CN111514922B - DPF catalyst with better dispersity and preparation method thereof - Google Patents

DPF catalyst with better dispersity and preparation method thereof Download PDF

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CN111514922B
CN111514922B CN202010384153.6A CN202010384153A CN111514922B CN 111514922 B CN111514922 B CN 111514922B CN 202010384153 A CN202010384153 A CN 202010384153A CN 111514922 B CN111514922 B CN 111514922B
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coating
noble metal
carrier
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solution
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CN111514922A (en
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柯峰
纪坤鹏
莫俊杰
王刚
张元�
王秀庭
岳军
贾莉伟
徐岘
王家明
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Wuxi Weifu Environmental Protection Catalyst Co Ltd
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
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    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/42—Platinum
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
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    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
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    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
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    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/20—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state
    • B01J35/23—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state in a colloidal state
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0215—Coating
    • B01J37/0228—Coating in several steps
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts

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Abstract

The invention relates to a DPF catalyst with better dispersion and a preparation method thereof, and the DPF catalyst comprises a carrier and a coating coated on the carrier, wherein the coating is loaded with noble metal, the coating amount of the noble metal is 0.10-1.10 g/L, and the coating amount of a coating material is 5-30g/L; the noble metal is one or two of Pt and Pd, the coating material contains gamma-alumina, and the coating material also contains SiO 2 、CeO 2 、ZrO 2 、TiO 2 And a molecular sieve. The preparation method comprises the following steps: preparing coating slurry, ball-milling the coating slurry, preparing a noble metal solution, adding the noble metal solution, coating the noble metal slurry, drying water in the carrier, drying a reducing agent in the carrier and roasting the carrier. The DPF catalyst prepared by the method has smaller particle size of active components, is uniformly distributed, and has better activity after being subjected to higher working temperature compared with the catalyst prepared by the conventional impregnation method.

Description

DPF catalyst with better dispersity and preparation method thereof
Technical Field
The invention belongs to the technical field of catalyst preparation, and particularly relates to a DPF catalyst with better dispersity and a preparation method thereof.
Background
The current diesel wall-flow particulate trap (DPF) and its system have become the conventional solutions to meet the emission regulation for diesel Particulate (PM) restriction, and are indispensable components in the diesel vehicle exhaust treatment system. The DPF catalyst is generally used in a downstream of a catalyst such as a Diesel Oxidation Catalyst (DOC). Through the special wall-flow structure, the separation of PM and air flow in the tail gas of the diesel engine is realized. If the exhaust temperature is high enough, the catalyst coating coated on the DPF is contacted with PM, so that the particulate matters are continuously subjected to passive regeneration and are catalytically converted into harmless gases. Or active regeneration is carried out, namely fuel oil is sprayed on the DOC in a mode of in-cylinder post-injection and the like, and PM in the DPF catalyst is catalytically oxidized and converted into harmless gas through high temperature generated by catalytic oxidation of the fuel oil on the DOC.
A method commonly used for manufacturing a DPF catalyst is called an impregnation method. The method mainly comprises the steps of adding a precursor (compound of precious metals such as platinum, palladium and the like) containing active components of the catalyst (simple substances of precious metals such as platinum, palladium and the like, and precious metal monomer particles such as oxides or alloys and the like) into coating material slurry with a high specific surface area, adding a dispersing agent to ensure that the active components of the catalyst are uniformly distributed in the slurry, then coating the slurry on a wall-flow carrier which is made of materials such as cordierite, silicon carbide (SiC) or Aluminum Titanate (AT) and has a microporous structure and a large specific surface area, drying moisture in the carrier, roasting to decompose the precursor, and uniformly distributing the active components of the catalyst on the surface of the carrier.
In the case where the wall flow type carrier has a certain specific surface area, the amount of the noble metal slurry applied may have a large influence on the dispersing effect of the catalyst active component. Under the condition of small coating amount, the dispersion degree of the active component is still enough; if the coating amount is large, the particle size distribution of the active ingredient becomes broad, and the particle size as a whole increases, resulting in a significant decrease in its dispersion. Under the high-temperature condition during PM regeneration, active components on the surface of the catalyst prepared by the impregnation method are more easily agglomerated, and the catalytic activity of the catalyst is reduced along with the agglomeration.
The amount of noble metal used may be increased to ensure the activity of the catalyst. The high price of the noble metal will increase the manufacturing cost of the catalyst, which is completely against the requirement of practical application. Then, it is considered how to reduce the particle size of the active component of the catalyst, distribute it more uniformly, and slow down the agglomeration process after undergoing the high temperature of the DPF catalyst in operation by improving the preparation method while ensuring the coating amount. There is a continuing need for improved coating of DPF catalysts and techniques for their application to extend their useful life.
Disclosure of Invention
One of the objects of the present invention is to overcome the disadvantages of the prior art and to provide a DPF catalyst having better dispersion of noble metals, thereby slowing down the agglomeration of active components of the catalyst caused by high temperature occurring when the DPF catalyst treats particulate matter.
Another object of the present invention is to provide a method for preparing a DPF catalyst having a better dispersion.
According to the technical scheme provided by the invention, the DPF catalyst with better dispersion degree comprises a carrier and a coating coated on the carrier, wherein the coating is loaded with noble metals, the coating amount of the noble metals is 0.10-1.10 g/L, and the coating amount of a coating material is 5-30 g/L; the noble metal is one or two of Pt and Pd, the coating material contains gamma-alumina, and the coating material also contains SiO 2 、CeO 2 、ZrO 2 、TiO 2 And a molecular sieve.
Preferably, when the noble metal is Pt and Pd, the mass ratio of the noble metal Pt to the noble metal Pd is 1 to 99.
Preferably, in the coating material, the mass ratio of the gamma-alumina to other substances is 2 to 99.
Preferably, the carrier is cordierite, siC or AT, and the mesh number of the carrier is 200-350 meshes.
The preparation method of the DPF catalyst with better dispersity comprises the following steps:
(1) Preparation of coating slurry: respectively weighing gamma-alumina and SiO according to the coating amount of the slurry which is determined in advance 2 、CeO 2 、ZrO 2 、TiO 2 Mixing at least one of the molecular sieves according to the mass ratio of gamma-alumina to other substances of 2-99;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 Is 2 to 20 μm;
(3) Preparing a noble metal solution: measuring a corresponding noble metal precursor solution according to the predetermined noble metal dosage, dropwise adding polyalcohol serving as a reducing agent into the noble metal precursor solution, and fully and uniformly stirring to ensure that noble metal monomer particles are fully reduced;
(4) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 4-8 h, and adding nitric acid to adjust the pH value to be below 7.0;
(5) Coating of noble metal slurry: quantitatively coating the prepared noble metal slurry on the wall flow type carrier by using a special quantitative coating special machine according to the determined slurry coating amount;
(6) Drying moisture in the carrier: putting the coated carrier into an oven, and drying at 70-80 ℃ for 3-4 h to dry the moisture in the carrier;
(7) Drying a reducing agent in the carrier: raising the temperature of the oven, and drying the polyol in the carrier at a temperature lower than the boiling point of the polyol;
(8) Roasting of the carrier: and (3) roasting the carrier at the temperature of 550-600 ℃ for 3-6 h by raising the temperature of the oven, and obtaining the DPF catalyst after roasting.
Preferably, in the step (2), after the ball milling of the coating slurry is finished, 10g of the coating slurry is put into a small crucible, the crucible is dried at 120 ℃ for 30min, then is transferred into a muffle furnace at 550-600 ℃ to be roasted for 10-20 min, and is cooled to room temperature, the mass of the powder is weighed, and the solid content of the coating slurry is measured by dividing the mass of the powder by 10 g.
Preferably, in the step (3), the polyol used as the reducing agent is one or more of ethylene glycol, polyethylene glycol and polyalkylene glycol.
Preferably, in the step (4), the auxiliary agent for adjusting the coating slurry is nitric acid, and the pH is adjusted to 6.0 or less.
Preferably, the precursor solution of the noble metal Pt is a platinum nitrate solution or Pt (NH) 3 ) 2 (NO 2 ) 2 Solution or [ Pt (NH) ] 3 ) 4 ](OH) 2 And (3) solution.
Preferably, the precursor solution of the noble metal Pd is a palladium nitrate solution or Pd (NH) 3 ) 2 (NO 2 ) 2 Solution or [ Pd (NH) ] 3 ) 4 ](OH) 2 And (3) solution.
The present invention provides a method for manufacturing a DPF catalyst having a better dispersion degree. Compared with the common impregnation method, the method has the advantages of better noble metal dispersibility, better catalytic performance, lower comprehensive cost, longer service life and the like.
The impregnation method is to add a dispersant, such as carboxymethyl cellulose, polyvinylpyrrolidone, etc., in order to prevent agglomeration of the reduced noble metal monomer particles when processing the noble metal precursor solution. The macromolecules of the dispersing agent can form sol with protection function, and the noble metal monomer particles are wrapped in the sol to keep a certain distance from each other in a liquid phase, so that the noble metal monomer particles are prevented from agglomerating due to higher surface energy of the noble metal monomer particles.
In the method, no additional dispersant is needed. Instead, the polyol is used as a reducing agent to uniformly reduce the monomer particles of the noble metal in the liquid phase onto the coating material. After the slurry of the coating material is applied to the wall-flow support, the water is first dried and the polyol is then evaporated at a temperature close to the boiling point of the polyol used. Finally, the coating material is fixed on the wall flow type carrier through roasting, so that the uniform distribution of the precious metal monomer particles is maintained. The whole drying and roasting process can be completed in the same equipment, and only the required temperature and duration time need to be controlled by a program.
The DPF catalyst prepared by the method has smaller particle size of active components, is uniformly distributed, and has better activity after being subjected to higher working temperature compared with the catalyst prepared by the conventional impregnation method. And the preparation process is similar to the common dipping method. When the method is put into large-scale production, the production can be directly carried out without equipment investment or process change.
Drawings
FIG. 1 is a TEM scan of the fresh state of example 1 of the present invention.
FIG. 2 is a TEM scan of the fresh state of comparative example 1.
FIG. 3 is a TEM scan of example 1 of the present invention after aging.
FIG. 4 is a TEM scan of comparative example 1 after aging.
Figure 5 is an XRD pattern of the fresh state of example 2 of the present invention and comparative example 2.
Figure 6 is an XRD pattern after aging of example 2 of the present invention and comparative example 2.
FIG. 7 is a graph showing fresh state activity evaluation performance in example 8 of the present invention.
Detailed Description
The present invention will be further described with reference to the following specific examples.
Example 1
A DPF catalyst with better dispersity is prepared from Pt as noble metal and the coating amount of noble metal is 1.10g/L. The coating material used is a coating material containing SiO 2 Gamma-alumina, molecular sieves; quality of gamma-alumina and SiO 2 Compared with the added mass of the molecular sieve, the ratio is 29. The reducing agent used was ethylene glycol. Make it possible toThe carrier used was SiC, with a volume of 3.08L and a pore density of 350 mesh/square foot.
A preparation method of a DPF catalyst with better dispersity comprises the following steps:
(1) Preparing coating slurry: according to the mass of gamma-alumina and SiO 2 The mass ratio of the molecular sieve phase 29, siO contained by each weight 2 Adding deionized water into the gamma-alumina and the molecular sieve which are 300g in total to prepare coating slurry, and fully and uniformly stirring the slurry;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 2.2 mu m, after ball milling, taking 10g of coating slurry into a small crucible, placing the crucible in a muffle furnace at 120 ℃ for drying for 30min, then transferring the crucible to a muffle furnace at 600 ℃ for roasting for 10min, cooling to room temperature, weighing the powder mass, and dividing the powder mass by 10g to obtain the coating slurry with the solid content of about 25%;
(3) Preparation of noble metal solution: according to the total amount of platinum of 11g, measuring a corresponding platinum nitrate solution, dropwise adding ethylene glycol serving as a reducing agent into the solution, and fully and uniformly stirring.
(4) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 7h, and adding nitric acid to adjust the pH value to be below 7.0.
(5) Coating of noble metal slurry: and quantitatively coating the prepared precious metal slurry on the wall flow type carrier by using a special quantitative coating special machine according to the determined slurry coating amount of 30g/L.
(6) Drying moisture in the carrier: and (3) putting the coated carrier into an oven, adjusting the temperature to 80 ℃, and drying for 4 hours to dry the moisture in the carrier.
(7) Drying a reducing agent in the carrier: and raising the temperature of the oven to 170 ℃, and drying for 2h to dry the glycol in the carrier.
(8) Roasting of the carrier: and raising the temperature of the oven to 600 ℃, roasting for 3h, and roasting the carrier to obtain the DPF catalyst.
The noble metal slurry for coating on the carrier in the step (5) was taken out 20g into another small crucible and subjected to the steps (6), (7), (8) as well, to be made into a catalyst powder for detection.
Example 2
A DPF catalyst with better dispersity is prepared from Pd as noble metal through coating noble metal by 0.90g/L. The coating materials used are gamma-alumina and CeO 2 And ZrO 2 The composite oxide and the molecular sieve of (4); mass of gamma-alumina and CeO 2 、ZrO 2 Compared with the mass of the molecular sieve phase, the ratio is 39. The reducing agent used was ethylene glycol. The carrier used was SiC, with a volume of 3.08L and a pore density of 350 mesh/square foot.
A preparation method of a DPF catalyst with better dispersity comprises the following steps:
(1) Preparing coating slurry: according to the mass of the gamma-alumina and CeO 2 、ZrO 2 And the added mass ratio of the molecular sieve 39, gamma-alumina and CeO were weighed respectively 2 And ZrO 2 Adding deionized water into the composite oxide and the molecular sieve to prepare coating slurry, and fully and uniformly stirring the coating slurry;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 The particle size is 2.3 mu m, 10g of coating slurry is taken to be put into a small crucible after ball milling, the crucible is placed at 120 ℃ and dried for 30min, then the crucible is transferred to a 600 ℃ muffle furnace to be roasted for 10min, the temperature is cooled to room temperature, the mass of the powder is weighed, and the solid content of the coating slurry is measured to be about 25 percent by dividing the mass of the powder by 10 g;
(3) Preparing a noble metal solution: according to the condition that the total amount of palladium is 9g, measuring a corresponding palladium nitrate solution, dropwise adding glycol serving as a reducing agent into the solution, and fully and uniformly stirring.
(4) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 6h, and adding nitric acid to adjust the pH value to be below 7.0.
(5) Coating of noble metal slurry: and quantitatively coating the prepared precious metal slurry on the wall flow type carrier by using a special quantitative coating special machine according to the determined slurry coating amount of 25g/L.
(6) Drying moisture in the carrier: and (3) putting the coated carrier into an oven, adjusting the temperature to 80 ℃, and drying for 4h to dry the moisture in the carrier.
(7) Drying a reducing agent in the carrier: and raising the temperature of the oven to 170 ℃, and drying for 2h to dry the glycol in the carrier.
(8) Roasting of the carrier: and raising the temperature of the oven to 600 ℃, roasting for 3h, and roasting the carrier to obtain the DPF catalyst.
The noble metal slurry for coating on the carrier in the step (5) was taken out 20g into another small crucible and subjected to the same steps (6), (7), (8) to prepare a catalyst powder for detection.
Example 3
A DPF catalyst with better dispersity is prepared from Pt as noble metal and the coating amount of noble metal is 0.70g/L. The used coating materials are gamma-alumina, molecular sieve and titanium dioxide; mass of gamma-alumina and TiO 2 Compared with the added mass of the molecular sieve, the ratio is 99. The reducing agent is polyethylene glycol with molecular weight of 2000-20000. The support used was AT, with a volume of 3.08L and a pore density of 300 mesh/sq ft.
A preparation method of a DPF catalyst with better dispersity comprises the following steps:
(1) Preparing coating slurry: according to the mass of gamma-alumina and TiO 2 Respectively weighing 200g of gamma-alumina, the molecular sieve and titanium dioxide in a total mass ratio of 99;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 The particle size is 6.9 mu m, 10g of coating slurry is taken to be put into a small crucible after ball milling, the crucible is placed at 120 ℃ and dried for 30min, then the crucible is transferred to a 600 ℃ muffle furnace to be roasted for 10min, the temperature is cooled to room temperature, the mass of the powder is weighed, and the solid content of the coating slurry is measured to be about 25 percent by dividing the mass of the powder by 10 g;
(3) Noble metal dissolving devicePreparation of liquid: measuring corresponding Pt (NH) according to the total amount of the platinum being 7g 3 ) 2 (NO 2 ) 2 And (3) adding polyethylene glycol serving as a reducing agent into the solution dropwise, and fully and uniformly stirring.
(4) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 5h, and adding nitric acid to adjust the pH value to be below 7.0.
(5) Coating of noble metal slurry: and quantitatively coating the prepared precious metal slurry on the wall flow type carrier by using a special quantitative coating special machine according to the determined slurry coating amount of 20g/L.
(6) Drying moisture in the carrier: and (3) putting the coated carrier into an oven, adjusting the temperature to 80 ℃, and drying for 3 hours to dry the moisture in the carrier.
(7) Drying a reducing agent in the carrier: the temperature of the oven is raised to 170 ℃ and the carrier is dried for 1.5h to dry the polyethylene glycol in the carrier.
(8) Roasting of the carrier: and raising the temperature of the oven to 600 ℃, roasting for 3h, and roasting the carrier to obtain the DPF catalyst.
The noble metal slurry for coating on the carrier in the step (5) was taken out 20g into another small crucible and subjected to the same steps (6), (7), (8) to prepare a catalyst powder for detection.
Example 4
A DPF catalyst with better dispersity is prepared by using platinum and palladium as noble metals, wherein the mass ratio of the platinum to the palladium is 99. The coating material used is a coating material containing SiO 2 Gamma-alumina, titanium dioxide; quality of gamma-alumina and SiO 2 、TiO 2 The ratio of the added mass ratios is 1.5. The reducing agent is polyethylene glycol with molecular weight of 2000-20000. The carrier used was cordierite, with a volume of 8.2L and a pore density of 200 mesh/sq ft.
A preparation method of a DPF catalyst with better dispersity comprises the following steps:
(1) Preparation of coating slurry: according to the mass of gamma-alumina and SiO 2 、TiO 2 1.5, siO-containing material was weighed in a ratio of 1.5 2 Adding deionized water into the gamma-alumina and the titanium dioxide of 300g in total to prepare coating slurry, and fully and uniformly stirring the slurry;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 The particle size is 12.5 mu m, 10g of coating slurry is taken to be put into a small crucible after ball milling, the crucible is placed at 120 ℃ and dried for 30min, then the crucible is transferred to a 600 ℃ muffle furnace to be roasted for 10min, the temperature is cooled to room temperature, the mass of the powder is weighed, and the solid content of the coating slurry is measured to be about 25 percent by dividing the mass of the powder by 10 g;
(3) Preparation of noble metal solution: according to the condition that the total amount of platinum and palladium is 10g and the mass ratio of the platinum to the palladium is 99 3 ) 2 (NO 2 ) 2 And Pd (NH) 3 ) 2 (NO 2 ) 2 And (3) adding polyethylene glycol serving as a reducing agent into the solution dropwise, and fully and uniformly stirring.
(4) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 8h, and adding nitric acid to adjust the pH value to be below 7.0.
(5) Coating of noble metal slurry: and quantitatively coating the prepared precious metal slurry on the wall flow type carrier by using a special quantitative coating special machine according to the determined slurry coating amount of 15g/L.
(6) Drying moisture in the carrier: and (3) putting the coated carrier into an oven, adjusting the temperature to 70 ℃, and drying for 4h to dry the moisture in the carrier.
(7) Drying a reducing agent in the carrier: and raising the temperature of the oven to 170 ℃, and drying for 2 hours to dry the polyethylene glycol in the carrier.
(8) Roasting the carrier: and raising the temperature of the oven to 600 ℃, roasting for 6 hours, and roasting the carrier to obtain the DPF catalyst.
The noble metal slurry for coating on the carrier in the step (5) was taken out 20g into another small crucible and subjected to the same steps (6), (7), (8) to prepare a catalyst powder for detection.
Example 5
The DPF catalyst with better dispersity uses platinum and palladium as noble metals, the mass ratio of the platinum to the palladium is 4:1, and the coating amount of the noble metals is 0.10g/L. The coating material used is a coating material containing SiO 2 Gamma-alumina of (a); mass of gamma-alumina and SiO 2 Compared with the mass ratio of 19, the coating amount is 5g/L. The reducing agent used is a polyalkylene glycol having a molecular weight of 2000-20000. The carrier used was cordierite, with a volume of 8.2L and a pore density of 200 mesh/sq ft.
A preparation method of a DPF catalyst with better dispersity comprises the following steps:
(1) Preparing coating slurry: weighing contains 5% by weight of SiO 2 Adding deionized water into 200g of gamma-alumina to prepare coating slurry, and fully and uniformly stirring;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 The particle size is 12.8 mu m, 10g of coating slurry is taken to be put into a small crucible after ball milling, the crucible is placed at 120 ℃ and dried for 30min, then the crucible is transferred to a muffle furnace at 550 ℃ and roasted for 20min, the temperature is cooled to room temperature, the mass of the powder is weighed, and the solid content of the coating slurry is measured to be about 25 percent by dividing the mass of the powder by 10 g;
(3) Preparation of noble metal solution: measuring corresponding [ Pt (NH) according to the mass ratio of 4:1 of the total amount of 4g of platinum and palladium 3 ) 4 ](OH) 2 And [ Pd (NH) ] 3 ) 4 ](OH) 2 And (3) adding the polyalkylene glycol serving as a reducing agent into the solution dropwise, and fully and uniformly stirring.
(4) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 6h, and adding nitric acid to adjust the pH value to be below 7.0.
(5) Coating of noble metal slurry: and quantitatively coating the prepared precious metal slurry on the wall flow type carrier by using a special quantitative coating special machine according to the determined slurry coating amount of 5g/L.
(6) Drying moisture in the carrier: and (3) putting the coated carrier into an oven, adjusting the temperature to 70 ℃, and drying for 4h to dry the moisture in the carrier.
(7) Drying a reducing agent in the carrier: the temperature of the oven is raised to 180 ℃ and dried for 2h to dry the polyalkylene glycol in the carrier.
(8) Roasting the carrier: and raising the temperature of the oven to 550 ℃, roasting for 6 hours, and roasting the carrier to obtain the DPF catalyst.
The noble metal slurry for coating on the carrier in the step (5) was taken out 20g into another small crucible and subjected to the same steps (6), (7), (8) to prepare a catalyst powder for detection.
Example 6
The DPF catalyst with better dispersity uses platinum and palladium as noble metals, the mass ratio of the platinum to the palladium is 3:1, and the coating amount of the noble metals is 0.35g/L. The coating materials used are gamma-alumina and CeO 2 And ZrO 2 A composite oxide of (a); mass of gamma-alumina and CeO 2 、ZrO 2 The ratio of the added masses was 2:1 and the coating application was 10g/L. The reducing agent is ethylene glycol with molecular weight of 2000-20000. The support used was AT, with a volume of 3.3L and a pore density of 300 mesh/sq ft.
A preparation method of a DPF catalyst with better dispersity comprises the following steps:
(1) Preparing coating slurry: according to the mass of the gamma-alumina and CeO 2 、ZrO 2 The added mass ratio of 2:1, gamma-alumina and CeO were weighed separately 2 And ZrO 2 Adding deionized water into the total amount of 200g of the composite oxide to prepare coating slurry, and fully and uniformly stirring the coating slurry;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 The particle size is 7.2 mu m, 10g of coating slurry is taken to be put into a small crucible after ball milling, the crucible is placed at 120 ℃ and dried for 30min, then the crucible is transferred to a 600 ℃ muffle furnace to be roasted for 10min, the temperature is cooled to room temperature, the mass of the powder is weighed, and the solid content of the coating slurry is measured to be about 25 percent by dividing the mass of the powder by 10 g;
(3) Preparation of noble metal solution: according to the method, corresponding platinum nitrate and palladium nitrate solutions are measured according to the condition that the total amount of platinum and palladium is 10g and the mass ratio of platinum to palladium is 3:1, ethylene glycol serving as a reducing agent is dropwise added into the solutions, and the solutions are fully and uniformly stirred.
(4) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 4h, and adding nitric acid to adjust the pH value to be below 7.0.
(5) Coating of noble metal slurry: and quantitatively coating the prepared precious metal slurry on the wall flow type carrier by using a special quantitative coating special machine according to the determined slurry coating amount of 10g/L.
(6) Drying moisture in the carrier: and (3) putting the coated carrier into an oven, adjusting the temperature to 80 ℃, and drying for 3h to dry the moisture in the carrier.
(7) Drying a reducing agent in the carrier: and raising the temperature of the oven to 170 ℃, and drying for 1h to dry the glycol in the carrier.
(8) Roasting of the carrier: and raising the temperature of the oven to 600 ℃, roasting for 4 hours, and roasting the carrier to obtain the DPF catalyst.
The noble metal slurry for coating on the carrier in the step (5) was taken out 20g into another small crucible and subjected to the same steps (6), (7), (8) to prepare a catalyst powder for detection.
Example 7
The DPF catalyst with better dispersity uses platinum and palladium as noble metals, the mass ratio of the platinum to the palladium is 1:1, and the coating amount of the noble metals is 0.35g/L. The coating material used is gamma-alumina, zrO 2 (ii) a Mass of gamma-alumina and ZrO 2 The ratio of the mass of the coating to the mass of the coating is 9:1, and the coating application amount is 10g/L. The reducing agent is ethylene glycol with molecular weight of 2000-20000. The support used was AT, with a volume of 3.3L and a pore density of 300 mesh/sq ft.
A preparation method of a DPF catalyst with better dispersity comprises the following steps:
(1) Preparation of coating slurry: according to the mass of gamma-alumina and ZrO 2 9:1, gamma-alumina and ZrO were weighed separately 2 In the total amount of 200g of the mixture,adding deionized water to prepare coating slurry, and fully and uniformly stirring;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 The particle size is 6.8 mu m, 10g of coating slurry is taken to be put into a small crucible after ball milling, the crucible is placed at 120 ℃ and dried for 30min, then the crucible is transferred to a 600 ℃ muffle furnace to be roasted for 10min, the temperature is cooled to room temperature, the mass of the powder is weighed, and the solid content of the coating slurry is measured to be about 25 percent by dividing the mass of the powder by 10 g;
(3) Preparing a noble metal solution: according to the method, corresponding platinum nitrate and palladium nitrate solutions are measured according to the condition that the total amount of platinum and palladium is 10g and the mass ratio of platinum to palladium is 1:1, ethylene glycol serving as a reducing agent is dropwise added into the solutions, and the solutions are fully and uniformly stirred.
(4) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 4h, and adding nitric acid to adjust the pH value to be below 7.0.
(5) Coating of noble metal slurry: and quantitatively coating the prepared precious metal slurry on the wall flow type carrier by using a special quantitative coating special machine according to the determined slurry coating amount of 10g/L.
(6) Drying moisture in the carrier: and (3) putting the coated carrier into an oven, adjusting the temperature to 80 ℃, and drying for 3h to dry the moisture in the carrier.
(7) Drying a reducing agent in the carrier: and raising the temperature of the oven to 170 ℃, and drying for 1h to dry the glycol in the carrier.
(8) Roasting of the carrier: and raising the temperature of the oven to 600 ℃, roasting for 4 hours, and roasting the carrier to obtain the DPF catalyst.
The noble metal slurry for coating on the carrier in the step (5) was taken out 20g into another small crucible and subjected to the same steps (6), (7), (8) to prepare a catalyst powder for detection.
Example 8
A DPF catalyst with better dispersity is prepared from platinum and palladium as noble metals, the mass ratio of the platinum to the palladium is 1.5. The coating material used is a coating material containingWith SiO 2 Of (2) gamma-alumina, ceO 2 A molecular sieve; mass of gamma-alumina and SiO 2 、CeO 2 Compared with the added mass of the molecular sieve, the ratio is 2.5. The reducing agent is ethylene glycol with molecular weight of 2000-20000. The carrier used was SiC, with a volume of 3.3L and a pore density of 350 mesh/square foot.
A preparation method of a DPF catalyst with better dispersity comprises the following steps:
(1) Preparing coating slurry: according to the mass of gamma-alumina and SiO 2 、CeO 2 The mass ratio of the molecular sieve addition was 2.5, and SiO-containing components were weighed 2 Of (2) gamma-alumina, ceO 2 Adding deionized water into the total amount of 200g of molecular sieve to prepare coating slurry, and fully and uniformly stirring the coating slurry;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 The particle size is 2.1 mu m, 10g of coating slurry is taken to be put into a small crucible after ball milling, the crucible is placed at 120 ℃ and dried for 30min, then the crucible is transferred to a 600 ℃ muffle furnace to be roasted for 10min, the temperature is cooled to room temperature, the mass of the powder is weighed, and the solid content of the coating slurry is measured to be about 25 percent by dividing the mass of the powder by 10 g;
(3) Preparation of noble metal solution: according to the method, according to the condition that the total amount of platinum and palladium is 10g and the mass ratio of platinum to palladium is 1.5.
(4) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 4 hours, and adding nitric acid to adjust the pH value to be below 7.0.
(5) Coating of noble metal slurry: and quantitatively coating the prepared precious metal slurry on the wall flow type carrier by using a special quantitative coating special machine according to the determined slurry coating amount of 10g/L.
(6) Drying moisture in the carrier: and (3) putting the coated carrier into an oven, adjusting the temperature to 80 ℃, and drying for 3 hours to dry the moisture in the carrier.
(7) Drying a reducing agent in the carrier: and raising the temperature of the oven to 170 ℃, and drying for 1h to dry the glycol in the carrier.
(8) Roasting of the carrier: and raising the temperature of the oven to 600 ℃, roasting for 4 hours, and roasting the carrier to obtain the DPF catalyst.
The noble metal slurry for coating on the carrier in the step (5) was taken out 20g into another small crucible and subjected to the steps (6), (7), (8) as well, to be made into a catalyst powder for detection.
Comparative example 1
The DPF catalyst was prepared by the impregnation method, and the noble metal and the coating material used were the same as in example 1. The noble metal used in the catalyst was platinum, and the coating amount of the noble metal was 1.10g/L. The coating material used is a coating material containing SiO 2 Gamma-alumina, molecular sieves; quality of gamma-alumina and SiO 2 Compared with the mass of the molecular sieve phase, the ratio is 29. The reducing agent used is citric acid. The dispersant used was polyvinylpyrrolidone. The carrier used was SiC, with a volume of 3.08L and a pore density of 350 mesh/square foot.
The preparation method of the DPF catalyst by the impregnation method comprises the following steps:
(1) Preparing coating slurry: according to the mass of gamma-alumina and SiO 2 The mass ratio of the molecular sieve phase 29, siO contained by each weight 2 Adding deionized water into the gamma-alumina and the molecular sieve which are 300g in total to prepare coating slurry, and fully and uniformly stirring the slurry;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 The particle size is 2.5 mu m, 10g of coating slurry is taken to be put into a small crucible after ball milling, the crucible is placed at 120 ℃ and dried for 30min, then the crucible is transferred to a 600 ℃ muffle furnace to be roasted for 10min, the temperature is cooled to room temperature, the mass of the powder is weighed, and the solid content of the coating slurry is measured to be about 25 percent by dividing the mass of the powder by 10 g;
(3) Reduction of the noble metal precursor solution: according to the total amount of platinum of 11g, measuring a corresponding platinum nitrate solution, dropwise adding a citric acid solution serving as a reducing agent into the solution, and fully and uniformly stirring.
(4) Dispersion of noble metal active ingredient: and adding polyvinylpyrrolidone into the reduced noble metal precursor solution, and fully and uniformly stirring to prepare the noble metal solution.
(5) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 7h, and adding nitric acid to adjust the pH value to be below 7.0.
(6) Coating of noble metal slurry: and quantitatively coating the prepared precious metal slurry on the wall flow type carrier by using a special quantitative coating special machine according to the determined slurry coating amount of 30g/L.
(7) Drying moisture in the carrier: and (3) putting the coated carrier into an oven, adjusting the temperature to 80 ℃, and drying for 4h to dry the moisture in the carrier.
(8) Roasting of the carrier: and raising the temperature of the oven to 600 ℃, roasting for 3h, and roasting the carrier to obtain the DPF catalyst.
The noble metal slurry for coating on the carrier in the step (6) was taken out 20g into another small crucible, and subjected to the same steps (7), (8) to prepare a catalyst powder for detection.
Comparative example 2
The DPF catalyst was prepared by the impregnation method, and the noble metal and the coating material used were the same as in example 2. The noble metal used in the catalyst was palladium, and the coating amount of the noble metal was 0.90g/L. The coating materials used are gamma-alumina and CeO 2 And ZrO 2 The composite oxide and the molecular sieve of (4); mass of gamma-alumina and CeO 2 、ZrO 2 Compared with the mass of the molecular sieve phase, the ratio is 39. The reducing agent used is citric acid. The dispersant used was polyvinylpyrrolidone. The carrier used was SiC, with a volume of 3.08L and a pore density of 350 mesh/square foot.
The preparation method of the DPF catalyst by the impregnation method comprises the following steps:
(1) Preparing coating slurry: according to the mass of the gamma-alumina and CeO 2 、ZrO 2 And the added mass ratio of the molecular sieve 39, gamma-alumina and CeO were weighed respectively 2 And ZrO 2 Adding deionized water into the composite oxide and the molecular sieve to prepare coating slurry, and fully and uniformly stirring the coating slurry;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 The particle size is 2.5 mu m, 10g of coating slurry is taken to be put into a small crucible after ball milling, the crucible is placed at 120 ℃ and dried for 30min, then the crucible is transferred to a 600 ℃ muffle furnace to be roasted for 10min, the temperature is cooled to room temperature, the mass of the powder is weighed, and the solid content of the coating slurry is measured to be about 25 percent by dividing the mass of the powder by 10 g;
(3) Reduction of the noble metal precursor solution: according to the condition that the total amount of palladium is 9g, measuring a corresponding palladium nitrate solution, dropwise adding a citric acid solution serving as a reducing agent into the solution, and fully and uniformly stirring.
(4) Dispersion of noble metal active ingredient: and adding polyvinylpyrrolidone into the reduced noble metal precursor solution, and fully and uniformly stirring to prepare the noble metal solution.
(5) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 6h, and adding nitric acid to adjust the pH value to be below 7.0.
(6) Coating of noble metal slurry: and quantitatively coating the prepared precious metal slurry on the wall flow type carrier by using a special quantitative coating special machine according to the determined slurry coating amount of 25g/L.
(7) Drying moisture in the carrier: and (3) putting the coated carrier into an oven, adjusting the temperature to 80 ℃, and drying for 4h to dry the moisture in the carrier.
(8) Roasting of the carrier: and raising the temperature of the oven to 600 ℃, roasting for 3h, and roasting the carrier to obtain the DPF catalyst.
The noble metal slurry for coating on the carrier in the step (6) was taken out 20g into another small crucible, and subjected to the same steps (7), (8) to prepare a catalyst powder for detection.
Comparative example 3
DPF catalyst prepared by simulating the method of the present invention, catalyst and coating material used in the same manner as in example 8, citric acid was used instead of polyolAs a reducing agent, no dispersant was used. The noble metal used in the catalyst is platinum and palladium, the mass ratio of platinum to palladium is 1.5. The coating material used is a coating material containing SiO 2 Of gamma-alumina, ceO 2 A molecular sieve; quality of gamma-alumina and SiO 2 、CeO 2 Compared with the added mass of the molecular sieve, the ratio is 2.5. The reducing agent used is citric acid. The carrier used was SiC, with a volume of 3.3L and a pore density of 350 mesh/square foot.
The preparation method of the DPF catalyst simulating the invention comprises the following steps:
(1) Preparing coating slurry: according to the mass of gamma-alumina and SiO 2 、CeO 2 The mass ratio of the molecular sieve addition was 2.5, and SiO-containing components were weighed 2 Of gamma-alumina, ceO 2 Adding deionized water into the total amount of 200g of molecular sieve to prepare coating slurry, and fully and uniformly stirring the coating slurry;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 2.5 mu m, after ball milling, taking 10g of coating slurry to a small crucible, placing the crucible at 120 ℃ for drying for 30min, then transferring the crucible to a muffle furnace at 600 ℃ for roasting for 10min, cooling to room temperature, weighing the powder mass, and dividing the powder mass by 10g to obtain the coating slurry with the solid content of about 25%;
(3) Preparation of noble metal solution: according to the method, the total amount of platinum and palladium is 10g, the mass ratio of the platinum to the palladium is 1.5.
(4) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 4 hours, and adding nitric acid to adjust the pH value to be below 7.0.
(5) Coating of noble metal slurry: and quantitatively coating the prepared precious metal slurry on the wall flow type carrier by using a special quantitative coating special machine according to the determined slurry coating amount of 10g/L.
(6) Drying moisture in the carrier: and (3) putting the coated carrier into an oven, adjusting the temperature to 80 ℃, and drying for 3 hours to dry the moisture in the carrier.
(7) Roasting of the carrier: and raising the temperature of the oven to 600 ℃, roasting for 4 hours, and roasting the carrier to obtain the DPF catalyst.
The noble metal slurry for coating on the carrier in the step (5) was taken out 20g into another small crucible, and subjected to the same steps (6), (7) to prepare a catalyst powder for detection.
Comparative example 4
The DPF catalyst was prepared by simulating the present method, using the same coating material as in example 8, and using 2 times as much noble metal as in example 8. Citric acid was used as a reducing agent instead of polyol, and no dispersant was used. The noble metal used in the catalyst is platinum and palladium, the mass ratio of platinum to palladium is 1.5. The coating material used is a coating material containing SiO 2 Of gamma-alumina, ceO 2 A molecular sieve; quality of gamma-alumina and SiO 2 、CeO 2 Compared with the mass of the molecular sieve phase, the ratio is 2.5. The reducing agent used is citric acid. The carrier used was SiC, with a volume of 3.3L and a pore density of 350 mesh/square foot.
The preparation method of the DPF catalyst simulating the method comprises the following steps:
(1) Preparing coating slurry: according to the mass of gamma-alumina and SiO 2 、CeO 2 The mass ratio of the molecular sieve addition was 2.5, and SiO-containing components were weighed 2 Of gamma-alumina, ceO 2 Adding deionized water into the total amount of 200g of molecular sieve to prepare coating slurry, and fully and uniformly stirring the coating slurry;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 2.5 mu m, after ball milling, taking 10g of coating slurry to a small crucible, placing the crucible at 120 ℃ for drying for 30min, then transferring the crucible to a muffle furnace at 600 ℃ for roasting for 10min, cooling to room temperature, weighing the powder mass, and dividing the powder mass by 10g to obtain the coating slurry with the solid content of about 25%;
(3) Preparation of noble metal solution: according to the method, the total amount of platinum and palladium is 20g, the mass ratio of the platinum to the palladium is 1.5.
(4) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 4h, and adding nitric acid to adjust the pH value to be below 7.0.
(5) Coating of noble metal slurry: and quantitatively coating the prepared precious metal slurry on the wall flow type carrier by using a special quantitative coating special machine according to the determined slurry coating amount of 10g/L.
(6) Drying moisture in the carrier: and (3) putting the coated carrier into an oven, adjusting the temperature to 80 ℃, and drying for 3h to dry the moisture in the carrier.
(7) Roasting of the carrier: and raising the temperature of the oven to 600 ℃, roasting for 4 hours, and roasting the carrier to obtain the DPF catalyst.
The noble metal slurry for coating on the carrier in the step (5) was taken out 20g into another small crucible, and subjected to the same steps (6), (7) to prepare a catalyst powder for detection.
Comparison of coating Dispersion effects: in order to compare the dispersion effect of the noble metal monomer particles of each example, a small amount of the catalyst coating was removed from the same position on the surface of the catalyst of each example, and TEM analysis was performed in a fresh state and after aging at 750 ℃ for 24 hours. Representative examples 1 and comparative examples 1 were selected for comparative description.
As can be seen from FIGS. 1 to 4, the dispersion degree of the comparative example 1 and that of the experimental example 1 in the fresh state were not greatly different from each other, and both were agglomerated after aging. The noble metal monomer particles of experimental example 1 prepared by this method had the maximum particle size not exceeding 20nm and were distributed more uniformly. In contrast, the noble metal monomer particles in comparative example 1 are mostly over 30nm, and the agglomeration condition is obviously better than that in experimental example 1.
Noble metal crystal form comparison: in order to compare the crystal forms of the noble metals of the examples, a small amount of the catalyst coating is removed from the same position on the surface of the catalyst of each example, and XRD analysis is carried out respectively in a fresh state and after aging at 750 ℃ for 24 hours. Representative examples 2 and comparative examples 2 were selected for comparative description.
As can be seen from fig. 5 to 6, the noble metals in experimental example 2 and comparative example 2 exhibited slightly different peaks in the fresh state, and both were somewhat changed after aging. In which comparative example 2 was significantly more deteriorated than experimental example 2 prepared by the present method.
Evaluation and comparison of Activity: the catalyst powders prepared in the respective examples and comparative examples were weighed to 300mg, and placed in a tube furnace for evaluation and comparison of activity.
And (3) testing conditions are as follows: will contain C 3 H 6 、CO、CO 2 、NO、H 2 Introducing a mixed gas of O into the tube furnace, wherein C 3 H 6 ：300ppm、CO：300ppm、NO：300ppm、CO 2 ：6％、H 2 O：6％、O 2 :10 percent. The temperature is raised from 50 ℃ to 500 ℃ at a heating rate of 10 ℃/min. The gas conversion curves of the respective schemes are plotted as shown in FIG. 7, and the HC conversion light-off temperatures T of the respective schemes are counted 50 。
Comparing the results of the schemes to select a representative scheme for discussion. It was found that the HC conversion light-off temperature T of example 8 was equal to the HC conversion light-off temperature T of example 4, example 6, example 7, example 8 and comparative example 3 in which the noble metal coating amount was the same 50 And the lowest. The catalyst powders of example 8, comparative example 3 and comparative example 4 were further aged at 750 ℃ for 24 hours and then tested again under the same test conditions. The test results are summarized in table 1.
TABLE 1
Categories T of fresh HC 50 /℃ Aged HC T 50 /℃
Example 4 227 -
Example 6 219 -
Example 7 213 -
Example 8 206 228
Comparative example 3 217 250
Comparative example 4 192 241
In comparative example 4, example 6, example 7, and example 8, the noble metal coating amount was the same, and the ratio of the noble metal to the platinum: palladium =1.5: example 8 of 1 gave the best results. Further comparison of fresh and aged HC's T of example 8, comparative example 3, comparative example 4 50 And (3) finding that: comparative example 3 simulates the process and uses a conventional dipping process without the addition of a dispersant, although the same amount of noble metal coating, the same coating material and T as in example 8, is used 50 But higher than in example 8. After aging, the degree of deterioration is far fromGreater than in experimental example 8. Comparative example 4 simulates the process and in fact uses a conventional dipping process without the addition of a dispersant, using a 2-fold amount of noble metal and the same coating material as in example 8, and although in a fresh state better than example 8, also after aging, the deterioration rate is severe and rather inferior to example 8.
Through the experimental comparison, the manufacturing method of the DPF catalyst with better dispersity provided by the invention is fully proved to have the advantages of better precious metal dispersity, better catalytic performance, lower comprehensive cost, better ageing resistance, longer service life and the like compared with the common impregnation method.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way. Any simple modification, change and equivalent changes of the above embodiments according to the principles of the present invention are still within the protection scope of the technical solution of the present invention.

Claims (6)

1. A preparation method of a DPF catalyst with better dispersity is characterized by comprising the following steps: the method comprises the following steps:
(1) Preparing coating slurry: respectively weighing gamma-alumina and SiO according to the coating amount of the slurry which is determined in advance 2 、CeO 2 、ZrO 2 、TiO 2 Mixing at least one of the molecular sieves according to the mass ratio of gamma-alumina to other substances of 2-99, adding deionized water to prepare coating slurry, and fully and uniformly stirring;
(2) Ball milling of coating slurry: treating the coating slurry by ball milling process to adjust the granularity of the coating slurry to D 90 2 to 20 mu m;
(3) Preparing a noble metal solution: measuring a corresponding noble metal precursor solution according to the predetermined noble metal dosage, dropwise adding polyalcohol serving as a reducing agent into the noble metal precursor solution, and fully and uniformly stirring to ensure that noble metal monomer particles are fully reduced;
(4) Adding a noble metal solution: adding the prepared noble metal solution into the coating slurry, stirring for 4 to 8 hours, and adding nitric acid to adjust the pH value to be below 7.0;
(5) Coating of noble metal slurry: quantitatively coating the prepared precious metal slurry on a wall-flow carrier by using a special quantitative coating special machine according to the determined slurry coating amount;
(6) Drying moisture in the carrier: putting the coated carrier into an oven, drying at 70-80 ℃ for 3-4 h, and drying the water in the carrier;
(7) Drying a reducing agent in the carrier: raising the temperature of the oven, and drying the polyol in the carrier at a temperature lower than the boiling point of the polyol;
(8) Roasting the carrier: and (3) increasing the temperature of the oven to roast the carrier, wherein the roasting temperature is 550-600 ℃, the roasting time is 3-6 h, and the DPF catalyst is prepared after the roasting is finished.
2. The method for preparing a DPF catalyst having a higher dispersibility according to claim 1, comprising: in the step (2), after the ball milling of the coating slurry is finished, 10g of the coating slurry is taken out and put into a small crucible, the crucible is placed at 120 ℃ and dried for 30min, then the crucible is transferred into a muffle furnace at 550 to 600 ℃ and roasted for 10 to 20min, the crucible is cooled to room temperature, the powder mass is weighed, and the solid content of the coating slurry is measured by dividing the powder mass by 10 g.
3. The method for preparing a DPF catalyst having a higher dispersibility according to claim 1, comprising: in the step (3), the polyol used as the reducing agent is one or more of ethylene glycol, polyethylene glycol and polyalkylene glycol.
4. The method for preparing a DPF catalyst having a higher dispersibility according to claim 1, comprising: in the step (4), the auxiliary agent for adjusting the coating slurry is nitric acid, and the pH value is adjusted to be below 6.0.
5. The method for preparing a DPF catalyst having a higher dispersibility according to claim 1, comprising: front of said noble metal PtThe precursor solution is platinum nitrate solution or Pt (NH) 3 ) 2 (NO 2 ) 2 Solution or [ Pt (NH) 3 ) 4 ](OH) 2 And (3) solution.
6. The method for preparing a DPF catalyst having a higher dispersibility according to claim 1, comprising: the precursor solution of the noble metal Pd is a palladium nitrate solution or Pd (NH) 3 ) 2 (NO 2 ) 2 Solution or [ Pd (NH) ] 3 ) 4 ](OH) 2 And (3) solution.
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