CN118002195A - Coupling type three-way catalyst for diesel engine and preparation method thereof - Google Patents
Coupling type three-way catalyst for diesel engine and preparation method thereof Download PDFInfo
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- CN118002195A CN118002195A CN202410417460.8A CN202410417460A CN118002195A CN 118002195 A CN118002195 A CN 118002195A CN 202410417460 A CN202410417460 A CN 202410417460A CN 118002195 A CN118002195 A CN 118002195A
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- 238000002360 preparation method Methods 0.000 title claims abstract description 12
- 238000000576 coating method Methods 0.000 claims abstract description 177
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- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 83
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 claims abstract description 68
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- 239000010948 rhodium Substances 0.000 claims abstract description 38
- 229910052697 platinum Inorganic materials 0.000 claims abstract description 36
- 229910052703 rhodium Inorganic materials 0.000 claims abstract description 35
- -1 rhodium modified molecular sieve Chemical class 0.000 claims abstract description 31
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 30
- 230000003647 oxidation Effects 0.000 claims abstract description 24
- 229910052878 cordierite Inorganic materials 0.000 claims abstract description 23
- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 claims abstract description 22
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- 238000011068 loading method Methods 0.000 claims description 33
- 238000001035 drying Methods 0.000 claims description 21
- 239000002245 particle Substances 0.000 claims description 21
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 19
- 239000011247 coating layer Substances 0.000 claims description 14
- 229910000510 noble metal Inorganic materials 0.000 claims description 13
- 239000002002 slurry Substances 0.000 claims description 12
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 12
- 239000007864 aqueous solution Substances 0.000 claims description 9
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- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 claims description 4
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 3
- 239000002253 acid Substances 0.000 claims description 3
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- VXNYVYJABGOSBX-UHFFFAOYSA-N rhodium(3+);trinitrate Chemical compound [Rh+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VXNYVYJABGOSBX-UHFFFAOYSA-N 0.000 claims description 2
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Classifications
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- 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
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- Catalysts (AREA)
Abstract
The invention discloses a coupling type three-way catalyst for a diesel engine and a preparation method thereof, and belongs to the technical field of catalysts. The catalyst of the present invention comprises a cordierite support, a first coating, a second coating, and a third coating; the first coating is a mixture of platinum-based alumina and rhodium modified molecular sieve, has NH 3 oxidation and N 2 O removal functions and is positioned in the front region of the cordierite carrier; the second coating is an Fe molecular sieve and has the functions of reducing NOx and removing N 2 O, and is positioned on the first coating; the third coating is a rhodium modified molecular sieve, has an N 2 O removing function and is positioned at the rear area of the carrier. The catalyst has three functions of NH 3 oxidation, N 2 O removal and NOx reduction, the ignition temperature of NH 3 is less than 200 ℃, the ignition temperature of N 2 O is less than or equal to 275 ℃, the conversion efficiency of NOx at 300 ℃ is 99%, and the leakage amount of NH 3、N2 O, NOx at 200-500 ℃ is effectively reduced.
Description
Technical Field
The invention belongs to the technical field of catalysts, and particularly relates to a coupling type three-way catalyst for a diesel engine and a preparation method thereof.
Background
The exhaust gas of the Guohu diesel engine comprises carbon oxides (CO, CO 2), hydrocarbon (HC), nitrogen-containing compounds (NOx), ammonia (NH 3) and Particulate Matters (PM), laughing gas (N 2O）.N2 O is derived from secondary pollutants generated by combustion in an engine cylinder and reaction of a post-treatment catalyst, and is listed as third greenhouse gas, the greenhouse effect is 298 times of that of carbon dioxide and is more serious than that of CO 2.
Disclosure of Invention
In view of the above, the invention aims to provide a coupling type three-way catalyst for a diesel engine, which has a multi-coating coupling and compact structure, can realize simultaneous removal of three pollutants of NH 3、N2 O, NOx, realizes high-efficiency conversion of NH 3、N2 O, NOx at low temperature and solves the problem of leakage of NH 3、N2 O, NOx at 200-500 ℃.
Based on the above objects, the technical scheme of the invention is as follows: the technical scheme of the invention is as follows:
A coupled three-way catalyst for a diesel engine, comprising a cordierite carrier 101, a first coating 102, a second coating 103 and a third coating 104; the first coating 102 has NH 3 oxidation and N 2 O removal functions and is positioned at the front region of the carrier 101; the second coating layer 103 has the functions of NOx reduction and N 2 O removal and is positioned on the first coating layer 102; the third coating 104 has an N 2 O removing function and is located at a rear region of the carrier 101.
The first coating 102 is subjected to high-temperature heat treatment, and the roasting temperature is 650-750 ℃ and the roasting time is 3-5h. The high-temperature heat treatment is used for increasing the size of active metal Pt particles in the platinum-based alumina catalytic material at the bottom layer of the front region, exposing more active sites and defects by utilizing the large-size effect, improving the adsorption and dissociation rate of O 2, promoting the NH 3 oxidation reaction and enhancing the NH 3 oxidation capability at low temperature.
Preferably, the ratio of the application length of the first coating layer 102 and the second coating layer 103 to the application length of the third coating layer 104 is (1-2.3): 1.
Preferably, the first coating 102 is a mixture of platinum-based alumina and rhodium-modified molecular sieves.
Preferably, the mass ratio of the platinum-based alumina to the rhodium modified molecular sieve is (60-80): (20-40).
Preferably, the rhodium-modified molecular sieve type is one or two of CHA type molecular sieve and ERI type molecular sieve.
Preferably, the molar ratio of SiO 2 to Al 2O3 in the rhodium-modified molecular sieve is (10-15): 1.
Preferably, the rhodium element in the rhodium modified molecular sieve accounts for 0.98-6.12% of the molecular sieve carrier.
Preferably, the second coating layer 103 is an Fe molecular sieve, wherein the mass of the iron element is 2.0% -4.0% of the mass of the molecular sieve carrier.
Preferably, the third coating 104 is a rhodium modified molecular sieve, consistent with the rhodium modified molecular sieve in the first coating 102.
Preferably, the ratio of the total loading of the first coating 102 and the second coating 103 to the loading of the third coating 104 is (0.94-1.67): 1, wherein the loading of the first coating 102 is 50-100g/L, and the loading of the second coating 103 is 100-150g/L; the third coating 104 has a loading of 120-160g/L.
Preferably, the particle diameters D90 of the first coating 102, the second coating 103 and the third coating 104 are respectively 9-11 mu m, 4-6 mu m and 3-5 mu m, and the viscosities are respectively 1200-1400cp, 2100-2300cp and 1000-1200cp.
The mechanism of the invention is as follows:
The coupled three-way catalyst of the present invention includes a cordierite support 101, a first coating layer 102, a second coating layer 103, and a third coating layer 104. The first coating 102 has NH 3 oxidation and N 2 O removal functions, and the NH 3 oxidation coating material is composed of platinum-based alumina, and an ammoxidation reaction occurs to generate N 2 and byproducts N 2 O and NO (see the following reaction formulas 1, 2 and 3), so that NH 3 leakage is reduced; the N 2 O removing coating material consists of a rhodium modified molecular sieve, N 2 O is subjected to decomposition reaction (see the following reaction formulas 4, 5 and 6), wherein by-product NO generated by the NH 3 oxidation reaction, unreacted NO in the air flow and unreacted NH 3 in a low temperature area are further diffused to the upper surface of the rhodium modified molecular sieve to be adsorbed, and both NH 3 and NO can react with N 2 O (see the following reaction formulas 4 and 5), so that N 2O、NH3 and NO leakage is reduced; by performing a high temperature heat treatment on the first coating 102, the active metal Pt particle size in the platinum-based alumina catalytic material is increased, and by utilizing the large size effect, more active sites and defects are exposed, so that the O 2 adsorption and dissociation rates are improved, the NH 3 oxidation reaction is promoted, and the NH 3 oxidation capability at low temperature is enhanced. The second coating 103 has NOx reduction and N 2 O decomposition functions, the coating is composed of Fe molecular sieve, has NOx conversion function, and generates NOx selective catalytic reduction reaction to reduce NOx to N 2 (see the following reaction formulas 7, 8 and 9), so that NO in the exhaust gas and the underlayer NH 3 can be oxidized to generate byproduct NO to reduce to N 2, reduce NOx leakage, and simultaneously has N 2 O decomposition function above 400 ℃ (see the following reaction formulas 4, 5 and 6), and provides N 2 O decomposition function in high temperature region. The third coating 104 has a low temperature N 2 O decomposition function (see equations 4, 5, 6 listed below) to further purge the upstream leaking N 2 O. The invention reduces leakage of NH 3、NOx、N2 O at 200-500 ℃.
The invention has the following beneficial effects:
(1) The invention adopts rhodium modified molecular sieve as the catalytic material for N 2 O decomposition, the N 2 O decomposition rate reaches more than 50% at 275 ℃, and the catalyst has excellent low-temperature N 2 O decomposition activity.
Rh modified molecular sieve is used as an N 2 O decomposition catalyst, wherein Rh is used as an active component, has better adsorptivity to N 2 O and excellent low-temperature N 2 O removal activity compared with transition metal; secondly, molecular sieve is adopted as noble metal carrier material, and compared with rare earth oxide, other metal oxide and other carrier materials, the noble metal carrier material is characterized in that: 1) The molecular sieve material has higher specific surface area and rich pores, can greatly improve the dispersity of the surface noble metal rhodium, and provides more reactive sites, thereby reducing the removal temperature of N 2 O; 2) The molecular sieve material has high ammonia adsorption capacity and N 2 O adsorption capacity at low temperature due to the high specific surface area and rich acid sites on the surface, and on the one hand, the adsorbed NH 3 can be used as a reducing agent to react with the adsorbed N 2 O to generate N 2 (see the following reaction formula 4); on the other hand, the molecular sieve is utilized to adsorb N 2 O at low temperature and is subjected to high-temperature desorption and decomposition, so that the leakage of low-temperature N 2 O can be effectively reduced, and the removal temperature of N 2 O is reduced; 3) The CHA type molecular sieve material and the ERI type molecular sieve material with excellent hydrothermal stability are selected, so that the water-resistant stability is improved, and the decomposition rate of N 2 O at 275 ℃ is realized by the functions of the three aspects and reaches more than 50%.
(2) According to the invention, through high-temperature heat treatment on the first coating 102, the size of active metal Pt particles in the platinum-based alumina catalytic material is increased, the adsorption and dissociation rate of O 2 is increased, the oxidation reaction of NH 3 is promoted, the oxidation capability of NH 3 at low temperature is enhanced, and the oxidation efficiency of NH 3 is improved by at least 10 points at 200 ℃ compared with that of a non-pretreated bifunctional ASC catalyst.
(3) According to the invention, the N 2 O is used for removing the secondary regionalization distribution of the catalytic material, so that the decomposition temperature of N 2 O is effectively reduced. Firstly, fully utilizing interface reaction, in the first coating 102, rh modified molecular sieve and Pt-based alumina exist in the form of mixture, rh modified molecular sieve is in direct contact with Pt-based alumina, N 2 O and NO byproducts generated by NH 3 oxidation reaction of Pt-based alumina (see the following reaction formulas 1, 2 and 3) can be rapidly diffused to the surface of noble metal modified molecular sieve for adsorption, NO and NH 3 are used as reactants to react with N 2 O (see the following reaction formulas 4, 5 and 6), so that N 2 O and NO in upstream tail gas and N 2 O and NO generated by Pt-based alumina are reduced; secondly, N 2 O is removed and catalytic material is distributed in the third coating 104, N 2 O leaked from the upstream is not completely reacted through the first coating 102, and then N 2 O adsorption and decomposition reaction is carried out through the Rh modified molecular sieve of the third coating 104, so that leakage of the whole N 2 O, NO and NH 3 is effectively reduced.
(4) According to the invention, through the design of a three-effect coating area, the NH 3 oxidation coating, the N 2 O removal coating and the NOx reduction coating are organically combined, and through the organic coordinated coupling of a certain proportion, the advantages of the three are fully exerted, and the leakage quantity of three pollutants is effectively reduced; meanwhile, the three-way catalyst reduces the post-treatment packaging space, saves the cost, realizes the function of treating three pollutants of NH 3、NOx、N2 O simultaneously, and reduces the leakage of NH 3、N2 O, NOx at 200-500 ℃.
NH 3 oxidation reaction:
4NH3+ 3O2 2N2+ 6H2O (1)
2NH3+ 2O2 N2O+3H2O (2)
4NH3+5O2 4NO+6H2O (3)
n 2 O decomposition reaction:
2NH3+3N2O 4N2+3H2O (4)
NO+N2O NO2+N2 (5)
N2O O2+N2 (6)
NOx selective catalytic reduction reaction:
4NH3+4NO+O2 6H2O +4N2 (7)
8NH3+6NO2 12H2O +7N2 (8)
2NH3+NO+NO2 3H2O +2N2 (9)
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a coupling type three-way catalyst for a diesel engine according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the comparative example structure of the present invention, and FIGS. 2a to 2e are schematic diagrams of the catalyst structures of comparative example 10 to comparative example 14, respectively;
FIG. 3 is a schematic diagram of the installation position of a coupling type three-way catalyst for a diesel engine in a post-treatment system according to an embodiment of the present invention;
In fig. 1-3: a 101-cordierite carrier; 102-first coating (NH 3 oxidation and N 2 O removal mix coating); 103-a second coating (NOx reduction coating); 104-third coating (N 2 O removal coating); 105-NH 3 oxide coating; 1-an engine; 2-DOC catalyst; a 3-CDPF catalyst; a 4-SCR catalyst; a 5-three-way catalyst;
FIG. 4 is a graph of ammonia conversion efficiency versus reaction temperature for the catalysts of example 1 and comparative examples 1,2 provided by the present invention;
FIG. 5 is a graph of laughing gas conversion efficiency versus reaction temperature for the catalysts of example 1 and comparative examples 1, 2 provided by the present invention;
FIG. 6 is a graph of nitrogen oxide conversion efficiency versus reaction temperature for the catalysts of example 1 and comparative examples 1, 2 provided by the present invention;
FIG. 7 is a graph of ammonia conversion efficiency versus reaction temperature for the catalysts of comparative examples 3, 4 provided herein;
FIG. 8 is a graph of laughing gas conversion efficiency versus reaction temperature for the catalysts of comparative examples 3, 4 provided herein;
FIG. 9 is a graph of nitrogen oxide conversion efficiency versus reaction temperature for the catalysts of comparative examples 3, 4 provided herein;
FIG. 10 is a graph of ammonia conversion efficiency versus reaction temperature for the catalysts of examples 1, 3 and comparative examples 4-9 provided herein;
FIG. 11 is a graph showing the conversion efficiency of laughing gas versus reaction temperature for the catalysts of examples 1, 3 and comparative examples 4-9 provided by the present invention;
FIG. 12 is a graph of nitrogen oxide conversion efficiency versus reaction temperature for the catalysts of examples 1, 3 and comparative examples 4-9 provided herein;
FIG. 13 is a graph of ammonia conversion efficiency versus reaction temperature for the catalysts of example 1 and comparative examples 10-14 provided herein;
FIG. 14 is a graph showing the relationship between the conversion efficiency of laughing gas and the reaction temperature of the catalysts of examples 1 to 4 and comparative examples 10 to 14 provided in the present invention;
FIG. 15 is a graph of nitrogen oxide conversion efficiency versus reaction temperature for the catalysts of examples 1-4 and comparative examples 10-14 provided herein;
FIG. 16 is a graph of ammonia conversion efficiency versus reaction temperature for the catalysts of examples 1-4 and comparative example 4 provided herein;
FIG. 17 is a graph of laughing gas conversion efficiency versus reaction temperature for the catalysts of examples 1-4 and comparative example 4 provided herein;
FIG. 18 is a graph of nitrogen oxide conversion efficiency versus reaction temperature for the catalysts of examples 1-4 and comparative example 4 provided herein.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely, and it is apparent that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention provides a coupling type three-way catalyst for a diesel engine, which comprises a cordierite carrier 101, a first coating 102, a second coating 103 and a third coating 104; the ratio of the coating length of the first coating 102 and the second coating 103 to the coating length of the third coating 104 is (1-2.3): 1; specifically, the ratio of the raw materials can be 1:1, 1.5: 1. 2: 1. 2.3:1, a step of; the first coating 102 has NH 3 oxidation and N 2 O removal functions, is positioned on the front area part of the carrier 101, and the first coating 102 is a mixture of platinum-based alumina and rhodium modified molecular sieve; the mass ratio of the platinum-based alumina to the rhodium modified molecular sieve is (60-80): (20-40). Preferably, it may be 60:40, 70:30, 80:20; the mass of the platinum element in the platinum-based alumina accounts for 0.39% -3.57%, preferably 0.58% -1.96%, and particularly can be 0.39%, 0.58%, 0.77%, 0.97%, 1.15%,1.37%, 1.56%, 1.77%, 1.96%, 2.15%, 2.56%, 2.76%, 2.94%, 3.12%, 3.37% and 3.57% of the mass of the alumina.
Preferably, the rhodium-modified molecular sieve type is one or two of CHA type molecular sieve and ERI type molecular sieve. The molar ratio of SiO 2 to Al 2O3 (silicon-aluminum ratio) in the molecular sieve carrier is preferably (10-15): 1, which may be specifically 10:1, 11:1, 12:1, 13:1, 14:1, 15:1; preferably, the rhodium element mass in the rhodium modified molecular sieve accounts for 0.98-6.12% of the molecular sieve carrier mass; preferably 1.35% -4.55%, in particular it may be 0.98%、1.24%、1.35%、1.42%,1.48%、1.52%、1.58%、1.62%、1.74%、1.95%、2.38%、2.67%,3.58%、3.72%、4.68%、4.95%、5.42%,5.78%、6.12%.
The second coating 103 has NOx reduction and N 2 O decomposition functions and is located on the first coating 102.
The second coating 103 is an Fe molecular sieve, wherein the Fe molecular sieve comprises a molecular sieve carrier and iron element; preferably, the mass of Fe element in the Fe molecular sieve accounts for 2.0% -4.0% of the mass of the molecular sieve carrier. Preferably 2.2% -2.9%, in particular 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.7%, 2.9%,3%, 3.2%, 3.5%, 3.7%, 4.0%.
The third coating 104 has an N 2 O removal function and is positioned on the rear region of the cordierite carrier 101, and the third coating 104 is a rhodium modified molecular sieve and is consistent with the rhodium modified molecular sieve in the first coating 102.
Preferably, the ratio of the total loading of the first coating 102 and the second coating 103 to the loading of the third coating 104 is (0.94-1.67): 1, in particular 0.94:1、1.00:1、1.06：1、1.07：1、1.13：1、1.14：1、1.19：1、1.20：1、1.21：1、1.25:1、1.27：1、1.29：1、1.33:1、1.36：1、1.38：1、1.43:1、1.46:1、1.50:1、1.54:1、1.58:1、1.67:1;, wherein the loading of the first coating 102 is 50-100g/L, in particular 50, 60, 70, 80, 90, 100g/L, and the loading of the second coating 103 is 100-150g/L; specifically, the concentration of the active ingredients can be 100, 110, 120, 130, 140 and 150g/L; the third coating 104 has a loading of 120-160g/L. Specifically, the concentration of the active ingredients can be 120, 130, 140, 150 and 160g/L.
Preferably, the baking temperature of the first coating layer 102 is 650-750 ℃, specifically 650, 700 ℃, 750 ℃, and the baking time is preferably 3-5h, specifically 3 h, 4h, 5 h.
Preferably, the particle diameters D90 of the first coating 102, the second coating 103 and the third coating 104 are respectively 9-11 mu m, 4-6 mu m and 3-5 mu m, and the viscosities are respectively 1200-1400cp, 2100-2300cp and 1000-1200cp.
For the sake of clarity, the following examples and comparative examples are described in detail.
Example 1
(1) Preparing a platinum-based alumina coating slurry:
Needle-like alumina powder 242.46g was added to deionized water 2205g and stirred well. According to the mass of Pt atoms in the platinum-based alumina accounting for 0.58% of the mass of the alumina, 7.65g of chloroplatinic acid aqueous solution is taken and added into the aqueous solution of the alumina, and the mixture is stirred for 1h to obtain the platinum-based alumina coating slurry.
(2) Preparing rhodium modified molecular sieve coating slurry:
412.5g of CHA type molecular sieve powder (molecular sieve of H-SSZ-13, silica-alumina ratio of 15) was added to 2940g of deionized water and stirred well. According to the condition that noble metal in the noble metal modified molecular sieve accounts for 0.98% of the mass of the molecular sieve, 22.92g of rhodium nitrate aqueous solution is taken and added into the aqueous solution of the molecular sieve, and the aqueous solution is fully stirred and ground to the grain diameter D90=3.5 mu m, and the viscosity is regulated to 1050cp, so that the noble metal rhodium modified molecular sieve coating slurry is obtained.
(3) Preparing mixed coating slurry of platinum-based alumina and rhodium modified molecular sieve:
Sampling and mixing the components (1) and (2) according to the proportion of 80:20, stirring for 30min, drying at 120 ℃ for 1h, and roasting at 650 ℃ for 3h in a muffle furnace. The calcined powder was thoroughly mixed with water and ground to a particle size d90=9.2 μm, and the viscosity was adjusted to 1320cp to obtain a mixed coating slurry of platinum-based alumina and rhodium-modified molecular sieve.
(4) Preparing Fe molecular sieve coating slurry:
500g of Fe-ZSM-5 (molecular sieve with a silicon-aluminum ratio of 22) is taken, 545g of deionized water is added, and the mixture is fully stirred and ground to a particle size D90=5.1 mu m, and the viscosity is adjusted to 2150cp, so that Fe molecular sieve coating slurry is obtained.
(5) The preparation of the coupling type three-way catalyst for the diesel engine comprises the following steps:
And (3) coating the mixed coating slurry of the platinum-based alumina and the rhodium modified molecular sieve prepared in the step (3) on a front region of a cordierite carrier 101, wherein the carrier specification is 190.5mm x 101.6mm, the loading capacity is 50g/L, the coating length is 50mm, and drying is carried out at 120 ℃ for 2 hours to obtain the first coating 102. Then coating the molecular sieve slurry in the step (4) on the first coating 102, wherein the loading capacity is 150g/L, the coating length is 50mm, and drying is carried out at 120 ℃ for 2 hours to obtain a second coating 103; finally, the rhodium modified molecular sieve slurry in (2) is coated on the back region of the cordierite carrier 101, the loading capacity is 120g/L, the coating length is 50mm, and the third coating 104 is obtained after drying for 2 hours at 120 ℃. Roasting in air at 550 deg.c for 3 hr. The coupling type three-way catalyst for the diesel engine is obtained.
Example 2
Steps (1), (2), (3), (4) and (5) of example 1 were repeated, wherein (3) was prepared in a ratio of 70:30, to obtain a coupled three-way catalyst for diesel engines.
Example 3
Steps (1), (2), (3), (4) and (5) of example 1 were repeated, wherein (3) was prepared in a ratio of 60:40, to obtain a coupled three-way catalyst for diesel engines.
Example 4
Repeating steps (1), (2), (3), (4), (5) of example 1, wherein the first coating 102 was applied at a length of 63mm and a loading of 50g/L; the loading of the second coating 103 is 150g/L, the coating length of the third coating 104 is 38mm, and the loading is 160g/L, so that the coupling type three-way catalyst for the diesel engine is obtained.
Comparative example 1
Steps (1), (2), (3), (4), (5) of example 1 were repeated, wherein the coating slurries prepared in steps (2), (3), (4) had a grinding particle size d90=2.5 μm, d90=8.4 μm, d90=3.2 μm, respectively, to give a three-way catalyst with NH 3、NOx、N2 O removal.
Comparative example 2
Steps (1), (2), (3), (4), (5) of example 1 were repeated, wherein the coating slurries prepared in steps (2), (3), (4) had a grinding particle size d90=6.4 μm, d90=12.3 μm, d90=7.4 μm, respectively, to give a three-way catalyst with NH 3、NOx、N2 O removal.
Comparative example 3
(1) Preparing a platinum-based alumina coating slurry:
example 1, step (1), was repeated, wherein the platinum-based alumina slurry was dried at 120℃for 1 hour and calcined in a muffle furnace at 650℃for 3 hours. The calcined powder was thoroughly mixed with water, and ground to a particle size d90=9.8 μm, and the viscosity was adjusted to 1380cp, to obtain a platinum-based alumina coating slurry.
(2) Preparing Fe molecular sieve coating slurry:
500g of Fe-ZSM-5 (molecular sieve with a silicon-aluminum ratio of 22) is taken, 545g of deionized water is added, and the mixture is sufficiently stirred and ground to a particle size D90=5.1 mu m, and the viscosity is adjusted to 2230cp, so that Fe molecular sieve coating slurry is obtained.
(3) Preparation of a bifunctional catalyst:
Coating the coating slurry prepared in the step (1) on a cordierite carrier 101, wherein the carrier specification is 190.5mm x 101.6mm, the loading amount is 50g/L, the coating length is 50mm, drying is carried out at 120 ℃ for 2 hours to obtain an ammonia oxidation coating, then coating the molecular sieve slurry in the step (2) on an NH 3 oxidation coating, the loading amount is 150g/L, the coating length is 50mm, drying is carried out at 120 ℃ for 2 hours, and roasting is carried out in air at 550 ℃ for 3 hours. The double-function catalyst for removing NH 3 and NOx is obtained.
Comparative example 4
(1) Preparing a platinum-based alumina coating slurry:
step (1) of example 1 was repeated, and the slurry was ground to a particle size d90=10 μm, and the viscosity was adjusted to 1320cp.
(2) Preparing Fe molecular sieve coating slurry:
comparative example 3, step (2), was repeated.
(3) Preparation of a bifunctional catalyst:
Comparative example 3 step (3) was repeated.
Comparative example 5
Steps (1), (2), (3), (4), (5) of example 1 were repeated, wherein (3) was prepared in a ratio of 10:90 to give a three-way catalyst with NH 3、NOx、N2 O removal.
Comparative example 6
Steps (1), (2), (3), (4), (5) of example 1 were repeated, wherein (3) was prepared in a ratio of 20:80 to give a three-way catalyst with NH 3、NOx、N2 O removal.
Comparative example 7
Steps (1), (2), (3), (4), (5) of example 1 were repeated, wherein (3) was prepared in a ratio of 30:70 to give a three-way catalyst with NH 3、NOx、N2 O removal.
Comparative example 8
Steps (1), (2), (3), (4), (5) of example 1 were repeated, wherein (3) was prepared in a ratio of 40:60 to give a three-way catalyst with NH 3、NOx、N2 O removal.
Comparative example 9
Steps (1), (2), (3), (4), (5) of example 1 were repeated, wherein (3) was prepared in a 50:50 ratio to give a three-way catalyst with NH 3、NOx、N2 O removal.
Comparative example 10
(1) Repeating steps (1), (2), (3) and (4) of example 1.
(2) And (3) coating the coating slurry prepared in the step (3) on a front region of the cordierite carrier 101, wherein the carrier specification is 190.5mm x 101.6mm, the loading capacity is 50g/L, the coating length is 101.6mm, and drying is carried out at 120 ℃ for 2 hours to obtain the first coating 102. Then coating the molecular sieve slurry in the step (4) on the first coating 102, wherein the loading capacity is 150g/L, the coating length is 101.6mm, and drying is carried out at 120 ℃ for 2 hours to obtain a second coating 103; roasting in air at 550 deg.c for 3 hr. A three-way catalyst with NH 3、NOx、N2 O removal was obtained.
The structure of the catalyst of this comparative example is shown in fig. 2 a.
Comparative example 11
(1) Steps (1), (2) and (4) of example 1 were repeated, wherein (1) was ground to a particle size d90=10 μm, and the viscosity was adjusted to 1320cp.
(2) Coating the coating slurry prepared in the step (1) on a front region of a cordierite carrier 101, wherein the carrier specification is 190.5mm x 101.6mm, the loading capacity is 25g/L, the coating length is 50mm, and drying is carried out at 120 ℃ for 2 hours to obtain an NH 3 oxidation coating 105. The slurry in (2) was then applied to the rear region of the support 101 at a loading of 25g/L, a length of 50mm, and dried at 120℃for 2 hours to give a third coating 104. Finally, the slurry in the step (4) is coated on the NH 3 oxidation coating 105 and the third coating 104, the loading capacity is 150g/L, the coating length is 101mm, the drying is carried out for 2 hours at 120 ℃, the second coating 103 is obtained, and the baking is carried out in air at 550 ℃ for 3 hours. A three-way catalyst with NH 3、NOx、N2 O removal was obtained.
The structure of the catalyst of this comparative example is shown in fig. 2 b.
Comparative example 12
(1) Repeating steps (1), (2), (3) and (4) of example 1.
(2) And (3) coating the coating slurry prepared in the step (3) on a rear region of the cordierite carrier 101, wherein the carrier specification is 190.5mm x 101.6mm, the loading capacity is 50g/L, the coating length is 50mm, and drying is carried out at 120 ℃ for 2 hours to obtain the first coating 102. And (3) coating the coating slurry prepared in the step (4) on the whole carrier of the cordierite carrier 101, wherein the carrier specification is 190.5mm x 101.6mm, the loading capacity is 150g/L, the coating length is 101mm, and drying is carried out at 120 ℃ for 2 hours to obtain the second coating 103. Roasting in air at 550 deg.c for 3 hr. A three-way catalyst with NH 3、NOx、N2 O removal was obtained.
The structure of the catalyst of this comparative example is shown in fig. 2 c.
Comparative example 13
(1) Steps (1), (2) and (4) of example 1 were repeated, wherein (1) was ground to a particle size d90=10 μm, and the viscosity was adjusted to 1320cp.
(2) Coating the coating slurry prepared in the step (1) on a rear region of a cordierite carrier 101, wherein the carrier specification is 190.5mm x 101.6mm, the loading capacity is 25g/L, the coating length is 50mm, and drying is carried out at 120 ℃ for 2 hours to obtain an NH 3 oxidation coating 105. And then coating the slurry in the step (2) on the NH 3 oxidation coating 105 with the loading of 25g/L and the coating length of 50mm, and drying at 120 ℃ for 2 hours to obtain the third coating 104. Finally, the slurry in the step (4) is coated on the front area of the carrier 101, the loading capacity is 150g/L, the coating length is 50mm, the drying is carried out for 2 hours at 120 ℃, the second coating 103 is obtained, and the baking is carried out in air, wherein the baking temperature is 550 ℃ and the baking time is 3 hours. A three-way catalyst with NH 3、NOx、N2 O removal was obtained.
The structure of the catalyst of this comparative example is shown in fig. 2 d.
Comparative example 14
(1) Repeating steps (1), (2), (3) and (4) of example 1.
(2) And (3) coating the coating slurry prepared in the step (3) on a rear region of the cordierite carrier 101, wherein the carrier specification is 190.5mm x 101.6mm, the loading capacity is 50g/L, the coating length is 50mm, and drying is carried out at 120 ℃ for 2 hours to obtain the first coating 102. Coating the coating slurry prepared in the step (4) on the front region of the cordierite carrier 101, wherein the loading capacity is 150g/L, the coating length is 50mm, and drying is carried out at 120 ℃ for 2 hours to obtain a second coating 103. Roasting in air at 550 deg.c for 3 hr. A three-way catalyst with NH 3、NOx、N2 O removal was obtained.
The structure of the catalyst of this comparative example is shown in fig. 2 e.
The catalysts prepared in example 1, example 2, example 3, example 4 and comparative examples 1,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 were subjected to the falling rate test, and the test results were: the falling rates of the examples 1-4 and the comparative examples 3-8 and 10-14 are all less than 0.1%, and no visual dust exists; the falling rate of comparative examples 1 and 2 is more than 2%, and obvious dust falling is achieved.
The catalysts prepared in examples 1-4 and comparative examples 1-14 were evaluated for performance under the following test conditions: [ NH 3]=200ppm,[NO]=100ppm,[O2]=10%,[H2O]=7%,[N2O]=50ppm,N2 balance gas, space velocity 100000h -1, reaction temperature 200-500 ℃.
The prepared test samples were subjected to activity investigation on a fixed bed reactor, and the results were as follows:
1) Fig. 4 is a graph of ammonia conversion efficiency versus reaction temperature for the catalysts of example 1 and comparative examples 1,2 provided by the present invention. As can be seen from FIG. 4, the catalyst prepared in example 1 of the present invention has a NH 3 light-off temperature of < 200 ℃, and the conversion efficiency of NH 3 at 200 ℃ is over 75%. And the conversion efficiency of the low-temperature ammonia gas of the catalysts prepared in comparative examples 1 and 2 is obviously reduced compared with that of the catalyst prepared in example 1. In particular, the conversion efficiency to NH 3 at 200℃was 57% and 45%, respectively. This is because the coating sizes of comparative examples 1 and 2 do not match the cordierite carrier, and the coating is severely exfoliated, resulting in reduced performance.
2) Fig. 5 is a graph showing the conversion efficiency of laughing gas versus reaction temperature of the catalysts of example 1 and comparative examples 1 and 2 provided by the present invention. As can be seen from FIG. 5, the catalyst prepared in the embodiment 1 of the invention has higher low-temperature N 2 O conversion efficiency, the ignition temperature of N 2 O is 275 ℃, and the conversion efficiency of N 2 O reaches over 67% under the condition of 300 ℃. The catalysts prepared in comparative examples 1 and 2 had a conversion efficiency of 55% and 41% in N 2 O at 300℃because the particle sizes of the coatings in comparative examples 1 and 2 were not matched with those of the cordierite carrier, and the coatings were severely peeled off, resulting in a decrease in performance.
3) FIG. 6 is a graph of nitrogen oxide conversion efficiency versus reaction temperature for the catalysts of example 1 and comparative examples 1,2 provided by the present invention; as can be seen from fig. 6, the NOx conversion efficiency of example 1 of the present invention at 300 ℃ reached 99%, which was substantially completely converted, whereas the NOx conversion efficiencies of the catalysts prepared in comparative examples 1 and 2 were 80% and 75%, respectively, at 300 ℃, because the coating particle diameters of comparative examples 1 and 2 were not matched with the cordierite carrier, the coating falling off was serious, resulting in performance degradation.
4) FIG. 7 is a graph of ammonia conversion efficiency versus reaction temperature for the catalysts of comparative examples 3, 4. As can be seen from fig. 7, the ammonia conversion efficiency of comparative example 3is overall superior to that of comparative example 4, and the ammonia conversion efficiency of comparative example 3 at 200 ℃ is 10% higher than that of comparative example 4, because the platinum-based alumina coating layer of comparative example 3 was subjected to heat treatment at 650 ℃ for 3 hours, the Pt particle size was increased, and the NH 3 low Wen Qiran capacity was improved, so that the ammonia oxidation performance was higher than that of the catalyst prepared in comparative example 4.
5) FIG. 8 is a graph showing the conversion efficiency of laughing gas versus reaction temperature for the catalysts of comparative examples 3 and 4. As can be seen from fig. 8, the catalysts prepared by the catalysts of comparative examples 3 and 4 all have negative N 2 O conversion efficiency below 300 ℃, and the N 2 O conversion efficiency of comparative example 3 is lower than that of comparative example 4, because in the low temperature section, the dual-function ASC catalyst undergoes ammoxidation reaction to generate the byproduct N 2 O, resulting in no decrease in the reaction of N 2 O, negative conversion efficiency occurs, and the catalyst of comparative example 3 has improved ammoxidation capability after heat treatment, and the amount of the byproduct N 2 O generated increases, resulting in the conversion efficiency of N 2 O of comparative example 3 being lower than that of comparative example 4; above 300 ℃, as the reaction temperature increases, the conversion efficiency of N 2 O increases, because the outer layer of the bi-functional catalyst iron molecular sieve has a decomposition effect on N 2 O in a medium-high temperature region, contributing to the conversion efficiency of N 2 O.
6) FIG. 9 is a graph of nitrogen oxide conversion efficiency versus reaction temperature for the catalysts of comparative examples 3, 4; as can be seen from fig. 9, the catalysts of comparative examples 3, 4 increased with increasing temperature below 300 ℃; the conversion efficiency of NOx is reduced with the rise of the reaction temperature at 300 ℃ and above which the conversion efficiency of NOx is reduced due to the fact that NOx which is a byproduct is generated by the ammoxidation reaction at the high Wen Duangui metal layer, and the conversion efficiency of NOx is reduced in a high temperature region; since the catalyst of comparative example 3 was heat-treated to improve the ammonia oxidizing ability, the by-product NOx generation amount was also increased, resulting in lower NOx conversion efficiency of comparative example 3 than comparative example 4.
7) FIG. 10 is a graph of ammonia conversion efficiency versus reaction temperature for the catalysts of examples 1, 3 and comparative examples 4-9 provided by the present invention. As can be seen from FIG. 10, the NH 3 light-off temperature of the catalysts prepared in examples 1 and 3 of the invention is less than 200 ℃, and the conversion efficiency of NH 3 under the condition of 200 ℃ is over 70%. And the conversion efficiency of the low-temperature ammonia gas of the catalysts of comparative examples 4-9 is obviously reduced compared with that of the catalysts of examples 1 and 3. The conversion efficiency of comparative example 4 was 58% at 200℃and the conversion efficiency of the catalysts of comparative examples 5-9 to NH 3 at 200℃was 35% -63%. This is due to the increased Pt particle size and improved NH 3 low Wen Qiran capacity of examples 1, 3 over comparative examples 4-9 by heat treating the platinum-based alumina. In addition, since the mass ratio range of the platinum-based alumina and the noble metal modified molecular sieve in the catalysts of comparative examples 5 to 9 is smaller than that of the catalysts of examples 1 and 3, the mass content of the platinum-based alumina is lower, resulting in lower oxidation efficiency of NH 3 at low temperature of comparative examples 5 to 9.
8) FIG. 11 is a graph showing the relationship between the conversion efficiency of laughing gas and the reaction temperature of the catalysts of examples 1 and 3 and comparative examples 4 to 9 provided by the present invention. As can be seen from FIG. 11, the catalysts prepared in comparative examples 5-9 have higher low temperature N 2 O conversion efficiency, the ignition temperature of N 2 O is less than 250 ℃, the conversion efficiency of N 2 O is over 80% at 300 ℃, and examples 1 and 3 are over 67% at 300 ℃, because the mass ratio of the platinum-based alumina to the noble metal modified molecular sieve in comparative examples 5-9 is higher than that in examples 1 and 3, the mass ratio of the noble metal modified molecular sieve is improved, and the decomposition efficiency of N 2 O is improved. The catalyst prepared in comparative example 4 had overall lower conversion efficiency to N 2 O than examples 1,3 and comparative examples 5-9 and negative conversion efficiency below 300 c because of the addition of the rhodium-modified molecular sieves of the present invention to examples 1,3 and comparative examples 5-9, which had N 2 O decomposition functionality, resulted in overall higher conversion efficiency to N 2 O of examples 1,3 and comparative examples 5-9 than the dual-function ASC catalyst of comparative example 4.
9) FIG. 12 is a graph of nitrogen oxide conversion efficiency versus reaction temperature for the catalysts of examples 1, 3 and comparative examples 4-9 provided herein; as can be seen from fig. 12, the catalysts of examples 1, 3 and comparative examples 4-9 of the present invention had substantially similar conversion efficiencies, with NOx conversion efficiencies of up to 99% at 275 c, and had been completely converted.
10 FIG. 13 is a graph showing the relationship between ammonia conversion efficiency and reaction temperature of the catalysts of example 1 and comparative examples 10 to 14 provided in the present invention. As can be seen from fig. 13, the ammonia conversion efficiency of example 1 reached 75% at 200 ℃ and was close to that of comparative examples 10-14, and the three-way catalyst structure of example 1 ensured good NH 3 conversion efficiency at low temperatures.
11 FIG. 14 is a graph showing the relationship between the conversion efficiency of laughing gas and the reaction temperature of the catalysts of example 1 and comparative examples 10-14 provided in the present invention. As can be seen from fig. 14, the catalyst prepared in example 1 of the present invention has a high conversion efficiency of low temperature N 2 O, and the conversion efficiency of N 2 O at 300 ℃ reaches 67%. Whereas the conversion efficiency of N 2 O at 300℃of the catalysts of comparative examples 10-14 was 48% -58%, 9-19 points lower than that of example 1, because the three-way catalyst structure of comparative examples 10-14 was different from the coating structure of example 1 of the present invention, the N 2 O decomposition coating was secondarily distributed in the catalyst in the coating structure of example 1, and the N 2 O emission was effectively reduced in both the front zone bottom layer and the rear zone. The coupled three-way catalyst structure for the diesel engine is favorable for improving the N 2 O decomposition activity.
12 FIG. 15 is a graph of nitrogen oxide conversion efficiency versus reaction temperature for the catalysts of example 1 and comparative examples 10-14 provided by the present invention; as can be seen from FIG. 15, the catalyst conversion efficiency of the present invention was close to that of the catalyst of example 1 and comparative examples 10-12, the NOx conversion efficiency at 200℃was 88% -90%, and the efficiency of comparative examples 13-14 was lower than that of example 1 and comparative examples 10-13 by nearly 10-12 points. This is because the outer NOx reduction coating of comparative examples 10, 11, 12 completely covers the entire catalyst and the byproduct NOx of the underlying ammonia oxidation coating reaction is reduced to N 2. The ammonia oxidation coating was not covered by the NOx reduction coating in the structures of comparative examples 13, 14, resulting in low NOx conversion efficiency. The coupled three-way catalyst structure for the diesel engine is beneficial to improving the NOx conversion efficiency. As can be seen from fig. 13 to 15, the three-way catalyst structure of the present invention has high N 2 O, NOx conversion efficiency while guaranteeing low-temperature ammoxidation efficiency.
13 FIG. 16 is a graph of ammonia conversion efficiency versus reaction temperature for the catalysts of examples 1-4 and comparative example 4 provided herein. As can be seen from FIG. 16, the NH 3 light-off temperature of the catalysts prepared in examples 1-4 of the present invention is less than 200deg.C, the conversion efficiency of NH 3 at 200deg.C is more than 68%, while the double-function ASC catalyst of comparative example 4 has an oxidation efficiency of NH 3 at 200deg.C of 58% which is at least 10 points lower than that of example 4, which indicates that the coupling type three-way catalyst for diesel engine of the present invention has excellent low temperature NH 3 oxidation activity.
14 FIG. 17 is a graph showing the relationship between the conversion efficiency of laughing gas and the reaction temperature of the catalysts of examples 1 to 4 and comparative example 4 provided in the present invention. As can be seen from FIG. 17, the catalysts prepared in examples 1-4 of the present invention have high low temperature N 2 O conversion efficiency, the ignition temperature of N 2 O is less than or equal to 275 ℃, and the conversion efficiency of N 2 O at 300 ℃ is over 67%. Whereas the dual-function ASC catalyst of comparative example 4 has a conversion efficiency of N 2 O of 10% at 300 ℃ which is at least 57 points lower than that of examples 1-4, it is demonstrated that the coupled three-way catalyst for diesel engine of the present invention has excellent low temperature N 2 O decomposition activity.
15 FIG. 18 is a graph of nitrogen oxide conversion efficiency versus reaction temperature for the catalysts of examples 1-4 and comparative example 4 provided herein; as can be seen from fig. 18, the catalysts prepared in examples 1to 4 and comparative example 4 of the present invention had substantially similar NOx conversion efficiencies to 99% at 275 ℃ and had been completely converted; the coupled three-way catalyst for the diesel engine has NOx conversion efficiency.
The coupled three-way catalyst for the diesel engine provided by the invention has the NH 3 ignition temperature of less than 200 ℃ and the N 2 O ignition temperature of less than or equal to 275 ℃ under the conditions of 100000h -1, 10% O 2 and 7%H 2 O, the conversion efficiency of NOx at 300 ℃ is 99%, and the leakage quantity of NH 3、NOx、N2 O at 200-500 ℃ is effectively reduced.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (9)
1. A coupled three-way catalyst for a diesel engine, comprising a cordierite carrier (101), a first coating (102), a second coating (103) and a third coating (104); the first coating (102) is positioned at the front area of the carrier (101) and is used for realizing NH 3 oxidation and N 2 O removal; the second coating (103) is positioned on the first coating (102) and is used for realizing NOx reduction and N 2 O removal; the third coating (104) is positioned at the rear area of the carrier (101) and is used for removing N 2 O; the ratio of the coating length of the first coating (102) to the coating length of the second coating (103) to the coating length of the third coating (104) is 1-2.3:1;
The first coating (102) is a mixture of platinum-based alumina and rhodium modified molecular sieve, and the mass ratio of the platinum-based alumina to the rhodium modified molecular sieve is 60-80: 20-40 parts; the molar ratio of SiO 2 to Al 2O3 in the rhodium modified molecular sieve is 10-15: 1, the mass of rhodium element in the rhodium modified molecular sieve accounts for 0.98% -6.12% of the mass of the molecular sieve carrier; the first coating (102) is subjected to high temperature heat treatment;
The second coating (103) is an Fe molecular sieve, wherein the mass of iron element accounts for 2.0% -4.0% of the mass of the molecular sieve carrier;
the third coating (104) is a rhodium modified molecular sieve and is consistent with the rhodium modified molecular sieve in the first coating (102);
The ratio of the total load of the first coating (102) to the second coating (103) to the load of the third coating (104) is 0.94-1.67: 1, wherein the load capacity of the first coating (102) is 50-100 g/L, and the load capacity of the second coating (103) is 100-150 g/L; the load capacity of the third coating (104) is 120-160 g/L.
2. The coupled three-way catalyst for a diesel engine according to claim 1, wherein the first coating (102) is baked at 650-750 ℃ for 3-5 hours.
3. The coupling type three-way catalyst for the diesel engine according to claim 1, wherein the mass of the platinum element in the platinum-based alumina accounts for 0.39% -3.57% of the mass of the alumina.
4. A coupled three-way catalyst for a diesel engine according to any one of claims 1 to 3, wherein the particle diameters D90 of the first coating layer (102), the second coating layer (103) and the third coating layer (104) are 9 to 11 μm, 4 to 6 μm and 3 to 5 μm, respectively, and the viscosities thereof are 1200 to 1400cp, 2100 to 2300cp and 1000 to 1200cp, respectively.
5. A coupled three-way catalyst for a diesel engine according to any one of claims 1 to 3, wherein the rhodium-modified molecular sieve is one or both of CHA-type molecular sieve and ERI-type molecular sieve.
6. A method for preparing a coupled three-way catalyst for a diesel engine according to any one of claims 1 to 5, comprising the steps of:
(1) Preparation of platinum-based alumina coating slurry
Adding 242.46g of needle-shaped alumina powder into 2205g of deionized water, and fully stirring; taking 7.65g of chloroplatinic acid aqueous solution according to the condition that Pt atoms in the platinum-based alumina account for 0.58% of the mass of the alumina, adding the solution into the aqueous solution of the alumina, and stirring for 1h to obtain platinum-based alumina coating slurry;
(2) Preparation of rhodium modified molecular sieve coating slurry
Adding 412.5g of CHA molecular sieve powder into 2940g of deionized water, and fully stirring; adding 22.92g of rhodium nitrate aqueous solution into the aqueous solution of the molecular sieve according to the condition that the noble metal in the noble metal modified molecular sieve accounts for 0.98% of the mass of the molecular sieve, fully stirring, grinding to the grain diameter D90=3.5 mu m, and adjusting the viscosity to 1050cp to obtain the noble metal rhodium modified molecular sieve coating slurry;
(3) Preparation of mixed coating slurry of platinum-based alumina and rhodium modified molecular sieve
Sampling and mixing the steps (1) and (2) according to the proportion of 80:20, stirring for 30min, drying at 120 ℃ for 1h, and roasting at 650 ℃ for 3h in a muffle furnace; fully mixing calcined powder and water, grinding to a particle size D90=9.2 mu m, and adjusting the viscosity to 1320cp to obtain mixed coating slurry of platinum-based alumina and rhodium modified molecular sieve;
(4) Preparation of Fe molecular sieve coating slurry
Taking 500g of Fe-ZSM-5 molecular sieve powder, adding 545g of deionized water, fully stirring, grinding to a particle size D90=5.1 mu m, and adjusting the viscosity to 2150cp to obtain Fe molecular sieve coating slurry;
(5) Preparation of the catalyst
Coating the mixed coating slurry of the platinum-based alumina and the rhodium modified molecular sieve prepared in the step (3) on a front region of cordierite Dan Zaiti (101), wherein the specification of a carrier is 190.5mm x 101.6mm, the loading capacity is 50g/L, the coating length is 50mm, and drying is carried out at 120 ℃ for 2 hours to obtain a first coating (102); then coating the molecular sieve slurry in the step (4) on the first coating (102), wherein the loading capacity is 150g/L, the coating length is 50mm, and drying is carried out at 120 ℃ for 2 hours to obtain a second coating (103); finally, coating rhodium modified molecular sieve slurry in the step (2) on a rear region of the cordierite carrier (101), wherein the loading capacity is 120g/L, the coating length is 50mm, and drying is carried out at 120 ℃ for 2 hours to obtain a third coating (104); roasting in air to obtain the coupling type three-way catalyst for the diesel engine.
7. The method of claim 6, wherein the CHA-type molecular sieve is H-SSZ-13 and has a silica to alumina ratio of 15.
8. The method of claim 6, wherein the Fe-ZSM-5 molecular sieve has a silica to alumina ratio of 22.
9. The process of claim 6, wherein the catalyst is calcined in air in step (5) at 550℃for 3 hours.
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