A pure silicon beta molecular sieve encapsulated metal catalyst, and a preparation method and application thereof

Abstract

The application discloses a pure-silicon Beta molecular sieve encapsulated metal catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: dissolving a silicon source, a template agent, a ligand, a metal salt and a mineralizer in water to perform a crystallization reaction at 120-200 DEG C, and then performing calcination treatment and reduction treatment on the solid after crystallization to obtain the pure-silicon Beta molecular sieve encapsulated metal catalyst. The pure-silicon twelve-membered ring large-pore Beta molecular sieve encapsulated metal catalyst is prepared through a ligand protection in-situ hydrothermal synthesis strategy, which can not only reduce the size of metal nanoclusters and improve the high-temperature thermal stability of the metal nanoclusters, but also can control the adsorption and diffusion process of guest molecules, and thus exhibits excellent catalytic performance in catalyzing propane dehydrogenation reaction and methylcyclohexane dehydrogenation reaction, and realizes efficient and stable propane and methylcyclohexane dehydrogenation performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molecular sieve encapsulated metal catalysts, in particular to a pure-silicon Beta molecular sieve encapsulated metal catalyst and a preparation method and application thereof. BACKGROUND

[0002] Hydrogen energy has the advantages of environmental friendliness, cleanliness, carbon-free and diverse sources. In the "production, storage, transportation and use" whole industry chain of hydrogen energy, hydrogen energy storage and transportation is the core link of the whole industry chain, and is also the main bottleneck restricting the rapid development of the current hydrogen energy industry. Organic liquid hydrogen storage technology realizes the safe and efficient storage and release of hydrogen energy through the hydrogenation and dehydrogenation processes of organic liquid hydrogen storage materials, and becomes a key technology to break through the current hydrogen energy storage and transportation bottleneck. Methylcyclohexane has the advantages of high hydrogen storage capacity, stable chemical properties and convenient transportation, and is an organic liquid hydrogen storage material with great development prospects. Designing and developing efficient and stable dehydrogenation catalysts is the key to promoting the development of organic liquid hydrogen storage technology using methylcyclohexane as a medium.

[0003] Among them, Pt-based catalysts have excellent C-H bond activation ability and weak C-C bond cleavage ability, and are the most widely studied alkane (propane, methylcyclohexane, etc.) dehydrogenation catalysts. However, the high methylcyclohexane dehydrogenation temperature increases the occurrence of demethylation and disproportionation side reactions in the reaction process, resulting in a decrease in the hydrogen selectivity of the catalyst; and the traditional supported Pt-based catalysts are prone to metal agglomeration sintering and carbon deposition during continuous high-temperature reaction, resulting in rapid deactivation of the catalysts during propane dehydrogenation and methylcyclohexane dehydrogenation.

[0004] Molecular sieve has a regular pore structure, excellent thermal stability and chemical stability, and is considered as an ideal carrier for encapsulating ultra-small metal nanoclusters. Encapsulating metal species inside the pore channel of the molecular sieve not only helps to reduce the size of the metal species and improve its high-temperature thermal stability, but also the pore channel confinement of the molecular sieve can regulate the adsorption and diffusion behavior of the guest molecules. Encapsulating Pt species inside the pore channel of the molecular sieve is expected to improve the dehydrogenation activity and stability of the catalyst. At present, the literature mainly focuses on the encapsulation of metal species in the ten-membered ring medium pore silicalite-1 (S-1) molecular sieve, but the pore size of the S-1 molecular sieve is similar to the kinetic diameters of the reactant methylcyclohexane and the product toluene, and there is obvious diffusion and mass transfer limitation, so the ideal catalytic performance cannot be achieved. For example, Guo et al. prepared a supported Pt / S-1 catalyst by using S-1 molecular sieve as the carrier and impregnation method, and the average methylcyclohexane conversion rate of the catalyst was only 17.7% at 350℃, and the catalyst gradually deactivated during the reaction and completely deactivated after 5h of reaction. Furukawa et al. prepared a Pt / SiO2 catalyst by using SiO2 as the carrier and impregnation method, and although the initial methylcyclohexane conversion rate of the catalyst could approach 100% at 400℃, the catalyst rapidly deactivated during the continuous reaction, and the conversion rate rapidly decreased to less than 10% after about 150min, which showed poor catalytic stability. SUMMARY

[0005] To solve the technical problems that the traditional supported Pt-based catalyst has a large metal size and the metal species are distributed on the outer surface of the catalyst, the metal clusters are easily sintered during the continuous high-temperature reaction, and coke is produced, which leads to low initial dehydrogenation performance of the catalyst during the dehydrogenation of propane and methylcyclohexane, and the catalyst also rapidly deactivates, and the high-efficiency and stable dehydrogenation performance of propane and methylcyclohexane cannot be achieved, the present application provides a pure-silicon Beta molecular sieve encapsulated metal catalyst and a preparation method and application thereof, a pure-silicon twelve-membered ring Beta molecular sieve with a larger pore size is prepared by optimizing the synthesis strategy to encapsulate metal species, which can not only reduce the size of the metal species and improve its high-temperature thermal stability, but also improve the diffusion and mass transfer limitations of the reactant methylcyclohexane and the product toluene, and further improve the dehydrogenation performance of propane and methylcyclohexane.

[0006] The present application is realized by the following technical solutions:

[0007] The present application is realized by the following technical solutions:

[0008] The silicon source, the template agent, the ligand, the metal salt and the mineralizer are dissolved in water, a crystallization reaction is carried out at 120-200℃, and then the solid after crystallization is calcined and reduced to obtain the pure-silicon Beta molecular sieve encapsulated metal catalyst.

[0009] The ligand is selected from one or more of ammonia, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, ethylenediaminetetraacetic acid, tartaric acid and citric acid; and the metal in the metal salt is selected from one or more of platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), osmium (Os), gold (Au), iridium (Ir), silver (Ag), titanium (Ti), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), zirconium (Zr), molybdenum (Mo), indium (In), tin (Sn), tungsten (W), lanthanum (La) and cerium (Ce).

[0010] The pure-silicon Beta molecular sieve of the present application can encapsulate noble metals (such as Pt, Pd, Ru, Rh, Os, Au, Ir, Ag, etc.), non-noble metals (such as Ti, Mn, Fe, Co, Ni, Cu, Zn, Ga, Zr, Mo, In, Sn, W, Ce, etc.), rare earth metals (La, etc.) and double / multiple metals. The encapsulation of the metal catalyst by the pure-silicon Beta molecular sieve hydrothermally synthesized in situ with ligand protection promotes the catalytic activity and stability of the catalyst in the catalytic dehydrogenation of propane and methylcyclohexane. The doping of metal promoters (such as Ti, Mn, Fe, Co, Ni, Cu, Zn, Ga, Zr, Mo, In, Sn, W, Ce, etc.) can promote the catalytic activity and stability of the Pt-based catalyst in the catalytic dehydrogenation of methylcyclohexane. The doping of Zn can improve the propane dehydrogenation activity and stability of the Pt-based catalyst, and the further doping of Mg can inhibit the loss of Zn species, thereby showing more stable propane dehydrogenation performance. The encapsulation of the metal species by the pure-silicon Beta molecular sieve channels improves the high-temperature thermal stability of Pt nanoclusters and inhibits the aggregation and sintering of Pt nanoclusters during high-temperature reaction. The pore confinement effect regulates the adsorption and diffusion behavior of the reactant methylcyclohexane and the product toluene, so that the metal catalyst encapsulated by the pure-silicon Beta molecular sieve channels exhibits high-efficiency and stable dehydrogenation reaction activity.

[0011] The present application encapsulates metal nanoclusters by pure-silicon twelve-membered ring large-pore Beta molecular sieve channels prepared by the strategy of in-situ hydrothermal synthesis with ligand protection, to improve the high-temperature thermal stability of the metal nanoclusters, regulate the adsorption and diffusion behavior of the reactant methylcyclohexane and the product toluene, and achieve high-efficiency and stable propane and methylcyclohexane dehydrogenation performance.

[0012] Further, the silicon source is selected from one or more of tetraethyl orthosilicate, white carbon black, silica sol and sodium silicate.

[0013] Further, the template agent is selected from one or more of tetramethylammonium hydroxide (TMAOH), tetraethylammonium hydroxide (TEAOH), tetrapropylammonium hydroxide (TPAOH), tetrabutylammonium hydroxide (TBAOH), and tetrabutylphosphonium hydroxide (TBPOH).

[0014] Further, the mineralizing agent is selected from one or more of hydrofluoric acid, ammonium fluoride, sodium fluoride, and magnesium fluoride.

[0015] Further, the molar ratio of the silicon source, the template agent, and water is 1: (0.2-0.5): (5-10).

[0016] Further, the molar ratio of the silicon source and the metal salt is 1: (0.0005-0.01).

[0017] Further, the molar ratio of the silicon source and the mineralizing agent is 1: (0.1-0.5).

[0018] Further, the crystallization reaction is a static crystallization reaction.

[0019] Further, the method further comprises a step of adding an alkali metal salt or an alkali metal hydroxide to the water, which can improve the thermal stability and catalytic activity of the catalyst.

[0020] Further, the alkali metal salt is selected from one or more of chlorides, nitrates, nitrites, acetates, molybdates, sulfates, and tungstates of sodium (Na), potassium (K), and cesium (Cs).

[0021] Further, the alkali metal hydroxide is selected from one or more of hydroxides of sodium, potassium, and cesium.

[0022] Further, the molar ratio of the silicon source and the alkali metal salt is 1: (0.01-0.05).

[0023] Further, the molar ratio of the silicon source and the alkali metal hydroxide is 1: (0.01-0.05).

[0024] Further, the method further comprises a step of centrifuging, washing, and drying the solid product before the calcination treatment.

[0025] Further, the calcination treatment is performed at a temperature increasing rate of 1-10℃ / min to 300-500℃, and the calcination is performed at 300-500℃ for 2-6h.

[0026] Further, the reduction treatment is performed in a hydrogen atmosphere at 300-500℃ for 1-2h.

[0027] In the specific embodiment, the ligand and the metal salt are combined to form a metal complex solution, which is added to a synthesis gel of pure silicon Beta molecular sieve, and after crystallization at a certain temperature for a certain time, a pure silicon Beta molecular sieve encapsulated metal species is obtained, which is then subjected to calcination and reduction treatment to obtain a pure silicon Beta molecular sieve encapsulated metal catalyst.

[0028] The second aspect of the present application provides a pure silicon Beta molecular sieve encapsulated metal catalyst prepared by the method of the first aspect.

[0029] The third aspect of the present application provides an application of the pure silicon Beta molecular sieve encapsulated metal catalyst of the second aspect in catalyzing a propane dehydrogenation reaction or a methylcyclohexane dehydrogenation reaction.

[0030] The beneficial effects of the present application are:

[0031] The pure silicon Beta molecular sieve of the present application can encapsulate noble metals, non-noble metals, rare earth metals, and double / multiple metals. The pure silicon Beta molecular sieve encapsulated metal catalyst synthesized in situ by ligand protection hydrothermal synthesis can promote the catalytic activity and stability of the catalyst in catalyzing a propane dehydrogenation reaction and a methylcyclohexane dehydrogenation reaction, and the doping of metal additives (noble metals, non-noble metals, rare earth metals, and double / multiple metals) can promote the performance of Pt-based catalysts in catalyzing a propane dehydrogenation reaction and a methylcyclohexane dehydrogenation reaction, further improving the activity and stability of the catalyst in a propane dehydrogenation reaction and a methylcyclohexane dehydrogenation reaction.

[0032] The present application prepares pure silicon twelve-membered ring large-pore Beta molecular sieve channel encapsulated metal nanoclusters by the strategy of ligand protection in situ hydrothermal synthesis, which not only can reduce the size of the metal nanoclusters and improve the high-temperature thermal stability of the metal nanoclusters, but also can regulate the adsorption and diffusion process of the guest molecules, thereby exhibiting excellent catalytic performance in a propane and a methylcyclohexane dehydrogenation reaction. In particular, in the catalysis of a large-molecule methylcyclohexane dehydrogenation, the larger pore size of the pure silicon twelve-membered ring large-pore Beta molecular sieve improves the diffusion and mass transfer limitations of the reactant methylcyclohexane and the product toluene, realizing high-efficiency and stable methylcyclohexane dehydrogenation performance. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Performance diagram of Pt / S-1 catalyst and Pt / SiO2 catalyst in catalyzing methylcyclohexane dehydrogenation; wherein a is Pt / S-1 catalyst, and b is Pt / SiO2 catalyst.

[0034] Figure 2X-ray powder diffraction patterns of the Pt@Si-Beta catalyst prepared in Example 1, the PtGa@Si-Beta catalyst prepared in Example 2, the Pt / Si-Beta-im catalyst prepared in Comparative Example 2 and the Pt@Amorphous SiO2 catalyst prepared in Comparative Example 4.

[0035] Figure 3 Scanning transmission electron microscopy image of the Pt@Si-Beta catalyst prepared in Example 1.

[0036] Figure 4 Conversion data graphs of the catalysts prepared in Examples 1-8 and Comparative Examples 1-3 for catalyzing the dehydrogenation reaction of methylcyclohexane; wherein a is the Pt@Si-Beta catalyst and the Pt / Si-Beta-im catalyst, b is the Pt@Si-Beta catalyst and the Pt@S-1 catalyst, c is the Pt@Si-Beta catalyst and the Pt@Al-Beta catalyst, d is the Pt@Si-Beta catalyst, the PtMn@Si-Beta catalyst, the PtFe@Si-Beta catalyst, the PtZn@Si-Beta catalyst, the PtIn@Si-Beta catalyst, the PtSn@Si-Beta catalyst, the PtGa@Si-Beta catalyst and the PtCe@Si-Beta catalyst.

[0037] Figure 5 Conversion data graphs of the catalysts prepared in Examples 1, 5 and 9 for catalyzing the dehydrogenation reaction of propane; wherein a is the conversion data graph of propane, b is the selectivity data graph of propylene. DETAILED DESCRIPTION

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0039] In the background art, Guo et al. prepared a supported Pt / S-1 catalyst using S-1 molecular sieve as the support by impregnation method, and the dehydrogenation performance of methylcyclohexane of the catalyst was as shown in Table a in the background art. The average conversion rate of methylcyclohexane of the catalyst was only 17.7% at 350°C, and the catalyst gradually deactivated during the reaction and completely deactivated after 5h of reaction. Figure 1 In the background art, Guo et al. prepared a supported Pt / S-1 catalyst using S-1 molecular sieve as the support by impregnation method, and the dehydrogenation performance of methylcyclohexane of the catalyst was as shown in Table a in the background art. The average conversion rate of methylcyclohexane of the catalyst was only 17.7% at 350°C, and the catalyst gradually deactivated during the reaction and completely deactivated after 5h of reaction. Figure 1As shown in FIG. b. Although the initial methylcyclohexane conversion of Pt / SiO2 catalyst (b) at 400℃ can approach 100%, it is rapidly deactivated in the continuous reaction, and the conversion rapidly decreases to less than 10% after about 150 min, showing poor catalytic stability. Figure 1 As shown in FIG. b. Although the initial methylcyclohexane conversion of Pt / SiO2 catalyst (b) at 400℃ can approach 100%, it is rapidly deactivated in the continuous reaction, and the conversion rapidly decreases to less than 10% after about 150 min, showing poor catalytic stability.

[0040] The application provides a preparation method of a pure-silicon Beta molecular sieve encapsulated metal catalyst, comprising the following steps: dissolving a silicon source, a template agent, a ligand, a metal salt and a mineralizer in water, performing a crystallization reaction at 120-200℃, and then performing calcination treatment and reduction treatment on the crystallized solid to obtain the pure-silicon Beta molecular sieve encapsulated metal catalyst.

[0041] In the specific embodiment, the ligand and the metal salt are combined to form a metal complex solution, which is added to a synthesis gel of the pure-silicon Beta molecular sieve, and the pure-silicon Beta molecular sieve encapsulated metal species is obtained after crystallization at a certain temperature for a certain time, and then the pure-silicon Beta molecular sieve encapsulated metal catalyst is obtained after calcination and reduction treatment.

[0042] The application will be further described in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the application and implement it, but the embodiments are not limiting to the application.

[0043] In the following examples, the experimental methods are conventional methods unless otherwise specified, and the materials, reagents, etc. used are commercially available unless otherwise specified.

[0044] Example 1

[0045] A preparation method of a pure-silicon Beta molecular sieve encapsulated Pt (Pt@Si-Beta) catalyst, wherein the molar ratio of SiO2:TEAOH:Pt(NH2CH2CH2NH2)2Cl2:CsCl:HF:H2O is 1:0.4:0.001:0.016:0.2:6.0, specifically comprising the following steps:

[0046] (1) 6.74 g of tetraethylammonium hydroxide aqueous solution (35 wt%) and 0.106 g of CsCl were added to a 25 mL polytetrafluoroethylene-lined reaction kettle, stirred at room temperature for 10 min to obtain a mixed solution;

[0047] (2) 2.4 g of white carbon black was added into the mixed solution obtained in step (1) in three steps, and stirred in an 80℃ oil bath. After fully stirring to make it completely dissolved, 450 μL of ethylenediamine platinum chloride (Pt(NH2CH2CH2NH2)2Cl2) solution (0.09 mol / L) was added, and then 350 μL of hydrofluoric acid was added dropwise to obtain a gel mixture; the 0.09 mol / L ethylenediamine platinum chloride solution was prepared by the following method: 0.24 g of PtCl2 solid was added into a mixed solution of 1 mL of ethylenediamine and 2 mL of deionized water, and then fully stirred at 60℃ water bath to make it completely dissolved, and finally diluted to 10 mL to obtain the ethylenediamine platinum chloride solution (0.09 mol / L);

[0048] (3) The gel mixture obtained in step (2) was loaded into a stainless steel high-pressure reaction kettle, and statically crystallized at 140℃ for 4 days. The crystallized sample was centrifuged and washed, and the obtained solid product was dried in an 80℃ oven overnight;

[0049] (4) The dried solid product was placed in a muffle furnace, and heated from room temperature to 500℃ at a rate of 1.5℃ / min, and then calcined at 500℃ to remove the molecular sieve template agent, and then reduced in a hydrogen atmosphere (50 mL / min) at 400℃ for 1 h to obtain a Pt@Si-Beta catalyst.

[0050] Example 2

[0051] A preparation method of a pure silicon Beta molecular sieve encapsulated PtGa (PtGa@Si-Beta) catalyst, wherein the molar ratio of SiO2:TEAOH:Pt(NH2CH2CH2NH2)2Cl2:Ga(NO3)3:CsCl:HF:H2O is 1:0.4:0.001:0.001:0.016:0.2:6.0, specifically comprising the following steps:

[0052] (1) 6.74 g of tetraethylammonium hydroxide aqueous solution (35 wt%) and 0.106 g of CsCl were added into a 25 mL polytetrafluoroethylene-lined reaction kettle, and stirred at room temperature for 10 min to obtain a mixed solution;

[0053] (2) 2.4 g of white carbon black was added into the mixed solution obtained in step (1) in three steps, and stirred in an 80℃ oil bath. After fully stirring to make it completely dissolved, 450 μL of ethylenediamine platinum chloride (Pt(NH2CH2CH2NH2)2Cl2) solution (0.09 mol / L) was added, and then 350 μL of hydrofluoric acid was added dropwise to obtain a gel mixture;

[0054] (3) The gel mixture obtained in step (2) is loaded into a stainless steel autoclave and statically crystallized at 140℃ for 4 days. The crystallized sample is centrifuged and washed, and the obtained solid product is dried in an oven at 80℃ overnight;

[0055] (4) The dried solid product is placed in a muffle furnace, heated from room temperature to 500℃ at a rate of 1.5℃ / min, and calcined at 500℃ to remove the molecular sieve template agent, and then reduced in a hydrogen atmosphere (50mL / min) at 400℃ for 1h to obtain a PtGa@Si-Beta catalyst.

[0056] Example 3

[0057] A preparation method of a pure-silicon Beta molecular sieve encapsulated PtMn (PtMn@Si-Beta) catalyst, wherein the molar ratio of SiO2:TEAOH:Pt(NH2CH2CH2NH2)2Cl2:[Mn(NH2CH2CH2NHCH2CH2)2NH]Cl2:CsCl:HF:H2O is 1:0.4:0.001:0.001:0.016:0.2:6.0, and the preparation method is basically the same as that of Example 2, except that in step (2), the Ga(NO3)3 solution (0.09mol / L) is replaced by a [Mn(NH2CH2CH2NHCH2CH2)2NH]Cl2 solution (0.09mol / L). The preparation of the [Mn(NH2CH2CH2NHCH2CH2)2NH]Cl2 solution is basically similar to that of the Pt(NH2CH2CH2NH2)2Cl2 solution, except that tetraethylenepentamine is used as the ligand and manganese chloride is used as the metal salt.

[0058] Example 4

[0059] A preparation method of a pure-silicon Beta molecular sieve encapsulated PtFe (PtFe@Si-Beta) catalyst, wherein the molar ratio of SiO2:TEAOH:Pt(NH2CH2CH2NH2)2Cl2:Fe-EDTA:CsCl:HF:H2O is 1:0.4:0.001:0.001:0.016:0.2:6.0, and the preparation method is basically the same as that of Example 2, except that in step (2), the Ga(NO3)3 solution (0.09mol / L) is replaced by a Fe-EDTA solution (0.09mol / L). The preparation of the Fe-EDTA solution is basically similar to that of the Pt(NH2CH2CH2NH2)2Cl2 solution, except that ethylenediaminetetraacetic acid is used as the ligand and ferric nitrate is used as the metal salt.

[0060] Example 5

[0061] A preparation method of a pure silicon Beta molecular sieve encapsulated PtZn (PtZn@Si-Beta) catalyst, wherein the molar ratio of SiO2:TEAOH:Pt(NH2CH2CH2NH2)2Cl2:[Zn(NH2CH2CH2NH2)3](OAc)2:CsCl:HF:H2O is 1:0.4:0.001:0.001:0.016:0.2:6.0, and the preparation method is basically the same as that of Example 2, except that in step (2), the Ga(NO3)3 solution (0.09 mol / L) is replaced by the [Zn(NH2CH2CH2NH2)3](OAc)2 solution (0.09 mol / L). The preparation of the [Zn(NH2CH2CH2NH2)3](OAc)2 solution is basically similar to that of the Pt(NH2CH2CH2NH2)2Cl2 solution, except that ethylenediamine is used as a ligand and zinc acetate is used as a metal salt.

[0062] Example 6

[0063] A preparation method of a pure silicon Beta molecular sieve encapsulated PtIn (PtIn@Si-Beta) catalyst, wherein the molar ratio of SiO2:TEAOH:Pt(NH2CH2CH2NH2)2Cl2:In(NO3)3:CsCl:HF:H2O is 1:0.4:0.001:0.001:0.016:0.2:6.0, and the preparation method is basically the same as that of Example 2, except that in step (2), the Ga(NO3)3 solution (0.09 mol / L) is replaced by the In(NO3)3 solution (0.09 mol / L).

[0064] Example 7

[0065] A preparation method of a pure silicon Beta molecular sieve encapsulated PtSn (PtSn@Si-Beta) catalyst, wherein the molar ratio of SiO2:TEAOH:Pt(NH2CH2CH2NH2)2Cl2:SnCl4:CsCl:HF:H2O is 1:0.4:0.001:0.001:0.016:0.2:6.0, and the preparation method is basically the same as that of Example 2, except that in step (2), the Ga(NO3)3 solution (0.09 mol / L) is replaced by the SnCl4 solution (0.09 mol / L).

[0066] Example 8

[0067] A preparation method of a pure silicon Beta molecular sieve encapsulated PtCe (PtCe@Si-Beta) catalyst, wherein the molar ratio of SiO2:TEAOH:Pt(NH2CH2CH2NH2)2Cl2:Ce(NO3)3:CsCl:HF:H2O is 1:0.4:0.001:0.001:0.016:0.2:6.0, and the preparation method is basically the same as that of Example 2, except that in step (2), the Ga(NO3)3 solution (0.09 mol / L) is replaced by the Ce(NO3)3 solution (0.09 mol / L).

[0068] Example 9

[0069] A preparation method of a pure silicon Beta molecular sieve encapsulated PtZnMg (PtZnMg@Si-Beta) catalyst, wherein the molar ratio of SiO2:TEAOH:Pt(NH2CH2CH2NH2)2Cl2:[Zn(NH2CH2CH2NH2)3](OAc)2:MgCl:CsCl:HF:H2O is 1:0.4:0.001:0.002:0.002:0.016:0.2:6.0, and the preparation method is basically the same as that of Example 2, except that in step (2), the 450 μL Ga(NO3)3 solution (0.09 mol / L) is replaced by 900 μL of zinc ethylenediamine acetate solution (0.09 mol / L) and 900 μL of MgCl solution (0.09 mol / L).

[0070] Comparative Example 1

[0071] A preparation method of a silicon-aluminum Beta molecular sieve encapsulated Pt (Pt@Al-Beta) catalyst, wherein the molar ratio of SiO2:TEAOH:Al2O3:Pt(NH2CH2CH2NH2)2Cl2:CsCl:HF:H2O is 1:0.4:0.04:0.001:0.016:0.2:6.0, and the preparation method comprises the following steps:

[0072] (1) 6.74 g of tetraethylammonium hydroxide aqueous solution (35 wt%), 0.106 g of CsCl, and 0.066 g of sodium metaaluminate were added to a 25 mL polytetrafluoroethylene-lined reaction kettle, stirred at room temperature for 10 min, and a mixed solution was obtained;

[0073] (2) 2.4 g of white carbon black was added to the mixed solution obtained in step (1) in three steps, heated and stirred in an 80°C oil bath, and after sufficient stirring to completely dissolve, 450 μL of ethylenediamine platinum chloride solution (0.09 mol / L) was added, then 350 μL of hydrofluoric acid was added dropwise, and a gel mixture was obtained;

[0074] (3) The gel mixture obtained in step (2) was loaded into a stainless steel autoclave and statically crystallized at 140°C for 4 days. The crystallized sample was centrifuged and washed, and the obtained solid product was dried in an oven at 80°C overnight;

[0075] (4) The dried solid product was placed in a muffle furnace and heated at a rate of 1.5°C / min from room temperature to 500°C, and calcined at 500°C to remove the molecular sieve template agent, and then reduced at 400°C in a hydrogen atmosphere (50 mL / min) for 1 h to obtain a Pt@Al-Beta catalyst.

[0076] Comparative Example 2

[0077] A method for preparing a Si-Beta molecular sieve supported Pt (Pt / Si-Beta-im) catalyst, using calcined Si-Beta molecular sieve as a catalyst carrier and hexahydrate chloroplatinic acid as a platinum source, synthesized by an impregnation method, specifically including the following steps:

[0078] 0.12 mL of chloroplatinic acid solution (0.064 mol / L) was added dropwise to 0.5 g of calcined Si-Beta molecular sieve at a stirring speed of 300 rpm, and the mixture was stirred to ensure full contact and then dried in an oven at 80°C overnight. Finally, the dried sample was reduced at 400°C in a hydrogen atmosphere (50 mL / min) for 1 h to obtain a Pt / Si-Beta-im catalyst.

[0079] Comparative Example 3

[0080] A method for preparing a S-1 molecular sieve encapsulated Pt (Pt@S-1) catalyst, wherein the molar ratio of SiO2:TPAOH:Pt(NH2CH2CH2NH2)2Cl2:H2O is 1:0.4:0.001:35, specifically including the following steps:

[0081] (1) 13.0 g of aqueous tetrapropylammonium hydroxide solution (25 wt%) was added to 15.0 g of deionized water, stirred for 10 min, and then 8.32 g of tetraethyl silicate was added. The mixture was continuously stirred for 6 h to ensure complete hydrolysis, and a uniform transparent solution was obtained;

[0082] (2) 450 μL of ethylenediamine platinum chloride solution (0.09 mol / L) was added to the solution of step (1) and stirred for 1 h. The uniform mixture solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave, and statically crystallized at 170°C for 3 days;

[0083] (3) The crystallized sample was centrifuged and washed, and the obtained solid product was dried in an oven at 80°C overnight. The obtained solid product was reduced by direct hydrogen reduction at 400°C under hydrogen atmosphere (50 mL / min) for 1 h to obtain the Pt@S-1 catalyst.

[0084] Comparative Example 4

[0085] A preparation method of an amorphous SiO2 encapsulated Pt (Pt@Amorphous SiO2) catalyst, wherein the molar ratio of SiO2:TEAOH:Pt(NH2CH2CH2NH2)2Cl2:CsCl:H2O is 1:0.4:0.001:0.2:6.0, specifically comprising the following steps:

[0086] (1) 6.74 g of aqueous tetraethylammonium hydroxide (35 wt%) and 0.106 g of CsCl were added to a 25 mL polytetrafluoroethylene-lined reaction kettle, stirred at room temperature for 10 min to obtain a mixed solution;

[0087] (2) 2.4 g of white carbon black was added to the mixed solution obtained in step (1) in three steps, and heated and stirred in an 80°C oil bath. After complete dissolution, 450 μL of ethylenediamine platinum chloride solution (0.09 mol / L) was added to obtain a mixed solution;

[0088] (3) The mixed solution obtained in step (2) was loaded into a stainless steel high-pressure reaction kettle, and crystallized statically at 140°C for 4 days. The crystallized sample was centrifuged and washed, and the obtained solid product was dried in an oven at 80°C overnight;

[0089] (4) The dried solid product was placed in a muffle furnace, and heated from room temperature to 500°C at a rate of 1.5°C / min, and then calcined at 500°C to remove the molecular sieve template agent. Then, the product was reduced at 400°C under hydrogen atmosphere (50 mL / min) for 1 h to obtain the Pt@Amorphous SiO2 catalyst.

[0090] Figure 2The powder X-ray diffraction patterns of the Pt@Si-Beta catalyst prepared in Example 1, the PtGa@Si-Beta catalyst prepared in Example 2, the Pt / Si-Beta-im catalyst prepared in Comparative Example 2 and the Pt@Amorphous SiO2 catalyst prepared in Comparative Example 4 were measured. The catalysts prepared in Examples 1 and 2 had typical Beta zeolite topology and no diffraction peaks corresponding to Pt foil were observed, proving that small-sized Pt nanoclusters were formed. However, the Pt / Si-Beta-im catalyst synthesized by the impregnation method had a characteristic peak corresponding to Pt foil at 2θ = ~40°, proving that the catalyst synthesized by the impregnation method had undergone agglomeration and sintering of Pt species during the heat treatment process, forming large-sized Pt nanoparticles. When no fluorine species was added to the synthesis gel in Comparative Example 4, the Pt@Amorphous SiO2 catalyst did not exhibit Beta zeolite topology, proving that the method could not synthesize a Pt catalyst encapsulated by a pure-silicon Beta zeolite.

[0091] Figure 3 The scanning transmission electron microscopy image of the Pt@Si-Beta catalyst prepared in Example 1 showed that the Pt nanoclusters had high metal dispersion in the channels of the Beta zeolite.

[0092] The catalysts prepared in Examples 1-8 and Comparative Examples 1-3 were used to catalyze the dehydrogenation of methylcyclohexane. The reaction conditions for the dehydrogenation of methylcyclohexane were as follows: 0.11 g of the catalyst (40-60 mesh) was mixed with 1.0 g of quartz sand, the flow rate of methylcyclohexane was 3.0 mL / h, the flow rate of nitrogen carrier gas was 30 mL / min, the reaction temperature was 400°C, and the mass hourly space velocity was 21 h -1 In addition, except for the Pt@Al-Beta catalyst prepared in Comparative Example 1, no other byproducts were detected in the process of catalyzing the dehydrogenation of methylcyclohexane, indicating that the prepared catalysts had hydrogen selectivity of about 100%.

[0093] Figure 4The conversion rate data chart of the catalysts prepared for Examples 1-8 and Comparative Examples 1-3 for catalyzing the dehydrogenation reaction of methylcyclohexane; wherein a is the Pt@Si-Beta catalyst and the Pt / Si-Beta-im catalyst, b is the Pt@Si-Beta catalyst and the Pt@S-1 catalyst, c is the Pt@Si-Beta catalyst and the Pt@Al-Beta catalyst, d is the Pt@Si-Beta catalyst, the PtMn@Si-Beta catalyst, the PtFe@Si-Beta catalyst, the PtZn@Si-Beta catalyst, the PtIn@Si-Beta catalyst, the PtSn@Si-Beta catalyst, the PtGa@Si-Beta catalyst and the PtCe@Si-Beta catalyst. From Figure 4 It can be seen from a that the Pt@Si-Beta catalyst has a methylcyclohexane conversion rate of 46.4% at 400°C and 21h -1 The initial methylcyclohexane conversion rate of the Pt / Si-Beta-im catalyst synthesized by the impregnation method is only 8.6%, and it rapidly deactivates as the reaction continuously develops. The above results prove that, compared with the impregnation method, the Pt catalyst encapsulated by the pure silicon Beta molecular sieve helps to improve the high-temperature thermal stability of the Pt nanoclusters and inhibit the sintering and aggregation of the metal species during the reaction; at the same time, the pore channel limitation can regulate the adsorption and diffusion process of the substrate methylcyclohexane and the product toluene, avoid the adsorption on the catalytically active sites, and make it maintain stable dehydrogenation activity. From Figure 4 It can be seen from b that the Pt@S-1 catalyst does not exhibit the methylcyclohexane dehydrogenation performance under the high space velocity condition (21h -1 ), which is mainly due to the fact that the pore size of the S-1 molecular sieve (-0.55 nm) is close to the kinetic diameter of the substrate methylcyclohexane and the product toluene (-0.6 nm), and the catalytically active sites inside the pore channel cannot be contacted, losing the methylcyclohexane dehydrogenation catalytic performance. Therefore, the design and synthesis of the Pt nanoclusters encapsulated by the pure silicon twelve-membered ring large-pore Beta molecular sieve with a larger pore size play a key role in improving the diffusion and mass transfer efficiency of the macromolecular methylcyclohexane and its catalytic performance. Figure 4 c explores the influence of the acidity of the Beta molecular sieve itself on the methylcyclohexane dehydrogenation performance, and the introduction of the acid sites has an obvious inhibitory effect on the methylcyclohexane dehydrogenation performance of the Pt@Al-Beta catalyst, which is attributed to the fact that the acid sites can accelerate the occurrence of the demethylation and disproportionation and other side reactions, produce carbon deposition on the surface of the catalyst, cover the catalytically active sites, and cause the rapid deactivation of the catalysis. Figure 4The effects of doping metal promoters on the performance of the Pt@Si-Beta catalyst in the dehydrogenation of methylcyclohexane were investigated, and the results showed that doping Mn, Fe, Zn, In, Sn, Ga and Ce promoters could effectively improve the reactivity and stability of the Pt@Si-Beta catalyst in the dehydrogenation of methylcyclohexane.

[0094] The catalysts prepared in Examples 1, 5 and 9 were used to catalyze the dehydrogenation of propane, and the reaction conditions of the dehydrogenation of propane were as follows: 0.11 g of the catalyst (40-60 mesh) was mixed with 1.0 g of quartz sand, the flow rate of propane was 10 mL / min, the flow rate of nitrogen carrier gas was 30 mL / min, the reaction temperature was 600 DEG C, and the mass space velocity was 10 h-1. -1 .

[0095] Figure 5 The data graphs of the conversion rate of propane and the selectivity of propylene in the dehydrogenation of propane catalyzed by the Pt@Si-Beta, PtZn@Si-Beta and PtZnMg@Si-Beta catalysts prepared in Examples 1, 5 and 9 were prepared, wherein a is the data graph of the conversion rate of propane, and b is the data graph of the selectivity of propylene. Figure 5 It can be found from the data graphs that doping Zn can improve the dehydrogenation activity and stability of the Pt@Si-Beta catalyst in the dehydrogenation of propane and the selectivity of propylene, and further doping Mg can inhibit the loss of Zn species, thereby showing more stable dehydrogenation performance of propane.

[0096] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Those skilled in the art should understand that on the basis of the above description, other different forms of changes or variations can also be made. Here, all the embodiments need not and cannot be exhausted. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the claims of the present application.

Claims

1. A method for preparing a pure silica Beta molecular sieve encapsulated metal catalyst, characterized in that, The method comprises the following steps: The silicon source, template agent, ligand, metal salt and mineralizer are dissolved in water, an alkali metal salt or alkali metal hydroxide is added, a crystallization reaction is carried out at 120-200 DEG C, and then the crystallized solid is subjected to calcination treatment and reduction treatment to obtain the pure-silicon Beta molecular sieve encapsulated metal catalyst; The metal in the metal salt is selected from one or more of platinum, palladium, ruthenium, rhodium, osmium, gold, iridium, silver, titanium, manganese, iron, cobalt, nickel, copper, zinc, gallium, zirconium, molybdenum, indium, tin, tungsten, lanthanum and cerium; the mineralizer is selected from one or more of hydrofluoric acid, ammonium fluoride, sodium fluoride and magnesium fluoride; the alkali metal salt is selected from one or more of chlorides, nitrates, nitrites, acetates, molybdates, sulfates and tungstates of sodium, potassium and cesium; the alkali metal hydroxide is selected from one or more of hydroxides of sodium, potassium and cesium; and the molar ratio of the silicon source to the alkali metal salt is 1:(0.01-0.05). The calcination treatment is carried out at a temperature increasing rate of 1-10 DEG C / min to 300-500 DEG C, and the calcination is carried out at 300-500 DEG C for 2-6 h; and the reduction treatment is carried out at 300-500 DEG C for 1-2 h in a hydrogen atmosphere.

2. The production method according to claim 1, characterized by, The template agent is selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide and tetrabutylphosphonium hydroxide.

3. The production method according to claim 1, characterized by, The molar ratio of the silicon source to the template agent to water is 1:(0.2-0.5):(5-10).

4. The method of claim 1, wherein, The molar ratio of the silicon source to the metal salt is 1:(0.0005-0.01).

5. The pure-silicon Beta molecular sieve encapsulated metal catalyst prepared by the method of any one of claims 1-4.

6. The use of the pure-silicon Beta molecular sieve encapsulated metal catalyst of claim 5 in catalyzing a propane dehydrogenation reaction or a methylcyclohexane dehydrogenation reaction.

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