Preparation method and application of wide-temperature-range MnCe hydrotalcite derivative catalyst for SCR (Selective Catalytic Reduction) degradation
The MnCe hydrotalcite derived catalyst prepared by co-precipitation method and radio frequency plasma treatment solves the problems of poor low temperature activity and narrow operating temperature window of existing SCR catalysts, and achieves efficient degradation of NOx in the mobile source exhaust gas, which is suitable for industrial production.
Patent Information
- Application Number
- CN202510080164.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-19
- Publication Date
- 2025-04-25
- Estimated Expiration
- Not applicable · inactive patent
AI Technical Summary
The existing SCR catalysts have poor catalytic activity at low temperatures, narrow operating temperature windows, and traditional V2O5/TiO2 catalysts have biotoxicity problems, making it difficult to effectively degrade NOx in the exhaust gas of the mobile source.
A hydrotalcite precursor with Mn as an active component and doped with Ce metal was prepared by co-precipitation method, and a wide temperature domain MnCe hydrotalcite derived catalyst was prepared by radio frequency plasma treatment to enhance its low temperature activity and operating temperature window.
The NO conversion rate at 150°C is achieved to reach 91%, the NO conversion rate at the optimal active temperature of 150-200°C reaches 93.33%, and the operating temperature window T80 is 150-300°C. At the same time, the process is simple and the cost is low, which is suitable for industrial production.
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Abstract
Description
Technical Field
[0001] The invention relates to a preparation method and application of a wide temperature range MnCe hydrotalcite-derived catalyst for SCR degradation, specifically a catalyst for effectively degrading the air pollutant NO, belonging to the field of waste gas treatment technology and environmental catalytic environment. Background Art
[0002] Nitrogen oxides (NO x ) is one of the main air pollutants, which not only harms human health, but also causes environmental pollution such as acid rain and photochemical smog. x The emission of NO is increasing year by year with the increase of mobile and fixed sources. Therefore, it is necessary to control NO x The emission of pollutants has become a mandatory law in our country and is one of the important contents of current air pollution control.
[0003] C3H6-SCR technology is currently the most promising technology for NO removal from mobile exhaust x One of the purification technologies, the core of which is the catalyst. Under the action of the catalyst, the external reducing agent or the reducing substance in the tail gas selectively converts NO x Reduced to N2, making NO in the exhaust gas x Therefore, C3H6-SCR degrades NO x The development of catalysts is imperative.
[0004] The traditional SCR catalyst V2O5 / TiO2 has a narrow operating window (300-400℃) and poor low-temperature catalytic activity, which limits its use as a catalyst for removing NO from mobile exhaust. x application, and V2O5 is biologically toxic. Layered double hydroxide (LDHs) catalysts show potential application prospects in stationary source denitrification reactions due to their good structural adjustability, high specific surface area and good redox properties. According to literature reports, some people have tried to introduce LDHs into stationary source denitrification and prepare Mn-based LDO-derived catalysts by combined calcination activation. The catalysts prepared by this activation method have a small specific surface area, uneven dispersion of active components, low denitrification conversion rate, and a narrow operating temperature window. Therefore, in mobile source denitrification, there is an urgent need to modify LDHs catalysts to improve their low-temperature activity and broaden their operating temperature window.
[0005] The design idea of this patent is to screen green, low-cost, non-toxic LDHs denitrification catalysts with better low-temperature denitrification activity and a wide temperature operating window. Literature reports that Mn-based catalysts have better low-temperature activity. We have done a lot of exploration work. We first used the co-precipitation method to explore the catalysts derived from LDHs precursors with different Mn contents as active components, and found that the effects were not ideal; literature reported that doping with metal additives can significantly improve the low-temperature activity of the catalyst, so we explored adding Co, Ni, Cu, Ce, Fe, La, and Zr additives to further improve the low-temperature activity of the catalyst. The effects of Co, Cu, Fe, La and Zr additives were not satisfactory. The study found that only Ce doping has certain low-temperature activity, but it still cannot achieve higher NO in a wide temperature range (150-400°C). x Removal rate (>50%). Summary of the invention
[0006] The purpose of the present invention is to provide a preparation method and application of a wide temperature range MnCe hydrotalcite-derived catalyst for SCR degradation. The catalyst has good catalytic activity for the reaction of selective reduction of NO using a reducing agent C3H6, and denitrifies to generate harmless N2, H2O, and CO2. After a large number of exploratory experiments, we found that the composite metal oxide-type catalyst derived from a hydrotalcite precursor doped with Ce metal and prepared by co-precipitation method with Mn as the active component combined with radio frequency (RF) plasma (5min, 100W) treatment has high catalytic low-temperature activity and a wide operating temperature window. The NO conversion rate at 150°C is 91%, and when the optimal active temperature of 150-200°C is reached, the NO conversion rate reaches 93.33%, and the operating temperature window T 80 150~300℃. In addition, the preparation method is simple in process, the preparation conditions are easy to control, and it is suitable for industrial production. The first problem solved by the present invention is to develop a highly active composite metal oxide catalyst with independent intellectual property rights; the second problem solved by the present invention is to broaden the operating temperature window of the catalyst, especially its low-temperature activity; the third problem solved by the present invention is to use a co-precipitation method combined with radio frequency plasma (RF) treatment, the preparation process and method are simple, easy to realize industrial production and low cost.
[0007] To achieve the above object, the technical solution adopted by the present invention is:
[0008] A method for preparing a wide temperature range MnCe hydrotalcite-derived catalyst for SCR degradation comprises the following steps:
[0009] (1) Weigh the active component Mn(NO3)2·4H2O and the auxiliary agent Ce(NO3)3·6H2O in a stoichiometric ratio, add 40 ml of deionized water, and stir until they are completely dissolved to obtain a transparent metal salt solution; add the metal salt solution dropwise to the precipitant under constant temperature, and use a stabilizer to adjust the pH during the process;
[0010] (2) After the addition is completed, the suspension is aged for 12 h under vigorous stirring at a constant temperature; then, the pH value of the supernatant is neutralized by several centrifugal washings, and the obtained precipitate is further dissolved in 100 mL of anhydrous ethanol and stirred for 2 h; and dried overnight;
[0011] The sample obtained in step (2) is ground into fine powder to obtain a MnCe-LDHs precursor, which is activated by radio frequency plasma (RF) treatment to obtain a MnCe hydrotalcite-derived NO degradation catalyst.
[0012] According to the above scheme, the precipitant is Na2CO3, the stabilizer is NaOH, and the activation method is radio frequency plasma (RF).
[0013] According to the above scheme, the RF plasma treatment time is 3 to 12 minutes, and the power is 50 to 250W;
[0014] According to the above scheme, the molar ratio of the metal elements in the metal salt solution is: 2+ ):n(Ce 3+ )=1:n(n=0.25, 0.5, 0.75, 1).
[0015] According to the above scheme, the metal salt solution is added at a dripping speed of 1 ml / min, and the precipitant NaOH is slowly added during the process to maintain the pH of the precursor solution ≈ 10, thereby obtaining the MnCe hydrotalcite-derived precursor.
[0016] Preferably, the constant temperature aging stirring temperature is 70°C; (1) dissolving the active component and the metal additive in deionized water, adding an alkaline precipitant, stirring and aging for 12 hours to obtain a precursor solution; (2) washing until the pH is neutral, stirring in anhydrous ethanol for 2 h, drying, removing by RF plasma, pressing, and grinding into a catalyst with a mesh size of 20 to 40, which is a wide temperature range MnCe hydrotalcite-derived denitrification catalyst.
[0017] The present invention also provides the use of a C3H6-SCR NO degradation catalyst prepared by the preparation method described in any one of the above technical solutions in tail gas denitrification.
[0018] The present invention has the following advantages:
[0019] 1. Use C3H6 produced by internal combustion engines as a reducing agent instead of traditional NH3 as a reducing agent, and remove NO produced by internal combustion engines at the same time x and C3H6 are two major pollutants;
[0020] 2. The composite metal oxide catalyst derived from MnCe hydrotalcite has excellent low-temperature catalytic activity and a wide temperature operating window. x The conversion rate is over 50%.
[0021] 3. The MnCe hydrotalcite-derived composite metal oxide catalyst is prepared by co-precipitation method. The preparation method has simple process, low cost, high catalytic activity for SCR reaction, and can purify C3H6 in motor vehicle exhaust gas. The preparation conditions are simple, easy to control, and suitable for industrial production.
[0022] Figure 1 These are the catalytic activity test graphs of the catalysts prepared in Examples 1, 2, 3, 4, 5 and 6.
[0023] Figure 2 These are the catalytic activity test graphs of the catalysts prepared in Examples 3, 7, and 8.
[0024] Figure 3 These are the catalytic activity test graphs of the catalysts prepared in Examples 8, 9, 10 and 11.
[0025] Figure 4 These are the catalytic activity test graphs of the catalysts prepared in Examples 8, 12, 13, 14 and 15.
[0026] Figure 5 These are the catalytic activity test graphs of the catalysts prepared in Examples 8, 16, 17, 18, and 19.
[0027] Figure 6 The XRD spectra of the catalysts prepared in Examples 3, 7 and 8 are shown.
[0028] Figure 7 The XPS spectra of the catalysts prepared in Examples 3, 7 and 8 are shown. DETAILED DESCRIPTION
[0029] The present invention will be further described below through some implementation examples, but the present invention is not limited thereto.
[0030] Example 1
[0031] Weigh 2.3243g of Mn(NO3)2·4H2O in a certain proportion, add 40ml of deionized water to dissolve it to obtain a mixed metal salt solution; weigh 3.2g of NaOH and dissolve it in 20ml of deionized water to obtain a stabilizer, weigh 1.325g of sodium carbonate and dissolve it in 50ml of water to obtain a precipitant; add the mixed metal salt solution dropwise to the precipitant sodium carbonate stirred at a constant temperature of 70°C, and add the precipitant NaOH dropwise during the process to maintain the solution pH≈10. After the addition is completed, continue stirring for 12h to obtain a Mn-LDHs hydrotalcite precursor solution. Then filter and wash until the pH is neutral, stir the slurry in an ethanol solution for 2h, and finally dry and grind it at 80°C and place it in a muffle furnace for calcination at 400°C for 5h. Press the calcined powder into a tablet press at a pressure of 10Mpa and crush it to 20-40 meshes to obtain a Mn-C catalyst.
[0032] Catalyst Evaluation
[0033] The activity evaluation of the catalyst was carried out in a homemade continuous flow fixed bed reactor. The reaction tube is a quartz tube with an inner diameter of 6mm and a length of 33cm. The reaction temperature is measured by a thermocouple placed in the middle of the reaction tube, and the reaction temperature is controlled by a program temperature controller. The gas flow is controlled by a mass flow meter. The reaction raw gas: 400ppm C3H6, 400ppm NO, 6% O2 and balance gas Ar. In the experiment, the catalyst dosage is 0.2g, the reaction temperature is 150℃~450℃, and sampling is performed every 50℃. The detection is carried out with a flue gas analyzer (MRU, VARIO PLUS) to calculate the conversion rate of NO. The NO conversion curve of the catalyst at different temperature points is shown in the figure below. Figure 1 shown.
[0034] Embodiments 2 to 6
[0035] Compared with Example 1, only n(Mn 2+ ): n(Ce 3+ )=1:0.25-1, and the other processes are the same as those in Example 1 to obtain the finished composite metal oxide catalysts. The catalyst compositions of Examples 2 to 6 are shown in Table 1.
[0036] Catalyst Evaluation
[0037] According to the evaluation method of Example 1, the conversion curve of the catalyst to NO at different temperature points is as follows: Figure 1 Its conversion rate and operating window temperature at 150°C are shown in Table 1.
[0038] Embodiment 7-8
[0039] The difference from Example 3 is that the activation methods of MnCe-LDHs precursor are 400°C calcination (C), dielectric barrier discharge (DBD) plasma (Air, 10 min, 100 W), and radio frequency plasma (RF) (H2, 10 min, 100 W). The catalyst compositions of Examples 7 and 8 are shown in Table 1.
[0040] Catalyst Evaluation
[0041] According to the evaluation method of Example 1, the conversion curve of the catalyst to NO at different temperature points is as follows: Figure 2 Its conversion rate and operating window temperature at 150°C are shown in Table 1.
[0042] Embodiments 9 to 11
[0043] The difference from Example 8 is that the precursor MnCe-LDHs hydrotalcite is treated with radio frequency plasma in an atmosphere of H2, N2, Air, and Ar. The catalyst compositions of Examples 9 to 11 are shown in Table 1.
[0044] Catalyst Evaluation
[0045] According to the evaluation method of Example 1, the conversion curve of the catalyst to NO at different temperature points is as follows: Figure 3 Its conversion rate and operating window temperature at 150°C are shown in Table 1.
[0046] Embodiments 12 to 15
[0047] The difference from Example 1 is that the radio frequency plasma treatment time during the activation of the MnCe hydrotalcite precursor is 3 to 12 minutes. The catalyst compositions of Examples 12 to 15 are shown in Table 1.
[0048] Catalyst Evaluation
[0049] According to the evaluation method of Example 1, the conversion curve of the catalyst to NO at different temperature points is as follows: Figure 4 Its conversion rate and operating window temperature at 150°C are shown in Table 1.
[0050] Embodiments 16 to 19
[0051] The difference from Example 1 is that the radio frequency plasma treatment power during activation of the MnCe hydrotalcite precursor is 50-250 W. The catalyst compositions of Examples 16 to 19 are shown in Table 1
[0052] According to the evaluation method of Example 1, the conversion curve of the catalyst to NO at different temperature points is as follows: Figure 5 Its conversion rate and operating window temperature at 150°C are shown in Table 1.
[0053] Example Metal oxide catalyst composition and surface activity evaluation results: The composition and activity evaluation results of the hydrotalcite-derived composite metal oxide catalyst are shown in Table 1:
[0054] The data in Table 1 show that the denitrification efficiency of catalysts prepared by different ratios of active components to additives, different powers and different times of radio frequency plasma (RF) treatment, and different activation methods are different. Among them, Mn1Ce was prepared by coprecipitation method, treated under RF plasma Air for 5 min (100 W), and the ratio of active component Mn to additive Ce metal ion was 1:0.25. 0.25 -RF-Air-5min-100W wide temperature (150-300℃)NO x The removal effect is best.
[0055] XRD characterization
[0056] Figure 6 (a) Through the Mn1Ce 0.25 -LDHs, Mn-LDHs precursor structure, Mn1Ce 0.25 -LDHs precursors showed 003, 006 and other crystal faces belonging to hydrotalcite, indicating the formation of carbonate intercalated LDHs. Figure 6 (b) The precursor LDHs is converted into metal oxide mixtures such as Mn-C and Mn1Ce under different activation methods. 0.25 -RF、Mn1Ce 0.25 -DBD catalyst XRD spectrum, observed that the characteristic diffraction peaks attributed to LDHs disappeared, indicating that the layered structure collapsed, while the Mn-C catalyst showed characteristic peaks attributed to Mn3O4 (PDF#19-0803). The catalyst after plasma activation showed CeO2 diffraction peaks. The radius of Ce ions is larger than that of Mn ions, and they are more inclined to form MO-Ce chemical bonds on the surface of oxide crystals to form solid solutions) (PDF#37-0630).
[0057] XPS characterization
[0058] In order to study the effects of the valence state and composition of the catalyst surface elements on the catalyst performance, XPS analysis was performed on a series of catalysts. Figure 7 The XPS results of different samples of Mn 2p, Ce 3d, and O 1s are given. Figure 7In (a), the O1s spectra of the three catalysts are well deconvoluted into three peaks: the characteristic peak at a lower binding energy of about 529.38 eV is attributed to lattice oxygen (Olat), while the characteristic peaks at 531.1 and 532.2 eV are attributed to surface chemically adsorbed oxygen (Oads) and oxygen from hydroxyl species or surface adsorbed water (OH), respectively. α The mobility is greater than O β The mobility of O α O β More reactive. Therefore, the O α The more it is, the more favorable it is for the redox reaction. Figure 7 (b)Mn1Ce 0.25 The XPS peaks corresponding to the Mn 2p3 / 2 and Mn 2p1 / 2 orbitals of the derivative catalyst activated by -LDHs in the XPS spectrum of Mn 2p are 641.8e V and 653.6e V, respectively. After the peak separation operation of the two catalysts, it was determined that the characteristic peaks of manganese in three different valence states are Mn 4+ (644.5e V) and Mn 3+ (642.1e V) and Mn 2+ (640.6 e V). This indicates that the manganese oxide species in the two catalysts are mainly in the form of high-valent Mn 4+ and Mn 3+ Exist in the form of Mn 4+ Species and Mn 4+ / Mn 3+ The species plays an important role in promoting the low-temperature C3H6-SCR reaction of the catalyst, which is beneficial to improving the low-temperature catalytic activity of the catalyst. Figure 7 (c) Mn1Ce 0.25 The characteristic peaks of the XPS spectrum of the Ce 3d of -LDHs-derived catalysts are composed of two parts, which are attributed to the spin-orbit peak splitting of 3d5 / 2 and 3d3 / 2, respectively. 3+ It consists of two peaks with binding energies of 884.9 eV and 903.7 eV, corresponding to Ce 3+ 3d5 / 2 and Ce 3+ 3d3 / 2. The characteristic peaks at 882.2eV, 888.7eV and 898.3eV are attributed to Ce 4+ 3d5 / 2, while the characteristic peaks at 900.9eV, 907.7eV and 916.6eV are attributed to Ce 4+ 3d3 / 2. During the reaction in the low temperature zone, Ce on the catalyst surface 3+ The higher the content, the more beneficial it is to Ce 4+ and Ce 3+The mutual conversion between ions can produce more oxygen vacancies, which is more conducive to the catalytic reaction.
Claims
1. A preparation method and application of a wide temperature range MnCe hydrotalcite-derived catalyst for SCR degradation, characterized in that: The method comprises the following steps: (1) Weigh the active component Mn(NO3)2·4H2O and the auxiliary agent Ce(NO3)3·6H2O in a stoichiometric ratio, add 40 ml of deionized water, and stir until they are completely dissolved to obtain a transparent metal salt solution; add the metal salt solution dropwise to the precipitant under constant temperature, and use a stabilizer to adjust the pH during the process; (2) After the addition is completed, the suspension is aged under vigorous stirring at a constant temperature; Subsequently, after several centrifugal washings to make the pH value of the supernatant neutral, the obtained precipitate was further dissolved in 100 mL of anhydrous ethanol and stirred; and dried overnight; (3) Grinding the sample obtained in step (2) into fine powder to obtain a MnCe-LDHs precursor, and activating the precursor by radio frequency plasma (RF) treatment to obtain a MnCe hydrotalcite-derived NO degradation catalyst.
2. The method for preparing a wide temperature range MnCe hydrotalcite-derived catalyst for SCR NO degradation catalyst according to claim 1, characterized in that: The preparation method is a co-precipitation method, and the activation method is a radio frequency plasma (RF).
3. The method for preparing a wide temperature range MnCe hydrotalcite-derived catalyst for SCR NO degradation catalyst according to claim 1-2, characterized in that: The RF plasma treatment time is 3 to 12 minutes, and the power is 50 to 250W.
4. The method for preparing the wide temperature range MnCe hydrotalcite-derived catalyst for SCR NO degradation catalyst according to any one of claims 1 to 4, characterized in that: The molar ratio of the metal elements in the metal salt solution is: 2 + ):n(Ce 3+ )=1:n(n=0.25, 0.5, 0.75, 1).
5. The method for preparing the wide temperature range MnCe hydrotalcite-derived catalyst for SCR NO degradation catalyst according to any one of claims 1 to 4, characterized in that: The metal salt solution was added at a dropping speed of 1 ml / min, and the precipitant NaOH was slowly added dropwise during the process to maintain the pH of the precursor solution at ≈ 10, thereby obtaining the MnCe hydrotalcite-derived precursor.
6. The method for preparing the wide temperature range MnCe hydrotalcite-derived catalyst for SCR NO degradation catalyst according to any one of claims 1 to 5, characterized in that: The atmosphere of the RF plasma treatment is N2, H2, Air, or Ar.
7. The method for preparing the wide temperature range MnCe hydrotalcite-derived catalyst for SCR NO degradation catalyst according to any one of claims 1 to 6, characterized in that: The constant temperature aging stirring temperature is 70°C; (1) dissolving the active component and the metal additive in deionized water, adding an alkaline precipitant, stirring and aging for 12 hours to obtain a precursor solution; (2) washing until the pH is neutral, stirring in anhydrous ethanol for 2 h, drying, removing by RF plasma, pressing, and grinding into a catalyst with a mesh size of 20 to 40, which is a wide temperature range MnCe hydrotalcite-derived denitrification catalyst.
8. Use of the MnCe hydrotalcite-derived catalyst for wide temperature range as a catalyst for SCR NO degradation according to any one of claims 1 to 7.