Preparation method and application of plasma MnZr hydrotalcite derivative catalyst for wide-temperature SCR (Selective Catalytic Reduction) degradation

Abstract

The invention relates to a preparation method and application of a MnZr catalyst prepared by a hydrotalcite precursor through a coprecipitation method in combination with radio frequency plasma (RF) activation treatment. Active species are inserted between hydrotalcite layers through a coprecipitation method, and then RF activation treatment is performed to prepare the high-dispersion composite metal oxide type catalyst. The preparation method comprises the following steps: firstly, respectively preparing a MnZr mixed metal salt solution, a Na2CO3 precipitant solution and a NaOH stabilizer solution, dropwise adding the metal salt solution into a precipitant under constant-temperature stirring, and controlling the pH value to be about 10; and after the dropwise adding is finished, stirring and aging the turbid liquid for 12 hours at a constant temperature, filtering and drying, treating for 15 minutes by using RF (Radio Frequency) under the power of 100 W in an air atmosphere, tabletting and grinding to obtain the Mn1Zr0.75-RF-H2-15-100 W catalyst. The Mn1Zr0.75-RF-H2-15min-100W catalyst disclosed by the invention has the characteristics of high dispersity, uniform active site distribution, small crystal grains, large specific surface area and the like, so that the catalyst has relatively high C3H6-SCR catalytic activity in the whole temperature range.

Description

Technical Field

[0001] The invention relates to a preparation method and application of a plasma MnZr hydrotalcite-derived catalyst for wide-temperature SCR degradation, and is 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] C 3 H 6 -SCR technology is currently the most promising technology for mobile source exhaust NO 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 Restore to N 2 , making the NO in the exhaust gas x Therefore, C 3 H 6 -SCR degradation of NO x The development of catalysts is imperative.

[0004] Conventional SCR Catalyst V 2 O 5 / TiO 2 The operating window is narrow (300-400℃), and its low-temperature catalytic activity is poor, which limits its use as a catalyst for removing NO from mobile exhaust. x application, and V 2 O 5 It has biological toxicity. 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 calcination activation. The catalysts prepared by this activation method have high energy consumption, long time, cumbersome operation, small specific surface area, uneven dispersion of active components, low denitrification conversion rate, and narrow operating temperature window. Therefore, in mobile source denitrification, there is an urgent need to modify LDHs catalysts to save energy, be convenient and quick to operate, and 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; there are literature reports that doping with metal additives can significantly improve the low-temperature activity of the catalyst, so we explored adding Co, Ni, Cu, 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 the denitrification conversion rate of Zr doping at 200°C was >80% (better than Co, Ni, Cu, Ce, Fe, La), but it still cannot achieve a higher NO in a wide temperature range (150-400°C). x The removal rate is high (>50%), and the activation method has high energy consumption and long time. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a plasma MnZr hydrotalcite-derived catalyst for wide temperature SCR degradation and its application. 3 H 6 The selective reduction of NO has good catalytic activity, denitrification generates harmless N 2 and H 2 O、CO 2 After a lot of exploratory experiments, we found that the composite metal oxide catalyst derived from the hydrotalcite precursor doped with Zr metal and prepared by co-precipitation method has high catalytic low-temperature activity and a wide operating temperature window. The NO conversion rate is 86.67% at 150°C. When the optimal activity temperature is 150-300°C, the NO conversion rate reaches 96.33%. 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 purpose, the technical solution adopted by the present invention is:

[0008] A method for preparing a wide temperature range MnZr hydrotalcite-derived catalyst for SCR degradation, comprising the following steps:

[0009] (1) Weigh the active component Mn(NO 3 ) 2 ·4H 2 O, additive Zr(NO 3 ) 4 ·5H 2 O, add 40 ml of deionized water and stir until it is completely dissolved to obtain a transparent metal salt solution; add the metal salt solution dropwise to the precipitant under constant temperature conditions, 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 MnZr-LDHs precursor, which is activated by radio frequency plasma (RF) treatment to obtain a MnZr hydrotalcite-derived NO degradation catalyst.

[0012] According to the above scheme, the precipitant is Na 2 CO 3 , 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 5 to 20 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(Zr 4+ )=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 MnZr 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 plasma-treated wide temperature range MnZr hydrotalcite-derived denitrification catalyst.

[0017] The present invention also provides C prepared by the preparation method described in any one of the above technical solutions 3 H 6 -Application of SCR NO degradation catalyst in exhaust gas denitrification.

[0018] The present invention has the following advantages:

[0019] 1. Using C generated by internal combustion engine 3 H 6 As a reducing agent to replace traditional NH 3 As a reducing agent, it also removes NO generated by internal combustion engines x and C 3 H 6 Two major pollutants;

[0020] 2. The composite metal oxide catalyst derived from MnZr hydrotalcite has excellent low-temperature catalytic activity and a wide temperature operating window. x The conversion rate is over 50%.

[0021] 3. The MnZr hydrotalcite-derived composite metal oxide catalyst was prepared by coprecipitation. The preparation method is simple, low-cost, and has high catalytic activity for SCR reaction. 3 H 6 Purification is achieved, the preparation conditions are simple, it is easy to control, and it is 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 5, 7, and 8.

[0024] Figure 3 These are the catalytic activity test graphs of the catalysts prepared in Examples 5, 8, 9, 10 and 11.

[0025] Figure 4 These are the catalytic activity test graphs of the catalysts prepared in Examples 5, 12, 13, 14 and 15.

[0026] Figure 5 These are the catalytic activity test graphs of the catalysts prepared in Examples 5, 16, 17, 18, and 19.

[0027] Figure 6 The XRD spectra of the catalysts prepared in Examples 5, 7 and 8 are shown.

[0028] Figure 7H is the catalyst prepared in Example 3, Example 7, and Example 8. 2 -TPR spectrum. 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 2.3243 g of Mn(NO 3 ) 2 ·4H 2 O, add 40ml of deionized water to dissolve it to obtain a mixed metal salt solution; weigh 3.2g NaOH and dissolve it in 20ml of deionized water to obtain a stabilizer, weigh 1.325g 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 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 at 80°C and place it in a muffle furnace for calcination at 400°C for 5h. The calcined powder is pressed into a tablet under a pressure of 10Mpa by a tablet press and crushed 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 self-made continuous flow fixed bed reactor. The reaction tube was a quartz tube with an inner diameter of 6 mm and a length of 33 cm. The reaction temperature was measured by a thermocouple placed in the middle of the reaction tube and controlled by a program temperature controller. The gas flow was controlled by a mass flow meter. The reaction raw gas: 400 ppm C 3 H 6 、400ppm NO、6%O 2 and balance gas Ar. In the experiment, the catalyst dosage was 0.2g, the reaction temperature was 150℃~450℃, and samples were taken every 50℃. The flue gas analyzer (MRU, VARIO PLUS) was used to detect and calculate the NO conversion rate. The NO conversion curve of the catalyst at different temperature points is shown in the figure Figure 1 shown.

[0034] Embodiments 2 to 6

[0035] Compared with Example 1, only n(Mn 2+ ): n(Zr 4+)=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 the MnZr-LDHs precursor are calcination at 400°C (C), dielectric barrier discharge (DBD) plasma (Air, 10 min, 100 W), radio frequency plasma (RF) (H 2 , 10min, 100W). 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 MnZr-LDHs hydrotalcite is treated with radio frequency plasma in an atmosphere of H 2 、N 2 , Air, 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 power of the radio frequency plasma treatment during the activation of the MnZr hydrotalcite precursor is 50-250 W. 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 RF plasma treatment time during the activation of the MnZr hydrotalcite precursor is 3 to 12 minutes. 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, the co-precipitation method was used to treat the catalyst under RF plasma Air for 10 min (100 W), and the ratio of active component Mn to additive Zr metal ion was 1:0.75 to obtain Mn. 1 Zr 0.75 -RF-H 2 -15min-100W wide temperature (150-350℃)NO x The removal effect is best.

[0055] XRD characterization

[0056] Figure 6 In (a), Mn 1 Zr 0.75 -LDHs, Mn-LDHs precursor structures were studied. 1 Zr 0.75 -LDHs precursors have 003, 012, 1010, 110 crystal planes belonging to hydrotalcite at 11.64°, 34.48°, 52.86°, and 60.12°, indicating the formation of carbonate intercalated LDHs. Both precursors belong to Mn(OH) 2 impurity peak. Figure 6 (b) The precursor LDHs is converted into Mn metal oxide mixture under different activation methods. 1 Zr0.75 --C, Mn 1 Zr 0.75 -RF、Mn 1 Zr 0.75 In the XRD spectrum of the -DBD catalyst, the characteristic diffraction peaks attributed to LDHs disappeared, indicating that the layered structure collapsed, while the Mn-C catalyst showed the characteristic diffraction peaks attributed to Mn 2 O 3 The catalyst after plasma activation shows a ZrO diffraction peak. The Zr ion radius is larger than that of the Mn ion, and it is more inclined to form MO-Zr chemical bonds on the surface of the oxide crystal to form a solid solution).

[0057] H 2 -TPR Characterization

[0058] In order to study the reduction and oxidation ability of the catalysts, a series of catalysts were subjected to H 2 -TPR analysis. Figure 7 Given Mn 1 Zr 0.75 -C, Mn 1 Zr 0.75 -RF、Mn 1 Zr 0.75 -DBD catalyst 2 -TPR results, in Figure 7 Among the three MnZr catalysts at 200-450 °C, the plasma-treated catalyst showed three peaks, the calcined catalyst showed two peaks, and the peak at 240-290 °C was attributed to MnO 2 / Mn 2 O 3 The peak at 360-375 °C is attributed to Mn 2 O 3 / Mn 3 O 4 The peak at 417-430℃ is attributed to Mn 3 O 4 In terms of the reduction of Mn / MnO, the temperature between 500 and 600 °C is attributed to the co-reduction of Mn and Zr, among which the catalyst produced by radio frequency (RF) plasma has the strongest co-reduction ability, and the reduction peak of the catalyst treated by plasma shifts to the low temperature region, which is beneficial to the low temperature activity of the catalyst.

Claims

1. A preparation method and application of a plasma MnZr hydrotalcite-derived catalyst for wide temperature SCR degradation, characterized in that: The method comprises the following steps: (1) stirring and dissolving a metal salt, NaOH, and Na2CO3 in deionized water to obtain a metal salt solution, a precipitant, and a stabilizer; (2) adding the metal salt solution dropwise to the precipitant, adding a stabilizer dropwise during the process to maintain the pH value of the mixed solution stable, and after the addition is completed, the mixture is stirred and aged at a constant temperature, and centrifuged and washed to make the pH value of the supernatant neutral, and the obtained precipitate is further dissolved in 100 mL of anhydrous ethanol and stirred; and dried overnight to obtain a MnZr-LDHs precursor; (3) Grinding the sample obtained in step (2) into fine powder, and activating it by radio frequency plasma (RF) treatment to obtain a MnZr hydrotalcite-derived NO degradation catalyst.

2. The method for preparing a wide temperature range MnZr hydrotalcite-derived catalyst for SCR NO degradation catalyst according to claim 1, characterized in that: The molar ratio of the metal elements in the metal salt solution in the preparation method is: 2+ ):n(Sm 3+ )=1:n(n=0.25, 0.5, 0.75, 1).

3. The method for preparing a wide temperature range MnZr hydrotalcite-derived catalyst for SCR NO degradation catalyst according to claim 1, characterized in that: The precipitant is Na2CO3 and the stabilizer is NaOH.

4. The method for preparing a wide temperature range MnZr hydrotalcite-derived catalyst for SCR NO degradation catalyst according to claims 1-3, characterized in that: The preparation method is a co-precipitation method, and the activation method is a radio frequency plasma (RF).

5. The method for preparing a wide temperature range MnZr hydrotalcite-derived catalyst for SCR NO degradation catalyst according to claims 1-4, characterized in that: The RF plasma treatment lasts for 5 to 20 minutes and has a power of 50 to 250W.

6. The method for preparing the wide temperature range MnZr 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 MnZr 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 to maintain the pH value at 10, 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 MnZr hydrotalcite-derived denitrification catalyst.

8. Use of the wide temperature range MnZr hydrotalcite-derived catalyst according to any one of claims 1 to 7 as an SCR NO degradation catalyst.

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