Integral difunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs (volatile organic compounds) and preparation method of integral difunctional Mn-based composite metal oxide catalyst

Abstract

The invention discloses an integral difunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs (Volatile Organic Compounds) and a preparation method of the integral difunctional Mn-based composite metal oxide catalyst. The Mn-based composite metal oxide catalyst is grown on the three-dimensional foam structure material in situ, the adsorption performance of the catalyst is remarkably enhanced by adding a small amount of adsorbent, and the activity of the catalyst is improved. When being used for NH3-SCR catalysis, the high-activity integral Mn-based composite metal oxide catalyst doped with a small amount of adsorbent has a wide temperature window and a nitrogen oxide (NOx) conversion rate gt in a medium-low temperature section; the temperature interval of 80% is 80-305 DEG C; when the catalyst is used for catalytic combustion of VOCs, the temperature for degrading 90% toluene is lower than 150 DEG C, and the low-temperature catalytic activity of the catalyst is even superior to that of numerous noble metal-loaded catalysts. In addition, the catalyst has good stability, H2O poisoning resistance and S poisoning resistance, and can be regenerated after simple heat treatment, so that the catalyst can be efficiently applied to actual flue gas treatment at low cost.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental catalytic purification, and specifically relates to an integral bifunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs and a preparation method thereof. Background Art

[0002] Thermal catalysis is an effective means of current flue gas terminal treatment. This method is economical, efficient and environmentally friendly. Although great progress has been made in the thermal catalytic degradation of VOCs and NH3-SCR denitrification catalysts, the limited low-temperature activity of non-precious metal catalysts when used for VOCs catalytic elimination, the high denitrification temperature window, and the poor resistance of the catalysts to water and sulfur poisoning have caused certain obstacles to the use of existing catalysts in flue gas treatment in non-power fields. In addition, fine powder catalysts are difficult to meet the flue gas treatment needs in actual production processes, and the use of in-situ growth to synthesize monolithic catalysts has opened up a new perspective in this field.

[0003] Patent application number CN202310237401.8 discloses a method for NO x The method requires the use of vapor deposition method to silanize the SiO2 carrier with the help of organic reagents such as trimethylchlorosilane. Although it can be used for NO and VOCs synergistic catalysis under mild reaction conditions, x The catalyst is a bifunctional catalyst for the removal of chlorobenzene and catalytic elimination of VOCs, but the reaction time is long, the introduction of multiple organic reagents is not only environmentally unfriendly but also adds additional costs, and the catalyst has a low chlorobenzene conversion rate and NO at T = 300 °C. x The removal efficiency is still less than 90%.

[0004] Patent application number CN202110594610.9 discloses a multi-shell V-Mn-Co-based catalyst with good NH3-SCR denitrification activity in a wide temperature range. The obtained V2O5 / MnCo2O4 catalyst can obtain NO in the temperature range of 125-400 °C. x The conversion rate is >90% and the catalyst has good N2 selectivity. However, the solvothermal method used to synthesize the catalyst involves a variety of organic reagents, and the main component of the obtained catalyst contains V2O5, which has extremely strong biological toxicity. The used V-based catalyst has been included in the "National Hazardous Waste List (2021)" (China), which further highlights the environmental risks of such catalysts.

[0005] Patent application number CN202210319910.0 discloses a catalyst for the catalytic combustion of VOCs. The catalyst uses diatomite as a carrier and the active components are MnO2, CeO2, and CuO. Although the preparation process is simple, the repeatability is good, and it is convenient for large-scale production and utilization, the active components are simply added and do not form a composite oxide, making it difficult to exert the synergistic effect between metals. In addition, the large amount of diatomite added is only used as a carrier and does not play the role of a catalytic aid. When the catalyst is used for the catalytic combustion of C1-C4 compounds, the temperature is relatively high (T 98 ≥ 290 ℃). Summary of the invention

[0006] In view of the limitations and shortcomings of the existing catalysts mentioned in the background technology, the purpose of the present invention is to provide an integral bifunctional Mn-based composite metal oxide catalyst for the removal of nitrogen oxides and VOCs and a preparation method. The catalyst of the present invention is environmentally friendly, the preparation method is simple, and the repeatability is high. It not only has a wide denitrification temperature window in the medium and low temperature range, but also can efficiently remove VOCs in the lower temperature range, and is suitable for industrial flue gas NO in non-electrical fields. x and elimination of VOCs.

[0007] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing an integral bifunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs, comprising the following steps: The pretreated three-dimensional foam structure material and adsorbent are added to distilled water, and after being uniformly dispersed, a precursor solution containing manganese salt and M salt is added dropwise, and after being stirred evenly, a hydrothermal reaction is carried out, and the obtained product is calcined to obtain an adsorbent-doped integral bifunctional Mn-based composite metal oxide catalyst; Wherein, the M salt is at least one of a rare earth soluble salt or a non-precious metal transition element soluble salt.

[0008] Furthermore, the temperature of the distilled water is 40-70°C.

[0009] Furthermore, the three-dimensional foam structure material is at least one of foam nickel, foam copper, and foam silicon; and the pretreatment thereof refers to ultrasonic treatment in a hydrochloric acid solution, followed by soaking and cleaning with deionized water and anhydrous ethanol, and drying for standby use. The concentration of the hydrochloric acid solution is preferably 1-5 mol / L, and the ultrasonic treatment time is preferably 1-30 min, more preferably 5-10 min.

[0010] Furthermore, the adsorbent is a porous carbon material or a clay mineral; the pretreatment thereof refers to soaking in hydrogen peroxide, then soaking and cleaning with deionized water and anhydrous ethanol, and drying for use. The mass fraction of hydrogen peroxide is preferably 12%-30%, and ultrasonic treatment can also be applied for 1-60 min during the hydrogen peroxide soaking process; the porous carbon material is preferably activated carbon, and the clay mineral is preferably kaolin, diatomaceous earth or attapulgite.

[0011] Furthermore, the adsorbent accounts for 1 wt.%-10 wt.% of the total amount of manganese salt and M salt in the precursor solution.

[0012] Furthermore, in the precursor solution containing manganese salt and M salt: the manganese salt is composed of potassium permanganate and at least one other soluble manganese salt. Preferably, the manganese salt is composed of potassium permanganate and manganese nitrate, and the M salt is preferably cerium nitrate, cobalt nitrate or copper nitrate. The concentration of the M salt is preferably 0.01-2.0 mol / L.

[0013] Furthermore, the molar ratio of M salt, potassium permanganate and other soluble manganese salts is (1-4):(1-2):(1-5).

[0014] Furthermore, the temperature of the hydrothermal reaction is 80-180°C, and the reaction time is 2-8 h.

[0015] Furthermore, the calcination adopts gradient heating: the first heating is to 100-200°C, and the second heating is to 350-600°C; the heating rate of the first heating is not more than 10°C / min, and the heating rate of the first heating is greater than that of the second heating.

[0016] The present invention also provides an integral bifunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs obtained by the above preparation method, wherein the catalyst comprises a solid solution of a manganese oxide compound (one or more of MnO2, Mn2O3, Mn3O4), a rare earth oxide and / or a non-precious metal transition metal oxide.

[0017] The beneficial effects of the present invention are: The present invention adopts the in-situ growth method to synthesize the monolithic catalyst, and the different metals have strong synergistic effects. A small amount of adsorbent doping can greatly improve the activity of the catalyst. The obtained monolithic Mn-based composite metal oxide catalyst can be used for flue gas denitrification in the medium and low temperature range, and can also be used for the efficient elimination of VOCs: when used for NH3-SCR catalysis, it has a wide temperature window in the medium and low temperature range, and the temperature range of nitrogen oxide conversion rate>80% is 80-305 ℃; when used for VOCs catalytic combustion, the temperature of degrading 90% of toluene is lower than 150 ℃, and its low-temperature catalytic activity is even better than many loaded precious metal catalysts. In addition, the catalyst has good stability and resistance to H2O and S poisoning, and can be regenerated after simple heat treatment, so it can be used in actual flue gas treatment with high efficiency and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 NO corresponding to different catalysts x Conversion rate curve.

[0019] Figure 2 This is the anti-poisoning performance of the catalyst synthesized in Example 3.

[0020] Figure 3 The toluene conversion curves corresponding to different catalysts.

[0021] Figure 4 This is the SEM image of the catalyst synthesized in Example 4.

[0022] Figure 5 This is the XRD pattern of the catalyst synthesized in Example 4.

[0023] Figure 6 This is the adsorption-desorption curve of the catalyst synthesized in Example 4.

[0024] Figure 7 This is the pore size distribution diagram of the catalyst synthesized in Example 4. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0027] Example 1 1. Cut a 1 cm × 1 cm nickel foam sheet, place it in a 2 mol / L hydrochloric acid solution for ultrasonic cleaning for 10 min, then soak and clean it repeatedly with deionized water and anhydrous ethanol, and dry it for later use. Place kaolin in 15% hydrogen peroxide for ultrasonic cleaning for 10 min, then soak and clean it repeatedly with deionized water and anhydrous ethanol, and dry it for later use. Dissolve 0.5 mmol potassium permanganate and 0.5 mmol cerium nitrate in 30 mL and 10 mL of distilled water respectively and set it aside.

[0028] 2. Take 20 mL of distilled water and heat it to 50 °C, add the pretreated nickel foam flakes and 0.045 g (8 wt.% of the total weight of the precursor salt) pretreated kaolin, and stir evenly. Add the prepared potassium permanganate solution and cerium nitrate solution and 0.347 mL of manganese nitrate solution (containing 1.5 mmol of manganese nitrate) dropwise, stir for 30 min, transfer to a reactor with a 100 mL polytetrafluoroethylene liner, and keep it at 120 °C for 5 h for hydrothermal reaction. After the reaction, the product is washed with distilled water and anhydrous ethanol to pH = 7, transferred to a vacuum oven, and dried at 80 °C overnight. Then placed in a tubular furnace, heated to 120 °C at a heating rate of 10 °C / min in an air atmosphere for calcination for 2 h, and then heated to 400 °C at a heating rate of 5 °C / min for calcination for 4 h, and finally a monolithic Mn-Ce-based composite metal oxide catalyst is obtained.

[0029] Example 2 The parameters of the steps in Example 1 are as follows, except that: 1. Replace nickel foam with copper foam and ultrasonically clean it in 1 mol / L hydrochloric acid solution for 15 min. 2. Replace cerium nitrate with an equal molar amount of cobalt nitrate and prepare a solution for standby use. 3. Change the mass of kaolin added to 5 wt.% of the total mass of soluble metal precursor salt. Finally, a monolithic Mn-Co-based composite metal oxide catalyst is obtained.

[0030] Example 3 The parameters of the steps in Example 1 are as follows, except that: 1. The mass of potassium permanganate was changed to 0.063 g (0.4 mmol), and cerium nitrate was replaced with an equal molar amount of cobalt nitrate, and a solution was prepared for use. 2. The amount of manganese nitrate solution was changed to 0.395 mL (containing 1.7 mmol manganese nitrate), and the molar ratio of cobalt nitrate, potassium permanganate, and manganese nitrate was 0.5:0.4:1.7. Finally, a monolithic Mn-Co-based composite metal oxide catalyst was obtained.

[0031] Example 4 The parameters of the steps in Example 1 are as follows, except that: 1. The mass of potassium permanganate was changed to 0.047 g (0.3 mmol), the amount of manganese nitrate solution was changed to 0.209 mL (containing 0.9 mmol manganese nitrate), and the molar ratio of cerium nitrate, potassium permanganate, and manganese nitrate was 0.5:0.3:0.9. 2. Kaolin was replaced with diatomaceous earth, and the added mass was changed to 5 wt.% of the total mass of the soluble metal precursor salt. Finally, a monolithic Mn-Ce-based composite metal oxide catalyst was obtained.

[0032] Example 5 The parameters of the steps in Example 1 are as follows, except that: 1. Replace nickel foam with copper foam. 2. Change the mass of potassium permanganate to 0.047 g (0.3 mmol), replace cerium nitrate with copper nitrate, and prepare a solution for standby use. The molar ratio of copper nitrate, potassium permanganate, and manganese nitrate is 0.6:0.3:1.5. 3. Replace kaolin with attapulgite, and the added mass is changed to 6 wt.% of the total mass of the soluble metal precursor salt. Finally, a monolithic Mn-Cu-based composite metal oxide catalyst is obtained.

[0033] Test example The monolithic catalyst sample obtained in the above example was cut into pieces, 0.5 g was weighed and placed in a solid bed reactor, the mass space velocity was controlled to be 60000 mL / (g·h), the NO and NH3 concentrations were both 500 ppm, the O2 concentration was 5%, and the NO x The temperature range for conversion rate>80% is shown in Table 1. x The conversion rate curve is as follows Figure 1 shown.

[0034] Table 1. NO x Removal performance evaluation results

[0035] It can be seen that Example 3 shows the widest temperature window (80-305 °C) in the medium and low temperature range, and the temperature window range of all example samples is in the medium and low temperature range, indicating that the samples have the potential to be applied to flue gas denitrification in non-electrical fields. Figure 2 The results of the thermal stability and anti-H2O and anti-S poisoning performance tests of the catalyst prepared in Example 3 at 230°C are shown in Table 1. xThe conversion rate decreased slightly, and the catalyst activity increased significantly after the water vapor supply was stopped, indicating that there was competitive adsorption between water vapor and reactant molecules, which would cause a slight decrease in catalyst activity. When 100 ppm SO2 was introduced, the catalyst activity decreased significantly, and the activity did not improve after the SO2 supply was stopped, but the catalyst activity was largely restored after a simple heat treatment of the catalyst, indicating that the poisoning caused by SO2 was mainly due to the coverage of active sites caused by the generated (NH4)2SO4 and (NH4)HSO4, rather than permanent deactivation caused by MnSO4. In summary, the above catalyst has good resistance to H2O and S poisoning, and can be recycled.

[0036] The monolithic catalyst sample obtained in the above example was cut into pieces, weighed 0.25 g and placed in a fixed bed reactor. The mass space velocity was controlled to be 45000 mL / (g·h). With 3000 ppm toluene as the target VOCs, the core temperature of the fixed bed reactor was first raised to 270 °C to activate the catalyst, and then the catalyst activity was tested by gradient cooling. The toluene conversion data corresponding to different temperature sections are shown in Tables 2 and 3. Figure 3 shown.

[0037] Table 2. Evaluation results of toluene catalytic elimination performance

[0038] The temperature at which the toluene conversion rate is 50% (T 50 ) represents the low temperature activity of the catalyst, and the temperature at which the toluene conversion rate reaches 90% (T 90 ).Depend on Figure 3 It can be seen that the T 50 All of them are below 160 ℃, which indicates that the monolithic Mn-based composite metal oxide synthesized by the above method has good low-temperature activity. By comparison, it is found that the catalyst prepared in Example 4 has the best catalytic activity when used for catalytic combustion of toluene. 50 and T 90 124 ℃ and 143 ℃ respectively.

[0039] Depend on Figure 4 It can be seen from the SEM image that the catalyst grown on the nickel foam substrate in Example 4 is composed of small particles piled up, and the loosely piled structure can provide more contact sites for the reactant molecules, which is conducive to improving the activity. Figure 5 The XRD diagram of the catalyst synthesized in Example 4 shows that the sample has an amorphous structure, which can provide a large number of structural defects and is an important reason for the high activity of the catalyst.

[0040] Figure 6 This is the adsorption-desorption curve of the catalyst synthesized in Example 4. It can be seen that the sample has two pore structures: internal pores and stacked pores. Figure 7 This is the pore size distribution diagram of the catalyst prepared in Example 4. The suitable pore structure is one of the reasons why the catalyst has high activity.

[0041] The embodiments described above only express several preferred embodiments of the present invention, and the descriptions thereof are relatively specific and detailed, but are not intended to limit the present invention. It should be noted that for those skilled in the art, the present invention may also have various changes and modifications, and any modifications, equivalent substitutions, improvements, etc. made within the concept and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing an integral bifunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs, characterized in that: The steps include: The pretreated three-dimensional foam structure material and adsorbent are added to distilled water, and after being uniformly dispersed, a precursor solution containing manganese salt and M salt is added dropwise, and after being stirred evenly, a hydrothermal reaction is carried out, and the obtained product is calcined to obtain an adsorbent-doped integral bifunctional Mn-based composite metal oxide catalyst; Wherein, the M salt is at least one of a rare earth soluble salt or a non-precious metal transition element soluble salt.

2. The method for preparing the integral bifunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs according to claim 1, characterized in that: The three-dimensional foam structure material is at least one of foam nickel, foam copper and foam silicon; the pretreatment thereof refers to ultrasonic treatment in a hydrochloric acid solution, followed by soaking and cleaning with deionized water and anhydrous ethanol, and drying for standby use.

3. The method for preparing the integral bifunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs according to claim 1, characterized in that: The adsorbent is a porous carbon material or a clay mineral; the pretreatment thereof is to soak it in hydrogen peroxide, then soak and clean it with deionized water and anhydrous ethanol, and dry it for use.

4. The method for preparing the integral bifunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs according to claim 1, characterized in that: The adsorbent accounts for 1 wt.%-10 wt.% of the total amount of manganese salt and M salt in the precursor solution.

5. The method for preparing the integral bifunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs according to claim 1, characterized in that: In the precursor solution containing manganese salt and M salt: the manganese salt consists of potassium permanganate and at least one other soluble manganese salt.

6. The method for preparing the integral bifunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs according to claim 5, characterized in that: The molar ratio of M salt, potassium permanganate and other soluble manganese salts is (1-4):(1-2):(1-5).

7. The method for preparing the integral bifunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs according to claim 1, characterized in that: The temperature of the hydrothermal reaction is 80-180°C, and the reaction time is 2-8 h.

8. The method for preparing the integral bifunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs according to claim 1, characterized in that: The calcination adopts gradient heating: the first heating is to 100-200°C, and the second heating is to 350-600°C; the heating rate of the first heating is greater than that of the second heating.

9. An integral bifunctional Mn-based composite metal oxide catalyst for eliminating nitrogen oxides and VOCs obtained by the preparation method according to any one of claims 1 to 8.

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