A hollow structure catalyst, a preparation method and application thereof, and a method for preparing low-carbon olefins by dehydrogenation of low-carbon alkanes

Abstract

The application provides a hollow structure catalyst and a preparation method and application thereof, and a method for preparing low-carbon olefins by dehydrogenation of low-carbon alkanes, and relates to the technical field of catalysts.The hollow structure catalyst provided by the application takes Pt as an active component and takes hollow silicalite-1 molecular sieve as a carrier;the carrier has specific pore structure and rich hydroxyl nests, molecular size pore structure, easy-to-diffuse hollow structure and shape-selective catalytic characteristics, can effectively limit Pt metal nanoclusters, inhibit migration and growth of Pt particles, promote dispersion of the Pt nanoclusters, the limiting effect of the molecular sieve pores can greatly inhibit migration and agglomeration of the Pt metal, improve selectivity of the hollow structure catalyst to low-carbon olefins, and also improve stability of the hollow structure catalyst at high temperatures.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a hollow structure catalyst, its preparation method and application, and a method for dehydrogenating low-carbon alkanes to prepare low-carbon olefins. Background Technology

[0002] The coal-to-oil and coal-to-olefins processes generate a large amount of low-carbon alkanes. Converting them into high-value-added olefins not only enriches the economics of the products but also promotes the optimization of the energy structure, achieves economical use of energy, and reduces reaction energy consumption, which is of great significance.

[0003] Currently, the commonly used industrial catalysts for the dehydrogenation of low-carbon alkanes to olefins are those with Al2O3 as the support, Pt as the active component, and auxiliary metals such as Sn, Zn, and Ga. However, due to the harsh reaction conditions (high temperature 500-600℃), the catalysts deactivate quickly, have poor stability, and low selectivity, especially with severe sintering of the active metal. To address this problem, the pore confinement effect can be used to highly disperse metal particles within or on the molecular sieve framework, which can greatly reduce the degree of sintering of metal particles at high temperatures and improve the stability of the catalyst. For example, Liu Lichen (Liu L, Lopez-Haro M, Lopes CW, et al. Regioselective generation and reactivity control of subnanometric platinum clusters inzeolites for high-temperature catalysis[J]. Nature Materials,2019,18(8)) reported that PtSn particles were highly dispersed in MFI molecular sieves using a hydrothermal synthesis method. The PtSn@MFI catalyst was used in the propane dehydrogenation reaction and showed significantly enhanced activity and propylene selectivity. However, the PtSn@MFI catalyst only showed about one-third of its initial reactive activity in the third cycle, indicating poor catalyst stability. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a hollow structure catalyst, its preparation method and application, and a method for the dehydrogenation of low-carbon alkanes to prepare low-carbon olefins. The hollow structure catalyst provided by this invention is used to catalyze the dehydrogenation of low-carbon alkanes to prepare low-carbon olefins, exhibiting high selectivity for low-carbon olefins and strong stability.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a hollow structure catalyst, comprising a hollow silicate-1 molecular sieve and an active component supported on the hollow silicate-1 molecular sieve;

[0007] The hollow silicalite-1 molecular sieve has a mesopore size of 2–10 nm and a specific surface area of ​​250–500 m². 2 / g, mesoporous pore volume is 0.20~0.35cm³ 3 / g;

[0008] The active component includes elemental platinum.

[0009] Preferably, the active component further includes an auxiliary metal, which forms an alloy phase with elemental platinum;

[0010] The auxiliary metals include one or more of Sn, La, Ga, Ce, In, and Zn.

[0011] Preferably, in the hollow structure catalyst for dehydrogenation of low-carbon alkane, the mass fraction of platinum is 0.05-2%, and the mass fraction of auxiliary metal elements is 0.05-4%.

[0012] This invention provides a method for preparing the hollow structure catalyst described in the above technical solution, comprising the following steps:

[0013] An alkaline substance, silicalite-1 molecular sieve, and water are mixed and aged to obtain a mixed alkaline solution.

[0014] A platinum precursor solution was obtained by mixing a water-soluble platinum source, a first organic amine ligand, and water.

[0015] The mixed alkaline solution was mixed with a platinum precursor solution and subjected to hydrothermal crystallization to obtain the crystallized product.

[0016] The crystallized product was subjected to calcination and reduction treatments in sequence to obtain a hollow structure catalyst.

[0017] Preferably, the alkaline substance includes inorganic substances and organic bases;

[0018] The inorganic substances include one or more of alkali metal hydroxides, alkali metal nitrates and alkali metal carbonates;

[0019] The organic base includes one or more of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium hydroxide, and tetrabutylammonium hydroxide;

[0020] The aging temperature is 5–240 min.

[0021] Preferably, the step of mixing the mixed alkaline solution with the platinum precursor solution is replaced by:

[0022] A water-soluble auxiliary metal source, a second organic amine ligand, and water are mixed to obtain an auxiliary metal precursor solution.

[0023] The mixed alkaline solution is mixed with a platinum precursor solution and an auxiliary metal precursor solution.

[0024] Preferably, the first organic amine ligand and the second organic amine ligand independently comprise one or more of ethylamine, ethylenediamine, butylamine, cyclohexylamine, cyclohexylimine, hexamethylenediamine, cyclohexanediamine, and diamine;

[0025] The molar ratio of platinum to the first organic amine ligand in the water-soluble platinum source is 1:20 to 400;

[0026] The molar ratio of the auxiliary metal and the second organic amine ligand in the water-soluble auxiliary metal source is 1:20 to 400;

[0027] The molar ratio of the auxiliary metal in the water-soluble auxiliary metal source to the platinum in the water-soluble platinum source is ≤10.

[0028] The hydrothermal crystallization temperature is 120–200℃, and the time is 12–96 h.

[0029] Preferably, the calcination temperature is 350–600°C, the holding time is 3–12 h, and the calcination atmosphere is air, hydrogen, or nitrogen.

[0030] The reduction treatment is carried out at a temperature of 150–700°C for 1–5 hours, and the reducing agent used includes carbon monoxide or hydrogen.

[0031] This invention provides the application of the hollow structure catalyst described in the above technical solution or the hollow structure catalyst prepared by the above technical solution in the dehydrogenation of low-carbon alkanes.

[0032] This invention also provides a method for preparing low-carbon olefins by dehydrogenation of low-carbon alkanes, comprising the following steps:

[0033] The dehydrogenation reaction is carried out in the presence of a catalyst to obtain low-carbon olefins.

[0034] The catalyst is the hollow structure catalyst described in the above technical solution or the hollow structure catalyst prepared by the preparation method described in the above technical solution;

[0035] The reaction atmosphere includes low-carbon alkanes and an auxiliary atmosphere, wherein the auxiliary atmosphere includes one or more of nitrogen, hydrogen and carbon dioxide; the molar ratio of the auxiliary atmosphere to the low-carbon alkanes is 0 to 10:1.

[0036] The dehydrogenation reaction temperature is 450–650 °C, and the mass hourly space velocity (WHSV) of the low-carbon alkanes is 1–200 h⁻¹.-1 .

[0037] This invention provides a hollow structure catalyst, comprising a hollow silicate-1 molecular sieve and an active component supported on the hollow silicate-1 molecular sieve; the mesopore size of the hollow silicate-1 molecular sieve is 2–10 nm, and the specific surface area is 250–500 m². 2 / g; the active component includes elemental platinum. Traditional supports cannot effectively inhibit the migration and growth of noble metal particles, leading to catalyst deactivation. This invention uses hollow silicalite-1 molecular sieve as a support, which has a specific pore structure and abundant hydroxyl nests. The molecular-sized pore structure, easily diffused hollow structure, and shape-selective catalytic properties can effectively confine Pt metal nanoclusters, inhibiting the migration and growth of Pt particles. Compared with traditional Pt-supported oxide supports (e.g., Al2O3), it can further promote the dispersion of Pt nanoclusters. Its strong hydrothermal stability can greatly inhibit the migration and aggregation of Pt metal, and improve the stability of hollow structure catalysts at high temperatures. In addition, the hollow structure can also promote the diffusion of low-carbon olefin products, reduce the occurrence of side reactions such as polymerization and cyclization of low-carbon alkanes, and improve the selectivity of low-carbon olefins.

[0038] Furthermore, when the active component also includes a promoter metal, the promoter metal forms an alloy phase with elemental platinum. In this invention, the promoter metal interacts with platinum electronically (the promoter metal provides electrons to Pt), thereby increasing the electron cloud density around Pt, promoting the activation and breaking of CH bonds, and enhancing the selectivity for low-carbon olefins. The presence of the promoter metal also improves the catalyst's dehydrogenation activity and enhances the dispersibility of platinum. This invention uses hollow silicalite-1 molecular sieve as a support. This support has a specific pore structure and abundant hydroxyl nests. The molecular-sized pore structure, easily diffused hollow structure, and shape-selective catalytic properties can effectively confine Pt and promoter metal particles. Compared with traditional oxide supports for Pt, it can further promote the dispersion of Pt nanoclusters and their interaction with promoter metals. Its strong hydrothermal stability can greatly inhibit the migration and aggregation of Pt metal, improving the catalytic activity and stability of the catalyst for the dehydrogenation of low-carbon alkanes.

[0039] As shown in the test results of the examples, the hollow structure catalyst provided by the present invention, when applied to the dehydrogenation reaction of propane, can achieve a selectivity of up to 99.7% for propylene. According to the catalyst activity lifetime test results, the propylene selectivity is maintained at 97% within 200 hours, indicating that the hollow structure catalyst provided by the present invention has excellent catalytic activity, stability and regeneration performance.

[0040] This invention provides a method for preparing the hollow structure catalyst described in the above-mentioned technical solution. This invention utilizes alkaline substances to treat silicalite-1 molecular sieves, creating abundant defect sites that react with Pt, stably confining it within the hollow silicalite-1 molecular sieve. Furthermore, the hollow structure promotes the diffusion of olefin products, inhibits side reactions, and improves product selectivity and catalyst stability. This invention employs an in-situ introduction method using crystallization treatment of silicalite-1 molecular sieves, enabling the stable introduction of Pt into the molecular sieve channels, improving Pt dispersion, and precisely controlling the geometric and electronic structure of Pt, thereby further enhancing the selectivity for low-carbon olefins and catalyst stability. Moreover, the preparation method provided by this invention is simple, low-cost, environmentally friendly, and suitable for industrial production. Attached Figure Description

[0041] Figure 1 For the application of the PtIn@S1-H catalyst in Example 1 (550℃, 3.6h) catalysis -1 The evaluation results of the propane dehydrogenation reaction are shown in the figure.

[0042] Figure 2 The graph shows the evaluation results of the propane dehydrogenation reaction catalyzed by the PtSn@S1-H catalyst in Example 2.

[0043] Figure 3 The graph shows the evaluation results of the propane dehydrogenation reaction catalyzed by the PtLa@S1-H catalyst in Example 3.

[0044] Figure 4 The graph shows the evaluation results of the propane dehydrogenation reaction catalyzed by the PtCe@S1-H catalyst in Example 4.

[0045] Figure 5 The graph shows the evaluation results of the propane dehydrogenation reaction catalyzed by the PtGa@S1-H catalyst in Example 5.

[0046] Figure 6 The graph shows the evaluation results of the propane dehydrogenation reaction catalyzed by the PtZn@S1-H catalyst in Example 6.

[0047] Figure 7 The graph shows the evaluation results of the propane dehydrogenation reaction catalyzed by the Pt@S1-H catalyst in Example 7.

[0048] Figure 8 For the application of the PtIn@S1-H catalyst in Example 1 (580℃, 3.6h) catalysis -1 The evaluation results of the ethane dehydrogenation reaction are shown in the figure.

[0049] Figure 9 For the application of the PtIn@S1-H catalyst in Example 1 (530℃, 3.6h) catalysis -1The evaluation results of the propane dehydrogenation reaction lifetime are shown in the figure.

[0050] Figure 10 For the application of the PtIn@S1-H catalyst in Example 1 (530℃, 100h) -1 ) Evaluation results of high-space velocity propane dehydrogenation;

[0051] Figure 11 The graph shows the evaluation results of the propane dehydrogenation reaction lifetime catalyzed by the Pt@S1 catalyst in Application Example 1 for comparison.

[0052] Figure 12 The graph shows the evaluation results of the lifetime of the propane dehydrogenation reaction catalyzed by the PtIn / Al2O3 catalyst in Application Example 2 for comparison.

[0053] Figure 13 The graph shows the evaluation results of the propane dehydrogenation reaction lifetime in Example 3 using the PtIn / S1-H catalyst-impregnation method.

[0054] Figure 14 The graph shows the evaluation results of the propane dehydrogenation reaction lifetime using the PtSn / S1 catalyst-impregnation method in Example 4 for comparison.

[0055] Figure 15 The PtIn@S1-H catalyst prepared in Example 1 was used for catalysis (530℃, 3.6h). -1 Figure 1 shows the performance and stability of propane dehydrogenation reaction.

[0056] Figure 16 TEM images of the catalysts prepared in Examples 1 to 7, where a is Example 1, b is Example 2, c is Example 3, d is Example 4, e is Example 5, f is Example 6, and g is Example 7;

[0057] Figure 17 The BET adsorption curve of the PtIn@S1-H catalyst prepared in Example 1 is shown. Detailed Implementation

[0058] The present invention provides a hollow structure catalyst, comprising a hollow silicate-1 molecular sieve and an active component supported on the hollow silicate-1 molecular sieve.

[0059] In this invention, the mesopore size of the hollow silicate-1 molecular sieve is 2–10 nm, preferably 3–5 nm; the specific surface area of ​​the hollow silicate-1 molecular sieve is 250–500 m². 2 / g, preferably 400-500m 2 / g; the mesopore volume of the hollow silicalite-1 molecular sieve is 0.20–0.35 cm³.3 / g, preferably 0.25~0.3cm 3 / g.

[0060] In this invention, the active component includes elemental platinum, which preferably exists in the form of platinum nanoclusters. In this invention, the mass fraction of platinum in the hollow catalyst is preferably 0.05–2%, more preferably 0.2–1%, further preferably 0.3–0.5%, and specifically preferably 0.35%, 0.40%, 0.45%, 0.46%, or 0.47%.

[0061] In this invention, the active component preferably further includes an auxiliary metal, which forms an alloy phase with elemental platinum; the auxiliary metal includes one or more of Sn, La, Ga, Ce, In, and Zn; the alloy phase is preferably PtM. x Nanoclusters, wherein M is an auxiliary metal, and x preferably ranges from 0.05% to 4%. In this invention, the mass fraction of platinum in the hollow catalyst is preferably 0.05% to 2%, more preferably 0.2% to 1%, further preferably 0.3% to 0.5%, and specifically preferably 0.35%, 0.40%, 0.45%, 0.46%, or 0.47%. In this invention, the mass fraction of the auxiliary metal in the hollow catalyst is preferably 0.05% to 4%, more preferably 0.2% to 2%, further preferably 0.3% to 1%, and specifically preferably 0.45%, 0.50%, 0.51%, 0.52%, or 0.55%.

[0062] In this invention, the particle size of the hollow catalyst is preferably 20-40 mesh. In this invention, the active component is preferably supported at the cross-cavities of the hollow silicate-1 molecular sieve.

[0063] This invention provides a method for preparing the hollow structure catalyst described in the above technical solution, comprising the following steps:

[0064] An alkaline substance, silicalite-1 molecular sieve, and water are mixed and aged to obtain a mixed alkaline solution.

[0065] A platinum precursor solution was obtained by mixing a water-soluble platinum source, a first organic amine ligand, and water.

[0066] The mixed alkaline solution was mixed with a platinum precursor solution and subjected to hydrothermal crystallization to obtain the crystallized product.

[0067] The crystallized product was subjected to calcination and reduction treatments in sequence to obtain a hollow structure catalyst.

[0068] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0069] This invention involves mixing an alkaline substance, a silicalite-1 molecular sieve, and water, and then aging the mixture to obtain a mixed alkaline solution.

[0070] In this invention, the alkaline substance preferably comprises inorganic substances and organic bases; the inorganic substances preferably comprise one or more of alkali metal hydroxides, alkali metal nitrates, and alkali metal carbonates; the alkali metal hydroxides preferably comprise one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide; the alkali metal nitrates preferably comprise one or more of lithium nitrate, sodium nitrate, potassium nitrate, and cesium nitrate; the alkali metal carbonates preferably comprise one or more of lithium carbonate, sodium carbonate, potassium carbonate, and cesium carbonate; and the organic base preferably comprises one or more of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium hydroxide, and tetrabutylammonium hydroxide. In this invention, the molar ratio of the inorganic substance to the organic base is preferably 1:0.1 to 100, more preferably 1:0.2 to 10.

[0071] In this invention, the mixing of the alkaline substance, the silicalite-1 molecular sieve, and water is preferably carried out by dissolving the alkaline substance in water to obtain an alkaline solution, and then mixing the alkaline solution with the silicalite-1 molecular sieve. In this invention, the concentration of the alkaline solution is preferably 0.005–1 mol / L, more preferably 0.01–0.9 mol / L, and even more preferably 0.1–0.8 mol / L. In this invention, the mixing time between the alkali and the molecular sieve carrier is preferably 5–240 min, more preferably 30–100 min.

[0072] In this invention, the aging temperature is preferably room temperature, and the aging time is preferably 5–240 min, more preferably 30–200 min, and even more preferably 60–120 min. This invention utilizes alkaline substances to treat silicalite-1 molecular sieves, which can create abundant defect sites within the silicalite-1 molecular sieve, facilitating interaction with Pt and its stable confinement within the hollow silicalite-1 molecular sieve. When an auxiliary metal is added, Pt can interact with the auxiliary metal to promote the formation of an alloy phase. Furthermore, the hollow structure can promote the diffusion of olefin products, suppress side reactions, and improve product selectivity and catalyst stability.

[0073] In this invention, the particle size of the silicalite-1 molecular sieve is preferably 100-450 nm, more preferably 170-200 nm; the silicalite-1 molecular sieve is preferably purchased directly or made in-house.

[0074] In this invention, the preparation method of the silicalite-1 molecular sieve preferably includes the following steps:

[0075] The initial gel was obtained by mixing and aging a silicon source, an organic template agent, and water.

[0076] The initial gel was subjected to hydrothermal crystallization and then calcined to obtain silicalite-1 molecular sieve.

[0077] This invention involves mixing and aging a silicon source, an organic template agent, and water to obtain an initial gel. In this invention, the silicon source preferably includes one or more of tetraethyl orthosilicate, methyl orthosilicate, propyl orthosilicate, and butyl orthosilicate. In this invention, the organic template agent preferably includes tetrapropylammonium hydroxide (TPAOH), and the organic template agent is preferably used in the form of an aqueous solution, with a mass fraction preferably of 20-30%, more preferably 25%. In this invention, the molar ratio of SiO2 to the organic template agent in the initial gel is preferably 1:0.1-0.7, more preferably 1:0.2-0.5, and even more preferably 1:0.3-0.4; the molar ratio of SiO2 to water in the initial gel is preferably 1:20-100, more preferably 1:30-80, and even more preferably 1:40-50. In this invention, the mixed aging is preferably carried out by mixing an aqueous solution of an organic template agent with water, and then adding a silicon source dropwise under stirring conditions. This invention does not have a special limitation on the dropwise addition rate; it can be added dropwise at a uniform rate. The stirring and mixing temperature is preferably room temperature, and the stirring and mixing time is preferably 1 to 5 hours, more preferably 1 to 2 hours. The aging temperature is preferably room temperature, and the aging time is preferably 2 to 48 hours, more preferably 5 to 24 hours.

[0078] After obtaining the initial gel, the present invention performs hydrothermal crystallization on the initial gel to obtain silicalite-1 molecular sieve. In the present invention, the temperature of the hydrothermal crystallization is preferably 150-220℃, more preferably 170-210℃, and even more preferably 190-200℃; the holding time of the hydrothermal crystallization is preferably 2-5 days, more preferably 3-5 days, and even more preferably 4-5 days.

[0079] After the hydrothermal crystallization is completed, the present invention preferably further includes: performing solid-liquid separation on the obtained crystallized product, and drying the obtained solid product. The present invention does not have special requirements for the method of solid-liquid separation; any solid-liquid separation method well known in the art can be used, such as centrifugation, filtration, or vacuum filtration. In the present invention, the drying temperature is preferably 80–100°C, more preferably 90–100°C; the drying time is preferably 6–12 hours, more preferably 10–12 hours.

[0080] In this invention, the calcination temperature is preferably 350-600℃, more preferably 500-600℃, and even more preferably 550℃; the calcination holding time is preferably 3-12h, more preferably 6-12h, and even more preferably 8-10h; the calcination atmosphere is preferably air, hydrogen, or nitrogen.

[0081] This invention involves mixing a water-soluble platinum source, a first organic amine ligand, and water to obtain a platinum precursor solution. In this invention, the water-soluble platinum source preferably includes one or more of chloroplatinic acid, tetraammineplatinum chloride, tetraammineplatinum nitrate, ethylenediamineplatinum chloride, (trimethyl)methylcyclopentadiene platinum(IV), sodium hexachloroplatinate, or tetra(triphenylphosphine)platinum. In this invention, the first organic amine ligand preferably includes one or more of ethylamine, ethylenediamine, butylamine, cyclohexylamine, cycloheximine, hexamethylenediamine, cyclohexanediamine, and diamine. In this invention, the molar ratio of platinum in the water-soluble platinum source to the first organic amine ligand is preferably 1:20–400, more preferably 1:20–200. In this invention, the mass ratio of the silicalite-1 molecular sieve in the mixed alkaline solution to the platinum in the water-soluble platinum source is preferably 1:20–100, more preferably 1:20–80. This invention does not have a specific limitation on the amount of water used, as long as it is sufficient to dissolve the water-soluble platinum source. In this invention, platinum in the water-soluble platinum source serves as the active component. The organic amine ligands (first organic amine ligand and second organic amine ligand) can act as templates for the silicalite-1 molecular sieve and coordinate with metal ions (platinum particles and auxiliary metal ions), thereby introducing platinum into the channels of the silicalite-1 molecular sieve and improving the dispersibility and stability of platinum.

[0082] When the active component is elemental platinum, after obtaining the platinum precursor solution, the present invention mixes the mixed alkaline solution with the platinum precursor solution and performs hydrothermal crystallization to obtain the crystallized product.

[0083] In this invention, the temperature of the hydrothermal crystallization (secondary crystallization) is preferably 120-200°C, more preferably 150-200°C, and even more preferably 150-170°C; the time of the hydrothermal crystallization is preferably 12-96 hours, more preferably 24-72 hours, and even more preferably 24-48 hours.

[0084] Following the hydrothermal crystallization, the present invention preferably further includes post-processing, which preferably includes: solid-liquid separation of the obtained hydrothermal crystallization system, washing and drying the obtained solid product ethanol to obtain the crystallized product. The present invention does not have special requirements for the solid-liquid separation method; any solid-liquid separation method well-known in the art can be used, such as centrifugation, filtration, or vacuum filtration. In the present invention, the washing is preferably water washing. In the present invention, the drying temperature is preferably 80–100°C, more preferably 90–100°C; the drying time is preferably 6–12 hours, more preferably 10–12 hours.

[0085] When the active component further includes an auxiliary metal, the present invention mixes a water-soluble auxiliary metal source, a second organic amine ligand, and water to obtain an auxiliary metal precursor solution; the mixed alkaline solution is then mixed with a platinum precursor solution and the auxiliary metal precursor solution for hydrothermal crystallization to obtain a crystallized product. In the present invention, the metal element in the water-soluble auxiliary metal source is the same as the auxiliary metal in the hollow structure catalyst; the water-soluble auxiliary metal source is preferably a water-soluble auxiliary metal salt, more preferably a nitrate, chloride, carbonate, or sulfate of a water-soluble auxiliary metal. In a specific embodiment of the present invention, the water-soluble auxiliary metal salt is SnCl4·5H2O, La(NO3)3, Ce(NO3)3, In(NO3)3, Zn(NO3)2, or Ga(NO3)3. In the present invention, the optional type of the second organic amine is preferably the same as the optional type of the first organic amine ligand, and will not be elaborated further here. In this invention, the molar ratio of the auxiliary metal in the water-soluble auxiliary metal source to the second organic amine ligand is 1:20 to 400, more preferably 1:20 to 200. In this invention, the molar ratio of the auxiliary metal in the water-soluble auxiliary metal source to platinum in the water-soluble platinum source is preferably ≤10, more preferably 1 to 5:1. This invention does not have a special limitation on the amount of water used, as long as it is sufficient to dissolve the water-soluble auxiliary metal source. In this invention, the hydrothermal crystallization and subsequent post-crystallization are the same as the preparation conditions when the active component is elemental platinum, and will not be repeated here.

[0086] This invention employs an in-situ introduction method of hydrothermal crystallization treatment of silicalite-1 molecular sieve, which enables Pt to be stably introduced into the molecular sieve channels, improving the dispersion of Pt and its interaction with auxiliary metals, and precisely controlling the geometry and electronic structure of Pt, thereby further enhancing the selectivity of olefins and the stability of the catalyst.

[0087] After obtaining the crystallized product, the present invention sequentially calcines and reduces the crystallized product to obtain a hollow structure catalyst.

[0088] In this invention, the calcination temperature is preferably 350-600℃, more preferably 450-560℃, and even more preferably 500-550℃; the calcination holding time is preferably 3-12h, more preferably 4-12h, and even more preferably 4-8h; the calcination atmosphere is preferably air, hydrogen, or nitrogen.

[0089] In this invention, the reduction treatment temperature is preferably 150–700°C, more preferably 250–600°C, and even more preferably 450–550°C; the holding time for the reduction treatment is preferably 1–5 h, more preferably 2–4 h, and even more preferably 2–3 h; the reducing agent used in the reduction treatment preferably includes carbon monoxide or hydrogen. In this invention, the reduction treatment reduces Pt and the auxiliary metal to elemental metals. During the reduction process, a partial alloy is formed between Pt and the auxiliary metal, exhibiting electronic and geometric effects. The geometric effect improves the dispersion of Pt and prevents Pt agglomeration; the electronic effect can promote the activation of CH bonds, thereby improving the catalytic activity of the catalyst.

[0090] This invention obtains PtM by controlling the parameters of the hydrothermal crystallization process. x A core-shell catalyst with highly dispersed nanoclusters on hollow silicate-1; this invention achieves precise control over the geometry and electronic structure of metal (Pt and M) particles by regulating conditions such as the type of alkali metal ions in the alkaline substance, the type of auxiliary metal, and the method of metal introduction.

[0091] This invention provides the application of the hollow structure catalyst described in the above technical solution or the hollow structure catalyst prepared by the above technical solution in the dehydrogenation of low-carbon alkanes.

[0092] This invention provides a method for preparing low-carbon olefins by dehydrogenation of low-carbon alkanes, comprising the following steps: carrying out a dehydrogenation reaction in a reaction atmosphere under the action of a catalyst to obtain low-carbon olefins; wherein the catalyst is a hollow structure catalyst as described in the above technical solution or a hollow structure catalyst prepared by the preparation method described in the above technical solution.

[0093] In this invention, the reaction atmosphere preferably includes low-carbon alkanes and an auxiliary atmosphere, wherein the auxiliary atmosphere preferably includes one or more of nitrogen, hydrogen and carbon dioxide; the molar ratio of the auxiliary atmosphere to the low-carbon alkanes is preferably 0 to 10:1, more preferably 0 to 5:1.

[0094] In this invention, the dehydrogenation reaction temperature is preferably 450–650°C, more preferably 500–600°C, and specifically preferably 450°C, 500°C, 530°C, or 650°C; the mass hourly space velocity (WHSV) of the low-carbon alkane is preferably 1–200 h⁻¹. -1 More preferably 1 to 100 h-1 Further preferably 1-20h -1 .

[0095] To further illustrate the present invention, the hollow structure catalyst, its preparation method and application, and the method for dehydrogenating low-carbon alkanes to prepare low-carbon olefins 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.

[0096] Example 1

[0097] A 25% TPAOH aqueous solution was added sequentially to water and stirred at 500 rpm for 2 hours. Tetraethyl orthosilicate (TEOS) was then slowly added dropwise, and the mixture was stirred and aged at room temperature for 6 hours to obtain an initial gel with a molar composition of 40H₂O: 0.3TPAOH: 1SiO₂. This initial gel was added to a 100 mL high-pressure reactor and hydrothermally crystallized at 200 °C for 120 hours. The reactor was then removed, and the sample was washed with water and centrifuged three times. The resulting solid product was dried at 100 °C for 12 hours and then calcined in a muffle furnace at 550 °C in air for 10 hours to obtain silicalite-1 molecular sieve.

[0098] 0.04 g NaOH and 1.6215 g TPAOH aqueous solution (mass fraction of 25%) were added sequentially to 8.7799 g water and stirred at 300 rpm for 0.5 h to obtain an initial alkali concentration of 0.3 M. Then, 1 g silicalite-1 molecular sieve was added and the mixture was stirred and aged at room temperature for 2 h to obtain a mixed alkali solution.

[0099] 2.5 mL of a 0.5123 M platinum solution (diluted with chloroplatinic acid) was added to a mixture of 2.5 mL of deionized water and 1.5 mL of ethylenediamine to obtain a Pt precursor solution; 0.08 g of indium nitrate was added to a mixture of 5 mL of deionized water and 0.1 mL of ethylenediamine to obtain an In precursor solution.

[0100] The Pt precursor solution and In precursor solution were added to the mixed alkaline solution and mixed for 5 min. The mixture was then loaded into a 100 mL high-pressure reactor and hydrothermally crystallized at 170 °C for 36 h. The reactor was then removed, and the sample was washed with water and centrifuged twice. The resulting solid product was dried at 100 °C for 12 h, and then calcined at 550 °C for 5 h in an air atmosphere in a muffle furnace. The product was then tableted, pulverized, and sieved. Particles of 20–40 mesh were taken and reduced at 550 °C in a hydrogen atmosphere for 2 h to obtain a high-stability low-carbon alkane dehydrogenation hollow structure catalyst (PtIn@S1-H catalyst, with a Pt mass fraction of 0.45% and an In mass fraction of 0.50%).

[0101] Example 2

[0102] 0.32 g NaOH and 1.6215 g TPAOH aqueous solution (mass fraction of 25%) were added sequentially to 8.7799 g water and stirred at 300 rpm for 0.5 h to obtain an initial alkali concentration of 0.8 M. Then, 1 g of silicalite-1 molecular sieve prepared in Example 1 was added and the mixture was stirred and aged at room temperature for 5 min to obtain a mixed alkali solution.

[0103] 2.5 mL of a 0.5123 M platinum solution (diluted with chloroplatinic acid) was added to a mixture of 2.5 mL of deionized water and 1.0 mL of ethylenediamine to obtain a Pt precursor solution; 0.098 g of tin nitrate was added to a mixture of 5 mL of deionized water and 0.1 mL of ethylenediamine to obtain a Sn precursor solution.

[0104] The Pt precursor solution and Sn precursor solution were added to the mixed alkaline solution and mixed for 60 min. The mixture was then loaded into a 100 mL high-pressure reactor and hydrothermally crystallized at 200 °C for 96 h. The reactor was then removed, and the sample was washed with water and centrifuged twice. It was dried at 60 °C for 8 h and then calcined at 600 °C for 3 h in an air atmosphere in a muffle furnace. The sample was then pressed into tablets, pulverized, and sieved. Particles of 20–40 mesh were taken and reduced at 550 °C in a hydrogen atmosphere for 2 h to obtain a high-stability low-carbon alkane dehydrogenation hollow structure catalyst (PtSn@S1-H catalyst, with a Pt mass fraction of 0.40% and a Sn mass fraction of 0.51%).

[0105] Example 3

[0106] 0.2027 g of TPAOH aqueous solution (mass fraction of 25%) was added to 8.7799 g of water and stirred at 300 rpm for 0.5 h. The corresponding initial alkali concentration was 0.005 M. Then, 1 g of silicalite-1 molecular sieve prepared in Example 1 was added and stirred and aged at room temperature for 4 h.

[0107] 2.5 mL of a 0.5123 M platinum solution (diluted with chloroplatinic acid) was added to a mixture of 2.5 mL of deionized water and 3.0 mL of ethylenediamine to obtain a Pt precursor solution; 0.087 g of lanthanum nitrate was added to a mixture of 5 mL of deionized water and 0.1 mL of ethylenediamine to obtain a La precursor solution.

[0108] The Pt precursor solution and La precursor solution were added to the mixed alkaline solution and then placed in a 100 mL high-pressure reactor. After hydrothermal crystallization at 120 °C for 96 h, the reactor was removed, the sample was washed with water and centrifuged twice, dried at 120 °C for 8 h, and then calcined at 350 °C for 12 h in an air atmosphere in a muffle furnace. The sample was then pressed into tablets, pulverized, and sieved. Particles of 20–40 mesh were taken and reduced at 550 °C in a hydrogen atmosphere for 2 h to obtain a high-stability low-carbon alkane dehydrogenation hollow structure catalyst (PtLa@S1-H catalyst, with a Pt mass fraction of 0.35% and a La mass fraction of 0.45%).

[0109] Example 4

[0110] 0.04 g NaOH and 1.6215 g TPAOH aqueous solution (mass fraction of 25%) were added sequentially to 8.7799 g water and stirred at 300 rpm for 0.5 h to obtain an initial alkali concentration of 0.03 M. Then, 1 g of silicalite-1 molecular sieve prepared in Example 1 was added and stirred and aged at room temperature for 3 h to obtain a mixed alkali solution.

[0111] 2.5 mL of a 0.5123 M platinum solution (diluted with chloroplatinic acid) was added to a mixture of 2.5 mL of deionized water and 0.02 mL of ethylenediamine to obtain a Pt precursor solution; 0.087 g of cerium nitrate was added to a mixture of 5 mL of deionized water and 0.1 mL of ethylenediamine to obtain a Ce precursor solution.

[0112] The Pt precursor solution and Ce precursor solution were added to the mixed alkaline solution and then loaded into a 100 mL high-pressure reactor. After hydrothermal crystallization at 170 °C for 12 h, the reactor was removed, the sample was washed with water and centrifuged twice, dried at 80 °C for 24 h, and then calcined at 500 °C for 6 h in an air atmosphere in a muffle furnace. The sample was then pressed into tablets, pulverized, and sieved. Particles of 20–40 mesh were taken and reduced at 550 °C in a hydrogen atmosphere for 2 h to obtain a high-stability low-carbon alkane dehydrogenation hollow structure catalyst (PtCe@S1-H catalyst, with a Pt mass fraction of 0.47% and a Ce mass fraction of 0.52%).

[0113] Example 5

[0114] 0.04 g NaOH and 1.6215 g TPAOH aqueous solution (mass fraction of 25%) were added sequentially to 8.7799 g water and stirred at 300 rpm for 0.5 h to obtain an initial alkali concentration of 0.03 M. Then, 1 g of silicalite-1 molecular sieve prepared in Example 1 was added and stirred and aged at room temperature for 3 h to obtain a mixed alkali solution.

[0115] 2.5 mL of a 0.5123 M platinum solution (diluted with chloroplatinic acid) was added to a mixture of 2.5 mL of deionized water and 1.2 mL of ethylenediamine to obtain a Pt precursor solution; 0.068 g of gallium nitrate was added to a mixture of 5 mL of deionized water and 0.1 mL of ethylenediamine to obtain a Ga precursor solution.

[0116] The Pt precursor solution and Ga precursor solution were added to the mixed alkaline solution and then placed in a 100 mL high-pressure reactor. After hydrothermal crystallization at 150 °C for 48 h, the reactor was removed, the sample was washed with water and centrifuged twice, dried at 60 °C for 24 h, and then calcined at 550 °C for 5 h in an air atmosphere in a muffle furnace. The sample was then pressed into tablets, pulverized, and sieved. Particles of 20–40 mesh were taken and reduced at 550 °C in a hydrogen atmosphere for 2 h to obtain a high-stability low-carbon alkane dehydrogenation hollow structure catalyst (PtGa@S1-H catalyst, with a Pt mass fraction of 0.46% and a Ga mass fraction of 0.50%).

[0117] Example 6

[0118] 0.04 g NaOH and 1.6215 g TPAOH aqueous solution (mass fraction of 25%) were added sequentially to 8.7799 g water and stirred at 300 rpm for 0.5 h to obtain an initial alkali concentration of 0.03 M. Then, 1 g of silicalite-1 molecular sieve prepared in Example 1 was added and stirred and aged at room temperature for 3 h to obtain a mixed alkali solution.

[0119] 2.5 mL of a 0.5123 M platinum solution (diluted with chloroplatinic acid) was added to a mixture of 2.5 mL of deionized water and 1.5 mL of ethylenediamine to obtain a Pt precursor solution; 0.051 g of zinc nitrate was added to a mixture of 5 mL of deionized water and 0.1 mL of ethylenediamine to obtain a Zn precursor solution.

[0120] The Pt and Zn precursor solutions were added to the mixed alkaline solution and then placed in a 100 mL high-pressure reactor. After hydrothermal crystallization at 170 °C for 36 h, the reactor was removed, the sample was washed with water and centrifuged twice, dried at 100 °C for 12 h, and then calcined at 550 °C for 6 h in an air atmosphere in a muffle furnace. The sample was then pressed into tablets, pulverized, and sieved. Particles of 20–40 mesh were taken and reduced at 550 °C in a hydrogen atmosphere for 2 h to obtain a high-stability low-carbon alkane dehydrogenation hollow structure catalyst (PtZn@Si-H catalyst, with a Pt mass fraction of 0.45% and a Ga mass fraction of 0.55%).

[0121] Example 7

[0122] 0.04 g NaOH and 1.6215 g TPAOH aqueous solution (mass fraction of 25%) were added sequentially to 8.7799 g water and stirred at 300 rpm for 0.5 h to obtain an initial alkali concentration of 0.03 M. Then, 1 g of silicalite-1 molecular sieve prepared in Example 1 was added and stirred and aged at room temperature for 3 h to obtain a mixed alkali solution.

[0123] Add 2.5 mL of a 0.5123 M platinum solution (diluted with chloroplatinic acid) to a mixture of 2.5 mL of deionized water and 1.5 mL of ethylenediamine to obtain a Pt precursor solution.

[0124] The Pt precursor solution was added to the mixed alkaline solution and then placed into a 100 mL high-pressure reactor. After hydrothermal crystallization at 170 °C for 36 h, the reactor was removed, the sample was washed with water and centrifuged twice, dried at 100 °C for 12 h, and then calcined at 550 °C for 6 h in an air atmosphere in a muffle furnace. The sample was then pressed into tablets, pulverized, and sieved. Particles of 20–40 mesh were taken and reduced at 550 °C in a hydrogen atmosphere for 2 h to obtain a high-stability low-carbon alkane dehydrogenation hollow structure catalyst (Pt@S1-H catalyst, with a Pt mass fraction of 0.40%).

[0125] Comparative Example 1 (a carrier with a non-hollow structure)

[0126] 0.202 g NaOH and 12.511 g TPAOH aqueous solution (25% by mass) were sequentially added to 27.596 g water and stirred at 500 rpm until clear. Then, 10.7 g tetraethyl orthosilicate (TEOS) was slowly added dropwise. The mixture was stirred and aged at room temperature for 24 h. All the hydrolyzed ethanol was removed in a 60 °C water bath. The initial gel molar composition was 40H₂O: 0.1Na₂O: 0.3TPAOH: 1SiO₂. 1.54 mL of 0.0513 mol / L chloroplatinic acid solution, 0.9 g ethylenediamine, and 1.5 g water were mixed thoroughly at room temperature to obtain a Pt precursor solution. The Pt precursor solution was added to the initial gel and stirred for 5 min. The sample was then transferred to a 100 mL high-pressure reactor and hydrothermally crystallized at 170 °C for 72 h. After removal from the reactor, the sample was washed with water, centrifuged three times, dried at 100 °C for 12 h, and then calcined at 550 °C for 5 h in an air atmosphere in a muffle furnace. The sample was then tableted, pulverized, and sieved. Particles of 20–40 mesh were taken and reduced at 550 °C in a hydrogen atmosphere for 2 h to obtain the Pt@S1 catalyst (Pt mass content was 0.49%).

[0127] Comparative Example 2 (Al2O3 as support)

[0128] 0.5 mL of 0.0513 mol / L chloroplatinic acid solution, 0.015 g of indium nitrate, 0.5 g of ethylenediamine, and 1.5 g of water were mixed at room temperature. Al2O3 was then added, and the mixture was dried at 80 °C for 12 h. The mixture was then calcined at 550 °C for 5 h in an air atmosphere in a muffle furnace. The mixture was then pressed into tablets, pulverized, and sieved. Particles of 20–40 mesh were taken and reduced at 550 °C for 2 h in a hydrogen atmosphere to obtain the PtIn / Al2O3 catalyst (Pt mass content was 0.48%).

[0129] Comparative Example 3 (Introduction of Active Components via Impregnation Method)

[0130] 0.202 g NaOH and 12.511 g TPAOH aqueous solution (mass fraction 25%) were sequentially added to 27.596 g water and stirred at 500 rpm until clear. Then, 10.7 g tetraethyl orthosilicate (TEOS) was slowly added dropwise, and the mixture was stirred and aged at room temperature for 24 h. All the hydrolyzed ethanol was removed in a 60 °C water bath, and the initial gel molar composition was 40H2O:0.1Na2O:0.3TPAOH:1SiO2. The gel was then transferred to a 100 mL high-pressure reactor and hydrothermally crystallized at 170 °C for 72 h. The reactor was then removed, the sample was washed with water and centrifuged three times, dried at 100 °C for 12 h, and then calcined in a muffle furnace at 550 °C in air atmosphere for 10 h to obtain silicalite-1 molecular sieve.

[0131] Mix 0.5 mL of 0.0513 mol / L chloroplatinic acid solution, 0.015 g of indium nitrate, 0.5 g of ethylenediamine, and 1.5 g of water at room temperature. Then add the above-mentioned silicalite-1 molecular sieve and let it stand for 12 h. Dry it at 80 °C for 12 h, then calcine it at 550 °C for 10 h in an air atmosphere in a muffle furnace. Press it into tablets, crush it, and sieve it. Take 20-40 mesh particles and reduce them at 550 °C for 2 h in a hydrogen atmosphere to obtain PtIn / Si-H catalyst-impregnation method (Pt mass content is 0.47%).

[0132] Comparative Example 4

[0133] Liu L, Lopez-Haro M, Lopes CW, et al. Regioselective generation and reactivity control of subnanometric platinum clusters in zeolites for high-temperature catalysis[J]. Nature Materials, 2019, 18(8)) Catalyst PtSn@MFI synthesized by hydrothermal synthesis.

[0134] Application Examples 1-7

[0135] The catalysts prepared in Examples 1-7 and Comparative Examples 1-3 were used in a continuous flow fixed-bed microreactor for catalytic dehydrogenation of low-carbon alkanes (propane or ethane). The reaction conditions for each application example are as follows:

[0136] Application Example 1 Reaction conditions: (1) The catalyst prepared in Example 1 was used, with a catalyst loading of 0.3 g, atmospheric pressure, temperature of 550 °C, and propane mass hourly space velocity of 3.6 h⁻¹. -1 The nitrogen:propane volume ratio was 3:1, and the catalytic results were as follows: Figure 1 As shown; (2) The catalyst prepared in Example 1 was used at atmospheric pressure, at a temperature of 580°C, with a catalyst loading of 0.3 g and an ethane mass hourly space velocity of 3.6 h⁻¹. -1 The nitrogen:propane volume ratio was 3:1, and the catalytic results were as follows: Figure 8 As shown; (3) Catalytic stability (catalyst lifetime): The catalyst prepared in Example 1 was used at atmospheric pressure, temperature of 530℃, catalyst loading of 0.3g, and ethane mass hourly space velocity of 3.6h. -1 With a nitrogen:propane volume ratio of 3:1 and a reaction time extended to 200 h, the catalytic results are as follows: Figure 9 As shown; (4) High space velocity: The catalyst prepared in Example 1 was used at atmospheric pressure and a temperature of 530°C. The catalyst loading was 0.03 g, and the mass space velocity of ethane was 100 h⁻¹. -1 The catalytic results are as follows Figure 10 As shown.

[0137] Application Example 2 Reaction Conditions: The catalyst prepared in Example 2 was used, with a catalyst loading of 0.3 g, at atmospheric pressure, a temperature of 450 °C, and a propane mass hourly space velocity of 3.6 h⁻¹. -1 The nitrogen:propane volume ratio was 3:1, and the catalytic results were as follows: Figure 2 As shown.

[0138] Application Example 3: Reaction conditions: The catalyst prepared in Example 3 was used, with a catalyst loading of 0.3 g, at atmospheric pressure, at a temperature of 530 °C, and a propane mass hourly space velocity of 3.6 h⁻¹. -1 The nitrogen:propane volume ratio was 3:1, and the catalytic results were as follows: Figure 3 As shown.

[0139] The reaction conditions for Application Example 4 were as follows: using the catalyst prepared in Example 4, with a catalyst loading of 0.3 g, atmospheric pressure, a temperature of 530 °C, and a propane mass hourly space velocity of 3.6 h⁻¹. -1 The nitrogen:propane volume ratio was 3:1, and the catalytic results were as follows: Figure 4 As shown.

[0140] The reaction conditions for Application Example 5 were as follows: using the catalyst prepared in Example 5, with a catalyst loading of 0.3 g, at atmospheric pressure, at a temperature of 530 °C, and a propane mass hourly space velocity of 3.6 h⁻¹. -1 The nitrogen:propane volume ratio was 3:1, and the catalytic results were as follows: Figure 5 As shown.

[0141] The reaction conditions for Application Example 6 were as follows: using the catalyst prepared in Example 6, with a catalyst loading of 0.3 g, atmospheric pressure, a temperature of 530 °C, and a propane mass hourly space velocity of 3.6 h⁻¹. -1 The nitrogen:propane volume ratio was 3:1, and the catalytic results were as follows: Figure 6 As shown.

[0142] The reaction conditions for Application Example 7 were as follows: using the catalyst prepared in Example 7, with a catalyst loading of 0.3 g, at atmospheric pressure, a temperature of 650 °C, and a propane mass hourly space velocity of 3.6 h⁻¹. -1 The nitrogen:propane volume ratio was 3:1, and the catalytic results were as follows: Figure 7 As shown.

[0143] Comparative Application Examples 1-3

[0144] Comparative application example 1 reaction conditions: using the catalyst prepared in Comparative Example 1, atmospheric pressure, temperature of 530℃, and propane mass hourly space velocity of 3.6 h⁻¹. -1 The volume ratio of nitrogen to propane was 3:1, and the catalytic results were as follows: Figure 11 As shown.

[0145] Comparative application of Example 2 reaction conditions: using the catalyst prepared in Comparative Example 2, atmospheric pressure, temperature of 530℃, and propane mass hourly space velocity of 3.6 h⁻¹. -1 The volume ratio of nitrogen to propane was 3:1, and the catalytic results were as follows: Figure 12 As shown.

[0146] Comparative application of Example 3 reaction conditions: using the catalyst prepared in Comparative Example 3, atmospheric pressure, temperature of 530℃, and propane mass hourly space velocity of 3.6 h⁻¹. -1 The volume ratio of nitrogen to propane was 3:1, and the catalytic results were as follows: Figure 13 As shown.

[0147] Comparative application of Example 4 reaction conditions: using the catalyst prepared in Comparative Example 4, atmospheric pressure, temperature of 530℃, and propane mass hourly space velocity of 3.6 h⁻¹. -1 The volume ratio of nitrogen to propane was 3:1, and the catalytic results were as follows: Figure 14 As shown.

[0148] The reaction products of Application Examples 1-7 and Comparative Application Examples 1-4 were analyzed by Agilent 7890B gas chromatography and Agilent 7890A oil chromatography. The reaction evaluation results are as follows: Figures 1-14As shown in Table 1.

[0149] Table 1 shows the initial reactivity of the catalyst in the propane dehydrogenation reaction in the application examples.

[0150]

[0151]

[0152] From Table 1 and Figures 1-14 It is evident that metal promoters can increase the dispersion of Pt, thereby improving the propane dehydrogenation activity and propylene selectivity. Meanwhile, the catalyst prepared in Example 1 exhibits excellent propane dehydrogenation stability and a long reaction lifetime. In the high-space-velocity propane dehydrogenation reaction, the propane dehydrogenation activity reaches as high as 29%, and the propylene selectivity is 99%. The hollow structure catalyst demonstrates excellent stability and regeneration performance.

[0153] Figure 15 The PtIn@S1-H catalyst prepared in Example 1 was reacted at a temperature of 530°C and a pure propane space velocity of 3.6 h⁻¹. -1 The reaction performance and stability are shown in the figure. As can be seen from the figure, the propane conversion rate is as high as 39%, the propylene selectivity is 97%, and the catalytic activity remains unchanged within 200 h, indicating that the catalyst provided by this invention has excellent catalytic stability.

[0154] Figure 16 The figures show TEM images of the catalysts prepared in Examples 1-7, where a represents Example 1, b represents Example 2, c represents Example 3, d represents Example 4, e represents Example 5, f represents Example 6, and g represents Example 7. As can be seen from the figures, the catalysts prepared in this invention do not have Pt particle aggregation and do not form large PtM (M = In, Sn, La, Ce, Ga, Zn) nanoclusters, indicating that the metal promoter M can increase the dispersion of Pt, thereby improving the propane dehydrogenation activity and propylene selectivity.

[0155] Figure 17 The figure shows the BET adsorption curve of the PtIn@S1-H catalyst prepared in Example 1. As can be seen from the figure, the hollow silicalite-1 molecular sieve has an obvious hysteresis loop, which, together with the TEM image, proves the formation of a hollow molecular sieve.

[0156] In summary, the catalyst provided by this invention can significantly improve the dispersion of active metal Pt, inhibit the sintering and growth of metal particles under high temperature conditions, and enhance the stability of the catalyst.

[0157] 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 hollow structure catalyst, characterized in that, It includes a hollow silicalite-1 molecular sieve and an active component supported on the hollow silicalite-1 molecular sieve; The hollow silicalite-1 molecular sieve has a mesopore size of 2~10 nm and a specific surface area of ​​250~500 m². 2 / g, mesoporous pore volume is 0.20~0.35cm³ 3 / g; The active component is an alloy phase formed by an auxiliary metal and elemental platinum; the auxiliary metal includes one or more of Sn, La, Ga, Ce, In and Zn; the active component is loaded at the cross-cavities of the hollow silicalite-1 molecular sieve. In the hollow structure catalyst, the mass fraction of platinum is 0.05~2%, and the mass fraction of the auxiliary metal element is 0.05~4%. The preparation method of the hollow structure catalyst includes the following steps: An alkaline substance, silicalite-1 molecular sieve, and water are mixed and aged to obtain a mixed alkaline solution. A platinum precursor solution was obtained by mixing a water-soluble platinum source, a first organic amine ligand, and water. A water-soluble auxiliary metal source, a second organic amine ligand, and water are mixed to obtain an auxiliary metal precursor solution. The mixed alkaline solution is mixed with a platinum precursor solution and an auxiliary metal precursor solution, and then subjected to hydrothermal crystallization to obtain a crystallized product. The crystallized product was subjected to calcination and reduction treatments in sequence to obtain a hollow structure catalyst.

2. The method for preparing the hollow structure catalyst according to claim 1, characterized in that, Includes the following steps: An alkaline substance, silicalite-1 molecular sieve, and water are mixed and aged to obtain a mixed alkaline solution. A platinum precursor solution was obtained by mixing a water-soluble platinum source, a first organic amine ligand, and water. A water-soluble auxiliary metal source, a second organic amine ligand, and water are mixed to obtain an auxiliary metal precursor solution. The mixed alkaline solution is mixed with a platinum precursor solution and an auxiliary metal precursor solution, and then subjected to hydrothermal crystallization to obtain a crystallized product. The crystallized product was subjected to calcination and reduction treatments in sequence to obtain a hollow structure catalyst.

3. The preparation method according to claim 2, characterized in that, The alkaline substances include inorganic substances and organic bases; The inorganic substances include one or more of alkali metal hydroxides, alkali metal nitrates and alkali metal carbonates; The organic base includes one or more of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium hydroxide, and tetrabutylammonium hydroxide; The aging time is 5~240 minutes.

4. The preparation method according to claim 2, characterized in that, The first organic amine ligand and the second organic amine ligand independently include one or more of ethylamine, ethylenediamine, butylamine, cyclohexylamine, cycloheximine, hexamethylenediamine, cyclohexanediamine, and diamine; The molar ratio of platinum to the first organic amine ligand in the water-soluble platinum source is 1:20~400; The molar ratio of the auxiliary metal and the second organic amine ligand in the water-soluble auxiliary metal source is 1:20~400; The molar ratio of the auxiliary metal in the water-soluble auxiliary metal source to the platinum in the water-soluble platinum source is ≤10. The hydrothermal crystallization temperature is 120~200℃, and the time is 12~96h.

5. The preparation method according to claim 2, characterized in that, The calcination temperature is 350~600℃, the holding time is 3~12h, and the calcination atmosphere is air, hydrogen or nitrogen. The reduction treatment is carried out at a temperature of 150~700℃ for 1~5 hours, and the reducing agent used includes carbon monoxide or hydrogen.

6. The application of the hollow structure catalyst according to claim 1 or the hollow structure catalyst prepared by any one of claims 2 to 5 in the dehydrogenation of low-carbon alkanes.

7. A method for preparing low-carbon olefins by dehydrogenation of low-carbon alkanes, characterized in that, Includes the following steps: The dehydrogenation reaction is carried out in the presence of a catalyst to obtain low-carbon olefins. The catalyst is the hollow structure catalyst according to claim 1 or the hollow structure catalyst prepared by any one of claims 2 to 5; The reaction atmosphere includes low-carbon alkanes and an auxiliary atmosphere, wherein the auxiliary atmosphere includes one or more of nitrogen, hydrogen and carbon dioxide; the molar ratio of the auxiliary atmosphere to the low-carbon alkanes is 0 to 10:

1. The dehydrogenation reaction temperature is 450~650℃, and the mass hourly space velocity (WHSV) of the low-carbon alkanes is 1~200 h⁻¹. -1 .

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