A rare-earth-based hollow nanotube denitration catalyst, a preparation method and application thereof

Abstract

The application discloses a rare earth-based hollow nanotube denitration catalyst and a preparation method and application thereof, and relates to the technical field of denitration catalysts. The catalyst takes TiOCl2-Al2O3 hollow nanotubes as a carrier, takes rare earth oxides as an active component, and takes MoO3 as a cocatalyst. The method first synthesizes the TiOCl2-Al2O3 hollow nanotube carrier through a microfluidic electrospinning technology, then impregnates the active component and the cocatalyst precursor, and fixes elements by adding a reducing agent, and finally synthesizes the finished catalyst through calcination. The hollow nanotube denitration catalyst synthesized by the application has a large specific surface area, a high conversion rate, and excellent denitration effects at high, medium and low temperature sections.

Description

TECHNICAL FIELD

[0001] The present application relates to a rare earth-based hollow nanotube denitration catalyst, a preparation method and application thereof, and belongs to the field of air pollution control. BACKGROUND

[0002] With the rapid development of urbanization and industrialization, a large amount of nitrogen oxides (NOx) is emitted into the atmosphere, which is the main factor causing acid rain, haze, photochemical smog and other disasters.

[0003] At present, the main means for NOx control is selective oxidation reduction (SCR) and selective non-catalytic reduction (SNCR), among which SCR technology is widely used in various denitration fields due to its high conversion rate and low energy consumption. The key to SCR technology is the catalyst, and the most common SCR denitration catalyst is vanadium-titanium catalyst. For example, patent CN103706409B discloses a flat plate type denitration catalyst, which is prepared by coating titanium dioxide, vanadium pentoxide, ammonium heptamolybdate, lactic acid, glass fiber and silicon dioxide on a substrate and then calcining. The catalyst has high strength, high conversion rate and is easy to recover. Patent CN102225333B discloses a denitration catalyst and a preparation method thereof, which is a V-Ti-based catalyst with the addition of A.K sugar to increase the strength of the catalyst. Patent CN108246283B prepares a denitration catalyst by combining a mixed concentrated solution of V, W and Mo precursors with a carrier, achieving high loading of active components. V2O5 has been proven to have excellent denitration performance due to its strong oxidation-reduction ability and easy valence change. However, V2O5 is a toxic chemical and has strong toxicity. Discarded vanadium-based denitration catalysts are often difficult to dispose, so it is necessary to find a substitute for the active element.

[0004] In the current research, rare earth elements Ce and La are good substitutes for V, and some research has been conducted on rare earth-based denitration catalysts. For example, patent CN116943635A discloses a CeMnOx@TiO2 core-shell structure SCR denitration catalyst, a preparation method and application thereof, which can maintain a denitration activity of more than 90% for a long time within 80-260℃. Patent CN115672312A discloses a hollow structure vanadium-free rare earth-based wide-temperature denitration catalyst and a preparation method thereof, which uses cerium-manganese composite oxide as the active component and has excellent catalytic activity within 140-335℃. Developing denitration catalysts with Ce, La and other rare earth elements as active components can not only effectively reduce the pollution of NOx to the atmosphere, but also avoid the secondary pollution of toxic element V to the environment. SUMMARY

[0005] The present application aims at the current situation and existing problems of the fixed bed denitration, and provides a preparation method and application of a rare earth-based hollow nanotube denitration catalyst.

[0006] The present application can be realized by the following technical scheme: a rare earth-based hollow nanotube denitration catalyst, which takes hollow nanotube TiOCl2-Al2O3 as a carrier, takes rare earth metal oxide as an active component, and takes MoO3 as a cocatalyst. The key of the present application lies in the synthesis of the hollow nanotube TiOCl2-Al2O3 carrier. The combination of TiOCl2 and Al2O3 can enhance the surface acidity of the carrier. The hollow nanotube structure can not only increase the specific surface area, but also further improve the catalyst performance due to the confinement effect formed by the unique structure.

[0007] A preparation method of a rare earth-based hollow nanotube denitration catalyst, which takes TiOCl2-Al2O3 hollow nanotube as a carrier, takes rare earth metal oxide as an active component, and takes MoO3 as a cocatalyst. The mass percentage of the active component is 5-10% and the mass percentage of the cocatalyst is 1-3% based on the mass of the carrier.

[0008] The synthesis steps of the catalyst are as follows:

[0009] (1) Dissolve polyacrylonitrile in dimethylformamide and carbon tetrachloride to obtain a mixed solution, then add anhydrous aluminum chloride and tetrabutyl titanate into the mixed solution in sequence to obtain a spinning solution;

[0010] (2) Perform spinning by using microfluidic spinning technology, dry the filamentous material, and then transfer the filamentous material to a muffle furnace for calcination to prepare a hollow nanotube carrier;

[0011] (3) Prepare a mixed solution of active component and cocatalyst precursor, immerse the carrier in the mixed solution for impregnation adsorption, then perform reduction treatment by adding a reducing agent, and perform suction filtration, washing and drying;

[0012] (4) Transfer the dried sample of step (3) to a muffle furnace for calcination to obtain a finished catalyst.

[0013] In the technical scheme of the present application, the rare earth metal oxide is CeO2 and / or La2O3.

[0014] In the technical scheme of the present application, the mass ratio of polyacrylonitrile, dimethylformamide and carbon tetrachloride in step (1) is (30-50):(80-100):(20-30).

[0015] The addition amount of aluminum chloride in step (1) is 3-5% of the mass of the mixed solution, and the addition amount of tetrabutyl titanate is 30-50% of the mass of the mixed solution.

[0016] In the technical scheme of the present application, the voltage for spinning in step (2) is 15-25kV, the feeding speed for spinning is 0.5-1.5mL / h, and the drying temperature is 60-80℃.

[0017] The roasting environment in step (2) is air, the roasting temperature is 500-600℃, and the roasting time is 4-6h.

[0018] In the technical scheme of the present application, the active component precursor in step (3) is nitrate or chloride, and the co-catalyst precursor is ammonium tetramolybdate or ammonium heptamolybdate.

[0019] In the technical scheme of the present application, the mass ratio of the mixed solution to the carrier in step (3) is (8-17):1, and the impregnation time in step (3) is 4-8h.

[0020] The reducing agent in step (3) is hydrazine hydrate, sodium borohydride or potassium borohydride, and the mass excess of the reducing agent is 300-500%.

[0021] In the technical scheme of the present application, the roasting environment in step (4) is air, the roasting temperature is 500-550℃, and the roasting time is 2-4h.

[0022] A rare earth-based hollow nanotube denitration catalyst is prepared by the above method.

[0023] In the technical scheme of the present application, the catalyst prepared by the method is used in denitration.

[0024] Beneficial effects:

[0025] The application discloses a preparation method and application of a rare earth-based hollow nanotube denitration catalyst, and the key of the catalyst lies in synthesis of a hollow nanotube TiOCl2-Al2O3 carrier. In the application, a mixed solution of polyacrylonitrile, dimethyl ether formamide and carbon tetrachloride is used as a solvent to dissolve aluminum chloride and tetrabutyl titanate, and then a hollow nanotube carrier is prepared through micro-fluid electrospinning and calcination. Although common electrospinning can form a hollow nanotube micro-morphology, TiOCl2 cannot be formed. TiOCl2 has not only the oxidation-reduction performance of TiO2, but also chlorine ions, so that the surface acidity of the carrier is improved, and a binary solid acid is formed by coupling with Al2O3, thereby further strengthening the surface acidity and improving the NH3 adsorption performance. Although TiCl4 can prepare TiOCl2, it cannot form a hollow nanotube microstructure. The hollow nanotube structure can not only improve the specific surface area of the carrier and enhance the contact between the surface active component and the reaction molecules, but also further improve the catalytic reaction performance due to the confinement effect of the hollow nanotube. In the scheme, the synthesis of the hollow nanotube micro-morphology and TiOCl2 is realized at the same time, so that the carrier has the advantages of large surface area and strong surface acidity. Then, the active component and the promoter are loaded through an impregnation adsorption method, and the active elements are uniformly dispersed on the surface of the carrier, thereby preventing performance reduction caused by agglomeration. The rare earth-based hollow nanotube denitration catalyst synthesized in the application has excellent denitration activity in the range of 180-420 DEG C, and has a wide reaction temperature range. Meanwhile, the catalyst has a simple synthesis process, common raw materials, high stability, high economic value and market application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0026] BRIEF DESCRIPTION OF DRAWINGS Figure 1 FIG. 2 is a FE-SEM diagram of the carrier in Example 3;

[0027] BRIEF DESCRIPTION OF DRAWINGS Figure 2 FIG. 3 is a FE-SEM diagram of the finished catalyst in Example 3;

[0028] BRIEF DESCRIPTION OF DRAWINGS Figure 3 FIG. 4 is a FE-SEM diagram of the finished catalyst in Comparative Example 1;

[0029] BRIEF DESCRIPTION OF DRAWINGS Figure 4 DETAILED DESCRIPTION NOx conversion rate DETAILED DESCRIPTION

[0030] The application will be further described below through examples. The examples are implemented on the premise of the technical scheme of the application, and detailed implementation modes and specific operation processes are given, but the protection scope of the application is not limited to the following examples.

[0031] Performance evaluation: NH3-SCR performance evaluation was carried out in a fixed bed reaction system. 2 ml of catalyst was weighed and placed in the middle position of a quartz reactor (inner diameter 10 mm), and quartz wool was fixed in front and back. The reactor was transferred to a muffle furnace, and a simulated gas was introduced. The simulated gas composition was NO 1000 ppm, NH3 1000 ppm, O2 10%, and N2 as the carrier gas. The space velocity was controlled at 50000 h -1 -1. The reaction interval was set to 180-420℃, and the tail gas NO concentration was recorded every 30℃ for 30 min.

[0032]

[0033] Example 1

[0034] (1) Preparation of catalyst carrier

[0035] 40 g of dimethylformamide and 15 g of carbon tetrachloride were weighed and mixed uniformly, and then 15 g of polyacrylonitrile was dissolved in the mixture to prepare a mixed solution. 3.5 g of anhydrous aluminum chloride was added to the mixed solution and stirred to dissolve, and then 28 g of titanium tetrabutoxide solution was continuously added. After mixing uniformly, a spinning solution was prepared.

[0036] The spinning solution was taken with a syringe, the syringe was connected to a single channel of a microfluidic chip, and then spinning was carried out by using the single channel of the microfluidic chip through a microfluidic electrostatic integrated machine (Nanjing Jetnas New Materials Co., Ltd.). The spinning voltage was 20 kV, and the injection rate of the syringe was 1.5 mL / h.

[0037] The obtained electrospun material was completely dried at 70℃, and then transferred to a muffle furnace and calcined at 600℃ under air atmosphere for 4 h to obtain a catalyst carrier, a total of 11.2263 g.

[0038] (2) Preparation of catalyst

[0039] 2.5608 g of La(NO3)3·6H2O and 1.1817 g of (NH4)6Mo7O 24 ·4H2O were dissolved in 112.3 g of deionized water, and then the carrier was immersed in the solution and gently stirred for several times, and then placed for 4 h to allow the carrier to fully adsorb. Then 2.0144 g of hydrazine hydrate (excess 300%) was added, and the active elements were fully reduced after gentle stirring for several times and standing for 2 h. After filtration, washing and drying, a semi-finished catalyst was obtained. Finally, the finished catalyst was obtained by calcining at 550℃ for 2 h in a muffle furnace.

[0040] Example 2

[0041] (1) Preparation of catalyst carrier

[0042] Weigh 50 g of dimethylformamide and 10 g of carbon tetrachloride and mix them evenly, then dissolve 20 g of polyacrylonitrile in them to prepare a mixed solution. Add 2.4 g of anhydrous aluminum chloride to the mixed solution and stir to dissolve, then continue to add 24 g of tetrabutyl titanate solution, mix evenly to prepare a spinning solution.

[0043] Suck the spinning solution with a syringe, connect the syringe to the single channel of the microfluidic chip, and then use the single channel of the microfluidic chip to spin through the microfluidic electrostatic integrated machine (Nanjing Jetnas New Materials Co., Ltd.) with a spinning voltage of 15 kV and a syringe injection rate of 1 mL / h.

[0044] The obtained electrospun material is completely dried at 70°C, then transferred to a muffle furnace and calcined at 500°C for 5h under air atmosphere to obtain a catalyst carrier, a total of 8.8251 g.

[0045] (2) Preparation of the catalyst

[0046] Dissolve 1.2189 g of CeCl3·7H2O and 0.6906 g of (NH4)6Mo7O 24 ·4H2O in 105.9 g of deionized water, then immerse the carrier in the solution and stir gently for several turns, then stand for 8 h to allow the carrier to fully adsorb. Then add 3.4574 g of sodium borohydride (excess 400%) and stir gently for several turns, then stand for 2 h to allow the active elements to be fully reduced. After suction filtration, washing and drying, a semi-finished catalyst is obtained. Finally, the finished catalyst is obtained by calcining in a muffle furnace at 520°C for 2h.

[0047] Example 3

[0048] (1) Preparation of the catalyst carrier

[0049] Weigh 50 g of dimethylformamide and 12.5 g of carbon tetrachloride and mix them evenly, then dissolve 25 g of polyacrylonitrile in them to prepare a mixed solution. Add 2.625 g of anhydrous aluminum chloride to the mixed solution and stir to dissolve, then continue to add 35 g of tetrabutyl titanate solution, mix evenly to prepare a spinning solution.

[0050] Suck the spinning solution with a syringe, connect the syringe to the single channel of the microfluidic chip, and then use the single channel of the microfluidic chip to spin through the microfluidic electrostatic integrated machine (Nanjing Jetnas New Materials Co., Ltd.) with a spinning voltage of 25 kV and a syringe injection rate of 0.5 mL / h.

[0051] The obtained electrospun material is completely dried at 60°C, then transferred to a muffle furnace and calcined at 550°C for 6h under air atmosphere to obtain a catalyst carrier, a total of 11.3967 g.

[0052] (2) Preparation of the catalyst

[0053] 1.5538 g of Ce(N03)3-6H20 and 0.7102 g of (NH4)2Mo40 13 ·2H20 were dissolved in 170.9 g of deionized water, and then the support was immersed in the solution and left to stand for 6 h after gentle stirring for several rounds to allow the support to fully adsorb. Then 1.9316 g of hydrazine hydrate (excess 500%) was added, and left to stand for 2 h after gentle stirring for several rounds to allow the active elements to be fully reduced. After suction filtration, washing and drying, a semi-finished catalyst was obtained. Finally, the finished catalyst was obtained by calcination in a muffle furnace at 500°C for 3 h.

[0054] Example 4

[0055] (1) Preparation of catalyst support

[0056] 45 g of dimethylformamide and 10 g of carbon tetrachloride were weighed and mixed uniformly, and then 20 g of polyacrylonitrile was dissolved therein to prepare a mixed solution. 3 g of anhydrous aluminum chloride was added to the mixed solution and stirred to dissolve, and then 37.5 g of tetrabutyl titanate solution was continuously added, and the mixture was mixed uniformly to prepare a spinning solution.

[0057] The spinning solution was taken up with a syringe, the syringe was connected to a single channel of a microfluidic chip, and then spinning was performed by using the single channel of the microfluidic chip through a microfluidic electrostatic integrated machine (Nanjing Jetnas New Materials Co., Ltd.). The spinning voltage was 20 kV, and the injection rate of the syringe was 0.5 mL / h.

[0058] The obtained electrospun material was completely dried at 80°C, and then transferred to a muffle furnace, and calcined at 600°C for 4 h under an air atmosphere to obtain a catalyst support, a total of 12.2153 g.

[0059] (2) Preparation of catalyst

[0060] 3.0754 g of LaCl3-7H20 and 1.5556 g of (NH4)2Mo40 13 ·2H20 were dissolved in 97.7 g of deionized water, and then the support was immersed in the solution and left to stand for 6 h after gentle stirring for several rounds to allow the support to fully adsorb. Then 11.8112 g of potassium borohydride (excess 400%) was added, and left to stand for 2 h after gentle stirring for several rounds to allow the active elements to be fully reduced. After suction filtration, washing and drying, a semi-finished catalyst was obtained. Finally, the finished catalyst was obtained by calcination in a muffle furnace at 500°C for 4 h.

[0061] Comparative Example 1

[0062] 1.7018 g of Ce(N03)3-6H20 and 0.8274 g of (NH4)6Mo70 24• 4H2O was dissolved in 100 g of deionized water to prepare a mixed solution for use. 10 g of titanium white powder was dispersed in the mixed solution, stirred gently for several circles and then left to stand for 4 h for full adsorption. Then 4.1418 g of sodium borohydride was added, stirred gently for several circles, left to stand for 2 h for full reduction of active elements. The catalyst semi-finished product was obtained by filtration, washing and drying, and then transferred to a muffle furnace for calcination at 550 °C for 3 h to obtain the finished catalyst.

[0063] Comparative effect: compared with Example 3, the catalyst has a significant decrease in NOx conversion rate in the temperature range of 180-420 °C.

Claims

1. A method for preparing a rare earth-based hollow nanotube denitration catalyst, characterized in that: This catalyst uses TiOCl2-Al2O3 hollow nanotubes as a support, rare earth metal oxides as the active component, and MoO3 as a co-catalyst; based on the mass of the support, the mass percentage of the active component is 5-10%, and the mass percentage of the co-catalyst is 1-3%. The synthesis steps of this catalyst are as follows: (1) Polyacrylonitrile was dissolved in dimethylformamide and carbon tetrachloride to obtain a mixture, and then anhydrous aluminum chloride and tetrabutyl titanate were added to the mixture to obtain a spinning solution. (2) The filaments were spun using microfluidic spinning technology, dried, and then transferred to a muffle furnace for calcination to prepare hollow nanotube carriers. (3) Prepare a mixed solution of active component and co-catalyst precursor, immerse the support in the mixed solution for impregnation and adsorption, then reduce it by adding a reducing agent, filter, wash and dry. (4) The sample dried in step (3) is transferred to a muffle furnace for calcination to obtain the finished catalyst; The rare earth metal oxides are CeO2 and / or La2O3.

2. The preparation method according to claim 1, characterized in that: The mass ratio of polyacrylonitrile, dimethylformamide and carbon tetrachloride in step (1) is (30~50):(80~100):(20~30); The amount of anhydrous aluminum chloride added in step (1) is 3-5% of the mass of the mixture, and the amount of tetrabutyl titanate added is 30-50% of the mass of the mixture.

3. The preparation method according to claim 1, characterized in that: The spinning voltage in step (2) is 15~25kV, the spinning feed rate is 0.5~1.5mL / h, and the drying temperature is 60~80℃; The roasting environment described in step (2) is an empty atmosphere, the roasting temperature is 500~600℃, and the roasting time is 4~6h.

4. The preparation method according to claim 1, characterized in that: The active component precursor in step (3) is a nitrate or a chloride, and the cocatalyst precursor is ammonium tetramolybdate or ammonium heptamolybdate.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the mixed solution to the carrier in step (3) is (8~17):1; the immersion time in step (3) is 4~8h; The reducing agent mentioned in step (3) is hydrazine hydrate, sodium borohydride, or potassium borohydride.

6. The preparation method according to claim 1, characterized in that: The roasting environment in step (4) is an empty atmosphere, the roasting temperature is 500~550℃, and the roasting time is 2~4h.

7. A rare earth-based hollow nanotube denitration catalyst, characterized in that: The catalyst is prepared by the method described in any one of claims 1 to 6.

8. The application of the catalyst prepared by the method of claim 1 in denitrification.

9. The application according to claim 8, characterized in that: The operating temperature range is 180~420℃.

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