Three-dimensional porous CuFeAlO for synergistically removing nitric mercury x Sulfur tolerant catalyst and method for making same

Abstract

The application discloses a three-dimensional porous structure sulfur-resistant catalyst for synergistically removing nitric mercury and a preparation method thereof. The catalyst is composed of CuO, Fe2O3 and Al2O3, wherein the mass percentage of CuO in the catalyst is 6-12%, the mass percentage of Fe2O3 in the catalyst is 78-84%, and the rest is Al2O3. The catalyst is prepared from Fe(NO3)3.9H2O, Cu(NO3)2.3H2O and Al(NO3)3.9H2O as metal sources by using a double-template method (polymethyl methacrylate (PMMA) as a hard template and cetyltrimethylammonium bromide (CTAB) as a soft template). The catalyst prepared by the application has both macroporous and mesoporous structures, has a large specific surface area, can make active components better dispersed, improves the sulfur poisoning resistance of the catalyst, can synergistically control mercury while removing nitric oxide, and has a good industrial application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of porous composite metal oxide catalyst preparation, and specifically relates to a three-dimensional porous CuFeAlO catalyst for synergistically removing mercury nitrate. x Sulfur-resistant catalyst and preparation method thereof. Background Art

[0002] Coal-fired industrial boilers are NO x and Hg 0 An important source of emissions. NO emitted into the atmosphere x and Hg 0 It has a significant impact on the ecological environment and human health. x O3 pollution, PM 2.5 Mercury is an important precursor of pollution phenomena such as NO and photochemical smog. Mercury is volatile, highly toxic and bioaccumulative, which can cause great harm to the natural environment and human health. Therefore, effective control of NO x and Hg 0 It becomes particularly important.

[0003] NH3-SCR is currently the most widely used x The mercury released into the atmosphere is usually in the form of Hg 0 The researchers found that SCR catalysts can reduce Hg 0 Oxidized to Hg 2+ , the generated Hg 2+ It can be removed by the subsequent wet flue gas desulfurization (WFGD) device to achieve the removal of Hg 0 The purpose of removing NO and Hg is to 0 In contrast, NH3-SCR technology is used to collaboratively control NO and Hg 0 This technology requires no additional investment in equipment or site, making it a highly competitive option. Due to production demands, industrial boiler operating loads fluctuate significantly, leading to significant variations in flue gas temperature and a high concentration of SO₂ in the flue gas. However, current commercial catalysts have drawbacks for this type of flue gas, such as a narrow activity window, SO₂ poisoning of the catalyst, and the biotoxicity of vanadium. Therefore, the development of wide-temperature, sulfur-resistant, vanadium-free catalysts for synergistic denitrification and mercury removal is particularly important.

[0004] In recent years, iron-based catalysts have been widely studied due to their advantages such as high oxygen carrying capacity, non-toxicity and price advantage. However, iron-based catalysts are prone to form iron oxide particles or agglomerates during the preparation process, which is not conducive to the efficiency of NH3-SCR. In addition, below 300°C, SO2 has a great influence on the performance of iron-based catalysts. Therefore, broadening the temperature window of iron-based catalysts and improving the low-temperature SO2 resistance of NH3-SCR catalysts are of great significance for their application. Adding additional components or changing the structure of the catalyst is a strategy to solve the above problems. Copper-based catalysts exhibit good catalytic activity at low temperatures. Researchers have found that the catalyst formed by the combination of copper and iron oxides can significantly improve the catalytic activity and reduce the active temperature. The surface acidity and redox ability of the catalyst play an important role in the performance of NH3-SCR catalysts and are key factors in achieving wide-temperature synergistic denitrification and mercury removal. Al2O3 has high dispersibility and strong stability. It is an acidic oxide and is often used as a catalyst support for NH3-SCR. It has catalytic activity at medium and high temperatures. By doping Al ions in CuO-Fe2O3, the surface acidity and redox properties of the catalyst can be adjusted to achieve NO and Hg 0 Synergistic control over a wide temperature range. Mixing Al2O3 with CuO-Fe2O3 to prepare CuO-Fe2O3-Al2O3 catalysts is expected to broaden their temperature window and optimize their catalytic performance. However, in order to achieve industrial application of catalysts, highly sulfur-resistant catalysts remain a difficult and key research topic. Two common causes of SO2 poisoning are: 1) At low temperatures, sulfur oxides and ammonia generate ammonium sulfate salts that cover the active sites, leading to catalyst deactivation; 2) At high temperatures, metal oxides at the active sites are sulfated, leading to catalyst poisoning and deactivation. In order to avoid SO2 poisoning of the catalyst, it is necessary to inhibit ammonium sulfate at low temperatures and inhibit the sulfidation of metal oxides at high temperatures. Studies have found that porous catalysts are conducive to the decomposition of ammonium sulfate and can significantly improve the SO2 resistance of the catalyst; and CuO can act as a sacrificial active site to preferentially react with SO2, thereby protecting the active sites of the catalyst. Therefore, the present invention uses Fe(NO3)3·9H2O, Cu(NO3)2·3H2O, Al(NO3)3·9H2O as catalyst precursors and PMMA as a template to prepare three-dimensional porous CuFeAlO x Catalyst, the prepared catalyst is used for selective catalytic reduction of NO in industrial flue gas and synergistic catalytic oxidation of Hg 0 . Summary of the Invention

[0005] For the above selective catalytic reduction of NO, the synergistic catalytic oxidation of Hg 0 The present invention provides a method for synergistically removing nitric oxide (NO) and mercury (Hg 0) a three-dimensional porous sulfur-resistant catalyst and a preparation method thereof, wherein the catalyst is prepared by a dual-template method (CTAB as a soft template and PMMA as a hard template).

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

[0007] A three-dimensional porous CuFeAlO for synergistic removal of mercury nitrate x Sulfur-resistant catalyst, the catalyst is composed of transition metal CuO, Fe2O3 and Al2O3, and the catalyst is recorded as CuFeAlO x .

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

[0009] CuO: 6% to 12% (more preferably 6% to 8%), Fe2O3: 78% to 84% (more preferably 82% to 84%), the remainder is the mass percentage of Al2O3, and the sum of the mass percentages of the three components is 100%.

[0010] Furthermore, the catalyst has a rich pore structure, and its specific surface area, total pore volume and average pore diameter are 30 to 80 m 2 / g, 0.05~0.2cm 3 / g, 6~20nm.

[0011] The above catalytic reduction of NO synergistically catalyzes the oxidation of Hg 0 Three-dimensional porous CuFeAlO x The preparation method of the catalyst comprises the following steps:

[0012] (1) PMMA emulsion was prepared by soap-free emulsion polymerization, and then the PMMA solution was evaporated and self-assembled using a constant temperature suspension film forming method to prepare a PMMA colloidal crystal hard template;

[0013] (2) CTAB is used as a soft template agent and mixed with a metal precursor in an ethanol solution to form micelles. Under the action of CTAB, the metal salt molecules are distributed in a certain sequence to form mesopores, thereby obtaining a CTAB-assisted metal precursor solution;

[0014] (3) pouring the metal precursor solution prepared in step (2) onto 2-5 g of the PMMA hard template prepared in step (1) so that the solution fills the gaps in the PMMA template. After pouring, vacuum drying is performed to allow the solution to more fully fill the gaps. After drying, calcination is performed to burn off the CTAB and PMMA template, and finally a metal oxide with a macroporous structure and a mesoporous wall is obtained, that is, a three-dimensional porous structure catalyst is obtained.

[0015] Furthermore, the specific preparation method of the PMMA template in step (1) is as follows: 110-115 ml of methyl methacrylate containing 0.03% by mass of p-hydroxybenzoic acid is added to 1000-1500 ml of deionized water and stirred evenly, the polymerization temperature is controlled to 70±1°C, N2 is continuously introduced into the reaction device to keep the reaction under anaerobic conditions, 0.3-0.8 g of initiator prepared by potassium persulfate is added after the reaction for 10-30 minutes, the emulsification time is controlled to be 40-50 minutes, and then the emulsified liquid is poured into cooled deionized water to dilute 1-1.5 times to stop the polymerization reaction, and after cooling, an emulsion of polymethyl methacrylate is obtained, the cooled emulsion is centrifuged at a speed of 3500-5500 rpm for 30-60 minutes, and after centrifugation, the precipitate is diluted 50-100 times with deionized water, and the precipitate is dispersed by ultrasound. The dispersed solution is evaporated at a constant temperature in a water area of ​​70-100°C to finally obtain a self-assembled three-dimensional PMMA template.

[0016] Furthermore, the ethanol solution in step (2) is obtained by mixing 10-13 ml of ethanol and 0.5-1 ml of deionized water; the mass ratio of the metal precursors Fe(NO3)3·9H2O, Cu(NO3)2·3H2O and Al(NO3)3·9H2O is (1-3):(17-19):(3-5).

[0017] Furthermore, step (3) is specifically as follows: pouring the metal precursor solution on a 2-5g PMMA template, and after the PMMA is soaked, placing the soaked PMMA in a vacuum drying oven at room temperature for 16-19 hours to allow the solution to more fully fill the gaps. After aging, the mixture is taken out and rinsed with anhydrous ethanol solution, and the excess solution is filtered off with a Buchner funnel. The washed filter cake is dried in an oven at 45-55°C for 16-19 hours, and the dried solid is placed in a muffle furnace for calcination, rising from room temperature to 300-350°C and maintaining for 3-4 hours at a heating rate of 1-2°C / min; then the temperature is raised to 450-550°C at the same heating rate as in the previous stage and maintained for 3-4 hours, and finally cooled to room temperature to obtain a three-dimensional porous catalyst.

[0018] The present invention will be further described below:

[0019] The present invention uses CTAB as a soft template and PMMA as a hard template to prepare a three-dimensional CuFeAlO with both macroporous and mesoporous structures. x Catalyst for synergistic control of NO and Hg in industrial boiler flue gas 0 Doping Cu and Al into the iron-based catalyst inhibits the crystallization and agglomeration of the iron-based catalyst, which helps the formation of lattice defects (such as oxygen vacancies), thereby changing the physical and chemical properties of the catalyst and improving the redox properties and surface acidity of the catalyst. xThe catalyst is prepared into a three-dimensional porous structure, which can reduce the grain size and effectively increase the specific surface area, thereby increasing the NO and Hg 0 The effective contact area with the active sites of the catalyst further promotes the catalytic reduction of NO and Hg 0 The three-dimensional porous catalyst's rich pore structure accelerates the decomposition of ammonium sulfate at low temperatures. Furthermore, the introduction of Cu preferentially reacts with SO₂, protecting the catalyst's active sites at high temperatures. Therefore, this catalyst has excellent application prospects in industrial boiler flue gases.

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

[0021] The catalyst prepared by the present invention has a multi-level pore structure, so that the active components of the catalyst are well dispersed on the catalyst surface, and can effectively and synergistically control NO and Hg in the presence of SO2. 0 , effectively avoiding the deposition of ammonium sulfate on the catalyst surface and the sulfation of active sites, and improving the stability of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 For Example 4, CuFeAlO x Scanning electron microscopy image of the catalyst.

[0023] Figure 2 For Example 4, CuFeAlO x Curve chart of N2 adsorption and desorption test of the catalyst.

[0024] Figure 3 CuFeAlO in Example 4 x Catalyst pore size distribution test results.

[0025] Figure 4 For Example 5, CuFeAlO x XRD spectrum 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 specific preparation method of PMMA template is as follows:

[0029] 115 ml of methyl methacrylate containing 0.03% by mass of p-hydroxybenzoic acid was added to 1300 ml of deionized water and stirred evenly. The polymerization temperature was controlled at 70°C, and N2 was continuously introduced into the reaction apparatus to keep the reaction under anaerobic conditions. After the reaction for 15 minutes, 0.4 g of initiator prepared with potassium persulfate was added, and the emulsification time was controlled at 45 minutes. The emulsified liquid was then poured into cooled deionized water and diluted 1.15 times to stop the polymerization reaction. After cooling, an emulsion of polymethyl methacrylate was obtained. The cooled emulsion was centrifuged at 4000 rpm for 45 minutes. After centrifugation, the precipitate was diluted 100 times with deionized water, and the precipitate was dispersed by ultrasound. The dispersed solution was evaporated at a constant temperature in water at 80°C to finally obtain a self-assembled three-dimensional PMMA template.

[0030] Example 2

[0031] The three-dimensional porous CuFeAlO x The preparation method of the sulfur-resistant catalyst comprises the following steps:

[0032] (1) Add 12 ml of anhydrous ethanol and 0.5 ml of deionized water to a 100 ml beaker at 30°C to prepare 10 g of a 95 wt% ethanol solution, and then dissolve 1 g of CTAB in the ethanol solution.

[0033] (2) 3.1325 g of Fe(NO3)3·9H2O, 0.1834 g of Cu(NO3)2·3H2O, and 0.5556 g of Al(NO3)3·9H2O were dissolved in the ethanol solution prepared in step (1) and stirred for 6 h to obtain a metal precursor solution;

[0034] (3) The metal precursor solution prepared in step (2) is poured on a 3g PMMA hard template. After the PMMA is soaked, the soaked PMMA is placed in a vacuum drying oven at room temperature for 18 hours to allow the solution to more fully fill the gaps. After aging, the mixture is taken out and rinsed with anhydrous ethanol solution, and the excess solution is filtered off with a Buchner funnel. The washed filter cake is dried in an oven at 50°C for 18 hours. The dried solid is placed in a muffle furnace and calcined from room temperature to 300°C and maintained for 2 hours at a heating rate of 1°C / min; then the temperature is raised to 500°C at the same rate as in the previous stage and maintained for 3 hours, and then cooled to room temperature to obtain a three-dimensional porous catalyst. The catalyst is sieved through an 80-100 mesh sieve for later use.

[0035] Example 3

[0036] The catalyst prepared by the present invention is used to catalyze the reduction of NO and synergistically oxidize Hg 0 performance.

[0037] The three-dimensional porous CuFeAlO prepared in Example 2 of the present inventionx The catalyst was used as the experimental object. 0.2 g of catalyst was loaded into the catalytic reactor, the total gas flow rate was 200 ml / min, and the gas composition was: 6 vol% O2, 500 ppm NO, 500 ppm NH3, 150 ppm SO2, 65 μg / m 3 Hg 0 , balance gas N2; space velocity is 40000h -1 The reaction temperature was controlled at 100-450°C, and the catalyst was tested for catalytic reduction of NO and synergistic oxidation of Hg 0 performance.

[0038] Example 4

[0039] BET and SEM tests of the catalyst of the present invention.

[0040] The specific surface area and pore structure of all catalysts in the present invention were measured using a Micromeritics Tristar II 3020 surface area and pore size distribution analyzer (Micromeritics Instrument Corp., USA). Transmission electron microscope (TEM) analysis was performed using a Hitachi JEM-2010 TEM. Figure 1 , Figure 2 and Figure 3 The results show that the CuFeAlO prepared by the present invention x The catalyst has a three-dimensional porous structure with a specific surface area of ​​34.26 m 2 / g.

[0041] Example 5

[0042] XRD test of the catalyst of the present invention.

[0043] The physical structure of the catalyst of the present invention was analyzed and characterized by a Rigaku rotaflex D / MAX-2500 / pc X-ray diffractometer of Hitachi, Japan. The test conditions were Cu target Ka radiation (λ=1.5406A), scanning 2θ range 10-80°, scanning speed 10° / min, and the test results were as follows: Figure 4 The results showed that only FeO was detected in x The diffraction peak of AlO was not detected. x and CuO x The diffraction peak of AlO x and CuO xIt exists in highly dispersed amorphous or very small crystalline phases. The diffraction peaks of magnetite Fe4O3 (PDF#75-0449) and hematite α-Fe2O3 (PDF#99-0060) were detected. 2+ , Fe in the spinel part 2+ It may play an important role in the NH3-SCR process. The redox reaction favors the catalytic reduction of NO and the synergistic catalytic oxidation of Hg. 0 active.

Claims

1. A three-dimensional porous structure sulfur-resistant catalyst for synergistically removing mercuric nitrate, characterized in that: The catalyst is composed of CuO, Fe2O3 and Al2O3, and the three-dimensional porous structure sulfur-resistant catalyst is recorded as CuFeAlO x The preparation method of the three-dimensional porous structure sulfur-resistant catalyst for synergistically removing mercuric nitrate comprises the following steps: (1) PMMA emulsion was prepared by soap-free emulsion polymerization, and then the PMMA solution was evaporated and self-assembled using a constant temperature suspension film formation method to prepare a PMMA colloidal crystal hard template; (2) CTAB is used as a soft template and mixed with a metal precursor in an ethanol solution to form micelles. Under the action of CTAB, the metal salt molecules are distributed in a certain sequence to form mesopores, and a CTAB-assisted metal precursor solution is obtained; (3) The metal precursor solution prepared in step (2) is poured on 2-5 g of the PMMA colloidal crystal hard template prepared in step (1) to fill the voids of the PMMA colloidal crystal hard template with the solution. After pouring, vacuum drying is performed to allow the solution to more fully fill the voids. After drying, calcination is performed to burn off the CTAB and the PMMA colloidal crystal hard template, and finally a metal oxide with a macroporous structure and a mesoporous wall is obtained, that is, a three-dimensional porous structure sulfur-resistant catalyst is obtained.

2. The three-dimensional porous structure sulfur-resistant catalyst for synergistically removing mercuric nitrate according to claim 1, characterized in that: The catalyst is composed of the following mass percentages: 6%≤CuO≤12%, 78%≤Fe2O3≤84%, and the remainder is the mass percentage of Al2O3, and the sum of the mass percentages of the three components is 100%.

3. The three-dimensional porous structure sulfur-resistant catalyst for synergistically removing mercuric nitrate according to claim 1, characterized in that: The catalyst has a rich pore structure, and its specific surface area, total pore volume and average pore diameter are 30-80 m 2 / g, 0.05~0.2cm 3 / g, 6~20 nm.

4. The method for preparing the three-dimensional porous structure sulfur-resistant catalyst for synergistically removing mercuric nitrate according to any one of claims 1 to 3, characterized in that: The steps include: (1) PMMA emulsion was prepared by soap-free emulsion polymerization, and then the PMMA solution was evaporated and self-assembled using a constant temperature suspension film formation method to prepare a PMMA colloidal crystal hard template; (2) CTAB is used as a soft template and mixed with a metal precursor in an ethanol solution to form micelles. Under the action of CTAB, the metal salt molecules are distributed in a certain sequence to form mesopores, and a CTAB-assisted metal precursor solution is obtained; (3) The metal precursor solution prepared in step (2) is poured on 2-5 g of the PMMA colloidal crystal hard template prepared in step (1) to fill the voids of the PMMA colloidal crystal hard template with the solution. After pouring, vacuum drying is performed to allow the solution to more fully fill the voids. After drying, calcination is performed to burn off the CTAB and the PMMA colloidal crystal hard template, and finally a metal oxide with a macroporous structure and a mesoporous wall is obtained, that is, a three-dimensional porous structure sulfur-resistant catalyst is obtained.

5. The method for preparing a three-dimensional porous structure sulfur-resistant catalyst for synergistically removing mercuric nitrate according to claim 4, characterized in that: The specific preparation method of the PMMA colloidal crystal hard template in step (1) is as follows: 110-115 ml of methyl methacrylate containing 0.03% by mass of p-hydroxybenzoic acid is added to 1000-1500 ml of deionized water and stirred evenly, the polymerization temperature is controlled to be 70±1°C, N2 is continuously introduced into the reaction device to keep the reaction under anaerobic conditions, 0.3-0.8 g of initiator prepared by potassium persulfate is added after the reaction for 10-30 minutes, the emulsification time is controlled to be 40-50 minutes, and then the emulsified liquid is poured into cooled deionized water to dilute 1-1.5 times to stop the polymerization reaction, and the polymethyl methacrylate emulsion is obtained after cooling, and the cooled emulsion is centrifuged at a speed of 3500-5500 rpm for 30-60 minutes. After centrifugation, the precipitate is diluted 50-100 times with deionized water, and the precipitate is dispersed by ultrasound. The dispersed solution is stirred at 70-100 ℃ constant temperature evaporation in a water bath finally yielded a self-assembled three-dimensional PMMA colloidal crystal hard template.

6. The preparation method according to claim 4, characterized in that The ethanol solution in step (2) is obtained by mixing 10-13 ml of ethanol and 0.5-1 ml of deionized water; the amount of CTAB used is 0.5-2.5 g, and the amounts of the metal precursors Fe(NO3)3·9H2O, Cu(NO3)2·3H2O and Al(NO3)3·9H2O are 0.1-0.3 g, 2-4 g and 0.5-0.7 g, respectively.

7. The preparation method according to claim 4, characterized in that Step (3) is specifically as follows: pouring the metal precursor solution on a 2-5 g PMMA colloidal crystal hard template, and after the PMMA colloidal crystal hard template is soaked, placing the soaked PMMA colloidal crystal hard template in a vacuum drying oven at room temperature for 16-19 hours to allow the solution to more fully fill the gaps; after aging, taking it out and rinsing it with anhydrous ethanol solution, and filtering off the excess solution with a Buchner funnel, drying the washed filter cake in an oven at 45-55 ° C for 16-19 hours, and calcining the dried solid in a muffle furnace, raising the temperature from room temperature to 300-350 ° C and maintaining it for 3-4 hours, with a heating rate of 1-2 ° C / min; then raising the temperature to 450-550 ° C at the same rate as in the previous stage and maintaining it for 3-4 hours, and finally cooling it to room temperature to obtain a three-dimensional porous structure sulfur-resistant catalyst.

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