High-efficiency HC-SCR catalyst and preparation method thereof

Abstract

The invention belongs to the technical field of engine tail gas aftertreatment, and particularly relates to an efficient HC-SCR catalyst and a preparation method thereof. The HC-SCR catalyst comprises a carrier, a first coating and a second coating, the first coating is a Cu-based molecular sieve and is coated on the carrier, and the second coating is coated on the first coating; the second coating contains Ag and Al2O3, and the mass content of Ag is 2%-10%; the second coating further contains at least one of Co and Ni, and the total mass content of Co and Ni is 2%-6%. By adopting the double-layer coating design, the HC-SCR reaction activity of the catalyst is improved, the low-temperature NOx conversion efficiency is high, the temperature window is relatively wide, and the generation amount of N2O is relatively low. The catalyst can replace an NH3-SCR catalyst to be applied to a diesel engine / lean burn gasoline engine tail gas aftertreatment system, the system structure can be simplified, the size can be reduced, the cost can be reduced, and the reliability can be improved.

Description

Technical Field

[0001] This invention belongs to the field of engine exhaust aftertreatment technology, specifically relating to a high-efficiency 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 (Selective Catalytic Reduction) 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 and the generation of the byproduct N2O, 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-based molecular sieves or Ag / Al2O3 coating technology. For example, invention patent CN103159242A discloses a method for catalytic purification of NOx on an Ag / Al2O3 catalyst by adding hydrocarbons at temperatures of 150-600℃. Invention patent CN115814844A discloses a method for preparing an HC-SCR catalyst using Cu-based molecular sieves with added cerium-zirconium composite oxides, exhibiting good resistance to hydrothermal aging.

[0006] Existing publicly reported HC-SCR catalysts still have performance shortcomings such as low NOx conversion rate, narrow temperature window, and high N2O generation. In particular, the NOx conversion rate is low in the low-temperature range (below 300℃). Therefore, further research is needed to develop an HC-SCR catalyst with higher low-temperature NOx conversion rate, wider temperature window, and lower N2O generation. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a highly efficient HC-SCR catalyst and its preparation method. The HC-SCR catalyst of this invention employs a Cu-based molecular sieve + Co / Ni-Ag-Al2O3 bilayer coating design, which improves the HC-SCR reactivity of the catalyst, resulting in high NOx conversion efficiency at low temperatures, a wide temperature window, and low N2O formation.

[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 high-efficiency HC-SCR catalyst, comprising a support and a first coating and a second coating, wherein the first coating is a Cu-based molecular sieve coating coated on the support, and the second coating is coated on the first coating; The second coating contains Ag and Al2O3, with the Ag content being 2%-10% by mass. The second coating also contains at least one of Co and Ni, with a total mass content of 2%-6% for Co and Ni. The second coating is denoted as Co / Ni-Ag-Al2O3.

[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, the Cu-based molecular sieve has a CHA configuration, preferably an SSZ-13 type molecular sieve.

[0011] Furthermore, in the Cu-based molecular sieve, the mass content of Cu, calculated as oxides, is 2%-5%, preferably 3%-5%.

[0012] Furthermore, the silicon-to-aluminum ratio in the Cu-based molecular sieve is 12-22, preferably 12-16.

[0013] Furthermore, in the second coating, the mass content of Ag is 2%-6%.

[0014] Furthermore, in the second coating, the total mass content of Co and Ni is 2%-4%.

[0015] Furthermore, the precursor of Ag in the second coating is at least one of Ag2O, Ag2SO4, AgNO3 and C2H3AgO2; The precursor of Co is at least one of CoCl2, CoSO4 and Co(NO3)2; The precursor of Ni is at least one of NiCl2, NiSO4 and Ni(NO3)2.

[0016] Furthermore, the coating amount of the first coating is 100-140 g / L; the coating amount of the second coating is 60-100 g / L, preferably 80-100 g / L.

[0017] Secondly, embodiments of the present invention provide a method for preparing the high-efficiency HC-SCR catalyst described in the first aspect, comprising the following steps: Step S1: Prepare the first coating slurry: Weigh the Cu-based molecular sieve according to the measured value, add sufficient deionized water and 5% of the mass of Cu-based molecular sieve binder, stir evenly, and ball mill to obtain the first coating slurry; Step S2: Preparation of the second coating slurry: Weigh Ag and Co / Ni precursors according to the measured values, add sufficient deionized water, add citric acid at 5-10 times the total mass of Ag and Co / Ni precursors, stir to dissolve and form Ag / Co / Ni precursor solution, add Al2O3 and mix evenly, heat to 80-100℃ and stir continuously for 4-8 hours, ball mill to obtain the second coating slurry; Step S3: Apply the first coating slurry onto the carrier, dry it thoroughly, and calcine it at 400-600℃ for 1-3 hours to form a carrier with the first coating. Step S4: Apply the second coating slurry onto the carrier with the first coating, dry it thoroughly, and calcine it at 400-600℃ for 1-3 hours to obtain the finished catalyst.

[0018] Compared with existing technologies, the high-efficiency HC-SCR catalyst provided by this invention has the following advantages: 1. The HC-SCR catalyst of the present invention adopts a Cu-based molecular sieve + Co / Ni-Ag-Al2O3 double-layer coating design, which improves the HC-SCR reaction activity of the catalyst, resulting in high NOx conversion efficiency at low temperature, a wide temperature window, and low N2O generation.

[0019] 2. The preparation method of the HC-SCR catalyst of the present invention is simple, the process is easy to control, and it is easy to produce on a large scale and stably.

[0020] 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

[0021] Figure 1 This is a schematic diagram of the structure of the HC-SCR catalyst provided by the present invention.

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

[0023] Figure 3 These are the N2O generation curves of the HC-SCR catalysts in Examples 1-2 and Comparative Examples 1-2.

[0024] Explanation of reference numerals in the attached drawings: 1-carrier; 2-first coating; 3-second coating. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] Example 1 like Figure 1 As shown, a high-efficiency HC-SCR catalyst includes a support 1, a first coating 2, and a second coating 3. The first coating 2 is a Cu-based molecular sieve coated on the support 1; the second coating 3 is Co-Ag-Al2O3 coated on the first coating 2. The support 1 is a straight-through cordierite material with dimensions of D143.8mm*L101.6mm, a mesh size of 400cpsi, and a wall thickness of 4mil.

[0027] The Cu-based molecular sieve in the first coating is SSZ-13 type molecular sieve, with a Cu mass content of 5%, a silicon-to-aluminum ratio of 12, and a coating amount of 100g / L.

[0028] The second coating comprises Co, Ag, and Al2O3, with Ag having a mass content of 2% and AgNO3 as the precursor; Co having a mass content of 4% and Co(NO3)2 as the precursor; and the coating amount of the second coating being 100 g / L.

[0029] The preparation method of the above-mentioned high-efficiency HC-SCR catalyst includes the following steps: Step S1: Preparation of the first coating slurry: Weigh 165g of Cu-based molecular sieve with a Cu mass content of 5% and a silicon-to-aluminum ratio of 12, add 300g of deionized water and 8g of binder silica sol, stir evenly, and ball mill to obtain the first coating slurry. Step S2: Preparation of the second coating slurry: Weigh 5.2g AgNO3 and 20.5g Co(NO3)2, add 300g deionized water and 128.5g citric acid, stir to dissolve and form Ag-Co precursor solution, add 155.1g Al2O3 to the precursor solution and mix evenly, heat to 80℃ and stir continuously for 8h, ball mill to obtain the second coating slurry; Step S3: Apply the first coating slurry onto the carrier, dry it thoroughly, and calcine it at 500°C for 2 hours to form a carrier with the first coating. Step S4: Apply the second coating slurry onto the carrier with the first coating, dry it thoroughly, and calcine it at 500°C for 2 hours to obtain the finished catalyst.

[0030] Example 2 A high-efficiency HC-SCR catalyst includes a support 1, a first coating 2, and a second coating 3. The first coating 2 is a Cu-based molecular sieve coated on the support 1. The second coating 3 is Ni-Ag-Al2O3 coated on the first coating 2. The support 1 is made of a straight-through cordierite material with dimensions of D143.8mm*L101.6mm, a mesh size of 400cpsi, and a wall thickness of 4mil.

[0031] The first coating uses a Cu-based molecular sieve of type SSZ-13, with a Cu content of 3% by mass, a silicon-to-aluminum ratio of 16, and a coating amount of 140 g / L.

[0032] The second coating comprises Ni, Ag, and Al2O3, with Ag having a mass content of 6% and C2H3AgO2 as the precursor; Ni having a mass content of 2% and NiCl2 as the precursor; and the coating amount of the second coating being 80 g / L.

[0033] The preparation method of the above-mentioned high-efficiency HC-SCR catalyst includes the following steps: Step S1: Preparation of the first coating slurry: Weigh 231g of Cu-based molecular sieve with a Cu mass content of 3% and a silicon-to-aluminum ratio of 16, add 500g of deionized water and 12g of binder silica sol, stir evenly, and ball mill to obtain the first coating slurry. Step S2, Second Coating Slurry: Weigh 12.2g C2H3AgO2 and 5.8g NiCl2, add 300g deionized water and 180g citric acid, stir to dissolve and form Ag-Ni precursor solution, add 121.4g Al2O3 to the precursor solution and mix evenly, heat to 80℃ and stir continuously for 8h, ball mill to obtain the second coating slurry; Step S3: Apply the first coating slurry onto the carrier, dry it thoroughly, and calcine it at 500°C for 2 hours to form a carrier with the first coating. Step S4: Apply the second coating slurry onto the carrier with the first coating, dry it thoroughly, and calcine it at 500°C for 2 hours to obtain the finished catalyst.

[0034] Comparative Example 1 An HC-SCR catalyst includes a support 1 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.

[0035] The coating is made of SSZ-13 Cu-based molecular sieve, with a Cu content of 5% by mass, a silicon-to-aluminum ratio of 12, and a coating amount of 200 g / L.

[0036] The preparation method of the above-mentioned HC-SCR catalyst includes the following steps: Step S1: Preparation of coating slurry: Weigh 462g of Cu-based molecular sieve with a Cu mass content of 5% and a silicon-to-aluminum ratio of 12, add 1000g of deionized water and 23g of binder silica sol, stir evenly, and ball mill to obtain coating slurry; Step S2: Apply the coating slurry onto the carrier, dry it thoroughly, and calcine it at 500℃ for 2 hours to obtain the finished catalyst.

[0037] Comparative Example 2 An HC-SCR catalyst includes a support 1 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 Co-Ag-Al2O3, in which the mass content of Ag is 2% and the precursor is AgNO3. The mass content of Co is 4% and the precursor is Co(NO3)2. The coating amount is 200g / L.

[0039] The preparation method of the above-mentioned HC-SCR catalyst includes the following steps: Step S1: Preparation of coating slurry: Weigh 10.4g of AgNO3 and 40.9g of Co(NO3)2, add 600g of deionized water and 52g of citric acid, stir to dissolve and form Ag / Co precursor solution, add 310.2g of Al2O3 to Ag / Co precursor solution and mix evenly, heat to 80℃ and stir continuously for 8h, ball mill to obtain coating slurry; Step S2: Apply the coating slurry onto the carrier, dry it thoroughly, and calcine it at 500℃ for 2 hours to obtain the finished catalyst.

[0040] NO in Examples 1-2 and Comparative Examples 1-2 of the HC-SCR catalyst of the present invention x Conversion efficiency, such as Figure 2 As shown, the amount of N2O generated is as follows Figure 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.

[0041] from Figure 2-3 It can be seen that the HC-SCR catalysts of Examples 1-2 have higher NOx conversion efficiency and a wider temperature window, with significantly higher efficiency in the low-temperature range (below 300℃) compared to Comparative Examples 1-2. They also exhibit excellent N2 selectivity, with a significant reduction in N2O generation compared to Comparative Examples 1-2. The Cu molecular sieve coating used in Comparative Example 1 is the mainstream technology for NH3-SCR in the current China VI emission standard stage, but its conversion efficiency in HC-SCR is relatively low, and the N2O generation is also relatively high. The Co-Ag-Al2O3 coating used in Comparative Example 2 is an optimization of the widely studied Ag-Al2O3 coating technology for HC-SCR catalysts, but its performance is weaker than that of Examples 1 and 2.

[0042] 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 high-efficiency HC-SCR catalyst, characterized in that, It includes a carrier and a first coating and a second coating. The first coating is a Cu-based molecular sieve coating applied to the carrier, and the second coating is applied to the first coating. The second coating contains Ag and Al2O3, with the Ag content being 2%-10% by mass. The second coating also contains at least one of Co and Ni, with a total mass content of 2%-6% for Co and Ni.

2. The high-efficiency 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 high-efficiency HC-SCR catalyst according to claim 1, characterized in that, The Cu-based molecular sieve has a CHA configuration.

4. The high-efficiency HC-SCR catalyst according to claim 1, characterized in that, In the Cu-based molecular sieve, the mass content of Cu, calculated as oxides, is 2%-5%.

5. The high-efficiency HC-SCR catalyst according to claim 1, characterized in that, The silicon-to-aluminum ratio in the Cu-based molecular sieve is 12-22.

6. The high-efficiency HC-SCR catalyst according to claim 1, characterized in that, In the second coating, the mass content of Ag is 2%-6%.

7. The high-efficiency HC-SCR catalyst according to claim 1, characterized in that, In the second coating, the total mass content of Co and Ni is 2%-4%.

8. The high-efficiency HC-SCR catalyst according to claim 1, characterized in that, The precursor of Ag in the second coating is at least one of Ag2O, Ag2SO4, AgNO3 and C2H3AgO2; The precursor of Co is at least one of CoCl2, CoSO4 and Co(NO3)2; The precursor of Ni is at least one of NiCl2, NiSO4 and Ni(NO3)2.

9. The high-efficiency HC-SCR catalyst according to claim 1, characterized in that, The coating amount of the first coating is 100-140 g / L; the coating amount of the second coating is 60-100 g / L.

10. The method for preparing the high-efficiency HC-SCR catalyst according to any one of claims 1-9, characterized in that, Includes the following steps: Step S1: Preparation of the first coating slurry: Weigh the Cu-based molecular sieve according to the measured value, add deionized water and binder, stir evenly, and ball mill to obtain the first coating slurry; Step S2: Preparation of the second coating slurry: Weigh Ag and Co / Ni precursors according to the measured values, add deionized water, add citric acid at 5-10 times the total mass of Ag and Co / Ni precursors, stir to dissolve and form Ag-Co / Ni precursor solution, add Al2O3 and mix evenly, heat to 80-100℃ and stir continuously for 4-8 hours, ball mill to obtain the second coating slurry; Step S3: Apply the first coating slurry onto the carrier, dry it thoroughly, and calcine it at 400-600℃ for 1-3 hours to form a carrier with the first coating. Step S4: Apply the second coating slurry onto the carrier with the first coating, dry it thoroughly, and calcine it at 400-600℃ for 1-3 hours to obtain the finished catalyst.

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