CN116688976A - Diesel vehicle oxidation catalyst and preparation method thereof - Google Patents
Diesel vehicle oxidation catalyst and preparation method thereof Download PDFInfo
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- 229910002651 NO3 Inorganic materials 0.000 claims abstract description 23
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims abstract description 23
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 12
- 150000002823 nitrates Chemical class 0.000 claims abstract description 11
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- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
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Classifications
-
- 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
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
- F01N3/28—Construction of catalytic reactors
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Health & Medical Sciences (AREA)
- Toxicology (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Catalysts (AREA)
Abstract
The invention provides a diesel vehicle oxidation catalyst and a preparation method thereof. The preparation method of the diesel oxidation catalyst comprises the following steps: the catalyst is prepared by coating slurry containing a noble metal nitrate salt and a supporting material on a carrier and then roasting the slurry at 350-550 ℃ in a nitrogen atmosphere, wherein the noble metal nitrate salt is the nitrate of Pt and the nitrate of Pd. According to the invention, the noble metal slurry serving as the raw material of the catalyst is coated on the same carrier according to a proper proportion, and nitrogen treatment is carried out at a proper temperature to promote the generation of Pt-Pd alloy, so that the synergistic effect of Pt and Pd is enhanced, and the effect of improving the catalytic performance is achieved.
Description
Technical Field
The invention relates to a diesel vehicle oxidation catalyst and a preparation method thereof, in particular to a Pt-Pd-containing high-activity diesel vehicle exhaust oxidation catalyst and a preparation method thereof.
Background
With the continuous strictness of the national automobile exhaust emission standard, the requirements on the performance of the exhaust purification catalyst are correspondingly improved. Among them, the purification of exhaust gas from diesel vehicles is a subject to be improved. Diesel oxidation catalysts (Diesel Oxidation Catalyst, DOC) are important components in diesel exhaust gas purification systems (typically consisting of DOC, DPF, SCR and/or ASC). Under the action of DOC, CO and Hydrocarbon (HC) generated after diesel combustion are oxidized into CO 2 And H 2 O, which increases the temperature of the exhaust gas and converts NO to NO having oxidizing ability 2 To oxidize particulate matter trapped by a subsequent diesel particulate filter (Diesel Particulate Filter, DPF), such as soluble organic components (Soluble Organic Fraction, SOF), soot (boot), etc.
In general, a simple way to improve catalyst performance is to increase the amount of metal as the active site of the catalyst. The main active sites of DOC are Pt and Pd. Pt has a higher NO 2 The conversion capability and the sulfur ageing resistance capability, but the capability of adsorbing CO at low temperature is strong, and the ignition characteristics of the CO are affected. Further, pt is likely to move under oxygen-enriched conditions, and the particles may become coarse and the active sites may decrease, or the Pt may be deactivated by the formation of stable Pt oxide. Pd has CO oxidizing ability and stability under oxygen-enriched condition, therefore, the existence of Pd can ensure the ignition performance and NO of Pt 2 Conversion ability and high temperature aging resistance.
Currently, in order to improve catalyst performance, DOC of diesel vehicles may improve light-off performance by increasing the amount of noble metal, but the use of noble metal in large amounts causes an increase in cost. Furthermore, in practical applications, it was found that DOCs using bimetallic Pt-Pd are superior in performance to DOCs using Pt or Pd alone. Further, if Pt and Pd are kept at an appropriate distance to enhance interaction between them, it can be advantageous to improve catalytic performance. Therefore, the preparation of a bimetallic Pt-Pd catalyst to exert the synergistic effect of Pt-Pd is one of means for reducing the amount of noble metal used. Currently, commercial DOC catalysts typically perform sample preparation by air calcination at temperatures below 600 ℃. Since in air below 600 ℃, the following occurs: part of Pt is a simple metal, the other part is an oxide, and most of Pd is PdO (decomposition temperature 860 ℃), so that it is unfavorable for the formation of pt—pd alloy.
JP 2019-76853 discloses the preparation of Pt with large specific surface area by a treatment method of heated hydrogen reduction, wherein the optimal starting treatment temperature of heated hydrogen reduction is 300-600 ℃, thereby realizing a high-activity Pt catalyst.
JP 2008-272659 discloses a method of dispersing a Pt simple substance and a (Pt-Pd) alloy on a heat-resistant inorganic material, respectively, and then mixing the materials into a whole. The distance between the noble metal particles is controlled according to the surface area of the support material. Wherein, for the high performance catalyst, the shortest distance between noble metal particles is made to be 5-50nm, and the distance between 50% -70% of noble metal particles is made to be 5-300nm, most preferably 10-200nm, so as to inhibit sintering of noble metal particles and balance adsorption of reactants and reaction between each other. The disadvantage of this technique is that when noble metal-containing powder is baked several times, the powder flies up to cause the loss of raw materials and the process flow time is long, and the baking under air cannot ensure the preparation of an alloy of pt—pd ratio required by the design.
Fei Dong et al, catalysis Today Volume 376 (2021), P47-54 disclose a DOC with a weight ratio of Pt (1.0% wt.%) -Pd (0.5% wt.%) using a Pt-Pd nano-alloy colloid as a precursor (pre-reactor) to prepare a catalyst with lower light-off temperature and better performance.
JP 2013-5343138 discloses a metal sol solution and a method for preparing the same, which uses precious metal nano alloy particles, and has complicated steps and large precious metal loss.
In summary, although the prior art literature discloses methods for improving the performance of single noble metal Pt, such as treatment by hydrogen atmosphere, for the solution for improving the performance and stability of bimetallic Pt-Pd catalysts, methods for using Pt-Pd nano alloy particles as precursors and multiple calcination are also disclosed. However, these methods are complicated in steps, labor-consuming, and expensive in noble metal loss, resulting in increased costs.
Disclosure of Invention
Aiming at the problems in the prior art, the invention does not adopt a method for treating nano noble metal particles and hydrogen with high preparation cost, does not adopt time-consuming, energy-consuming and lost multiple times of roasting of noble metal, but adopts the method that noble metal slurry serving as a catalyst raw material is coated on the same carrier (supporting material) according to a proper proportion, and nitrogen treatment is carried out at a proper temperature to promote the generation of Pt-Pd alloy, thereby enhancing the synergistic effect of Pt and Pd to achieve the effect of improving the catalytic performance.
The technical scheme of the invention is as follows:
the preparation method of the diesel vehicle oxidation catalyst comprises the following steps: after applying a slurry containing a noble metal nitrate salt and a support material to a carrier, the carrier was treated with nitrogen (N) 2 ) Roasting at 350-550 ℃ in the atmosphere of the catalyst, wherein the nitrate noble metal salt is the nitrate of Pt and the nitrate of Pd.
According to the prior art, as described in JP 2008-272659, a Pt-Pd type diesel oxidation catalyst generally contains independent Pt and (Pt-Pd) alloy, and the spacing of noble metals of active points is controlled by adopting a stable carrier material and proper addition amount so as to achieve the improvement of ageing resistance. Alternatively, the use of Pt-Pd nano-alloy colloids as precursors (procursor) can significantly improve the light-off properties as described by Fei Dong et al. Currently, catalysts are generally prepared by calcination in air to decompose noble metal salts and other salts.
However, in the present invention, the inventors considered to use a nitrogen atmosphere for the treatment. The effect of the air firing and the nitrogen treatment may be different in that whether or not an oxide is formed as a product. Under air calcination, pt (NO 3 ) 4 Generating PtO 2 ，Pd(NO 3 ) 2 PdO is generated. The PdO melting point is 860 ℃ and is relatively stable. PtO (PtO) 2 Melting point is 450 ℃, ptO is carried out at the air roasting temperature above 450 DEG C 2 Will melt. Its melting pointThe melt-out may cause fluidity, which may cause undesirable fusion between Pt and Pd, and may cause the noble metal itself to become coarse. Regarding the nitrogen-treated product, it is presumed that: ptO under nitrogen 2 Is easily deoxidized and decomposed into Pt, the melting point of Pt is 1768 ℃, and the Pt is relatively not easy to move on a carrier material.
Air-firing Pt (NO) 3 ) 4 →Pt/PtO 2 +NO 2 +O 2
Pd(NO 3 ) 2 →Pd/PdO+NOx
N 2 Treatment of Pt (NO) 3 ) 4 →Pt+NO X
Pd(NO 3 ) 2 →Pd+NOx
The inventors of the present invention found that since the Pt salt and Pd salt form oxides by calcination in air, a Pt-Pd alloy of a designed ratio could not be formed even if they were placed on the same carrier. For this, the inventors compared the test data of the aged samples, i.e., 1% Pt/Al air-calcined 2 O 3 Air-calcined (1% Pt-1% Pd)/Al 2 O 3 And N 2 Treated (1% Pt-1% Pd)/Al 2 O 3 XRD test data of (test equipment model Rigaku Miniflex 600C, scan speed 0.5 °/min). The results show that air-calcined (1% Pt-1% Pd)/Al 2 O 3 After 50 hours aging of the sample at 700℃the peak ascribed to PdO (around 2. Theta. -33.96 ℃) is evident, indicating that a portion of Pd is present as PdO. In addition, 1% Pt/Al compared to the single metal 2 O 3 The peak ascribed to Pt (around 2 theta-39.85 deg.) shifted by 0.15 deg., the crystal grain size was about 22nm. On the other hand, via N 2 Treated (1% Pt-1% Pd)/Al 2 O 3 No significant peak ascribed to PdO was found in the sample even after aging, and the peak ascribed to Pt was at 39.98 deg., shifted 0.28 deg. to the Pd (40.12 deg.) direction, with the crystal particles being about 9nm. This means N 2 The treatment is more favorable for the generation of Pt-Pd and the inhibition of the enlargement of Pt particles. That is, if one wants to stabilize Pt with a small amount of Pd, N 2 The treatment effect will be better (refer to fig. 1).
Furthermore, the inventors compared a catalyst in which Pt and Pd were mixed in advance and then supported on a support (see comparative example-1A in the examples section) with a catalyst in which Pt and Pd were supported on different supports in advance respectively (see comparative example-1B in the examples section), and after air-firing at 550 ℃, the performances of both were substantially the same (see fig. 2). It is presumed that there may be two reasons for this, one is that Pt moves to the position of Pd under air firing conditions at 550 ℃; another more important reason is that even if two metals are placed on the same support material, pt and Pd remain independent of each other, resulting in a very limited pt—pd.
The inventors also compared two samples, wherein the first sample was obtained by mixing Pt and Pd in advance and then placing them on a support material, and the second sample was obtained by placing Pt and Pd on different support materials in advance, wherein the first sample was calcined at 550℃in air (comparative example-1A), and the second sample was calcined at 550℃in N 2 Treatment (comparative example-1C). The performance test results show that the test result is that through N 2 The catalyst performance of the treated comparative example-1C was inferior to that of comparative example-1A (refer to FIG. 3) subjected to air calcination. From this, it can be seen that if Pt and Pd are not carried together on the same support material in advance, N 2 It is difficult to obtain a synergistic effect of Pt-Pd together like air calcination for the treated catalyst.
Based on the above test results, the inventors considered that both the firing conditions and the mounting manner become important factors affecting the characteristics of Pt and pt—pd. Under air firing conditions, even if two metals are placed on the same support material, a designed ratio of pt—pd alloy cannot be produced, and thus a finished product of Pt and pt—pd alloy in a desired ratio cannot be produced. In addition, as in the prior art, the reducing gas hydrogen (H 2 ) The safety requirements on mass production equipment are strict, and the production cost can be greatly increased. The invention uses the ratio H 2 Inexpensive and safe inert gas nitrogen (N) 2 ) By optimizing N 2 Treatment conditions, N 2 The positive effect of reducing the amount of noble metal used due to the treatment conditions is greater than the negative effect on equipment investment and the like.
According to an embodiment of the invention, the carrier is a honeycomb carrier.
According to an embodiment of the present invention, the slurry containing a noble metal nitrate salt and a support material contains a Pt slurry and a pt—pd concurrent slurry. By using such a slurry, it is easy to prepare a bimetallic catalyst containing both individual single metal Pt and pt—pd alloy particles.
According to an embodiment of the present invention, the Pt slurry contains nitrate of Pt and a supporting material, wherein the Pt content is 10wt% to 90wt%, preferably 15wt% to 75wt%, more preferably 20wt% to 60wt%, still more preferably 25wt% to 50wt% of the total Pt feeding amount. For example, the slurry containing the noble metal nitrate salt and the support material may contain 25% pt slurry and 75% pt—pd concurrent slurry, or contain 50% pt slurry and 50% pt—pd concurrent slurry.
According to an embodiment of the present invention, the supporting material may be Al 2 O 3 、SiO 2 /Al 2 O 3 、CeO 2 /Al 2 O 3 、BaO/Al 2 O 3 、ZrO 2 /Al 2 O 3 Etc., preferably Al 2 O 3 。
According to an embodiment of the invention, the concentration of Pt in the support material in the Pt slurry is 0.1 to 3wt%, preferably 0.15 to 2.5wt%, more preferably 0.3 to 1.1wt%.
According to an embodiment of the invention, the pH of the Pt slurry is >3.5 and the amount of free Pt ions is less than 1wt% of the nitrate addition of Pt.
According to an embodiment of the invention, the Pt-Pd concurrent slurry comprises a nitrate of Pt, a nitrate of Pd and a support material, wherein the weight ratio of the nitrate of Pt to the nitrate of Pd is 0.2:1 to 3:1, and the concentration of the sum of Pt and Pd in the support material is 0.1 to 3wt%, preferably 0.15 to 2.5wt%, more preferably 0.3 to 1.1wt%. The support material may be selected in the same range as the support material in the Pt slurry.
According to an embodiment of the invention, the pH of the Pt-Pd concurrent slurry is >3.5, and the amounts of free Pt and Pd ions are less than 1wt% of the nitrate of Pt and the nitrate addition of Pd, respectively.
According to an embodiment of the invention, the slurry comprising the noble metal nitrate salt and the support material has a solids content of 20% to 60%, preferably 40%.
According to an embodiment of the present invention, the preparation method further comprises: the slurry containing the noble metal nitrate salt and the support material is ground to an average particle size of 3 to 8 μm prior to application to the support.
According to an embodiment of the present invention, the method of applying the slurry may be a coating method commonly used in the art, such as a dip coating method, a spray coating method, a roll coating method, or the like.
According to an embodiment of the present invention, when a slurry containing a noble metal nitrate salt and a support material is applied to a carrier, the total coating dry weight of the catalyst is 0.2 to 5.0g/inch 3 Preferably 1.0 to 4.0g/inch 3 Exemplary is 1.5g/inch 3 。
According to an embodiment of the present invention, the preparation method further comprises: after the slurry containing the noble metal nitrate salt and the support material is applied to the carrier, drying is carried out at 100 to 150 ℃, preferably 120 ℃ for 0.5 to 5 hours, preferably 1 hour. By drying, 90% or more of the water can be removed.
According to an embodiment of the present invention, the nitrogen (N 2 ) Is heated at a rate of 5-20 deg.c/min, preferably 10 deg.c/min, until the firing temperature is reached.
According to an embodiment of the invention, the calcination time is 0.5 to 5 hours, preferably 1 hour.
According to an embodiment of the present invention, after firing, it may be cooled to 90℃to complete N 2 And (5) processing.
According to an embodiment of the present invention, the firing temperature may be set to 350 ℃ or higher and less than 600 ℃. As shown in the examples below, the samples were thermogravimetric tested at N 2 The temperature was raised in the atmosphere, and no significant change in weight was found after exceeding 350 ℃. N is also found 2 The catalyst performance does not change much at a treatment temperature of 350-550 ℃, if N is to be added 2 The treatment temperature is set at 600 ℃, and the catalysis is carried outThe performance of the catalyst is reduced (see FIG. 4-1, FIG. 4-2, FIG. 5-1, FIG. 5-2). In addition, comprehensively consider the energy-saving problem, N 2 The recommended temperature for treatment is 350-400 ℃.
In summary, the present invention utilizes Pt in N 2 The catalyst is not easy to move in atmosphere and easy to generate Pt-Pd alloy, and the catalyst containing both independent single noble metal such as Pt and double noble metal of Pt-Pd alloy particles is prepared, namely, the purpose of reproducing the design scheme of the catalyst by a simple process is achieved.
The invention also provides a diesel vehicle oxidation catalyst prepared by the method.
Advantageous effects
According to the invention, by selecting proper slurry configuration conditions and processing with reasonable temperature and atmosphere, complex production processes (such as using expensive noble metal nano particles, consuming time and energy for multiple roasting) can be avoided, and the bimetallic Pt-Pd catalyst with better performance can be obtained. Wherein noble metals Pt and Pd exist in independent states or alloy states on a support material, and Pt is more resistant to high-temperature aging.
Drawings
FIG. 1 is an X-ray diffraction pattern of a sample after aging at 700℃for 50 hours, wherein a black solid line is a 550℃air-calcined 1% Pt-containing single metal sample (1% Pt/Al) 2 O 3 (Air)), the black dotted line is 550 ℃ Air-calcined sample containing 1% pt and 1% pd in the same material ((1% pt-1% pd)/Al) 2 O 3 (Air)), the dotted line is a sample of 550℃nitrogen treated with 1% Pt and 1% Pd in the same material ((1% Pt-1% Pd)/Al) 2 O 3 (N 2 ))。
FIG. 2 is a comparison of the light-off properties T50 of comparative example-1A and comparative example-1B, the samples being fresh samples.
FIG. 3 is a comparison of the light-off properties T50 of comparative example-1A and comparative example-1C, the samples being fresh samples.
FIG. 4-1 shows the difference between N 2 Examples of treatment temperatures-1A, 1B,1C,1D light-off T50 comparison. The aging conditions of the test sample were 10% H 2 Atmosphere of OAging for 50 hours at 700 ℃.
FIG. 4-2 shows the difference between N 2 Examples of treatment temperatures-1A, 1B,1C,1D NO 2 A performance comparison is generated. The aging conditions of the test sample were 10% H 2 Aging was carried out at 700℃for 50 hours under an air atmosphere of O.
FIG. 4-3 is a comparison of the light-off properties T50 of comparative example-2 and example-1A. The aging conditions of the test sample were 10% H 2 Aging was carried out at 700℃for 50 hours under an air atmosphere of O.
FIGS. 4-4 are NO of comparative example-2 and example-1A 2 A performance comparison is generated. The aging conditions of the test sample were 10% H 2 Aging was carried out at 700℃for 50 hours under an air atmosphere of O.
FIG. 5-1 shows the difference between N 2 Examples of treatment temperatures-2A, 2B,2C,2D light-off T50 comparison. The aging conditions of the test sample were 10% H 2 Aging was carried out at 700℃for 50 hours under an air atmosphere of O.
FIG. 5-2 shows the difference between N 2 Examples of treatment temperatures-NO of 2A,2B,2C,2D 2 A performance comparison is generated. The aging conditions of the test sample were 10% H 2 Aging was carried out at 700℃for 50 hours under an air atmosphere of O.
FIG. 5-3 is a comparison of the light-off properties T50 of comparative example-3 and example-2A. The aging conditions of the test sample were 10% H 2 Aging was carried out at 700℃for 50 hours under an air atmosphere of O.
FIGS. 5-4 are NO of comparative example-3 and example-2A 2 A performance comparison is generated. The aging conditions of the test sample were 10% H 2 Aging was carried out at 700℃for 50 hours under an air atmosphere of O.
Detailed Description
The technical scheme of the invention will be further described in detail below with reference to specific embodiments. It is to be understood that the following examples are illustrative only and are not to be construed as limiting the scope of the invention. All techniques implemented based on the above description of the invention are intended to be included within the scope of the invention.
Unless otherwise indicated, the starting materials and reagents used in the following examples were either commercially available or may be prepared by known methods.
Examples and comparative examples of the present invention basically employed 3 types of slurries, including (1) Pt slurry, (2) Pd slurry and (3) pt—pd concurrent slurry. Each slurry was prepared as follows.
(1) Preparation of Pt slurry: al in a predetermined dry weight 2 O 3 Added to deionized water and stirred for 10 minutes, and a specified amount of Pt (in 10% Pt (NO) 3 ) 4 In the form of (c) was added to the slurry and stirred for 60 minutes. Slurry pH>3.5, the amount of free Pt ions is less than 1wt% of the input amount.
(2) Preparation of Pd slurry: al in a predetermined dry weight 2 O 3 Added to deionized water and stirred for 10 minutes, and the desired amount of Pd (as 10% Pd (NO) 3 ) 2 In the form of (c) was added to the slurry and stirred for 60 minutes. Slurry pH>3.5, the amount of free Pd ions is less than 1wt% of the input amount.
(3) Preparation of Pt-Pd concurrent slurry: al in a predetermined dry weight 2 O 3 Adding deionized water, stirring for 10 min, and stirring to obtain 10% Pt (NO) 3 ) 4 And Pd (NO) 3 ) 2 Added to the slurry and stirred for 60 minutes. Slurry pH>3.5, the amount of free Pt and Pd ions is less than 1wt% of the input amount.
Mixing the components (1), (2) and/or (3) in a certain proportion, stirring for 60 minutes, and grinding into slurry with the average particle size of 3-8 mu m and the solid content of 40%.
The roasting modes are 2 kinds, (1) Air (Air) roasting, (2) nitrogen (N) 2 ) And (5) processing.
(1) Roasting in air;
the slurry containing the noble metal nitrate and the supporting material is coated on a honeycomb carrier, dried for 1h at 120 ℃, and then placed after more than 90% of water is removed.
The temperature was raised to a set temperature (e.g., 550 ℃) at a rate of 10℃per minute in a conventional electric furnace, and after maintaining the set temperature (e.g., 550 ℃) for 1 hour, the temperature was cooled to 200℃to complete the air firing. The dry weight of the total coating of the catalyst was 1.5g/inch 3 。
(2) Nitrogen treatment
The slurry containing the noble metal nitrate and the supporting material is coated on a honeycomb carrier, dried for 1h at 120 ℃, and then placed after more than 90% of water is removed.
Under nitrogen (N) 2 ) Is heated at a rate of 10 ℃/min until the firing temperature (e.g., 350 ℃, 450 ℃, 550 ℃, or 600 ℃) is reached. The calcination time was 1 hour. After calcination, cooling to 90℃to complete N 2 And (5) processing. The dry weight of the total coating of the catalyst was 1.5g/inch 3 。
The raw material compositions and firing atmospheres and temperatures of the examples and comparative examples are shown in tables 1 and 2.
TABLE 1 composition of comparative examples and conditions of calcination or treatment
TABLE 2 composition of examples and comparative examples and conditions of calcination or treatment
Test case
Catalytic reaction test
The catalyst was heated at 700℃and 10% H 2 In the presence of O, the mixture was subjected to hydrothermal aging for 50 hours. The test specimen was 1 inch in diameter and 3 inches in length. The conditions described in Table 3 below test the light-off characteristics and NO of DOC 2 Conversion rate.
Testing the aged catalyst for oxidation of CO, C3H6, C10H22 and nitrogen oxides to NO by passing the gas mixture into a reactor containing a catalyst having a diameter of 1 inch and a length of 3 inches 2 Conversion rate. The reaction is carried out for 50,000 hours at the temperature of 100-550 DEG C -1 Is carried out at a space velocity. The light-off temperature T50 is defined as the inlet temperature at which the catalyst outlet concentration is reduced to 50% of the catalyst inlet concentration. NO at 200 ℃, 250 ℃ and 300 DEG C 2 Conversion is defined as NO when the inlet temperature reaches 200 ℃, 250 ℃ and 300 DEG C 2 Concentration to catalyst inlet NOx concentration.
TABLE 3 catalyst sample test gas conditions
FIG. 4-1 shows the difference between N 2 Examples of treatment temperatures-1A, 1B,1C,1D light-off T50 comparison. As can be seen from FIG. 4-1, the T50 performance does not change much at 350-550℃if N is to be added 2 The treatment temperature was set at 600 ℃, and the T50 performance was reduced.
FIG. 4-2 shows the difference between N 2 Examples of treatment temperatures-1A, 1B,1C,1D NO 2 A performance comparison is generated. As can be seen from FIG. 4-2, NO is present at 350-550℃ 2 The generation efficiency does not change much if N 2 The treatment temperature is set at 600 ℃, NO 2 The production efficiency is lowered.
FIG. 4-3 is a comparison of the light-off properties T50 of comparative example-2 and example-1A. As can be seen from FIGS. 4-3, the temperature of the mixture is 350 ℃ N 2 The treated example-1A had better T50 performance than the air calcined comparative example-2.
FIGS. 4-4 are NO of comparative example-2 and example-1A 2 A performance comparison is generated. As can be seen from FIGS. 4-4, the temperature of the mixture is 350 ℃ N 2 Treated example-1A has a better NO than air-calcined comparative example-2 2 Generating efficiency.
FIG. 5-1 shows the difference between N 2 Examples of treatment temperatures-2A, 2B,2C,2D light-off T50 comparison. As can be seen from FIG. 5-1, the T50 performance does not change much at 350-550℃if N is to be added 2 The treatment temperature was set at 600 ℃, and the T50 performance was reduced.
FIG. 5-2 shows the difference between N 2 Examples of treatment temperatures-NO of 2A,2B,2C,2D 2 A performance comparison is generated. As can be seen from FIG. 5-2, NO is present at 350-550℃ 2 The generation efficiency does not change much if N 2 The treatment temperature was set to 600℃and NO 2 The production efficiency is lowered.
FIG. 5-3 is a comparison of the light-off properties T50 of comparative example-3 and example-2A. As can be seen from fig. 5-3Through 350 ℃ N 2 The treated example-2A had better T50 performance than the air calcined comparative example-3.
FIGS. 5-4 are NO of comparative example-3 and example-2A 2 A performance comparison is generated. As can be seen from FIGS. 5-4, the temperature of the mixture is 350 ℃ N 2 example-2A treated had a better NO than comparative example-3, which was air-calcined 2 Generating efficiency.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The preparation method of the diesel vehicle oxidation catalyst is characterized by comprising the following steps of: coating slurry containing nitric acid noble metal salt and supporting material on a carrier, roasting at 350-550 ℃ in nitrogen atmosphere to prepare the catalyst,
wherein the nitrate noble metal salt is the nitrate of Pt and the nitrate of Pd.
2. The method of claim 1, wherein the slurry comprising a noble metal nitrate salt and a support material comprises a Pt slurry and a Pt-Pd concurrent slurry.
3. The method according to claim 2, wherein the Pt slurry comprises a nitrate of Pt and a supporting material, wherein the Pt content is 10wt% to 90wt% of the total Pt feeding amount,
preferably, the support material is Al 2 O 3 、SiO 2 /Al 2 O 3 、CeO 2 /Al 2 O 3 、BaO/Al 2 O 3 、ZrO 2 /Al 2 O 3 Etc., preferably Al 2 O 3 ，
Preferably, the concentration of Pt in the support material is 0.1 to 3wt%.
4. A production method according to claim 2 or 3, characterized in that the Pt-Pd concurrent slurry contains a nitrate of Pt, a nitrate of Pd and a support material, wherein the weight ratio of the nitrate of Pt and the nitrate of Pd is 0.2:1 to 3:1, and the concentration of the sum of Pt and Pd in the support material is 0.1 to 3wt%.
5. The method according to any one of claims 1 to 4, characterized in that the temperature is raised at a rate of 5-20 ℃/min, preferably 10 ℃/min, under an atmosphere of nitrogen until the calcination temperature is reached.
6. The method according to any one of claims 1 to 5, wherein the calcination time is 0.5 to 5 hours, preferably 1 hour.
7. The method according to any one of claims 1 to 6, wherein the firing temperature is 350 ℃ to 400 ℃.
8. The production method according to any one of claims 1 to 7, characterized in that the production method further comprises: after the slurry containing the noble metal nitrate salt and the support material is applied to the carrier, drying is carried out at 100 to 150 ℃, preferably 120 ℃ for 0.5 to 5 hours, preferably 1 hour.
9. An oxidation catalyst for diesel vehicles, characterized by being obtained by the preparation method according to any one of claims 1 to 8.
10. The catalyst according to claim 9, characterized in that it comprises: single noble metal Pt and double noble metals of pt—pd alloy particles.
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Effective date of registration: 20231024 Address after: 3rd Floor, Building 5, Yard 8, Haixin Road, Daxing District, Beijing 102600 Applicant after: China Chemical Environmental Protection Catalyst Co.,Ltd. Address before: 102488 block B, building 4, yard 1, Jiaotong West Street, Doudian Town, Fangshan District, Beijing Applicant before: China Chemical Science and Technology Research Co.,Ltd. |