Carbon sponge supported nanometer array monolithic catalyst, its preparation method and application

Abstract

The application belongs to the field of catalysis technology, and discloses a carbon sponge supported nanometer array monolithic catalyst, a preparation method and application thereof, and comprises the following steps: (1) preparing nitrogen-doped carbon sponge; (2) preparing a precursor solution: dissolving metal salt in water, then adding a precipitant to prepare the precursor solution; the metal salt is manganese acetate and metal nitrate, and the metal nitrate is rare earth metal nitrate and / or transition metal nitrate; (3) adding a template agent to the precursor solution, stirring until completely dissolved, adding nitrogen-doped carbon sponge, then performing hydrothermal reaction, cooling, washing, and drying to obtain the carbon sponge supported nanometer array monolithic catalyst. The preparation method is green and efficient, the denitration efficiency of the prepared catalyst can reach 100%, the catalyst has high sulfur and water resistance, and the waste catalyst is easy to handle.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, specifically relating to a method for preparing and applying a highly efficient, sulfur-resistant, integral flexible catalyst for low-temperature denitrification. Background Technology

[0002] Industrial flue gas denitrification is one of the important measures to improve the atmospheric environment. In response to the practical needs of ultra-low emissions and low-temperature flue gas treatment, research on low-temperature denitrification technology is increasingly urgent. NH3-SCR technology, due to its excellent catalytic activity and low operating costs, has been widely used for NOx removal in industrial boilers. V2O5-WO3(MoO3) / TiO2 is the most widely used commercial catalyst. However, the biotoxicity of vanadium species and its narrow operating temperature window (300-400℃) make it difficult to directly apply to low-temperature flue gas denitrification. Especially in non-power industries, where flue gas temperatures are generally low and emissions are large, it has become the main battleground for improving environmental quality. Transition metal oxide catalysts have good low-temperature SCR activity and have become a research focus in the field of denitrification in recent years. In particular, Mn oxide catalysts have received widespread attention due to their excellent low-temperature catalytic activity and inherent environmental friendliness. However, Mn oxide catalysts are very sensitive to SO2, which severely limits their industrial application. Although Mn oxide catalysts have been extensively studied, powdered catalysts typically exhibit excellent low-temperature activity under laboratory conditions, but their application under practical engineering conditions remains a significant challenge because industrial applications often require the fabrication of monolithic structures to reduce bed resistance.

[0003] Currently used monolithic catalysts are mostly prepared by extrusion molding or coating methods. Sample preparation is complex and expensive, and the active components are prone to detachment. Therefore, directly coating the active material onto a three-dimensional porous matrix to prepare monolithic catalysts is one of the new development directions for low-temperature SCR catalysts. Three-dimensional porous matrices possess a three-dimensional interconnected network, which can provide a larger contact area and lower bed pressure drop for the reactant gases. This characteristic makes them promising candidates for catalyst supports. However, due to the complexity of the preparation process and the high cost of most three-dimensional porous supports, large-scale production is difficult. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a method for preparing and applying a highly efficient, sulfur-resistant, monolithic flexible catalyst for low-temperature denitrification. The catalyst uses a nitrogen-doped carbon sponge as a substrate, leveraging its high porosity of up to 97% to reduce catalyst bed resistance and provide more active sites, while also incorporating the high redox properties of nano-metal oxides. The catalyst prepared by this method exhibits excellent flexibility, strong adhesion of active components, good low-temperature catalytic activity and stability, a wide operating temperature window, and good water and sulfur resistance.

[0005] The technical problems to be solved are: the preparation process of manganese-based monolithic denitrification catalysts currently used in industry is complex, costly, the active components are easy to fall off, the low-temperature activity is poor and the resistance to sulfur poisoning is weak, and the cost of treating waste catalysts is high.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for preparing a carbon sponge-supported nanoarray monolithic catalyst includes the following steps:

[0008] (1) Preparation of nitrogen-doped carbon sponge;

[0009] (2) Preparation of precursor solution: Dissolve the metal salt in water, and then add a precipitant to prepare a precursor solution; the metal salt is manganese acetate and metal nitrate, and the metal nitrate is rare earth metal nitrate and / or transition metal nitrate;

[0010] (3) Add template agent to precursor solution, stir until completely dissolved, add nitrogen-doped carbon sponge, then carry out hydrothermal reaction, cool, wash and dry to obtain carbon sponge supported nanoarray monolithic catalyst.

[0011] Preferably, the nitrogen-doped carbon sponge in step (1) is prepared by carbonizing melamine sponge at 500-800°C in a protective atmosphere and then cooling it to obtain nitrogen-doped carbon sponge.

[0012] Preferably, the carbonization heating rate is 1-5℃ / min, the carbonization temperature is 700±100℃, and the carbonization time is 3±2h.

[0013] Preferably, the molar ratio of manganese acetate to metal nitrate in step (2) is 1-10; the molar ratio of precipitant to metal ion is 0.6±0.3; and the molar ratio of metal salt to template agent in step (3) is 0.5-5.0.

[0014] Preferably, the metal nitrate in step (2) is one or more of cerium nitrate, cobalt nitrate, ferric nitrate, copper nitrate, and nickel nitrate; and the precipitant is one or more of urea, ammonium carbonate, and hexamethylenetetramine.

[0015] Preferably, the molar ratio of manganese acetate to metal nitrate in step (2) is 2-5.

[0016] Preferably, the temperature of the hydrothermal reaction in step (3) is 250-400℃, the time of the hydrothermal reaction is 12-36h, and the heating rate of the hydrothermal reaction is 1-5℃ / min.

[0017] Preferably, the template agent in step (3) is nitrogen tetrafluoride or hexadecyltrimethylammonium bromide, and the molar ratio of the metal salt to the template agent is 1-4; the drying is freeze drying, supercritical drying or vacuum drying.

[0018] Application of the carbon sponge-supported nanoarray monolithic catalyst prepared by the above method in low-temperature denitrification.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) In this invention, nitrogen-doped carbon sponge with a three-dimensional interconnected network structure is used as a flexible carrier, which can provide a larger contact area, which is beneficial to the dispersion and chemical stability of the active components (composite metal oxides). In addition, its unique network structure is conducive to the diffusion and adsorption of reactant gases in the catalytic reaction. At the same time, the bed resistance is small during application and it has good processability, making it adaptable to different application environments. Compared with traditional rigid substrates, nitrogen-doped carbon sponge has unique advantages such as low cost, light weight, high porosity, and strong processability, and the pyridine-N, pyrrole-N, and quaternary ammonium-N functional groups on the surface can improve the denitrification efficiency of carbon materials.

[0021] (2) The present invention uses environmentally friendly transition metal elements, the synthesis method is green and efficient, the catalyst has excellent performance, and the waste catalyst is easy to handle, such as direct combustion or compression and landfill, which will hardly produce solid waste.

[0022] (3) The catalyst prepared in this invention has a surface rich in active surface oxygen and a large amount of Mn. 3+ and Mn 4+ And Lewis acid sites. Most importantly, it follows different reaction mechanisms in different temperature ranges, thus exhibiting excellent catalytic activity in the 100℃-400℃ range. Attached Figure Description

[0023] Figure 1 This is a microscopic morphology image of the catalyst obtained in Example 1. The electron microscope in the image is model SU8020, the accelerating voltage is 3.0kV, and the magnification is 150. Each small division on the scale bar at the bottom of the image represents 300 micrometers.

[0024] Figure 2 This is a microscopic morphology image of the catalyst obtained in Example 1. The electron microscope in the image is SU8020, the accelerating voltage is 3.0kV, and the magnification is 1000. Each small division on the scale bar below the image represents 50 micrometers.

[0025] Figure 3 This is a microscopic morphology image of the catalyst obtained in Example 1. The electron microscope in the image is SU8020, the accelerating voltage is 3.0kV, and the magnification is 20000. Each small division on the scale bar at the bottom of the image represents 2 micrometers.

[0026] Figure 4 Stability of the catalysts prepared in Examples 1-5.

[0027] Figure 5 The sulfur and water resistance properties of the catalysts prepared in Examples 1-5 at 200°C.

[0028] Figure 6 Pressure-strain curve of the catalyst in Example 2. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0030] Example 1

[0031] Step 1: The melamine sponge is heated to 600℃ in a nitrogen atmosphere at a heating rate of 2℃ / min for 3 hours, and then naturally cooled to room temperature to obtain nitrogen-doped carbon sponge.

[0032] Step 2: Prepare the active precursor solution. Dissolve 4 mmol manganese acetate and 1 mmol cerium nitrate (molar ratio 4:1) in 40 mL of deionized water to form a homogeneous precursor solution. Then add 3 mmol urea (the molar ratio of precipitant to metal ions is 0.6:1) to the precursor solution to prepare a mixed solution.

[0033] Step 3: Add 5 mmol of nitrogen tetrafluoride (molar ratio of template agent to metal ions is 1:1) to the mixed solution prepared in Step 2, and stir continuously until completely dissolved.

[0034] Step 4: Add a piece of nitrogen-doped carbon sponge prepared in Step 1 to the solution prepared in Step 3, then transfer it to a hydrothermal reactor and heat it to 300℃ at a heating rate of 2℃ / min for 12 hours. Allow it to cool naturally to room temperature and wash it with deionized water.

[0035] Step 5: Freeze-dry the catalyst prepared in Step 4 at -60℃ for 24 hours to obtain the carbon sponge-supported nanoarray monolithic catalyst.

[0036] Example 2

[0037] Step 1: The melamine sponge is heated to 700℃ in a nitrogen atmosphere at a heating rate of 5℃ / min for 3 hours, and then naturally cooled to room temperature to obtain nitrogen-doped carbon sponge.

[0038] Step 2: Prepare the active precursor solution. Dissolve 4 mmol manganese acetate and 2 mmol cerium nitrate (molar ratio 2:1) in 40 mL of deionized water to form a homogeneous precursor solution. Then add 3.6 mmol urea (the molar ratio of precipitant to metal ions is 0.6:1) to the precursor solution to prepare a mixed solution.

[0039] Step 3: Add 3 mmol of nitrogen tetrafluoride (molar ratio of template agent to metal ions is 1:2) to the mixed solution prepared in Step 2, and stir continuously until completely dissolved.

[0040] Step 4: Add a piece of nitrogen-doped carbon sponge prepared in Step 1 to the solution prepared in Step 3, then transfer it to a hydrothermal reactor and heat it to 250℃ at a heating rate of 3℃ / min for 12 hours. Allow it to cool naturally to room temperature and wash it with deionized water.

[0041] Step 5: Dry the catalyst prepared in step 4 under vacuum at 100°C for 12 hours to obtain the carbon sponge-supported nanoarray monolithic catalyst.

[0042] Example 3

[0043] Step 1: The melamine sponge is heated to 800℃ in a nitrogen atmosphere at a heating rate of 3℃ / min for 2 hours, and then naturally cooled to room temperature to obtain nitrogen-doped carbon sponge.

[0044] Step 2: Prepare the active precursor solution. Dissolve 5 mmol of manganese acetate and 1 mmol of ferric nitrate (molar ratio 5:1) in 40 mL of deionized water to form a homogeneous precursor solution. Then add 3.6 mmol of urea (molar ratio of precipitant to metal ions is 0.6:1) to the precursor solution to prepare a mixed solution. Step 3: Add 1.5 mmol of hexadecyltrimethylammonium bromide (molar ratio of template agent to metal ions is 1:4) to the mixed solution prepared in Step 2, and stir continuously until completely dissolved.

[0045] Step 4: Add a piece of nitrogen-doped carbon sponge prepared in Step 1 to the solution prepared in Step 3, then transfer it to a hydrothermal reactor and heat it to 400℃ at a heating rate of 5℃ / min for 24 hours. Allow it to cool naturally to room temperature and wash it with deionized water.

[0046] Step 5: Supercritically dry the catalyst prepared in Step 4 for 12 hours to obtain the carbon sponge-supported nanoarray monolithic catalyst.

[0047] Example 4

[0048] Step 1: The melamine sponge is heated to 600℃ in a nitrogen atmosphere at a heating rate of 5℃ / min for 3 hours, and then naturally cooled to room temperature to obtain nitrogen-doped carbon sponge.

[0049] Step 2: Prepare the active precursor solution. Dissolve 4 mmol manganese acetate, 1 mmol cerium nitrate and 1 mmol cobalt nitrate (molar ratio 4:1:1) in 40 mL of deionized water to form a homogeneous precursor solution. Then add 3.6 mmol urea (the molar ratio of precipitant to metal ions is 0.6:1) to the precursor solution to prepare a mixed solution.

[0050] Step 3: Add 2 mmol of nitrogen tetrafluoride (molar ratio of template agent to metal ions is 1:3) to the mixed solution prepared in Step 2, and stir continuously until completely dissolved.

[0051] Step 4: Add a piece of nitrogen-doped carbon sponge prepared in Step 1 to the solution prepared in Step 3, then transfer it to a hydrothermal reactor and heat it to 250℃ at a heating rate of 5℃ / min for 36 hours. Allow it to cool naturally to room temperature and wash it with deionized water.

[0052] Step 5: Freeze-dry the catalyst prepared in Step 4 at -60℃ for 24 hours to obtain the carbon sponge-supported nanoarray monolithic catalyst.

[0053] Example 5

[0054] Step 1: The melamine sponge is heated to 600℃ in a nitrogen atmosphere at a heating rate of 2℃ / min for 3 hours, and then naturally cooled to room temperature to obtain nitrogen-doped carbon sponge.

[0055] Step 2: Prepare the active precursor solution. Dissolve 4 mmol manganese acetate, 1 mmol cerium nitrate and 1 mmol nickel nitrate (molar ratio 4:1:1) in 40 mL of deionized water to form a homogeneous precursor solution. Then add 3.6 mmol urea (the molar ratio of precipitant to metal ions is 0.6:1) to the precursor solution to prepare a mixed solution.

[0056] Step 3: Add 2 mmol of cetyltrimethylammonium bromide (molar ratio of template agent to metal ions is 1:3) to the mixed solution prepared in Step 2, and stir continuously until completely dissolved.

[0057] Step 4: Add a piece of nitrogen-doped carbon sponge prepared in Step 1 to the solution prepared in Step 3, then transfer it to a hydrothermal reactor and heat it to 400℃ at a heating rate of 2℃ / min for 12 hours. Allow it to cool naturally to room temperature and wash it with deionized water.

[0058] Step 5: Dry the catalyst prepared in step 4 under vacuum at 100°C for 12 hours to obtain the carbon sponge-supported nanoarray monolithic catalyst.

[0059] The analytical and catalytic performance test results of the samples in each embodiment are as follows:

[0060] The product obtained in Example 1 of this invention was observed using a scanning electron microscope, and the results are as follows: Figure 1-3 As shown in the figure, the active components of the catalyst prepared in this invention are uniformly distributed on the nitrogen-doped carbon sponge substrate, and the surface exhibits a uniformly distributed nanoarray structure, indicating that the active components are well bonded to the substrate.

[0061] The test conditions for denitrification performance are as follows: gas flow rate 200 mL / min, NO concentration 500 ppm, NH3 concentration 500 ppm, O2 concentration 5%, N2 as balance gas, SO2 concentration 200 ppm (in use), H2O concentration 5% vol% (in use), and space velocity 12000 h⁻¹. -1 The denitrification efficiencies of the catalysts in each embodiment are shown in Table 1. It can be seen that the catalysts prepared in each embodiment exhibit high denitrification activity within a temperature range of 100℃-400℃, exceeding 80% at 100℃ and reaching over 95% at 400℃. This indicates that the catalysts prepared in this invention have a wide activity window, significantly higher than similar monolithic catalysts reported in the literature.

[0062] Table 1. Performance test results of catalysts prepared in each preparation example.

[0063]

[0064] The stability test results of the catalysts prepared in each example show that all five catalysts exhibit good stability at different test temperatures. Figure 4 SO2 and H2O in flue gas have a strong inhibitory effect on low-temperature SCR reactions. Therefore, the anti-sulfur and anti-water poisoning ability of low-temperature denitrification catalysts is an important indicator for evaluating catalyst performance. In the anti-water and anti-sulfur performance tests (reaction at 200℃) of each embodiment, when 5% vol of H2O and 200 ppm of SO2 were simultaneously introduced into the reaction system (… Figure 5 Although the denitrification efficiency decreased to some extent, the decrease was relatively small, especially in Examples 4 and 5 where it decreased by 7% and 11%, respectively. After stopping the introduction of H2O and SO2, the efficiency rebounded to some extent. This indicates that the catalyst prepared using the method of this invention still possesses high sulfur and water resistance in the presence of H2O and SO2.

[0065] During the mechanical property testing of the catalyst prepared in Example 2, it was found that the compression curve showed almost complete recovery after 60% strain. Figure 6 At 60% strain, the stress was 1.6 kPa, indicating that the catalyst possesses excellent flexibility. Furthermore, the compressive stress-strain curve of the 5th cycle showed no significant change compared to the 1st cycle, demonstrating the excellent elasticity of the catalyst prepared in this example.

[0066] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a carbon sponge-supported nanoarray monolithic catalyst, characterized in that, Includes the following steps: (1) Preparation of nitrogen-doped carbon sponge; (2) Preparation of precursor solution: Dissolve the metal salt in water and then add a precipitant to prepare a precursor solution; the metal salt is manganese acetate and metal nitrate, and the metal nitrate is rare earth metal nitrate and / or transition metal nitrate; (3) Add template agent to precursor solution and stir until completely dissolved. Add nitrogen-doped carbon sponge and then carry out hydrothermal reaction. The hydrothermal reaction temperature is 250-400 ℃ and the hydrothermal reaction time is 12-36 h. Cool, wash and dry to obtain carbon sponge supported nanoarray monolithic catalyst.

2. The preparation method according to claim 1, characterized in that, Preparation of nitrogen-doped carbon sponge in step (1): melamine sponge is carbonized at 500-800 °C in a protective atmosphere and then cooled to obtain nitrogen-doped carbon sponge.

3. The preparation method according to claim 2, characterized in that, The carbonization heating rate is 1-5 ℃ / min, the carbonization temperature is 700±100 ℃, and the carbonization time is 3±2h.

4. The preparation method according to claim 1, characterized in that, In step (2), the molar ratio of manganese acetate to metal nitrate is 1-10; the molar ratio of precipitant to metal ion is 0.6±0.3; and in step (3), the molar ratio of metal salt to template agent is 0.5-5.

0.

5. The preparation method according to claim 4, characterized in that, The metal nitrate in step (2) is one or more of cerium nitrate, cobalt nitrate, iron nitrate, copper nitrate, and nickel nitrate; the precipitant is one or more of urea, ammonium carbonate, and hexamethylenetetramine.

6. The preparation method according to claim 5, characterized in that, The molar ratio of manganese acetate to metal nitrate in step (2) is 2-5.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The heating rate of the hydrothermal reaction in step (3) is 1-5 °C / min.

8. The preparation method according to claim 7, characterized in that, The template agent in step (3) is hexadecyltrimethylammonium bromide, and the molar ratio of the metal salt to the template agent is 1-4; the drying is freeze drying, supercritical drying or vacuum drying.

9. A carbon sponge-supported nanoarray monolithic catalyst prepared by the method according to any one of claims 1 to 8.

10. The application of the catalyst according to claim 9 in low-temperature denitrification.

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