Catalysed particulate filter for diesel exhaust aftertreatment and method of manufacture

Abstract

This invention provides a catalytic particulate filter for diesel engine exhaust aftertreatment with higher regeneration efficiency and its manufacturing method. The catalytic particulate filter of this invention includes a DPF carrier and a catalyst coating coated on the DPF carrier. The catalyst coating has a cerium-zirconium composite oxide as the inner coating and a cerium-manganese-nickel composite oxide as the outer coating. The manufacturing method includes preparing the cerium-zirconium composite oxide, coating the inner coating and coating the outer coating to obtain the catalytic particulate filter. It does not use expensive precious metal catalysts at all, reducing the consumption of precious metals and has broad application value.

Description

Technical Field

[0001] This invention relates to a particulate catalytic filter for diesel engine exhaust aftertreatment that uses non-precious metals as catalysts and its manufacturing method. Background Technology

[0002] Existing catalytic converter particulate filters (CDPFs) for diesel engine exhaust aftertreatment use precious metal catalysts. These catalysts are first dispersed on a carrier such as alumina / cerium oxide, and then coated onto the DPF filter. To improve the catalytic combustion efficiency of particulate matter, a larger amount of precious metal coating is needed; a higher coating amount results in better catalytic performance. However, precious metals are expensive, making them unaffordable for many users. Currently, the precious metal coating amount in DPFs is typically only 3 g / ft³. Therefore, the elimination of particulate matter in the DPF relies solely on the oxidation capacity of DOC at its upstream end.

[0003] CN114251158A discloses a diesel engine exhaust particulate catalytic filter and its manufacturing method that do not require a precious metal catalyst. The catalytic particulate filter includes a DPF support and a catalyst coating coated on the DPF support. The catalyst coating has a cerium-zirconium composite oxide as the inner coating and a lanthanum-manganese-copper composite oxide as the outer coating. The manufacturing method includes preparing the cerium-zirconium composite oxide, applying the inner coating, preparing a lanthanum-manganese-copper solution for applying the outer coating, and sintering by heating. This particulate filter can improve the combustion rate of particulate matter. Summary of the Invention

[0004] The purpose of this invention is to improve upon the particulate catalytic filter disclosed in CN114251158A, and to provide a catalytic particulate filter for diesel engine exhaust aftertreatment with higher regeneration efficiency and its manufacturing method.

[0005] The catalytic particulate filter of the present invention includes a DPF carrier and a catalyst coating coated on the DPF carrier. The catalyst coating has a cerium-zirconium composite oxide as the inner coating and a cerium-manganese-nickel composite oxide as the outer coating. The molar ratio of cerium to zirconium in the cerium-zirconium composite oxide is 1:0.1-0.4, and the molar ratio of cerium to manganese to nickel in the cerium-manganese-nickel composite oxide is 1:1.2-10:0-3. The coating amount of the inner coating is 15-40 g / L based on the volume of the DPF, and the weight ratio of the outer coating to the inner coating is 0.5-1.2:1.

[0006] Preferably, in the cerium-manganese-nickel composite oxide, the molar ratio of cerium to nickel is 1:2-3.

[0007] The molar ratio of cerium and zirconium in the cerium-zirconium composite oxide is 1:0.2-0.3.

[0008] In the cerium-manganese-nickel composite oxide, the molar ratio of cerium to manganese is 1:3-6.

[0009] The method for manufacturing the catalytic particulate filter of the present invention includes the following steps: A. Preparation of cerium-zirconium composite oxide: Cerium nitrate and zirconium nitrate are dissolved in water according to the molar ratio of cerium and zirconium elements. Citric acid is added at 1-1.5 times the total molar amount of cerium and zirconium. The mixture is stirred and heated at 80-100℃ until dry. Then, it is heated to 550-650℃ at a rate of 50-100℃ / hour and kept at that temperature for 1-3 hours. After cooling, the mixture is ball-milled for 8-24 hours to obtain cerium-zirconium composite oxide. B. Preparation of alumina sol: Mix boehmite, concentrated nitric acid and water in a mass ratio of 1:0.75-1:10, heat and stir in an 80°C water bath for 3-8 hours to obtain alumina sol; C. Inner coating: Prepare a coating solution with a weight percentage of 5-20% cerium-zirconium composite oxide, 10-30% alumina sol, and the balance being water. Coat the coating solution onto the DPF, dry it, heat it to 550-650℃ at a rate of 50-100℃ / hour, hold it at that temperature for 1-3 hours, and then cool it. D. Repeat step C until the amount of the inner coating layer is reached; E. Coating the outer layer: Dissolve cerium nitrate, manganese nitrate and nickel nitrate in water according to the molar ratio of cerium, manganese and nickel elements, and add citric acid at 1 to 1.1 times the total molar amount of cerium, manganese and nickel to prepare a solution with a total concentration of cerium, manganese and nickel ions of 0.5 to 3 mol / L. Immerse the DPF coated with the inner layer in the solution, take it out and dry it, then heat it to 550 to 650°C at a rate of 50 to 100°C / hour, keep it at that temperature for 1 to 3 hours, and then cool it. F. Repeat step E until the amount of the outer coating is reached to obtain a catalytic particulate filter.

[0010] Preferably, in step C, the proportion of the coating liquid is 8-10% cerium-zirconium composite oxide, 10-20% alumina sol, and the remainder is water.

[0011] In step E, the total concentration of cerium, manganese, and nickel ions is 1.5–2.5 mol / L. This invention does not use expensive precious metal catalysts, thus reducing the consumption of precious metals. Its performance is superior to the catalytic particulate filter disclosed in CN114251158A, and it has broad application value. Detailed Implementation

[0012] The following examples use a cylindrical wall-flow cordierite carrier with a diameter of 143.8 mm, a length of 152.4 mm, a mesh size of 200, and a volume of 2.47 L. Example

[0013] Preparation of cerium-zirconium composite oxide: Cerium nitrate, zirconium nitrate, and citric acid were dissolved in water in a molar ratio of 1:0.25:1.25 to prepare a solution with a total metal ion concentration of 1.5 mol / L. The solution was heated and concentrated to dryness in a water bath at 80-100℃ with stirring. The solution was then heated to 600℃ at a rate of 100℃ / hour and held for 1 hour. The resulting solid cerium-zirconium composite oxide was ball-milled for 16 hours.

[0014] Preparation of alumina sol: Boehmite, concentrated nitric acid and water were mixed in a mass ratio of 1:0.75:10 and heated and stirred in a water bath at 80°C for 6 hours to obtain alumina sol.

[0015] Inner coating: The inner coating solution is prepared by weight percentage of 9% cerium-zirconium composite oxide, 15% alumina sol, and 76% water. Under stirring, the coating solution is drawn into the honeycomb pores of the DPF carrier under negative pressure. The negative pressure is then removed to allow the coating solution to flow out naturally to complete the coating. After the carrier dries, it is heated to 600℃ at a rate of 100℃ / hour and held at that temperature for 1 hour. It is then cooled with the furnace to complete the first layer coating. The coating amount of the inner coating is 28g / L according to the test.

[0016] Outer coating: Cerium nitrate, manganese nitrate, and citric acid are dissolved in water at a molar ratio of 1:2:3 to prepare a solution with a total metal ion concentration of 2 mol / L. The DPF with the inner coating is immersed in the solution for 1-2 minutes to complete the coating. After drying, it is heated to 600℃ at a rate of 100℃ / hour and held at that temperature for 1 hour. It is then cooled in the furnace to obtain the finished product. The coating amount of the outer coating is tested to be 28 g / L. Example

[0017] Preparation of cerium-zirconium composite oxide: Cerium nitrate, zirconium nitrate, and citric acid were dissolved in water in a molar ratio of 1:0.30:1.30 to prepare a solution with a total metal ion concentration of 1.5 mol / L. The solution was heated and concentrated to dryness in a water bath at 80-100℃ with stirring. The solution was then heated to 600℃ at a rate of 100℃ / hour and held for 1 hour. The resulting solid cerium-zirconium composite oxide was ball-milled for 16 hours.

[0018] Preparation of alumina sol: Boehmite, concentrated nitric acid and water were mixed in a mass ratio of 1:0.75:10 and heated and stirred in a water bath at 80°C for 6 hours to obtain alumina sol.

[0019] Inner coating application: The inner coating solution was prepared by weight percentage of 9% cerium-zirconium composite oxide, 15% alumina sol, and 76% water. Under stirring, the solution was drawn into the honeycomb pores of the DPF carrier under negative pressure. The negative pressure was then removed, allowing the solution to flow out naturally to complete the coating. After drying, the solution was heated to 600℃ at a rate of 100℃ / hour and held for 1 hour, followed by furnace cooling to complete the inner coating application. The measured coating amount was 31 g / L.

[0020] Outer coating: Dissolve cerium nitrate, manganese nitrate, nickel nitrate, and citric acid in water at a molar ratio of 1:5:3:9 to prepare a solution with a total metal ion concentration of 2 mol / L. Immerse the DPF with the inner coating in the solution for 1-2 minutes to complete the coating. After drying, heat to 600℃ at a rate of 100℃ / hour and hold for 1 hour. Cool in the furnace to obtain the finished product. The coating amount of the outer coating was tested to be 25 g / L. Example

[0021] Preparation of cerium-zirconium composite oxide: Cerium nitrate, zirconium nitrate, and citric acid were dissolved in water in a molar ratio of 1:0.30:1.30 to prepare a solution with a total metal ion concentration of 1.5 mol / L. The solution was heated and concentrated to dryness in a water bath at 80-100℃ with stirring. The solution was then heated to 600℃ at a rate of 100℃ / hour and held for 1 hour. The resulting solid cerium-zirconium composite oxide was ball-milled for 16 hours.

[0022] Preparation of alumina sol: Boehmite, concentrated nitric acid and water were mixed in a mass ratio of 1:0.75:10 and heated and stirred in a water bath at 80°C for 6 hours to obtain alumina sol.

[0023] Inner coating application: The inner coating solution was prepared by weight percentage of 9% cerium-zirconium composite oxide, 15% alumina sol, and 76% water. Under stirring, the solution was drawn into the honeycomb pores of the DPF carrier under negative pressure. The negative pressure was then removed, allowing the solution to flow out naturally to complete the coating. After drying, the solution was heated to 600℃ at a rate of 100℃ / hour and held for 1 hour, followed by furnace cooling to complete the inner coating application. The coating amount was tested to be 22 g / L.

[0024] Outer coating: Dissolve cerium nitrate, manganese nitrate, nickel nitrate, and citric acid in water at a molar ratio of 1:4:2.5:9 to prepare a solution with a total metal ion concentration of 2 mol / L. Immerse the DPF with the inner coating in the solution for 1-2 minutes to complete the coating. After drying, heat to 600℃ at a rate of 100℃ / hour and hold for 1 hour. Cool in the furnace to obtain the finished product. The coating amount of the outer coating was tested to be 24 g / L.

[0025] Performance testing Test method: The DPF packages of Examples 1-3 were connected to the exhaust systems of diesel engines respectively.

[0026] PM treatment efficiency testing: On a dynamometer bench equipped with a 55KW diesel engine, different exhaust temperatures were obtained by adjusting the output power at a fixed speed of 1600r / min. A DPF without any catalyst coating was used to measure the engine's hourly PM emissions at each exhaust temperature. The DPF was initially set to accumulate PM at an engine exhaust temperature of 250℃ to 1.5-2g / L. After running the DPF for one hour at each exhaust temperature, the weight of the DPF was measured. The processing capacity per liter per hour of the DPF was calculated as: (Initial weight + Engine hourly PM emissions at that temperature - DPF weight after running) / DPF volume.

[0027] The DPF's PM removal efficiency at various engine exhaust temperatures is as follows:

[0028] It is evident that the DPF obtained by this invention is significantly superior to the DPF of CN114251158A.

Claims

1. A catalytic particulate filter for diesel engine exhaust aftertreatment, comprising a DPF carrier and a catalyst coating coated on the DPF carrier, characterized in that, The catalyst coating consists of a cerium-zirconium composite oxide as the inner coating and a cerium-manganese-nickel composite oxide as the outer coating. The molar ratio of cerium to zirconium in the cerium-zirconium composite oxide is 1:0.1-0.4, and the molar ratio of cerium to manganese to nickel in the cerium-manganese-nickel composite oxide is 1:1-10:0-3. The coating amount of the inner coating is 15-40 g / L based on the volume of DPF, and the weight ratio of the outer coating to the inner coating is 0.5-1.2:

1.

2. The catalytic particulate filter according to claim 1, characterized in that, In the cerium-manganese-nickel composite oxide, the molar ratio of cerium to nickel is 1:2-3.

3. The catalytic particulate filter according to claim 1 or 2, characterized in that, The molar ratio of cerium and zirconium in the cerium-zirconium composite oxide is 1:0.2-0.

3.

4. The catalytic particulate filter according to claim 1 or 2, characterized in that, In the cerium-manganese-nickel composite oxide, the molar ratio of cerium to manganese is 1:3-6.

5. A method for manufacturing a catalytic particulate filter according to any one of claims 1-4, characterized in that, Includes the following steps: A. Preparation of cerium-zirconium composite oxide: Cerium nitrate and zirconium nitrate are dissolved in water according to the molar ratio of cerium and zirconium elements. Citric acid is added at 1-1.5 times the total molar amount of cerium and zirconium. The mixture is stirred and heated at 80-100℃ until dry. Then, it is heated to 550-650℃ at a rate of 50-100℃ / hour and kept at that temperature for 1-3 hours. After cooling, the mixture is ball-milled for 8-24 hours to obtain cerium-zirconium composite oxide. B. Preparation of alumina sol: Mix boehmite, concentrated nitric acid and water in a mass ratio of 1:0.75-1:10, heat and stir in an 80°C water bath for 3-8 hours to obtain alumina sol; C. Inner coating: Prepare a coating solution with a weight percentage of 5-20% cerium-zirconium composite oxide, 10-30% alumina sol, and the balance being water. Coat the coating solution onto the DPF, dry it, heat it to 550-650℃ at a rate of 50-100℃ / hour, hold it at that temperature for 1-3 hours, and then cool it. D. Repeat step C until the amount of the inner coating layer is reached; E. Coating the outer layer: Dissolve cerium nitrate, manganese nitrate and nickel nitrate in water according to the molar ratio of cerium, manganese and nickel elements, and add citric acid at 1 to 1.1 times the total molar amount of cerium, manganese and nickel to prepare a solution with a total concentration of cerium, manganese and nickel ions of 0.5 to 3 mol / L. Immerse the DPF coated with the inner layer in the solution, take it out and dry it, then heat it to 550 to 650°C at a rate of 50 to 100°C / hour, keep it at that temperature for 1 to 3 hours, and then cool it. F. Repeat step E until the amount of the outer coating is reached to obtain a catalytic particulate filter.

6. The method for manufacturing the catalytic particulate filter according to claim 5, characterized in that, In step C, the coating liquid consists of 8-10% cerium-zirconium composite oxide, 10-20% alumina sol, and the remainder is water.

7. The method for manufacturing a catalytic particulate filter according to claim 5 or 6, characterized in that, In step E, the total concentration of cerium, manganese, and nickel ions is 1.5–2.5 mol / L.

Images