Hydrothermal-resistant HC-SCR catalyst and preparation method thereof

Abstract

The invention belongs to the technical field of engine tail gas aftertreatment, and particularly relates to a hydrothermal-resistant HC-SCR catalyst and a preparation method thereof. The hydrothermal-resistant HC-SCR catalyst comprises a carrier, a first coating and a second coating, the carrier is coated with the first coating, and the first coating is coated with the second coating; the first coating is a cerium-zirconium-manganese composite oxide and is marked as CeZrMnOx; the second coating is a yttrium modified copper molecular sieve. According to the HC-SCR catalyst, the double-coating design is adopted, so that the HC-SCR reaction activity of the catalyst is improved, the low-temperature NOx conversion efficiency is high, the temperature window is wide, and the hydrothermal thermal aging resistance is high. The HC-SCR catalyst can replace an NH3-SCR catalyst to be applied to a diesel engine / lean burn gasoline engine tail gas aftertreatment system, the system size can be greatly reduced, the cost is reduced, and the reliability is improved.

Description

Technical Field

[0001] This invention belongs to the field of engine exhaust aftertreatment technology, specifically relating to a hydrothermal resistant HC-SCR catalyst and its preparation method. Background Technology

[0002] my country currently implements the sixth stage of motor vehicle emission regulations (referred to as China VI), and the China VII regulations are under development. Referring to the already released Euro VII emission regulations, the emission limits for nitrogen oxides (NOx) will be further tightened, and new restrictions on nitrous oxide (N2O) emissions will be added, which poses a great challenge to current exhaust aftertreatment catalyst technology.

[0003] Currently, the NH3-SCR catalyst technology is widely used in diesel vehicle exhaust aftertreatment devices. This technology requires the injection of urea solution as a reducing agent, necessitating a complete urea injection system, including a urea tank, urea pump, urea nozzle, urea mixing chamber, and urea concentration sensor. This not only results in a large, complex, unreliable, and costly system, but also leads to side reactions, generating the byproduct N2O and exhibiting low N2 selectivity. 2NH3 + 2O2 → N2O + 3H2O; N2O is harmful to the human body and the environment, and can easily cause high blood pressure, fainting, anemia and damage to the central nervous system. Its greenhouse effect is about 300 times that of CO2.

[0004] The HC-SCR technology route, which uses hydrocarbons (HC) and carbon monoxide (CO) as reducing agents, is still under research. Theoretically, both HC and CO in engine exhaust can be used as reducing agents in HC-SCR. In a suitable HC-SCR catalyst, they react with NOx to reduce NOx emissions. This approach eliminates the need for urea as a reducing agent, which can simplify the system structure, reduce size, lower costs, and improve reliability.

[0005] Currently, the most widely studied HC-SCR technology routes employ Cu molecular sieves or Ag / Al2O3 coating technology. For example, CN103159242A discloses a method for catalytic purification of NOx on Ag / Al2O3 catalysts by adding hydrocarbons at temperatures of 150-600℃; CN115814844A discloses a method for preparing HC-SCR catalysts with Cu molecular sieves containing cerium-zirconium composite oxides, which exhibits good resistance to hydrothermal aging.

[0006] Existing publicly reported HC-SCR catalysts generally suffer from problems such as low NOx conversion rate, narrow temperature window, and insufficient resistance to hydrothermal aging. In particular, their performance deteriorates severely after hydrothermal aging. Therefore, further research is needed to develop an HC-SCR catalyst with high NOx conversion rate at low temperature, wide temperature window, and resistance to hydrothermal aging. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a hydrothermal-resistant HC-SCR catalyst and its preparation method. The HC-SCR catalyst of this invention employs a CeZrMnOx+Y@Cu-ZSM-5 double-layer coating design, which improves the catalyst's HC-SCR reactivity and hydrothermal resistance, resulting in high low-temperature NOx conversion efficiency, a wide temperature window, and excellent hydrothermal resistance.

[0008] To achieve the above technical objectives, the present invention provides the following technical solutions: In a first aspect, embodiments of the present invention provide a hydrothermal resistant HC-SCR catalyst, comprising a support, a first coating, and a second coating, wherein the first coating is coated on the support, and the second coating is coated on the first coating; the first coating is a cerium-zirconium-manganese composite oxide, denoted as CeZrMnOx; and the second coating is a yttrium-modified copper molecular sieve.

[0009] Furthermore, the carrier is one of a straight-through honeycomb ceramic carrier, a honeycomb metal carrier, and a wall-flow carrier, preferably a straight-through honeycomb ceramic carrier.

[0010] Furthermore, in the first coating, the molar ratio of each element is Ce:Zr:Mn=(2-5):1:(3-10).

[0011] Furthermore, in the first coating, the precursor of Ce is at least one of CeCl4, Ce(NO3)4 and Ce(Ac)3; The precursor of Zr is at least one of Zr(OH)4, ZrO(NO3)2 and Zr(Ac)4; The precursor of Mn is at least one of MnCl2, Mn(Ac)2 and Mn(NO3)2.

[0012] Furthermore, the copper molecular sieve in the second coating has a ZSM-5 configuration.

[0013] Furthermore, by weight fraction, the second coating contains 2-5% Cu, preferably 3-5%, and 1-4% yttrium, preferably 1-2%.

[0014] Furthermore, the yttrium precursor in the second coating is at least one of YCl3, Y(NO3)3, and Y(Ac)3.

[0015] Furthermore, the coating amount of the first coating is 60-100 g / L; the coating amount of the second coating is 60-100 g / L, preferably 100-160 g / L.

[0016] Secondly, embodiments of the present invention provide a method for preparing the hydrothermal resistant HC-SCR catalyst described in the first aspect, comprising the following steps: (1) Add the precursors of Ce, Zr and Mn to sufficient deionized water and stir to mix. Add 2-5 times the total mass of Ce / Mn elements in citric acid and stir for 2-4 hours. Add ammonia water to adjust the pH value to 9-11. Filter the solution and wash the precipitate with deionized water until the pH value remains unchanged. After completely drying, calcine at 300-400℃ for 1-2 hours to obtain the first coating material CeZrMnOx. (2) Add the first coating material CeZrMnOx to sufficient deionized water, add 2-10% (preferably 5%-10%) of binder to the total amount of cured material, stir evenly, and ball mill to obtain the first coating slurry; (3) The first coating slurry is coated onto the carrier, completely dried, and calcined at 400-600℃ for 1-3 hours, preferably at 500℃ for 2 hours, to form a carrier with the first coating. (4) Add copper molecular sieve to sufficient deionized water and stir to mix. Add yttrium precursor, heat to 80-100℃ and stir continuously for 4-10 hours. Add 2%-10% (preferably 5%-10%) of binder to the total amount of solidified material and stir evenly. Ball mill to obtain the second coating slurry. (5) The second coating slurry is coated onto the carrier with the first coating, completely dried, and calcined at 400-600℃ for 1-3 hours, preferably at 500℃ for 2 hours, to obtain the finished catalyst.

[0017] Compared with the prior art, the hydrothermal resistant HC-SCR catalyst provided by the present invention has the following advantages: 1. The HC-SCR catalyst of the present invention adopts a CeZrMnOx+Y@Cu-ZSM-5 double-layer coating design, which improves the HC-SCR reaction activity and hydrothermal resistance of the catalyst, resulting in high low-temperature NOx conversion efficiency, wide temperature window, and excellent hydrothermal resistance.

[0018] 2. The preparation method of the HC-SCR catalyst of the present invention is simple, easy to control, and easy to produce on a large scale and stably.

[0019] 3. The HC-SCR catalyst of the present invention does not require urea as a reducing agent. It can use reducing components such as hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas of gasoline, diesel or synthetic HC fuel engines to replace NH3 as a reducing agent. It can be applied to the exhaust gas aftertreatment system of diesel engine / lean-burn gasoline engine and placed in front of the existing engine oxidation catalyst, which simplifies the system structure, reduces volume, lowers cost and improves reliability. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the HC-SCR catalyst in the embodiments of the present invention.

[0021] Figure 2 These are the NOx conversion curves of the fresh HC-SCR catalysts in Examples 1-2 and Comparative Example 1.

[0022] Figure 3 These are the NOx conversion curves of the aged HC-SCR catalysts in Examples 1-2 and Comparative Example 1.

[0023] Explanation of reference numerals in the attached drawings: 1-carrier; 2-first coating; 3-second coating. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] Example 1 like Figure 1 As shown, a hydrothermal resistant HC-SCR catalyst includes a support 1 and a first coating 2 and a second coating 3. The first coating 2 is coated on the support 1, and the second coating 3 is coated on the first coating 2.

[0026] The first coating is a cerium-zirconium-manganese composite oxide, denoted as CeZrMnOx; the second coating is a yttrium-modified copper molecular sieve with a ZSM-5 configuration, denoted as Y@Cu-ZSM-5.

[0027] The carrier is made of straight-through cordierite material, with dimensions of D143.8mm*L101.6mm, mesh size of 400cpsi, and wall thickness of 4mil.

[0028] The coating amount of the first coating CeZrMnOx is 100g / L, and the molar ratio of each element is Ce:Zr:Mn=2:1:10. The precursor of Ce is Ce(Ac)3, the precursor of Zr is Zr(Ac)4, and the precursor of Mn is Mn(Ac)2.

[0029] The coating amount of the second coating Y@Cu-ZSM-5 is 100g / L. By weight fraction, the Cu content is 4%, the Y content is 1%, and the precursor of Y is Y(Ac)3.

[0030] The preparation method of the above-mentioned hydrothermal resistant HC-SCR catalyst includes the following steps: (1) Weigh Ce(Ac)3, Zr(Ac)4, and Mn(Ac)2 according to the calculated amount and add them to sufficient deionized water and stir to mix. Add citric acid with a total mass of Ce and Mn of 2 times and stir for 4 hours. Add ammonia water to adjust the pH value to 9. Filter the solution and wash the resulting precipitate with deionized water until the pH value remains unchanged. After completely drying, calcine at 400℃ for 2 hours to obtain the first coating material CeZrMnOx. (2) Add the first coating material CeZrMnOx to sufficient deionized water, add 5% of the binder silica sol of the total mass of the cured material, stir evenly, and ball mill to obtain the first coating slurry; (3) The first coating slurry is coated onto the carrier, dried completely, and calcined at 500°C for 2 hours to form a carrier with the first coating. (4) Weigh out Cu-ZSM-5 molecular sieve according to the calculated amount and add it to sufficient deionized water and stir to mix. Add Y(Ac)3, heat to 80℃ and stir continuously for 4 hours. Add 5% of the binder silica sol of the total mass of the solidified material and stir evenly. Ball mill to obtain the second coating slurry. (5) The second coating slurry is coated onto the carrier with the first coating, completely dried, and calcined at 500°C for 2 hours to obtain the finished catalyst.

[0031] Example 2 like Figure 1 As shown, a hydrothermal resistant HC-SCR catalyst includes a support 1 and a first coating 2 and a second coating 3. The first coating 2 is coated on the support 1, and the second coating 3 is coated on the first coating 2.

[0032] The first coating is a cerium-zirconium-manganese composite oxide, denoted as CeZrMnOx; the second coating is a yttrium-modified copper molecular sieve with a ZSM-5 configuration, denoted as Y@Cu-ZSM-5.

[0033] The carrier is made of straight-through cordierite material, with dimensions of D143.8mm*L101.6mm, mesh size of 400cpsi, and wall thickness of 4mil.

[0034] The coating amount of the first coating CeZrMnOx is 80g / L, and the molar ratio of each element is Ce:Zr:Mn=5:1:4. The precursor of Ce is Ce(NO3)4, the precursor of Zr is ZrO(NO3)2, and the precursor of Mn is Mn((NO3)2.

[0035] The coating amount of the second coating Y@Cu-ZSM-5 is 160g / L. By weight fraction, the content of Cu is 2%, the content of Y is 2%, and the precursor of Y is Y((NO3)3.

[0036] The preparation method of the above-mentioned hydrothermal resistant HC-SCR catalyst includes the following steps: (1) Weigh Ce(NO3)3, ZrO(NO3)2 and Mn(NO3)2 according to the calculated amount and add them to sufficient deionized water and stir to mix. Add citric acid with a mass of 5 times the total mass of Ce and Mn, stir for 4 hours, add ammonia water to adjust the pH value to 9, filter the solution, wash the obtained precipitate with deionized water and the pH value remains unchanged, dry it completely, and calcine it at 400℃ for 2 hours to obtain the first coating material CeZrMnOx; (2) Add the first coating material CeZrMnOx to sufficient deionized water, add 5% of the binder silica sol of the total mass of the cured material, stir evenly, and ball mill to obtain the first coating slurry; (3) The first coating slurry is coated onto the carrier, dried completely, and calcined at 500°C for 2 hours to form a carrier with the first coating. (4) Weigh out Cu-ZSM-5 molecular sieve according to the calculated amount and add it to sufficient deionized water and stir to mix. Add Y(NO3)3, heat to 80℃ and stir continuously for 4 hours. Add 5% of the binder silica sol of the total mass of the solidified material and stir evenly. Ball mill to obtain the second coating slurry. (5) The second coating slurry is coated onto the carrier with the first coating, completely dried, and calcined at 500°C for 2 hours to obtain the finished catalyst.

[0037] Comparative Example 1 An HC-SCR catalyst includes a support and a coating, wherein the support is a straight-through cordierite material with dimensions of D143.8mm*L101.6mm, a mesh size of 400cpsi, and a wall thickness of 4mil.

[0038] The coating is Y@Cu-ZSM-5, with a coating amount of 200 g / L. By weight fraction, the coating contains 4% Cu and 1% Y, and the precursor of Y is Y(Ac)3.

[0039] The preparation method of the above-mentioned HC-SCR catalyst includes the following steps: (1) Weigh out Cu-ZSM-5 molecular sieve according to the calculated amount and add it to sufficient deionized water and stir to mix. Add Y(Ac)3, heat to 80℃ and stir continuously for 4 hours. Add 5% of the binder silica sol of the total mass of the cured material and stir evenly. Ball mill to obtain coating slurry. (2) The coating slurry is coated onto the carrier, dried completely, and calcined at 500°C for 2 hours to obtain the finished catalyst.

[0040] Comparative Example 2 An HC-SCR catalyst includes a support and a coating, wherein the support is a straight-through cordierite material with dimensions of D143.8mm*L101.6mm, a mesh size of 400cpsi, and a wall thickness of 4mil.

[0041] The coating is a single layer with a coating amount of 200g / L.

[0042] The coating material is a mixture of CeZrMnOx and Y@Cu-ZSM-5, with each accounting for 50% of the total mass of the coating. The molar ratio of each element in CeZrMnOx is Ce:Zr:Mn = 2:1:10. The precursor of Ce is Ce(Ac)3, the precursor of Zr is Zr(Ac)4, and the precursor of Mn is Mn(Ac)2. By weight fraction, Y@Cu-ZSM-5 contains 4% Cu and 1% Y, with Y(Ac)3 as its precursor.

[0043] The preparation method of the above-mentioned HC-SCR catalyst includes the following steps: Weigh out Ce(Ac)3, Zr(Ac)4, and Mn(Ac)2 according to the calculated amounts, add them to sufficient deionized water and stir to mix. Add citric acid in an amount twice the total mass of Ce and Mn, stir for 4 hours, add ammonia water to adjust the pH value to 9, filter the solution, wash the resulting precipitate with deionized water until the pH value remains unchanged, dry it completely, and calcine it at 400℃ for 2 hours to obtain CeZrMnOx. Weigh out Cu-ZSM-5 molecular sieve according to the calculated amount and add it to sufficient deionized water and stir to mix. Add Y(Ac)3, heat to 80℃ and stir continuously for 4 hours. Add CeZrMnOx to it, add 5% of the binder silica sol according to the total amount of the cured material and stir evenly. Ball mill to obtain the coating slurry. The coating slurry was coated onto the carrier, dried thoroughly, and calcined at 500℃ for 2 hours to obtain the finished catalyst.

[0044] Fresh / aged NO content of the HC-SCR catalysts prepared in Examples 1-2 and Comparative Examples 1-2 of this invention x Conversion efficiencies are respectively as follows Figures 2-3 As shown. The test atmosphere composition was 500 ppm NO, 1350 ppm C3H6, 500 ppm CO, 10 vol.% O2, 3 vol.% H2O, with N2 as the balance gas, and a space velocity of 50 km / h. -1 The test temperature range is 150-600℃, and the heating rate is 10℃ / min. The aging conditions are 650℃*100h and 10%H2O.

[0045] from Figure 2 , 3 As can be seen, the HC-SCR catalysts of Examples 1-2 exhibit higher NOx conversion efficiency and a wider temperature window, with the mid-temperature range (250-400℃) significantly exceeding that of Comparative Examples 1-2. They also demonstrate excellent resistance to hydrothermal aging; the performance of the aged catalysts of Examples 1-2 is significantly better than that of the aged catalysts of Comparative Examples 1-2, showcasing the performance advantages of the dual-layer coating design of this invention. Comparative Example 1 uses a single-layer coating with yttrium-modified copper molecular sieve Y@Cu-ZSM-5 as the coating material. Its performance in the fresh low-temperature range is acceptable, but the conversion rate in the mid-to-high temperature range is low. Comparative Example 2 uses a single-layer coating design with a mixture of CeZrMnOx and Y@Cu-ZSM-5 as the coating material. Its performance in the high-temperature range is improved compared to Comparative Example 1, but the low-temperature conversion rate is low. Furthermore, the catalysts of Comparative Examples 1-2 all suffer from poor resistance to hydrothermal aging and significant deterioration in performance in the aged state compared to the fresh state.

[0046] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A hydrothermal resistant HC-SCR catalyst, characterized in that, It includes a carrier, a first coating, and a second coating. The first coating is applied to the carrier, and the second coating is applied to the first coating. The first coating is a cerium-zirconium-manganese composite oxide, denoted as CeZrMnOx. The second coating is a yttrium-modified copper molecular sieve.

2. The hydrothermal resistant HC-SCR catalyst according to claim 1, characterized in that, The carrier is one of the following: a through-type honeycomb ceramic carrier, a honeycomb metal carrier, and a wall-flow carrier.

3. The hydrothermal resistant HC-SCR catalyst according to claim 1, characterized in that, In the first coating, the molar ratio of each element is Ce:Zr:Mn=(2-5):1:(3-10).

4. The hydrothermal resistant HC-SCR catalyst according to claim 1, characterized in that, In the first coating, the precursor of Ce is at least one of CeCl4, Ce(NO3)4 and Ce(Ac)3; The precursor of Zr is at least one of Zr(OH)4, ZrO(NO3)2 and Zr(Ac)4; The precursor of Mn is at least one of MnCl2, Mn(Ac)2 and Mn(NO3)2.

5. The hydrothermal resistant HC-SCR catalyst according to claim 1, characterized in that, The copper molecular sieve in the second coating has a ZSM-5 configuration.

6. The hydrothermal resistant HC-SCR catalyst according to claim 1, characterized in that, By weight fraction, the second coating contains 1%-4% yttrium and 2%-5% Cu.

7. The hydrothermal resistant HC-SCR catalyst according to claim 1, characterized in that, The precursor of yttrium in the second coating is at least one of YCl3, Y(NO3)3 and Y(Ac)3.

8. The hydrothermal resistant HC-SCR catalyst according to claim 1, characterized in that, The first coating has a coating amount of 60-100 g / L; the second coating has a coating amount of 60-100 g / L.

9. The method for preparing the hydrothermal resistant HC-SCR catalyst according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Add the precursors of Ce, Zr and Mn to sufficient deionized water and stir to mix. Add citric acid with a total mass of Ce and Mn of 2-5 times and stir for 2-4 hours. Add ammonia to adjust the pH value to 9-11. Filter the solution and wash the precipitate with deionized water until the pH value remains unchanged. After completely drying, calcine at 300-400℃ for 1-2 hours to obtain the first coating material CeZrMnOx. (2) Add the first coating material CeZrMnOx to sufficient deionized water, add 2-10% of the binder of the total amount of cured material, stir evenly, and ball mill to obtain the first coating slurry; (3) The first coating slurry is coated onto the carrier, dried completely, and calcined at 400-600℃ for 1-3 hours to form a carrier with the first coating. (4) Add copper molecular sieve to sufficient deionized water and stir to mix. Add yttrium precursor, heat to 80-100℃ and stir continuously for 4-10h. Add binder accounting for 2-10% of the total amount of solidified material and stir evenly. Ball mill to obtain the second coating slurry. (5) The second coating slurry is coated onto the carrier with the first coating, completely dried, and calcined at 400-600℃ for 1-3 hours to obtain the finished catalyst.

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