SCR (Selective Catalytic Reduction) denitration catalyst with gradient functional active sites and preparation method thereof

Abstract

The invention relates to the technical field of SCR denitration, in particular to an SCR denitration catalyst with gradient functional active sites and a preparation method thereof.The SCR denitration catalyst comprises a honeycomb ceramic carrier and functional layers coating the side walls of pore channels of the honeycomb ceramic carrier, and the functional layers are arranged in the flue gas flowing direction. The functional layer comprises a protection pretreatment layer, a main reaction antitoxic layer and a capture purification layer, and the protection pretreatment layer, the main reaction antitoxic layer and the capture purification layer all take TiO2-SiO2 composite aerogel as a carrier; fe2O3, MnOx and precious metal are loaded on the surface of a carrier of the protective pretreatment layer; a composite oxide of CeO2, MnOx and Fe2O3 and an anti-arsenic additive are loaded on the surface of a carrier of the main reaction anti-toxic layer; and solid superacid and nano MgO are loaded on the surface of a carrier of the capturing and purifying layer. The SCR denitration catalyst provided by the invention has excellent low-temperature activity and strong anti-poisoning ability, and has huge industrial application prospects and economic values.

Description

Technical Field

[0001] This invention relates to the field of SCR denitrification technology, and in particular to an SCR denitrification catalyst with gradient functional active sites and its preparation method. Background Technology

[0002] Nitrogen oxides (NO) x NO is one of the major air pollutants, posing a serious threat to human health and the ecological environment. Selective catalytic reduction (SCR) technology is currently the most widely used and mature method internationally for addressing NO from stationary sources such as power plant boilers and industrial kilns. x Purification technology. Its core is to use a reducing agent (such as ammonia) to remove NO under the action of a catalyst. x It is selectively reduced to harmless nitrogen (N2) and water (H2O).

[0003] Commercial SCR catalysts typically use TiO2 as a support, V2O5 as the main active component, and add WO3 or MoO3 as promoters to improve thermal stability and acidity. Although these vanadium-based catalysts exhibit good activity in the mid-temperature range (300-400°C), they still face many severe challenges in practical applications. For example, the active temperature window is narrow: traditional vanadium-titanium catalysts have poor activity in the low-temperature range (<250°C), making it difficult to meet the denitrification requirements of non-electric industries (such as steel, cement, and glass) under low-load or start-stop conditions; while in the high-temperature range (>450°C), the active component sintering deactivates and side reactions (such as SO2 oxidation and ammonia oxidation) intensify, leading to a decrease in denitrification efficiency and an increase in operational risks; insufficient resistance to poisoning: various impurities in flue gas can cause catalyst poisoning and deactivation. Alkali metals (K, Na) and alkaline earth metals (Ca) neutralize the acidic sites of the catalyst, irreversibly destroying its ability to activate NH3; arsenic (As) and phosphorus (P) clog the catalyst pores and react with the active sites; in particular, the presence of SO2 and H2O not only competes for adsorption, but more importantly, SO2 is easily oxidized to SO3, which then reacts with escaped NH3 to form viscous ammonium bisulfate (ABS). ABS condenses in the low-temperature region, clogging the catalyst pores and downstream air preheater, causing a surge in system pressure drop and equipment corrosion. This is the core problem restricting the long-term stable operation of SCR systems; Environmental and health risks: V2O5 itself has certain biotoxicity, and the treatment and disposal of waste catalysts face increasingly stringent environmental regulations. Developing environmentally friendly non-vanadium-based catalysts has become an important trend.

[0004] To address these challenges, those skilled in the art have conducted extensive research. On one hand, efforts have been focused on developing novel non-vanadium cryogenic catalysts, such as catalyst systems based on transition metal oxides like manganese (Mn), cerium (Ce), and iron (Fe). These catalysts exhibit excellent redox performance at low temperatures, showing potential to replace vanadium-based catalysts. However, these catalysts generally suffer from new problems such as poor N2 selectivity and inadequate resistance to sulfur and water. On the other hand, in catalyst structure design, schemes such as partitioned coating and bilayer structures have emerged. For example, an oxide layer is placed at the catalyst front end to generate NO2 to promote the "fast SCR" reaction. However, existing designs often have limited functionality and synergistic effects between different regions, failing to systematically and simultaneously solve problems related to activity, resistance to toxicity, and ammonia slip.

[0005] It is evident that existing SCR catalyst technologies, whether traditional vanadium-based systems or emerging non-vanadium systems, have significant shortcomings in terms of activity temperature window, overall resistance to poisoning, and system synergy.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide an SCR denitration catalyst with gradient functional active sites and its preparation method. This SCR denitration catalyst has excellent low-temperature activity and strong resistance to poisoning.

[0008] In a first aspect, the present invention provides an SCR denitrification catalyst with gradient functional active sites, comprising a honeycomb ceramic support and a functional layer coated on the sidewalls of the pores of the honeycomb ceramic support. Along the direction of flue gas flow, the functional layer includes a protective pretreatment layer, a main reaction anti-poisoning layer, and a capture and purification layer. The protective pretreatment layer, the main reaction antitoxic layer, and the capture and purification layer all use TiO2-SiO2 composite aerogel as a carrier. The protective pretreatment layer has Fe2O3 and MnO loaded on its carrier surface. x and precious metals; The carrier surface of the main reactive antitoxic layer is loaded with CeO2 and MnO. x Composite oxides of Fe2O3 and arsenic-resistant additives; The carrier surface of the capture and purification layer is loaded with solid superacid and nano-MgO. Preferably, the precious metal includes either Pt or Pd; Preferably, the arsenic-resistant additive includes any one or both of WO3 and MoO3; Preferably, the solid superacid includes either S-ZrO2 or WO3-ZrO2, and is more preferably S-ZrO2.

[0009] In a preferred embodiment of this technical solution, the protective pretreatment layer accounts for 20%-40% of the overall length of the catalyst; The main reaction anti-poison layer accounts for 40%-60% of the total length of the catalyst; The capture and purification layer accounts for 10%-30% of the total length of the catalyst.

[0010] The protective pretreatment layer, main reaction antitoxic layer, and capture and purification layer of the present invention have a very narrow transition zone between the layers, which can avoid the problem of weak bonding caused by sharp interfaces.

[0011] In a preferred embodiment of this technical solution, the protective pretreatment layer contains Fe2O3 with a loading of 1wt%-5wt% and MnO. x The loading of Pt is 3wt%-8wt%, and the loading of Pt and / or Pd is 0.05wt%-0.5wt%.

[0012] In a preferred embodiment of this technical solution, the main reactive antitoxic layer contains CeO2 with a loading of 5wt%-15wt% (based on oxides) and MnO2. x The loading amounts are 5wt%-10wt%, Fe2O3 is 3wt%-8wt%, and WO3 and / or MoO3 is 2wt%-8wt%. This loading amount can effectively prevent excessive Mn from covering the active sites of Ce and reducing oxygen storage capacity.

[0013] As a preferred embodiment of this technical solution, in the capture and purification layer, the loading of nano-MgO is 3wt%-10wt%, and the loading of S-ZrO2 and / or WO3-ZrO2 is 5wt%-15wt%.

[0014] In a preferred embodiment of this technical solution, the molar ratio of TiO2 to SiO2 in the TiO2-SiO2 composite aerogel carrier is (7:3)-(9:1), and its specific surface area is not less than 350 m². 2 / g, and has a hierarchical pore structure.

[0015] Secondly, the present invention also provides a method for preparing the above-mentioned SCR denitration catalyst with gradient functional active sites, comprising the following steps: S1. Preparation of TiO2-SiO2 composite aerogel carrier powder; S2. Using TiO2-SiO2 composite aerogel as a carrier, catalyst powders for the protective pretreatment layer, the main reaction anti-poisoning layer, and the capture and purification layer were prepared respectively. S3. The catalyst powders obtained in step S2 are mixed with deionized water, binder, thickener and dispersant respectively, and ball-milled to obtain coating slurries corresponding to the three functional layers. S4. Pre-treat the honeycomb ceramic carrier, and then use the gradient vacuum coating method to coat the coating slurry corresponding to the three functional layers onto the pre-treated honeycomb ceramic carrier in sequence by controlling the immersion depth, lifting speed and vacuum degree, to form three continuous functional layers. S5. The coated support is subjected to programmed step sintering to obtain an SCR denitrification catalyst with gradient functional active sites.

[0016] As a preferred embodiment of this technical solution, in step S1, the preparation method of the TiO2-SiO2 composite aerogel carrier powder includes: A wet gel of TiO2-SiO2 was prepared by the sol-gel method; The wet gel was placed in a supercritical drying vessel and dried using ethanol as the medium at a temperature of 200-300℃ and a pressure of 5-10MPa to obtain TiO2-SiO2 composite aerogel blocks. TiO2-SiO2 composite aerogel blocks were ground into fine powder and calcined at 400-500℃ for 3-5 hours to obtain TiO2-SiO2 composite aerogel carrier powder.

[0017] As a preferred embodiment of this technical solution, in step S2, the method for preparing the catalyst powder of the protective pretreatment layer includes: A mixed solution of soluble salts of Mn and Fe was prepared and then mixed with a TiO2-SiO2 composite aerogel carrier powder suspension. The pH was adjusted to 9-10 using ammonia water, and the mixture was continuously stirred and aged at 70-90℃ for 5-7 hours. After filtration, washing, and drying, the active component powder was obtained. The active component powder is immersed in a soluble salt solution of Pt and / or Pd for 10-15 hours and then dried to obtain the protective pretreatment layer catalyst powder.

[0018] Among them, the loading of precious metals after co-precipitation of transition metals by the "impregnation method" can effectively avoid the adverse effects of high-temperature calcination on precious metals.

[0019] As a preferred embodiment of this technical solution, the preparation method of the main reaction anti-poisoning layer catalyst powder in step S2 includes: Soluble salts of Ce, Mn, Fe, W, and Mo were prepared into a mixed solution and then mixed with a TiO2-SiO2 composite aerogel carrier powder suspension. Using urea solution as a precipitant, the reaction is carried out at 90-95℃ and aged for 6-10 hours. After filtration, washing and drying, the main reaction anti-poisoning layer catalyst powder is obtained.

[0020] As a preferred embodiment of this technical solution, the method for preparing the catalyst powder for the capture and purification layer in step S2 includes: TiO2-SiO2 composite aerogel carrier powder, nano MgO powder, S-ZrO2 and / or WO3-ZrO2 powder are mechanically mixed to obtain the catalyst powder for the capture and purification layer.

[0021] As a preferred embodiment of this technical solution, in the gradient vacuum coating method, after the coating slurry corresponding to each functional layer is coated on the pretreated honeycomb ceramic carrier, it is subjected to preliminary drying treatment at 100-120℃.

[0022] In a preferred embodiment of this technical solution, during the programmed step sintering in step S5, the temperature is first increased to 120°C at a rate of 1-2°C / min and held for 2 hours to remove moisture; then the temperature is increased to 350°C at a rate of 1-2°C / min and held for 3 hours to remove organic matter; finally, the temperature is increased to 450-550°C at a rate of 2-3°C / min and held for 4-8 hours for qualitative analysis, followed by natural cooling to room temperature. This programmed step sintering method not only ensures a strong bond between the active component and the carrier but also avoids over-sintering of precious metals and active components.

[0023] The SCR denitration catalyst with gradient functional active sites of the present invention has at least the following beneficial effects: 1. The present invention provides an SCR denitration catalyst with gradient functional active sites, comprising a honeycomb ceramic support and a functional layer coated on the sidewall of the honeycomb ceramic support pores. The functional layers are all supported by TiO2-SiO2 composite aerogel. The TiO2-SiO2 composite aerogel support not only has an ultra-high specific surface area, but its three-dimensional network structure also endows the coating with excellent mechanical strength and wear resistance, significantly improving the mechanical strength and stability of the catalyst. 2. The SCR denitrification catalyst of the present invention has gradient functional active sites. Along the direction of flue gas flow, the functional layer includes a protective pretreatment layer, a main reaction anti-poisoning layer, and a capture and purification layer. In the protective pretreatment layer, the active components are highly dispersed Fe2O3 and MnO. x The substrate is primarily composed of Pt / Pd nanoparticles, with a small amount of Pt / Pd nanoparticles loaded onto it, in a combination of noble metals (Pt / Pd) and transition metals (Fe / Mn-O). x With the synergistic effect of [the active ingredient], NO can be efficiently oxidized to NO2 at low temperatures, generating an optimal NO / NO2 ratio (≈1:1), thereby initiating a "fast SCR" pathway with an extremely high reaction rate, laying the foundation for high activity at low temperatures; at the same time, this active component can also preferentially oxidize and solidify some SO2 and Hg. 0 This protects the main active area behind it; in the main reaction anti-toxic layer, the active components are mainly Ce-Mn-Fe-W-Mo multi-component composite oxides, with CeO2 having excellent oxygen storage capacity and MnO... xThe strong low-temperature redox properties, the excellent medium- and high-temperature activity of Fe2O3, and the N2 selectivity complement each other, achieving full temperature coverage from low to high temperatures with an extremely wide activity window. Therefore, the SCR denitrification catalyst of this invention can maintain a denitrification efficiency of over 90% in an ultra-wide temperature range of 180-450℃, completely solving the problems of low-temperature deactivation and high-temperature sintering of traditional vanadium-titanium catalysts. 3. The SCR denitration catalyst of this invention, with its gradient functional active sites, preferentially occupies SO2 oxidation active sites in the main reaction anti-poisoning layer due to the introduction of W / Mo promoters, significantly inhibiting the conversion of SO2 to SO3 and suppressing the formation of ammonium bisulfate at its source. Simultaneously, the macroporous structure of the TiO2-SiO2 composite aerogel also reduces the physical blockage of ammonium bisulfate. The Ce-based catalyst also inhibits K... + Na + Ca 2+ The neutralization effect itself is not sensitive, and the highly acidic S-ZrO2 (capture and purification layer) can also capture some alkali metals, protecting the main active sites; finally, the introduction of SiO2 component also greatly enhances the support's resistance to As2O3 and P2O5 poisoning, preventing them from reacting with the active components. Therefore, the SCR catalyst of this invention exhibits extremely strong tolerance to common poisons such as alkali metals (K, Na), SO2, arsenic, and phosphorus, and possesses excellent anti-poisoning performance and service life; 4. The SCR denitrification catalyst of this invention has gradient functional active sites. The capture and purification layer is supported on a solid superacid and a nano-MgO alkaline adsorbent. The solid superacid has a strong chemical adsorption and fixation capacity for escaped NH3, while the nano-MgO, as an alkaline adsorbent, can efficiently capture residual SO3 and generate stable MgSO4. Therefore, the SCR catalyst of this invention systematically solves the downstream problems caused by ammonia escape and SO3, ensuring the long-term stable operation of the entire flue gas purification system. 5. This invention's SCR denitration catalyst with gradient functional active sites significantly reduces or avoids the use of toxic heavy metal vanadium (V), lowering the difficulty of waste catalyst disposal and environmental risks. Although the initial cost may be slightly higher due to the precious metal and complex process, its longer lifespan, higher reliability, and protection of downstream equipment result in a significantly lower total lifespan cost compared to traditional catalysts.

[0024] Therefore, the SCR denitrification catalyst of the present invention has excellent low-temperature activity and strong resistance to poisoning, and has great prospects for industrial application and economic value. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is a flowchart illustrating the preparation method of the SCR denitration catalyst with gradient functional active sites according to the present invention. Figure 2 This is a schematic diagram of the honeycomb ceramic carrier of the present invention. Figure 3 This is a schematic diagram of the SCR denitrification catalyst with gradient functional active sites of the present invention. Detailed Implementation

[0027] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0028] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1 like Figure 1-3 As shown, this embodiment provides a method for preparing an SCR denitration catalyst with gradient functional active sites: 1. Preparation of TiO2-SiO2 composite aerogel carrier powder TBOT and TEOS with a molar ratio of (Ti:Si = 9:1) were dissolved in anhydrous ethanol and denoted as solution A. Mix deionized water, ethanol, and glacial acetic acid, and label the mixture as solution B. Under vigorous stirring, solution B was slowly added dropwise to solution A. After the addition was complete, stirring was continued for 2 hours to form a transparent sol. The sol was transferred to a sealed container and aged at 40°C for 24 hours to form a wet gel. The wet gel was subjected to multiple solvent replacements with anhydrous ethanol to remove moisture and byproducts. The wet gel was placed in a supercritical drying vessel and dried using ethanol as the medium at a temperature of 260°C and a pressure of 7 MPa to obtain TiO2-SiO2 composite aerogel blocks. The aerogel block was ground into fine powder (<45 μm) and calcined at 450°C for 4 hours to remove residual organic matter and stabilize the crystal phase, thus obtaining TiO2-SiO2 composite aerogel carrier powder.

[0031] 2. Preparation of catalyst slurry for protective pretreatment layer (active components Fe2O3 (3 wt%), MnO2 (5 wt%), Pt (0.1 wt%)) A mixed solution of soluble salts of Mn and Fe was prepared and mixed with a TiO2-SiO2 composite aerogel carrier powder suspension, and stirred for 2 hours. The pH was adjusted to 9-10 using ammonia water, and the mixture was continuously stirred and aged at 80°C for 6 hours. After filtration and washing until neutral, the mixture was dried at 110°C for 12 hours to obtain the active component powder. The active component powder was immersed in chloroplatinic acid solution for 12 hours and then dried to obtain the protective pretreatment layer catalyst powder. The catalyst powder of the protective pretreatment layer is mixed with deionized water, silica sol, PEG-400 and CTAB in a certain proportion and ball-milled until the viscosity is in the range of 3000-5000 mPa·s.

[0032] 3. Preparation of catalyst slurry for the main reaction anti-poisoning layer (active components: CeO2 (10 wt%), MnO) x (8 wt%), Fe2O3(5 wt%), WO3(5 wt%), MoO3(3 wt%)) Soluble salts of Ce, Mn, Fe, W, and Mo were prepared into a mixed solution, which was then mixed with a TiO2-SiO2 composite aerogel carrier powder suspension and stirred for 2 hours. Using urea solution as a precipitant, urea is slowly hydrolyzed at 90-95℃ to uniformly co-precipitate metal ions. After aging for 8 hours, the catalyst powder for the main reaction anti-poisoning layer is obtained after filtration, washing, and drying. The main reaction anti-toxic layer catalyst powder was mixed with deionized water, silica sol, PEG-400 and CTAB in a certain proportion, and ball-milled until the viscosity was similar to that of the protective pretreatment layer catalyst slurry.

[0033] 4. Preparation of catalyst powder for the capture and purification layer (active component (S-ZrO2, 10 wt%), nano MgO (5 wt%)) TiO2-SiO2 composite aerogel carrier powder, nano MgO powder, and S-ZrO2 powder are mechanically mixed to obtain the catalyst powder for the capture and purification layer. The catalyst powder of the capture and purification layer is mixed with deionized water, silica sol, PEG-400 and CTAB in a certain proportion, and ball-milled until the viscosity is similar to that of the catalyst slurry of the protective pretreatment layer.

[0034] 5. Preparation of SCR denitration catalysts with gradient functional active sites The honeycomb ceramic carrier was cleaned with deionized water in an ultrasonic cleaner to remove dust, and then dried at 110℃ for 2 hours to obtain the pretreated honeycomb ceramic carrier. The dried honeycomb ceramic carrier is vertically fixed in a precision vacuum coating machine. The lower end of the honeycomb ceramic carrier (flue gas inlet end) is immersed in the protective pretreatment layer catalyst slurry. By precisely controlling the vacuum degree and the lifting speed, the slurry is precisely coated to 30% of the total length of the carrier. After removal, it is initially dried at 110℃ for 10 minutes. The carrier coated with the protective pretreatment layer is then immersed again in the main reaction anti-poisoning layer catalyst slurry. The immersion depth is controlled so that the main reaction anti-poisoning layer catalyst slurry covers the remaining 50% of the length (with a small overlap with the protective pretreatment layer), and then initially dried. Finally, the end of the honeycomb ceramic carrier is immersed in the capture and purification layer catalyst slurry, coating the remaining 20% ​​of the length, and then initially dried.

[0035] The coated honeycomb catalyst was placed in a muffle furnace and heated to 120°C at a rate of 1-2°C / min and held for 2 hours to remove moisture. Then, the temperature was increased to 350°C at a rate of 1-2°C / min and held for 3 hours to remove organic matter. Finally, the temperature was increased to 500°C at a rate of 2-3°C / min and held for 6 hours for qualitative analysis. The catalyst was then allowed to cool naturally to room temperature to obtain an SCR denitrification catalyst with gradient functional active sites.

[0036] Example 2 This embodiment is basically the same as Embodiment 1, except that: the protective pretreatment layer accounts for 20% of the total length of the catalyst, the main reaction anti-poisoning layer accounts for 60% of the total length of the catalyst, and the capture and purification layer accounts for 20% of the total length of the catalyst.

[0037] Example 3 This embodiment is basically the same as Embodiment 1, except that: the active components of the protective pretreatment layer are Fe2O3 (5 wt%), MnO2 (8 wt%), and Pt (0.05 wt%), and the active components of the main reactive antitoxic layer are CeO2 (15 wt%) and MnO2 (0.05 wt%).x The active components for the preparation of the catalyst powder for the capture and purification layer are: Fe2O3 (8 wt%), WO3 (2 wt%), MoO3 (3 wt%), and nano MgO (10 wt%).

[0038] Compare with Example 1 Commercial vanadium-titanium catalyst (V2O5-WO3 / TiO2).

[0039] Compare with Example 2 Ordinary non-vanadium catalyst (Ce-Mn / TiO2 prepared by co-precipitation method, uniformly coated on a honeycomb support).

[0040] Experimental Example 1 To investigate the activity of the denitrification catalysts prepared in the above examples and control examples, their denitrification efficiency was tested at flue gas temperatures of 150-500℃. The test results are shown in Table 1.

[0041] The test conditions are as follows: The test temperature was 150-500℃, the volume fraction of NH3 was 0.05%, the NH3 / NO ratio was 1, the O2 content was 5%, the equilibrium gas was N2, and the GHSV was 60000h. -1 .

[0042] The volume fractions of NO and NO2 in the post-reaction mixture were analyzed using a GA-21plus flue gas analyzer (Madur GmbH, Austria), and the denitrification efficiency ηNO (%) was calculated using the following formula. The denitrification efficiency of the denitrification catalyst at different temperatures was obtained using this formula, and the results are detailed in Table 1.

[0043] ηNO (%) = ([NO] in -[NO] out -[NO2] out ) / [NO] in ×100% Table 1. Denitrification efficiency of denitrification catalysts

[0044] As shown in Table 1, Examples 1-3 of this invention all exhibit an ultra-wide activity temperature window (efficiency >90% within 200-450℃). Their low-temperature activity (150-250℃) far exceeds that of traditional vanadium-titanium catalysts (Comparative Example 1), which is attributed to the noble metals and MnO in the inlet region. X Its low-temperature oxidation capability is superior. Its high-temperature activity (400-500℃) and stability are significantly better than those of ordinary non-vanadium catalysts (Comparative Example 2), which is attributed to the thermal stability of the Ce-Mn-Fe system and the specific design of the main reaction zone.

[0045] Experimental Example 2 At the optimal reaction temperature (350℃), flue gas containing 300ppm SO2 was introduced. The volume fraction of SO2 at the inlet and outlet was measured using a flue gas analyzer, and the SO2 oxidation rate ηSO2 (%) was calculated according to the following formula. The results are shown in Table 2.

[0046] ηSO2 (%) = ([SO2] out - [SO2] in ) / [SO2] in × 100% Table 2 SO2 oxidation rate of denitrification catalysts

[0047] As shown in Table 2, the catalysts obtained in Examples 1-3 of the present invention exhibit extremely low SO2 oxidation rates, significantly lower than 1%, compared to Control Examples 1-2. This fully demonstrates the effectiveness of the W / Mo additive in suppressing SO2 oxidation, reducing the risk of ammonium bisulfate (ABS) formation at the source.

[0048] Experimental Example 3 At the reactor outlet, the concentration of unreacted NH3 was detected online using Fourier transform infrared spectroscopy (FTIR), and the ammonia slip was monitored throughout the entire temperature window. The results are shown in Table 3.

[0049] Table 3 Ammonia slip of denitrification catalyst

[0050] Depend on Figure 3 It can be seen that the catalysts obtained in Examples 1-3 of this invention maintained a stable ammonia slip below 2 ppm throughout the entire test temperature range, further demonstrating the efficient ammonia capture and purification layer (S-ZrO2+MgO). In Control Example 1, ammonia slip increased due to insufficient activity at low temperatures and side reactions at high temperatures. Control Example 2 suffered from severe ammonia slip due to its poor N2 selectivity and high-temperature stability.

[0051] Test Example 4 An arsenic-poisoned denitration catalyst was prepared using a simulated poisoning method, as follows: The denitration catalyst was placed in a tubular furnace, and a certain amount of As₂O₃ was placed at the front end of the catalyst. N₂ containing 3 vol% H₂O was introduced into the tubular furnace, and the furnace was heated to 350°C. The As₂O₃ vapor was loaded onto the denitration catalyst with the gas flow. Subsequently, the denitration catalyst was treated at 370°C for 10 hours in an N₂ atmosphere containing 3 vol% O₂ to obtain the arsenic-poisoned denitration catalyst.

[0052] The denitrification efficiency of the arsenic poisoning denitrification catalyst was further tested using the method of Experiment Example 1 at the optimal reaction temperature (350℃), and the results are shown in Table 4.

[0053] Table 4. Denitrification efficiency of denitrification catalysts in arsenic poisoning

[0054] As shown in Table 4, the catalysts prepared in Examples 1-3 of the present invention showed a very small decrease in activity after poisoning (<7%), demonstrating excellent resistance to arsenic poisoning.

[0055] Experimental Example 5 Take 100 cm 3 Catalyst samples with a mesh size of 20-30 were placed in a roller wear tester and rotated at 60 rpm for 60 minutes. After that, they were taken out, weighed, and the wear rate was calculated according to the following formula. The results are shown in Table 5.

[0056] Wear rate = (Weight before wear - Weight after wear) / Weight before wear × 100% Table 5 Wear rate of denitrification catalyst

[0057] As shown in Table 5, the wear rate of the catalysts prepared in Examples 1-3 of this invention is less than 0.5%, which meets and exceeds the industrial application standard (<1%), indicating that the TiO2-SiO2 composite aerogel support and good sintering process endow the catalyst with high mechanical strength.

[0058] In summary, the SCR denitrification catalyst of this invention possesses excellent low-temperature activity and strong resistance to poisoning, and has great prospects for industrial application and economic value.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An SCR denitration catalyst having a gradient function active site, characterized by, The catalyst comprises a honeycomb ceramic carrier and functional layers coated on the side walls of the honeycomb ceramic carrier, and the functional layers comprise, in the direction of flue gas flow, a protective pretreatment layer, a main reaction anti-poisoning layer, and a capture purification layer, The protective pretreatment layer, the main reaction anti-poisoning layer, and the capture purification layer all use TiO2-SiO2 composite aerogel as a carrier; The carrier surface of the protective pretreatment layer is loaded with Fe2O3, MnO x and noble metals; The support surface of the main reaction antitoxic layer is loaded with a complex oxide of CeO2, MnO x , Fe2O3 and an arsenic-resistant additive; The carrier surface of the capture purification layer is loaded with solid superacid and nano-MgO; Preferably, the noble metal includes any one of Pt and Pd; Preferably, the arsenic-resistant additive includes any one or both of WO3 and MoO3; Preferably, the solid superacid includes any one of S-ZrO2 and WO3-ZrO2. 2.The SCR De-NOx catalyst with gradient functional active sites according to claim 1, characterized in that, The protective pretreatment layer accounts for 20%-40% of the overall length of the catalyst; The main reaction anti-poisoning layer accounts for 40%-60% of the overall length of the catalyst; The capture purification layer accounts for 10%-30% of the overall length of the catalyst. 3.The SCR De-NOx catalyst with gradient functional active sites according to claim 1, characterized in that, The protective pretreatment layer has Fe2O3 loading of 1wt%-5wt%, MnO x loading of 3wt%-8wt%, and Pt and / or Pd loading of 0.05wt%-0.5wt%. 4.The SCR de-NOx catalyst with gradient functional active sites according to claim 1, characterized in that, The loading of CeO2 in the main reaction poison-resistant layer is 5wt%-15wt%, the loading of MnO x is 5wt%-10wt%, the loading of Fe2O3 is 3wt%-8wt%, and the loading of WO3 and / or MoO3 is 2wt%-8wt%. 5.The SCR De-NOx catalyst with gradient functional active sites according to claim 1, wherein, In the capture purification layer, the loading amount of nano-MgO is 3wt%-10wt%, and the loading amount of S-ZrO2 and / or WO3-ZrO2 is 5wt%-15wt%. 6.The SCR de-NOx catalyst with gradient functional active sites according to claim 1, characterized in that, The TiO2-SiO2 composite aerogel carrier has a molar ratio of TiO2 to SiO2 of (7:3)-(9:1), a specific surface area of not less than 350 m 2 / g, and has a hierarchical pore structure.

7. A method for preparing an SCR denitration catalyst having a gradient functionally active site, characterized by, The method comprises the following steps: S1. Preparing TiO2-SiO2 composite aerogel carrier powder; S2. Using TiO2-SiO2 composite aerogel as a carrier, preparing catalyst powders of the protective pretreatment layer, the main reaction anti-poisoning layer, and the capture purification layer, respectively; S3. Mixing, ball-milling, and preparing coating slurry of each functional layer by using deionized water, a binder, a thickening agent, and a dispersant; S4. Preprocessing the honeycomb ceramic carrier, and then using gradient vacuum coating method to coat the coating slurry of each functional layer on the preprocessed honeycomb ceramic carrier in sequence to form three continuous functional layers; S5. Programmed step sintering the coated carrier to obtain an SCR denitration catalyst with gradient functional active sites.

8. The preparation method according to claim 7, characterized in that, In step S1, the preparation method of the TiO2-SiO2 composite aerogel carrier powder comprises: Preparation of TiO2-SiO2 wet gel by sol-gel method; Supercritical drying of the wet gel in a supercritical drying kettle with ethanol as a medium under the conditions of a temperature of 200-300℃ and a pressure of 5-10MPa to obtain TiO2-SiO2 composite aerogel blocks; Grinding the TiO2-SiO2 composite aerogel blocks into fine powder, and calcining the fine powder at 400-500℃ for 3-5h to obtain TiO2-SiO2 composite aerogel carrier powder.

9. The preparation method according to claim 7, characterized in that, In step S2, the preparation method of the protective pretreatment layer catalyst powder comprises: Mixing soluble salts of Mn and Fe into a mixed solution, and mixing with a TiO2-SiO2 composite aerogel carrier powder suspension; Adjusting the pH to 9-10 by using ammonia water, and continuously stirring and aging at 70-90℃ for 5-7h to obtain active component powder after filtration, washing, and drying; Immersion of the active component powder into a soluble salt solution of Pt and / or Pd, and drying after immersion for 10-15h to obtain the protective pretreatment layer catalyst powder; Preferably, the preparation method of the main reaction anti-poison layer catalyst powder comprises: The soluble salts of Ce, Mn, Fe, W and Mo are mixed into a mixed solution, which is mixed with the TiO2-SiO2 composite aerogel carrier powder suspension; The main reaction anti-poison layer catalyst powder is obtained by using urea solution as a precipitant, reacting and aging at 90-95°C for 6-10h, and then filtering, washing and drying. Preferably, the preparation method of the capture purification layer catalyst powder comprises: The TiO2-SiO2 composite aerogel carrier powder, nano-MgO powder, S-ZrO2 and / or WO3-ZrO2 powder are mechanically mixed to obtain the capture purification layer catalyst powder.

10. The preparation method according to claim 7, characterized in that, In step S5, the programmed step sintering is performed as follows: first, the temperature is raised to 120°C at a rate of 1-2°C / min and kept for 2h; then, the temperature is raised to 350°C at a rate of 1-2°C / min and kept for 3h; finally, the temperature is raised to 450-550°C at a rate of 2-3°C / min and kept for 4-8h, and then naturally cooled to room temperature.

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