Vanadium-tungsten-titanium type SCR denitration catalyst and preparation method thereof

Abstract

The invention discloses a vanadium-tungsten-titanium type SCR denitration catalyst and a preparation method thereof, and relates to the technical field of catalysts. According to the technical scheme, the preparation method comprises the following steps: S1, preparing a TiO2-coated ZrO2 core-shell composite carrier; s2, electromagnetic coupling field auxiliary tungsten loading; s3, microwave-enhanced vanadium loading; s4, depositing a coating: coating a polyacrylic acid-b-polystyrene layer on a product in the step S3 through atomic layer deposition to obtain the vanadium-tungsten-titanium type SCR denitration catalyst. The vanadium-tungsten-titanium type SCR denitration catalyst has excellent low-temperature activity and toxicity resistance, the replacement period of a catalyst module is prolonged to 6 years, and the service life is greatly prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a vanadium-tungsten-titanium type SCR denitration catalyst and a preparation method thereof. Background Art

[0002] Vanadium-tungsten-titanium catalyst is a denitrification catalyst widely used in selective catalytic reduction technology. Its main active components are V2O5, WO3 and TiO2. This catalyst can effectively promote the reduction of nitrogen oxides (NO x ) reacts with ammonia (NH3) at high temperature to generate nitrogen and water, thereby achieving NO in flue gas. x effective removal.

[0003] Although vanadium-tungsten-titanium catalysts are widely used in the field of denitrification, the following problems still exist:

[0004] (1) Narrow temperature window

[0005] The suitable operating temperature range of vanadium-tungsten-titanium catalyst is 300-420℃. Below 200℃, NO x The conversion rate drops significantly, typically below 50%, making it difficult to meet the requirements of low-load conditions. In low-load operation of coal-fired power plants or certain low-temperature flue gas treatment scenarios (such as the coking and cement industries), the flue gas temperature is low, and the catalyst activity is insufficient, resulting in a significant reduction in denitrification efficiency.

[0006] (2) Poor anti-poisoning performance

[0007] The active components of the catalyst (such as V2O5) are more sensitive to poisoning substances such as SO3, which will react with the active sites on the catalyst surface, causing catalyst deactivation or shortening of life.

[0008] In summary, the vanadium-tungsten-titanium catalyst is a highly efficient denitrification catalyst, exhibiting excellent denitrification performance within the 300-420°C range. However, its narrow temperature window and insufficient resistance to poisoning limit its application in low-temperature conditions and complex flue gas environments. Therefore, further improvements are needed to address these issues and provide new possibilities for future industrial applications. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a vanadium-tungsten-titanium SCR denitrification catalyst and its preparation method, which has excellent low-temperature activity and resistance to poisoning, and the catalyst module replacement cycle is extended to 6 years, greatly extending the service life.

[0010] The technical solution of the present invention is:

[0011] In one aspect, the present invention provides a method for preparing a vanadium-tungsten-titanium SCR denitration catalyst, comprising the following steps:

[0012] S1 Preparation of TiO2@ZrO2 core-shell composite support: TiO2 nanoparticles were synthesized by sol-gel method using tetrabutyl titanate as precursor, and then coated with ZrO2 shell in ZrOCl2·8H2O ethanol solution; 4+ With W 6+ Strong electronic interaction inhibits the migration of active components;

[0013] S2 electromagnetic coupling field assisted tungsten loading: The TiO2@ZrO2 core-shell composite carrier is impregnated in an impregnation solution containing ammonium metatungstate, [Bmim]PF6 ionic liquid and citric acid, and a pulsed magnetic field and ultrasonic waves are applied. The mixture is treated at 50-70°C for 2-3h and pre-calcined at 400-500°C.

[0014] S3 Microwave-enhanced vanadium loading: The product of step S2 is immersed in a solution containing ammonium metavanadate, EDTA and Ce. 0.7 La 0.3 O x The impregnation solution was treated with pulse microwave and calcined at 350-450℃; wherein Ce 0.7 La 0.3 O x The oxygen vacancy density is greatly increased compared to pure CeO2, which promotes the adsorption of NH3 and SO3 2- Oxidation inhibition;

[0015] S4 deposition coating: coating the product of step S3 with a polyacrylic acid-b-polystyrene layer by atomic layer deposition (ALD) to obtain a vanadium-tungsten-titanium type SCR denitration catalyst.

[0016] Preferably, the specific operations of step S1 are as follows:

[0017] S11 Precursor Prehydrolysis: Tetrabutyl titanate (TBT) and acetic acid were mixed in a nitrogen-protected reactor; acetic acid reacted with Ti through the carboxylic acid group. 4+ Coordinate to inhibit the rapid hydrolysis of TBT;

[0018] S12 hydrolysis reaction: add ethanol-water mixture with a pH of 2.5-3.5 dropwise, maintaining the reaction temperature at 38-42°C; after the addition is completed, continue stirring to form a uniform and transparent TiO2 sol; wherein an acidic environment with a pH of 2.5-3.5 can achieve controlled hydrolysis;

[0019] S13 Sol-Gel Conversion: Raise the temperature to 60-65°C, adjust the pH to 5.5-6, and carry out polycondensation to prepare a wet gel. The viscosity of the system gradually increases, forming a three-dimensional network gel. The gelation time is monitored by a rheometer (the gelation is completed when the storage modulus G'> the loss modulus G");

[0020] S14 aging and drying: The wet gel is statically aged for 20-28 hours to strengthen the network structure; it is then dried using supercritical CO2 to prevent pore collapse and obtain a dry gel;

[0021] S15 crystallization and calcination: Place the dry gel in a muffle furnace, heat it to 450-500°C at a rate of 1.8-2.2°C / min under air atmosphere, and keep it at this temperature for 2-3 hours to obtain anatase TiO2 nanoparticles;

[0022] S16 TiO2 surface pretreatment: Disperse TiO2 nanoparticles in an ethanol-water mixture and ultrasonicate to obtain a uniform TiO2 suspension; adjust the pH to 2-2.5 to protonate the TiO2 surface (Zeta potential +25 mV) and enhance electrostatic adsorption with the ZrO2 precursor;

[0023] S17 zirconium source hydrolysis and interface nucleation: ZrOCl2·8H2O and CTAB were dissolved in an ethanol-water mixture to prepare a zirconium source solution; under nitrogen protection, the zirconium source solution was added dropwise to the TiO2 suspension; ammonia water was added dropwise simultaneously to maintain the pH of the system at 4.5-5, which promoted the hydrolysis of ZrOCl2·8H2O and interface nucleation. 4+ It preferentially hydrolyzes to form Zr(OH)4 nuclei on the TiO2 surface rather than in the bulk;

[0024] S18 ZrO2 shell growth: After the addition is complete, the temperature is raised to 70-75°C and aged for 5-7 hours; CTAB micelles adsorb on the Zr(OH)4 surface, guiding the formation of mesoporous structure through the lyotropic liquid crystal template effect;

[0025] S19 template removal and crystallization: The product was centrifuged and washed to remove free CTAB. The washed wet gel was vacuum dried and then placed in a muffle furnace. The temperature was raised to 400-450°C at a rate of 0.8-1.2°C / min in an air atmosphere and kept at this temperature for 2-3 hours to obtain a TiO2@ZrO2 core-shell composite carrier.

[0026] In preparing a TiO2@ZrO2 core-shell composite carrier, the present invention overcomes the bottleneck of easy agglomeration in the traditional sol-gel method through acetic acid complexation and pH segmented control, achieving the controllable preparation of highly dispersed and narrowly distributed TiO2 nanoparticles, laying the structural foundation for the construction of a gradient pore composite carrier. Simultaneously, by matching pH with Zeta potential, heterogeneous nucleation of ZrO2 on the TiO2 surface is achieved. Through CTAB template confinement and interface nucleation control, the present invention overcomes the bottleneck of dense shell and limited mass transfer in traditional coating methods, constructing a high-specific-surface-area mesoporous ZrO2 / TiO2 core-shell structure and significantly improving catalytic stability.

[0027] Preferably, in step S11, the acetic acid is 10-15% by mass of tetrabutyl titanate; in step S12, in the ethanol-water mixture, the volume ratio of ethanol to tetrabutyl titanate is (2-3):1, and the molar ratio of water to tetrabutyl titanate is (4-8):1; in step S16, in the ethanol-water mixture, the volume ratio of ethanol to water is (4-5):1, and the solid content of the TiO2 suspension is 4-8wt.%.

[0028] Preferably, in step S17, the volume ratio of ethanol to water in the ethanol-water mixture is (4-5):1, the concentration of the zirconium source solution is 0.1-0.2M; the mass ratio of ZrOCl2·8H2O to TiO2 is 1:(2-3) based on ZrO2, and CTAB is 20-30% of the mass of ZrO2; the zirconium source solution is added dropwise at a temperature of 50-60°C, stirred during addition, and the stirring rate is 500-800 rpm.

[0029] Preferably, in step S19, the vacuum drying temperature is 60-65° C., and the time is 10-14 h.

[0030] Preferably, in step S2, in the impregnation solution, ammonium metatungstate is 5-30wt.%, [Bmim]PF6 ionic liquid is 0.5-10wt.%, and citric acid is 1-15wt.%; the pulse magnetic field intensity is 0.5-1.2T, and the ultrasonic frequency is 15-25kHz.

[0031] Preferably, in step S3, the immersion solution contains 2-15 wt.% ammonium metavanadate, 0.5-10 wt.% EDTA, and Ce. 0.7 La 0.3 O x 5-15wt.%; pulse microwave frequency is 5-8GHz, power density is 2-3W / cm 3 , 10s on / 5s off, processing time is 20-40min.

[0032] Preferably, in steps S2 and S3, the impregnation process is carried out in an impregnation reactor, which includes a reaction chamber, in which the TiO2@ZrO2 core-shell composite carrier and the impregnation liquid are placed; the reaction chamber is equipped with an agitator, a microwave generator, an ultrasonic generator, a thermocouple and two Helmholtz coils arranged oppositely on the reaction chamber; and a circulating water constant temperature jacket is also provided on the outer wall of the reaction chamber.

[0033] Preferably, in step S4, the atomic layer deposition process is: introducing acrylic acid monomer and styrene monomer to polymerize under the conditions of 110-130° C. and 0.1-0.15 Torr to form a polyacrylic acid-b-polystyrene layer with a thickness of 20-30 nm.

[0034] On the other hand, the present invention provides a vanadium-tungsten-titanium type SCR denitration catalyst, which is prepared by the above-mentioned preparation method of the vanadium-tungsten-titanium type SCR denitration catalyst.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention: 1) uses a dual template method to prepare a TiO2@ZrO2 core-shell composite carrier with a porous structure, and constrains the nano-confined growth of the active component through the ZrO2 mesoporous shell, significantly improving the specific surface area and thermal stability; 2) innovates the electromagnetic coupling field assisted impregnation process, combines ionic liquid activation, pulse microwave and magnetic field synergy to achieve V / W atomic-level dispersion and improve metal loading efficiency; 3) uses atomic layer deposition (ALD) to coat a pH-responsive coating (i.e., a polyacrylic acid-b-polystyrene layer) to trigger polymer swelling when the SO3 concentration is greater than 10ppm, physically blocking poisoning substances, so that the catalyst can operate in flue gas containing 50ppm SO3 for 4000h with an activity decay of less than 5%; 4) introduces Ce 0.7 La 0.3 O x Solid solution, improving NH3 adsorption capacity and inhibiting SO3 by regulating oxygen vacancies 2- The vanadium-tungsten-titanium SCR denitration catalyst prepared by the present invention has excellent low-temperature activity and anti-poisoning: at 200℃, NO x The conversion rate is >94%, and the activity decay is <5% after operating for 4000 hours in flue gas containing 50ppm SO3. In addition, industrial pilot tests have shown that the catalyst module replacement cycle is extended to 6 years, greatly extending its service life. It is suitable for efficient purification of complex flue gas environments such as coal-fired power plants and steel metallurgy. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic structural diagram of the impregnation reactor of the present invention.

[0038] Figure 2This is a HAADF-STEM image of the TiO2@ZrO2 core-shell composite carrier prepared in the present invention.

[0039] Figure 3 The NO of the catalysts of Examples 1-3 and Comparative Examples 1-5 is x Conversion rate-temperature curve.

[0040] In the figure, 1. reaction chamber; 2. circulating water constant temperature jacket; 3. stirrer; 4. microwave generator; 5. ultrasonic generator; 6. Helmholtz coil. DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0042] In the following examples, during the preparation of the catalyst, an impregnation reactor with the following structure was used for impregnation: Figure 1 As shown, the impregnation reactor includes a reaction chamber 1, and the TiO2@ZrO2 core-shell composite carrier and the impregnation liquid are placed in the reaction chamber 1. The reaction chamber 1 is a cylindrical stainless steel sealed container (diameter 300mm, height 700mm), lined with a polytetrafluoroethylene anti-corrosion layer (thickness 2mm), with a temperature resistance range of -20 to 300°C and a working pressure of ≤0.5MPa. A circulating water constant temperature jacket 2 (water flow rate 5-10L / min) is provided on the outer wall of the reaction chamber 1 for real-time temperature control. At the same time, an agitator 3 and a microwave generator 4 are installed on the reaction chamber 1, an ultrasonic generator 5 is installed at the bottom of the reaction chamber 1, and a Pt100 thermocouple is installed inside to monitor the solution temperature in real time (accuracy ±0.5°C); two Helmholtz coils 6 are symmetrically arranged outside the reaction chamber 1, with a single coil 6 having 200 turns and a wire cross-sectional area of ​​4mm 2 .

[0043] Example 1

[0044] The preparation method of the vanadium-tungsten-titanium type SCR denitration catalyst of this embodiment comprises the following steps:

[0045] S1 Preparation of TiO2@ZrO2 core-shell composite carrier

[0046] Prehydrolysis of S11 precursor: In a nitrogen-protected reactor, tetrabutyl titanate and acetic acid were mixed with magnetic stirring at 25°C for 15 min. The acetic acid content was 12% of the mass of tetrabutyl titanate to form a light yellow transparent solution.

[0047] S12 hydrolysis reaction: add dropwise an ethanol-water mixture with a pH of 3, wherein the volume ratio of ethanol to tetrabutyl titanate is 2.5:1, and the molar ratio of water to tetrabutyl titanate is 5:1. The pH of the ethanol-water mixture is adjusted with nitric acid, and the reaction temperature is maintained at 40°C. The droplet acceleration rate is controlled at 2 mL / min by a peristaltic pump to avoid precipitation caused by excessive local concentration. After the droplet addition is completed, continue stirring to form a uniform and transparent TiO2 sol.

[0048] S13 Sol-Gel Conversion: The temperature was raised to 60°C, and 0.5 M ammonia was added to slowly adjust the pH to 5.8 for polycondensation to prepare a wet gel. The viscosity of the system gradually increased, forming a three-dimensional network gel. The gelation time was monitored by rheometer (the gelation was completed when the storage modulus G'> the loss modulus G").

[0049] S14 Aging and Drying: The wet gel was statically aged for 24 h to strengthen the network structure; it was then dried using supercritical CO2 (critical conditions: 31°C, 7.38 MPa) to avoid pore collapse and obtain a high specific surface area dry gel;

[0050] S15 crystallization and calcination: The dry gel was placed in a muffle furnace and heated to 450°C at a rate of 2°C / min under air atmosphere and kept at this temperature for 2 hours; the crystal transformation was monitored by XRD to obtain anatase TiO2 nanoparticles;

[0051] S16 TiO2 surface pretreatment: TiO2 nanoparticles were dispersed in an ethanol-water mixture with a volume ratio of 4.5:1 and ultrasonicated to obtain a uniform TiO2 suspension with a solid content of 5 wt.%. 0.1 M nitric acid solution was added to adjust the pH to 2.3 to protonate the TiO2 surface (Zeta potential +25 mV) and enhance electrostatic adsorption with the ZrO2 precursor.

[0052] S17 zirconium source hydrolysis and interfacial nucleation: ZrOCl2·8H2O and CTAB were dissolved in an ethanol-water mixture to prepare a 0.1M zirconium source solution with a volume ratio of ethanol to water of 4.5:1. Under nitrogen protection, the zirconium source solution was added dropwise to the TiO2 suspension at a rate of 1 mL / min at 50°C and a stirring rate of 500 rpm. The mass ratio of ZrOCl2·8H2O to TiO2 was 1:2.5 based on ZrO2, and CTAB was 25% of the mass of ZrO2. Ammonia was added dropwise to maintain the pH of the system at 4.8 through online pH monitoring to promote the hydrolysis of ZrOCl2·8H2O and TiO2. 4+ It preferentially hydrolyzes to form Zr(OH)4 nuclei on the TiO2 surface rather than in the bulk;

[0053] S18 ZrO2 shell growth: After the addition, the temperature was raised to 70℃ and aged for 6h. CTAB micelles were adsorbed on the Zr(OH)4 surface, guiding the formation of mesoporous structure through the lyotropic liquid crystal template effect;

[0054] S19 template removal and crystallization: The product was centrifuged and washed three times with ethanol and acetone to remove free CTAB. The washed wet gel was vacuum dried at 60°C for 12 h, then placed in a muffle furnace and heated to 400°C at a rate of 1°C / min in an air atmosphere and kept warm for 2 h to obtain the TiO2@ZrO2 core-shell composite carrier.

[0055] S2 electromagnetic coupling field assisted tungsten load

[0056] The TiO2@ZrO2 core-shell composite support was impregnated in an impregnation solution (solvent: water) containing 10 wt.% ammonium metatungstate, 5 wt.% [Bmim]PF6 ionic liquid, and 2 wt.% citric acid. A 1 T pulsed magnetic field and 20 kHz ultrasonic waves were applied at 60°C for 2 h, followed by pre-calcination at 450°C.

[0057] S3 microwave enhanced vanadium loading

[0058] The product of step S2 is immersed in a solution containing 5 wt.% ammonium metavanadate, 1.5 wt.% EDTA and 8 wt.% Ce. 0.7 La 0.3 O 1.85 The immersion liquid (solvent is water) was heated by 5.8 GHz pulse microwave (power density is 2 W / cm 3 , 10s on / 5s off) for 30min, and calcined at 350°C;

[0059] S4 deposition coating

[0060] At 120° C. and 0.1 Torr, acrylic acid monomer and styrene monomer were introduced for polymerization, and a polyacrylic acid-b-polystyrene layer with a thickness of 20 nm was formed on the product of step S3 by ALD to obtain a vanadium-tungsten-titanium SCR denitration catalyst.

[0061] Depend on Figure 2 It can be seen that the vanadium-tungsten-titanium SCR denitration catalyst prepared in this example has a core-shell structure: Figure 2 It shows that the interface between the continuous ZrO2 shell and the TiO2 core is clear.

[0062] Example 2

[0063] The preparation method of the vanadium-tungsten-titanium type SCR denitration catalyst of this embodiment comprises the following steps:

[0064] S1 Preparation of TiO2@ZrO2 core-shell composite carrier

[0065] Prehydrolysis of S11 precursor: In a nitrogen-protected reactor, tetrabutyl titanate and acetic acid were mixed with magnetic stirring at 25°C for 15 min. The acetic acid content was 15% of the mass of tetrabutyl titanate to form a light yellow transparent solution.

[0066] S12 hydrolysis reaction: add dropwise an ethanol-water mixture with a pH of 3.5, wherein the volume ratio of ethanol to tetrabutyl titanate is 3:1, and the molar ratio of water to tetrabutyl titanate is 8:1. The pH of the ethanol-water mixture is adjusted with nitric acid, and the reaction temperature is maintained at 42°C. The droplet acceleration rate is controlled at 2 mL / min by a peristaltic pump to avoid precipitation caused by excessive local concentration. After the droplet addition is completed, continue stirring to form a uniform and transparent TiO2 sol.

[0067] S13 Sol-Gel Conversion: The temperature was raised to 65°C, and 0.5 M ammonia was added to slowly adjust the pH to 6 for polycondensation to prepare a wet gel. The viscosity of the system gradually increased, forming a three-dimensional network gel. The gelation time was monitored by rheometer (the gelation was completed when the storage modulus G'> the loss modulus G").

[0068] S14 Aging and Drying: The wet gel was statically aged for 28 h to strengthen the network structure; it was then dried using supercritical CO2 (critical conditions: 31°C, 7.38 MPa) to avoid pore collapse and obtain a high specific surface area dry gel;

[0069] S15 crystallization and calcination: The dry gel was placed in a muffle furnace and heated to 500°C at a rate of 2.2°C / min under air atmosphere and kept at this temperature for 2 hours; the crystal transformation was monitored by XRD to obtain anatase TiO2 nanoparticles;

[0070] S16 TiO2 surface pretreatment: TiO2 nanoparticles were dispersed in an ethanol-water mixture with a volume ratio of 5:1 and ultrasonicated to obtain a uniform TiO2 suspension with a solid content of 8 wt.%. 0.1 M nitric acid solution was added to adjust the pH to 2.5 to protonate the TiO2 surface (Zeta potential +25 mV) and enhance electrostatic adsorption with the ZrO2 precursor.

[0071] S17 zirconium source hydrolysis and interfacial nucleation: ZrOCl2·8H2O and CTAB were dissolved in an ethanol-water mixture to prepare a 0.2M zirconium source solution with a volume ratio of ethanol to water of 5:1. Under nitrogen protection, the zirconium source solution was added dropwise to the TiO2 suspension at a rate of 1 mL / min at 60°C and a stirring rate of 800 rpm. The mass ratio of ZrOCl2·8H2O to TiO2 was 1:3 based on ZrO2, and CTAB was 30% of the mass of ZrO2. Ammonia was added dropwise to maintain the pH of the system at 5 by online pH monitoring to promote the hydrolysis of ZrOCl2·8H2O and TiO2. 4+ It preferentially hydrolyzes to form Zr(OH)4 nuclei on the TiO2 surface rather than in the bulk;

[0072] S18 ZrO2 shell growth: After the addition, the temperature was raised to 75℃ and aged for 5h. CTAB micelles were adsorbed on the Zr(OH)4 surface, guiding the formation of mesoporous structure through the lyotropic liquid crystal template effect.

[0073] S19 template removal and crystallization: The product was centrifuged and washed three times with ethanol and acetone to remove free CTAB. The washed wet gel was vacuum dried at 65°C for 10 h, then placed in a muffle furnace and heated to 450°C at a rate of 1.2°C / min in an air atmosphere and kept warm for 2 h to obtain the TiO2@ZrO2 core-shell composite carrier.

[0074] S2 electromagnetic coupling field assisted tungsten load

[0075] The TiO2@ZrO2 core-shell composite support was impregnated in an impregnation solution (solvent: water) containing 30 wt.% ammonium metatungstate, 10 wt.% [Bmim]PF6 ionic liquid, and 15 wt.% citric acid. A 1.2 T pulsed magnetic field and 25 kHz ultrasonic waves were applied at 70°C for 2 h, followed by pre-calcination at 500°C.

[0076] S3 microwave enhanced vanadium loading

[0077] The product of step S2 is immersed in a solution containing 15 wt.% ammonium metavanadate, 10 wt.% EDTA and 15 wt.% Ce. 0.7 La 0.3 O 1.85 The immersion liquid (solvent is water) was heated by 8 GHz pulse microwave (power density is 3 W / cm 3 , 10s on / 5s off) for 40min, and calcined at 450℃;

[0078] S4 deposition coating

[0079] At 130° C. and 0.15 Torr, acrylic acid monomer and styrene monomer were introduced for polymerization, and a polyacrylic acid-b-polystyrene layer with a thickness of 30 nm was formed on the product of step S3 by ALD to obtain a vanadium-tungsten-titanium SCR denitration catalyst.

[0080] Example 3

[0081] The preparation method of the vanadium-tungsten-titanium type SCR denitration catalyst of this embodiment comprises the following steps:

[0082] S1 Preparation of TiO2@ZrO2 core-shell composite carrier

[0083] Prehydrolysis of S11 precursor: In a nitrogen-protected reactor, tetrabutyl titanate and acetic acid were mixed with magnetic stirring at 25°C for 15 min. The acetic acid content was 10% of the mass of tetrabutyl titanate to form a light yellow transparent solution.

[0084] S12 hydrolysis reaction: add dropwise an ethanol-water mixture with a pH of 2.5, wherein the volume ratio of ethanol to tetrabutyl titanate is 2:1, and the molar ratio of water to tetrabutyl titanate is 4:1. The pH of the ethanol-water mixture is adjusted with nitric acid, and the reaction temperature is maintained at 38°C. The droplet acceleration rate is controlled at 2 mL / min by a peristaltic pump to avoid precipitation caused by excessive local concentration. After the droplet addition is completed, continue stirring to form a uniform and transparent TiO2 sol.

[0085] S13 Sol-Gel Conversion: The temperature was raised to 62°C, and 0.5 M ammonia was added to slowly adjust the pH to 5.5 for polycondensation to prepare a wet gel. The viscosity of the system gradually increased, forming a three-dimensional network gel. The gelation time was monitored by rheometer (the gelation was completed when the storage modulus G'> the loss modulus G").

[0086] S14 Aging and Drying: The wet gel was statically aged for 20 h to strengthen the network structure; it was then dried using supercritical CO2 (critical conditions: 31°C, 7.38 MPa) to avoid pore collapse and obtain a high specific surface area dry gel;

[0087] S15 crystallization and calcination: The dry gel was placed in a muffle furnace and heated to 480°C at a rate of 1.8°C / min under air atmosphere and kept at this temperature for 3 hours; the crystal transformation was monitored by XRD to obtain anatase TiO2 nanoparticles;

[0088] S16 TiO2 surface pretreatment: TiO2 nanoparticles were dispersed in an ethanol-water mixture with a volume ratio of 4:1 and ultrasonicated to obtain a uniform TiO2 suspension with a solid content of 4 wt.%. 0.1 M nitric acid solution was added to adjust the pH to 2 to protonate the TiO2 surface (Zeta potential +25 mV) and enhance electrostatic adsorption with the ZrO2 precursor.

[0089] S17 zirconium source hydrolysis and interfacial nucleation: ZrOCl2·8H2O and CTAB were dissolved in an ethanol-water mixture to prepare a 0.1M zirconium source solution with a volume ratio of ethanol to water of 4:1. Under nitrogen protection, the zirconium source solution was added dropwise to the TiO2 suspension at a rate of 1 mL / min at 55°C and a stirring rate of 600 rpm. The mass ratio of ZrOCl2·8H2O to TiO2 was 1:2 based on ZrO2, and CTAB was 20% of the mass of ZrO2. Ammonia was added dropwise to maintain the pH of the system at 4.5 through online pH monitoring to promote the hydrolysis of ZrOCl2·8H2O and TiO2. 4+ It preferentially hydrolyzes to form Zr(OH)4 nuclei on the TiO2 surface rather than in the bulk;

[0090] S18 ZrO2 shell growth: After the addition, the temperature was raised to 72℃ and aged for 7h. CTAB micelles were adsorbed on the Zr(OH)4 surface, guiding the formation of mesoporous structure through the lyotropic liquid crystal template effect.

[0091] S19 template removal and crystallization: The product was centrifuged and washed three times with ethanol and acetone to remove free CTAB. The washed wet gel was vacuum dried at 62°C for 14 h, then placed in a muffle furnace and heated to 420°C at a rate of 0.8°C / min in an air atmosphere and kept warm for 3 h to obtain a TiO2@ZrO2 core-shell composite carrier.

[0092] S2 electromagnetic coupling field assisted tungsten load

[0093] The TiO2@ZrO2 core-shell composite support was impregnated in an impregnation solution (solvent: water) containing 5 wt.% ammonium metatungstate, 0.5 wt.% [Bmim]PF6 ionic liquid, and 1 wt.% citric acid. A 0.5 T pulsed magnetic field and 15 kHz ultrasonic waves were applied at 50°C for 3 h, and the resulting product was pre-calcined at 400°C.

[0094] S3 microwave enhanced vanadium loading

[0095] The product of step S2 is immersed in a solution containing 2 wt.% ammonium metavanadate, 0.5 wt.% EDTA and 5 wt.% Ce. 0.7 La 0.3 O 1.85 The immersion liquid (solvent is water) was heated by 5 GHz pulse microwave (power density is 3 W / cm 3 , 10s on / 5s off) for 20min, and calcined at 400℃;

[0096] S4 deposition coating

[0097] At 110° C. and 0.1 Torr, acrylic acid monomer and styrene monomer were introduced for polymerization, and a polyacrylic acid-b-polystyrene layer with a thickness of 25 nm was formed on the product of step S3 by ALD to obtain a vanadium-tungsten-titanium SCR denitration catalyst.

[0098] Comparative Example 1

[0099] The difference from Example 1 is that steps S16 to S19 are not performed.

[0100] Comparative Example 2

[0101] The difference from Example 1 is that in step S2, no pulsed magnetic field and no ultrasonic waves are applied during the immersion process.

[0102] Comparative Example 3

[0103] The difference from Example 1 is that in step S3, no microwave treatment is performed during the immersion process.

[0104] Comparative Example 4

[0105] The difference from Example 1 is that in step S3, Ce is not added to the impregnation solution. 0.7 La 0.3 O x .

[0106] Comparative Example 5

[0107] The difference from Example 1 is that step S4 is not performed.

[0108] The performance of the SCR denitration catalysts prepared in Examples 1-3 and Comparative Examples 1-5 was tested. The test results are as follows: Figure 3 As shown in Table 1. Among them, the detection method of anti-sulfur aging (4000h) is as follows:

[0109] 1. Preparation before the test

[0110] (1) Catalyst sample preparation: The sample was loaded into a quartz tube fixed bed reactor;

[0111] (2) Simulated flue gas composition: NO 500ppm, NH3 550ppm, SO2 200ppm, O2 5% (vol / vol), H2O 10% (vol / vol), N2; air velocity 30000h -1 ;

[0112] (3) Test equipment and monitoring system

[0113] Reactor: Quartz tube fixed bed reactor (inner diameter 8 mm) equipped with electric heating furnace (temperature control accuracy ± 2 ° C).

[0114] Online analyzer: NO / NO2 / NH3 concentration: chemiluminescence analyzer (CLD, accuracy ±1ppm); SO2 concentration: UV fluorescence analyzer (accuracy ±0.5ppm); O2 concentration: paramagnetic oxygen analyzer (accuracy ±0.1%); Data acquisition: outlet gas concentration, temperature and pressure are recorded every 10 minutes.

[0115] 2. Test operation process

[0116] (1) Initial performance baseline test

[0117] Conditions: In clean flue gas without SO2 (other parameters are the same as above), 200-400℃ step-by-step temperature test (stable for 1 hour at each 50℃), draw NO x Conversion rate-temperature curve (LT 90 HT 90 window).

[0118] (2) Long-term sulfur aging test

[0119] Temperature control: Select the optimal activity temperature of the catalyst (such as 200℃±5℃).

[0120] Operation cycle: Continuously introduce simulated flue gas containing SO2 for 4000 hours; pause for 1 hour every 24 hours, cool to room temperature and then conduct physical impact test (simulating start-stop conditions).

[0121] Stability monitoring:

[0122] Daily: Record NO x Conversion rate, SO2 conversion rate, and pressure drop changes.

[0123] Weekly: Shut down and take samples to test the following indicators:

[0124] Sulfate accumulation: The amount of sulfate accumulation was determined by thermogravimetric-differential scanning calorimetry (TG-DSC, heating rate 10°C / min to 800°C).

[0125] Surface sulfur species: in situ diffuse reflectance infrared spectroscopy (in situ DRIFTS, wavenumber range 4000-600 cm -1 ).

[0126] Oxygen vacancy concentration: electron paramagnetic resonance (EPR, g-factor analysis).

[0127] Table 1 Performance test results of SCR denitration catalysts of Examples 1-3 and Comparative Examples 1-5

[0128]

[0129] Depend on Figure 3 As can be seen from Table 1, compared with Example 1, after the comparative example 1 lacks the ZrO2 shell, the acidity of the carrier surface is reduced, resulting in a decrease in the amount of NH3 adsorption and a decrease in the activity of the SCR denitrification catalyst; and without the ZrO2 shell, SO2 directly attacks the active sites (such as V=O bonds) to generate thermally stable VOSO4, resulting in permanent deactivation of the catalyst. In addition, sulfate is more likely to accumulate on the TiO2 surface, blocking the pores and covering the active sites. Comparative Example 2 does not apply pulsed magnetic fields and ultrasonic waves during the impregnation process, and Comparative Example 3 does not apply microwaves during the impregnation process, which affects the dispersion and loading uniformity of tungsten and vanadium, resulting in agglomeration of active components, affecting the activity and sulfur resistance of the catalyst. Ce is not added to the impregnation solution of Comparative Example 4. 0.7 La 0.3 O x, which affects the redox ability of the catalyst, reduces surface acidic sites, and loses the sulfur shielding effect of Ce-La, resulting in a decrease in catalyst activity and sulfur resistance. The lack of a polyacrylic acid-b-polystyrene layer in Comparative Example 5 allows SO2 to directly contact the active components, causing them to quickly deactivate and affecting the catalyst's sulfur resistance.

Claims

1. A method for preparing a vanadium-tungsten-titanium SCR denitration catalyst, characterized in that: The following steps are involved: S1 Preparation of TiO2@ZrO2 core-shell composite supports: TiO2 nanoparticles were synthesized by sol-gel method using tetrabutyl titanate as a precursor, and then coated with ZrO2 shell in ZrOCl2·8H2O ethanol solution; S2 electromagnetic coupling field assisted tungsten loading: The TiO2@ZrO2 core-shell composite carrier is impregnated in an impregnation solution containing ammonium metatungstate, [Bmim]PF6 ionic liquid and citric acid, and a pulsed magnetic field and ultrasonic waves are applied. The mixture is treated at 50-70°C for 2-3h and pre-calcined at 400-500°C. S3 Microwave-enhanced vanadium loading: The product of step S2 is immersed in a solution containing ammonium metavanadate, EDTA and Ce. 0.7 La 0.3 O x The impregnation solution is treated with pulse microwave and calcined at 350-450°C; S4 deposition coating: coating the product of step S3 with a polyacrylic acid-b-polystyrene layer by atomic layer deposition to obtain a vanadium-tungsten-titanium type SCR denitration catalyst.

2. The method for preparing the vanadium-tungsten-titanium type SCR denitration catalyst according to claim 1, characterized in that: The specific operations of step S1 are as follows: S11 Precursor pre-hydrolysis: In a nitrogen-protected reactor, tetrabutyl titanate and acetic acid were mixed; S12 hydrolysis reaction: add ethanol-water mixture with a pH of 2.5-3.5 dropwise, maintaining the reaction temperature at 38-42°C; after the addition is complete, continue stirring to form a uniform and transparent TiO2 sol; S13 sol-gel conversion: heating to 60-65°C, adjusting the pH to 5.5-6, and performing polycondensation to prepare a wet gel; S14 aging and drying: The wet gel was statically aged for 20-28 h and then dried using supercritical CO2 to obtain a dry gel; S15 crystallization and calcination: Place the dry gel in a muffle furnace, heat it to 450-500°C at a rate of 1.8-2.2°C / min under air atmosphere, and keep it at this temperature for 2-3 hours to obtain anatase TiO2 nanoparticles; S16 TiO2 surface pretreatment: Disperse TiO2 nanoparticles in an ethanol-water mixture and ultrasonicate to obtain a uniform TiO2 suspension; adjust the pH to 2-2.5; S17 zirconium source hydrolysis and interfacial nucleation: ZrOCl2·8H2O and CTAB were dissolved in an ethanol-water mixture to prepare a zirconium source solution. Under nitrogen protection, the zirconium source solution was added dropwise to the TiO2 suspension. Ammonia was simultaneously added dropwise to maintain the system pH at 4.5-5. S18 ZrO2 shell growth: After the addition is complete, heat to 70-75°C and age for 5-7 hours; S19 template removal and crystallization: centrifugation of the product and washing to remove free CTAB; The washed wet gel is vacuum dried, then placed in a muffle furnace, heated to 400-450°C at a rate of 0.8-1.2°C / min in an air atmosphere, and kept warm for 2-3 hours to obtain a TiO2@ZrO2 core-shell composite carrier.

3. The method for preparing the vanadium-tungsten-titanium type SCR denitration catalyst according to claim 2, characterized in that: In step S11, the acetic acid content is 10-15% by mass of tetrabutyl titanate; in step S12, the volume ratio of ethanol to tetrabutyl titanate in the ethanol-water mixture is (2-3):1, and the molar ratio of water to tetrabutyl titanate is (4-8):1; in step S16, the volume ratio of ethanol to water in the ethanol-water mixture is (4-5):1, and the solid content of the TiO2 suspension is 4-8 wt.%.

4. The method for preparing the vanadium-tungsten-titanium type SCR denitration catalyst according to claim 2, characterized in that: In step S17, the volume ratio of ethanol to water in the ethanol-water mixture is (4-5):1, the concentration of the zirconium source solution is 0.1-0.2M; the mass ratio of ZrOCl2·8H2O to TiO2 is 1:(2-3) based on ZrO2, and the CTAB content is 20-30% of the mass of ZrO2; the zirconium source solution is added dropwise at a temperature of 50-60°C, stirred during addition, and a stirring rate of 500-800 rpm.

5. The method for preparing the vanadium-tungsten-titanium type SCR denitration catalyst according to claim 2, characterized in that: In step S19, the vacuum drying temperature is 60-65° C. and the time is 10-14 h.

6. The method for preparing the vanadium-tungsten-titanium type SCR denitration catalyst according to claim 1, characterized in that: In step S2, in the impregnation solution, ammonium metatungstate is 5-30wt.%, [Bmim]PF6 ionic liquid is 0.5-10wt.%, and citric acid is 1-15wt.%; the pulse magnetic field intensity is 0.5-1.2T, and the ultrasonic frequency is 15-25kHz.

7. The method for preparing the vanadium-tungsten-titanium type SCR denitration catalyst according to claim 1, characterized in that: In step S3, the immersion solution contains 2-15 wt.% ammonium metavanadate, 0.5-10 wt.% EDTA, and Ce. 0.7 La 0.3 O x 5-15wt.%; pulse microwave frequency is 5-8GHz, power density is 2-3W / cm 3 , 10s on / 5s off, processing time is 20-40min.

8. The method for preparing the vanadium-tungsten-titanium type SCR denitration catalyst according to claim 1, characterized in that: In steps S2 and S3, the impregnation process is carried out in an impregnation reactor, which includes a reaction chamber (1), in which the TiO2@ZrO2 core-shell composite carrier and the impregnation liquid are placed; the reaction chamber (1) is equipped with an agitator (3), a microwave generator (4), an ultrasonic generator (5), a thermocouple, and two Helmholtz coils (6) arranged opposite to each other on the reaction chamber (1); and a circulating water constant temperature jacket (2) is also provided on the outer wall of the reaction chamber (1).

9. The method for preparing the vanadium-tungsten-titanium type SCR denitration catalyst according to claim 1, characterized in that: In step S4, the atomic layer deposition process is as follows: acrylic acid monomer and styrene monomer are introduced to polymerize at 110-130° C. and 0.1-0.15 Torr to form a polyacrylic acid-b-polystyrene layer with a thickness of 20-30 nm.

10. Vanadium-tungsten-titanium type SCR denitration catalyst, characterized in that: The catalyst is prepared by the method for preparing the vanadium-tungsten-titanium SCR denitration catalyst according to any one of claims 1 to 9.

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