A diesel oxidation catalyst and a method for manufacturing the same

Abstract

The application provides a diesel vehicle oxidation catalyst and a preparation method thereof. The preparation method of the diesel vehicle oxidation catalyst comprises the following steps: coating a slurry containing a noble metal nitrate salt and a supporting material on a carrier, and performing calcination at 350-550 DEG C under a nitrogen atmosphere to prepare the catalyst, wherein the noble metal nitrate salt is a nitrate salt of Pt and a nitrate salt of Pd. According to the application, the noble metal slurry as a catalyst raw material is coated on the same carrier in a proper ratio, and nitrogen treatment is performed at a proper temperature to promote the generation of Pt-Pd alloy, so that the synergistic effect of Pt and Pd is enhanced to improve the catalytic performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a diesel vehicle oxidation catalyst and a preparation method thereof, in particular to a high-activity diesel vehicle exhaust oxidation catalyst containing Pt-Pd and a preparation method thereof. BACKGROUND

[0002] With the increasingly stringent standards for automobile exhaust emission in China, the performance requirements for exhaust purification catalysts are also correspondingly improved. Among them, the exhaust purification of diesel vehicles is an urgent issue to be improved. Diesel oxidation catalyst (DOC) is an important component in the diesel exhaust purification system (generally composed of DOC, DPF, SCR and / or ASC). Under the action of DOC, CO and hydrocarbons (HC) generated after diesel combustion are oxidized to CO2 and H2O, which can increase the temperature of the exhaust gas, and at the same time, NO is converted into NO2 with oxidation ability to oxidize the particulate matter such as soluble organic fraction (SOF), soot, etc. captured by the subsequent diesel particulate filter (DPF).

[0003] Generally speaking, a simple method to improve the performance of the catalyst is to increase the amount of metal as the active point of the catalyst. The main active points of DOC are Pt and Pd. Pt has high NO2 conversion ability, sulfur aging resistance, but has strong CO adsorption ability at low temperature, which will affect its light-off characteristics. Moreover, Pt is easy to move under oxygen-rich conditions, which may cause the particles to become coarse and the active points to decrease, or lose activity due to the formation of stable Pt oxides. Pd has CO oxidation ability and stability under oxygen-rich conditions, therefore, the presence of Pd can ensure the light-off property, NO2 conversion ability and high-temperature aging resistance of Pt.

[0004] Currently, in order to improve the performance of the catalyst, the DOC of the diesel vehicle can increase the amount of noble metal to improve the light-off performance, but the large use of noble metal will cause the increase of cost. In addition, it is found in practical application that the DOC using double metal Pt-Pd is superior in performance to the DOC using only Pt or Pd. Moreover, if Pt and Pd are kept at an appropriate distance to enhance the interaction between them, the catalytic performance can be improved. Therefore, the preparation of double metal Pt-Pd catalyst to play the synergistic effect of Pt-Pd is one of the means to reduce the amount of noble metal used. Currently, the industrial DOC catalyst generally completes sample preparation by air calcination below 600℃. Since in air below 600℃, the following situations occur: part of Pt is in the form of metal, and the other part is in the form of oxide, while most of Pd is in the form of PdO (decomposition temperature 860℃), thus being not conducive to the formation of Pt-Pd alloy.

[0005] JP 2019-76853 discloses a method of preparing Pt with a large specific surface area by using a heated hydrogen reduction process, thereby achieving a high-activity Pt catalyst, wherein the optimal starting treatment temperature of the heated hydrogen reduction is 300-600°C.

[0006] JP 2008-272659 discloses a method of dispersing Pt single elements and (Pt-Pd) alloys on heat-resistant inorganic materials respectively, and then mixing them together. The distance between the noble metal particles is controlled according to the surface area of the carrier material. For high-performance catalysts, the shortest distance between the noble metal particles is 5-50 nm, and the distance between 50%-70% of the noble metal particles is 5-300 nm, and most preferably 10-200 nm, in order to inhibit the sintering of the noble metal particles and balance the adsorption of reactants and reactions between them. The disadvantage of this technology is that when the noble metal-containing powder is calcined multiple times, the powder flies, causing loss of raw materials and a longer process flow time, and calcination in air cannot guarantee the preparation of the designed Pt-Pd ratio alloy.

[0007] An article by Fei Dong et al. published in Catalysis Today Volume 376 (2021), P47-54 discloses a DOC with a weight ratio of Pt (1.0% wt%) - Pd (0.5% wt%) prepared using a Pt-Pd nano-alloy colloid as a precursor, which has a lower light-off temperature and better performance.

[0008] JP 2013-5343138 discloses a metal sol solution and a method for preparing the same, which uses noble metal nano-alloy particles, has a complicated process and a large amount of noble metal loss.

[0009] In summary, although the prior art documents disclose methods for improving the performance of a single noble metal Pt, such as by treating it in a hydrogen atmosphere, and methods for improving the performance and stability of a bimetallic Pt-Pd catalyst, such as by using Pt-Pd nano-alloy particles as a precursor and multiple calcination processes. However, these methods are complicated, time-consuming and have a large amount of noble metal loss, resulting in increased costs. SUMMARY

[0010] To solve the problems in the prior art described above, the present application does not use the method of treating nano noble metal particles with hydrogen, which has a high preparation cost, nor does it use the multiple calcination process, which is time-consuming, energy-consuming and loses noble metals. Instead, the present application coats the noble metal slurry as a catalyst raw material on the same carrier (supporting material) in the appropriate ratio, and performs nitrogen treatment at an appropriate temperature to promote the formation of Pt-Pd alloy, thereby enhancing the synergistic effect of Pt and Pd to achieve the effect of improving the catalytic performance.

[0011] The technical solution of the present application is as follows:

[0012] The preparation method of the diesel vehicle oxidation catalyst comprises the following steps: coating slurry containing noble metal nitrate salt and support material on the carrier, and then performing calcination at 350-550 DEG C under the atmosphere of nitrogen (N2) to obtain the catalyst, wherein the noble metal nitrate salt is Pt nitrate and Pd nitrate.

[0013] According to the description of the prior art such as JP 2008-272659, the diesel oxidation catalyst of Pt-Pd type generally contains independent Pt and (Pt-Pd) alloy, and the distance between the active point noble metals is controlled by using stable carrier material and appropriate additive amount to achieve the improvement of aging resistance. Alternatively, as described by Fei Dong et al., the light-off characteristics can be significantly improved by using Pt-Pd nano-alloy colloid as precursor. At present, the catalyst is generally prepared by calcining and decomposing noble metal salt and other salts in air.

[0014] However, in the present application, the inventors consider using nitrogen atmosphere for treatment. The difference between the effects brought by air calcination and nitrogen treatment may lie in whether oxide is generated as product. Under air calcination, Pt(NO3)4 generates PtO2, and Pd(NO3)2 generates PdO. The melting point of PdO is 860 DEG C, and it is relatively stable. The melting point of PtO2 is 450 DEG C, and PtO2 will melt at the air calcination temperature above 450 DEG C. The melting thereof generates fluidity, which may bring undesired fusion between Pt and Pd, and also may cause the noble metal itself to become coarse. Regarding the product of nitrogen treatment, it is speculated that PtO2 is easy to be deoxidized and decomposed into Pt under nitrogen condition, and the melting point of Pt is 1768 DEG C, which is relatively not easy to move on the carrier material.

[0015] Air calcination Pt(NO3)4→Pt / PtO2+NO2+O2

[0016] Pd(NO3)2→Pd / PdO+NOx

[0017] N2 treatment Pt(NO3)4→Pt+NO X

[0018] Pd(NO3)2→Pd+NOx

[0019] The inventors of the present invention found that Pt and Pd salts, when calcined in air, form oxides and thus Pt-Pd alloys cannot be formed even when they are placed on the same support. In this regard, the inventors compared the test data of the aged samples, i.e. XRD test data (test equipment model Rigaku Miniflex 600C, scan speed 0.5° / min) of 1% Pt / Al203 calcined in air, (1% Pt-1% Pd) / Al203 calcined in air and (1% Pt-1% Pd) / Al203 treated in N2. The results showed that the peak attributed to PdO (2Θ - around 33.96°) was very clear in the (1% Pt-1% Pd) / Al203 sample calcined in air after 50 hours of aging at 700°C, indicating that part of the Pd existed in the form of PdO. In addition, the peak attributed to Pt (2Θ - around 39.85°) in this sample was shifted by 0.15° compared to the diffraction peak of the monometallic 1% Pt / Al203 (39.70°), and the crystal particle size was about 22 nm. On the other hand, no clear peak attributed to PdO was found in the (1% Pt-1% Pd) / Al203 sample treated in N2 even after aging, and the peak attributed to Pt was at 39.98°, shifted by 0.28° towards Pd (40.12°), and the crystal particle was about 9 nm. This indicates that N2 treatment is more conducive to the formation of Pt-Pd and the inhibition of the increase of Pt particles. That is, if a small amount of Pd is used to stabilize Pt, N2 treatment will have a better effect (see Figure 1 ).

[0020] In addition, the inventors also compared a catalyst in which Pt and Pd were mixed beforehand and then placed on a support material (see Comparative Example-1A in the Examples section) and a catalyst in which Pt and Pd were placed on different support materials beforehand (see Comparative Example-1B in the Examples section), and the performance of the two was roughly the same after calcination in air at 550°C (see Figure 2 ). It is speculated that there can be two reasons for this. One is that Pt moves to the position of Pd under the condition of calcination in air at 550°C; the other, a more important reason, is that even if the two metals are placed on the same support material, Pt and Pd remain independent of each other, and the Pt-Pd formed is very limited.

[0021] In addition, the inventors also compared two samples, the first of which was a catalyst in which Pt and Pd were mixed beforehand and then placed on a support material, and the second of which was a catalyst in which Pt and Pd were placed on different support materials beforehand, and the first of which was calcined in air at 550°C (Comparative Example-1A) and the second of which was treated in N2 at 550°C (Comparative Example-1C). The performance test results showed that the performance of the catalyst of Comparative Example-1C treated in N2 was inferior to that of Comparative Example-1A calcined in air (seeFigure 3 ). Thus, if Pt and Pd are not placed together on the same support material in advance, the N2-treated catalyst cannot obtain the synergistic effect of Pt-Pd together as in the case of air calcination.

[0022] Based on the above test results, the inventors believe that both the calcination conditions and the placement method are important factors affecting the characteristics of Pt and Pt-Pd. Under the air calcination conditions, even if the two metals are placed on the same support material, a Pt-Pd alloy of the designed ratio cannot be formed, and thus a finished product of Pt and Pt-Pd alloy of the desired ratio cannot be prepared. In addition, as in the prior art, treatment with the reducing gas hydrogen (H2) is strictly required for the safety of mass production equipment, and can greatly increase the production cost. The present application uses the non-reactive gas nitrogen (N2) which is cheaper and safer than H2, and by optimizing the N2 treatment conditions, the positive effect of reducing the amount of noble metal brought by the N2 treatment conditions will be greater than the negative effect caused by the investment in equipment, etc.

[0023] According to an embodiment of the present application, the support is a honeycomb support.

[0024] According to an embodiment of the present application, the slurry containing a noble metal nitrate salt and a support material includes a Pt slurry and a Pt-Pd coexisting slurry. By using such a slurry, it is easy to prepare a bimetallic catalyst containing both independent single metal Pt and Pt-Pd alloy particles.

[0025] According to an embodiment of the present application, the Pt slurry contains a Pt nitrate salt and a support material, wherein the Pt content is 10 wt% to 90 wt% of the total Pt feed amount, preferably 15 wt% to 75 wt%, more preferably 20 wt% to 60 wt%, and further preferably 25 wt% to 50 wt%. For example, the slurry containing a noble metal nitrate salt and a support material can contain 25% Pt slurry and 75% Pt-Pd coexisting slurry, or 50% Pt slurry and 50% Pt-Pd coexisting slurry.

[0026] According to an embodiment of the present application, the support material can be AI2O3, SiO2 / AI2O3, CeO2 / AI2O3, BaO / AI2O3, ZrO2 / AI2O3, etc., and is preferably AI2O3.

[0027] According to an embodiment of the present application, in the Pt slurry, the concentration of Pt in the support material is 0.1 to 3 wt%, preferably 0.15 to 2.5 wt%, and more preferably 0.3 to 1.1 wt%.

[0028] According to an embodiment of the present application, the pH of the Pt slurry is > 3.5, and the amount of free Pt ions is 1 wt% or less of the amount of the Pt nitrate salt added.

[0029] According to an embodiment of the present application, the Pt-Pd coexisting slurry comprises a nitrate salt of Pt, a nitrate salt of Pd, and a support material, wherein the weight ratio of the nitrate salt of Pt to the nitrate salt of Pd is 0.2:1 to 3:1, and the total concentration of Pt and Pd in the support material is 0.1 to 3 wt%, preferably 0.15 to 2.5 wt%, and more preferably 0.3 to 1.1 wt%. The support material can be selected from the same range as the support material in the Pt slurry.

[0030] According to an embodiment of the present application, the pH of the Pt-Pd coexisting slurry is greater than 3.5, and the amount of free Pt and Pd ions is each less than 1 wt% of the amount of the added nitrate salt of Pt and the nitrate salt of Pd.

[0031] According to an embodiment of the present application, the solid content of the slurry containing the noble metal nitrate salt and the support material is 20 to 60%, and preferably 40%.

[0032] According to an embodiment of the present application, the preparation method further comprises grinding the slurry containing the noble metal nitrate salt and the support material to have an average particle size of 3 to 8 μm before being coated on the support.

[0033] According to an embodiment of the present application, the method of coating the slurry can be a coating method commonly used in the art, such as dip coating, spray coating, roll coating, etc.

[0034] According to an embodiment of the present application, when the slurry containing the noble metal nitrate salt and the support material is coated on the support, the total dry weight of the catalyst coating is 0.2 to 5.0 g / inch 3 , preferably 1.0 to 4.0 g / inch 3 , and exemplarily 1.5 g / inch 3 .

[0035] According to an embodiment of the present application, the preparation method further comprises drying the slurry containing the noble metal nitrate salt and the support material at 100 to 150°C, and preferably 120°C, for 0.5 to 5 hours, and preferably 1 hour after being coated on the support. By drying, more than 90% of the water can be removed.

[0036] According to an embodiment of the present application, the temperature is increased at a rate of 5 to 20°C / min, and preferably 10°C / min, until the calcination temperature is reached, in an atmosphere of nitrogen (N2).

[0037] According to an embodiment of the present application, the calcination time is 0.5 to 5 hours, and preferably 1 hour.

[0038] According to an embodiment of the present application, after the calcination, the temperature can be cooled down to 90°C, thereby completing the N2 treatment.

[0039] According to the embodiment of the present application, the calcination temperature can be set at above 350°C and less than 600°C. As shown in the following examples, the sample was tested by thermogravimetry method, and it was found that the weight did not change significantly after 350°C under N2 atmosphere. It was also found that the catalyst performance did not change much when the N2 treatment temperature was set at 350-550°C, and the catalyst performance would decrease if the N2 treatment temperature was set at 600°C (see Table 1). Figure 4-1 , Figure 4-2 , Figure 5-1 , Figure 5-2 In addition, considering the energy saving, the recommended N2 treatment temperature is 350-400°C.

[0040] In summary, the present application utilizes the characteristics that Pt is not easy to move under N2 atmosphere and Pt-Pd alloy is easy to form, and prepares a dual noble metal catalyst containing both independent single noble metal such as Pt and Pt-Pd alloy particles, i.e. achieves the purpose of reproducing the design scheme of the catalyst by a simple process.

[0041] The present application also provides a diesel vehicle oxidation catalyst prepared by the above method.

[0042] Advantages

[0043] The present application can avoid using a complex production process (such as using expensive noble metal nanoparticles, consuming time and energy, and multiple calcinations) to obtain a dual metal Pt-Pd catalyst with good performance by selecting appropriate slurry configuration conditions, and processing with reasonable temperature and atmosphere. The noble metals Pt and Pd exist in an independent state or an alloy state on the support material, and Pt is more resistant to high temperature aging. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 X-ray diffraction pattern of the sample after aging at 700°C for 50 hours, wherein the black solid line is the 1% Pt-containing single metal sample calcined at 550°C in air (1% Pt / Al2O3(Air)), the black dotted line is the sample containing 1% Pt and 1% Pd in the same material calcined at 550°C in air ((1% Pt-1% Pd) / Al2O3(Air)), and the dotted line is the sample containing 1% Pt and 1% Pd in the same material treated at 550°C in nitrogen ((1% Pt-1% Pd) / Al2O3(N2)).

[0045] Figure 2 The light-off performance T50 of Comparative Example-1A and Comparative Example-1B was compared, and the sample was a fresh sample.

[0046] Figure 3 The light-off performance T50 of Comparative Example-1A and Comparative Example-1C was compared, and the sample was a fresh sample.

[0047] Figure 4-1 The ignition performance T50 of Examples-1A, 1B, 1C, 1D at different N2treatment temperatures were compared. The aging condition of the tested samples was 700°C aging for 50 hours in air atmosphere containing 10% H2O.

[0048] Figure 4-2 The NO2generation performance of Examples-1A, 1B, 1C, 1D at different N2treatment temperatures were compared. The aging condition of the tested samples was 700°C aging for 50 hours in air atmosphere containing 10% H2O.

[0049] Figure 4-3 The ignition performance T50 of Comparative Example-2 and Example-1A were compared. The aging condition of the tested samples was 700°C aging for 50 hours in air atmosphere containing 10% H2O.

[0050] Figure 4-4 The NO2generation performance of Comparative Example-2 and Example-1A were compared. The aging condition of the tested samples was 700°C aging for 50 hours in air atmosphere containing 10% H2O.

[0051] Figure 5-1 The ignition performance T50 of Examples-2A, 2B, 2C, 2D at different N2treatment temperatures were compared. The aging condition of the tested samples was 700°C aging for 50 hours in air atmosphere containing 10% H2O.

[0052] Figure 5-2 The NO2generation performance of Examples-2A, 2B, 2C, 2D at different N2treatment temperatures were compared. The aging condition of the tested samples was 700°C aging for 50 hours in air atmosphere containing 10% H2O.

[0053] Figure 5-3 The ignition performance T50 of Comparative Example-3 and Example-2A were compared. The aging condition of the tested samples was 700°C aging for 50 hours in air atmosphere containing 10% H2O.

[0054] Figure 5-4 The NO2generation performance of Comparative Example-3 and Example-2A were compared. The aging condition of the tested samples was 700°C aging for 50 hours in air atmosphere containing 10% H2O. DETAILED DESCRIPTION

[0055] The technical solutions of the present application will be further described in detail below in combination with specific examples. It should be understood that the following examples are only illustratively used to explain and describe the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above description of the present application is covered within the scope of protection intended by the present application.

[0056] The starting materials and reagents used in the following examples are commercially available or can be prepared by known methods unless otherwise stated.

[0057] The examples and comparative examples of the present application basically use three types of slurry, including (1) Pt slurry, (2) Pd slurry and (3) Pt-Pd coexisting slurry. Each slurry is prepared as follows.

[0058] (1) Preparation of Pt slurry: A predetermined dry weight of Al2O3 is added to deionized water and stirred for 10 minutes, and a predetermined amount of Pt (in the form of 10% Pt(NO3)4) solution is added to the slurry while stirring, and stirred for 60 minutes. The slurry has a pH of more than 3.5, and the amount of free Pt ions is 1 wt% or less of the amount of Pt added.

[0059] (2) Preparation of Pd slurry: A predetermined dry weight of Al2O3 is added to deionized water and stirred for 10 minutes, and a predetermined amount of Pd (in the form of 10% Pd(NO3)2) solution is added to the slurry while stirring, and stirred for 60 minutes. The slurry has a pH of more than 3.5, and the amount of free Pd ions is 1 wt% or less of the amount of Pd added.

[0060] (3) Preparation of Pt-Pd coexisting slurry: A predetermined dry weight of Al2O3 is added to deionized water and stirred for 10 minutes, and 10% Pt(NO3)4 and Pd(NO3)2 are added to the slurry while stirring, and stirred for 60 minutes. The slurry has a pH of more than 3.5, and the amount of free Pt and Pd ions is 1 wt% or less of the amount of Pt and Pd added.

[0061] The predetermined proportions of (1), (2) and / or (3) are mixed and stirred for 60 minutes, and then ground to a slurry having an average particle diameter of 3-8 μm and a solid content of 40%.

[0062] There are two types of calcination, (1) air (Air) calcination, and (2) nitrogen (N2) treatment.

[0063] (1) Air calcination

[0064] After the slurry containing the noble metal nitrate salt and the support material is applied to the honeycomb support, it is dried at 120°C for 1 hour to remove 90% or more of the water, and then left to stand.

[0065] In a general electric furnace, the temperature is raised to a set temperature (e.g., 550°C) at a rate of 10°C / min, and after maintaining the set temperature (e.g., 550°C) for 1 hour, the temperature is cooled to 200°C, thereby completing the air calcination. The total dry weight of the catalyst coating is 1.5 g / inch 3 .

[0066] (2) Nitrogen treatment

[0067] The slurry containing the noble metal nitrate salt and the support material was coated on the honeycomb support, dried at 120°C for 1 hour to remove more than 90% of the water, and then aged.

[0068] The temperature was increased at a rate of 10°C / min under a nitrogen (N2) atmosphere until the calcination temperature (e.g., 350°C, 450°C, 550°C, or 600°C) was reached. The calcination time was 1 hour. After calcination, the temperature was decreased to 90°C to complete the N2treatment. The total coating dry weight of the catalyst was 1.5 g / inch 3 .

[0069] The raw material composition and calcination atmosphere and temperature for the examples and comparative examples are shown in Tables 1 and 2.

[0070] Table 1. Comparative Example Sample Composition and Calcination or Treatment Conditions

[0071]

[0072] Table 2. Example and Comparative Example Sample Composition and Calcination or Treatment Conditions

[0073]

[0074] Test Examples

[0075] Catalytic Reaction Testing

[0076] The catalysts were hydrothermally aged at 700°C in the presence of 10% H2O for 50 hours. The test samples had a diameter of 1 inch and a length of 3 inches. The light-off characteristics and NO2conversion of the DOCs were tested under the conditions described in Table 3 below.

[0077] The oxidation of CO, C3H6, C10H22, and nitrogen oxides to NO2conversion of the aged catalysts was tested by passing the above gas mixture into a reactor containing a catalyst having a diameter of 1 inch and a length of 3 inches. The reaction was performed at a space velocity of 50,000 h -1 over a temperature range of 100°C to 550°C. The light-off temperature T50was defined as the inlet temperature at which the concentration at the outlet of the catalyst was reduced to 50% of the concentration at the inlet of the catalyst. The NO2conversion at 200°C, 250°C, and 300°C was defined as the ratio of the NO2concentration to the NOxconcentration at the inlet of the catalyst when the inlet temperature reached 200°C, 250°C, and 300°C, respectively.

[0078] Table 3. Catalyst Sample Test Gas Conditions

[0079]

[0080] Figure 4-1 The light-off performance T50of Examples-1A, 1B, 1C, and 1D at different N2treatment temperatures were compared. The results are shown in Table 4. Figure 4-1It can be seen that the performance of T50 does not change much between 350-550℃, but if the N2 treatment temperature is set at 600℃, the performance of T50 decreases.

[0081] Figure 4-2 A comparison of NO2 generation performance of Examples 1A, 1B, 1C, and 1D at different N2 treatment temperatures. Figure 4-2 It can be seen that the NO2 generation efficiency does not change much between 350-550℃, but if the N2 treatment temperature is set at 600℃, the NO2 generation efficiency decreases.

[0082] Figure 4-3 For the comparison of ignition performance T50 between Comparative Example-2 and Example-1A. (From...) Figure 4-3 It can be seen that Example-1A, which was treated with N2 at 350℃, has better T50 performance than Comparative Example-2, which was calcined in air.

[0083] Figure 4-4 For the comparison of NO2 generation performance between Comparative Example-2 and Example-1A. Figure 4-4 It can be seen that Example-1A, which was treated with N2 at 350℃, had a better NO2 generation efficiency than Comparative Example-2, which was roasted in air.

[0084] Figure 5-1 A comparison of the ignition performance (T50) of Examples 2A, 2B, 2C, and 2D at different N2 treatment temperatures. (By...) Figure 5-1 It can be seen that the performance of T50 does not change much between 350-550℃, but if the N2 treatment temperature is set to 600℃, the performance of T50 decreases.

[0085] Figure 5-2 A comparison of NO2 generation performance of Examples 2A, 2B, 2C, and 2D at different N2 treatment temperatures. Figure 5-2 It can be seen that the NO2 generation efficiency does not change much between 350-550℃, but if the N2 treatment temperature is set to 600℃, the NO2 generation efficiency decreases.

[0086] Figure 5-3 For the comparison of ignition performance T50 between Comparative Example-3 and Example-2A. (From...) Figure 5-3 It can be seen that Example-2A, which was treated with N2 at 350℃, has better T50 performance than Comparative Example-3, which was calcined in air.

[0087] Figure 5-4 For the comparison of NO2 generation performance between Comparative Example-3 and Example-2A. Figure 5-4 It can be seen that Example-2A, which was treated with N2 at 350℃, had a better NO2 generation efficiency than Comparative Example-3, which was roasted in air.

[0088] The above describes the embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, and the like made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A method for producing a diesel oxidation catalyst, characterized by, The method comprises the following steps: The slurry containing the noble metal nitrate salt and the support material is coated on the carrier, and then calcination is performed at 350-550℃ under the atmosphere of nitrogen to prepare the catalyst. The noble metal nitrate salt is a nitrate salt of Pt and a nitrate salt of Pd. The slurry containing the noble metal nitrate salt and the support material comprises a Pt slurry and a Pt-Pd coexisting slurry. The Pt slurry comprises the nitrate salt of Pt and the support material, wherein the content of Pt is 15wt%-75wt% of the total amount of Pt raw materials. The Pt-Pd coexisting slurry comprises the nitrate salt of Pt, the nitrate salt of Pd and the support material, wherein the weight ratio of the nitrate salt of Pt to the nitrate salt of Pd is 0.2:1-3:1, and the total concentration of Pt and Pd in the support material is 0.1-3wt%.

2. The production method according to claim 1, characterized by, The support material in the Pt slurry is Al2O3, SiO2 / Al2O3, CeO2 / Al2O3, BaO / Al2O3 or ZrO2 / Al2O3.

3. The preparation method according to claim 2, characterized in that, The support material is Al2O3.

4. The production method according to any one of claims 1 to 3, characterized by, The concentration of Pt in the support material in the Pt slurry is 0.1-3wt%.

5. The preparation method according to claim 1, characterized in that, The support material in the Pt-Pd coexisting slurry is Al2O3, SiO2 / Al2O3, CeO2 / Al2O3, BaO / Al2O3 or ZrO2 / Al2O3.

6. The preparation method according to claim 5, characterized in that, The support material in the Pt-Pd coexisting slurry is Al2O3.

7. The production method according to any one of claims 1 to 3, 5 to 6, characterized by, The temperature is raised at a speed of 5-20℃ / min until the calcination temperature is reached under the atmosphere of nitrogen.

8. The preparation method according to claim 7, characterized in that, The temperature is raised at a speed of 10℃ / min until the calcination temperature is reached under the atmosphere of nitrogen.

9. The production method according to any one of claims 1 to 3, 5 to 6, characterized by, The calcination time is 0.5-5h.

10. The method of claim 9, wherein, The calcination time is 1h.

11. The production method according to any one of claims 1 to 3, 5 to 6, characterized by, The calcination temperature is 350℃-400℃.

12. The production method according to any one of claims 1 to 3, 5 to 6, characterized by, The preparation method further comprises: after the slurry containing the noble metal nitrate salt and the support material is coated on the carrier, drying is performed at 100-150℃, and the drying time is 0.5-5h.

13. The method of claim 12, wherein, After the slurry containing the noble metal nitrate salt and the support material is coated on the carrier, drying is performed at 120℃, and the drying time is 1h.

14. A diesel oxidation catalyst characterized by comprising: The catalyst is obtained by the preparation method in any one of claims 1-13, and the catalyst comprises: independent single noble metal Pt and Pt-Pd alloy particles.

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