A 3D spherical chrysanthemum-like structure FeWAl x Water-resistant calcium sulfate denitrification catalyst and its preparation method and application

Abstract

The present invention discloses a 3D spherical chrysanthemum-shaped structure FeWAl x Anti-water sulfur calcium denitrification catalyst and its preparation method and application. The catalyst is composed of a composite metal oxide of Fe2O3 and WO3 loaded on Al2O3, and is prepared by the interaction of PMMA colloidal template microspheres and F127 to form a macroporous, mesoporous and microporous interwoven structure. The catalyst of the present invention presents a 3D chrysanthemum-like structure. Its interconnected pores and large pore volume and pore size accelerate the formation and sublimation of ammonium sulfate salt on the catalyst surface. The more dispersed active components are difficult to contact with SO2 and H2O, protecting the active sites. The addition of Al2O3 promotes electron transfer between Fe‑O‑W, produces more active oxygen, and improves NO x It can also provide enough acidic sites for the catalyst to neutralize the toxicity of CaO, and can achieve the removal of NO in complex industrial flue gas. x Efficient removal.

Description

Technical Field

[0001] The present invention belongs to the field of denitration catalyst preparation, and specifically relates to a 3D spherical chrysanthemum structure FeWAl x Water-resistant calcium sulfate denitrification catalyst, preparation method and application thereof. Background Art

[0002] It is urgent to reduce air pollution such as ozone and particulate matter. Therefore, NO, one of its main precursors, is urgently needed. x With the implementation of ultra-low emissions in the power industry and the gradual completion of ultra-low emissions (ULE) transformation in China's steel industry, the control of NO x The focus of efficient removal has gradually shifted to stationary emission sources of complex industrial flue gases such as the cement industry. Currently, ammonia selective catalytic reduction (NH3-SCR) has been widely used for NO x However, the current commercial VWTi catalyst will be poisoned and deactivated when facing complex industrial flue gas containing SO2, H2O and alkaline (earth) metals, making it difficult to achieve stable and efficient NO x Therefore, it is particularly important to develop an efficient denitrification catalyst that is suitable for complex industrial flue gas containing SO2, H2O and alkaline (earth) metals.

[0003] There are two main reasons why SO2 causes poisoning and deactivation of SCR catalysts: one is the sulfidation of active sites at higher temperatures, which leads to catalyst deactivation; the other is the deposition of ammonium sulfate salts formed by the reaction of sulfur oxides and ammonia at lower temperatures on the catalyst surface, covering the catalyst surface and preventing active molecules from contacting the catalyst, thereby affecting the performance of the catalyst. Therefore, if deep sulfidation can be suppressed and the deposition of ammonium sulfate salts on the catalyst surface can be reduced, the SO2 poisoning problem can be solved. Researchers generally believe that H2O deactivates SCR catalysts due to competitive adsorption of H2O and NH3 and the formation of additional surface hydroxyl groups (-OH) on the catalyst. It is reported that the CaO content in complex industrial flue gas is as high as 80%. CaO will block the catalyst pores and reduce the adsorption of NH3 on the catalyst. The 3D chrysanthemum-like structure has a uniform macropore and mesopore structure, a large specific surface area and a controllable pore size. Its special 3D chrysanthemum-like structure can highly disperse the active components, increase the contact area between the reactants and the active sites, and enhance the interaction between the active components and the carrier. The macropore and mesopore structure of the catalyst is conducive to the sublimation and decomposition of ammonium sulfate salts, thereby reducing the deposition of ammonium sulfate salts; at the same time, the larger pore size can prevent the condensation of H2O on the catalyst, ensuring that the catalyst can efficiently remove NO. x ability.

[0004] Fe2O3-based catalysts have many advantages, such as Fe 3+ and Fe 2+ It has sufficient redox performance and low cost, and has good anti-SO2 activity at medium and high temperatures, which has attracted special attention. At the same time, the introduction of WO3 into Fe2O3 can enhance the surface acidity and electronic properties, and form α-Fe2O3 and FeWO4 species through strong Fe-W interaction, thereby improving SCR activity. Al2O3 is a potential additive for iron-based catalysts. It is a catalyst promoter that can provide neutral acidity to the catalyst, thereby inhibiting the adsorption of SO2 and neutralizing the alkalinity of CaO, and can increase the specific surface area of ​​the catalyst, forming more surface adsorbed oxygen, significantly reducing the thermal stability of ABS and promoting the decomposition of ABS. The prepared 3D spherical chrysanthemum structure FeWAl x Denitrification catalyst can face the complex flue gas environment of SO2, H2O and alkaline (earth) metals to achieve NO x Efficient removal. Summary of the Invention

[0005] Aiming at the technical problems of the commercial VWTi catalyst facing the poisoning of the water-sulfur calcium component of complex industrial flue gas on the denitrification catalyst, the present invention provides a 3D chrysanthemum-shaped FeWAl x The invention relates to a water-resistant calcium sulfate denitrification catalyst, a preparation method thereof, and an application thereof. The catalyst is prepared with the assistance of PMMA microspheres and F127 (poloxamer), and has a 3D porous structure with macropores, mesopores, and micropores interwoven.

[0006] In order to achieve the above object, the technical solution provided by the present invention is:

[0007] A 3D spherical chrysanthemum-like structure FeWAl x Water-resistant sulfur calcium denitrification catalyst, composed of Al2O3 loaded with Fe2O3 and WO3 composite transition metal oxides, denoted as FeWAl x , where x is the percentage of Al2O3 in the total mass of the catalyst, 5<x≤50%.

[0008] Furthermore, the above catalyst is composed of the following components in percentage by mass:

[0009] WO3 0% to 45% (preferably 5% to 40%, more preferably 30% to 35%), Al2O3 content accounts for 5% to 50% (preferably 15% to 20%), and the balance is Fe2O3. The sum of the mass percentages of each component is 100%.

[0010] Furthermore, the catalyst has a 3D structure of ping-pong balls interwoven with macropores, mesopores and micropores, with a specific surface area of ​​50 to 150 m 2 / g, with a total pore volume of 0.15 to 0.30 cm3 / g, and the average pore size is 2 to 20 nm.

[0011] The preparation method of the above catalyst comprises the following steps:

[0012] (1) PMMA emulsion was synthesized by modified soap-free emulsion polymerization, and then PMMA colloidal crystal template microspheres were prepared by constant temperature suspension film formation method;

[0013] (2) Using F127 (poloxamer) as a pulling agent, micelles are formed through intermolecular forces with the metal precursor solution of iron, tungsten, and aluminum to obtain a metal oxide precursor solution capable of forming mesopores;

[0014] (3) immersing the PMMA microspheres prepared in step (1) in the metal oxide precursor solution obtained in step (2) until the metal oxide precursor solution completely fills the voids of the PMMA microspheres, and finally removing the PMMA colloidal template by calcination to form a 3D porous metal oxide catalyst composed of macropores, mesopores and micropores interwoven, i.e., a 3D spherical chrysanthemum structure FeWAl x Denitrification catalyst.

[0015] Furthermore, in step (1), the preparation method of PMMA colloidal template microspheres is specifically as follows: continuously introducing inert gas into ultrapure water and heating it to 60-75°C, adding methyl methacrylate to the ultrapure water and stirring for 30-50 minutes, reacting with potassium persulfate as an initiator for 40-50 minutes, and the amount ratio of potassium persulfate to methyl methacrylate is 0.3-0.5g:100-120mL. After the reaction is completed, pouring into ultrapure water at a temperature of 5-20°C to prepare a polymethyl methacrylate emulsion, packaging the obtained liquid and centrifuging to remove the supernatant, then adding ultrapure water to the white precipitate for ultrasonic dispersion, and evaporating at a constant temperature to form ordered PMMA microsphere crystals.

[0016] Furthermore, step (2) is specifically as follows: F127 (poloxamer), anhydrous methanol, ethylene glycol, citric acid and anhydrous oxalic acid are stirred at 15-40°C to form a uniform solution, and then Fe(NO3)2·3H2O, (NH4) 10 [H2W 12 O 42 ]·4H2O, Al(NO3)3·9H2O, and then stirred at 35-65℃ for 2-4h to form a uniform colloid, F127, anhydrous methanol, ethylene glycol, citric acid, anhydrous oxalic acid, Fe(NO3)2·3H2O, (NH4) 10 [H2W 12 O 42The usage ratio of ]·4H2O and Al(NO3)3·9H2O is 2~3g:10~30mL:5~20mL:3~6g:2~4g:2~10g:0.5~2g:0.5~5g.

[0017] Furthermore, step (3) is specifically as follows: immersing the metal oxide precursor solution in the PMMA microspheres for 5-10 hours, removing the excess precursor solution with a funnel, and eluting with anhydrous methanol to obtain a filter cake, placing the filter cake in an oven to dry, and then calcining it in a muffle furnace, heating it from room temperature to 100-250°C and maintaining it for 4-5 hours, then heating it to 350-450°C and maintaining it for 4-6 hours, and then cooling it to room temperature to obtain a 3D spherical chrysanthemum structure FeWAl x Denitrification catalyst.

[0018] The above catalyst can achieve good results in denitrification and is applied to industrial flue gas with remarkable effects, especially when facing complex industrial flue gas rich in SO2, H2O and alkaline (earth) metals, it can still achieve NO x Efficient removal.

[0019] The present invention uses PMMA microspheres and F127 (poloxamer) to construct a 3D spherical chrysanthemum structure FeWAl with macropores, mesopores and micropores interwoven. x Denitrification catalyst, with good denitrification effect, is used for complex industrial flue gas rich in SO2, H2O and alkaline (earth) metals and other components, and can achieve NO x Efficient removal. The catalyst's 3D chrysanthemum-like structure, with its interconnected pores and large pore volume, accelerates the formation and sublimation of ammonium sulfate on the catalyst surface. The more dispersed active components are less likely to come into contact with SO2 and H2O, protecting the active sites. The addition of an appropriate amount of Al2O3 promotes electron transfer between Fe-OW, generating more active oxygen and improving NO removal capacity. It also provides the catalyst with sufficient acidic sites to neutralize the toxicity of CaO.

[0020] The beneficial effects of the present invention are:

[0021] The catalyst prepared by the present invention has a special 3D chrysanthemum-shaped structure with a large number of macropores, mesopores and micropores interwoven, which can promote the good dispersion of surface active components and the exposure of active sites, accelerate the dynamic balance of formation and sublimation of ammonium sulfate on the catalyst surface, inhibit SO2 adsorption and neutralize the alkalinity of CaO, and significantly improve the catalyst NO x Removal capacity, for complex industrial flue gas rich in SO2, H2O and alkaline (earth) metals, it can achieve NO x Efficient removal. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1The three-dimensional porous FeWAl prepared in Example 3 x Test activity diagram of the catalyst.

[0023] Figure 2 The three-dimensional porous FeWAl prepared in Example 2 x Scanning electron microscopy image of the catalyst.

[0024] Figure 3 The three-dimensional porous FeWAl prepared in Example 2 x N2 adsorption-desorption curves and pore size distribution of the catalyst.

[0025] Figure 4 The three-dimensional porous FeWAl prepared in Example 2 x XRD patterns of the catalyst. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited thereto.

[0027] Example 1

[0028] The PMMA production steps:

[0029] Inert gas is continuously introduced into ultrapure water and heated to 65°C. Methyl methacrylate is added to the ultrapure water and stirred for 30 to 50 minutes. Potassium persulfate is used as an initiator to react for 40 to 50 minutes. The amount ratio of potassium persulfate to methyl methacrylate is 0.4g:115mL. After the reaction is completed, the mixture is poured into ultrapure water at a temperature of 5 to 20°C to prepare a polymethyl methacrylate emulsion. The obtained liquid is packaged and centrifuged to remove the supernatant. Then, the white precipitate is ultrasonically dispersed in ultrapure water and evaporated at a constant temperature to form ordered PMMA microsphere crystals.

[0030] Example 2

[0031] 3D spherical chrysanthemum structure FeWAl x The preparation method of the water-resistant calcium sulfate denitrification catalyst comprises the following steps:

[0032] (1) Dissolve 2 g of F127 (poloxamer), 2 g of anhydrous oxalic acid, and 4.8 g of citric acid in a mixture of 24 mL of anhydrous methanol and 16 mL of ethylene glycol in a 35°C water bath and stir for 2 h until the solution becomes transparent.

[0033] (2) Add 5.0030g Fe(NO3)3·9H2O and 0.5766g (NH4) to the solution obtained in step (1) in sequence under stirring. 10 [H2W 12 O 42]·4H2O, 1.9843gAl(NO3)3·9H2O, heat to 50℃ and stir for 2h until the solution becomes clear and sol-like, then reduce the temperature to 35℃ and continue stirring for 1h;

[0034] (3) Immersing the metal oxide precursor solution obtained in step (2) in 6 g of PMMA microspheres for 6 h, removing excess precursor solution with a funnel, and rinsing with anhydrous methanol to obtain a filter cake;

[0035] (4) Dry the filter cake in a vacuum drying oven at 50°C for 24 hours;

[0036] (5) After drying, the precursor was placed in a muffle furnace and calcined at a rate of 3°C / min from room temperature to 250°C and maintained for 5 h, then raised to 450°C at a rate of 1°C / min and maintained for 6 h. After cooling to room temperature, a 3D spherical chrysanthemum-like structure of FeWAl was obtained. x Catalyst: Pass the catalyst through a 40-60 mesh sieve for later use.

[0037] Example 3

[0038] 3D spherical chrysanthemum structure FeWAl x The preparation method of the water-resistant calcium sulfate denitrification catalyst comprises the following steps:

[0039] (1) Add 0.084 g of Ca(NO3)2·4H2O to 20 mL of deionized water and stir until completely dissolved.

[0040] (2) Add 2 g of fresh catalyst to the aqueous solution prepared in step (1) and stir thoroughly for 6 h;

[0041] (3) After stirring, the catalyst was placed in an oven at 105°C and dried for 16 hours;

[0042] (4) The dried sample was placed in a muffle furnace and calcined at a rate of 10°C / min from room temperature to 500°C for 5 h. After cooling to room temperature, a CaO-supported 3D spherical chrysanthemum-like structure of FeWAl was obtained. x The catalyst is ready for use.

[0043] Example 4

[0044] Evaluation of catalyst resistance to aqueous calcium sulfate denitrification.

[0045] The 3D spherical chrysanthemum structure FeWAl prepared by the alkali metal in Example 3 of the present invention xThe catalyst was used as the target. 0.15 g of catalyst was placed in a quartz tube and fixed in the reactor. The simulated reaction flue gas consisted of 500 ppm NH3, 500 ppm NO, 400 ppm SO2, 6 vol.% O2, 10 vol.% H2O and the balance gas N2. The total gas flow rate was maintained at 200 mL / min and the volume space velocity (GHSV) was 100,000 h -1 The reaction temperature was controlled in the range of 200-500℃, and the ability of the catalyst to resist the removal of NOx by calcium sulfate was tested. The test results are as follows: Figure 1 As shown, the results show that the catalyst has the ability to effectively resist the removal of NO by calcium sulfate at 300-500℃.

[0046] Example 5

[0047] SEM and BET tests of catalysts

[0048] The scanning electron microscopy (SEM) analysis of the catalyst was performed using a Hitachi JEOL JSM-6360LV electron scanning microscope. The specific surface area and pore structure analysis were performed using a Quantachrom instrument (USA) Micromeritics Tristar II 3020. Taking the test results of the product obtained in Example 2 as an example, the test results are as follows: Figure 2 and Figure 3 As shown, the results show that the FeWAl prepared by the present invention x The catalyst has a 3D spherical structure with a surface area of ​​124.46 m 2 / g, with a total pore volume of 0.3 cm 3 / g, and the average pore diameter is 9.77nm.

[0049] Example 6

[0050] XRD test of catalyst

[0051] The catalyst's phase composition and crystal structure were determined using XRD, using a Rigaku Ultima IV powder X-ray diffractometer. The test conditions were Cu-Kα radiation (λ = 1.5406A), a maximum operating voltage and current of 60 kV, and a maximum operating current of 300 mA. The experimental data were analyzed using Jade 8.0 software. Taking the test results of the product in Example 2 as an example, the obtained XRD patterns were used to identify the crystal phases with reference to JCPDS data. Figure 4 As shown. Three-dimensional spherical chrysanthemum-shaped porous FeWAl xThe sample exhibited characteristic diffraction peaks at 2θ values ​​of 30.24, 35.62, 54.62, 57.28, and 62.92°, which can be attributed to the (220), (311), (430), (511), and (440) lattice planes of γ-Fe2O3 in a typical spinel structure (JCPDS#39-1346). γ-Fe2O3 is more active than α-Fe2O3 in medium-temperature SCR. In addition, no diffraction peaks of the Al2O3 crystalline phase were detected, indicating that the Al2O3 is in an amorphous state or highly dispersed on the surface of the composite oxide.

Claims

1. A 3D spherical chrysanthemum-like structure FeWAl x The water-resistant calcium sulfate denitrification catalyst is characterized by: It is composed of a composite transition metal oxide of Fe2O3 and WO3 loaded on Al2O3, and is recorded as FeWAl x , where x is the percentage of Al2O3 in the total mass of the catalyst, 5<x≤50%; The catalyst is composed of the following components in percentage by mass: WO3 0%~45% (excluding endpoint 0), Al2O3 5%~50%, the balance is Fe2O3, and the sum of the mass percentages of each component is 100%; The catalyst has a 3D structure of ping-pong balls shaped by interweaving macropores, mesopores and micropores, and a specific surface area of ​​50-150 m 2 / g, with a total pore volume of 0.15–0.30 cm 3 / g, and the average pore size is 2~20 nm.

2. The 3D spherical chrysanthemum-shaped structure FeWAl according to claim 1 x The water-resistant calcium sulfate denitrification catalyst is characterized by: The catalyst is composed of the following components in percentage by mass: WO3 30%~35%, Al2O3 15%~20%, the balance is Fe2O3, and the sum of the mass percentages of each component is 100%.

3. The 3D spherical chrysanthemum-shaped structure FeWAl according to claim 1 or 2 x The preparation method of water-resistant calcium sulfate denitrification catalyst is characterized in that: The steps include: (1) A modified soap-free emulsion polymerization method is used to synthesize PMMA emulsion, and then PMMA colloidal crystal template microspheres are prepared by a constant temperature suspension film forming method. The preparation method of the PMMA colloidal crystal template microspheres is as follows: inert gas is continuously introduced into ultrapure water and heated to 60-75°C, methyl methacrylate is added to the ultrapure water and stirred for 30-50 min, potassium persulfate is used as an initiator to react for 40-50 min, and the amount ratio of potassium persulfate to methyl methacrylate is 0.3-0.5 g: 100-120 mL. After the reaction is completed, the mixture is poured into ultrapure water at a temperature of 5-20°C to prepare polymethyl methacrylate emulsion, the prepared liquid is divided and centrifuged to remove the supernatant, and then the white precipitate is added to ultrapure water for ultrasonic dispersion, and evaporated at a constant temperature to form ordered PMMA colloidal crystal template microspheres; (2) Using F127 as a pulling agent, micelles are formed through intermolecular forces with the metal precursor solution of iron, tungsten, and aluminum to obtain a metal oxide precursor solution capable of forming mesopores; (3) The PMMA colloidal crystal template microspheres prepared in step (1) are immersed in the metal oxide precursor solution obtained in step (2) until the metal oxide precursor solution completely fills the voids of the PMMA colloidal crystal template microspheres. Finally, the colloidal crystal template of the PMMA colloidal crystal template microspheres is removed by calcination to form a 3D porous metal oxide catalyst composed of macropores, mesopores and micropores interwoven, i.e., a 3D spherical chrysanthemum structure FeWAl x Water-resistant calcium sulfate denitrification catalyst.

4. The preparation method according to claim 3, characterized in that Step (2) is as follows: F127, anhydrous methanol, ethylene glycol, citric acid and anhydrous oxalic acid are stirred at 15-40 °C to form a uniform solution, and then Fe(NO3)2·3H2O, (NH4) 10 [H2W 12 O 42 ]·4H2O, Al(NO3)3·9H2O, and then stirred at 35~65℃ for 2~4 h to form a uniform colloid, F127, anhydrous methanol, ethylene glycol, citric acid, anhydrous oxalic acid, Fe(NO3)2·3H2O, (NH4) 10 [H2W 12 O 42 The usage ratio of ]·4H2O and Al(NO3)3·9H2O is 2~3 g:10~30 mL:5~20 mL:3~6 g:2~4 g:2~10 g:0.5~2 g:0.5~5g.

5. The preparation method according to claim 3, characterized in that Step (3) is specifically as follows: immerse the metal oxide precursor solution in the PMMA colloidal crystal template microspheres for 5-10 hours, remove the excess precursor solution with a funnel, and rinse with anhydrous methanol to obtain a filter cake. The filter cake is placed in an oven to dry, and then calcined in a muffle furnace. The temperature is raised from room temperature to 100-250 ° C and maintained for 4-5 hours, then raised to 350-450 ° C and maintained for 4-6 hours. After cooling to room temperature, a 3D spherical chrysanthemum structure FeWAl is obtained. x Water-resistant calcium sulfate denitrification catalyst.

6. The 3D spherical chrysanthemum-shaped structure FeWAl according to claim 1 or 2 x Application of water-resistant calcium sulfate denitrification catalyst in industrial flue gas denitrification.

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