Cerium-based modified red mud denitration catalyst and preparation method thereof

Abstract

The invention discloses a cerium-based modified red mud denitration catalyst and a preparation method thereof, and belongs to the technical field of denitration catalyst preparation. The preparation method comprises the following steps: a mixed reaction solution containing red mud and cerium salt is subjected to a variable-temperature hydrothermal reaction, so that cerium oxide is loaded on the red mud in an amorphous state, and the variable-temperature hydrothermal reaction comprises the following steps: the mixed reaction solution is heated to 170-190 DEG C from room temperature at a heating rate of 0.1-2 DEG C / min, then heat preservation is performed for 0.5-2 h, and finally, the mixed reaction solution is cooled to room temperature at a cooling rate of 0.1-2 DEG C / min. By adopting the preparation method, the specific surface area of the cerium-based modified red mud and the number of defects such as pores can be effectively increased, so that the denitration catalytic activity is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of denitration catalyst preparation, and more specifically, to a cerium-based modified red mud denitration catalyst and a preparation method thereof. Background Art

[0002] Nitrogen oxides (NO x ) is one of the gaseous pollutants emitted by power plants, industrial plants, and automobile transportation vehicles. It is the basic substance for the generation of atmospheric pollution phenomena such as acid rain, photochemical smog, and particulate matter (PM2.5), which seriously damages the ecological environment. In addition, the human body inhales NO x It can cause chronic lung diseases, and long-term inhalation may cause acute poisoning, which can have fatal consequences. Therefore, it is necessary to conduct NO x Research work on emission reduction technologies.

[0003] Selective catalytic reduction of NO using ammonia as a reducing agent (NH3-SCR) x It is the most widely used flue gas denitrification technology. As a commercially mature denitrification catalyst, V2O5-WO3 / TiO2 catalyst has significant advantages, but due to the toxicity of vanadium, high cost, high reaction temperature (300-400℃) and strong oxidation of NH3 and SO2, it is not suitable for emission reduction applications with a wider operating temperature window. Among NH3-SCR catalysts, Fe2O3-based catalysts are a type of metal oxide with abundant reserves, low cost, and good SCR reaction performance. It has the characteristics of good medium and high temperature activity, high N2 selectivity, and strong resistance to SO2 poisoning. Therefore, it has attracted the attention of most researchers and has become a research hotspot in this field.

[0004] Red mud RM (Red Mud) has a complex composition, and its main components include Fe2O3, TiO2, SiO2, Al2O3, etc., among which iron oxide content accounts for the highest proportion. This solid waste with active components and carriers has attracted the attention of researchers, and it is used as a denitrification catalyst in NH3-SCR reactions. However, studies have shown that the activity of pure red mud RM is not ideal, because red mud contains a large amount of highly alkaline substances, such as calcium oxide, sodium oxide, magnesium oxide, etc., which cause alkali poisoning of the red mud catalyst, destroying and blocking the active sites on the catalyst surface, resulting in reduced activity. Using acidic solutions to remove alkaline substances has become an effective solution. At the same time, metal oxide catalysts with CeO2 as a component have been widely studied. CeO2 has excellent redox properties, high oxygen storage / release capacity and Ce 3+ / Ce 4+ The conversion performance of NH3-SCR can be improved by modifying red mud with CeO2, optimizing the structure and properties of the catalyst.

[0005] For example, the application case of Chinese patent application No. 202110281930.9 discloses a method for preparing a red mud SCR catalyst, which includes acid-treating the red mud, loading the metal additive Ce, and then filtering, drying, and roasting; the method for loading the metal additive Ce is as follows: adding the additive Ce to the turbid liquid of the red mud, and stirring in a 70°C water bath for 0.5h. Slowly drip ammonia water with a concentration of 2mol / L until the pH value of the solution is 9-10, and continue stirring for 1h. The catalyst particles prepared in this way are relatively large, and ultrasonic treatment is required to refine the catalyst particles.

[0006] In addition, the catalytic activity of the CeO2-modified red mud catalyst prepared using the existing process still needs to be further improved. Summary of the invention

[0007] In view of the problem that the existing CeO2-loaded denitrification catalyst has low activity, the present invention provides a cerium-based modified red mud denitrification catalyst and a preparation method thereof. The present invention optimizes the design of the process of loading Ce on red mud, especially by adopting a variable temperature hydrothermal method to load Ce, thereby effectively improving the denitrification catalytic activity of the cerium-based modified red mud.

[0008] In order to achieve the above object, the technical solution provided by the present invention is:

[0009] The first aspect of the present invention provides a method for preparing a cerium-based modified red mud denitrification catalyst, comprising the following steps: subjecting a mixed reaction liquid containing red mud and a cerium salt to a variable temperature hydrothermal reaction so that cerium oxide is loaded on the red mud in an amorphous state, the variable temperature hydrothermal reaction comprising: heating the mixed reaction liquid from room temperature to 170-190°C at a heating rate of 0.1-2°C / min, then keeping the temperature for 0.5-2h, and finally cooling the mixed reaction liquid to room temperature at a cooling rate of 0.1-2°C / min.

[0010] In the prior art, there are related publications on the use of cerium oxide to modify red mud denitration catalysts, but the catalytic activity of existing cerium oxide-modified red mud denitration catalysts is still relatively low. Based on this situation, the present invention effectively increases the specific surface area and the number of defects of the obtained catalyst by subjecting the mixed reaction liquid containing red mud and cerium salt to a variable temperature hydrothermal reaction, and loads cerium oxide on red mud in an amorphous and highly dispersed state, thereby improving the catalytic activity of the obtained catalyst, and the nitrogen oxide conversion rate is relatively high in the range of 200 to 400°C. The heating rate of the mixed reaction liquid is further preferably 0.1-1°C / min.

[0011] Furthermore, the mixed reaction liquid is stirred during the variable temperature hydrothermal reaction, which can improve the uniformity of the reaction and the dispersibility of cerium oxide in red mud on the one hand, and on the other hand, and more importantly, the stirring can effectively refine the particle size of the catalyst, increase its specific surface area and the number of defects such as pores in the catalyst, which is beneficial to further improve the catalytic activity of the obtained catalyst.

[0012] Further, the stirring speed is 300-900r / min. In the catalyst preparation process, the stirring speed has a great influence on the performance of the catalyst. When the stirring speed is not selected properly, it will lead to uneven dispersion of the reaction solution and insufficient number of defects such as pores in the catalyst, and will also affect the specific surface area of ​​the obtained catalyst. The stirring speed is further preferably 500-700r / min, and more preferably 600r / min.

[0013] Furthermore, the variable temperature hydrothermal reaction is carried out in a high pressure reactor.

[0014] Furthermore, the method further comprises: calcining the product obtained by the temperature-variable hydrothermal reaction, thereby effectively improving the crystal stability of the obtained catalyst.

[0015] Furthermore, vacuum calcination is used to increase the oxygen negative sites of the cerium oxide modified red mud catalyst, which is beneficial to further improve the catalytic activity of the catalyst.

[0016] Furthermore, the heating rate of the calcination is 2-3°C / min, the calcination temperature is 350-600°C, and the calcination time is 4h-6h. Further preferably, the calcination temperature is 400°C. If the calcination temperature is too low, the sample may not reach the activation temperature and cannot meet the subsequent reaction, resulting in reduced activity. If the vacuum calcination temperature is too high, on the one hand, it will increase unnecessary energy consumption, and on the other hand, the high temperature will cause the sample to sinter.

[0017] Furthermore, it also includes: dissolving red mud in an acid solution to form a red mud solution; and / or mixing the formed red mud solution with a cerium salt solution to form a mixed reaction solution; and / or adjusting the pH value of the mixed reaction solution containing red mud and cerium salt to 8-10 before performing the variable temperature hydrothermal reaction.

[0018] Furthermore, the red mud is dissolved in an acid solution to form a red mud solution, specifically, red mud powder is dissolved in dilute sulfuric acid, and hydrothermally treated at 170-190°C for 10-12h; the particle size of the red mud powder is less than 200 mesh, and the concentration of dilute sulfuric acid is 1-3 mol / L. The red mud modified by dilute sulfuric acid dredges the pore structure of the catalyst, and cerium dioxide adds more reactive sites to the surface of the catalyst, which better promotes the improvement of the redox property and surface acidity of the red mud, promotes the occurrence of NH3-SCR reaction, and improves the denitrification activity.

[0019] The second aspect of the present invention also provides a cerium-based modified red mud denitrification catalyst prepared according to any one of the preparation methods described in the first aspect.

[0020] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0021] (1) The present invention subjects the mixed reaction liquid of red mud and cerium salt to a variable temperature hydrothermal reaction and optimizes the specific temperature control process, thereby effectively increasing the specific surface area and the number of defects of the resulting catalyst, and allowing cerium oxide to be loaded on the red mud in an amorphous, highly dispersed state, thereby effectively improving the catalytic activity of the resulting catalyst.

[0022] (2) The present invention performs stirring during the variable temperature hydrothermal reaction, which, on the one hand, is conducive to more uniform mixing of the cerium salt and the red mud, thereby ensuring the uniformity of the loading of cerium oxide; on the other hand, it is also conducive to refining the grain size of the catalyst, increasing the specific surface area and the number of defects of the catalyst, and generating a denitrification catalyst with more active pores.

[0023] (3) The present invention further performs a vacuum calcination treatment on the product obtained by the variable temperature hydrothermal reaction, thereby not only improving the crystal stability of the obtained catalyst, but also providing more oxygen negative sites for the red mud catalyst loaded with cerium oxide, thereby facilitating further improving the catalytic activity of the cerium-based red mud. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The NO conversion rate of the catalysts prepared in Example 1 of the present invention and Comparative Examples 1, 2, 3, and 4 varies with temperature.

[0025] Figure 2 The XRD spectra of the catalysts prepared in Example 1 and Comparative Examples 1, 2, 3 and 4 of the present invention are shown.

[0026] Figure 3 The H2-TPR results of the catalysts prepared in Example 1 of the present invention and Comparative Examples 1, 2, 3, and 4 are shown.

[0027] Figure 4 NH3-TPD diagrams of Example 1 of the present invention and comparative samples 1, 2, 3, and 4.

[0028] Description of labels:

[0029] 1. 10% CeO2 / RM(R) is the catalyst prepared in Example 1.

[0030] 2. 10% CeO2 / RM(S) is the catalyst prepared in Comparative Example 1.

[0031] 3. 10% CeO2 / RM(V) is the catalyst prepared in Comparative Example 2.

[0032] 4. 10% CeO2 / RM(H) is the catalyst prepared in Comparative Example 3.

[0033] 5. 10% CeO2 / RM(N) is the catalyst prepared in Comparative Example 4. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0035] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0036] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0037] In the following examples and comparative examples, cerium salts are all hydrated cerium nitrate as an example. In fact, other soluble cerium salts or hydrated cerium salts can also be selected, such as CeCl3·6H2O, Ce2(SO4)3, Ce(SO4)2·4H2O, Ce(CH3COO)3, etc. Red mud is dissolved in an acid solution, not limited to dilute sulfuric acid, and in fact, other acid solutions can also be selected, such as dilute hydrochloric acid and dilute nitric acid solutions.

[0038] Example 1

[0039] Preparation of 10% CeO2 / RM(R) catalyst:

[0040] (1) First, the blocky red mud is ball-milled to collect red mud powder with a sample particle size of less than 200 mesh. Then, the red mud powder is dissolved in a 2 mol / L sulfuric acid solution, mixed evenly, and hydrothermally treated at 180°C for 12 hours, and the solution is collected as solution A.

[0041] (2) Dissolve cerium nitrate hexahydrate in 20 ml of water and stir to obtain solution B.

[0042] (3) Mix and stir the above solutions A and B evenly, add ammonia solution dropwise, adjust the pH of the solution to between 9 and 10, continue stirring for 1 hour, transfer to a high-pressure reactor with stirring for variable temperature hydrothermal reaction, the stirring speed is 600r / min, and the variable temperature hydrothermal reaction conditions are: the temperature in the high-pressure reactor is slowly increased from room temperature to 180°C at a rate of 0.1°C / min, then kept at 180°C for 1 hour, and finally cooled to room temperature at a rate of 0.1°C / min. The obtained precipitate is washed several times with ultrapure water until the solution is neutral to obtain a precipitate; the precipitate is dried at 110°C for 12 hours.

[0043] (4) Grinding the dried sample and then calcining it in vacuum at a heating rate of 2-3°C / min to 400°C for 5 hours. After calcination, a cerium dioxide-modified red mud denitrification catalyst is obtained, which is marked as 10% CeO2 / RM(R).

[0044] Comparative Example 1

[0045] The difference between this comparative example and Example 1 is that in step 3), stirring is not performed during the variable temperature hydrothermal reaction. Specifically, the reaction is transferred to a high pressure reactor without stirring, and the rest of the preparation process is the same as that of Example 1. The obtained product is marked as 10% CeO2 / RM(S).

[0046] Comparative Example 2

[0047] The difference between this comparative example and Example 1 is that the calcination in step 4) is not performed by vacuum calcination. Specifically, the dried sample is ground and then calcined in ordinary air at a heating rate of 2-3°C / min to 400°C for 5 hours. The rest of the preparation process is the same as that in Example 1, and the obtained product is marked as 10% CeO2 / RM(V).

[0048] Comparative Example 3

[0049] The difference between this comparative example and Example 1 is that the variable temperature hydrothermal condition in Example 1 is not used in step 3). Specifically, the temperature in the autoclave is quickly raised from room temperature to 180°C, then kept at 180°C for 1 hour, and finally quickly lowered to room temperature. The rest of the preparation process is the same as that in Example 1, and the obtained product is marked as 10% CeO2 / RM(H).

[0050] Comparative Example 4

[0051] The difference between this comparative example and Example 1 is that in step 3), the variable temperature hydrothermal reaction is not stirred during the process, and the variable temperature hydrothermal conditions in Example 1 are not used; and in step 4), vacuum roasting is not used. Specifically, in step 3), the autoclave is transferred without stirring, and the temperature in the autoclave is quickly raised from room temperature to 180°C, then kept at 180°C for 1h, and finally quickly lowered to room temperature; in step 4), the roasting is ordinary air roasting, and the temperature is raised to 400°C at a heating rate of 2-3°C / min, and the roasting time is 5h. The rest of the preparation process is the same as in Example 1, and the obtained product is marked as 10% CeO2 / RM(N).

[0052] The denitration activities of the catalysts prepared in Example 1 and Comparative Examples 1-4 were measured as follows:

[0053] (1) Testing the NO conversion rate of the catalysts prepared in Example 1 and Comparative Examples 1-4

[0054] The main process is as follows:

[0055] 0.1 g of sample was weighed and placed in a quartz tube with an inner diameter of 5 mm, which was then placed in the heating furnace of the SCR device. N2 was purged at 200 °C for more than 1 h, and the sample was heated at 120,000 mL·g at different temperatures. -1 ·h -1 The reaction was carried out at an air velocity ratio of 15 minutes. After stabilization, the tail gas was collected and the nitrogen oxide concentration was measured by an ECOM-J2KN flue gas analyzer. The conversion rate of nitrogen oxides was calculated by the following formula:

[0056]

[0057] In the above formula [NO x ] in Indicates the intake concentration of nitrogen oxides before the reaction, [NO x ] out Indicates the concentration of nitrogen oxide tail gas after the reaction.

[0058] The reaction gas components involved in the NH3-SCR reaction under the steady state are NH3=500ppm, NO=500ppm, O2=5vol%, N2 is used as the balance gas, and the total gas flow rate is 100mL / min (NH3 is 10mL / min, NO is 10mL / min, O2 is 80mL / min). The trend of NO conversion rate changing with temperature is shown in the figure below: Figure 1 shown.

[0059] Table 1 NO2 of the catalysts prepared in Example 1 and Comparative Examples 1-4 at different temperatures x Conversion rate

[0060]

[0061]

[0062] from Figure 1 As can be seen from Table 1, in the temperature range of 200-400°C, the NO conversion rate of the 10% CeO2 / RM(N) catalyst prepared in Comparative Example 4 is not ideal, with the highest being only 55%. However, the NO conversion rate of the 10% CeO2 / RM(R) catalyst prepared in Example 1 by using variable temperature hydrothermal, stirring in a reactor and vacuum calcination is very high. x The conversion rate increases with the increase of temperature. At 400℃, NO x The conversion rate was increased to 97%. At the same time, within the range of 200-400°C, the catalytic performance of the 10% CeO2 / RM(R) catalyst prepared in Example 1 was significantly better than that of the catalysts in Comparative Examples 1, 2, 3, and 4.

[0063] (2) Testing the specific surface area of ​​the catalysts prepared in Example 1 and Comparative Examples 1-4

[0064] The specific surface area of ​​the catalyst was tested by performing nitrogen adsorption and desorption experiments on the catalysts obtained in Example 1 and Comparative Examples 1-4. The samples were dried under vacuum at 300° C. for 5 hours. The specific surface areas of the catalysts in Example 1 and Comparative Examples 1-4 are shown in Table 2.

[0065] Table 2 Specific surface area of ​​the catalysts prepared in Example 1 and Comparative Examples 1-4

[0066]

[0067] From the experimental data in Table 2, it can be seen that the specific surface area of ​​the 10% CeO2 / RM(N) catalyst is the smallest, only 57.3352 m 2 / g. Among the catalysts prepared in Example 1 and Comparative Examples 1-4, the 10% CeO2 / RM(R) catalyst has the largest specific surface area under the same test conditions, reaching 151.4145 m 2 / g. The particle's texture parameters such as specific surface area and pores will affect the adsorption probability of reactant molecules and active sites, thereby changing the denitration performance of the catalyst. The larger the specific surface area, the more conducive it is to increase the number of reactant molecules adsorbed on the catalyst surface, thereby improving the SCR reaction activity.

[0068] (3) XRD spectra of the catalysts prepared in Example 1 and Comparative Examples 1-4

[0069] like Figure 2As shown, the diffraction peaks at 24.1°, 33.1°, 35.6°, 40.8°, 49.4°, 54.0°, 62.4°, and 63.9° are attributed to the characteristic peaks of α-Fe2O3, which is consistent with the standard card of hematite-type α-Fe2O3 (PDF#33-0664). Its characteristic diffraction peak is sharp, indicating that its degree of crystallization is high. After adding CeO2, the catalyst showed an obvious characteristic diffraction peak at 28.5°, which is attributed to the characteristic peak of CeO2, which is consistent with the standard card of cubic fluorite structure CeO2 (PDF#34-0394). The 10% CeO2 / RM(R) catalyst did not see the typical characteristic peaks of iron oxide and cerium oxide, and its peak shape was wide and narrow, indicating that it was amorphous and highly dispersed, which was conducive to the improvement of activity. The highest combined activity showed that it was one of the factors affecting the denitrification activity.

[0070] (4) H2-TPR graphs of the catalysts prepared in Example 1 and Comparative Examples 1-4

[0071] like Figure 3 As shown in the figure, it can be seen that the reduction peak temperature shifts to a lower temperature, which means that the redox property of the catalyst is enhanced, which is conducive to the adsorption and activation of ammonia. At the same time, the peak area of ​​the 10% CeO2 / RM(R) catalyst represents the hydrogen consumption. Figure 3 Its hydrogen consumption is the largest, indicating that it has the most reducing species and more active sites, which is one of the main reasons why 10%CeO2 / RM(R) catalyst has the best activity.

[0072] (5) NH3-TPD diagram of the catalysts prepared in Example 1 and Comparative Examples 1-4

[0073] like Figure 4 As shown, the ammonia desorption experiment can illustrate the acid strength and quantity properties of the catalyst. The amount of acid is crucial to the adsorption of ammonia. From the figure, we can see that the 10% CeO2 / RM(R) catalyst has the largest number of acid sites, which proves that it can adsorb more ammonia for activation and promote the improvement of denitrification activity. Acidity is one of the important factors in maintaining catalytic activity.

[0074] Example 2

[0075] The difference between this embodiment and embodiment 1 is that the stirring speed in the high-pressure reactor in step 3) is adjusted to 300 r / min, and the rest of the preparation process is the same as that in embodiment 1.

[0076] Example 3

[0077] The difference between this embodiment and embodiment 1 is that the stirring speed in the high-pressure reactor in step 3) is adjusted to 500 r / min, and the rest of the preparation process is the same as that in embodiment 1.

[0078] Example 4

[0079] The difference between this embodiment and embodiment 1 is that the stirring speed in the high-pressure reactor in step 3) is adjusted to 700 r / min, and the rest of the preparation process is the same as that in embodiment 1.

[0080] Example 5

[0081] The difference between this embodiment and embodiment 1 is that the stirring speed in the high-pressure reactor in step 3) is adjusted to 900 r / min, and the rest of the preparation process is the same as that in embodiment 1.

[0082] Comparative Example 5

[0083] The difference between this comparative example and Example 1 is that the stirring speed in the high-pressure reactor in step 3) is adjusted to 1200 r / min, and the rest of the preparation process is the same as that in Example 1.

[0084] The catalysts prepared in Examples 1-5 and Comparative Example 5 were subjected to a catalyst activity evaluation experiment to measure the NO conversion rate at 350° C. and evaluate their performance.

[0085] Table 3 Effect of different stirring speeds on the performance of the prepared catalyst

[0086] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 5 Speed ​​r / min 600 300 500 700 900 1200 NO conversion rate 95.14％ 78.40％ 83.20％ 80.12％ 76.50％ 72.10％

[0087] It can be seen from Table 3 that the stirring speed of the present invention has a significant effect on the catalyst performance. When the stirring speed is too low, the stirring is not sufficient and the sample may not be completely dispersed. 600 r / min is the best stirring rate to ensure the catalyst performance.

[0088] Example 6

[0089] The difference between this embodiment and embodiment 1 is that the vacuum calcination temperature in step 4) is adjusted to 350° C., and the rest of the preparation process is the same as that of embodiment 1.

[0090] Example 7

[0091] The difference between this embodiment and embodiment 1 is that the vacuum calcination temperature in step 4) is adjusted to 450° C., and the rest of the preparation process is the same as that of embodiment 1.

[0092] Example 8

[0093] The difference between this embodiment and embodiment 1 is that the vacuum calcination temperature in step 4) is adjusted to 500° C., and the rest of the preparation process is the same as that of embodiment 1.

[0094] Example 9

[0095] The difference between this embodiment and embodiment 1 is that the vacuum calcination temperature in step 4) is adjusted to 600° C., and the rest of the preparation process is the same as that of embodiment 1.

[0096] Comparative Example 6

[0097] The difference between this comparative example and Example 1 is that the vacuum calcination temperature in step 4) is adjusted to 300° C., and the rest of the preparation process is the same as that of Example 1.

[0098] The catalysts prepared in Example 1, Examples 6-9, and Comparative Example 6 were subjected to a catalyst activity evaluation experiment to measure the NO conversion rates at 350° C. and evaluate their performance.

[0099] Table 4 Effect of different vacuum calcination temperatures on catalyst performance

[0100] Example 1 Example 6 Example 7 Example 8 Example 9 Comparative Example 6 Calcination temperature 400℃ 350 450 500℃ 600℃ 300℃ NO conversion rate 95.14％ 87.30％ 85.36％ 79.60％ 78.50％ 75.10％

[0101] As can be seen from Table 4, different vacuum calcination temperatures of the present invention have a significant impact on the performance of the catalyst, wherein the best performance of the catalyst is obtained when the vacuum calcination temperature is about 400°C. This is because when the temperature is too low, the sample may not reach the activation temperature and cannot meet the subsequent reaction, resulting in reduced activity. When the vacuum calcination temperature is too high, on the one hand, unnecessary energy consumption will be increased, and on the other hand, the high temperature will cause the sample to sinter.

[0102] Example 10

[0103] The difference between this embodiment and embodiment 1 is that the variable temperature hydrothermal reaction in step 3) is adjusted. The variable temperature hydrothermal reaction conditions are: the temperature in the high-pressure reactor is increased from room temperature to 180°C at a heating rate of 1°C / min, then kept at 180°C for 1h, and finally cooled to room temperature at a cooling rate of 1°C / min.

[0104] Embodiment 11

[0105] The difference between this embodiment and embodiment 1 is that the variable temperature hydrothermal reaction in step 3) is adjusted. The variable temperature hydrothermal reaction conditions are: the temperature in the high pressure reactor is slowly increased from room temperature to 180°C at a rate of 2°C / min, then kept at 180°C for 1 hour, and finally cooled to room temperature at a rate of 2°C / min.

[0106] The catalysts prepared in Example 1 and Examples 10-11 were subjected to a catalyst activity evaluation experiment to measure the NO conversion rate at 350° C. and evaluate their performance.

[0107] Table 5 Effect of different variable temperature hydrothermal rates on the performance of the prepared catalyst

[0108] Example 1 Example 10 Embodiment 11 Temperature change rate 0.1℃ / min 1℃ / min 2℃ / min NO conversion rate 95.14％ 85.25％ 79.02％

[0109] It can be seen from Table 5 that the variable temperature hydrothermal rate prepared by the present invention has a significant effect on the catalyst performance. The catalyst performance is best when the variable temperature hydrothermal rate is 0.1°C / min. This may be because the lower variable temperature rate affects the progress of the catalytic reaction and changes the activation energy of the reaction process.

[0110] Example 12

[0111] The difference between this embodiment and embodiment 1 is that in step 1), the red mud powder is dissolved in a sulfuric acid solution with a concentration of 1 mol / L, and the red mud powder is hydrothermally treated at 170°C for 11 h; in step 3), the pH of the solution is adjusted to between 8 and 9, and the variable temperature hydrothermal reaction conditions are: the temperature in the high pressure reactor is slowly increased from room temperature to 170°C at a rate of 0.1°C / min, then kept at 170°C for 2 h, and finally cooled to room temperature at a cooling rate of 0.1°C / min; the calcination time in step 4) is 4 h; and the rest of the preparation process is the same as that in embodiment 1.

[0112] The catalysts prepared in Example 1 and Example 12 were subjected to a catalyst activity evaluation experiment to measure the NO conversion rate at 350°C. The denitration conversion rate of Example 12 was slightly lower than that of Example 1.

[0113] Example 13

[0114] The difference between this embodiment and embodiment 1 is that in step 1), the red mud powder is dissolved with a sulfuric acid solution having a concentration of 3 mol / L, and the red mud powder is hydrothermally treated at 190°C for 10 h; in step 3), the pH of the solution is adjusted to between 8 and 9, and the variable temperature hydrothermal reaction conditions are: the temperature in the high pressure reactor is slowly increased from room temperature to 190°C at a rate of 0.1°C / min, then kept at 190°C for 0.5 h, and finally cooled to room temperature at a cooling rate of 0.1°C / min; the calcination time in step 4) is 6 h; and the rest of the preparation process is the same as that in embodiment 1.

[0115] The catalysts prepared in Example 1 and Example 13 were subjected to a catalyst activity evaluation experiment to measure the NO conversion rate at 350°C. The denitration conversion rate of Example 13 was slightly lower than that of Example 1.

[0116] The present invention and its embodiments are described schematically above, and the description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by it and designs a structural method and an embodiment similar to the technical solution without creativity without departing from the purpose of the invention, they shall all fall within the protection scope of the present invention.

Claims

1. A method for preparing a cerium-based modified red mud denitration catalyst, characterized in that: include: The mixed reaction liquid containing red mud and cerium salt is subjected to a variable temperature hydrothermal reaction so that cerium oxide is supported on the red mud in an amorphous state. The variable temperature hydrothermal reaction comprises: The mixed reaction solution was heated from room temperature to 170-190°C at a heating rate of 0.1-2°C / min, then kept warm for 0.5-2h, and finally cooled to room temperature at a cooling rate of 0.1-2°C / min.

2. The method for preparing the cerium-based modified red mud denitration catalyst according to claim 1, characterized in that: The mixed reaction liquid is stirred during the variable temperature hydrothermal reaction.

3. The method for preparing the cerium-based modified red mud denitration catalyst according to claim 2, characterized in that: The stirring speed is 300-900r / min.

4. The method for preparing a cerium-based modified red mud denitration catalyst according to any one of claims 1 to 3, characterized in that: The variable temperature hydrothermal reaction is carried out in a high pressure reactor.

5. The method for preparing a cerium-based modified red mud denitration catalyst according to any one of claims 1 to 3, characterized in that: Also includes: The product obtained by the temperature-variable hydrothermal reaction is calcined.

6. The method for preparing the cerium-based modified red mud denitration catalyst according to claim 5, characterized in that: The calcination is performed by vacuum calcination.

7. The method for preparing the cerium-based modified red mud denitration catalyst according to claim 5, characterized in that: The heating rate of the calcination is 2-3°C / min, the calcination temperature is 350-600°C, and the calcination time is 4h-6h.

8. The method for preparing the cerium-based modified red mud denitration catalyst according to claim 5, characterized in that: Also includes: dissolving red mud in an acid solution to form a red mud solution; and / or mixing the formed red mud solution with the cerium salt solution to form a mixed reaction solution; and / or Before the variable temperature hydrothermal reaction, the pH value of the mixed reaction liquid containing red mud and cerium salt is adjusted to 8-10.

9. The method for preparing the cerium-based modified red mud denitration catalyst according to claim 8, characterized in that: The red mud is dissolved in an acid solution to form a red mud solution, specifically, red mud powder is dissolved in dilute sulfuric acid and hydrothermally treated at 170-190° C. for 10-12 hours; the particle size of the red mud powder is less than 200 mesh, and the concentration of the dilute sulfuric acid is 1-3 mol / L.

10. A denitration catalyst product obtained by the preparation method according to any one of claims 1 to 9.

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