Efficient trapping and regenerating CDPF catalyst and preparation method thereof

Abstract

The invention discloses an efficient trapping and regenerating CDPF catalyst and a preparation method thereof.The CDPF catalyst comprises a wall flow type DPF carrier, a first coating and a second coating, the first coating and the second coating are applied to the DPF carrier, the first coating is composed of aluminum oxide and / or silicon-aluminum oxide with low apparent density and rhombic, needle-shaped, fiber-shaped and three-dimensional porous structures and a binder, and the second coating is composed of silicon-aluminum oxide and / or silicon-aluminum oxide with the rhombic, needle-shaped, fiber-shaped and three-dimensional porous structures. The particles are distributed in a DPF carrier pore channel; the second coating is a catalytic active layer containing single platinum or platinum-palladium bimetal and is distributed on the outer wall of the air inlet side of the DPF carrier. According to the CDPF catalyst, the collision frequency of the first coating and particulate matter can be increased, the particulate matter trapping efficiency can be improved, the airflow flowing resistance can be reduced, the back pressure can be reduced, the contact area of soot and the active coating is increased through the catalytic active layer of the second coating, passive regeneration is promoted, and the service life of the catalyst is prolonged. Therefore, the passive regeneration capacity and the trapping efficiency of the CDPF are both improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of diesel engine exhaust catalytic purification technology, and particularly relates to a CDPF catalyst for diesel engine high-efficiency trapping and regeneration and a preparation method thereof. BACKGROUND

[0002] Particulate matter emitted by diesel vehicles is extremely harmful to human bodies and ecological environment, and is the most important problem in the post-processing of exhaust emission control. The wall-flow particulate trap is a recognized most effective technical means for particulate control of motor vehicles. With the large-scale use of the national sixth diesel vehicles, more and more problems are exposed in the actual application process. Among them, the PN emission easy to exceed the standard and the high back pressure OBD alarm in the actual road vehicle PEMS test have become the two most prominent problems at the present stage, which seriously affect the smooth progress of the national sixth emission regulations.

[0003] In the PEMS test, the PN emission is easy to exceed the standard. The main reason is that the trapping efficiency of the conventional CDPF catalyst in the fresh state is insufficient (≤95%). When the vehicle runs at high speed, the CDPF will undergo high-temperature regeneration to restore to the fresh state, resulting in a sharp increase in the penetration rate of particulate matter, which causes the emission to exceed the standard. The high back pressure OBD alarm is usually caused by two reasons: on the one hand, the trapping efficiency of the CDPF is improved by increasing the coating load or reducing the pore size of the carrier (a common means in the prior art), which causes the back pressure to increase dramatically; on the other hand, the regeneration ability of the CDPF is insufficient, which causes the accumulation of particulate matter (PM) and leads to the increase of back pressure, triggering the back pressure OBD alarm. At present, the related research based on the CDPF mainly focuses on the improvement of the single aspect performance of the activity or trapping efficiency of the catalytic coating and the back pressure.

[0004] The Chinese patent CN115680828A discloses a high-efficiency particulate matter capturing catalytic diesel particulate filter, which comprises an inorganic coating layer coated on a blank DPF carrier, a catalytically active coating layer coated on the inorganic coating layer, and the coating layer and the catalytically active layer are both distributed inside the pores of the DPF carrier. It realizes selective penetration of the coating layer into the large pores inside the carrier wall by matching the particle size of the coating slurry with the pore size of the blank DPF carrier, fills the part of the pore channel of the large pores prone to soot leakage, reduces the proportion of large pores in the carrier wall, prevents small particles from leaking from the large pores, intercepts more soot particles, and achieves the purpose of improving the capture efficiency. However, there are still some defects, mainly in the following two aspects: first, the coating layer material is a conventional spherical silicon aluminum material that modifies the pore channel, which is not conducive to the collision and rapid settlement of particles in irregular Brownian motion, and is also not conducive to the air permeability, increasing the air flow resistance; second, when the CDPF catalyst captures soot, it first fills the internal pores of the DPF (deep bed capture stage), and when the internal pores of the porous medium are quickly filled with captured particles, soot will accumulate on the outer wall of the DPF pores (soot layer capture stage). Compared to coating the catalytically active layer inside the DPF pores, coating the catalytically active layer on the outer wall of the DPF carrier on the gas inlet side reduces the contact area between the soot and the active coating, which is not conducive to soot regeneration. SUMMARY

[0005] The present application aims to address the dual problems of passive regeneration efficiency deficiency and PMES working condition particulate matter exceeding the standard of existing CDPF catalysts, to solve the deficiencies of existing CDPF technology, and to provide a CDPF catalyst with high efficiency of capture and regeneration and a preparation method thereof.

[0006] The technical solutions adopted by the present application are as follows: The CDPF catalyst with high efficiency of capture and regeneration comprises a wall-flow DPF carrier, a first coating layer and a second coating layer applied to the DPF carrier, wherein the first coating layer is a low bulk density, rhombic, needle-like, fibrous, three-dimensional porous structure of aluminum oxide and / or silicon aluminum oxide and a binder, distributed inside the pores of the DPF carrier, and the pore diameter of the three-dimensional porous structure is 10-100 nm; the second coating layer is a catalytically active layer containing single platinum or platinum-palladium bimetal, distributed on the outer wall of the DPF carrier on the gas inlet side.

[0007] Further, the bulk density of the aluminum oxide or silicon aluminum oxide of the first coating layer is 0.05-0.25 g / cm 3 .

[0008] Further, the binder used in the first coating layer is one or more of alumina gel, silica gel and zirconium gel, and the usage amount is 2-10 wt.% of the total dry weight of the oxide in the first coating layer. Further, the median pore size of the wall flow DPF carrier is 7-16 μm.

[0009] Further, the particle size or particle size of the particles in the first coating slurry is less than the pore size of the DPF carrier.

[0010] Further, the particle size D50 or particle size of the particles in the first coating slurry is 0.1-10 μm.

[0011] The preparation method of the high-efficiency trapping and regenerative CDPF catalyst according to the present application comprises the following steps: (1) adding the alumina or silica-alumina oxide used in the first coating layer into deionized water and a binder, and adding cellulose, and stirring uniformly to obtain a first coating slurry; (2) coating the first coating slurry into the pores of the wall flow DPF carrier by vacuum suction, and drying and calcining to make the loading amount of the first layer be 3-10 g / L, thereby obtaining the high-efficiency trapping and regenerative CDPF catalyst semi-product; (3) loading a catalytically active layer on the high-efficiency trapping and regenerative CDPF catalyst semi-product on the outer wall of the DPF carrier on the gas inlet side, so that the loading amount of the second layer is 5-15 g / L, thereby preparing the high-efficiency trapping and regenerative CDPF catalyst.

[0012] The high-efficiency trapping and regenerative CDPF catalyst according to the present application has a two-layer coating structure, wherein the first coating layer is distributed inside the pores of the DPF carrier, and the low bulk density coating layer is loosely filled inside the pores of the carrier with a small loading amount, and the space structure formed by the rhombic, needle-like, fibrous, three-dimensional porous and mutual stacking thereof can increase the collision frequency with the particles in random Brownian motion, so that the soot which is easy to leak through the carrier wall realizes rapid settling, improves the particle trapping efficiency, and due to the characteristics of low bulk density and low loading, the airflow resistance can be reduced and the back pressure can be reduced, and the catalytically active layer of the second coating layer is distributed on the outer wall of the DPF carrier on the gas inlet side, which increases the contact area of the soot and the active coating layer, promotes passive regeneration, thereby realizing the dual improvement of the passive regeneration ability and trapping efficiency of the CDPF. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The figure is a schematic diagram of the high-efficiency trapping and regenerative CDPF catalyst according to the present application; Figure 2Passive regeneration efficiency of the conventional single coating CDPF catalyst prepared by using the CDPF catalyst obtained in Examples 1-5 and the catalytically active layer loaded with the same loading amount of platinum-palladium bimetal. DETAILED DESCRIPTION

[0014] To further illustrate the technical solutions of the present application and their effects, the content of the present application is further illustrated below in conjunction with the accompanying drawings of the specification and through examples.

[0015] Figure 1 A schematic diagram of the high-efficiency trapping and regenerating CDPF catalyst of the present application, as can be seen from the diagram, the high-efficiency trapping and regenerating CDPF catalyst comprises a wall-flow DPF carrier 1, a first coating layer 2 and a second coating layer 3 applied on the DPF carrier, the wall-flow DPF carrier is respectively provided with an inlet end plug 1a and an outlet end plug 1b, wherein the first coating layer is composed of alumina and / or silicon-aluminum oxide with low bulk density, rhombic, needle-like, fibrous, three-dimensional porous structure and a binder, and is distributed inside the pore channels of the DPF carrier, wherein the pore channels of the three-dimensional porous structure have a diameter of 10-100 nm, and the second coating layer is a catalytically active layer containing single platinum or platinum-palladium bimetal, and is distributed on the outer wall of the inlet side of the DPF carrier. The bulk density of the alumina or silicon-aluminum oxide of the first coating layer is 0.05-0.25 g / cm 3 The binder used is one or more of aluminum sol, silicon sol and zirconium sol, and the usage amount is 2-10 wt.% of the total dry weight of the oxides of the first coating layer. The median pore diameter of the wall-flow DPF carrier is 7-16 μm. Further, to enable the first coating slurry to enter the inside of the wall pore channels of the DPF carrier when vacuum suction is performed, the particle size or particle size of the particles in the first coating slurry is less than the loose pore diameter 1c in the DPF carrier, and preferably, the particle size D50 or particle size of the particles in the first coating slurry is 0.1-10 μm.

[0016] The first coating layer is distributed inside the pore channels of the DPF carrier, and the low bulk density coating layer is loosely filled in the inside of the pore channels of the DPF carrier with a small loading amount, and the rhombic, needle-like, fibrous, three-dimensional porous structure and the space structure formed by the mutual accumulation thereof increase the collision frequency of the bulk density coating layer and the particles in random Brownian motion, so that the soot which is easy to pass through the carrier wall to cause leakage can be quickly settled, the particulate matter trapping efficiency is improved, and moreover, due to the characteristics of low bulk density and low loading, the airflow flow resistance can also be reduced, and the back pressure is reduced, and the catalytically active layer is distributed on the outer wall of the inlet side of the DPF carrier, the contact area of the soot and the active coating layer is increased, and the passive regeneration is promoted; thereby realizing the dual improvement of the passive regeneration capability and the trapping efficiency of the CDPF.

[0017] The preparation method of the high-efficiency trapping and regenerating CDPF catalyst of the present application is as follows: (1) adding alumina or silicon-alumina oxide used for the first coating layer into deionized water and a binder, adding cellulose, and stirring to obtain a first coating layer slurry; (2) coating the first coating layer slurry into the wall flow DPF carrier channel by vacuum suction, and drying and calcining to make the first layer loading amount 3-10 g / L, thereby obtaining a high-efficiency trapping and regenerating CDPF catalyst semi-finished product; (3) loading a catalytically active layer on the high-efficiency trapping and regenerating CDPF catalyst semi-finished product on the outer wall of the DPF carrier on the air inlet side, and making the second layer loading amount 5-15 g / L, thereby obtaining the high-efficiency trapping and regenerating CDPF catalyst.

[0018] The catalytically active coating layer material in the application can be commercially available or prepared by the prior art, and is a catalytically active layer containing single platinum or platinum-palladium bimetal in any ratio, and the noble metal concentration can be 2-10 g / cft. In order to facilitate comparison, the CDPF catalysts obtained in Examples 1-5 below and the conventional single-coating CDPF catalysts all use platinum-palladium bimetal as the noble metal, and the noble metal concentration is 3 g / cft, and the platinum-palladium ratio is 3:1. Example 1

[0019] A preparation method of a high-efficiency trapping and regenerating CDPF catalyst, the steps being as follows: (1) adding alumina with a needle-like morphology and a loose bulk density of 0.25 g / cm 3 into deionized water and stirring to obtain a first coating layer slurry, adding 5 wt.% of silica gel, and then adding cellulose and stirring to obtain the first coating layer slurry, wherein the particle size in the first coating layer slurry is 0.1 μm; (2) using a commonly used vacuum suction coating device, first coating the first coating layer slurry into the wall flow DPF carrier channel, and drying and calcining to make the first layer loading amount 10 g / L, thereby obtaining the high-efficiency trapping and regenerating CDPF catalyst semi-finished product. The wall flow DPF carrier used has a median pore size of 16 μm; (3) loading a catalytically active layer on the high-efficiency trapping and regenerating CDPF catalyst semi-finished product on the outer wall of the DPF carrier on the air inlet side, and making the second layer loading amount 5 g / L, thereby obtaining the high-efficiency trapping and regenerating CDPF catalyst.

[0020] The PN emission and passive regeneration efficiency of the high-efficiency trapping and regenerating CDPF catalyst obtained in this example were tested, and the results are shown in Figure 2 and Table 1. Example 2

[0021] A preparation method of a high-efficiency trapping and regenerating CDPF catalyst, the steps being as follows: (1) The first coating is rhomboid in shape with a bulk density of 0.15 g / cm³. 3 A composite of alumina and silica was added to deionized water and stirred until homogeneous. Then, 4 wt.% silica gel was added, followed by cellulose. The mixture was stirred until homogeneous to obtain a first coating slurry, wherein the particle size in the first coating slurry was 10 μm. (2) The first coating slurry was coated into the pores of the wall-flow DPF support by vacuum suction, and after drying and calcination, the loading of the first layer was 5 g / L, thus obtaining the semi-finished product of the highly efficient capture and regeneration CDPF catalyst. The median pore size of the wall-flow DPF support used was 7 μm; (3) On the CDPF catalyst semi-finished product with high efficiency capture and regeneration, a catalytic active layer is loaded on the outer wall of the DPF support on the inlet side with a loading amount of 10 g / L to obtain the CDPF catalyst with high efficiency capture and regeneration.

[0022] The PN emission and passive regeneration efficiency of the CDPF catalyst with high efficiency in trapping and regenerating obtained in this embodiment were tested. See the results for details. Figure 2 See Table 1. Example 3

[0023] A method for preparing a highly efficient CDPF catalyst for capture and regeneration includes the following steps: (1) The first coating is fibrous in shape with a bulk density of 0.05 g / cm³. 3 A composite of alumina and silica was added to deionized water and stirred until homogeneous. Then, 5 wt.% silica gel was added, followed by cellulose. The mixture was stirred until homogeneous to obtain a first coating slurry, wherein the particle size in the first coating slurry was 1.5 μm. (2) The first coating slurry was coated into the pores of the wall-flow DPF support by vacuum suction, and after drying and calcination, the loading of the first layer was 8 g / L, thus obtaining the semi-finished product of the highly efficient capture and regeneration CDPF catalyst. The median pore size of the wall-flow DPF support used was 11 μm; (3) On the CDPF catalyst semi-finished product with high efficiency capture and regeneration, a catalytic active layer is loaded on the outer wall of the DPF support on the inlet side, so that the loading of the second layer is 15g / L, and the CDPF catalyst with high efficiency capture and regeneration is obtained.

[0024] The PN emission and passive regeneration efficiency of the CDPF catalyst with high efficiency in trapping and regenerating obtained in this embodiment were tested. See the results for details. Figure 2 See Table 1. Example 4

[0025] A method for preparing a highly efficient CDPF catalyst for capture and regeneration includes the following steps: (1) The first coating uses a three-dimensional porous structure with a pore diameter of 10-50 nm and a loose packing density of 0.2 g / cm³. 3 Alumina is added to deionized water and stirred evenly. 2 wt.% aluminum and silica gel are added, wherein the ratio of aluminum gel to silica gel is 1:1. Cellulose is then added and stirred evenly to obtain the first coating slurry, wherein the particle size D50 of the particles in the first coating slurry is 4 μm. (2) The first coating slurry was coated into the pores of the wall-flow DPF support by vacuum suction, and after drying and calcination, the loading of the first layer was 4 g / L, thus obtaining the highly efficient CDPF catalyst semi-finished product for capture and regeneration. The median pore size of the wall-flow DPF support used was 9.5 μm; (3) On the CDPF catalyst semi-finished product with high efficiency capture and regeneration, a catalytic active layer is loaded on the outer wall of the DPF support on the inlet side, so that the loading of the second layer is 12g / L, and the CDPF catalyst with high efficiency capture and regeneration is obtained.

[0026] The PN emission and passive regeneration efficiency of the CDPF catalyst with high efficiency in trapping and regenerating obtained in this embodiment were tested. See the results for details. Figure 2 See Table 1. Example 5

[0027] A method for preparing a highly efficient CDPF catalyst for capture and regeneration includes the following steps: (1) The first coating uses a three-dimensional porous structure with a pore diameter of 10-50 nm and a loose packing density of 0.10 g / cm³. 3 A composite of alumina and silica is added to deionized water and stirred evenly. Then, 6 wt.% of aluminum, silica and zirconium glue are added, wherein the ratio of aluminum glue, silica glue and zirconium glue is 1:1:1. Cellulose is then added and stirred evenly to obtain the first coating slurry, wherein the particle size D50 of the particles in the first coating slurry is 8 μm. (2) The first coating slurry was coated into the pores of the wall-flow DPF support by vacuum suction, and after drying and calcination, the loading of the first layer was 4 g / L, thus obtaining the semi-finished product of the highly efficient capture and regeneration CDPF catalyst. The median pore size of the wall-flow DPF support used was 12.5 μm; (3) On the CDPF catalyst semi-finished product with high efficiency capture and regeneration, a catalytic active layer is loaded on the outer wall of the DPF support on the inlet side, so that the loading of the second layer is 5g / L, and the CDPF catalyst with high efficiency capture and regeneration is obtained.

[0028] The PN emission and passive regeneration efficiency of the CDPF catalyst with high efficiency in trapping and regenerating obtained in this embodiment were tested. See the results for details. Figure 2 See Table 1.

[0029] The cellulose used in the above embodiments is any type of cellulose commonly used in this technical field and is commercially available. It is mainly used to improve the fluidity and water retention of the coating slurry.

[0030] Table 1 shows the PN emission test results under WHTC cycle conditions for the CDPF catalysts obtained in Examples 1-5 and conventional single-coated CDPF catalysts (i.e., CDPF catalysts with a platinum-palladium bimetallic catalytic active layer coated on the outside of the inlet side of a wall-flow DPF support with the same loading amount as in the examples). In Table 1, source emissions refer to exhaust gas directly emitted by the engine without catalyst treatment and exhaust gas refers to exhaust gas emitted after catalyst treatment.

[0031] Figure 2 The passive regeneration efficiency of a conventional single-coated CDPF catalyst prepared according to the CDPF catalysts obtained in Examples 1-5 and with a platinum-palladium bimetallic catalytic active layer with the same loading amount as in the examples was measured. The passive regeneration efficiency test method was as follows: The CDPF catalyst was loaded with soot to a concentration of 4 g / L. The engine was kept at its maximum torque speed, and the CDPF inlet temperature was stabilized at (280±5) °C by adjusting the load. The operation was continued for 10 min, and the inlet temperature was increased at 20 °C intervals, with each condition being maintained for 10 min. The process continued until the inlet temperature reached 420 °C. Data such as CDPF inlet temperature, pressure drop, and gas emissions were recorded during this process. The regeneration efficiency was calculated based on the thermogravimetric changes of the CDPF before and after active and passive regeneration.

[0032] Depend on Figure 2 As shown in Table 1, the high-efficiency capture and regeneration CDPF catalyst of this invention exhibits superior particulate capture and passive regeneration capabilities compared to conventional CDPF catalyst technology. This high-efficiency capture and regeneration CDPF catalyst can be widely applied to the control of particulate matter emissions from diesel engine exhaust from mobile sources, off-road sources, and stationary sources.

[0033] The wall-flow DPF carrier used in this invention can be commercially available or prepared according to existing technology. The material of the wall-flow DPF carrier is one of cordierite, silicon carbide, aluminum titanate, mullite, etc.

[0034] Unless otherwise stated, all percentages mentioned in this invention are mass percentages.

[0035] Table 1. Comparison of PN emissions between the high-efficiency capture and regeneration CDPF catalyst of this invention and conventional single-coated CDPF catalyst. .

Claims

1. A CDPF catalyst with high efficiency in trapping and regenerating, characterized in that, The device includes a wall-flow DPF support, a first coating and a second coating applied to the DPF support. The first coating is composed of alumina and / or aluminosilicate oxides with a low bulk density and a rhomboid, needle-like, fibrous, three-dimensional porous structure, and a binder, distributed inside the pores of the DPF support. The diameter of the three-dimensional porous pores is 10-100 nm. The second coating is a catalytically active layer containing monoplatinum or platinum-palladium bimetals, distributed on the outer wall of the DPF support on the inlet side.

2. The highly efficient CDPF catalyst for capture and regeneration according to claim 1, characterized in that, The bulk density of the alumina or aluminosilicate in the first coating is 0.05-0.25 g / cm³. 3 .

3. The highly efficient CDPF catalyst for capture and regeneration according to claim 1 or 2, characterized in that, The binder used for the first coating is one or more of aluminum glue, silicone glue, and zirconium glue, and the amount used is 2-10 wt.% of the total dry weight of the oxide in the first coating.

4. The highly efficient CDPF catalyst for capture and regeneration according to claim 1 or 2, characterized in that, The median pore size of the wall-flow DPF carrier is 7-16 μm.

5. The highly efficient CDPF catalyst for capture and regeneration according to claim 1 or 2, characterized in that, The particle size or particle size of the particles in the first coating slurry is smaller than the pore size of the DPF carrier channel.

6. The highly efficient CDPF catalyst for capture and regeneration according to claim 5, characterized in that, The particle size D50 or particle size of the particles in the first coating slurry is 0.1-10μm.

7. The method for preparing the highly efficient CDPF catalyst for capture and regeneration as described in any one of claims 1-6, characterized in that, The steps are as follows: (1) Add the alumina or silica-alumina oxide used in the first coating to deionized water and binder, then add cellulose, and stir evenly to obtain the first coating slurry; (2) The first coating slurry is coated into the pores of the wall-flow DPF support by vacuum suction, and after drying and calcination, the loading of the first layer is 3-10 g / L, so as to obtain a CDPF catalyst semi-finished product with high efficiency of capture and regeneration. (3) On the CDPF catalyst semi-finished product with high efficiency capture and regeneration, a catalytic active layer is loaded on the outer wall of the DPF support on the inlet side, so that the loading of the second layer is 5-15 g / L, and the CDPF catalyst with high efficiency capture and regeneration is prepared.

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