High-activity SCR (Selective Catalytic Reduction) catalyst applied to low-temperature environment and preparation method thereof
By using a composite treatment of fly ash support and metal salt, a high-active SCR catalyst was prepared, which solved the problem of poor denitrification effect of biomass gas boilers in low temperature environments, and achieved the effect of efficient denitrification, anti-alkali metal poisoning and long service life.
Patent Information
- Application Number
- CN202510383951.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-28
- Publication Date
- 2025-06-27
AI Technical Summary
In the low-temperature environment, biomass gas boilers have a limited denitrification effect due to the wide distribution and large emission of alkali metals, and are susceptible to alkali metal poisoning, which affects their service life.
Fly ash is used as a carrier, and through hydrothermal activation and acidification treatment, combined with cupric ammonia complex, sodium hydroxide and template agent to form a carrier with high load capacity and temperature adaptability. Then, the vanadium salt, tungsten salt and cerium salt were dispersed in the oxalic acid solution, and the metal ions were uniformly supported on the support by ion exchange method and plasma modification, thereby preparing a highly active SCR catalyst.
It significantly improves the denitrification efficiency of SCR catalysts in low temperature environments, extends its service life, and enhances its resistance to alkali metal poisoning and sulfur resistance. The denitrification rate can reach 71.1% at 150-200℃, reach 89.3% at 300-350℃, and the compressive strength is no less than 2.13MPa.
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Abstract
Description
Technical Field
[0001] The present application relates to the technical field of biomass, and in particular to a highly active SCR catalyst applied to low-temperature environments and a preparation method thereof. Background Art
[0002] Biomass refers to all organic substances produced through photosynthesis, including plants, animals, microorganisms, and their derivatives. It is a renewable energy source because biomass can be continuously regenerated through natural processes, in sharp contrast to the limited reserves of fossil fuels. The sources of biomass are extensive, including but not limited to: agricultural waste, forestry residues, municipal solid waste, industrial waste, energy crops, and animal manure, etc. The development and utilization of biomass energy are of great significance for reducing greenhouse gas emissions, enhancing energy security, promoting rural development, and resource utilization of waste.
[0003] Among them, burning biomass can convert organic waste into heat energy or electrical energy, realizing the recycling of energy, reducing greenhouse gas emissions. The carbon dioxide generated by biomass combustion can be offset by the carbon dioxide absorbed during the growth process of biomass. It can also reduce the volume of organic waste, reduce landfill requirements, and reduce the emissions of greenhouse gases such as methane.
[0004] During this combustion process, a certain amount of nitrogen oxides (NO x ) will be generated. These pollutants will have certain negative impacts on the environment and human health. Therefore, technicians use selective catalytic reduction (SCR) technology to reduce the content of NO in the system x and add an SCR catalyst to promote the denitrification rate of the system. However, due to the characteristics of biomass gas boilers, such as low flue gas temperature, wide distribution and large emissions of alkali metals, the combustion of alkali metals will become fly ash and cover the surface of the SCR catalyst, preventing the reactants from contacting the SCR catalyst. Moreover, the alkali metals inside the reactants in contact with the SCR catalyst will also occupy the active sites of the catalyst. That is to say, the existing SCR catalyst (vanadium tungsten titanium catalyst) has limited catalytic effect on denitrification. Therefore, it is very necessary to provide a highly active SCR catalyst that can be flexibly applied to low-temperature environments. Summary of the Invention
[0005] To solve the above technical problems, the present application provides a highly active SCR catalyst applied to low-temperature environments and a preparation method thereof.
[0006] In the first aspect, the present application provides a preparation method of a highly active SCR catalyst applied to low-temperature environments, including the following steps: S1. Preparation of support: Hydrothermally activate fly ash under alkaline conditions, mix it with silica sol, copper ammonia complex, sodium hydroxide and template agent, raise the temperature for crystallization, cool, filter, wash until neutral, and dry to obtain a crude support. Then, after acidification, calcination and shaping, the support is obtained. S2. Preparation of precursor solution: Disperse metal salts in oxalic acid solution to obtain a precursor solution with a metal salt concentration of 0.1 - 0.2 mol / L. The metal salts include vanadium salt, tungsten salt and cerium salt with a molar ratio of 2:4:(0.5 - 0.7). S3. Preparation of SCR catalyst: Mix the support obtained in step S1 and the precursor solution obtained in step S2, impregnate, filter, wash, dry, and perform plasma modification under H2 atmosphere or N2 atmosphere to obtain the SCR catalyst.
[0007] Specifically, the operation of step S3 is as follows: Mix the support obtained in step S1 and the precursor solution obtained in step S2, impregnate, dry at 80°C for 1 h first, and then dry at 110°C for 12 h. Place the dried material in H2 atmosphere or N2 atmosphere, and perform plasma modification under the conditions of a treatment power of 120 - 280 W and a treatment duration of 10 - 120 min to obtain the SCR catalyst.
[0008] By adopting the above technical solutions, the present application first uses fly ash for in-situ crystallization conversion reaction, blends it with copper ammonia complex, sodium hydroxide and template agent, and then obtains a support with good loading capacity and temperature adaptability through acidification treatment. Acidification treatment can increase the number of acid sites on the support surface, help capture and consume alkali metal ions, reduce the possibility and coverage area of alkali metal covering the surface of the SCR catalyst, so as to keep the active sites of the SCR catalyst unblocked. The present application also adopts a fine shaping process, including steps such as wet mixing, stirring, kneading, aging, extrusion molding, cutting, and segmented drying, to make the support have higher mechanical strength and better pore structure, further improving the stability and service life of the SCR catalyst.
[0009] Next, the present application disperses vanadium salt, tungsten salt and cerium salt in oxalic acid solution to obtain a precursor solution with a certain metal salt concentration, ensuring the uniform distribution and efficient loading of active components on the support surface, enhancing the overall activity of the SCR catalyst. The addition of cerium element can broaden the active temperature window of the SCR catalyst and effectively reduce the adsorption of SO2, thus significantly improving the resistance of the SCR catalyst to SO2, enhancing the redox performance of the SCR catalyst, and further improving the catalytic activity. In the present application, ammonium metavanadate, ammonium metatungstate and cerium nitrate hexahydrate are respectively used as vanadium salt, tungsten salt and cerium salt. Those skilled in the art can make conventional adjustments according to actual situations, and the protection scope of the present application cannot be limited thereby.
[0010] Finally, the present application uses the ion exchange method and plasma modification to uniformly load metal ions in the precursor solution onto the carrier. Compared with the calcination loading method, the plasma treatment of the present application has stronger dispersion-promoting properties, enabling the metal elements to be loaded onto the carrier more stably and uniformly. Finally, an SCR catalyst with multiple active substances is obtained.
[0011] In summary, the preparation method of the present application not only improves the denitrification efficiency of the SCR catalyst in a low-temperature environment but also extends the service life of the SCR catalyst, enhancing its resistance to alkali metal poisoning and sulfur resistance. Specifically, after alkali poisoning treatment, the denitrification rate of the SCR catalyst of the present application can reach up to 71.1% in the denitrification environment of 150 - 200 °C; in the denitrification environment of 300 - 350 °C, the denitrification rate can reach up to 89.3%.
[0012] Preferably, in the step S2, the concentration of the metal salt in the precursor solution is 0.065 mol / L.
[0013] By adopting the above technical solution, the present application can ensure the uniform loading of the active components on the carrier by controlling the concentration of the metal salt in the precursor solution, thereby improving the denitrification rate of the SCR catalyst. If the concentration of the metal salt is too low, it will lead to insufficient loading of the active components, resulting in a reduction in the number of active sites of the SCR catalyst and affecting the denitrification efficiency, and it cannot effectively reduce the emission of NO x . On the other hand, if the concentration of the metal salt is too high, it will cause the active components to aggregate excessively on the carrier, forming an agglomeration phenomenon, which will also affect the activity and stability of the SCR catalyst and may even block the pores of the SCR catalyst, reducing the service life of the SCR catalyst. Therefore, by controlling the concentration of the metal salt in the precursor solution at 0.065 mol / L, the present application can balance the uniform loading of the active components and the high-efficiency and stable performance of the catalyst.
[0014] Preferably, the molar ratio of the vanadium salt, tungsten salt, and cerium salt is 2:4:0.65.
[0015] By adopting the above technical solution, the present application controls the molar ratio of the vanadium salt, tungsten salt, and cerium salt to 2:4:0.65, enabling a better synergistic effect to be formed among tungsten, vanadium, and titanium, further improving the denitrification efficiency of the catalyst and enhancing the stability of the catalyst in a low-temperature environment, enabling it to maintain a more efficient denitrification ability.
[0016] Preferably, in the step S2, the metal salt further includes an iron salt, and the molar ratio of the vanadium salt to the iron salt is 2:(1 - 1.5).
[0017] By adopting the above technical solution, iron salt is further added to the precursor liquid in the present application, thereby introducing new active components into the carrier. There is a strong synergistic effect between iron and vanadium, with charge transfer and strong charge interaction. At the same time, the addition of iron increases the specific surface area of the SCR catalyst, enabling it to maintain a relatively high acid amount even after contacting alkali metals. Therefore, by adding iron and compounding it with vanadium and other active components in the present application, the good synergistic effect between them is fully exerted, thereby significantly improving the catalytic activity of the SCR catalyst and broadening the temperature window. Iron nitrate nonahydrate is taken as an example to illustrate the iron salt in the present application. Those skilled in the art can make conventional adjustments according to the actual situation, and the protection scope of the present application cannot be limited thereby.
[0018] Preferably, the molar ratio of the vanadium salt to the iron salt is 2:1.2.
[0019] By adopting the above technical solution, the present application strictly controls the molar ratio of the vanadium salt to the iron salt to optimize the performance of the SCR catalyst. When the molar proportion of the iron salt is too low, there are insufficient active sites on the SCR catalyst, resulting in a reduction in denitrification efficiency, especially being more obvious in a low-temperature and high-alkali metal environment; while when the molar proportion of the iron salt is too high, excessive iron ions will cause agglomeration on the surface of the SCR catalyst, affecting the dispersibility and specific surface area of the SCR catalyst, and further reducing the overall activity and stability of the SCR catalyst. The present application strictly controls the molar ratio of the two to 2:1.2, which can balance the activity and stability of the SCR catalyst to the greatest extent and improve its denitrification efficiency in a low-temperature environment.
[0020] Preferably, in the step S1, the specific operation of shaping is as follows: The solid obtained after roasting is ground until its particle size reaches 200 - 300 mesh to obtain the precursor carrier powder. Subsequently, a reinforcing agent, a binder, and a pore-forming agent are added for dry mixing, and then water and a lubricant are added for wet mixing, stirring, kneading, aging, extrusion molding, cutting, and segmented drying to obtain the carrier. The weight ratio of the precursor carrier powder, the reinforcing agent, the binder, the pore-forming agent, water, and the lubricant is 100:10:(5 - 10):(4 - 6):33:4.
[0021] By adopting the above technical solution, the present application first grinds the SCR catalyst to a certain particle size, and then adds a certain amount of a reinforcing agent, a binder, a pore-forming agent, water, and a lubricant. After dry mixing, wet mixing, stirring, kneading, and aging to form the SCR catalyst embryo, it is extruded into shape by an extruder, cut into an appropriate length, and finally the formed SCR catalyst can be obtained through drying and calcination. In addition, the forming shape of the extruded SCR catalyst can be adjusted according to the mold. The process is simple, efficient, with good forming effect, and at the same time, the SCR catalyst also has good mechanical properties. After testing, its compressive strength is not less than 2.13 MPa.
[0022] Preferably, the weight ratio of the front carrier powder, reinforcing agent, binder, pore-forming agent, water and lubricant is 100:10:8:5:33:4.
[0023] Optionally, the reinforcing agent is glass fiber, the binder is any one of polyacrylamide, guar gum, carboxymethyl cellulose and sesbania powder, the pore-forming agent is any one of starch, polyethylene glycol, activated carbon and ammonium carbonate, and the lubricant is glycerol.
[0024] Preferably, the reinforcing agent is glass fiber, the binder is guar gum, the pore-forming agent is polyethylene glycol, and the lubricant is glycerol.
[0025] By adopting the above technical solution, the present application strictly controls the weight ratio of the front carrier powder, reinforcing agent, binder, pore-forming agent, water and lubricant. At this time, the surface of the SCR catalyst embryo is smooth, and the extruded SCR catalyst does not crack, with good forming effect, having both good mechanical strength and catalytic activity, and at the same time having a large specific surface area and active site exposure. Experimental data shows that at this time, the compressive strength of the SCR catalyst can be increased by 0.32 - 0.35 MPa.
[0026] Preferably, in step S3, after being modified by N2 atmosphere plasma, an SCR catalyst is obtained.
[0027] By adopting the above technical solution, the present application selects N2 atmosphere plasma modification, which can exert better dispersion-promoting ability in the system of the present application compared with H2 atmosphere plasma modification. The active components on the finally obtained SCR catalyst are more evenly loaded, the distribution density is most suitable, and thus it has better catalytic ability and catalytic stability.
[0028] In the second aspect, the present application provides a highly active SCR catalyst for low-temperature environments prepared by the above preparation method.
[0029] By adopting the above technical solution, the highly active SCR catalyst for low-temperature environments of the present application has good denitrification efficiency in low-temperature environments, excellent alkali metal poisoning resistance and sulfur resistance, and at the same time has good mechanical stability and a long service life, with high practical utilization value. Specifically, the SCR catalyst of the present application can still reach a denitrification rate of 68.9% in a denitrification environment of 150 - 200 °C; in a denitrification environment of 300 - 350 °C, its denitrification rate can reach 86.8%; and the compressive strength is not less than 2.13 MPa.
[0030] In summary, the present application has the following beneficial technical effects: 1. The preparation method of this application utilizes fly ash to carry out in-situ transformation crystallization reaction, and then blends it with copper ammonia complex, sodium hydroxide and template agent. Acidification treatment is carried out on it to obtain a crude carrier with high loading capacity and high stability. Next, the ion exchange method is adopted to load metal ions in the precursor solution onto the carrier. A variety of optimized operations improve the denitrification efficiency of the SCR catalyst in low-temperature environments, extend the service life of the SCR catalyst, and enhance its alkali metal poisoning resistance and sulfur resistance; 2. This application also adds iron salt to the precursor solution to introduce new active components into the carrier. The complexation of iron, vanadium and other active components gives full play to the good synergistic effect among them, thereby significantly enhancing the catalytic activity of the SCR catalyst and broadening the temperature window; 3. The highly active SCR catalyst applied in low-temperature environments of this application has good denitrification efficiency in low-temperature environments, excellent alkali metal poisoning resistance and sulfur resistance, and also has good mechanical stability, long service life, and high practical utilization value. Specifically, the SCR catalyst of this application has a maximum denitrification rate of up to 71.1% in the denitrification environment of 150 - 200 °C; in the denitrification environment of 300 - 350 °C, its maximum denitrification rate can reach 89.3%; the compressive strength is not less than 2.13 MPa. Specific embodiments
[0031] Material sources Except as otherwise specified, the raw materials used in this application are all commercially available products, specifically: Fly ash is purchased from Xishan Coal and Electricity Co., Ltd.; Tetraethylenepentamine is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; TMAda-OH is purchased from Sichuan Zhongbang Technology Development Co., Ltd., and the CAS number is 53075-09-5; Silica sol is purchased from Qingdao Ocean Chemistry Co., Ltd., with an effective content of 30 wt%; Glass fiber is purchased from Guangdong Mineral New Materials, 200 mesh; Guar gum is purchased from Qingzhou Rongmeier; Polyethylene glycol is purchased from Jiangxi Yipusen; Glycerol is purchased from Sinopharm Chemical Reagent Co., Ltd.; Ammonium metavanadate is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Ammonium metatungstate is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Cerium nitrate hexahydrate is purchased from Sinopharm Chemical Reagent Co., Ltd.; Polyacrylamide is purchased from Sinopharm Chemical Reagent Co., Ltd.; Carboxymethyl cellulose is purchased from Tianjin Kemiou Chemical Reagent Co., Ltd.; Sesbania powder was purchased from Shanghai Wangwang Industrial Co., Ltd.; Starch was purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; Activated carbon was purchased from Sinopharm Chemical Reagent Co., Ltd.; Ammonium carbonate was purchased from Tianjin Kemiou Chemical Reagent Co., Ltd.; Ferric nitrate nonahydrate was purchased from Sinopharm Chemical Reagent Co., Ltd.
[0032] The present application will be further described in detail below in conjunction with examples and comparative examples.
[0033] Example 1.1 A preparation method of a highly active SCR catalyst for use in a low-temperature environment, comprising the following steps: S1. Prepare the support: Place fly ash at a temperature of 350 °C and hydrothermally activate it with a NaOH solution with a concentration of 2.0 mol·L -1 for 2 h. After cooling, filter, wash, and dry to obtain heat-treated fly ash for standby. Disperse 1.6 kg of copper sulfate pentahydrate and 1.2 kg of tetraethylenepentamine in 8.5 L of water, continuously stir for 20 min to form a copper ammonia complex, then add 10.5 kg of TMAda-OH and 1.5 kg of sodium hydroxide to the system, stir for 15 min, then add 500 g of the above-prepared heat-treated fly ash and 10 kg of silica sol, mix evenly, place in an oven, crystallize at a temperature of 160 °C for 72 h, naturally cool to room temperature, filter with suction, wash until neutral, and dry in an oven at a temperature of 110 °C for 12 h to obtain a crude support. Mix the obtained crude support with an HNO3 solution with a concentration of 0.1 mol·L -1 in a solid-liquid ratio of 1:100, stir at a temperature of 80 °C for 6 h, then calcine in an air atmosphere at a temperature of 550 °C for 8 h, grind the calcined solid until its particle size reaches 250 mesh to obtain a pre-support powder. Subsequently, add a reinforcing agent (glass fiber), a binder (guar gum), and a pore-forming agent (polyethylene glycol) for dry mixing, then add water and a lubricant (glycerol) for wet mixing, stir for 2 h, knead for 2 h, and age for 2 h to form a catalyst embryo. Then, the embryo is extruded into strips through a catalyst forming and extruding device. The formed support is cut into formed particles of 450 mm × 300 mm × 300 mm. Finally, the formed particles are placed in a constant-temperature drying oven for segmented drying. First, dry at 55 °C for 4 h, and finally dry at 105 °C for 4 h to finally obtain the formed support, where the weight ratio of the pre-support powder, reinforcing agent, binder, pore-forming agent, water, and lubricant is 100:10:8:5:33:4; S2. Prepare the precursor solution: Ammonium metavanadate, ammonium metatungstate, and cerium nitrate hexahydrate with a molar ratio of 2:4:0.65 are dispersed in an oxalic acid solution. The amount of oxalic acid added in the oxalic acid solution is twice the amount of ammonium metavanadate. After stirring evenly, a precursor solution with a metal salt concentration of 0.165 mol / L is obtained. S3. Prepare the SCR catalyst: Mix and stir the carrier obtained in step S1 and the precursor solution obtained in step S2 for 45 min, filter, wash, dry first at 80 °C for 1 h, and then dry at 110 °C for 12 h. Place the dried material in an H2 atmosphere and perform plasma modification under the conditions of a treatment power of 120 W and a treatment duration of 120 min to obtain the SCR catalyst.
[0034] Example 1.2 A preparation method of a highly active SCR catalyst for low-temperature environments, comprising the following steps: S1. Prepare the carrier: Place fly ash at a temperature of 350 °C and hydrothermally activate it with a NaOH solution with a concentration of 2.0 mol·L -1 for 2 h. After cooling, filter, wash, and dry to obtain heat-treated fly ash for standby. Disperse 1.6 kg of copper sulfate pentahydrate and 1.2 kg of tetraethylenepentamine in 8.5 L of water, continuously stir for 20 min to form a copper ammonia complex, then add 10.5 kg of TMAda-OH and 1.5 kg of sodium hydroxide to the system, stir for 15 min, add 500 g of the above-mentioned standby heat-treated fly ash and 10 kg of silica sol, mix evenly, place in an oven, crystallize at a temperature of 160 °C for 72 h, naturally cool to room temperature, filter with suction, wash until neutral, dry in an oven at a temperature of 110 °C for 12 h to obtain a crude carrier. Mix the obtained crude carrier with an HNO3 solution with a concentration of 0.1 mol·L -1 in a solid-liquid ratio of 1:100 and stir at a temperature of 80 °C for 6 h. Then calcine in an air atmosphere at a temperature of 550 °C for 8 h, grind the calcined solid until its particle size reaches 250 mesh to obtain a pre-carrier powder. Subsequently, add a reinforcing agent (glass fiber), a binder (guar gum), and a pore-forming agent (polyethylene glycol) for dry mixing, and then add water and a lubricant (glycerol) for wet mixing. Stir for 2 h, knead for 2 h, and age for 2 h to form a catalyst embryo. Then, the embryo is extruded into strips through a catalyst forming and extruding device. The formed carrier is cut into formed particles with dimensions of 450 mm × 300 mm × 300 mm. Finally, place the formed particles in a constant-temperature drying oven for segmented drying. First, dry at 55 °C for 4 h, and finally dry at 105 °C for 4 h to finally obtain the formed carrier, where the weight ratio of the pre-carrier powder, reinforcing agent, binder, pore-forming agent, water, and lubricant is 100:10:8:5:33:4; S2. Prepare the precursor solution: Ammonium metavanadate, ammonium metatungstate, and cerium nitrate hexahydrate with a molar ratio of 2:4:0.65 are dispersed in an oxalic acid solution. The amount of oxalic acid added in the oxalic acid solution is twice the amount of ammonium metavanadate. After stirring evenly, a precursor solution with a metal salt concentration of 0.165 mol / L is obtained. S3. Prepare the SCR catalyst: Mix and stir the carrier obtained in step S1 and the precursor solution obtained in step S2 for 45 minutes, filter, wash, dry at 80 °C for 1 hour first, and then dry at 110 °C for 12 hours. Place the dried material in an H2 atmosphere and perform plasma modification under the conditions of a treatment power of 280 W and a treatment duration of 10 minutes to obtain the SCR catalyst.
[0035] Example 2.1 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S2, the concentration of the metal salt in the precursor solution is 0.1 mol / L, and the rest are the same as in Example 1.1.
[0036] Example 2.2 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S2, the concentration of the metal salt in the precursor solution is 0.135 mol / L, and the rest are the same as in Example 1.1.
[0037] Example 2.3 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S2, the concentration of the metal salt in the precursor solution is 0.185 mol / L, and the rest are the same as in Example 1.1.
[0038] Example 2.4 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S2, the concentration of the metal salt in the precursor solution is 0.2 mol / L, and the rest are the same as in Example 1.1.
[0039] Example 3.1 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S2, the molar ratio of ammonium metavanadate, ammonium metatungstate, and cerium nitrate hexahydrate is 2:4:0.5, and the rest are the same as in Example 1.1.
[0040] Example 3.2 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S2, the molar ratio of ammonium metavanadate, ammonium metatungstate, and cerium nitrate hexahydrate is 2:4:0.7, and the rest are the same as in Example 1.1.
[0041] Example 3.3 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S2, the molar ratio of ammonium metavanadate, ammonium metatungstate, and cerium nitrate hexahydrate is 2:4:0.6, and the rest are the same as in Example 1.1.
[0042] Example 3.4 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S2, the molar ratio of ammonium metavanadate, ammonium metatungstate, and cerium nitrate hexahydrate is 2:4:0.55, and the rest are the same as in Example 1.1.
[0043] Example 4.1 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S1, the weight ratio of the pre-carrier powder, reinforcing agent, binder, pore-forming agent, water, and lubricant is 100:10:5:6:33:4, and the rest are the same as in Example 1.1.
[0044] Example 4.2 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S1, the weight ratio of the pre-carrier powder, reinforcing agent, binder, pore-forming agent, water, and lubricant is 100:10:10:4:33:4, and the rest are the same as in Example 1.1.
[0045] Examples 4.3 - 4.5 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S1, guar gum is replaced with polyacrylamide, carboxymethyl cellulose, and sesbania powder respectively, and the rest are the same as in Example 1.1.
[0046] Examples 4.6 - 4.8 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S1, polyethylene glycol is replaced with starch, activated carbon, and ammonium carbonate respectively, and the rest are the same as in Example 1.1.
[0047] Example 5.1 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S2, the metal salt further includes an iron salt, and the molar ratio of the vanadium salt to the iron salt is 2:1, and the rest are the same as in Example 1.1.
[0048] Example 5.2 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S2, the metal salt further includes an iron salt, and the molar ratio of the vanadium salt to the iron salt is 2:1.5, and the rest are the same as in Example 1.1.
[0049] Example 5.3 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 5.1 in that in step S2, the molar ratio of the vanadium salt to the iron salt is 2:1.2, and the rest are the same as in Example 5.1.
[0050] Example 6 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 1.1 in that in step S3, the dried substance is placed in an N2 atmosphere and subjected to plasma modification under the conditions of a treatment power of 120 W and a treatment duration of 120 min to obtain an SCR catalyst, and the rest are the same as in Example 1.1.
[0051] Example 7.1 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 6 in that in step S3, plasma modification is carried out under the conditions of a treatment power of 200 W and a treatment duration of 60 min to obtain an SCR catalyst, and the rest are the same as in Example 6.
[0052] Example 7.2 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 6 in that in step S3, plasma modification is carried out under the condition of a treatment duration of 60 min to obtain an SCR catalyst, and the rest are the same as in Example 6.
[0053] Example 7.3 A preparation method of a highly active SCR catalyst for low-temperature environments, which is different from Example 6 in that in step S3, plasma modification is carried out under the condition of a treatment power of 200 W to obtain an SCR catalyst, and the rest are the same as in Example 6.
[0054] Comparative Example 1 Including the following steps: S1. Prepare a support: Place fly ash at a temperature of 350 °C and mix it with a concentration of 2.0 mol·L-1 The NaOH solution was hydrothermally activated for 2 h, cooled, filtered, washed, and dried to obtain heat-treated fly ash for standby. 1.6 kg of copper sulfate pentahydrate and 1.2 kg of tetraethylenepentamine were dispersed in 8.5 L of water, and continuously stirred for 20 min to form a copper ammonia complex. Then, 10.5 kg of TMAda-OH and 1.5 kg of sodium hydroxide were added to the system. After stirring for 15 min, 500 g of the above-mentioned standby heat-treated fly ash and 10 kg of silica sol were added. After mixing evenly, it was placed in an oven and crystallized at a temperature of 160 °C for 72 h. It was naturally cooled to room temperature, filtered, washed until neutral, and dried in an oven at a temperature of 110 °C for 12 h to obtain a crude carrier. Subsequently, it was calcined in an air atmosphere at a temperature of 550 °C for 8 h, and the solid obtained after calcination was ground until its particle size reached 250 mesh to obtain a pre-carrier powder. Subsequently, a reinforcing agent (glass fiber), a binder (guar gum), and a pore-forming agent (polyethylene glycol) were added for dry mixing, and then water and a lubricant (glycerol) were added for wet mixing. It was stirred for 2 h, kneaded for 2 h, and aged for 2 h to form a catalyst embryo. Then, the embryo was extruded into strips through a catalyst forming and extruding device, and the formed carrier was cut into formed particles of 450 mm × 300 mm × 300 mm. Finally, the formed particles were placed in a constant temperature drying oven for segmented drying. First, it was dried at 55 °C for 4 h, and finally dried at 105 °C for 4 h to finally obtain the formed carrier, where the weight ratio of the pre-carrier powder, the reinforcing agent, the binder, the pore-forming agent, water, and the lubricant is 100:10:8:5:33:4; S2. Prepare the precursor solution: Ammonium metavanadate, ammonium metatungstate, and cerium nitrate hexahydrate with a molar ratio of 2:4:0.65 were dispersed in an oxalic acid solution. The amount of oxalic acid added in the oxalic acid solution was twice the amount of ammonium metavanadate. After stirring evenly, a precursor solution with a metal salt concentration of 0.065 mol / L was obtained; S3. Prepare the SCR catalyst: The carrier obtained in step S1 and the precursor solution obtained in step S2 were mixed and stirred for 3 h, filtered, washed, dried, and then calcined in an air atmosphere at a temperature of 600 °C to obtain the SCR catalyst.
[0055] Comparative Example 2 It is different from Example 1.1 in that in step S2, cerium nitrate hexahydrate was removed, and the rest was the same as in Example 1.1.
[0056] Comparative Example 3 It is different from Example 1.1 in that in step S2, the metal salt concentration of the precursor solution was 0.05 mol / L, and the rest was the same as in Example 1.1.
[0057] Comparative Example 4 It is different from Example 1.1 in that in step S2, the metal salt concentration of the precursor solution is 0.25 mol / L, and the rest are the same as in Example 1.1.
[0058] Comparative Example 5 It is different from Example 1.1 in that the specific operation of step S3 is as follows: The carrier obtained in step S1 and the precursor solution obtained in step S2 are mixed and stirred for 3 h, filtered, washed, dried, and then calcined in an air atmosphere at a temperature of 600 °C to obtain an SCR catalyst.
[0059] Performance detection The SCR catalysts prepared in the examples and comparative examples were subjected to alkali poisoning treatment. Specifically: First, KCl particles were put into a ball mill and ground at high speed for 1 h, then sieved through a 150-mesh sieve, and then dried in a constant-temperature drying oven for 4 h to obtain KCl solid powder. The mass ratio of the SCR catalyst to KCl was taken as 1:2, and the two were put into a crucible to ensure that the sample was completely immersed in the KCl solid powder to ensure full contact, and calcined in a muffle furnace for 6 h. The calcination temperature was set at 500 °C. After the calcination was completed, the sample was taken out, and the KCl floating powder on the surface was blown off with a blower to obtain the catalyst treated with alkali metal poisoning.
[0060] 1. Determination of denitrification rate: The SCR catalyst after alkali poisoning treatment was placed in a tubular fixed-bed reactor. The reaction gas composition was: 1000 ppm NO x , 500 ppm NH3, 400 ppm SO2, 6% O2, 12% H2O, with N2 as the carrier gas, and the space velocity was 48000 h -1 . The reaction temperatures were 150 - 200 °C and 300 - 350 °C respectively, and the 6-h denitrification rate was recorded in Table 1; 2. Determination of compressive strength: A universal testing machine was used to conduct a compressive performance test on the SCR catalysts prepared in the examples and comparative examples. During the test, axial uniform force was applied. When the pressure suddenly disappeared, the maximum value was read, and the average value was taken after multiple tests. The results were recorded in Table 1.
[0061] Table 1 Performance detection table Data analysis: As can be seen from Table 1, the SCR catalysts of Examples 1.1 - 1.2 achieved a denitrification rate of 68.7 - 68.9% at 150 - 200 °C and 86.3 - 86.8% at 300 - 350 °C after alkali metal poisoning treatment. The compressive strength was as high as 2.47 - 2.48 MPa, proving that the preparation method of this application not only improved the denitrification efficiency of the SCR catalyst in a low - temperature environment, but also extended the service life of the SCR catalyst, enhanced its alkali - metal poisoning resistance and sulfur resistance. Moreover, through a series of carrier shaping treatments, the SCR catalyst also has good mechanical properties.
[0062] The difference between Examples 2.1 - 2.4 and Example 1.1 is the concentration of metal salts in the precursor solution. The data shows that the denitrification rates at 150 - 200 °C and 300 - 350 °C of Examples 2.1 - 2.4 are lower than those of Example 1.1, proving that by controlling the concentration of metal salts in the precursor solution in this application, the uniform loading of active components on the carrier can be ensured, thereby improving the denitrification rate of the SCR catalyst. If the concentration of metal salts is too low, the loading amount of active components will be insufficient, resulting in a reduction in the number of active sites of the SCR catalyst and affecting the denitrification efficiency, and it cannot effectively reduce the emission of NO x . On the other hand, if the concentration of metal salts is too high, the active components will agglomerate excessively on the carrier, forming an agglomeration phenomenon, which will also affect the activity and stability of the SCR catalyst, and may even block the pores of the SCR catalyst, reducing the service life of the SCR catalyst.
[0063] For the SCR catalysts of Examples 3.1 - 3.4, the denitrification rates at 150 - 200 °C and 300 - 350 °C are lower than those of Example 1.1, proving that by controlling the molar ratios of ammonium metavanadate, ammonium metatungstate and cerium nitrate hexahydrate in this application, the performance of the catalyst is further optimized, enabling it to maintain a more efficient denitrification ability.
[0064] For the SCR catalysts of Examples 4.1 - 4.2, the denitrification rates at 150 - 200 °C and 300 - 350 °C are lower than those of Example 1.1, and at the same time, the compressive strength is also significantly lower than that of Example 1.1, proving that by controlling the weight ratios of the precursor carrier powder, reinforcing agent, binder, pore - forming agent, water and lubricant in this application, the surface of the SCR catalyst green body is smooth, and the extruded SCR catalyst does not crack, with good forming effect, having both good mechanical strength and catalytic activity, and at the same time having a large specific surface area and active site exposure degree.
[0065] The SCR catalysts of Examples 4.3 - 4.8 have lower denitrification rates at 150 - 200 °C and 300 - 350 °C than those of Example 1.1, and their compressive strengths are also significantly lower than that of Example 1.1, which proves that by using guar gum as a binder and polyethylene glycol as a pore former in this application, the catalytic activity and mechanical stability of the SCR catalyst can be further improved.
[0066] The SCR catalysts of Examples 5.1 - 5.3 have significantly higher denitrification rates at 150 - 200 °C and 300 - 350 °C than those of Example 1.1, which proves that by adding ferric nitrate nonahydrate to the precursor solution in this application, new active components are introduced into the carrier. There is a strong synergistic effect between iron and vanadium, with charge transfer and strong charge interaction. At the same time, the addition of iron increases the specific surface area of the SCR catalyst, enabling it to maintain a relatively high acid amount even after contacting alkali metals. Therefore, by adding and compounding iron with vanadium and other active components in this application, the good synergistic effect between them is fully exerted, thereby significantly improving the catalytic activity of the SCR catalyst and broadening the temperature window.
[0067] The 150 - 200 °C and 300 - 350 °C denitrification rates of the SCR catalyst of Example 5.3 are higher than those of Example 5.1, which proves that by strictly controlling the molar ratio of vanadium salt to iron salt in this application, the performance of the SCR catalyst can be optimized. When the molar proportion of ferric nitrate nonahydrate is too low, the active sites of the SCR catalyst are insufficient, resulting in a decrease in denitrification efficiency, especially being more obvious in a low - temperature and high - alkali - metal environment; while when the molar proportion of ferric nitrate nonahydrate is too high, excessive iron ions will cause agglomeration on the surface of the SCR catalyst, affecting the dispersibility and specific surface area of the SCR catalyst, and thus reducing the overall activity and stability of the SCR catalyst.
[0068] The SCR catalysts of Example 6 have significantly higher denitrification rates at 150 - 200 °C and 300 - 350 °C than those of Example 1.1, which proves that by selecting N2 - atmosphere plasma modification in this application, compared with H2 - atmosphere plasma modification, it can exhibit more excellent dispersion - promoting ability in the system of this application. The active components on the finally obtained SCR catalyst are more evenly loaded, with the most suitable distribution density, and thus have better catalytic ability and catalytic stability.
[0069] The 150 - 200 °C denitrification rate of the SCR catalyst of Comparative Example 1 is 0, and its 300 - 350 °C denitrification rate is much lower than that of Example 1.1, which proves that by acidification treatment in this application, the number of acid sites on the carrier surface is increased, which helps to capture and consume alkali metal ions, reducing the possibility and coverage area of alkali metals covering the surface of the SCR catalyst, thereby keeping the active sites of the SCR catalyst unobstructed.
[0070] For the SCR catalyst of Comparative Example 2, the denitration rates at 150 - 200 °C and 300 - 350 °C are both lower than those of Example 1.1, which proves that the addition of cerium element can broaden the active temperature window of the SCR catalyst, effectively reduce the adsorption of SO2, thereby significantly improving the resistance of the SCR catalyst to SO2, enhancing the redox performance of the SCR catalyst, and further improving the catalytic activity.
[0071] For the SCR catalysts of Comparative Examples 3 - 4, the denitration rates at 150 - 200 °C and 300 - 350 °C are both lower than those of Example 1.1, which proves that by controlling the concentration of metal salts in the precursor solution in this application, the uniform loading of active components on the carrier can be ensured, and then the denitration rate of the SCR catalyst can be improved. If the concentration of metal salts is too low, the loading amount of active components will be insufficient, resulting in a reduction in the number of active sites of the SCR catalyst, affecting the denitration efficiency and being unable to effectively reduce the emission of NO x . On the other hand, if the concentration of metal salts is too high, it will lead to excessive aggregation of active components on the carrier, forming an agglomeration phenomenon, which will also affect the activity and stability of the SCR catalyst, and may even block the pores of the SCR catalyst, reducing the service life of the SCR catalyst.
[0072] For the SCR catalyst of Comparative Example 5, the denitration rates at 150 - 200 °C and 300 - 350 °C are far lower than those of Example 1.1, which proves that by using the ion exchange method and plasma modification in this application, the metal ions in the precursor solution are uniformly loaded on the carrier. Compared with the calcination loading method, the plasma treatment in this application has stronger dispersion promotion, enabling the metal elements to be more stably and uniformly loaded on the carrier, and finally obtaining an SCR catalyst with multiple active substances.
[0073] The examples of this specific embodiment are all preferred embodiments of this application, and do not limit the protection scope of this application accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of this application should be covered within the protection scope of this application.
Claims
1. A method for preparing a high-activity SCR catalyst for use in a low-temperature environment, characterized in that: The following steps are involved: S1. Preparation of carrier: hydrothermally activate fly ash under alkaline conditions, mix with silica sol, copper ammonia complex, sodium hydroxide and template, heat up for crystallization, cool, filter, wash to neutrality, dry to obtain a crude carrier, and then acidify, roast and shape to obtain a carrier; S2. Preparing a precursor solution: dispersing a metal salt in an oxalic acid solution to obtain a precursor solution with a metal salt concentration of 0.1-0.2 mol / L, wherein the metal salt includes a vanadium salt, a tungsten salt and a cerium salt in a molar ratio of 2:4:(0.5-0.7); S3, preparing SCR catalyst: mixing the carrier obtained in step S1 and the precursor solution obtained in step S2, impregnating, filtering, washing, drying, and subjecting to plasma modification in H2 atmosphere or N2 atmosphere to obtain SCR catalyst.
2. The method for preparing a high-activity SCR catalyst for use in a low-temperature environment according to claim 1, characterized in that: In step S2, the concentration of the metal salt in the precursor solution is 0.165 mol / L.
3. The method for preparing a high-activity SCR catalyst for use in a low-temperature environment according to claim 1, characterized in that: In the step S2, the molar ratio of the vanadium salt, the tungsten salt and the cerium salt is 2:4:0.
65.
4. The method for preparing a high-activity SCR catalyst for use in a low-temperature environment according to claim 1, characterized in that: In the step S2, the metal salt further includes an iron salt, and the molar ratio of the vanadium salt to the iron salt is 2:(1-1.5).
5. The method for preparing a high-activity SCR catalyst for use in a low-temperature environment according to claim 4, characterized in that: The molar ratio of the vanadium salt to the iron salt is 2:1.
2.
6. The method for preparing a high-activity SCR catalyst for use in a low-temperature environment according to claim 1, characterized in that: In step S1, the specific operation of shaping is: The solid obtained after roasting is ground until its particle size reaches 200-300 meshes to obtain a pre-carrier powder, and then a reinforcing agent, a binder and a pore-forming agent are added for dry mixing, and then water and a lubricant are added for wet mixing, stirring, kneading, aging, extrusion molding, cutting, and segmented drying to obtain a carrier. The weight ratio of the pre-carrier powder, the reinforcing agent, the binder, the pore-forming agent, the water and the lubricant is 100:10:(5-10):(4-6):33:
4.
7. The method for preparing a high-activity SCR catalyst for use in a low-temperature environment according to claim 6, characterized in that: The weight ratio of the front carrier powder, reinforcing agent, binder, pore-forming agent, water and lubricant is 100:10:8:5:33:
4.
8. The method for preparing a high-activity SCR catalyst for use in a low-temperature environment according to claim 6, characterized in that: The reinforcing agent is glass fiber, the binder is guar gum, the pore-forming agent is polyethylene glycol, and the lubricant is glycerol.
9. The method for preparing a high-activity SCR catalyst for use in a low-temperature environment according to claim 1, characterized in that: In the step S3, the SCR catalyst is obtained by N2 atmosphere plasma modification.
10. An SCR catalyst obtained by the method for preparing a high-activity SCR catalyst for use in a low-temperature environment as claimed in any one of claims 1 to 9.