Method for preparing protonated hbeta molecular sieve catalyst by modification with acid, prepared catalyst and application

Abstract

This invention discloses a method for preparing a protonated Hβ molecular sieve catalyst using acid treatment modification, the obtained catalyst, and its application. A β molecular sieve is mixed with an ammonium chloride solution, and after sufficient ion exchange, the resulting mixture is transferred to a centrifuge tube, centrifuged, and washed several times with water. The lower solid layer is dried and ground. After grinding, the solid is placed in a crucible, which is then placed in a muffle furnace for a first calcination at high temperature, yielding an H-type β molecular sieve. The obtained H-type β molecular sieve is mixed with an inorganic acid solution, and after sufficient acid leaching, the resulting mixture is allowed to cool to room temperature, filtered, and washed several times with water. The upper solid layer is dried and ground. After grinding, the solid is placed in a crucible, which is then placed in a muffle furnace for a second calcination at high temperature, yielding a protonated Hβ molecular sieve catalyst. This invention first hydrogenates the molecular sieve and then modifies it with an acid solution to construct highly efficient and stable active sites, thereby achieving efficient NO removal.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a method for preparing protonated Hβ molecular sieve catalysts by acid treatment modification, the obtained catalysts, and their applications. Background Technology

[0002] China is a major global producer and consumer of coal, with coal dominating its energy structure. Despite efforts to reduce its reliance on coal, it is projected to remain a primary energy source until 2035. Coal use leads to high NOx emissions, making NOx control a crucial environmental task for China. Pollutants such as nitrogen oxides (NOx) and VOCs emitted from coal-fired power plants cause various environmental problems and seriously endanger human health. Traditional NOx removal methods include selective catalytic reduction (SCR), which offers high removal efficiency but suffers from high investment and operating costs, catalyst poisoning, and significant ammonia escape. Furthermore, over 95% of nitrogen oxides exist as insoluble NO, but higher-valence NO oxides can react with water to form HNO3. Therefore, efficient NO oxidation is key to denitrification. The choice of oxidant is crucial. Compared to common oxidants such as KMnO4, NaClO2, K2S2O8, and O3, H2O2 is an environmentally friendly oxidant because it primarily decomposes into hydroxyl radicals without generating harmful byproducts. In the field of catalytic oxidation of NO using gas-phase H2O2, the catalysts used in the synergistic removal of NO and VOCs by H2O2 decomposition are almost all supported catalysts, such as iron-based catalysts and copper-based catalysts. There is very little research on the technology of synergistic removal of NO and VOCs by H2O2 decomposition without supporting any metals, using zeolite as the catalyst directly.

[0003] Patent CN1769169A discloses a β-zeolite particle with multi-level channels and its preparation method. The β-zeolite preparation process adopts a hydrothermal synthesis method with optimized conditions. After the synthesis process, an ammonium salt treatment process is carried out first. The zeolite is then subjected to acid treatment and hydrothermal treatment under suitable conditions to obtain the final β-zeolite product.

[0004] β-zeolite not only possesses strong acidity but also exhibits excellent hydrothermal stability. Compared to CHA-type (chamferrocene) catalysts, β-zeolite has a larger pore size, making it less prone to clogging by surface-formed oxide shells. Therefore, acid modification of β-zeolite removes aluminum and silicon species from the molecular sieve, increasing the specific surface area of ​​the product molecular sieve and forming numerous secondary pores, while preserving the pore structure of the molecular sieve itself. This allows the molecular sieve to catalyze the generation of more hydroxyl radicals from H₂O₂ for efficient oxidation of NO. Summary of the Invention

[0005] In view of the low efficiency of hydrogen peroxide oxidizing NO, poor stability of catalyst and difficulty in constructing effective active sites in the prior art, the application provides a preparation method of an acid-modified molecular sieve catalyst and application of the catalyst in catalytic oxidation of NO by H2O2.The method first hydrogenates the molecular sieve, and then modifies the molecular sieve by nitric acid, sulfuric acid or phosphoric acid, and constructs high-efficiency and stable active sites by adjusting acid concentration, treatment temperature and treatment time, so as to realize high-efficiency removal of NO.

[0006] To solve the above technical problems, the application adopts the following technical solutions:

[0007] A method for preparing a protonated Hβ molecular sieve catalyst by acid treatment and modification, comprising the following steps:

[0008] (1) hydrogenation of β molecular sieve: β molecular sieve and an ammonium chloride solution are mixed according to a certain solid-liquid ratio, and stirred at a certain temperature on a constant-temperature stirrer for a period of time; after ion exchange is completed, the obtained mixed solution is moved into a centrifuge tube, centrifuged and washed with water for several times; the lower solid is dried and ground; and after grinding, the solid is placed in a crucible, the crucible is placed in a muffle furnace for primary calcination under high-temperature conditions; and H-type β molecular sieve is obtained after calcination.

[0009] (2) acid-modified Hβ molecular sieve: the hydrogenated β molecular sieve (H-type β molecular sieve) in step (1) is mixed with an inorganic acid solution according to a certain solid-liquid ratio, and stirred at a certain temperature on a constant-temperature stirrer for a period of time; after acid immersion is completed, the obtained mixed solution is cooled to room temperature by standing; the upper solid is dried and ground after being filtered and washed with water for several times; and the solid is placed in a crucible, the crucible is placed in a muffle furnace for secondary calcination under high-temperature conditions; and a protonated Hβ molecular sieve catalyst is obtained after calcination.

[0010] As a preferred technical solution of the present invention, in step (1), the concentration of ammonium chloride solution is 0.5-2 mol / L, the solid-liquid ratio of β molecular sieve and ammonium chloride solution is 0.1-0.5 g / mL, the stirring temperature is 60-100℃, and the stirring time is 0.5-2 hours. In the ion exchange process of step (1), the concentration of ammonium chloride solution, the solid-liquid ratio, and the stirring temperature have a significant impact on the degree of cation exchange in β molecular sieve, and thus directly affect the number and distribution of acidic centers of Hβ molecular sieve obtained subsequently. Among them, if the concentration of ammonium chloride solution is too low, the exchange will be insufficient and the metal cations in the original molecular sieve cannot be effectively converted into ammonium form; if the concentration is too high, it may cause waste of resources and may have an adverse effect on the stability of the molecular sieve framework. The solid-liquid ratio determines the degree of effective contact in the ion exchange system. A solid-liquid ratio that is too small or too large is not conducive to the balance between exchange efficiency and process economy. The stirring temperature affects the ion migration rate and the exchange reaction rate. Appropriately increasing the temperature is beneficial to improving the degree of exchange, but excessively high temperature may cause damage to the molecular sieve structure. Therefore, the above parameters are all key process conditions that have a significant impact on the present invention.

[0011] In step (1), the initial calcination temperature is 400-600℃, and the initial calcination time is 2-6 hours. The initial calcination temperature and time have a significant impact on the conversion of ammonium-type β-zeolite to hydrogen-type β-zeolite and are important conditions for the formation of effective acid centers. If the calcination temperature is too low or the time is insufficient, the ammonium ions will not decompose completely, resulting in insufficient formation of Hβ-zeolite and affecting the basis for subsequent acid treatment modification. Conversely, if the calcination temperature is too high or the time is too long, it may cause local collapse of the zeolite framework or loss of acid sites, reducing the stability and catalytic performance of the material. Therefore, the initial calcination conditions have an important impact on the structural integrity and acid regulation effect of the final modified zeolite of this invention.

[0012] As a preferred technical solution of the present invention, in step (2), the concentration of the inorganic acid solution is 0.1-2.0 mol / L, and the inorganic acid is any one of phosphoric acid, nitric acid, or sulfuric acid. The solid-liquid ratio of the hydrogenated β-zeolite to the inorganic acid solution is 0.1-0.5 g / mL. In the acid treatment process of step (2), the type of inorganic acid, the concentration of inorganic acid, and the solid-liquid ratio have a significant impact on the degree of dealuminization, pore structure adjustment, and acidity optimization of the zeolite. Among them, the concentration of inorganic acid directly determines the intensity of acid leaching treatment. If the concentration is too low, it is difficult to achieve effective dealuminization and acidity control. If the concentration is too high, it is easy to cause excessive loss of framework aluminum, thereby destroying the crystal structure of the zeolite. Different types of inorganic acids have different effects on the control of zeolite structure and surface acidity due to differences in acidity, anionic properties, and interaction modes with framework aluminum. Therefore, the choice of acid type has a significant impact on the final modification effect. The solid-liquid ratio affects the sufficiency of contact between the acid solution and the zeolite and the uniformity of treatment. It is an important factor affecting the uniformity of dealuminization and the reproducibility of modification. Therefore, the above parameters are all key influencing factors of this invention.

[0013] As a preferred technical solution of the present invention, in step (2), the acid treatment temperature is 60-100℃, the treatment time is 0.5-2 hours, and the number of acid leaching treatments (only after filtration, a new acid solution is used for treatment) is 1-3 times. The acid treatment temperature, treatment time, and number of acid leaching treatments are the core parameters for controlling the degree of dealuminization of the molecular sieve and the adjustment range of the silicon-aluminum ratio, and have a significant impact on the technical effect of the present invention. Increasing the acid treatment temperature is beneficial to improving the dealuminization rate, but excessively high temperatures may cause damage to the pore structure; if the treatment time is too short, the modification will be insufficient, and if the time is too long, too much skeletal aluminum may be lost, affecting the crystallinity and mechanical stability of the molecular sieve. The number of acid leaching treatments further determines the modification depth. Multiple acid leaching treatments are beneficial to gradually increase the silicon-aluminum ratio and optimize the distribution of acid centers, but too many treatments may easily cause excessive dealuminization of the structure. Therefore, the above conditions need to be controlled in a coordinated manner to take into account both the structural stability of the molecular sieve and the acid modulation effect.

[0014] As a preferred embodiment of the present invention, in step (2), the secondary calcination temperature is 400-600℃, and the secondary calcination time is 2-6 hours. The temperature and time of the secondary calcination have a significant impact on the structural stabilization and active site fixation of the molecular sieve after acid treatment. Suitable secondary calcination can effectively remove residual acid radicals, moisture, and impurities, making the modified Hβ molecular sieve structure more stable, and at the same time, it is conducive to the redistribution and stable existence of acid centers. If the calcination conditions are insufficient, it will not be conducive to the thorough removal of post-treatment impurities and the stability of material properties; if the calcination conditions are too strong, it may further damage the molecular sieve framework, causing a decrease in specific surface area or deterioration of pore structure. Therefore, the secondary calcination conditions are also an important process parameter affecting the performance of the final product of the present invention.

[0015] As a preferred embodiment of the present invention, in step (2), the Si / Al molar ratio of the acid-treated modified Hβ molecular sieve is 10-100. The Si / Al molar ratio of the acid-treated modified Hβ molecular sieve is a key parameter characterizing the modification effect of the present invention, and has a significant impact on the acidity, acid center density, hydrophobicity, and catalytic selectivity of the material. If the Si / Al molar ratio is too low, it indicates insufficient dealuminization, and the improvement of the molecular sieve's acidity and pore environment is limited; if the Si / Al molar ratio is too high, it may mean excessive dealuminization, leading to an increase in framework defects, a decrease in the number of acid centers, or even a decrease in crystal structure stability. Therefore, controlling the Si / Al molar ratio within the range of 10-100 is beneficial to balancing the structural integrity of the molecular sieve and the improvement of its catalytic performance. This indicator is of great significance in demonstrating the technical effect of the present invention.

[0016] This invention also provides an acid-treated modified Hβ molecular sieve catalyst prepared by the aforementioned method. The acid-treated Hβ molecular sieve catalyst undergoes non-framework external aluminum removal, exposing more acidic sites and thereby adjusting the ratio of Brønsted acid sites to Lewis acid sites.

[0017] This invention also provides the application of the acid-treated modified β-molecular sieve catalyst in the catalytic oxidation of NO and VOCs, characterized by comprising the following steps:

[0018] The acid-modified Hβ molecular sieve is packed into a reactor, and the gas to be treated containing NO and VOCs is introduced. At the same time, hydrogen peroxide is introduced as an oxidant, and a catalytic oxidation reaction is carried out at 20-250℃, so that NO is oxidized to NO2 or nitrate, and VOCs are oxidized to CO2 and H2O.

[0019] As a preferred embodiment of the present invention, the molar ratio of hydrogen peroxide to NO is 0.5-10, the molar ratio of hydrogen peroxide to VOCs is 0.5-10, the catalyst dosage is 0.05-0.3 g, and the synergistic oxidation reaction of NO and VOCs is achieved at 50-250 °C.

[0020] The process and method of the present invention have the following features and advantages:

[0021] 1. This invention adopts a two-step preparation route of "preparing Hβ molecular sieve by exchanging β molecular sieve with ammonium chloride, followed by inorganic acid impregnation and secondary calcination modification". By removing the non-framework aluminum and adjusting the ratio of Brønsted acid sites to Lewis acid sites, the catalytic performance is improved.

[0022] 2. Improve the effective utilization rate of H2O2: Acid treatment can regulate the acidity and pore structure of molecular sieves, promote the efficient activation of H2O2 on the surface and directional oxidation of NO, reduce the ineffective decomposition of H2O2, and thus improve the oxidation efficiency.

[0023] 3. High activity and stability at low temperature: The catalyst can maintain a high NO conversion capacity at low temperature. The acidic sites, larger specific surface area, and pore structure help to improve the NO oxidation efficiency.

[0024] 4. Simple preparation: The steps of acid washing, washing, drying and calcination are easy to operate, the process conditions are mild, which is conducive to mass production, and the catalyst loading operation is also more convenient.

[0025] 5. Adaptable to various working conditions: The molecular sieve type and acid treatment intensity can be matched with the NO concentration, temperature, space velocity, etc. of the flue gas, making it suitable for industrial flue gas treatment scenarios. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This describes the preparation process of nitric oxide catalytic oxidation by acid-treated modified molecular sieves; Figure 2 The efficiency of NO oxidation by catalysts modified with different concentrations of nitric acid under different hydrogen peroxide concentrations; Figure 3 The efficiency of NO oxidation under different inorganic acid-modified catalysts and different hydrogen peroxide concentrations; Figure 4 The efficiency of NO oxidation under different hydrogen peroxide concentrations at different acid modification temperatures; Figure 5 The efficiency of 2NHβ-60 in oxidizing NO at different catalytic temperatures and hydrogen peroxide concentrations; Figure 6 Nitrogen adsorption-desorption curves for nitric acid-treated modified Hβ molecular sieves. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above-described invention.

[0029] This invention utilizes an acid-treated modified molecular sieve to catalyze the oxidation of nitric oxide by peroxide. The preparation process is as follows: Figure 1As shown. This invention provides an acid-treated modified molecular sieve catalyst for activating H2O2 to oxidize NO. Its core features are: (1) first obtaining an H-type molecular sieve using ammonium chloride; (2) controlling the Si / Al ratio, acidic sites (B / L ratio), and pore structure defects of the molecular sieve through acid treatment; (3) forming active oxygen species by decomposing the catalyst H2O2 at the gas-solid interface, thereby improving the selective oxidation ability of NO.

[0030] Example 1

[0031] This embodiment utilizes an acid-treated modified β-zeolite catalyst preparation method, the steps of which are as follows:

[0032] (1) The preparation process of H-type molecular sieves includes the following steps:

[0033] Accurately weigh 3 g of commercial β (Si / Al: 20-30), then dissolve the weighed commercial β in 10 ml of 1.0 mol / L NH4Cl solution, and perform ion exchange at room temperature for 2 hours (repeated three times). Filter the sample, wash with distilled water, dry the precipitate at 80 °C for 12 hours, and then calcine at 550 °C for 2 hours to obtain Hβ.

[0034] (2) The preparation process of acid-modified molecular sieves includes the following steps:

[0035] Prepare a 0.1 mol / L nitric acid solution. Add accurately weighed Hβ to the acid solution at a solid-liquid ratio of 0.1 g / mL. Stir and acid leaching treatment at 60℃ for 2 hours. After filtration, wash with deionized water until the pH of the filtrate is approximately 6-7. Dry the filter residue in an oven at 80℃ for 2 hours and calcine it in a muffle furnace at 550℃ for 2 hours to obtain the acid-treated modified molecular sieve, namely the protonated Hβ molecular sieve catalyst (denoted as 0.1NHβ-60).

[0036] Example 2

[0037] This embodiment utilizes an acid-treated modified β-zeolite catalyst preparation method, the steps of which are as follows:

[0038] (1) The preparation process of H-type molecular sieves includes the following steps:

[0039] Accurately weigh 3 g of commercial β (Si / Al: 20-30), then dissolve the weighed commercial β in 10 ml of 1.0 mol / L NH4Cl solution, and perform ion exchange at room temperature for 2 hours (repeated three times). Filter the sample, wash with distilled water, dry the precipitate at 80 °C for 12 hours, and then calcine at 550 °C for 2 hours to obtain Hβ.

[0040] (2) The preparation process of acid-modified molecular sieves includes the following steps:

[0041] Prepare a 1 mol / L nitric acid solution. Accurately weighed Hβ is added to the acid solution at a solid-liquid ratio of 0.1 g / mL. The solution is stirred and acid-leached at 60℃ for 2 hours. After filtration, the solution is washed with deionized water until the pH of the filtrate is approximately 6-7. The filter residue is dried in an oven at 80℃ for 2 hours and calcined in a muffle furnace at 550℃ for 2 hours to obtain the acid-treated modified molecular sieve, i.e., the protonated Hβ molecular sieve catalyst (denoted as 1NHβ-60).

[0042] Example 3

[0043] This embodiment utilizes an acid-treated modified β-zeolite catalyst preparation method, the steps of which are as follows:

[0044] (1) The preparation process of H-type molecular sieve includes the following steps: accurately weigh 3 g of commercial β (Si / Al: 20-30), then dissolve the weighed commercial β in 10 ml of 1.0 mol / L NH4Cl solution, ion exchange at room temperature for 2 hours (repeated three times), filter the sample, wash with distilled water, dry the sludge at 80℃ for 12 hours, and then calcine at 550℃ for 2 hours to obtain Hβ.

[0045] (2) The preparation process of acid-modified molecular sieves includes the following steps:

[0046] Prepare a 2 mol / L nitric acid solution. Add accurately weighed Hβ to the acid solution at a solid-liquid ratio of 0.1 g / mL. Stir and acid leaching treatment at 60℃ for 2 hours. After filtration, wash with deionized water until the pH of the filtrate is ≈6-7. Dry the filter residue in an oven at 80℃ for 2 hours and calcine it in a muffle furnace at 550℃ for 2 hours to obtain the acid-treated modified molecular sieve, namely the protonated Hβ molecular sieve catalyst (denoted as 2NHβ-60).

[0047] The pore data of the protonated Hβ molecular sieve catalysts prepared in Examples 1-3 are recorded in Table 1.

[0048] Table 1 Pore data of nitric acid-modified Hβ

[0049]

[0050] Based on Table 1 Figure 2 It is known that the catalyst can maintain a high NO conversion capacity at low temperatures, and the acidic sites, larger specific surface area, and pore structure help to improve the NO oxidation efficiency.

[0051] Example 4

[0052] Replace the 2 mol / L nitric acid solution in step (2) of Example 3 with a 2 mol / L phosphoric acid solution, and perform the other operations as in Example 3 to obtain the protonated Hβ molecular sieve catalyst (denoted as 2PHβ-60).

[0053] Example 5

[0054] Replace the 2 mol / L phosphoric acid solution in step (2) of Example 3 with a 2 mol / L sulfuric acid solution, and perform the same other operations as in Example 3 to obtain the protonated Hβ molecular sieve catalyst (denoted as 2SHβ-60).

[0055] Example 6

[0056] In step (2) of Example 3, the acid leaching treatment at 60°C for 2 hours was adjusted to acid leaching treatment at 20°C for 2 hours. Other operations were the same as in Example 3, and protonated Hβ molecular sieve catalyst (denoted as 2NHβ-20) was obtained.

[0057] Example 7

[0058] In step (2) of Example 3, the acid leaching treatment at 60°C for 2 hours was adjusted to acid leaching treatment at 40°C for 2 hours. Other operations were the same as in Example 3, and protonated Hβ molecular sieve catalyst (denoted as 2NHβ-40) was obtained.

[0059] Example 8

[0060] In step (2) of Example 3, the acid leaching treatment at 60°C for 2 hours was changed to acid leaching treatment at 80°C for 2 hours. Other operations were the same as in Example 3, and protonated Hβ molecular sieve catalyst (denoted as 2NHβ-80) was obtained.

[0061] Comparative Example 1

[0062] This comparative example uses a commercially available β-molecular sieve that has not undergone ammonium exchange and acid treatment as a catalyst. The steps are as follows:

[0063] 3 g of commercial β-zeolite (Si / Al: 20-30) was accurately weighed. Without ion exchange treatment with NH4Cl solution or acid modification, the commercial β-zeolite was directly dried at 80 °C for 12 hours and used as a catalyst. The resulting commercial β-zeolite was directly used to test its performance in oxidizing NO with H2O2 solution.

[0064] Comparative Example 2

[0065] This comparative example uses untreated Hβ molecular sieve as a catalyst, and the steps are as follows:

[0066] Accurately weigh 3 g of commercial β-zeolite (Si / Al: 20-30), add the weighed commercial β-zeolite to 10 mL of 1.0 mol / L NH4Cl solution, and perform ion exchange at room temperature for 2 hours (repeated three times). Filter the sample, wash with distilled water, dry the precipitate at 80 ℃ for 12 hours, and then calcine at 550 ℃ for 2 hours to obtain Hβ-zeolite. The obtained Hβ-zeolite is not subjected to further acid treatment or secondary calcination and is directly used as a catalyst for testing its performance in oxidizing NO with H2O2 solution.

[0067] Application Example 1

[0068] 100 mg of the catalyst sample (2NHβ-60) from Example 3 was weighed and packed into a quartz tube lined with silica wool. The NO oxidation performance was tested in a reactor at different catalytic temperatures and with a total gas flow rate of 500 mL / min, an oxygen volume fraction of 2.5%, a NO concentration of 400 ppm, an H2O2 purge gas flow rate of 10 mL / min. The results are shown below. Figure 5 And Table 2.

[0069] Table 2. Efficiency of NO oxidation by 2NHβ-60 at different catalytic temperatures and different hydrogen peroxide concentrations

[0070]

[0071] Depend on Figure 5 As shown in Table 2, the oxidation performance of 2NHβ-60 on NO is affected by both the reaction temperature and the H2O2 / NO molar ratio. As the reaction temperature increases from 100 °C to 175 °C, the NO conversion rate gradually increases; however, as the temperature continues to rise, the NO conversion rate decreases. Simultaneously, as the H2O2 / NO molar ratio increases, the NO conversion rate increases accordingly. Preferably, at 175 °C and with an H2O2 / NO ratio of 8, the NO conversion rate of 2NHβ-60 reaches 96.37%. This indicates that the material provided by this invention can achieve high NO oxidation efficiency in the presence of hydrogen peroxide and has good application prospects.

[0072] Application Example 2

[0073] 100 mg of catalyst sample (Examples 1-8 and Comparative Examples 1-2) was weighed and filled into a quartz tube lined with quartz wool. The NO oxidation performance was tested in a reactor with a total gas flow rate of 500 mL / min, an oxygen volume fraction of 2.5%, a NO concentration of 400 ppm, an H2O2 purge gas flow rate of 10 mL / min, and a temperature of 175 °C.

[0074] Examples 1-8 above investigated the effects of different acid types, acid concentrations, and acid treatment temperatures on the modification effect of β-zeolites. Comparative Examples 1 and 2 are used to illustrate the differences in NO oxidation performance between commercially available and unmodified Hβ-zeolites and the acid-modified Hβ-zeolites of this invention.

[0075] like Figure 2 As shown, compared with Comparative Example 1, the catalysts prepared in Examples 1-3, after ammonium exchange and calcination treatment, formed Hβ molecular sieves, which is beneficial for increasing the number of Brønsted acid centers and improving the acidic environment on the surface of the molecular sieve. Therefore, they exhibit better catalytic activity when combined with H2O2 for NO oxidation. Comparative Example 1, compared with the examples, omitted the ion exchange preparation of Hβ molecular sieves and the subsequent acid treatment modification steps. Typically, untreated commercial β molecular sieves have less than ideal acid center types and distributions, and their pore environment and surface properties are not further optimized; therefore, their promoting effect on H2O2 activation and NO oxidation is relatively weak. By comparing with the embodiments of the present invention, it can be further demonstrated that the modification process described in this invention has a positive effect on improving catalyst performance.

[0076] like Figure 2 As shown, compared with Comparative Example 2, Examples 1-3 further modified the Hβ molecular sieve with inorganic acid treatment, resulting in improved catalytic performance. This indicates that the acid treatment process has a significant effect on improving the performance of the molecular sieve. Analysis suggests that acid treatment can remove framework or non-framework aluminum species to a certain extent, adjust the Si / Al molar ratio of the molecular sieve, optimize the type, strength, and distribution of acid centers, and improve pore permeability and surface properties, thereby enhancing the interaction between the catalyst and reactants and improving NO oxidation efficiency.

[0077] The results show that the acid-treated modified β-zeolite catalyst exhibits superior NO oxidation performance compared to the unmodified sample. This indicates that the ion exchange-calcination-acid treatment-secondary calcination modification route employed in this invention can effectively improve the surface acidity, pore structure, and active site distribution of β-zeolite, thereby enhancing its activation capacity for H2O2 and further promoting the conversion of NO to higher valence nitrogen oxides.

[0078] In summary, the test results of Comparative Examples 1 and 2 demonstrate the effectiveness of the modification process of this invention from a comparative perspective. That is, after commercial β molecular sieves are converted into Hβ by ammonium exchange, they are further modified by inorganic acid treatment and secondary calcination, which can significantly improve their performance in oxidizing NO with H2O2 solution, demonstrating the superiority of the method of this invention in catalyst preparation.

[0079] Figure 3 This is a graph showing the efficiency of NO oxidation at 175 °C for different inorganic acid-modified catalysts and different hydrogen peroxide concentrations. Figure 3It can be seen that, at 175 °C, both the H₂O₂ / NO molar ratio and the type of inorganic acid used for modification affect the oxidation performance of NO by the Hβ catalyst. With increasing H₂O₂ / NO molar ratio, the NO conversion rate generally increases. Under the same conditions, the nitric acid-modified catalyst 2NHβ exhibits the best performance, followed by the sulfuric acid-modified catalyst 2SHβ, and the phosphoric acid-modified catalyst 2PHβ shows the lowest performance. This indicates that nitric acid modification is more beneficial for improving the catalytic oxidation of NO by Hβ molecular sieves.

[0080] Figure 4 This is a graph showing the efficiency of NO oxidation at different acid modification temperatures (175℃) and different hydrogen peroxide concentrations for catalysts. Figure 4 It is evident that, at 175℃, both the H2O2 / NO molar ratio and the acid modification temperature affect the NO oxidation performance of the nitric acid-modified Hβ catalyst. With increasing H2O2 / NO molar ratio, the NO conversion rate of all samples generally increases. Under the same conditions, 2NHβ-60 consistently exhibits the highest NO conversion rate, indicating that 60℃ is the optimal acid modification temperature. This suggests that excessively low acid modification temperatures result in insufficient modification, while excessively high temperatures may adversely affect the catalyst structure or effective active sites, thus hindering further improvement in NO oxidation performance.

[0081] Figure 6 Nitrogen adsorption-desorption curves for nitric acid-treated modified Hβ molecular sieves. Figure 6 The N2 adsorption-desorption results showed that both the original Hβ and nitric acid-modified samples retained the predominantly microporous pore structure characteristics, while also exhibiting some mesoporous features. After nitric acid modification, the overall N2 adsorption capacity of the samples increased, indicating an improvement in both specific surface area and pore volume. Among them, 2NHβ-60 showed the highest adsorption capacity, indicating the most significant pore structure optimization effect. This demonstrates that appropriate nitric acid modification is beneficial for improving the pore structure of Hβ molecular sieves, providing a structural basis for enhancing their catalytic performance. It also shows that nitric acid modification has a certain optimizing effect on the pore structure parameters of Hβ molecular sieves without altering their basic pore structure characteristics.

[0082] Furthermore, the different types, concentrations, and processing temperatures of inorganic acids used in different embodiments lead to variations in the structural properties and acidity characteristics of the resulting modified β-zeolites, resulting in different NO oxidation performances. This indicates that the type of inorganic acid and acid treatment conditions have a significant impact on the degree of dealumination, framework retention, and active site formation of the zeolite, and are important factors affecting the catalyst performance of this invention. By controlling the process parameters within the limits defined in this invention, effective regulation of acidity and pore structure can be achieved while ensuring the stability of the β-zeolite crystal structure, thereby obtaining superior catalytic effects.

[0083] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing protonated Hβ molecular sieve catalysts by acid treatment modification, characterized in that, Includes the following steps: (1) β molecular sieve hydrogenation: β molecular sieve and ammonium chloride solution are mixed at a certain solid-liquid ratio and stirred at a certain temperature for a period of time on a constant temperature stirrer. After sufficient ion exchange, the resulting mixture is transferred into a centrifuge tube, centrifuged and washed with water several times. The lower solid is dried and ground. After grinding, the solid is placed in a crucible and the crucible is placed in a muffle furnace for calcination at high temperature. After calcination, H-type β molecular sieve is obtained. (2) Acid-modified Hβ molecular sieve: The H-type β molecular sieve obtained in step (1) is mixed with an inorganic acid solution at a certain solid-liquid ratio. The mixture is stirred at a certain temperature for a period of time on a constant temperature stirrer. After the acid leaching is completed, the resulting mixture is allowed to stand and cool to room temperature. It is then filtered and washed with water several times. The upper solid is dried and ground. After grinding, the solid is placed in a crucible. The crucible is placed in a muffle furnace and calcined twice under high temperature conditions. After calcination, a protonated Hβ molecular sieve catalyst is obtained.

2. The method for preparing protonated Hβ molecular sieve catalyst by acid treatment modification according to claim 1, characterized in that, In step (1), the concentration of ammonium chloride solution is 0.5-2 mol / L, the solid-liquid ratio of β molecular sieve and ammonium chloride solution is 0.1-0.5 g / mL, the stirring temperature is 60-100℃, and the stirring time is 0.5-2 hours.

3. The method for preparing protonated Hβ molecular sieve catalysts by acid treatment modification according to claim 1, characterized in that, In step (1), the calcination temperature is 400-600℃ and the calcination time is 2-6 hours.

4. The method for preparing protonated Hβ molecular sieve catalyst by acid treatment modification according to claim 1, characterized in that, In step (2), the concentration of the inorganic acid solution is 0.1-2.0 mol / L, the inorganic acid is any one of phosphoric acid, nitric acid or sulfuric acid, and the solid-liquid ratio of the hydrogenated β molecular sieve to the inorganic acid solution is 0.1-0.5 g / mL.

5. The method for preparing protonated Hβ molecular sieve catalyst by acid treatment modification according to claim 1, characterized in that, In step (2), the acid leaching temperature is 60-100℃, the treatment time is 0.5-2 hours, and the acid leaching is performed 1-3 times.

6. The method for preparing protonated Hβ molecular sieve catalyst by acid treatment modification according to claim 1, characterized in that, In step (2), the secondary calcination temperature is 400-600℃ and the secondary calcination time is 2-6 hours.

7. The method for preparing protonated Hβ molecular sieve catalyst by acid treatment modification according to claim 1, characterized in that, In step (2), the Si / Al molar ratio of the H-type β molecular sieve after acid leaching is 10-100.

8. The protonated Hβ molecular sieve catalyst prepared by the method according to any one of claims 1-7, characterized in that, Protonated Hβ molecular sieve catalysts remove aluminum from the non-framework, exposing more acidic sites and thus regulating the ratio of Brønsted acid sites to Lewis acid sites.

9. The application of the acid-treated modified Hβ molecular sieve catalyst according to claim 8 in the activation of NO and VOCs by hydrogen peroxide oxidation, characterized in that, Includes the following steps: The protonated Hβ molecular sieve catalyst is packed into a reactor, and the gas to be treated containing NO and VOCs is introduced. Hydrogen peroxide is introduced as an oxidant, and a catalytic oxidation reaction is carried out at 20-250°C, so that NO is oxidized to NO2 or nitrate, and VOCs are oxidized to CO2 and H2O.

10. The application according to claim 9, characterized in that: The molar ratio of hydrogen peroxide to NO is 0.5-10, and the molar ratio of hydrogen peroxide to VOCs is 0.5-10; the amount of protonated Hβ molecular sieve catalyst is 0.05-0.3 g; and the synergistic oxidation reaction of NO and VOCs is achieved under the conditions of 50-250 °C.

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