An SBA molecular sieve encapsulated with nano-metal particles, its preparation method and application

Abstract

This invention relates to an SBA molecular sieve encapsulated with nano-metal particles, its preparation method, and its application. The preparation method includes the following steps: S1: Passivating the raw SBA molecular sieve powder to obtain passivated SBA molecular sieve powder; S2: Adding an alkaline solution to the passivated SBA molecular sieve powder obtained in step S1 to obtain an SBA molecular sieve powder intermediate; S3: Adding a metal complex solution to the SBA molecular sieve powder intermediate obtained in step S2 to obtain product A, wherein the metal particles in the metal complex are iron, cobalt, or nickel particles; S4: Uniformly mixing an organic template agent, water, a silicon source, and an acid to form a gel to obtain product B; S5: Mixing product A obtained in step S3 and product B obtained in step S4, and performing crystallization treatment, followed by washing, drying, and calcination to obtain the target product. The nanoparticles in the molecular sieve prepared by this invention are all located within the molecular sieve channels, improving the catalytic performance of the catalyst.

Description

Technical Field

[0001] This invention provides an SBA molecular sieve encapsulated with nano-metal particles, its preparation method, and its application. Background Technology

[0002] Since Mobil's successful synthesis of regular MCM-41 in 1992, mesoporous materials have shown great potential application value as adsorbents, catalysts, and catalyst supports. In 1998, Zhao Dongyuan successfully synthesized the first novel mesoporous materials SBA-15 and SBA-16, which have a larger specific surface area, regular pore size distribution, thicker pore walls, and better thermal stability than M41S molecular sieves. These materials have shown greater application value in catalysts. Compared with conventional M41S series molecular sieves, the three-dimensional channels allow reactants to enter the molecular sieve interior more easily without causing pore blockage. However, pure silicon SBA molecular sieves themselves do not contain any acidic, basic, or redox centers; their surface only has one functional group—silanol (Si-OH)—which greatly limits their application in certain fields. In recent years, the introduction of impurities into mesoporous molecular sieves to improve their acidity and stability has attracted increasing attention. Almost all transition metals and main group elements can be introduced into molecular sieves via hydrothermal synthesis and impregnation methods to serve as catalytic active centers and enhance the catalytic activity of the sieves. Among these heteroparticles, mesoporous iron, cobalt, and nickel silicates also exhibit excellent catalytic performance in many homogeneous oxidation reactions, such as phenol hydroxylation, adsorption desulfurization, and oxidative desulfurization. The state of these heteroparticles within the molecular sieve directly determines its catalytic performance.

[0003] Nanoparticle catalysts can be used in the production of fine chemicals, fuel improvement, hydrogen production, solar energy utilization, and pollutant removal. However, in some high-temperature reactions, metal particles often aggregate or become deactivated due to metal leaching. Significant efforts have been made to address the stability of nanoparticles, including enhancing the interaction between the metal and the supported material, adding promoters, and adjusting the diameter or morphology of the metal particles. The encapsulation of nanoparticles in molecular sieves can be mainly divided into two strategies: post-synthesis and in-situ confinement. Post-synthesis involves introducing nanoparticles after the zeolite structure has been constructed. In contrast, in-situ confinement requires the co-crystallization of the zeolite and the metal precursor, followed by in-situ reduction to obtain the nanoparticles.

[0004] In-situ confinement synthesis involves introducing nano-metal particles or precursors into the interior of molecular sieve crystals via a one-step hydrothermal synthesis method. This method first mixes the synthesized nano-metal particles or soluble metal precursors with the molecular sieve synthesis gel, followed by high-temperature crystallization. The synthesized product is then further calcined to remove organic matter, and reduced to nano-metal particles under a reducing agent. This method is simple and effective; however, because the metal particles are larger than the molecular sieve pores, the reduced metal expands the pore structure of the molecular sieve during reduction, causing structural damage and reducing the catalytic effect. Post-synthesis synthesis is widely used due to its advantage of not limiting the type of molecular sieve framework. By impregnating the molecular sieve support in a metal colloid or soluble metal precursor, nano-metal particles can enter the pores inside the molecular sieve. However, with this method, most of the nano-metal particles remain on the surface of the molecular sieve, with only a small portion entering the pores, thus failing to exert their catalytic effect. Summary of the Invention

[0005] In order to solve at least one of the above-mentioned problems in the prior art, the present invention proposes an SBA molecular sieve encapsulated with nano-metal particles, its preparation method and application.

[0006] The objective of this invention is achieved through the following technical solutions.

[0007] The inventors of this application discovered that by using a passivating agent to passivate the silanol groups on the outer surface of SBA molecular sieves, these passivated outer surfaces of SBA molecular sieves will not undergo desilication reaction under the action of alkaline substances, thus protecting the outer surface of the SBA molecular sieves. Subsequently, the alkaline substances undergo a desilication reaction inside the molecular sieve channels, forming new mesopores and macropores. Then, metal particles are embedded into the channels of the molecular sieve. The size of the nano-metal particles can be adjusted at any time according to the size of the molecular sieve channels. Finally, secondary crystallization is used to encapsulate the outer channels etched by the alkaline substances, thereby utilizing the confinement effect in the molecular sieve channels to prevent the nano-metal particles from agglomerating.

[0008] In a first aspect, the present invention provides a method for preparing an SBA molecular sieve encapsulated with nano-metal particles, comprising the following steps:

[0009] S1: Passivate the raw SBA molecular sieve powder to obtain passivated SBA molecular sieve powder.

[0010] S2: Add an alkaline solution to the SBA molecular sieve powder after passivation treatment in step S1 to obtain an SBA molecular sieve powder intermediate.

[0011] S3: Add a metal complex solution to the SBA molecular sieve powder intermediate obtained in step S2 to obtain product A, wherein the metal particles in the metal complex are iron, cobalt or nickel particles.

[0012] S4: Mix the organic template agent, water, silicon source and acid evenly to form a gel, and obtain product B;

[0013] S5: Mix product A obtained in step S3 and product B obtained in step S4, and perform crystallization treatment. After washing, drying and calcination, the target product is obtained.

[0014] Preferably, step S1 includes: mixing SBA molecular sieve raw powder with a passivating agent and performing passivation treatment under stirring.

[0015] Preferably, the passivation treatment conditions are as follows: temperature is 50-80℃, and time is preferably 2-6h.

[0016] Preferably, the passivating agent in step S1 includes general formula R a R b R c SiR d The organosilane shown, wherein R a R b R c and R d Same or different, independently selected from hydrogen, halogen, C1-C 20 Alkyl, C1-C 20 alkoxy groups, C3-C 20 cycloalkyl, C6-C 20 aryl and C1-C 20 Any one of the haloalkyl groups, and R a R b R c and R d Not simultaneously hydrogen and / or halogen; preferably, R d For halogens, R a R b and R c The passivating agent may not be hydrogen or halogen at the same time; more preferably, the passivating agent includes at least one of diphenyldichlorosilane, trimethylchlorosilane and dimethyldichlorosilane.

[0017] Preferably, the mass ratio of the passivating agent to the SBA molecular sieve powder is 4:5-1:10.

[0018] Preferably, the SBA molecular sieve raw powder is SBA-15 molecular sieve raw powder or SBA-16 molecular sieve raw powder.

[0019] Preferably, step S2 includes: adding an alkaline solution to the SBA molecular sieve powder after passivation treatment in step S1, reacting at room temperature for 1-2 hours to obtain an SBA molecular sieve powder intermediate.

[0020] Preferably, the alkaline solution in step S2 is a sodium hydroxide solution with a mass fraction of 1%-5%;

[0021] Preferably, the mass ratio of the alkaline solution to the SBA molecular sieve powder in step S2 is 1:20 to 1:10.

[0022] Preferably, step S5 includes: mixing product A obtained in step S3 and product B obtained in step S4, crystallizing at 80-130°C for 24-90 hours, filtering, washing, drying and calcining the crystallized product to obtain the target product, denoted as M@SBA molecular sieve.

[0023] Preferably, the drying temperature in step S5 is 100-140°C.

[0024] Preferably, the calcination temperature in step S5 is 400-700℃, and the calcination time is 5-8h.

[0025] Preferably, the mass ratio of the metal complex solution to the SBA molecular sieve powder is 0.5-1:5.

[0026] Preferably, the metal complex is a complex of at least one iron source complex selected from potassium ferrocyanide, potassium ferrous ferrocyanide and ferric nitrate with ethylenediaminetetraacetic acid, or a complex of ferric chloride with ethylenediaminetetraacetic acid.

[0027] Preferably, step S4 includes: uniformly mixing the organic template agent, water, silicon source, and alkali source in step S4 to form a gel, wherein product B has SiO2:a H2O:b R:c H + Wherein, R is an organic template agent, the value of a is 80~200, preferably 80~120, the value of b is 0.005~0.030, and the value of c is 0.10~0.25.

[0028] Preferably, the organic template agent in step S4 is the amphiphilic nonionic triblock surfactant F127 (EO). 106 PO 70 EO 106 ), F108 (EO) 132 PO 50 EO 132 ), hexamethylenetetramine (HMTA), P123 (EO) 20 PO 70 EO 20 ) or P104 (EO 27 PO 61 EO27 One or more of the following: When the SBA molecular sieve raw powder is SBA-15 molecular sieve raw powder, the organic template agent is one or more of P123 or P104; and / or when the SBA molecular sieve raw powder is SBA-16 molecular sieve raw powder, the organic template agent is one or more of F127, F108 or HMTA.

[0029] Preferably, the silicon source is one or more of silica, tetraethyl orthosilicate, sodium silicate, or silica sol, and the acid is one of hydrochloric acid, sulfuric acid, or nitric acid.

[0030] Secondly, the present invention provides an SBA molecular sieve encapsulated with nano-metal particles prepared by the aforementioned method for preparing SBA molecular sieves encapsulated with nano-metal particles.

[0031] In this invention, the nano-metal particles in the SBA molecular sieve encapsulated with nano-metal particles exist in the SBA molecular sieve in elemental form.

[0032] Preferably, the specific surface area is 940-1100 m². 2 / g, and / or the size of the nano-metal particles can be controlled between 5-50 nm.

[0033] Preferably, when the metal particle is Fe, the XPS of Fe atoms is 706 eV; when the metal particle is Co, the XPS of Co atoms is 778 eV; and when the metal particle is Ni, the XPS of Ni atoms is 852 eV.

[0034] Thirdly, the present invention provides the use of the SBA molecular sieve encapsulated with nano-metal particles in adsorbing arsenic in water.

[0035] This invention has the following advantages:

[0036] In the preparation method and the resulting molecular sieve of the present invention, passivation treatment is first used, in particular, a passivating agent is used to protect the silanol groups on the outside of the molecular sieve. Alkaline substances enter the molecular sieve channels and etch from the inside without etching or damaging the outer surface of the molecular sieve. The two independent pore structures of the internal molecular sieve are interconnected due to the etching by the alkaline substances, forming new macropore and mesopore structures. The size of the internal pore structure of the molecular sieve is adjusted according to the concentration and amount of alkaline substances. Subsequently, nano-metal particles are introduced into the molecular sieve channels. Due to the confinement effect of the molecular sieve channel structure, the nano-metal particles will not exceed the size of the molecular sieve channels and damage the internal structure of the molecular sieve. Finally, secondary crystallization is used to re-encapsulate the etched channels inside, completely encapsulating the nano-metal particles in the molecular sieve channels. Attached Figure Description

[0037] Figure 1 This is an HRTEM image of the Fe@SBA-16 molecular sieve obtained in Example 1;

[0038] Figure 2 This is the small-angle XRD pattern of Fe@SBA-16 molecular sieve obtained in Example 3;

[0039] Figure 3 This is an HRTEM image of the Fe@SBA-16 molecular sieve obtained in Example 3;

[0040] Figure 4 This is the XPS image of the Fe@SBA-16 molecular sieve obtained in Example 3;

[0041] Figure 5 This is an HRTEM image of the Fe@SBA-16 molecular sieve obtained in Example 4. Detailed Implementation

[0042] The present invention will be further explained below with reference to specific embodiments.

[0043] The present invention is described in detail through the following embodiments, which enable those skilled in the art to have a more comprehensive understanding of the present invention, but these embodiments do not constitute any limitation on the scope of the present invention.

[0044] In this embodiment, XRD was performed using a Philips X-Pert series X-ray diffractometer to determine the structure of the molecular sieve; HRTEM was performed using a Rigku Jem-3010 high-resolution transmission electron microscope to determine the regularity of the molecular sieve; XPS was performed using a Thermo ESCALAB 250 spectrometer to determine the bonding of metal particles; and BET was performed using a Micromeritics ASAP2020 fully automated surface area analyzer. In this invention, the silicon source is calculated as SiO2, the iron source as Fe, the cobalt source as Co, the nickel source as Ni, and the acid as H... + Solvents are calculated as H2O, and organic template agents are calculated as R.

[0045] Example 1

[0046] Take 5.0 g of SBA-16 molecular sieve raw powder and 2.1 g of trimethylchlorosilane and stir at 50 °C for 2 h. Then mix the product with 0.4 g of 1% sodium hydroxide solution and stir at room temperature for 1 h. Then filter and wash the product to obtain solution D. Add 2.0 g of potassium ferrocyanide to it to obtain solution A.

[0047] 1.6 g of F127 and 34.5 g of deionized water were added sequentially to the reactor and stirred until homogeneous. Then, 24.1 mL of 0.1 mol / L hydrochloric acid solution was added, and stirring continued. 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. The resulting reaction mixture had the following molar ratio: SiO2:80 H2O:0.005 R:0.1 H + Solution B was prepared by mixing B and A and transferring the mixture to a crystallization vessel. The temperature was raised to 90℃ and crystallized at this temperature for 40 h. After complete crystallization, the temperature was allowed to drop to room temperature. The resulting mixture was then separated, washed, and dried at 100℃. Finally, it was calcined at 400℃ for 8 h to obtain Fe@SBA-16 molecular sieve. The specific surface area of ​​the product obtained by BET analysis is shown in Table 1, and the high-magnification transmission electron microscopy image of the sample is shown in [Table 1]. Figure 1 The obtained samples were used for arsenic adsorption experiments, and the results are shown in Table 1.

[0048] For the arsenic adsorption test, 1.0 g of Fe@SBA-16 molecular sieve was dispersed in 50 mL of distilled water. After adjusting the pH to 7.5, 10 mg / L arsenic stock solution was added to obtain a molecular sieve suspension. The pH of the system was adjusted with NaOH and HCl to maintain a constant pH. After 24 h of adsorption, a certain amount of suspension was taken, centrifuged for 10 min, and the supernatant was removed, filtered, and sealed for later testing. The arsenic concentration in the liquid phase was determined using a particle fluorescence spectrophotometer, with a detection limit of 0.1 μg / L. All glassware used in the experiment was soaked in 1% HNO3 for at least 12 h after cleaning, and then rinsed thoroughly with distilled water.

[0049] Example 2

[0050] The procedure is basically the same as in Example 1, except that the passivating agent is changed to dimethyldichlorosilane, the amount is changed to 0.56 g, the passivation temperature is changed to 60℃, the passivation time is changed to 3 h, the mass fraction of sodium hydroxide solution is changed to 2%, the amount is 0.3 g, the Fe source complex is changed to a complex of ferric nitrate and ethylenediaminetetraacetic acid (where the molar ratio of ferric nitrate and ethylenediaminetetraacetic acid is 1:1), the amount is 1.5 g, the template agent is changed to F108, the amount is 4.4 g, the amount of water is changed to 54 g, the silicon source is changed to silica (silicon dioxide content is 90 wt%), the amount is 2 g, the acid is changed to sulfuric acid, the amount is 44.8 mL, the crystallization temperature is changed to 100℃, the crystallization time is changed to 50 h, the drying temperature is changed to 110℃, the calcination temperature is changed to 500℃, the calcination time is changed to 6 h, and the remaining components and synthesis conditions remain unchanged. The molar ratio of the resulting reaction mixture is SiO2:100 H2O:0.01 R:0.15 H + The specific surface area of ​​the product obtained by BET analysis of the sample is shown in Table 1. The obtained sample was used for arsenic adsorption experiment, and the results are shown in Table 1.

[0051] Example 3

[0052] The procedure is basically the same as in Example 1, except that the passivating agent is changed to diphenyldichlorosilane, the amount is changed to 1.25 g, the passivation temperature is changed to 70℃, the passivation time is changed to 4 h, the mass fraction of sodium hydroxide solution is changed to 3%, the amount is 0.35 g, the reaction time is changed to 2 h, the template agent is changed to HMTA, the amount is 0.15 g, the amount of water is changed to 82.5 g, the silicon source is changed to silica sol (SW-25, silica content 25wt%), the amount is 10 g, the acid source is changed to nitric acid, the amount is 83 mL, the Fe source complex is changed to potassium ferricyanide, the amount is 1.0 g, the crystallization temperature is changed to 110℃, the crystallization time is changed to 60 h, the drying temperature is changed to 120℃, the calcination temperature is changed to 550℃, the calcination time is changed to 7 h, and the remaining components and synthesis conditions remain unchanged. The molar ratio of the resulting reaction mixture is SiO2:110 H2O:0.025 R:0.2 H + The specific surface area of ​​the products obtained by BET analysis of the samples is shown in Table 1. The small-angle powder XRD diffraction of the samples is shown in Table 1. Figure 2 High-magnification transmission electron microscopy image can be found in [the image]. Figure 3 The state analysis of iron particles in the molecular sieve (XPS) is shown in [link to XPS]. Figure 4 The obtained samples were used for arsenic adsorption experiments, and the results are shown in Table 1.

[0053] Example 4

[0054] The procedure is basically the same as in Example 3, except that the mass fraction of the sodium hydroxide solution is changed to 4%, while the remaining components and synthesis conditions remain unchanged. A high-magnification transmission electron microscope image of the sample is shown below. Figure 5 The specific surface area of ​​the product obtained by BET analysis of the sample is shown in Table 1. The obtained sample was used for arsenic adsorption experiment, and the results are shown in Table 1.

[0055] Example 5

[0056] Take 5.0 g of SBA-15 molecular sieve raw powder and 2.1 g of trimethylchlorosilane and stir at 50 ℃ for 2 h. Then mix the product with 0.4 g of 1% sodium hydroxide solution and stir at room temperature for 1 h. Then filter and wash the product to obtain solution D. Take 3.6 g of cobalt nitrate and 20 ml of 1 mol / L ethylenediaminetetraacetic acid solution and mix them evenly to form a complex. Then add 1.0 g of the solution to solution D to obtain solution A.

[0057] 4.2 g of P104 and 38.9 g of deionized water were added sequentially to the reactor and stirred until homogeneous. Then, 60 mL of 0.1 mol / L hydrochloric acid solution was added, and stirring continued. 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. The resulting reaction mixture had the following molar ratio: SiO2:90 H2O:0.03 R:0.25 H + Solution B was prepared by mixing B and A and transferring the mixture to a crystallization vessel. The temperature was raised to 130℃ and crystallized at this temperature for 90 h. After complete crystallization, the mixture was allowed to cool to room temperature, then separated, washed, and dried at 130℃. Finally, it was calcined at 400℃ for 8 h to obtain Co@SBA-15 molecular sieve. The specific surface area of ​​the product obtained by BET analysis is shown in Table 1. The obtained sample was used for arsenic adsorption experiments, and the results are shown in Table 1.

[0058] Example 6

[0059] Take 5.0 g of SBA-15 molecular sieve raw powder and 2.1 g of trimethylchlorosilane and stir at 50 ℃ for 2 h. Then mix the product with 0.4 g of 1% sodium hydroxide solution and stir at room temperature for 1 h. Then filter and wash the product to obtain solution D. Take 3.6 g of nickel nitrate and 20 ml of 1 mol / L citric acid solution and mix them evenly to form a complex. Then add 1.0 g of the solution to solution D to obtain solution A.

[0060] 4.2 g of P104 and 38.9 g of deionized water were added sequentially to the reactor and stirred until homogeneous. Then, 60 mL of 0.1 mol / L hydrochloric acid solution was added, and stirring continued. 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. The resulting reaction mixture had the following molar ratio: SiO2:90 H2O:0.03 R:0.25 H + Solution B was prepared by mixing B and A and transferring the mixture to a crystallization vessel. The temperature was raised to 130℃ and crystallized at this temperature for 90 h. After complete crystallization, the mixture was allowed to cool to room temperature, then separated, washed, and dried at 130℃. Finally, it was calcined at 400℃ for 8 h to obtain Ni@SBA-15 molecular sieve. The specific surface area of ​​the product obtained by BET analysis is shown in Table 1. The obtained sample was used for arsenic adsorption experiments, and the results are shown in Table 1.

[0061] Comparative Example 1

[0062] 1.6 g of F127 and 34.5 g of deionized water were added sequentially to the reactor and stirred until homogeneous. Then, 24.1 mL of 0.1 mol / L hydrochloric acid solution and 2.0 g of potassium ferrocyanide were added, and stirring continued. 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. The resulting reaction mixture had the following molar ratio: SiO2:80 H2O:0.005 R:0.1 H + The mixed solution was transferred to a crystallization vessel, heated to 90℃, and crystallized at that temperature for 40 h. After complete crystallization, the temperature was allowed to drop to room temperature. The reaction mixture was then separated, washed, and dried at 100℃. Finally, it was calcined at 400℃ for 8 h to obtain Fe-SBA-16 molecular sieve. The Fe-SBA-16 molecular sieve was placed at the bottom of a quartz tube and hydrogen gas was introduced. The temperature was increased to 400℃ at a rate of 3° / min and held for 2 h. The final product was Fe@SBA-16 molecular sieve. The specific surface area of ​​the product obtained by BET analysis is shown in Table 1. The obtained sample was used for arsenic adsorption experiments, and the results are shown in Table 1.

[0063] Comparative Example 2

[0064] 1.6 g of F127 and 34.5 g of deionized water were added sequentially to the reactor and stirred until homogeneous. Then, 24.1 mL of 0.1 mol / L hydrochloric acid solution was added and stirred until homogeneous. Finally, 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. The resulting reaction mixture had the following molar ratio: SiO2:80 H2O:0.005 R:0.1 H + The mixed solution was transferred to a crystallization vessel, heated to 90℃, and crystallized at that temperature for 40 h. After complete crystallization, the temperature was allowed to drop to room temperature. The reaction mixture was then separated, washed, and dried at 100℃. Finally, it was calcined at 400℃ for 8 h to obtain SBA-16 molecular sieve raw powder. SBA-16 molecular sieve, 2.0 g potassium ferrocyanide, and 50 ml deionized water were mixed evenly. The reaction mixture was then separated, washed, and dried at 100℃. Finally, it was calcined at 400℃ for 8 h to obtain Fe / SBA-16 molecular sieve. The specific surface area of ​​the product obtained by BET analysis is shown in Table 1. The obtained sample was used for arsenic adsorption experiments, and the results are shown in Table 1.

[0065] Table 1 Results of Arsenic Adsorption Experiment

[0066]

[0067] As shown in Table 1 of Comparative Examples 1-2 and Example 1, Fe@SBA-16 was prepared using the in-situ constraint method in Comparative Example 1. This method is quite simple and convenient, requiring only H2 reduction to pull the metal out of the framework at the end. However, this method has two drawbacks: firstly, it forcibly pulls the metal particles out of the framework, thus destroying the framework structure of the molecular sieve; secondly, the metal particles precipitated from the framework are larger than the pores, which also has a certain destructive effect on the pore structure. Therefore, the overall structure of the molecular sieve will be significantly altered, resulting in lower catalytic performance of the catalyst obtained by this method. In contrast, Comparative Example 2 uses a post-synthesis strategy, which is basically the same as the ordinary loading method. The metal is ultimately loaded on the surface of the molecular sieve in the form of oxides, which will cause the overall loss of metal during the reaction, thus affecting the performance of the catalyst.

[0068] Depend on Figure 2 It can be seen that the Fe@SBA-16 molecular sieve obtained by the method provided by the present invention still has the characteristic peaks of high regularity of SBA-16 molecular sieve in small-angle XRD, indicating that the metal modification did not destroy the structure of the molecular sieve itself; Figure 3 and Figure 4 It is known that the iron in the Fe@SBA-16 molecular sieve obtained by the method provided by the present invention is in the form of elemental ( Figure 4 It exists in the form of elemental iron (Fe2p3 / 2 orbital) at 706.5 eV, and the size of the metal particles is clearly visible in the electron microscope image to be around 5 nm.

[0069] Depend on Figure 1 , Figure 3 and Figure 5 It can be seen that by changing the amount of alkali, the size of the nano-metal element can be adjusted at any time, and the metal element can vary from 5 to 50 nm.

[0070] As shown in Table 1, the catalytic activity improves with increasing size of the nano-metal particles. However, when the nano-metal particles are too large, although they do not damage the structure of the molecular sieve itself, the etching by the alkali will increase the interconnection of the internal pores of the molecular sieve, which will reduce the strength of the molecular sieve itself. Therefore, the catalytic performance will decrease to a certain extent.

[0071] In summary, the molecular sieve prepared according to the method of the present invention first uses a passivating agent to protect the silanol groups on the outside of the molecular sieve. Alkaline substances enter the molecular sieve channels and etch from the inside without etching or damaging the outer surface of the molecular sieve. The two independent pore structures inside the molecular sieve are interconnected due to the etching by the alkaline substances, forming new macropores and mesopores. The size of the internal pore structure of the molecular sieve is adjusted according to the concentration and amount of alkaline substances. Subsequently, nano-metal particles are introduced into the molecular sieve channels. Due to the confinement effect of the molecular sieve channel structure, the nano-metal particles will not exceed the size of the molecular sieve channels and damage the internal structure of the molecular sieve. Finally, secondary crystallization is used to re-encapsulate the etched channels inside, completely encapsulating the nano-metal particles in the molecular sieve channels.

[0072] Compared to conventional post-processing methods, which can only load most of the nano-metal particles onto the outer surface of the molecular sieve, the nano-metal particles, exposed to the outside, will continue to aggregate or even be lost after high-temperature treatment, resulting in a decrease in catalytic efficiency. Compared to conventional one-step hydrothermal synthesis, the one-step method is simpler, but it requires reduction to convert the nano-particles into their metallic elemental state. However, the reduced nano-metal particles are much larger than the pores of the molecular sieve itself, inevitably causing some of the internal structure of the molecular sieve pores to be enlarged and damaged, thus leading to a decrease in the catalyst's catalytic performance.

[0073] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88… and 69-71 and 70-71, etc. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0074] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing SBA molecular sieves encapsulated with nano-metal particles, characterized in that, Includes the following steps: S1: Passivate the raw SBA molecular sieve powder to obtain passivated SBA molecular sieve powder. S2: Add an alkaline solution to the SBA molecular sieve powder after passivation treatment in step S1 to obtain an SBA molecular sieve powder intermediate. S3: Add a metal complex solution to the SBA molecular sieve powder intermediate obtained in step S2 to obtain product A, wherein the metal particles in the metal complex are iron, cobalt or nickel particles. S4: Mix the organic template agent, water, silicon source and acid evenly to form a gel, and obtain product B; S5: Mix product A obtained in step S3 and product B obtained in step S4, and perform crystallization treatment. After washing, drying and calcination, the target product is obtained. Step S1 includes: mixing SBA molecular sieve raw powder with a passivating agent and performing passivation treatment under stirring; the passivating agent in step S1 includes general formula R a R b R c SiR d The organosilane shown, wherein R a R b R c and R d Same or different, independently selected from hydrogen, halogen, C1-C 20 Alkyl, C1-C 20 alkoxy groups, C3-C 20 cycloalkyl, C6-C 20 aryl and C1-C 20 Any one of the haloalkyl groups, and R a R b R c and R d It is not simultaneously hydrogen and / or halogen.

2. The method for preparing SBA molecular sieve encapsulated with nano-metal particles according to claim 1, characterized in that, The passivation treatment conditions are as follows: temperature 50-80℃, time 2-6h.

3. The method for preparing SBA molecular sieve encapsulated with nano-metal particles according to claim 1, characterized in that, In the general formula of the passivating agent, R d For halogens, R a R b and R c It is not simultaneously hydrogen or halogen.

4. The method for preparing SBA molecular sieve encapsulated with nano-metal particles according to claim 3, characterized in that, The passivating agent includes at least one of diphenyldichlorosilane, trimethylchlorosilane, and dimethyldichlorosilane.

5. The method for preparing SBA molecular sieves encapsulated with nano-metal particles according to any one of claims 1-4, characterized in that, The mass ratio of the passivating agent to the SBA molecular sieve raw powder is 4:5-1:

10.

6. The method for preparing SBA molecular sieves encapsulated with nano-metal particles according to any one of claims 1-4, characterized in that, The SBA molecular sieve raw powder is either SBA-15 molecular sieve raw powder or SBA-16 molecular sieve raw powder.

7. The method for preparing SBA molecular sieves encapsulated with nano-metal particles according to any one of claims 1-4, characterized in that, Step S2 includes: adding an alkaline solution to the SBA molecular sieve powder after passivation treatment in step S1, reacting at room temperature for 1-2 hours to obtain an SBA molecular sieve powder intermediate.

8. The method for preparing SBA molecular sieve encapsulated with nano-metal particles according to claim 7, characterized in that, The alkaline solution in step S2 is a sodium hydroxide solution with a mass fraction of 1%-5%.

9. The method for preparing SBA molecular sieve encapsulated with nano-metal particles according to claim 7, characterized in that, The mass ratio of the alkaline solution to the raw SBA molecular sieve powder in step S2 is 1:20-1:

10.

10. The method for preparing SBA molecular sieves encapsulated with nano-metal particles according to any one of claims 1-4, characterized in that, Step S5 includes: mixing product A obtained in step S3 and product B obtained in step S4, and crystallizing at 80-130℃ for 24-90h. The crystallized product is then filtered, washed, dried, and calcined to obtain the target product, denoted as M@SBA molecular sieve.

11. The method for preparing SBA molecular sieve encapsulated with nano-metal particles according to claim 10, characterized in that, The drying temperature in step S5 is 100-140℃.

12. The method for preparing SBA molecular sieve encapsulated with nano-metal particles according to claim 10, characterized in that, The roasting temperature in step S5 is 400-700℃, and the roasting time is 5-8h.

13. The method for preparing SBA molecular sieves encapsulated with nano-metal particles according to any one of claims 1-4, characterized in that, The mass ratio of the metal complex solution to the SBA molecular sieve powder is 0.5-1:

5.

14. The method for preparing SBA molecular sieve encapsulated with nano-metal particles according to claim 13, characterized in that, The metal complex is a complex of at least one iron source complex selected from potassium ferrocyanide and potassium ferrous ferrocyanide with ethylenediaminetetraacetic acid, or a complex of one of ferric nitrate and ferric chloride with ethylenediaminetetraacetic acid.

15. The method for preparing SBA molecular sieves encapsulated with nano-metal particles according to any one of claims 1-4, characterized in that, Step S4 includes: uniformly mixing an organic template agent, water, a silicon source, and an alkali source to form a gel, wherein product B has the following composition: SiO2:aH2O:bR:cH + The molar ratios are as follows: where R is an organic template agent, a is 80~200, b is 0.005~0.030, and c is 0.10~0.

25.

16. The method for preparing SBA molecular sieves encapsulated with nano-metal particles according to any one of claims 1-4, characterized in that, The organic template agent in step S4 is one or more of the following: amphiphilic nonionic triblock surfactants F127, F108, hexamethylenetetramine, P123, or P104.

17. The method for preparing SBA molecular sieves encapsulated with nano-metal particles according to any one of claims 1-4, characterized in that, When the SBA molecular sieve raw powder is SBA-15 molecular sieve raw powder, the organic template agent is selected from one or more of P123 or P104.

18. The method for preparing SBA molecular sieves encapsulated with nano-metal particles according to any one of claims 1-4, characterized in that, When the SBA molecular sieve raw powder is SBA-16 molecular sieve raw powder, the organic template agent is selected from one or more of F127, F108 or HMTA.

19. The method for preparing SBA molecular sieve encapsulated with nano-metal particles according to claim 15, characterized in that, In product B, the value of a is 80~120.

20. The method for preparing SBA molecular sieves encapsulated with nano-metal particles according to any one of claims 1-4, characterized in that, The silicon source is one or more of silica, tetraethyl orthosilicate, sodium silicate, or silica sol, and the acid is one of hydrochloric acid, sulfuric acid, or nitric acid.

21. An SBA molecular sieve encapsulated with nano-metal particles prepared by the method for preparing SBA molecular sieve encapsulated with nano-metal particles according to any one of claims 1-20.

22. The SBA molecular sieve encapsulated with nano-metal particles according to claim 21, characterized in that, The SBA molecular sieve encapsulated with nano-metal particles has a specific surface area of ​​940-1100 m². 2 / g, and / or the size of the nano-metal particles can be controlled between 5-50 nm.

23. The SBA molecular sieve encapsulated with nano-metal particles according to claim 21, characterized in that, In the SBA molecular sieve encapsulated with nano-metal particles, the XPS of Fe atoms is 706.5 eV when the metal particles are Fe; the XPS of Co atoms is 778 eV when the metal particles are Co; and the XPS of Ni atoms is 852 eV when the metal particles are Ni.

24. Use of an SBA molecular sieve encapsulated with nano-metal particles according to any one of claims 21-23 for the adsorption of arsenic in water.

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