A strong-resistance high-activity ozone decomposition catalyst, a preparation method and application thereof

Abstract

The application belongs to the technical field of atmospheric pollution control, and particularly relates to a strong-resistance high-activity ozone decomposition catalyst and a preparation method and application thereof. The application provides a preparation method of a strong-resistance high-activity ozone decomposition catalyst. The catalyst prepared by the method has a multi-stage pore structure, a large specific surface area, rich and dispersed multi-activity sites, rich oxygen vacancies, excellent hydrophobicity, strong resistance to sulfur and water poisoning, high activity, and a long service life. The strong-resistance high-activity ozone decomposition catalyst has the ability to efficiently and stably decompose ozone under water-containing and sulfur-containing conditions. In addition to being used for indoor air ozone treatment, the catalyst can also be used for ozone treatment of industrial flue gas directly discharged from smelting and sintering, industrial furnaces and kilns.

Description

Technical Field

[0001] This invention belongs to the field of air pollution control technology, specifically relating to a highly resistant and active ozone decomposition catalyst, its preparation method, and its application. Background Technology

[0002] Tropospheric ozone is a greenhouse gas that determines the atmosphere's oxidation capacity. Long-term exposure to ozone is harmful to ecosystems and leads to human health risks such as dizziness, headaches, respiratory diseases, and decreased immune function.

[0003] Ozone removal generally employs methods such as thermal decomposition, liquid absorption, activated carbon adsorption, and catalytic decomposition. Among these, catalytic decomposition of ozone (deO3) is the most widely used due to its high efficiency, mild reaction conditions, and economic stability. Noble metal catalysts (silver, gold, platinum, palladium, etc.) exhibit high activity for ozone decomposition, but their high cost limits their industrial application. Transition metal oxides (manganese, cobalt, nickel, copper, etc.) are inexpensive and readily available, possessing variable valence states, abundant surface oxygen vacancies, different morphologies, and tunable phase states, resulting in excellent deO3 efficiency. Studies have shown that oxygen vacancies are the main active sites for catalytic ozone decomposition, and increasing the oxygen vacancy content of the catalyst is key to improving ozone decomposition activity. Furthermore, indoor air often contains a certain amount of moisture, and H2O in industrial flue gas, as a combustion product of hydrocarbon fuels, is also an unavoidable component (5-20% by volume). H2O molecules compete with ozone for oxygen vacancies, occupying active sites. Excessive H2O can form a dense water film on the catalyst surface, hindering contact between ozone and active sites, thus leading to catalyst deactivation. Industrial flue gas, in addition to containing a large amount of water vapor, also contains a high concentration of SO2. Even after desulfurization, the SO2 concentration still ranges from 30 to 150 mg / m³. 3 The concentration of ozone in indoor air is much higher than that of SO2 in the atmosphere. Commercially available manganese-based catalysts for indoor ozone decomposition are easily poisoned and deactivated under conditions of high water and sulfur content, highlighting the urgent need to develop more efficient ozone decomposition catalysts with stronger resistance to poisoning. Summary of the Invention

[0004] To overcome the shortcomings of existing catalysts, the primary objective of this invention is to provide a method for preparing a highly resistant and active ozone decomposition catalyst.

[0005] Another objective of this invention is to provide a highly resistant and active ozone decomposition catalyst prepared by the above method. The catalyst obtained by this preparation method has a hierarchical porous structure, a large specific surface area, abundant and dispersed multiple active sites, abundant oxygen vacancies, and excellent hydrophobicity.

[0006] Another objective of this invention is to provide the application of the above-mentioned highly resistant and active ozone decomposition catalyst, which has the ability to efficiently and stably decompose ozone under conditions containing water and sulfur. In addition to being used for indoor air ozone treatment, it can also be used for ozone treatment of direct emissions from industrial flue gas such as smelting and sintering, and industrial furnaces and kilns.

[0007] This invention is achieved through the following technical solution:

[0008] A method for preparing a highly resistant and active ozone decomposition catalyst includes the following steps:

[0009] S1. Biochar is activated by high-temperature steam and then mixed with urea for secondary pyrolysis to prepare nitrogen-rich hierarchical porous biochar (HAC).

[0010] S2. Nitrogen-rich hierarchical porous biochar was added to a solution of manganese salt, cerium salt, and nickel salt. After thorough stirring, it was dried, calcined, and then ground to obtain Mn-Ce-Ni / HAC with a particle size of 40-60 mesh.

[0011] S3. Gaseous carbon source is passed through Mn-Ce-Ni / HAC at a specific temperature and reacted under the induction of magnetic field to obtain Mn-Ce-Ni@CNTs / HAC with regular carbon nanotube growth.

[0012] S4. Mn-Ce-Ni@CNTs / HAC was modified using a rapid Joule heating method with gradient heating to obtain a highly resistant and active ozone decomposition catalyst.

[0013] Further, the biochar mentioned in step S1 is one or more of straw charcoal, wood charcoal, rice husk charcoal, sludge charcoal, and coconut shell charcoal;

[0014] The biochar activation process is controlled at a temperature of 600–900℃, a water vapor volume of 5–20%, and an activation time of 0.5–20 h.

[0015] Further, in step S1, the mass ratio of biochar to urea is 1:0.1-3, the temperature of the secondary pyrolysis is 500-800℃, the time of the secondary pyrolysis is 0.5-5h, the heating rate is 1-10℃ / min, and the atmosphere is nitrogen or argon.

[0016] Furthermore, the nitrogen-rich hierarchical porous biochar prepared in step S1 has a specific surface area of ​​500–800 m². 2 / g, pore volume is 0.1~1cm³ 3 / g, of which micropore volume accounts for 30-45%, mesopore volume accounts for 40-55%, macropore volume accounts for 10-25%, and has a multi-level pore structure dominated by mesopores, with a nitrogen content of 2-10wt%.

[0017] Further, the manganese salt mentioned in step S2 is one or more of manganese nitrate and manganese acetate, the cerium salt is one or more of cerium nitrate and cerium acetate, and the nickel salt is one or more of nickel nitrate and nickel acetate. The loading of nickel, manganese and cerium in the Mn-Ce-Ni / HAC is 5 to 15 wt%.

[0018] Furthermore, the calcination temperature in step S2 is 300–800°C, the calcination atmosphere is nitrogen or argon, and the calcination time is 1–6 hours.

[0019] Furthermore, the gaseous carbon source mentioned in step S3 is tar produced by biomass gasification, with a tar concentration of 1–30 g / m³. 3 ;

[0020] The reaction atmosphere is nitrogen or argon, the reaction temperature is 500–900℃, the reaction time is 0.2–5h, and the magnetic field strength is 0.01–5T.

[0021] Further, the gradient heating temperatures in step S4 are 200-300℃, 400-500℃, and 600-1200℃, respectively, with a heating rate of 1000-100000℃ / s. After the rapid Joule heat treatment reaches the set temperature of each gradient, it is held for 50-500ms, and then the temperature is increased to the next gradient temperature. After reaching the final set temperature, it is cooled, and then the heating cycle is repeated 1-20 times.

[0022] Furthermore, the atmosphere for rapid Joule heating described in step S4 is argon or vacuum.

[0023] A method for decomposing ozone using a highly resistant and active ozone decomposition catalyst includes the following steps: placing the catalyst in an ozone-containing environment at a temperature of 20–120°C, an ozone concentration of 25–200 ppm, a moisture content of 0–15 vol%, an SO2 concentration of 0–150 ppm, and a space velocity ratio of 30,000–600,000 mL / (g·h).

[0024] The present invention has the following advantages over the prior art:

[0025] 1. This invention provides a method for preparing a highly resistant and active ozone decomposition catalyst. The catalyst prepared by this method has a hierarchical porous structure, a large specific surface area, abundant and dispersed active sites, abundant oxygen vacancies, and excellent hydrophobicity. It has the advantages of strong resistance to sulfur and water poisoning, high activity, and long lifespan. The highly resistant and active ozone decomposition catalyst of this invention has the ability to efficiently and stably decompose ozone under water and sulfur-containing conditions. In addition to being used for indoor air ozone treatment, it can also be used for ozone treatment of direct emissions from industrial flue gas such as smelting and sintering, and industrial furnaces and kilns.

[0026] 2. The biochar selected in this invention has a large specific surface area. After activation with steam, the specific surface area is further increased, creating a multi-level pore structure with micropores, mesopores, and macropores evenly distributed, mainly mesopores. Furthermore, the secondary pyrolysis of urea can achieve nitrogen doping, increase the content of nitrogen-containing functional groups on the surface of biochar, enhance its anchoring ability for metal ions, facilitate the uniform loading of active metals such as nickel, manganese, and cerium, avoid agglomeration, and improve the activity of the supported catalyst.

[0027] 3. The manganese, cerium and nickel multi-metal interaction of the present invention promotes inter-metal electron transfer, generates more oxygen vacancies as ozone decomposition active sites, and improves the ozone decomposition activity of the catalyst.

[0028] 4. The gaseous carbon source of this invention undergoes a reaction with Mn-Ce-Ni / HAC, resulting in the in-situ growth of carbon nanotubes on nickel metal through the principle of "dissociation-diffusion-deposition." Active nickel metal is encapsulated within the carbon nanotubes. Under the induction of a magnetic field, the growth direction and density of the carbon nanotubes are controlled, and through magnetic field orientation, a three-dimensional conductive network is constructed, accelerating electron transfer. Due to the physical barrier of the carbon nanotubes, impurities such as SO2 and H2O in ozone-containing gaseous environments are isolated outside the carbon nanotubes, preventing their toxic effects on the active nickel metal. Meanwhile, manganese and cerium on the surface of the carbon nanotubes and the hierarchical porous activated carbon act as sacrificial sites, preferentially reacting with SO2. Simultaneously, the mesoporous structure of the hierarchical porous biochar and carbon nanotubes inhibits capillary condensation of water molecules, reducing water accumulation, thus exhibiting excellent sulfur and water resistance properties.

[0029] 5. Rapid Joule heating post-treatment of catalysts can improve oxygen vacancy content and hydrophobicity. Short-term high-temperature induced defects and surface oxygen desorption promote oxygen vacancy generation, while rapid cooling can "freeze" the metastable oxygen vacancy structure, avoiding oxygen vacancy recombination during traditional slow cooling. This invention employs gradient heat treatment, avoiding structural collapse caused by single high-temperature treatment. High-temperature instantaneous decomposition of oxygen- and hydrogen-containing polar groups (such as –OH, –COOH) reduces surface hydrophilicity; defect edges are reconstructed at high temperature to form sp... 2 Hybridized carbon domains reduce polar adsorption sites caused by dangling bonds; high-temperature volatilization and reconstruction of the carbon matrix produce a micro-mesoporous composite structure, increasing surface roughness and enhancing the hydrophobic effect of the Cassie-Baxter state (air trapping); directional Joule heating makes the graphene sheets stack more densely, reducing capillary water absorption channels. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments. However, the examples below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0031] Unless otherwise specified, all reagents used in the examples are commercially available.

[0032] Example 1

[0033] The preparation of the Mn-Ce-Ni@CNTs / HAC#1 catalyst includes the following steps:

[0034] S1. 100g of pine charcoal was activated at 800℃ for 1h with 15% water vapor and the remainder nitrogen. Then, urea and biochar were mixed in a mass ratio of 1 and pyrolyzed for a second time at 550℃ for 1h with a heating rate of 5℃ / min and a nitrogen atmosphere to obtain nitrogen-rich hierarchical porous biochar (HAC).

[0035] S2. Add 14.86g of nickel nitrate hexahydrate, 6.51g of manganese nitrate, and 6.20g of cerium nitrate hexahydrate to 100mL of ethanol solution and stir thoroughly. Then add 13g of the hierarchical porous biochar obtained in step S1 and stir thoroughly at 80℃ until the ethanol is fully evaporated. After drying the sample at 105℃ for 12h, calcine it at 700℃ in a nitrogen atmosphere for 4h and grind it to a particle size of 40-60 mesh. The mass fractions of nickel, manganese, and cerium in the obtained Mn-Ce-Ni / HAC are 15%, 10%, and 10%, respectively.

[0036] S3. The Mn-Ce-Ni / HAC obtained in S2 is stabilized at 800℃ under a nitrogen atmosphere for 5 min, and the biomass gasification tar (concentration of 10 g / m³) is then used. 3 After dehydration with silica gel, the sample was fully reacted with Mn-Ce-Ni / HAC for 0.5 h. The reaction apparatus was placed in a magnetic field with a strength of 0.2 T. After the reaction, the gas inlet was turned off and the sample was cooled and collected.

[0037] S4. Using a rapid Joule heating method, the Mn-Ce-Ni@CNTs / HAC obtained in step S3 was rapidly heated to 200, 400, and 600 °C respectively under an argon atmosphere at a heating rate of 10000 °C / s. After holding the temperature for 100 ms, the temperature was cooled. This heating was repeated 5 times. The gas inlet was then turned off and the reaction sample Mn-Ce-Ni@CNTs / HAC#1 catalyst was collected after cooling.

[0038] Example 2

[0039] The preparation of the Mn-Ce-Ni@CNTs / HAC#2 catalyst includes the following steps:

[0040] S1. 100g of pine charcoal was activated at 800℃ for 1h with 15% water vapor and the remainder nitrogen. Then, urea and biochar were mixed in a mass ratio of 1 and pyrolyzed for a second time at 550℃ for 1h with a heating rate of 5℃ / min and a nitrogen atmosphere to obtain nitrogen-rich hierarchical porous biochar (HAC).

[0041] S2. Add 9.90g of nickel nitrate hexahydrate, 6.51g of manganese nitrate, and 6.20g of cerium nitrate hexahydrate to 100mL of ethanol solution and stir thoroughly. Then add 14g of the hierarchical porous biochar obtained in step one and stir thoroughly at 80℃ until the ethanol is fully evaporated. After drying the obtained sample at 105℃ for 12h, calcine it at 700℃ in a nitrogen atmosphere for 4h and grind it to a particle size of 40-60 mesh. The mass fractions of nickel, manganese, and cerium in the obtained Mn-Ce-Ni / HAC are 10%, 10%, and 10%, respectively.

[0042] S3. Stabilize the Mn-Ce-Ni / HAC obtained in step S2 at 800℃ under a nitrogen atmosphere for 5 min, and then gasify the biomass tar (concentration of 10 g / m³). 3 After dehydration with silica gel, the sample was fully reacted with Mn-Ce-Ni / HAC for 0.5 h. The reaction apparatus was placed in a magnetic field with a strength of 0.2 T. After the reaction, the gas inlet was turned off and the sample was cooled and collected.

[0043] S4. Using a rapid Joule heating method, the Mn-Ce-Ni@CNTs / HAC obtained in step S3 was rapidly heated to 200, 400, and 600 °C respectively under an argon atmosphere at a heating rate of 10000 °C / s. After holding the temperature for 100 ms, the temperature was cooled. This heating process was repeated 5 times. The gas inlet was then turned off and the reaction sample Mn-Ce-Ni@CNTs / HAC#2 catalyst was collected after cooling.

[0044] Example 3

[0045] Mn-Ce-Ni@CNTs / HAC#3 catalyst

[0046] The difference from Example 1 is the nickel mass fraction, which is 5%. The rest of the technical solutions are the same as those in Example 1.

[0047] Example 4

[0048] Mn-Ce-Ni@CNTs / HAC#4 catalyst

[0049] The difference from Example 1 is the nickel mass fraction, which is 20%. The rest of the technical solutions are the same as those in Example 1.

[0050] Example 5

[0051] Mn-Ce-Ni@CNTs / HAC#5 catalyst

[0052] The difference from Example 1 lies in the rapid Joule heat treatment temperature, which is 300, 500, and 1000°C. The rest of the technical solutions are the same as those in Example 1.

[0053] Comparative Example 1

[0054] Mn-Ce-Ni@CNTs / HAC#5 catalyst

[0055] The difference between this comparative example and Example 1 is that the Mn-Ce-Ni@CNTs / HAC obtained in step S3 does not undergo the gradient heating rapid Joule heat treatment in step S4. The rest of the technical solutions are the same as those in the example.

[0056] Comparative Example 2

[0057] The difference between this comparative example and Example 1 is that the Mn-Ce-Ni / HAC obtained in step S2 is not treated by magnetic field-induced chemical vapor deposition in step S3, and therefore cannot generate regular carbon nanotubes. The rest of the technical solutions are the same as those in the example.

[0058] Comparative Example 3

[0059] The difference between this comparative example and Example 1 is that the pine charcoal in step S1 is not activated by steam and then subjected to a secondary pyrolysis treatment with urea, so it cannot form an ideal nitrogen-rich surface multi-level porous structure. The rest of the technical solutions are the same as those in the example.

[0060] Comparative Example 4

[0061] The difference between this comparative example and Example 1 is that manganese nitrate and cerium nitrate hexahydrate are not added in step S2, and only active metal nickel is retained in the resulting catalyst. The rest of the technical solutions are the same as those in the example.

[0062] The performance test results of the obtained catalyst are shown in Table 1.

[0063] Performance testing

[0064] Table 1 shows the catalysts and their performance obtained in each example and comparative example. The reaction conditions were: ozone concentration 50 ppm, SO2 concentration 50 ppm, moisture content 5 vol%, oxygen concentration 3.5 vol%, nitrogen as the balance gas, gas flow rate 300 mL / min, space velocity ratio 300000 mL / (g·h), and temperature 60℃.

[0065] Table 1

[0066]

[0067]

[0068] As shown in Table 1, the catalysts prepared in Examples 1 to 5 exhibited excellent ozone decomposition activity and stability under sulfur-containing and water-containing conditions by adjusting the conditions of biochar steam activation and nitrogen doping, active metal loading, magnetic field-induced chemical vapor deposition treatment, and gradient heating Joule heat treatment. Among them, the Mn-Ce-Ni@CNTs / HAC#1 catalyst in Example 1 had the best performance.

[0069] A comparison of the performance test results of Example 1 and Comparative Examples 1-4 reveals that steam activation and nitrogen doping of biochar, active metal loading, magnetic field-induced chemical vapor deposition (CVD) treatment, and gradient heating rapid Joule heat treatment all significantly affect the catalyst's activity and resistance to sulfur and water. Steam activation forms an ideal hierarchical porous structure in biochar, reducing the proportion of micropores and increasing the proportion of mesopores and macropores. Urea-based mixed pyrolysis enables nitrogen doping, increasing the content of nitrogen-containing functional groups on the biochar surface, enhancing its anchoring ability for metal ions, and contributing to the uniform loading of active metals, the free growth of carbon nanotubes, and the diffusion and decomposition of ozone molecules. Nickel serves as the main active site for ozone decomposition. Manganese and cerium, in addition to decomposing ozone, more importantly act as sacrificial sites on the outside of carbon nanotubes, preferentially reacting with SO2 to prevent SO2 from reacting with nickel inside the carbon nanotubes, thereby improving resistance to poisoning. In the treatment of gaseous carbon-source biomass gasification tar, under the induction of a magnetic field, relatively regular carbon nanotubes can be grown on the catalyst surface. Nickel is encapsulated within the carbon nanotubes. Due to the physical barrier effect of the carbon nanotubes, SO2 and water cannot enter the tubes. At the same time, the hydrophobicity of the carbon nanotubes and the mesoporous structure also inhibit the capillary condensation of water, thereby improving the sulfur and water resistance. Gradient heating rapid Joule heat treatment promotes the generation of oxygen vacancies through short-term high-temperature induction of defects and surface oxygen desorption. Rapid cooling can "freeze" the metastable oxygen vacancy structure, avoiding oxygen vacancy recombination in traditional slow cooling. Gradient heating can avoid structural collapse caused by single high-temperature treatment. High-temperature instantaneous decomposition of oxygen-containing / hydrogen-containing polar groups reduces surface hydrophilicity, and the defect edges are reconstructed at high temperature to form sp. 2 Hybridized carbon domains reduce polar adsorption sites caused by dangling bonds. At high temperatures, the volatilization and reconstruction of the carbon matrix produce a micro-mesoporous composite structure, increasing surface roughness and enhancing the hydrophobic effect of the Cassie-Baxter state (air retention). Therefore, rapid Joule heat treatment can improve the oxygen vacancy content and hydrophobicity of the catalyst, thereby enhancing its activity and anti-poisoning performance.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a highly resistant and active ozone decomposition catalyst, characterized in that, Includes the following steps: S1. Biochar was activated by high-temperature steam and then mixed with urea for secondary pyrolysis to prepare nitrogen-rich hierarchical porous biochar HAC. S2. Nitrogen-rich hierarchical porous biochar was added to a solution of manganese salt, cerium salt, and nickel salt. After thorough stirring, it was dried, calcined, and then ground to obtain Mn-Ce-Ni / HAC with a particle size of 40-60 mesh. The loadings of nickel, manganese, and cerium in the Mn-Ce-Ni / HAC are all 5~15 wt%; S3. Gaseous carbon source is passed through Mn-Ce-Ni / HAC at a specific temperature and reacted under the induction of magnetic field to obtain Mn-Ce-Ni@CNTs / HAC with regular carbon nanotube growth. The reaction atmosphere is nitrogen or argon, the reaction temperature is 500~900°C, the reaction time is 0.2~5h, and the magnetic field strength is 0.01~5T; S4. Mn-Ce-Ni@CNTs / HAC was modified using a rapid Joule heating method with gradient heating to obtain a highly resistant and active ozone decomposition catalyst. The gradient heating temperatures are 200~300℃, 400~500℃, and 600~1200℃, with a heating rate of 1000~100000℃ / s. After the rapid Joule heat treatment reaches the set temperature of each gradient, it is held for 50~500ms, and then the temperature is increased to the next gradient temperature. After reaching the final set temperature, it is cooled, and then the heating cycle is repeated 1~20 times.

2. The method for preparing a highly resistant and active ozone decomposition catalyst according to claim 1, characterized in that, The biochar mentioned in step S1 is one or more of the following: straw charcoal, wood charcoal, rice husk charcoal, sludge charcoal, and coconut shell charcoal. The biochar activation process is controlled at a temperature of 600-900℃, a water vapor volume fraction of 5-20%, and an activation time of 0.5-20h.

3. The method for preparing a highly resistant and active ozone decomposition catalyst according to claim 1, characterized in that, In step S1, the mass ratio of biochar to urea is 1:0.1~3, the temperature of the secondary pyrolysis is 500~800℃, the time of the secondary pyrolysis is 0.5~5h, the heating rate is 1~10℃ / min, and the atmosphere is nitrogen or argon.

4. The method for preparing a highly resistant and active ozone decomposition catalyst according to claim 1, characterized in that, The manganese salt mentioned in step S2 is one or more of manganese nitrate and manganese acetate, the cerium salt is one or more of cerium nitrate and cerium acetate, and the nickel salt is one or more of nickel nitrate and nickel acetate.

5. The method for preparing a highly resistant and active ozone decomposition catalyst according to claim 1, characterized in that, The calcination temperature in step S2 is 300~800℃, the calcination atmosphere is nitrogen or argon, and the calcination time is 1~6h.

6. The method for preparing a highly resistant and active ozone decomposition catalyst according to claim 1, characterized in that, The gaseous carbon source mentioned in step S3 is tar produced by biomass gasification, with a tar concentration of 1~30 g / m³. 3 .

7. The method for preparing a highly resistant and active ozone decomposition catalyst according to claim 1, characterized in that, The atmosphere for rapid Joule heating in step S4 is argon or vacuum.

8. A highly resistant and active ozone decomposition catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the highly resistant and active ozone decomposition catalyst as described in claim 8 in ozone control, characterized in that, The specific application involves placing the catalyst in an ozone-containing environment at a temperature of 20-120°C, an ozone concentration of 25-200 ppm, a moisture content of 0-15 vol%, an SO2 concentration of 0-150 ppm, and a space velocity ratio of 30,000-600,000 mL / g. . h -1 The content of moisture and SO2 is not zero.

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