Diesel vehicle oxidation catalyst and preparation method thereof

Abstract

The present invention provides a diesel vehicle oxidation catalyst and a preparation method thereof, and relates to the technical field of oxidation catalysts of diesel engine tail gas purification systems, the catalyst comprises a carrier, a lower layer coating coated on the carrier and an upper layer coating coated on the lower layer coating, the lower layer coating comprises a noble metal Pt and a manganese-containing composite oxide, and the upper layer coating comprises a noble metal Pt and a manganese-containing composite oxide. The upper coating comprises precious metal Pt, precious metal Pd and silicon-aluminum composite oxide; the coating amount of the lower-layer coating is 60-100 g / L, and the coating amount of the upper-layer coating is 70-90 g / L. According to the diesel vehicle oxidation catalyst and the preparation method thereof, through the synergistic oxidation effect of the rare earth manganese zirconium material and the platinum group metal, the usage amount of the platinum group noble metal can be reduced, the oxidation performance of the catalyst is improved, the usage amount of the platinum group noble metal in the catalyst is small, the cost is low, the ignition temperature is low, the NO oxidation capacity is high, and CO / HC combustion can be catalyzed at a low temperature.

Description

Technical Field

[0001] The invention relates to the technical field of oxidation catalysts for diesel engine tail gas purification systems, in particular to an oxidation catalyst for diesel vehicles and a preparation method thereof. Background Art

[0002] The main functions of a 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. Part of the NO2 produced is used for passive and continuous regeneration of particulate matter, and the other part is used for rapid SCR reaction to improve the denitrification efficiency under low-temperature conditions.

[0003] DOC catalysts for medium and heavy-duty diesel vehicles generally use Pt / Pd dual precious metal coatings, and the mainstream DOC catalysts in the National VI stage use 0.7-0.9 g / L of platinum group precious metals. In view of the demand for efficient utilization of precious metals and cost reduction of diesel vehicle aftertreatment, there is an urgent need to develop low-precious metal DOC to meet the requirements of diesel vehicle fuel ignition, active and passive regeneration of carbon soot, and system reliability with low precious metal dosage. Manganese-based catalysts have good oxidation activity, but their poor thermal stability restricts their application in diesel vehicle aftertreatment systems. High-stability rare earth manganese-zirconium composite catalytic materials can replace part of the platinum group metals, which is one of the promising development directions for low-platinum group metal DOC catalysts. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a diesel vehicle oxidation catalyst and a preparation method thereof, which adopts a layered design and uses a rare earth manganese zirconium composite catalytic material to replace part of the platinum group metals to reduce the amount of precious metals used; the NO / HC / CO oxidation efficiency of the catalyst is improved through the synergistic oxidation effect of the rare earth manganese zirconium material and the platinum group metals.

[0005] The technical solution adopted by the present invention is:

[0006] A diesel vehicle oxidation catalyst, comprising: a carrier, a lower coating layer coated on the carrier, and an upper coating layer coated on the lower coating layer, wherein the lower coating layer comprises a precious metal Pt and a manganese-containing composite oxide, and the upper coating layer comprises a precious metal Pt, a precious metal Pd, and a silicon-aluminum composite oxide; the coating amount of the lower coating layer is 60-100 g / L, and the coating amount of the upper coating layer is 70-90 g / L.

[0007] Preferably, in the diesel vehicle oxidation catalyst, the amount of precious metal Pt in the lower coating layer is 0.05-0.1 g / L.

[0008] Preferably, in the diesel vehicle oxidation catalyst, the total amount of precious metal Pt and precious metal Pd in ​​the upper coating is 0.35-0.5 g / L, and the mass ratio of precious metal Pt and precious metal Pd is 2:1-5:1.

[0009] Preferably, the diesel vehicle oxidation catalyst comprises, by mass percentage, 10-20% manganese dioxide, 20-30% cerium dioxide, 5-10% lanthanum oxide, and 40-65% zirconium dioxide in the manganese-containing composite oxide.

[0010] Preferably, in the diesel vehicle oxidation catalyst, the silicon-aluminum composite oxide comprises 5-10% silicon dioxide and 90-95% aluminum oxide in terms of mass percentage.

[0011] The present invention also provides a method for preparing a diesel vehicle oxidation catalyst, which comprises the following steps:

[0012] Step S1. Preparation of manganese-containing composite oxide: according to the mass ratio of manganese dioxide, cerium dioxide, lanthanum oxide and zirconium dioxide of 2-4:4-6:1-2:8-13, manganese nitrate, cerous nitrate, lanthanum nitrate and zirconium oxynitrate are configured into a metal ion solution, and then manganese nitrate, cerous nitrate, lanthanum nitrate and zirconium oxynitrate are added dropwise to excess ammonia water, the pH of the reaction system is controlled to be 9-10, and then 5% polyethylene glycol by mass of the manganese-containing composite oxide is added to the solution, stirred for 10-20 minutes to obtain a suspension, and then the obtained suspension is aged in a 70-80°C water bath for 8-12 hours, filtered, the filter cake is washed with distilled water for 3-5 times, and then spray-dried to obtain a precursor powder, and the precursor powder is calcined to obtain the manganese-containing composite oxide;

[0013] Step S2. Preparation of the lower coating: impregnate the platinum nitrate solution onto the manganese-containing composite oxide by an equal volume impregnation method to obtain a mixed solution, add deionized water to the mixed solution to form a Pt / MnO2-CeO2-La2O3-ZrO2 slurry, and ball-mill the slurry to a particle size of D 90 The particle size is 10-15 μm, and finally the slurry is coated on the carrier and dried to obtain a semi-finished catalyst;

[0014] Step S3. Preparation of the upper coating: impregnate the mixed solution of platinum nitrate and palladium nitrate onto the silicon-aluminum composite oxide by an equal volume impregnation method, let it stand for 6-10 hours, then add it to deionized water, control the solid content to 25-30%, stir evenly, form a Pt / Pd / SiO2-Al2O3 slurry, and ball-mill the slurry to a particle size of D 90 The particle size is 15-20 μm. Finally, the slurry is coated on the semi-finished catalyst, dried, and calcined to obtain the finished catalyst.

[0015] Preferably, in the method for preparing the diesel vehicle oxidation catalyst, the temperature of the spray drying in step S1 is 200-300°C.

[0016] Preferably, in the method for preparing the diesel vehicle oxidation catalyst, the calcination temperature in step S1 is 500-600° C. and the calcination time is 3-5 h.

[0017] Preferably, in the method for preparing the diesel vehicle oxidation catalyst, the drying temperatures in step S2 and step S3 are both 100-150° C., and the drying time is both 10-15 min.

[0018] Preferably, in the method for preparing the diesel vehicle oxidation catalyst, the calcination temperature in step S3 is 500-600° C. and the calcination time is 2-3 h.

[0019] Advantages of the present invention:

[0020] The diesel vehicle oxidation catalyst of the present invention and the preparation method thereof, the catalyst comprises a carrier, a lower coating layer coated on the carrier and an upper coating layer coated on the lower coating layer, the lower coating layer comprises a precious metal Pt and a manganese-containing composite oxide; the upper coating layer comprises a precious metal Pt, a precious metal Pd, and a silicon-aluminum composite oxide, through the synergistic oxidation effect of rare earth manganese-zirconium materials and platinum group metals, the usage of platinum group precious metals can be reduced, and the oxidation performance of the catalyst is improved, the usage of platinum group precious metals in the catalyst is small, the cost is low, the ignition temperature is low, the NO oxidation ability is high, the stability is high, and the CO / HC combustion can be catalyzed at a relatively low temperature. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific embodiments.

[0022] Example 1

[0023] A diesel vehicle oxidation catalyst comprises a 400-mesh cordierite ceramic carrier, a lower coating layer coated on the 400-mesh cordierite ceramic, and an upper coating layer coated on the lower coating layer, wherein the volume of the cordierite ceramic carrier is 1.65 L, the lower coating layer comprises a precious metal Pt and a manganese-containing composite oxide, and the upper coating layer comprises a precious metal Pt, a precious metal Pd, and a silicon-aluminum composite oxide; the coating amount of the lower coating layer is 60 g / L, the coating amount of the upper coating layer is 70 g / L, and the total coating amount of the coating layer is 130 g / L.

[0024] The amount of precious metal Pt in the lower coating is 0.05 g / L; the total amount of precious metal Pt and precious metal Pd in ​​the upper coating is 0.35 g / L, and the mass ratio of precious metal Pt and precious metal Pd is 5:1; in terms of mass percentage, the manganese-containing composite oxide includes 10% manganese dioxide, 20% cerium dioxide, 5% lanthanum oxide, and 65% zirconium dioxide; in terms of mass percentage, the silicon-aluminum composite oxide includes 8% silicon dioxide and 92% aluminum oxide.

[0025] The preparation method of the diesel vehicle oxidation catalyst of this embodiment comprises the following steps:

[0026] Step S1. Preparation of manganese-containing composite oxide: manganese nitrate, cerous nitrate, lanthanum nitrate and zirconium oxynitrate are configured into a metal ion solution according to the mass ratio of manganese dioxide, cerium dioxide, lanthanum oxide and zirconium dioxide of 2:4:1:13, and then manganese nitrate, cerous nitrate, lanthanum nitrate and zirconium oxynitrate are added dropwise to excess ammonia water, the pH of the reaction system is controlled to be 9.5, and then 5% polyethylene glycol by mass of the manganese-containing composite oxide is added to the solution, stirred for 15 minutes to obtain a suspension, and then the obtained suspension is aged in a 70°C water bath for 12 hours, filtered, and the filter cake is washed with distilled water 4 times, and then spray-dried at 260°C to obtain a precursor powder, and the precursor powder is air-bathed at 550°C for 5 hours to obtain a manganese-containing composite oxide;

[0027] Step S2. Preparation of the lower coating: impregnate the platinum nitrate solution onto the manganese-containing composite oxide by an equal volume impregnation method to obtain a mixed solution, add deionized water to the mixed solution to form a Pt / MnO2-CeO2-La2O3-ZrO2 slurry, and ball-mill the slurry to a particle size of D 90 The particle size of the catalyst was 12.6 μm, and the slurry was finally coated on a cordierite ceramic carrier and dried at 120°C for 10 min to obtain a semi-finished catalyst.

[0028] Step S3. Preparation of the upper coating: impregnate a mixed solution of platinum nitrate and palladium nitrate onto a silicon-aluminum composite oxide (the silicon-aluminum composite oxide includes 8% SiO2 and 92% alumina) by an equal volume impregnation method, let it stand for 8 hours, then add it to deionized water, control the solid content to 27%, stir evenly, and form a Pt / Pd / SiO2-Al2O3 slurry. Ball-mill the Pt / Pd / SiO2-Al2O3 slurry to a particle size of D 90 The particle size of the catalyst is 16.0 μm. Finally, the slurry is coated on the semi-finished catalyst, dried at 120°C for 10 min, and calcined at 550°C for 2 h to obtain the finished catalyst.

[0029] Example 2

[0030] The preparation method of Example 2 is the same as that of Example 1, except that the mass ratio of manganese dioxide, cerium dioxide, lanthanum oxide and zirconium dioxide in the manganese-containing composite oxide is 2:3:1:4.

[0031] Example 3

[0032] The preparation method of Example 3 is the same as that of Example 1, except that the mass ratio of precious metal Pt to precious metal Pd in ​​the upper coating is 2:1.

[0033] Example 4

[0034] The preparation method of Example 4 is the same as that of Example 1, except that the total coating amount is 190 g / L, the coating amount of the lower coating is 100 g / L, the coating amount of the upper coating is 90 g / L, the loading amount of the precious metal Pt in the lower coating is 0.1 g / L, and the total loading amount of the precious metal in the upper coating is 0.5 g / L, wherein the mass ratio of the precious metal Pt to the precious metal Pd is 4:1.

[0035] Comparative Example 1

[0036] The coating coating amount is 130g / L, and the precious metal loading amount is 0.4g / L. The Pt / MnO2-CeO2-La2O3-ZrO2 slurry prepared in step S2 of Example 1 is mixed with the Pt / Pd / SiO2-Al2O3 slurry prepared in step S3, stirred evenly and then coated on the carrier, quickly dried at 120°C for 10min, and calcined at 550°C for 2h to obtain the catalyst of Comparative Example 1.

[0037] Comparative Example 2

[0038] The coating coating amount is 90g / L, the precious metal loading amount is 0.42g / L, wherein the mass ratio of Pt / Pd is 6:1, and the mixed solution of platinum nitrate and palladium nitrate is impregnated onto the silicon-aluminum composite oxide (the silicon-aluminum composite oxide includes 8% SiO2 and 92% alumina) by using the equal volume impregnation method, and then allowed to stand for 8h, and then added to deionized water, the solid content is 28%, and stirred evenly to form a slurry, and the slurry is ball-milled to a particle size of D 90 The slurry was then coated on a cordierite ceramic carrier, quickly dried at 120°C for 10 min, and calcined at 550°C for 2 h to obtain the catalyst of Comparative Example 2.

[0039] NO x Transformation efficiency evaluation

[0040] The catalyst oxidation performance was evaluated 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, and N2 as the balance gas. The volumetric space velocity was 80,000h -1 ; The outlet product concentration was detected using a Fourier transform infrared spectroscopy (FTIR) analyzer, and the NO conversion rate and HC / CO-T of the samples at different temperatures were calculated. 50 (Temperature at the catalyst inlet when the conversion rate is 50%). The catalysts prepared in Examples 1-4 and Comparative Examples 1-2 were evaluated for performance. The results are shown in Table 1.

[0041] Table 1

[0042] sample Maximum NO conversion rate (%) <![CDATA[HC T 50 (℃)]]> <![CDATA[CO T 50 (℃)]]> Example 1 54.0 181 135 Example 2 56.4 177 128 Example 3 49.1 172 131 Example 4 58.9 166 126 Comparative Example 1 47.2 195 154 Comparative Example 2 44.7 198 165

[0043] It can be seen from Table 1 that under the same amount and ratio of precious metals, the oxidation performance of the diesel vehicle oxidation catalyst obtained by the preparation method of the present invention in Examples 1-4 is significantly better than that of the comparative example.

[0044] 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, characterized in that: The invention comprises a carrier, a lower coating layer coated on the carrier and an upper coating layer coated on the lower coating layer, wherein the lower coating layer comprises precious metal Pt and a manganese-containing composite oxide, and the upper coating layer comprises precious metal Pt, precious metal Pd and a silicon-aluminum composite oxide; the coating amount of the lower coating layer is 60-100 g / L, and the coating amount of the upper coating layer is 70-90 g / L.

2. The diesel vehicle oxidation catalyst according to claim 1, characterized in that: The amount of precious metal Pt in the lower coating is 0.05-0.1 g / L.

3. The diesel vehicle oxidation catalyst according to claim 1, characterized in that: The total amount of precious metal Pt and precious metal Pd in ​​the upper coating is 0.35-0.5 g / L, and the mass ratio of precious metal Pt and precious metal Pd is 2:1-5:

1.

4. The diesel vehicle oxidation catalyst according to claim 1, characterized in that: The manganese-containing composite oxide comprises, by mass percentage, 10-20% manganese dioxide, 20-30% cerium dioxide, 5-10% lanthanum oxide, and 40-65% zirconium dioxide.

5. The diesel vehicle oxidation catalyst according to claim 1, characterized in that: Calculated by mass percentage, the silicon-aluminum composite oxide includes 5-10% silicon dioxide and 90-95% aluminum oxide.

6. The method for preparing a diesel vehicle oxidation catalyst according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step S1. Preparation of manganese-containing composite oxide: according to the mass ratio of manganese dioxide, cerium dioxide, lanthanum oxide and zirconium dioxide being 2-4:4-6:1-2:8-13, manganese nitrate, cerous nitrate, lanthanum nitrate and zirconium oxynitrate are configured into a metal ion solution, and then manganese nitrate, cerous nitrate, lanthanum nitrate and zirconium oxynitrate are added dropwise to excess ammonia water, the pH of the reaction system is controlled to be 9-10, and then 5% polyethylene glycol by mass of the manganese-containing composite oxide is added to the solution, stirred for 10-20 minutes to obtain a suspension, and then the obtained suspension is aged in a 70-80°C water bath for 8-12 hours, filtered, the filter cake is washed with distilled water for 3-5 times, and then spray-dried to obtain a precursor powder, and the precursor powder is calcined to obtain the manganese-containing composite oxide; Step S2. Preparation of the lower coating: impregnate the platinum nitrate solution onto the manganese-containing composite oxide by an equal volume impregnation method to obtain a mixed solution, add deionized water to the mixed solution to form a Pt / MnO2-CeO2-La2O3-ZrO2 slurry, and ball-mill the slurry to a particle size of D 90 The particle size is 10-15 μm, and finally the slurry is coated on the carrier and dried to obtain a semi-finished catalyst; Step S3. Preparation of the upper coating: impregnate the mixed solution of platinum nitrate and palladium nitrate onto the silicon-aluminum composite oxide by an equal volume impregnation method, let it stand for 6-10 hours, then add it to deionized water, control the solid content to 25-30%, stir evenly, form a Pt / Pd / SiO2-Al2O3 slurry, and ball-mill the slurry to a particle size of D 90 The particle size is 15-20 μm. Finally, the slurry is coated on the semi-finished catalyst, dried, and calcined to obtain the finished catalyst.

7. The method for preparing a diesel vehicle oxidation catalyst according to claim 6, characterized in that: The spray drying temperature in step S1 is 200-300°C.

8. The method for preparing a diesel vehicle oxidation catalyst according to claim 6, characterized in that: In step S1, the calcination temperature is 500-600° C. and the calcination time is 3-5 h.

9. The method for preparing a diesel vehicle oxidation catalyst according to claim 6, characterized in that: In step S2 and step S3, the drying temperature is 100-150° C. and the drying time is 10-15 min.

10. The method for preparing a diesel vehicle oxidation catalyst according to claim 6, characterized in that: In step S3, the calcination temperature is 500-600° C. and the calcination time is 2-3 h.