Method for preparing molecular sieve confinement active metal catalyst and application of catalyst

Abstract

The invention relates to a method for preparing a molecular sieve confinement active metal catalyst and application of the catalyst. According to the preparation method of the molecular sieve confinement active metal catalyst, a traditional organic structure directing agent is replaced with a seed crystal method, and a metal-molecular sieve catalyst is prepared in an in-situ confinement mode by directly adding molecular sieve seed crystals into a metal silicon-aluminum sol precursor. The metal-coated molecular sieve prepared by the method has metal species with smaller size, the synthesis method is simple and convenient, the use of an organic structure-directing agent is saved, and the cost of the catalyst is reduced. The metal scale of the metal-at-molecular sieve is monatomic, sub-nano, and nano-scale. The sub-nano palladium-coated molecular sieve catalyst is applied to catalysis of semi-hydrogenation reaction of phenylacetylene, has excellent catalytic performance, and shows accurate catalytic selectivity on alkyne molecules less than # imgabs0 #.

Description

Technical Field

[0001] The present invention relates to the preparation of a molecular sieve-confined active metal catalyst and the application of the catalyst in the field of alkyne semi-hydrogenation technology, belonging to the field of chemical engineering technology. Background Art

[0002] Molecular sieves are well-known for their ordered porous structure, uniform pores, and extremely high thermal and chemical stabilities. These excellent properties make molecular sieves ideal carriers for confining the synthesis of metal catalysts. In-situ confining and anchoring metal clusters in molecular sieves not only enhances the interaction between the metal and the molecular sieve structure, inhibits the aggregation of metal clusters, but also effectively improves the catalytic activity and chemical stability of the catalyst. Currently, the method of in-situ coating of ultra-small clusters in molecular sieves mainly relies on the ligand protection method, which is prepared by inducing nucleation using traditional organic templating agents. The preparation process is cumbersome and the synthesis cycle is long. More importantly, the temperature required for the addition of the templating agent and the calcination removal process is too high, which easily causes the aggregation of metal atoms with high surface energy and is not conducive to anchoring single atoms or sub-nanoscale metal clusters in the molecular sieve framework.

[0003] Styrene is an important chemical intermediate for the production of polystyrene, ABS resin, styrene-butadiene rubber, etc., with an annual output as high as 37 million tons. The by-product phenylacetylene produced by naphtha cracking is a key factor affecting the production of polymer-grade styrene. To ensure the quality of downstream products, catalytic semi-hydrogenation of alkynes to remove a small amount of by-product phenylacetylene has become an important way to improve the quality of styrene. Since palladium (Pd) particle catalysts have high catalytic activity, they are widely used in the catalytic semi-hydrogenation reaction of phenylacetylene. However, β-PdH species are easily formed on the subsurface of the exposed large palladium particles, resulting in over-hydrogenation reactions. Moreover, the methods reported subsequently by doping a second metal or masking some palladium active sites, although increasing the olefin selectivity, result in low utilization rate of palladium atoms and high cost of the catalyst. Although isolated palladium atom sites can coordinate with electronegative heteroatoms (N, O, etc.) to reduce the electron density of palladium, weaken the activation of intermediate olefins, and thus improve the olefin selectivity, this also reduces its ability to adsorb and dissociate hydrogen.

[0004] Therefore, it is necessary to find a simple method to in-situ confine single atoms or sub-nanoscale metals inside the molecular sieve framework to form a molecular sieve-based single atom or sub-nanoscale metal catalyst. Summary of the Invention

[0005] To overcome the problem of the difficulty in in-situ confining the preparation of sub-nanoscale metal cluster molecular sieve catalysts by using an organic structure-directing agent through a hydrothermal synthesis method.

[0006] The present invention provides a method for preparing a molecular sieve encapsulated active metal catalyst. By using molecular sieve seeds instead of organic structure-directing agents, single-atom, sub-nanoscale or nanoscale metal@molecular sieve catalysts are in-situ confined and prepared by directly adding molecular sieve seeds into a silica-alumina sol containing a palladium metal precursor.

[0007] Specifically, the present invention provides a method for preparing an M@molecular sieve material, including:

[0008] Step S1. Prepare an aqueous solution of a metal M complex by mixing a metal M salt and a ligand compound to form the aqueous solution. The ligand compound is selected from N-containing compounds, such as NH3, ethylenediamine, diethylenetriamine, triethylenetetramine or tetraethylenepentamine.

[0009] The metal M salt is an inorganic or organic salt of metal M, such as nitrate, chloride, sulfate, phosphate, oxalate, citrate, etc.

[0010] Step S2. Prepare an M@molecular sieve silica-alumina sol precursor solution by dropping the aqueous metal complex solution obtained in Step S1 into the silica-alumina sol precursor solution and stirring at room temperature.

[0011] Step S3. Add molecular sieve seeds to the metal silica-alumina sol solution in Step S2, stir at room temperature for 1 - 2 h, then transfer the mixed solution to a reaction kettle, carry out static crystallization at 120°C - 180°C for 12 h - 72 h, cool to room temperature, wash with water, and dry.

[0012] Step S4. Calcinate the sample powder obtained in Step S3 at 300°C - 500°C to obtain the sample.

[0013] Among them, M is selected from noble metals, Group IB metals, and Group IIB metals; in M@molecular sieve, metal M is in-situ confined in the molecular sieve framework structure, and metal M exists in the form of single-atom sites, sub-nanoscale clusters or n-nanoscale states respectively, where n is between 2 - 5 nm.

[0014] The selected molecular sieve is not limited in type, and any molecular sieve that can use seeds instead of it as a structure-directing agent to assist in synthesis can be used in the method of the present invention. During the synthesis of the molecular sieve, there is no need to add traditional organic templating agents. The molecular sieve is selected from MFI-type molecular sieves, BEA* -type molecular sieves, FAU-type molecular sieves, RTH-type molecular sieves, MTW-type molecular sieves, LEV-type molecular sieves, FER-type molecular sieves, MEL-type molecular sieves. The preferred molecular sieve is an MFI-type molecular sieve or a BEA* -type molecular sieve. The aforementioned "molecular sieve that can use seeds instead of it as a structure-directing agent to assist in synthesis" and the specific synthesis scheme can refer to Microporous and mesoporous materials, 2014, 189, 22 - 30.

[0015] The silica-alumina sol precursor solution is a commonly used precursor solution for preparing molecular sieves in the art. The silica-alumina sol precursor is generally a mixture of a silicon source, an aluminum source, an alkali source, a template, and water. Common silicon sources include ethyl orthosilicate, silica sol, and sodium silicate. The aluminum sources include aluminum isopropoxide, aluminum nitrate, and sodium metaaluminate. The alkali sources include sodium hydroxide and potassium hydroxide. The template is a structure-directing agent. Different molecular sieves have different structure-directing agents. For example, the template for MFI is tetrapropylammonium hydroxide, while for BEA* molecular sieve it is tetraethylammonium hydroxide.

[0016] Preferably, the N-containing compound in step S1 is ethylenediamine.

[0017] Preferably, the stirring time in step S2 is 4-5 hours.

[0018] Preferably, the static crystallization time in step S3 is 24h-72h,

[0019] In step S4, the calcination temperature is 350° C.-450° C., and the calcination time is 2 h-3 h.

[0020] In fact, according to the method of the present invention, the molecular sieve encapsulates part of the metal in a single atomic state, and part of the metal exists in a state where several atoms are clustered together or in a state of nanoparticles. But it is obvious that the size of the active metal in the metal@molecular sieve catalyst prepared by the seed crystal method is smaller than that of the metal@molecular sieve catalyst obtained by the traditional organic structure directing agent method. The possible reason is that the method of the present invention avoids the use of organic templates to preferentially fill and form the molecular sieve pores, which easily leads to the concentrated distribution of metal complexes in the molecular sieve framework. At the same time, the removal of the organic template requires a long period of high-temperature calcination (550°C, more than 6h) under air conditions, which easily leads to the migration and agglomeration of metal single atoms or sub-nano particles with high surface energy in the molecular sieve framework structure, resulting in an increase in the scale of its active center.

[0021] The present invention selects to use zeolite molecular sieve seeds instead of traditional organic structure directing agents, and in situ confines the preparation of single-atom, sub-nanometer or nanometer-sized metal molecular sieve catalysts (such as nano-Ag@Zeolite, sub-nanometer Pd@Zeolite, Co@Zeolite, Ni@Zeoltie, single-atom Rh@Zeolite, Cu@Zeolite, Pt@Zeolite, Zn@Zeolite). The in situ confinement of the sub-nanometer metal molecular sieve catalyst using the seed crystal method can accelerate the crystallization rate of the molecular sieve, shorten the catalyst preparation cycle, and eliminate the need for high-temperature calcination to remove the organic structure directing agent. The obtained sub-nanometer palladium cluster molecular sieve catalyst (Pd@Zeolite) can be used to efficiently catalyze the semi-hydrogenation reaction of phenylacetylene, thereby achieving the purpose of the present invention.

[0022] The zeolite seeds can be commercially available or prepared by the common methods for preparing zeolites in the art. For the specific synthesis scheme, reference can be made to Microporous and mesoporous materials, 2014, 189, 22 - 30.

[0023] As an example, the present invention discloses a method for preparing MFI zeolite seeds, and the specific operation is as follows:

[0024] (1) Preparation: silicon source, tetraethyl orthosilicate or 40% aqueous silica solution, organic structure - directing agent, tetrapropylammonium hydroxide;

[0025] (2) Prepare a zeolite seed silica precursor solution. Add the required silicon source, water and organic template agent in a ratio of TEOS / TPAOH / H2O = 1.0:0.28:9.6 to a plastic beaker and stir at room temperature. The resulting solution is the zeolite seed silica precursor solution.

[0026] (3) After stirring for 6 h - 12 h, transfer the obtained silica solution to a reaction kettle and carry out static crystallization at 120 °C - 140 °C for 12 h - 72 h. After cooling to room temperature, wash the obtained precipitate powder sample with water and dry it overnight at 60 °C - 80 °C or freeze - dry it overnight. Remove the organic structure - directing agent through a high - temperature calcination process at 500 °C - 600 °C for 6 h - 10 h. The obtained powder is the MFI zeolite seed.

[0027] In addition, in the confined synthesis of the sub - nanoscale palladium zeolite catalyst of the present invention, the size of the palladium metal is between that of nanoparticles and single - atom catalysts, and it has the advantages of high activity of palladium particles and high selectivity of palladium single - atom catalysts in the semi - hydrogenation reaction of phenylacetylene.

[0028] The present invention further provides a method for the semi - hydrogenation of R1C≡CH alkynes. React R1C≡CH with hydrogen to obtain the product R1CH = CH2, where R1 is a phenyl group, a phenyl group substituted by C 1-6 alkyl, C 1-6 alkoxy, halogen, OH or amino - substituted phenyl group. It is characterized in that Pd@Zeolite is used as a catalyst, and this catalyst is prepared by the aforementioned method.

[0029] Preferably, R1 is 4 - methylphenyl, phenyl.

[0030] Furthermore, the method is carried out under the conditions of a H2 pressure of 0.5 - 3 MPa and a temperature of 40 °C to 80 °C. Preferably, the reaction temperature of the reaction is 60 °C to 80 °C, and the reaction time is 2 h to 3 h.

[0031] Term description

[0032] Sub-nanoscale: It refers to objects describing tiny scales, between the nanoscale and the atomic scale, generally defined as below 2 nm in size.

[0033] Confinement effect: It refers to the phenomenon that when a substance is in a confined space, its physical and chemical properties change significantly due to the restricted movement.

[0034] Shape-selective catalysis: It refers to the unique catalytic performance of a type of molecular sieve. When the catalytic active center is restricted inside the pore structure of this type of molecular sieve, the reaction occurs in the pore channels of the molecular sieve crystal; only specific molecules with sizes and shapes matching the pore channels of the molecular sieve and capable of diffusing into the pore channels can react with the catalytic active center to form products.

[0035] Beneficial effects

[0036] The present invention provides a method for confining the synthesis of single-atom, sub-nanoscale, and nanoscale metal catalysts by the seed method. The catalyst is an M@zeolite catalyst. This method has broad applicability, is suitable for industrial production, and compared with the traditional method of confining the preparation of M@zeolite catalysts using organic templates, it has the advantages of small active metal size, low cost, and greater industrialization prospects.

[0037] In addition, the present invention provides a method for semi-hydrogenation of phenylacetylene. The conversion rate of this method is 98%, and the selectivity of styrene is 97%. The TOF value of the semi-hydrogenation of phenylacetylene is as high as 48576 mol Pd / mol C＝C / h. Brief description of the drawings

[0038] Figure 1 It is a transmission electron microscope image of MFI-type zeolite seeds.

[0039] Figure 2 It is a spherical aberration electron microscope image of Pd@ZSM-5.

[0040] Figure 3 It is a spherical aberration electron microscope image of Ag@ZSM-5.

[0041] Figure 4 It is a spherical aberration electron microscope image of Rh1@ZSM-5.

[0042] Figure 5 It is a high-resolution electron microscope image of Pd@ZSM-5-T.

[0043] Figure 6 It is a high-resolution electron microscope image of Pd / ZSM-5. Detailed implementation manners

[0044] Specific implementation cases will be described in detail here. The specific operation steps in the following implementation cases do not represent all implementation manners consistent with the present invention, but they are only the most representative examples in the present invention. These implementation cases can better highlight the actual application effects of the present invention.

[0045] The technical solution of the present invention will be described in detail below with specific implementation cases.

[0046] Example 1 Sub-nanoscale Pd@Zeolite Catalyst

[0047] Step 1. Prepare MFI-type zeolite seeds. That is, add 16 g of tetrapropylammonium hydroxide (25%, aqueous solution) and 14.4 g of tetraethyl orthosilicate to a 50 mL plastic flask and stir at room temperature for 12 h. Subsequently, transfer the mixed solution to a reaction kettle equipped with a 100 mL polytetrafluoroethylene liner and carry out static crystallization at 120 °C for 12 h. After the reaction is completed, wait for the reaction kettle to cool to room temperature, centrifuge to remove the upper liquid, wash with distilled water 3-4 times, and freeze-dry overnight to obtain a white powder sample. The white powder sample is calcined at 550 °C for 6 h to obtain MFI-type zeolite seeds with a particle size of about 50 nm to 100 nm ( Figure 1 ).

[0048] Step 2. Prepare an aqueous solution of 0.09 M [Pd(NH2CH2CH2NH2)2]Cl2. Dissolve 0.16 g of palladium dichloride in 2 mL of aqueous solution, then add 1 mL of excess ethylenediamine solution and stir at room temperature for 10 minutes. Subsequently, transfer the [Pd(NH2CH2CH2NH2)2]Cl2 aqueous solution to a 10 mL volumetric flask and make up the volume to 10 mL with distilled water.

[0049] Step 3. Prepare a palladium sub-nanocluster zeolite aluminosilicate sol precursor solution. Dissolve 0.216 g of sodium aluminate and 0.382 g of sodium hydroxide in 22.84 mL of distilled water. Add 0.24 mL of the [Pd(NH2CH2CH2NH2)2]Cl2 solution prepared in Step 2 to the above mixed solution, stir at room temperature for 10 minutes, then add 5.765 g of silica sol (40%, aqueous solution), and continue to stir at room temperature for 5 h.

[0050] Step 4. Add the seeds prepared in Step 1 to the aluminosilicate sol solution prepared in Step 3. After stirring at room temperature for 1 h, transfer the mixed solution to a 100 mL reaction kettle and carry out static crystallization at 180 °C for 24 h. After cooling to room temperature, centrifuge and wash with water, and dry the sample overnight at 80 °C.

[0051] Step 5. Remove the metal protecting group ethylenediamine. The sample powder obtained in Step 4 is calcined in air at 400 °C for 2 h to remove the ethylenediamine ligand, and the sample obtained by reducing with H2 at 300 °C for 2 h is Pd@ZSM-5. The aberration-corrected electron microscope image is Figure 2 。

[0052] After the above steps, the white powder palladium sub-nanocluster molecular sieve catalyst (Pd@ZSM-5) of the present invention is obtained.

[0053] Example 2 Nano-scale Ag@Molecular Sieve Catalyst

[0054] Step 1. Prepare MFI-type molecular sieve seeds, that is, add 16 g of tetrapropylammonium hydroxide (25%, aqueous solution) and 14.4 g of tetraethyl orthosilicate to a 50 mL plastic flask, and stir at room temperature for 12 h. Subsequently, transfer the mixed solution to a reaction kettle equipped with a 100 mL polytetrafluoroethylene liner, and carry out static crystallization at 120 °C for 12 h. After the reaction is completed, wait for the reaction kettle to cool to room temperature, centrifuge to remove the upper liquid, wash with distilled water 3-4 times, and freeze-dry overnight to obtain a white powder sample. The white powder sample is calcined at 550 °C for 6 h to obtain MFI-type molecular sieve seeds with a particle size of about 50 nm to 100 nm ( Figure 1 )。

[0055] Step 2. Prepare a 0.09 M [Ag(NH2CH2CH2NH2)2]Cl aqueous solution. Dissolve 0.15 g of silver nitrate in 2 mL of aqueous solution, then add 1 mL of excess ethylenediamine solution, stir at room temperature for 10 minutes, and then transfer the [Ag(NH2CH2CH2NH2)2]Cl aqueous solution to a 10 mL volumetric flask and make up to 10 mL with distilled water.

[0056] Step 3. Prepare a silver-based nanoparticle molecular sieve silica-alumina sol precursor solution. Dissolve 0.216 g of sodium aluminate and 0.382 g of sodium hydroxide in 20.7 mL of distilled water. Add 2.564 mL of the [Ag(NH2CH2CH2NH2)2]Cl solution prepared in Step 2 to the above mixed solution, stir at room temperature for 10 minutes, then add 5.765 g of silica sol (40%, aqueous solution), and continue to stir at room temperature for 5 h.

[0057] Step 4. Add the seeds prepared in Step 1 to the silica-alumina sol solution prepared in Step 3. After stirring at room temperature for 1 h, transfer the mixed solution to a 100 mL reaction kettle, carry out static crystallization at 180 °C for 24 h, cool to room temperature, centrifuge and wash with water, and dry the sample overnight at 80 °C.

[0058] Step 5. Removal of the metal protecting group ethylenediamine. The sample powder obtained in Step 4 is calcined in air at 400 °C for 2 h to remove the ethylenediamine ligand, and the sample obtained by reducing with H2 at 300 °C for 2 h is Ag@ZSM-5, and the aberration-corrected electron microscope image is Figure 3 。

[0059] Example 3 Single-atom-scale Rh1@Molecular Sieve Catalyst

[0060] Step 1. Prepare MFI type molecular sieve seed crystals, that is, add 16g of tetrapropylammonium hydroxide (25%, aqueous solution) and 14.4g of tetraethyl orthosilicate into a 50mL plastic flask and stir at room temperature for 12h. Subsequently, transfer the mixed solution to a reactor equipped with a 100mL polytetrafluoroethylene liner and statically crystallize for 12h at 120°C. After the reaction is completed, wait for the reactor to cool to room temperature, centrifuge to remove the upper liquid, wash with distilled water 3-4 times, and freeze-dry overnight to obtain a white powder sample. The white powder sample was calcined at 550°C for 6h to obtain MFI type molecular sieve seed crystals with a particle size of about 50nm to 100nm ( Figure 1 ).

[0061] Step 2. Prepare 0.09M [Rh(NH2CH2CH2NH2)3]Cl3 aqueous solution, take 0.19g rhodium trichloride and dissolve it in 2mL aqueous solution, then add 1mL excess ethylenediamine solution, stir at room temperature for 10 minutes, then transfer the [Rh(NH2CH2CH2NH2)3]Cl3 aqueous solution to a 10mL volumetric flask and dilute to 10mL with distilled water.

[0062] Step 3. Prepare a rhodium-based single-atom molecular sieve silica gel precursor solution, take 0.216g of sodium aluminate and 0.382g of sodium hydroxide and dissolve them in 22.84mL of distilled water, take 0.25mL of the [Rh(NH2CH2CH2NH2)3]Cl3 solution in step 2 and add it to the above mixed solution. After stirring at room temperature for 10 minutes, add 5.765g of silica sol (40%, aqueous solution) and continue stirring at room temperature for 5h.

[0063] Step 4. Add the seed crystals in step 1 to the silica gel solution in step 3. After stirring at room temperature for 1 hour, transfer the mixed solution to a 100 mL reactor and statically crystallize at 180°C for 24 hours. After cooling to room temperature, centrifuge and wash with water. Dry the sample at 80°C overnight.

[0064] Step 5. Removal of the metal protecting group ethylenediamine. The powder sample obtained in step 4 was calcined in air at 400℃ for 2h to remove the ethylenediamine ligand. The obtained sample is Rh1@ZSM-5. The spherical aberration electron microscope image is Figure 4 .

[0065] Through the above steps, the white powder rhodium-based single-atom molecular sieve catalyst (Rh1@ZSM-5) of the present invention is obtained.

[0066] Example 4 Single-atom scale Cu1@ZSM-5

[0067] The specific preparation method is the same as that of Example 3, except that the metal salt in step 2 is 0.217 g of Cu(NO3)2·3H2O, and the catalyst is named Cu1@ZSM-5.

[0068] Example 5 Single-atom Scale Zn1@ZSM-5

[0069] The specific preparation method is the same as that of Example 3, except that in step 2, the metal salt is 0.268 g of Zn(NO3)2·6H2O, and the catalyst is named Zn1@ZSM-5.

[0070] Example 6 Single-atom Scale Pt1@ZSM-5

[0071] The specific preparation method is the same as that of Example 3, except that in step 2, the metal salt is 0.239 g of PtCl2, and the catalyst is named Pt1@ZSM-5.

[0072] Example 7 Single-atom Scale Rh1@Beta

[0073] Step 1. Prepare BEA* type molecular sieve seeds. That is, add 0.282 g of NaOH, 0.32 g of H2O, 10.4 g of tetraethylammonium hydroxide (25%, aqueous solution) and 10 g of silica sol (40%, aqueous solution) into a 50 mL plastic flask, and stir at room temperature for 10 min. Subsequently, add 0.274 g of NaAlO2, transfer the mixed solution to a reaction kettle equipped with a 100 mL polytetrafluoroethylene liner, and carry out static crystallization at 120 °C for 72 h. After the reaction is completed, wait for the reaction kettle to cool to room temperature, centrifuge to remove the upper liquid, wash with distilled water 3-4 times, and freeze-dry overnight to obtain a white powder sample. The white powder sample is calcined at 550 °C for 6 h to obtain BEA* type molecular sieve seeds.

[0074] Step 2. Prepare a 0.09 M [Rh(NH2CH2CH2NH2)3]Cl3 aqueous solution. Dissolve 0.19 g of rhodium trichloride in 2 mL of aqueous solution, then add 1 mL of excess ethylenediamine solution, stir at room temperature for 10 minutes, and then transfer the [Rh(NH2CH2CH2NH2)3]Cl3 aqueous solution to a 10 mL volumetric flask, and make up the volume to 10 mL with distilled water.

[0075] Step 3. Prepare a rhodium-based single-atom molecular sieve silica gel precursor solution. Dissolve 1.28 g of sodium aluminate and 2.24 g of sodium hydroxide in 13.6 mL of distilled water. Add 0.64 mL of the [Rh(NH2CH2CH2NH2)3]Cl3 solution in step 2 to the above mixed solution, stir at room temperature for 10 minutes, then add 8 g of white carbon black, and continue to stir at room temperature for 12 h.

[0076] Step 4. Add 0.4 g of the seed crystals in Step 1 to the silica gel solution in Step 3. After stirring at room temperature for 10 min, transfer the mixed solution to a 100 mL autoclave, and carry out static crystallization at 120 °C for 72 h. After cooling to room temperature, carry out centrifugation and washing with water, and dry the sample overnight at 80 °C.

[0077] Step 5. Removal of the metal protecting group ethylenediamine. The sample powder obtained in Step 4 is calcined in air at 400 °C for 2 h to remove the ethylenediamine ligand, and the obtained sample is Rh1@Beta.

[0078] Through the above steps, the white powder rhodium-based single-atom molecular sieve catalyst (Rh1@Beta) of the present invention is obtained.

[0079] Example 7 Single-atom scale Cu1@Beta

[0080] The specific preparation method is the same as that of Example 6, and the difference is that the metal salt in Step 2 is 0.217 g of Cu(NO3)2·3H2O, and the catalyst is named Cu1@Beta.

[0081] Example 8 Single-atom scale Zn1@Beta

[0082] The specific preparation method is the same as that of Example 6, and the difference is that the metal salt in Step 2 is 0.268 g of Zn(NO3)2·6H2O, and the catalyst is named Zn1@Beta.

[0083] Example 9 Single-atom scale Pt1@Beta

[0084] The specific preparation method is the same as that of Example 6, and the difference is that the metal salt in Step 2 is 0.239 g of PtCl2, and the catalyst is named Pt1@Beta.

[0085] Comparative Example 1

[0086] Using an organic template as a molecular sieve structure directing agent, a palladium-based molecular sieve catalyst (Pd@ZSM-5-T) is in-situ synthesized for the catalytic semi-hydrogenation reaction of phenylacetylene, which is a comparative sample of the in-situ confinement preparation of palladium sub-nanocluster catalysts by the seed crystal method. The specific synthesis steps are as follows:

[0087] Step 1. Prepare a 0.09 M aqueous solution of [Pd(NH2CH2CH2NH2)2]Cl2. Take 0.16 g of palladium dichloride and dissolve it in 2 mL of aqueous solution, then add 1 mL of excessive ethylenediamine solution, stir at room temperature for 10 minutes, and then transfer the aqueous solution of [Pd(NH2CH2CH2NH2)2]Cl2 to a 10 mL volumetric flask and make up the volume to 10 mL with distilled water.

[0088] Step 2. Preparation of palladium-based molecular sieve silica-alumina sol precursor solution. Take 3.23 g of organic template tetrapropylammonium hydroxide and 0.32 g of sodium hydroxide and dissolve them in 29.7 mL of distilled water. Stir at room temperature for 10 minutes, then successively add 0.24 mL of the [Pd(NH2CH2CH2NH2)2]Cl2 solution in Step 2 and 8.26 g of tetraethyl orthosilicate, and continue to stir at room temperature for 10 minutes. Subsequently, add 0.41 g of Al(NO3)3·9H2O. After the obtained mixed solution is continuously stirred at room temperature for 6 h, transfer the solution to a 100 mL autoclave and carry out static crystallization at 170 °C for 120 h. After cooling to room temperature, centrifuge and wash with water 3-4 times, and dry the sample overnight at 80 °C.

[0089] Step 3. Removal of template. The powder sample obtained in Step 2 is calcined in air at 550 °C for 6 h to remove tetrapropylammonium hydroxide, and the white powder sample obtained by reducing with H2 at 300 °C for 2 h is Pd@ZSM-5-T. The transmission electron microscope image is Figure 5 .

[0090] Through the above steps, the comparative sample palladium-based molecular sieve catalyst (Pd@ZSM-5-T) is obtained.

[0091] Comparative Example 2

[0092] Synthesize pure ZSM-5 molecular sieve by the seed method, prepare palladium-based supported molecular sieve catalyst (Pd / ZSM-5) by the traditional impregnation method, and apply it to the catalytic semi-hydrogenation reaction of phenylacetylene. It is a comparative sample of the in-situ confinement preparation of palladium sub-nanocluster catalyst by the seed method. The specific synthesis steps are as follows:

[0093] Step 1. Preparation of MFI-type molecular sieve seeds. That is, add 16 g of tetrapropylammonium hydroxide (25%, aqueous solution) and 14.4 g of tetraethyl orthosilicate to a 50 mL plastic flask and stir at room temperature for 12 h. Subsequently, transfer the mixed solution to an autoclave equipped with a 100 mL polytetrafluoroethylene liner and carry out static crystallization at 120 °C for 12 h. After the reaction is completed, wait for the autoclave to cool to room temperature, centrifuge to remove the upper liquid, and wash with distilled water 3-4 times, and freeze-dry overnight to obtain a white powder sample. The white powder sample is calcined at 550 °C for 6 h to obtain MFI-type molecular sieve seeds with a particle size of about 50 nm to 100 nm ( Figure 1 ).

[0094] Step 2. Preparation of molecular sieve silica-alumina sol precursor solution. Take 0.216 g of sodium metaaluminate and 0.382 g of sodium hydroxide and dissolve them in 23 mL of distilled water. Stir at room temperature for 10 minutes, then add 5.765 g of silica sol (40%, aqueous solution), and continue to stir at room temperature for 5 h.

[0095] Step 3. Add the seeds in Step 1 to the silica-alumina sol in Step 2. After stirring at room temperature for 1 h, transfer the mixed solution to a 100 mL autoclave, crystallize statically at 180 °C for 24 h, cool to room temperature, then centrifuge and wash with water, and dry the sample overnight at 80 °C.

[0096] Step 4. Take 1 g of the sample obtained after drying in Step 3, add 2 mL of 2.2 mM aqueous Na2PdCl4 solution, stir at 70 °C for 6 h, and slowly evaporate the water solvent to obtain a solid powder sample.

[0097] Step 5. The powder sample obtained in Step 4 is calcined in air at 400 °C for 2 h and then reduced with H2 at 300 °C for 2 h. The obtained sample is Pd / ZSM-5, and the transmission electron microscope image is Figure 6 .

[0098] Through the above steps, a comparative sample palladium-based molecular sieve supported catalyst (Pd / ZSM-5) is obtained.

[0099] Comparative Example 3

[0100] Take 7.52×10 -5 mmol of commercially available Lindlar catalyst, from Shanghai Merck Chemical Technology Co., Ltd., with the product number M67205-5G.

[0101] Application test experiments and data

[0102] 1. Content test

[0103] Perform component tests on the catalysts obtained in Example 1 and Comparative Examples 1-2. The test results are shown in Table 1:

[0104] Table 1. Pd content of the products in Example 1 and Comparative Examples 1-2.

[0105] Example 1 Comparative Example 1 Comparative Example 2 Pd content (wt, %) 0.04 0.04 0.04

[0106] 2. Test results of phenylacetylene semi-hydrogenation

[0107] Dissolve 7.5 mmol of monomers (phenylacetylene, 4-methylphenylacetylene, 2-methylphenylacetylene, 3-methylphenylacetylene, 1-ethynylnaphthalene, diphenylacetylene, 4-fluorophenylacetylene, 4-chlorophenylacetylene, 4-ethynylaniline) and 20 μL of n-dodecane internal standard molecules in 10 mL of n-hexane solution. Then add 20 mg of the catalyst prepared in the example to the above mixed solution and disperse it evenly.

[0108] After replacing the air in the reaction kettle with H2 three times, the pressure in the kettle was maintained at 1 MPa, and the reaction solution was stirred for 3 h at 65 °C. After centrifuging the obtained solution, the chemical components in it were analyzed by gas chromatography-mass spectrometry. After calculation, the conversion rate of alkynes and the selectivity of alkenes were obtained. The catalytic efficiency and TOF value of the catalyst were calculated according to the conversion rate and aldehyde selectivity. The results are shown in Tables 2 and 3.

[0109] The catalysts used were the catalysts of Example 1 and Comparative Examples 1-3. Among them, the addition amounts of the catalysts of Example 1 and Comparative Examples 1-2 were 20 mg; the addition amount of the catalyst of Comparative Example 3 was 7.52×10 -5 mmol.

[0110] Table 2. Comparison of the performance of catalytic semi-hydrogenation of phenylacetylene.

[0111] Substrate Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Phenylacetylene conversion rate (%) 98 55 78 6 Styrene selectivity (%) 97 87 93 90 <![CDATA[TOF value (mol C＝C / mol Pd / h)]]> 48576 19360 33000 1992

[0112] The results in Table 2 show that the conversion rate of catalytic semi-hydrogenation of phenylacetylene and the selectivity of styrene of the sub-nanoscale Pd@ZSM-5 catalyst are higher than those of the nano-scale Pd@ZSM-5-T, Pd / ZSM-5 catalysts and commercial Lindlar catalyst in the comparative examples.

[0113] Table 3. Performance of the product of Example 1 in catalytic semi-hydrogenation of different alkyne substrate molecules.

[0114] Substrate Example 1 4-Methylphenylacetylene conversion rate (%) 100 4-Methylstyrene selectivity (%) 94 2-Methylphenylacetylene conversion rate (%) 12 2-Methylstyrene selectivity (%) 95 3-Methylphenylacetylene conversion rate (%) 35 3-Methylstyrene selectivity (%) 95 1-Ethynaphthalene conversion rate (%) 1-vinylnaphthalene selectivity (%) Conversion rate of diphenylacetylene (%) 1,2-Styrene selectivity (%) 4-Fluorophenylacetylene conversion rate (%) 23 4-Fluorostyrene selectivity (%) 98 4-Chlorophenylacetylene conversion rate (%) 63 4-Chlorostyrene selectivity (%) 96 4-Ethynylaniline conversion rate (%) 92 4-vinylaniline selectivity (%) 87

[0115] The results in Table 3 show that: Since the sub-nanoscale Pd clusters are in-situ confined inside the molecular sieve framework, they have an obvious shape-selective catalytic effect on alkyne molecules smaller than the molecular sieve pores. In addition, the Pd@ZSM-5 catalyst has good catalytic activity for 4-ethynylaniline molecules with an electron-donating group at the para position. On the contrary, when the para position is an electron-withdrawing group, the Pd@ZSM-5 catalyst has a low efficiency in catalytic semi-hydrogenation of alkynes.

[0116] Conclusion:

[0117] The present method provides a general synthesis method for seed-mediated confinement synthesis of metal-based molecular sieves, which can obtain metal@molecular sieve materials with metal scales of single atoms, sub-nanometers or nanometers. This method has obtained a variety of metal M@molecular sieve materials. Among them, the molecular sieve materials with encapsulated metal M being Rh, Pt, Cu, and Zn are proven to be single-atom metal@molecular sieves by synchrotron radiation. In the prepared example products proven by synchrotron radiation, only M-O bonds exist for metal M, and no M-M bonds exist. For the example products with M being Pd, Ag, Co, and Ni, after verification by synchrotron radiation and aberration-corrected electron microscopy, the materials with metal M being Pd, Co, or Ni are sub-nanometer@molecular sieve materials, and the material obtained with M being Ag is a nanoscale material.

[0118] Furthermore, the present invention demonstrates that compared with traditional Lindlar catalysts, Pd@ZSM5-T catalysts in-situ confined by an organic templating agent method, and supported Pd / ZSM-5 catalysts, the palladium sub-nanocluster molecular sieve catalyst Pd@ZSM-5 prepared by the seed-mediated in-situ confinement method of the present invention has higher catalytic performance for the semi-hydrogenation of phenylacetylene and stronger stability under the same noble metal usage, and at the same time has a shape-selective catalytic effect on alkyne molecules smaller than Therefore, this invention has good industrial application prospects.

Claims

1. A method for preparing an M@zeolite catalyst, characterized in that zeolite seeds are used instead of an organic structure-directing agent, and a single-atom, sub-nanoscale or nanoscale metal@zeolite catalyst is prepared by in-situ confinement by adding zeolite seeds to a silica-alumina sol containing a palladium metal precursor, and the M@zeolite is that the active metal is encapsulated in the zeolite.

2. The method according to claim 1, comprising: Step S1. Prepare an aqueous solution of a metal M complex by mixing a metal salt with a ligand compound to form the aqueous solution, and the ligand compound is selected from N-containing compounds, selected from NH3, ethylenediamine, diethylenetriamine, triethylenetetramine or tetraethylenepentamine; Step S2. Prepare an M@zeolite silica-alumina sol precursor solution, and add the aqueous metal complex solution obtained in Step S1 dropwise to the silica-alumina sol precursor solution, and stir at room temperature; Step S3. Add zeolite seeds to the metal silica-alumina sol solution in Step S2, stir at room temperature for 1-2 h, then transfer the mixed solution to a reaction kettle, carry out static crystallization at 150°C - 180°C for 12 h - 72 h, cool to room temperature, wash with water, and dry; Step S4. Calcinate the sample powder obtained in Step S3 at 300°C - 500°C to obtain a sample; Wherein, M is selected from noble metals, Group IB metals, and Group IIB metals; in M@zeolite, the metal M is in-situ confined in the zeolite framework structure, and the metal M exists in a single-atom site state, sub-nanoscale or n-nanoscale state, and n is between 2 - 5 nm; The metal M salt is an inorganic or organic salt of metal M, preferably nitrate, chloride, sulfate, phosphate, oxalate or citrate; The silica-alumina sol precursor solution is a material mixture of a silicon source, an aluminum source, a base source, a template agent and water; the silicon source is tetraethyl orthosilicate, silica sol or sodium silicate; the aluminum source is aluminum isopropoxide, aluminum nitrate or sodium metaaluminate; the base source is sodium hydroxide or potassium hydroxide; the template agent is a structure-directing agent, preferably tetrapropylammonium hydroxide or tetraethylammonium hydroxide.

3. The method according to claim 1 or 2, wherein The selected zeolite is selected from MFI-type zeolite, BEA* -type zeolite, FAU-type zeolite, RTH-type zeolite, MTW-type zeolite, LEV-type zeolite, FER-type zeolite, MEL-type zeolite; preferably MFI-type zeolite or BEA* -type zeolite.

4. The method according to claim 1 or 2, wherein The stirring time in Step S2 is 4 - 5 h; the static crystallization time in Step S3 is 24 h - 72 h; in Step S4, the calcination temperature is 350°C - 450°C and the time is 2 h - 3 h.

5. The method according to claim 1 or 2, wherein the zeolite seeds can be commercially purchased or prepared by a commonly used method for preparing zeolites in the art.

6. The method according to claim 1 or 2, wherein The catalyst obtained according to the method is selected from Ag@Zeolite, Pd@Zeolite, Zn@Zeolite, Co@Zeolite, Ni@Zeoltie, Rh@Zeolite, Cu@Zeolite, or Pt@Zeolite.

7. A method for semi-hydrogenation of R1C≡CH alkyne, the method comprising reacting R1C≡CH with hydrogen to obtain the product R1CH=CH2, where R1 is phenyl, phenyl substituted at the para position with C 1-6 alkyl, C 1-6 alkoxy, halogen, OH or amino, and is characterized in that Using Pd@Zeolite as a catalyst, the catalyst is prepared by the method according to any one of claims 1 - 6.

8. The method according to claim 7, wherein, R1 is preferably phenyl or 4-methylphenyl.

9. The method according to claim 7 or 8 is carried out under a H2 pressure of 0.5 - 3 MPa and at a temperature of 40°C to 80°C.

10. The method according to claim 9, wherein, The reaction temperature of the said reaction is 60°C to 80°C, and the reaction time is 2 h to 3 h.

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