Pure silicon molecular sieve confined Pt-based bimetallic catalyst for preparing propylene through propane dehydrogenation

Abstract

The invention provides an all-silicon molecular sieve confined Pt-based bimetallic catalyst and application thereof in preparation of propylene through propane dehydrogenation. The preparation method comprises the following steps: mixing a silicon source, a template agent, a Pt precursor, an auxiliary element Cu precursor and the like by adopting an in-situ synthesis method, synthesizing under a hydrothermal condition, washing, drying, roasting and reducing to obtain the Pt-based bimetallic molecular sieve catalyst. According to the present invention, the pure silicon molecular sieve Silicalite-1 (S-1) is adopted as the carrier, such that the good carrier characteristics of high thermal stability, low acidity, rich pore structure and the like are provided, and the silicon hydroxyl group (Si-OH) in the S-1 pore channel can further provide the metal species anchoring effect so as to easily disperse and limit the active site; and the Cu auxiliary agent improves the metallicity of Pt. The synergy of the two significantly improves the performance of propylene preparation by direct dehydrogenation of propane. The synthesized PtCu-coated S-1 catalyst is low in Pt loading capacity, Pt and Cu are highly dispersed, side reactions such as deep dehydrogenation of propylene can be inhibited, and good stability is achieved.

Description

Technical Field

[0001] This invention belongs to the field of propane dehydrogenation to propylene catalyst technology, specifically relating to a Pt-based bimetallic catalyst confined in a pure silicon molecular sieve for propane dehydrogenation to propylene. Background Technology

[0002] Light olefins such as ethylene and propylene are important raw materials in the chemical industry and have significant applications in chemical manufacturing, including the synthesis of polymers such as polyethylene and polypropylene, as well as oxygen-containing compounds such as ethylene glycol, ethylene oxide, and propylene oxide. Propylene, in particular, is used to prepare the polymer polypropylene (PP), and other polymer-related precursors such as acrylic acid and propylene oxide. The downstream applications of propylene are extensive, and its consumption is expected to continue to expand globally.

[0003] Traditional propylene production processes include steam cracking, fluid catalytic cracking (FCC), and coal-to-olefins. Among these, FCC is widely used in refineries to produce light olefins, such as propylene, from heavy petroleum fractions. While FCC offers advantages such as inexpensive feedstocks and a wide variety of products, it also has limitations, including low selectivity and yield of propylene, high separation costs and energy consumption, and a shortage of petroleum feedstocks. Shale gas is a clean energy source, primarily composed of short-chain alkanes such as propane and butane. Compared to conventional fossil resources like oil and natural gas, it boasts advantages such as a long exploitation life and abundant reserves. In recent years, shale gas extraction technology has made significant progress, resulting in more efficient extraction and lower shale gas prices. Furthermore, the direct dehydrogenation of propane to propylene under anaerobic conditions offers advantages such as a simple process, high economic efficiency, and the production of hydrogen as a byproduct, making it highly valuable. Therefore, developing more efficient direct alkane dehydrogenation technology using more economical shale gas as feedstock has become an urgent problem for the chemical industry.

[0004] Pt metal has a high affinity for CH bonds, making it an excellent catalyst for propane dehydrogenation and the most widely used catalyst in industrial propane dehydrogenation reactions. However, the direct propane dehydrogenation process is a strongly endothermic reaction, and the conversion rate is difficult to improve due to thermodynamic equilibrium limitations, often requiring relatively high temperatures (500-650℃). Excessive temperatures exacerbate the breaking of C-C bonds, producing coke deposits or other low-carbon side products, leading to reduced propylene selectivity. Furthermore, metal particles are prone to Ostwald ripening at high temperatures, and metal sintering causes rapid catalyst deactivation, necessitating frequent catalyst regeneration, thus incurring additional energy consumption and costs.

[0005] To achieve high selectivity for propylene in propane dehydrogenation, a second component is introduced to modify Pt to suppress undesirable C-C bond dissociation, such as adding promoters like Sn, Zn, and Fe. Studies have shown that PtCu single-atom alloy catalysts have a unique effect in lowering the CH bond energy barrier during activation; therefore, we chose Cu as the second metal promoter to improve the catalytic activity of Pt. Furthermore, we selected pure silica molecular sieve Silicalite-1 (S-1) as the support, which possesses excellent support properties such as high thermal stability, low acidity, and abundant pore structure, exhibiting significant advantages in propane dehydrogenation. Moreover, the silanol groups (Si-OH) within the S-1 channels can also act as anchors for metal species. This invention selects a Pt-based bimetallic catalyst for propane dehydrogenation to propylene synthesized in situ. Using a molecular sieve as a support, the active metal is dispersed through its pore and framework structure, resulting in a molecular sieve-confined catalyst, PtCu@S-1, with extremely low Pt loading. The synthesized PtCu@S-1 catalyst has highly dispersed Pt and Cu, exhibiting high activity and stability; while the co-impregnated PtCu / S-1 catalyst shows obvious particle aggregation and very low activity. Summary of the Invention

[0006] The purpose of this invention is to address the poor stability and easy sintering and deactivation of Pt-based catalysts by providing a Pt-Cu bimetallic molecular sieve confined catalyst for propane dehydrogenation to propylene. By utilizing the channels and framework of S-1 to confine Pt and Cu, the Pt loading is reduced, providing a new approach for the industrial development of low-cost Pt-based industrial catalysts.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] The Pt-based bimetallic catalyst confined in a pure silica molecular sieve for propane dehydrogenation to propylene, designated PtCu@S-1, is prepared by in-situ synthesis, with the following steps:

[0009] (1) Pt source and Cu source were added dropwise to ultrapure water at a certain temperature, and then a certain proportion of ethylenediamine was added. The mixture was stirred in a container for 1-5 hours to obtain two precursor solutions.

[0010] (2) Mix the two precursor solutions mentioned above and add them to an aqueous solution containing a certain proportion of silicon source and template agent, and stir for 2-6 hours.

[0011] (3) Add isopropanol (IPA) dropwise to the solution obtained in step (2) at a certain molar ratio and stir for 1-2 hours;

[0012] (4) Transfer the solution to a hydrothermal reactor and crystallize it at a certain temperature for 3 days;

[0013] (5) The solid obtained in step (4) is separated by centrifugation, washed with ultrapure water and centrifuged four times. The solid is then transferred to an oven to dry and finally calcined in air at a certain heating rate. After reduction, the target product is obtained.

[0014] Further, in step (1), the Pt source is chloroplatinic acid hexahydrate or platinum nitrate, and the Cu source is copper sulfate pentahydrate, copper nitrate, copper acetate, copper oxalate, or copper chloride. The molar ratio of the metal to ethylenediamine is 1:4-52.8. In step (2), the silicon source is tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TEOS), and the template agent is tetrapropylammonium hydroxide (TPAOH). The molar ratio is 1.0TEOS:0.4-1.0TPAOH:5.0-10H2O. In step (3), the molar ratio is 1SiO2:4IPA. In step (4), the crystallization temperature is 160-180℃. In step (5), the centrifugation speed is 9000 r / min, the drying temperature is 60℃, and the drying time is 12 hours; the heating rate is 1° / min, and the calcination is carried out at 600℃ for 4 hours; the reducing gas is hydrogen and helium, the volume flow rate ratio is 1:3, and the total volume flow rate is 15 mL / min.

[0015] The above-mentioned application of the all-silica molecular sieve-confined Pt-based bimetallic catalyst for propane dehydrogenation to propylene: The propane dehydrogenation to propylene reaction is carried out in a fixed bed at a reaction temperature of 600°C. The reaction gas (propane / H2 / Ar = 1 / 1 / 3) is introduced into a reactor containing the all-silica molecular sieve-confined Pt-based bimetallic catalyst for propane dehydrogenation to propylene.

[0016] Compared with the prior art, the beneficial results achieved by the technical solution of this invention are:

[0017] 1. This invention uses an in-situ synthesis method to confine Pt and Cu within the pores of a molecular sieve. After 50 hours of reaction, no large particles formed by sintering were observed, demonstrating good metal dispersion and resistance to sintering.

[0018] 2. The PtCu@S-1 catalyst synthesized by this method has high reactivity and still maintains good reactivity at high space velocities;

[0019] 3. The PtCu@S-1 catalyst synthesized by this method can achieve a propylene yield of 471.8 mol C3H8·g after 50 h of reaction. -1 ·h -1 It has the highest propylene formation rate among Pt-based catalysts, and the deactivation rate is only 0.006 h⁻¹. -1 In contrast, the PtCu / S-1 catalyst prepared by the impregnation method showed a continuous decrease in reaction activity under the same conditions.

[0020] 4. This method introduces Cu element in situ, forming metallic Cu within the molecular sieve framework. 0 The species can transfer electrons to Pt to promote the desorption of the product propylene, inhibit the deep dehydrogenation reaction, and improve the catalyst activity, selectivity and stability; in addition, the molecular sieve cage stabilizes the Pt introduced in situ by hydrothermal treatment, which greatly inhibits the occurrence of sintering and also improves the stability of the catalyst. Attached Figure Description Figure 1 This is a schematic diagram of the stability experiment of the PtCu@S-1 catalyst at different space velocities in Example 1 of this invention. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1

[0023] A) Weigh a certain amount of chloroplatinic acid hexahydrate and prepare a 3.8% solution by elemental mass fraction; weigh a certain amount of copper sulfate pentahydrate and prepare a 5% solution by elemental mass fraction; weigh 0.0263g of 3.8% Pt solution and dissolve it in 0.016g of ethylenediamine and 10mL of ultrapure water at a Pt:EDA molar ratio of 1:52.8; weigh 0.0800g of 5% Cu solution and dissolve it in 0.197g of ethylenediamine and 10mL of ultrapure water at a Cu:EDA molar ratio of 1:52.8. Control the stirring temperature at 15℃ and stir for 1h.

[0024] B) Weigh 3.47g of tetraethyl orthosilicate, 5.423g of tetrapropylammonium hydroxide solution (25wt%) and 1.5g of ultrapure water, mix them in a beaker and add the two solutions mentioned above and stir for 3h;

[0025] C) Weigh 4.00 g of isopropanol and add it to the above solution, then stir for 1 hour;

[0026] D) Transfer the above clarified liquid to a 100mL stainless steel crystallization vessel and let it stand in a 170℃ oven for 3 days to crystallize.

[0027] E) Wash and centrifuge the solid obtained in the previous step with ultrapure water four times. At this time, the liquid changes from alkaline to neutral. Then, transfer the solid to a 60°C oven and dry it for 12 hours. Then, calcine it in air at 600°C for 4 hours at a heating rate of 1° / min to obtain the target catalyst product, which is denoted as 0.1Pt0.4Cu@S-1 based on the elemental mass fraction as the nominal loading.

[0028] F) The catalyst needs to be reduced before the reaction. The reducing gas is hydrogen and helium with a volume flow ratio of 1:3 and a total volume flow rate of 15 mL / min.

[0029] Example 2

[0030] The only difference from Example 1 is that the Pt precursor is platinum nitrate, and the ratio of Pt to ethylenediamine is Pt:EDA = 1:2.

[0031] Example 3

[0032] The only difference from Example 1 is that the Pt precursor is platinum nitrate, and the ratio of Pt to ethylenediamine is Pt:EDA = 1:52.8.

[0033] Example 4

[0034] The only difference from Example 1 is that the catalyst is 0.02Pt0.4Cu@S-1.

[0035] Example 5

[0036] The only difference from Example 1 is that the catalyst is 0.2Pt0.4Cu@S-1.

[0037] Example 6

[0038] The only difference from Example 1 is that the catalyst is 0.1Pt0.1Cu@S-1.

[0039] Example 7

[0040] The only difference from Example 1 is that the catalyst is 0.1Pt0.8Cu@S-1.

[0041] Example 8

[0042] The only difference from Example 1 is that the Cu precursor is copper nitrate, and the ratio of Cu to ethylenediamine is Cu:EDA = 1:2.

[0043] Example 9

[0044] The only difference from Example 1 is that the Cu precursor is copper acetate, and the ratio of Cu to ethylenediamine is Cu:EDA = 1:52.8.

[0045] Example 10

[0046] The only difference from Example 1 is that the Cu precursor is copper oxalate, and the ratio of Cu to ethylenediamine is Cu:EDA = 1:25.

[0047] Example 11

[0048] The only difference from Example 1 is that the Cu precursor is copper chloride.

[0049] Example 12

[0050] The only difference from Example 1 is that the amount of water added in step B) is 2.0g, and the stirring time is 1h.

[0051] Example 13

[0052] The only difference from Example 1 is that the amount of water added in step B) is 3.0g, and the stirring time is 5h.

[0053] Example 14

[0054] The only difference from Example 1 is that the amount of template agent solution added in step B) is 8.135g.

[0055] Example 15

[0056] The only difference from Example 1 is that the amount of template agent solution added in step B) is 13.558g.

[0057] Example 16

[0058] The only difference from Example 1 is that the stirring temperature in step A) is 10°C and the stirring time is 5 hours.

[0059] Example 17

[0060] The only difference from Example 1 is that the stirring temperature in step A) is 20°C and the stirring time is 1 hour.

[0061] Example 18

[0062] The only difference from Example 1 is that the crystallization temperature in step D) is 160°C and the crystallization time is 4 days.

[0063] Example 19

[0064] The only difference from Example 1 is that the crystallization temperature in step D) is 180°C.

[0065] Example 20

[0066] The only difference from Example 1 is that the calcination temperature in step E) is 500°C.

[0067] Example 21

[0068] The only difference from Example 1 is that the calcination temperature in step E) is 700°C.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that 0.0263 g of chloroplatinic acid hexahydrate solution (with a Pt mass fraction of 3.8%) and 0.0800 g of copper sulfate pentahydrate solution (with a Cu mass fraction of 5%) were added dropwise to the prepared S-1 molecular sieve. After continuous stirring, the mixture was ultrasonicated for 30 minutes and dried at 60°C for 12 hours. Finally, the catalyst was calcined at 600°C for 4 hours to obtain 0.1Pt0.4Cu / S-1 synthesized by the impregnation method.

[0071] Comparative Example 2

[0072] The difference from Example 1 is that no Cu solution or other corresponding solutions were added during catalyst preparation, and the resulting catalyst was 0.1Pt@S-1.

[0073] Comparative Example 3

[0074] The difference from Example 1 is that, in step A), no Pt solution or other corresponding solutions are added. After calcination, 0.0263 g of chloroplatinic acid hexahydrate solution (with a Pt mass fraction of 3.8%) is added dropwise to the prepared Cu@S-1 molecular sieve. After continuous stirring, the mixture is ultrasonicated for 30 minutes and dried at 60°C for 12 hours. Finally, the catalyst is calcined at 600°C for 4 hours to obtain 0.1Pt / 0.4Cu@S-1 synthesized by the impregnation method.

[0075] Propane dehydrogenation reaction performance test:

[0076] Propane dehydrogenation was carried out in a fixed-bed reactor using a quartz tube. Before each experiment, 0.100 g of sieved 40-60 mesh catalyst was placed in a quartz tube, fixed with quartz wool, and heated to 600 °C at a rate of 10 °C / min. Simultaneously, a mixed gas (Ar: 15 mL / min, H2: 5 mL / min) was blown in at a rate of 20 mL / min and maintained for 1 hour to allow for complete reduction. Then, C3H8 was introduced at a rate of 5 mL / min for propane dehydrogenation (propane / H2 / Ar = 1 / 1 / 3). The gases were uniformly mixed in a mixing tank before entering the reactor. The gaseous products were analyzed using an online gas chromatograph (GC2060) and a flame ionization detector (FID).

[0077] Table 1: Results of catalysts in each example after reaction at 600°C for 8 hours (space velocity 5h) -1 )as follows:

[0078] catalyst Propane conversion rate / % Propylene selectivity / % Example 1 54.5 97.2 Example 2 50.2 97.1 Example 3 48.0 97.3 Example 4 34.2 97.0 Example 5 43.4 95.4 Example 6 33.1 98.5 Example 7 35.6 98.2 Example 8 50.2 97.2 Example 9 49.9 97.4 Example 10 46.3 96.8 Example 11 48.7 95.7 Example 12 46.8 96.5 Example 13 50.9 96.2 Example 14 49.8 95.3 Example 15 49.2 96.6 Example 16 45.7 96.0 Example 17 50.5 96.9 Example 18 51.6 95.7 Example 19 50.1 94.4 Example 20 46.3 95.2 Example 21 32.9 93.1

[0079] Table 2: Results of each comparative catalyst after reaction at 600℃ for 8 hours (space velocity 5h) -1 )as follows:

[0080]

[0081]

[0082] The reaction performance of each catalyst shows that PtCu@S-1 exhibits the best activity for propane dehydrogenation, maintaining a propylene selectivity of 99% even after 8 hours of reaction. Meanwhile, compared to Pt@S-1, the introduction of Cu improved the propylene selectivity of other Pt catalysts synthesized by impregnation and in-situ methods.

[0083] The above embodiments provide a detailed description of the present invention, but they are merely examples and are not intended to limit the scope of the patent. Any equivalent modifications and substitutions made to the present invention based on this specification are also within the scope of the present invention and are included within the patent protection scope of the present invention.

Claims

1. A Pt-based bimetallic catalyst confined within an all-silica molecular sieve for the dehydrogenation of propane to propylene, the catalyst exhibiting high space-time yield and stability at extremely low Pt loadings, characterized in that: The catalyst is designated as PtCu@S-1, with Pt as the active component, Cu as the first promoter, and S-1 (Silicalite-1) as the support; wherein the mass percentage of the active component Pt is 0.02-0.20%, the mass percentage of the first promoter Cu is 0.10-0.80%, and the remainder is all-silica molecular sieve Silicalite-1. The catalyst was prepared using an in-situ hydrothermal method, and the steps are as follows: (1) Add Pt precursor and Cu precursor to deionized water and a certain proportion of ethylenediamine respectively, and stir and mix them at a certain temperature. (2) Mix and stir the silicon source, template agent and deionized water at a certain temperature; (3) Mix the solution in step (1) with the solution in step (2) and stir for a certain period of time; (4) Add isopropanol to the homogeneous liquid from step (3) and stir continuously; (5) Transfer the liquid obtained in step (4) to a stainless steel high-pressure hydrothermal crystallization kettle and let it stand in an oven at a certain temperature to crystallize. (6) The product obtained in step (5) is washed with deionized water, centrifuged, dried, calcined and reduced to obtain a Pt-based bimetallic catalyst for propane dehydrogenation to propylene. The silicon source is tetraethyl orthosilicate or tetramethyl orthosilicate, the template agent is tetrapropyl ammonium hydroxide, the Pt precursor is chloroplatinic acid hexahydrate or platinum nitrate, and the Cu precursor is copper sulfate hexahydrate, copper nitrate, copper acetate, copper oxalate, or copper chloride.

2. The Pt-based bimetallic catalyst confined within an all-silica molecular sieve for propane dehydrogenation to propylene according to claim 1, characterized in that: In step (1), the molar ratio of metal ions to ethylenediamine is 1M:2-52.8EDA, where M is Cu or Pt; in step (2), the molar ratio of silicon source, template agent and ultrapure water is 1.0:0.4-1:5.0-10; in step (4), the molar ratio of added isopropanol (IPA) is 1SiO2:4IPA.

3. The Pt-based bimetallic catalyst confined within an all-silica molecular sieve for propane dehydrogenation to propylene according to claim 1, characterized in that: In step (1), the stirring temperature is controlled at 10-25℃ and the stirring time is 1-5 hours; in step (3), the stirring time after mixing the solution is 2-6 hours; in step (4), the stirring time after adding isopropanol is 1-2 hours.

4. The Pt-based bimetallic catalyst confined within an all-silica molecular sieve for propane dehydrogenation to propylene according to claim 1, characterized in that: The crystallization temperature in step (5) is 160℃-180℃, and the time is 2-4 days.

5. The Pt-based bimetallic catalyst confined within an all-silica molecular sieve for propane dehydrogenation to propylene according to claim 1, characterized in that: The drying temperature in step (6) is 60℃, and the calcination temperature is 500-700℃.

6. The Pt-based bimetallic catalyst confined within an all-silica molecular sieve for propane dehydrogenation to propylene according to claim 1, characterized in that: The gases used in the reduction reaction in step (6) are hydrogen and argon, with a volume flow ratio of 1:3 between hydrogen and argon.

7. The application of the Pt-based bimetallic catalyst confined within an all-silica molecular sieve according to claim 1 for the dehydrogenation of propane to propylene, characterized in that: The propane dehydrogenation to propylene reaction is carried out in a fixed bed at a reaction temperature of 600°C. The reaction gas (propane / H2 / Ar = 1 / 1 / 3) is introduced into a reactor containing a Pt-based bimetallic catalyst confined within an all-silica molecular sieve for propane dehydrogenation to propylene.

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