Mcm molecular sieve encapsulating nanometal atoms, method for preparing the same, and use thereof in preparing cyclohexanone and cyclohexanol

Abstract

The application discloses encapsulated nanometer metal atom MCM molecular sieve and a preparation method and application thereof in preparation of cyclohexanone and cyclohexanol. The encapsulated nanometer metal atom MCM molecular sieve, wherein the metal atom exists in the form of an element in the MCM molecular sieve. The preparation method of the encapsulated nanometer metal atom MCM molecular sieve comprises the following steps: 1) mixing MCM molecular sieve raw powder with a passivation agent to perform a first reaction, then mixing with an alkaline solution to perform a second reaction, filtering, washing, and mixing with a metal complex solution to obtain solution A; 2) mixing an organic template agent, water, a silicon source and an alkali source into glue to obtain solution B; 3) mixing the solution A with the solution B and performing hydrothermal crystallization, filtering, washing, drying and calcining. The catalyst has better catalytic performance. In the molecular sieve prepared by the method, the nanometer particles are in the molecular sieve channel, and the catalytic performance of the catalyst can be improved.

Description

Technical Field

[0001] The present invention relates to a preparation method of nanometer metal atoms encapsulated in MCM molecular sieve, the obtained MCM molecular sieve encapsulating nanometer metal atoms, and application of the MCM molecular sieve in the preparation of cyclohexanone and cyclohexanol. Background Art

[0002] MCM-41 and other M41S series molecular sieves possess large specific surface area, pore volume, and uniform pore size. The emergence of M41S mesoporous materials has not only broadened the application range of molecular sieves but also addressed the shortcomings 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 centers to enhance their catalytic activity. Among these heteroatoms, vanadium and titanium atoms, as variable-valence metals, exhibit excellent catalytic performance in redox reactions, particularly in the selective oxidation of cyclohexane to cyclohexanone and cyclohexanol. The activity of vanadium catalysts is directly related to the vanadium content and binding state.

[0003] Metal nanoparticle 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 metal nanoparticle stability, 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 metal nanoparticles 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 metal nanoparticles after the zeolite structure is constructed. In contrast, the in-situ confinement method requires the co-crystallization of zeolite and metal precursor, and obtains metal nanoparticles by in situ reduction.

[0004] In situ confinement method is that metal nanoparticles or precursors can be introduced into the interior of the molecular sieve crystal by one-step hydrothermal synthesis method. The method first mixes the synthesized metal nanoparticles or soluble metal precursors with the synthesis gel of the molecular sieve, and then performs high-temperature crystallization. The synthesized product is further calcined to remove organic matter, and is reduced by a reducing agent to generate metal nanoparticles. This method is simple and effective, but because the metal particles are larger than the molecular sieve channels, the reduced metal will expand the pore structure of the molecular sieve during reduction, causing the structure of the molecular sieve itself to be destroyed and thus reducing the catalytic effect of the catalyst. The post-synthesis method is widely used because it does not limit the type of molecular sieve framework. By impregnating the molecular sieve carrier in the metal colloid or soluble metal precursor, the metal nanoparticles can enter the channels in the interior of the molecular sieve. However, most of the metal nanoparticles are actually on the surface of the molecular sieve, and only a small part can enter the channels of the molecular sieve, so that the catalytic effect of the metal nanoparticles cannot be fully exerted. SUMMARY

[0005] In view of the above problems existing in the prior art, the present application provides a new preparation method of MCM molecular sieve encapsulating nanometer metal atoms, in which the nanometer particles are in the channels of the molecular sieve, thereby improving the catalytic performance of the catalyst. Specifically, in the method, the silicon hydroxyl groups on the outer surface of the MCM-41 molecular sieve are passivated by using a passivating agent. The outer surface after the passivation treatment will not undergo desilication reaction under the action of the alkaline substance, thereby protecting the outer surface of the MCM-41 molecular sieve. Then, the alkaline substance causes desilication reaction in the interior of the channels of the molecular sieve, forming new mesoporous and macroporous channels. Then, the metal particles are embedded into the channels of the molecular sieve, and the size of the metal nanoparticles is adjusted according to the size of the channels of the molecular sieve. Finally, the outer channels etched by the alkaline substance are encapsulated by secondary crystallization, so that the confinement effect in the channels of the molecular sieve is utilized without agglomeration.

[0006] The first aspect of the present application provides an MCM molecular sieve encapsulating nanometer metal atoms, wherein the metal atoms exist in the MCM molecular sieve in the form of an element.

[0007] In the present application, for example but not limited to, it can be proved that the metal atoms exist in the MCM molecular sieve only in the form of an element and not in the form of an oxide by XPS determination, the XPS of vanadium atoms is 512 eV, and the XPS of titanium atoms is 454 eV. Moreover, they exist only in the interior of the MCM molecular sieve and not on the surface of the MCM molecular sieve. If they exist in the form of an oxide or on the surface of the MCM molecular sieve, the XPS of vanadium atoms is 524.5 eV, and the XPS of titanium atoms is 458.5 eV.

[0008] According to some embodiments of the molecular sieve of the present invention, preferably, the metal atom is a vanadium atom and / or a titanium atom.

[0009] According to some embodiments of the molecular sieve of the present invention, preferably, when the metal atom is a vanadium atom, the XPS of the vanadium atom is 512 eV.

[0010] According to some embodiments of the molecular sieve of the present invention, preferably, when the metal atom is a titanium atom, the XPS of the titanium atom is 454 eV.

[0011] According to some embodiments of the molecular sieve of the present invention, preferably, the MCM is MCM-41, and the MCM molecular sieve encapsulating nano-metal atoms is denoted as M@MCM-41.

[0012] According to some embodiments of the molecular sieve of the present invention, preferably, the specific surface area of ​​the M@MCM-41 is 910-990 m 2 The MCM molecular sieve encapsulated with nano-metal atoms of the present invention has a larger specific surface area, thereby improving the conversion rate and selectivity.

[0013] According to some embodiments of the molecular sieve of the present invention, preferably, the size of the metal nanoparticles in the M@MCM-41 can be controlled to be 5 to 25 nm.

[0014] The second aspect of the present invention provides a method for preparing nano-metal atoms (M) encapsulated in MCM molecular sieves, comprising the following steps:

[0015] 1) Mixing MCM molecular sieve raw powder with a passivating agent for a first reaction, then mixing with an alkaline solution for a second reaction, filtering, washing, and mixing with a metal complex solution to obtain solution A;

[0016] 2) mixing an organic template, water, a silicon source, and an alkali source into a gel to obtain a solution B;

[0017] 3) mixing the solution A and the solution B and performing hydrothermal crystallization, filtering, washing, drying and calcining.

[0018] According to some embodiments of the preparation method of the present invention, preferably, the MCM molecular sieve is MCM-41 molecular sieve.

[0019] According to some embodiments of the preparation method of the present invention, preferably, the passivating agent comprises a general formula R a R b R c SiR d The organosilane shown, wherein R a 、R b 、Rc and R d are each independently selected from any one of hydrogen, halogen, C1-C 20 alkyl, C1-C 20 alkoxy, C3-C 20 cycloalkyl, C6-C 20 aryl and C1-C 20 haloalkyl, and R a , R b , R c and R d are not simultaneously hydrogen and / or halogen; preferably, R d is halogen, R a , R b and R c are not simultaneously hydrogen and / or halogen; the passivating agent is further preferably selected from at least one of diphenyldichlorosilane, trimethylchlorosilane and dimethyldichlorosilane.

[0020] According to some embodiments of the preparation method of the present application, preferably, the weight ratio of the passivating agent to the raw MCM molecular sieve is 4:5-1:10, preferably 3:5-1:10, further preferably 3:7-1:9.

[0021] According to some embodiments of the preparation method of the present application, preferably, the content of the base in the alkaline solution is 1-5% by weight.

[0022] According to some embodiments of the preparation method of the present application, preferably, the alkaline solution is a sodium hydroxide solution.

[0023] According to some embodiments of the preparation method of the present application, preferably, the weight ratio of the alkaline solution to the raw MCM molecular sieve is 1:20-1:10, preferably 3:50-2:25.

[0024] According to some embodiments of the preparation method of the present application, preferably, the metal complex solution comprises a metal atom source and a solution capable of complexing with the metal atom source, wherein the metal is vanadium and / or titanium, and the metal atom source is a vanadium-containing source oxalic acid solution and / or a titanium source.

[0025] According to some embodiments of the preparation method of the present application, preferably, the vanadium source is selected from at least one of ammonium metavanadate, sodium orthovanadate and sodium pyrovanadate.

[0026] According to some embodiments of the preparation method of the present application, preferably, the molar ratio of oxalic acid to the vanadium source is greater than 2. For example, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 10:1, 20:1, 50:1, etc.

[0027] According to some embodiments of the preparation method of the present application, preferably, the titanium source is selected from at least one of tetrabutyl titanate, titanium tetrachloride and titanium sulfate.

[0028] According to some embodiments of the preparation method of the present application, preferably, the solution capable of complexing with the metal atom source is selected from at least one of citric acid, tartaric acid and triethanol.

[0029] According to some embodiments of the preparation method of the present application, preferably, the content of the metal atom source in the metal complex solution is not more than 8% by weight.

[0030] According to some embodiments of the preparation method of the present application, preferably, the weight ratio of the metal complex solution to the original powder of molecular sieve is 0.5-1:5.

[0031] According to some embodiments of the preparation method of the present application, preferably, the conditions of the first reaction include: temperature of 50-80°C, preferably 60-70°C; time of 2-6h, preferably 3-5h.

[0032] According to some embodiments of the preparation method of the present application, preferably, the conditions of the second reaction include: temperature of 20-40°C, time of 1-2h.

[0033] According to some embodiments of the preparation method of the present application, preferably, the organic template agent is selected from at least one of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride and cetyltriethylammonium bromide. Preferably, cetyltrimethylammonium chloride.

[0034] According to some embodiments of the preparation method of the present application, preferably, the silicon source is selected from at least one of white carbon black, tetraethyl orthosilicate, sodium silicate and silica sol. Preferably, tetraethyl orthosilicate.

[0035] According to some embodiments of the preparation method of the present application, preferably, the alkali source is selected from at least one of sodium hydroxide, tetramethylammonium hydroxide and ammonia. Preferably, ammonia.

[0036] According to some embodiments of the preparation method of the present application, preferably, the solution B satisfies SiO2:a H2O:b R:c OH - , in which R is an organic template agent, the value of a is 80-160, preferably 100-140; the value of b is 0.1-0.7, preferably 0.2-0.5; the value of c is 2-7, preferably 4-5. In the present application, the silicon source is calculated as SiO2, the vanadium source is calculated as V, the titanium source is calculated as Ti, the alkali is calculated as OH - , the solvent is calculated as H2O, and the organic template agent is calculated as R.

[0037] According to some embodiments of the preparation method, preferably, the conditions of the hydrothermal crystallization include: temperature of 110-140℃, preferably 120-130℃; time of 72-108h, preferably 84-100h.

[0038] According to some embodiments of the preparation method, preferably, the conditions of the drying include: temperature of 100-140℃, preferably 110-130℃; time of 4-6h. Through drying, the water and organic template on the surface of the molecular sieve are removed.

[0039] According to some embodiments of the preparation method, preferably, the conditions of the calcination include: temperature of 400-700℃, preferably 500-600℃; calcination time of 5-8h. Through calcination, the organic template and water in the pores of the molecular sieve are removed, and the strength of the molecular sieve framework is increased, etc.

[0040] According to some embodiments of the preparation method, preferably, the preparation method of the MCM molecular sieve encapsulating nano metal atoms (M) includes but is not limited to the following steps:

[0041] (1) stirring the MCM-41 molecular sieve powder with a passivation agent at a certain temperature for a period of time, then adding an alkaline solution to the obtained product, reacting at room temperature for a period of time, then filtering and washing the product, and then mixing the washed product with a metal complex solution to obtain A;

[0042] (2) uniformly mixing an organic template, water, a silicon source and an alkali into a gel, and the molar ratio of the obtained reaction mixture is SiO2:a H2O:b R:c OH - , wherein R is an organic template, the value of a is 80-160, the value of b is 0.1-0.7, and the value of c is 2-7, and the mixed solution is B;

[0043] (3) adding B to A and hydrothermally crystallizing at a certain crystallization temperature for a period of time, filtering, washing, drying and calcining the product to obtain M@MCM-41 molecular sieve.

[0044] The third aspect of the present application provides a MCM molecular sieve encapsulating nano metal atoms prepared by the above preparation method, and the metal atoms exist in the MCM molecular sieve in the form of an element.

[0045] M@MCM refers to a MCM molecular sieve encapsulating nano metal atoms M.

[0046] In the present application, for example but not limited to, XPS of vanadium atom is 512eV and XPS of titanium atom is 454eV, which can prove that the metal atoms exist only in the form of simple substance in the MCM molecular sieve, and do not exist in the form of oxide. Moreover, they exist only in the interior of the MCM molecular sieve, and do not exist on the surface of the MCM molecular sieve. If the oxide form exists or exists on the surface of the MCM molecular sieve, XPS of vanadium atom is 524.5eV and XPS of titanium atom is 458.5eV.

[0047] According to some embodiments of the molecular sieve of the present application, preferably, when the metal atom is a vanadium atom, XPS of the vanadium atom is 512eV.

[0048] According to some embodiments of the molecular sieve of the present application, preferably, when the metal atom is a titanium atom, XPS of the titanium atom is 454eV.

[0049] According to some embodiments of the molecular sieve of the present application, preferably, the MCM is MCM-41, and the MCM molecular sieve encapsulating the nanometal atom is denoted as M@MCM-41.

[0050] According to some embodiments of the molecular sieve of the present application, preferably, the M@MCM-41 has a specific surface area of 910-990m 2 / g. The MCM molecular sieve encapsulating the nanometal atom of the present application has a larger specific surface area, thereby being capable of improving conversion rate and selectivity.

[0051] According to some embodiments of the molecular sieve of the present application, preferably, the metal nanoparticle size in the M@MCM-41 can be controlled in the range of 5-25nm.

[0052] The fourth aspect of the present application provides the use of the MCM molecular sieve encapsulating the nanometal atom prepared by the above method or the above MCM molecular sieve encapsulating the nanometal atom in the preparation of cyclohexanone and cyclohexanol by selective oxidation of cyclohexane.

[0053] The present application has the following beneficial effects:

[0054] The present application firstly protects the silicon hydroxyl outside the molecular sieve by using a passivation agent, the alkaline substance can enter the molecular sieve channel to etch from the inside without etching and damaging the outer surface of the molecular sieve, the two independent channel structures of the internal molecular sieve are connected to form new macropore and mesopore structures due to the etching of the alkaline substance, the size of the internal channel structure of the molecular sieve is adjusted according to the concentration and amount of the alkaline substance, then the metal nanoparticles are introduced into the molecular sieve channel, due to the confinement effect of the molecular sieve channel structure, the metal nanoparticles will not exceed the size of the molecular sieve channel to damage the internal structure of the molecular sieve, finally the etched channel inside is re-encapsulated by using secondary crystallization, and the metal nanoparticles are completely encapsulated in the molecular sieve channel. Compared with the conventional post-treatment method, most of the metal nanoparticles can be loaded on the outer surface of the molecular sieve by the post-treatment method, and due to the exposure of the metal nanoparticles, the metal nanoparticles will continue to agglomerate and even be lost after high-temperature treatment, thereby causing the decline of the catalytic effect. Compared with the conventional one-step hydrothermal synthesis method, the one-step method is simple, but the nanoparticles must be reduced to metal single state by reduction, and the specific surface area of the metal nanoparticles after reduction is much larger than the channel of the molecular sieve itself, so it is inevitable that a part of the internal structure of the molecular sieve channel will be expanded and damaged, thereby causing the decline of the catalytic performance of the catalyst. Therefore, the method of the present application can effectively solve the problems existing in the prior art and improve the catalytic performance of the catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 HRTEM diagram of V@MCM-41 molecular sieve obtained in Example 1 of the present application;

[0056] Figure 2 Small-angle XRD diagram of V@MCM-41 molecular sieve obtained in Example 3 of the present application;

[0057] Figure 3 HRTEM diagram of V@MCM-41 molecular sieve obtained in Example 3 of the present application;

[0058] Figure 4 XPS diagram of V@MCM-41 molecular sieve obtained in Example 3 of the present application;

[0059] Figure 5 HRTEM diagram of V@MCM-41 molecular sieve obtained in Example 4 of the present application;

[0060] Figure 6 XPS diagram of Ti@MCM-41 molecular sieve obtained in Example 5 of the present application. DETAILED DESCRIPTION

[0061] In order to make the present application easier to understand, the present application will be described in detail below in conjunction with examples, which only serve to illustrate the present application and are not limited to the scope of application of the present application.

[0062] The test method of the present application and the equipment used in the test are as follows:

[0063] (1) The XRD is determined by using the X-Pert series X-ray diffractometer of Philips Company to determine the structure of the molecular sieve.

[0064] (2) The HRTEM is determined by using the Jem-3010 type high-resolution transmission electron microscope of Rigku Company to determine the regularity of the molecular sieve.

[0065] (3) The XPS is determined by using the ESCALAB 250 spectrometer type X-ray photoelectron spectrometer of Thermo Company to determine the bonding of the metal particles.

[0066] (4) The BET is determined by using the ASAP2020 type full-automatic specific surface analyzer of Micromeritics Company.

[0067] The silicon source is calculated as SiO2, the vanadium source is calculated as V, the titanium source is calculated as Ti, the base is calculated as OH - , the solvent is calculated as H2O, and the organic template agent is calculated as R.

[0068]

Example 1

[0069] 5.0 g of MCM-41 molecular sieve raw powder is stirred with 2.1 g of trimethylsilyl chloride at 50℃ for 2h, then the product is mixed with 0.4 g of 1wt% sodium hydroxide solution uniformly, and stirred at room temperature for 1h, then the product is filtered and washed, which is solution D. 2g of ammonium metavanadate and 2.5g of oxalic acid are fully stirred to a blue clear solution, then 4.8g of tartaric acid is added, which is solution C. 1.0g of solution C is taken out and added to D and mixed uniformly to obtain solution A.

[0070] 4.4g of cetyltrimethylammonium bromide (CTAB) and 38.9g of deionized water are sequentially added to the reactor and stirred uniformly, 5g of tetraethyl orthosilicate (TEOS) is slowly added dropwise, 4.8g of NaOH is added to adjust the pH of the solution to 11-13, which is solution B. The molar ratio of the obtained reaction mixture is SiO2:90H2O:0.5R:5OH - After mixing B and A, it is transferred to the crystallization kettle, heated to 110℃, and crystallized at constant temperature for 72h. After the crystallization is completed, the temperature is reduced to room temperature, the reacted mixture is separated, washed, and dried at 110℃. Finally, after calcination at 400℃ for 8h, the V@MCM-41 molecular sieve is obtained. The high-magnification transmission electron microscope image of the sample is shown in Figure 1 , and the specific surface area of the product obtained by BET analysis is shown in Table 1.

[0071] Example 2

[0072] The difference from Example 1 is that the passivator 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 weight fraction of sodium hydroxide solution is changed to 2 wt%, the amount is 0.3 g, the template agent is changed to cetyltrimethylammonium 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 amount of vanadium source complex solution C is changed to 0.5 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, and the rest of the components and synthesis conditions remain unchanged. The molar ratio of the obtained reaction mixture is Si02:80H20:0.4R:6OH - The specific surface area of the product obtained by BET analysis of the sample is shown in Table 1.

[0073] Example 3

[0074] The difference from Example 1 is that the passivator 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 weight fraction of sodium hydroxide solution is changed to 3 wt%, the amount is 0.35 g, the reaction time is changed to 2 h, the template agent is changed to cetyltrimethylammonium 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 base source is changed to ammonia water, the amount is 2.0 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 rest of the components and synthesis conditions remain unchanged. The molar ratio of the obtained reaction mixture is Si02:100H20:0.3R:4OH - The small-angle powder XRD diffraction of the sample is shown in Figure 2 The high-magnification transmission electron micrograph of the sample is shown in Figure 3 The XPS analysis of the state of vanadium atoms in the molecular sieve is shown in Figure 4 The specific surface area of the product obtained by BET analysis of the sample is shown in Table 1.

[0075] Example 4

[0076] The difference from Example 3 is that the weight fraction of sodium hydroxide solution is changed to 4 wt%, and the rest of the components and synthesis conditions remain unchanged. The high-magnification transmission electron micrograph of the sample is shown in Figure 5 The specific surface area of the product obtained by BET analysis of the sample is shown in Table 1.

[0077] Example 5

[0078] Take 5.0 g MCM-41 molecular sieve powder and 2.1 g trimethyl chlorosilane under the condition of 50 °C stirring for 2 h, then mix the product with 0.4 g 1 wt% sodium hydroxide solution uniformly and stir for 1 h at room temperature, then filter and wash the product, which is solution D. Add 2 g tetrabutyl titanate to it and mix uniformly, which is solution A.

[0079] Add 4.4 g cetyltrimethylammonium bromide (CTAB) and 38.9 g deionized water into the reactor in turn, stir uniformly, slowly add 5 g tetraethyl orthosilicate (TEOS) drop by drop, add 4.8 g NaOH to adjust the solution pH to 11-13, which is solution B. The molar ratio of the obtained reaction mixture is SiO2:90H2O:0.5R:5OH - After mixing B and A, transfer to the crystallization kettle, heat to 110 °C, and keep constant temperature for 72 h. After complete crystallization, when the temperature drops to room temperature, separate, wash and dry the reacted mixture at 110 °C, and finally calcine at 400 °C for 8 h to obtain Ti@MCM-41 molecular sieve. The specific surface area of the product obtained by BET analysis is shown in Table 1. The state analysis of titanium atoms in the molecular sieve is XPS Figure 6 .

[0080]

Example 6

[0081] The difference from Example 5 is that the passivator is changed to diphenyldichlorosilane, the amount is changed to 0.56 g, the passivation temperature is changed to 70 °C, the passivation time is changed to 5 h, the weight fraction of sodium hydroxide solution is changed to 3 wt%, the amount is changed to 0.3 g, the amount of tetrabutyl titanate is changed to 3 g, the reaction time is changed to 2 h, the template agent is changed to cetyltriethylammonium bromide, the amount is changed to 0.7 g, the amount of water is changed to 19.5 g, the silicon source is changed to silica sol (JN-25, silica content is 25 wt%), the amount is changed to 2 g, the alkali source is changed to tetramethylammonium hydroxide, the amount is changed to 1.5 g, the crystallization temperature is changed to 140 °C, the crystallization time is changed to 100 h, the drying temperature is changed to 140 °C, the calcination temperature is changed to 600 °C, and the calcination time is changed to 5 h. The rest of the components and synthesis conditions remain unchanged. The molar ratio of the obtained reaction mixture is SiO2:130H2O:0.2R:2OH - The specific surface area of the product obtained by BET analysis is shown in Table 1.

[0082]

Comparative Example 1

[0083] Mix 2 g ammonium metavanadate and 2.5 g oxalic acid to a blue clear solution, then add 4.8 g tartaric acid, which is solution C;

[0084] Into the reactor, 4.4 g of cetyltrimethylammonium bromide (CTAB) and 38.9 g of deionized water were sequentially added and stirred until uniform, 1.0 g of solution C was removed and added thereto and mixed until uniform, stirring was continued, 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise, 4.8 g of NaOH was added to adjust the pH of the solution to 11-13, and the molar ratio of the resulting reaction mixture was SiO2:90H2O:0.5R:5OH - The mixed solution was transferred to a crystallization kettle, warmed to 110°C, and held at constant temperature for crystallization for 72 h. After crystallization was complete, the temperature was allowed to drop to room temperature, the reacted mixture was separated, washed, and dried at 110°C, and finally calcined at 400°C for 8 h to obtain V-MCM-41 molecular sieve. The V-MCM-41 molecular sieve was placed at the bottom of a quartz tube and hydrogen was introduced, the temperature was increased to 400°C at a rate of 3° / min and held for 2 h, and finally V@MCM-41 molecular sieve was obtained. The specific surface area of the product obtained by BET analysis is shown in Table 1.

[0085]

Comparative Example 2

[0086] 2 g of ammonium metavanadate and 2.5 g of oxalic acid were stirred until uniform to form a blue clear solution, and then 4.8 g of tartaric acid was added to form solution C;

[0087] Into the reactor, 4.4 g of cetyltrimethylammonium bromide (CTAB) and 38.9 g of deionized water were sequentially added and stirred until uniform, 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise, 4.8 g of NaOH was added to adjust the pH of the solution to 11-13, and the molar ratio of the resulting reaction mixture was SiO2:90H2O:0.5R:5OH - The mixed solution was transferred to a crystallization kettle, warmed to 110°C, and held at constant temperature for crystallization for 72 h. After crystallization was complete, the temperature was allowed to drop to room temperature, the reacted mixture was separated, washed, and dried at 110°C, and finally calcined at 400°C for 8 h to obtain V-MCM-41 molecular sieve. The V-MCM-41 molecular sieve was placed at the bottom of a quartz tube and hydrogen was introduced, the temperature was increased to 400°C at a rate of 3° / min and held for 2 h, and finally V@MCM-41 molecular sieve was obtained. The specific surface area of the product obtained by BET analysis is shown in Table 1.

[0088]

Comparative Example 3

[0089] Take 5.0 g of MCM-41 molecular sieve raw powder and 0.4 g of 1 wt% sodium hydroxide solution, mix well, and stir at room temperature for 1 h, then filter and wash the product to obtain solution D. Take 2 g of ammonium metavanadate and 2.5 g of oxalic acid, mix well to form a blue clear solution, then add 4.8 g of tartaric acid to form solution C. Take 1.0 g of solution C and add to solution D to obtain solution A.

[0090] Add 4.4 g of cetyltrimethylammonium bromide (CTAB) and 38.9 g of deionized water to the reactor in sequence, stir well, slowly add 5 g of tetraethyl orthosilicate (TEOS) drop by drop, and finally add 4.8 g of NaOH to adjust the pH of the solution to 11-13 to obtain solution B. The molar ratio of the obtained reaction mixture is SiO2:90H2O:0.5R:5OH. - After mixing B and A, transfer to the crystallization kettle, heat to 110°C, and crystallize at constant temperature for 72 h. After crystallization is complete, wait for the temperature to drop to room temperature, separate, wash, and dry at 110°C. Finally, calcine at 400°C for 8 h to obtain V / MCM-41 molecular sieve. The specific surface area of the product obtained by BET analysis is shown in Table 1.

[0091]

Test Example

[0092] The samples obtained in Examples 1-6 and Comparative Examples 1-3 were used in the experiment of selective oxidation of cyclohexane to prepare cyclohexanone and cyclohexanol, and the results are shown in Table 1.

[0093] The experiment of selective oxidation of cyclohexane to prepare cyclohexanone and cyclohexanol was carried out in a fixed bed microreactor (H200 mm x φ10 mm). The specific reaction process was as follows: 5.4 mL of cyclohexane, 1.5 g of catalyst, and 1.5 mL of H2O2 (cyclohexane:H2O2 = 1:1) were sequentially added to the fixed bed microreactor, and the reaction was carried out at 70°C for 7 h. After the reaction was completed, the liquid product was collected after cooling. The obtained product was analyzed by gas chromatography.

[0094] Table 1. Results of selective oxidation of cyclohexane to prepare cyclohexanone and cyclohexanol

[0095] Cyclohexane conversion (%) Cyclohexanol selectivity (%) Specific surface area (m 2 / g) Example 1 38.1 88.6 917 Example 2 40.4 92.8 955 Example 3 42.3 95.2 987 Example 4 45.9 94.0 978 Example 5 38.6 89.5 928 Example 6 41.5 94.1 979 Comparative Example 1 36.2 68.7 415 Comparative Example 2 14.3 32.9 290 Comparative Example 3 4.9 11.2 119

[0096] From Comparative Examples 1-2 and Example 1, Table 1 shows that in Comparative Example 1, V@MCM-41 is prepared by an in-situ constraint method. The process of this method is quite simple and convenient. It is only necessary to use H2 reduction to pull the metal out of the skeleton. However, this method will force the metal atoms in the skeleton to be pulled out of the skeleton, thereby destroying the skeleton structure of the molecular sieve. Secondly, the metal atoms precipitated from the skeleton will be larger than the pores, which will also have a certain destructive effect on the structure of the pores. Therefore, the overall structure of the molecular sieve will be greatly changed, so the catalytic performance of the catalyst obtained by this method is low; while Comparative Example 2 adopts a post-synthesis strategy method, which is basically the same as the ordinary loading method. The metal atoms are ultimately loaded on the surface of the molecular sieve in the form of oxides, which will cause the overall loss of metal atoms during the reaction and are easily deactivated in the catalytic reaction; in Comparative Example 3, since no passivating agent is used, the added alkali will directly etch the skeleton structure of the molecular sieve surface, and the molecular sieve structure is damaged to a certain extent. Subsequently, when a metal source is added, the metal atoms cannot be encapsulated inside the pores of the molecular sieve, resulting in poor reaction performance of the catalyst.

[0097] Depend on Figure 2 It can be seen that the V@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 atoms does not destroy the structure of the molecular sieve itself; Figure 3 and Figure 4 It can be seen that the vanadium atoms in the V@MCM-41 molecular sieve obtained by the method provided by the present invention are in the form of single substance ( Figure 4 The vanadium element exists in the form of V2p3 orbital (512eV), and it can be clearly seen in the electron microscope image that the size of the metal element is about 10nm.

[0098] Depend on Figure 1 、 Figure 3 and Figure 5 It can be seen that by changing the amount of alkali, the size of the metal nanoparticles can be controlled at any time, and the size of the metal nanoparticles varies from 5 to 25 nm.

[0099] As can be seen from Table 1, as the size of metal nanoparticles increases, the catalytic activity becomes better and better. However, when the metal nanoparticles are too large, although the structure of the molecular sieve itself will not be destroyed, the alkali etching will increase the interconnectivity of the pores inside the molecular sieve, weakening the shape-selective catalytic effect of the molecular sieve itself. Therefore, the selectivity will decrease to a certain extent.

[0100] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, under the technical enlightenment provided by the present invention, as common knowledge in the art, other equivalent variations and improvements can be made, which should also be considered as the scope of protection of the present invention.

Claims

1. An MCM molecular sieve encapsulated with nano-metal atoms, wherein: The metal atoms exist in the pores of the MCM molecular sieve in the form of a single substance, and the metal atoms are vanadium atoms and / or titanium atoms; When the metal atom is a vanadium atom, the XPS of the vanadium atom is 512 eV; When the metal atom is a titanium atom, the XPS of the titanium atom is 454 eV; The preparation method of the MCM molecular sieve encapsulated with nano-metal atoms comprises the following steps: 1) Mixing MCM molecular sieve raw powder with a passivating agent for a first reaction, then mixing with an alkaline solution for a second reaction, filtering, washing, and mixing with a metal complex solution to obtain solution A; The passivating agent 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, each 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; the metal complex solution comprises a metal atom source and a solution capable of complexing with the metal atom source, wherein the metal is vanadium and / or titanium, and the metal atom source is an oxalic acid solution containing a vanadium source and / or a titanium source; 2) mixing an organic template, water, a silicon source, and an alkali source into a gel to obtain solution B; 3) mixing the solution A and the solution B and performing hydrothermal crystallization, filtering, washing, drying and calcining.

2. The molecular sieve according to claim 1, characterized in that The MCM is MCM-41, and the MCM molecular sieve encapsulating nano-metal atoms is denoted as M@MCM-41.

3. The molecular sieve according to claim 2, characterized in that The specific surface area of ​​M@MCM-41 is 910-990m 2 / g.

4. The molecular sieve according to claim 2, characterized in that The size of the metal nanoparticles in the M@MCM-41 is controlled to be 5 to 25 nm.

5. A method for preparing nano-metal atoms encapsulated in MCM molecular sieves, comprising the following steps: 1) Mixing MCM molecular sieve raw powder with a passivating agent for a first reaction, then mixing with an alkaline solution for a second reaction, filtering, washing, and mixing with a metal complex solution to obtain solution A; The passivating agent 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, each 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; the metal complex solution comprises a metal atom source and a solution capable of complexing with the metal atom source, wherein the metal is vanadium and / or titanium, and the metal atom source is an oxalic acid solution containing a vanadium source and / or a titanium source; 2) mixing an organic template, water, a silicon source, and an alkali source into a gel to obtain solution B; 3) mixing the solution A and the solution B and performing hydrothermal crystallization, filtering, washing, drying and calcining.

6. The preparation method according to claim 5, characterized in that The MCM molecular sieve is MCM-41 molecular sieve.

7. The preparation method according to claim 5, characterized in that R d is halogen, R a 、R b and R c It is not hydrogen and / or halogen at the same time.

8. The preparation method according to claim 5, characterized in that The passivating agent is selected from at least one of diphenyldichlorosilane, trimethylchlorosilane and dimethyldichlorosilane; and / or, The weight ratio of the passivating agent to the molecular sieve raw powder is 4:5 to 1:

10.

9. The preparation method according to claim 8, characterized in that The weight ratio of the passivating agent to the molecular sieve raw powder is 3:5 to 1:

10.

10. The preparation method according to claim 8, characterized in that The weight ratio of the passivator to the molecular sieve raw powder is 3:7 to 1:

9.

11. The preparation method according to any one of claims 5 to 10, characterized in that: In the alkaline solution, the content of the alkali is 1 to 5% by weight.

12. The preparation method according to any one of claims 5 to 10, characterized in that: The alkaline solution is a sodium hydroxide solution; and / or, The weight ratio of the alkaline solution to the MCM molecular sieve raw powder is 1:20 to 1:

10.

13. The preparation method according to claim 12, characterized in that The weight ratio of the alkaline solution to the MCM molecular sieve raw powder is 3:50 to 2:

25.

14. The preparation method according to any one of claims 5 to 10, characterized in that: The vanadium source is selected from at least one of ammonium metavanadate, sodium orthovanadate and sodium pyrovanadate.

15. The preparation method according to any one of claims 5 to 10, characterized in that: The titanium source is selected from at least one of tetrabutyl titanate, titanium tetrachloride and titanium sulfate.

16. The preparation method according to any one of claims 5 to 10, characterized in that: The solution capable of complexing with the metal atom source is selected from at least one of citric acid, tartaric acid and triethanol.

17. The preparation method according to any one of claims 5 to 10, characterized in that: The weight ratio of the metal complex solution to the molecular sieve raw powder is 0.5 to 1:

5.

18. The preparation method according to any one of claims 5 to 10, characterized in that: The conditions of the first reaction include: temperature of 50-80°C; time of 2-6 hours; and / or, The conditions of the second reaction include: temperature of 20-40° C. and time of 1-2 h.

19. The preparation method according to claim 18, characterized in that The conditions of the first reaction include: temperature of 60-70° C.; time of 3-5 h.

20. The preparation method according to any one of claims 5 to 10, characterized in that: The organic template is at least one selected from cetyltrimethylammonium bromide, cetyltrimethylammonium chloride and cetyltriethylammonium bromide; and / or, The silicon source is selected from at least one of white carbon black, ethyl orthosilicate, sodium silicate and silica sol; and / or, The alkaline source is selected from at least one of sodium hydroxide, tetramethylammonium hydroxide and ammonia water; and / or, The solution B satisfies, in moles, SiO2:a H2O:b R:c OH - , wherein R is an organic template, the value of a is 80 to 160; the value of b is 0.1 to 0.7; and the value of c is 2 to 7.

21. The preparation method according to claim 20, characterized in that The value of a is 100 to 140.

22. The preparation method according to claim 20, characterized in that The value of b is 0.2 to 0.

5.

23. The preparation method according to claim 20, characterized in that The value of c is 4 to 5.

24. The preparation method according to any one of claims 5 to 10, characterized in that: The conditions for the hydrothermal crystallization include: a temperature of 110 to 140° C.; a time of 72 to 108 hours; and / or, The drying conditions include: a temperature of 100 to 140° C.; a time of 4 to 6 hours; and / or, The calcination conditions include: a temperature of 400 to 700° C.; and a calcination time of 5 to 8 hours.

25. The preparation method according to claim 24, characterized in that The conditions for the hydrothermal crystallization include: a temperature of 120 to 130° C.; a time of 84 to 100 hours; and / or, The drying conditions include: a temperature of 110 to 130° C.; a time of 4 to 6 hours; and / or, The calcination conditions include: a temperature of 500-600° C.; and a calcination time of 5-8 hours.

26. An MCM molecular sieve encapsulating nano-metal atoms, which is prepared according to the preparation method according to any one of claims 5 to 25, wherein the metal atoms exist in the MCM molecular sieve in a simple form.

27. The MCM molecular sieve encapsulated with nano-metal atoms according to claim 26, characterized in that: When the metal atom is a vanadium atom, the XPS of the vanadium atom is 512 eV; When the metal atom is a titanium atom, the XPS wavelength of the titanium atom is 454 eV.

28. The MCM molecular sieve encapsulated with nano-metal atoms according to claim 26, characterized in that: The MCM is MCM-41, and the MCM molecular sieve encapsulating nano-metal atoms is denoted as M@MCM-41.

29. The MCM molecular sieve encapsulated with nano-metal atoms according to claim 28, characterized in that: The specific surface area of ​​M@MCM-41 is 910-990m 2 / g.

30. The MCM molecular sieve encapsulated with nano-metal atoms according to claim 28, characterized in that: The size of the metal nanoparticles in the M@MCM-41 can be controlled to be 5 to 25 nm.

31. Use of the MCM molecular sieve encapsulating nano-metal atoms obtained by the preparation method according to any one of claims 5 to 25 or the MCM molecular sieve encapsulating nano-metal atoms according to any one of claims 1 to 4 in the selective oxidation of cyclohexane to prepare cyclohexanone and cyclohexanol.

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