Preparation method and application of zeolite encapsulated metal bifunctional catalyst

Abstract

The application discloses a preparation method of a zeolite encapsulated metal bifunctional catalyst and application thereof, and belongs to the technical field of bifunctional catalysts, and comprises the following steps: dissolving a salt containing a metal to be encapsulated into a certain amount of deionized water, then adding a certain proportion of an organic ligand as a complexing agent, and uniformly stirring to obtain a metal complex aqueous solution; adopting an in-situ synthesis method to obtain a zeolite initial gel; dropping the metal complex aqueous solution into the zeolite initial gel, uniformly stirring to obtain a gel mixture; transferring the gel mixture into a crystallization kettle for crystallization, and after washing, drying, calcining and ammonium exchange, a zeolite encapsulated metal bifunctional catalyst is obtained. The bifunctional catalyst prepared by the application has the performance advantages of high crystallinity and high dispersion; the encapsulated metal is in close contact with the carrier molecular sieve, a suitable active component spacing promotes mutual coordination between the metal center and the acid center, and the low-temperature activity of the metal component is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bifunctional catalysts, in particular to a preparation method of a zeolite encapsulated metal bifunctional catalyst and application thereof. BACKGROUND

[0002] The preparation and modification methods of bifunctional catalysts are roughly divided into post-treatment methods and in-situ encapsulation methods. The post-treatment methods include ion exchange and impregnation methods. Traditional silicoaluminate zeolite frameworks have negative charges, and the cations used to balance them can move freely and can also be exchanged with other metal cations (such as filtered metal cations in solution). Generally speaking, the traditional exchange process needs to repeat the exchange steps to achieve the desired metal loading. The molecular sieves with neutral frameworks (such as pure silica molecular sieves and aluminum phosphate molecular sieves) cannot be ion-exchanged. For molecular sieves with neutral frameworks, impregnation is a widely used method to introduce metal precursors. Generally, the metal precursors are mainly introduced into the pores of the molecular sieve through physical adsorption. The isochoric impregnation method is the most commonly used impregnation method, that is, the dehydrated molecular sieve is mixed with an equal volume of metal solution, and the solution is introduced into the pores of the molecular sieve. The metal components of the catalyst prepared by impregnation are mainly distributed on the outer surface and part of the pores of the molecular sieve, and have the disadvantage of low metal dispersion, which easily leads to accelerated carbon deposition and deactivation of the catalyst. In practical applications, in order to ensure sufficient catalytic activity, a high metal loading is required. However, the increase of metal loading will usually lead to the formation of large metal particles on the surface.

[0003] Compared with the post-treatment method, the in-situ encapsulation method is not limited by the pore size of the molecular sieve, because the encapsulation process of the metal is synchronized with the crystallization process of the molecular sieve. The in-situ encapsulation strategy is that the metal nanoparticles or precursors can be introduced into the zeolite crystal by one-step hydrothermal synthesis. This method first mixes the synthesized metal nanoparticles or soluble metal precursors with the synthesis gel of the zeolite (such as structure directing agent, silicon source, water, sodium hydroxide, etc.), and then performs high-temperature crystallization. The synthesized product is further calcined to remove organic matter. However, during the crystallization process of the molecular sieve under hydrothermal conditions, most metal cations are prone to precipitate in the form of hydroxide in the alkaline initial gel, which will lead to the formation of large particles on the surface of the molecular sieve crystal, and even lead to the separation of the metal species from the molecular sieve carrier. In addition, due to the high surface energy of the metal clusters, there is a serious tendency of aggregation in the molecular sieve precursor. Therefore, more protection methods need to be developed to limit the serious aggregation or rapid precipitation of the metal clusters encapsulated in the molecular sieve framework during the in-situ synthesis process.

[0004] Ligand-stabilization method is to use N- or S-containing organosilicon ligands to effectively solve the problem of metal species aggregation under the conditions of molecular sieve crystallization. Amine-based ligands, such as ammonia and ethylenediamine, are often used to stabilize metal cations when synthesizing molecular sieves encapsulating metals in situ, because these metal-amine complexes have good water solubility and excellent stability in high-pH synthesis systems. Some metal ions, such as Au 3+ ions are not easily stabilized by amine-based ligands, but in the presence of mercaptosilane, stable complexes can be formed, which remain stable even under alkaline hydrothermal conditions. Mercaptosilane is a strong ligand for stabilizing metal ions and encapsulating metal clusters within molecular sieves.

[0005] In addition to using organic ligands to stabilize metal ions, using amorphous silica precursors as stabilizers to immobilize metal clusters is also an effective method for in situ synthesis of molecular sieves encapsulating MNPs (metal nanoparticles). In this synthesis system, pre-prepared metal clusters are first embedded in a SiO2 matrix as a precursor for molecular sieve crystallization. Under hydrothermal conditions, the silica-coated metal cluster precursor is crystallized, and as the silica is consumed, the internal metal clusters are simultaneously encapsulated in the prepared molecular sieves. To overcome the problem of incomplete filling of MNPs inside the molecular sieves, researchers have developed a solvent-free method and improved the Kirkendall growth method to reduce the amount of solvent used during molecular sieve crystallization.

[0006] Zeolite molecular sieves are crystalline materials with uniform microporous structures and are widely used in the field of catalysis. For example, Y-type zeolites have been widely used in catalytic cracking (FCC) of heavy oil; ZSM-5-type molecular sieves with mesoporous channels have been used for upgrading of fuels. Researchers have successfully prepared zeolite molecular sieve-confined MNPs bifunctional catalysts and found that they have good catalytic performance in hydrogenation, dehydrogenation and cracking, and isomerization reactions. MNPs@zeolite molecular sieve materials have the advantages of both zeolite molecular sieves and high-activity MNPs: open nanopores facilitate molecular diffusion, allowing access to immobilized metal species; uniform nanopores can effectively separate molecules of different sizes, with smaller molecules diffusing into the nanopores and larger molecules being completely blocked; adjustable zeolite composition and structure enable mass transfer regulation at the molecular level; active centers in the framework cooperate with confined metal nanoparticles to form multifunctional catalysts. In addition, the zeolite molecular sieve channel structure stabilizes the MNPs, preventing aggregation or leaching during catalysis, and obtaining a sintering-resistant catalyst under high-temperature reaction conditions.

[0007] In some high-temperature reactions, metal particles tend to aggregate or be deactivated due to metal leaching. Metal nanoparticles are fixed in zeolites, which is superior to traditional supported catalysts. The catalyst prepared by in-situ encapsulation method can usually encapsulate the metal inside the pore channel of the molecular sieve, and often has good dispersion, easily exposes more effective active sites, high catalytic performance and good stability. Due to the inherent structural advantages of mesoporous zeolites and the constraint effect of immobilized metal nanoparticles, these composite catalysts exhibit superior catalytic activity in various catalytic reactions. For hydrogenation reactions, noble metals such as Pt, Rh, Ru and Pd show good catalytic performance, however, these metals face the problems of limited resources and high cost; some non-noble metals also face these problems. Coating the catalytically active component in the structure of the zeolite molecular sieve is an effective method to disperse and stabilize the metal component. The spatial confinement of the molecular sieve channel can effectively limit the aggregation of metal particles during catalyst preparation and reaction, so that they have very good sintering resistance. Thus, a high-activity zeolite molecular sieve encapsulated metal particle system is generated.

[0008] The MNPs@zeolite molecular sieve catalyst not only exhibits excellent catalytic activity, but also has high stability and shape-selective catalytic properties; in addition, the synergistic effect of the confined MNPs and the nanopore framework with active sites can further improve the catalytic activity of the composite catalyst. Due to the advantages of anti-leaching and anti-aggregation of zeolite immobilized metal nanoparticles, more and more scholars have paid attention to it. Synthesizing more metal@zeolite catalysts with unique characteristics and performing important industrial catalytic reactions on these metal@zeolite catalysts is the future research direction. SUMMARY

[0009] Based on the previous research and existing problems, the present application provides a preparation method of a zeolite encapsulated metal bifunctional catalyst and its application. The encapsulated metal-zeolite bifunctional catalyst prepared by the method provided by the present application enhances the anti-aggregation ability of the metal active component, can maintain the high crystallinity of the zeolite and the high dispersity of the metal, constructs a molecular sieve confined "metal-acid" dual active center, and improves the accessibility of the active sites of the catalyst and the low-temperature activity.

[0010] To achieve the above object, the present application provides the following technical scheme: a preparation method of a zeolite encapsulated metal bifunctional catalyst, and the specific method steps are as follows:

[0011] S1, dissolving a salt containing a metal to be encapsulated into a certain amount of deionized water, then adding a certain proportion of an organic ligand as a complexing agent, and stirring uniformly to obtain a metal complex aqueous solution;

[0012] S2, obtaining a zeolite initial gel by an in-situ synthesis method;

[0013] S3, drop the metal complex aqueous solution into the zeolite initial gel, stir to obtain a gel mixture;

[0014] S4, transfer the gel mixture to a crystallization kettle for crystallization, and obtain the zeolite encapsulated metal bifunctional catalyst after washing, drying, calcination and ammonium exchange.

[0015] Preferably, the encapsulated metal active component in S1 is any one or more of Pt, Pd, Ru, Cu, Co, Ni, Mo and W, and the metal is encapsulated in the form of clusters in the pores of the zeolite molecular sieve, and the metal salt solution is nitrate or chloride.

[0016] Preferably, the organic ligand is one of ammonia, ethylenediamine, diethylenetriamine, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and mercaptopropyltrimethoxysilane, and the molar ratio of the organic ligand to the metal salt is 1-10.

[0017] Preferably, the preparation method of the zeolite initial gel in S2 specifically comprises:

[0018] S101, mix and stir the silicon source, the template agent and a certain amount of deionized water for a certain time to obtain solution A;

[0019] S102, mix and stir the alkali source, the aluminum source and a certain amount of deionized water for a certain time to obtain solution B;

[0020] S103, drop solution B into solution A, and then stir for 3-6 hours to obtain a zeolite initial gel.

[0021] Preferably, in S101, the silicon source can be any one of nano-silicon dioxide, tetraethyl orthosilicate and solid silica gel.

[0022] Preferably, in S102, the aluminum source is sodium metaaluminate or aluminum nitrate.

[0023] Preferably, in the process of preparing the zeolite initial gel, the template agent is selected to be tetraethylammonium hydroxide, and the feeding ratio is silicon source: aluminum source: tetraethylammonium hydroxide: alkali source = 1: (0.005-0.025): 0.4: 0.0047.

[0024] Preferably, in the process of preparing the zeolite initial gel, the template agent is selected to be tetraethylammonium hydroxide, and the feeding ratio is silicon source: aluminum source: tetraethylammonium hydroxide: alkali source = 1: (0.005-0.025): 0.4: 0.0047.

[0025] Preferably, in S54, the crystallized gel mixture is washed with deionized water, the washing liquid has a pH of 7-8; drying is performed at 100-200°C for 6-12h, calcination is performed at 450-550°C for 6-8h; the ammonium exchange is performed at a mass ratio of catalyst to 1M NH4Cl of 1:10, and hydrothermal treatment is performed at 90°C for 3h.

[0026] The application also provides a use of the zeolite-encapsulated metal bifunctional catalyst, which is prepared by the method described above, and the catalyst can be used in a hydroisomerization reaction.

[0027] Compared with the prior art, the application provides a preparation method and use of a zeolite-encapsulated metal bifunctional catalyst, and has the following beneficial effects:

[0028] (1) The zeolite-encapsulated metal bifunctional catalyst prepared by the method provided by the application can keep high crystallinity of the zeolite and high dispersity of the metal by growing the zeolite molecular sieve on the outer surface of the metal and encapsulating the metal in the pore of the zeolite, effectively inhibits the aggregation of the metal particles, reduces the size of the active metal particles to sub-nanometer, significantly improves the accessibility of the active sites, and reduces the required temperature of the reaction; constructs a molecular sieve limited "metal-acid" dual active center, enhances the electron transfer effect between the metal and the carrier, and thus improves the selectivity and low-temperature activity of the catalyst.

[0029] (2) The zeolite-encapsulated metal bifunctional catalyst can be applied to a hydroisomerization reaction, the prepared zeolite-encapsulated metal bifunctional catalyst is subjected to performance evaluation, the zeolite-encapsulated metal bifunctional catalyst has metal hydrogenation, dehydrogenation activity and carrier molecular sieve ring-opening, isomerization and other acidic activity, a model compound tetrahydronaphthalene is used to simulate the reaction path of the catalytic cracking diesel in the hydroisomerization reaction, and the evaluation results show that the prepared catalyst has high raw material conversion rate, effectively improves the selectivity of the hydroisomerization product, and has a very broad application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 FIG. 4 is an XRD spectrum of the zeolite-encapsulated metal bifunctional catalyst in Examples 1-5;

[0031] Figure 2 FIG. 6 is an SEM image of the zeolite-encapsulated metal bifunctional catalyst in Examples 1-5. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments of the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0033] In order to more clearly and specifically introduce the preparation method of the preparation method of the zeolite encapsulated metal bifunctional catalyst provided by the embodiments of the present application, the following will be described in combination with specific embodiments.

[0034] Example 1

[0035] In a reaction kettle A, 600.00 g of nanosilica was weighed, 1400.00 g of deionized water and 2356.00 g of tetraethylammonium hydroxide (25 wt%) were added and stirred for 1 h to obtain solution A. At the same time, in a reaction kettle B, 775.00 g of deionized water, 19.00 g of sodium hydroxide and 83.00 g of Al(NO3)3·9H2O were added and stirred for 1 h to obtain solution B. Then, solution B was added dropwise to solution A and continued to be stirred for aging for 3 h to obtain a zeolite initial gel. Then, in a reaction kettle C, 300.00 g of deionized water, 29.00 g of Ni(NO3)2·6H2O and 12.00 g of ethylenediamine were added, and after being stirred and dissolved, they were added dropwise to the zeolite initial gel. Then, it was stirred for another 30 min. The stirred zeolite gel was crystallized at 150℃ for 5 days. After the crystallization was completed, the light green solid generated was washed to neutral with deionized water and dried at 100℃, and then calcined at 550℃ for 6 h to prepare an encapsulated Ni@Na-Beta bifunctional catalyst with a silicon-aluminum ratio of 45 and a Ni content of 1 wt%. The prepared Ni@Na-Beta was added to a 1M NH4Cl solution at a mass ratio of 1 / 10, and exchanged under hydrothermal conditions at 90℃ for 3 h, and then washed and dried at 100℃. After being calcined at 550℃ for 6 h, a Ni@H-Beta bifunctional catalyst with catalytic effect was obtained. The pore structure properties of the catalyst are shown in Table 1.

[0036] In a high-pressure fixed-bed reactor loaded with 50 ml of the catalyst prepared in Example 1, a 20 wt% tetrahydro naphthalene-cyclohexane solution was used as a model compound to simulate the catalytic cracking diesel hydroisomerization reaction, the reaction temperature was 300℃, the liquid hourly space velocity was 2.0 h -1 , and the reaction pressure was 4 MPa. The conversion rate of tetrahydro naphthalene was 47.48%, and the selectivity of isomerization products was 16.63%. The results are shown in Table 2.

[0037] Example 2

[0038] Take 600.00 g of nano-silicon dioxide in a reaction kettle A, add 1400.00 g of deionized water and 2356.00 g of tetrapropylammonium hydroxide (25 wt%) and stir for 1 h to obtain solution A. At the same time, in reaction kettle B, add 775.00 g of deionized water, 19.00 g of sodium hydroxide and 165.00 g of Al(NO3)3·9H2O and stir for 1 h to obtain solution B. Then add solution B to solution A dropwise and continue to stir for 5 h to obtain a zeolite initial gel. Then add 300.00 g of deionized water, 29.00 g of Ni(NO3)2·6H2O and 12.00 g of ethylenediamine in a reaction kettle C, stir to dissolve, and then add them dropwise to the zeolite initial gel. Then stir for another 30 min. The stirred zeolite gel is crystallized at 170°C for 3 days. After crystallization, the generated solid is washed to neutral with deionized water and dried at 100°C, and then calcined at 550°C for 6 h to prepare an encapsulated Ni@ZSM-5 bifunctional catalyst with a silicon-aluminum ratio of 20 and a Ni content of 1 wt%. The prepared Ni@Na-ZSM-5 is added to a 1M NH4Cl solution at a mass ratio of 1 / 10, and exchanged under hydrothermal conditions at 90°C for 3 h, then washed, dried at 100°C, and calcined at 550°C for 6 h to obtain a Ni@H-ZSM-5 bifunctional catalyst with catalytic effect. The pore structure properties of the catalyst are shown in Table 1.

[0039] In a high-pressure fixed-bed reactor loaded with 50 ml of the catalyst prepared in Example 2, a 20 wt% tetrahydro naphthalene-cyclohexane solution was used as a model compound to simulate the catalytic cracking diesel hydroisomerization reaction under the conditions of a reaction temperature of 300°C, a liquid hourly space velocity of 2.0 h-1, and a reaction pressure of 4 MPa. The conversion rate of tetrahydro naphthalene was 33.36%, and the selectivity of isomerization products was 14.55%. The results are shown in Table 2. -1

[0040] Example 3

[0041] Take 600.00 g of nano-silicon dioxide in a reaction kettle A, add 1400.00 g of deionized water and 2356.00 g of tetrapropylammonium hydroxide (25 wt%) and stir for 1 h to obtain solution A. At the same time, in reaction kettle B, add 775.00 g of deionized water, 19.00 g of sodium hydroxide and 165.00 g of Al(NO3)3·9H2O and stir for 1 h to obtain solution B. Then add solution B to solution A dropwise and continue to stir for 5 h to obtain a zeolite initial gel. Then add 300.00 g of deionized water, 29.00 g of Ni(NO3)2·6H2O and 12.00 g of ethylenediamine in a reaction kettle C, stir to dissolve, and then add them dropwise to the zeolite initial gel. Then stir for another 30 min. The stirred zeolite gel is crystallized at 170°C for 3 days. After crystallization, the generated solid is washed to neutral with deionized water and dried at 100°C, and then calcined at 550°C for 6 h to prepare an encapsulated Ni@ZSM-5 bifunctional catalyst with a silicon-aluminum ratio of 20 and a Ni content of 1 wt%. The prepared Ni@Na-ZSM-5 is added to a 1M NH4Cl solution at a mass ratio of 1 / 10, and exchanged under hydrothermal conditions at 90°C for 3 h, then washed, dried at 100°C, and calcined at 550°C for 6 h to obtain a Ni@H-ZSM-5 bifunctional catalyst with catalytic effect. The pore structure properties of the catalyst are shown in Table 1. 24 ​·4H2O and 8.00g of ethylenediamine were dissolved by stirring and then added dropwise to the initial zeolite gel. The mixture was then stirred for 30 min. The stirred zeolite gel was crystallized at 150℃ for 5 days. After crystallization, the resulting pale yellow solid was washed with deionized water until neutral, dried at 100℃, and then calcined at 550℃ for 6 h to obtain an encapsulated Mo@Na-Beta bifunctional catalyst with a silicon-to-aluminum ratio of 45 and a Mo content of 1wt%. The obtained Mo@Na-Beta was added to a 1M NH4Cl solution at a mass ratio of 1 / 10, and subjected to hydrothermal exchange at 90℃ for 3 h. After washing, drying at 100℃, and calcining at 550℃ for 6 h, a Mo@H-Beta bifunctional catalyst with catalytic effect was obtained. The pore structure properties of the catalyst are shown in Table 1.

[0042] In a high-pressure fixed-bed reactor packed with 50 ml of the catalyst prepared in Example 3, a 20 wt% tetrahydronaphthalene-cyclohexane solution was used as a model compound to simulate the hydroisomerization reaction of catalytic cracking diesel fuel. The reaction temperature was 300 °C and the liquid hourly space velocity was 2.0 h⁻¹. -1 Under a reaction pressure of 4 MPa, the conversion rate of tetrahydronaphthalene was 58.22%, and the selectivity of the isomer was 11.71%. The results are listed in Table 2.

[0043] Example 4

[0044] 600.00 g of nano-silica was weighed into reactor A, and 1400.00 g of deionized water and 2356.00 g of tetraethylammonium hydroxide (25 wt%) were added and stirred for 1 h to obtain solution A. Simultaneously, 775.00 g of deionized water, 19.00 g of sodium hydroxide, and 83.00 g of Al(NO3)3·9H2O were added to reactor B and stirred for 1 h to obtain solution B. Solution B was then added dropwise to solution A, and stirring and aging continued for 3 h to obtain the initial zeolite gel. Afterwards, 300.00 g of deionized water and 8.00 g of (NH4)6H2O were added to reactor C. 12 O 40 4.00 g of ethylenediamine was dissolved by stirring and then added dropwise to the initial zeolite gel. The mixture was then stirred for 30 min. The stirred zeolite gel was crystallized at 150 °C for 5 days. After crystallization, the resulting solid was washed with deionized water until neutral, dried at 100 °C, and then calcined at 550 °C for 6 h to obtain an encapsulated W@Na-Beta bifunctional catalyst with a silicon-to-aluminum ratio of 45 and a W content of 1 wt%. The obtained W@Na-Beta was added to a 1 M NH4Cl solution at a mass ratio of 1 / 10, and subjected to hydrothermal exchange at 90 °C for 3 h. After washing, drying at 100 °C, and calcining at 550 °C for 6 h, a W@H-Beta bifunctional catalyst with catalytic effect was obtained. The pore structure properties of the catalyst are shown in Table 1.

[0045] In a high-pressure fixed-bed reactor packed with 50 ml of the catalyst prepared in Example 4, a 20 wt% tetrahydronaphthalene-cyclohexane solution was used as a model compound to simulate the hydroisomerization reaction of catalytic cracking diesel. The reaction temperature was 300 °C and the liquid hourly space velocity was 2.0 h⁻¹. -1 Under a reaction pressure of 4 MPa, the conversion rate of tetrahydronaphthalene was 42.96%, and the selectivity of the isomer was 13.12%. The results are listed in Table 2.

[0046] Example 5

[0047] In reactor A, 100.00 g of sodium aluminate (NaAlO2) was weighed and dissolved in 1210.00 g of H2O. Then, 134.00 g of NaOH was added and mixed thoroughly. Next, 300.00 g of TPAOH was added and ultrasonically mixed until homogeneous. Under vigorous stirring, 1230.00 g of silica sol (SiO2·6.5H2O) with a mass fraction of 30% was added dropwise to the mixture. The silica sol was calculated as SiO2, forming a synthetic Y molecular sieve system and obtaining the initial zeolite gel. In reactor B, 300.00 g of deionized water, 18.00 g of Ni(NO3)2·6H2O, and 8.00 g of ethylenediamine were added and stirred until dissolved. This solution was then added dropwise to the initial zeolite gel. The mixture was stirred for another 30 minutes. The mixture was then subjected to static crystallization at 110℃ for 10 days. After crystallization, the solution was filtered, washed, and dried. The sample was calcined at 350℃ for 2 h to obtain an encapsulated Ni@Na-Y bifunctional catalyst with a silicon-to-aluminum ratio of 12 and a Ni content of 1 wt%. The prepared Ni@Na-Y was added to a 1M NH4Cl solution at a mass ratio of 1 / 10, and the mixture was subjected to hydrothermal exchange at 90℃ for 3 h. After washing, drying at 100℃, and calcining at 550℃ for 6 h, a Ni@HY bifunctional catalyst with catalytic activity was obtained. The pore structure properties of the catalyst are shown in Table 1.

[0048] In a high-pressure fixed-bed reactor packed with 50 ml of the catalyst prepared in Example 5, a 20 wt% tetrahydronaphthalene-cyclohexane solution was used as a model compound to simulate the hydroisomerization reaction of catalytic cracking diesel. The reaction temperature was 300 °C and the liquid hourly space velocity was 2.0 h⁻¹. -1 Under a reaction pressure of 4 MPa, the conversion rate of tetrahydronaphthalene was 22.81%, and the selectivity of the isomer was 16.58%. The results are listed in Table 2.

[0049] Table 1. Main properties of the pore structure of zeolite-encapsulated metal bifunctional catalysts

[0050]

[0051]

[0052] As shown in Table 1, the pore structure properties of different types of zeolite-encapsulated metal bifunctional catalysts are not significantly different, indicating that the prepared catalysts have uniform specific surface area, pore size, and pore volume.

[0053] Table 2 Results of hydroisomerization reaction using zeolite-encapsulated metal bifunctional catalysts

[0054] Catalyst tetrahydronaphthalene conversion (%) isomeric product selectivity (%) Example 1 47.48 16.63 Example 2 33.36 14.55 Example 3 58.22 11.71 Example 4 42.96 13.12 Example 5 22.81 16.58

[0055] Table 2 shows the results of the hydroisomerization reaction. The zeolite-encapsulated metal bifunctional catalyst exhibits high feed conversion and isomer selectivity, indicating that the prepared catalyst maintains high crystallinity of the zeolite and high dispersion of the metal, improving the accessibility of active sites and low-temperature activity. Examples 1, 3, and 4 show that the metal hydrogenation activity varies when different metals are encapsulated in β-zeolites. Example 1, under conditions of high feed conversion, shows the highest selectivity for isomers, indicating a high synergistic effect between the metal center and the acidic center. Examples 1, 2, and 5 show that different types of zeolites encapsulating the same metal result in significant differences in catalyst performance. The three-dimensional channels and BEA topology of β-zeolites exhibit stable catalytic activity in the hydrocracking reaction of polycyclic aromatic hydrocarbons, along with high feed conversion and isomer selectivity.

[0056] Depend on Figure 1 The XRD patterns of the zeolite-encapsulated metal bifunctional catalyst show that the characteristic diffraction peaks of different types of zeolite are highly intense, while the characteristic diffraction peaks of the unencapsulated metal are absent, indicating that the synthesized molecular sieve maintains the high crystallinity of the zeolite; combined with Figure 2 The SEM image of the zeolite-encapsulated metal bifunctional catalyst shows that there are no large metal clusters attached to the surface of the molecular sieve, indicating that the zeolite-encapsulated metal catalyst has been successfully synthesized. The metal is mainly distributed inside the molecular sieve channels, which enhances the synergistic effect between the metal center and the acid center, thereby improving the catalytic performance of the catalyst.

[0057] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by the present invention.

Claims

1. Use of a zeolite encapsulated metal bifunctional catalyst in tetralin hydroisomerization reactions, characterized in that, The method steps are as follows: S1, dissolve the salt containing the metal to be encapsulated into a certain amount of deionized water, then add a certain proportion of organic ligand as a complexing agent, stir uniformly to obtain a metal complex aqueous solution; S2, obtain a zeolite initial gel by in-situ synthesis; S3, add the metal complex aqueous solution to the zeolite initial gel, stir uniformly to obtain a gel mixture; S4, transfer the gel mixture to a crystallization kettle for crystallization, after washing, drying, calcination and ammonium exchange, obtain a zeolite encapsulated metal bifunctional catalyst; The organic ligand is one of ethylenediamine, diethylenetriamine, N-(2-aminoethyl)-3-aminopropyl trimethoxysilane and mercaptopropyl trimethoxysilane, and the molar ratio of the organic ligand to the metal salt is 1-10; The metal active component encapsulated in S1 is any one or more of Pt, Pd, Ru, Cu, Co, Ni, Mo and W, and the metal is encapsulated in the form of clusters in the pores of the zeolite molecular sieve; The preparation method of the zeolite initial gel in S2 specifically includes: S101, mix and stir the silicon source, template agent and a certain amount of deionized water for a certain time to obtain solution A; S102, mix and stir the alkali source, aluminum source and a certain amount of deionized water for a certain time to obtain solution B; S103, add solution B to solution A, then stir for 3-6h to obtain a zeolite initial gel; In S4, the conditions for ammonium exchange are that the mass ratio of the catalyst to 1M NH4Cl is 1:10, and the hydrothermal treatment is carried out at 90℃ for 3h.

2. Use of a zeolite encapsulated metal bifunctional catalyst according to claim 1 in tetralin hydroisomerization reactions, characterized in that, The metal salt solution in S1 is nitrate or chloride.

3. Use of a zeolite encapsulated metal bifunctional catalyst according to claim 1 in tetralin hydroisomerization reactions, characterized in that, In S101, the silicon source can be any one of nano silicon dioxide, tetraethyl orthosilicate and solid silica gel.

4. Use of a zeolite encapsulated metal bifunctional catalyst according to claim 1 or 3 in tetralin hydroisomerization reactions, characterized in that, In S102, the aluminum source is sodium metaaluminate or aluminum nitrate.

5. Use of a zeolite encapsulated metal bifunctional catalyst according to claim 1 in tetralin hydroisomerization reactions, characterized in that, In S4, the gel mixture after crystallization is washed with deionized water, the washing liquid pH is 7-8; drying is carried out at 100-200℃ for 6-12h, the calcination temperature is 450-550℃, and the calcination is carried out for 6-8h.

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