Ceo2 modified pd-based ammonia production catalyst for pscr system and preparation method thereof

Abstract

The application provides a CeO2 modified Pd-based ammonia production catalyst for a pSCR system, the catalyst comprising a carrier, the carrier being coated with an active coating layer, the active coating layer comprising a noble metal Pd, a cerium-aluminum composite oxide CeO2-Al2O3 and a lanthanum-aluminum composite oxide La2O3-Al2O3; the mass ratio of the cerium-aluminum composite oxide to the lanthanum-aluminum composite oxide being 1:5-1:19. The application also provides a preparation method of the CeO2 modified Pd-based ammonia production catalyst for a pSCR system, which adopts conventional processes such as ball milling, coating, drying and calcination, does not need special equipment, is compatible with the existing industrial production line of automobile exhaust catalysts, uses commercial conventional chemical raw materials as the raw materials, is easy to obtain and controllable in cost, and is suitable for large-scale mass production. The CeO2 modified Pd-based ammonia production catalyst provided by the application realizes high conversion efficiency and high NH3 production rate through the synergistic effect of the oxygen storage component and the dispersion stabilizing component, is simple in process, low in cost and suitable for large-scale mass production, and is an ideal catalyst for the pSCR exhaust purification system of a lean burn engine.

Description

Technical Field

[0001] This invention belongs to the field of automotive exhaust purification catalyst technology, specifically relating to a CeO2-modified Pd-based ammonia production catalyst for pSCR systems and its preparation method. Background Technology

[0002] Lean-burn engines have a significant advantage in fuel economy and are more promising for application than traditional stoichiometric gasoline engines. However, their oxygen-rich combustion environment leads to increased NO content. X Emissions have increased significantly, making it difficult to meet stringent vehicle exhaust emission standards.

[0003] Passive selective catalytic reduction (pSCR) technology generates NH3 in situ under stoichiometric or slightly fuel-rich conditions via tightly coupled TWC. The NH3 is then adsorbed onto the downstream SCR catalyst, reducing NO under lean conditions. X No additional urea is needed, making it a solution for lean combustion engines. X The preferred emission control method is as follows: Al2O3-supported Pd-based three-way catalyst (TWC) can promote the water-gas shift (WGS) reaction to produce H2, thereby assisting the reduction of NO to NH3, and has the potential for pSCR application; however, the CO / HC / NO conversion efficiency and NH3 generation of this system are still difficult to meet the actual vehicle installation requirements.

[0004] CeO2, as a commonly used modifying component in commercial TWC, has advantages such as promoting the dispersion of precious metals and storing and releasing oxygen. Therefore, developing an optimized Pd / Al2O3 / CeO2 three-way catalyst to simultaneously improve the conversion efficiency of CO / HC / NO and the amount of NH3 generated, and to meet the needs of pSCR systems, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a CeO2-modified Pd-based ammonia production catalyst for pSCR systems and its preparation method, in order to solve the problems of insufficient CO / HC / NO conversion efficiency and limited NH3 generation in the existing Pd / Al2O3 three-way catalyst in pSCR applications.

[0006] To achieve the above and other related objectives, the present invention provides a CeO2-modified Pd-based ammonia production catalyst for a pSCR system. The catalyst includes a support coated with an active coating, which includes the noble metal Pd, the cerium-aluminum composite oxide CeO2-Al2O3, and the lanthanum-aluminum composite oxide La2O3-Al2O3. The mass ratio of the cerium-aluminum composite oxide to the lanthanum-aluminum composite oxide is 1:5 to 1:19.

[0007] Preferably, the amount of the active coating is 120-150 g / L.

[0008] Preferably, the amount of the noble metal in the active coating is 0.5 to 0.9 g / L.

[0009] Preferably, the mass percentage of cerium oxide in the cerium-aluminum composite oxide is 80% to 100%.

[0010] Preferably, the mass percentage of lanthanum oxide in the lanthanum-aluminum composite oxide is 3% to 5%.

[0011] Preferably, the carrier is a cordierite honeycomb ceramic or a metal carrier with a pore density of 400 to 600 meshes per square inch.

[0012] The present invention also provides a method for preparing a CeO2-modified Pd-based ammonia-producing catalyst for a pSCR system according to the above-described method, comprising the following steps: S1. Pretreatment of precious metals: Add the precursor of precious metal Pd to deionized water to prepare a Pd precursor solution and mix until the solution is homogeneous. S2. Preparation of active coating slurry: Cerium aluminum composite oxide and lanthanum aluminum composite oxide are added to deionized water according to the mass ratio and stirred to form slurry I. After ball milling, the Pd precursor solution prepared in step S1 is slowly added to the ball-milled slurry and stirred to obtain active coating slurry II. S3. Catalyst preparation: The active coating slurry II obtained in step S2 is coated onto the support, dried, calcined, and cooled to room temperature to obtain an ammonia production catalyst suitable for the pSCR system.

[0013] Preferably, in step S1, the concentration of the Pd precursor solution is 10~20wt%.

[0014] Preferably, in step S1, the mixing is carried out by stirring at room temperature, and the stirring time is 1~2 hours.

[0015] Preferably, in step S2, the solid content of the slurry I is 30~45 wt%.

[0016] Preferably, in step S2, the ball milling process uses zirconia balls as the milling medium.

[0017] Preferably, in step S2, the ball milling process takes 0.5 to 1 hour.

[0018] Preferably, in step S2, the ball milling process is performed until the slurry particle size D90 is 10~20μm.

[0019] Preferably, in step S3, the drying temperature is 100~120℃.

[0020] Preferably, in step S3, the drying time is 2 to 5 hours.

[0021] Preferably, in step S3, the calcination temperature is 500~600℃.

[0022] Preferably, in step S3, the roasting time is 1 to 3 hours.

[0023] As described above, the CeO2-modified Pd-based ammonia production catalyst for pSCR systems and its preparation method of the present invention have the following beneficial effects: 1. The CeO2-modified Pd-based ammonia production catalyst for pSCR systems of the present invention utilizes a cerium-aluminum composite oxide (oxygen storage material) with high CeO2 content in the active coating. Under a fuel-rich atmosphere, it can release oxygen, increase the probability of HC reforming reaction and water gas (CO+H2O) reaction, and promote H2 generation while ensuring the conversion efficiency of CO, HC and NO, thereby increasing the H2 / NO ratio in the atmosphere and significantly improving NH3 production.

[0024] 2. In the CeO2-modified Pd-based ammonia production catalyst for pSCR systems of the present invention, the large specific surface area of ​​the lanthanum-aluminum composite oxide can effectively improve the dispersion of the precious metal Pd, avoid Pd particle agglomeration, and at the same time play a role in stabilizing the valence state of the precious metal Pd, ensuring the long-term activity and stability of the catalyst; Pd, as the active center, forms a synergistic effect with the cerium-aluminum composite oxide and the lanthanum-aluminum composite oxide, achieving a dual improvement in CO / HC / NO conversion efficiency and NH3 production, adapting to the pSCR system for fuel-rich ammonia production and lean-burn NO reduction. x The core work requirements.

[0025] 3. The preparation method of the present invention adopts conventional processes such as ball milling, coating, drying and calcination, which do not require special equipment, are compatible with existing industrial production lines for automotive exhaust catalysts, and use commercial conventional chemical raw materials that are readily available and cost-controllable, making them suitable for large-scale mass production.

[0026] 4. The CeO2-modified Pd-based ammonia production catalyst provided by this invention achieves high conversion efficiency and high NH3 yield through the synergistic effect of oxygen storage components and dispersion stabilizing components. The process is simple, low-cost, and can be mass-produced, making it an ideal catalyst for pSCR exhaust gas purification systems in lean-burn engines. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0028] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included. For example, a specified range from “1 to 10” should be considered to include any and all subranges between the minimum value 1 and the maximum value 10. Exemplary subranges of the range 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0029] Furthermore, it should be understood that the one or more method steps mentioned in this invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated; moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as within the scope of the invention.

[0030] The first aspect of the present invention provides a CeO2-modified Pd-based ammonia production catalyst for a pSCR system, the catalyst comprising a support, wherein the support is coated with an active coating, the active coating comprising noble metal Pd, cerium-aluminum composite oxide CeO2-Al2O3 and lanthanum-aluminum composite oxide La2O3-Al2O3; The mass ratio of the cerium-aluminum composite oxide to the lanthanum-aluminum composite oxide is 1:5 to 1:19. For example, it is 1:5 to 1:7, 1:7 to 1:9, 1:9 to 1:10, 1:10 to 1:12, 1:12 to 1:14, 1:14 to 1:15, 1:15 to 1:17, or 1:17 to 1:19.

[0031] In some embodiments of the present invention, the amount of the active coating is 120-150 g / L. For example, it is 120-125 g / L, 125-130 g / L, 130-135 g / L, 135-140 g / L, 140-145 g / L, or 145-150 g / L.

[0032] In some embodiments of the present invention, the amount of the noble metal coated in the active coating is 0.5–0.9 g / L. For example, it is 0.5–0.6 g / L, 0.6–0.7 g / L, 0.7–0.8 g / L, or 0.8–0.9 g / L.

[0033] In some embodiments of the present invention, the mass percentage of cerium oxide in the cerium-aluminum composite oxide is 80% to 100%. For example, it is 80% to 85%, 85% to 90%, 90% to 95%, or 95% to 100%.

[0034] In some embodiments of the present invention, the mass percentage of lanthanum oxide in the lanthanum-aluminum composite oxide is 3% to 5%. For example, it is 3% to 3.4%, 3.4% to 3.8%, 3.8% to 4.2%, 4.2% to 4.6%, or 4.6% to 5%.

[0035] In some embodiments of the present invention, the carrier is a cordierite honeycomb ceramic or a metal carrier with a pore density of 400 to 600 meshes per square inch. For example, it is 400 to 450 meshes per square inch, 450 to 500 meshes per square inch, 500 to 550 meshes per square inch, or 550 to 600 meshes per square inch.

[0036] A second aspect of the present invention provides a method for preparing a CeO2-modified Pd-based ammonia-producing catalyst for a pSCR system as described above, comprising the following steps: S1. Pretreatment of precious metals: Add the precursor of precious metal Pd to deionized water to prepare a Pd precursor solution and mix until the solution is homogeneous. S2. Preparation of active coating slurry: Cerium aluminum composite oxide and lanthanum aluminum composite oxide are added to deionized water according to the mass ratio and stirred to form slurry I. After ball milling, the Pd precursor solution prepared in step S1 is slowly added to the ball-milled slurry and stirred to obtain active coating slurry II. S3. Catalyst preparation: The active coating slurry II obtained in step S2 is coated onto the support, dried, calcined, and cooled to room temperature to obtain an ammonia production catalyst suitable for the pSCR system.

[0037] In some embodiments of the present invention, in step S1, the concentration of the Pd precursor solution is 10-20 wt%. For example, it is 10-12 wt%, 12-14 wt%, 14-15 wt%, 15-17 wt%, 17-19 wt%, or 19-20 wt%.

[0038] In some embodiments of the present invention, in step S1, the mixing is performed by stirring at room temperature, and the stirring time is 1 to 2 hours. For example, it is 1 to 1.5 hours or 1.5 to 2 hours.

[0039] In some embodiments of the present invention, in step S2, the solid content of the slurry I is 30-45 wt%. For example, it is 30-32 wt%, 32-34 wt%, 34-35 wt%, 35-37 wt%, 37-39 wt%, 39-40 wt%, 40-42 wt%, 42-44 wt%, or 44-45 wt%.

[0040] In some embodiments of the present invention, in step S2, the ball milling process uses zirconia balls as the milling medium.

[0041] In some embodiments of the present invention, the ball milling process in step S2 is performed for 0.5 to 1 hour. For example, it is 0.5 to 0.7 hours, 0.7 to 0.9 hours, or 0.9 to 1 hour.

[0042] In some embodiments of the present invention, in step S2, the ball milling process is performed until the slurry particle size D90 is 10~20 μm. For example, it is 10~12 μm, 12~14 μm, 14~15 μm, 15~17 μm, 17~19 μm, or 19~20 μm.

[0043] In some embodiments of the present invention, the drying temperature in step S3 is 100-120°C. For example, it is 100-105°C, 105-110°C, 110-115°C, or 115-120°C.

[0044] In some embodiments of the present invention, the drying time in step S3 is 2 to 5 hours. For example, it is 2 to 3 hours, 3 to 4 hours, or 4 to 5 hours.

[0045] In some embodiments of the present invention, the calcination temperature in step S3 is 500-600°C. For example, it is 500-520°C, 520-540°C, 540-550°C, 550-570°C, 570-590°C, or 590-600°C.

[0046] In some embodiments of the present invention, the calcination time in step S3 is 1 to 3 hours. For example, it is 1 to 1.5 hours, 1.5 to 2 hours, 2 to 2.5 hours, or 2.5 to 3 hours.

[0047] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. The described embodiments are only for explaining the present invention and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the equipment used in the following embodiments is conventional equipment in the art; unless otherwise specified, the reagents used are commercially available products or prepared by conventional methods in the art. Items not described in detail in the following embodiments can be achieved using conventional experimental methods in the art.

[0048] Example 1 A CeO2-modified Pd-based ammonia production catalyst for pSCR systems, wherein the mass ratio of cerium-aluminum composite oxide to lanthanum-aluminum composite oxide is 1:19, the active coating amount is 130 g / L, and the amount of noble metal Pd in ​​the active coating is 0.706 g / L.

[0049] The preparation method is as follows: S1. Pretreatment of precious metals: Add an appropriate amount of deionized water to the palladium nitrate solution, mix and stir at room temperature for 1 hour to prepare a Pd precursor solution with a concentration of 15wt%. S2. Preparation of active coating slurry: 11.8g of cerium aluminum oxide (95%CeO2, 5%Al2O3) and 224.2g of lanthanum aluminum composite oxide (4.6%LaO2, 95.4%Al2O3) were added to deionized water and stirred to form a slurry. The solid content of the slurry was 35wt%, and the mass ratio of the total oxide mass to the deionized water was 5:16. The slurry was then ground until the particle size D90 was 12.5μm. The palladium nitrate solution obtained in step S1 was added dropwise to the above slurry and stirred at room temperature for 3h to obtain the active coating slurry. S3. Preparation of catalyst: The active coating slurry is uniformly coated onto a cordierite honeycomb ceramic support (pore density of 400~600 mesh / square inch), dried at 110℃ for 2h, calcined at 550℃ for 2h, and cooled to room temperature to obtain the target Pd-based catalyst.

[0050] Example 2 A CeO2-modified Pd-based ammonia production catalyst for pSCR systems, wherein the mass ratio of cerium-aluminum composite oxide to lanthanum-aluminum composite oxide is 1:15, the active coating amount is 130 g / L, and the amount of noble metal Pd in ​​the active coating is 0.706 g / L.

[0051] The preparation method is basically the same as in Example 1, except that the amount of cerium aluminum composite oxide used is 14.75g and the amount of lanthanum aluminum composite oxide used is 221.25g.

[0052] Example 3 A CeO2-modified Pd-based ammonia production catalyst for pSCR systems, wherein the mass ratio of cerium-aluminum composite oxide to lanthanum-aluminum composite oxide is 1:10, the active coating amount is 130 g / L, and the amount of noble metal Pd in ​​the active coating is 0.706 g / L.

[0053] The preparation method is basically the same as in Example 1, except that the amount of cerium aluminum composite oxide used is 21.45g and the amount of lanthanum aluminum composite oxide used is 214.55g.

[0054] Example 4 A CeO2-modified Pd-based ammonia production catalyst for pSCR systems, wherein the mass ratio of cerium-aluminum composite oxide to lanthanum-aluminum composite oxide is 1:5, the active coating amount is 130 g / L, and the amount of noble metal Pd in ​​the active coating is 0.706 g / L.

[0055] The preparation method is basically the same as in Example 1, except that the amount of cerium aluminum composite oxide used is 39.33g and the amount of lanthanum aluminum composite oxide used is 196.67g.

[0056] Comparative Example 1 A Pd-based catalyst, without the addition of cerium-aluminum composite oxide, with other parameters consistent with Example 1.

[0057] The preparation method is basically the same as in Example 1, except that the amount of cerium aluminum composite oxide is 0g and the amount of lanthanum aluminum composite oxide is 236g.

[0058] Comparative Example 2 A Pd-based catalyst, without the addition of lanthanum-aluminum composite oxide, with other parameters consistent with Example 1.

[0059] The preparation method is basically the same as in Example 1, except that the amount of cerium aluminum composite oxide used is 236g and the amount of lanthanum aluminum composite oxide used is 0g.

[0060] Comparative Example 3 Commercial Pd / Al2O3 catalyst with Pd coating amount of 0.706 g / L and active coating amount of 130 g / L, modified without cerium aluminum or lanthanum aluminum composite oxide.

[0061] Performance testing Test conditions: The actual exhaust gas composition of a lean-burn engine with alternating lean and rich combustion was simulated, and the test conditions are shown in Table 1. The conversion efficiencies of the catalyst for CO, HC, and NO, as well as the amount of NH3 generated, were measured. The inlet and outlet gas components were analyzed using a Fourier transform infrared spectroscopy (FTIR). The test temperature was 350℃, and the space velocity was 200,000 h⁻¹. -1 .

[0062] Table 1 Test Results Under the four operating conditions shown in Table 1, the catalyst performance test results of each embodiment and comparative example are shown in Tables 2, 3, 4, and 5 respectively.

[0063] Table 2 Table 3 Table 4 Table 5 Based on the examples, comparative examples, and Tables 1-5 above, it can be seen that: in Comparative Example 1, without the addition of cerium-aluminum composite oxide, the amount of NH3 generated was significantly lower than that in each example, proving that CeO2 can effectively promote H2 generation and increase the yield of NH3; and as the amount of CeO2 increases (the mass ratio of cerium-aluminum to lanthanum-aluminum changes from 1:19 to 1:5), the amount of NH3 generated shows a gradual upward trend, indicating the promoting effect of high CeO2 content on ammonia production.

[0064] Comparative Example 2, without the addition of lanthanum-aluminum composite oxide, showed the lowest conversion efficiencies and NH3 generation, demonstrating that lanthanum-aluminum composite oxide is crucial for improving Pd dispersion and ensuring catalyst activity.

[0065] Compared to the commercial Pd / Al2O3 catalyst in Comparative Example 3, the NH3 production in each example increased by more than 30%, and the NO conversion efficiency was also improved. This demonstrates that the CeO2 modification and lanthanum-aluminum composite oxide of the present invention work synergistically to make the prepared CeO2-modified Pd-based ammonia production catalyst for pSCR system significantly superior to the traditional Pd / Al2O3 catalyst.

[0066] The HC conversion efficiency in each embodiment is slightly lower than that in Comparative Example 1 because some HC is not directly oxidized but participates in the HC reforming reaction to generate H2, providing raw materials for NH3 generation. This phenomenon has no negative impact on the core requirement of the pSCR system for fuel-rich ammonia production; on the contrary, it increases the overall NO emission of the system. X Reduction efficiency.

[0067] Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0068] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A CeO2-modified Pd-based ammonia production catalyst for pSCR systems, characterized in that, The catalyst includes a support coated with an active coating, the active coating comprising noble metal Pd, cerium-aluminum composite oxide CeO2-Al2O3 and lanthanum-aluminum composite oxide La2O3-Al2O3; The mass ratio of the cerium-aluminum composite oxide to the lanthanum-aluminum composite oxide is 1:5 to 1:

19.

2. The CeO2-modified Pd-based ammonia production catalyst for pSCR systems according to claim 1, characterized in that, The active coating is applied at a rate of 120-150 g / L.

3. The CeO2-modified Pd-based ammonia production catalyst for pSCR systems according to claim 1, characterized in that, The amount of the precious metal in the active coating is 0.5 to 0.9 g / L.

4. The CeO2-modified Pd-based ammonia production catalyst for pSCR systems according to claim 1, characterized in that, The mass percentage of cerium oxide in the cerium-aluminum composite oxide is 80% to 100%.

5. The CeO2-modified Pd-based ammonia production catalyst for pSCR systems according to claim 1, characterized in that, The mass percentage of lanthanum oxide in the lanthanum-aluminum composite oxide is 3% to 5%.

6. The CeO2-modified Pd-based ammonia production catalyst for pSCR systems according to claim 1, characterized in that, The carrier is a cordierite honeycomb ceramic or a metal carrier with a pore density of 400 to 600 meshes per square inch.

7. A method for preparing a CeO2-modified Pd-based ammonia production catalyst for a pSCR system according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Pretreatment of precious metals: Add the precursor of precious metal Pd to deionized water to prepare a Pd precursor solution and mix until the solution is homogeneous. S2. Preparation of active coating slurry: Cerium aluminum composite oxide and lanthanum aluminum composite oxide are added to deionized water according to the mass ratio and stirred to form slurry I. After ball milling, the Pd precursor solution prepared in step S1 is slowly added to the ball-milled slurry and stirred to obtain active coating slurry II. S3. Catalyst preparation: The active coating slurry II obtained in step S2 is coated onto the support, dried, calcined, and cooled to room temperature to obtain an ammonia production catalyst suitable for the pSCR system.

8. The method for preparing the CeO2-modified Pd-based ammonia production catalyst for pSCR systems according to claim 7, characterized in that, It also includes one or more of the following features: 11) In step S1, the concentration of the Pd precursor solution is 10~20 wt%; 12) In step S1, the mixing is carried out by stirring at room temperature, and the stirring time is 1~2 hours.

9. The method for preparing the CeO2-modified Pd-based ammonia production catalyst for a pSCR system according to claim 7, characterized in that, It also includes one or more of the following features: 21) In step S2, the solid content of the slurry I is 30~45wt%; 22) In step S2, the ball milling process uses zirconia balls as the milling medium; 23) In step S2, the ball milling process takes 0.5 to 1 hour; 24) In step S2, the ball milling process is carried out until the slurry particle size D90 is 10~20μm.

10. The method for preparing the CeO2-modified Pd-based ammonia production catalyst for a pSCR system according to claim 7, characterized in that, It also includes one or more of the following features: 31) In step S3, the drying temperature is 100~120℃; 32) In step S3, the drying time is 2 to 5 hours; 33) In step S3, the calcination temperature is 500 ~ 600℃; 34) In step S3, the roasting time is 1 to 3 hours.

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