Hollow mesoporous SiO2 nanoreactor as well as preparation method and application thereof

Abstract

The invention discloses a mesoporous hollow SiO2 nanoreactor as well as a preparation method and application thereof. The preparation method comprises the following steps: combining a cationic cluster with a hollow structure, which is formed by coordination and complexation of polyethyleneimine and metal ions, with a surfactant to form a micelle as a template, hydrolyzing tetraethyl orthosilicate to form silicified nano SiO2 spheres, and limiting the metal ions in a cavity, so as to obtain the nano SiO2 nanospheres. And roasting at high temperature to obtain the SiO2 nano reactor with the hollow mesoporous structure. When the hollow structure is used as a catalyst, the influence of mass transfer on catalytic reaction is eliminated, and meanwhile, the hollow structure can remarkably increase effective collision between active components of the catalyst and reactants through a confinement effect, so that the catalytic reaction is accelerated; the catalyst disclosed by the invention is simple in preparation process, has the advantages of uniformity, good thermal stability and high repeatability, is easy to realize automatic production, and is suitable for large-scale popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and in particular to a hollow mesoporous SiO2 nanoreactor and a preparation method and application thereof. Background Art

[0002] Cyclohexanone, a high-value-added industrial raw material, is an important intermediate in the manufacture of nylon, caprolactam, and adipic acid. It is also a crucial organic solvent, used in paints, organophosphorus insecticides, pesticides, and dyes. Industrially, cyclohexanone is produced through the oxidation of cyclohexane. However, this process requires relatively harsh conditions, with a cyclohexane conversion rate of approximately 4% and a cyclohexanone selectivity of 82-84%, resulting in complex collection and separation steps. Therefore, a more environmentally friendly cyclohexanone production method is urgently needed to address the technical challenges of high conversion rates and complex production processes.

[0003] On the other hand, due to the increase in the supply of phenol in the coal chemical industry, the method for producing cyclohexanone using phenol as raw material has received increasing attention. In the prior art, the catalytic system types applied to chlorophenol catalytic hydrodechlorination are more, but mostly focus on supported catalysts, and supported catalysts are due to the problem of poor thermal stability and easy loss of reaction components, often leading to the deactivation of catalysts and a large amount of loss of reaction components leading to secondary pollution of water bodies; Compared to supported catalysts, hollow mesoporous nanoreactors can effectively suppress the loss of metal due to the protection of the shell, and the presence of confinement effect can increase the progress of deep hydrogenation reaction, which is conducive to the deep catalytic hydrogenation of phenol into cyclohexanone. However, due to the synthetic process of the current hollow nanoreactor synthesis method, most of them are more complicated, and the nanoreactor pore size and specific surface area of ​​the synthesis are usually too small, which causes mass transfer resistance to have a great impact in catalytic hydrogenation, so that the catalytic reaction efficiency is low.

[0004] In summary, the present invention provides a hollow mesoporous SiO2 nanoreactor and a preparation method thereof, which solves the technical problems existing in the hollow mesoporous catalyst in the prior art and can also provide a method for producing cyclohexanone. Summary of the Invention

[0005] The purpose of the present invention is to provide a hollow mesoporous SiO2 nanoreactor and its preparation method and application.

[0006] To achieve the aforementioned purpose of the invention, the present invention provides a method for preparing a mesoporous hollow SiO2 nanoreactor, which adopts a reverse microemulsion method to coordinate and complex a template agent and metal ions to form cationic clusters with a hollow structure, and contains metal ions in the hollow structure; the cationic clusters are combined with a surfactant through electrostatic attraction to form micelles; using the micelles as templates, tetraethyl orthosilicate is hydrolyzed to form silicified nano-SiO2 balls with a cavity structure, and after high-temperature calcination, a SiO2 nanoreactor containing metal or metal oxide with a hollow mesoporous structure is obtained; the SiO2 nanoreactor forms a shell structure with silicon dioxide, which has a hollow mesoporous structure, and the metal ions are confined in the hollow cavity. This method has good controllability for the pores, hollow size and metal loading rate of the hollow SiO2 nanoreactor.

[0007] As one of the preferred embodiments, the method for preparing the mesoporous hollow SiO2 nanoreactor comprises the following steps:

[0008] Step 1: Preparation of microemulsion: Dissolve the surfactant in the organic phase and heat and stir under stirring at room temperature;

[0009] Step 2: Template preparation: Add template agent, metal salt solution, and alkali solution to form a uniform and transparent solution;

[0010] Step 3: Preparation of nano-SiO2 spheres: Tetraethyl orthosilicate is added to the solution, and tetraethyl orthosilicate undergoes hydrolysis and polymerization reaction, and the reaction product encapsulates the metal ions to form a core-shell structure;

[0011] Step 4: Preparation of the reactor: After the reaction is completed, the emulsion is broken, and the product is post-treated and then calcined at high temperature to obtain a mesoporous hollow SiO2 nanoreactor containing metal or metal oxide.

[0012] As one of the preferred embodiments, in step 1, the surfactant includes hexadecyl polyoxyethylene ether carboxylic acid.

[0013] As one of the preferred embodiments, the organic phase is cyclohexane.

[0014] As one of the preferred implementations, the added amount of the surfactant is 0.1-1 g / 5 mL of the organic phase. The pore size of the mesoporous hollow SiO2 nanoreactor can be strictly adjusted by varying the added amount of the surfactant.

[0015] As one of the preferred embodiments, the heating temperature is 40-60°C.

[0016] As one of the preferred embodiments, in step 2, the metal salt solution is a metal chlorate or nitrate solution.

[0017] As one of the preferred embodiments, the alkali solution is aqueous ammonia.

[0018] As one of the preferred embodiments, the template is polyethyleneimine.

[0019] As one of the preferred embodiments, the molar ratio of the template to the metal salt is 1:1 to 13:1.

[0020] As one of the preferred embodiments, in step 3, the molar ratio of tetraethyl silicate to the metal salt is 20:1 to 180:1.

[0021] As one of the preferred embodiments, in step 3, the post-treatment includes centrifugal washing with deionized water and ethanol and then drying, and the drying temperature is 60-80°C.

[0022] As one of the preferred implementations, the high-temperature calcination is carried out at a temperature of 300 to 400° C. and for a time of 2 to 6 hours.

[0023] As one of the preferred embodiments, the reduction temperature is 200-300°C and the time is 2-6 hours.

[0024] As the second purpose of the invention, the present invention also provides a mesoporous hollow SiO2 nanoreactor, which is prepared by the preparation method described above.

[0025] As the third object of the invention, the present invention also provides a mesoporous hollow SiO2 nanoreactor prepared by the preparation method as described above, or the use of the mesoporous hollow SiO2 nanoreactor as described above in the catalytic hydrogenation reaction of phenol.

[0026] As the fourth object of the invention, the present invention also provides a catalyst, including a mesoporous hollow SiO2 nanoreactor prepared by the preparation method as described above, or a mesoporous hollow SiO2 nanoreactor as described above, which can be used for the catalytic hydrogenation reaction of phenol to prepare cyclohexanone; the yield of cyclohexanone is ≥99.8%.

[0027] As the fifth object of the invention, the present invention also provides a cyclohexanone, which is prepared by using phenol as a raw material through a catalytic reaction under the action of the catalyst as described above.

[0028] Compared with the prior art, the advantages of the present invention include:

[0029] 1. By adopting the technical solution of the present invention, a hollow mesoporous SiO2 nanoreactor is realized in a one-step method in a reverse microemulsion. The synthesized nanoreactor has the advantages of large pore size and high specific surface area, and the pore size, specific surface area, mesopore size and metal loading rate of the material are all excellently controllable.

[0030] 2. The present invention confines metal ions in the nanoreactor by adding polyethyleneimine as a template and complexing agent, and uses a surfactant as a pore-forming agent to form a mesoporous structure with large pore size and high specific surface area, which can eliminate the influence of mass transfer on the core-shell catalyst during the catalytic reaction. In addition, due to the presence of the mesoporous structure, the effective collision probability between the active components of the catalyst and the reactants can be significantly increased through the confinement effect, thereby accelerating the catalytic reaction.

[0031] 3. The present invention can obtain a SiO2 nanoreactor with a hollow structure after removing the surfactant through high-temperature calcination. The shell of the nanoreactor has a mesoporous structure with a high specific surface area and large pore size. The prepared catalyst is uniform and highly repeatable, and the automated production of catalyst preparation is easy to realize. The synthesized catalyst has good thermal stability and high reusability, and is suitable for large-scale promotion and production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 TEM and magnified images of the hollow mesoporous SiO2 nanoreactor prepared in Example 1 of the present invention.

[0034] Figure 2 This is the XRD pattern of the hollow mesoporous SiO2 nanoreactor prepared in Example 1 of the present invention.

[0035] Figure 3a and Figure 3b They are respectively the BET diagram and pore size distribution diagram of the hollow mesoporous SiO2 nanoreactor prepared in Example 1 of the present invention.

[0036] Figure 4 This is a TEM image of the hollow mesoporous SiO2 nanoreactor prepared in Example 2 of the present invention.

[0037] Figure 5a and Figure 5b 2 are the BET diagram and pore size distribution diagram of the SiO2 nanoreactor prepared in Example 2 of the present invention.

[0038] Figure 6 This is a TEM image of the SiO2 nanoreactor prepared in Example 3 of the present invention.

[0039] Figure 7This is a TEM image of the SiO2 nanoreactor prepared in Example 4 of the present invention.

[0040] Figure 8 This is a TEM image of the SiO2 nanoreactor prepared in Example 5 of the present invention.

[0041] Figure 9 This is a TEM image of the SiO2 nanoreactor prepared in Comparative Example 1 of the present invention.

[0042] Figure 10 This is the XRD pattern of the SiO2 nanoreactor prepared in Comparative Example 1 of the present invention.

[0043] Figure 11a and Figure 11b They are respectively the BET diagram and pore size distribution diagram of the SiO2 nanoreactor prepared in Comparative Example 1 of the present invention.

[0044] Figure 12 It is a TEM image of the supported catalyst prepared in Comparative Example 2 of the present invention.

[0045] Figure 13 It is the XRD pattern of the supported catalyst prepared in Comparative Example 2 of the present invention.

[0046] Figure 14 It is a TEM image of the catalyst prepared in Comparative Example 3 of the present invention.

[0047] Figure 15 This is a TEM image of the supported catalyst prepared in Comparative Example 4 of the present invention.

[0048] Figure 16a and Figure 16b Comparison charts of multiple catalytic cycle stability tests of the catalysts of Example 1 and Comparative Example 2, respectively. DETAILED DESCRIPTION

[0049] In view of the deficiencies in the prior art, the inventors of this case have proposed the technical solution of the present invention after long-term research and extensive practice. The main purpose is to provide a hollow mesoporous SiO2 nanoreactor and a preparation method thereof. Cationic clusters with a hollow structure formed by coordination and complexation of polyethyleneimine and metal ions are formed by the reverse microemulsion method. The micelles formed by electrostatic bonding with anionic surfactants are used as templates. Tetraethyl orthosilicate is hydrolyzed to form silicified nano-SiO2 spheres. The metal ions are confined in the cavity. After high-temperature calcination, a SiO2 nanoreactor with a hollow mesoporous structure is obtained.

[0050] In some specific embodiments, the surfactant is hexadecyl polyoxyethylene ether carboxylic acid.

[0051] In some specific embodiments, the template is polyethyleneimine.

[0052] In some specific embodiments, a reverse microemulsion method is used, in which cationic clusters are formed by coordination and complexation of polyethyleneimine and metal ions, and the cationic clusters are combined with hexadecyl polyoxyethylene ether carboxylic acid by electrostatic attraction to form micelles as templates. After hydrolysis and polymerization of tetraethyl orthosilicate, siliconized nano-SiO2 spheres are formed, and after high-temperature calcination to remove the surfactant, a hollow mesoporous nanoreactor with a high specific surface area and a large pore size is obtained.

[0053] The cationic clusters formed by the coordination and complexation of polyethyleneimine and metal ions form a hollow structure for the material, while confining the metal ions in the cavity. The use of hexadecyl polyoxyethylene ether carboxylic acid forms large-sized mesopores for the material. This eliminates the influence of mass transfer on the catalytic reaction when the hollow nanoreactor is used as a catalyst. At the same time, the hollow structure can significantly increase the effective collision between the active components of the catalyst and the reactants through the confinement effect, thereby accelerating the catalytic reaction. The catalyst preparation process of the present invention is simple, the synthesized catalyst is uniform and highly reproducible, and it is easy to realize the automated production of catalyst preparation; the synthesized catalyst has good thermal stability and high reusability.

[0054] The technical solution, its implementation process and principles are further explained below.

[0055] As one aspect of the technical solution of the present invention, the present invention provides a method for preparing a hollow mesoporous SiO2 nanoreactor with a mesoporous structure, a high specific surface area and a high metal dispersion, the specific steps comprising:

[0056] Step 1: Add hexadecyl polyoxyethylene ether carboxylic acid and cyclohexane to a reaction flask with stirring at room temperature. Heat to form a clear solution. Then, add a metal salt solution, alkali solution, and ethanol to form a homogeneous, transparent solution. Add the required amount of tetraethyl orthosilicate to this solution and allow to react overnight.

[0057] Step 2: Transfer the reaction solution to a centrifuge tube, add ethanol to break the emulsion, let the solution stand for 1.0 h, and obtain the reaction product, which is centrifuged, washed, dried, and calcined to obtain a hollow mesoporous SiO2 nanoreactor containing metal or metal oxide.

[0058] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments and the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The experimental methods in the following examples where specific conditions are not specified are generally based on conventional conditions or the conditions recommended by the manufacturer.

[0059] Example 1

[0060] This embodiment provides a method for preparing a hollow mesoporous SiO2 nanoreactor with large pore size, high specific surface area and metal dispersion. Specifically, the preparation steps include:

[0061] (1) At room temperature, weigh 2.0 g of hexadecyl polyoxyethylene ether carboxylic acid and 10 mL of cyclohexane, heat to 50°C, and completely dissolve the hexadecyl polyoxyethylene ether carboxylic acid. At room temperature, add aqueous polyethyleneimine solution (number average molecular weight 3500) and aqueous potassium tetrachloropalladate solution (mass ratio of polyethyleneimine to metal ion 13:1) and stir until a clear solution is obtained. Then, add 150 μL of aqueous ammonia (concentration 37 wt%) and stir the reaction mixture for 0.5 h. Add 72.4 μL of tetraethyl orthosilicate and react for 9.0 h at a stirring speed of 500 rpm.

[0062] (2) After the reaction is completed, stirring is stopped and an equal volume of ethanol is added to the reaction solution to break the emulsion. After the product is precipitated, it is collected by centrifugation and washed with deionized water and ethanol three times each. It is placed in an oven and dried overnight at 60°C, and then calcined in a muffle furnace at 300°C and reduced in a tubular furnace at 250°C to obtain a highly dispersed Pd-containing hollow SiO2 nanoreactor.

[0063] like Figure 1 The figure shows the TEM image of the Pd hollow mesoporous SiO2 nanoreactor obtained in this example. It can be seen from the figure that the morphology of the prepared catalyst is a hollow mesoporous structure with a hollow size of 20nm, and the Pd metal nanoparticles are highly dispersed in the nanoreactor.

[0064] Figure 2 2 is the XRD pattern of this embodiment. It can be seen from the figure that the diffraction peaks of the product correspond to the SiO2 and Pd standard card patterns (JCPDS29-0085; JCPDS 460-1043), and no other impurity peaks appear.

[0065] Figure 3a and Figure 3b They are the BET diagram and pore size distribution of this embodiment respectively. It can be seen from the diagram that the material has abundant micropores and large-pore mesoporous structure.

[0066] Example 2

[0067] This example provides the effect of surfactants on catalyst structure. Specifically, the preparation steps include:

[0068] (1) At room temperature, 0.5 g of hexadecyl polyoxyethylene ether carboxylic acid and 10 mL of cyclohexane were weighed and completely dissolved under heating at 50°C. A polyethyleneimine aqueous solution (number average molecular weight 3500) and a potassium tetrachloropalladate aqueous solution (mass ratio of polyethyleneimine to metal ions 13:1) were added to the solution at room temperature and stirred until a clear solution was obtained. 150 μL of ammonia water (concentration 37 wt%) was then added to the solution. 72.4 μL of tetraethyl orthosilicate was then added to the solution and the reaction was continued for 9.0 h at a stirring speed of 500 rpm.

[0069] (2) After the reaction is completed, stirring is stopped and an equal volume of ethanol is added to the reaction solution to break the emulsion. After the product is precipitated, it is collected by centrifugation and washed with deionized water and ethanol three times each. It is placed in an oven and dried overnight at 60°C, and then calcined in a muffle furnace at 300°C and reduced in a tubular furnace at 250°C to obtain a highly dispersed Pd-containing hollow SiO2 nanoreactor.

[0070] Figure 4 This is a TEM image of the sample obtained in Example 2. It can be seen from the image that the prepared catalyst has a hollow structure with a hollow size of 20 nm, and the Pd metal nanoparticles are highly dispersed in the nanoreactor.

[0071] Figure 5a and Figure 5b 1 and 2 are BET diagrams and pore size distribution of Example 2, respectively. It can be seen from the diagram that the pores of the material are significantly smaller than those of Example 1, and the specific surface area is also significantly reduced.

[0072] Example 3

[0073] This example provides information on the effect of polyethyleneimine molecular weight on material structure. Specifically, the preparation steps include:

[0074] (1) At room temperature, weigh 2 g of hexadecyl polyoxyethylene ether carboxylic acid and 10 mL of cyclohexane, and heat at 50°C to completely dissolve the hexadecyl polyoxyethylene ether carboxylic acid. Add polyethyleneimine aqueous solution (number average molecular weight 300) and potassium tetrachloropalladate aqueous solution (mass ratio of polyethyleneimine to metal ion 13:1) at room temperature and stir until a clear solution is obtained. Then add 150 μL of ammonia water (concentration 37 wt%) and 72.4 μL of tetraethyl orthosilicate. The reaction is continued for 9.0 h at a stirring speed of 500 rpm.

[0075] (2) After the reaction is completed, stirring is stopped and an equal volume of ethanol is added to the reaction solution to break the emulsion. After the product is precipitated, it is collected by centrifugation and washed with deionized water and ethanol three times each. It is placed in an oven and dried overnight at 60°C, and then calcined in a muffle furnace at 300°C and reduced in a tubular furnace at 250°C to obtain a highly dispersed Pd-containing hollow SiO2 nanoreactor.

[0076] Figure 6 This is a TEM image of the sample obtained in Example 3. It can be seen from the image that the prepared catalyst has a hollow structure with a hollow size of 5 nm.

[0077] Example 4

[0078] This example provides the effect of the amount of tetraethyl silicate on the structure. Specifically, the preparation steps include:

[0079] (1) At room temperature, weigh 2 g of hexadecyl polyoxyethylene ether carboxylic acid and 10 mL of cyclohexane, and heat at 50°C to completely dissolve the hexadecyl polyoxyethylene ether carboxylic acid. At room temperature, add a polyethyleneimine aqueous solution (number average molecular weight 3500) and a potassium tetrachloropalladate aqueous solution (mass ratio of polyethyleneimine to metal ion 13:1) and stir until a clear solution is obtained. Then, add 150 μL of ammonia water (concentration 37 wt%) and 145 μL of tetraethyl orthosilicate. The mixture is reacted for 9.0 h at a stirring speed of 500 rpm.

[0080] (2) After the reaction is completed, stirring is stopped and an equal volume of ethanol is added to the reaction solution to break the emulsion. After the product is precipitated, it is collected by centrifugation and washed with deionized water and ethanol three times each. It is placed in an oven and dried overnight at 60°C, and then calcined in a muffle furnace at 300°C and reduced in a tubular furnace at 250°C to obtain a highly dispersed Pd-containing hollow SiO2 nanoreactor.

[0081] Figure 7 This is a TEM image of the sample obtained in Example 4. It can be seen from the image that the thickness of the catalyst shell layer is significantly thickened and the metal loading rate is reduced.

[0082] Example 5

[0083] This example provides the effect of calcination temperature on catalyst structure. Specifically, the preparation steps include:

[0084] (1) At room temperature, weigh 2 g of hexadecyl polyoxyethylene ether carboxylic acid and 10 mL of cyclohexane, and heat at 50°C to completely dissolve the hexadecyl polyoxyethylene ether carboxylic acid. At room temperature, add a polyethyleneimine aqueous solution (number average molecular weight 3500) and a potassium tetrachloropalladate aqueous solution (mass ratio of polyethyleneimine to metal ion 13:1) and stir until a clear solution is obtained. Then, add 150 μL of ammonia water (concentration 37 wt%) and 145 μL of tetraethyl orthosilicate. The mixture is reacted for 9.0 h at a stirring speed of 500 rpm.

[0085] (2) After the reaction is completed, stirring is stopped and an equal volume of ethanol is added to the reaction solution to break the emulsion. After the product is precipitated, it is collected by centrifugation and washed with deionized water and ethanol three times each. It is placed in an oven and dried overnight at 60°C, and then calcined in a muffle furnace at 800°C and reduced in a tubular furnace at 250°C to obtain a highly dispersed Pd-containing hollow SiO2 nanoreactor.

[0086] Figure 8 This is a TEM image of the sample obtained in this example. It can be seen from the image that after high-temperature calcination, the shell of the catalyst becomes obviously denser and the hollow structure shrinks.

[0087] Comparative Example 1

[0088] This comparative example provides a Pd hollow mesoporous SiO2 nanoreactor synthesized by traditional reverse microemulsion. Specifically, the steps are as follows:

[0089] (1) At room temperature, 3 g of hexadecyl polyoxyethylene ether alcohol and 20 mL of cyclohexane were weighed and heated at 50°C to completely dissolve the hexadecyl polyoxyethylene ether alcohol. At room temperature, an aqueous solution of polyethyleneimine (number average molecular weight of 75W) and an aqueous solution of potassium tetrachloropalladate (the molar ratio of polyethyleneimine to metal ions was 1:1) were added and stirred until a clear solution was obtained. 150 μL of aqueous ammonia (concentration of 37 wt%) was then added, followed by 72.4 μL of tetraethyl orthosilicate. The mixture was reacted for 9.0 h at a stirring speed of 500 rpm.

[0090] (2) After the reaction is completed, stirring is stopped and an equal volume of ethanol is added to the reaction solution to break the emulsion. After the product is precipitated, it is collected by centrifugation and washed with deionized water and ethanol three times each. It is placed in an oven and dried overnight at 60°C, and then calcined in a muffle furnace at 800°C and reduced in a tubular furnace at 250°C to obtain a highly dispersed Pd-containing hollow SiO2 nanoreactor.

[0091] Figure 9 This is a TEM image of the sample obtained in Comparative Example 1. It can be seen from the image that the catalyst has a hollow mesoporous structure and Pd is loaded in the hollow structure.

[0092] Figure 10 This is the XRD pattern of this comparative example. It can be seen from the figure that the diffraction peaks of the product correspond to the SiO2 and Pd standard card patterns (JCPDS29-0085; JCPDS 460-1043), and no other impurity peaks appear.

[0093] Figure 11a and Figure 11b They are the BET diagram and pore size distribution of this comparative example, from which it can be seen that the material has only a microporous structure.

[0094] Comparative Example 2

[0095] This comparative example provides a method for preparing a supported catalyst. Specifically, the preparation steps include:

[0096] Step 1: At 160°C and 700 rpm, add 20 mL of octadecene to a three-necked flask, add 3 mL of oleylamine solution containing 5.8 mg of potassium tetrachloropalladate, and heat and stir for 3 hours. Under nitrogen protection, after removing water from the solvent, transfer 2 mL of n-butyl lithium solution into the above solution to form a black Pd nanoparticle solution. Stir for 3 hours. After the reaction, centrifuge the reaction solution, wash with acetone three times, and dissolve the Pd in ​​ethanol for later use.

[0097] Step 2: Add 200 mg of SiO2 powder and Pd solution dissolved in ethanol to a three-necked flask. Under nitrogen protection at 70°C, dry the ethanol in the reaction flask. Dry the powder in an oven at 60°C, calcine it in a muffle furnace at 300°C, and reduce it in a tubular furnace at 250°C to obtain a comparative supported catalyst.

[0098] Figure 12 and Figure 13 TEM and XRD patterns of the supported catalyst of Comparative Example 2; Figure 12 It can be seen that the material obtained in this comparative example is solid and has no hollow mesoporous structure, which is obviously different from the hollow structure obtained in the example.

[0099] Figure 13 It can be seen that the diffraction peaks of the product correspond to the SiO2 and Pd standard card patterns (JCPDS29-0085; JCPDS 460-1043), and no other impurity peaks appear.

[0100] Comparative Example 3

[0101] This comparative example provides the effect of adding surfactant beyond the range on the material structure. Specifically, the preparation steps are as follows:

[0102] (1) At room temperature, weigh 3.0 g of hexadecyl polyoxyethylene ether carboxylic acid and 10 mL of cyclohexane, heat to 50°C, and completely dissolve the hexadecyl polyoxyethylene ether carboxylic acid. At room temperature, add polyethyleneimine aqueous solution (number average molecular weight 3500) and potassium tetrachloropalladate aqueous solution (mass ratio of polyethyleneimine to metal ion 13:1) and stir until a clear solution is obtained. Then, add 150 μL of ammonia water (concentration 37 wt%) and stir the reaction mixture for 0.5 h. Add 72.4 μL of tetraethyl orthosilicate and react for 9.0 h at a stirring speed of 500 rpm.

[0103] (2) After the reaction is completed, stirring is stopped and an equal volume of ethanol is added to the reaction solution to break the emulsion. After the product is precipitated, it is collected by centrifugation and washed with deionized water and ethanol three times each. It is placed in an oven and dried overnight at 60°C, and then calcined in a muffle furnace at 300°C and reduced in a tubular furnace at 250°C to obtain a highly dispersed Pd-containing hollow SiO2 nanoreactor.

[0104] like Figure 14 The TEM image of the material obtained in this comparative example is shown. It can be seen from the figure that the material is broken.

[0105] Comparative Example 4

[0106] This comparative example provides the effect of exceeding the template and metal ratio range on the material structure. Specifically, the preparation steps are as follows:

[0107] (1) At room temperature, weigh 2.0 g of hexadecyl polyoxyethylene ether carboxylic acid and 10 mL of cyclohexane, heat to 50°C, and completely dissolve the hexadecyl polyoxyethylene ether carboxylic acid. At room temperature, add polyethyleneimine aqueous solution (number average molecular weight 3500) and potassium tetrachloropalladate aqueous solution (mass ratio of polyethyleneimine to metal ion 16:1) and stir until a clear solution is obtained. Then, add 150 μL of ammonia water (concentration 37 wt%) and stir the reaction mixture for 0.5 h. Add 72.4 μL of tetraethyl orthosilicate and react for 9.0 h at a stirring speed of 500 rpm.

[0108] (2) After the reaction is completed, stirring is stopped and an equal volume of ethanol is added to the reaction solution to break the emulsion. After the product is precipitated, it is collected by centrifugation and washed with deionized water and ethanol three times each. It is placed in an oven and dried overnight at 60°C, and then calcined in a muffle furnace at 300°C and reduced in a tubular furnace at 250°C to obtain a highly dispersed Pd-containing hollow SiO2 nanoreactor.

[0109] like Figure 15 Shown is the TEM image of the material obtained in this comparison. It can be seen from the image that the corresponding hollow mesoporous structure cannot be formed.

[0110] Furthermore, the catalysts obtained in Examples 1-5 and Comparative Example 1 were used for the catalytic hydrogenation of phenol to produce cyclohexanone. The specific method was as follows: 5 mg of catalyst, 100 mg of phenol and 20 mL of ethanol were added to a reaction flask, and the reaction was carried out for 2.0 h under the conditions of magnetic stirring, heating at 45°C and hydrogen bubbling. The conversion rate of phenol and the selectivity of cyclohexanone of the liquid after the reaction were determined by gas chromatography. The test results are shown in Table 1. At the same time, in order to verify the stability of the catalysts in Example 1 and Comparative Example 2, the catalysts were subjected to multiple cycle stability tests according to the above method. The test data are shown in Table 1. Figure 16a and Figure 16bAs shown in the figure, it can be seen that the mesoporous hollow nanoreactor has better catalytic stability than the supported catalyst.

[0111] Table 1 Comparison of catalytic performance of the catalysts obtained in the examples and comparative examples

[0112] sample Phenol conversion rate / % Cyclohexanone selectivity / % Cyclohexanone yield / % Example 1 99.8％ 100.0％ 99.8％ Example 2 30.0％ 98％ 29.4％ Example 3 60.0％ 100％ 60.0％ Example 4 70.0％ 95.0％ 73.7％ Example 5 23.5％ 97.0％ 22.8％ Comparative Example 1 30.0％ 60.0％ 18.0％ Comparative Example 2 0％ 0％ 0％

[0113] It can be seen from the test results in Table 1 that the Pd-containing hollow mesoporous SiO2 nanoreactor (Example 1) prepared by this method has excellent catalytic activity and selectivity in the catalytic hydrogenation of phenol to cyclohexanone. Comparative Example 1 (synthesis of traditional hollow nanoreactor) basically has no reaction and Comparative Example 2 (supported catalyst) has poor reaction activity and selectivity. The main reason is that the hollow mesoporous nanoreactor catalyst synthesized by the present invention eliminates the influence of mass transfer resistance on the catalytic reaction due to its large pore size and high specific surface area; the protection of the nanoreactor shell inhibits the loss and agglomeration of the metal; at the same time, the presence of the hollow structure enables the catalyst to further accelerate the occurrence of deep hydrogenation reaction through the confinement effect, thereby significantly improving the rate and selectivity of the catalytic reaction.

[0114] The various aspects, embodiments, features and examples of the present invention should be considered as illustrative in all respects and are not intended to limit the present invention, the scope of which is defined solely by the claims. Other embodiments, modifications and uses will be apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0115] Throughout this disclosure, where compositions are described as having, containing, or comprising particular components, or where processes are described as having, containing, or comprising particular process steps, it is contemplated that the compositions taught by this disclosure also consist essentially of, or consist of, the recited components, and that the processes taught by this disclosure also consist essentially of, or consist of, the recited process steps.

[0116] Should be understood that, the order of each step or the order in which specific action is performed is not very important, as long as the present invention teachings remain operable.In addition, two or more steps or actions can be performed simultaneously.

[0117] Although the present invention has been described with reference to illustrative embodiments, it will be understood by those skilled in the art that various other changes, omissions, and / or additions may be made and that substantial equivalents may be substituted for elements of the described embodiments without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from the scope of the invention. Therefore, it is not intended that the present invention be limited to the specific embodiments disclosed for carrying out the invention, but rather that the invention will encompass all embodiments falling within the scope of the appended claims.

Claims

1. A method for preparing a mesoporous hollow SiO2 nanoreactor, characterized in that: A reverse microemulsion method is used to coordinate and complex the template agent with the metal ion to form a cationic cluster with a hollow structure, and the metal ion is contained in the hollow structure; The cationic clusters are combined with surfactants through electrostatic attraction to form micelles; Using the micelle as a template, the hydrolysis product of tetraethyl orthosilicate is formed into a silicified nano-SiO2 ball with a cavity structure, and after high-temperature calcination, a SiO2 nanoreactor containing metal or metal oxide with a hollow mesoporous structure is obtained.

2. The method for preparing a mesoporous hollow SiO2 nanoreactor according to claim 1, characterized in that: The following steps are involved: Step 1: Preparation of microemulsion: Dissolve the surfactant in the organic phase and heat and stir under stirring at room temperature; Step 2: Template preparation: Add template agent, metal salt solution, and alkali solution to form a uniform and transparent solution; Step 3: Preparation of nano-SiO2 spheres: Tetraethyl orthosilicate is added to the solution, and tetraethyl orthosilicate undergoes hydrolysis and polymerization reaction, and the reaction product encapsulates the metal ions to form a core-shell structure; Step 4: Preparation of the reactor: After the reaction is completed, the emulsion is broken, and the product is post-treated and then calcined at high temperature to obtain a mesoporous hollow SiO2 nanoreactor containing metal or metal oxide.

3. The method for preparing a mesoporous hollow SiO2 nanoreactor according to claim 2, characterized in that: In step 1, the surfactant includes hexadecyl polyoxyethylene ether carboxylic acid; the organic phase is cyclohexane; The amount of the surfactant added is 0.1-1 g per 5 mL of the organic phase; And / or, the heating temperature is 40-60°C.

4. The controllable preparation method of the mesoporous hollow SiO2 nanoreactor according to claim 2, characterized in that: In step 2, the metal salt solution is a metal chlorate or nitrate solution; and / or, the alkali solution is aqueous ammonia; And / or, the template agent is polyethyleneimine, and the molecular weight of polyethyleneimine is 300-75w; And / or, the molar ratio of the template to the metal salt is 1:1 to 1:

13.

5. The method for preparing a mesoporous hollow SiO2 nanoreactor according to claim 3, characterized in that: In step 3, the molar ratio of tetraethyl silicate to the metal salt is 20:1 to 180:1; In step 4, the mesoporous hollow SiO2 nanoreactor obtained has a mesopore size of 5-30 nm.

6. The method for preparing a mesoporous hollow SiO2 nanoreactor according to claim 1, characterized in that: In step 4, the post-treatment includes centrifugal washing with deionized water and ethanol and then drying, and the drying temperature is 60-80°C; The high temperature calcination temperature is 300-400°C and the time is 2-6h; The reduction temperature is 200-300° C., and the reduction time is 2-6 hours.

7. A mesoporous hollow SiO2 nanoreactor prepared by the preparation method according to any one of claims 1 to 6.

8. Use of a mesoporous hollow SiO2 nanoreactor prepared by the preparation method according to any one of claims 1 to 6, or a mesoporous hollow SiO2 nanoreactor according to claim 7 in catalytic hydrogenation of phenol.

9. A catalyst comprising a mesoporous hollow SiO2 nanoreactor prepared by the preparation method according to any one of claims 1 to 6, or a mesoporous hollow SiO2 nanoreactor according to claim 7, which can be used for the catalytic hydrogenation of phenol to produce cyclohexanone; the yield of cyclohexanone is ≥99.8%.

10. Cyclohexanone prepared by using phenol as a raw material through a catalytic reaction under the action of the catalyst according to claim 9.

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