Medium and low temperature denitration catalyst with meerscham-TiO2 composite carrier loaded with manganese and cerium as well as preparation method and application of medium and low temperature denitration catalyst

Abstract

The invention belongs to the technical field of denitration catalyst preparation, and discloses a meerscham-TiO2 composite carrier loaded manganese cerium medium and low temperature denitration catalyst and a preparation method and application thereof, the preparation method comprises the following steps: (1) mixing meerschaum and nitric acid, then heating and stirring for reaction, then carrying out suction filtration and washing, and drying to obtain a meerschaum-TiO2 composite carrier loaded manganese cerium medium and low temperature denitration catalyst; after the treated sepiolite is drained, drying and screening are conducted, and nitric acid acidified sepiolite is obtained; and (2) mixing the meerschaum acidified by nitric acid and TiO2, then adding the manganese source precursor solution into the acidified meerscham-TiO2, then dipping and stirring, dropwise adding a potassium permanganate solution into the solution, then adding a cerium nitrate solution, stirring and then carrying out suction filtration, drying, grinding and screening the obtained filter cake, and then calcining to obtain the catalyst. According to the invention, the acidified sepiolite and TiO2 are compounded, so that complementary advantages of the two carrier materials are realized, and the obtained catalyst not only has good denitration efficiency, but also can significantly reduce the production cost.

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] A composite titanium dioxide powder for high specific surface denitration catalyst and a preparation method thereof are disclosed in Chinese patent application CN109603922A in 2019. The composite titanium dioxide powder is composed of titanium dioxide, activated diatomite, sepiolite powder, zirconium oxide, ammonium paratungstate, cerium oxide, bridged silsesquioxane, and hyperdispersant. The problems of poor plasticity, low specific surface area, and difficulty in breaking through the 94% efficiency upper limit of denitration efficiency of traditional titanium dioxide carriers are solved. The preparation method is as follows: titanium dioxide, activated diatomite, zirconium oxide, ammonium paratungstate, cerium oxide, bridged silsesquioxane (KH560-660 and KH560-540), and desalted water are mixed to form a suspension. The obtained suspension is placed in a ball mill, and hyperdispersant (mercaptoacetamide polyacrylate) is added for wet ball milling. After ball milling, the composite powder is washed and dried. The dried composite powder is mixed with sepiolite powder in a stirrer to obtain the composite titanium dioxide powder. Compared with traditional titanium dioxide, the extrusion speed, specific surface area, denitration efficiency, and plasticity index of the composite titanium dioxide powder are significantly improved. The innovation lies in that the particle size distribution design of activated diatomite and activated sepiolite powder can improve the plasticity of the catalyst, the bridged silsesquioxane as a surfactant can improve the powder viscosity, and the bridged agent can form a large number of pores in the catalyst after calcination to increase the specific surface area of the catalyst. However, the sepiolite powder is directly dry-mixed after ball milling and does not participate in the wet ball milling and dispersion process, which makes it difficult to ensure uniform dispersion in the titanium dioxide matrix and leads to uneven catalyst structure, affecting the specific surface area and active site distribution. Moreover, the active components such as ammonium paratungstate and molybdenum oxide are only mixed by low-temperature stirring, without calcination and other steps, which makes it difficult to load the active components firmly on the surface of the carrier and leads to migration and agglomeration in subsequent use, reducing the long-term stability of the catalytic efficiency.

[0006] A nitrogen-doped porous carbon-TiO2 composite carrier, a preparation method thereof, and a low-temperature denitration catalyst are disclosed in Chinese patent application CN120022921A in 2025. The nitrogen-doped porous carbon has a two-dimensional carbon sheet-like structure with dual-stage pores. The TiO2 is nano-titanium dioxide with a particle size of 3-8 nm, uniformly dispersed on the surface of the two-dimensional carbon sheet-like structure, accounting for 75-90 wt% of the total weight. The specific surface area of the composite carrier can reach 180-400 m 2 / g. Its preparation method is: (1) synthesis of nitrogen-doped porous carbon ① raw material mixing: the carbon source is potassium / sodium citrate or potassium sorbate (alkali metal salt), the nitrogen source is a polyamino compound (diphenyl carbazide, phenylenediamine, melamine, etc.), and the crosslinking agent is aniline (0.5-1.0 mL of alkali metal salt), the mass ratio of alkali metal salt: polyamino compound = 2-5:1; ② heterogeneous reaction: 160-200℃ for 6-12h to form a prepolymer; ③ staged heat treatment: the first stage is 250-300℃ / 2-4h (pre-carbonization), and the second stage is 650-800℃ / 2-3h (alkali metal in-situ pore forming); ④ post-treatment: washing with dilute hydrochloric acid to remove metal residues, washing with water until neutral, and then vacuum drying at 80℃ for 12h; (2) in-situ loading of nano-TiO2 ① mixing nitrogen-doped porous carbon and solid titanium salt (titanium sulfate, titanium oxalate, etc.) ② heat treatment: 400-600℃ / 2-5h in an inert atmosphere. The innovation lies in that the alkali metal salt generates mesopores, the polyamino compound generates micropores, and the dual pore system can make the specific surface area reach 180-400m 2 / g; nitrogen doping can improve the reducibility of the carbon layer; nano-TiO2 is dispersed on the surface of the two-dimensional carbon sheet layered structure, which can solve the problems of easy agglomeration of nano-TiO2 and low specific surface area; high specific surface area and hierarchical pores can strengthen the adsorption and mass transfer of reactants, and nitrogen-doped carbon enhances the reduction ability of the active component. However, the solid titanium salt (such as titanium sulfate) releases SO3 gas during thermal decomposition, which is strongly corrosive; the nitrogen-containing group has hydrophilicity, which may exacerbate the adsorption of H2O in flue gas; the two-stage heat treatment and the thermal decomposition of titanium salt have high energy consumption, which greatly increases the production cost; the polyamino compound (such as diphenyl carbazide) is expensive, and aniline is highly toxic. SUMMARY

[0007] The present application aims to provide a sepiolite-TiO2 composite carrier loaded with manganese cerium for a medium-low temperature denitration catalyst and its preparation method and application, and the core purpose is to overcome the limitations of traditional single carriers, to realize the complementary advantages of the two carrier materials by compounding a specific proportion of acidified sepiolite and TiO2, to significantly reduce the production cost under the premise of ensuring the good denitration efficiency of the catalyst, and at the same time, the composite carrier design is dedicated to comprehensively improving the comprehensive performance and application value of the catalyst, so that it is improved in environmental friendliness, economy, safety and industrial applicability, etc., and an innovative solution is provided to break through the bottleneck of the traditional vanadium-titanium system.

[0008] In order to realize the above technical purpose, the technical scheme adopted by the present application is as follows:

[0009] A preparation method of a sepiolite-TiO2 composite carrier loaded with manganese cerium for a medium-low temperature denitration catalyst, comprising the following steps:

[0010] (1) The natural sepiolite is mixed with 0.2-0.4 mol / L nitric acid, heated and stirred in an oil bath, after the reaction is completed, the filtration is performed, and the sepiolite is washed with water for multiple times, after the treatment, the sepiolite is dried in a forced air drying machine at 80-110℃ for 10-12 h, then sieved by 100-300 mesh screen, to obtain the nitric acid acidified sepiolite, which is sealed for use;

[0011] (2) The nitric acid acidified sepiolite and TiO2 are weighed and mixed, the manganese source is mixed with water to obtain a manganese source precursor solution, which is added to the acidified sepiolite-TiO2, and then the solution is stirred at room temperature, then the potassium permanganate solution is added dropwise, after the dropwise addition is completed, the cerium nitrate solution is added, and the stirring at room temperature is continued for 12-24 h, after the filtrate is colorless, the filter cake is dried at 80-110℃ for 10-12 h, and ground and sieved to 20-60 mesh particles, which are calcined in a muffle furnace, to obtain the Ce-Mn / TiO2-SEP catalyst.

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

[0013] Preferably, in step (1), the sepiolite is washed with water for multiple times until the pH value of the washing liquid is neutral.

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

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

[0016] Preferably, in step (2), the stirring at room temperature is performed for 12-24 h.

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

[0018] Preferably, in step (2), the calcination in the muffle furnace is performed at 300-500℃ for 2-3 h.

[0019] The application also provides a sepiolite-TiO2 composite carrier loaded manganese-cerium low-temperature denitration catalyst, and the ratio of Ce:Mn of the Ce-Mn / TiO2-SEP catalyst is (1-5):(1-4).

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

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

[0022] The prior art has obvious carrier defects: the traditional single TiO2 has high cost, and the Brønsted acid site is scarce, the single sepiolite has poor thermal stability and insufficient active metal dispersion; in the prior art patent application CN109603922A, the sepiolite is only "ball milled and then directly dry mixed", which is easy to cause uneven dispersion and structural imbalance; the prior art patent application CN120022921A relies on nitrogen-doped porous carbon-TiO2, which needs a complex pore-making process.

[0023] The present application is compounded by 5-25wt% nitric acid sepiolite and 75-95wt% TiO2, which not only retains the high thermal stability and good dispersibility of TiO2 (avoiding the problem of poor thermal stability of sepiolite), but also replaces part of TiO2 with cheap natural sepiolite to reduce raw material cost, and at the same time makes up for the defect of insufficient acidity of TiO2 mainly with Lewis acid site by using the rich Brønsted acid site provided by acidified sepiolite, realizing the synergistic optimization of "cost-performance-stability".

[0024] 2. The pretreatment of sepiolite is more precise, which significantly improves the interface performance and dispersibility of the carrier

[0025] The prior art handles sepiolite roughly: the prior art patent application CN109603922A does not acidify or pretreat sepiolite, but directly dry mixes it, which is difficult to eliminate impurities and cannot strengthen its surface activity; the traditional sepiolite has weak surface acidity and is easy to agglomerate when not treated.

[0026] The present application adopts a whole-process pretreatment of "nitric acid acidification-oil bath heating and stirring-neutral washing-drying and screening" (0.2-0.4mol / L nitric acid, 60-90℃ oil bath stirring for 8-10h, 100-300 mesh screening after washing to neutral pH), which not only removes impurities and dredges the nanofiber channels of sepiolite, but also significantly increases the number of surface Brønsted acid sites; at the same time, when the pretreated sepiolite is mixed with TiO2, agglomeration can be avoided, ensuring uniform dispersion in the matrix and providing a better interface environment for subsequent active component loading.

[0027] 3. The active component loading process is more scientific, which improves the loading firmness and long-term stability

[0028] The prior art has key defects in active component loading: in the prior art patent application CN109603922A, the active components such as ammonium paratungstate are only mixed by "low-temperature stirring", without calcination, which makes it difficult to load the active components firmly and easy to migrate and agglomerate; the traditional loading process often ignores the proportion regulation of active components.

[0029] The application adopts a "step-by-step impregnation-precise proportioning-high temperature calcination" loading process: first, using manganese nitrate as a manganese source and potassium permanganate as an oxidizing agent (mole ratio of Mn(NO3)2 to KMnO4 is 3:2), adding cerium nitrate dropwise, stirring at room temperature for 12-24 hours to ensure uniform adsorption of active components, and finally realizing strong interaction of Mn, Ce and the carrier by calcining at 300-500 DEG C for 2-3 hours; at the same time, the ratio of Ce:Mn is strictly controlled at (1-5):(1-4), which not only avoids migration and agglomeration of active components, but also optimizes the distribution of active sites, significantly improving the long-term stability of the catalyst.

[0030] 4. Significant optimization of economic efficiency and environmental friendliness, reducing the threshold of industrial application

[0031] The prior art has the problems of "high cost, high energy consumption and high pollution": the prior art patent application CN120022921A uses expensive polyamino compounds (such as diphenylcarbazide) and toxic aniline (crosslinking agent), and requires two-stage high-temperature heat treatment (250-300 DEG C pre-carbonization, 650-800 DEG C pore forming), which has very high energy consumption, and the pyrolysis of solid titanium salt produces SO3 strong corrosive gas.

[0032] The application is optimized by three means: ① using cheap natural sepiolite to replace part of TiO2 to reduce raw material cost; ② no toxic and harmful raw materials (such as aniline and polyamino compounds) to avoid environmental pollution; ③ calcination temperature is only 300-500 DEG C, which is much lower than the high-temperature process of the prior art patent application CN120022921A, energy consumption is reduced by more than 40%, and no corrosive gas is produced, which takes into account economic efficiency and environmental friendliness, and is more in line with the needs of industrial scale application.

[0033] 5. Acid site synergistic strengthening, breaking the bottleneck of low-temperature denitration activity

[0034] The low-temperature activity of the carrier in the prior art is restricted by insufficient acidity: traditional TiO2 mainly has Lewis acid sites, and the number of Brønsted acid sites is small and the strength is weak, which is difficult to meet the adsorption and activation requirements of reactants at medium and low temperatures (<250 DEG C); although the prior art patent application CN109603922A introduces sepiolite, the acidity is not strengthened by acidification, and the synergistic effect is poor.

[0035] The application significantly improves the number and richness of total acid sites of the carrier through the synergy of "TiO2 Lewis acid site + acidified sepiolite Brønsted acid site": a large number of Brønsted acid sites provided by acidified sepiolite can efficiently adsorb NH3, and the Lewis acid sites of TiO2 are beneficial to the activation of NO x , and the two synergistically promote "NH3-NO xThe reaction efficiency at the active site fundamentally breaks the low-temperature denitration activity bottleneck caused by the insufficient acidity of the traditional carrier, and is more suitable for low-temperature industrial flue gas scenes such as cement and chemical industry. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 A preparation flowchart of the Ce-Mn / TiO2-SEP catalyst is shown in the following figure:

[0037] Figure 2 A figure showing the influence of different acidification sepiolite doping amounts on the NH3-SCR performance of the Mn / TiO2-SEP(x) catalyst is shown in the following figure:

[0038] Figure 3 A figure showing the influence of different Ce loadings on the NH3-SCR performance of the Ce(x)-Mn / TiO2-SEP catalyst is shown in the following figure:

[0039] Figure 4 SEM images of the catalyst are shown in the following figures: Figure 4 (a) and Figure 4 (b) are SEM (20K, 5K) images of the Mn / TiO2-20%SEP catalyst, Figure 4 (c) and Figure 4 (d) are SEM (20K, 5K) images of the Ce-Mn / TiO2-20%SEP catalyst.

[0040] Figure 5 N2 adsorption-desorption curves and pore size distribution curves of the catalyst are shown in the following figures:

[0041] Figure 6 XRD patterns of the Mn / TiO2-SEP(x) catalyst are shown in the following figure:

[0042] Figure 7 XRD patterns of the Ce(x)-Mn / TiO2-SEP catalyst are shown in the following figure. DETAILED DESCRIPTION

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

[0044] If the specific experimental steps or conditions are not specified in the examples, the conventional experimental steps are operated according to the field. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products obtained by market purchase.

[0045] The abbreviations and key terms involved in the present application are defined as follows:

[0046] SCR: selective catalytic reduction technology;

[0047] NO x : nitrogen oxide;

[0048] SEP: Sepiolite acidified with nitric acid;

[0049] Ce-Mn / TiO2-SEP: a low-medium temperature denitration catalyst with manganese cerium oxide supported on a composite carrier of TiO2 and sepiolite acidified with nitric acid;

[0050] TiO2: P25 anatase titanium dioxide

[0051] As shown in the embodiments of the present application, a preparation method of a low-medium temperature denitration catalyst with manganese cerium oxide supported on a composite carrier of sepiolite-TiO2, comprises the following steps: Figure 1

[0052] (1) Mix natural sepiolite with 0.2-0.4 mol / L nitric acid according to a solid-liquid ratio of 1:15, heat and stir in an oil bath pot at 60-90°C for 8-10 h, after the reaction is completed, perform suction filtration, and wash with purified water for multiple times until the pH value of the washing liquid is neutral. After the treated sepiolite is dried by filtration, it is placed in a blast drying machine at 80-110°C for 10-12 h, then sieved through a 100-300 mesh sieve to obtain nitric acid acidified sepiolite, which is 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, and add it to the acidified sepiolite-TiO2, and immerse and stir at room temperature for 12-24 h. Then slowly add potassium permanganate solution to the solution, wherein n(Mn(NO3)2) / n(KMnO4)=3:2, after the addition is completed, add cerium nitrate solution, and continue to stir at room temperature for 12-24 h. After washing by suction filtration until the filtrate is colorless, dry the filter cake at 80-110°C for 10-12 h, and grind and sieve to particles of 20-60 mesh, and calcine in a muffle furnace at 300-500°C for 2-3 h to obtain the Ce-Mn / TiO2-SEP catalyst, wherein the mass fraction of Mn elements in the Ce-Mn / TiO2-SEP catalyst in the manganese nitrate and potassium permanganate is 4-10 wt%.

[0054] Technical principle of the present application:

[0055] I. Mechanism of action of each raw material

[0056] 1. Natural sepiolite (SEP)

[0057] Basic carrier skeleton: natural sepiolite has a multi-level pore structure composed of micropores and mesopores and a high specific surface area (primary about 150-200 m 2 / g), which provides loading sites for active components; but its pores are easily blocked by impurities (such as carbonates and metal oxides), which need to be activated by acidification modification.​

[0058] Synergistic adsorption: The modified porous structure can enhance the adsorption capacity of NO X , NH3, prolong the residence time of reactants on the catalyst surface, and improve the reaction probability.

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

[0060] Modification and purification: Impurities in the pores of sepiolite are removed by acidolysis reaction (such as CaCO3 + 2HNO3 = Ca(NO3)2 + CO2↑ + H2O), avoiding impurities occupying active sites; at the same time, the pore wall is etched, the specific surface area is improved, and the pore size is expanded, creating conditions for the subsequent penetration of active components.

[0061] Regulation of surface properties: Introducing hydroxyl groups (-OH) on the surface of sepiolite enhances the interaction with TiO2 and manganese cerium active components, reducing the shedding of active components.

[0062] 3. Titanium dioxide (TiO2)

[0063] Synergistic effect of composite carrier: TiO2 has excellent chemical stability (acid-resistant and high-temperature-resistant), forming a "porous-stable" composite system with sepiolite - sepiolite provides specific surface area and abundant pore structure, which is beneficial to the high dispersion of active components, and its fibrous structure can effectively inhibit the phase change of TiO2 after high-temperature calcination, so that the composite carrier can still maintain a high specific surface area after heat treatment. TiO2 has excellent chemical stability and mechanical strength, providing an ideal carrier surface for active components, while the activation of O2 is achieved through the oxidation-reduction cycle of active components, improving the oxidation-reduction capacity.

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

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

[0066] Active component supply: Manganese nitrate provides Mn 2+ , potassium permanganate provides Mn 7+ , and the two undergo an oxidation-reduction reaction (3Mn 2+ + 2MnO4 - + 2H2O = 5MnO2↓ + 4H + ) to generate highly active MnO2, forming a Mn 4+ / Mn 3+ redox cycle to provide an electron transfer channel for NO x reduction (NO + Mn 4+ → NO2 + Mn3+ ).

[0067] Active site regulation: This ratio can accurately control the Mn valence state distribution (Mn 4+ accounts for 60%-70%), avoiding excessive Mn 7+ reacting with the main product MnO2 to further generate unstable or low-activity manganese oxides, which further leads to the non-selective oxidation of NH3 to generate byproducts N2O and NO; excessive Mn 2+ will remain in the product, reducing the catalytic activity, thereby 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, CeO2 with excellent oxygen storage and release capacity and rich surface oxygen vacancies is formed, and its Ce 3+ / Ce 4+ redox can efficiently activate O2 and convert it into highly active surface adsorbed oxygen species, thereby providing abundant active oxygen species for the adjacent Mn active sites to maintain their high oxidation state, thereby improving the medium-low temperature SCR reaction rate; at the same time, CeO2 can form surface nitrate intermediates with NO2, promoting the reduction of NO x .

[0070] Anti-poisoning protection: When SO2 is present, the active component cerium oxide can preferentially react with SO2 to form stable Ce2(SO4)3, avoiding the combination of SO2 with Mn active sites to form inactive MnSO4, thereby improving the sulfur resistance of the catalyst.

[0071] TiO2 raw materials and energy consumption costs are significantly higher than natural mineral carriers, which directly affects the overall economy of the catalyst, especially in large-scale industrial applications; and TiO2 (anatase) itself mainly has Lewis acid sites, with limited number and weak strength of Brønsted acid sites. The thermal stability of sepiolite itself is relatively limited, and its surface is not conducive to the high uniform dispersion and strong interaction of active metal components. By combining the two carriers, the inexpensive acidified sepiolite can partially replace TiO2, effectively reducing the raw material cost of the catalyst and improving its overall economy. At the same time, the acid-treated sepiolite can provide abundant Brønsted acid sites, effectively making up for the lack of TiO2 surface acidity. After the combination of the two, new acid sites can be generated to maintain the stability of the carrier structure and the high dispersion of the active components. Ultimately, a carrier with better overall performance and more industrial applicability is obtained, which has the potential to improve the adsorption performance, medium-low temperature denitrification performance, and stability of the catalyst.

[0072] II. The necessity and importance of raw material dosage optimization

[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] The other process parameters are fixed as in Example 1, only the ratio of Ce:Mn is changed, which is 0:1, 1:4, 1:2, 3:4, 1:1, and 5:4, respectively, to prepare different Ce-Mn / TiO2-SEP catalysts. The catalysts are tested for denitration activity. During the test, the temperature is kept at 100-300°C for 20 minutes at each temperature point. The NO concentration is measured using a flue gas analyzer when the remaining holding time is 10, 5, and 1 minute, respectively. The average of the three test results is taken as the final measurement result, and the error is within 1%. The results are shown in Table 2. Figure 3

[0090] As can be seen from Figure 3 the denitration performance test, the best denitration efficiency is achieved when the ratio of cerium to manganese is 1:1, which is more than 90% in the medium temperature range of 175-300°C.

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

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

[0093]

[0094] As can be seen from Table 1, when the concentration is less than 0.2 mol / L, the acidification of sepiolite by nitric acid is not sufficient, only part of the impurities can be removed, and the carrier pore channel cannot be effectively etched, resulting in small specific surface area of the carrier and small number of surface hydroxyl groups. The subsequent active components (Mn, Ce) have insufficient adsorption sites, low loading and uneven distribution, and the number of active sites (MnO x -CeO2 solid solution) is small, and the NO conversion rate is low.

[0095] When the concentration is greater than 0.4 mol / L, the silicon-oxygen skeleton of sepiolite is excessively corroded by nitric acid, resulting in collapse of the carrier pore structure and even amorphization. At the same time, excessive H⁺ can damage the stability of the sepiolite and TiO2 composite, and the carrier agglomeration phenomenon is obvious. The active components are easily agglomerated into large particles, the active sites are covered, and the NO conversion rate is significantly reduced.

[0096] ​In summary, the preferred 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 acid acidification reaction and the NO conversion rate of the subsequent catalyst

[0098] While fixing other process parameters as in Example 1, only the oil bath temperature in step (1) is changed, the variable level (℃) is 50, 60, 70, 80, 90, 100, and other fixed parameters are: the nitric acid concentration is 0.3 mol / L, the acidified sepiolite doping amount is 20%, and the Ce:Mn ratio is 1:1. Different Ce-Mn / TiO2-SEP catalysts are prepared, and the denitration activity of the catalysts is tested. During the test, the temperature is 150℃, the flue gas analyzer is used to measure the NO concentration, and the average value of three test results is taken as the final measurement result. The measurement error is within 1%, and the NO conversion rate test results are shown in Table 2.

[0099]

[0100] As shown in Table 2, when the temperature is less than 60℃, the reaction kinetics rate of nitric acid and sepiolite is low, the acidification reaction is incomplete, there are many impurities on the surface of the carrier, the pore channel is not well connected, the active components cannot be effectively loaded, and the NO conversion rate is low.

[0101] When the temperature is greater than 90℃, the volatilization rate of nitric acid increases, the effective H + concentration in the system decreases, the acidification efficiency decreases, and high temperature can cause local overreaction of sepiolite, damage the crystal structure, reduce the specific surface area of the carrier, and possibly cause the TiO2 precursor to agglomerate prematurely, thereby reducing the activity of the catalyst.

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

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

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

[0105]

[0106] From Table 3, when the time is less than 8h, the nitric acid is not fully contacted with the sepiolite, the local acidification degree is greatly different (part of the area is not acidified, and part of the area is slightly acidified), the hydroxyl group on the surface of the carrier is unevenly distributed; the subsequent active component loading appears "hot spots" (local overload) and "cold spots" (local empty load), the number of active sites is insufficient and the distribution is disordered, and the NO conversion rate is low.

[0107] When the time is greater than 10h, excessive stirring causes the sepiolite fiber structure to break, and the specific surface area of the carrier decreases; at the same time, long-time stirring can aggravate the carrier agglomeration, reduce the active component adsorption site, and reduce the NO conversion rate.

[0108] In summary, the preferred stirring time is 8-10h, and the best stirring time is 9h.

[0109] Single factor experiment 6: effect of different manganese loadings in step (2) on NO conversion rate of the catalyst

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

[0111]

[0112] From Table 4, when the manganese loading is less than 4wt%, the number of active sites is insufficient, the NO oxidation and reduction reaction is blocked, and the NO conversion rate is low.

[0113] When the manganese loading is greater than 10wt%, the adsorbed Mn 2+ occurs secondary agglomeration, the particle size increases, the specific surface area decreases significantly, and the NO conversion rate decreases.

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

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

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

[0117]

[0118] From Table 5, when the temperature is less than 300℃, the manganese nitrate and cerium nitrate precursors are not completely decomposed, and the residual nitrate covers the active sites; and high-activity MnO x -CeO2 solid solution is not formed, and only a small amount of MnO is generated, and the NO conversion rate is low.

[0119] When the temperature is greater than 500℃, the active components sinter, the CeO2 lattice shrinks, and the Mn 4+ / Mn 3+ ratio significantly decreases (high-activity Mn 4+ decreases); at the same time, the carrier and the active component have a strong interaction (Si-O-Mn bond is generated), and the active site is fixed and cannot participate in the denitration reaction, so the NO conversion rate decreases.

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

[0121] Catalyst characterization test:

[0122] 1. The Mn / TiO2-SEP catalyst with the best sepiolite doping amount (i.e. 20wt%) and the Ce-Mn / TiO2-SEP catalyst with the best cerium manganese ratio (i.e. Ce:Mn=1:1) were characterized by SEM

[0123] Figure 4 (a) and Figure 4 (b) are Mn / TiO2-SEP catalysts prepared by fixing other process parameters as in Example 1, and the amount of nitric acid sepiolite is 20wt%, and no cerium nitrate solution is added. Figure 4 (c) and Figure 4 (d) are Ce-Mn / TiO2-SEP catalysts prepared in Example 1. The results are shown in Figure 4 Figure 4 (a) and​Figure 4 (b) TEM (20K, 5K) images of Mn / TiO2-20% SEP respectively, Figure 4 (c) and Figure 4 (d) TEM (20K, 5K) images of Ce:Mn = 1:1 / TiO2-20% SEP respectively. From Figure 4 (a) and Figure 4 (b) can be seen that more dispersed nanoscale active component particles are loaded on the surface of TiO2 and acidified sepiolite, and slight agglomeration occurs. Poor dispersion results in clogging of the surface pores of the composite carrier; sepiolite with a fibrous structure is embedded in the particles and is well combined with TiO2, with no significant phase separation, no obvious cracks or large holes, indicating that the mechanical stability of the material after doping is good, thus indicating that 20% sepiolite doping optimizes the carrier structure, forming a porous composite carrier with high specific surface area. From Figure 4 (c) and Figure 5 (d) can be seen that the surface of the carrier is covered with smaller nanoparticles (<50 nm), increasing the density of surface active sites, which may be Mn-Ce active components. The sepiolite sheet structure is still clear, but a large number of active component particles are attached to the surface, indicating that the addition of Ce promotes the dispersion of the active component, forming a high-coverage active site.

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

[0125] The preparation method is the same as that in the SEM section. Table 6 is the specific surface area, pore volume and average pore diameter of pure natural sepiolite, Mn / TiO2-20wt% SEP and Ce:Mn = 1:1 / TiO2-SEP catalysts, Figure 5 are the N2 adsorption-desorption curves and pore size distribution graphs of Mn / TiO2-20wt% SEP and Ce:Mn = 1:1 / TiO2-SEP catalysts. From Table 1, it can be seen that after acidification, natural sepiolite exposes a rich microporous / mesoporous structure, and a high specific surface area is suitable as a carrier matrix. Although the specific surface area of Mn / TiO2-SEP is greatly reduced compared to pure acidified sepiolite, it forms a hierarchical pore with a mesopore of 11-13 nm as the main channel, which is beneficial to gas diffusion; after adding cerium, the specific surface area further decreases, the pore size continues to increase, but the pore volume decreases, indicating that the active component preferentially fills the small pores (<10 nm), forming a more uniform mesoporous system, indicating that the Mn-Ce active component blocks part of the micropores, but optimizes the mesoporous channel. From Figure 6The N2 adsorption-desorption curves and pore size distribution of the two can be seen as IV type curve + H3 type hysteresis ring, and the mesoporous structure is dominant. In summary, the specific surface area of the Ce-Mn sample is lower, but the mesopore proportion is improved, which offsets the adverse effect of the loss of specific surface area on mass transfer; the larger pore size reduces the diffusion resistance and accelerates the entry of NO x / NH3 into the active site; the pore volume decreases but the pore size is optimized, indicating that the ineffective micropores are reduced and the proportion of effective reaction channels is increased.

[0126]

[0127] 3. XRD pattern test of different catalysts

[0128] The other process parameters are fixed as in Example 1, and the amount of nitric acid- acidified sepiolite is changed to 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 50 wt%, 75 wt% and 100 wt%, respectively, and no cerium nitrate solution is added, to prepare different Mn / TiO2-SEP catalysts without loading Ce, and the catalysts are subjected to XRD pattern test, and the results are shown in Figure 6 .

[0129] As can be seen from Figure 7 , the doping of sepiolite does not change the anatase crystal phase of TiO2, indicating that the crystal structure of the carrier is not destroyed, and with the increase of the proportion of sepiolite, the intensity of the anatase characteristic peak decreases (due to the decrease of TiO2 content), and at the same time, the characteristic peak of sepiolite appears.

[0130] The other process parameters are fixed as in Example 1, and only the ratio of Ce:Mn is changed to 0:1, 1:4, 1:2, 3:4, 1:1 and 5:4, respectively, to prepare different Ce-Mn / TiO2-SEP catalysts, and the catalysts are subjected to XRD pattern test, and the results are shown in Figure 7 .

[0131] As can be seen from ​ , the characteristic peaks of manganese and cerium oxides, the active components, are not detected, indicating that the active components are highly dispersed or exist in amorphous form.

[0132] The above describes the preferred embodiments of the present application, but it is not intended to limit the present application. Those skilled in the art can make improvements and changes to the embodiments disclosed herein without departing from the scope and spirit of the present application.

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, Comprising 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 suction filtration operation, and using water for multiple washing treatment, after the treated sepiolite is dried by filtration, it is placed in a 80-110℃ blast drying machine for 10-12 h, then sieving with 100-300 mesh screen, obtaining nitric acid acidified sepiolite, sealing for use; (2) weighing the nitric acid acidified sepiolite and TiO2 and mixing, mixing manganese source with water to obtain manganese source precursor solution, adding to the acidified sepiolite-TiO2, dipping and stirring at room temperature, then adding potassium permanganate solution dropwise to the solution, after the dropwise addition is completed, adding cerium nitrate solution, continuing to stir at room temperature for 12-24 h, after washing the filter cake by suction filtration until the filtrate is colorless, drying the filter cake at 80-110℃ for 10-12 h, and grinding and sieving to 20-60 mesh particles, calcining in a muffle furnace, obtaining Ce-Mn / TiO2-SEP catalyst.

2. The method for preparing a sepiolite-TiO2 composite support loaded manganese cerium medium-low temperature denitration catalyst according to claim 1, characterized in that, The temperature of the oil bath in step (1) is 60-90℃, and the stirring time is 8-10 h.

3. The method for preparing a sepiolite-TiO2 composite support loaded manganese cerium medium-low temperature denitration catalyst according to claim 1, characterized in that, In step (1), the water is used for multiple washing until the pH value of the washing liquid is neutral.

4. The method for preparing a sepiolite-TiO2 composite support loaded manganese cerium medium-low temperature denitration catalyst according to claim 1, characterized in that, In step (2), the manganese source is manganese nitrate.

5. The method for preparing the sepiolite-TiO2 composite support loaded manganese cerium medium-low temperature denitration catalyst according to claim 1, characterized in that, In step (2), the nitric acid acidified sepiolite is 5-25 wt%, and TiO2 is 75-95 wt%.

6. The method for preparing a sepiolite-TiO2 composite support loaded manganese cerium medium-low temperature denitration catalyst according to claim 1, characterized in that, In step (2), the dipping and stirring at room temperature is 12-24 h.

7. The method for preparing the sepiolite-TiO2 composite support loaded manganese cerium medium-low temperature denitration catalyst according to claim 1, characterized in that, In step (2), the calcining in the muffle furnace is at 300-500℃ for 2-3 h.

8. A low-medium temperature denitration catalyst of manganese cerium supported on a sepiolite-TiO2 composite carrier prepared by the method according to any one of claims 1-7, characterized in that, The ratio of Ce:Mn of the Ce-Mn / TiO2-SEP catalyst is (1-5):(1-4).

9. Use of a catalyst according to claim 8, characterized in that, It is applied to low-temperature denitration.

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