A diesel oxidation catalyst for reducing n2o emissions and a method for manufacturing the same

Abstract

The application discloses a diesel oxidation catalyst for reducing N2O emission and a preparation method thereof. First and second catalytic coating layers of the catalyst are continuously coated on a carrier in sections, a third catalytic coating layer is located on the upper layer of the first catalytic coating layer, and a fourth catalytic coating layer is located on the upper layer of the second catalytic coating layer. The first and second catalytic coating layers are used for purifying HC / CO pollutants and oxidizing NOx into NO2. The third noble metal active component of the third catalytic coating layer is composed of Pt or a mixture of Pt and Pd, and the ratio of Pt / Pd is 5:1-1:0. The fourth noble metal active component of the fourth catalytic coating layer is one or more of Pt, Pd, Rh and Ru. The third catalytic coating layer is used for reducing the selectivity of the DOC catalyst to N2O when oxidizing NH3 and the selectivity to N2O when the HC-SCR reaction is performed. The fourth catalytic coating layer adopts a coating layer with N2O decomposition capacity, and the N2O selectively generated in the upstream section is decomposed into N2. The catalyst coating layers are mutually cooperative, have basic DOC catalytic performance, and can reduce N2O emission.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, and in particular to a diesel oxidation catalyst for reducing N2O emissions and its preparation method. Background Technology

[0002] In November 2022, the initial draft of the Euro 7 emission regulations was released, and the draft of the Euro 7 emission regulations was updated in September 2023. At present, my country has fully upgraded to the China VI emission regulations. In the future, the China VII emission regulations will be further tightened, and the China VII emission regulations are likely to refer to the Euro VII standard. The main differences between the China VI emission regulations and the Euro VII standard draft are: (1) The NOx emission limit is greatly reduced, which is the first challenge of the next step of exhaust gas after-treatment technology; (2) The assessment of unconventional pollutant N2O has been added. The N2O emission is below 0.2g / W•h, with an average of about 11ppm. Based on the current exhaust gas after-treatment catalyst technology, this is the second challenge.

[0003] Based on the emission limits of the Euro 7 standard draft and the current level of catalyst technology, possible after-treatment technology routes for the future China VII emission standard were analyzed. If the current China VI technology route (DOC+DPF+SCR+ASC) is adopted, and cold-start testing is conducted separately, the long cold-start time will result in emissions far exceeding the limits. Furthermore, due to the aggressive urea injection strategy to reduce NOx, the risk of exceeding PN pollutant emission standards will be high. Therefore, possible after-treatment technology routes for the future China VII emission standard include the following:

[0004] (1) China VII technical route 1: Add thermal management (enhanced thermal management + DOC + DPF + large volume SCR + ASC) to the current China VI technical route. This technical route can shorten the cold start time to a certain extent, but it is still far from the Euro VII cold state emission limit.

[0005] (2) China VII technical route 2: The dual-injection mode of pre-positioned CCSCR in the traditional route (CCSCR+DOC+DPF+SCR+ASC). This technical route can shorten the cold start time to a certain extent, but it is still far from the Euro VII cold start emission limit. However, since some urea is injected before CDPF, it will be slightly more favorable for PN emission reduction than the previous two routes. However, if the urea injection strategy of CCSCR is not handled well, NH3 leakage to the chassis DOC will generate a large amount of N2O. ２ O has a high emission risk;

[0006] (3) National VII technology route 3: Add thermal management (enhanced thermal management + ccSCR + DOC + DPF + SCR + ASC) to National VII technology route 2. Compared with National VII technology route 2, National VII technology route 3 adds thermal management, which is more friendly to NOx emissions and PN emissions. If the NH3 leakage problem of ccSCR is handled well, the risk of N2O will also be lower.

[0007] (4) National VII technology route 4: Add ccDOC (enhanced thermal management + ccDOC + ccSCR + DOC + DPF + SCR + ASC) to National VII technology route 3. Under the condition of not changing thermal management, the addition of ccDOC will prolong the cold start time of ccSCR. Relatively speaking, the NOx emission risk is slightly higher, but considering desulfurization and regeneration, it is better than National VII technology route 3.

[0008] (5) National VII technical route 5: Add PNA (PNA+ccSCR+DOC+DPF+SCR+ASC) to National VII technical route 2. Due to the difficulty of calibration of PNA catalyst at low temperature adsorption and high temperature release, and the easy thermal degradation and poisoning of PNA catalyst, calibration is still a difficult point. Therefore, this technical route is not mature at present.

[0009] Currently, China VII emission standards routes 3 and 4 are potential after-treatment technologies for future China VII emission standards. However, these technologies present some technical challenges, primarily in the following aspects: NH3 escapes from the ccSCR / ASC system and reacts in the downstream chassis DOC, easily oxidizing to N2O. The reaction equations are: NH3 + O2 → N2O + H2O, NH3 + NO2 → NH4NO3, NH4NO3 → N2O + H2O. A small amount of HC produced by the engine reacts in the DOC, easily undergoing an HC-SCR reaction, also generating N2O. The reaction equation is: CxHy + NOx → N2O + CO2 + H2O. The aforementioned NH3 will be oxidized to N2O, and the HC will undergo an HC-SCR reaction to generate N2O, resulting in a double reaction that leads to excessive N2O emissions. Prior to China VI emission standards, heavy-duty emission regulations did not address N2O generation, and there was no NH3 present before the DOC catalyst. Furthermore, the HC content in the original emissions of light-duty vehicles was low. Therefore, the absolute amount of N2O generated by HC-SCR was not high. According to light-duty vehicle emission regulations, the N2O limit for light-duty vehicles is 20 mg / km. Thus, DOC catalysts prior to China VI did not specifically inhibit N2O generation. For China VII emission standards, significant optimization is required to meet the N2O emission limits. Therefore, for China VII emission standards, DOC catalysts must meet both normal DOC function requirements and the newly added requirement for low N2O selectivity. This necessitates improvements over DOC catalysts prior to China VI. Based on the current treatment levels of aftertreatment catalysts such as SCR, the maximum N2O emission limit after DOC catalyst treatment is 5 ppm. However, current DOC catalysts cannot reduce N2O generation, necessitating the development of new DOC catalysts. Summary of the Invention

[0010] The purpose of this invention is to overcome the above-mentioned shortcomings in the prior art and provide a diesel oxidation catalyst for reducing N2O emissions and its preparation method. Under the condition that DOC has NH3 and HC present, it inhibits the formation of N2O and contributes to the overall N2O emission reduction.

[0011] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0012] A diesel oxidation catalyst for reducing N2O emissions includes a support and a coating applied to the support. The coating includes a first catalytic coating, a second catalytic coating, a third catalytic coating, and a fourth catalytic coating. The first and second catalytic coatings are applied segmentally and continuously to the support. The first catalytic coating is located at the air inlet end of the support; the third catalytic coating is located at the air inlet end of the support and is above the first catalytic coating; the fourth catalytic coating is located at the air outlet end of the support and is above the second catalytic coating.

[0013] The first and second catalytic coatings are used to purify HC and CO pollutants and oxidize NO to NO2;

[0014] The third catalytic coating comprises a third catalytic material, a third noble metal active component, and a third auxiliary agent. The third noble metal active component is composed of Pt or a mixture of Pt and Pd. When the third noble metal active component is a mixture of Pt and Pd, the Pt / Pd ratio is 5:1 to 2:1. The third auxiliary agent is composed of one or more salts containing Ba, Sr, and Mg.

[0015] The fourth catalytic coating comprises a fourth catalytic material, a fourth noble metal active component, and a fourth auxiliary agent. The fourth noble metal active component is one or more of Pt, Pd, Rh, and Ru. The fourth auxiliary agent is composed of one or more of Ba, Sr, and Mg salts.

[0016] In the above technical solution, the first catalytic coating is located at the inlet end of the carrier, and the second catalytic coating is located at the outlet end of the carrier. The first and second catalytic coatings are the basic coatings of the DOC catalyst, achieving the purification of HC / CO and the oxidation of NO to NO2, promoting the passive regeneration of the CDPF catalyst and the active regeneration of the CDPF catalyst through fuel ignition. The third catalytic coating is located at the inlet end of the carrier and is situated above the first catalytic coating. The noble metal in the third catalytic coating is either high in Pt or single Pt. The inventors have found that the higher the Pt content in the catalytic coating, the lower the selectivity for N2O. Furthermore, the coating contains alkaline earth metals, which makes the third catalytic coating act as a suppressor... The N2O generation coating reduces NH3 adsorption, preventing NH3 from reacting on the DOC catalyst to generate N2O, thus reducing N2O formation. It also selectively oxidizes NH3 to N2 in the presence of NH3 and allows for HC-SCR reaction in the presence of HC, inhibiting the formation of the byproduct N2O. The fourth catalytic coating is located at the outlet end of the support and above the second catalytic coating. The noble metal in the fourth catalytic coating is one or more of Pt, Pd, Rh, and Ru, and the coating contains alkaline earth metals. This allows the fourth catalytic coating to decompose N2O generated by the upstream catalyst, reducing N2O emissions after DOC. The diesel oxidation catalyst of this invention exhibits synergistic effects among its various catalyst coatings, purifying HC / CO and oxidizing NO to NO2 to promote passive regeneration of CDPF and rapid SCR reaction. It also features active CDPF regeneration promoted by fuel ignition and is a DOC catalyst with a low N2O generation rate.

[0017] As a preferred embodiment of the present invention, the carrier is a permeable substrate, such as a honeycomb ceramic carrier.

[0018] In a preferred embodiment of the present invention, the first catalytic coating comprises a first catalytic material and a first noble metal active component, wherein the first noble metal active component is composed of Pt and Pd, the Pt / Pd ratio is 1:2 to 10:1, and the content of the first noble metal active component is 10 to 100 g / ft. 3 The first catalytic coating of the DOC catalyst of this invention has a high content of precious metals, including a certain amount of Pd, which is beneficial to the oxidation of HC and CO and the ignition of fuel oil.

[0019] In a preferred embodiment of the present invention, the second catalytic coating comprises a second catalytic material and a second noble metal active component, wherein the second noble metal active component is composed of Pt and / or Pd, the Pt / Pd ratio is 2:1 to 1:0, and the content of the second noble metal active component is 1 to 20 g / ft. 3The second catalytic coating of the DOC catalyst of this invention has a slightly lower noble metal content than the first catalytic coating, with a low or even zero Pd content, which is beneficial for NO oxidation and can assist in the oxidation of the remaining fuel at the relatively high bed temperature for fuel ignition.

[0020] In the above technical solution, the first catalytic coating and the second catalytic coating are continuously coated in a segmented manner, covering the entire length of the support, and the content of the first noble metal active component is 10~100g / ft. 3 The content of the second precious metal active component is 1~20g / ft. 3 The first catalytic coating at the front end has a high content of precious metals, while the second catalytic coating at the back end has a low content of precious metals. Using them in a matching manner can reduce the cost of precious metals on the one hand, and greatly improve the overall catalytic performance of the catalyst on the other.

[0021] In a more preferred embodiment of the present invention, the coating length of the first catalytic coating is 10-80% of the length of the carrier, and the coating length of the second catalytic coating is 20-90% of the length of the carrier. The total length of the first and second catalytic coatings is the length of the carrier. Preferably, the coating length of the first catalytic coating is 30-60% of the length of the carrier, and the coating length of the second catalytic coating is 40-70% of the length of the carrier.

[0022] As a preferred embodiment of the present invention, the first catalytic material is composed of a metal oxide and / or a molecular sieve. The metal oxide includes one or more of alumina, modified alumina, titanium oxide, and silicon oxide, and the molecular sieve is composed of one or more of β, CHA, ZSM-5, X, Y, and AEI structures. The second catalytic material is composed of a metal oxide and / or a molecular sieve. The metal oxide includes one or more of alumina, modified alumina, titanium oxide, and silicon oxide, and the molecular sieve is composed of one or more of β, CHA, ZSM-5, X, Y, and AEI structures. The modified alumina mentioned above is one or more of lanthanum-modified alumina, silicon-modified alumina, titanium-modified alumina, and tungsten-modified alumina, and the content of lanthanum, silicon, titanium, and tungsten elements is 0.1-10 wt% based on oxides. In the present invention, the selection and amount of the first catalytic material and the second catalytic material are independent of each other and can be the same or different.

[0023] As a more preferred embodiment of the present invention, the first catalytic coating further includes a first additive, which is composed of one or more soluble salts containing Ce, Zr, W, Mo, Sn, and Zn, specifically cerium nitrate, cerium carbonate, zirconium acetate, zirconium carbonate, ammonium metatungstate, ammonium paratungstate, tin nitrate, zinc nitrate, etc.; the amount of the first additive is 0.5 to 10% wt of the first catalytic material.

[0024] As a more preferred embodiment of the present invention, the second catalytic coating further includes a second auxiliary agent, which is composed of one or more soluble salts containing Ce, Zr, W, Mo, Sn, and Zn, specifically cerium nitrate, cerium carbonate, zirconium acetate, zirconium carbonate, ammonium metatungstate, ammonium paratungstate, tin nitrate, zinc nitrate, etc.; the amount of the second auxiliary agent is 0.5-10%wt of the second catalytic material. In the present invention, the selection and amount of the first and second auxiliary agents are independent of each other, and they can be the same or different.

[0025] As a more preferred embodiment of the present invention, the third auxiliary agent is composed of one or more salts containing Ba, Sr, and Mg; specifically, it is barium hydroxide, barium sulfate, barium carbonate, strontium nitrate, magnesium nitrate, etc., and the amount of the third auxiliary agent is 0.5-10%wt of the third catalytic material; the fourth auxiliary agent is composed of one or more salts containing Ba, Sr, and Mg, specifically, it is barium hydroxide, barium sulfate, barium carbonate, strontium nitrate, magnesium nitrate, etc., and the amount of the fourth auxiliary agent is 0.5-10%wt of the fourth catalytic material.

[0026] As a more preferred embodiment of the present invention, the coating length of the third catalytic coating is 10-20% of the length of the first catalytic coating, and the coating length of the fourth catalytic coating is 5-20% of the length of the second catalytic coating. In the above technical solution, the precious metal in the third catalytic coating is a high Pt content or a single Pt, which makes the fuel ignition effect of the third catalytic coating lower than that of a coating containing a certain amount of Pd. Furthermore, since it covers the first catalytic coating, this may reduce the fuel ignition performance of the first catalytic coating. To achieve the effect of inhibiting N2O generation, the coating length of the third catalytic coating is as short as possible to reduce the impact on the basic function of the DOC catalyst. The fourth catalytic coating contains a single Pd, and its NO oxidation efficiency is lower than that of the second catalytic coating containing a high Pt content. Covering the second catalytic coating may reduce the NO oxidation performance of the second catalytic coating. To achieve the effect of decomposing N2O, the coating length of the fourth catalytic coating is as short as possible to reduce the impact on the NO oxidation efficiency in the later stages of DOC and the oxidation of the remaining fuel in the later stages.

[0027] As a more preferred embodiment of the present invention, the coating length of the third catalytic coating is 10-15% of the length of the first catalytic coating, and the coating length of the fourth catalytic coating is 10-15% of the length of the second catalytic coating.

[0028] In a preferred embodiment of the present invention, the front end of the third catalytic coating is flush with the inlet port of the carrier, and the end end of the fourth catalytic coating is flush with the outlet port of the carrier. In the catalytic reaction, the fourth catalytic coating is positioned at the tail end to decompose the N2O generated upstream as much as possible, thereby reducing N2O emissions.

[0029] As a preferred embodiment of the present invention, the content of the third noble metal active component is 1~100g / ft. 3 The content of the fourth precious metal active component is 1~100g / ft. 3 More preferably, the content of the third noble metal active component is 1~15 g / ft. 3 The content of the fourth precious metal active component is 5~50g / ft. 3 More preferably, the content of the third noble metal active component is 1~5 g / ft. 3 The content of the fourth precious metal active component is 5~30g / ft. 3 .

[0030] As a preferred embodiment of the present invention, the third catalytic material is composed of metal oxides and / or molecular sieves, wherein the metal oxides include one or more of alumina, modified alumina, cerium oxide and its modified oxides, zirconium oxide and its modified oxides, and the molecular sieves are mainly composed of one or more of β, CHA, ZSM-5, X, Y, and AEI structures; the fourth catalytic material is composed of metal oxides and / or molecular sieves, wherein the metal oxides include one or more of alumina, modified alumina, iron oxide, nickel oxide, and cobalt oxide, and the molecular sieves include one or more of β, CHA, ZSM-5, X, Y, and AEI structures.

[0031] More preferably, the fourth catalytic material is nickel oxide or cobalt oxide. In the above technical solution, the fourth catalytic coating uses NiO or cobalt oxide as the catalytic support and Pd as the active component. The addition of alkaline earth metal additives activates the adsorption of Ni or Co elements on N2O, which can improve the generation of N2O by the fourth catalytic coating and reduce N2O emissions.

[0032] This invention also provides a method for preparing a diesel oxidation catalyst that reduces N2O emissions, used in the preparation of the above-mentioned catalyst, the preparation method comprising the following steps:

[0033] S1. Prepare the first slurry and the second slurry;

[0034] Preparation of the third slurry: The precursor solution of the third noble metal active component is dispersed in the raw material of the third catalytic material, and then the third auxiliary agent and the third binder are added and mixed. The mixture is then ball-milled to obtain the third slurry.

[0035] Preparation of the fourth slurry: The precursor solution of the fourth noble metal active component is dispersed in the raw material of the fourth catalytic material, and then the fourth auxiliary agent and the fourth binder are added and mixed. The mixture is then ball-milled to obtain the fourth slurry.

[0036] S2. The first slurry is coated on the air inlet end of the carrier, and the second slurry is coated on the air outlet end of the carrier, and then dried.

[0037] S3. The third slurry is coated onto the coating formed by the first slurry, and the fourth slurry is coated onto the coating formed by the second slurry. The mixture is then dried and calcined to obtain a diesel vehicle oxidation catalyst.

[0038] As a preferred embodiment of the present invention, the first slurry is prepared by dispersing the precursor solution of the first noble metal active component in the raw material of the first catalytic material, adding the first binder and mixing, and ball milling to obtain the first slurry.

[0039] Preparation of the second slurry: The precursor solution of the second noble metal active component is dispersed in the raw material of the second catalytic material, and then the second binder is added and mixed. The mixture is ball-milled to obtain the second slurry.

[0040] As a preferred embodiment of the present invention, the third adhesive includes one or more of aluminum sol, silica sol, zirconium sol, and their self-made sols; the fourth adhesive includes one or more of aluminum sol, silica sol, zirconium sol, and their self-made sols; the selected third adhesive, the type of the third adhesive, and the amount of the third adhesive are independent of each other and can be the same or different.

[0041] As a preferred embodiment of the present invention, when applying the slurry in step S2 or S3, the drying conditions after coating are 120-150℃ for 5-20 minutes.

[0042] As a preferred embodiment of the present invention, in step S4, the calcination conditions are: calcination at 350-650°C for 1-6 hours.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] 1. The diesel oxidation catalyst of this invention has four coating designs. The first and second catalytic coatings are the basic coatings of the DOC catalyst, which purify HC / CO and oxidize NO to NO2. The third catalytic coating uses a high Pt ratio or even single Pt noble metal active component and adds alkaline earth metal oxides to reduce the selectivity of the DOC catalyst for N2O when oxidizing NH3 and the selectivity of the HC-SCR reaction for N2O. The fourth catalytic coating is a coating with N2O decomposition ability, which decomposes the N2O selectively generated in the upstream section into N2. The various catalyst coatings work together to reduce N2O emissions while maintaining the basic DOC catalytic performance, thus meeting the N2O emission requirements of Euro VII / China VII.

[0045] 2. The diesel oxidation catalyst of the present invention has a higher content of precious metals in the upper and lower layers of the front section than in the rear section, which is beneficial to HC / CO oxidation. After the interference of HC / CO in the rear section, the NO oxidation efficiency is higher. Moreover, according to the axial bed temperature distribution characteristics of fuel ignition, the high content of precious metals in the front section is beneficial to fuel ignition. After fuel ignition, the bed temperature rises, and the downstream section can realize the conversion of the remaining fuel with a lower content of precious metals. Therefore, the fuel ignition performance is also extremely high.

[0046] 3. The diesel oxidation catalyst of the present invention has good catalytic performance and low N2O selectivity while being a low-precious-metal DOC catalyst, thus achieving the purpose of cost reduction and efficiency improvement. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the structure of an oxidation catalyst for diesel vehicles.

[0048] In the figure, the labels are: 1-carrier, 2-first catalytic coating, 3-second catalytic coating, 4-third catalytic coating, and 5-fourth catalytic coating. Detailed Implementation

[0049] To more clearly describe the inventive objectives, technical solutions, and advantages of the specific embodiments of this invention, the solutions in the specific embodiments will be described in detail below with reference to the accompanying drawings. The specific technical solutions involved in the following embodiments are merely for the purpose of clearly and completely describing the innovative technical solutions of this invention. They are only a part of the specific implementation methods that this invention can adopt, not all embodiments, and should not be construed as limiting the innovative solutions of this invention. Any solution that adopts the same inventive concept as this invention should be included within the protection scope of this invention.

[0050] Secondly, the descriptions in the accompanying drawings of the specific embodiments of this invention are merely for the convenience of those skilled in the art to understand the invention. The details shown in the drawings are for the purpose of clearly presenting the technical solution, and should not be construed as including all technical features in the drawings in the specific implementation examples, nor should the details in the drawings be considered as additional limitations on the innovative technical solution of this invention. The components in the various embodiments described and shown in the drawings can be combined and arranged in different configurations. These variations in combination and arrangement should be considered as part of all embodiments of the innovative solution of this invention and included within the scope of protection of this invention.

[0051] In summary, the solutions or descriptions presented in the specific embodiments and accompanying drawings of this invention are not intended to limit the scope of protection claimed, but merely to illustrate selected embodiments / examples to help those skilled in the art understand the relevant innovative solutions. All other equivalent or parallel embodiments obtained by those skilled in the art based on these embodiments without inventive effort are within the scope of protection claimed by this invention.

[0052] Example 1

[0053] like Figure 1 As shown, a diesel oxidation catalyst for reducing N2O emissions includes a support 1, a first catalytic coating 2, a second catalytic coating 3, a third catalytic coating 4, and a fourth catalytic coating 5. From the air intake direction of the support 1, the first catalytic coating 2 and the second catalytic coating 3 are continuously coated on the support in segments. The third catalytic coating 4 is located at the air intake end of the support 1 and is above the first catalytic coating 2. The fourth catalytic coating 5 is located at the air outlet end of the support 1 and is above the second catalytic coating 3. In this embodiment, the catalyst support 1 is a cordierite support with dimensions of 190.5*76.2 / 400-4.

[0054] The preparation method of diesel oxidation catalyst includes the following steps:

[0055] S1. Preparation of the first slurry SA1: Weigh 7.4333g of platinum chloride and 3.7167g of palladium chloride (based on elemental metal content), add 1500ml of deionized water, and stir until homogeneous to obtain the prepared first noble metal precursor solution; weigh 986.85g of lanthanum-modified alumina as the first catalyst material into a stirred tank, add the first noble metal precursor solution to it, and stir for 1 hour using the excess impregnation method; weigh 2.74g of ammonium molybdate and add it to the stirred first noble metal precursor solution, stir for 2 hours, and after stirring, determine that the solid content of the solution is 40%; transfer 950g of the above slurry (based on dry basis) to a ball mill jar; weigh 50g of silica sol (based on dry basis) and add it, ball mill, D 50 The first slurry, SA1, was obtained by controlling the micrometer size to 3-5 micrometers, the solid content to 40%, and the pH to 4.5.

[0056] Preparation of the second slurry SB1: Weigh 3.3450g of platinum chloride and 0.3717g of palladium chloride (based on elemental metal content), add a total of 1500ml of deionized water, and stir to mix evenly to obtain the prepared second noble metal precursor solution; weigh 994.28g of β-structured molecular sieve as the second catalyst material into a stirred tank, add the second noble metal precursor solution to it, and stir for 1 hour using the excess impregnation method; weigh 2.86g of cerium chloride and add it to the stirred second noble metal precursor solution, stir for 2 hours, and after stirring, determine that the solid content of the solution is 40%; transfer 950g of the above slurry (based on dry basis) to a ball mill jar; weigh 50g of silica sol (based on dry basis) and add it, ball mill, D 50 The sample was controlled at 3-5 micrometers, with a solid content of 40% and a pH of 4.5 to obtain the second slurry, SB1.

[0057] Preparation of the third slurry SC1: Weigh 3.7167g of platinum chloride (based on elemental metal), add 1500ml of deionized water, and stir until homogeneous to obtain the prepared third noble metal precursor solution; weigh 994.28g of lanthanum-modified alumina as the third catalyst material into a stirred tank, add the third noble metal precursor solution to it, and stir for 1 hour using the excess impregnation method; weigh 4.1176g of barium hydroxide, add it to the stirred third noble metal precursor solution, and stir for 2 hours. After stirring, the solid content of the solution is measured to be 40%; transfer 950g of the above slurry (based on dry weight) to a ball mill jar; weigh 50g of silica sol (based on dry weight) and add it, then ball mill, D 50 The slurry was controlled at 3-5 micrometers, with a solid content of 40% and a pH of 4.5 to obtain the third slurry, SC1.

[0058] Preparation of the fourth slurry SD1: Weigh 3.7167g of palladium chloride (based on elemental metal), add 1500ml of deionized water, and stir until homogeneous to obtain the prepared fourth noble metal precursor solution; weigh 994.28g of lanthanum-modified alumina as the fourth catalyst material into a stirred tank, add the fourth noble metal precursor solution to it, and stir for 1 hour using the excess impregnation method; weigh 7.4g of magnesium nitrate, add it to the stirred fourth noble metal precursor solution, and stir for 2 hours. After stirring, the solid content of the solution is measured to be 40%; transfer 950g of the above slurry (based on dry weight) to a ball mill jar; weigh 50g of silica sol (based on dry weight), add it, and ball mill; D 50 The fourth slurry, SD1, was obtained by controlling the particle size to 3-5 micrometers, the solid content to 40%, and the pH to 4.5.

[0059] S2. The first slurry SA1 and the second slurry SB1 are coated in sections on the air inlet and air outlet of the carrier, respectively. The coating length of the first slurry is 38.1 mm, the dry basis loading of the first slurry is 100 g / L, and the dry basis loading of the second slurry is 100 g / L. The coating is dried at 150°C for 20 min.

[0060] S3. Apply the third slurry SC1 onto the coating formed by the first slurry, ensuring the leading edge of the third catalytic coating is flush with the inlet port of the support. The dry basis loading of the third slurry is 50 g / L, and the coating length is 6 mm. Then, apply the fourth slurry SD1 onto the coating formed by the second slurry, ensuring the trailing edge of the fourth catalytic coating is flush with the outlet port of the support. The dry basis loading of the fourth slurry is 50 g / L, and the coating length is 6 mm. Dry at 150°C for 20 min, then calcine to obtain the diesel vehicle oxidation catalyst. The noble metal content of the first catalytic coating in the catalyst is 30 g / ft. 3 The ratio of precious metals Pt to Pd is 2:1; the content of precious metals in the second catalytic coating is 10 g / ft. 3 The ratio of precious metals Pt to Pd is 10:1; the content of precious metals in the third catalytic coating is 5 g / ft. 3 The fourth catalytic coating contains 5 g / ft of precious metals. 3 The total precious metal content of the catalyst coating is 20.79 g / ft. 3 .

[0061] Example 2

[0062] The catalyst in this embodiment is similar to that in Example 1, except that the preparation of the third slurry is different.

[0063] The preparation method of diesel oxidation catalyst includes the following steps:

[0064] S1. The preparation of the first slurry SA2 is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the second slurry SB2 is the same as the preparation of the second slurry SB1 in Example 1; the preparation of the fourth slurry SD2 is the same as the preparation of the fourth slurry SD1 in Example 1.

[0065] Preparation of the third slurry SC2: Weigh 2.4778g of platinum chloride and 1.2389g of palladium-platinum chloride (based on elemental metal content), add a total of 1500ml of deionized water, and stir until homogeneous to obtain the prepared third noble metal precursor solution; weigh 994.28g of lanthanum-modified alumina as the third catalyst material into a stirred tank, add it to the third noble metal precursor solution, and stir for 1 hour using the excess impregnation method; weigh 4.1176g of barium hydroxide and add it to the stirred third noble metal precursor solution, stir for 2 hours, and after stirring, determine that the solid content of the solution is 40%; transfer 950g of the above slurry (based on dry basis) to a ball mill jar; weigh 50g of silica sol (based on dry basis) and add it, ball mill, D 50 The slurry was controlled at 3-5 micrometers, with a solid content of 40% and a pH of 4.5 to obtain the third slurry, SC2.

[0066] S2. The first slurry SA2 and the second slurry SB2 are coated in sections on the air inlet and air outlet of the carrier, respectively. The coating length of the first slurry is 38.1 mm, the dry basis loading of the first slurry is 100 g / L, and the dry basis loading of the second slurry is 100 g / L. The coating is dried at 150°C for 20 min.

[0067] S3. The third slurry SC2 is coated onto the coating formed by the first slurry, with the leading edge of the third catalytic coating flush with the inlet port of the support. The dry basis loading of the third slurry is 50 g / L, and the coating length is 6 mm. Then, the fourth slurry SD2 is coated onto the coating formed by the second slurry, with the trailing edge of the fourth catalytic coating flush with the outlet port of the support. The dry basis loading of the fourth slurry is 50 g / L, and the coating length is 6 mm. The mixture is dried at 150°C for 20 min and calcined to obtain a diesel vehicle oxidation catalyst. The noble metal content of the first catalytic coating in the catalyst is 30 g / ft. 3 The ratio of precious metals Pt to Pd is 2:1; the content of precious metals in the second catalytic coating is 10 g / ft. 3 The ratio of precious metals Pt to Pd is 9:1; the precious metal content of the third catalytic coating is 5 g / ft. 3 The ratio of precious metals Pt to Pd is 2:1, and the content of precious metals in the fourth catalytic coating is 5 g / ft. 3 The total precious metal content of the catalyst coating is 20.79 g / ft. 3 .

[0068] Example 3

[0069] The catalyst in this embodiment is similar to that in Example 1, except that the fourth slurry is different.

[0070] The preparation method of diesel oxidation catalyst includes the following steps:

[0071] S1. The preparation of the first slurry SA3 is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the second slurry SB3 is the same as the preparation of the second slurry SB1 in Example 1; the preparation of the third slurry SC3 is the same as the preparation of the third slurry SC3 in Example 1.

[0072] Preparation of the fourth slurry SD3: Weigh 3.7167g of rhodium chloride (based on elemental metal), add 1500ml of deionized water, and stir until homogeneous to obtain the prepared fourth noble metal precursor solution; weigh 994.28g of lanthanum-modified alumina as the fourth catalyst material into a stirred tank, add the fourth noble metal precursor solution to it, and stir for 1 hour using the excess impregnation method; weigh 7.4g of magnesium nitrate, add it to the stirred fourth noble metal precursor solution, and stir for 2 hours. After stirring, the solid content of the solution is measured to be 40%; transfer 950g of the above slurry (based on dry weight) to a ball mill jar; weigh 50g of silica sol (based on dry weight), add it, and ball mill; D 50 The fourth slurry, SD3, was obtained by controlling the particle size to 3-5 micrometers, the solid content to 40%, and the pH to 4.5.

[0073] S2. The first slurry SA3 and the second slurry SB3 are coated in sections on the air inlet and air outlet of the carrier, respectively. The coating length of the first slurry is 38.1 mm, the dry basis loading of the first slurry is 100 g / L, and the dry basis loading of the second slurry is 100 g / L. The coating is dried at 150°C for 20 min.

[0074] S3. A third slurry, SC3, is coated onto the coating formed by the first slurry, with the leading edge of the third catalytic coating flush with the inlet port of the support. The dry basis loading of the third slurry is 50 g / L, and the coating length is 6 mm. Then, a fourth slurry, SD3, is coated onto the coating formed by the second slurry, with the trailing edge of the fourth catalytic coating flush with the outlet port of the support. The dry basis loading of the fourth slurry is 50 g / L, and the coating length is 6 mm. The mixture is dried at 150°C for 20 min and calcined to obtain a diesel vehicle oxidation catalyst. The noble metal content of the first catalytic coating in the catalyst is 30 g / ft. 3 The ratio of precious metals Pt to Pd is 2:1; the content of precious metals in the second catalytic coating is 10 g / ft. 3 The ratio of precious metals Pt to Pd is 9:1; the precious metal content of the third catalytic coating is 5 g / ft. 3， The fourth catalytic coating contains 5 g / ft of precious metals. 3 The total precious metal content of the catalyst coating is 20.79 g / ft. 3 .

[0075] Example 4

[0076] The catalyst in this embodiment is similar to that in Example 1, except that the coating length of the third catalytic coating is different.

[0077] The preparation method of diesel oxidation catalyst includes the following steps:

[0078] S1. The preparation of the first slurry SA4 is the same as that of the first slurry SA1 in Example 1; the preparation of the second slurry SB4 is the same as that of the second slurry SB1 in Example 1; the preparation of the third slurry SC4 is the same as that of the third slurry SC3 in Example 1; the preparation of the fourth slurry SD4 is the same as that of the fourth slurry SD1 in Example 1.

[0079] S2. The first slurry SA4 and the second slurry SB4 are coated in sections on the air inlet and air outlet of the carrier, respectively. The coating length of the first slurry is 38.1 mm, the dry basis loading of the first slurry is 100 g / L, and the dry basis loading of the second slurry is 100 g / L. The coating is dried at 150°C for 20 min.

[0080] S3. Apply the third slurry SC4 onto the coating formed by the first slurry, so that the front end of the third catalytic coating is flush with the port of the inlet end of the carrier. The dry basis loading of the third slurry is 50 g / L, and the coating length of the third slurry is 15 mm. Then apply the fourth slurry SD4 onto the coating formed by the second slurry, so that the rear end of the fourth catalytic coating is flush with the port of the outlet end of the carrier. The dry basis loading of the fourth slurry is 50 g / L, and the coating length of the fourth slurry is 6 mm. Dry at 150°C for 20 min, and calcine to obtain the diesel vehicle oxidation catalyst.

[0081] Example 5

[0082] The catalyst in this embodiment is similar to that in Example 1, except that the coating length of the third catalytic coating is different.

[0083] The preparation method of diesel oxidation catalyst includes the following steps:

[0084] S1. The preparation of the first slurry SA5 is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the second slurry SB5 is the same as the preparation of the second slurry SB1 in Example 1; the preparation of the third slurry SC5 is the same as the preparation of the third slurry SC1 in Example 1; the preparation of the fourth slurry SD5 is the same as the preparation of the fourth slurry SD1 in Example 1.

[0085] S2. The first slurry SA5 and the second slurry SB5 are coated in sections on the air inlet and air outlet of the carrier, respectively. The coating length of the first slurry is 38.1 mm, the dry basis loading of the first slurry is 100 g / L, and the dry basis loading of the second slurry is 100 g / L. The coating is dried at 150°C for 20 min.

[0086] S3. Apply the third slurry SC5 onto the coating formed by the first slurry, so that the front end of the third catalytic coating is flush with the port of the inlet end of the carrier. The dry basis loading of the third slurry is 50 g / L, and the coating length of the third slurry is 6 mm. Then apply the fourth slurry SD5 onto the coating formed by the second slurry, so that the rear end of the fourth catalytic coating is flush with the port of the outlet end of the carrier. The dry basis loading of the fourth slurry is 50 g / L, and the coating length of the fourth slurry is 15 mm. Dry at 150°C for 20 min, and calcine to obtain the diesel vehicle oxidation catalyst.

[0087] Example 6

[0088] The catalyst in this embodiment is similar to that in Example 1, except that the fourth slurry is different.

[0089] The preparation method of diesel oxidation catalyst includes the following steps:

[0090] S1. The preparation of the first slurry SA6 is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the second slurry SB6 is the same as the preparation of the second slurry SB1 in Example 1; the preparation of the third slurry SC6 is the same as the preparation of the third slurry SC1 in Example 1.

[0091] Preparation of the fourth slurry SD6: Weigh 3.7167g of palladium chloride (based on elemental metal), add 1500ml of deionized water, and stir until homogeneous to obtain the prepared fourth noble metal precursor solution; weigh 994.28g of NiO as the fourth catalyst material into a stirred tank, add the fourth noble metal precursor solution to it, and stir for 1 hour using the excess impregnation method; weigh 7.4g of magnesium nitrate, add it to the stirred fourth noble metal precursor solution, and stir for 2 hours. After stirring, the solid content of the solution is measured to be 40%; transfer 950g of the above slurry (based on dry weight) to a ball mill jar; weigh 50g of silica sol (based on dry weight), add it, and ball mill; D 50 The fourth slurry, SD6, was obtained by controlling the particle size to 3-5 micrometers, the solid content to 40%, and the pH to 4.5.

[0092] S2. The first slurry SA1 and the second slurry SB1 are coated in sections on the air inlet and air outlet of the carrier, respectively. The coating length of the first slurry is 38.1 mm, the dry basis loading of the first slurry is 100 g / L, and the dry basis loading of the second slurry is 100 g / L. The coating is dried at 150°C for 20 min.

[0093] S3. Apply the third slurry SC6 onto the coating formed by the first slurry, so that the front end of the third catalytic coating is flush with the port of the inlet end of the carrier. The dry basis loading of the third slurry is 50 g / L, and the coating length of the third slurry is 6 mm. Then apply the fourth slurry SD6 onto the coating formed by the second slurry, so that the rear end of the fourth catalytic coating is flush with the port of the outlet end of the carrier. The dry basis loading of the fourth slurry is 50 g / L, and the coating length of the fourth slurry is 6 mm. Dry at 150°C for 20 min, and calcine to obtain the diesel vehicle oxidation catalyst.

[0094] Example 7

[0095] The catalyst in this embodiment is similar to that in Example 1, except that the fourth slurry is different.

[0096] The preparation method of diesel oxidation catalyst includes the following steps:

[0097] S1. The preparation of the first slurry SA7 is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the second slurry SB7 is the same as the preparation of the second slurry SB1 in Example 1; the preparation of the third slurry SC7 is the same as the preparation of the third slurry SC3 in Example 1.

[0098] Preparation of the fourth slurry SD7: Weigh 3.7167g of palladium chloride (based on elemental metal), add 1500ml of deionized water, and stir until homogeneous to obtain the prepared fourth noble metal precursor solution; weigh 994.28g of cobalt oxide as the fourth catalyst material into a stirred tank, add the fourth noble metal precursor solution to it, and stir for 1 hour using the excess impregnation method; weigh 7.4g of magnesium nitrate, add it to the stirred fourth noble metal precursor solution, and stir for 2 hours. After stirring, the solid content of the solution is measured to be 40%; transfer 950g of the above slurry (based on dry weight) to a ball mill jar; weigh 50g of silica sol (based on dry weight), add it, and ball mill; D 50 The fourth slurry, SD7, was obtained by controlling the particle size to 3-5 micrometers, the solid content to 40%, and the pH to 4.5.

[0099] S2. The first slurry SA7 and the second slurry SB7 are coated in sections on the air inlet and air outlet of the carrier, respectively. The coating length of the first slurry is 38.1 mm, the dry basis loading of the first slurry is 100 g / L, and the dry basis loading of the second slurry is 100 g / L. The coating is dried at 150°C for 20 min.

[0100] S3. Apply the third slurry SC7 onto the coating formed by the first slurry, so that the front end of the third catalytic coating is flush with the port of the inlet end of the carrier. The dry basis loading of the third slurry is 50 g / L, and the coating length of the third slurry is 6 mm. Then apply the fourth slurry SD7 onto the coating formed by the second slurry, so that the rear end of the fourth catalytic coating is flush with the port of the outlet end of the carrier. The dry basis loading of the fourth slurry is 50 g / L, and the coating length of the fourth slurry is 6 mm. Dry at 150°C for 20 min, and calcine to obtain the diesel vehicle oxidation catalyst.

[0101] Example 8

[0102] The catalyst in this embodiment is similar to that in Example 1, except that the preparation of the third and fourth slurries is different.

[0103] The preparation method of diesel oxidation catalyst includes the following steps:

[0104] S1. The preparation of the first slurry SA8 is the same as that of the first slurry SA1 in Example 1; the preparation of the second slurry SB8 is the same as that of the second slurry SB1 in Example 1.

[0105] Preparation of the third slurry SC8: Weigh 14.8668g of platinum chloride (based on elemental metal), add 1500ml of deionized water, and stir until homogeneous to obtain the prepared third noble metal precursor solution; weigh 994.28g of lanthanum-modified alumina as the third catalyst material into a stirred tank, add the third noble metal precursor solution to it, and stir for 1 hour using the excess impregnation method; weigh 4.1176g of barium hydroxide, add it to the stirred third noble metal precursor solution, and stir for 2 hours. After stirring, the solid content of the solution is measured to be 40%; transfer 950g of the above slurry (based on dry weight) to a ball mill jar; weigh 50g of silica sol (based on dry weight) and add it, then ball mill. 50 The slurry was controlled at 3-5 microns, with a solid content of 40% and a pH of 4.5 to obtain the third slurry, SC8.

[0106] Preparation of the fourth slurry SD8: Weigh 14.8668 g of palladium chloride (based on elemental metal), add 1500 ml of deionized water, and stir until homogeneous to obtain the prepared fourth noble metal precursor solution; weigh 994.28 g of lanthanum-modified alumina as the fourth catalyst material into a stirred tank, add the fourth noble metal precursor solution to it, and stir for 1 h using the excess impregnation method; weigh 7.4 g of magnesium nitrate, add it to the stirred fourth noble metal precursor solution, and stir for 2 h. After stirring, the solid content of the solution is measured to be 40%; transfer 950 g of the above slurry (based on dry weight) to a ball mill jar; weigh 50 g of silica sol (based on dry weight), add it, and ball mill; D 50The fourth slurry, SD8, was obtained by controlling the particle size to 3-5 micrometers, the solid content to 40%, and the pH to 4.5.

[0107] S2. The first slurry SA8 and the second slurry SB8 are coated in sections on the air inlet and air outlet of the carrier, respectively. The coating length of the first slurry is 38.1 mm, the dry basis loading of the first slurry is 100 g / L, and the dry basis loading of the second slurry is 100 g / L. The coating is dried at 150°C for 20 min.

[0108] S3. A third slurry, SC8, is coated onto the coating formed by the first slurry, with the leading edge of the third catalytic coating flush with the inlet port of the support. The dry basis loading of the third slurry is 50 g / L, and the coating length is 6 mm. Then, a fourth slurry, SD8, is coated onto the coating formed by the second slurry, with the trailing edge of the fourth catalytic coating flush with the outlet port of the support. The dry basis loading of the fourth slurry is 50 g / L, and the coating length is 6 mm. The mixture is dried at 150°C for 20 min and calcined to obtain a diesel vehicle oxidation catalyst. The noble metal content of the first catalytic coating in the catalyst is 30 g / ft. 3 The ratio of precious metals Pt to Pd is 2:1; the content of precious metals in the second catalytic coating is 10 g / ft. 3 The ratio of precious metals Pt to Pd is 10:1; the content of precious metals in the third catalytic coating is 20 g / ft. 3 The fourth catalytic coating contains 20 g / ft of precious metals. 3 The total precious metal content of the catalyst coating is 23.16 g / ft. 3 .

[0109] Comparative Example 1

[0110] The catalyst in this comparative example is similar to the catalyst in Example 1, except that the first and second catalytic coatings are not applied in segments, and the coating at the bottom of the support is an integral coating formed by applying the first slurry.

[0111] The preparation method of diesel oxidation catalyst includes the following steps:

[0112] S1, the preparation of the first slurry DA1 is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the third slurry DC1 is the same as the preparation of the third slurry SC1 in Example 1; the preparation of the fourth slurry DD1 is the same as the preparation of the fourth slurry SD1 in Example 1;

[0113] S2. The first slurry DA1 is coated onto the carrier. The dry basis loading of the first slurry is 67.7 g / L. It is then dried at 120℃ for 20 min.

[0114] S3. The third slurry DC1 is coated onto the coating formed by the first slurry, with the leading edge of the third catalytic coating flush with the inlet port of the carrier. The dry basis loading of the third slurry is 50 g / L, and the coating length is 6 mm. Then, the fourth slurry DD1 is coated onto the coating formed by the second slurry, with the trailing edge of the fourth catalytic coating flush with the outlet port of the carrier. The dry basis loading of the fourth slurry is 50 g / L, and the coating length is 6 mm. The mixture is then dried at 120°C for 20 min and calcined to obtain a diesel vehicle oxidation catalyst. The noble metal content of the first catalytic coating in the catalyst is 30 g / ft. 3 The ratio of precious metals Pt to Pd is 2:1; the precious metal content of the third catalytic coating is 5 g / ft. 3， The fourth catalytic coating contains 5 g / ft of precious metals. 3 The total precious metal content of the catalyst coating is 20.79 g / ft. 3 .

[0115] Comparative Example 2

[0116] The catalyst in this comparative example is similar to the catalyst in Example 1, except that the first catalytic coating and the second catalytic coating are not applied in segments, but are applied in layers.

[0117] The preparation method of diesel oxidation catalyst includes the following steps:

[0118] S1. The preparation of the first slurry DA2 is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the second slurry DA2 is the same as the preparation of the second slurry SB2 in Example 1; the preparation of the third slurry DC3 is the same as the preparation of the third slurry SC1 in Example 1; the preparation of the fourth slurry DD2 is the same as the preparation of the fourth slurry SD1 in Example 1.

[0119] S2. First, the second slurry DB2 is coated onto the carrier. The coating length of the second slurry is 76.2 mm and the dry basis loading of the second slurry is 50 g / L. Then, the first slurry DA2 is coated onto the formed second slurry. The dry basis loading of the first slurry is 50 g / L. Dry at 150°C for 20 min.

[0120] S3. Apply the third slurry DC2 onto the coating formed by the first and second slurries, ensuring the leading edge of the third catalytic coating is flush with the inlet port of the support. The dry basis loading of the third slurry is 50 g / L, and the coating length is 6 mm. Then, apply the fourth slurry DD2 onto the coating formed by the first and second slurries, ensuring the trailing edge of the fourth catalytic coating is flush with the outlet port of the support. The dry basis loading of the fourth slurry is 50 g / L, and the coating length is 6 mm. Dry at 150°C for 20 min, then calcine to obtain the diesel vehicle oxidation catalyst. The noble metal content of the first catalytic coating in the catalyst is 30 g / ft. 3 The ratio of precious metals Pt to Pd is 2:1; the content of precious metals in the second catalytic coating is 10 g / ft. 3 The ratio of precious metals Pt to Pd is 9:1; the precious metal content of the third catalytic coating is 5 g / ft. 3 The fourth catalytic coating contains 5 g / ft of precious metals. 3 The total precious metal content of the catalyst coating is 20.79 g / ft. 3 .

[0121] Comparative Example 3

[0122] The catalyst in this comparative example is similar to the catalyst in Example 1, except that the catalyst does not contain a third catalytic coating.

[0123] The preparation method of diesel oxidation catalyst includes the following steps:

[0124] S1. The preparation of the first slurry DA3 is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the second slurry DA3 is the same as the preparation of the second slurry SD1 in Example 1; the preparation of the fourth slurry DD3 is the same as the preparation of the fourth slurry SD1 in Example 1.

[0125] S2. First, coat the first slurry DA3 onto the carrier. The coating length of the first slurry is 38.1 mm and the dry basis loading of the first slurry is 100 g / L. Then coat the second slurry DB3 onto the formed first slurry. The dry basis loading of the second slurry is 100 g / L. Dry at 150°C for 20 min.

[0126] S3. Then, the fourth slurry DD3 is coated onto the coating formed by the second slurry, so that the rear end of the fourth catalytic coating is flush with the outlet port of the support. The dry basis loading of the fourth slurry is 50 g / L, and the coating length of the fourth slurry is 6 mm. It is dried at 150°C for 20 min and calcined to obtain the diesel vehicle oxidation catalyst. The noble metal content of the first catalytic coating in the catalyst is 30 g / L. 3 The ratio of precious metals Pt to Pd is 2:1; the content of precious metals in the second catalytic coating is 10 g / ft. 3The ratio of precious metals Pt to Pd is 9:1; the content of precious metals in the fourth catalytic coating is 5 g / ft. 3 The total precious metal content of the catalyst coating is 20.40 g / ft. 3 .

[0127] Comparative Example 4

[0128] The catalyst in this comparative example is similar to the catalyst in Example 1, except that the catalyst does not contain a fourth catalytic coating.

[0129] The preparation method of diesel oxidation catalyst includes the following steps:

[0130] S1. The preparation of the first slurry DA4 is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the second slurry DA4 is the same as the preparation of the first slurry SB1 in Example 1; the preparation of the third slurry DC4 is the same as the preparation of the third slurry SC1 in Example 1.

[0131] S2. First, coat the first slurry DA4 onto the carrier. The coating length of the first slurry is 38.1 mm and the dry basis loading of the first slurry is 100 g / L. Then coat the second slurry DB4 onto the formed first slurry. The dry basis loading of the second slurry is 100 g / L. Dry at 150°C for 20 min.

[0132] S3. Apply the third slurry DC4 onto the coating formed by the first slurry, ensuring the leading edge of the third catalytic coating is flush with the inlet port of the carrier. The dry basis loading of the third slurry is 50 g / L, and the coating length is 6 mm. Dry at 150°C for 20 min, then calcine to obtain the diesel vehicle oxidation catalyst. The noble metal content of the first catalytic coating in the catalyst is 30 g / L. 3 The ratio of precious metals Pt to Pd is 2:1; the content of precious metals in the second catalytic coating is 10 g / ft. 3 The ratio of precious metals Pt to Pd is 9:1; the precious metal content of the third catalytic coating is 5 g / ft. 3 The total precious metal content of the catalyst coating is 20.4 g / ft. 3 .

[0133] Comparative Example 5

[0134] The catalyst in this comparative example is similar to the catalyst in Example 1, except that the positions of the third and fourth catalytic coatings are different.

[0135] The preparation method of diesel oxidation catalyst includes the following steps:

[0136] S1. The preparation of the first slurry DA6 is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the second slurry DB6 is the same as the preparation of the second slurry SB1 in Example 1; the preparation of the third slurry DC6 is the same as the preparation of the third slurry SC1 in Example 1; the preparation of the fourth slurry DD6 is the same as the preparation of the fourth slurry SD1 in Example 1.

[0137] S2. The first slurry DA6 and the second slurry DB6 are coated in sections on the air inlet and air outlet of the carrier, respectively. The coating length of the first slurry is 38.1 mm, the dry basis loading of the first slurry is 100 g / L, and the dry basis loading of the second slurry is 100 g / L. The coating is dried at 150°C for 20 min.

[0138] S3. Apply the fourth slurry DD6 onto the coating formed by the first slurry, making the front end of the fourth catalytic coating flush with the front end of the coating formed by the first slurry. The dry basis loading of the fourth slurry is 50 g / L, and the coating length of the fourth slurry is 6 mm. Then apply the third slurry DC6 onto the coating formed by the second slurry, making the rear end of the third catalytic coating flush with the rear end of the coating formed by the second slurry. The dry basis loading of the fourth slurry is 50 g / L, and the coating length of the fourth slurry is 6 mm. Dry at 150°C for 20 min, and calcine to obtain the diesel vehicle oxidation catalyst.

[0139] Comparative Example 6

[0140] The catalyst in this comparative example is similar to that in Example 2, except that the preparation of the third slurry is different.

[0141] The preparation method of diesel oxidation catalyst includes the following steps:

[0142] S1. The preparation of the first slurry DA6 is the same as the preparation of the first slurry SA1 in Example 2; the preparation of the second slurry DB6 is the same as the preparation of the second slurry SB6 in Example 2; the preparation of the fourth slurry DD6 is the same as the preparation of the fourth slurry SD2 in Example 2.

[0143] Preparation of the third slurry DC6: Weigh 1.2389g of platinum chloride and 2.4778g of palladium-platinum chloride (based on elemental metal content), add a total of 1500ml of deionized water, and stir to mix evenly to obtain the prepared third noble metal precursor solution; Weigh 994.28g of lanthanum-modified alumina as the third catalyst material into a stirred tank, add the third noble metal precursor solution to it, and stir for 1 hour using the excess impregnation method; Weigh 4.1176g of barium hydroxide and add it to the stirred third noble metal precursor solution, stir for 2 hours, and after stirring, determine that the solid content of the solution is 40%; Transfer 950g of the above slurry (based on dry basis) to a ball mill jar; Weigh 50g of silica sol (based on dry basis) and add it, ball mill, DC6... 50The slurry was controlled at 3-5 micrometers, with a solid content of 40% and a pH of 4.5 to obtain the third slurry, DC6.

[0144] S2. The first slurry DA6 and the second slurry DB6 are coated in sections on the air inlet and air outlet of the carrier, respectively. The coating length of the first slurry is 38.1 mm, the dry basis loading of the first slurry is 100 g / L, and the dry basis loading of the second slurry is 100 g / L. The coating is dried at 150°C for 20 min.

[0145] S3. Apply the third slurry DC6 onto the coating formed by the first slurry, ensuring the leading edge of the third catalytic coating is flush with the inlet port of the support. The dry basis loading of the third slurry is 50 g / L, and the coating length is 6 mm. Then, apply the fourth slurry DD6 onto the coating formed by the second slurry, ensuring the trailing edge of the fourth catalytic coating is flush with the outlet port of the support. The dry basis loading of the fourth slurry is 50 g / L, and the coating length is 6 mm. Dry at 150°C for 20 min, then calcine to obtain the diesel vehicle oxidation catalyst. The noble metal content of the first catalytic coating in the catalyst is 30 g / ft. 3 The ratio of precious metals Pt to Pd is 2:1; the content of precious metals in the second catalytic coating is 10 g / ft. 3 The ratio of precious metals Pt to Pd is 9:1; the precious metal content of the third catalytic coating is 5 g / ft. 3， The ratio of precious metals Pt to Pd is 1:2, and the content of precious metals in the fourth catalytic coating is 5 g / ft. 3 The total precious metal content of the catalyst coating is 20.79 g / ft. 3 .

[0146] Comparative Example 7

[0147] The catalyst in this comparative example is similar to the catalyst in Example 1, except that the preparation of the third slurry is different, and no third auxiliary agent is added during the preparation of the third slurry.

[0148] The preparation method of diesel oxidation catalyst includes the following steps:

[0149] S1. The preparation of the first slurry DA7 is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the second slurry DB7 is the same as the preparation of the second slurry SB1 in Example 1; the preparation of the fourth slurry DD7 is the same as the preparation of the fourth slurry SD1 in Example 1.

[0150] Preparation of the third slurry (DC7): Weigh 3.7167 g of platinum chloride (based on elemental metal), add 1500 ml of deionized water, and stir until homogeneous to obtain the prepared third noble metal precursor solution; weigh 996.28 g of lanthanum-modified alumina as the third catalyst material into a stirred tank, add the third noble metal precursor solution to it, and stir for 1 hour using the excess impregnation method; after stirring, the solid content of the solution is measured to be 40%; transfer 950 g of the above slurry (based on dry weight) to a ball mill jar; weigh 50 g of silica sol (based on dry weight) and add it, ball mill, DC7... 50 The slurry was controlled at 3-5 micrometers, with a solid content of 40% and a pH of 4.5 to obtain the third slurry, DC7.

[0151] S2. The first slurry DA7 and the second slurry DB7 are coated in sections on the air inlet and air outlet of the carrier, respectively. The coating length of the first slurry is 38.1 mm, the dry basis loading of the first slurry is 100 g / L, and the dry basis loading of the second slurry is 100 g / L. The coating is dried at 150°C for 20 min.

[0152] S3. Apply the third slurry DC7 onto the coating formed by the first slurry, so that the front end of the third catalytic coating is flush with the port of the inlet end of the carrier. The dry basis loading of the third slurry is 50 g / L, and the coating length of the third slurry is 6 mm. Then apply the fourth slurry DD7 onto the coating formed by the second slurry, so that the rear end of the fourth catalytic coating is flush with the port of the outlet end of the carrier. The dry basis loading of the fourth slurry is 50 g / L, and the coating length of the fourth slurry is 6 mm. Dry at 150°C for 20 min, and calcine to obtain the diesel vehicle oxidation catalyst.

[0153] Comparative Example 8

[0154] The catalyst in this comparative example is similar to the catalyst in Example 1, except that the preparation of the fourth slurry is different, and no fourth auxiliary agent is added during the preparation of the fourth slurry.

[0155] The preparation method of diesel oxidation catalyst includes the following steps:

[0156] S1. The preparation of the first slurry DA8 is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the second slurry DB8 is the same as the preparation of the second slurry SB1 in Example 1; the preparation of the fourth slurry DD8 is the same as the preparation of the fourth slurry SD1 in Example 1.

[0157] Preparation of the fourth slurry DD8: Weigh 3.7167g of palladium chloride (based on elemental metal), add 1500ml of deionized water, and stir until homogeneous to obtain the prepared fourth noble metal precursor solution; weigh 996.28g of lanthanum-modified alumina as the fourth catalyst material into a stirred tank, add the fourth noble metal precursor solution to it, and stir for 1 hour using the excess impregnation method. After stirring, the solid content of the solution is measured to be 40%; transfer 950g of the above slurry (based on dry weight) to a ball mill jar; weigh 50g of silica sol (based on dry weight) and add it, then ball mill, D... 50 The fourth slurry, DD8, was obtained by controlling the particle size to 3-5 micrometers, the solid content to 40%, and the pH to 4.5.

[0158] S2. The first slurry DA8 and the second slurry DB8 are coated in sections on the air inlet and air outlet of the carrier, respectively. The coating length of the first slurry is 38.1 mm, the dry basis loading of the first slurry is 100 g / L, and the dry basis loading of the second slurry is 100 g / L. The coating is dried at 150°C for 20 min.

[0159] S3. Apply the third slurry DC8 onto the coating formed by the first slurry, so that the front end of the third catalytic coating is flush with the port of the inlet end of the carrier. The dry basis loading of the third slurry is 50 g / L, and the coating length of the third slurry is 6 mm. Then apply the fourth slurry DD8 onto the coating formed by the second slurry, so that the rear end of the fourth catalytic coating is flush with the port of the outlet end of the carrier. The dry basis loading of the fourth slurry is 50 g / L, and the coating length of the fourth slurry is 6 mm. Dry at 150°C for 20 min, and calcine to obtain the diesel vehicle oxidation catalyst.

[0160] Comparative Example 9

[0161] This comparative example prepares an N2O removal catalyst, including a first catalytic coating, a second catalytic coating and a third catalytic coating. This comparative example is prepared with reference to Chinese patent document CN 107921416 B.

[0162] The preparation of the first slurry DA9 for the first catalytic coating is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the second slurry DB9 for the second catalytic coating is the same as the preparation of the second slurry SB1 in Example 1.

[0163] The preparation method of the third slurry DC9 is as follows: Weigh 3.7167g of ruthenium chloride (based on elemental metal), add 1500ml of deionized water, stir and mix evenly to obtain the prepared third noble metal precursor solution; weigh 996.28g of cerium dioxide as the fourth catalyst material into a stirred tank, add the fourth noble metal precursor solution into it, and stir for 1 hour using the excess impregnation method; after stirring, the solid content of the solution is measured to be 40%; transfer 900g of the above slurry (based on dry basis) to a ball mill jar; weigh 50g of ferric nitrate (based on Fe2O3) and add it to the ball mill jar; weigh 50g of silica sol (based on dry basis) and add it, ball mill, DC9... 50 The fourth slurry, DC9, was obtained by controlling the particle size to 3-5 micrometers, the solid content to 40%, and the pH to 4.5.

[0164] S2. The first slurry DA9 and the second slurry DB9 are coated in sections on the air inlet and air outlet of the carrier, respectively. The coating length of the first slurry is 38.1 mm, the dry basis loading of the first slurry is 100 g / L, and the dry basis loading of the second slurry is 100 g / L. The coating is dried at 150°C for 20 min.

[0165] S3. The third slurry DC9 is coated onto the coating formed by the first slurry, so that the front end of the third catalytic coating is flush with the port of the air inlet end of the carrier. The dry basis loading of the third slurry is 50 g / L, and the coating length of the third slurry is 6 mm. It is dried at 150°C for 20 min and calcined to obtain the diesel vehicle oxidation catalyst.

[0166] Comparative Example 10

[0167] The catalyst in this comparative example is similar to the catalyst in Example 1, except that the coating method is different.

[0168] The preparation method of diesel oxidation catalyst includes the following steps:

[0169] S1. The preparation of the first slurry DA10 is the same as the preparation of the first slurry SA1 in Example 1; the preparation of the second slurry DB10 is the same as the preparation of the second slurry SB1 in Example 1; the preparation of the third slurry DC10 is the same as the preparation of the third slurry SC1 in Example 1; the preparation of the fourth slurry DD10 is the same as the preparation of the fourth slurry SD1 in Example 1.

[0170] S2. First slurry DA10 is coated onto the inlet end of the carrier, with a coating length of 41.5 mm, forming a first catalytic coating. The front end of the first catalytic coating is flush with the port of the inlet end of the carrier. The dry basis loading of the first slurry is 100 g / L. Then, second slurry DB10 is coated onto the coating formed by the first slurry, with the same coating length as the first slurry. The dry basis loading of the first slurry is 100 g / L. Then, third slurry DC10 is coated onto the coating formed by the second slurry, with the same coating length as the first slurry. The dry basis loading of the third slurry is 50 g / L. Dry at 150℃ for 20 min.

[0171] S3. The fourth slurry DD11 is coated onto the support, so that the rear end of the fourth catalytic coating is flush with the gas outlet end of the support. The dry loading of the fourth slurry is 50 g / L, and the coating length of the fourth slurry is 27.6 mm. It is then dried at 150 °C for 20 min and calcined to obtain a diesel vehicle oxidation catalyst. In this comparative example, there is a blank section between the coatings formed by the first, second, and third slurries and the coating formed by the fourth slurry, with a length of 6.9 mm.

[0172] Test Example 1

[0173] (1) Fuel ignition performance test

[0174] The diesel vehicle oxidation catalysts described in Examples 1-7 and Comparative Examples 1-10 were fitted with metal casings and installed in the exhaust pipe of a diesel engine bench. The ignition performance of the DOC catalysts on fuel was tested. The engine operating conditions were adjusted to achieve a catalyst test space velocity of 100,000 rpm and a DOC inlet temperature of 250°C. The post-injection fuel quantity was set to achieve a target DOC inlet temperature of 600°C. The target temperature was checked and recorded after DOC. After stabilization, the HC component concentration in the exhaust gas after DOC was checked and recorded. The test results are shown in Table 1.

[0175] Table 1. Test results of diesel vehicle oxidative catalyst fuel ignition performance in the examples and comparative examples.

[0176] Serial Number Airspeed (10000h⁻¹) DOC pre-temperature (°C) Temperature after DOC (°C) HC component concentration (ppm) Example 1 10 250 600 230 Example 2 10 250 600 180 Example 3 10 250 600 238 Example 4 10 250 600 852 Example 5 10 250 600 923 Example 6 10 250 600 652 Example 7 10 250 600 956 Example 8 10 250 600 238 Comparative Example 1 10 250 600 521 Comparative Example 2 10 250 600 1560 Comparative Example 3 10 250 600 105 Comparative Example 4 10 250 600 188 Comparative Example 5 10 250 400 7000+ Comparative Example 6 10 250 600 280 Comparative Example 7 10 250 600 195 Comparative Example 8 10 250 600 256 Comparative Example 9 10 250 600 265 Comparative Example 10 10 250 600 350

[0177] Note: The HC slip of 7000+ ppm in the test results indicates that the HC concentration is too high and may contaminate the analyzer. Therefore, the test was stopped when the analyzer reading reached 7000. The actual HC concentration was higher than 7000.

[0178] (2) DOC oxidation performance test and N2O selectivity under normal mode

[0179] The diesel vehicle oxidation catalysts described in Examples 1-7 and Comparative Examples 1-10 were fitted with metal casings and installed in the exhaust pipe of a diesel engine test bench to test the oxidation performance of the DOC catalysts for NO. Engine operating conditions were adjusted to achieve a catalyst test space velocity of 100,000 rpm and DOC inlet temperatures of 200, 250, 300, 350, and 400°C. After stabilization for 10 minutes, the concentrations of HC, CO, NO, NO2, and N2O components in the exhaust before and after the DOC were measured and recorded. The oxidation performance of the DOC for HC, CO, and NO, as well as its selectivity for N2O, were calculated. In the test results, the catalysts of the examples and comparative examples showed high conversion rates for HC and CO under conventional conditions, which are not presented here. The test results for the oxidation performance of NO and the selectivity for N2O are shown in Tables 2 and 3.

[0180] Table 2. NO oxidation performance results (%) of the diesel vehicle oxidation catalysts in the examples and comparative examples.

[0181] Serial Number 200℃ 250℃ 300℃ 350℃ 400℃ Example 1 18 36 51 60 48 Example 2 19 35 53 59 47 Example 3 18 37 52 61 49 Example 4 15 33 48 55 47 Example 5 14 29 45 52 41 Example 6 16 32 49 55 48 Example 7 17 31 48 56 49 Example 8 19 36 52 61 48 Comparative Example 1 12 26 39 49 38 Comparative Example 2 11 23 35 47 33 Comparative Example 3 19 37 51 60 46 Comparative Example 4 19 38 52 63 50 Comparative Example 5 17 36 52 59 48 Comparative Example 6 18 36 52 61 49 Comparative Example 7 18 37 51 62 49 Comparative Example 8 17 36 51 62 48 Comparative Example 9 17 32 47 55 46 Comparative Example 10 6 17 32 45 31

[0182] Table 3. N2O generation results (ppm) of diesel vehicle oxidation catalysts in the examples and comparative examples.

[0183] Serial Number 180℃ 200℃ 250℃ 300℃ 350℃ Example 1 0.5 0 0 0 0 Example 2 2 0 0 0 0 Example 3 0.5 0 0 0 0 Example 4 0 0 0 0 0 Example 5 0 0 0 0 0 Example 6 0 0 0 0 0 Example 7 0.5 0 0 0 0 Example 8 2 0 0 0 0 Comparative Example 1 0.5 0 0 0 0 Comparative Example 2 0.5 0 0 0 0 Comparative Example 3 3 0 0 0 0 Comparative Example 4 3 0 0 0 0 Comparative Example 5 3 0 0 0 0 Comparative Example 6 3 0 0 0 0 Comparative Example 7 2 0 0 0 0 Comparative Example 8 2 0 0 0 0 Comparative Example 9 3 0 0 0 0 Comparative Example 10 1 0 0 0 0

[0184] (3) Selectivity test of N2O under NH3 conditions

[0185] The catalyst was fitted with a metal casing and installed in the exhaust pipe of a diesel engine test bench. The selectivity of the DOC catalyst for N2O in the presence of NH3 was tested. The engine operating conditions were adjusted to achieve a catalyst test space velocity of 100,000 rpm and DOC inlet temperatures of 200, 250, 300, 350, and 400°C. 100 ppm NH3 was introduced into the exhaust pipe, and the concentrations of HC, CO, NO, NO2, and N2O components in the exhaust before and after DOC were measured and recorded. The oxidation performance of DOC for HC, CO, and NO, as well as its selectivity for N2O, were calculated. The test results showed that the catalysts of the examples and comparative examples had high conversion rates for HC, CO, and NO under NH3 conditions, but these were not presented. The test results for N2O selectivity are shown in Table 4.

[0186] Table 4. N2O generation rate (ppm) of the diesel vehicle oxidation catalysts in the examples and comparative examples under the condition of NH3 presence.

[0187] Serial Number 180℃ 200℃ 250℃ 300℃ 350℃ 400℃ Example 1 1 5 3 2 1 0 Example 2 2 9 5 3 1 0 Example 3 2 10 4 2 1 0 Example 4 1 5 2 2 1 0 Example 5 1 4 3 2 1 0 Example 6 0 2 2 1 0 0 Example 7 1 2 2 1 0 0 Example 8 1 2 2 1 0 0 Comparative Example 1 1 5 3 2 1 0 Comparative Example 2 1 5 3 2 1 0 Comparative Example 3 4 15 12 10 2 0 Comparative Example 4 5 20 15 12 3 0 Comparative Example 5 0 2 2 1 1 0 Comparative Example 6 5 25 18 12 3 0 Comparative Example 7 3 12 9 4 2 0 Comparative Example 8 2 10 8 3 1 0 Comparative Example 9 2 12 9 5 2 0 Comparative Example 10 3 15 9 5 2 0

[0188] Regarding the above test results, it can be seen that compared to Example 1, in Example 2, the third noble metal active component is a mixture of Pt and Pd. The basic performance of the DOC catalyst in Example 2 is unaffected, but the N2O selectivity of HC-SCR is increased. The N2O generation at 200°C in the presence of NH3 is 4 ppm greater than that in Example 1. This is because the addition of Pd increases the N2O selectivity during NH3 oxidation and the N2O selectivity during HC-SCR. In Example 3, the fourth noble metal active component in the fourth catalytic coating is rhodium. The basic performance of the DOC catalyst in Example 3 is unaffected, but the N2O selectivity of HC-SCR is increased. The N2O generation at 200°C in the presence of NH3 is 5 ppm greater than that in Example 1. This is because the difference in the fourth active component means that the N2O generated by NH3 oxidation and HC-SCR is not effectively decomposed on the fourth catalyst, resulting in a higher final generation. In Example 4, the length of the third catalytic coating exceeds 30%. The basic performance of the DOC catalyst deteriorates, manifested in high HC leakage and reduced NO oxidation performance during fuel ignition. This is mainly due to the length of the third catalytic coating, which covers the first catalytic coating, thus reducing the basic function of the DOC catalyst. However, the amount of N2O generated is essentially unaffected. In Example 5, the length of the fourth catalytic coating exceeds 30%. The basic performance of the DOC catalyst in Example 5 deteriorates, manifested in high HC leakage and reduced NO oxidation performance during fuel ignition. This is mainly due to the length of the fourth catalytic coating, which covers the second catalytic coating, thus reducing the basic function of the DOC catalyst. However, the amount of N2O generated is slightly lower, mainly because the longer fourth catalytic coating is beneficial for the decomposition of upstream N2O. In Example 6, the catalytic material for the fourth catalytic coating is NiO. The basic performance of the DOC catalyst in Example 6 deteriorates, manifested in high HC leakage and reduced NO oxidation performance during fuel ignition. This is mainly because the fourth catalytic coating is NiO, which has lower oxidation performance for HC and NO than alumina in Example 1. However, the NiO fourth catalytic coating is beneficial for the decomposition of N2O, therefore the amount of N2O generated is slightly lower than in Example 1. In Example 7, the catalytic material for the fourth catalytic coating is cobalt oxide. The basic performance of the DOC catalyst declined, manifested in high HC leakage and reduced NO oxidation performance during fuel ignition. This was primarily due to the fourth catalytic coating being cobalt oxide, which has lower HC and NO oxidation performance than the alumina in Example 1. However, the cobalt oxide coating is beneficial for N2O decomposition, thus slightly reducing N2O generation compared to Example 1. In Example 8, the third and fourth noble metal active components were higher than in Example 1, so the basic performance of the DOC catalyst in Example 8 was unaffected. The N2O selectivity of HC-SCR increased because the third catalyst had a high noble metal content and strong oxidizing power, resulting in high N2O selectivity. The N2O generation was lower in the presence of NH3 than in Example 1 because the higher content of the fourth active component provided better N2O decomposition.

[0189] For the comparative examples, Comparative Example 1 uses a different coating method compared to Example 1. The ignition performance of DOC fuel is essentially unaffected, but the NO oxidation performance is reduced. This is because Comparative Example 1 uses a first catalyst coating at the bottom layer, which is beneficial for fuel ignition. However, since the Pd content is higher than in the second catalyst coating, the NO oxidation performance is reduced. Since the third and fourth catalyst coatings remain unchanged, the N2O generation is essentially unaffected. Comparative Example 2 uses a layered coating method for the first and second catalyst coatings compared to Example 1. When DOC fuel ignites, HC leakage increases, and NO oxidation performance decreases. This is because the first and second catalyst coatings in Comparative Example 2 are used in layers, preventing them from fully utilizing their respective functions. However, since the third and fourth catalyst coatings remain unchanged, the N2O generation is essentially unaffected. Comparative Example 3 does not contain a third catalyst coating compared to Example 1. The ignition performance of DOC fuel and NO oxidation performance are improved, but the N2O generation is increased. This is because Comparative Example 3 lacks a third catalyst coating, and NH3 is directly oxidized in the first catalyst coating, resulting in a large amount of N2O. However, because there is no obstruction from the third coating, the catalyst performance of the first coating is fully utilized, thus reducing HC leakage. Comparative Example 4, unlike Example 1, does not contain a fourth catalytic coating. While it improves the ignition performance of DOC fuel and NO oxidation performance, it also increases N2O generation. This is because Comparative Example 4 lacks a fourth catalytic coating, preventing the upstream N2O from decomposing within it. However, without the obstruction of the fourth coating, the second catalytic layer performs optimally, resulting in reduced HC leakage and increased NO oxidation. In Comparative Example 5, the fourth and third catalytic coatings are the opposite of those in Example 1. Comparative Example 5 shows a significant decrease in the ignition performance of DOC fuel and NO oxidation performance, but also a decrease in N2O generation. This is because the third and fourth catalytic coatings in Comparative Example 5 effectively control N2O generation and decomposition, but their coverage over the first and second catalytic coatings prevents them from fully functioning, thus reducing the basic function of DOC. Compared to Example 1, Comparative Example 6 has a higher Pd content in its third catalytic coating. While the ignition performance and NO oxidation performance of Comparative Example 6 remain essentially unchanged, N2O generation is significantly increased. This is because the third and fourth catalytic coatings in Comparative Example 6 exchange, preventing the generated N2O from decomposing in the downstream third catalytic coating. Compared to Example 1, the third catalytic coating of Comparative Example 7 does not contain the third auxiliary agent, and the fourth catalytic coating of Comparative Example 8 does not contain the fourth auxiliary agent. The basic DOC function of Comparative Examples 8 and 9 is unaffected. However, due to the absence of auxiliary agents in the third and fourth catalytic coatings, the selectivity for N2O is high and the decomposition of N2O is low, resulting in a high final N2O formation. Compared to Example 1, Comparative Example 9 uses different catalytic coatings to prepare the catalyst. The basic DOC function is unaffected, but the N2O formation is increased. The main reason is that even with the addition of the N2O inhibitor Fe, N2O formation increases in the absence of a fourth catalytic decomposition.Compared to Example 1, Comparative Example 10 used a different coating method to prepare the catalyst, resulting in reduced fuel ignition performance, reduced NO oxidation performance, and increased N2O generation. The main reason is that the first, second, and third catalytic coatings overlap, leading to the loss of the basic function of DOC. Furthermore, the excessively high content of precious metals after upstream overlap results in excessive N2O generation during NH3 oxidation, while insufficient downstream decomposition capacity leads to increased N2O generation.

[0190] For those skilled in the art, when understanding the solutions described in the specific embodiments of the present invention, conventional technical manuals in the field can be consulted. At the same time, appropriate understandings or adjustments can be made to the above-mentioned terms to deduce the same or similar technical solutions without creative effort.

[0191] The above embodiments describe only the basic principles, main features and / or advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and the description of the invention content in the specification are only the principles or specific cases of the present invention. Without departing from the essence of the innovative idea of ​​the present invention, there are various changes and improvements to the innovative solution of the present invention, and all such changes and improvements fall within the scope of protection claimed by the present invention.

Claims

1. A diesel oxidation catalyst for reducing N2O emissions, said catalyst comprising a support and a coating applied to said support, characterized in that, The coating includes a first catalytic coating, a second catalytic coating, a third catalytic coating, and a fourth catalytic coating. The first catalytic coating and the second catalytic coating are applied to the carrier in segments and continuously. The first catalytic coating is located at the air inlet end of the carrier. The third catalytic coating is located at the air inlet end of the carrier and is located on top of the first catalytic coating; The fourth catalytic coating is located at the gas outlet end of the carrier and is located on top of the second catalytic coating; The total length of the first and second catalytic coatings is equal to the length of the carrier. The front end of the third catalytic coating is flush with the inlet port of the carrier, and the end of the fourth catalytic coating is flush with the outlet port of the carrier. The coating length of the third catalytic coating is 10-20% of the length of the first catalytic coating, and the coating length of the fourth catalytic coating is 5-20% of the length of the second catalytic coating. The coating length of the first catalytic coating is 10-80% of the length of the carrier, and the coating length of the second catalytic coating is 20-90% of the length of the carrier. The first and second catalytic coatings are used to purify HC and CO pollutants and oxidize NO to NO2; The third catalytic coating comprises a third catalytic material, a third noble metal active component, and a third auxiliary agent. The third catalytic material is composed of metal oxides and / or molecular sieves. The third noble metal active component is composed of Pt or a mixture of Pt and Pd. When the third noble metal active component is a mixture of Pt and Pd, the Pt / Pd ratio is 5:1 to 2:

1. The third auxiliary agent is composed of one or more salts containing Ba, Sr, and Mg. The fourth catalytic coating comprises a fourth catalytic material, a fourth noble metal active component and a fourth auxiliary agent, the fourth catalytic material is composed of a metal oxide and / or a molecular sieve, the fourth noble metal active component is one or more of Pt, Pd, Rh and Ru; the fourth auxiliary agent is composed of one or more of Ba, Sr and Mg-containing salts, the content of the third noble metal active component is 1-100 g / ft 3 ; the content of the fourth noble metal active component is 1-100 g / ft 3 .

2. The diesel oxidation catalyst for reducing N2O emissions according to claim 1, characterized in that, The first catalytic coating comprises a first catalytic material and a first noble metal active component. The first noble metal active component is composed of Pt and Pd, with a Pt / Pd ratio of 1:2 to 10:1, and the content of the first noble metal active component is 10 to 100 g / ft. 3 .

3. The diesel oxidation catalyst for reducing N2O emissions according to claim 1 or 2, characterized in that, The second catalytic coating comprises a second catalytic material and a second noble metal active component, wherein the second noble metal active component is composed of Pt and / or Pd, the Pt / Pd ratio is 2:1 to 1:0, and the content of the second noble metal active component is 1 to 20 g / ft. 3 .

4. The diesel oxidation catalyst for reducing N2O emissions according to claim 1, characterized in that, The coating length of the first catalytic coating is 10-80% of the length of the carrier, and the coating length of the second catalytic coating is 20-90% of the length of the carrier.

5. The diesel oxidation catalyst for reducing N2O emissions according to claim 1, characterized in that, The third catalytic material is composed of metal oxides and / or molecular sieves. The metal oxides include one or more of alumina, modified alumina, cerium oxide and its modified oxides, and zirconium oxide and its modified oxides. The molecular sieves mainly consist of one or more of the β, CHA, ZSM-5, X, Y, and AEI structures. The fourth catalytic material is composed of metal oxides and / or molecular sieves. The metal oxides include one or more of alumina, modified alumina, iron oxide, nickel oxide, and cobalt oxide. The molecular sieves include one or more of the β, CHA, ZSM-5, X, Y, and AEI structures.

6. The diesel oxidation catalyst for reducing N2O emissions according to claim 5, characterized in that, The fourth catalytic material is nickel oxide or cobalt oxide.

7. A method for preparing a diesel oxidation catalyst for reducing N2O emissions as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Prepare the first slurry and the second slurry; Preparation of the third slurry: The precursor solution of the third noble metal active component is dispersed in the raw material of the third catalytic material, and then the third auxiliary agent and the third binder are added and mixed. The mixture is then ball-milled to obtain the third slurry. Preparation of the fourth slurry: The precursor solution of the fourth noble metal active component is dispersed in the raw material of the fourth catalytic material, and then the fourth auxiliary agent and the fourth binder are added and mixed. The mixture is then ball-milled to obtain the fourth slurry. S2. The first slurry is coated on the air inlet end of the carrier, and the second slurry is coated on the air outlet end of the carrier, and then dried. S3. The third slurry is coated onto the coating formed by the first slurry, and the fourth slurry is coated onto the coating formed by the second slurry. The mixture is then dried and calcined to obtain a diesel vehicle oxidation catalyst.

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