Partitioned DPF catalyst and preparation method thereof

Abstract

The invention belongs to the technical field of diesel engine tail gas aftertreatment, and particularly relates to a partitioned DPF catalyst and a preparation method thereof.The catalyst comprises a carrier, a first coating, a second coating and a third coating; the first coating is coated from the air inlet end, and the length of the first coating accounts for 100% of the length of the carrier; the first coating is coated with the second coating from the air inlet end, and the length of the second coating accounts for 60-90% of the length of the carrier; the third coating is coated on the second coating from the air inlet end, and the length of the third coating accounts for 30-50% of the length of the carrier; the first coating contains a first catalytic material; the second coating contains a second catalytic material; the third coating contains precious metal and a third catalytic material, and the content of the precious metal is 15-30 g / cfu. The DPF catalyst disclosed by the invention does not need to be matched with a diesel oxidation type catalyst, is low in precious metal consumption, good in active regeneration performance, high in aging resistance and high in particulate trapping efficiency, and can reduce the overall volume of a post-treatment device.

Description

Technical Field

[0001] The invention belongs to the technical field of diesel engine exhaust post-treatment, and in particular relates to a partitioned DPF catalyst and a preparation method thereof. Background Art

[0002] The mainstream post-treatment system for diesel vehicles currently in the National VI stage adopts the DOC+CDPF+SCR+ASC technology route. The DOC catalyst plays an oxidizing role, converting CO and HC in the exhaust gas into CO2 and H2O, and converting part of NO into NO2; the CDPF catalyst mainly plays a role in particle capture, and also has a partial oxidation effect to improve active / passive regeneration performance.

[0003] The regeneration of CDPF is divided into active regeneration and passive regeneration: during passive regeneration, NOx in the exhaust gas at 220-400℃ reacts with soot. At this time, the role of DOC is to convert part of NO into NO2 to increase the passive regeneration rate; active regeneration is the reaction of the remaining oxygen in the exhaust gas above 450℃ with soot. At this time, the role of DOC is to catalyze the oxidation of fuel, greatly increase the exhaust gas temperature, and thus remove soot.

[0004] At present, the precious metals used in the National VI stage DOC catalyst are Pt and Pd, and the dosage is generally 25-35g / cft. The large dosage leads to high costs. If the dosage of precious metals is reduced, the oxidation capacity will be reduced, especially during active regeneration under low temperature and high space velocity conditions. The ability to raise the temperature of the exhaust gas is a major technical difficulty.

[0005] Long-term and frequent active regeneration keeps the DOC catalyst in a high-temperature state (above 600°C) for a long time. Precious metals are prone to sintering, which reduces the performance of the catalyst. Therefore, ensuring its heat-resistant aging performance is also a technical difficulty.

[0006] During active regeneration, the soot stored in the DPF undergoes an oxidation reaction and burns violently, and is discharged together with a small amount of unburned HC, causing the PN emission value to increase sharply, with the risk of exceeding the regulatory limit. This is also one of the technical difficulties of the current DPF catalyst coating technology.

[0007] On the other hand, since the vehicle chassis space is very limited, there are very strict requirements on the size and shape of the after-treatment system, especially for light diesel vehicles, off-road engineering machinery, agricultural machinery and other vehicles, the layout of the after-treatment system is more difficult. Summary of the invention

[0008] The purpose of the present invention is to overcome the problems in the prior art of high precious metal usage, high cost, high PN emission value during active regeneration, large volume of post-processing device and limited loading of diesel vehicle DOC and DPF catalysts, and provide a partitioned DPF catalyst and a preparation method thereof.

[0009] In order to achieve the above technical objectives, the present invention provides the following technical solutions:

[0010] In a first aspect, an embodiment of the present invention provides a partitioned DPF catalyst, comprising a carrier and a first coating, a second coating and a third coating sequentially coated on the carrier, wherein the two axial ends of the carrier are an inlet end and an outlet end respectively; the first coating is coated from the inlet end of the carrier, and the length of the first coating accounts for 100% of the length of the carrier; the second coating is coated on the first coating from the inlet end, and the length of the second coating accounts for 60-90% of the length of the carrier; the third coating is coated on the second coating from the inlet end, and the length of the third coating accounts for 30-50% of the length of the carrier;

[0011] The first coating layer contains a first catalytic material; the second coating layer contains a second catalytic material; the third coating layer contains a noble metal and a third catalytic material, and the content of the noble metal is 15-30 g / cft.

[0012] Furthermore, the carrier is a wall-flow structure, and the material is one of cordierite, silicon carbide, aluminum titanate and metal foam.

[0013] Furthermore, the first catalytic material contains at least one of cerium oxide, modified aluminum oxide and silicon aluminum oxide.

[0014] Furthermore, the second catalytic material contains at least one of cerium oxide, cerium-zirconium composite oxide, cerium-zirconium-aluminum oxide and cerium-aluminum oxide, and manganese.

[0015] Furthermore, the manganese, calculated as MnO2, accounts for 5-20% by weight in the second coating.

[0016] Furthermore, the third catalytic material contains at least one of aluminum oxide, modified aluminum oxide, silicon aluminum oxide and cerium aluminum oxide.

[0017] Furthermore, the precious metals of the third coating are platinum Pt and palladium Pd, and the mass ratio of Pt to Pd is 2:1-12:1.

[0018] In a second aspect, an embodiment of the present invention provides a method for preparing the partitioned DPF catalyst according to the first aspect, comprising the following steps:

[0019] Step S1, adding a raw material of the first catalytic material into an appropriate amount of deionized water and stirring evenly, adding 2-4% of a binder and 1-2% of a dispersant by dry weight, and ball milling to obtain a first slurry;

[0020] Add the raw material of the second catalytic material into an appropriate amount of deionized water and stir evenly, wherein the raw material of Mn is a soluble manganese salt, and 2-6% of a binder and 1-3% of a dispersant are added on a dry basis weight basis, and the second slurry is obtained by ball milling;

[0021] Dispersing the precursor solution of the noble metal in the raw material of the third catalytic material, adding an appropriate amount of deionized water, adding 2-8% of a binder and 1-5% of a dispersant by dry weight, and ball milling to obtain a third slurry;

[0022] Step S2, coating the first slurry from the air inlet end of the carrier, and completely drying at 100-200° C., the dry basis coating amount of the first coating is 5-15 g / L;

[0023] Step S3, coating the second slurry on the first coating in step S2 from the air inlet end, and completely drying at 100-200° C., and calcining at 450-600° C. for 1-4 hours, the dry basis coating amount of the second coating is 10-40 g / L;

[0024] Step S4, apply the third slurry from the air inlet end to the second coating in step S3, completely dry at 100-200°C, and calcine at 450-600°C for 1-4h. The dry coating amount of the third coating is 10-40g / L to obtain a partitioned DPF catalyst product.

[0025] Furthermore, in step S1, the soluble manganese salt is at least one of manganese acetate, manganese nitrate and potassium permanganate.

[0026] Furthermore, in step S1, the binder is at least one of silica sol, aluminum sol, titanium sol and zirconium sol; and the dispersant is at least one of PEG, PVP, PVA and carboxymethyl cellulose.

[0027] Compared with the prior art, the partitioned DPF catalyst of the present invention has the following advantages:

[0028] 1. The amount of precious metal used in the DPF catalyst of the present invention is significantly less than that of the existing DOC+DPF catalyst, which greatly reduces the cost and can significantly reduce the overall volume of the post-treatment device, making it easier to install on the vehicle.

[0029] 2. The DPF catalyst of the present invention has good active regeneration performance and good heat aging resistance.

[0030] 3. The DPF catalyst of the present invention still has a very high PN capture efficiency during active regeneration, and the PN emission value is significantly lower than that of the DPF catalyst of the prior art, thereby reducing the risk of excessive PN emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the structure of a partitioned DPF catalyst.

[0032] Explanation of reference numerals: 1 - first coating layer; 2 - second coating layer; 3 - third coating layer; 4 - DPF carrier.

[0033] Figure 2 It is a schematic diagram comparing the packaging structure of the DOC+DPF catalyst combination and the partitioned DPF catalyst. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] Example 1

[0036] A zoned DPF catalyst, such as Figure 1 As shown, it includes a carrier 4 and a first coating 1, a second coating 2, and a third coating 3 coated on the carrier, and the two ends of the carrier along the axial direction are an air inlet end and an air outlet end respectively; the first coating is coated from the air inlet end, and the length of the first coating accounts for 100% of the length of the carrier; the second coating is coated on the first coating from the air inlet end, and the length of the second coating accounts for 90% of the length of the carrier; the third coating is coated on the second coating from the air inlet end, and the length of the third coating accounts for 30% of the length of the carrier.

[0037] The carrier adopts a wall-flow silicon carbide carrier with specifications of φ190.5mm*152.4mm, 300 mesh, and a wall thickness of 10mil.

[0038] The first coating contains cerium oxide.

[0039] The second coating layer contains cerium zirconium aluminum oxide and manganese (Mn), and the weight content of Mn in the second coating layer is 20% (calculated as MnO2).

[0040] The third coating layer contains silicon aluminum oxide, in which the weight content of silicon is 5% (calculated as SiO2).

[0041] The precious metals of the third coating layer are platinum (Pt) and palladium (Pd), with a total amount of 30 g / cft and a mass ratio of Pt to Pd of 12:1.

[0042] The preparation method of the partitioned DPF catalyst comprises the following steps:

[0043] Step S1: Weigh 147 g of cerium nitrate, a precursor of cerium oxide, add 529 g of deionized water and stir evenly, add 6.5 g of silica sol (solid content 40%) as a binder and 0.65 g of PEG as a dispersant, and obtain a first slurry by ball milling. The slurry particle size is D 90 =10μm;

[0044] Weigh 31g of cerium zirconium aluminum oxide powder (comprising the following components by weight: 40% CeO2, 30% ZrO2 and 30% Al2O3), add 279g of deionized water and stir evenly; weigh 25g of manganese nitrate, a precursor of Mn, add 25g of deionized water and stir to dissolve and clarify to obtain a manganese precursor solution, add the solution to the stirring slurry of cerium zirconium aluminum oxide, add 7.8g of aluminum sol (solid content 20%) as a binder and 0.78g of PVA as a dispersant, and obtain a second slurry by ball milling. The slurry particle size D 90 =20μm;

[0045] Weigh the calculated amount of Pt and Pd precursors - platinum nitrate and palladium nitrate solutions, add 100g of deionized water and stir evenly to obtain a precious metal precursor solution; weigh 52g of silicon aluminum oxide powder (components are SiO2 5%, Al2O3 95%), add 208g of deionized water and stir evenly, add the precious metal precursor solution thereto, continue stirring for 1h, add 5.2g of binder silica sol (solid content 40%) and 0.52g of dispersant PEG, and obtain the third slurry by ball milling. The slurry particle size D 90 =20μm;

[0046] Step S2, coating the first slurry from the air inlet end of the carrier, and completely drying at 200° C., the first coating dry basis coating amount is 15 g / L;

[0047] Step S3, coating the second slurry from the catalyst inlet end after step S2, completely drying at 150° C., calcining at 450° C. for 4 hours, and the dry coating amount of the second coating is 10 g / L;

[0048] Step S4, coating the third slurry from the catalyst inlet end after step S3, completely drying at 100°C, calcining at 600°C for 1h, the third coating dry coating amount is 40g / L, and a partitioned DPF catalyst product is obtained.

[0049] Example 2

[0050] A partitioned DPF catalyst, such as Figure 1As shown, it includes a carrier 4 and a first coating 1, a second coating 2, and a third coating 3 coated on the carrier, and the two ends of the carrier along the axial direction are an air inlet end and an air outlet end respectively; the first coating is coated from the air inlet end, and the length of the first coating accounts for 100% of the length of the carrier; the second coating is coated on the first coating from the air inlet end, and the length of the second coating accounts for 60% of the length of the carrier; the third coating is coated on the second coating from the air inlet end, and the length of the third coating accounts for 50% of the length of the carrier.

[0051] The carrier adopts a wall-flow silicon carbide carrier with specifications of φ190.5mm*152.4mm, 300 mesh, and a wall thickness of 10mil.

[0052] The first coating contains cerium oxide.

[0053] The second coating layer contains cerium zirconium aluminum oxide and manganese (Mn), and the weight content of Mn in the second coating layer is 5% (calculated as MnO2).

[0054] The third coating layer contains silicon aluminum oxide, wherein the weight content of silicon is 5% (calculated as SiO2).

[0055] The precious metals of the third coating layer are platinum (Pt) and palladium (Pd), with a total amount of 15 g / cft and a mass ratio of Pt to Pd of 2:1.

[0056] The preparation method of the partitioned DPF catalyst comprises the following steps:

[0057] Step S1: Weigh 49 g of cerium nitrate, a precursor of cerium oxide, add 176 g of deionized water and stir evenly, add 2.2 g of silica sol (solid content 40%) as a binder and 0.22 g of PEG as a dispersant, and obtain a first slurry by ball milling. The slurry particle size is D 90 =10μm;

[0058] Weigh 83g of cerium zirconium aluminum oxide powder (comprising the following components by weight: 40% CeO2, 30% ZrO2 and 30% Al2O3), add 744g of deionized water and stir evenly; weigh 17g of manganese nitrate, a precursor of Mn, add 17g of deionized water, stir to dissolve and clarify, and obtain a manganese precursor solution, add the solution to the stirring cerium zirconium aluminum oxide solution, add 20.8g of aluminum sol (solid content 20%) as a binder and 2.08g of PVA as a dispersant, and obtain a second slurry by ball milling. The slurry has a particle size of D 90 =20μm;

[0059] Weigh the calculated amount of Pt and Pd precursors - platinum nitrate and palladium nitrate solutions, add 100g of deionized water and stir evenly to obtain a precious metal precursor solution; weigh 22g of silicon aluminum oxide powder (by weight fraction, including the following components: SiO25% and Al2O3 95%), add 88g of deionized water and stir evenly, add the precious metal precursor solution thereto, continue stirring for 1h, add 2.2g of binder silica sol (solid content 40%) and 0.22g of dispersant PEG, and obtain the third slurry by ball milling. The slurry particle size D 90 =20μm;

[0060] Step S2, coating the first slurry from the air inlet end of the carrier, and completely drying at 200° C., the first coating dry basis coating amount is 5 g / L;

[0061] Step S3, coating the catalyst through step S2 with the second slurry from the air inlet end, completely drying at 150° C., and calcining at 450° C. for 4 hours, with the second coating having a dry coating amount of 40 g / L;

[0062] Step S4, coating the third slurry from the catalyst inlet end after step S3, completely drying at 100°C, calcining at 600°C for 1h, the third coating dry basis coating amount is 10g / L, and a partitioned DPF catalyst product is obtained.

[0063] Comparative Example 1

[0064] A partitioned DPF catalyst is the same as Example 1 except that it does not contain a first coating layer.

[0065] Comparative Example 2

[0066] A partitioned DPF catalyst is the same as Example 1 except that it does not contain a second coating layer.

[0067] Comparative Example 3

[0068] A combination of DOC+DPF catalyst, the packaging structure diagram is as follows Figure 2 shown.

[0069] The DOC catalyst carrier is a 400-mesh straight-through ceramic honeycomb carrier with specifications of φ190.5mm*101.6mm, 400 mesh, wall thickness of 4mil, precious metal dosage of 20g / cft, mass ratio of Pt and Pd of 4:1, DOC coating contains silicon aluminum oxide, in which the silicon content is 5% (in terms of SiO2), and the dry basis coating amount is 100g / L.

[0070] The DPF catalyst is the same as the partitioned DPF catalyst in Example 1 except that it does not contain the third coating layer.

[0071] The DPF catalysts of Examples 1-2 and Comparative Examples 1-2 and the DOC+DPF catalyst combination in Comparative Example 3 were tested and characterized, including active regeneration, hydrothermal aging and PN capture, as shown below:

[0072] Active regeneration: The DPF catalysts of Examples 1-2 and Comparative Examples 1-2 and the DOC+DPF catalyst combination of Comparative Example 3 were tested on a diesel engine bench for fuel injection ignition performance. The test conditions were engine exhaust temperature after turbine: 240°C, airspeed: 60k / h -1 , diesel is injected into the engine cylinder, the injection amount: 5.0mg / hub.

[0073] Hydrothermal aging: The DPF catalysts of Examples 1-2 and Comparative Examples 1-2 and the DOC+DPF catalyst combination of Comparative Example 3 were subjected to hydrothermal aging, aging conditions: 750° C.*20 h, 10% H 2 O.

[0074] The catalysts in fresh state and after hydrothermal aging were tested, and the results of active regeneration temperature raising capability of the catalyst and HC leakage are shown in Tables 2 and 3.

[0075] PN capture: The PN capture capability of the catalyst was tested on a diesel engine bench. The test condition was the NRTC cycle. Three cycles were run continuously and the average value of the three cycles was taken. The test results are shown in Table 4.

[0076] The total amount of precious metals used in DPF catalyst Examples 1-2 and Comparative Examples 1-3 of the present invention is shown in Table 1.

[0077] Table 1 Amount of precious metals used in DPF catalysts in Examples 1-4 and Comparative Examples 1-2

[0078] Compare Projects Pt / g Pd / g Example 1 1.27 0.11 Example 2 0.77 0.38 Comparative Example 1 1.27 0.11 Comparative Example 2 1.27 0.11 Comparative Example 3 1.64 0.41

[0079] As can be seen from Table 1, the amount of precious metals Pt and Pd used in the partitioned DPF catalyst of Examples 1-2 is significantly lower than that of the DOC+DPF catalyst combination of Comparative Example 3, with the total amount reduced by 30% and 40% or more, respectively. The DOC+DPF catalyst combination is the mainstream technical route in the current National VI regulatory stage. Therefore, the partitioned DPF catalyst provided by the present invention can significantly reduce the catalyst cost, while combining Figure 2 Comparing the schematic diagrams of the two catalyst packaging structures, the partitioned DPF catalyst can also reduce the volume of the post-treatment device, facilitating the vehicle chassis space layout, and has obvious advantages.

[0080] Table 2 Comparison of active regeneration temperature raising capability of fresh catalyst in the present invention

[0081] Compare Projects DPF exhaust temperature / ℃ HC leakage / ppm Example 1 592 67 Example 2 585 81 Comparative Example 1 586 75 Comparative Example 2 542 247 Comparative Example 3 587 58

[0082] Table 3 Comparison of active regeneration temperature raising capability of aged catalysts in the present invention

[0083] Compare Projects DPF exhaust temperature / ℃ HC leakage / ppm Example 1 564 152 Example 2 554 169 Comparative Example 1 558 165 Comparative Example 2 526 397 Comparative Example 3 557 214

[0084] As can be seen from Table 2 and Table 3, the partitioned DPF catalysts of Examples 1 and 2 have excellent active regeneration performance, and both the fresh state and the hydrothermal aging state can increase the exhaust temperature after the DPF to above 550°C, and the aging resistance is good. The HC leakage does not exceed 200ppm, and the leakage is extremely low. Comparative Example 2 lacks a second coating, so the active regeneration ability is relatively weak, the exhaust temperature after the DPF does not reach 550°C, and the HC leakage exceeds 200ppm, and the aging state is close to 400ppm. The active regeneration performance is somewhat different from that of Examples 1 and 2.

[0085] Table 4 Comparison of PN capture capacity of the catalysts in the present invention

[0086] Compare Projects PN emission value / kW·h PN capture rate / % Example 1 2.67E+11 99.68％ Example 2 4.19E+11 99.50％ Comparative Example 1 1.48E+12 98.22％ Comparative Example 2 8.74E+11 98.95％ Comparative Example 3 3.53E+11 99.58％ Original row 8.21E+13 ——

[0087] As can be seen from Table 4, Examples 1 and 2 have excellent PN capture capabilities due to the coating of the first coating, and the PN emission values ​​in the NRTC cycle are 2.67E+11 and 4.19E+11 respectively, and the PN capture rates are both above 99.5%. Comparative Example 1 has a significantly lower PN capture capability due to the lack of the first coating, with a PN value as high as 1.48E+12 and a capture rate of only 98.22%; in addition to the first coating mainly playing the role of PN capture, the second coating also plays an auxiliary role in PN capture, so the PN value of Comparative Example 2 is also significantly higher than that of Examples 1 and 2, reaching 8.74E+11, and the capture rate does not reach 99%.

[0088] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A partitioned DPF catalyst, characterized in that: The invention comprises a carrier and a first coating, a second coating and a third coating sequentially coated on the carrier, wherein the two ends of the carrier along the axial direction are an air inlet end and an air outlet end respectively; the first coating is coated from the air inlet end of the carrier, and the length of the first coating accounts for 100% of the length of the carrier; the second coating is coated on the first coating from the air inlet end, and the length of the second coating accounts for 60-90% of the length of the carrier; the third coating is coated on the second coating from the air inlet end, and the length of the third coating accounts for 30-50% of the length of the carrier; The first coating layer contains a first catalytic material; the second coating layer contains a second catalytic material; the third coating layer contains a noble metal and a third catalytic material, and the content of the noble metal is 15-30 g / cft.

2. The zoned DPF catalyst according to claim 1, characterized in that: The carrier is a wall-flow structure, and the material is one of cordierite, silicon carbide, aluminum titanate and metal foam.

3. The zoned DPF catalyst according to claim 1, characterized in that: The first catalytic material contains at least one of cerium oxide, modified aluminum oxide and silicon aluminum oxide.

4. The zoned DPF catalyst according to claim 1, characterized in that: The second catalytic material contains at least one of cerium oxide, cerium-zirconium composite oxide, cerium-zirconium aluminum oxide, and cerium aluminum oxide, and manganese.

5. The zoned DPF catalyst according to claim 4, characterized in that: The manganese is calculated as MnO2, and its weight proportion in the second coating layer is 5-20%.

6. The zoned DPF catalyst according to claim 1, characterized in that: The third catalytic material contains at least one of aluminum oxide, modified aluminum oxide, silicon aluminum oxide and cerium aluminum oxide.

7. The zoned DPF catalyst according to claim 1, characterized in that: The precious metals of the third coating are platinum Pt and palladium Pd, and the mass ratio of Pt to Pd is 2:1-12:

1.

8. The method for preparing the partitioned DPF catalyst according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step S1, adding a raw material of the first catalytic material into an appropriate amount of deionized water and stirring evenly, adding 2-4% of a binder and 1-2% of a dispersant by dry weight, and ball milling to obtain a first slurry; Add the raw material of the second catalytic material into an appropriate amount of deionized water and stir evenly, wherein the raw material of Mn is a soluble manganese salt, and 2-6% of a binder and 1-3% of a dispersant are added on a dry basis weight basis, and the second slurry is obtained by ball milling; Dispersing the precursor solution of the noble metal in the raw material of the third catalytic material, adding an appropriate amount of deionized water, adding 2-8% of a binder and 1-5% of a dispersant by dry weight, and ball milling to obtain a third slurry; Step S2, coating the first slurry from the air inlet end of the carrier, and completely drying at 100-200° C., the dry basis coating amount of the first coating is 5-15 g / L; Step S3, coating the second slurry on the first coating in step S2 from the air inlet end, and completely drying at 100-200° C., and calcining at 450-600° C. for 1-4 hours, the dry basis coating amount of the second coating is 10-40 g / L; Step S4, apply the third slurry from the air inlet end to the second coating in step S3, completely dry at 100-200°C, and calcine at 450-600°C for 1-4h. The dry coating amount of the third coating is 10-40g / L to obtain a partitioned DPF catalyst product.

9. The method for preparing a zoned DPF catalyst according to claim 8, characterized in that: In step S1, the soluble manganese salt is at least one of manganese acetate, manganese nitrate and potassium permanganate.

10. The method for preparing a zoned DPF catalyst according to claim 8, characterized in that: In step S1, the binder is at least one of silica sol, aluminum sol, titanium sol and zirconium sol; the dispersant is at least one of PEG, PVP, PVA and carboxymethyl cellulose.

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