Method for preparing low-temperature denitration catalyst under assistance of active auxiliary agent

Abstract

The invention relates to the technical field of catalyst preparation, in particular to a method for preparing a low-temperature denitration catalyst under the assistance of an active auxiliary agent. The method comprises the following steps: 1) phosphorus-doped modified activated carbon; 2) co-precipitating and loading manganese ferrite; 3) grafting modification of ammonium molybdate; according to the preparation method, activated carbon is doped with phosphorus, coordination sites of metal ions are constructed on the activated carbon, Fe < 2 + > and Mn < 2 + > are adsorbed by the sites to form a precursor of manganese ferrite, and the catalyst P-AC / MnFe2O4 / MoOx is obtained after ammonium molybdate grafting modification and high-temperature calcination. According to the invention, P is doped with a strong acid site, manganese ferrite is co-precipitated, spinel is formed for concerted catalytic denitration, P and MoOx are used as sacrificial agents, SO2 / H2O poisoning is reduced, high efficiency and stability of active components are actively protected, the fundamental industrial problem that low-temperature activity, poisoning resistance and high selectivity are difficult to consider at the same time is successfully solved, and comprehensive and remarkable performance advantages and application potential are shown.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of organic chemical technology, and in particular to a method for preparing a low-temperature denitration catalyst with the assistance of an active additive. BACKGROUND

[0002] Nitrogen oxides (NO x ) are one of the main atmospheric pollutants, posing a serious threat to the environment and human health. Selective catalytic reduction (SCR) technology is the most widely used and most efficient industrial denitration technology. Traditional commercial SCR catalysts are represented by V2O5-WO3 / TiO2 or V2O5-MoO3 / TiO2, which have high denitration activity and stability in a high-temperature window of 350-400℃. However, this system has several fundamental defects that are difficult to overcome: First, its active core is highly dispersed polymeric V 5+ =O species, which has good redox ability at medium and high temperatures, but at low temperatures (<250℃), the redox cycle (V 5+ / V 4+ ) of vanadium is slow, resulting in a sharp decrease in catalyst activity at low temperatures. This makes it necessary to reheat the flue gas in practical applications, resulting in a huge energy consumption burden and operating cost.

[0003] Second, the acidity of existing catalysts is mainly provided by the addition of WO3 or MoO3 to provide Lewis acid sites, which has limited acid strength and acid amount, insufficient adsorption and activation of NH3, and insufficient synergy between V2O5 redox sites, limiting the reaction efficiency at low temperatures.

[0004] Third, this system is abnormally sensitive to SO2 and H2O in the flue gas. SO2 is easily oxidized to SO3 on the V2O5 active site, and then reacts with escaped NH3 to form sticky ammonium bisulfate (NH4HSO4), which seriously blocks the catalyst pores and covers the active sites; at the same time, SO2 also reacts with the V-OH group of the catalyst to form stable VOSO4, causing permanent deactivation of the active center. Water vapor competes with reactant molecules for adsorption on active sites, further inhibiting the reaction.

[0005] In addition, vanadium (V) is a biotoxic metal, and its catalysts pose potential ecological and human health risks during production, use, disposal, and regeneration, which does not meet the development trend of green chemical industry.

[0006] To solve the above problems, the development of non-vanadium-based low-temperature SCR catalysts with excellent low-temperature activity, strong resistance to sulfur and water, and environmental friendliness has become a research hotspot and urgent need in this field. Among them, catalysts with manganese (Mn), iron (Fe) and other non-vanadium transition metal oxides as the core show good low-temperature catalytic potential. However, how to simultaneously achieve high activity, high stability, high selectivity and strong resistance to poison is still the main challenge faced by current researchers. Single-component catalysts often cannot meet all performance requirements, for example: high-activity manganese-based catalysts are prone to SO2 poisoning and hydrothermal sintering; high-stability iron-based catalysts have insufficient low-temperature activity. Therefore, constructing new composite catalyst systems through multi-component synergy, carrier functional modification and interface structure design is the key to breaking through the existing technical bottlenecks and promoting the application of low-temperature SCR technology. SUMMARY

[0007] The purpose of the present application is to solve the problems existing in the prior art and to provide a method for preparing a low-temperature denitration catalyst with the assistance of an active additive.

[0008] Based on the above purpose, the present application provides a method for preparing a low-temperature denitration catalyst with the assistance of an active additive, comprising the following steps: S1. Phosphorus-doped modified activated carbon: The activated carbon is washed with deionized water until it is neutral, and then dried in an oven for standby; ammonium dihydrogen phosphate is dissolved in deionized water to prepare an impregnation solution; The pretreated activated carbon is put into the impregnation solution, stirred at a constant temperature of 40-50℃, and then filtered. After drying, the filter cake is transferred to a muffle furnace, heated to 500℃ under N2 atmosphere, and calcined for 4-5h; Phosphate ions enter the large pore system of activated carbon (AC) through diffusion during stirring and are attached to the carbon surface through physical adsorption and electrostatic attraction; under heating conditions of 500℃, ammonium phosphate salt decomposes and reacts with functional groups on the carbon surface, such as -OH and -COOH, to form chemical bonds in the form of C-O-P=O or C-P, anchoring phosphorus atoms on the carbon skeleton.

[0009] Natural cooling to room temperature gives phosphorus-doped activated carbon, i.e. P-AC, which is sealed and stored; The introduced P=O and P-OH groups can serve as coordination sites for subsequent metal ions (Fe 2+ , Mn 2+ ), allowing them to be uniformly distributed on the surface of the carrier, preventing agglomeration at high temperatures, and being strong Brønsted acid sites, greatly enhancing the ability of the catalyst surface to adsorb and activate NH3; P compounds form a protective film on the surface of AC, inhibiting the oxidation of carbon at high temperatures, thereby improving the durability of the carrier in the reaction environment.

[0010] S2. Co-precipitation of manganese ferrite: In a reaction kettle, FeSO4·7H2O and MnSO4·H2O were dissolved in ethylene glycol with vigorous stirring; cetyltrimethylammonium bromide (CTAB) was added and continued to be stirred until completely dissolved; P-AC was slowly added to the above solution and ultrasonic treatment was performed to fully disperse it; NaOH solution was slowly added to adjust the pH value of the system to 10-11 to obtain a mixed slurry; Fe ions in solution 2+ and Mn 2+ ions are adsorbed and fixed by the oxygen-containing and phosphorus-containing functional groups on the surface of P-AC. In the high-temperature and high-pressure ethylene glycol environment, OH - reacts with metal ions to generate M(OH) n colloid particles co-precipitate, and ethylene glycol acts as a mild reducing agent and complexing agent to control the generation rate of crystal nuclei; The reaction kettle was placed in an oven at 200-220°C and reacted for 24h; after natural cooling, it was suction filtered and washed repeatedly with deionized water and ethanol until the filtrate was neutral; the filter cake was vacuum dried to obtain the P-AC / MnFe2O4 precursor; Under the long-time hydrothermal conditions at 200°C, the amorphous hydroxide colloid dehydrates and rearranges to finally crystallize into MnFe2O4 nanoparticles with a spinel structure and firmly grow on the surface of P-AC; due to the bridging effect of P, the combination between MnFe2O4 and the AC carrier is no longer a simple physical adhesion, but a stronger chemical interaction, which makes the active component more stable and less likely to sinter and fall off.

[0011] CTAB is a cationic surfactant, and its hydrophilic positively charged head (-N + (CH3)3) selectively adsorbs on specific crystal faces to inhibit the growth rate of the crystal faces, and the difference in growth rates of different crystal faces leads to a change in the final crystal morphology from a cube to an octahedron, exposing more active crystal faces; Mn and Fe ions in the spinel structure exist in tetrahedral and octahedral interstices, and the valence state changes flexibly (Mn 2+ / Mn 3+ / Mn 4+ , Fe 2+ / Fe 3+ ), providing excellent electron transfer and lattice oxygen migration ability, which is the key to oxidizing NO to NO2 at low temperatures.

[0012] S3. Ammonium molybdate graft modification: The ammonium molybdate is dissolved in deionized water, the P-AC / MnFe2O4 precursor is added, and the mixture is stirred and impregnated at 50-60℃ for 6-8h; after filtration, the dried sample is calcined at 400℃ in an air atmosphere for 4h; after natural cooling, the final catalyst product P-AC / MnFe2O4 / MoO x .

[0013] The molybdate ion (Mo7O 24 6- ) is negatively charged in water, and it can be adsorbed on the positively charged areas on the surface of the catalyst, such as the protonated phosphorus-containing groups or metal sites, by electrostatic interaction; under calcination at 400℃, the ammonium molybdate decomposes to form highly dispersed MoO x , mainly MoO3, which is grafted on the surface of MnFe2O4 and AC in the form of a monolayer or small islands. MoO3 itself is a Lewis acid, and its introduction further increases the total acid amount on the surface of the catalyst, especially the medium-strong acid sites, promoting the adsorption of NH3.

[0014] MoO x species will cover or modify a part of the over-oxidized active sites, such as some high-activity Mn 4+ sites, preventing NH3 from being over-oxidized to N2O at these sites, thereby guiding the reaction towards the path of generating N2.

[0015] At the same time, SO2 will preferentially react with MoO3 to form relatively stable molybdenum sulfate, rather than reacting with the core MnFe2O4 to form difficult-to-decompose manganese sulfate; MoO x serves as a sacrificial site, protecting the main active center, thereby significantly enhancing the SO2 poisoning resistance of the catalyst.

[0016] Preferably, in S1, the mass ratio of the pretreated activated carbon to ammonium dihydrogen phosphate is 5-7:1.

[0017] Preferably, in S2, the mass ratio of P-AC, FeSO4·7H2O, MnSO4·H2O, and cetyltrimethylammonium bromide is 1:1-1.2:0.304-0.365:1.2-1.8. Preferably, in S2, the molar ratio of Mn to Fe is 1:2.

[0018] Preferably, in S3, the mass ratio of P-AC / MnFe2O4 to ammonium molybdate is 9-11:1.

[0019] The application also provides a low-temperature denitration catalyst prepared by the method, wherein the catalytic temperature window of the low-temperature denitration catalyst is 150-350℃, the optimal activity interval is 200-300℃, and in the optimal temperature interval, the conversion rate of NOx The conversion rate can be consistently maintained at >95%.

[0020] The beneficial effects of this invention are: 1. The active core of existing technologies is highly dispersed polymeric V. 5+ =O, its redox cycle (V 5+ / V 4+ The kinetics are slow at low temperatures, resulting in poor low-temperature activity of the catalyst. It must be raised to above 350°C to operate efficiently, which results in high energy consumption.

[0021] The core innovation of this invention lies in constructing a composite structure of highly ordered manganese, iron, and oxygen at the atomic level, using spinel-type MnFe2O4 as a low-temperature redox center. Its greatest advantage is the creation of a Mn... 3+ -O-Fe 3+ This unique electron channel enables an extremely efficient synergistic redox cycle: Mn 3+ +Fe 3+ ⇌Mn 2+ +Fe 4+ ; The Fe produced therein 4+ It is a very powerful oxide species at low temperatures, capable of instantly oxidizing NO to NO2. This allows the catalyst to efficiently initiate and dominate the extremely fast "fast SCR" pathway, namely NO + NO2 + 2NH3 → 2N2 + 3H2O, within the low temperature range of 150℃-250℃. The rate is several orders of magnitude faster than the traditional "standard SCR" pathway, achieving excellent low-temperature activity.

[0022] 2. Existing technologies mainly provide Lewis acidity by adding WO3 or MoO3, but the acidity is limited and the synergistic effect with the redox sites of V2O5 is not strong enough.

[0023] This invention functionalizes activated carbon supports through phosphorus (P) doping. P forms stable, strong Brønsted acid sites such as P-OH and -POOH on the carbon surface. The acidity and strength of these sites far exceed those of traditional catalysts; they exhibit extremely strong adsorption and activation capabilities for NH3 molecules. More importantly, these chemically bonded strong acid sites are closely adjacent to the redox sites of MnFe2O4, allowing NH3 to react immediately with activated NOx species after adsorption and activation, following a highly efficient Eley-Rideal (ER) mechanism. This significantly shortens the reaction pathway and improves reaction efficiency.

[0024] 3. Existing technologies are very vulnerable to SO2 and H2O in flue gas. SO2 is easily oxidized to SO3 on V2O5, and then reacts with NH3 to form ammonium bisulfate (NH4HSO4), which blocks the pores and covers the active sites; at the same time, it can also react with V-OH to form VOSO4, which permanently destroys the active centers.

[0025] This invention constructs an active defense system—first, the oxygen-containing groups introduced by P doping preferentially combine with SO2 to form thermally stable phosphates, thereby protecting the core MnFe2O4 active sites from being sulfided into deactivated manganese sulfate; second, MoO… x The grafting further inhibits the oxidation process of SO2 to SO3, cutting off the formation chain of NH4HSO4 at its source. Furthermore, the large specific surface area of ​​the activated carbon support provides numerous inactive adsorption sites for H2O molecules, greatly mitigating the competitive adsorption effect between H2O and reactants at active sites. This multi-layered synergistic protection mechanism enables the invention to exhibit extremely excellent stability in harsh sulfur-containing and water-containing environments.

[0026] 4. Existing technologies use highly toxic V2O5 as the active ingredient, and its production, use, and disposal all pose environmental and health risks.

[0027] This invention completely eliminates vanadium, using environmentally friendly elements such as Mn, Fe, Mo, P, and C, representing a greener and more sustainable technological route. Furthermore, thanks to the system's superior low-temperature activity, this invention enables the denitrification reaction to proceed efficiently at flue gas emission temperatures (e.g., 150-300℃), eliminating the enormous energy consumption of reheating the flue gas to above 350℃, thus significantly reducing operating costs.

[0028] In summary, this invention utilizes P doping at strong acid sites to co-precipitate manganese ferrite, forming spinel-based synergistic catalytic denitration, followed by the use of P and MoO2. x As a sacrificial agent, it reduces SO2 / H2O poisoning and actively protects the high efficiency and stability of active ingredients. It successfully solves the fundamental industry problem of balancing low-temperature activity, anti-poisoning ability and high selectivity, demonstrating comprehensive and significant performance advantages and application potential. Attached Figure Description

[0029] Figure 1 This is a summary chart of the conversion rate of nitrogen oxides for the low-temperature denitrification catalyst produced by this invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0031] The purity and manufacturers of the various drugs used in the experiment are shown in Table 1. Table 1. Raw Material Drug Information

[0032] Example 1: A method for preparing a low-temperature denitration catalyst with the assistance of an active additive includes the following steps: S1. Phosphorus-doped modified activated carbon: Wash the activated carbon with deionized water until neutral, dry it in an oven and set it aside; dissolve ammonium dihydrogen phosphate in deionized water to prepare an impregnation solution; The pretreated activated carbon was put into the impregnation solution, stirred at a constant temperature of 45°C, and then filtered. After drying, the filter cake was transferred into a muffle furnace and calcined at 500°C for 4-5 hours under N2 atmosphere protection. After naturally cooling to room temperature, phosphorus-doped activated carbon, i.e., P-AC, is obtained and stored in a sealed container. S2. Co-precipitated manganese ferrite: In the reactor, FeSO4·7H2O and MnSO4·H2O were dissolved in ethylene glycol and stirred vigorously; hexadecyltrimethylammonium bromide was added and stirring was continued until completely dissolved; P-AC was slowly added to the above solution and ultrasonically treated to ensure full dispersion; NaOH solution was slowly added to adjust the pH of the system to 10, resulting in a mixed slurry. The reactor was placed in an oven at 210℃ and reacted for 24 hours. After natural cooling, it was filtered and repeatedly washed with deionized water and ethanol until the filtrate was neutral. The filter cake was dried under vacuum to obtain the P-AC / MnFe2O4 precursor. S3. Ammonium molybdate grafting modification: Ammonium molybdate was dissolved in deionized water, and P-AC / MnFe2O4 precursor was added. The mixture was stirred and impregnated at 55°C for 7 hours. After filtration, the sample was dried at high temperature. The dried sample was then calcined in air at 400°C for 4 hours. After natural cooling, the final catalyst product P-AC / MnFe2O4 / MoO was obtained. x .

[0033] In S1, the mass ratio of pretreated activated carbon to ammonium dihydrogen phosphate is 7:1.

[0034] In S2, the mass ratio of P-AC, FeSO4·7H2O, MnSO4·H2O, and hexadecyltrimethylammonium bromide is 1:1:0.304:1.2. In S2, the molar ratio of Mn to Fe is 1:2.

[0035] In S3, the mass ratio of P-AC / MnFe2O4 to ammonium molybdate is 11:1.

[0036] Unlike Example 1, Examples 2-3 were designed and implemented: Example 2: In S1, the mass ratio of pretreated activated carbon to ammonium dihydrogen phosphate is 6:1.

[0037] In S2, the mass ratio of P-AC, FeSO4·7H2O, MnSO4·H2O, and hexadecyltrimethylammonium bromide is 1:1.1:0.334:1.5. In S2, the molar ratio of Mn to Fe is 1:2.

[0038] In S3, the mass ratio of P-AC / MnFe2O4 to ammonium molybdate is 10:1.

[0039] Example 3: In S1, the mass ratio of pretreated activated carbon to ammonium dihydrogen phosphate is 5:1.

[0040] In S2, the mass ratio of P-AC, FeSO4·7H2O, MnSO4·H2O, and hexadecyltrimethylammonium bromide is 1:1.2:0.365:1.8. In S2, the molar ratio of Mn to Fe is 1:2.

[0041] In S3, the mass ratio of P-AC / MnFe2O4 to ammonium molybdate is 9:1.

[0042] Based on this, the following design was also created: Comparative Example 1: The formulation and experimental method are the same as those in Example 2, but the mass ratio of pretreated activated carbon to ammonium dihydrogen phosphate is 10:1.

[0043] Comparative Example 2: The formulation and experimental method are the same as in Example 2, but the mass ratio of pretreated activated carbon to ammonium dihydrogen phosphate is 2:1.

[0044] Comparative Example 3: The formulation and experimental methods were the same as in Example 2, but the mass ratio of P-AC, FeSO4·7H2O, MnSO4·H2O, and hexadecyltrimethylammonium bromide was 1:0.5:0.167:1.5; Comparative Example 4: The formulation and experimental methods were the same as in Example 2, but the mass ratio of P-AC, FeSO4·7H2O, MnSO4·H2O, and hexadecyltrimethylammonium bromide was 1:3:1:1.5. Comparative Example 5: The formulation and experimental methods were the same as in Example 2, but the mass ratio of P-AC, FeSO4·7H2O, MnSO4·H2O, and hexadecyltrimethylammonium bromide was 1:1.1:0.334:0.5. Comparative Example 6: The formulation and experimental methods were the same as in Example 2, but the mass ratio of P-AC, FeSO4·7H2O, MnSO4·H2O, and hexadecyltrimethylammonium bromide was 1:1.1:0.334:3; Comparative Example 7: The formulation and experimental method are the same as those in Example 2, but in S3, the mass ratio of P-AC / MnFe2O4 to ammonium molybdate is 5:1.

[0045] Comparative Example 8: The formulation and experimental method are the same as those in Example 2, but in S3, the mass ratio of P-AC / MnFe2O4 to ammonium molybdate is 20:1.

[0046] The specific surface area was tested according to GB / T 19587-2004 Gas Adsorption BET Method for Determination of Specific Surface Area of ​​Solid Substances; the mechanical strength and thermal stability were tested according to GB / T 31590-2015 Flue Gas Denitrification Catalysts; and the leaching amount of heavy metals was tested according to HJ 557-2010 Solid Waste Leaching Toxicity Leaching Method Horizontal Oscillation Method. A fixed-bed reactor was constructed to simulate the actual flue gas composition. The gas composition of the mixed gas used for testing was: 500ppm NO, 500ppm NH3, 5% vol O2, 200ppm SO2, with N2 as the balance gas; the total gas flow rate was 500mL / min, 1mL of catalyst was added, and the gas flow rate was 30000h. -1 The temperature range covers the 150℃-350℃ requirement specified in the patent, with a focus on testing the optimal range of 200℃-300℃. Samples are taken after each temperature point has stabilized for 30-60 minutes, and the concentration of pollutants in the exhaust gas is simultaneously measured to test the NO content of this invention. x Conversion rate, N2 selectivity, NH3 escape rate, sulfur / water resistance; The corresponding results are shown below: The performance test data are summarized and plotted in Table 2: Table 2.1. Performance test data of low-temperature denitrification catalyst (Part 1)

[0047] Table 2.2. Performance test data of low-temperature denitrification catalyst (Part II)

[0048] Data Analysis: By comparing Example 2, Comparative Example 1, and Comparative Example 2, it can be seen that: Appropriate phosphorus doping can form stable PC and POC structures on the surface of activated carbon, increase the pore structure and surface acidic sites, improve the specific surface area, enhance the structural stability of the carbon skeleton, stabilize the MnFe2O4 structure, prevent high-temperature sintering, and enhance the interaction between the metal and the support, inhibiting the migration and dissolution of metal ions. However, the phosphorus content in Comparative Example 1 is too low, the doping is insufficient, the modification effect is inadequate, and there are few surface functional groups, resulting in a low specific surface area and uneven metal loading. The phosphorus content in Comparative Example 2 is too high, which causes some pores to be blocked, the specific surface area to decrease, and excessive phosphorus may form inactive phosphates with the metal, reducing the number of active sites.

[0049] By comparing Example 2, Comparative Example 3, and Comparative Example 4, it can be seen that: The phosphorus-doped activated carbon (P-AC) support provides a sufficiently large specific surface area and abundant anchoring sites for the active component (MnFe2O4), enabling it to achieve high dispersion and uniform loading. It exists in the form of small nanoparticles. The reasonable loading amount maximizes the number of active sites without severely clogging the support pores, providing a sufficient interface for the catalytic reaction. The moderate loading amount avoids particle agglomeration and sintering at high temperatures, resulting in good stability. At the same time, the interaction between MnFe2O4 and the P-AC support is strongest at the optimal loading amount, and the active component is firmly anchored on the support surface, making it difficult to leach out in the reaction environment.

[0050] The low loading in Comparative Example 3 resulted in insufficient total active components in the system, although the specific surface area per unit mass of carrier was higher at 350 m² due to less pore blockage. 2 While the total number of active sites is low, resulting in minimal heavy metal leaching and a limited upper limit for catalytic activity, the low loading also has minimal impact on the support framework, leading to acceptable mechanical strength. Comparative Example 4, with its high loading, exhibits excessive metal salt precursor co-precipitation on the support surface, which easily leads to overgrowth and aggregation of MnFe2O4 nanoparticles, forming larger particles. These large particles severely clog the pores of the activated carbon, causing a sharp decrease in specific surface area to 280 m². 2 / g, particle agglomeration is more likely to sinter and deactivate during thermal aging, and the diffusion of reactants is hindered, resulting in the worst thermal stability; and an excessively thick load layer will weaken the mechanical support of the carrier itself, leading to a significant reduction in mechanical strength.

[0051] By comparing Example 2, Comparative Example 5, and Comparative Example 6, it can be seen that: CTAB molecules form micelles in solution, guiding the nucleation and growth of metal oxides (MnFe2O4), which helps to form more regular pore structures and smaller nanoparticles. Its long-chain alkyl structure can be adsorbed on the particle surface, preventing the aggregation of nanoparticles through steric hindrance, making it highly dispersed on the carrier surface. It has both template and dispersing effects, playing a key role as a soft template and dispersant in the coprecipitation process. In Example 2, the appropriate amount of CTAB effectively formed a micelle template, guiding the formation of small and uniform MnFe2O4 particles and highly dispersing them on the surface and within the pores of the P-AC support. This not only created a rich mesoporous structure but also provided a large specific surface area (412 m²). 2 The amount of CTAB ( / g) also ensures sufficient exposure of active sites, and the appropriate amount of CTAB avoids the damage to the structure caused by a large amount of residual carbon during subsequent calcination. Therefore, the mechanical strength is up to 19.5 N / cm. In contrast, the amount of CTAB in Comparative Example 5 was insufficient, resulting in weak template and dispersion effects. Consequently, MnFe2O4 particles tended to agglomerate during the formation process, forming larger and more uneven particles that blocked some of the pores of the carrier, reducing the specific surface area. At the same time, the agglomeration of larger particles weakened the uniformity of the carrier structure, leading to a decrease in mechanical strength. In Comparative Example 6, the amount of CTAB used was seriously excessive. Excessive CTAB micelles would make the system too complex, which would destroy the formation of an ordered structure. More importantly, in the subsequent calcination process, a large amount of residual CTAB carbonized to form amorphous carbon residues, which would severely block the micropores and mesopores of the catalyst, resulting in a sharp decrease in specific surface area. These carbon residues could also destroy the integrity of the catalyst skeleton, encapsulate some active sites, and lead to a significant reduction in mechanical strength and catalytic activity.

[0052] By comparing Example 2, Comparative Example 7, and Comparative Example 8, it can be seen that: Molybdenum exists as a co-catalyst in the system, MoO x Lewis acid sites can be introduced onto the catalyst surface, preferentially adsorbing and activating NH3 molecules, greatly increasing the rate of the SCR reaction. 6+ Having variable valence states, it can act as a "bridge" for electron transfer, promoting Fe 2+ / Fe 3+ and Mn 3+ / Mn 4+ During redox cycles, molybdenum accelerates the oxidation of NO and subsequent reactions. It can also preferentially combine with SO2 in flue gas to form relatively stable molybdates, thereby protecting the main active components (Mn, Fe) from sulfation and reducing catalyst poisoning.

[0053] In the proportions of Example 2, molybdenum species were successfully grafted onto the surfaces of MnFe2O4 and P-AC in a highly dispersed monolayer or submonolayer form, maximizing beneficial acidic sites and optimizing electron conduction channels without significantly blocking the inherent pore structure of the support. Therefore, the specific surface area remained maximized, resulting in the highest catalytic activity and thermal stability. Appropriate amounts of MoO2... x The coating layer acts like a protective layer for the active components, effectively inhibiting the dissolution of Mn and Fe.

[0054] In Comparative Example 7, excess ammonium molybdate precursor readily forms crystalline MoO3 particles or multilayered aggregates of MoO3 after calcination. x The larger particles physically block some of the pores of the carrier, resulting in a decrease in specific surface area. The aggregated MoO3 itself has poor low-temperature SCR activity, but it will cover some of the active sites of MnFe2O4. Although its sulfur resistance is further enhanced, too much molybdenum covering will hinder the contact between the reactants and the main active center, which will result in its optimal activity and thermal stability being lower than that of Example 2. At the same time, MoO3 has a certain degree of volatility in humid environments, and excessive loading will affect long-term stability. The amount of molybdenum species in Comparative Example 8 was insufficient to form an effective and continuous modification layer on the catalyst surface, resulting in limited enhancement of surface acidic sites and insufficient regulation of electronic structure. More importantly, its sulfur resistance protection was inadequate. During thermal aging or sulfur resistance testing, some MnFe2O4 active centers were directly exposed to the sulfur-containing atmosphere, undergoing sulfation poisoning, such as the formation of MnSO4 and Fe2(SO4)3, leading to a decrease in activity. This is the main reason for its relatively poor thermal stability. Due to insufficient protection, its metal leaching amount was also higher than that in Example 2.

[0055] 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 low-temperature de-NOx catalyst with the aid of an activity aid, characterized by, Comprising the following steps: S1. Phosphorus-doped modified activated carbon: The activated carbon is washed with deionized water until neutral, and then dried in an oven for standby; ammonium dihydrogen phosphate is dissolved in deionized water to prepare an impregnation solution; The pretreated activated carbon is put into the impregnation solution, stirred at 40-50℃, and then filtered. After drying, the filter cake is transferred into a muffle furnace, heated to 500℃ under N2 atmosphere, and calcined for 4-5h; Natural cooling to room temperature, to obtain phosphorus-doped activated carbon, P-AC, sealed storage; S2. Co-precipitation loading manganese ferrite: In the reaction kettle, FeSO4·7H2O and MnSO4·H2O are dissolved in ethylene glycol with vigorous stirring; cetyltrimethylammonium bromide is added and continues to stir until completely dissolved; P-AC is slowly added to the above solution, and ultrasonic treatment is performed to fully disperse; NaOH solution is slowly added to adjust the pH value of the system to 10-11, to obtain a mixed slurry; The reaction kettle is placed in an oven at 200℃-220℃ for 24h; after natural cooling, suction filtration is performed, and deionized water and ethanol are repeatedly washed until the filtrate is neutral. After vacuum drying of the filter cake, P-AC / MnFe2O4 precursor is obtained; S3. Ammonium molybdate graft modification: Ammonium molybdate was dissolved in deionized water, and the P-AC / MnFe2O4 precursor was added, and the mixture was stirred and impregnated at 50-60°C for 6-8h; after filtration, the sample was dried at high temperature, and the dried sample was calcined in an air atmosphere at 400°C for 4h; after natural cooling, the final catalyst product P-AC / MnFe2O4 / MoO x was obtained.

2. The method for preparing a low-temperature de-NOx catalyst with the aid of an activity aid according to claim 1, characterized by, In S1, the mass ratio of pretreated activated carbon to ammonium dihydrogen phosphate is 5-7:

1.

3. The method for preparing a low-temperature de-NOx catalyst with the aid of an activity aid according to claim 1, characterized by, In S2, the mass ratio of P-AC, FeSO4·7H2O, MnSO4·H2O, and cetyltrimethylammonium bromide is 1:1-1.2:0.304-0.365:1.2-1.

8.

4. The method for preparing a low-temperature de-NOx catalyst with the aid of an activity aid according to claim 1, characterized by, In S2, the molar ratio of Mn to Fe is 1:

2.

5. The method for preparing a low-temperature denitration catalyst with the assistance of an active additive according to claim 1, characterized in that, In S3, the mass ratio of P-AC / MnFe2O4 to ammonium molybdate is 9-11:

1.

6. The low-temperature de-NOx catalyst produced by the method according to any one of claims 1 to 5, characterized by, The catalytic temperature window of the low-temperature denitration catalyst is 150-350°C, the optimal active interval is 200-300°C, and the NO x The conversion rate can be stably maintained at >95%.

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