CN111514922A - DPF catalyst with better dispersity and preparation method thereof - Google Patents
DPF catalyst with better dispersity and preparation method thereof Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 34
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- 238000000576 coating method Methods 0.000 claims abstract description 158
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- 238000000034 method Methods 0.000 claims abstract description 56
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- 239000000463 material Substances 0.000 claims abstract description 41
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- 229910052697 platinum Inorganic materials 0.000 claims abstract description 34
- 229910052763 palladium Inorganic materials 0.000 claims abstract description 33
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- 229910000422 cerium(IV) oxide Inorganic materials 0.000 claims abstract description 26
- 229910052681 coesite Inorganic materials 0.000 claims abstract description 25
- 229910052906 cristobalite Inorganic materials 0.000 claims abstract description 25
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 25
- 229910052682 stishovite Inorganic materials 0.000 claims abstract description 25
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- GWEVSGVZZGPLCZ-UHFFFAOYSA-N titanium dioxide Inorganic materials O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims abstract description 17
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- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 75
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- 238000003756 stirring Methods 0.000 claims description 39
- 230000008569 process Effects 0.000 claims description 20
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- 239000002243 precursor Substances 0.000 claims description 15
- 238000007581 slurry coating method Methods 0.000 claims description 14
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- 239000008367 deionised water Substances 0.000 claims description 13
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- GPNDARIEYHPYAY-UHFFFAOYSA-N palladium(ii) nitrate Chemical compound [Pd+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O GPNDARIEYHPYAY-UHFFFAOYSA-N 0.000 claims description 9
- NWAHZABTSDUXMJ-UHFFFAOYSA-N platinum(2+);dinitrate Chemical group [Pt+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O NWAHZABTSDUXMJ-UHFFFAOYSA-N 0.000 claims description 9
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- 238000005470 impregnation Methods 0.000 abstract description 11
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- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 30
- 230000000052 comparative effect Effects 0.000 description 27
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- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 9
- 239000012071 phase Substances 0.000 description 8
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- JRTYPQGPARWINR-UHFFFAOYSA-N palladium platinum Chemical compound [Pd].[Pt] JRTYPQGPARWINR-UHFFFAOYSA-N 0.000 description 1
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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
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- 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
- 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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- 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
- 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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- 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
- 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
- B01J23/44—Palladium
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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
- B01J23/54—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
- B01J23/63—Platinum group metals with rare earths or actinides
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- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/20—Carbon compounds
- B01J27/22—Carbides
- B01J27/224—Silicon carbide
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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
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- 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
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Abstract
The invention relates to a DPF catalyst with better dispersity 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 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 SiO2、CeO2、ZrO2、TiO2And a molecular sieve. The manufacture thereofThe 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
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
At present, a diesel wall-flow particulate filter (DPF) and a system thereof become a conventional scheme for meeting the restriction of an emission regulation on diesel Particulates (PM), and are indispensable components in an exhaust gas treatment system of a diesel vehicle. 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 passive regeneration of the particulate matters continuously occurs, and the particulate matters 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 of a wall flow type carrier having a constant specific surface area, the amount of the noble metal slurry applied may have a large influence on the dispersion 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 dispersity 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 SiO2、CeO2、ZrO2、TiO2And a molecular sieve.
Preferably, when the noble metal is Pt and Pd, the mass ratio of the noble metal Pt and the noble metal Pd is 1-99: 1.
Preferably, in the coating material, the mass ratio of the gamma-alumina to other substances is 2-99: 1.
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) preparing coating slurry: respectively weighing gamma-alumina and SiO according to the coating amount of the slurry which is determined in advance2、CeO2、ZrO2、TiO2Mixing at least one of the molecular sieves according to the mass ratio of 2-99: 1 of gamma-alumina to other substances, 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 D902-20 μm;
(3) preparation of 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 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, and drying at the temperature of 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 by raising the temperature of the oven, wherein the roasting temperature is 550-600 ℃, the roasting time is 3-6 h, and the DPF catalyst is prepared after roasting is finished.
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 the crucible is transferred to a muffle furnace at 550-600 ℃ to be roasted for 10-20 min, the crucible 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(NO2)2Solution or [ Pt (NH)3)4](OH)2And (3) solution.
Preferably, the precursor solution of the noble metal Pd is a palladium nitrate solution or Pd (N)H3)2(NO2)2Solution or [ Pd (NH) ]3)4](OH)2And (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 carrier, the water is first dried and the polyol is then evaporated at a temperature close to or below 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 1.10 g/L. The coating material used is a coating material containing SiO2Gamma-alumina, molecular sieves; quality of gamma-alumina and SiO2Compared with the added mass of the molecular sieve, the ratio of the molecular sieve to the added mass is 29:1, and the coating amount of the coating is 30 g/L. 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 gamma-alumina and SiO2The mass ratio of the molecular sieve phase is 29:1, and SiO is weighed respectively2Adding 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 D90The particle size is 2.2 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 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 30 g/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 2
A DPF catalyst with better dispersity is prepared from Pd as noble metal through coating noble metal by 0.90 g/L. The coating materials used are gamma-alumina and CeO2And ZrO2The composite oxide and the molecular sieve of (4); mass of gamma-alumina and CeO2、ZrO2The ratio of the mass of the molecular sieve phase to the mass of the molecular sieve phase is 39:1, and the coating amount of the coating is 25 g/L. 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 CeO2、ZrO2The mass ratio of the molecular sieve to the total mass is 39:1, and gamma-alumina and CeO are respectively weighed2And ZrO2The total amount of the composite oxide and the molecular sieve of (2) is 250g, andpreparing coating slurry by using ionized water, 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 D90The 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) preparation of 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 25 g/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 0.70 g/L. The used coating materials are gamma-alumina, molecular sieve and titanium dioxide; mass of gamma-alumina and TiO2Molecular sieve addition massIn contrast, the ratio was 99:1 and the coating weight was 20 g/L. The reducing agent used is polyethylene glycol with a molecular weight of 2000-. 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 TiO2Respectively weighing 200g of gamma-alumina, the molecular sieve and titanium dioxide in a mass ratio of 99:1, 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 D90The 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) preparation of noble metal solution: measuring the corresponding Pt (NH) according to the total amount of the platinum being 7g3)2(NO2)2And (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 20 g/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 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 from the noble metals platinum and palladium in a mass ratio of 99:1, and the coating amount of the noble metals is 0.35 g/L. The coating material used is a coating material containing SiO2Gamma-alumina, titanium dioxide; quality of gamma-alumina and SiO2、TiO2The ratio of the added masses was 1.5:1 and the coating weight was 15 g/L. The reducing agent used is polyethylene glycol with a molecular weight of 2000-. 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: according to the mass of gamma-alumina and SiO2、TiO2The sum of the mass ratios 1.5:1, respectively, containing SiO2Adding 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 D90The 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: measuring corresponding Pt (NH) according to the mass ratio of the platinum to the palladium of 10g and 99:13)2(NO2)2And Pd (NH)3)2(NO2)2And (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 15 g/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 2h to dry the polyethylene glycol in the carrier.
(8) Roasting of 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
A DPF catalyst with better dispersity is prepared from the noble metals platinum and palladium in a mass ratio of 4:1, and the coating amount of the noble metals is 0.10 g/L. The coating material used is a coating material containing SiO2Gamma-alumina of (a); quality of gamma-alumina and SiO2Compared with the prior art, the ratio of the mass of the coating to the mass of the coating is 19:1, and the coating amount of the coating is 5 g/L. The reducing agent used was a polyalkylene glycol having a molecular weight of 2000-. 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: weighed to contain 5% wt SiO2Adding 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 D9012.8 μm, ball milling, placing 10g of coating slurry into a small crucible, and placing the crucible in a vacuum ovenDrying at 120 ℃ for 30min, then transferring to a muffle furnace at 550 ℃ for roasting for 20min, 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: corresponding [ Pt (NH) was measured in an amount such that the total amount of platinum and palladium was 4g and the mass ratio of platinum to palladium was 4:13)4](OH)2And [ Pd (NH)3)4](OH)2And (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 5 g/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 of 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
A DPF catalyst with better dispersity is prepared from the noble metals platinum and palladium in a mass ratio of 3:1, and the coating amount of the noble metals is 0.35 g/L. The coating materials used are gamma-alumina and CeO2And ZrO2A composite oxide of (a); mass of gamma-alumina and CeO2、ZrO2The ratio of the added masses was 2:1 and the coating weight was 10 g/L. Make itThe reducing agent used is ethylene glycol with a 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 CeO2、ZrO2The added mass ratio is 2:1, and the gamma-alumina and the CeO are respectively weighed2And ZrO2Adding 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 D90The 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, 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 3:1, corresponding platinum nitrate and palladium nitrate solutions are measured, 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 10 g/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
A 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 0.35 g/L. The coating material is gamma-alumina or ZrO2(ii) a Mass of gamma-alumina and ZrO2The ratio of the mass of the coating to the mass of the coating is 9:1, and the coating amount of the coating is 10 g/L. The reducing agent used was ethylene glycol, molecular weight 2000-. 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 gamma-alumina and ZrO2In a mass ratio of 9:1, gamma-alumina and ZrO were weighed respectively2Adding deionized water into the total amount of 200g 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 D90The 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) 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 the platinum to the palladium is 1:1, corresponding platinum nitrate and palladium nitrate solutions are measured, 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 10 g/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 the noble metals platinum and palladium in a mass ratio of 1.5:1, and the coating amount of the noble metals is 0.35 g/L. The coating material used is a coating material containing SiO2Of gamma-alumina, CeO2A molecular sieve; quality of gamma-alumina and SiO2、CeO2Compared with the added mass of the molecular sieve, the ratio of the molecular sieve to the added mass is 2.5:1, and the coating amount of the coating is 10 g/L. The reducing agent used was ethylene glycol, molecular weight 2000-. 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 SiO2、CeO2The mass ratio of the molecular sieve to the total weight of the mixture is 2.5:1, and SiO is weighed respectively2Of gamma-alumina, CeO2Adding 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 D902.1 μm, ball milling, placing 10g of coating slurry into a small crucible, drying the crucible at 120 deg.C for 30min, and transferring to a containerRoasting in a muffle furnace at 600 ℃ for 10min, cooling to room temperature, weighing the powder mass, and dividing the powder mass by 10g to obtain coating slurry with the solid content of about 25%;
(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 the platinum to the palladium is 1.5:1, corresponding platinum nitrate and palladium nitrate solutions are measured, 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 10 g/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.
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 1.10 g/L. The coating material used is a coating material containing SiO2Gamma-alumina, molecular sieves; quality of gamma-alumina and SiO2Compared with the added mass of the molecular sieve, the ratio of the molecular sieve to the added mass is 29:1, and the coating amount of the coating is 30 g/L. The reducing agent used is citric acid. The dispersant used was polyvinylpyrrolidone. The carrier used was SiC, the volume was 3.08L, and the pore density was 350 mesh/sq.EnglishAnd (6) measuring.
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 SiO2The mass ratio of the molecular sieve phase is 29:1, and SiO is weighed respectively2Adding 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 D90The 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 30 g/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 0.90 g/L. The coating materials used are gamma-alumina and CeO2And ZrO2The composite oxide and the molecular sieve of (4); mass of gamma-alumina and CeO2、ZrO2The ratio of the mass of the molecular sieve phase to the mass of the molecular sieve phase is 39:1, and the coating amount of the coating is 25 g/L. 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 CeO2、ZrO2The mass ratio of the molecular sieve to the total mass is 39:1, and gamma-alumina and CeO are respectively weighed2And ZrO2Adding 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 D90The 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 25 g/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
The DPF catalyst was prepared by simulating the method of the present invention, using the same catalyst and coating material as in example 8, using citric acid as a reducing agent instead of polyol, and no dispersant. The noble metal used in the catalyst is platinum and palladium, the mass ratio of the platinum to the palladium is 1.5:1, and the coating amount of the noble metal is 0.35 g/L. The coating material used is a coating material containing SiO2Of gamma-alumina, CeO2A molecular sieve; quality of gamma-alumina and SiO2、CeO2Compared with the added mass of the molecular sieve, the ratio of the molecular sieve to the added mass is 2.5:1, and the coating amount of the coating is 10 g/L. 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 SiO2、CeO2The mass ratio of the molecular sieve to the total weight of the mixture is 2.5:1, and SiO is weighed respectively2Of gamma-alumina, CeO2Adding 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 millingParticle size is adjusted to D90The 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) 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 the platinum to the palladium is 1.5:1, corresponding platinum nitrate and palladium nitrate solutions are measured, a citric acid solution 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 10 g/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.
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 the platinum to the palladium is 1.5:1, and the coating amount of the noble metal is 0.70 g/L. The coating material used is a coating material containing SiO2Of gamma-alumina, CeO2A molecular sieve; quality of gamma-alumina and SiO2、CeO2The mass ratio of the molecular sieve phase to the molecular sieve phase is 2.5:1, and the coating is coatedThe coverage was 10 g/L. 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 SiO2、CeO2The mass ratio of the molecular sieve to the total weight of the mixture is 2.5:1, and SiO is weighed respectively2Of gamma-alumina, CeO2Adding 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 D90The 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) preparation of noble metal solution: according to the method, according to the condition that the total amount of platinum and palladium is 20g and the mass ratio of the platinum to the palladium is 1.5:1, corresponding platinum nitrate and palladium nitrate solutions are measured, a citric acid solution 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 10 g/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 Effect: 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 experimental example 1 and that of the comparative example 1 are not greatly different in the fresh state, and both are 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.
It can be seen from fig. 5 to 6 that the noble metals in experimental example 2 and comparative example 2 exhibited slightly different peaks in the fresh state, and both of them underwent some change 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 C3H6、CO、CO2、NO、H2Introducing a mixed gas of O into the tube furnace, wherein C3H6：300ppm、CO：300ppm、NO：300ppm、CO2：6％、H2O：6％、O2: 10 percent. The temperature is raised from 50 ℃ to 500 ℃ at a heating rate of 10 ℃/min. The gas conversion curves for each protocol were plotted as in FIG. 7Making out and counting the HC conversion light-off temperature T of each scheme50。
Comparing the results of each scheme, and selecting 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 same50And 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 HC50/℃ | Aged HC T50/℃ |
| 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 450And (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 used50But higher than in example 8. After aging, the degree of deterioration was also much greater 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 for the 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 (10)
1. A DPF catalyst with better dispersity is characterized in that: it is composed of a base, a cover and a coverThe coating 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 SiO2、CeO2、ZrO2、TiO2And a molecular sieve.
2. The better dispersed DPF catalyst of claim 1, wherein: when the noble metal is Pt and Pd, the mass ratio of the noble metal Pt to the noble metal Pd is 1-99: 1.
3. The better dispersed DPF catalyst of claim 1, wherein: in the coating material, the mass ratio of gamma-alumina to other substances is 2-99: 1.
4. The better dispersed DPF catalyst of claim 1, wherein: the carrier is cordierite, SiC or AT and the like, and the mesh number of the carrier is 200-350 meshes.
5. The preparation method of the DPF catalyst with better dispersity 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 advance2、CeO2、ZrO2、TiO2Mixing at least one of the molecular sieves according to the mass ratio of 2-99: 1 of gamma-alumina to other substances, 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 D902-20 μm;
(3) preparation of 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 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 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 by raising the temperature of the oven, wherein the roasting temperature is 550-600 ℃, the roasting time is 3-6 h, and the DPF catalyst is prepared after roasting is finished.
6. The method for preparing a DPF catalyst having a higher dispersibility according to claim 5, wherein: 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 550-600 ℃ and roasted for 10-20 min, the crucible 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.
7. The method for preparing a DPF catalyst having a higher dispersibility according to claim 5, wherein: in the step (3), the polyol used as the reducing agent is one or more of ethylene glycol, polyethylene glycol and polyalkylene glycol.
8. The method for preparing a DPF catalyst having a higher dispersibility according to claim 5, wherein: 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.
9. The method for preparing a DPF catalyst having a higher dispersibility according to claim 5, wherein: the precursor solution of the noble metal Pt is platinum nitrate solution or Pt (NH)3)2(NO2)2Solution or [ Pt (NH)3)4](OH)2And (3) solution.
10. The method for preparing a DPF catalyst having a higher dispersibility according to claim 5, wherein: the precursor solution of the noble metal Pd is a palladium nitrate solution or Pd (NH)3)2(NO2)2Solution or [ Pd (NH) ]3)4](OH)2And (3) solution.
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