Diesel vehicle oxidation catalyst for improving CO low-temperature light-off performance and preparation method thereof

Abstract

The invention provides a diesel vehicle oxidation type catalyst for improving CO low-temperature light-off performance, and relates to the technical field of catalysts.The catalyst comprises a carrier and an active coating, the carrier is coated with the active coating, precious metal Pt and precious metal Pd are loaded in the active coating, the active coating comprises cerium oxide and bismuth-lanthanum-aluminum composite oxide, and the bismuth-lanthanum-aluminum composite oxide is loaded in the active coating. The coating amount of the active coating is 90-120 g / L, and the coating amount of the noble metal is 0.5-0.9 g / L. According to the diesel vehicle oxidation type catalyst for improving the CO low-temperature light-off performance and the preparation method of the diesel vehicle oxidation type catalyst, the bismuth-lanthanum-aluminum composite oxide is prepared through an equivalent-volume impregnation method, the bismuth-lanthanum-aluminum composite oxide serves as an active coating substrate, the anchoring effect of a coating on precious metal Pt / Pd can be effectively enhanced, and the CO low-temperature light-off performance can be improved. Meanwhile, a certain proportion of cerium oxide is added into the formula of the active coating, so that the low-temperature CO ignition activity of the coating is further improved; the diesel vehicle oxidation type catalyst prepared by the invention is low in ignition temperature, simple in preparation method and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to an oxidation catalyst for diesel vehicles capable of improving the low-temperature ignition performance of CO and a preparation method thereof. Background Art

[0002] HC (including various chain hydrocarbons and aromatic hydrocarbons) and CO in diesel vehicle exhaust are produced by incomplete combustion of diesel and lubricating oil, and the content in exhaust varies under different working conditions. Usually, more HC and CO are produced during cold start. The concentration of HC and CO in exhaust is very low under the traditional combustion mode of diesel engine, but in the new combustion mode (such as premixed compression ignition, which can reduce NO at the same time), the concentration of HC and CO in exhaust is very low. x and PM production), a considerable amount of HC and CO will be produced.

[0003] The main functions of diesel oxidation catalyst (DOC) are: (1) converting pollutants such as carbon monoxide (CO), hydrocarbons (HC) and soluble organic matter (SOF) in particulate matter (PM) in diesel engine exhaust into non-toxic CO2 and H2O; (2) oxidizing NO, with part of the produced NO2 being used for passive and continuous regeneration of particulate matter and the other part being used for rapid SCR reaction to improve the denitrification efficiency under low-temperature conditions; the exhaust temperature of diesel vehicles under most driving conditions is below 250°C, which directly leads to insufficient conversion rate of HC / CO by DOC; increasing the amount of precious metals in DOC can improve the low-temperature ignition activity of the coating to a certain extent, but the large amount of HC / CO emitted during the cold start phase cannot be effectively treated.

[0004] With the further upgrading of national motor vehicle exhaust emission regulations, DOC's HC and CO gas phase pollution treatment capabilities face severe challenges; DOC products currently on the market generally have problems such as poor low-temperature ignition activity and high T50 (the temperature at which the pollutant conversion rate is 50%), so it is particularly critical to improve DOC's low-temperature ignition capability. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a diesel vehicle oxidation catalyst for improving the CO low-temperature ignition performance and a preparation method thereof. The catalyst has the advantage of a low CO ignition temperature.

[0006] The technical solution adopted by the present invention is:

[0007] A diesel vehicle oxidation catalyst for improving the low-temperature ignition performance of CO, comprising a carrier and an active coating coated on the carrier, wherein the active coating comprises cerium oxide and a bismuth-lanthanum-aluminum composite oxide, the active coating is loaded with precious metals Pt and Pd, the coating amount of the active coating is 90-120 g / L, and the coating amount of the precious metal is 0.5-0.9 g / L.

[0008] Preferably, in the diesel vehicle oxidation catalyst for improving the CO low temperature ignition performance, the mass ratio of the precious metal Pt to the precious metal Pd is 2 to 9:1.

[0009] Preferably, in the diesel vehicle oxidation catalyst for improving the CO low temperature ignition performance, the mass ratio of the cerium oxide to the bismuth-lanthanum-aluminum composite oxide is 1:49-69.

[0010] Preferably, in the diesel vehicle oxidation catalyst for improving the CO low temperature ignition performance, the mass ratio of bismuth oxide, lanthanum oxide and aluminum oxide in the bismuth-lanthanum-aluminum composite oxide is 2 to 3:3:97.

[0011] The present invention also provides a method for preparing a diesel vehicle oxidation catalyst for improving CO low temperature ignition performance, which comprises the following steps:

[0012] Step S1. preparing bismuth-lanthanum-aluminum composite oxide by equal volume impregnation method: weighing bismuth nitrate and lanthanum-aluminum composite oxide respectively according to the mass ratio of bismuth oxide to lanthanum-aluminum composite oxide material of 2 to 3:100, preparing bismuth nitrate aqueous solution according to the saturated adsorption amount of lanthanum-aluminum composite oxide, adding the prepared bismuth nitrate aqueous solution dropwise to lanthanum-aluminum composite oxide and continuously stirring for 2 to 4 hours, then aging, drying, and calcining to obtain bismuth-lanthanum-aluminum composite oxide;

[0013] Step S2. Preparation of active coating slurry: adding cerium acetate and bismuth-lanthanum-aluminum composite oxide to deionized water in a mass ratio of cerium oxide to bismuth-lanthanum-aluminum composite oxide of 1:49-69, stirring to form a slurry, then ball-milling the slurry, and then adding precious metal Pt and Pd precursor solutions to the ball-milled slurry, stirring evenly, to form an active coating slurry;

[0014] Step S3. Active slurry coating: soak the carrier in the active coating slurry for 0.5 to 5 minutes and then take it out. Then, use compressed air to blow the channels inside the carrier. Then, dry and calcine the carrier to obtain a diesel vehicle oxidation catalyst with improved CO low-temperature ignition performance.

[0015] Preferably, the method for preparing a diesel vehicle oxidation catalyst for improving the low-temperature ignition performance of CO is as follows: the aging time in step S1 is 6 to 10 hours, the drying temperature is 100 to 150°C, the drying time is 4 to 8 hours, the calcination temperature is 500 to 600°C, and the calcination time is 2 to 4 hours.

[0016] Preferably, the method for preparing a diesel vehicle oxidation catalyst for improving CO low temperature ignition performance, wherein: in step S2, the mass ratio of the total mass of the oxide in the slurry to the mass of the deionized water is 1:2-3, and the particle size D of the slurry after ball milling is90 10~20μm.

[0017] Preferably, in the method for preparing a diesel vehicle oxidation catalyst for improving CO low temperature ignition performance, the precious metal Pt precursor in step S2 is platinum oxalate.

[0018] Preferably, in the method for preparing the diesel vehicle oxidation catalyst for improving the CO low temperature ignition performance, the purge time in step S3 is 0.5 to 3 minutes.

[0019] Preferably, the method for preparing a diesel vehicle oxidation catalyst for improving the CO low temperature ignition performance, wherein: in step S3, the drying temperature is 100-150°C, the drying time is 4-8h, the calcination temperature is 450-550°C, and the calcination time is 1-2h.

[0020] Advantages of the present invention:

[0021] The diesel vehicle oxidation catalyst for improving the CO low-temperature ignition performance of the present invention and the preparation method thereof, prepare the bismuth-lanthanum-aluminum composite oxide by an equal volume impregnation method, use it as the active coating substrate, can effectively enhance the anchoring effect of the coating on the precious metal Pt / Pd, and at the same time add a certain proportion of cerium oxide to the active coating, further improve the low-temperature CO ignition activity of the coating; the diesel vehicle oxidation catalyst prepared by the present invention has a low ignition temperature, and the preparation method is simple and suitable for industrial production. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with specific embodiments.

[0023] Example 1

[0024] A diesel vehicle oxidation catalyst for improving CO low-temperature ignition performance comprises a cordierite honeycomb ceramic carrier and an active coating coated on the cordierite honeycomb ceramic carrier, wherein the volume of the cordierite honeycomb ceramic is 1.6 liters and the pore density is 400 meshes / square foot, the active coating comprises cerium oxide and a bismuth-lanthanum-aluminum composite oxide, the active coating is loaded with precious metals Pt and Pd, the coating amount of the active coating is 100 g / L, and the coating amount of the precious metal is 0.5 g / L; the mass ratio of the precious metals Pt and Pd is 3:1; the mass ratio of bismuth oxide to lanthanum-aluminum composite oxide is 1:50, the mass ratio of cerium oxide to bismuth-lanthanum-aluminum composite oxide is 1:49; the mass ratio of bismuth oxide, lanthanum oxide and aluminum oxide in the bismuth-lanthanum-aluminum composite oxide is 2:3:97.

[0025] The method for preparing a diesel vehicle oxidation catalyst for improving CO low temperature ignition performance of this embodiment comprises the following steps:

[0026] Step S1. preparing bismuth-lanthanum-aluminum composite oxide by equal volume impregnation method: according to the mass ratio of bismuth oxide to commercial lanthanum-aluminum composite oxide material of 2:100, 41.7 g of bismuth nitrate pentahydrate and 1000 g of lanthanum-aluminum composite oxide are weighed respectively, and a bismuth nitrate aqueous solution is prepared according to the saturated adsorption amount of lanthanum-aluminum composite oxide, and the prepared bismuth nitrate aqueous solution is added dropwise to the lanthanum-aluminum composite oxide and stirred for 3 hours, then aged for 3 hours, and then dried and roasted to obtain bismuth-lanthanum-aluminum composite oxide, the drying temperature is 110° C., the drying time is 8 hours, the roasting temperature is 500° C., and the roasting time is 3 hours;

[0027] Step S2. Preparation of active coating slurry: According to the mass ratio of cerium oxide to bismuth-lanthanum-aluminum composite oxide of 1:49, weigh 1900 g of deionized water, add 800 g of bismuth-lanthanum-aluminum composite oxide and 29 g of cerium acetate to the deionized water, stir evenly to form a slurry, and then ball-mill the slurry to a particle size D 90 The particle size is 18 μm, and then platinum oxalate solution and palladium nitrate solution are added to the ball-milled slurry and stirred for 4 hours to form an active coating slurry;

[0028] Step S3. Active slurry coating: soak the cordierite ceramic honeycomb carrier in the active slurry for 1 minute and then take it out. Then, use compressed air to blow the channels inside the carrier for 1 minute. Then, dry and calcine the carrier to obtain a diesel vehicle oxidation catalyst with improved CO low-temperature ignition performance. The drying temperature is 120°C, the drying time is 6 hours, the calcination temperature is 500°C, and the calcination time is 2 hours.

[0029] Example 2

[0030] The preparation method of Example 2 is the same as that of Example 1, except that the mass ratio of bismuth oxide to lanthanum-aluminum composite oxide (mass ratio of lanthanum oxide to aluminum oxide is 3:97) in the bismuth-lanthanum-aluminum composite oxide is 3:100.

[0031] Example 3

[0032] The preparation method of Example 3 is the same as that of Example 1, except that the mass ratio of cerium oxide to bismuth-lanthanum-aluminum composite oxide in the active coating is 1:69.

[0033] Example 4

[0034] The preparation method of Example 4 is the same as that of Example 1, except that the mass ratio of precious metal Pt to precious metal Pd in ​​the active coating is 9:1.

[0035] Example 5

[0036] The preparation method of Example 4 is the same as that of Example 1, except that the coating amount is 120 g / L and the coating amount of the precious metal is 0.9 g / L.

[0037] Comparative Example 1

[0038] The preparation method of Comparative Example 1 is the same as that of Example 1, except that the precursor of the precious metal Pt in the active coating is platinum nitrate.

[0039] Comparative Example 2

[0040] The preparation method of Comparative Example 2 is the same as that of Example 1, except that the precursor of the precious metal Pt in the active coating is platinum nitrate, and cerium oxide is not added to the coating.

[0041] The preparation method of Comparative Example 2 is as follows:

[0042] Step S1. preparing bismuth-lanthanum-aluminum composite oxide by equal volume impregnation method: according to the mass ratio of bismuth oxide to lanthanum-aluminum composite oxide material of 2:100, 41.7 g of bismuth nitrate pentahydrate and 1000 g of commercial lanthanum-aluminum composite oxide are weighed respectively, and a bismuth nitrate aqueous solution is prepared according to the saturated adsorption amount of lanthanum-aluminum composite oxide, and the prepared bismuth nitrate aqueous solution is added dropwise to the lanthanum-aluminum composite oxide and stirred for 3 hours, then aged for 3 hours, and then dried and roasted to obtain bismuth-lanthanum-aluminum composite oxide, the drying temperature is 110° C., the drying time is 8 hours, the roasting temperature is 500° C., and the roasting time is 3 hours;

[0043] Step S2. Preparation of active coating slurry: Weigh 1900 g of deionized water, add 800 g of bismuth-lanthanum-aluminum composite oxide to the deionized water, stir evenly to form a slurry, and then ball-mill the slurry to a particle size D 90 The particle size was 18 μm, and then platinum nitrate solution and palladium nitrate solution were added to the ball-milled slurry and stirred for 4 hours to form an active coating slurry;

[0044] Step S3. Active slurry coating: soak the cordierite ceramic honeycomb carrier in the active slurry for 1 minute and then take it out, then use compressed air to blow the channels inside the carrier for 1 minute, and then dry and calcine the carrier to obtain a diesel vehicle oxidation catalyst with improved CO low-temperature ignition performance, the drying temperature is 120°C, the drying time is 6 hours, the calcination temperature is 500°C, and the calcination time is 2 hours. Comparative Example 3

[0045] The preparation method of Comparative Example 3 is the same as that of Example 1, except that the precursor of the precious metal Pt in the active coating is platinum nitrate, and cerium oxide and bismuth oxide are not added to the coating.

[0046] The coating amount is 100 g / L, the precious metal loading is 0.5 g / L, and the Pt / Pd mass ratio is 3:1.

[0047] Comparative Example 3 Preparation of coating slurry: Weigh 1980 g of deionized water, add 820 g of lanthanum-aluminum composite oxide to the deionized water, stir evenly to form a slurry, and then ball-mill the slurry to a particle size D 90 The surface of the active coating slurry is 16.8 μm, and then platinum nitrate solution and palladium nitrate solution are added to the slurry after ball milling and stirred for 4 hours to form an active coating slurry; the coating slurry of comparative example 3 is applied in the same way as in the embodiment.

[0048] Catalyst ignition performance evaluation

[0049] The catalyst ignition performance evaluation was carried out at 100-500°C, starting at 100°C and heating to 500°C at a rate of 5°C / min. The evaluation atmosphere contained 500ppm NO, 200ppm C3H6, 500ppm CO, 8% O2, 10% H2O, 8% CO2, with N2 as the balance gas; the volume space velocity was 80,000h -1 The concentration of the outlet product was detected using a Fourier transform infrared spectroscopy (FTIR) analyzer, from which the conversion rate of the sample at different temperatures was calculated, and the T 50 (Temperature of catalyst inlet when conversion rate is 50%) T of HC and CO 50 The lower the temperature, the better the ignition performance of the catalyst. The performance of the catalysts prepared in Examples 1-5 and Comparative Examples 1-3 was evaluated, and the results are shown in Table 1.

[0050] Table 1

[0051] sample <![CDATA[HC T 50 (℃)]]> <![CDATA[CO T 50 (℃)]]> Example 1 173 122 Example 2 174 120 Example 3 171 121 Example 4 188 126 Example 5 162 111 Comparative Example 1 176 138 Comparative Example 2 171 145 Comparative Example 3 170 153

[0052] As shown in Table 1, the CO T of the diesel vehicle oxidation catalyst obtained by the preparation method of the present invention in Examples 1-5 is 50 The temperature is relatively low, especially in Examples 1-3 and Example 5, and the low-temperature CO and HC ignition performance is excellent.

[0053] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A diesel vehicle oxidation catalyst for improving CO low temperature ignition performance, characterized in that: The invention comprises a carrier and an active coating coated on the carrier, wherein the active coating comprises cerium oxide and bismuth-lanthanum-aluminum composite oxide, the active coating is loaded with precious metals Pt and Pd, the coating amount of the active coating is 90-120 g / L, and the coating amount of the precious metal is 0.5-0.9 g / L.

2. The diesel vehicle oxidation catalyst for improving CO low temperature ignition performance according to claim 1, characterized in that: The mass ratio of the noble metal Pt to the noble metal Pd is 2-9:

1.

3. The diesel vehicle oxidation catalyst for improving CO low temperature ignition performance according to claim 1, characterized in that: The mass ratio of the cerium oxide to the bismuth-lanthanum-aluminum composite oxide is 1:49-69.

4. The diesel vehicle oxidation catalyst for improving CO low temperature ignition performance according to claim 1, characterized in that: The mass ratio of bismuth oxide, lanthanum oxide and aluminum oxide in the bismuth-lanthanum-aluminum composite oxide is 2-3:3:

97.

5. The method for preparing a diesel vehicle oxidation catalyst for improving CO low temperature ignition performance according to any one of claims 1 to 4, characterized in that: The steps include: Step S1. preparing bismuth-lanthanum-aluminum composite oxide by an equal volume impregnation method: weighing bismuth nitrate and lanthanum-aluminum composite oxide respectively according to a mass ratio of bismuth oxide to lanthanum-aluminum composite oxide material of 2-3:100, preparing a bismuth nitrate aqueous solution according to the saturated adsorption amount of lanthanum-aluminum composite oxide, dropping the prepared bismuth nitrate aqueous solution into the lanthanum-aluminum composite oxide and continuously stirring for 2-4 hours, then aging, drying, and calcining to obtain bismuth-lanthanum-aluminum composite oxide; Step S2. Preparation of active coating slurry: adding cerium acetate and bismuth-lanthanum-aluminum composite oxide to deionized water in a mass ratio of cerium oxide to bismuth-lanthanum-aluminum composite oxide of 1:49-69, stirring to form a slurry, then ball-milling the slurry, and then adding precious metal Pt and Pd precursor solutions to the ball-milled slurry, stirring evenly, to form an active coating slurry; Step S3. Active slurry coating: soak the carrier in the active coating slurry for 0.5-5 minutes and then take it out. Then, use compressed air to blow the channels inside the carrier. Then, dry the carrier and calcine it to obtain a diesel vehicle oxidation catalyst with improved CO low-temperature ignition performance.

6. The method for preparing a diesel vehicle oxidation catalyst for improving CO low temperature ignition performance according to claim 5, characterized in that: In step S1, the aging time is 6 to 10 hours, the drying temperature is 100 to 150° C., the drying time is 4 to 8 hours, the roasting temperature is 500 to 600° C., and the roasting time is 2 to 4 hours.

7. The method for preparing a diesel vehicle oxidation catalyst for improving CO low temperature ignition performance according to claim 5, characterized in that: The mass ratio of the total mass of the oxide in the slurry to the mass of the deionized water in step S2 is 1:2-3, and the particle size D of the slurry after ball milling is 90 10~20μm.

8. The method for preparing a diesel vehicle oxidation catalyst for improving CO low temperature ignition performance according to claim 5, characterized in that: In step S2, the noble metal Pt precursor is platinum oxalate.

9. The method for preparing a diesel vehicle oxidation catalyst for improving CO low temperature ignition performance according to claim 5, characterized in that: The purge time in step S3 is 0.5 to 3 minutes.

10. The method for preparing a diesel vehicle oxidation catalyst for improving CO low temperature ignition performance according to claim 5, characterized in that: In step S3, the drying temperature is 100-150° C., the drying time is 4-8 hours, the roasting temperature is 450-550° C., and the roasting time is 1-2 hours.