Preparation method and application of a propane dehydrogenation catalyst with carbon nanotube-wrapped iron and iron carbide mixture structure

Abstract

The application belongs to the technical field of low carbon alkane dehydrogenation, and particularly relates to a preparation method of a propane dehydrogenation catalyst with a structure of a carbon nanotube-wrapped iron and iron carbide mixture. The method comprises the following steps: dissolving ferrocene and thiophene in ethanol together, performing ultrasonic dispersion at normal temperature, and transferring the mixed solution to a syringe after the ferrocene is completely dissolved in the ethanol solution. Argon is introduced into a tube furnace, the syringe is placed on a sample injector, and the syringe is injected into the tube furnace at a slow injection rate. After the reaction is completed, the catalyst on the wall of the tube furnace is scraped off, and the Fe@C catalyst is prepared.

Description

Technical Field

[0001] This invention relates to a catalyst for the dehydrogenation reaction of low-carbon alkanes and its preparation method. Specifically, it relates to a dehydrogenation catalyst with a multi-walled carbon nanotube-encapsulated iron carbide structure, its preparation method, and its application. Background Technology

[0002] Propylene is one of the most important industrial raw materials for the production of chemical products such as polypropylene, acrylic acid, isopropanol, acrylonitrile, and propylene oxide. It is mainly derived from steam cracking and catalytic cracking processes, but these two processes are far from meeting the demand for propylene. The shale gas revolution, with its abundant propane resources, has provided an effective propane dehydrogenation (PDH) method for propylene production.

[0003] For the direct propane dehydrogenation process, Pt-based catalysts remain a key research focus. Supported Pt-based catalysts exhibit excellent CH bond activation performance and are considered ideal PDH catalysts for this process. Over the past few decades, a wide variety of heterogeneous catalysts have emerged, including metal-based catalysts, metal oxide-based catalysts, and non-oxide-based catalysts (such as Pt, CrO₂). x VO x GaO x Platinum (Pt), ZrO2, carbides, and nitrides, among others, exhibit high performance due to their affinity for carbon-hydrogen bonds and low activity in carbon-carbon bond cleavage, and have been developed for direct PDH reactions. However, most propane dehydrogenation research has focused on Pt-based and Cr-based catalysts. The high cost of platinum and the toxicity of chromium severely limit their further application; worse still, they all rapidly deactivate due to carbon deposition.

[0004] To improve the catalytic activity and lifespan of catalysts, extensive research has been conducted on suppressing the aggregation of active metals, regulating the distribution of active components, optimizing electronic effects, and optimizing support structures. In addition, various non-noble metal-based dehydrogenation catalysts (such as Zn, V, Ga, Fe, Co, Ru, and Zr) have been developed, exhibiting excellent performance and serving as ideal alternatives to Pt-based catalysts; however, many practical problems still exist.

[0005] Currently, the research focus in the field of PDH catalysts remains on developing highly stable and active Pt-based catalysts. However, the Pt-Pt ensemble can trigger undesirable side reactions (cracking and deep dehydrogenation), leading to poor activity and stability. Abundant metal carbides have attracted widespread attention as alternative non-noble metal catalysts. Studies have found that metal carbides can effectively improve heterogeneous catalytic processes. Summary of the Invention

[0006] The purpose of this invention is to provide a simple method for preparing a high-conversion catalyst. The catalyst consists of a mixture of iron and iron carbide encapsulated in multi-walled carbon nanotubes. Ferrocene, ethanol, and a small amount of thiophene are used in a programmed temperature rise and high-temperature calcination process. This causes the ethanol to decompose into carbon nanotubes with a small number of defect sites, and a small amount of ferrocene, as a precursor to iron and iron carbide, is retained in the carbon nanotubes. The resulting catalyst maintains a stable propane dehydrogenation conversion rate at high temperatures and can be repeatedly recycled.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A propane dehydrogenation catalyst with a structure of iron and iron carbide encapsulated in carbon nanotubes is prepared by the following steps:

[0009] 1) Weigh out appropriate amounts of carbon source, iron source and additives, and dissolve them by sonication to completely mix the three substances together. Place the resulting mixture into an injection syringe.

[0010] 2) Using the mixture as a precursor, it is injected into a tube furnace filled with inert gas at a slow injection rate for high-temperature pyrolysis. After pyrolysis, it is allowed to stand at room temperature to obtain the catalyst containing iron and iron carbide encapsulated by multi-walled carbon nanotubes.

[0011] Furthermore, the mass ratio of carbon source, iron source and additives used in step 1) is 1000:10:1.

[0012] Further, in step 1), the carbon source is ethanol, the iron source is ferrocene, and the auxiliary is thiophene.

[0013] Furthermore, the ultrasonic dissolution time in step 1) is 10–15 min.

[0014] Furthermore, the syringe mentioned in step 1) is 20 mL.

[0015] Furthermore, the slow injection rate described in step 2) is 0.2 mL / min.

[0016] Furthermore, the high-temperature pyrolysis temperature mentioned in step 2) is 1000℃, the heating rate is 10℃ / min, and the tubular furnace should be heated to 1000℃ before injection; the high-temperature pyrolysis time is 1h.

[0017] Furthermore, the inert gas in the tube furnace filled with inert gas mentioned in step 2) is argon.

[0018] Furthermore, the inert gas flow rate in the tubular furnace described in step 2) should be 10 mL / min.

[0019] The catalysts obtained above, which contain carbon defect sites and encapsulate iron and iron carbide in carbon nanotubes, can be used for dehydrogenation to prepare unsaturated hydrocarbons such as propylene, butene, or pentene. The dehydrogenation reaction temperature is 500–700 °C, the pressure is 1.1–1.2 MPa, and the reaction time is 0–20 h.

[0020] The significant advantages of this invention are:

[0021] This invention utilizes a simple preparation method to fabricate multi-walled carbon nanotubes containing defect sites, ensuring that iron particles are smoothly and uniformly encapsulated within the carbon nanotubes. Even after three cycles, the catalyst maintains excellent propane conversion. This differs from traditional precious metal catalysts, which rely on expensive raw materials. The raw materials used in this invention are readily available and inexpensive, reducing the use of precious metals. This saves on catalyst production costs and offers greater industrial application value. Attached Figure Description

[0022] Figure 1 This is a SEM image of the Fe@C catalyst obtained in Example 1.

[0023] Figure 2 This is a TEM image of the Fe@C catalyst obtained in Example 1.

[0024] Figure 3 This is a particle size distribution diagram of the Fe@C catalyst obtained in Example 1.

[0025] Figure 4 The image shows the Raman diagram of the catalyst obtained in Example 1.

[0026] Figure 5 The image shows the Raman plot of the catalyst obtained in Comparative Example 1. Detailed Implementation

[0027] A method for preparing a propane dehydrogenation catalyst with a structure of carbon nanotube-encapsulated iron and iron carbide mixture includes the following steps:

[0028] 1) Dissolve ferrocene and thiophene together in ethanol, and then ultrasonically disperse them at room temperature until the ferrocene is completely dissolved in the ethanol solution. Transfer the mixture to an injection container. Before injection, preheat the tubular furnace to 1000°C at a heating rate of 10°C / min, and purge the furnace with argon gas at a rate of 10 mL / min.

[0029] 2) Place the syringe on the injector and slowly inject the sample into the tube furnace at an injection rate of 0.2 mL / min. After injection, maintain the temperature at 1000℃ for 1 hour. After the reaction is complete, allow it to stand at room temperature, scrape off the catalyst from the tube furnace wall, and obtain the Fe@C catalyst.

[0030] In step 1), the mass ratio of ethanol, ferrocene, and thiophene is 1000:10:1.

[0031] To make the content of this invention easier to understand, the technical solution of this invention will be further described below in conjunction with specific embodiments, but this invention is not limited thereto.

[0032] Example 1

[0033] (1) Add 0.1g of ferrocene and 0.01g of thiophene to 10g of ethanol solution, then sonicate for 10 minutes until the ferrocene and thiophene are completely dissolved in the ethanol solution. Pour the mixture into a 20mL syringe for later use. Then turn on the argon gas at a flow rate of 10mL / min and continue to purge the argon gas for 30min. After that, program the temperature of the tube furnace to 1000℃ at a heating rate of 10℃ / min.

[0034] (2) Place the spare syringe into the syringe and slowly inject it into the tube furnace at an injection rate of 0.2 mL / min. After the mixture in the syringe is injected, maintain the temperature of the tube furnace at 1000℃ for 1 hour to carry out the pyrolysis reaction. After the reaction is completed in 1 hour, let it stand and wait for the tube furnace to cool to room temperature. Scrape off the catalyst on the tube wall to obtain Fe@C.

[0035] Comparative Example 1

[0036] Weigh 0.1 g of multi-walled carbon nanotubes to obtain a comparative catalyst.

[0037] Application Example 1

[0038] Evaluation of the propane dehydrogenation performance of the catalyst: 0.1 g of the obtained Fe@C catalyst was loaded into a microreactor. A mixture of propane and N2 with a propane volume fraction of 5% was used as the reactant, with a total flow rate of 60 mL / min. The reaction was carried out at 600 °C, 1 MPa, and a propane feed mass hourly space velocity of 1.8 h⁻¹. -1 The dehydrogenation reaction was carried out under the specified conditions. The catalyst used in the examples and the results after 10 hours of reaction are shown in Table 1.

[0039] Application Example 2

[0040] 0.1 g of the Fe@C catalyst reacted in Example 1 was loaded into a microreactor. A mixture of propane (5% propane by volume) and N2 was used as the reactants, with a total flow rate of 60 mL / min. The reaction was carried out at 600 °C, 1 MPa, and a propane feed mass hourly space velocity of 1.8 h⁻¹. -1 The dehydrogenation reaction was carried out under the specified conditions. The catalyst used in the examples and the results after 10 hours of reaction are shown in Table 2.

[0041] Application Example 3

[0042] 0.1 g of the Fe@C catalyst reacted in Example 2 was loaded into a microreactor. A mixture of propane (5% propane by volume) and N2 was used as the reactants, with a total flow rate of 60 mL / min. The reaction was carried out at 600 °C, 1 MPa, and a propane feed mass hourly space velocity of 1.8 h⁻¹. -1 The dehydrogenation reaction was carried out under the specified conditions. The catalyst used in the examples and the results after 10 hours of reaction are shown in Table 3.

[0043] Application Example 4

[0044] 0.1 g of the catalyst from Comparative Example 1 was loaded into a microreactor. A mixture of propane (5% propane by volume) and N2 was used as the reactants. The total flow rate was 60 mL / min, and the reaction was carried out at 600 °C, 1 MPa, and a propane feed mass hourly space velocity of 1.8 h⁻¹. -1 The dehydrogenation reaction was carried out under the specified conditions, and the results after 10 hours are shown in Table 4. Table 4 shows that the propane dehydrogenation propane conversion rate was worse compared to that of the CNT catalyst.

[0045] Table 1 Catalytic data of Fe@C dehydrogenation reaction after 10 h.

[0046]

[0047] Table 2 Catalytic data for the dehydrogenation reaction of the catalyst used in Application Example 2 after 10 h.

[0048]

[0049] Table 3. Catalytic data for the dehydrogenation reaction of the catalyst used in Application Example 3 after 10 hours.

[0050]

[0051]

[0052] Table 4 Catalytic data for the dehydrogenation reaction of the catalyst in Application Example 4 after 10 h.

[0053]

[0054] Comparing the catalytic performance of the catalysts obtained in Example 1 and Comparative Example 1 for propane dehydrogenation reveals that the Fe@C catalyst exhibits excellent stability within 10 hours of reaction, with its conversion rate stabilizing at around 20%. In contrast, simple multi-walled carbon nanotubes show almost no activity in the 10-hour propane dehydrogenation reaction. The catalyst in Example 1 demonstrates superior activity and stability compared to the catalyst in Comparative Example 1. Furthermore, repeated use of the catalyst in Example 1 shows that its activity remains highly stable during the reaction, and even after the third reaction, the propane conversion rate still reaches approximately 6%.

[0055] Figure 1This is a SEM image of the Fe@C catalyst obtained in Example 1. The image shows that the carbon nanotubes are randomly dispersed around the edges.

[0056] Figure 2 , Figure 3 The images show the TEM image and particle size distribution of the Fe@C catalyst obtained in Example 1. As can be seen from the images, the Fe particles are uniformly dispersed within the multi-walled carbon nanotubes, and the particle size distribution indicates that the Fe particle size is in the range of 2-8 nm.

[0057] Figure 4 The image shows the Raman diagram of the catalyst obtained in Example 1. Figure 5 The Raman plot of the catalyst obtained in Comparative Example 1 shows that the I of Fe@C D / I G The value is the highest, at 1.14, which indicates that Fe@C has the highest carbon defect content, which is the reason why the catalyst has a stable conversion rate and stable activity.

[0058] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. The application of a propane dehydrogenation catalyst with a structure of carbon nanotube-encapsulated iron and iron carbide mixture in the propane dehydrogenation to propylene, characterized in that: The catalyst is prepared by weighing a carbon source, an iron source, and an additive, performing ultrasonic dissolution, and using the resulting mixture as a precursor. This mixture is then injected into a tube furnace for high-temperature pyrolysis to obtain a catalyst containing carbon nanotubes encapsulating iron and iron carbide. The mass ratio of the carbon source, iron source, and additive is 1000:10:

1. The carbon source is ethanol, the iron source is ferrocene, and the additive is thiophene. The high-temperature pyrolysis temperature is 1000℃, the heating rate is 10℃ / min, the tube furnace should be heated to 1000℃ before injection, and the high-temperature pyrolysis time is 1 hour. The catalyst has an I content of... D / I G It is 1.

14.

2. The application according to claim 1, characterized in that: The ultrasonic dissolution time is 10-15 minutes.

3. The application according to claim 1, characterized in that: The injection rate is 0.2 mL / min.

4. The application according to claim 1, characterized in that: The tubular furnace is filled with inert gas; the inert gas flow rate is 10 mL / min.

Images