SBA molecular sieve encapsulated with nano-metal atoms, preparation method thereof, and application in direct epoxidation of propylene in gas phase

Abstract

The present invention discloses an SBA molecular sieve encapsulated with nano-metal atoms, its preparation method, and its application in the direct vapor-phase epoxidation of propylene. The preparation method comprises the following steps: 1) mixing SBA 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, wherein the metal complex is selected from at least one of haloauric acid, haloauric acid salt, haloplatinic acid, haloplatinic acid salt, sodium chloropalladate, palladium trifluoroacetate, and sodium tetrabromopalladate; 2) mixing an organic template, water, an acid, and a silicon source to form a gel to obtain solution B; 3) mixing solutions A and B and performing hydrothermal crystallization, filtering, washing, drying, and calcining. In the molecular sieve prepared by this method, the nanoparticles are all located in the molecular sieve pores, thereby improving the catalytic performance of the catalyst. During the direct vapor-phase epoxidation of propylene, the catalyst exhibits excellent propylene oxide selectivity.

Description

Technical Field

[0001] The present invention relates to a preparation method of nano-metal atoms encapsulated in SBA molecular sieve, the obtained SBA molecular sieve encapsulating nano-metal atoms, and application of the SBA molecular sieve in gas-phase direct epoxidation of propylene. Background Art

[0002] Since Mobil Corporation first successfully synthesized the well-structured MCM-41 in 1992, mesoporous materials have shown a wide range of potential applications in adsorbents, catalysts, and catalyst supports. In 1998, Zhao Dongyuan successfully synthesized the novel mesoporous materials SBA-15 and SBA-16, which exhibited a larger surface area, more regular pore size distribution, thicker pore walls, and improved thermal stability compared to the M41S series of molecular sieves. These materials have shown even greater potential in catalytic applications. Compared to conventional M41S series molecular sieves, their three-dimensional pores allow reactants to enter the sieve more easily for reaction without causing pore blockage. However, pure silicon SBA molecular sieves lack any acidic, basic, or redox centers, and possess only one surface functional group—silanol (Si-OH)—which significantly limits their application in certain applications. 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 introduced into molecular sieves through hydrothermal synthesis and impregnation methods to serve as catalytic active centers to improve the catalytic activity of molecular sieves. Among these heteroatoms, noble metals have shown excellent catalytic performance in reactions, and the state and particle size of the noble metals in the molecular sieve will directly determine the catalytic performance of the molecular sieve.

[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] 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 a soluble metal precursor with a molecular sieve synthesis gel, followed by high-temperature crystallization. The resulting product is further calcined to remove organic matter and then 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 molecular 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 incorporated 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 response to the above-mentioned problems existing in the prior art, the present invention provides a new method for preparing nano-metal atoms encapsulated in SBA molecular sieves. In the molecular sieve prepared by this method, the nanoparticles are all in the molecular sieve pores, thereby being able to improve the catalytic performance of the catalyst and having a better effect in the application of direct epoxidation of propylene in gas phase. Specifically, the method first uses a passivating agent to passivate the silanol groups on the outer surface of the SBA molecular sieve. These passivated outer surfaces will not undergo desiliconization under the action of alkaline substances, thereby protecting the outer surface of the SBA molecular sieve. Then, the alkaline substance carries out a desiliconization reaction inside the molecular sieve pores, forming new mesopores and macropores. Then, the metal particles are embedded in the pores of the molecular sieve, and the size of the metal nanoparticles is regulated at any time according to the size of the molecular sieve pores. Finally, the outer pores etched by the alkaline substance are encapsulated by secondary crystallization, thereby utilizing the confinement effect in the molecular sieve pores without agglomeration.

[0006] The first aspect of the present invention provides a method for preparing nano-metal atoms (M) encapsulated in SBA molecular sieve, comprising the following steps:

[0007] 1) mixing SBA 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 to obtain a solution A, wherein the metal complex is selected from at least one of haloauric acid, haloauric acid salt, haloplatinic acid, haloplatinate, sodium chloropalladate, palladium trifluoroacetate, and sodium tetrabromopalladate;

[0008] 2) mixing an organic template, water, an acid, and a silicon source into a gel to obtain a solution B;

[0009] 3) mixing the solution A and the solution B and performing hydrothermal crystallization, filtering, washing, drying and calcining.

[0010] 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 、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; preferably, R d is halogen, R a 、R b and R c It is not hydrogen and / or halogen at the same time; the passivating agent is further preferably selected from at least one of diphenyldichlorosilane, trimethylchlorosilane and dimethyldichlorosilane.

[0011] According to some embodiments of the preparation method of the present invention, preferably, the weight ratio of the passivating agent to the molecular sieve raw powder is 4:5 to 1:10, preferably 3:5 to 1:10, and more preferably 3:7 to 1:9.

[0012] According to some embodiments of the preparation method of the present invention, preferably, the SBA molecular sieve is SBA-15 molecular sieve and / or SBA-16 molecular sieve.

[0013] According to some embodiments of the preparation method of the present invention, preferably, in the alkaline solution, the content of alkali is 1 to 5 weight %.

[0014] According to some embodiments of the preparation method of the present invention, preferably, the alkaline solution is a sodium hydroxide solution.

[0015] According to some embodiments of the preparation method of the present invention, preferably, the weight ratio of the alkaline solution to the molecular sieve raw powder is 1:20 to 1:10, preferably 3:50 to 2:25.

[0016] According to some embodiments of the preparation method of the present invention, preferably, the metal complex is formed by a metal atom source and a solution capable of complexing with the metal atom source. Preferably, the metal complex is selected from at least one of haloauric acid (HAuX4, X = F, Cl, Br or I), haloauric acid salts, haloplatinic acid (HAuX4, X = F, Cl or Br), haloplatinic acid salts, sodium chloropalladate (Na2PdCl4), palladium trifluoroacetate and sodium tetrabromopalladate.

[0017] According to some embodiments of the preparation method of the present invention, preferably, the weight ratio of the metal complex solution to the molecular sieve raw powder is 0.5 to 1:5.

[0018] According to some embodiments of the preparation method of the present invention, preferably, the conditions of the first reaction include: temperature of 50-80° C., preferably 60-70° C.; time of 2-6 h, preferably 3-5 h.

[0019] According to some embodiments of the preparation method of the present invention, preferably, the conditions of the second reaction include: temperature of 20-40° C., and time of 1-2 h.

[0020] According to some embodiments of the preparation method of the present invention, preferably, the organic template R is an amphiphilic nonionic triblock surfactant, preferably F127 (EO 106 PO 70 EO 106 )、F108(EO 132 PO 50 EO 132 )、hexamethylenetetramine (HMTA), P123 (EO 20 PO 70 EO 20 ) and P104(EO 27 PO 61 EO 27 ). More preferably, when the prepared molecular sieve is SBA-15, the organic template R is selected from P123 and / or P104; when the prepared molecular sieve is SBA-16, the organic template R is selected from at least one of F127, F108 and HMTA.

[0021] According to some embodiments of the preparation method of the present invention, preferably, the silicon source is selected from at least one of white carbon black, tetraethyl orthosilicate, sodium silicate and silica sol, preferably tetraethyl orthosilicate.

[0022] According to some embodiments of the preparation method of the present invention, preferably, the acid is selected from at least one of hydrochloric acid, sulfuric acid and nitric acid, preferably hydrochloric acid.

[0023] According to some embodiments of the preparation method of the present invention, preferably, the solution B satisfies, on a molar basis, SiO2:a H2O:b R:c H + , wherein R is an organic template, a is 80 to 200, preferably 100 to 160; b is 0.005 to 0.030, preferably 0.010 to 0.025; c is 0.10 to 0.25, preferably 0.15 to 0.20. In the present invention, the silicon source is calculated as SiO2, the vanadium source is calculated as V, the titanium source is calculated as Ti, and the acid is calculated as H + The solvent is calculated as H2O, and the organic template is calculated as R.

[0024] According to some embodiments of the preparation method of the present invention, preferably, the hydrothermal crystallization conditions include: a temperature of 80 to 130° C., preferably 90 to 120° C.; and a time of 24 to 90 hours, preferably 40 to 70 hours.

[0025] According to some embodiments of the preparation method of the present invention, preferably, the drying conditions include: a temperature of 100-140° C., preferably 110-130° C., and a time of 4-6 hours. The drying removes moisture and organic templates on the surface of the molecular sieve.

[0026] According to some embodiments of the preparation method of the present invention, preferably, the calcination conditions include: a temperature of 400-700°C, preferably 500-600°C, and a calcination time of 5-8 hours. The calcination removes organic templates and moisture from the molecular sieve pores, thereby increasing the molecular sieve framework strength.

[0027] According to some specific embodiments of the preparation method of the present invention, preferably, the preparation method of encapsulating nano-metal atoms (M) in SBA molecular sieve includes but is not limited to the following steps:

[0028] (1) SBA molecular sieve powder and a passivating agent are stirred at a certain temperature for a period of time, and then an alkaline solution is added to the resulting product. After reacting at room temperature for a period of time, the product is filtered and washed, and then the washed product is mixed with a metal complex solution to obtain A;

[0029] (2) The organic template, water, acid and silicon source are mixed into a gel, and the molar ratio of the obtained reaction mixture is SiO2:aH2O:bR:cH + , wherein R is an organic template, the value of a is 80-200, the value of b is 0.005-0.030, and the value of c is 0.10-0.25. The mixed solution is B;

[0030] (3) Add B to A and hydrothermally crystallize at a certain crystallization temperature for a period of time. The product is filtered, washed, dried and calcined to obtain M@SBA molecular sieve.

[0031] The second aspect of the present invention provides an SBA molecular sieve encapsulated with nano-metal atoms prepared according to the above preparation method, wherein the metal atom M is at least one of a gold atom, a platinum atom and a palladium atom, denoted as M@SBA.

[0032] M@SBA refers to SBA molecular sieve encapsulated with nano-metal atoms M.

[0033] According to some embodiments of the molecular sieve of the present invention, preferably, the metal atoms exist in the SBA molecular sieve in the form of a single substance.

[0034] In the present invention, for example, but not limited to, XPS can be measured, the XPS of platinum atoms is 71eV, the XPS of palladium atoms is 335eV, and the XPS of gold atoms is 84eV, which can prove that the metal atoms are only present in the SBA molecular sieve in the form of a simple substance, and do not exist in the form of an oxide. And they are only present inside the SBA molecular sieve, and not on the surface of the SBA molecular sieve. For example, if platinum exists in the form of an oxide, PtO is 72.4eV, PtO2 is 74.9eV, and if it is on the surface, it is generally PtO2. For another example, if palladium exists in the form of an oxide or is present on the surface of the SBA molecular sieve, the XPS of the palladium atoms is 336.7eV. Using H2-TPR test, if there is a gold oxide, a reduction peak will appear when reduced with hydrogen, and if there is no reduction peak, it is explained that it is a gold simple substance. When the SBA molecular sieve encapsulated with nano-metal atoms (gold atoms) of the present invention is subjected to H2-TPR test, no reduction peak occurs, indicating that the gold atoms are present in the SBA molecular sieve in the form of a simple substance.

[0035] According to some embodiments of the molecular sieve of the present invention, preferably, the specific surface area of ​​the M@SBA is 910-990 m 2 The M@SBA of the present invention has a larger specific surface area, thereby improving conversion rate and selectivity.

[0036] According to some embodiments of the molecular sieve of the present invention, preferably, the size of the metal nanoparticles in the M@SBA can be controlled to be 5 to 25 nm.

[0037] According to some embodiments of the molecular sieve of the present invention, preferably, when the metal atom is a platinum atom, the XPS of the platinum atom is 71 eV.

[0038] According to some embodiments of the molecular sieve of the present invention, preferably, when the metal atom is a palladium atom, the XPS of the palladium atom is 335 eV.

[0039] According to some embodiments of the molecular sieve of the present invention, preferably, when the metal atom is a gold atom, the XPS of the gold atom is 84 eV.

[0040] The third aspect of the present invention provides the use of the above-mentioned preparation method or the above-mentioned SBA molecular sieve encapsulated with nano-metal atoms in the gas-phase direct epoxidation of propylene.

[0041] Beneficial effects of the present invention:

[0042] The present invention first utilizes a passivating agent to protect the silanol group on the outside of the molecular sieve, an alkaline substance can enter the molecular sieve pores and etch from the inside without etching the outer surface of the molecular sieve, two sets of independent pore structures of the internal molecular sieve are interconnected to form new macropores and mesoporous structures due to the etching of the alkaline substance, the size of the internal pore structure of the molecular sieve is regulated according to the concentration and amount of the alkaline substance, then metal nanoparticles are introduced into the molecular sieve pores, due to the confinement effect of the molecular sieve pore structure, the metal nanoparticles will not exceed the size of the molecular sieve pores and destroy the internal structure of the molecular sieve, finally secondary crystallization is utilized to repackage the internal etched pores, and the metal nanoparticles are thoroughly encapsulated in the molecular sieve pores. Compared with conventional post-processing methods, the post-processing method can only load most of the metal nanoparticles on the outer surface of the molecular sieve, and simultaneously because the metal nanoparticles are exposed to the outside, after treatment such as high temperature, the metal nanoparticles will continue to agglomerate or even lose, thereby causing a decline in catalytic effect. Compared to conventional one-step hydrothermal synthesis, the one-step method is simpler but requires reduction to convert the nanoparticles to a metallic state. However, the pores of the reduced metal nanoparticles are much larger than those of the molecular sieve itself, which inevitably enlarges and destroys the internal structure of some molecular sieve pores, thereby reducing the catalytic performance of the catalyst. The method of the present invention effectively addresses these issues, improves the catalytic performance of the catalyst, and demonstrates significant results in the vapor-phase direct epoxidation of propylene. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is the HRTEM image of Au@SBA-16 molecular sieve obtained in Example 1 of the present invention;

[0044] Figure 2 This is the low-angle XRD pattern of Au@SBA-16 molecular sieve obtained in Example 3 of the present invention;

[0045] Figure 3 This is the HRTEM image of Au@SBA-16 molecular sieve obtained in Example 3 of the present invention;

[0046] Figure 4 This is the XPS graph of Au@SBA-16 molecular sieve obtained in Example 3 of the present invention;

[0047] Figure 5 This is the HRTEM image of Au@SBA-16 molecular sieve obtained in Example 4 of the present invention.

[0048] Figure 6 This is the XPS graph of the Pd@SBA-15 molecular sieve obtained in Example 5 of the present invention;

[0049] Figure 7 This is the XPS graph of the Pt@SBA-15 molecular sieve obtained in Example 6 of the present invention. DETAILED DESCRIPTION

[0050] In order to make the present invention easier to understand, the present invention will be described in detail below with reference to embodiments. These embodiments are only for illustration and do not limit the scope of application of the present invention.

[0051] The test method of the present invention and the equipment used in the test are as follows:

[0052] (1) XRD uses Philips X-Pert series X-ray diffractometer to determine the structure of molecular sieves.

[0053] (2) HRTEM uses the Jem-3010 high-resolution transmission electron microscope of Rigku Company to determine the regularity of the molecular sieve.

[0054] (3) XPS uses Thermo Scientific's ESCALAB 250 spectrometer to measure the bonding of metal particles.

[0055] (4) BET was measured using a Micromeritics ASAP2020 fully automatic surface area analyzer.

[0056] The silicon source of the present invention is calculated as SiO2, the vanadium source is calculated as V, the titanium source is calculated as Ti, and the acid is calculated as H + The solvent is calculated as H2O, and the organic template is calculated as R.

[0057] In the following embodiments

[0058] Template F127 was purchased from Sigma-Aldrich;

[0059] Template F108 was purchased from Sigma-Aldrich;

[0060] The template agent HMTA was purchased from Sigma-Aldrich;

[0061] Template agent P123 was purchased from Sigma-Aldrich.

[0062] [Example 1]

[0063] 5.0 g of SBA-16 molecular sieve raw powder was stirred with 2.1 g of trimethylsilyl chloride at 50 ° C for 2 h, and then the product was mixed with 0.4 g of 1 wt% sodium hydroxide solution and stirred at room temperature for 1 h. The product was then filtered and washed to obtain solution D. 2.0 g of chloroauric acid was added thereto to obtain solution A.

[0064] 1.6 g of F127 and 34.5 g of deionized water were added to the reactor in sequence and stirred evenly. Then 24.1 mL of 0.1 mol / L hydrochloric acid solution was added. Stirring was continued and 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. The molar ratio of the reaction mixture was SiO2: 80 H2O: 0.005 R: 0.1 H + , which is solution B. B and A are mixed and transferred to a crystallization kettle, heated to 90°C, and crystallized at a constant temperature for 40 hours. After the crystallization is complete, the temperature is lowered to room temperature, the reaction mixture is separated, washed, and dried at 100°C. Finally, it is calcined at 400°C for 8 hours to obtain Au@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 Figure 1 .

[0065] [Example 2]

[0066] The difference from Example 1 is that the passivating agent is changed to dimethyldichlorosilane, the amount is changed to 0.56g, the passivation temperature is changed to 60°C, the passivation time is changed to 3h, the weight fraction of the sodium hydroxide solution is changed to 2% by weight, the amount is 0.3g, the Au source complex is changed to sodium chloroaurate, the amount is 1.5g, the template agent is changed to F108, the amount is 4.4g, the amount of water is changed to 54g, the silicon source is changed to white carbon black (silicon dioxide content is 90% by weight), the amount is 2g, the acid is changed to sulfuric acid, the amount is 44.8mL, the crystallization temperature is changed to 100°C, the crystallization time is changed to 50h, the drying temperature is changed to 110°C, the calcination temperature is changed to 500°C, the calcination time is changed to 6h, the other components and synthesis conditions remain unchanged, and the molar ratio of the reaction mixture obtained is SiO2:100H2O:0.01R:0.15H + The specific surface area of ​​the product obtained by BET analysis is shown in Table 1.

[0067] [Example 3]

[0068] The difference from Example 1 is that the passivator is changed to diphenyldichlorosilane, the amount is changed to 1.25g, the passivation temperature is changed to 70°C, the passivation time is changed to 4h, the weight fraction of sodium hydroxide solution is changed to 3wt%, the amount is 0.35g, the reaction time is changed to 2h, the template agent is changed to HMTA, the amount is 0.15g, the amount of water is changed to 82.5g, the silicon source is changed to silica sol (SW-25, silica content is 25wt%), the amount is 10g, the acid source is changed to nitric acid, the amount is 83mL, the amount of Au source complex is changed to 1.0g, the crystallization temperature is changed to 110°C, the crystallization time is changed to 60h, the drying temperature is changed to 120°C, the calcination temperature is changed to 550°C, the calcination time is changed to 7h, the other components and synthesis conditions remain unchanged, and the molar ratio of the reaction mixture obtained is SiO2:110H2O:0.025R:0.2H + The specific surface area of ​​the product obtained by BET analysis is shown in Table 1, and 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 gold atoms in the molecular sieve is analyzed by XPS. Figure 4 .

[0069] [Example 4]

[0070] The difference from Example 3 is that the weight fraction of the sodium hydroxide solution is changed to 4 weight percent, and the other components and synthesis conditions remain unchanged. Figure 5 The specific surface area of ​​the product obtained by BET analysis is shown in Table 1.

[0071] [Example 5]

[0072] 5.0 g of SBA-15 molecular sieve raw powder was stirred with 2.1 g of trimethylsilyl chloride at 50 ° C for 2 h, and then the product was mixed evenly with 0.4 g of 1 wt% sodium hydroxide solution and stirred at room temperature for 1 h. The product was then filtered and washed to obtain solution D. Subsequently, 2.0 g of sodium chloropalladate was added to solution D to obtain solution A.

[0073] 4.2 g of P104 and 38.9 g of deionized water were added to the reactor in sequence and stirred evenly. Then, 60 mL of 0.1 mol / L hydrochloric acid solution was added. Stirring was continued and 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. The molar ratio of the reaction mixture was SiO2: 90 H2O: 0.03 R: 0.25 H +, which is solution B. B and A are mixed and transferred to a crystallization kettle, heated to 130°C, and crystallized at a constant temperature for 90 hours. After the crystallization is complete, the temperature is lowered to room temperature, the reaction mixture is separated, washed, and dried at 130°C. Finally, it is calcined at 400°C for 8 hours to obtain Pd@SBA-15 molecular sieve. The specific surface area of ​​the product obtained by BET analysis of the sample is shown in Table 1. The state analysis of Pd atoms in the molecular sieve by XPS is shown in Figure 6 .

[0074] [Example 6]

[0075] 5.0 g of SBA-15 molecular sieve raw powder was stirred with 2.1 g of trimethylsilyl chloride at 50° C. for 2 h. The product was then mixed evenly with 0.4 g of 1 wt% sodium hydroxide solution and stirred at room temperature for 1 h. The product was then filtered and washed to obtain solution D. 2.0 g of chloroplatinic acid was added to solution D to obtain solution A.

[0076] 4.2 g of P104 and 38.9 g of deionized water were added to the reactor in sequence and stirred evenly. Then, 60 mL of 0.1 mol / L hydrochloric acid solution was added. Stirring was continued and 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. The molar ratio of the reaction mixture was SiO2: 90 H2O: 0.03 R: 0.25 H + , which is solution B. B and A are mixed and transferred to a crystallization kettle, heated to 130°C, and crystallized at a constant temperature for 90 hours. After the crystallization is complete, the temperature is lowered to room temperature, the reaction mixture is separated, washed, and dried at 130°C. Finally, it is calcined at 400°C for 8 hours to obtain Pt@SBA-15 molecular sieve. The specific surface area of ​​the product obtained by BET analysis of the sample is shown in Table 1. The state analysis of Pt atoms in the molecular sieve by XPS is shown in Figure 7 .

[0077] [Comparative Example 1]

[0078] 1.6 g of F127 and 34.5 g of deionized water were added to the reactor in sequence and stirred evenly. Then, 24.1 mL of 0.1 mol / L hydrochloric acid solution was added, 2.0 g of chloroauric acid was added, stirring was continued, and 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. The molar ratio of the reaction mixture was SiO2: 80 H2O: 0.005 R: 0.1 H +The mixed solution was transferred to a crystallization kettle, heated to 90°C, and crystallized at this constant temperature for 40 hours. After complete crystallization, the temperature was lowered to room temperature, and the reaction mixture was separated, washed, and dried at 100°C. Finally, it was calcined at 400°C for 8 hours to obtain the Au-SBA-16 molecular sieve raw powder. The Au-SBA-16 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 final product was Au@SBA-16 molecular sieve. The specific surface area of ​​the product obtained by BET analysis is shown in Table 1.

[0079] [Comparative Example 2]

[0080] 1.6 g of F127 and 34.5 g of deionized water were added to the reactor in sequence and stirred evenly. Then 24.1 mL of 0.1 mol / L hydrochloric acid solution was added and stirred evenly. 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. The molar ratio of the reaction mixture was SiO2: 80 H2O: 0.005 R: 0.1 H + The mixed solution was transferred to a crystallization kettle, heated to 90°C, and crystallized at a constant temperature for 40 hours. After complete crystallization, the temperature was lowered to room temperature, and the reaction mixture was separated, washed, and dried at 100°C. Finally, it was calcined at 400°C for 8 hours to obtain the SBA-16 molecular sieve raw powder. The SBA-16 molecular sieve, 2.0g of chloroauric acid, and 50mL of deionized water were mixed uniformly. Subsequently, the reaction mixture was separated, washed, and dried at 100°C. Finally, it was calcined at 400°C for 8 hours to obtain the Au / SBA-16 molecular sieve. The specific surface area of ​​the product obtained by BET analysis is shown in Table 1.

[0081] [Comparative Example 3]

[0082] 5.0 g of SBA-16 molecular sieve raw powder was mixed evenly with 0.4 g of 1 wt% sodium hydroxide solution and stirred at room temperature for 1 h. The product was then filtered and washed to obtain solution D. 2.0 g of chloroauric acid was added thereto to obtain solution A.

[0083] 1.6 g of F127 and 34.5 g of deionized water were added to the reactor in sequence and stirred evenly. Then 24.1 mL of 0.1 mol / L hydrochloric acid solution was added. Stirring was continued and 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. The molar ratio of the reaction mixture was SiO2: 80 H2O: 0.005 R: 0.1 H +, which is solution B. B and A were mixed and transferred to a crystallization kettle. The temperature was raised to 90°C and crystallized at this constant temperature for 40 hours. After complete crystallization, the temperature was lowered to room temperature. The reaction mixture was separated, washed, and dried at 100°C. Finally, it was calcined at 400°C for 8 hours to obtain the Fe@SBA-16 molecular sieve. The specific surface area of ​​the product obtained by BET analysis is shown in Table 1.

[0084] Test Example

[0085] The samples obtained in Examples 1-6 and Comparative Examples 1-3 were respectively used in gas-phase direct epoxidation experiments of propylene. The results are shown in Table 1.

[0086] The catalyst activity evaluation of the direct epoxidation of propylene in the gas phase was carried out in a fixed-bed microreactor at atmospheric pressure. The catalyst dosage was 0.30 g. The reaction gas composition was regulated by a mass flow meter to a volume ratio of C3H6:H2:O2:N2 of 1:1:1:7. After mixing, the gas passed through the catalyst bed at a space velocity of 7000 mL·(g·h). -1 Before the reaction, the catalyst was pretreated as follows: 10% (volume ratio, the same below) H2 / N2 and 10% O2 / N2, heat treated for 0.5 h in succession, and then under N2 atmosphere, the reaction temperature was lowered to 423 K, all reaction gases were turned on, and after the reaction was carried out for 0.5 h, the reaction products were qualitatively and quantitatively analyzed using gas chromatography.

[0087] Table 1. Results of direct vapor phase epoxidation of propylene

[0088] Propylene oxide PO selectivity (%) <![CDATA[Specific surface area (m 2 / g)]]> Example 1 72.3 947 Example 2 78.2 1012 Example 3 80.7 1075 Example 4 79.2 1033 Example 5 72.1 945 Example 6 80.3 1061 Comparative Example 1 27.6 448 Comparative Example 2 10.4 177 Comparative Example 3 5.6 79

[0089] From Comparative Examples 1-2 and Example 1, Table 1 shows that in Comparative Example 1, Au@SBA-16 is prepared by the in-situ constraint method. The process of this method is quite simple and convenient. It only requires the metal to be pulled out of the skeleton by H2 reduction. 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. Therefore, 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, thereby affecting the performance of the catalyst; 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 will be 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.

[0090] Depend on Figure 2 It can be seen that the Au@SBA-16 molecular sieve obtained by the method provided by the present invention still has the characteristic peak of high regularity of SBA-16 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 Au@SBA-16 molecular sieve obtained by the method provided by the present invention are in the form of single substance ( Figure 4 It exists in the form of gold elemental 4f7 / 2 / orbital with a wavelength of 84eV, and it can be clearly seen in the electron microscope image that the size of the metal element is about 5nm.

[0091] 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 metal nanoparticles vary from 5 to 50 nm.

[0092] 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 damaged, the alkali etching will increase the interconnectivity of the pores inside the molecular sieve, causing the strength of the molecular sieve itself to decrease, and thus the catalytic performance will decrease to a certain extent.

[0093] 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. A method for preparing nano-metal atoms encapsulated in SBA molecular sieves, comprising the following steps: 1) mixing SBA 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 to obtain a solution A, wherein the metal complex is selected from at least one of haloauric acid, haloauric acid salt, haloplatinic acid, haloplatinate, sodium chloropalladate, palladium trifluoroacetate, and sodium tetrabromopalladate; 2) mixing an organic template, water, an acid, and a silicon source into a gel to obtain a solution B; 3) mixing the solution A and the solution B and performing hydrothermal crystallization, filtering, washing, drying and calcining; Wherein, the passivating agent includes 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 It is not hydrogen and / or halogen at the same time.

2. The preparation method according to claim 1, characterized in that R d is halogen, R a 、R b and R c are not hydrogen and / or halogen at the same time; and / or The weight ratio of the passivating agent to the molecular sieve raw powder is 4:5 to 1:

10.

3. The preparation method according to claim 2, 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 3:5 to 1:

10.

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

9.

5. The preparation method according to claim 1, characterized in that The SBA molecular sieve is SBA-15 molecular sieve and / or SBA-16 molecular sieve.

6. The preparation method according to any one of claims 1 to 5, characterized in that In the alkaline solution, the content of alkali is 1 to 5% by weight; and / or, The weight ratio of the alkaline solution to the molecular sieve raw powder is 1:20 to 1:

10.

7. The preparation method according to claim 6, characterized in that The alkaline solution is a sodium hydroxide solution; and / or the weight ratio of the alkaline solution to the molecular sieve raw powder is 3:50 to 2:

25.

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

5.

9. The preparation method according to any one of claims 1 to 5, 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.

10. The preparation method according to claim 9, characterized in that The conditions of the first reaction include: temperature of 60-70° C.; time of 3-5 h.

11. The preparation method according to any one of claims 1 to 5, characterized in that The organic template is an amphiphilic nonionic triblock surfactant; 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 acid is selected from at least one of hydrochloric acid, sulfuric acid and nitric acid; and / or, The solution B satisfies, on a molar basis, SiO2:a H2O:b R:c H + , wherein R is an organic template, the value of a is 80 to 200; the value of b is 0.005 to 0.030; and the value of c is 0.10 to 0.

25.

12. The preparation method according to claim 11, characterized in that The organic template is at least one of F127, F108, hexamethylenetetramine, P123 and P104; and / or, In the solution B, the value of a is 100 to 160; the value of b is 0.010 to 0.025; and the value of c is 0.15 to 0.

20.

13. The preparation method according to any one of claims 1 to 5, characterized in that The conditions for the hydrothermal crystallization include: a temperature of 80 to 130° C.; a time of 24 to 90 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.

14. The preparation method according to claim 13, characterized in that The conditions for the hydrothermal crystallization include: a temperature of 90 to 120° C.; a time of 40 to 70 hours; and / or, The drying conditions include: a temperature of 110 to 130° C.; and / or, The calcination conditions include: a temperature of 500-600°C.

15. An SBA molecular sieve encapsulated with nano-metal atoms, prepared by the method according to any one of claims 1 to 14, wherein the metal atom M is at least one of a gold atom, a platinum atom and a palladium atom, denoted as M@SBA.

16. The molecular sieve according to claim 15, characterized in that The metal atoms exist in the SBA molecular sieve in the form of a single substance.

17. The molecular sieve according to claim 15, characterized in that The specific surface area of ​​the M@SBA is 940-1100 m 2 / g.

18. The molecular sieve according to claim 15, characterized in that The size of the metal nanoparticles in the M@SBA can be controlled to be 5 to 50 nm.

19. The molecular sieve according to any one of claims 15 to 18, characterized in that When the metal atom is a platinum atom, the XPS of the platinum atom is 71 eV; when the metal atom is a palladium atom, the XPS of the palladium atom is 335 eV; when the metal atom is a gold atom, the XPS of the gold atom is 84 eV.

20. Use of the SBA molecular sieve encapsulating nano-metal atoms prepared by the preparation method according to any one of claims 1 to 14 or the SBA molecular sieve encapsulating nano-metal atoms according to any one of claims 15 to 19 in gas-phase direct epoxidation of propylene.

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