λ<1.0)条件下产生，被下游ASC吸附(被吸附的氨在偏富条件下并不能被氧化或者消除)，当排气被切换到偏稀(λ>1.0)的状态(包括减速断油等发动机运行模式)时，氨在富氧条件下主要在氧化层被氧化掉，ASC对氨的吸附量越大，氧化效率越高，降低当量运行发动机废气中氨的泄漏能力越强。
如上所述，目前典型的ASC催化剂由表层的吸附层和底层的氨氧化层组成(如图1)，为了提高ASC降低氨泄漏的效率，必须尽可能增加氨吸附材料的量，因此ASC中吸附层的量通常达到150克/升催化剂载体以上，氨氧化层的量在50克/升载体以下，目前的ASC普遍存在以下缺陷：(1)即使总涂敷量在200克/升载体以上，ASC的氨吸附量仍显不足，吸附效率低；(2)氨的氧化主要是在氨从分子筛材料脱附到再被分子筛材料吸附之间的短暂时间里通过氨氧化层完成，反应时间短，限制了转化效率；(3)吸附层和氨氧化层的特定组合，决定了ASC必须独立应用(与 其它催化剂分别采用不同载体或者分区涂敷)，这样会增加后处理系统的载体、封装等成本，同时可能给有限底盘空间的合理布置带来困难。
降低发动机尾气氨泄漏已经引起包括环保和整车企业等领域的重视，要求更为严格的欧七(EU7)/国七(CN7)排放标准预计也将于2026年前后推出，ASC被应用于降低发动机尾气氨气泄漏已经是一个重要选项了，如何进一步提高ASC的效率、降低ASC产品成本、以及提高ASC应用的灵活性仍然是本领域技术人员亟待解决的技术问题。
发明内容
本发明提供一种氨吸附催化剂，具有氨吸附/转化效率高、成本低、应用灵活等优点，能够有效改进现有技术存在的缺陷。
本发明的一方面，提供一种氨吸附催化剂，包括载体、以及位于所述载体表面的吸附层，所述吸附层包含含有贵金属的分子筛吸附材料。
根据本发明的一实施方式，所述贵金属包括铂和/或钯。
根据本发明的一实施方式，所述含有贵金属的分子筛吸附材料中贵金属的含量为1～20克/立方英尺。
根据本发明的一实施方式，所述含有贵金属的分子筛吸附材料是通过离子交换法将贵金属交换到分子筛中得到，所述分子筛包括β分子筛、Y分子筛、ZSM-5分子筛中的至少一种。
根据本发明的一实施方式，所述吸附层中含有贵金属的分子筛吸附材料的质量含量为90～100％。
根据本发明的一实施方式，所述含有贵金属的分子筛吸附材料与所述载体的质量体积比为30-200g：1L。
根据本发明的一实施方式，所述载体包括堇青石、碳化硅、金属载体中的至少一种。
本发明的另一方面，提供一种上述氨吸附催化剂的制备方法，包括：采用贵金属前驱体对分子筛进行离子交换处理，得到含有贵金属的分子筛吸附材料；将含有贵金属的分子筛吸附材料与粘结剂、溶剂混合，制成浆料；将所述浆料涂覆于载体上，经干燥、焙烧后形成吸附层，得到所述氨吸附催化剂。
本发明的再一方面，提供一种上述氨吸附催化剂在发动机后处理系统中的应用。
根据本发明的一实施方式，所述发动机后处理系统包括当量运行发动机后处理系统。
根据本发明的一实施方式，所述发动机后处理系统包括三效催化剂，所述发动机后处理系统中的待处理气体先经过三效催化剂处理后再经所述氨吸附催化剂处理；或者，所述发动机后处理系统包括选择性氧化还原催化剂，所述发动机后处理系统中的待处理气体先经过选择性氧化还原催化剂处理后再经所述氨吸附催化剂处理。
根据本发明的一实施方式，所述氨吸附催化剂与三效催化剂复配使用，所述复配方式包括如下方式A和方式B中的至少一种：方式A：所述氨吸附催化剂的吸附层与所述载体之间设有由三效催化剂形成的三效催化剂层；方式B：所述氨吸附催化剂的吸附层中还含有所述三效催化剂。
本发明中，在分子筛吸附材料中引入贵金属，无需再在载体上涂覆氨氧化层，简化了催化剂的制作工序，降低了制作难度，降低成本，同时节约空间，能够在载体上负载更多的分子筛吸附材料，增加氨的吸附量，并且吸附在分子筛吸附材料中的氨可以直接在分子筛吸附材料中被催化氧化，增加了氨的氧化反应时间，从而提高了氨的转化率；此外，本发明的氨吸附催化剂还可以结合其他催化剂使用(例如和三效催化剂(TWC)涂层复配使用，排气偏富(λ<1.0)时吸附氨，排气偏稀(λ＞1.0)时氧化氨)，应用更加灵活；另外，研究表明，相对于常规的其他金属原子置换的分子筛(如Cu-分子筛)和氢型分子筛(H-分子筛)，本发明中引入贵金属的分子筛吸附材料(置换在分子筛中的贵金属替代分子筛中布朗斯特酸位点H +)不仅能够增加氨吸附量，还表现出更好的热稳定性，在热老化温度(650～750℃)下也能表现出相对更好的氨吸附性能，热老化温度一般高于实际应用温度，催化剂应用过程中的温度一般为200～500℃，本发明的氨吸附催化剂能够在200～500℃甚至更高温度下使用。由此，本发明的氨吸附催化剂兼具氨吸附/转化效率高、成本低、应用灵活、热稳定性好等优点，对于实际产业化应用具有重要意义。
附图说明
图1为现有ASC的结构及应用过程的示意图。
图2为本发明一实施例中新鲜和老化以后同样分子筛负载量的不同氨吸附催化剂ASC的氨吸附量随温度的变化曲线图；
图3(λ>1)为本发明一实施例中的氨吸附催化剂和对比例中的ASC在稀燃条件下的氨转化效率随温度的变化曲线图。
附图标记说明：1：吸附层；2：氨氧化层；3：载体；f：气流。
具体实施方式
为使本领域技术人员更好地理解本发明的方案，下面对本发明作进一步地详细说明。以下所列举具体实施方式只是对本发明的原理和特征进行描述，所举实例仅用于解释本发明，并非限定本发明的范围。基于本发明实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施方式，都属于本发明保护的范围。
本发明的氨吸附催化剂包括载体、以及位于载体表面的吸附层，吸附层包含含有贵金属的分子筛吸附材料。
本发明中，分子筛吸附材料对氨具有良好的吸附和催化氧化能力，其中，引入到分子筛吸附材料中的贵金属主要起到催化氧化氨的功能，该贵金属例如可以包括铂(Pt)、钯(Pd)、铑(Rh)中的至少一种，但不局限于此，在一些优选实施例中，贵金属包括铂和/或钯，利于进一步提高氨吸附催化氧化效率，同时节约成本。
相对而言，贵金属的含量过高，会增加成本，而贵金属含量过低，会在一定程度上影响氨吸附催化剂对氨的吸附转化性能，因此，综合考虑该些因素，一般可以控制含有贵金属的分子筛吸附材料中贵金属的含量为1～20克/立方英尺，例如1克/立方英尺、3克/立方英尺、5克/立方英尺、7克/立方英尺、10克/立方英尺、12克/立方英尺、15克/立方英尺、18克/立方英尺、20克/立方英尺或其中的任意两者组成的范围，一般优选3～5克/立方英尺。
本发明中，上述含有贵金属的分子筛吸附材料可以是通过离子交换法将贵金属交换到分子筛中得到，在一些实施例中，所用分子筛可以包括β分子筛、Y分子筛、ZSM-5中的至少一种。其中，分子筛吸附材料的体积基本等于所用分子筛的体积，在分子筛吸附材料的制备过程中，可以控制贵金属和 分子筛的用量满足3～5克：1立方英尺，以获得贵金属的含量为3～5克/立方英尺的分子筛吸附材料。当然，本发明不局限于离子交换法，也可以通过喷雾法等方式将贵金属交换到分子筛上。
具体地，离子交换法的过程一般可以包括：将贵金属前驱体溶于溶剂中形成浸渍液，采用该浸渍液对分子筛进行浸渍，例如等体积浸渍等，然后干燥、煅烧，制得含有贵金属的分子筛吸附材料；其中，贵金属前驱体一般可以包括贵金属的盐等含有贵金属的化合物，具体可以包括贵金属的可溶性盐，例如硝酸盐，如硝酸铂和/或硝酸钯等，在干燥、煅烧过程中通常可以使硝酸根等阴离子分解，从而从分子筛材料中脱离。
一般情况下，上述吸附层中还可以含有粘结剂和/或辅料(辅助材料)，利于粘结上述含有贵金属的分子筛吸附材料以形成涂层(即吸附层)，优化吸附层的强度及稳定性等性能，在一些实施例中，吸附层中的含有贵金属的分子筛吸附材料的质量含量为90～100％，余量可以是粘结剂及辅助材料。可选地，粘结剂可以包括铝胶和/或硅胶等，辅料可以包括铈材料和/或锆材料等。
具体地，可以将上述含有贵金属的分子筛吸附材料涂覆在载体表面以形成吸附层，具体实施时，可以将该分子筛吸附材料与粘结剂、溶剂混合制成浆料，将该浆料涂布在载体表面，经烘干后形成吸附层。
经进一步研究，上述含有贵金属的分子筛吸附材料与载体的质量体积比可以为30-280g：1L，例如30g：1L、50g：1L、80g：1L、100g：1L、120g：1L、150g：1L、180g：1L、200g：1L、230g：1L、250g：1L、280g：1L或其中的任意两个比例组成的范围。具体实施时，可以根据汽车的底盘空间调控吸附层厚度(分子筛吸附材料在载体上的涂覆量)，可以尽可能多的涂覆分子筛吸附材料，以提高氨吸附量。一般情况下，优选吸附层的质量与载体的体积之比为150g～230g：1L。
本发明可采用本领域常规载体，在一些优选实施例中，载体包括堇青石(一般为陶瓷蜂窝状)、碳化硅和金属载体等中的至少一种。载体的结构例如是颗粒捕集器(GPF)等，本发明对此不作特别限制。
本发明提供的氨吸附催化剂的制备方法包括：采用贵金属前驱体对分子筛进行离子交换处理(即通过离子交换法将贵金属交换至分子筛中)，得到含有贵金属的分子筛吸附材料；将含有贵金属的分子筛吸附材料与粘结剂、 溶剂混合，制成浆料；将浆料涂覆于载体表面上，经80-90℃干燥，去掉大量溶剂，再在100-200℃干燥，去掉残余溶剂，然后在500-650℃焙烧，在载体表面形成吸附层，得到氨吸附催化剂；其中焙烧时间可以为1～2小时，但不局限于此。
本发明中，上述氨吸附催化剂可以直接使用，也可以和其他催化剂或其功能成分复配，例如，可以将上述氨吸附催化剂与TWC结合形成多功能催化剂，具体地，可以在吸附层中引入TWC，即将含有贵金属的分子筛吸附材料与TWC混合形成吸附层，即上述吸附层中还含有TWC催化剂；或者，除吸附层外，载体表面还可以设有由TWC形成的TWC涂层，吸附层与TWC涂层位于载体表面的不同区域(即在载体表面分区设置)，二者可以相接或不相接(即间隔一段距离)；或者，TWC涂层与吸附层在载体表面分层设置，TWC涂层位于载体表面和吸附层之间，或者吸附层位于TWC涂层与载体表面之间，优选吸附层位于TWC涂层与载体表面之间。
本发明还提供上述氨吸附催化剂在发动机后处理系统中的应用，该发动机后处理系统可以包括当量运行发动机后处理系统，即上述氨吸附催化剂可以用于当量运行发动机后处理系统，例如可以用在当量运行发动机后处理系统中的TWC后端(即发动机排气先经TWC处理后再经上述氨吸附催化气处理)，能够高效吸附转化氨。其中，发动机当量运行是在空燃比(λ)围绕当量(λ＝1.0)小幅度上下波动中完成运行(即在发动机运行过程中基本当量燃烧天然气等燃料)，当量运行发动机的空燃比一般为0.98～1.02(即λ＝0.98～1.02)。一般情况下，在具体发动机当量运行应用过程中，在偏富(λ＜1.0)条件下，氨在TWC上生成，由于含氧量较少，氨吸附催化剂基本不能氧化氨，而主要是以吸附氨为主，在偏稀(λ＞1.0)条件下，TWC上不再生成氨，氨吸附催化剂可以氧化氨，所以主要以氧化氨为主。
本发明的氨吸附催化剂可以用于当量运行发动机后处理系统，能够显著提高氨吸附量，同时也表现出良好的对氨的转化(催化氧化)性能。但不以当量运行发动机后处理系统为限，上述发动机后处理系统还可以包括稀燃(λ>1.0)运行发动机后处理系统，即上述氨吸附催化剂可以用于稀燃运行发动机后处理系统，例如用在稀燃运行发动机后处理系统中的SCR后端。
具体来说，氨吸附催化剂可以单独使用，在一些实施例中，发动机后处 理系统包括三效催化剂(TWC)，发动机后处理系统中的待处理气体(尾气)先经过三效催化剂处理后再经氨吸附催化剂处理，即氨吸附催化剂用于TWC后端。在另一些实施例中，发动机后处理系统包括选择性氧化还原催化剂(SCR)，发动机后处理系统中的待处理气体先经过选择性氧化还原催化剂处理后再经所述氨吸附催化剂处理，即氨吸附催化剂用于SCR催化剂后端。
本发明的应用不局限于上述方式，也可以将氨吸附催化剂与其他催化剂(如TWC等)或其功能成分结合，例如，在一些实施例中，氨吸附催化剂与三效催化剂复配使用，所述复配方式包括如下方式A和方式B中的至少一种：方式A：所述氨吸附催化剂的吸附层与所述载体之间设有由三效催化剂形成的三效催化剂层；方式B：所述氨吸附催化剂的吸附层中还含有所述三效催化剂。在应用时，具体可以用在发动机后处理系统中的TWC系统。
为使本发明的目的、技术方案和优点更加清楚，下面将结合具体实施例对本发明的技术方案进行清楚、完整地描述，显然，所描述的实施例是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
实施例1
本实施例的氨吸附催化剂(记为新鲜(Pt-分子筛))由载体、位于载体表面的氧化铝涂层和位于氧化铝涂层表面的吸附层组成，其中，氧化铝涂层由氧化铝材料和粘结剂涂布形成，吸附层由含有铂的分子筛吸附材料(Pt-分子筛)和粘结剂涂布形成；
吸附层的组分为粘结剂和含有铂的分子筛吸附材料(Pt-分子筛)，吸附层中Pt-分子筛的质量含量为97％，余量为粘结剂；
Pt-分子筛中铂的含量为5克/立方英尺；
Pt-分子筛是通过离子交换法将铂交换到分子筛中得到，所用分子筛为β分子筛；
Pt-分子筛与载体的质量体积比为150g：1L(即Pt-分子筛的负载量为150g/L)；
氧化铝涂层与载体的质量体积比为50g：1L(即氧化铝的负载量为50g/L)；
载体为堇青石；
实施例2
实施例2与实施例1的区别在于，氨吸附催化剂由载体和位于载体表面的吸附层组成(即没有氧化铝涂层)，Pt-分子筛与载体的质量体积比为200g：1L(即Pt-分子筛的负载量为200g/L)；
对比例1
该对比例1的催化剂(记为新鲜(Cu-分子筛))为常规ASC，由载体、位于载体表面的氨氧化层、位于氨吸附层表面的氨吸附层组成，氨吸附层是由Cu-分子筛和粘结剂涂布形成的涂层，氨氧化层是由负载有铂的氧化铝材料和粘结剂涂布形成的涂层(50g/L)；其中：
对比例1中的载体与实施例1中的载体相同；
对比例1中由氨吸附层和氨氧化层组成的总涂层中的铂含量与实施例1中吸附层中的铂含量相同；
对比例1中Cu-分子筛的负载量与实施例1中Pd-分子筛的负载量相同(150g/L)。
对比例2
该对比例2的催化剂(记为新鲜(H-分子筛))与对比例1的区别在于：采用H-分子筛替换Cu-分子筛，其余条件与对比例1相同。
催化剂性能测试
1、催化剂老化
使实施例1中的氨吸附催化剂在管式反应炉中在720℃、保持空速30000hr -1的条件下反应40小时，得到老化的氨吸附催化剂(记为老化(Pt-分子筛))；
按照上述老化过程，将对比例1中的催化剂进行老化，得到老化的催 化剂(记为老化(Cu-分子筛))；
按照上述老化过程，将对比例2中的催化剂进行老化，得到老化的催化剂(记为老化(H-分子筛))；
2、测试
分别采用上述新鲜(Pt-分子筛)、新鲜(Cu-分子筛)、新鲜(H-分子筛)、老化(Pt-分子筛)、老化(Cu-分子筛)、老化新鲜(H-分子筛)催化剂进行如下测试1和测试2，测得各催化剂在当量运行条件下的氨吸附量随温度的变化曲线(见图2)以及在稀燃运行条件下的氨转化率随温度的变化曲线(见图3)：
测试1：模拟当量运行发动机后处理系统经TWC后的排气组成(见表1中氨吸附实验合成气)，空速为170000hr -1，在该条件下测试催化剂的氨吸附量(存储量)随温度的变化曲线；
测试2：模拟稀燃运行发动机后处理系统中经SCR后的排气组成(见表1中氨氧化实验合成气)，空速为170000hr -1，在该条件下测试催化剂转化氨的效率(氨转化率)随温度的变化曲线。
表1
实验合成气 O 2(％) 水蒸气(％) CO 2(％) 氨(ppm) 氮气
氨吸附实验合成气 0 10 8 500 平衡
氨氧化实验合成气 5 10 8 100 平衡
从图2可以看出，催化剂的氨吸附量随温度的升高而减少，新鲜(Pd-分子筛)的氨吸附量从200℃时的2.79g/L降至500℃时的0.65g/L；老化也会影响催化剂的氨吸附性能，老化(Pd-分子筛)在200℃时的氨吸附量约为1.36g/L；此外，无论是新鲜还是老化后，实施例1的氨吸附催化剂的氨吸附量均高于对比例1和对比例2中的催化剂，表现出更好的氨吸附性能和热稳定性，新鲜(Pt-分子筛)、新鲜(Cu-分子筛)、新鲜(H-分子筛)在200℃下的氨吸附量依次是2.79g/L、2.4g/L、2.3g/L，老化(Pt-分子筛)、老化(Cu-分子筛)、老化新鲜(H-分子筛)的氨吸附量在200℃下的氨吸附量依次是1.36g/L、0.9g/L、0.67g/L。
结合图3可以看出，实施例1的氨吸附催化剂在增加氨吸附量的同时，还具有良好的氨转化性能，其与对比例1和对比例2中催化剂的氨转化率 接近；催化剂的氨转化率随着温度的升高呈增大趋势，老化后催化剂的氨转化性能有所衰减，但老化(Pt-分子筛)仍然能够保持较高的氨转化率。
一般情况下，当量运行发动机废气除氨过程可以分为偏富燃时产生氨并被ASC等催化剂吸附、偏稀燃时氧化氨两个相对独立且短暂的过程，如上所述，实施例1的氨吸附催化剂对氨的催化氧化效率与对比例1和2中的催化剂基本相当，在实施例1的氨吸附催化剂的氨吸附量显著优于对比例1和2的催化剂，而且实施例1的氨吸附催化剂在同样尺寸的载体情况下可以比对比例1和2多涂覆高达30％的氨吸附(分子筛)材料，在对氨的催化氧化效率基本相当的情况下，氨吸附量越大，对废气中氨的脱除效果越好。
本发明中，为尽可能减少变量影响，设计了上述实施例1，并列举了实施例1与对比例1的相关实验过程，证明了本发明的氨吸附催化剂相对于常规ASC具有更为优异的降氨效果，本发明进一步设计了实施例2，并对实施例2的催化剂进行了上述实验测试，结果显示实施例2的氨吸附性能、氨氧化性能以及热稳定性等性能均优于实施例1的氨吸附催化剂。
以上对本发明的实施方式进行了说明。但是，本发明不限定于上述实施方式。凡在本发明的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (12)

  1. 一种氨吸附催化剂，其特征在于，包括载体、以及位于所述载体表面的吸附层，所述吸附层包含含有贵金属的分子筛吸附材料。
  2. 根据权利要求1所述的氨吸附催化剂，其特征在于，所述贵金属包括铂和/或钯。
  3. 根据权利要求1或2所述的氨吸附催化剂，其特征在于，所述含有贵金属的分子筛吸附材料中贵金属的含量为1～20克/立方英尺。
  4. 根据权利要求1或2所述的氨吸附催化剂，其特征在于，所述含有贵金属的分子筛吸附材料是通过离子交换法将贵金属交换到分子筛中得到，所述分子筛包括β分子筛、Y分子筛、ZSM-5分子筛中的至少一种。
  5. 根据权利要求1所述的氨吸附催化剂，其特征在于，所述吸附层中含有贵金属的分子筛吸附材料的质量含量为90～100％。
  6. 根据权利要求1所述的氨吸附催化剂，其特征在于，所述含有贵金属的分子筛吸附材料与所述载体的质量体积比为30-200g：1L。
  7. 根据权利要求1或6所述的氨吸附催化剂，其特征在于，所述载体包括堇青石、碳化硅、金属载体中的至少一种。
  8. 权利要求1-7任一项所述的氨吸附催化剂的制备方法，其特征在于，包括：
    采用贵金属前驱体对分子筛进行离子交换处理，得到含有贵金属的分子筛吸附材料；
    将含有贵金属的分子筛吸附材料与粘结剂、溶剂混合，制成浆料；
    将所述浆料涂覆于载体上，经干燥、焙烧后形成吸附层，得到所述氨吸附催化剂。
  9. 权利要求1-7任一项所述的氨吸附催化剂在发动机后处理系统中的应用。
  10. 根据权利要求9所述的应用，其特征在于，所述发动机后处理系统包括当量运行发动机后处理系统。
  11. 根据权利要求9或10所述的应用，其特征在于，
    所述发动机后处理系统包括三效催化剂，所述发动机后处理系统中的待 处理气体先经过三效催化剂处理后再经所述氨吸附催化剂处理；
    或者，所述发动机后处理系统包括选择性氧化还原催化剂，所述发动机后处理系统中的待处理气体先经过选择性氧化还原催化剂处理后再经所述氨吸附催化剂处理。
  12. 根据权利要求9或10所述的应用，其特征在于，所述氨吸附催化剂与三效催化剂复配使用，所述复配方式包括如下方式A和方式B中的至少一种：
    方式A：所述氨吸附催化剂的吸附层与所述载体之间设有由三效催化剂形成的三效催化剂层；
    方式B：所述氨吸附催化剂的吸附层中还含有所述三效催化剂。
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