Preparation method and application of MCM molecular sieve encapsulated with nano-metal particles

Abstract

The present invention relates to an MCM molecular sieve encapsulated with nano-metal particles, and its preparation method and application. The preparation method comprises the following steps: S1: passivating MCM molecular sieve raw powder to obtain passivated MCM molecular sieve powder; S2: adding an alkaline solution to the passivated MCM molecular sieve powder in step S1 to obtain an MCM molecular sieve powder intermediate; S3: adding a metal complex solution to the MCM 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 atoms; S4: uniformly mixing an organic template, water, a silicon source, and an alkaline source to form a gel to obtain product B; S5: mixing product A obtained in step S3 and product B obtained in step S4, crystallizing the mixture, washing, drying, and calcining the mixture to obtain the target product. The nanoparticles in the molecular sieve prepared by the present invention are all located in the molecular sieve pores, significantly improving catalyst performance.

Description

Technical Field

[0001] The present invention provides an MCM molecular sieve encapsulating nano-metal particles, a preparation method thereof and an application thereof. Background Art

[0002] Due to their large surface area, pore volume, and uniform pore size, MCM-41 and other M41S series molecular sieves have attracted significant interest. The emergence of M41S mesoporous materials has not only broadened the application range of molecular sieves but also addressed the limitations of microporous materials. However, the low acidity of pure silicon MCM-41 has made it difficult to use as a catalyst in industrial production. In recent years, the introduction of heteroatoms into mesoporous molecular sieves to enhance their acidity and stability has attracted increasing attention. Almost all transition metals and main-group elements can be incorporated into molecular sieves through hydrothermal synthesis and impregnation methods, serving as catalytic active sites to enhance their catalytic activity. Among these heteroatoms, mesoporous iron, cobalt, and nickel silicates have demonstrated excellent catalytic performance in many homogeneous oxidation reactions, such as phenol hydroxylation, adsorptive desulfurization, and oxidative desulfurization. The state of the heteroatoms within the molecular sieve directly determines its catalytic performance.

[0003] Nano-metal particle catalysts can be used to produce fine chemicals, improve fuels, produce hydrogen, utilize solar energy, and eliminate pollutants. However, in certain high-temperature reactions, metal particles tend to aggregate or become inactivated due to metal leaching. In order to solve the problem of stability of nano-metal particles, people have made great efforts, including strengthening the interaction between metal and support, adding promoters, and adjusting the diameter or morphology of metal particles. The coating of nano-metal particles in molecular sieves can be mainly divided into two strategies: post-synthesis method and in-situ confinement method. The post-synthesis strategy refers to the introduction of nano-metal particles after the zeolite structure is constructed. In contrast, the in-situ confinement method requires the co-crystallization of zeolite and metal precursor, and obtains nano-metal particles by in situ reduction.

[0004] The in-situ confinement method involves introducing metal nanoparticles or precursors into the interior of molecular sieve crystals through a one-step hydrothermal synthesis process. This method first involves mixing synthesized metal nanoparticles or soluble metal precursors with a molecular sieve synthesis gel, followed by high-temperature crystallization. The resulting product is then calcined to remove organic matter and reduced in the presence of a reducing agent to yield metal nanoparticles. This method is simple and effective, but because metal particles are larger than the molecular sieve pores, the reduced metal expands the molecular sieve's pore structure during the reduction process, disrupting the sieve's structure and reducing the catalyst's effectiveness. The post-synthesis method is widely used because it offers the advantage of not being restricted to the type of molecular sieve framework. By impregnating the molecular sieve support with a metal colloid or soluble metal precursor, metal nanoparticles can be introduced into the molecular sieve's internal pores. However, this method results in the majority of the metal nanoparticles remaining on the molecular sieve's surface, with only a small fraction penetrating the pores, hindering their catalytic activity. Summary of the Invention

[0005] In order to solve at least one of the above problems in the prior art, the present invention provides an MCM molecular sieve encapsulated with nano-metal particles and a preparation method thereof.

[0006] The objectives of the present invention are achieved through the following technical solutions.

[0007] The inventors of the present application discovered that a passivating agent is used to passivate the silanol groups on the outer surface of the MCM-41 molecular sieve. The passivated outer surface of the MCM-41 molecular sieve will not undergo a desiliconization reaction under the action of an alkaline substance, thereby protecting the outer surface of the MCM-41 molecular sieve. The alkaline substance then causes a desiliconization reaction inside the molecular sieve pores, forming new mesopores and macropores. Metal particles are then embedded in the pores of the molecular sieve, and the size of the nano-metal particles is adjusted at any time according to the size of the molecular sieve pores. Finally, crystallization is used to encapsulate the outer pores etched by the alkaline substance, thereby utilizing the confinement effect in the molecular sieve pores to prevent the nano-metal particles from agglomerating.

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

[0009] S1: passivating the MCM molecular sieve raw powder to obtain the passivated MCM molecular sieve powder;

[0010] S2: adding an alkaline solution to the MCM molecular sieve powder after the passivation treatment in step S1 to obtain an MCM molecular sieve powder intermediate;

[0011] S3: adding a metal complex solution to the MCM 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 atoms;

[0012] S4: uniformly mixing the organic template, water, silicon source and alkali source into a gel to obtain product B;

[0013] S5: The product A obtained in step S3 and the product B obtained in step S4 are mixed and crystallized, and then washed, dried and calcined to obtain the target product.

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

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

[0016] Preferably, the passivating agent in step S1 comprises the general formula R a R b R c SiR d The organosilane shown, wherein R a 、R b 、R c and R d The same or different, independently selected from hydrogen, halogen, C1-C 20 Alkyl, C1-C 20 Alkoxy, C3-C 20 Cycloalkyl, C6-C 20 Aryl and C1-C 20 Any one of the halogenated alkyl groups, and R a 、R b 、R c and R d are not hydrogen and / or halogen at the same time; preferably, R d is halogen, R a 、R b and R c It is not hydrogen or halogen at the same time; further preferably, the passivating agent includes at least one of diphenyldichlorosilane, trimethylchlorosilane and dimethyldichlorosilane.

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

[0018] Preferably, step S2 comprises: adding an alkaline solution to the MCM molecular sieve powder after the passivation treatment in step S1, and reacting at room temperature for 1-2 hours to obtain an MCM molecular sieve powder intermediate.

[0019] Preferably, the alkaline solution in step S2 is a sodium hydroxide solution with a mass fraction of 1%-5%.

[0020] Preferably, the mass ratio of the alkaline solution to the MCM molecular sieve powder in step S2 is 1:20-1:10.

[0021] Preferably, step S5 comprises: mixing the product A obtained in step S3 and the product B obtained in step S4, and crystallizing them at 110-140° C. for 72-108 hours, filtering, washing, drying and calcining the crystallized product to obtain the target product, which is recorded as M@MCM molecular sieve.

[0022] Preferably, the drying temperature in step S5 is 100-140°C.

[0023] Preferably, the calcination temperature in step S5 is 400-700° C., and the calcination time is 5-8 hours.

[0024] Preferably, the mass ratio of the metal complex solution to the MCM molecular sieve powder is 0.5-1:5.

[0025] Preferably, the metal complex is a complex of at least one iron source complex selected from potassium ferrocyanide, potassium ferrocyanide and ferric nitrate and ethylenediaminetetraacetic acid, or a complex of ferric chloride and ethylenediaminetetraacetic acid.

[0026] Preferably, in step S4, the organic template, water, silicon source and alkali source are uniformly mixed to form a gel, and the product B has SiO2: aH2O: bR: cOH - The molar ratio of , wherein R is an organic template, the value of a is 80-160, the value of b is 0.1-0.7, the value of c is 2-7, and / or the organic template is one of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride or cetyltriethylammonium bromide, and / or the silicon source is one or more of white carbon black, ethyl orthosilicate, sodium silicate or silica sol, and / or the alkali source is one or more of sodium hydroxide, tetramethylammonium hydroxide or ammonia water.

[0027] Preferably, the MCM is MCM-41.

[0028] In a second aspect, the present invention provides an MCM molecular sieve encapsulating nano-metal particles, which is prepared by the method for preparing an MCM molecular sieve encapsulating nano-metal particles.

[0029] In the present invention, the nano-metal particles in the MCM molecular sieve encapsulating the nano-metal particles exist in the MCM molecular sieve in the form of a single substance.

[0030] Preferably, the specific surface area of the MCM molecular sieve encapsulated with nano-metal particles is 910-990 m2 / g, and / or the size of nano metal particles can be controlled between 5-25nm.

[0031] Preferably, when the metal particle is Fe, the XPS of the Fe atom is 706 eV; when the metal particle is Co, the XPS of the Co atom is 778 eV; when the metal particle is Ni, the XPS of the Ni atom is 852 eV.

[0032] In a third aspect, the present invention provides a method for preparing the MCM molecular sieve encapsulating nano-metal particles or a use of the MCM molecular sieve encapsulating nano-metal particles in adsorbing arsenic in water.

[0033] The present invention has the following advantages:

[0034] In the preparation method of the present invention, the MCM molecular sieve raw powder is passivated to allow the alkaline substance to be directed into the interior of the molecular sieve, forming a porous and macroporous structure without destroying the external structure of the molecular sieve. The metal is then embedded in the molecular sieve pores, and the alkali-etched structure is crystallized and encapsulated by crystallization to produce an MCM molecular sieve encapsulated with nano-metal particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the HRTEM image of the Fe@MCM-41 molecular sieve obtained in Example 1;

[0036] Figure 2 This is the low-angle XRD pattern of the Fe@MCM-41 molecular sieve obtained in Example 3;

[0037] Figure 3 This is the HRTEM image of the Fe@MCM-41 molecular sieve obtained in Example 3;

[0038] Figure 4 This is the XPS graph of Fe@MCM-41 molecular sieve obtained in Example 3;

[0039] Figure 5 This is the HRTEM image of the Fe@MCM-41 molecular sieve obtained in Example 4. DETAILED DESCRIPTION

[0040] The present invention will be further explained below with reference to specific embodiments.

[0041] The present invention is described in detail through the following examples, which can enable those skilled in the art to have a more comprehensive understanding of the present invention. However, these examples do not limit the scope of the present invention in any way. In the examples, XRD uses Philips' X-Pert series X-ray diffractometer to determine the structure of the molecular sieve, HRTEM uses Rigku's Jem-3010 high-resolution transmission electron microscope to determine the regularity of the molecular sieve, XPS uses Thermo's ESCALAB 250 spectrometer X-ray photoelectron spectrometer to determine the bonding of metal particles, and BET uses Micromeritics' ASAP2020 fully automatic specific surface analyzer to determine. In the present invention, the silicon source is measured as SiO2, the iron source is measured as Fe, the cobalt source is measured as Co, the nickel source is measured as Ni, and the alkali is measured as OH. - The solvent is calculated as H2O, and the organic template is calculated as R.

[0042] Example 1

[0043] Take 5.0g of pure silicon MCM-41 molecular sieve powder and 2.1g of trimethylchlorosilane and stir them at 50°C for 2h. Then mix the product with 0.4g of 1% sodium hydroxide solution and stir it at room temperature for 1h. Then filter and wash the product to obtain solution D. Add 2.0g of potassium ferrocyanide to obtain solution A.

[0044] 4.4 g of hexadecyltrimethylammonium bromide (CTAB) and 38.9 g of deionized water were added to the reactor in sequence, stirred evenly, and 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise to obtain a reaction mixture with a molar ratio of SiO2: 90 H2O: 0.5 R: 5 OH. - Finally, 4.8g NaOH was added to adjust the pH of the solution to 11-13, which is solution B. B and A were mixed and transferred to a crystallization kettle, heated to 110°C, and crystallized at a constant temperature for 72 hours. After the crystallization is complete, the temperature is lowered to room temperature, the reaction mixture is separated, washed, and dried at 110°C, and finally calcined at 400°C for 8 hours to obtain the Fe@MCM-41 molecular sieve raw powder. The specific surface area of the product obtained by BET analysis of the sample is shown in Table 1, and the high-magnification transmission electron microscope image of the sample is shown in Figure 1 The obtained samples were used for arsenic adsorption experiments, and the results are shown in Table 1.

[0045] For the arsenic adsorption test, 1.0g of Fe@MCM-41 molecular sieve was dispersed in 50mL of distilled water. After adjusting the pH to 7.5, a 10mg / L arsenic stock solution was added to create a molecular sieve suspension. The pH was then adjusted with NaOH and HCl to maintain a constant value. After 24 hours of adsorption, a certain amount of the suspension was centrifuged for 10 minutes. The supernatant was removed, filtered, and sealed for storage until further analysis. Arsenic concentrations in the liquid phase were determined using an atomic fluorescence spectrometer with a detection limit of 0.1μg / L. All glassware in the experiment was rinsed and then soaked in 1% HNO3 for at least 12 hours before being rinsed with distilled water.

[0046] Example 2

[0047] The operation is basically the same as that 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 ° C, the passivation time is changed to 3 h, the mass fraction of the sodium hydroxide solution is changed to 2%, the amount is 0.3 g, the template agent is changed to hexadecyltrimethylammonium chloride (CTAC), the amount is 1.8 g, the amount of water is changed to 20.3 g, the silicon source is changed to sodium silicate, the amount is 4 g, the amount of NaOH is changed to 3.4 g, the Fe source complex is changed to a complex of ferric nitrate and ethylenediaminetetraacetic acid (wherein the molar ratio of ferric nitrate to ethylenediaminetetraacetic acid is 1:1), the amount is 1.5 g, the crystallization temperature is changed to 120 ° C, the crystallization time is changed to 80 h, the drying temperature is changed to 120 ° C, the calcination temperature is changed to 500 ° C, the calcination time is changed to 6 h, the other components and synthesis conditions remain unchanged, and the molar ratio of the reaction mixture obtained is SiO2: 80H2O: 0.4R: 6OH - The obtained samples were used for arsenic adsorption experiments. The results are shown in Table 1. The specific surface areas of the products obtained by BET analysis of the samples are shown in Table 1.

[0048] Example 3

[0049] The operation is basically the same as that in Example 1, the only difference is that the passivating agent is changed to diphenyldichlorosilane, the amount is changed to 1.25 g, the passivation temperature is changed to 70 ° C, the passivation time is changed to 4 h, the mass fraction of the 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 hexadecyltrimethylammonium chloride (CTAC), the amount is 1.4 g, the amount of water is changed to 25.9 g, the amount of TEOS is changed to 3 g, the alkali source is changed to ammonia water, the amount is 2.0 g, the Fe source complex is changed to potassium ferrocyanide, the amount is 1.0 g, the crystallization temperature is changed to 130 ° C, the crystallization time is changed to 90 h, the drying temperature is changed to 130 ° C, the calcination temperature is changed to 550 ° C, the calcination time is changed to 7 h, and the other components and synthesis conditions remain unchanged. The molar ratio of the reaction mixture obtained is SiO2: 100H2O: 0.3R: 4OH - The small angle powder XRD diffraction of the sample is shown in Figure 2, high magnification transmission electron microscopy images are shown in Figure 3 , the state of iron atoms in the molecular sieve is analyzed by XPS Figure 4 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.

[0050] Example 4

[0051] The operation is basically the same as that of Example 3, except that the mass fraction of the sodium hydroxide solution is changed to 4%, and the other components and synthesis conditions remain unchanged. 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 Figure 5 The obtained samples were used for arsenic adsorption experiments, and the results are shown in Table 1.

[0052] Example 5

[0053] Take 5.0g of pure silicon MCM-41 molecular sieve powder and 2.1g of trimethylchlorosilane and stir at 50°C for 2h, then mix the product with 0.4g of 1% sodium hydroxide solution and stir at room temperature for 1h. Then filter and wash the product to obtain solution D. Take 3.6g of cobalt nitrate and 20ml (1mol / L) ethylenediaminetetraacetic acid solution and mix them evenly for complexation. Then take 1.0g of the solution and add it to solution D to obtain solution A.

[0054] 4.4 g of hexadecyltrimethylammonium bromide (CTAB) and 38.9 g of deionized water were added to the reactor in sequence, stirred evenly, and 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise to obtain a reaction mixture with a molar ratio of SiO2: 90 H2O: 0.5 R: 5 OH. - Finally, 4.8g of NaOH was added to adjust the solution pH to 11-13, forming Solution B. Solution B and Solution A were mixed and transferred to a crystallization kettle. The temperature was raised to 110°C and crystallized at this constant temperature for 72 hours. After complete crystallization, the temperature was lowered to room temperature. The reaction mixture was separated, washed, and dried at 110°C. Finally, it was calcined at 400°C for 8 hours to obtain the Co@MCM-41 molecular sieve raw powder. The specific surface area of the product obtained by BET analysis is shown in Table 1. The resulting sample was used in arsenic adsorption experiments, and the results are shown in Table 1.

[0055] Example 6

[0056] Take 5.0g of pure silicon MCM-41 molecular sieve powder and 2.1g of trimethylchlorosilane and stir them at 50°C for 2h, then mix the product with 0.4g of 1% sodium hydroxide solution and stir at room temperature for 1h. Then filter and wash the product to obtain solution D. Take 3.6g of nickel nitrate and 20ml (1mol / L) of citric acid solution and mix them evenly for complexation. Then take 1.0g of the solution and add it to solution D to obtain solution A.

[0057] 4.4 g of hexadecyltrimethylammonium bromide (CTAB) and 38.9 g of deionized water were added to the reactor in sequence, stirred evenly, and 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise to obtain a reaction mixture with a molar ratio of SiO2: 90 H2O: 0.5 R: 5 OH. - Finally, 4.8g of NaOH was added to adjust the solution pH to 11-13, forming Solution B. Solution B and Solution A were mixed and transferred to a crystallization kettle. The temperature was raised to 110°C and crystallized at this constant temperature for 72 hours. After complete crystallization, the temperature was lowered to room temperature. The reaction mixture was separated, washed, and dried at 110°C. Finally, it was calcined at 400°C for 8 hours to obtain the Ni@MCM-41 molecular sieve raw powder. The specific surface area of the product obtained by BET analysis is shown in Table 1. The resulting sample was used in arsenic adsorption experiments, and the results are shown in Table 1.

[0058] Comparative Example 1

[0059] 4.4 g of hexadecyltrimethylammonium bromide (CTAB) and 38.9 g of deionized water were added to the reactor in sequence and stirred evenly. 2.0 g of potassium ferrocyanide was added and continued stirring. 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. The molar ratio of the reaction mixture was SiO2: 90 H2O: 0.5 R: 5 OH. - Finally, 4.8g of NaOH was added to adjust the pH of the solution to 11-13. The mixed solution was transferred to a crystallization kettle, heated to 110°C, and crystallized at this constant temperature for 72 hours. After complete crystallization, the temperature was lowered to room temperature. The reaction mixture was separated, washed, and dried at 110°C. Finally, it was calcined at 400°C for 8 hours to obtain the Fe-MCM-41 molecular sieve raw powder. The Fe-MCM-41 molecular sieve was placed at the bottom of a quartz tube and hydrogen was introduced. The temperature was raised to 400°C at a rate of 3° / min and maintained for 2 hours. The resulting Fe@MCM-41 molecular sieve was obtained. The specific surface area of the product obtained by BET analysis is shown in Table 1. The obtained sample was used in arsenic adsorption experiments, and the results are shown in Table 1.

[0060] Comparative Example 2

[0061] 4.4 g of hexadecyltrimethylammonium bromide (CTAB) and 38.9 g of deionized water were added to the reactor in sequence, stirred evenly, and 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise to obtain a reaction mixture with a molar ratio of SiO2: 90 H2O: 0.5 R: 5 OH. - Finally, 4.8g of NaOH was added to adjust the pH of the solution to 11-13. The mixed solution was transferred to a crystallization kettle, heated to 110°C, and crystallized at a constant temperature for 72 hours. After complete crystallization, the temperature was lowered to room temperature. The reaction mixture was separated, washed, and dried at 110°C. Finally, it was calcined at 400°C for 8 hours to obtain MCM-41 molecular sieve raw powder. MCM-41 molecular sieve, 2.0g of potassium ferrocyanide, and 50ml of deionized water were mixed uniformly. The reaction mixture was then separated, washed, and dried at 110°C. Finally, it was calcined at 400°C for 8 hours to obtain Fe / MCM-41 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.

[0062] Table 1 Arsenic adsorption experimental results

[0063] Adsorption rate (%) <![CDATA[Specific surface area (m 2 / g)]]> Example 1 88.1 912 Example 2 89.2 942 Example 3 90.7 989 Example 4 90.0 985 Example 5 88.9 930 Example 6 89.8 948 Comparative Example 1 29.6 382 Comparative Example 2 11.2 129

[0064] From Comparative Examples 1-2 and Example 1, Table 1 shows that in Comparative Example 1, Fe@MCM-41 is prepared by the in-situ constraint method. The process of this method is quite simple and convenient. It only requires the use of H2 reduction to pull the metal out of the skeleton. However, this method will force the metal particles in the skeleton to be pulled out of the skeleton, thereby destroying the skeleton structure of the molecular sieve. Secondly, the metal particles precipitated from the skeleton will be larger than the pores, thereby having a certain destructive effect on the structure of the pores. Therefore, the overall structure of the molecular sieve will be greatly changed. Therefore, the catalytic performance of the catalyst obtained by this method is low. Comparative Example 2 adopts a post-synthesis strategy method, which is basically the same as the ordinary loading method. The metal particles are ultimately loaded on the surface of the molecular sieve in the form of oxides, which will cause the overall loss of metal particles during the reaction, thereby affecting the performance of the catalyst.

[0065] Depend on Figure 2 It can be seen that the Fe@MCM-41 molecular sieve obtained by the method provided by the present invention still has the characteristic peak of high regularity of MCM-41 molecular sieve in small-angle XRD, indicating that the modification of metal particles does not destroy the structure of the molecular sieve itself; Figure 3 and Figure 4 It can be seen that the iron atoms in the Fe@MCM-41 molecular sieve obtained by the method provided by the present invention are in the form of single substance ( Figure 4It exists in the form of iron element Fe2p3 / 2 orbital (706.5eV), and it can be clearly seen in the electron microscope image that the size of the metal element particles is about 5nm.

[0066] Depend on Figure 1 、 Figure 3 and Figure 5 It can be seen that by changing the amount of alkali, the size of nano-metal particles can be controlled at any time, and the size of the metal particles varies from 5-25nm.

[0067] As can be seen from Table 1, as the size of the nano-metal particles increases, the catalytic activity becomes better and better. However, when the nano-metal particles are too large, although the structure of the molecular sieve itself will not be destroyed, the alkali etching will increase the interconnectivity of the internal pores of the molecular sieve, causing the strength of the molecular sieve itself to decrease, and thus the catalytic performance will decrease to a certain extent.

[0068] In summary, according to the method of the present invention, the molecular sieve prepared is first protected by a passivating agent to protect the silicon hydroxyl groups on the outside of the molecular sieve. The alkaline substance will enter the molecular sieve pores and etch from the inside without etching and damaging the outer surface of the molecular sieve. The two independent pore structures of the internal molecular sieve are interconnected due to the etching of the alkaline substance to form new macropore and mesoporous structures. The size of the internal pore structure of the molecular sieve is adjusted according to the concentration and amount of the alkaline substance. Subsequently, nano-metal particles are introduced into the molecular sieve pores. Due to the confinement effect of the molecular sieve pore structure, the nano-metal particles will not exceed the size of the molecular sieve pores and destroy the internal structure of the molecular sieve. Finally, the internal etched pores are re-encapsulated by secondary crystallization to completely encapsulate the nano-metal particles in the molecular sieve pores.

[0069] Compared with conventional post-treatment methods, which can only load most of the nano-metal particles on the outer surface of the molecular sieve, and because the nano-metal particles are exposed to the outside, they will continue to agglomerate or even lose after high-temperature treatment, resulting in a decrease in catalytic effect. Compared with the conventional one-step hydrothermal synthesis, the one-step method is simpler, but it must be reduced to a metal elemental state. However, the nano-metal particles after reduction are much larger than the pores of the molecular sieve itself, so it is bound to cause the internal structure of the molecular sieve to be partially enlarged and damaged, resulting in a decrease in catalytic performance.

[0070] Any numerical value mentioned in the present invention includes all values that increase by one unit each time from the lowest value to the highest value if there is only a gap of two units between any minimum value and any maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, time, etc. is stated to be 50-90, it is meant in this specification to specifically list values such as 51-89, 52-88... and 69-71 and 70-71. For non-integer values, it is appropriate to consider units of 0.1, 0.01, 0.001 or 0.0001. These are just some special examples. In this application, in a similar manner, all possible combinations of numerical values between the listed lowest value and the listed highest value are considered to have been disclosed.

[0071] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation of 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 words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. 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 MCM molecular sieves encapsulated with nano-metal particles, characterized in that: The following steps are involved: S1: passivating the MCM molecular sieve raw powder to obtain the passivated MCM molecular sieve powder; S2: adding an alkaline solution to the MCM molecular sieve powder after the passivation treatment in step S1 to obtain an MCM molecular sieve powder intermediate; S3: adding a metal complex solution to the MCM 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 atoms; S4: uniformly mixing the organic template, water, silicon source and alkali source into a gel to obtain product B; S5: mixing the product A obtained in step S3 and the product B obtained in step S4, and performing crystallization treatment, washing, drying and roasting to obtain the target product; Step S1 includes: mixing the MCM molecular sieve raw powder with a passivating agent and performing a passivation treatment under stirring. The passivating agent in step S1 includes a general formula R a R b R c SiR d The organosilane shown, wherein R a 、R b 、R c and R d The same or different, independently selected from hydrogen, halogen, C1-C 20 Alkyl, C1-C 20 Alkoxy, C3-C 20 Cycloalkyl, C6-C 20 Aryl and C1-C 20 Any one of the halogenated alkyl groups, and R a 、R b 、R c and R d It is not hydrogen and / or halogen at the same time.

2. The method for preparing MCM molecular sieve encapsulated with nano-metal particles according to claim 1, characterized in that: The conditions of the passivation treatment are as follows: temperature is 50-80° C., and time is 2-6 hours.

3. The method for preparing MCM molecular sieve encapsulated with nano-metal particles according to claim 1, characterized in that: In the general formula of the passivating agent in step S1, R d is halogen, R a 、R b and R c Not hydrogen or halogen at the same time.

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

10.

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

7. The method for preparing MCM molecular sieve encapsulated with nano-metal particles according to claim 6, characterized in that: The alkaline solution in step S2 is a sodium hydroxide solution with a mass fraction of 1%-5%.

8. The method for preparing MCM molecular sieve encapsulated with nano-metal particles according to claim 6, characterized in that: The mass ratio of the alkaline solution to the original MCM molecular sieve powder in step S2 is 1:20-1:

10.

9. The method for preparing the MCM molecular sieve encapsulated with nano-metal particles according to any one of claims 1 to 4, characterized in that: Step S5 includes: mixing the product A obtained in step S3 and the product B obtained in step S4, and crystallizing them at 110-140° C. for 72-108 hours, filtering, washing, drying and calcining the crystallized product to obtain the target product, which is recorded as M@MCM molecular sieve.

10. The method for preparing MCM molecular sieve encapsulated with nano-metal particles according to claim 9, characterized in that: The drying temperature in step S5 is 100-140°C.

11. The method for preparing MCM molecular sieve encapsulated with nano-metal particles according to claim 9, characterized in that: The calcination temperature in step S5 is 400-700° C., and the calcination time is 5-8 hours.

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

5.

13. The method for preparing MCM molecular sieve encapsulated with nano-metal particles according to claim 12, characterized in that: The metal complex is an iron source complex of at least one selected from potassium ferrocyanide and potassium ferrocyanide, or a complex of at least one selected from ferric nitrate and ferric chloride and ethylenediaminetetraacetic acid.

14. The method for preparing the MCM molecular sieve encapsulated with nano-metal particles according to any one of claims 1 to 4, characterized in that: In step S4, the organic template, water, silicon source and alkali source are uniformly mixed to form a gel, and the product B has SiO2: a H2O: b R: c OH - The invention relates to a method for preparing an aqueous solution of at least one of the following materials: wherein R is an organic template, a is 80-160, b is 0.1-0.7, and c is 2-7, and / or the organic template is one of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, or cetyltriethylammonium bromide, and / or the silicon source is one or more of white carbon black, ethyl orthosilicate, sodium silicate, or silica sol, and / or the alkali source is one or more of sodium hydroxide, tetramethylammonium hydroxide, or ammonia water; and / or the MCM is MCM-41.

15. An MCM molecular sieve encapsulated with nano-metal particles prepared by the preparation method according to any one of claims 1 to 14.

16. The molecular sieve according to claim 15, characterized in that The specific surface area of the MCM molecular sieve encapsulated with nano-metal particles is 910-990 m 2 / g, and / or the size of nano metal particles can be controlled between 5-25nm.

17. The molecular sieve according to claim 15 or 16, characterized in that In the MCM molecular sieve encapsulated with nano-metal particles, when the metal particles are Fe, the XPS of the Fe atom is 706 eV; when the metal particles are Co, the XPS of the Co atom is 778 eV; when the metal particles are Ni, the XPS of the Ni atom is 852 eV.

18. Use of the MCM molecular sieve encapsulated with nano-metal particles according to any one of claims 15 to 17 in adsorbing arsenic in water.

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