A DPF coating structure and preparation method thereof

Abstract

The present application relates to the technical field of engine emission control, and more particularly to a DPF coating structure and a method for preparing the same. The DPF coating structure comprises a first coating applied to the surface of the DPF and a second coating applied to the surface of the first coating, wherein the first coating comprises a catalyst carrier, and the second coating comprises an activated carbon layer containing a catalyst precursor. The DPF coating structure of the present application improves the filtration efficiency of the DPF by pre-setting the activated carbon layer in the initial stage without increasing the back pressure of the DPF. After the engine has operated for a period of time, the DPF actively regenerates and activates the catalyst, which catalytically oxidizes PM. At the same time, the accumulated ash in the DPF helps improve the filtration efficiency, thereby enabling the DPF to maintain a high filtration efficiency.

Description

Technical Field

[0001] The present application relates to the technical field of engine emission control, and in particular to a DPF coating structure and a preparation method thereof. Background Art

[0002] Diesel engines have the significant advantages of high thermal efficiency and good economy, but they also emit a large amount of soot particulate matter (PM) and NO x As the environmental protection requirements of various countries are tightened, the emission of NO x The removal of PM has become an inevitable trend, especially the removal of PM. Diesel particulate filters (DPF) are used in existing diesel engines to capture PM to reduce PM emissions. DPF is a honeycomb porous ceramic material. Initially, the filtration efficiency of DPF is very low. It requires a carbon layer or ash accumulation before the filtration efficiency of DPF can be improved. However, random inspections of new cars are usually conducted in the initial state of DPF, so the problem of excessive particle number (PN) emissions is prone to occur in random inspections of new cars.

[0003] At present, the problem of low initial filtration efficiency of DPF is mainly solved by DPF ash coating technology. DPF ash coating technology refers to blowing alumina powder as simulated ash into the DPF pores after coating the surface of DPF with a catalyst to improve the filtration efficiency of DPF. However, the ash blown into the pores increases the back pressure of DPF, affecting the operating efficiency of the engine. Moreover, the ash cannot be effectively removed, increasing the risk of DPF clogging.

[0004] It is worth noting that after the DPF has been working for a period of time, the PM accumulated in the DPF gradually increases, and the DPF back pressure increases, resulting in a sharp increase in the pressure difference before and after the DPF. The operating efficiency of the engine is significantly affected. Therefore, it is necessary to regularly and effectively remove the captured PM so that the entire after-treatment system can be maintained at a lower back pressure state. At present, the DPF removes deposited PM through active regeneration or passive regeneration. Active regeneration uses external energy to provide the temperature inside the DPF so that the PM ignites and burns. Passive regeneration uses fuel additives or catalysts to lower the ignition temperature of PM so that PM can ignite and burn at normal diesel engine exhaust temperatures. The surface of existing DPFs is basically provided with a catalyst coating so that the DPF can optimize its own performance through passive regeneration. Passive regeneration will cause the carbon accumulated in the DPF to burn, and the carbon layer structure will become loose. Especially for the DPF in its initial state, it is easy to have PN emissions exceeding the standard. Summary of the Invention

[0005] The present application discloses a DPF coating structure and a preparation method thereof, which are used to solve the problem of low PN filtration efficiency of the DPF in the initial state.

[0006] To achieve the above objectives, in the first aspect, this application provides the following technical solutions:

[0007] A DPF coating structure comprises a first coating coated on the surface of the DPF and a second coating coated on the surface of the first coating, wherein the first coating comprises a catalyst carrier and the second coating is an activated carbon layer containing a catalyst precursor.

[0008] Furthermore, the catalyst precursor is a noble metal precursor or a non-noble metal precursor.

[0009] Furthermore, the noble metal precursor includes at least one of ethanolamine hydroxyplatinum, tetraammonium nitrosoplatinum, platinum nitrate, chloroplatinic acid, palladium nitrate, palladium acetate, palladium chloride, rhodium nitrate and rhodium acetate.

[0010] Furthermore, the catalyst carrier includes at least one of aluminum oxide, silicon oxide, titanium oxide, zirconium oxide and molecular sieve.

[0011] In a second aspect, a method for preparing a DPF coating structure comprises the following steps:

[0012] Applying the first coating layer: applying a slurry containing a catalyst carrier to the surface of the DPF, and obtaining a DPF coated with the first coating layer after a first drying and a first calcination, wherein the temperature of the first calcination is 550° C.-650° C.;

[0013] Applying the second coating: applying a mixed slurry of catalyst precursor and activated carbon on the surface of the first coating, and obtaining the DPF coating structure after a second drying, wherein the second drying is drying at room temperature.

[0014] Furthermore, before applying the first coating step, a slurry containing a catalyst carrier is prepared. The slurry containing the catalyst carrier is prepared by:

[0015] The catalyst support, the binder and the surfactant are mixed with the first solvent to obtain a slurry containing the catalyst support.

[0016] Furthermore, the slurry containing the catalyst carrier also includes a promoter, which is a compound of a rare earth element.

[0017] Furthermore, before applying the second coating step, a mixed slurry of a catalyst precursor and activated carbon is prepared, and the preparation of the mixed slurry includes:

[0018] The catalyst precursor, activated carbon powder, dispersant and the second solvent are mixed to obtain a mixed slurry.

[0019] Furthermore, the particle size of the activated carbon is 1um-50um.

[0020] Furthermore, the loading amount of the first coating layer is 5-20 g / L, the loading amount of the second coating layer is 1-10 g / L, and the total loading amount of the first coating layer and the second coating layer is 5-100 g / L.

[0021] The DPF coating structure provided in the present application has the following characteristics: in the initial state, the activated carbon of the second coating layer can adsorb PM, thereby improving the PN filtration efficiency of the DPF. At the same time, the catalyst precursor cannot directly contact the carrier, is not activated, and has basically no catalytic activity, thereby inhibiting the passive regeneration of the DPF; when the engine has been running for a period of time, when the carbon load of the DPF reaches the preset carbon load, the engine sprays oil, the DPF actively regenerates, the activated carbon layer of the second coating layer burns, part of the catalyst precursor is transferred to the first coating layer and reacts with the catalyst carrier, the catalyst is activated, and the catalyst catalytically oxidizes PM, thereby promoting the passive regeneration of the DPF. In summary, the DPF coating structure in the present application improves the filtration efficiency of the DPF by presetting the activated carbon layer in the initial stage, and the activated carbon layer can be burned and consumed later; when the engine has been running for a period of time, the DPF actively regenerates and activates the catalyst, and the catalyst catalytically oxidizes PM. At the same time, the ash accumulated in the DPF helps to improve the filtration efficiency, so that the DPF always maintains a high PN filtration efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic structural diagram of a DPF coating structure provided in an embodiment of the present application;

[0023] Figure 2 A schematic diagram of the initial state of a DPF coating structure provided in an embodiment of the present application;

[0024] Figure 3 A schematic diagram of a DPF coating structure provided in an embodiment of the present application after active DPF regeneration;

[0025] Figure 4 This is an electron microscope image of the DPF coating structure in Example 1 of the present application;

[0026] Figure 5 This is an electron microscope image of the DPF coating structure in Comparative Example 1 of this application.

[0027] Reference numerals: 100 -DPF; 200 -first coating layer; 210 -catalyst support; 300 -second coating layer; 310 -catalyst precursor; 320 -activated carbon layer. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0029] Figure 1 A schematic diagram of a DPF coating structure provided in an embodiment of the present application, referring to Figure 1 The DPF coating structure includes a first coating 200 coated on the surface of the DPF 100 and a second coating 300 coated on the surface of the first coating 200 . The first coating 200 includes a catalyst carrier 210 , and the second coating 300 is an activated carbon layer 320 containing a catalyst precursor 310 .

[0030] In an optional solution of the embodiment of the present application, the catalyst precursor is a noble metal precursor or a non-noble metal precursor.

[0031] Among them, when the catalyst precursor is a noble metal precursor, it can specifically be at least one of ethanolamine hydroxyplatinum, tetraammonium nitrosoplatinum, platinum nitrate, chloroplatinic acid, palladium nitrate, palladium acetate, palladium chloride, rhodium nitrate and rhodium acetate.

[0032] When the catalyst precursor is a non-noble metal precursor, it may specifically be a cesium-vanadium based non-noble metal catalyst precursor.

[0033] In an alternative embodiment of the present application, the catalyst carrier includes at least one of aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, and molecular sieves. The catalyst precursor reacts with the catalyst carrier to activate the catalyst, thereby catalytically oxidizing PM.

[0034] Based on the same inventive concept, an embodiment of the present application also provides a method for preparing a DPF coating structure, which comprises the following steps:

[0035] Applying the first coating layer: applying a slurry containing a catalyst carrier to the surface of the DPF, and obtaining a DPF coated with the first coating layer after a first drying and a first calcination, wherein the first drying temperature is 100°C-300°C, and the first calcination temperature is 550°C-650°C;

[0036] Applying a second coating: A mixed slurry of catalyst precursor and activated carbon is applied to the surface of the first coating. After a second drying process, the DPF coating structure is obtained. The second drying process is performed at room temperature. Optionally, the second drying process includes a second calcination process at a temperature of 300°C or less.

[0037] The first coating layer can be applied to the wall surface or the interior of the DPF, preferably to the wall surface of the DPF. The second coating layer is applied only to the surface of the DPF on the wall surface. The temperature of the first calcination is 550°C-650°C, for example 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C or 650°C. The temperature of the first drying is 100°C-300°C, for example 100°C, 120°C, 150°C, 180°C, 200°C, 250°C, 280°C or 300°C. It is understood that the drying method is not limited in this application. Specifically, baking can be selected.

[0038] The temperature of the second calcination is less than or equal to 300° C. It is understood that the second drying is room temperature drying and the second calcination is not high temperature calcination, so that the catalyst is in a compound or complex state and in an inactivated state.

[0039] In an optional solution of the embodiment of the present application, the particle size of the activated carbon is 1 μm-50 μm. The particle size of the activated carbon can be 1 μm, 5 μm, 10 μm, 15 μm, 30 μm, 40 μm or 50 μm.

[0040] In an optional solution of the embodiment of the present application, before applying the first coating step, a slurry containing a catalyst carrier is further prepared. The slurry containing the catalyst carrier is prepared including:

[0041] A catalyst support, a binder, and a surfactant are mixed with a first solvent to obtain a slurry containing the catalyst support, wherein the solid content of the catalyst support accounts for 85% to 95% of the total mass of the slurry, the mass of the binder accounts for 1% to 5% of the total mass of the slurry, and the mass of the surfactant accounts for 1% to 5% of the total mass of the slurry.

[0042] The binder may be at least one of silica gel or aluminum gel. The surfactant may be polyvinyl alcohol, ethoxylated alkylphenol, polyethylene glycol ether, or polyoxyethylene ethyl ether. The first solvent may be water.

[0043] In order to enhance the catalytic activity of the catalyst, the catalyst carrier slurry in the embodiments of the present application further includes a promoter, which is a rare earth element compound. Specifically, the rare earth element compound includes at least one of cerium oxide, zirconium oxide, lanthanum oxide, praseodymium oxide, yttrium oxide, or neodymium oxide.

[0044] In an optional solution of the embodiment of the present application, before applying the second coating step, a mixed slurry of a catalyst precursor and activated carbon is prepared. The preparation of the mixed slurry includes:

[0045] A catalyst precursor, activated carbon powder, a dispersant, and a second solvent are mixed to form a mixed slurry. The concentration of the catalyst precursor is designed based on the catalyst's functional requirements, and its absolute weight is 0.1g-15g, for example, 0.1g, 1g, 3g, 5g, 7g, 10g, 12g, or 15g. The activated carbon powder accounts for 85%-95% of the mixed slurry, and the dispersant accounts for 1%-5% of the mixed slurry.

[0046] The dispersant is polyvinyl alcohol or ethoxylated alkylphenol. The second solvent is water or ethanol. The active component of the catalyst can be one or a combination of two or more of the precious metals platinum, palladium, or rhodium. The loading is 1-50 g / cft to ensure the capture efficiency and oxidative removal capacity of the precious metals for PM. Examples include 1 g / cft, 5 g / cft, 10 g / cft, 20 g / cft, 30 g / cft, 40 g / cft, or 50 g / cft.

[0047] In some optional embodiments, the mixed slurry further includes a pH regulator, specifically, the pH regulator can be ammonia water or acetic acid. The pH regulator is used to adjust the pH of the mixed slurry to be between 7 and 9.

[0048] In an optional solution of the embodiment of the present application, the loading amount of the first coating layer is 5-20 g / L, the loading amount of the second coating layer is 3-10 g / L, and the total loading amount of the first coating layer and the second coating layer is 5-100 g / L.

[0049] The material of the DPF carrier in this application is wall-flow cordierite or silicon carbide honeycomb material, which can be a symmetrical or asymmetrical structure. In the initial state, the filtration efficiency of the DPF is very low.

[0050] Figure 2 A schematic diagram of the initial state of a DPF coating structure provided in an embodiment of the present application, referring to Figure 2 The DPF coating structure obtained by the preparation method in the embodiment of the present application, wherein the second coating layer 300 is an activated carbon layer 320 containing a catalyst precursor 310. The activated carbon has good adsorption properties and can improve the PM capture efficiency of the DPF 100. At the same time, the catalyst precursor 310 cannot directly contact the catalyst carrier 210, and the catalyst is in a dormant state, thereby inhibiting the passive regeneration of the DPF 100 and avoiding the consumption of the activated carbon by the passive regeneration, thereby making the DPF 100 in the initial state have a higher filtration efficiency and avoiding the problem of excessive PM emissions in the random inspection of new vehicles.

[0051] Figure 3 A schematic diagram of a DPF coating structure after active regeneration of the DPF provided in an embodiment of the present application, referring to Figure 3After the vehicle has run 2,000 to 3,000 kilometers, active regeneration is manually triggered, the activated carbon in the second coating 300 is burned and consumed, part of the catalyst precursor 310 is transferred to the first coating 200 and reacts with the catalyst carrier 210, the catalyst is activated, and the catalyst catalytically oxidizes PM, thereby improving the filtration efficiency of DPF 100. As the carbon layer accumulates, passive regeneration also occurs in DPF 100. As active regeneration and passive regeneration accumulate, the catalyst is fully activated. At the same time, as DPF 100 is used, the ash generated by the engine enters DPF 100 and is deposited. The ash cannot be regenerated and burned, which helps to improve the PM filtration efficiency. Therefore, the DPF 100 in this application will have a very high PM filtration efficiency after running for a period of time.

[0052] The DPF coating structure and preparation method thereof in this application will be further described in detail below with reference to specific embodiments and comparative examples.

[0053] Example 1

[0054] This embodiment is a DPF coating structure, which includes a first coating coated on the DPF surface and a second coating coated on the surface of the first coating, the first coating includes aluminum oxide, and the second coating is an activated carbon layer containing precious metals Pt and Pd; the median pore diameter of the DPF carrier is 11.5μm.

[0055] The preparation method of the above-mentioned DPF coating structure comprises the following steps:

[0056] S1: Al2O3, silica gel, aluminum gel and polyvinyl alcohol are mixed with water to obtain an aluminum oxide slurry, wherein the solid content of Al2O3 accounts for 85% of the total mass of the slurry, the mass of silica gel and aluminum gel accounts for 3% of the total mass of the slurry, and the mass of polyvinyl alcohol accounts for 2% of the total mass of the slurry;

[0057] S2: applying an alumina slurry to the surface of the DPF, wherein the first drying temperature is 200° C. and the first calcination temperature is 600° C., and after the first drying and first calcination, a DPF coated with an alumina coating is obtained;

[0058] S3: Platinum nitrate, activated carbon powder, ethoxylated alkylphenol and water are mixed to obtain a mixed slurry, and ammonia water is added to adjust the pH thereof to 7; wherein the platinum loading is 3 g / cft, the mass of the added platinum nitrate is calculated based on the precious metal content in the solid, the mass of the activated carbon powder accounts for 90% of the total mass of the coating solid, and the mass of the ethoxylated alkylphenol accounts for 1%-5% of the total mass of the slurry.

[0059] S4: coating the mixed slurry on the surface of the alumina coating, drying the mixture at room temperature for the second time, and calcining the mixture at 280° C. to obtain a DPF coating structure after drying the mixture at room temperature and calcining the mixture for the second time.

[0060] Figure 4 This is an electron microscope image of the DPF coating structure in Example 1 of the present application, referring to Figure 4 The DPF coating structure in Example 1 includes a double-layer coating structure, the first coating is a catalyst support layer coated on the DPF surface, and the second coating is an activated carbon layer coated on the catalyst support layer.

[0061] Comparative Example 1

[0062] This comparative example is a DPF coating structure, wherein the median pore size of the DPF substrate is 11.5 μm. The DPF coating structure comprises a single coating applied to the surface of the DPF. The specific preparation method thereof comprises the following steps:

[0063] S1: mixing platinum, rhodium, palladium noble metal solutions and activated alumina to obtain a mixed solution with a weight fraction of 30-70%;

[0064] S2: adding 25-60% by weight of a rare earth solution to the above mixed solution, then adding 1-5% by weight of aluminum gel and 1-5% by weight of a rare earth nitrate, and stirring for 6 hours to form a slurry;

[0065] S3: After the slurry is coated on the DPF wall, the coated honeycomb support ceramic is placed in a kiln at 550° C. and fired for 3-5 hours to obtain the DPF coating structure in Comparative Example 1.

[0066] Figure 5 This is an electron microscope image of the DPF coating structure in comparative example 1 of this application, refer to Figure 5 , the DPF coating structure in Comparative Example 1 is a single-layer coating structure.

[0067] The DPFs in Example 1 and Comparative Example 1 were subjected to PN emission tests, and the test results are listed in Table 1.

[0068] Table 1

[0069]

[0070] Referring to the data in Table 1, the PN emission value of the DPF in Example 1 is significantly lower than that of the comparative example 1, indicating that the DPF with a double-layer coating structure in the embodiment of the present application can significantly improve the PN filtration efficiency.

[0071] Obviously, those skilled in the art may make various changes and modifications to the embodiments of the present application without departing from the spirit and scope of the present application. Thus, if such modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include such modifications and variations.

Claims

1. A DPF coating structure, characterized in that: The method comprises a first coating layer applied on the surface of the DPF and a second coating layer applied on the surface of the first coating layer, wherein the first coating layer comprises a catalyst carrier and the second coating layer is an activated carbon layer containing a catalyst precursor; The catalyst precursor is a noble metal precursor or a non-noble metal precursor; The noble metal precursor includes at least one of ethanolamine hydroxyplatinum, tetraammonium nitrosoplatinum, platinum nitrate, chloroplatinic acid, palladium nitrate, palladium acetate, palladium chloride, rhodium nitrate and rhodium acetate; The non-noble metal precursor is cesium Precursors of vanadium-based non-noble metal catalysts; The catalyst carrier comprises at least one of aluminum oxide, silicon oxide, titanium oxide, zirconium oxide and molecular sieve; In the initial state, the catalyst precursor cannot directly contact the carrier and is not activated. After a period of time, the activated carbon layer burns, and part of the catalyst precursor is transferred to the first coating layer and reacts with the catalyst carrier, and the catalyst is activated.

2. A method for preparing a DPF coating structure according to claim 1, characterized in that: The steps include: Applying a first coating layer: applying a slurry containing the catalyst support to the surface of the DPF, and obtaining a DPF coated with the first coating layer after a first drying and a first calcination, wherein the temperature of the first calcination is 550° C.-650° C.; Applying the second coating layer: applying the mixed slurry of the catalyst precursor and activated carbon on the surface of the first coating layer, and obtaining the DPF coating structure after a second drying, wherein the second drying is drying at room temperature.

3. The preparation method according to claim 2, characterized in that Before the step of applying the first coating layer, a slurry containing a catalyst carrier is prepared. The slurry containing the catalyst carrier is prepared including: The catalyst support, the binder and the surfactant are mixed with the first solvent to obtain a slurry containing the catalyst support.

4. The preparation method according to claim 3, characterized in that The slurry containing the catalyst carrier also includes a promoter, which is a compound of a rare earth element.

5. The preparation method according to claim 2, characterized in that Before applying the second coating step, a mixed slurry of the catalyst precursor and activated carbon is prepared, and the mixed slurry is prepared including: The catalyst precursor, activated carbon powder, dispersant and the second solvent are mixed to obtain the mixed slurry.

6. The preparation method according to claim 2, characterized in that The particle size of the activated carbon is 1um-50um.

7. The preparation method according to any one of claims 2 to 6, characterized in that The loading amount of the first coating layer is 5-20 g / L, the loading amount of the second coating layer is 1-10 g / L, and the total loading amount of the first coating layer and the second coating layer is 5-100 g / L.

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