A molecular sieve confined metal catalyst, its preparation method and its use in alkane aromatization reactions

Abstract

The application belongs to the technical field of catalysts, and particularly relates to a molecular sieve confined metal catalyst, a preparation method thereof and application of the catalyst in an alkane aromatization reaction. The application provides a molecular sieve confined metal catalyst, which comprises a full-silicon ZSM-5 molecular sieve and Pt, K and Cr encapsulated in the pore channel of the full-silicon ZSM-5 molecular sieve. The Pt is a main active site for alkane dehydrogenation and aromatization reaction, and the K and Cr are important structure promoters; the introduction of the K and Cr can improve the dispersion of the Pt site and the adsorption capacity of the Pt site for alkane, thereby being favorable to improving the alkane conversion rate and the aromatic hydrocarbon selectivity. The application encapsulates the metal by using the molecular sieve, can inhibit the agglomeration of the metal site in the reaction process by the framework confinement effect of the molecular sieve, and thereby greatly improves the stability of the catalyst.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a molecular sieve confined metal catalyst, its preparation method, and its application in alkane aromatization reactions. Background Technology

[0002] Coal gasification and Fischer-Tropsch (FT) synthesis via indirect liquefaction to produce liquid fuels and petroleum products, along with coal-based methanol-to-hydrocarbon (MTH) technology, are the most important clean and efficient coal conversion routes and crucial methods for producing clean fuels and chemicals without petroleum involvement. However, these processes generate significant amounts of low-value alkanes, such as hexane, and the lack of effective utilization pathways leads to a substantial waste of carbon resources.

[0003] Aromatics are important basic organic chemical raw materials, used in the production of various chemical products and fine chemicals, such as synthetic rubber, synthetic fibers, and synthetic resins. Among them, light aromatics such as benzene, toluene, and xylene (BTX) have the widest applications. Traditional aromatics production processes, mainly through petroleum fraction catalytic reforming and gasoline cracking, can no longer meet the ever-increasing demand. Therefore, developing new aromatics production processes is of great significance. Converting low-value alkanes into high-value aromatics through aromatization provides a new aromatization route independent of petroleum resources, and has significant application value.

[0004] Currently, metal-modified molecular sieve catalysts are widely used in alkane aromatization reactions. For example, MFI and MWW type molecular sieve catalysts modified with Zn and / or Ga species are used for hexane aromatization, but the aromatic selectivity is not high (Synthesis of catalysis containing Zn and Ga for aromatization of n-hexane, Journal of the Japan Petroleum Institute). Furthermore, the Mo / H-ZSM-5 catalyst prepared by modifying H-ZSM-5 molecular sieve with Mo exhibits a high n-hexane conversion (77.5%) at 500℃, but a very low aromatic selectivity (19.9%), failing to achieve high aromatic yields (Aromatization of n-hexane over Ga, Mo and Znmodified H-ZSM-5 zeolite catalysts, Catalysis Communications).

[0005] Despite extensive research into the aromatization of hexane to aromatics, challenges remain regarding low alkane conversion and aromatic selectivity. In particular, alkane aromatization typically requires high reaction temperatures (400–600 °C), leading to rapid sintering of metal sites and significant carbon deposition, ultimately reducing catalyst stability. Therefore, there is an urgent need to develop a catalytic system that combines high hexane conversion, aromatic selectivity, and catalytic stability. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a molecular sieve-confined metal catalyst, its preparation method, and its application in alkane aromatization reactions. The catalyst of this invention, when used to catalyze the hexane aromatization reaction, exhibits advantages such as high hexane conversion, high aromatic selectivity and yield, and strong stability.

[0007] The present invention provides a molecular sieve confined metal catalyst, comprising an all-silica ZSM-5 molecular sieve and a metal oxide encapsulated within the pores of the all-silica ZSM-5 molecular sieve, wherein the metal in the metal oxide comprises Pt, K and Cr; The mass of Pt is 0.2-2% of the mass of the molecular sieve-confined metal catalyst; the mass of K is 0.2-5% of the mass of the molecular sieve-confined metal catalyst; and the mass of Cr is 0.05-1.0% of the mass of the molecular sieve-confined metal catalyst.

[0008] Preferably, the mass of Pt is 0.25-1.5% of the mass of the molecular sieve-confined metal catalyst, the mass of K is 0.5-4.0% of the mass of the molecular sieve-confined metal catalyst, and the mass of Cr is 0.1-0.8% of the mass of the molecular sieve-confined metal catalyst.

[0009] This invention also provides a method for preparing the molecular sieve-confined metal catalyst described in the above technical solution, comprising the following steps: A Pt-K-Cr-ligand mixed precursor solution was obtained by mixing a water-soluble platinum source, a water-soluble potassium source, a water-soluble chromium source, an organic amine ligand, and water. The Pt-K-Cr-ligand mixed precursor solution was mixed with the mother liquor for the synthesis of all-silica ZSM-5 molecular sieve and subjected to hydrothermal crystallization. The resulting solid was then dried and calcined to obtain the molecular sieve confined metal catalyst.

[0010] Preferably, the water-soluble platinum source includes platinum chloride and / or chloroplatinic acid; the water-soluble potassium source includes one or more of potassium nitrate, potassium sulfate, and potassium chloride; the water-soluble chromium source includes one or more of chromium nitrate, chromium sulfate, and chromium chloride; and the organic amine ligand includes one or more of ethylenediamine, cyclohexylamine, and cyclohexanediamine.

[0011] Preferably, the molar ratio of Pt, K, and Cr in the Pt-K-Cr-ligand mixture precursor solution is 1:(4~15):(0.1~5), and the molar ratio of the total amount of metal ions to the molar amount of organic amine ligands is 1:(1~10). The metal ions include platinum, potassium, and chromium ions.

[0012] Preferably, the mother liquor for the synthesis of all-silica ZSM-5 molecular sieve includes the active ingredient SiO2, a template agent, and H2O, wherein the molar ratio of the active ingredient SiO2, the template agent, and H2O is 1:(0.2~0.8):(20~100); the template agent includes one or more of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, and n-butylamine.

[0013] Preferably, the hydrothermal crystallization temperature is 150~200℃ and the time is 30~120h.

[0014] Preferably, the calcination temperature is 500~650℃ and the time is 5~10h.

[0015] The present invention also provides the application of the molecular sieve confined metal catalyst described in the above technical solution or the molecular sieve confined metal catalyst obtained by the above preparation method in the catalytic aromatization reaction of alkane.

[0016] This invention also provides a method for preparing aromatic hydrocarbons by hexane aromatization, comprising the following steps: Hexane-nitrogen mixture is subjected to aromatization reaction in the presence of a catalyst to obtain aromatic hydrocarbons; The catalyst is the molecular sieve-confined metal catalyst described in the above technical solution or the molecular sieve-confined metal catalyst obtained by the above preparation method; the aromatization reaction is carried out at a temperature of 400~600℃ and a mass hourly space velocity of 0.1~20h. -1 .

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a sieve-confined metal catalyst, comprising an all-silica ZSM-5 sieve and a metal oxide encapsulated within the pores of the all-silica ZSM-5 sieve. The metal oxide contains Pt, K, and Cr. Pt is the main active site for alkane dehydrogenation and aromatization reactions, while K and Cr are important structural promoters. The introduction of K and Cr can improve the dispersion of Pt sites and enhance their ability to adsorb alkanes, thereby improving alkane (e.g., hexane) conversion and aromatic selectivity. Furthermore, this invention uses a sieve to encapsulate the metal, which can suppress metal site aggregation during the reaction through the sieve's framework confinement effect, thus significantly improving catalyst stability. Using the catalyst provided by this invention for the catalytic hexane aromatization reaction exhibits advantages such as high hexane conversion, high aromatic selectivity and yield, and strong catalyst stability.

[0018] Test results show that the 0.6%Pt-1.5%K-0.3%Cr@S-1 composite catalyst prepared in this invention, when used for the hexane aromatization reaction, achieves good results at 550℃ and a hexane mass hourly space velocity of 7 h⁻¹. -1 Under the given conditions, the hexane conversion rate reached 78% after 24 hours of reaction, the aromatic selectivity remained at 65%, and the catalyst showed no significant deactivation after 100 hours of reaction.

[0019] This invention provides a method for preparing molecular sieve-confined metal catalysts as described above. The method is simple to operate, produces no secondary pollution, is environmentally friendly, has low production costs, and is suitable for industrial production applications. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 The XRD pattern of the 0.6%Pt-1.5%K-0.3%Cr@S-1 composite catalyst prepared in Example 1; Figure 2 TEM images of the 0.6%Pt-1.5%K-0.3%Cr@S-1 composite catalyst prepared in Example 1 at different magnifications; Figure 3 The figure shows the stability test results of the hexane aromatization reaction catalyzed by the 0.6%Pt-1.5%K-0.3%Cr@S-1 composite catalyst prepared in Example 1. Detailed Implementation

[0022] The present invention provides a molecular sieve confined metal catalyst, comprising an all-silica ZSM-5 molecular sieve and a metal oxide encapsulated within the pores of the all-silica ZSM-5 molecular sieve, wherein the metal in the metal oxide comprises Pt, K and Cr; The mass of Pt is 0.2-2% of the mass of the molecular sieve-confined metal catalyst; the mass of K is 0.2-5% of the mass of the molecular sieve-confined metal catalyst; and the mass of Cr is 0.05-1.0% of the mass of the molecular sieve-confined metal catalyst.

[0023] The molecular sieve-confined metal catalyst (denoted as x%Pt-y%Kz%Cr@S-1 composite catalyst) provided by this invention utilizes Pt, which is the main active site for alkane dehydrogenation and aromatization reactions, while K and Cr are important structural promoters. The introduction of K and Cr can improve the dispersion of Pt sites and enhance their ability to adsorb alkanes, thereby improving the conversion rate of alkane (such as hexane) and the selectivity of aromatics. Furthermore, this invention employs an all-silica ZSM-5 molecular sieve (denoted as S-1) to encapsulate the metal, which can suppress the aggregation of metal sites during the reaction process through the framework confinement effect of the molecular sieve, thus significantly improving the stability of the catalyst.

[0024] In this invention, the metal oxides include PtO2, K2O and Cr2O3, and the all-silica ZSM-5 molecular sieve is calculated as SiO2.

[0025] In this invention, the mass of Pt is preferably 0.25-1.5% of the mass of the molecular sieve confined metal catalyst, more preferably 0.30-1.25%, and specifically can be 0.4%, 0.6% or 0.8%.

[0026] In this invention, the mass of K is preferably 0.5 to 4.0% of the mass of the molecular sieve confined metal catalyst, more preferably 1.0 to 3.0%, and specifically can be 1.0%, 1.5% or 1.6%.

[0027] In this invention, the mass of Cr is preferably 0.1-0.8% of the mass of the molecular sieve confined metal catalyst, more preferably 0.2-0.6%, and specifically can be 0.15%, 0.16% or 0.3%.

[0028] In this invention, the particle size of the molecular sieve-confined metal catalyst is preferably 10-60 mesh, more preferably 20-50 mesh, and specifically 20-40 mesh. The catalyst particle size described in this invention is beneficial for better catalysis of the hexane aromatization reaction.

[0029] This invention provides a method for preparing the molecular sieve-confined metal catalyst described above, comprising the following steps: A Pt-K-Cr-ligand mixed precursor solution was obtained by mixing a water-soluble platinum source, a water-soluble potassium source, a water-soluble chromium source, an organic amine ligand, and water. The Pt-K-Cr-ligand mixed precursor solution was mixed with the mother liquor for the synthesis of all-silica ZSM-5 molecular sieve and subjected to hydrothermal crystallization. The resulting solid was then dried and calcined to obtain the molecular sieve confined metal catalyst.

[0030] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0031] This invention mixes a water-soluble platinum source, a water-soluble potassium source, a water-soluble chromium source, an organic amine ligand, and water to obtain a Pt-K-Cr-ligand mixed precursor solution.

[0032] In this invention, the water-soluble platinum source preferably includes platinum chloride and / or chloroplatinic acid, wherein the chloroplatinic acid is preferably used in its hydrate form, specifically hexachloroplatinic acid hexahydrate; the water-soluble potassium source preferably includes one or more of potassium nitrate, potassium sulfate, and potassium chloride, specifically potassium nitrate; the water-soluble chromium source preferably includes one or more of chromium nitrate and its hydrate (chromium nitrate), sulfate (chromium sulfate), and chloride (chromium chloride), wherein the chromium nitrate is preferably used in its hydrate form, specifically chromium nitrate nonahydrate.

[0033] In this invention, the water is preferably deionized water.

[0034] In this invention, the organic amine ligand preferably includes one or more of ethylenediamine, cyclohexylamine, and cyclohexanediamine, specifically ethylenediamine, cyclohexylamine, or cyclohexanediamine. The organic amine ligand can form a complex with metal ions, preventing premature precipitation of metal ions as hydroxides in strongly alkaline solutions.

[0035] In this invention, the mixing of the water-soluble platinum source, water-soluble potassium source, water-soluble chromium source, organic amine ligand, and water is preferably carried out by mixing an aqueous solution of the water-soluble platinum source, an aqueous solution of the water-soluble potassium source, an aqueous solution of the water-soluble chromium source, and the organic amine ligand; the concentrations of the aqueous solutions of the water-soluble platinum source, the water-soluble potassium source, and the water-soluble chromium source are all preferably 10 wt%, and the mass ratio of the water-soluble platinum source, the water-soluble potassium source, the water-soluble chromium source, and the organic amine ligand is preferably 0.29~0.38:0.62~0.99:0.3~0.6:0.27.

[0036] In this invention, the molar ratio of Pt, K, and Cr in the Pt-K-Cr-ligand mixed precursor solution is preferably 1:(4.0~15.0):(0.1~5.0), more preferably 1:(5.0~10.0):(0.5~0.3), and specifically 1:13:2; the molar ratio of the total amount of metal ions to the organic amine ligands in the Pt-K-Cr-ligand mixed precursor solution is preferably 1:(1~10), more preferably 1:(2~5).

[0037] After obtaining the Pt-K-Cr-ligand mixed precursor solution, the present invention mixes the Pt-K-Cr-ligand mixed precursor solution with the mother liquor for the synthesis of all-silica ZSM-5 molecular sieve and performs hydrothermal crystallization. The resulting solid is then dried and calcined sequentially to obtain the molecular sieve confined metal catalyst.

[0038] In this invention, the all-silica ZSM-5 molecular sieve synthesis mother liquor (initial gel) includes the active ingredient SiO2, a template agent, and H2O. The template agent preferably includes one or more of tetrapropylammonium hydroxide (TPAOH), tetraethylammonium hydroxide (TEAOH), and n-butylamine. The molar ratio of the active ingredient SiO2, the template agent, and H2O is preferably 1:(0.2~0.8):(20~100), more preferably 1:(0.3~0.7):(25~80), and even more preferably 1:(0.4~0.6):(30~50), specifically 1:0.4:35.

[0039] In this invention, the preparation method of the all-silicon ZSM-5 molecular sieve synthesis mother liquor preferably includes the following steps: mixing a silicon source, a template agent, and water, followed by aging, to obtain the all-silicon ZSM-5 molecular sieve synthesis mother liquor. The silicon source preferably includes one or more of tetramethyl orthosilicate, tetraethyl orthosilicate, and tetrabutyl orthosilicate, specifically tetraethyl or tetrabutyl orthosilicate. The template agent is preferably used in the form of an aqueous template agent solution; the mass fraction of the aqueous template agent solution is preferably 15-50%, more preferably 20-45%, specifically 25%. This invention does not have a special limitation on the mixing, as long as the raw materials are mixed evenly; the mixing temperature is preferably room temperature; in the embodiments of this invention, the mixing of the silicon source, template agent, and water is preferably: mixing the aqueous template agent solution with water until clear, and then adding the silicon source dropwise; this invention does not have a special limitation on the dropwise addition, as long as it is added dropwise at a uniform rate. The aging temperature is preferably room temperature (25°C), and the aging time is preferably 1-8 hours, more preferably 2-7 hours, specifically 6 hours.

[0040] The present invention obtains a gel solution by mixing the Pt-K-Cr-ligand mixed precursor solution with the mother liquor for the synthesis of all-silica ZSM-5 molecular sieve.

[0041] In this invention, the hydrothermal crystallization temperature is preferably 150-200℃, more preferably 160-190℃, and even more preferably 170-180℃, specifically 175℃; the hydrothermal crystallization time is preferably 30-120h, more preferably 50-100h, and even more preferably 60-80h, specifically 96h. During the hydrothermal crystallization process, the introduced organic amine ligand can protect the water-soluble platinum source, water-soluble potassium source, and water-soluble chromium source, promoting the encapsulation of Pt-K-Cr within the pores of the all-silicon ZSM-5 molecular sieve.

[0042] In this invention, the hydrothermal crystallization process preferably further includes solid-liquid separation of the obtained crystallization reaction solution. This invention does not specifically limit the method of solid-liquid separation; any solid-liquid separation method well-known to those skilled in the art can be used, such as centrifugation. This invention does not have special requirements for the drying conditions; drying to constant weight can be achieved using drying conditions well-known in the art, specifically drying in an 80°C oven for 12 hours.

[0043] In this invention, the calcination temperature is preferably 500-650℃, more preferably 530-620℃, and even more preferably 550-600℃; the calcination holding time is preferably 5-10h, more preferably 6-9h, and even more preferably 7-8h; the calcination atmosphere is preferably air. In an embodiment of this invention, the calcination specifically includes: calcination at 550℃ in an air atmosphere for 8h, followed by calcination at 600℃ for 2h.

[0044] In this invention, the roasting process preferably further includes: sequentially pressing, pulverizing, and sieving the obtained roasted product. This invention does not specifically limit the pressing, pulverizing, and sieving processes, but the particle size after sieving is preferably 10-60 mesh, specifically 20-40 mesh.

[0045] The present invention also provides the application of the molecular sieve confined metal catalyst described in the above technical solution or the molecular sieve confined metal catalyst obtained by the above preparation method in the catalytic aromatization reaction of alkane.

[0046] In this invention, the alkane is preferably hexane.

[0047] This invention also provides a method for preparing aromatic hydrocarbons by hexane aromatization, comprising the following steps: Hexane-nitrogen mixture is subjected to aromatization in the presence of a catalyst to obtain aromatic hydrocarbons. The catalyst is the molecular sieve confined metal catalyst described in the above technical solution or the molecular sieve confined metal catalyst obtained by the above preparation method.

[0048] In this invention, the catalyst is preferably subjected to a reduction treatment before use. The reduction treatment temperature is preferably 400~700℃, more preferably 450~650℃, and even more preferably 500~650℃, specifically 600℃. The reduction treatment time is preferably 1~8h, more preferably 1~6h, and even more preferably 1~5h. The reducing agent used in the reduction treatment is preferably hydrogen or a hydrogen-inert gas mixture. After the reduction treatment, PtO2 is reduced to metallic Pt.

[0049] In this invention, the volume ratio of hexane to nitrogen in the hexane-nitrogen mixture is preferably 1:(0~20), more preferably 1:(1~8), and specifically 1:2. Preferably, the hexane-nitrogen mixture is introduced into a reactor containing the catalyst, and the total gas velocity of the hexane-nitrogen mixture is preferably 15 mL / min. The temperature of the aromatization reaction is preferably 400~600℃, more preferably 520~580℃, specifically 500℃ or 550℃, the pressure is preferably atmospheric pressure (0.1 MPa), and the mass hourly space velocity is preferably 0.1~20 h⁻¹. -1 More preferably 0.2~15h -1 Specifically, it can be 3 hours. -1 or 7h -1 The preferred time is 2 to 300 hours, more preferably 10 to 200 hours, and even more preferably 20 to 100 hours.

[0050] To further illustrate the present invention, the molecular sieve confined metal catalyst, its preparation method, and its application in alkane aromatization reactions provided by the present invention are described in detail below with reference to the accompanying drawings and embodiments. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0051] Example 1 13.02 g of TPAOH aqueous solution (mass fraction of 25%) was added to 15 g of deionized water (H2O) and magnetically stirred until the solution was clear. 8.24 g of tetraethyl orthosilicate (TEOS) was added dropwise, and the mixture was aged for 6 h at room temperature with stirring to obtain the initial gel for the synthesis of all-silica ZSM-5 molecular sieve (molar composition of 35H2O:0.4TPAOH:1SiO2).

[0052] At room temperature, 0.38 g of 10 wt% hexachloroplatinic acid hexahydrate solution, 0.99 g of 10 wt% potassium nitrate solution, and 0.6 g of 10 wt% chromium nitrate nonahydrate solution were mixed with 0.27 g of ethylenediamine. The resulting Pt-K-Cr-ligand mixture precursor solution was added to the initial gel for the synthesis of the all-silica ZSM-5 molecular sieve and stirred until homogeneous. The mixture was then transferred to a 100 mL high-pressure reactor and hydrothermally crystallized at 175 °C for 96 h. After centrifugation, the resulting solid product was dried in an oven at 80 °C for 12 h, and then placed in a muffle furnace and calcined at 550 °C for 8 h in air atmosphere, followed by calcination at 600 °C for 2 h. The product was then tableted, pulverized, and sieved to obtain a catalyst with a particle size of 20-40 mesh, denoted as the 0.6%Pt-1.5%K-0.3%Cr@S-1 composite catalyst.

[0053] Figure 1The XRD pattern of the 0.6%Pt-1.5%K-0.3%Cr@S-1 catalyst prepared in Example 1 is shown in the figure. As can be seen from the figure, the prepared 0.6%Pt-1.5%K-0.3%Cr@S-1 composite catalyst exhibits typical diffraction peaks of ZSM-5 molecular sieves. No obvious characteristic peaks of Pt, K, or Cr were observed, indicating that these metal components are highly dispersed on the ZSM-5 molecular sieve.

[0054] Figure 2 The image shows a TEM image of the 0.6%Pt-1.5%K-0.3%Cr@S-1 composite catalyst prepared in Example 1. As can be seen from the image, the prepared 0.6%Pt-1.5%K-0.3%Cr@S-1 composite catalyst exhibits a coffin-like morphology with a particle size of approximately 400 nm.

[0055] Example 2 13.02 g of TPAOH aqueous solution (mass fraction of 25%) was added to 15 g of deionized water (H2O) and magnetically stirred until the solution was clear. 8.24 g of tetraethyl orthosilicate (TEOS) was added dropwise, and the mixture was aged for 6 h at room temperature with stirring to obtain the initial gel for the synthesis of all-silica ZSM-5 molecular sieve (molar composition of 35H2O:0.4TPAOH:1SiO2).

[0056] At room temperature, 0.29 g of 10 wt% hexachloroplatinic acid hexahydrate solution, 0.99 g of 10 wt% potassium nitrate solution, and 0.6 g of 10 wt% chromium nitrate nonahydrate solution were mixed with 0.27 g of ethylenediamine. The resulting Pt-K-Cr-ligand mixture precursor solution was added to the initial gel for the synthesis of the all-silica ZSM-5 molecular sieve and stirred until homogeneous. The mixture was then transferred to a 100 mL high-pressure reactor and hydrothermally crystallized at 175 °C for 96 h. After centrifugation, the resulting solid product was dried in an oven at 80 °C for 12 h, and then placed in a muffle furnace and calcined at 550 °C for 8 h in air atmosphere, followed by calcination at 600 °C for 2 h. The product was then tableted, pulverized, and sieved to obtain a catalyst with a particle size of 20-40 mesh, denoted as the 0.4%Pt-1.5%K-0.3%Cr@S-1 composite catalyst.

[0057] Example 3 13.02 g of TPAOH aqueous solution (mass fraction of 25%) was added to 15 g of deionized water (H2O) and magnetically stirred until the solution was clear. 8.24 g of tetraethyl orthosilicate (TEOS) was added dropwise, and the mixture was aged for 6 h at room temperature with stirring to obtain the initial gel for the synthesis of all-silica ZSM-5 molecular sieve (molar composition of 35H2O:0.4TPAOH:1SiO2).

[0058] At room temperature, 0.38 g of 10 wt% hexachloroplatinic acid hexahydrate solution, 0.62 g of 10 wt% potassium nitrate solution, and 0.6 g of 10 wt% chromium nitrate nonahydrate solution were mixed with 0.27 g of ethylenediamine. The resulting Pt-K-Cr-ligand mixture precursor solution was added to the initial gel for the synthesis of the all-silica ZSM-5 molecular sieve and stirred until homogeneous. The mixture was then transferred to a 100 mL high-pressure reactor and hydrothermally crystallized at 175 °C for 96 h. After centrifugation, the resulting solid product was dried in an oven at 80 °C for 12 h, and then placed in a muffle furnace and calcined at 550 °C in air for 8 h, followed by calcination at 600 °C for 2 h. The product was then tableted, pulverized, and sieved to obtain a catalyst with a particle size of 20-40 mesh, denoted as the 0.6%Pt-1.0%K-0.3%Cr@S-1 composite catalyst.

[0059] Example 4 13.02 g of TPAOH aqueous solution (mass fraction of 25%) was added to 15 g of deionized water (H2O) and magnetically stirred until the solution was clear. 8.24 g of tetraethyl orthosilicate (TEOS) was added dropwise, and the mixture was aged for 6 h at room temperature with stirring to obtain the initial gel for the synthesis of all-silica ZSM-5 molecular sieve (molar composition of 35H2O:0.4TPAOH:1SiO2).

[0060] At room temperature, 0.38 g of 10 wt% hexachloroplatinic acid hexahydrate solution, 0.99 g of 10 wt% potassium nitrate solution, and 0.3 g of 10 wt% chromium nitrate nonahydrate solution were mixed with 0.27 g of ethylenediamine. The resulting Pt-K-Cr-ligand mixture precursor solution was added to the initial gel for the synthesis of the all-silica ZSM-5 molecular sieve and stirred until homogeneous. The mixture was then transferred to a 100 mL high-pressure reactor and hydrothermally crystallized at 175 °C for 96 h. After centrifugation, the resulting solid product was dried in an oven at 80 °C for 12 h, and then placed in a muffle furnace and calcined at 550 °C in air for 8 h, followed by calcination at 600 °C for 2 h. The product was then tableted, pulverized, and sieved to obtain a catalyst with a particle size of 20-40 mesh, designated as the 0.6%Pt-1.5%K-0.16%Cr@S-1 composite catalyst.

[0061] Comparative Example 1 13.02 g of TPAOH aqueous solution (mass fraction of 25%) was added to 15 g of deionized water (H2O) and magnetically stirred until the solution was clear. 8.24 g of tetraethyl orthosilicate (TEOS) was added dropwise, and the mixture was aged for 6 h at room temperature with stirring to obtain the initial gel for the synthesis of all-silica ZSM-5 molecular sieve (molar composition of 35H2O:0.4TPAOH:1SiO2).

[0062] At room temperature, 0.38 g of 10 wt% hexachloroplatinic acid hexahydrate solution, 0.99 g of 10 wt% potassium nitrate solution, and 0.27 g of ethylenediamine were mixed evenly at room temperature. The resulting Pt-K-ligand mixture precursor solution was added to the initial gel for the synthesis of the all-silica ZSM-5 molecular sieve and stirred evenly. The mixture was then transferred to a 100 mL high-pressure reactor and hydrothermally crystallized at 175 °C for 96 h. After centrifugation, the resulting solid product was dried in an oven at 80 °C for 12 h, and then placed in a muffle furnace and calcined at 550 °C in air for 8 h, followed by calcination at 600 °C for 2 h. The product was then tableted, pulverized, and sieved to obtain a catalyst with a particle size of 20-40 mesh, denoted as the 0.6%Pt-1.5%K@S-1 composite catalyst.

[0063] Comparative Example 2 13.02 g of TPAOH aqueous solution (mass fraction of 25%) was added to 15 g of deionized water (H2O) and magnetically stirred until the solution was clear. 8.24 g of tetraethyl orthosilicate (TEOS) was added dropwise, and the mixture was aged for 6 h at room temperature with stirring to obtain the initial gel for the synthesis of all-silica ZSM-5 molecular sieve (molar composition of 35H2O:0.4TPAOH:1SiO2).

[0064] At room temperature, 0.38 g of 10 wt% hexachloroplatinic acid hexahydrate solution, 0.6 g of 10 wt% chromium nitrate nonahydrate solution, and 0.27 g of ethylenediamine were mixed evenly at room temperature. The resulting Pt-Cr-ligand mixture precursor solution was added to the initial gel for the synthesis of the all-silica ZSM-5 molecular sieve and stirred evenly. The mixture was then transferred to a 100 mL high-pressure reactor and hydrothermally crystallized at 175 °C for 96 h. After centrifugation, the resulting solid product was dried in an oven at 80 °C for 12 h, and then placed in a muffle furnace and calcined at 550 °C in air for 8 h, followed by calcination at 600 °C for 2 h. The product was then tableted, pulverized, and sieved to obtain a catalyst with a particle size of 20-40 mesh, denoted as the 0.6%Pt-0.3%Cr@S-1 composite catalyst.

[0065] Comparative Example 3 13.02 g of TPAOH aqueous solution (mass fraction of 25%) was added to 15 g of deionized water (H2O) and magnetically stirred until the solution was clear. 8.24 g of tetraethyl orthosilicate (TEOS) was added dropwise, and the mixture was aged for 6 h at room temperature with stirring to obtain the initial gel for the synthesis of all-silica ZSM-5 molecular sieve (molar composition of 35H2O:0.4TPAOH:1SiO2).

[0066] At room temperature, 0.99 g of 10 wt% potassium nitrate solution and 0.6 g of 10 wt% chromium nitrate nonahydrate solution were mixed with 0.27 g of ethylenediamine. The resulting K-Cr-ligand mixture precursor solution was added to the initial gel for the synthesis of the all-silica ZSM-5 molecular sieve and stirred until homogeneous. The mixture was then transferred to a 100 mL high-pressure reactor and hydrothermally crystallized at 175 °C for 96 h. After centrifugation, the resulting solid product was dried in an oven at 80 °C for 12 h, and then placed in a muffle furnace and calcined at 550 °C in air for 8 h, followed by calcination at 600 °C for 2 h. The product was then tableted, pulverized, and sieved to obtain a catalyst with a particle size of 20-40 mesh, denoted as the 1.6%K-0.3%Cr@S-1 composite catalyst.

[0067] Comparative Example 4 13.02 g of TPAOH aqueous solution (mass fraction of 25%) was added to 15 g of deionized water (H2O) and magnetically stirred until the solution was clear. 8.24 g of tetraethyl orthosilicate (TEOS) was added dropwise, and the mixture was aged for 6 h at room temperature with stirring to obtain the initial gel for the synthesis of all-silica ZSM-5 molecular sieve (molar composition of 35H2O:0.4TPAOH:1SiO2).

[0068] At room temperature, 0.38 g of 10 wt% hexachloroplatinic acid hexahydrate solution and 0.99 g of 10 wt% potassium nitrate solution were mixed with 0.27 g of ethylenediamine. The resulting Pt-K-ligand mixture precursor solution was added to the initial gel for the synthesis of the all-silica ZSM-5 molecular sieve and stirred until homogeneous. The mixture was then transferred to a 100 mL high-pressure reactor and hydrothermally crystallized at 175 °C for 96 h. After centrifugation, the resulting solid product was dried in an oven at 80 °C for 12 h and then placed in a muffle furnace for calcination at 550 °C in air for 8 h, followed by calcination at 600 °C for 2 h to obtain 0.6% Pt-1.5% K@S-1 composite catalyst powder.

[0069] Subsequently, chromium nitrate nonahydrate was dissolved in deionized water to prepare a 10wt% chromium nitrate nonahydrate solution. 0.6g of the chromium nitrate nonahydrate solution was added dropwise to 0.6%Pt-1.5%K@S-1, followed by the addition of an appropriate amount of deionized water to completely submerge the powder. After stirring evenly, the mixture was allowed to stand for 12h. 0.3%Cr was then loaded onto the 0.6%Pt-1.6%K@S-1 composite catalyst powder using an impregnation method. The resulting solid product was dried in an oven at 80℃ for 12h, then placed in a muffle furnace and calcined at 550℃ in air for 10h. The product was then tableted, pulverized, and sieved to obtain a catalyst with a particle size of 20~40 mesh, denoted as the 0.3%Cr / 0.6%Pt-1.5%K@S-1 composite catalyst.

[0070] Comparative Example 5 13.02 g of TPAOH aqueous solution (mass fraction of 25%) was added to 15 g of deionized water (H2O) and magnetically stirred until the solution was clear. 8.24 g of tetraethyl orthosilicate (TEOS) was added dropwise, and the mixture was aged for 6 h at room temperature with stirring to obtain the initial gel for the synthesis of all-silica ZSM-5 molecular sieve (molar composition of 35H2O:0.4TPAOH:1SiO2).

[0071] The synthesized initial gel was transferred to a 100 mL high-pressure reactor and hydrothermally crystallized at 175 °C for 96 h. After centrifugation, the resulting solid product was dried in an 80 °C oven for 12 h, and then placed in a muffle furnace and calcined at 550 °C in air for 8 h, and then calcined at 600 °C for 2 h to obtain S-1 carrier powder.

[0072] Subsequently, 0.38 g of hexachloroplatinic acid hexahydrate solution (10 wt%), 0.99 g of potassium nitrate solution (10 wt%), and 0.6 g of chromium nitrate nonahydrate solution (10 wt%) were mixed and added dropwise to the S-1 support powder. Deionized water was added to cover the powder. 0.6% Pt, 1.5% K, and 0.3% Cr were loaded onto the S-1 support powder by impregnation. The resulting solid product was dried in an oven at 80 °C for 12 h, and then placed in a muffle furnace and calcined at 550 °C in air for 10 h. The product was then tableted, pulverized, and sieved to obtain a catalyst with a particle size of 20-40 mesh, denoted as the 0.6% Pt-1.5% K-0.3% Cr / S-1 composite catalyst.

[0073] Comparative Example 6 13.02 g of TPAOH aqueous solution (mass fraction of 25%) was added to 15 g of deionized water (H2O) and magnetically stirred until the solution was clear. 8.24 g of tetraethyl orthosilicate (TEOS) was added dropwise, and the mixture was aged for 6 h at room temperature with stirring to obtain the initial gel for the synthesis of all-silica ZSM-5 molecular sieve (molar composition of 35H2O:0.4TPAOH:1SiO2).

[0074] At room temperature, 0.38 g of 10 wt% hexachloroplatinic acid hexahydrate solution, 0.99 g of 10 wt% potassium nitrate solution, and 0.31 g of 10 wt% gallium nitrate nonahydrate solution were mixed with 0.27 g of ethylenediamine. The resulting Pt-K-Ga-ligand mixture precursor solution was added to the initial gel for the synthesis of the all-silicon ZSM-5 molecular sieve and stirred until homogeneous. The mixture was then transferred to a 100 mL high-pressure reactor and hydrothermally crystallized at 175 °C for 96 h. After centrifugation, the resulting solid product was dried in an oven at 80 °C for 12 h, and then placed in a muffle furnace and calcined at 550 °C for 8 h in air atmosphere, followed by calcination at 600 °C for 2 h. The product was then tableted, pulverized, and sieved to obtain a catalyst with a particle size of 20-40 mesh, denoted as the 0.6%Pt-1.5%K-0.2%Ga@S-1 composite catalyst.

[0075] Application Example 1 The catalysts prepared in Examples 1-4 and Comparative Examples 1-6 were subjected to catalytic performance testing: The 0.15 g catalysts prepared in Examples 1-4 and Comparative Examples 1-6 were reduced at 600 °C under a hydrogen atmosphere for 1 h to obtain activated catalysts.

[0076] A hexane-nitrogen mixture (hexane:nitrogen volume ratio = 1:2) was introduced into a reactor containing the activated catalyst at a total gas velocity of 15 mL / min to carry out a catalytic dehydrogenation reaction, yielding aromatics. The catalytic performance of the catalysts prepared in Examples 1-4 and Comparative Examples 1-6 after 2 hours of reaction under the same catalytic reaction conditions is shown in Table 1.

[0077] Table 1 Catalytic performance of the catalysts prepared in Examples 1-4 and Comparative Examples 1-6

[0078] As shown in Table 1, the x%Pt-y%Kz%Cr@S-1 catalyst prepared in this invention, when used for the catalytic aromatization of hexane to aromatics, achieves an initial hexane conversion of 71% at 500℃, an aromatics selectivity of 72%, an aromatics yield of 51%, and a selectivity for the undesirable methane byproduct of only 9%. In contrast, without the auxiliary agent Cr, the hexane conversion, aromatics selectivity, and aromatics yield decrease to 39%, 56%, and 22%, respectively; without the auxiliary agent K, the hexane conversion, aromatics selectivity, and aromatics yield decrease to 35%, 62%, and 22%, respectively; and without metallic Pt, the above reactions are difficult to proceed, with hexane conversion below 1%. Meanwhile, when introducing the auxiliary agent Cr using the traditional impregnation method, the hexane conversion, aromatic selectivity, and aromatic yield were 43%, 32%, and 14%, respectively. In contrast, the Pt-K-Cr / S-1 prepared by the impregnation method only achieved 2%, 17%, and 0.34% hexane conversion, aromatic selectivity, and aromatic yield, respectively. For comparison, adding other auxiliary agents such as gallium resulted in hexane conversion, aromatic selectivity, and yield of only 53%, 52%, and 28%, respectively. These results demonstrate that the x%Pt-y%Kz%Cr@S-1 composite catalyst prepared in this invention simultaneously exhibits high hexane conversion, aromatic selectivity, and high aromatic yield in the catalytic hexane aromatization reaction.

[0079] Application Example 2 The catalytic stability of the 0.6%Pt-1.5%K-0.3%Cr@S-1 composite catalyst prepared in Example 1 was tested. The catalytic reaction conditions were: reaction temperature 550℃, atmospheric pressure, and hexane mass hourly space velocity (H₂S₀) of 7 h⁻¹. -1 .

[0080] The catalytic stability test results of the 0.6%Pt-1.5%K-0.3%Cr@S-1 catalyst are as follows: Figure 3 As shown. By Figure 3 It is evident that the 0.6%Pt-1.5%K-0.3%Cr@S-1 catalyst prepared in this invention exhibits excellent reaction stability in the catalytic hexane aromatization reaction. Even after reacting at a high temperature of 550℃ for 100 h, the hexane conversion, aromatic selectivity, and yield of the 0.5%Pt-1.5%K-0.3%Cr@S-1 composite catalyst can still be maintained at 69%, 59%, and 41%, respectively.

[0081] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A molecular sieve-confined metal catalyst, characterized in that, It includes an all-silica ZSM-5 molecular sieve and a metal oxide encapsulated within the pores of the all-silica ZSM-5 molecular sieve, wherein the metal oxide contains Pt, K and Cr; The mass of Pt is 0.2-2% of the mass of the molecular sieve-confined metal catalyst; the mass of K is 0.2-5% of the mass of the molecular sieve-confined metal catalyst; and the mass of Cr is 0.05-1.0% of the mass of the molecular sieve-confined metal catalyst.

2. The molecular sieve confined metal catalyst according to claim 1, characterized in that, The mass of Pt is 0.25-1.5% of the mass of the molecular sieve-confined metal catalyst, the mass of K is 0.5-4.0% of the mass of the molecular sieve-confined metal catalyst, and the mass of Cr is 0.1-0.8% of the mass of the molecular sieve-confined metal catalyst.

3. The method for preparing the molecular sieve confined metal catalyst according to claim 1 or 2, characterized in that, Includes the following steps: A Pt-K-Cr-ligand mixed precursor solution was obtained by mixing a water-soluble platinum source, a water-soluble potassium source, a water-soluble chromium source, an organic amine ligand, and water. The Pt-K-Cr-ligand mixed precursor solution was mixed with the mother liquor for the synthesis of all-silica ZSM-5 molecular sieve and subjected to hydrothermal crystallization. The resulting solid was then dried and calcined to obtain the molecular sieve confined metal catalyst.

4. The preparation method according to claim 3, characterized in that, The water-soluble platinum source includes platinum chloride and / or chloroplatinic acid; the water-soluble potassium source includes one or more of potassium nitrate, potassium sulfate, and potassium chloride; the water-soluble chromium source includes one or more of chromium nitrate, chromium sulfate, and chromium chloride; and the organic amine ligand includes one or more of ethylenediamine, cyclohexylamine, and cyclohexanediamine.

5. The preparation method according to claim 3, characterized in that, The molar ratio of Pt, K, and Cr in the Pt-K-Cr ligand mixture precursor solution is 1:(4~15):(0.1~5), and the ratio of the total molar amount of metal ions to the molar amount of organic amine ligands is 1:(1~10). The metal ions include platinum, potassium, and chromium ions.

6. The preparation method according to claim 3, characterized in that, The mother liquor for the synthesis of all-silica ZSM-5 molecular sieve includes active ingredients SiO2, a template agent, and H2O, wherein the molar ratio of active ingredients SiO2, template agent, and H2O is 1:(0.2~0.8):(20~100); the template agent includes one or more of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, and n-butylamine.

7. The preparation method according to claim 3, characterized in that, The hydrothermal crystallization temperature is 150~200℃, and the time is 30~120h.

8. The preparation method according to claim 3, characterized in that, The roasting temperature is 500~650℃ and the time is 5~10h.

9. The application of the molecular sieve confined metal catalyst according to claim 1 or 2, or the molecular sieve confined metal catalyst obtained by the preparation method according to any one of claims 3 to 8, in the catalytic aromatization reaction of alkane.

10. A method for preparing aromatic hydrocarbons by hexane aromatization, characterized in that, Includes the following steps: Hexane-nitrogen mixture is subjected to aromatization reaction in the presence of a catalyst to obtain aromatic hydrocarbons; The catalyst is the molecular sieve confined metal catalyst according to claim 1 or 2, or the molecular sieve confined metal catalyst obtained by the preparation method according to any one of claims 3 to 8; the aromatization reaction is carried out at a temperature of 400-600°C and a mass hourly space velocity of 0.1-20 h⁻¹. -1 .

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