A dual-functional motor vehicle exhaust denitration catalyst, a preparation method and application thereof

Abstract

The application discloses a kind of bifunctional motor vehicle exhaust denitration catalyst and its preparation method and application.Catalyst is prepared by three-step method, first by impregnation method Pd / SSZ-13, Pd / Beta is prepared, secondly using cobalt acetate, ethylene glycol solution and ammonium carbonate solution is prepared under hydrothermal stirring Co3O4.Last Co3O4 Prepared respectively and Pd / SSZ-13, Pd / Beta is mixed according to certain proportion, to obtain Co3O4-Pd / SSZ-13, Co3O4-Pd / Beta catalyst.The sample has higher low-temperature NO adsorption capacity, can be stored in the process of cold start adsorption and storage motor vehicle exhaust emission NO;The sample also has NO direct decomposition capacity, can be decomposed into N2 at 200-500 DEG C.NO.This catalyst is suitable for controlling motor vehicle cold start process exhaust nitrogen oxides emission.Catalyst preparation method in the application is simple and has strong repeatability, raw material is low in price and environmental protection, has very strong practical value and application potential.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and more specifically, to a catalyst that can both adsorb and store NO in exhaust gas during the cold start of a motor vehicle, and directly decompose NO in exhaust gas into N2 after the temperature is increased (200-500℃), as well as its preparation method and application. Background Technology

[0002] Currently, with the increase in the number of motor vehicles, air pollution caused by motor vehicle exhaust has attracted widespread attention. Among them, nitrogen oxides are one of the main pollutants causing air pollution. Of the thermal nitrogen oxides produced by the high-temperature combustion of motor vehicle internal combustion engines, 95% are NO. NO is easily oxidized in the air into other nitrogen oxides, further polluting the atmosphere.

[0003] Currently, NO emission control primarily relies on ammonia-selective catalytic reduction (NH3-SCR) or NO storage reduction (NSR) to eliminate NO over a relatively wide temperature range (200-500℃). However, in vehicles equipped with SCR or NSR systems, 80% of NOx emissions occur during cold starts (2-5 minutes), before the denitrification catalyst reaches its operating temperature. Future efforts will focus on reducing cold-start NO emissions. x Emissions control measures include controlling NO emissions from diesel engine exhaust. x The key to emissions.

[0004] Pd / SSZ-13 and Pd / Beta can adsorb and store NO in the exhaust gas during the cold start phase, and when the exhaust gas temperature reaches above 200°C, they can remove the NO. x Desorption occurs when the downstream SCR / NSR catalyst reaches its optimal catalytic temperature, allowing the desorbed NO to be released. x Elimination. Pd / SSZ-13 and Pd / Beta can reduce low-temperature NO emissions from vehicle exhaust. However, since Pd / SSZ-13 and Pd / Beta catalysts do not have the ability to convert NO, they increase the NO removal burden on downstream SCR / NSR catalysts. x The pressure. Therefore, it is necessary to improve the Pd / SSZ-13 and Pd / Beta catalysts to enable them to directly decompose NO adsorbed and stored at low temperatures. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this invention provides a dual-function vehicle exhaust denitrification catalyst, its preparation method, and its application. The catalyst can adsorb and store NO during the cold start process of a vehicle, and simultaneously, at 200-500℃, it can denitrate the adsorbed and stored NO. x It decomposes directly into N2. This catalyst is environmentally friendly, and its preparation process is simple, easy to operate and scale up.

[0006] One of the technical solutions adopted by this invention to solve its technical problem is:

[0007] A dual-function vehicle exhaust denitrification catalyst, wherein the catalyst is prepared by mixing Co3O4 and Pd / zeolite molecular sieve, and the mass ratio of Co3O4:Pd / zeolite molecular sieve is 1:0.1-10.

[0008] Furthermore, the Pd / zeolite molecular sieve uses a molecular sieve as a carrier, and Pd is loaded onto the molecular sieve carrier using an impregnation method. The loading amount of Pd is 1-5 wt.%. The Co3O4 is prepared by hydrothermal stirring of cobalt acetate, ethylene glycol solution, and ammonium carbonate solution.

[0009] Furthermore, the zeolite molecular sieve support is at least one of SSZ-13 or Beta. Furthermore, the active component Pd exists in ionic form, and Co3O4 exists in metal oxide form.

[0010] The present invention also provides the application of the aforementioned dual-function vehicle exhaust denitrification catalyst in vehicle exhaust treatment.

[0011] Furthermore, it is used for the emission control of nitrogen oxides in motor vehicle exhaust during cold start; the exhaust temperature is below 200℃ during cold start.

[0012] This invention also provides a method for preparing a dual-function vehicle exhaust denitrification catalyst, comprising the following steps:

[0013] Step (1): Pd is impregnated and loaded using the equal volume impregnation method. 1-5 wt.% of palladium nitrate aqueous solution is added to NH4 / SSZ-13 or NH4 / Beta molecular sieve, stirred until completely wetted, and then allowed to stand in air at room temperature (20-25℃) to achieve a Pd loading of 1-5 wt.%. After drying, it is calcined in air at 500-550℃ for 4-6 hours to obtain the Pd / SSZ-13 or Pd / Beta catalyst.

[0014] Step (2): Dissolve cobalt acetate in ethylene glycol solution, keep the temperature at 190°C in a magnetic stirrer, add (NH4)2CO3 aqueous solution while stirring, and after the reaction is complete, wash the obtained solid with deionized water, filter, dry, and calcine in air at 330-370°C for 1-3 hours to obtain Co3O4.

[0015] Step 3: Physically mix the prepared Co3O4 with Pd / SSZ-13 or Pd / Beta in a certain proportion to obtain Co3O4-Pd / SSZ-13 or Co3O4-Pd / Beta catalysts.

[0016] Furthermore, in step (1), the plant is left to stand for at least 10 hours, preferably 12-24 hours.

[0017] Further, in step (1), the equal volume impregnation method means that for every 1g of NH 4 / Palladium nitrate aqueous solution was added dropwise to SSZ-13 and NH4 / BETA molecular sieve supports, with a total addition of 1 mL. The mixture was stirred to ensure that the solution was evenly dispersed in the supports.

[0018] Furthermore, in step (2), calcination is carried out in an air atmosphere with a programmed heating rate of 1-5℃ / min.

[0019] Further, in step (3), the mixing mass ratio of Co3O4 and Pd / SSZ-13 or Pd / Beta is 1:0.1-10.

[0020] Compared to existing Pd / SSZ-13 and Pd / BEA catalysts, the Co3O4-Pd / SSZ-13 and Co3O4-Pd / BEA catalysts prepared in this invention exhibit almost identical NO adsorption capacities at low temperatures (<200℃). However, at high temperatures (>200℃), the mixed catalyst can directly decompose NO adsorbed and stored at low temperatures into N2. Therefore, the mixed catalyst possesses both low-temperature adsorption and high-temperature decomposition capabilities for NO, offering the advantage of high NO conversion efficiency. Figure 1 As shown, this device can be installed in front of the SCR catalyst in motor vehicle exhaust treatment to reduce emissions during cold start. Attached Figure Description

[0021] Figure 1 It is a catalyst component in the motor vehicle after-treatment system.

[0022] Figure 2 It is Pd / SSZ-13 and Co3O4-Pd / SSZ-13 low temperature NO x (NO and NO2) adsorption and high-temperature desorption performance graph, where the horizontal axis represents time and the left vertical axis represents NO. x The right vertical axis represents the concentration, and the right vertical axis represents the temperature.

[0023] Figure 3 It is Co3O4-Pd / Beta low-temperature NO x Adsorption and high-temperature desorption performance graph, where the horizontal axis represents time and the left vertical axis represents NO. x The right vertical axis represents the concentration, and the right vertical axis represents the temperature. Detailed Implementation

[0024] The technical solution of the present invention will be further explained and described below with reference to specific embodiments and accompanying drawings.

[0025] Example 1:

[0026] A Co3O4-Pd / SSZ-13 catalyst was prepared and used for low-temperature NO adsorption. The specific implementation steps are as follows:

[0027] (1) Place 1g of NH4 / SSZ-13 (Zhuoran Environmental Protection Technology (Dalian) Co., Ltd., ammonia-type SSZ-13 zeolite molecular sieve with a silicon-to-aluminum ratio of 10) in an agate mortar and add 1mL of 1wt.% Pd(NO3)2 solution dropwise onto NH4 / SSZ-13. Stir and grind continuously during the dropwise addition. After the wet catalyst is added, let it stand in an air atmosphere at room temperature (20-25℃) for 10 hours. After standing, calcine the catalyst in a muffle furnace at a heating rate of 10℃ / min to 550℃ for 5 hours to obtain Pd / SSZ-13.

[0028] (2) Dissolve 17.43 g of cobalt acetate in 210 mL of ethylene glycol solution, and put the resulting solution into a 1 L round-bottom three-necked flask. Keep the temperature at 190 °C in a magnetic stirrer, and add 0.2 mol / L of (NH4)2CO3 aqueous solution at a rate of 7 mL / min while stirring. React for 1 h, then wash the resulting mixed solution twice with deionized water, filter, and dry. Then calcine the catalyst in a muffle furnace at a heating rate of 2 °C / min to 350 °C for 2 hours to obtain Co3O4.

[0029] (3) The prepared Co3O4 and Pd / SSZ-13 are physically mixed in equal mass ratio to obtain Co3O4-Pd / SSZ-13.

[0030] Example 2:

[0031] The prepared Co3O4-Pd / Beta catalyst was used for low-temperature NO adsorption. The specific implementation steps are as follows:

[0032] (1) Place 1g of NH4 / Beta (Zhuoran Environmental Protection Technology (Dalian) Co., Ltd., ammonia-type Beta zeolite molecular sieve with a silicon-to-aluminum ratio of 10) in an agate grinding cloth, and add 1mL of 1wt.% Pd(NO3)2 solution dropwise to NH4 / SSZ-13. Stir and grind continuously during the dropwise addition. After the dropwise addition is completed, let the wet catalyst stand in an air atmosphere at room temperature of 20-25℃ for 10 hours. After standing, calcine the catalyst in a muffle furnace at a heating rate of 10℃ / min to 550℃ for 5 hours to obtain Pd / Beta.

[0033] (2) Dissolve 17.43 g of cobalt acetate in 210 mL of ethylene glycol solution, and put the resulting solution into a 1 L round-bottom three-necked flask. Add 0.2 mol / L of (NH4)2CO3 aqueous solution at a rate of 7 mL / min while stirring in a 190 °C water bath. React for 1 h, then wash the resulting mixed solution twice with deionized water, filter, and dry. Calcine the catalyst in a muffle furnace at a heating rate of 2 °C / min to 350 °C for 2 h to obtain Co3O4.

[0034] (3) The prepared Co3O4 and Pd / Beta were physically mixed at a mass ratio of 1:2 to obtain Co3O4-Pd / Beta.

[0035] Example 3

[0036] 75 mg (40-60 mesh) of the catalyst prepared in Example 1 was used for low-temperature NO adsorption performance testing. NO adsorption and subsequent desorption experiments were conducted in a fixed-bed quartz tube reactor (4 mm inner diameter) under simulated automotive exhaust conditions. The total flow rate was adjusted to 200 mL / min using a mass flow meter controller. The reaction gas contained 200 ppm NO, 5% H₂O, 5% O₂, and N₂ in equilibrium. Thermocouples monitored the bed temperature at the top and bottom of the quartz tube, and the gas tube was heated to 140°C using a heating belt to prevent water vapor condensation.

[0037] Before NO absorption and desorption, the sample was pretreated with 10% O2 / N2 at 600°C for 30 minutes, followed by cooling to 100°C. The feed gas was first stabilized in a bypass line for 5 minutes, then directed to the catalyst at 100°C and held for 10 minutes to ensure catalyst adsorption equilibrium. The temperature was then increased to 600°C at a heating rate of 10°C / min for NO absorption and desorption. x Desorption. NO adsorption and desorption by bifunctional catalysts, such as... Figure 1 As shown. Figure 1 During the adsorption-desorption process, NO is introduced into the reactor. x The concentration was 200 ppm; a baseline below 200 ppm represents NO. x The adsorption or decomposition of the sample is represented by a value above the baseline, indicating desorption.

[0038] like Figure 2 As shown, Co3O4-Pd / SSZ-13 adsorbs and stores NO at a low temperature of 100℃. With increasing temperature, NO adsorption decreases at ~385℃. x The concentration is below 200 ppm, which indicates that some of the NO was directly decomposed into N2 during the desorption process.

[0039] NO→N2+O2 (1)

[0040] Example 4

[0041] 150 mg (40-60 mesh) of the catalyst prepared in Example 2 was used for low-temperature NO adsorption performance testing. NO adsorption and subsequent desorption experiments were conducted in a fixed-bed quartz tube reactor (4 mm inner diameter) under simulated automotive exhaust conditions. The total flow rate was adjusted to 500 mL / min using a mass flow meter controller. The reaction gas contained 250 ppm NO, 5% H₂O, 5% O₂, and N₂ in equilibrium. Thermocouples monitored the bed temperature at the top and bottom of the quartz tube, and the gas tube was heated to 140°C using a heating belt to prevent water vapor condensation.

[0042] Before NO absorption and desorption, the sample was pretreated with 10% O2 / N2 at 600°C for 30 minutes, followed by cooling to 80°C. The feed gas was first stabilized in a bypass line for 10 minutes, then directed to the catalyst at 80°C and held for 10 minutes to ensure catalyst adsorption equilibrium. Afterwards, the temperature was increased to 600°C at a heating rate of 10°C / min for NO absorption and desorption. x Desorption. NO adsorption and desorption by bifunctional catalysts, such as... Figure 2 As shown. Figure 2 During the adsorption-desorption process, NO is introduced into the reactor. x The concentration was 250 ppm; a baseline below 250 ppm represents NO. x The adsorption or decomposition of the sample is represented by a value above the baseline, indicating desorption.

[0043] like Figure 3 As shown, Co3O4-Pd / Beta adsorbs and stores NO at a low temperature of 100℃. As the temperature increases, the adsorbed and stored NO is gradually released. At ~385℃, NO... x The concentration was below 200 ppm, which indicates that some of the NO was directly decomposed into N2 by the mixed catalyst during the desorption process.

[0044] NO → N2 + O2 (2)

[0045] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. Application of a dual-function vehicle exhaust denitrification catalyst in vehicle exhaust treatment; the dual-function vehicle exhaust denitrification catalyst is prepared by mixing Co3O4 and Pd / zeolite molecular sieve, with a Co3O4:Pd / zeolite molecular sieve mass ratio of 1:0.1-10; during the cold start of the vehicle, the catalyst adsorbs and stores NO in the exhaust gas; when the temperature is raised to 200-500℃, the NO in the exhaust gas is directly decomposed into N2; the preparation method of the dual-function vehicle exhaust denitrification catalyst includes the following steps: Step (1): Pd is impregnated and loaded using the equal volume impregnation method. 1-5 wt.% of palladium nitrate aqueous solution is added to NH4 / SSZ-13 or NH4 / Beta molecular sieve, stirred until completely wetted, and then allowed to stand in air at room temperature (20-25 ℃) to achieve a Pd loading of 1-5 wt.%. After drying, it is calcined in air at 500-550 ℃ for 4-6 hours to obtain the Pd / SSZ-13 or Pd / Beta catalyst. Step (2): Dissolve cobalt acetate in ethylene glycol solution, keep at 190 °C in a magnetic stirrer, add (NH4)2CO3 aqueous solution while stirring, and after the reaction is complete, wash the obtained solid with deionized water, filter, dry, and calcine in air at 330-370 °C for 1-3 hours to obtain Co3O4. Step 3: Physically mix the prepared Co3O4 with Pd / SSZ-13 or Pd / Beta in a certain proportion to obtain Co3O4-Pd / SSZ-13 or Co3O4-Pd / Beta catalysts.

2. The application according to claim 1, characterized in that, The zeolite molecular sieve support is at least one of SSZ-13 or Beta; the active component Pd exists in ionic form, and Co3O4 exists in metal oxide form.

3. The application according to claim 1, characterized in that, In step (1), let it stand for at least 10 hours.

4. The application according to claim 3, characterized in that, In step (1), let it stand for 12-24 hours.

5. The application according to claim 1, characterized in that, In step (1), the equal volume impregnation method means that for every 1 g of NH 4 / Add palladium nitrate aqueous solution dropwise to SSZ-13 or NH4 / Beta molecular sieve support, with a total addition of 1 mL, and stir to ensure the solution is evenly dispersed in the support.

6. The application according to claim 1, characterized in that, In step (2), calcination is carried out in an air atmosphere with a programmed heating rate of 1-5 ℃ / min.

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