A meerschaum-tiO2 composite carrier loaded manganese cerium medium-low temperature denitration catalyst and a preparation method and application thereof

Abstract

The application belongs to the technical field of preparation of denitration catalysts, and discloses a sepiolite-TiO2 composite carrier loaded manganese cerium medium-low temperature denitration catalyst and a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing sepiolite with nitric acid, then heating and stirring to react, and then performing suction filtration and washing; after the treated sepiolite is dried by filtration, the sepiolite is subjected to drying and sieving to obtain nitric acid acidified sepiolite; (2) mixing the nitric acid acidified sepiolite and TiO2, then adding a manganese source precursor solution into the acidified sepiolite-TiO2, and then performing immersion and stirring; potassium permanganate solution is added dropwise into the solution, and then cerium nitrate solution is added; after stirring, suction filtration is performed; the obtained filter cake is dried, ground, and sieved, and then calcination is performed to obtain the catalyst. The sepiolite is acidized and compounded with TiO2, the advantages of the two carrier materials are complemented, the obtained catalyst has good denitration efficiency, and the production cost can be significantly reduced.

Description

Technical Field

[0001] This invention belongs to the field of denitrification catalyst preparation technology, specifically relating to a medium- and low-temperature denitrification catalyst for manganese and cerium supported on a sepiolite-TiO2 composite support, its preparation method, and its application. Background Technology

[0002] Nitrogen oxides are major air pollutants, closely related to environmental problems such as smog, acid rain, and photochemical smog. Selective catalytic reduction (SCR) technology is currently the most widely used method for treating nitrogen oxides. x The core of the treatment method lies in using NH3 as a reducing agent through catalysis to reduce NO. x It is reduced to harmless N2 and H2O.

[0003] Traditional V2O5-WO3(MoO3) / TiO2 catalysts generally require denitrification temperatures above 350℃. However, in actual industrial scenarios such as cement and refining where lower processing temperatures are required, flue gas temperatures are often below 250℃. Furthermore, industrial waste gases contain large amounts of SO2, alkali metals, and other elements that poison catalysts. Therefore, the catalytic device must be placed after the desulfurization and dust removal device. Consequently, there is an urgent need to develop economical, efficient, and environmentally friendly medium- and low-temperature denitrification catalysts for use in practical industrial scenarios.

[0004] TiO2 possesses advantages such as high thermal stability, high mechanical strength, and good sulfur resistance, making it suitable as a support for various active components. Furthermore, TiO2 raw materials are environmentally friendly, making it the most commonly used support material for denitrification catalysts. However, the denitrification activity of TiO2-supported catalysts decreases significantly at low temperatures. This is partly due to the low surface area of ​​TiO2 limiting the mass transfer level at low temperatures, and partly because TiO2 particles are prone to agglomeration during synthesis due to their small size, weakening the interfacial effect with the active components. Compared to titanium dioxide, sepiolite, as a natural nanofiber-rich magnesium silicate mineral, is abundant, inexpensive, and readily available, possessing a large specific surface area and numerous acidic sites on its surface, thus exhibiting certain catalytic activity. However, sepiolite has a high silicon content; using sepiolite alone as a catalyst support cannot meet the silicon content requirements of the cement industry's denitrification standards, thus hindering its industrial application.

[0005] In 2019, Chinese patent application CN109603922A disclosed a composite titanium dioxide for use as a high specific surface area denitrification catalyst and its preparation method. The composite titanium dioxide is composed of titanium dioxide, activated diatomaceous earth, sepiolite powder, zirconium oxide, ammonium paratungstate, cerium oxide, bridged silsesquioxane, and a superdispersant. This design solves the problems of poor plasticity, low specific surface area, and difficulty in achieving a denitrification efficiency exceeding 94% associated with traditional titanium dioxide carriers. The preparation method involves mixing titanium dioxide, activated diatomaceous earth, zirconium oxide, ammonium paratungstate, cerium oxide, bridged silsesquioxane (KH560-660 and KH560-540), and demineralized water to form a suspension. The suspension is then placed in a ball mill, and a superdispersant (terminated mercaptoacetamide polymethyl acrylate) is added before wet ball milling. After milling, the mixture is washed and dried. The dried composite powder is then thoroughly mixed with sepiolite powder in a mixer to obtain the composite titanium dioxide. Compared to traditional titanium dioxide, its extrusion speed, specific surface area, denitrification efficiency, and plasticity index are significantly improved. Its innovation lies in the particle size distribution design of activated diatomaceous earth and activated sepiolite powder, which improves catalyst plasticity; the use of bridging silsesquioxane as a surfactant to enhance powder viscosity; and the formation of numerous pores within the catalyst after calcination of the bridging agent, thereby increasing the catalyst's specific surface area. However, directly adding sepiolite powder after ball milling without participating in the preceding wet ball milling and dispersion processes makes it difficult to ensure uniform dispersion within the titanium dioxide matrix, easily leading to uneven catalyst structure and affecting the specific surface area and active site distribution. Furthermore, the active components such as ammonium paratungstate and molybdenum oxide are only mixed through low-temperature stirring without calcination, making it difficult for the active components to be firmly loaded onto the carrier surface. This can lead to migration and agglomeration during subsequent use, reducing the long-term stability of catalytic efficiency.

[0006] Chinese patent application CN120022921A, filed in 2025, discloses a nitrogen-doped porous carbon-TiO2 composite support, its preparation method, and a low-temperature denitration catalyst. The nitrogen-doped porous carbon is a two-dimensional carbon sheet layered structure with bilevel pores; the TiO2 is nano-titanium dioxide (particle size 3-8 nm), uniformly dispersed on the surface of the two-dimensional carbon sheet layered structure, accounting for 75-90 wt% of the total weight. The specific surface area of ​​this composite support can reach 180-400 m². 2 / g. Its preparation method is as follows: (1) Synthesis of nitrogen-doped porous carbon ① Raw material mixing: carbon source is potassium citrate / sodium or potassium sorbate (alkali metal salt), nitrogen source is polyamine compound (diphenylcarbazide, phenylenediamine, melamine, etc.), crosslinking agent is aniline (0.5-1.0 mL alkali metal salt), mass ratio is alkali metal salt: polyamine compound = 2-5: 1; ② Heterogeneous reaction: react at 160-200℃ for 6-12h to form prepolymer; ③ Segmented heat treatment: first stage 250-300℃ / 2-4h (pre-carbonization), second stage 650-800℃ / 2-3h (alkali metal in-situ pore formation); ④ Post-treatment: wash away metal residue with dilute hydrochloric acid, wash with water until neutral, and then vacuum dry at 80℃ for 12h; (2) In-situ loading of nano-TiO2 ① Mix nitrogen-doped porous carbon and solid titanium salt (titanium sulfate, titanium oxalate, etc.) ② Heat treatment: 400-600℃ / 2-5h inert atmosphere. Its innovation lies in the fact that alkali metal salts generate mesopores, while polyamine compounds generate micropores; this dual-pore system can achieve a specific surface area of ​​180-400 m². 2 / g; Nitrogen doping can improve the reducibility of carbon layers; Nano-TiO2 dispersed on the surface of two-dimensional carbon sheet layered structure can solve the problems of easy agglomeration and low specific surface area of ​​nano-TiO2; High specific surface area and hierarchical channels can enhance the adsorption and mass transfer of reactants, and nitrogen-doped carbon enhances the reduction ability of active components. However, solid titanium salts (such as titanium sulfate) release SO3 gas through thermal decomposition, which is highly corrosive; Nitrogen-containing groups are hydrophilic, which may aggravate the adsorption of H2O in flue gas; Two-stage heat treatment and thermal decomposition of titanium salts consume too much energy, resulting in a sharp increase in production costs; Polyamine compounds (such as diphenylcarbazide) are expensive, and aniline is highly toxic. Summary of the Invention

[0007] This invention aims to provide a low-to-medium temperature denitration catalyst for manganese and cerium supported on a sepiolite-TiO2 composite support, along with its preparation method and application. Its core objective is to overcome the limitations of traditional single-support methods. By combining acidified sepiolite with TiO2 in a specific ratio, the advantages of the two support materials are complemented, significantly reducing production costs while ensuring good denitration efficiency. Furthermore, this composite support design is dedicated to comprehensively improving the catalyst's overall performance and application value, enhancing its environmental friendliness, economy, safety, and industrial applicability. This provides an innovative solution for overcoming the bottlenecks of traditional vanadium-titanium systems.

[0008] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a low-to-medium temperature denitration catalyst supported on a sepiolite-TiO2 composite support for manganese and cerium includes the following steps:

[0010] (1) Mix natural sepiolite with 0.2-0.4 mol / L nitric acid, heat and stir in an oil bath, and after the reaction is complete, perform a vacuum filtration operation and wash with water multiple times. After the sepiolite is dried by filtration, place it in a blower dryer at 80-110℃ for 10-12 h, and then sieve it through a 100-300 mesh screen to obtain nitric acid-acidified sepiolite, which is then sealed for later use.

[0011] (2) Weigh and mix nitric acid-acidified sepiolite and TiO2, mix manganese source with water to obtain manganese source precursor solution, add to acidified sepiolite-TiO2, impregnate and stir at room temperature, then add potassium permanganate solution dropwise to the solution, add cerium nitrate solution after the dropwise addition is complete, continue stirring at room temperature for 12-24h, filter and wash until the filtrate is colorless, dry the filter cake at 80-110℃ for 10-12h, grind and sieve to 20-60 mesh particles, calcine in muffle furnace to obtain Ce-Mn / TiO2-SEP catalyst.

[0012] Preferably, in step (1), the temperature of the oil bath is 60-90℃ and the stirring time is 8-10h.

[0013] Preferably, in step (1), water is used to wash repeatedly until the pH of the washing solution is neutral.

[0014] Preferably, the manganese source in step (2) is manganese nitrate.

[0015] Preferably, the nitric acid-acidified sepiolite in step (2) is 5-25 wt%, and the TiO2 is 75-95 wt%.

[0016] Preferably, in step (2), the soaking and stirring are carried out at room temperature for 12-24 hours.

[0017] Preferably, the potassium permanganate solution in step (2) contains Mn(NO3)2, and the molar ratio of Mn(NO3)2 to KMnO4 is 3:2.

[0018] Preferably, in step (2), the furnace is calcined at 300-500°C for 2-3 hours.

[0019] The present invention also provides a medium- and low-temperature denitrification catalyst for manganese and cerium supported on a sepiolite-TiO2 composite support, wherein the Ce:Mn ratio of the Ce-Mn / TiO2-SEP catalyst is (1-5):(1-4).

[0020] Compared with the prior art, the present invention has the following innovative points and technical advantages:

[0021] 1. The composite design of the carrier achieves "complementary advantages" and solves the inherent limitations of a single carrier.

[0022] Existing technologies have obvious carrier defects: traditional single TiO2 is costly and lacks Brønsted acid sites; single sepiolite has poor thermal stability and insufficient dispersion of active metals; in the existing patent application CN109603922A, sepiolite is only "directly dry-mixed after ball milling", which easily leads to uneven dispersion and structural imbalance; the existing patent application CN120022921A relies on nitrogen-doped porous carbon-TiO2, which requires a complex pore-forming process.

[0023] This invention combines 5-25wt% nitric acid-acidified sepiolite with 75-95wt% TiO2, which retains the high thermal stability and good dispersibility of TiO2 (avoiding the problem of poor thermal stability of sepiolite), while reducing raw material costs by replacing part of TiO2 with inexpensive natural sepiolite. At the same time, it utilizes the abundant Brønsted acid sites provided by acidified sepiolite to compensate for the deficiency of TiO2, which is mainly composed of Lewis acid sites and has insufficient acidity, thus achieving synergistic optimization of "cost-performance-stability".

[0024] 2. The finer pretreatment of sepiolite significantly improves the interfacial properties and dispersibility of the carrier.

[0025] Existing technologies treat sepiolite poorly: Existing patent application CN109603922A does not perform pretreatment such as acidification on sepiolite, but directly adds it dry, which makes it difficult to eliminate impurities and cannot enhance its surface activity; traditional sepiolite has weak surface acidity and is easy to agglomerate when untreated.

[0026] This invention employs a complete pretreatment process of "nitric acid acidification - oil bath heating and stirring - neutral washing - drying and sieving" (0.2-0.4 mol / L nitric acid, 60-90℃ oil bath stirring for 8-10 hours, washing until pH neutral and then sieving through 100-300 mesh). This process not only removes impurities from sepiolite and clears its nanofiber pores, but also significantly increases the number of Brønsted acid sites on the surface. At the same time, when the pretreated sepiolite is mixed with TiO2, agglomeration is avoided, ensuring uniform dispersion in the matrix and providing a better interfacial environment for subsequent loading of active components.

[0027] 3. The active component loading process is more scientific, improving loading strength and long-term stability.

[0028] The existing technology for loading active components has a key defect: In the existing patent application CN109603922A, active components such as ammonium paratungstate are only "mixed by low-temperature stirring" without calcination, which makes it difficult for the active components to be firmly loaded and easy to migrate and agglomerate; traditional loading processes often ignore the control of the proportion of active components.

[0029] This invention employs a "stepwise impregnation-precise proportioning-high-temperature calcination" loading process: first, manganese nitrate is used as the manganese source and potassium permanganate as the oxidant (Mn(NO3)2 to KMnO4 molar ratio 3:2). Cerium nitrate is then introduced dropwise, and the active components are stirred at room temperature for 12-24 hours to ensure uniform adsorption. Finally, strong interaction between Mn, Ce and the support is achieved through calcination at 300-500℃ for 2-3 hours. At the same time, the Ce:Mn ratio is strictly controlled at (1-5):(1-4), which not only avoids the migration and aggregation of active components but also optimizes the distribution of active sites, significantly improving the long-term stability of the catalyst.

[0030] 4. Significantly improved economic efficiency and environmental friendliness, lowering the threshold for industrial application.

[0031] Existing technologies suffer from "high cost, high energy consumption, and high pollution": Existing patent application CN120022921A uses expensive polyamine compounds (such as diphenylcarbazide) and toxic aniline (crosslinking agent), and requires two stages of high-temperature heat treatment (250-300℃ pre-carbonization and 650-800℃ pore formation), resulting in extremely high energy consumption. At the same time, the pyrolysis of solid titanium salts produces SO3, a highly corrosive gas.

[0032] This invention optimizes the process through three main means: ① replacing part of TiO2 with inexpensive natural sepiolite to reduce raw material costs; ② eliminating toxic and harmful raw materials (such as aniline and polyamine compounds) to avoid environmental pollution; ③ using a calcination temperature of only 300-500℃, which is far lower than the high-temperature process of the existing technology patent application CN120022921A, reducing energy consumption by more than 40% and producing no corrosive gases, thus balancing economic efficiency and environmental friendliness, and better meeting the needs of large-scale industrial applications.

[0033] 5. Synergistic enhancement of acidic sites, overcoming the bottleneck of denitrification activity at medium and low temperatures.

[0034] In the existing technology, the insufficient acidity of the carrier restricts the low-temperature activity: Traditional TiO2 is mainly composed of Lewis acid sites, with few Brønsted acid sites and weak strength, which makes it difficult to meet the adsorption and activation requirements of reactants at medium and low temperatures (<250℃); Although the existing technology patent application CN109603922A introduces sepiolite, it does not enhance the acidity through acidification, resulting in poor synergistic effect.

[0035] This invention significantly enhances the number and diversity of total acidic sites on the support through the synergistic effect of "TiO2 Lewis acid sites + acidified sepiolite Brønsted acid sites": the abundant Brønsted acid sites provided by acidified sepiolite can efficiently adsorb NH3, while the Lewis acid sites of TiO2 are beneficial for NO adsorption. x The activation of NH3-NO2, and the two work synergistically to promote the activation of NH3-NO2. x"The reaction efficiency at the active site fundamentally breaks through the bottleneck of low-temperature denitrification activity caused by insufficient acidity of traditional carriers, making it more suitable for low-temperature industrial flue gas scenarios such as cement and refining." Attached Figure Description

[0036] Figure 1 This is a flowchart illustrating the preparation process of the Ce-Mn / TiO2-SEP catalyst.

[0037] Figure 2 Figure 1 shows the effect of different acidified sepiolite doping amounts on the NH3-SCR performance of Mn / TiO2-SEP(x) catalyst;

[0038] Figure 3 Figure 1 shows the effect of different Ce loading on the NH3-SCR performance of Ce(x)-Mn / TiO2-SEP catalyst;

[0039] Figure 4 Here are SEM images of the catalyst, where, Figure 4 (a) and Figure 4 (b) SEM images (20K, 5K) of Mn / TiO2-20%SEP. Figure 4 (c) and Figure 4 (d) SEM images (20K, 5K) of Ce-Mn / TiO2-20%SEP;

[0040] Figure 5 The N2 adsorption-desorption curves and pore size distribution of the catalyst are shown.

[0041] Figure 6 XRD pattern of Mn / TiO2-SEP(x) catalyst;

[0042] Figure 7 The image shows the XRD pattern of the Ce(x)-Mn / TiO2-SEP catalyst. Detailed Implementation

[0043] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0044] For experiments not specifically described in the examples, follow standard experimental procedures in the field. Reagents or instruments not specifying manufacturers are commercially available products.

[0045] The abbreviations and key terms involved in this invention are defined as follows:

[0046] SCR: Selective Catalytic Reduction Technology;

[0047] NO x Nitrogen oxides;

[0048] SEP: nitric acid acidified sepiolite;

[0049] Ce-Mn / TiO2-SEP: A medium- and low-temperature denitration catalyst supported on TiO2 and nitric acid-acidified sepiolite;

[0050] TiO2: P25 anatase titanium dioxide

[0051] like Figure 1 As shown in this embodiment of the invention, a method for preparing a low-to-medium temperature denitration catalyst for manganese cerium oxide supported on an acidified sepiolite-TiO2 composite support includes the following steps:

[0052] (1) Mix natural sepiolite with 0.2-0.4 mol / L nitric acid at a solid-liquid ratio of 1:15, heat and stir in an oil bath at 60-90℃ for 8-10 hours. After the reaction is complete, perform a vacuum filtration operation and wash with pure water several times until the pH of the washing liquid is neutral. After the sepiolite is filtered dry, place it in a blower dryer at 80-110℃ for 10-12 hours, and then sieve it through a 100-300 mesh sieve to obtain nitric acid-acidified sepiolite, which is then sealed for later use.

[0053] (2) Weigh and mix 5-25 wt% nitric acid-acidified sepiolite and 75-95 wt% TiO2 (P25), mix manganese nitrate with deionized water to obtain a manganese source precursor solution, add it to the acidified sepiolite-TiO2, and impregnate and stir at room temperature for 12-24 h. Then slowly add potassium permanganate solution dropwise to the solution, where n(Mn(NO3)2) / n(KMnO4)=3:2. After the addition is complete, add cerium nitrate solution and continue stirring at room temperature for 12-24 h. After filtration and washing until the filtrate is colorless, the filter cake is dried at 80-110℃ for 10-12 h, ground and sieved to 20-60 mesh particles, and calcined in a muffle furnace at 300-500℃ for 2-3 h to obtain the Ce-Mn / TiO2-SEP catalyst. The mass fraction of Mn element in the manganese nitrate and potassium permanganate of the Ce-Mn / TiO2-SEP catalyst is 4-10 wt%.

[0054] Technical principle of the invention:

[0055] I. Mechanism of Action of Each Raw Material

[0056] 1. Natural sepiolite (SEP)

[0057] Basic carrier framework: Natural sepiolite has a multi-level pore structure composed of micropores and mesopores and a high specific surface area (approximately 150-200 m² in its original state). 2 / g), which provides loading sites for active components; however, its pores are easily blocked by impurities (such as carbonates and metal oxides), and need to be activated by acidification modification.

[0058] Synergistic adsorption: The porous structure retained after modification can enhance NO adsorption. X The adsorption capacity of NH3 prolongs the residence time of reactants on the catalyst surface, thereby increasing the reaction probability.

[0059] 2. Nitric acid (0.2-0.4 mol / L)

[0060] Modification and purification: Impurities in the sepiolite pores are removed by acid hydrolysis (e.g., CaCO3+2HNO3=Ca(NO3)2+CO2↑+H2O) to prevent impurities from occupying active sites; at the same time, the pore walls are etched to increase the specific surface area and expand the pore size, creating conditions for the subsequent penetration of active components.

[0061] Surface property regulation: Introducing hydroxyl groups (-OH) into the surface of sepiolite enhances the interaction with TiO2 and manganese cerium active components, and reduces the shedding of active components.

[0062] 3. Titanium dioxide (TiO2)

[0063] Synergistic effect of composite support: TiO2 exhibits excellent chemical stability (acid resistance, high temperature resistance), forming a "porous-stable" composite system with sepiolite. Sepiolite provides specific surface area and abundant pore structure, which is conducive to the high dispersion of active components. Its fibrous structure can effectively inhibit the phase transformation of TiO2 after high-temperature calcination, allowing the composite support to maintain a high specific surface area after heat treatment. TiO2 has excellent chemical stability and mechanical strength, providing an ideal support surface for active components, while O2 activation is achieved through the redox cycle of active components, enhancing redox capabilities.

[0064] Sintering inhibition: The lattice oxygen on the TiO2 surface can prevent the agglomeration of manganese cerium oxide particles and maintain the nanoscale dispersion of active components (particle size 2-5nm).

[0065] 4. Manganese source (manganese nitrate) and potassium permanganate (KMnO4)

[0066] Active component supply: Manganese nitrate provides Mn 2+ Potassium permanganate provides Mn 7+ The two undergo a redox reaction in a 3:2 molar ratio (3Mn). 2+ +2MnO4 - +2H₂O=5MnO₂↓+4H + ), generating highly active MnO2), forming Mn 4+ / Mn 3+ The redox loop is NO. x Reduction provides an electron transfer pathway (NO+Mn) 4+ →NO2+Mn3+ ).

[0067] Active site regulation: This ratio can precisely control the Mn valence state distribution (Mn 4+ (60%-70%), avoid Mn 7+ Excessive amounts will react further with the main product MnO2, potentially forming unstable or low-activity manganese oxides, which in turn leads to the non-selective oxidation of NH3, generating byproducts N2O and NO; Mn 2+ Excessive amounts will remain in the product, reducing catalytic activity and thus indirectly affecting the selectivity and activity of the catalyst.

[0068] 5. Cerium nitrate (Ce(NO3)3)

[0069] Synergistic catalysis: After the introduction of cerium components, the formed CeO2 exhibits excellent oxygen storage and release capacity and abundant surface oxygen vacancies. 3+ / Ce 4+ Redox reactions can efficiently activate O2, converting it into highly active surface-adsorbed oxygen species. This provides abundant active oxygen species for adjacent Mn active sites, maintaining their high oxidation state and thus enhancing the SCR reaction rate at medium and low temperatures. Simultaneously, CeO2 can form surface nitrate intermediates with NO2, promoting NO regeneration. x reduction.

[0070] Anti-poisoning protection: When SO2 is present, the active component cerium oxide can preferentially react with SO2 to generate stable Ce2(SO4)3, avoiding SO2 from combining with Mn active sites to form inactive MnSO4, thus improving the catalyst's anti-sulfur performance.

[0071] The raw material and energy costs of TiO2 are significantly higher than those of natural mineral supports, directly impacting the overall economics of the catalyst, especially in large-scale industrial applications. Furthermore, TiO2 (anatase) is primarily composed of Lewis acid sites, with a limited number and weak strength of Brønsted acid sites. Sepiolite, on the other hand, has relatively limited thermal stability, and its surface is not conducive to the highly uniform dispersion and strong interaction of active metal components. By combining the two supports and partially replacing TiO2 with inexpensive acidified sepiolite, the raw material cost of the catalyst can be effectively reduced, improving its overall economics. Simultaneously, the acidified sepiolite provides abundant Brønsted acid sites, effectively compensating for the insufficient acidity of the TiO2 surface. The combination of the two generates new acidic sites, jointly maintaining the structural stability of the support and the high dispersion of the active components. Ultimately, a support with superior overall performance and greater industrial applicability is obtained, with the potential to improve the catalyst's adsorption performance, low-to-medium temperature denitration performance, and stability.

[0072] II. The Necessity and Importance of Optimizing Raw Material Usage

[0073] 1. Nitric acid concentration (0.2-0.4 mol / L)

[0074] Necessity: When the concentration is <0.2mol / L, the acid hydrolysis reaction is insufficient, the impurity removal rate is low, the pore expansion effect is poor, the specific surface area is not increased enough, and the loading of subsequent active components is reduced; when the concentration is >0.4mol / L, excessive etching leads to the collapse of the sepiolite skeleton, the destruction of the pore structure, the specific surface area decreases, and the carrier's carrying capacity is lost.

[0075] Importance: This concentration range achieves a balance between "impurity removal, pore expansion, and structure preservation," laying the foundation for uniform loading of active components.

[0076] 2. Manganese source molar ratio (Mn(NO3)2:KMnO4=3:2)

[0077] Necessity: When the ratio deviates, the valence distribution of Mn becomes unbalanced—for example, at a ratio of 3:1, Mn... 2+ Excessive Mn 4+ When the proportion is less than 40%, the activity decreases by 40%; at a ratio of 2:3, Mn 7+ With excessive amounts, the NH3 oxidation rate increases to 25%, while the N2 selectivity decreases to 80%.

[0078] Importance: This ratio precisely generates highly active Mn. 4+ At the same time, the side reaction of NH3 oxidation is controlled, and the N2 selectivity is maintained at over 95%.

[0079] To make the present invention more fully disclosed, more specific embodiments are described below.

[0080] Example 1

[0081] A method for preparing a low-to-medium temperature denitration catalyst for manganese cerium oxide supported on an acidified sepiolite-TiO2 composite support includes the following steps:

[0082] (1) Natural sepiolite was mixed with 0.3 mol / L nitric acid at a solid-liquid ratio of 1:15 and heated and stirred in an oil bath at 80°C for 8 hours. After the reaction was completed, the mixture was filtered and washed repeatedly with pure water until the pH of the washing liquid was 7. The sepiolite was then dried in a forced-air dryer at 110°C for 10 hours and then sieved through a 300-mesh sieve to obtain nitric acid-acidified sepiolite, which was then sealed for later use.

[0083] (2) 20 wt% nitric acid-acidified sepiolite and 80 wt% TiO2 (P25) were weighed and mixed. Manganese nitrate was mixed with deionized water to obtain a manganese source precursor solution, which was added to the acidified sepiolite-TiO2 and impregnated and stirred at room temperature for 21 h. Subsequently, potassium permanganate solution was slowly added dropwise to the solution, where n(Mn(NO3)2) / n(KMnO4)=3:2. After the addition was completed, cerium nitrate solution was added, and stirring was continued at room temperature for 24 h. After filtration and washing until the filtrate was colorless, the filter cake was dried at 110℃ for 10 h, ground and sieved to 50 mesh particles, and calcined in a muffle furnace at 350℃ for 3 h to obtain the Ce-Mn / TiO2-SEP catalyst. The mass fraction of Mn element in the manganese nitrate and potassium permanganate in the Ce-Mn / TiO2-SEP catalyst was 8 wt%.

[0084] Single-factor experiments for screening key process parameters:

[0085] Single-factor experiment 1: Effect of different acidified sepiolite doping amounts on the NH3-SCR performance of Mn / TiO2-SEP(x) catalyst

[0086] With other process parameters fixed as in Example 1, the amount of nitric acid-acidified sepiolite was changed to 0 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, and 25 wt%, respectively. Cerium nitrate solution was not added. A series of Ce-unloaded Mn / TiO2-SEP(x) catalysts were prepared. The denitrification activity of the catalysts was tested. During the test, each temperature point was held for 20 minutes within the temperature range of 100-300℃. The NO concentration was measured using a flue gas analyzer at the remaining holding time of 10, 5, and 1 minute. The average of the three test results was taken as the final measurement result. The error of the measured result was within 1%. The results are as follows: Figure 2 As shown.

[0087] from Figure 2 As can be seen, the optimal doping content of acidified sepiolite is 20%, which not only meets the requirement of the denitrification industry for silicon content to be below 5.5%, but also reduces raw material costs while ensuring that the denitrification efficiency at medium and low temperatures is not significantly reduced.

[0088] Single-factor experiment 2: Effect of different Ce loading on the NH3-SCR performance of Ce(x)-Mn / TiO2-SEP catalyst

[0089] With other process parameters fixed as in Example 1, only the Ce:Mn ratio was changed to 0:1, 1:4, 1:2, 3:4, 1:1, and 5:4 to prepare different Ce-Mn / TiO2-SEP catalysts. The denitrification activity of the catalysts was tested. During the test, each temperature point was held for 20 minutes within the 100-300℃ temperature range. The NO concentration was measured using a flue gas analyzer at the remaining holding time of 10, 5, and 1 minutes, and the average of the three test results was taken as the final measurement result. The error of the measured result was within 1%. The results are as follows: Figure 3 As shown.

[0090] from Figure 3 As can be seen from the denitrification performance test, the denitrification efficiency is best when the cerium-manganese ratio is 1:1, and the denitrification efficiency can reach more than 90% in the medium temperature range of 175-300℃.

[0091] Single-factor experiment 3: Effect of different nitric acid concentrations in step (1) on the structure of acidified sepiolite support and the subsequent NO conversion rate of the catalyst.

[0092] With other process parameters fixed as in Example 1, only the nitric acid concentration in step (1) was changed. The variable levels (mol / L) were 0.1, 0.2, 0.3, 0.4, and 0.5. Other fixed parameters were: the acidified sepiolite doping amount was 20%, and the Ce:Mn ratio was 1:1. Different Ce-Mn / TiO2-SEP catalysts were prepared and their denitrification activity was tested. During the test, the temperature was 150°C. The NO concentration was measured using a flue gas analyzer, and the average value of the three test results was taken as the final measurement result. The error of the measured result was within 1%. The NO conversion rate test results are shown in Table 1.

[0093]

[0094] Table 1 shows that when the concentration is less than 0.2 mol / L, the acidification of sepiolite by nitric acid is insufficient, only removing some impurities and failing to effectively etch the carrier pores, resulting in a small specific surface area and a low number of surface hydroxyl groups. Consequently, the subsequent adsorption sites for active components (Mn, Ce) are insufficient, with low loading and uneven distribution. x The amount of -CeO2 solid solution is small, resulting in low NO conversion.

[0095] When the concentration is greater than 0.4 mol / L, excessive nitric acid corrodes the silica-oxygen framework of sepiolite, causing the carrier pore structure to collapse and even amorphization. At the same time, excessive H⁺ will destroy the composite stability of sepiolite and TiO2, the carrier agglomeration phenomenon is obvious, the active components are prone to agglomerate into large particles, the active sites are covered, and the NO conversion rate decreases significantly.

[0096] In summary, the optimal nitric acid concentration range is 0.2-0.4 mol / L, and the optimal nitric acid concentration is 0.3 mol / L.

[0097] Single-factor experiment 4: Effect of different oil bath temperatures in step (1) on the efficiency of nitric acidification reaction and the subsequent NO conversion rate of the catalyst.

[0098] With other process parameters fixed as in Example 1, only the oil bath temperature in step (1) was changed. The variable levels (°C) were 50, 60, 70, 80, 90, and 100. Other fixed parameters were: nitric acid concentration 0.3 mol / L, acidified sepiolite doping amount 20%, and Ce:Mn ratio 1:1. Different Ce-Mn / TiO2-SEP catalysts were prepared and their denitrification activity was tested. During the test, the temperature was 150°C. The NO concentration was measured using a flue gas analyzer, and the average value of the three test results was taken as the final measurement result. The error of the measured result was within 1%. The NO conversion rate test results are shown in Table 2.

[0099]

[0100] As shown in Table 2, when the temperature is below 60℃, the reaction kinetics of nitric acid and sepiolite are low, the acidification reaction is incomplete, there are many impurities remaining on the carrier surface, and the pore unblocking effect is poor; the subsequent active components cannot be effectively loaded, and the NO conversion rate is low.

[0101] When the temperature is above 90℃, the evaporation rate of nitric acid increases, and the effective H+ in the system increases. + As the concentration decreases, the acidification efficiency decreases; at the same time, high temperature can cause local overreaction of sepiolite, damage the crystal structure, reduce the specific surface area of ​​the support, and may cause premature aggregation of TiO2 precursor, thus reducing catalyst activity.

[0102] In summary, the optimal oil bath temperature is 60-90℃, and the best oil bath temperature is 80℃.

[0103] Single-factor experiment 5: Effect of different stirring times in step (1) on acidification uniformity and subsequent catalyst NO conversion rate

[0104] With other process parameters fixed as in Example 1, only the stirring time in step (1) was changed. The variable levels (h) were 7, 8, 9, 10, and 11. Other fixed parameters were: nitric acid concentration 0.3 mol / L, acidified sepiolite doping amount 20%, and Ce:Mn ratio 1:1. Different Ce-Mn / TiO2-SEP catalysts were prepared and their denitrification activity was tested. During the test, the temperature was 150℃. The NO concentration was measured using a flue gas analyzer, and the average value of the three test results was taken as the final measurement result. The error of the measured result was within 1%. The NO conversion rate test results are shown in Table 3.

[0105]

[0106] As shown in Table 3, when the time is less than 8 hours, the contact between nitric acid and sepiolite is insufficient, the degree of local acidification varies greatly (some areas are not acidified, and some areas are slightly acidified), and the hydroxyl groups on the carrier surface are unevenly distributed; the subsequent loading of active components shows "hot spots" (local overload) and "cold spots" (local vacancy), the number of active sites is insufficient and the distribution is disordered, and the NO conversion rate is low.

[0107] When the stirring time exceeds 10 hours, excessive stirring causes the sepiolite fiber structure to break and the specific surface area of ​​the carrier to decrease. At the same time, prolonged stirring will exacerbate carrier aggregation, reduce the adsorption sites of active components, and decrease the NO conversion rate.

[0108] In summary, the optimal mixing time is 8-10 hours, and the best mixing time is 9 hours.

[0109] Single-factor experiment 6: Effect of different manganese loading on NO conversion rate of catalyst in step (2)

[0110] With other process parameters fixed as in Example 1, only the loading of manganese in step (2) was changed. The variable levels (wt%) were 2, 4, 6, 8, and 10. Other fixed parameters were: nitric acid concentration 0.3 mol / L, stirring time in step (1) 9 h, acidified sepiolite doping amount 20%, and Ce:Mn ratio 1:1. Different Ce-Mn / TiO2-SEP catalysts were prepared and their denitrification activity was tested. During the test, the test was conducted at 150°C. The NO concentration was measured using a flue gas analyzer, and the average value of the three test results was taken as the final measurement result. The error of the measured result was within 1%. The NO conversion rate test results are shown in Table 4.

[0111]

[0112] As shown in Table 4, when the manganese loading is less than 4 wt%, the number of active sites is insufficient, the NO oxidation and reduction reactions are hindered, and the NO conversion rate is low.

[0113] When the manganese loading is greater than 10 wt%, the adsorbed Mn 2+ Secondary aggregation occurs, resulting in increased particle size, a significant decrease in specific surface area, and a decrease in NO conversion rate.

[0114] In summary, the preferred manganese loading is 4-10 wt%, and the optimal manganese loading is 8 wt%.

[0115] Single-factor experiment 7: Effect of different calcination temperatures in step (2) on precursor decomposition and subsequent catalyst NO conversion rate

[0116] With other process parameters fixed as in Example 1, only the calcination temperature in step (2) was changed. The variable levels (°C) were 250, 300, 350, 400, 450, 500, and 550. Other fixed parameters were: nitric acid concentration 0.3 mol / L, stirring time in step (1) 9 h, manganese loading in step (2) 8 wt%, acidified sepiolite doping amount 20%, and Ce:Mn ratio 1:1. Different Ce-Mn / TiO2-SEP catalysts were prepared and their denitrification activity was tested. During the test, the temperature was 150°C. The NO concentration was measured using a flue gas analyzer, and the average value of the three test results was taken as the final measurement result. The error of the measured result was within 1%. The NO conversion rate test results are shown in Table 5.

[0117]

[0118] Table 5 shows that when the temperature is below 300℃, the precursors of manganese nitrate and cerium nitrate decompose incompletely, leaving residual nitrates covering the active sites; and highly active MnO cannot be formed. x -CeO2 solid solution, only a small amount of MnO is generated, and the NO conversion rate is low.

[0119] When the temperature exceeds 500℃, the active component undergoes sintering, the CeO2 lattice shrinks, and the Mn... 4+ / Mn 3+ The proportion decreased significantly (highly active Mn) 4+ (Reduction); at the same time, the support and active components interact strongly (generating Si-O-Mn bonds), the active sites are fixed and cannot participate in the denitrification reaction, and the NO conversion rate decreases.

[0120] In summary, the optimal calcination temperature is 300-500℃, and the best calcination temperature is 400℃.

[0121] Catalyst characterization tests:

[0122] 1. SEM characterization was performed on the Mn / TiO2-SEP catalyst with the optimal sepiolite doping content (i.e., 20 wt%) and the Ce-Mn / TiO2-SEP catalyst with the optimal cerium-manganese ratio (i.e., Ce:Mn=1:1).

[0123] Figure 4 (a) and Figure 4 (b) With other process parameters fixed as in Example 1, the amount of sepiolite acidified with nitric acid was 20 wt%, and no cerium nitrate solution was added, to prepare an unloaded Ce Mn / TiO2-SEP catalyst. Figure 4 (c) and Figure 4 (d) is the Ce-Mn / TiO2-SEP catalyst prepared in Example 1. The results are as follows: Figure 4 As shown, Figure 4 (a) and Figure 4 (b) Electron microscopy images (20K and 5K) of Mn / TiO2-20%SEP, respectively. Figure 4 (c) and Figure 4 (d) Electron microscopy images (20K, 5K) of Ce:Mn=1:1 / TiO2-20%SEP. Figure 4 (a) and Figure 4 (b) It can be seen that a large number of dispersed nanoscale active component particles are loaded on the surface of TiO2 and acidified sepiolite, and slight agglomeration occurs. The poor dispersion leads to pore blockage on the surface of the composite carrier. The fibrous sepiolite is embedded in the particles and is well combined with TiO2, with no significant phase separation. The whole material has no obvious cracks or large pores, indicating that the mechanical stability of the doped material is good. This shows that 20% sepiolite doping optimizes the carrier structure and forms a porous composite carrier with high specific surface area. Figure 4 (c) and Figure 4 (d) It can be seen that the surface of the carrier is covered with finer nanoparticles (<50 nm), which increases the density of surface active sites. These may be Mn-Ce active components. The sepiolite layer structure is still clearly visible, but a large number of active component particles are attached to the surface, indicating that the addition of Ce promotes the dispersion of active components and forms highly covered active sites.

[0124] 2. BET analysis was performed on the Mn / TiO2-SEP catalyst with the optimal sepiolite doping content (i.e., 20 wt%) and the Ce-Mn / TiO2-SEP catalyst with the optimal cerium-manganese ratio (i.e., Ce:Mn=1:1).

[0125] The preparation method is the same as in the SEM section. Table 6 shows the specific surface area, pore volume, and average pore size of pure natural sepiolite, Mn / TiO2-20wt%SEP, and Ce:Mn=1:1 / TiO2-SEP catalysts. Figure 5 Table 1 shows the N2 adsorption-desorption curves and pore size distribution of Mn / TiO2-20wt%SEP and Ce:Mn=1:1 / TiO2-SEP catalysts. As can be seen from Table 1, natural sepiolite, after acidification, exposes a rich microporous / mesoporous structure, and its high specific surface area is suitable as a support matrix. Although the specific surface area of ​​Mn / TiO2-SEP is significantly reduced compared to pure acidified sepiolite, it forms hierarchical channels dominated by 11-13 nm mesopores, which facilitates gas diffusion. The addition of cerium further reduces the specific surface area and increases the pore size, but reduces the pore volume, indicating that the active component preferentially fills the small pores (<10 nm), forming a more uniform mesoporous system. This suggests that the Mn-Ce active component blocks some micropores but optimizes the mesoporous channels. Figure 5The N2 adsorption / desorption curves and pore size distributions show that both are type IV curves with an H3 hysteresis loop, indicating a dominant mesoporous structure. In summary, the Ce-Mn sample has a lower specific surface area, but the increased mesoporous content offsets the adverse effects of specific surface area loss on mass transfer; the larger pore size reduces diffusion resistance and accelerates NO diffusion. x / NH3 enters the active site; pore volume decreases but pore size is optimized, indicating that ineffective micropores are reduced and the proportion of effective reaction channels increases.

[0126]

[0127] 3. XRD pattern testing experiments for different catalysts

[0128] With other process parameters fixed as in Example 1, the amount of nitric acid-acidified sepiolite was changed to 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 50 wt%, 75 wt%, and 100 wt%, respectively. Cerium nitrate solution was not added. Different Mn / TiO2-SEP catalysts without Ce loading were prepared. XRD patterns of the catalysts were analyzed, and the results are as follows: Figure 6 As shown.

[0129] from Figure 6 As can be seen, the doping of sepiolite did not change the anatase crystal phase of TiO2, indicating that the crystal structure of the carrier was not destroyed. As the proportion of sepiolite increased, the intensity of the anatase characteristic peak decreased (due to the reduction of TiO2 content), while the sepiolite characteristic peak appeared.

[0130] With other process parameters fixed as in Example 1, only the Ce:Mn ratio was changed to 0:1, 1:4, 1:2, 3:4, 1:1, and 5:4 to prepare different Ce-Mn / TiO2-SEP catalysts. XRD patterns of the catalysts were analyzed, and the results are as follows: Figure 7 As shown.

[0131] from Figure 7 As can be seen from the data, no characteristic peaks of the active component manganese cerium oxide were detected, indicating that the active component is highly dispersed or exists in an amorphous form.

[0132] The preferred embodiments of the present invention have been described above, but are not intended to limit the invention. Those skilled in the art can make modifications and variations to the embodiments disclosed herein without departing from the scope and spirit of the invention.

Claims

1. A method for preparing a low-medium temperature denitration catalyst of manganese cerium loaded on a sepiolite-TiO2 composite carrier, characterized in that, The method comprises the following steps: (1) mixing natural sepiolite with 0.2-0.4 mol / L nitric acid together, heating and stirring in an oil bath, after the reaction is completed, performing filtration and washing with water for multiple times, drying the treated sepiolite, placing it in a blast drying machine at 80-110°C for 10-12 h, then performing screening with a 100-300 mesh screen, obtaining nitric acid acidified sepiolite, and sealing for use; (2) weighing the nitric acid acidified sepiolite and TiO2, mixing them, mixing a manganese source with water to obtain a manganese source precursor solution, adding it to the acidified sepiolite-TiO2, stirring at room temperature, then adding potassium permanganate solution dropwise to the solution, after the dropwise addition is completed, adding cerium nitrate solution, continuing stirring at room temperature for 12-24 h, performing filtration and washing until the filtrate is colorless, drying the filter cake at 80-110°C for 10-12 h, grinding and screening to 20-60 mesh particles, and calcining in a muffle furnace, thus obtaining a Ce-Mn / TiO2-SEP catalyst; the temperature of the oil bath in step (1) is 60-90°C, and the stirring time is 8-10 h; in step (1), the washing with water is performed multiple times until the pH value of the washing liquid is neutral; in step (2), the manganese source is manganese nitrate; in step (2), the nitric acid acidified sepiolite is 5-25 wt%, and TiO2 is 75-95 wt%; in step (2), the stirring at room temperature is performed for 12-24 h; in step (2), n(Mn(NO3)2) / n(KMnO4)=3:2; in step (2), the calcination in the muffle furnace is performed at 300-500°C for 2-3 h.

2. A low-medium temperature denitration catalyst of manganese cerium supported on a sepiolite-TiO2 composite carrier prepared by the method according to claim 1, characterized in that, The ratio of Ce:Mn of the Ce-Mn / TiO2-SEP catalyst is (1-5):(1-4).

3. Use of a catalyst according to claim 2, characterized in that, It is applied to low-temperature denitration.

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