Preparation method and application of iron-manganese-titanium-based catalyst with amorphous structure

Abstract

The application discloses a preparation method and application of an iron-manganese-titanium-based catalyst with an amorphous structure, and the catalyst prepared by the method has excellent performance in selective catalytic reduction of nitrogen oxides by ammonia. The iron-manganese-titanium catalyst with a special amorphous structure is synthesized by a sol-gel method by using tetrabutyl titanate, iron nitrate nine hydrate and manganese nitrate four hydrate as precursors. The catalyst has excellent low-temperature nitrogen oxide reduction capacity, low-temperature nitrogen selectivity, a wide reaction activity window and excellent regeneration performance, and effectively solves the problems of poor activity and a narrow activity window of a traditional vanadium-based catalyst under low-temperature conditions. The catalyst has great application potential in industries with low tail gas temperature, such as the cement and steel industries.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalysts for selective catalytic reduction of nitrogen oxides by ammonia, and in particular to a preparation method and application of an iron-manganese-titanium-based catalyst with amorphous structure. BACKGROUND

[0002] According to the 2022 China Ecological Environment Statistics Report, a total of 8.957 million tons of nitrogen oxides were emitted in China in 2022, of which 3.333 million tons were emitted from stationary sources, accounting for 37.2%. In the context of carbon reduction and pollution control in China, effectively controlling stationary source nitrogen oxide emissions is crucial to improving air environmental quality.

[0003] For the removal and control technology of nitrogen oxides, mainly includes selective catalytic reduction method, selective non-catalytic reduction method, microbial method, absorption method, adsorption method, plasma method, etc. Among them, the ammonia selective catalytic reduction of nitrogen oxides (NH3-SCR) is the most widely used NOx emission reduction technology. The catalyst is the core of this technology, which directly affects the denitrification effect. At present, vanadium-based catalyst is the most mature commercial NH3-SCR denitrification catalyst, which has been widely used in stationary source NOx emission control. However, this type of catalyst has poor low-temperature activity and narrow active temperature range, requiring high denitrification temperature and strict reaction conditions, which can easily cause energy waste and catalyst poisoning and deactivation in high-temperature and high-dust arrangement. Therefore, it is particularly important to develop new low-temperature and high-efficiency catalysts to meet the requirements of low-temperature and low-dust arrangement in industry.

[0004] In recent years, the most widely studied low-temperature non-vanadium-based SCR catalysts include noble metal catalysts, molecular sieve catalysts, and transition metal oxide catalysts. Noble metal catalysts have excellent activity at low temperatures, but the cost is high and they are difficult to be used on a large scale; molecular sieve catalysts show good low-temperature denitrification performance, but have poor stability and high preparation cost, which are not suitable for commercial application. Transition metal oxide catalysts are rich in types, and because the d-electron shell of the metal cation is easy to lose or steal electrons, they have strong oxidation and reduction capacity and coordination ability, and have attracted widespread attention in the field of NH3-SCR. For example, manganese oxides show excellent low-temperature SCR catalytic performance due to their variable valence and good redox ability, and have attracted much attention in the field of catalysis. However, manganese-based catalysts have a narrow NH3-SCR temperature window and low N2 selectivity, which limits their practical application. Therefore, by improving the formula of the catalyst, the structure, redox properties and acidity can be adjusted to design an NH3-SCR catalyst with high low-temperature activity and wide reaction activity temperature window. SUMMARY

[0005] The application provides an iron-manganese-titanium-based catalyst with a special amorphous structure, which is high in nitrogen oxide removal efficiency at low temperature, high in N2 selectivity at low temperature, wide in active temperature range and environmentally friendly, and application thereof.

[0006] The catalyst is composed of Fe, Mn and Ti elements with different proportions, and is synthesized by one-pot synthesis of a special ternary transition metal oxide catalyst with an amorphous structure through a sol-gel method. The special amorphous structure of the catalyst increases the specific surface area, the content of surface oxygen vacancies and the number of active sites. Meanwhile, the special amorphous structure promotes the dispersion of surface active species. In addition, the introduction of Ti elements increases the acid sites and improves the adsorption amount of ammonia on the catalyst surface. Compared with the traditional vanadium-based catalyst, the catalyst significantly improves the low-temperature conversion rate of nitrogen oxides, maintains high N2 selectivity at low temperature and widens the active temperature range.

[0007] A preparation method of an iron-manganese-titanium-based catalyst with a special amorphous structure, comprising the following steps:

[0008] (1) First step, synthesis of a mixed solution:

[0009] Mix acetic acid and ethanol uniformly, then add tetrabutyl titanate to stir to form a mixed solution; add a nitric acid solution to the mixed solution and stir to mix uniformly;

[0010] (2) Second step, synthesis of a mixed precursor:

[0011] Mix ultrapure water and ethanol uniformly, add an iron source precursor and a manganese source precursor to stir to dissolve and form a mixed precursor;

[0012] (3) Third step, sol-gel reaction:

[0013] Slowly drop the mixed precursor obtained in step (2) into the mixed solution obtained in step (1), stir at room temperature, then continue to stir after heating to form a gel; dry the obtained gel, and calcine in an air atmosphere to obtain an iron-manganese-titanium-based catalyst with an amorphous structure.

[0014] The ratio of the amount of tetrabutyl titanate in the mixed solution to the amount of the iron source precursor and the manganese source precursor in the mixed precursor is 1.0 g (calculated based on tetrabutyl titanate): 0.5-3.0 g (calculated based on iron nitrate nine hydrate): 0.5-1.5 g (calculated based on manganese nitrate four hydrate). The most preferred ratio is 1.0 g: 0.5 g: 0.5 g.

[0015] The concentration of the nitric acid solution added in step (1) is 65.0 vol% to 68.0 vol%, and the pH of the mixed solution is adjusted to 1.5 to 3.0.

[0016] The iron source precursor added in step (2) is ferric nitrate nine hydrate or ferric chloride six hydrate, and the manganese source precursor is manganese nitrate four hydrate or manganese acetate.

[0017] In step (3), the drying condition is drying at 70-90°C for 12-24h, and the calcination condition is programmed heating at a heating rate of 2-5°C / min to 480-520°C and then calcining at 480-520°C in air for 3-5h, and further preferably programmed heating at a heating rate of 2-5°C / min to 500°C and then calcining at 500°C in air for 4h.

[0018] The iron-manganese-titanium-based catalyst with the special amorphous structure is applied in selective catalytic reduction of nitrogen oxides by ammonia.

[0019] In the application, the nitrogen oxides are nitrogen oxides discharged by a fixed source, and the temperature of the nitrogen oxides is 100-300°C. The application specifically comprises the following steps:

[0020] The modified titanium dioxide catalyst with the special morphology is loaded into a fixed bed reactor, high-temperature activation is performed by inputting a mixed gas composed of 5-10% by volume O2 and 90-95% by volume N2, then a gas containing nitrogen oxides is inputted, and the selective catalytic reduction of nitrogen oxides by ammonia is performed.

[0021] The high-temperature activation condition is 500°C for 30min at the preparation temperature.

[0022] Specifically, the catalyst is loaded into a fixed bed reactor, high-temperature activation is performed, then the temperature is lowered, then a mixed reaction gas is inputted, and programmed heating is performed to start the selective catalytic reduction reaction (NH3-SCR).

[0023] The catalyst particles are 40-60 mesh;

[0024] The concentration composition of the simulated reaction mixed gas is 500ppm NO, 500ppm NH3, 5% O2 and N2 as the balance gas.

[0025] The total flow of the simulated reaction mixed gas is 500mL / min, and the space velocity is 75,000-3,000,00mL·h -1 ·g -1 ;

[0026] The programmed heating temperature range is 100-500°C.

[0027] Compared with the prior art, the application has the following beneficial effects:

[0028] The application utilizes tetrabutyl titanate, iron nitrate nine hydrates and manganese nitrate four hydrates as precursors to synthesize the iron-manganese-titanium catalyst with special amorphous structure through a sol-gel method. The introduction of Mn and Fe elements effectively improves the oxidation-reduction capacity of the catalyst, promotes the oxidation dehydrogenation of ammonia at low temperature; the introduction of Fe element effectively inhibits the excessive oxidation of ammonia on the surface of the catalyst, and improves the low-temperature N2 selectivity of the catalyst; the introduction of Ti element effectively improves the acidity of the catalyst, increases the number of acidic sites on the surface of the catalyst, and improves the adsorption and activation of ammonia on the surface of the catalyst. Meanwhile, the three elements exhibit synergistic catalysis, effectively improving the low-temperature nitrogen oxide conversion rate and low-temperature N2 selectivity of the catalyst. In addition, the special amorphous structure promotes the dispersion of surface active species, increases the specific surface area of the catalyst, exposes more defects, increases the content of surface oxygen vacancies, and increases the number of active sites.

[0029] The iron-manganese-titanium-based catalyst with special amorphous structure in the application. The catalyst is prepared by using Fe, Mn and Ti precursors which are widely available, easy to obtain and low in cost, and overcomes the potential harm of commercial vanadium-based catalysts to human body and environment. Compared with the vanadium-based catalyst, the iron-manganese-titanium-based catalyst exhibits more excellent activity at low temperature and has a wider applicable temperature range. This provides a new solution for tail gas treatment in the steel, cement, glass and metallurgy industries, and also provides the possibility for the fixed source tail gas treatment in coal-fired power plants to change from high-temperature and high-dust arrangement to low-temperature and low-dust arrangement, effectively reduces energy consumption, and realizes more environmentally friendly and economical denitration.

[0030] The method is simple and easy to operate, and the prepared catalyst exhibits excellent performance in the selective catalytic reduction of nitrogen oxides by ammonia. The catalyst not only has excellent low-temperature nitrogen oxide reduction capacity and low-temperature nitrogen selectivity, but also has a wide reaction activity window and excellent regeneration performance, effectively solving the problems of poor activity and narrow activity window of traditional vanadium-based catalysts at low temperature. In industries with low tail gas temperature, such as the cement and steel industries, this catalyst has great application potential. In addition, the catalyst contains Fe, Mn, Ti and O elements, which can effectively avoid the health hazards and environmental secondary pollution that may be caused by traditional vanadium-based catalysts when treating nitrogen oxides in waste gas, and has the advantages of economy, environmental friendliness and convenience of industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The effect diagram of the selective catalytic reduction of nitrogen oxides (NO x conversion rate) by ammonia of the iron-manganese-titanium-based catalyst with special amorphous structure in Example 1 of the application and the comparative sample;

[0032] Figure 2The figure of the effect of the iron-manganese-titanium-based catalyst with special amorphous structure in Example 1 of the present application and the comparative sample on the selective catalytic reduction of nitrogen oxides by ammonia (N2 selectivity) ;

[0033] Figure 3 The figure of the microstructure of the iron-manganese-titanium-based catalyst with special amorphous structure in Example 1 of the present application and the comparative sample;

[0034] Figure 4 The figure of the microstructure of the iron-manganese-titanium-based catalyst with special amorphous structure in Example 1 of the present application and the comparative sample;

[0035] Figure 5 The figure of the surface physicochemical property data of the iron-manganese-titanium-based catalyst with special amorphous structure in Example 1 of the present application and the comparative sample. DETAILED DESCRIPTION

[0036] The present application will be described in more detail below with reference to examples, which are selected examples only and are not intended to limit the entire scope of the present application in any way.

[0037] Example 1: Preparation of an iron-manganese-titanium-based catalyst with special amorphous structure

[0038] 2.0 g of acetic acid and 26.0 g of anhydrous ethanol were weighed into a beaker and stirred to form a uniform solution; then 8.0 g of tetrabutyl titanate was added to the solution, and a 66.0 vol% aqueous nitric acid solution was added while stirring and adjusting the pH to 2.5 to form solution A; 2.0 g of ultrapure water and 12.5 g of anhydrous ethanol were weighed into another beaker and stirred to form a uniform solution; then 4.0 g of Fe(NO3)3·9H2O and 4.3 g of Mn(NO3)2·4H2O were added to form solution B. Solution B was slowly dripped into solution A under magnetic stirring and stirred at room temperature 25°C for 1 h to form a uniform solution. Then, the gel was formed by heating and stirring at 80°C. The gel was dried at 90°C for 24 h. The product was calcined in a muffle furnace at a temperature increasing rate of 5°C / min to 500°C for 4 h to obtain an iron-manganese-titanium-based catalyst with special amorphous structure.

[0039] Example 2: Preparation of an iron-manganese-titanium-based catalyst with special amorphous structure

[0040] Take 2.0 g of acetic acid and 26.0 g of anhydrous ethanol in a beaker, stir to form a uniform solution; then add 8.0 g of tetrabutyl titanate to the solution, add a 66.0 vol% aqueous nitric acid solution with a concentration of 66.0 vol% and stir to adjust the pH to 2.5 to form solution A; take 2.0 g of ultrapure water and 12.5 g of anhydrous ethanol in another beaker, stir to form a uniform solution; then add 22.7 g of Fe(NO3)3·9H2O and 9.8 g of manganese acetate, stir to form B solution. Slowly drop B solution into A solution under magnetic stirring and stir for 1 h at room temperature 25℃ to form a uniform solution. Then, heat and stir to form a gel at 80℃. The gel is placed at 90℃ for drying for 24 h. The product is calcined in a muffle furnace at a temperature rising rate of 5℃ / min to 500℃ for 4 h to obtain an iron-manganese-titanium-based catalyst with a special amorphous structure.

[0041] Example 3: Preparation of an iron-manganese-titanium-based catalyst with a special amorphous structure

[0042] Take 2.0 g of acetic acid and 26.0 g of anhydrous ethanol in a beaker, stir to form a uniform solution; then add 8.0 g of tetrabutyl titanate to the solution, add a 66.0 vol% aqueous nitric acid solution with a concentration of 66.0 vol% and stir to adjust the pH to 2.5 to form solution A; take 2.0 g of ultrapure water and 12.5 g of anhydrous ethanol in another beaker, stir to form a uniform solution; then add 22.7 g of Fe(NO3)3·9H2O and 9.8 g of manganese acetate, stir to form B solution. Slowly drop B solution into A solution under magnetic stirring and stir for 1 h at room temperature 25℃ to form a uniform solution. Then, heat and stir to form a gel at 80℃. The gel is placed at 90℃ for drying for 24 h. The product is calcined in a muffle furnace at a temperature rising rate of 5℃ / min to 500℃ for 4 h to obtain an iron-manganese-titanium-based catalyst with a special amorphous structure.

[0043] Example 4: Test of the reaction activity of an amorphous iron-manganese-titanium-based catalyst

[0044] According to the preparation method in the application of Example 1, an amorphous iron-manganese-titanium-based catalyst is obtained. According to the preparation method in the application of Example 1, an iron-manganese-based catalyst is synthesized without adding a Ti source as a comparative sample. Its ammonia selective catalytic reduction of nitrogen oxides activity and selectivity are tested according to the following method.

[0045] The amorphous iron-manganese-titanium-based catalyst and the iron-manganese-based catalyst are respectively sieved into 40-60 mesh particles, 0.2 g of catalyst is weighed and placed in a quartz tube fixed bed reactor with an inner diameter of 0.6 cm, and the space velocity is 150,000 mL·h -1 ·g -1Firstly, the catalyst sample was activated and pretreated by passing 25 mL / min O2 and 475 mL / min N2, and the reactor was heated from room temperature to 500℃ at a rate of 5℃ / min, and maintained at 500℃ for 30 min. After the pretreatment, the temperature was lowered to room temperature, and the simulated mixed gas was passed through. After stabilization, the NH3-SCR reaction was started. The total flow rate of the simulated mixed gas used in the test was 500 mL / min, and the gas composition was 500 ppm NO, 500 ppm NH3, 5 vol% O2, and N2 as the carrier gas. The temperature-programmed control reaction was adopted. The reaction temperature was set to 100-400℃, and the temperature was raised to the set temperature at a certain rate. The test interval was 25℃. The temperature was kept constant for 30 min at each test temperature point to ensure that the catalytic reaction reached the equilibrium state. The data were measured as the average value of the test within 30 min. The concentration values of various gases at the inlet and outlet were measured by a Fourier infrared spectrometer equipped with a gas cell. Figure 1 As shown in Figure 2 .

[0046] As shown in Figure 1 , the nitrogen oxide conversion rate of the amorphous iron-manganese-titanium-based catalyst was over 80% in the range of 100-300℃, and the nitrogen oxide conversion rate was over 95% in the range of 125-275℃. The nitrogen oxide conversion rate of the iron-manganese-based catalyst was close to 90% only in the range of 150-175℃. As can be seen from the comparison, after the introduction of Ti element, the amorphous iron-manganese-titanium-based catalyst effectively improved the low-temperature nitrogen oxide conversion rate of the catalyst and widened the active temperature range. Figure 2 As can be seen from the comparison, after the introduction of Ti element, the amorphous iron-manganese-titanium-based catalyst effectively improved the low-temperature nitrogen oxide conversion rate of the catalyst and widened the active temperature range. Figure 1 As can be seen from the comparison, after the introduction of Ti element, the amorphous iron-manganese-titanium-based catalyst effectively improved the low-temperature nitrogen oxide conversion rate of the catalyst and widened the active temperature range.

[0047] Example 5: Micro-morphology structure of the amorphous iron-manganese-titanium-based catalyst

[0048] This example analyzes the micro-morphology and structure characteristics of the prepared amorphous iron-manganese-titanium-based catalyst, thereby providing basic data for analyzing the reaction mechanism of the new catalyst and establishing the structure-activity relationship of the catalyst.

[0049] The special amorphous structure iron-manganese-titanium-based catalyst prepared in Example 1 is observed for micro-morphology and structure characteristics according to the following method.

[0050] A small amount of the prepared catalyst in powder form is taken for X-ray diffraction (XRD) experiment, and the test conditions are as follows: scanning angle 10-90°, step length 0.02°, and dwell time 1 s / step.

[0051] As can be seen from Figure 3 , no diffraction peak of any crystal substance is observed for the iron-manganese-titanium-based catalyst in the present application, indicating that the iron-manganese-titanium-based catalyst in the present application has a special amorphous structure. In the comparative iron-manganese-based catalyst, not only the diffraction peak of α-Fe2O3 (PDF: 33-0664) is observed, but also β-MnO2 (PDF: 24-0735) exists. It is indicated that the iron-manganese-based catalyst without introducing Ti element does not completely form a doped structure. As a comparison, no diffraction peak of any crystal substance is observed for the iron-manganese-titanium-based catalyst in the present application, indicating that the iron-manganese-titanium-based catalyst in the present application has a special amorphous structure, and the introduction of Ti element is conducive to the formation of a special amorphous structure.

[0052] A small amount of the prepared catalyst in powder form is uniformly dispersed in ethanol, and a small amount of the dispersion liquid is dropped on a copper mesh covered with a common carbon film, and then naturally dried for high-resolution transmission electron microscopy (HR-TEM) observation.

[0053] As can be seen from Figure 4 , the iron-manganese-titanium-based catalyst in the present application has no specific morphology at a scale of 100 nm; and the EDS energy spectrum scanning result shows that the Fe, Mn and Ti elements in the amorphous iron-manganese-titanium catalyst in the present application are uniformly distributed. The above conclusion shows that the iron-manganese-titanium-based catalyst in the present application presents a special amorphous structure. At the same time, the iron-manganese-titanium-based catalyst in the present application has small particles, strong agglomeration, large specific surface area, and well-distributed active sites, which is helpful to the establishment of high ammonia selective catalytic reduction of nitrogen oxides activity, and has certain application and promotion significance.

[0054] Example 6: Surface physicochemical properties of the amorphous structure iron-manganese-titanium-based catalyst

[0055] This example analyzes the micro-morphology and structure characteristics of the prepared amorphous structure iron-manganese-titanium-based catalyst, thereby providing basic data for analyzing the reaction mechanism of the new catalyst and establishing the structure-activity relationship of the catalyst.

[0056] The special amorphous structure iron-manganese-titanium-based catalyst prepared in Example 1 is analyzed for surface physicochemical properties according to the following method.

[0057] A small amount of the prepared catalyst sample in powder form was placed in a reaction tube, and dried pretreated by programmed temperature rising from room temperature to 500 DEG C at a rate of 10 DEG C / min, then purged with a He gas flow of 30-50 mL / min for 1 h, and cooled to 100 DEG C. 10% NH3 / He mixed gas was introduced to adsorb the sample until saturation, then switched to He gas flow to purge for 1 h to remove the weakly physically adsorbed NH3 on the surface, and finally raised to 800 DEG C at a rate of 10 DEG C / min under He atmosphere to desorb, and the desorbed gas was detected by TCD.

[0058] A small amount of the prepared catalyst sample in powder form was placed in a BET tester for degassing treatment, and then cooled to liquid nitrogen temperature. Nitrogen was introduced to the surface of the sample at different relative pressures, and the adsorption amount of nitrogen was measured. The adsorption amount of nitrogen at different relative pressures was recorded to generate an adsorption isotherm. According to the BET theory, the specific surface area of the sample was calculated using the adsorption isotherm data.

[0059] The specific surface area of the iron-manganese-titanium-based catalyst with a special amorphous structure in the application is 7 times that of the comparative iron-manganese-based catalyst, which indicates that the iron-manganese-titanium-based catalyst with a special amorphous structure in the application has a larger specific surface area, and the amorphous structure significantly improves the specific surface area of the catalyst, which is beneficial to the exposure and dispersion of the surface active sites. Figure 5 It can be seen that, compared with the comparative iron-manganese-based catalyst, the adsorption amount of NH3 on the surface of the catalyst is larger, which indicates that the iron-manganese-titanium-based catalyst with a special amorphous structure in the application has a higher surface acid amount, and the number of weak acid centers below 250 DEG C is larger, which indicates that the special amorphous structure is beneficial to promoting the adsorption and diffusion of NH3 on the surface of the catalyst at low temperature, and is helpful to the establishment of high ammonia selective catalytic reduction of nitrogen oxide activity, and has certain application and promotion significance.

[0060] The application is not limited to the above best embodiment, and anyone can obtain other forms of products under the inspiration of the application. However, regardless of any changes in catalyst composition, morphology, structure and ratio, any technical solution with the same or similar technical solution as the present application belongs to the protection scope of the present application.

Claims

1. A method for preparing an amorphous iron-manganese-titanium-based catalyst for the selective catalytic reduction of nitrogen oxides with ammonia, characterized in that: The following steps are involved: (1) Acetic acid and ethanol are mixed uniformly, tetrabutyl titanate is added and stirred, and then a nitric acid aqueous solution is added and stirred to obtain a mixed solution; (2) Mix water and ethanol evenly, add iron source precursor and manganese source precursor, and stir to dissolve to form a mixed precursor; (3) adding the mixed precursor obtained in step (2) dropwise to the mixed solution obtained in step (1), stirring, heating and continuing stirring to form a gel; (4) drying the gel obtained in step (3) and calcining it in an air atmosphere to obtain an amorphous iron-manganese-titanium-based catalyst, wherein the iron-manganese-titanium-based catalyst does not have any diffraction peaks of crystalline substances.

2. The preparation method according to claim 1, characterized in that The mass ratio of tetrabutyl titanate in step (1) to the iron source precursor and manganese source precursor in step (2) is: 1.0: 0.5~3.0: 0.5~1.

5.

3. The preparation method according to claim 1, characterized in that In step (1), the concentration of the nitric acid aqueous solution is 65.0 vol% to 68.0 vol%; The pH of the mixed solution after adding nitric acid aqueous solution is 1.5~3.

0.

4. The preparation method according to claim 1, characterized in that In step (1), the iron source precursor is ferric nitrate nonahydrate or ferric chloride hexahydrate.

5. The preparation method according to claim 1, characterized in that In step (1), the manganese source precursor is manganese nitrate tetrahydrate or manganese acetate.

6. The preparation method according to claim 1, characterized in that In step (3), the temperature is raised to 70°C to 90°C and stirring is continued to form a gel.

7. The preparation method according to claim 1, characterized in that In step (4), the drying conditions are: drying at 70°C to 90°C for 12-24 hours.

8. The preparation method according to claim 1, characterized in that In step (4), the calcination conditions are as follows: heating the temperature to 480-520°C at a heating rate of 2-5°C / min and then calcining in an air atmosphere at 480-520°C for 3-5h.

9. Use of the iron-manganese-titanium-based catalyst having an amorphous structure prepared by the preparation method according to any one of claims 1 to 8 in the selective catalytic reduction of nitrogen oxides with ammonia.

10. The use according to claim 9, characterized in that The nitrogen oxides are nitrogen oxides emitted from stationary sources, and the temperature of the nitrogen oxides is 100~300°C.

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