Method for improving the denitration activity of iron oxide, modified iron oxide and method for denitration
By subjecting iron oxide to ultrasonic treatment, the modification process of iron oxide catalyst is simplified, its low-temperature denitrification activity is improved, the problem of insufficient activity in the existing technology is solved, and it has the potential for industrial application.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUODIAN SCI & TECH RES INST
- Filing Date
- 2024-03-13
- Publication Date
- 2026-07-24
AI Technical Summary
Existing iron oxide catalysts exhibit poor low-temperature denitrification activity, and existing optimization methods are complex, often requiring combination with other components.
Modified iron oxide was prepared for use as a denitrification catalyst by ultrasonic treatment of iron oxide in water for 1 to 15 minutes at a power of 80 to 150 W, followed by drying.
It significantly improves the low-temperature denitrification activity of iron oxide, the method is simple and does not require compounding with other components, and has potential industrial application prospects.
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Figure CN117960252B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of low-temperature denitrification catalyst technology, specifically to a method for improving the denitrification activity of iron oxide, modified iron oxide, and a denitrification method. Background Technology
[0002] Nitrogen oxides (NOx), as an air pollutant, have caused serious environmental problems, such as photochemical smog, acid rain, and the greenhouse effect. With increasing societal awareness of global environmental protection, people are paying more and more attention to NOx control. Ammonia selective catalytic reduction (NH3-SCR) of nitrogen oxides is recognized as the most effective and widely used NOx emission reduction technology.
[0003] Catalysts are crucial for NH3-SCR technology. Traditional commercial catalysts, such as V2O5-WO3(MoO3) / TiO2, are widely used in stationary source denitrification applications like coal-fired power plants, operating at high temperatures. However, flue gas temperatures from non-power industries (such as cement kilns) are typically 120-300℃. Therefore, there is an urgent need to develop NH3-SCR catalysts for low-temperature operation. Transition metal oxides are promising alternatives to vanadium-based catalysts. Among them, iron oxides are particularly valuable due to their excellent Fe... 3+ / Fe 2+ Its redox cycling capability and high SO2 resistance make it an excellent choice.
[0004] Pure Fe2O3 with Fe 3+ and O 2- Fe₂O₃ is classified into four crystal forms based on different arrangements, among which α-Fe₂O₃ and γ-Fe₂O₃ have been extensively studied. α-Fe₂O₃ exhibits high thermal stability but insufficient activity; while γ-Fe₂O₃ catalysts show superior low-temperature activity compared to α-Fe₂O₃ catalysts due to their greater surface chemical adsorption of oxygen and easier adsorption of reactant gases, they still cannot meet the needs of practical applications. Pure Fe₂O₃ catalysts still inevitably suffer from poor catalytic performance and thermal stability, leading to various optimization efforts for pure iron oxide catalysts in recent years. However, there is currently no simple method to improve the activity of pure iron oxide through optimization. Most methods involve modifying Fe₂O₃ catalysts by combining other components with Fe₂O₃, or exploring the advantages and disadvantages of pure iron oxide catalysts prepared using different methods, with different exposed crystal faces, or with different morphologies.
[0005] The optimization preparation process of iron oxide catalysts in the existing technology is relatively complex. Therefore, there is an urgent need to provide a relatively simple method to improve the low-temperature denitrification activity of pure iron oxide catalysts. Summary of the Invention
[0006] The purpose of this invention is to overcome the problems of poor low-temperature denitrification activity of pure iron oxide in existing technologies, and the complexity of existing methods for optimizing the denitrification activity of iron oxide, most of which require compounding with other components. This invention provides a method for improving the denitrification activity of iron oxide, as well as a method for modifying iron oxide and denitrifying it. This method is simple to operate, does not require compounding with other components, and can improve the low-temperature denitrification activity of pure iron oxide.
[0007] To achieve the above objectives, the first aspect of the present invention provides a method for improving the denitrification activity of iron oxide, the method comprising: ultrasonicating iron oxide in water, wherein the iron oxide is α-Fe2O3 and / or γ-Fe2O3.
[0008] Preferably, the ultrasound duration is 1 to 15 minutes, more preferably 5 to 10 minutes.
[0009] Preferably, the power of the ultrasound is 80-150W.
[0010] Preferably, the method specifically includes: sonicating iron oxide in water, then filtering and drying it.
[0011] Preferably, the drying conditions include a temperature of 80-120°C and a time of 10-15 hours.
[0012] A second aspect of the present invention provides a modified iron oxide prepared by the method described above.
[0013] A third aspect of the present invention provides a method for denitrification, the method comprising: contacting flue gas with a denitrification catalyst in a reactor;
[0014] The denitrification catalyst is the modified iron oxide prepared by the method described above or the modified iron oxide described above.
[0015] Preferably, the temperature of the contact reaction is 150-300℃, and more preferably 200-250℃.
[0016] Preferably, the flue gas composition includes: 400-600 ppm NOx, 400-600 ppm NH3 and 3-8% O2.
[0017] Preferably, the conditions for the contact reaction include: using an inert gas as the equilibrium gas; a total gas flow rate of 80-150 mL / min; and a gas hourly space velocity of 50,000-70,000 mL·g. -1 ·h -1 .
[0018] Compared with the prior art, the present invention has at least the following advantages:
[0019] (1) The present invention only requires ultrasonic treatment of pure iron oxide in water to effectively improve its low-temperature denitrification activity.
[0020] (2) The present invention uses ultrasound to improve the denitrification activity of iron oxide. The method is simple and quick and has potential industrial application prospects.
[0021] (3) The raw materials used in this invention are inexpensive, readily available, and abundant. Attached Figure Description
[0022] Figure 1 These are the XRD patterns of the α-Fe2O3 catalyst before and after ultrasonic treatment;
[0023] Figure 2 These are the XRD patterns of the γ-Fe2O3 catalyst before and after ultrasonic treatment;
[0024] Figure 3 The graph shows a comparison of the activity test results of the α-Fe2O3 catalyst after ultrasound and the original catalyst, as well as the effect of different ultrasound times on the NO conversion rate of the α-Fe2O3 catalyst.
[0025] Figure 4 The graph shows a comparison of the activity test results of the γ-Fe2O3 catalyst after ultrasound and the original catalyst, as well as the effect of different ultrasound times on the NO conversion rate of the γ-Fe2O3 catalyst.
[0026] Figure 5 These are NH3-TPD diagrams of the α-Fe2O3 catalyst before and after ultrasonic treatment;
[0027] Figure 6 These are H2-TPR images of the α-Fe2O3 catalyst before and after ultrasonic treatment. Detailed Implementation
[0028] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.
[0029] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0030] The first aspect of the present invention provides a method for improving the denitrification activity of iron oxide, the method comprising: ultrasonicating iron oxide in water, wherein the iron oxide is α-Fe2O3 and / or γ-Fe2O3.
[0031] The inventors of this invention discovered through research that the reason why the low-temperature denitrification activity of pure iron oxide can be improved by ultrasonic treatment in water may be that: the crystallinity of γ-Fe2O3 decreases and the defects increase; α-Fe2O3 not only has a decreased crystallinity and an increased defect, but also an improved redox capacity.
[0032] In this invention, the iron oxide can be any commercially available product. For example, α-Fe2O3 can be purchased from Sinopharm Chemical Reagent Co., Ltd. (particle size 100-500nm); γ-Fe2O3 can be purchased from Shanghai Maclean Biochemical Technology Co., Ltd. (particle size 20nm).
[0033] The ultrasound described in this invention can be performed in devices commonly used in the field; specifically, the ultrasound can be performed in an ultrasonic cleaning machine.
[0034] In a specific implementation, iron oxide is ultrasonically dissolved in water, and the ratio of iron oxide to water can be 1g:30-80mL.
[0035] In the method described in this invention, the power of ultrasonication on the iron oxide does not need to be too high to achieve the effect of improving its denitrification activity. In a specific embodiment, the power of the ultrasound can be 80-150W, for example, 80W, 100W, 120W or 150W.
[0036] In this invention, the denitrification activity of iron oxide can be improved simply and quickly by subjecting it to ultrasound for a short period of time.
[0037] In a specific implementation, the duration of the ultrasound can be 1 to 15 minutes, for example, 1 minute, 5 minutes, 10 minutes or 15 minutes.
[0038] In a preferred embodiment, in order to further improve the denitrification activity of iron oxide and increase the conversion rate of nitrogen oxides, the ultrasonication time is 5-10 minutes.
[0039] In a more specific embodiment, the method specifically includes: ultrasonicating iron oxide in water, followed by filtration and drying.
[0040] In this invention, the filtering is not particularly limited and can be performed according to conventional methods.
[0041] In this invention, the drying conditions can be chosen conventionally in the art. In a specific embodiment, the drying temperature can be 80-120℃, and the drying time can be 10-15 hours. After drying, a powder product with a substantially unchanged particle size is obtained.
[0042] In a specific implementation, the dried product can be placed into a sample press to compress tablets, sieved to 20-40 mesh and stored for testing, and then subjected to a denitrification reaction.
[0043] A second aspect of this invention provides a modified iron oxide prepared by the method described above. Using this modified iron oxide in a denitrification catalyst can improve the denitrification catalytic activity of the original iron oxide and increase the conversion rate of nitrogen oxides.
[0044] A third aspect of the present invention provides a method for denitrification, the method comprising: contacting flue gas with a denitrification catalyst in a reactor;
[0045] The denitrification catalyst is the modified iron oxide prepared by the method described above or the modified iron oxide described above.
[0046] In this invention, the source of the flue gas is not limited and can be flue gas generated by coal-fired power plants or industrial furnaces. The denitrification method of this invention is applicable not only to flue gas containing NOx, but also to flue gas containing both NOx and NH3, wherein NOx can be NO and / or NO2.
[0047] In a specific embodiment, the flue gas composition includes: 400-600 ppm NOx, 400-600 ppm NH3 and 3-8% O2.
[0048] In this invention, the denitrification method uses the modified iron oxide described above as a denitrification catalyst to carry out the denitrification reaction at low temperature.
[0049] In a specific embodiment, the temperature of the contact reaction can be 150-300℃, for example, 150℃, 200℃, 250℃ or 300℃. In a preferred embodiment, in order to further improve the catalytic activity of the modified iron oxide and further improve the conversion rate of nitric oxide, the temperature of the contact reaction is 200-250℃.
[0050] In this invention, the contact reaction between flue gas and the denitrification catalyst in a reactor needs to be carried out under conditions where an inert gas is used as the equilibrium gas. The role of this inert gas is to control the gas flow rate and maintain a constant concentration of the reactant gas. In specific embodiments, the inert gas can be argon, helium, nitrogen, etc.
[0051] In a specific embodiment, the total gas flow rate of the contact reaction can be 80-150 mL / min, for example, 80 mL / min, 100 mL / min, 120 mL / min, or 150 mL / min. In this document, the total gas flow rate refers to the sum of gases such as flue gas and inert gas.
[0052] In a specific embodiment, the gas space velocity of the contact reaction can be 50,000-70,000 mL·g. -1 ·h -1 For example, 50000 mL·g -1 ·h -1 60000mL·g -1 ·h -1 Or 70000 mL·g -1 ·h -1 The gas space velocity mentioned refers to the total gas space velocity.
[0053] In this invention, the reactor can be a common type of reactor in the art. In a specific embodiment, the reactor can be a fixed-bed continuous flow reactor.
[0054] In a specific implementation, before the catalyst undergoes denitration reaction after being ultrasonicated, it is purged with Ar at 120-180°C for 20-60 minutes to remove other impurities from the catalyst surface.
[0055] This invention uses ultrasound to treat pure iron oxide, resulting in modified iron oxide with significantly improved denitrification activity.
[0056] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto.
[0057] In the following examples and comparative examples, α-Fe2O3 is a commercially available product from Sinopharm Chemical Reagent Co., Ltd. with a particle size of 100-500nm (Sinopharm code 10012028); γ-Fe2O3 is a commercially available product from Shanghai Maclean Biochemical Technology Co., Ltd. with a particle size of 20nm (item number F809546).
[0058] Examples 1-3 illustrate methods for improving the denitrification activity of α-Fe2O3.
[0059] Example 1
[0060] Weigh 1.0g of α-Fe2O3 and dissolve it in 50mL of deionized water. Then place it in an ultrasonic cleaner and ultrasonically treat it at 100W power for 1 minute.
[0061] After sonication, the catalyst was filtered and placed in an oven to dry at 100°C for 12 hours to obtain sonicated α-Fe2O3 catalyst powder, denoted as α-Fe2O3(U1).
[0062] The prepared ultrasonically compressed catalyst was placed into a sample press and pressed into tablets, then sieved to 20-40 mesh and stored for later testing.
[0063] Example 2
[0064] Weigh 1.0g of α-Fe₂O₃ (XRD pattern as shown) Figure 1 Dissolve the sample in 50 mL of deionized water, then place it in an ultrasonic cleaner and ultrasonically treat it at 100 W for 5 minutes.
[0065] After ultrasonication, the catalyst was filtered and placed in an oven to dry at 100℃ for 12 hours to obtain ultrasonicated α-Fe2O3 catalyst powder, denoted as α-Fe2O3(U5). The XRD pattern is shown below. Figure 1 As shown.
[0066] The prepared ultrasonically compressed catalyst was placed into a sample press and pressed into tablets, then sieved to 20-40 mesh and stored for later testing.
[0067] Example 3
[0068] Weigh 1.0g of α-Fe2O3 and dissolve it in 50mL of deionized water. Then place it in an ultrasonic cleaner and ultrasonically treat it at 100W power for 10 minutes.
[0069] After sonication, the catalyst was filtered and placed in an oven to dry at 100°C for 12 hours to obtain sonicated α-Fe2O3 catalyst powder, denoted as α-Fe2O3(U10).
[0070] The prepared ultrasonically compressed catalyst was placed into a sample press and pressed into tablets, then sieved to 20-40 mesh and stored for later testing.
[0071] Comparative Example 1
[0072] Instead of ultrasonic treatment, α-Fe2O3 was directly placed into a sample press and pressed into tablets, then sieved to 20-40 mesh for later testing.
[0073] Examples 4-6 illustrate methods for improving the denitrification activity of γ-Fe2O3.
[0074] Example 4
[0075] Weigh 1.0g of γ-Fe2O3 and dissolve it in 50mL of deionized water. Then place it in an ultrasonic cleaner and ultrasonically treat it at 100W power for 1 minute.
[0076] After sonication, the catalyst was filtered and placed in an oven to dry at 100°C for 12 hours to obtain sonicated γ-Fe2O3 catalyst powder, denoted as γ-Fe2O3(U1).
[0077] The prepared ultrasonically compressed catalyst was placed into a sample press and pressed into tablets, then sieved to 20-40 mesh and stored for later testing.
[0078] Example 5
[0079] Weigh 1.0g of γ-Fe2O3 (XRD spectrum as shown) Figure 2 Dissolve the sample in 50 mL of deionized water, then place it in an ultrasonic cleaner and ultrasonically treat it at 100 W for 5 minutes.
[0080] After ultrasonication, the catalyst was filtered and placed in an oven to dry at 100℃ for 12 hours to obtain ultrasonicated γ-Fe2O3 catalyst powder, denoted as γ-Fe2O3(U5). The XRD pattern is shown below. Figure 2 As shown.
[0081] The prepared ultrasonically compressed catalyst was placed into a sample press and pressed into tablets, then sieved to 20-40 mesh and stored for later testing.
[0082] Example 6
[0083] Weigh 1.0g of γ-Fe2O3 and dissolve it in 50mL of deionized water. Then place it in an ultrasonic cleaner and ultrasonically treat it at 100W power for 10 minutes.
[0084] After sonication, the catalyst was filtered and placed in an oven to dry at 100°C for 12 hours to obtain sonicated γ-Fe2O3 catalyst powder, denoted as γ-Fe2O3(U10).
[0085] The prepared ultrasonically enhanced catalyst and the original catalyst γ-Fe2O3 were placed in a sample press and pressed into tablets, which were then sieved to 20-40 mesh and stored for later testing.
[0086] Comparative Example 2
[0087] Instead of ultrasonic treatment, α-Fe2O3 was directly placed into a sample press and pressed into tablets, then sieved to 20-40 mesh for later testing.
[0088] Test case
[0089] The products obtained in the examples and comparative examples were used as catalysts for catalytic performance testing, and the test conditions are shown below:
[0090] The catalytic reaction was tested in a fixed-bed continuous flow reactor. The catalyst particle size was 20-40 mesh, and the dosage was 100 mg. The reaction gas composition was: 500 ppm NO, 500 ppm NH3, 5% O2, with Ar as the equilibrium gas. The total gas flow rate was maintained at 100 mL / min, and the gas hourly space velocity (GHSV) was 60,000 mL·g⁻¹. -1 ·h -1 Before the reaction, the catalyst was purged with Ar at 150 °C for 0.5 h. The catalytic reaction was carried out at 150–350 °C, and activity data were collected after the reaction reached equilibrium.
[0091] NO conversion rate is calculated using the following formula:
[0092]
[0093] Wherein, [NO]in represents the initial concentration of NO in the reaction gas at the reactor inlet; [NO]out represents the concentration of NO in the reaction gas after the reaction.
[0094] The catalysts in the examples and comparative examples were evaluated for their structure and catalytic performance using X-ray diffraction (XRD) and catalytic performance testing (NH3-SCR reaction), the results of which are shown in the appendix. Figure 1-4 Furthermore, the α-Fe2O3 catalysts in the examples and comparative examples were further characterized using ammonia temperature-programmed desorption (NH3-TPD) and temperature-programmed reduction (H2-TPR) curves to evaluate their surface acidity sites and redox properties. The results are shown in the appendix. Figure 5-6 .
[0095] The comparison of the activity test results of the α-Fe2O3 catalyst after ultrasound (Examples 1-3) and the original α-Fe2O3 catalyst (Comparative Example 1), as well as the effect of different ultrasound times on the NO conversion rate of the α-Fe2O3 catalyst, are shown in the figure below. Figure 3 As shown in the figure; the comparison of the activity test results of the γ-Fe2O3 catalyst after ultrasound (Examples 4-6) and the original γ-Fe2O3 catalyst (Comparative Example 2), and the effect of different ultrasound times on the NO conversion rate of the γ-Fe2O3 catalyst are shown in the figure. Figure 4 As shown.
[0096] like Figure 1 As shown, XRD results indicate that ultrasonic treatment did not change the crystal form of the α-Fe₂O₃ catalyst, but its peak intensity decreased, indicating that ultrasonic treatment reduced the crystallinity of α-Fe₂O₃ and increased defects. The catalytic activity test data of the catalyst before and after ultrasonic treatment are shown below. Figure 3 As shown, it is evident that the untreated original catalyst α-Fe₂O₃ exhibits poor activity, with a maximum activity of only about 23% at 250℃. Furthermore, at higher temperatures (350℃), the strong oxidizing properties of iron oxide cause NH₃ to oxidize and generate NO, resulting in a negative NO conversion rate. From... Figure 2 The results show that ultrasound can very effectively improve the low-temperature denitrification activity of α-Fe2O3 catalysts, while the catalyst activity is almost the same at different ultrasound times. Taking 5 minutes of ultrasound as an example, at 200℃, the NO conversion rate of the ultrasound-treated catalyst is almost twice that of the original catalyst (approximately 30% and 15%, respectively); at 250℃, the NO conversion rate of the ultrasound-treated catalyst is approximately 1.6 times that of the original catalyst (approximately 37% and 23%, respectively).
[0097] In addition, NH3-TPD results ( Figure 5The results showed almost no difference in acidity between the α-Fe₂O₃ samples before and after ultrasonic treatment, indicating that their adsorption and activation capacity for NH₃ was not affected. H₂-TPR results ( Figure 6 The results show that the hydrogen consumption peak of the catalyst shifts to a lower temperature after ultrasonic treatment, indicating that ultrasonic treatment improves the redox performance of the α-Fe2O3 catalyst, thereby increasing the catalyst activity.
[0098] like Figure 2 As shown, XRD results indicate that ultrasonic treatment did not change the crystal form of the γ-Fe₂O₃ catalyst, but its peak intensity decreased, indicating that ultrasonic treatment reduced the crystallinity of γ-Fe₂O₃ and increased defects. The catalytic activity test data of the catalyst before and after ultrasonic treatment are shown below. Figure 4 As shown. Figure 4 It is quite evident that the activity of the untreated original catalyst γ-Fe2O3 is relatively low. Figure 3 The α-Fe₂O₃ catalyst performed better, but the overall results were still not ideal. Regarding the effect of ultrasonic treatment, the figures show that at 200-300℃, after 5 minutes of ultrasonication, the NO conversion rate of the catalyst was above 80%, reaching a maximum of 97% at 200℃, while the highest activity of untreated γ-Fe₂O₃ was only 70%. Ultrasound can very effectively improve the low-temperature denitrification activity of γ-Fe₂O₃ catalysts, and among the catalysts treated with ultrasound for 5 minutes, the catalyst with the best catalytic performance was observed.
[0099] The activity data of the catalytic reaction at 200℃ and 250℃ are shown in Table 1.
[0100] Table 1
[0101]
[0102]
[0103] As can be seen from the results in Table 1, the NO conversion rate of the catalyst obtained by ultrasonication of pure iron oxide using the method of the present invention is significantly improved.
[0104] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.
Claims
1. A method for improving the denitrification activity of iron oxide, characterized in that, The method includes: sonicating iron oxide in water, wherein the iron oxide is α-Fe2O3 and / or γ-Fe2O3; The duration of the ultrasound is 1 to 15 minutes. The power of the ultrasound is 100W; By sonicating iron oxide in water, the crystallinity of γ-Fe2O3 decreases and the number of defects increases; α-Fe2O3 not only has a decreased crystallinity and an increased number of defects, but also an increased redox capacity.
2. The method according to claim 1, characterized in that, The ultrasound session lasted 5-10 minutes.
3. The method according to claim 1 or 2, characterized in that, The method involves ultrasonicating iron oxide in water, followed by filtration and drying.
4. The method according to claim 3, characterized in that, The drying conditions include a temperature of 80-120 ℃ and a time of 10-15 h.
5. A method for denitrification, characterized in that, The method includes: contacting flue gas with a denitrification catalyst in a reactor; The preparation method of the denitrification catalyst includes: ultrasonicating iron oxide in water, then filtering and drying, wherein the iron oxide is α-Fe2O3 and / or γ-Fe2O3; The duration of the ultrasound is 1 to 15 minutes. The power of the ultrasound is 100W; By sonicating iron oxide in water, the crystallinity of γ-Fe2O3 decreases and the number of defects increases; α-Fe2O3 not only has a decreased crystallinity and an increased number of defects, but also an increased redox capacity.
6. The method according to claim 5, characterized in that, The temperature of the contact reaction is 150-300 ℃.
7. The method according to claim 6, characterized in that, The temperature of the contact reaction is 200-250 ℃.
8. The method according to claim 5 or 6, characterized in that, The composition of the flue gas includes: 400-600 ppm NO. x 400-600 ppm of NH3 and 3-8% of O2.
9. The method according to claim 5, characterized in that, The conditions for the contact reaction include: using an inert gas as the equilibrium gas; a total gas flow rate of 80-150 mL / min; and a gas hourly space velocity of 50,000-70,000 mL·g. -1 ·h -1 .