Hydrophobic denitration catalyst and method for preparing the same

Abstract

The present application belongs to the technical field of catalysts, and particularly relates to a hydrophobic denitration catalyst and a preparation method thereof. The hydrophobic denitration catalyst is prepared from the following components: 100 parts of titanium white, 1.7-8.3 parts of ammonium metavanadate, 4-16 parts of ammonium metatungstate, 15-17.5 parts of magnesium fluoride, 3-5 parts of hexagonal boron nitride nanosheet, and 2-5 parts of melamine cyanurate. The preparation method comprises the following steps: preparing two kinds of tartaric acid complex solutions from the ammonium metavanadate and the ammonium metatungstate; mixing and aging the two kinds of tartaric acid complex solutions to obtain an active impregnation solution; adding the titanium white, the magnesium fluoride, the hexagonal boron nitride nanosheet and the melamine cyanurate into the active impregnation solution to obtain a slurry; and finally drying and calcining the slurry to obtain the hydrophobic denitration catalyst. The present application solves the problem of catalyst life attenuation of the traditional vanadium-based catalyst in the low-temperature working condition and active regeneration by preparing a new hydrophobic denitration catalyst.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a hydrophobic denitrification catalyst and its preparation method. Background Technology

[0002] Nitrogen oxides (NO) x Air pollution, primarily consisting of NO and NO2, is one of the major air pollutants. Its sources include stationary sources such as thermal power plants, industrial boilers, kilns, waste incineration, and steel sintering, as well as mobile sources such as diesel vehicles, ships, and non-road machinery. Selective catalytic reduction (SCR) technology, using NH3 (or NH3 produced by urea hydrolysis) as a reducing agent, is currently the most widely used and mature NO reduction technology both domestically and internationally. x The core of SCR denitrification technology lies in the performance of the catalyst. Depending on the active component, SCR denitrification catalysts come in various types, including vanadium-based, manganese-based, iron-based, and copper-based. Among them, vanadium-based catalysts typically have a composition of V₂O₅-WO₃ / TiO₂, and have long dominated the stationary source denitrification market due to their mature preparation process, excellent mid-temperature activity, and good sulfur resistance. However, with the increasing complexity of application conditions, the inherent defects of vanadium-based catalysts have gradually become apparent, particularly in the scenarios of mobile source diesel vehicle exhaust and stationary source humid flue gas.

[0003] Firstly, vanadium-based catalysts operate in a low-temperature range (<250℃). Within this range, water vapor from mobile diesel vehicle exhaust and stationary humid flue gas can cause NO2-oxidation in vanadium-based catalysts. x The conversion rate is significantly reduced; and under combined operating conditions containing sulfur and water, deactivation is more pronounced and partially irreversible, affecting catalyst life. Secondly, during active regeneration of the DPF in diesel vehicles, the SCR inlet temperature can rise sharply to over 600℃. Vanadium-based catalysts exhibit poor stability under such high-temperature hydrothermal conditions, leading to NO... x The conversion efficiency decreases and the activity window narrows, ultimately leading to irreversible deactivation of vanadium-based catalysts under diesel particulate filter (DPF) regeneration conditions, thus affecting catalyst life.

[0004] Chinese patent CN110280315A discloses a method for improving the anti-ABS and water / dust-proof performance of low- and medium-temperature SCR catalysts. This patent involves placing a finished honeycomb vanadium-based or rare-earth-based denitrification catalyst in a hydrophobic organosilicon, followed by vapor deposition at 120-300℃ or impregnation with an organic solvent to form a hydrophobic layer on the surface. After drying, a hydrophobically modified low- and medium-temperature SCR catalyst is obtained. The hydrophobic organosilicon material is one or more of polydimethylsiloxane, octyltrimethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, cyclomethylsiloxane, vinyltrimethoxysilane, vinyltriethoxysilane, phenyltrimethoxysilane, perfluorooctyltrimethoxysilane, and perfluorodecyltrimethoxysilane. Such hydrophobic layers begin to oxidize and decompose at temperatures above 350℃, and the temperature during diesel vehicle DPF regeneration can exceed 600℃. The hydrophobic layer suffers irreversible loss of hydrophobicity, making its service life difficult to guarantee.

[0005] Chinese patent CN118719110A discloses a porous spherical water-resistant and sulfur-resistant low-temperature SCR denitrification catalyst. The preparation method of this low-temperature SCR denitrification catalyst is as follows: ① Oxalic acid-treated anatase TiO2 is ball-milled into porous spheres; ② It is impregnated in a solution containing one of vanadium salt, molybdenum salt, ammonium phosphate salt, Co / La / Zr oxides, and melamine (containing a nitrogen source); ③ Three-stage calcination; ④ A hydrophobic material (one or more of β-cyclodextrin, polydimethylsiloxane, and polydivinylbenzene, 1~10wt%) is introduced, followed by wet ball milling and drying to obtain the low-temperature SCR denitrification catalyst. Since hydrophobic materials such as β-cyclodextrin are carbon-containing organic compounds, they are prone to denaturation and decomposition at the calcination temperature (350~450℃) of the SCR catalyst. Furthermore, the exhaust gas from mobile source diesel vehicles exhibits a large temperature range, making it difficult to guarantee the long-term stability of the denitrification effect of the low-temperature SCR denitrification catalyst when used for diesel vehicle exhaust treatment. Summary of the Invention

[0006] The purpose of this invention is to provide a hydrophobic denitrification catalyst to solve the problem of catalyst life decay in traditional vanadium-based catalysts under low-temperature operating conditions and during active regeneration of diesel vehicle DPF; this invention also provides a method for preparing the hydrophobic denitrification catalyst.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The hydrophobic denitrification catalyst of the present invention comprises the following components by mass: 100 parts titanium dioxide, 1.7-8.3 parts ammonium metavanadate, 4-16 parts ammonium metatungstate, 15-17.5 parts magnesium fluoride, 3-5 parts hexagonal boron nitride nanosheets, and 2-5 parts melamine cyanurate.

[0008] in: The titanium dioxide mentioned is anatase nano-titanium dioxide, with a specific surface area of ​​95~105 m².2 / g.

[0009] The hydrophobic denitration catalyst has a water contact angle of 122~126° and a specific surface area of ​​83.9~95.2 m². 2 / g.

[0010] The preparation method of the hydrophobic denitrification catalyst of the present invention includes the following steps: (1) Prepare a vanadium-tartaric acid complex solution from ammonium metavanadate and a tungsten-tartaric acid complex solution from ammonium metatungstate; (2) Mix the vanadium-tartaric acid complex solution with the tungsten-tartaric acid complex solution, adjust the pH, and age to obtain the active impregnation solution; (3) Add titanium dioxide, magnesium fluoride, hexagonal boron nitride nanosheets and melamine cyanurate to the active impregnation solution and stir to obtain a slurry; (4) The slurry is dried and calcined to obtain a hydrophobic denitrification catalyst.

[0011] in: In step (1), the vanadium-tartaric acid complex solution is prepared by dissolving ammonium metavanadate in water, adding tartaric acid solution, stirring, and obtaining the vanadium-tartaric acid complex solution; the dissolution temperature is 90~95℃; the concentration of tartaric acid solution is 4.5~5.5mol / L, and the ratio of ammonium metavanadate:water:tartaric acid solution is (1.7~8.3):200:(35~80). Ammonium metavanadate is expressed in g, and water and tartaric acid solution are expressed in mL.

[0012] In step (1), the tungsten-tartaric acid complex solution is prepared by dissolving ammonium metatungstate in water, adding tartaric acid solution, stirring, and obtaining the tungsten-tartaric acid complex solution. The concentration of tartaric acid solution is 0.5~0.6 mol / L, and the ratio of ammonium metatungstate:water:tartaric acid solution is (4~16):150:(60~150). Ammonium metatungstate is expressed in g, and water and tartaric acid solution are expressed in mL.

[0013] In step (2), the pH is adjusted to 2.5-3.0 and the aging time is 1-2 hours.

[0014] In step (3), the stirring temperature is 30~50℃, the stirring speed is 200~300rpm, and the stirring time is 1.5~2.5h.

[0015] In step (4), the drying temperature is 60~70℃ and the drying time is 12~16h.

[0016] In step (4), during roasting, the temperature is increased to 450-520℃ at a rate of 2-3.5℃ / min and held for 8-10 hours to complete the roasting.

[0017] The beneficial effects of this invention are as follows: (1) During the calcination of the precursor to form the V2O5-WO3 / TiO2 catalyst matrix, melamine cyanurate (hereinafter referred to as MCA) acts as a sacrificial pore-forming agent, synergistically with magnesium fluoride (hereinafter referred to as MgF2) and hexagonal boron nitride nanosheets (hereinafter referred to as h-BN) to construct a multi-scale all-inorganic composite hydrophobic structure on the surface of the catalyst matrix; MCA is completely decomposed and removed during the calcination process, and no organic components remain in the final hydrophobic structure: During high-temperature calcination, MCA dissociates into melamine and cyanuric acid. The two sublimate and further decompose and oxidize, releasing gases such as NH3, CO2, H2O and a small amount of isocyanic acid (HNCO) and completely removing them, leaving interconnected multi-level channels in situ inside and on the surface of the catalyst. MgF2 and h-BN nanosheets are insoluble in water in the slurry and are uniformly dispersed in solid form. Under the combined effects of capillary shrinkage during the drying stage (water forms a meniscus in the capillaries between nano- or micro-sized materials, generating negative pressure, pulling the materials closer together, resulting in uniform shrinkage of the material as a whole) and MCA decomposition and gasification during the calcination stage, due to the large specific surface area and high bending stiffness of MgF2 and h-BN, their shrinkage is lower than that of ammonium metavanadate and ammonium metatungstate. Therefore, during calcination, MgF2 and h-BN are dispersed on the inner wall and pore opening of the newly formed channels: the basal surface of h-BN nanosheets is a chemically inert surface saturated with BN bonds, providing dispersion and anchoring points for the V2O5-WO3 active components; MgF2 does not decompose or melt at the calcination temperature of this invention, and is dispersed on the pore walls and TiO2 surface, forming a rough structure together with h-BN sheets and hierarchical channels. This rough structure can trap air and significantly reduce the actual solid-liquid contact area between water droplets and the surface. Furthermore, the h-BN inert basal plane and MgF2 cover and shield the hydrophilic sites rich in hydroxyl groups on the TiO2 support surface, reducing the surface's affinity for water. The coupling of the two results in a water contact angle of 122~126° on the catalyst surface, exhibiting stable hydrophobicity.

[0018] The stable hydrophobicity can trap air layers, significantly reducing the actual solid-liquid contact area; it shields some of the hydrophilic hydroxyl sites on the TiO2 support surface; it inhibits the competitive adsorption of water molecules on active sites; and it suppresses capillary condensation and water blockage within the pores. Furthermore, the hydrophobic structure of this invention is composed of inorganic components such as h-BN and MgF2, which do not decompose at the regeneration temperature. Therefore, the hydrophobic structure remains intact after multiple regeneration cycles, and the aforementioned water-resistant properties can continue to function when returning to low-temperature, water-containing conditions. This is the key to this invention's simultaneous achievement of both low-temperature water resistance and long lifespan under regeneration conditions.

[0019] Thus, the pore-forming process of MCA, the overlapping of h-BN sheets, and the enrichment of MgF2 work together to synergistically construct the aforementioned composite hydrophobic structure. Both h-BN and MgF2 ultimately retained in the catalyst are inorganic components: neither h-BN nor MgF2 decomposes at calcination and DPF regeneration temperatures. This allows the composite hydrophobic structure to maintain its structural integrity even in the high-temperature, water-containing atmosphere of active DPF regeneration in diesel vehicles. This overcomes the defects of existing technologies where organic hydrophobic layers, such as organosilicon (which decomposes at >350℃) and β-cyclodextrin / polydimethylsiloxane (PDMS, which decomposes at calcination temperatures), are oxidized and irreversibly lost under regeneration conditions.

[0020] (2) During active regeneration of the DPF in diesel vehicles, traditional V2O5-WO3 / TiO2 is prone to TiO2 rutile phase transformation and V / W species sintering and agglomeration, resulting in a decrease in specific surface area and the number of active sites. In this invention, the endothermic pore-forming effect of MCA during the calcination and forming stage is interconnected with the structural stabilizing effect of h-BN and MgF2 during the high-temperature service stage, synergistically inhibiting sintering from the following aspects: During the calcination and forming stage, the sublimation and decomposition of MCA is a strongly endothermic process, which can absorb and homogenize the heat released by the combustion of organic ligands such as tartaric acid and the decomposition and oxidation of precursors, suppressing local overheating and heat peaks inside the powder bed, and avoiding local over-sintering of active components during the phase formation process. The hierarchical porous structure left after the complete removal of MCA gives the catalyst a high initial specific surface area and reserves stress release space for subsequent thermal expansion at high temperatures and V2O5-WO3 / TiO2 rearrangement. During the high-temperature service phase of the hydrophobic denitration catalyst: h-BN nanosheets interspersed between V2O5-WO3 / TiO2 form a two-dimensional physical barrier, pinning the migration and merging of TiO2 grain boundaries. Furthermore, the high in-plane thermal conductivity of h-BN helps to homogenize the internal temperature distribution of V2O5-WO3 / TiO2 and alleviate local hot spots. MgF2, as a second phase, anchors at the TiO2 grain boundaries and the interface between h-BN sheets and TiO2, exerting a pinning effect and hindering grain boundary migration and merging. The hierarchical porous structure provides stress release and volume buffer space for high-temperature thermal expansion, inhibiting the close packing and densification of V2O5-WO3 / TiO2. The aforementioned two-dimensional physical barrier, second-phase pinning, and pore structure stress release work synergistically to slow down the rutile phase transformation of TiO2 and the sintering and agglomeration of V / W species. Thus, after aging, the specific surface area of ​​the hydrophobic denitration catalyst does not collapse, active sites are not lost, and the crystal form does not change. After high-temperature hydrothermal aging, NO... x The conversion rate remains high and the activity window does not narrow, thus avoiding irreversible deactivation under DPF regeneration conditions and helping to extend the catalyst life. Attached Figure Description

[0021] Figure 1 This is a SEM image of the hydrophobic denitrification catalyst in Example 1. Detailed Implementation

[0022] The present invention will now be described and illustrated in detail with reference to the embodiments.

[0023] The raw materials used in the following examples and comparative examples are all commercially available products.

[0024] Example 1 Take 200 mL of deionized water, heat it to 90 °C and keep it constant, add 5.0 g of ammonium metavanadate powder and stir to dissolve; while maintaining stirring, slowly add 50 mL of 4.5 mol / L tartaric acid solution, and continue stirring for 30 min to obtain vanadium-tartaric acid complex solution.

[0025] Take another 150 mL of deionized water, add 12.0 g of ammonium metatungstate powder and stir to dissolve; while maintaining stirring, add 130 mL of 0.6 mol / L tartaric acid solution dropwise at room temperature, and continue stirring for 40 min to obtain a tungsten-tartaric acid complex solution.

[0026] The vanadium-tartaric acid complex solution was slowly poured into the tungsten-tartaric acid complex solution. After mixing, tartaric acid was added to adjust the pH to 2.5-3.0. The mixture was then aged at room temperature for 1 hour to obtain the active impregnation solution for later use.

[0027] Weigh out 100g of titanium dioxide (anatase nano titanium dioxide, specific surface area 95.0m²). 2 15g of magnesium fluoride, 3g of hexagonal boron nitride nanosheets, and 2g of melamine cyanurate were added to the above active impregnation solution in a constant temperature water bath at 40℃ and stirred at 200rpm for 2 hours to obtain a slurry.

[0028] The slurry was vacuum dried at 60℃ for 14 h. The dried powder was then transferred to a muffle furnace and heated to 480℃ at a rate of 3.5℃ / min, held at that temperature for 9 h, and allowed to cool naturally to room temperature. The powder was then ground through a 100-mesh sieve to obtain the hydrophobic denitrification catalyst. SEM characterization of the hydrophobic denitrification catalyst is shown below. Figure 1 As shown, based on the mass of titanium dioxide (100wt%), the loading of V2O5 was 3.34wt% and the loading of WO3 was 10.21wt%.

[0029] The performance of hydrophobic denitrification catalysts was tested: Water contact angle: The water contact angle of the catalyst surface was measured to be 125° using a contact angle meter, indicating that it has excellent hydrophobicity.

[0030] Specific surface area: The specific surface area determined by the BET method is 85.0 m². 2 / g.

[0031] Denitrification activity test: A hydrophobic denitrification catalyst was loaded into a quartz tube reactor, and simulated flue gas was introduced. The simulated flue gas composition was 500 ppm NO, 500 ppm NH3, 15 vol% H2O, 5 vol% O2, and balance gas N2, with a space velocity of 30,000 h⁻¹. -1 Simulating the low-temperature operating conditions of the catalyst, i.e., continuous operation within a temperature window of 180~220℃, tests showed that NO... x The conversion rate was 92.8%; after continuous operation at 200℃ for 80 hours, NO... x The conversion rate decreased by 0.5%.

[0032] Hydrothermal aging resistance: Simulating multiple cycles of active regeneration of a diesel vehicle's DPF, i.e., aging the hydrophobic denitrification catalyst at 750℃ in air containing 15 vol% water vapor for 10 hours, the denitrification activity of the hydrophobic denitrification catalyst at 200℃ was retested. x The conversion rate was 88.2%.

[0033] Example 2 Take 200 mL of deionized water, heat it to 95 °C and keep it constant, add 1.7 g of ammonium metavanadate powder and stir to dissolve; while maintaining stirring, slowly add 35 mL of 5 mol / L tartaric acid solution, and continue stirring for 30 min to obtain vanadium-tartaric acid complex solution.

[0034] Take another 150 mL of deionized water, add 4.0 g of ammonium metatungstate powder and stir to dissolve; while maintaining stirring, add 60 mL of 0.5 mol / L tartaric acid solution dropwise at room temperature, and continue stirring for 40 min to obtain a tungsten-tartaric acid complex solution.

[0035] The vanadium-tartaric acid complex solution was slowly poured into the tungsten-tartaric acid complex solution. After mixing, tartaric acid was added to adjust the pH to 2.5-3.0. The solution was then aged at room temperature for 1.5 hours to obtain the active impregnation solution for later use.

[0036] Weigh out 100g of titanium dioxide (anatase nano titanium dioxide, specific surface area 95.0m²). 2 16g of magnesium fluoride, 4g of hexagonal boron nitride nanosheets, and 5g of melamine cyanurate were added to the above active impregnation solution in a constant temperature water bath at 30℃ and stirred at 300rpm for 1.5h to obtain a slurry.

[0037] The slurry was vacuum dried at 60℃ for 16 hours. The dried powder was then transferred to a muffle furnace and heated to 450℃ at a rate of 2.5℃ / min, held at that temperature for 10 hours, and allowed to cool naturally to room temperature. The powder was then ground through a 100-mesh sieve to obtain a hydrophobic denitrification catalyst. Analysis showed that, based on 100wt% titanium dioxide, the loading of V₂O₅ was 1.22wt% and the loading of WO₃ was 3.18wt%.

[0038] The performance of hydrophobic denitrification catalysts was tested: Water contact angle: The water contact angle of the catalyst surface was measured to be 122° using a contact angle meter, indicating that it has excellent hydrophobicity.

[0039] Specific surface area: The specific surface area determined by the BET method is 83.9 m². 2 / g.

[0040] Denitrification activity test: A hydrophobic denitrification catalyst was loaded into a quartz tube reactor, and simulated flue gas was introduced. The simulated flue gas composition was 500 ppm NO, 500 ppm NH3, 15 vol% H2O, 5 vol% O2, and balance gas N2, with a space velocity of 30,000 h⁻¹. -1 Simulating the low-temperature operating conditions of the catalyst, i.e., continuous operation within a temperature window of 180~220℃, tests showed that NO... x The conversion rate was 91.5%; after continuous operation at 200℃ for 80 hours, NO... x The conversion rate decreased by 0.4%.

[0041] Hydrothermal aging resistance: Simulating multiple cycles of active regeneration of a diesel vehicle's DPF, i.e., aging the hydrophobic denitrification catalyst at 750℃ in air containing 15 vol% water vapor for 10 hours, the denitrification activity of the hydrophobic denitrification catalyst at 200℃ was retested. x The conversion rate was 87.4%.

[0042] Example 3 Take 200 mL of deionized water, heat it to 93 °C and keep it constant, add 8.3 g of ammonium metavanadate powder and stir to dissolve; while maintaining stirring, slowly add 80 mL of 5.5 mol / L tartaric acid solution, and continue stirring for 30 min to obtain vanadium-tartaric acid complex solution.

[0043] Take another 150 mL of deionized water, add 16.0 g of ammonium metatungstate powder and stir to dissolve; while maintaining stirring, add 150 mL of 0.6 mol / L tartaric acid solution dropwise at room temperature, and continue stirring for 40 min to obtain a tungsten-tartaric acid complex solution.

[0044] The vanadium-tartaric acid complex solution was slowly poured into the tungsten-tartaric acid complex solution. After mixing, tartaric acid was added to adjust the pH to 2.5-3.0. The mixture was then aged at room temperature for 2 hours to obtain the active impregnation solution for later use.

[0045] Weigh 100g of titanium dioxide (anatase nano titanium dioxide, specific surface area 105m²). 217.5g of magnesium fluoride, 5g of hexagonal boron nitride nanosheets, and 4g of melamine cyanurate were added to the above active impregnation solution in a constant temperature water bath at 50℃ and stirred at 250rpm for 2.5h to obtain a slurry.

[0046] The slurry was vacuum dried at 70℃ for 12 hours. The dried powder was then transferred to a muffle furnace and heated to 520℃ at a rate of 2℃ / min, held at that temperature for 8 hours, and allowed to cool naturally to room temperature. The powder was then ground through a 100-mesh sieve to obtain a hydrophobic denitrification catalyst. Analysis showed that, based on 100wt% titanium dioxide, the loading of V₂O₅ was 5.87wt% and the loading of WO₃ was 13.84wt%.

[0047] The performance of hydrophobic denitrification catalysts was tested: Water contact angle: The water contact angle of the catalyst surface was measured to be 126° using a contact angle meter, indicating that it has excellent hydrophobicity.

[0048] Specific surface area: The specific surface area determined by the BET method is 95.2 m². 2 / g.

[0049] Denitrification activity test: A hydrophobic denitrification catalyst was loaded into a quartz tube reactor, and simulated flue gas was introduced. The simulated flue gas composition was 500 ppm NO, 500 ppm NH3, 15 vol% H2O, 5 vol% O2, and balance gas N2, with a space velocity of 30,000 h⁻¹. -1 Simulating the low-temperature operating conditions of the catalyst, i.e., continuous operation within a temperature window of 180~220℃, tests showed that NO... x The conversion rate was 94.7%; after continuous operation at 200℃ for 80 hours, NO... x The conversion rate decreased by 0.5%.

[0050] Hydrothermal aging resistance: Simulating multiple cycles of active regeneration of a diesel vehicle's DPF, i.e., aging the hydrophobic denitrification catalyst at 750℃ in air containing 15 vol% water vapor for 10 hours, the denitrification activity of the hydrophobic denitrification catalyst at 200℃ was retested. x The conversion rate was 90.5%.

[0051] Comparative Example 1 Without adding magnesium fluoride, the remaining procedures were the same as in Example 1 to obtain the denitration catalyst. The performance of the denitration catalyst was then tested. Water contact angle: The water contact angle on the catalyst surface was measured to be 93° using a contact angle measuring instrument.

[0052] Specific surface area: The specific surface area determined by the BET method is 90.6 m². 2 / g.

[0053] Denitrification activity test: The denitrification catalyst was loaded into a quartz tube reactor, and simulated flue gas was introduced. The simulated flue gas composition was 500 ppm NO, 500 ppm NH3, 15 vol% H2O, 5 vol% O2, and balance gas N2, with a space velocity of 30,000 h⁻¹. -1 Simulating the low-temperature operating conditions of the catalyst, i.e., continuous operation within a temperature window of 180~220℃, tests showed that NO... x The conversion rate was 80.6%; after continuous operation at 200℃ for 80 hours, NO... x The conversion rate decreased by 17%.

[0054] Hydrothermal aging resistance: Simulating multiple cycles of active regeneration of a diesel vehicle's DPF, i.e., aging the denitrification catalyst at 750℃ in air containing 15 vol% water vapor for 10 hours, the denitrification activity of the catalyst at 200℃ was retested. NO x Conversion rate: 63.5%.

[0055] Comparative Example 2 Without adding hexagonal boron nitride nanosheets, the remaining procedures were the same as in Example 1 to obtain the denitration catalyst. The performance of the denitration catalyst was then tested. Water contact angle: The water contact angle of the catalyst surface was measured to be 101° using a contact angle measuring instrument.

[0056] Specific surface area: The specific surface area determined by the BET method is 90.4 m². 2 / g.

[0057] Denitrification activity test: The denitrification catalyst was loaded into a quartz tube reactor, and simulated flue gas was introduced. The simulated flue gas composition was 500 ppm NO, 500 ppm NH3, 15 vol% H2O, 5 vol% O2, and balance gas N2, with a space velocity of 30,000 h⁻¹. -1 Simulating the low-temperature operating conditions of the catalyst, i.e., continuous operation within a temperature window of 180~220℃, tests showed that NO... x The conversion rate was 83.9%; after continuous operation at 200℃ for 80 hours, NO... x The conversion rate decreased by 14%.

[0058] Hydrothermal aging resistance: Simulating multiple cycles of active regeneration of a diesel vehicle's DPF, i.e., aging the denitrification catalyst at 750℃ in air containing 15 vol% water vapor for 10 hours, the denitrification activity of the catalyst at 200℃ was retested. NO x Conversion rate: 72.4%.

[0059] Comparative Example 3 Without adding melamine cyanurate, the remaining procedures were the same as in Example 1 to obtain the denitration catalyst. The performance of the denitration catalyst was then tested. Water contact angle: The water contact angle of the catalyst surface was measured to be 84° using a contact angle measuring instrument.

[0060] Specific surface area: The specific surface area determined by the BET method is 74.6 m². 2 / g.

[0061] Denitrification activity test: The denitrification catalyst was loaded into a quartz tube reactor, and simulated flue gas was introduced. The simulated flue gas composition was 500 ppm NO, 500 ppm NH3, 15 vol% H2O, 5 vol% O2, and balance gas N2, with a space velocity of 30,000 h⁻¹. -1 Simulating the low-temperature operating conditions of the catalyst, i.e., continuous operation within a temperature window of 180~220℃, tests showed that NO... x The conversion rate was 82.8%; after continuous operation at 200℃ for 80 hours, NO... x The conversion rate decreased by 13%.

[0062] Hydrothermal aging resistance: Simulating multiple cycles of active regeneration of a diesel vehicle's DPF, i.e., aging the denitrification catalyst at 750℃ in air containing 15 vol% water vapor for 10 hours, the denitrification activity of the catalyst at 200℃ was retested. NO x Conversion rate: 77.6%.

[0063] Implementation effect evaluation The water contact angles of Comparative Examples 1-3 were 93°, 101°, and 84°, respectively, all significantly lower than those of Example 1. Specifically, Comparative Example 3, lacking melamine cyanurate (MCA), had a water contact angle of only 84°, below the critical hydrophilic / hydrophobic angle of 90°, indicating a change in the catalyst surface from hydrophobic to hydrophilic. Comparative Example 1, lacking magnesium fluoride (MgF2), saw its water contact angle drop to 93°, only slightly above the critical angle. Comparative Example 2, lacking hexagonal boron nitride nanosheets (h-BN), had a water contact angle of 101°. This demonstrates that the significant decrease in water contact angles in each comparative example is due to changes in surface chemical composition and roughness structure resulting from the absence of the corresponding component. This aligns with the hydrophobic formation mechanism described in the beneficial effects: MCA is completely decomposed and removed during calcination, leaving interconnected hierarchical channels in situ. Under the combined effect of capillary shrinkage during drying and MCA decomposition and vaporization during calcination, MgF2 and h-BN nanosheets are dispersed on the inner walls and pore openings of the newly formed channels. Without MCA, the hierarchical channels and the dispersion of MgF2 and h-BN within the channels disappear, making it difficult to form a rough structure. Therefore, the contact angle in Comparative Example 3 drops below the critical angle. MgF2 does not decompose or melt at the calcination temperature, dispersing on the pore walls and TiO2 surface. Together with the inert basal surface of h-BN, it covers and shields the hydrophilic sites rich in hydroxyl groups on the TiO2 support surface and participates in the formation of the rough structure. Without MgF2, the hydrophilic sites are not effectively shielded, and the rough structure is incomplete. Therefore, the water contact angle in Comparative Example 1 decreases significantly. The basal surface of the h-BN nanosheets is a chemically inert surface saturated with BN bonds; the absence of h-BN results in the loss of this chemically inert surface, thus significantly reducing the water contact angle in Comparative Example 2. These results demonstrate that MCA pore formation, MgF2 dispersion shielding, and h-BN sheets work synergistically and are indispensable in the construction of the composite hydrophobic structure, collectively contributing to the high water contact angle (122–126°) and stable hydrophobicity of the catalysts obtained in the examples.

[0064] Comparative data from the low-temperature, water-containing denitrification activity tests of the examples and comparative examples show that: under simulated flue gas containing 15 vol% water vapor (500 ppm NO, 500 ppm NH3, 5 vol% O2, and balance gas N2) and a space velocity of 30,000 h⁻¹, the denitrification activity is: -1 Under a low-temperature window of 180~220℃, NO in Example 1 x The conversion rate reached 92.8%, while Comparative Examples 1-3 were significantly lower than Example 1. After continuous operation at 200°C for 80 hours, the NO content in Example 1 was significantly lower. x The conversion rate decreased by 0.5%; while the NO conversion rate in comparative examples 1-3 decreased by 0.5%. xThe conversion rates decreased by 17%, 14%, and 13%, respectively, indicating a significant deterioration in long-term stability. This suggests that under high humidity and low temperature conditions, the competitive adsorption and capillary condensation of water vapor on the catalyst surface are important reasons for the inhibition of vanadium-based catalyst activity and the gradual decline in activity. The composite hydrophobic structure constructed in this invention effectively blocks the enrichment of water molecules near the active sites, inhibits the competitive adsorption and capillary condensation of water vapor, and enables the V2O5-WO3 active centers to maintain a high and stable NO content in a water-containing atmosphere. x Conversion efficiency.

[0065] Comparing the high-temperature hydrothermal aging test data of the examples and comparative examples, it can be seen that after aging in air at 750℃ with 15 vol% water vapor for 10 hours (simulating multiple cycles of extreme conditions for active regeneration of a diesel vehicle's DPF), the denitrification activity at 200℃ was retested, and the NO content in Example 1 was [data missing]. x The conversion rate remained at 88.2%, while Comparative Examples 1-3 were significantly lower than Example 1. Before aging, NO in Example 1 was within a temperature window of 180-220°C. x The conversion rate was 92.8%. After the above-mentioned harsh hydrothermal aging, its NO content at 200℃ was [missing information]. x The conversion rate remained at 88.2%, indicating that the catalyst still possesses good low-temperature activity stability after hydrothermal aging at temperatures above 600℃. These results are consistent with the ternary synergistic anti-sintering mechanism described in the beneficial effects section: the stress release from the pore structure formed by MCA, the two-dimensional physical barrier of h-BN, and the pinning of the MgF2 second phase synergistically mitigate the rutile phase transformation of TiO2 and the sintering and agglomeration of V / W species. In contrast, the low-temperature activity of the comparative catalysts significantly decreased after hydrothermal aging due to the absence of corresponding components and the disruption of the synergistic mechanism.

Claims

1. A hydrophobic denitrification catalyst, characterized in that, The raw materials, by weight, include the following components: 100 parts titanium dioxide, 1.7 to 8.3 parts ammonium metavanadate, 4 to 16 parts ammonium metatungstate, 15 to 17.5 parts magnesium fluoride, 3 to 5 parts hexagonal boron nitride nanosheets, and 2 to 5 parts melamine cyanurate.

2. The hydrophobic denitrification catalyst according to claim 1, characterized in that, Titanium dioxide is anatase nano-titanium dioxide, with a specific surface area of ​​95~105 m². 2 / g.

3. The hydrophobic denitrification catalyst according to claim 1, characterized in that, The water contact angle of the hydrophobic denitration catalyst surface is 122~126°, and the specific surface area of ​​the hydrophobic denitration catalyst is 83.9~95.2 m². 2 / g.

4. A method for preparing the hydrophobic denitrification catalyst according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Prepare a vanadium-tartaric acid complex solution from ammonium metavanadate and a tungsten-tartaric acid complex solution from ammonium metatungstate; (2) Mix the vanadium-tartaric acid complex solution with the tungsten-tartaric acid complex solution, adjust the pH, and age to obtain the active impregnation solution; (3) Add titanium dioxide, magnesium fluoride, hexagonal boron nitride nanosheets and melamine cyanurate to the active impregnation solution and stir to obtain a slurry; (4) The slurry is dried and calcined to obtain a hydrophobic denitrification catalyst.

5. The method for preparing the hydrophobic denitrification catalyst according to claim 4, characterized in that, In step (1), the vanadium-tartaric acid complex solution is prepared by dissolving ammonium metavanadate in water, adding tartaric acid solution, stirring, and obtaining the vanadium-tartaric acid complex solution; the dissolution temperature is 90~95℃; the concentration of tartaric acid solution is 4.5~5.5mol / L, and the ratio of ammonium metavanadate:water:tartaric acid solution is (1.7~8.3):200:(35~80). Ammonium metavanadate is expressed in g, and water and tartaric acid solution are expressed in mL.

6. The method for preparing the hydrophobic denitrification catalyst according to claim 4, characterized in that, In step (1), the tungsten-tartaric acid complex solution is prepared by dissolving ammonium metatungstate in water, adding tartaric acid solution, stirring, and obtaining the tungsten-tartaric acid complex solution. The concentration of tartaric acid solution is 0.5~0.6 mol / L, and the ratio of ammonium metatungstate:water:tartaric acid solution is (4~16):150:(60~150). Ammonium metatungstate is expressed in g, and water and tartaric acid solution are expressed in mL.

7. The method for preparing the hydrophobic denitrification catalyst according to claim 4, characterized in that, In step (2), the pH is adjusted to 2.5-3.0 and the aging time is 1-2 hours.

8. The method for preparing the hydrophobic denitrification catalyst according to claim 4, characterized in that, In step (3), the stirring temperature is 30~50℃, the stirring speed is 200~300rpm, and the stirring time is 1.5~2.5h.

9. The method for preparing the hydrophobic denitrification catalyst according to claim 4, characterized in that, In step (4), the drying temperature is 60~70℃ and the drying time is 12~16h.

10. The method for preparing the hydrophobic denitrification catalyst according to claim 4, characterized in that, In step (4), during roasting, the temperature is increased to 450-520℃ at a rate of 2-3.5℃ / min and held for 8-10 hours to complete the roasting.

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