Pure silicon Beta molecular sieve packaged metal catalyst as well as preparation method and application thereof

Abstract

The invention discloses a pure silicon Beta molecular sieve packaging 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, carrying out a crystallization reaction at 120-200 DEG C, and carrying out calcination treatment and reduction treatment on the crystallized solid to obtain the pure silicon Beta molecular sieve packaging metal catalyst. The pure silicon Beta molecular sieve packaged metal catalyst is obtained. The pure silicon twelve-membered ring macroporous Beta molecular sieve encapsulated metal catalyst is prepared through a ligand protection in-situ hydrothermal synthesis strategy, so that the size of a metal nanocluster can be reduced, the high-temperature thermal stability of the metal nanocluster is improved, the adsorption and diffusion processes of guest molecules can be regulated and controlled, and the stability of the metal nanocluster is improved. Furthermore, the catalyst shows excellent catalytic performance when being used for catalyzing a propane dehydrogenation reaction and a methyl cyclohexane dehydrogenation reaction, and efficient and stable propane and methyl cyclohexane dehydrogenation performance is achieved.

Description

Technical Field

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

[0002] Hydrogen energy has the advantages of being environmentally friendly, clean and carbon-free, and having diverse sources. In the entire industry chain of hydrogen energy's "production, storage, transportation and use", hydrogen energy storage and transportation is the core link of the entire industry chain, and it is also the main bottleneck restricting the rapid development of the current hydrogen energy industry. Organic liquid hydrogen storage technology is to achieve safe and efficient storage and release of hydrogen energy through the hydrogenation and dehydrogenation process of organic liquid hydrogen storage materials, and has become a key technology to break through the current bottleneck of hydrogen energy storage and transportation. Methylcyclohexane has the advantages of high hydrogen storage capacity, stable chemical properties and convenient transportation. It is an organic liquid hydrogen storage material with great development prospects. The design and development of 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 CH bond activation ability and weak CC bond cracking ability, and are currently the most widely studied catalysts for dehydrogenation of alkanes (propane, methylcyclohexane, etc.). However, the higher methylcyclohexane dehydrogenation temperature increases the occurrence of side reactions such as demethylation and disproportionation during the reaction, resulting in a decrease in the hydrogen selectivity of the catalyst; and traditional supported Pt-based catalysts are prone to metal agglomeration and sintering during continuous high-temperature reactions, and produce carbon deposits, resulting in rapid deactivation of the catalyst during propane dehydrogenation and methylcyclohexane dehydrogenation.

[0004] Molecular sieves have regular pore structures, excellent thermal and chemical stability, and are considered to be an ideal carrier for encapsulating ultra-small metal nanoclusters. Encapsulating metal species into the pores of molecular sieves not only helps to reduce the size of metal species and improve their high-temperature thermal stability, but also the pore confinement of molecular sieves can regulate the adsorption and diffusion behavior of guest molecules. Encapsulating Pt species into the pores of molecular sieves is expected to improve the dehydrogenation activity and stability of the catalyst. At present, the literature mainly focuses on the encapsulation of metal species by ten-membered ring mesoporous silicalite-1 (S-1) molecular sieves. However, the pore size of S-1 molecular sieves is similar to the kinetic diameter of the reactant methylcyclohexane and the product toluene, and there are obvious diffusion and mass transfer limitations, so it is impossible to achieve ideal catalytic performance. For example, Guo et al. used S-1 molecular sieve as a carrier and prepared a supported Pt / S-1 catalyst by impregnation. The average methylcyclohexane conversion rate of the catalyst at 350°C was only 17.7%, and it gradually deactivated during the reaction and became fully active after 5 hours of reaction. Furukawa et al. used SiO2 as a carrier and prepared a Pt / SiO2 catalyst by impregnation method. Although the initial methylcyclohexane conversion rate at 400°C was close to 100%, it was rapidly deactivated during the continuous reaction process. After about 150 minutes, the conversion rate quickly dropped to below 10%, showing poor catalytic stability. Summary of the invention

[0005] In order to solve the technical problems that the conventional supported Pt-based catalyst has large metal size and metal species distributed on the outer surface of the catalyst, metal agglomeration and sintering are prone to occur during the continuous high-temperature reaction process, and carbon deposition is generated, resulting in low initial dehydrogenation performance of the catalyst in the propane dehydrogenation and methylcyclohexane dehydrogenation processes, rapid deactivation, and inability to achieve efficient and stable propane and methylcyclohexane dehydrogenation performance, the present invention provides a pure silicon Beta molecular sieve encapsulated metal catalyst and a preparation method and application thereof, and a pure silicon twelve-membered ring Beta molecular sieve with a larger pore size is prepared by optimizing the synthesis strategy to encapsulate the 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, thereby improving the propane and methylcyclohexane dehydrogenation performance.

[0006] The present invention is achieved through the following technical solutions:

[0007] The first aspect of the present invention provides a method for preparing a pure silicon Beta molecular sieve encapsulated metal catalyst, comprising the following steps:

[0008] Dissolving a silicon source, a template, a ligand, a metal salt and a mineralizer in water, performing a crystallization reaction at 120-200° C., and then calcining and reducing the crystallized solid to obtain the pure silicon Beta molecular sieve encapsulated metal catalyst;

[0009] The ligand is selected from one or more of ammonia water, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, ethylenediaminetetraacetic acid, tartaric acid and citric acid; 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 invention can encapsulate precious metals (such as Pt, Pd, Ru, Rh, Os, Au, Ir, Ag, etc.), non-precious 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 pure silicon Beta molecular sieve encapsulated metal catalyst synthesized by ligand protection in situ hydrothermal synthesis has a promoting effect on the catalytic activity and stability of the catalytic dehydrogenation reaction of propane and methylcyclohexane, and doping with metal additives (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 reaction of methylcyclohexane; doping with Zn can improve the propane dehydrogenation activity and stability of the Pt-based catalyst, and further doping with Mg can inhibit the loss of Zn species, thereby showing a more stable propane dehydrogenation performance. The present invention utilizes the encapsulation effect of pure silicon Beta molecular sieve channels on metal species to, on the one hand, improve the high-temperature thermal stability of Pt nanoclusters and inhibit the aggregation and sintering of Pt nanoclusters during high-temperature reactions; on the other hand, the adsorption and diffusion behaviors of the reactant methylcyclohexane and the product toluene are regulated through the channel confinement effect, so that the pure silicon Beta molecular sieve channel encapsulated metal catalyst exhibits efficient and stable dehydrogenation reaction activity.

[0011] The present invention prepares metal nanoclusters encapsulated in the pores of pure silicon twelve-membered ring macroporous Beta molecular sieve through a ligand-protected in-situ hydrothermal synthesis strategy to improve the high-temperature thermal stability of the metal nanoclusters, while regulating the adsorption and diffusion behaviors of the reactant methylcyclohexane and the product toluene, thereby achieving efficient and stable dehydrogenation performance of propane and methylcyclohexane.

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

[0013] Furthermore, 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] Furthermore, the mineralizer is selected from one or more of hydrofluoric acid, ammonium fluoride, sodium fluoride and magnesium fluoride.

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

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

[0017] Furthermore, the molar ratio of the silicon source to the mineralizer is 1:(0.1-0.5).

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

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

[0020] Furthermore, 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] Furthermore, the alkali metal hydroxide is selected from one or more of the hydroxides of sodium, potassium and cesium.

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

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

[0024] Furthermore, before the calcination treatment, the solid product is centrifuged, washed and dried.

[0025] Furthermore, the calcination treatment conditions are: heating to 300-500°C at a heating rate of 1-10°C / min, and calcining at 300-500°C for 2-6h.

[0026] Furthermore, the reduction treatment is carried out under the conditions of: reducing at 300-500° C. for 1-2 h in a hydrogen atmosphere.

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

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

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

[0030] Beneficial effects of the present invention:

[0031] The pure silicon Beta molecular sieve of the present invention can encapsulate precious metals, non-precious metals, rare earth metals and bi / multi-metals. The pure silicon Beta molecular sieve encapsulated metal catalyst synthesized by ligand protection in situ hydrothermal synthesis has a promoting effect on the catalytic activity and stability of catalytic propane dehydrogenation reaction and methylcyclohexane dehydrogenation reaction, and doping with metal additives (precious metals / non-precious metals / rare earth metals and bi / multi-metals) can promote the performance of Pt-based catalysts in catalytic propane dehydrogenation reaction and methylcyclohexane dehydrogenation reaction, further improving the catalyst's propane dehydrogenation reaction and methylcyclohexane dehydrogenation reaction activity and stability.

[0032] The present invention prepares metal nanoclusters encapsulated in the pores of pure silicon twelve-membered ring macroporous Beta molecular sieves through a ligand-protected in-situ hydrothermal synthesis strategy, which can not only reduce the size of the metal nanoclusters and improve the high-temperature thermal stability of the metal nanoclusters, but also regulate the adsorption and diffusion processes of guest molecules, thereby showing excellent catalytic performance in the dehydrogenation reaction of propane and methylcyclohexane. In particular, when catalyzing the dehydrogenation of macromolecular methylcyclohexane, the larger pore size of the pure silicon twelve-membered ring macroporous Beta molecular sieve improves the diffusion and mass transfer limitations of the reactant methylcyclohexane and the product toluene, thereby achieving efficient and stable methylcyclohexane dehydrogenation performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The performance diagram of methylcyclohexane dehydrogenation catalyzed by Pt / S-1 catalyst and Pt / SiO2 catalyst; among them, a is Pt / S-1 catalyst and b is Pt / SiO2 catalyst.

[0034] Figure 2Powder 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@AmorphousSiO2 catalyst prepared in Comparative Example 4.

[0035] Figure 3 This is a scanning transmission electron microscope image of the Pt@Si-Beta catalyst prepared in Example 1.

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

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

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0039] In the background technology, Guo et al. used S-1 molecular sieve as a carrier and prepared a supported Pt / S-1 catalyst by impregnation method. The dehydrogenation performance of methylcyclohexane was as follows: Figure 1 As shown in a, the average methylcyclohexane conversion rate of the catalyst at 350°C is only 17.7%, and it gradually deactivates during the reaction and becomes fully active after 5 hours of reaction. Furukawa et al. used SiO2 as a carrier and prepared the Pt / SiO2 catalyst by impregnation method. Figure 1As shown in b. Although Pt / SiO2 catalyst ( Figure 1 The initial methylcyclohexane conversion rate of Pt in (b) at 400°C was close to 100%, but it deactivated rapidly during the continuous reaction process. After about 150 minutes, the conversion rate dropped rapidly to below 10%, showing poor catalytic stability.

[0040] The present invention 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° C., and then performing a calcination treatment and a reduction treatment on the crystallized solid to obtain the pure silicon Beta molecular sieve encapsulated metal catalyst.

[0041] In a specific embodiment, a ligand and a metal salt are combined to form a metal complex solution, which is added to a synthetic gel of pure silicon Beta molecular sieve, and after crystallization at a certain temperature for a certain period of time, a metal species encapsulated in the pure silicon Beta molecular sieve is obtained, which is then calcined and reduced to obtain a pure silicon Beta molecular sieve encapsulated metal catalyst.

[0042] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0043] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods, and the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0044] Example 1

[0045] A method for preparing 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 reactor and stirred at room temperature for 10 min to obtain a mixed solution;

[0047] (2) 2.4 g of white carbon black was gradually added to the mixed solution obtained in step (1) three times, heated and stirred in an oil bath at 80° C., and after being fully stirred to completely dissolve, 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; 0.09 mol / L ethylenediamine platinum chloride solution was prepared by the following method: 0.24 g of PtCl2 solid was added to a mixed solution of 1 mL of ethylenediamine and 2 mL of deionized water, and then fully stirred in a water bath at 60° C. to completely dissolve it, and finally the volume was adjusted to 10 mL to obtain ethylenediamine platinum chloride solution (0.09 mol / L);

[0048] (3) placing the gel mixture obtained in step (2) into a stainless steel autoclave, statically crystallizing at 140° C. for 4 days, centrifuging and washing the crystallized sample, and drying the obtained solid product in an oven at 80° C. overnight;

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

[0050] Example 2

[0051] A method for preparing 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 to a 25 mL polytetrafluoroethylene-lined reactor and stirred at room temperature for 10 min to obtain a mixed solution;

[0053] (2) 2.4 g of white carbon black was gradually added to the mixed solution obtained in step (1) in three times, heated and stirred in an oil bath at 80° C., and after being fully stirred to completely dissolve, 450 μL of ethylenediamineplatinum chloride solution (0.09 mol / L) and 450 μL of Ga(NO3)3 solution (0.09 mol / L) were added, and then 350 μL of hydrofluoric acid was added dropwise to obtain a gel mixture;

[0054] (3) placing the gel mixture obtained in step (2) into a stainless steel autoclave, statically crystallizing at 140° C. for 4 days, centrifuging and washing the crystallized sample, and drying the obtained solid product in an oven at 80° C. overnight;

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

[0056] Example 3

[0057] A method for preparing 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, which is basically the same as the preparation method in Example 2, except that: in step (2), Ga(NO3)3 solution (0.09 mol / L) is replaced by [Mn(NH2CH2CH2NHCH2CH2)2NH]Cl2 solution (0.09 mol / L). The preparation of [Mn(NH2CH2CH2NHCH2CH2)2NH]Cl2 solution is basically similar to that of 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 method for preparing 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, which is basically the same as the preparation method of Example 2, except that in step (2), Ga(NO3)3 solution (0.09 mol / L) is replaced by Fe-EDTA solution (0.09 mol / L). The preparation of Fe-EDTA solution is basically similar to that of Pt(NH2CH2CH2NH2)2Cl2 solution, except that ethylenediaminetetraacetic acid is a ligand and ferric nitrate is a metal salt.

[0060] Example 5

[0061] A method for preparing 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, which is basically the same as the preparation method in Example 2, except that: in step (2), Ga(NO3)3 solution (0.09 mol / L) is replaced by [Zn(NH2CH2CH2NH2)3](OAc)2 solution (0.09 mol / L). The preparation of [Zn(NH2CH2CH2NH2)3](OAc)2 solution is basically similar to that of 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 method for preparing 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, which is basically the same as the preparation method in Example 2, except that: in step (2), Ga(NO3)3 solution (0.09 mol / L) is replaced by In(NO3)3 solution (0.09 mol / L).

[0064] Example 7

[0065] A method for preparing 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, which is basically the same as the preparation method of Example 2, except that: in step (2), Ga(NO3)3 solution (0.09 mol / L) is replaced by SnCl4 solution (0.09 mol / L).

[0066] Example 8

[0067] A method for preparing 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, which is basically the same as the preparation method of Example 2, except that: in step (2), Ga(NO3)3 solution (0.09 mol / L) is replaced by Ce(NO3)3 solution (0.09 mol / L).

[0068] Example 9

[0069] A method for preparing 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, which is basically the same as the preparation method of Example 2, except that: in step (2), 450 μL Ga(NO3)3 solution (0.09 mol / L) is replaced by 900 μL ethylenediamine zinc acetate solution (0.09 mol / L) and 900 μL MgCl solution (0.09 mol / L).

[0070] Comparative Example 1

[0071] A method for preparing a Pt@Al-Beta catalyst encapsulated with a silicon-aluminum Beta molecular sieve, 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, specifically comprising 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 aluminate were added to a 25 mL polytetrafluoroethylene-lined reactor and stirred at room temperature for 10 min to obtain a mixed solution;

[0073] (2) 2.4 g of white carbon black was gradually added to the mixed solution obtained in step (1) in three portions, and the mixture was heated and stirred in an oil bath at 80° C. After being stirred sufficiently to completely dissolve, 450 μL of ethylenediamineplatinum chloride solution (0.09 mol / L) was added, and then 350 μL of hydrofluoric acid was added dropwise to obtain a gel mixture;

[0074] (3) placing the gel mixture obtained in step (2) into a stainless steel autoclave, statically crystallizing at 140° C. for 4 days, centrifuging and washing the crystallized sample, and drying the obtained solid product in an oven at 80° C. overnight;

[0075] (4) The dried solid product was placed in a muffle furnace, and the temperature was raised from room temperature to 500°C at a rate of 1.5°C / min, and calcined at 500°C to remove the molecular sieve template, and then reduced in a hydrogen atmosphere at 400°C (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, wherein the calcined Si-Beta molecular sieve is used as a catalyst carrier, hexahydrate chloroplatinic acid is used as a platinum source, and the catalyst is synthesized by an impregnation method, and specifically comprises the following steps:

[0078] 0.12mL of chloroplatinic acid solution (0.064mol / L) was added dropwise to 0.5g of calcined Si-Beta molecular sieve at 300rpm, and the mixture was stirred to make it fully contacted and mixed, and then placed in an oven at 80℃ to dry overnight. Finally, the dried sample was reduced at 400℃ in a hydrogen atmosphere (50mL / min) for 1h to obtain a Pt / Si-Beta-im catalyst.

[0079] Comparative Example 3

[0080] A method for preparing an 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 comprising the following steps:

[0081] (1) 13.0 g of tetrapropylammonium hydroxide aqueous 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, and stirring was continued for 6 h to completely hydrolyze to obtain a uniform transparent solution;

[0082] (2) adding 450 μL of ethylenediamineplatinum chloride solution (0.09 mol / L) to the solution of step (1) and stirring for 1 h, transferring the above-mentioned uniformly mixed solution to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave, and statically crystallizing 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 directly reduced by hydrogen at 400°C in a hydrogen atmosphere (50 mL / min) for 1 h to obtain a Pt@S-1 catalyst.

[0084] Comparative Example 4

[0085] A method for preparing 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, and specifically comprises the following steps:

[0086] (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 reactor and stirred at room temperature for 10 min to obtain a mixed solution;

[0087] (2) 2.4 g of white carbon black was gradually added to the mixed solution obtained in step (1) in three portions, and the mixture was heated and stirred in an oil bath at 80° C. After being stirred sufficiently to completely dissolve, 450 μL of ethylenediamineplatinum chloride solution (0.09 mol / L) was added to obtain a mixed solution;

[0088] (3) the mixed solution obtained in step (2) was placed in 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;

[0089] (4) The dried solid product was placed in a muffle furnace, and the temperature was raised from room temperature to 500°C at a rate of 1.5°C / min, and calcined at 500°C to remove the molecular sieve template, and then reduced in a hydrogen atmosphere at 400°C (50 mL / min) for 1 h to obtain a 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@AmorphousSiO2 catalyst prepared in Comparative Example 4 show that the catalysts prepared in Example 1 and Example 2 have a typical Beta molecular sieve topological structure, and no diffraction peaks corresponding to Pt foil are observed, proving that small-sized Pt nanoclusters are formed. However, the Pt / Si-Beta-im catalyst synthesized by the impregnation method has a characteristic peak corresponding to Pt foil at 2θ=~40°, proving that the catalyst synthesized by the impregnation method undergoes agglomeration and sintering of Pt species during the heat treatment process, forming larger Pt nanoparticles. When no fluorine species is added to the synthetic gel in Comparative Example 4, the Pt@Amorphous SiO2 catalyst does not show the topological structure of the Beta molecular sieve, proving that this method cannot synthesize a Pt catalyst encapsulated in pure silicon Beta molecular sieve.

[0091] Figure 3 This is a scanning transmission electron microscope image of the Pt@Si-Beta catalyst prepared in Example 1. It can be found that the Pt nanoclusters have high metal dispersion in the Beta molecular sieve pores.

[0092] The catalysts prepared in Examples 1-8 and Comparative Examples 1-3 were used to catalyze the dehydrogenation of methylcyclohexane. The reaction conditions of the dehydrogenation of methylcyclohexane were as follows: 0.11 g of 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 space velocity was 21 h -1 In addition, except for the Pt@Al-Beta catalyst prepared in Comparative Example 1, only reactant methylcyclohexane and product toluene were detected in the process of catalytic dehydrogenation of methylcyclohexane by other prepared catalysts, and no other by-products were detected, indicating that the prepared catalysts have about 100% hydrogen selectivity.

[0093] Figure 4The data graph of the conversion rate of the catalysts prepared in Examples 1-8 and Comparative Examples 1-3 for catalyzing the dehydrogenation reaction of methylcyclohexane; wherein a is a Pt@Si-Beta catalyst and a Pt / Si-Beta-im catalyst, b is a Pt@Si-Beta catalyst and a Pt@S-1 catalyst, c is a Pt@Si-Beta catalyst and a Pt@Al-Beta catalyst, and d is a Pt@Si-Beta catalyst, a PtMn@Si-Beta catalyst, a PtFe@Si-Beta catalyst, a PtZn@Si-Beta catalyst, a PtIn@Si-Beta catalyst, a PtSn@Si-Beta catalyst, a PtGa@Si-Beta catalyst, and a PtCe@Si-Beta catalyst. Figure 4 As can be seen in a, the Pt@Si-Beta catalyst is heated to 400℃ and 21h. -1 The initial methylcyclohexane conversion rate under space velocity conditions can reach 46.4%, and finally achieve stable dehydrogenation performance. However, 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 continues. The above results prove that compared with the impregnation method, pure silicon Beta molecular sieve encapsulated Pt catalyst helps to improve the high-temperature thermal stability of Pt nanoclusters and inhibit the aggregation and sintering of metal species during the reaction; at the same time, pore confinement can regulate the adsorption and diffusion process of the substrate methylcyclohexane and the product toluene, avoiding adsorption on the catalytic active sites, so that it maintains stable dehydrogenation activity. Figure 4 As can be seen in b, the Pt@S-1 catalyst -1 ) did not show the performance of methylcyclohexane dehydrogenation, which is mainly due to the fact that the pore size of S-1 molecular sieve (~0.55nm) is close to the kinetic diameter of substrate methylcyclohexane and product toluene (~0.6nm), and it is unable to contact the catalytic active sites inside the pores, thus losing the catalytic performance of methylcyclohexane dehydrogenation. Therefore, the design and synthesis of Pt nanoclusters encapsulated in pure silicon twelve-membered ring macroporous Beta molecular sieve with larger pore size plays a key role in improving the diffusion mass transfer efficiency and catalytic performance of macromolecular methylcyclohexane. Figure 4 In c, the effect of the acidity of Beta zeolite itself on the dehydrogenation performance of methylcyclohexane was investigated. The introduction of acidic sites had a significant inhibitory effect on the dehydrogenation performance of methylcyclohexane of Pt@Al-Beta catalyst. This was attributed to the fact that the acidic sites would accelerate the occurrence of side reactions such as demethylation and disproportionation, produce carbon deposits on the catalyst surface, cover the catalytic active sites, and cause rapid deactivation of the catalyst. Figure 4Figure d investigates the effect of doping metal additives on the methylcyclohexane dehydrogenation performance of Pt@Si-Beta catalyst. Among them, doping with additives such as Mn, Fe, Zn, In, Sn, Ga and Ce can effectively improve the methylcyclohexane dehydrogenation reaction activity and stability of Pt@Si-Beta catalyst.

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

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

[0096] Obviously, the above embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art should understand that other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a pure silicon Beta molecular sieve encapsulated metal catalyst, characterized in that: The following steps are involved: Dissolving a silicon source, a template, a ligand, a metal salt and a mineralizer in water, performing a crystallization reaction at 120-200° C., and then calcining and reducing the crystallized solid to obtain the pure silicon Beta molecular sieve encapsulated metal catalyst; The ligand is selected from one or more of ammonia water, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, ethylenediaminetetraacetic acid, tartaric acid and citric acid; 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.

2. The preparation method according to claim 1, characterized in that: The template agent is selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide and tetrabutylphosphonium hydroxide; the mineralizer is selected from one or more of hydrofluoric acid, ammonium fluoride, sodium fluoride and magnesium fluoride.

3. The preparation method according to claim 1, characterized in that: The molar ratio of the silicon source, the template and water is 1:(0.2-0.5):(5-10).

4. The preparation method according to claim 1, characterized in that: The molar ratio of the silicon source to the metal salt is 1:(0.0005-0.01).

5. The preparation method according to claim 1, characterized in that: The method further comprises the step of adding an alkali metal salt or an alkali metal hydroxide to the water.

6. The preparation method according to claim 5, characterized in that: The molar ratio of the silicon source to the alkali metal salt is 1:(0.01-0.05).

7. The preparation method according to claim 1, characterized in that: The calcination treatment conditions are: heating to 300-500° C. at a heating rate of 1-10° C. / min, and calcining at 300-500° C. for 2-6 hours.

8. The preparation method according to claim 1, characterized in that: The reduction treatment conditions are: reduction at 300-500° C. for 1-2 h in a hydrogen atmosphere.

9. A pure silicon Beta molecular sieve encapsulated metal catalyst prepared by the method according to any one of claims 1 to 8.

10. Use of the pure silicon Beta molecular sieve encapsulated metal catalyst according to claim 9 in catalyzing propane dehydrogenation reaction or methylcyclohexane dehydrogenation reaction.

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