Preparation method of methane dry reforming catalyst and application thereof

Abstract

The application belongs to the chemical field and provides a preparation method of a catalyst for methane dry reforming; a 3D-Ti-Ce-O carrier is prepared, and Ni, Fe and Nb active metals are loaded on the 3D-Ti-Ce-O carrier to obtain a Ni-Fe-Nb / 3D-Ti-Ce-O catalyst. The application also simultaneously provides a methane dry reforming reaction; CH4 and CO2 are mixed according to a volume ratio of 1:1 and input into the inner cavity of a quartz tube as raw gas from a gas outlet, and then the raw gas is contacted with the catalyst and reacts under the action of plasma discharge to generate CO and H2. The Ni-Fe-Nb / 3D-Ti-Ce-O catalyst provided by the application has high methane and carbon dioxide conversion rate and long-term stability in DBD.

Description

Technical Field

[0001] This invention belongs to the field of chemistry, specifically relating to a supported catalyst, its preparation method, and its application in the dry reforming reaction of methane under dielectric barrier discharge conditions. Background Technology

[0002] Methane molecules have extremely high bond energies, and the dry reforming (DRM) reaction of methane is a strongly endothermic process that requires high temperatures to occur, and is accompanied by side reactions such as methane cracking and CO disproportionation. Plasma technology can input high-quality energy into the reaction system to activate the reactants, generating various active substances such as free radicals, ions, and electrons, thus allowing the reaction to proceed under milder conditions. Dielectric barrier discharge (DBD) is a commonly used plasma technique that has been proven to achieve dry reforming of methane under atmospheric pressure and near-room temperature conditions.

[0003] Adding catalysts to DBD can further improve the conversion rate and selectivity of the reaction. Most catalysts used in current research are active metal-supported catalysts, with commonly used metals including Fe, Cu, Pt, Ni, and Au, and supports such as Al₂O₃, MgO, SiO₂, and ZrO₂. During the reaction, problems such as changes in catalyst structure and deactivation can occur. Therefore, developing a catalyst with high activity and good stability is crucial for the advancement of DBD in methane dry reforming.

[0004] For example, patent CN114733528A discloses a method for preparing a nickel / cerium oxide catalyst. This method uses a precipitation method to prepare a basic cerium carbonate precursor and an impregnation method to load Ni to obtain a Ni / CeO2 catalyst, which improves the conversion rate of the reaction. However, after loading Ni, the catalyst support exhibits significant aggregation. Patent CN116393158A discloses a method for preparing and applying a catalyst for dry reforming of methane to syngas. Ni and Ce are loaded onto MCM-41 by an impregnation method, and then radio frequency plasma treatment is used to obtain a Ni-Ce / MCM-41 catalyst, which enhances the interaction between the active component, the promoter, and the support. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a methane dry reforming catalyst, its preparation method and its application in dielectric barrier discharge.

[0006] To address the aforementioned problems, this invention provides a method for preparing a catalyst for dry reforming of methane: preparing a 3D-Ti-Ce-O support, and loading active metals Ni, Fe, and Nb onto the 3D-Ti-Ce-O support to obtain a Ni-Fe-Nb / 3D-Ti-Ce-O catalyst.

[0007] An improvement to the preparation method of the catalyst for dry reforming of methane according to the present invention includes the following steps:

[0008] 1) Dissolve tetrabutyl titanate and cerium (Ce) salt in ethanol to form a system, add alkaline substances until the pH of the system is 9-10, thereby precipitating (the precipitation is then filtered).

[0009] The molar ratio of tetrabutyl titanate to cerium salt is 1:(1±0.05);

[0010] 2) The precipitate obtained in step 1) is first frozen in a liquid nitrogen environment (-196℃), and then subjected to vacuum freeze drying, grinding and calcination in sequence to obtain 3D-Ti-Ce-O support (3D-Ti-Ce-O scaffold support);

[0011] The calcination temperature is 200±20℃, and the calcination time is 3±0.5h;

[0012] 3) Weigh out soluble nickel salt, iron salt and niobium salt and dissolve them in water to obtain a metal salt solution;

[0013] The 3D-Ti-Ce-O support obtained in step 2) was immersed in a metal salt solution;

[0014] The Ni in the nickel salt is 5 to 20 wt% (preferably 5 to 15 wt%) of the weight of the 3D-Ti-Ce-O support, the Fe in the iron salt is 1 to 10 wt% (preferably 1 to 8 wt%) of the weight of the 3D-Ti-Ce-O support, and the Nb in the niobium salt is 0.5 to 5 wt% of the weight of the 3D-Ti-Ce-O support.

[0015] Note: The amount of water used in the metal salt solution should only be sufficient to ensure that the nickel, iron, and niobium salts are completely dissolved;

[0016] 4) Filter the material obtained in step 3), and dry the filter cake obtained by suction filtration (place it in an oven to dry) to obtain a dried solid;

[0017] 5) After the solid dried in step 4) is ground, it is placed in a muffle furnace for calcination at a temperature of 600±50℃ for 3 to 8 hours to obtain the Ni-Fe-Nb / 3D-Ti-Ce-O catalyst.

[0018] As a further improvement to the preparation method of the catalyst for dry reforming of methane of the present invention, the cerium salt in step 1) is cerium nitrate or cerium chloride.

[0019] As a further improvement to the preparation method of the catalyst for dry reforming of methane of the present invention, in step 1):

[0020] The alkaline substance is ammonia water, ammonium chloride aqueous solution, or sodium hydroxide aqueous solution.

[0021] For every 0.2 mol of tetrabutyl titanate, use 300±50 mL of ethanol.

[0022] As a further improvement to the preparation method of the catalyst for dry reforming of methane of the present invention, in step 3):

[0023] The soaking time is 4 to 8 hours;

[0024] Nickel salts are nickel nitrate, nickel chloride, or nickel sulfate; iron salts are ferric nitrate, ferric chloride, or ferric sulfate; and niobium salts are niobium oxalate.

[0025] As a further improvement to the preparation method of the catalyst for dry reforming of methane of the present invention, in step 2):

[0026] Freezing time in liquid nitrogen environment is 30 min to 1 h;

[0027] The vacuum freeze-drying temperature was -60±10℃, and the time was 48±2h;

[0028] Grind at room temperature until it passes through a 40-60 mesh sieve;

[0029] Then, the temperature is increased to the calcination temperature at a rate of 10±0.5℃ / min for calcination.

[0030] As a further improvement to the preparation method of the catalyst for dry reforming of methane of the present invention, the drying temperature in step 4) is 120±20℃ and the drying time is 12~48h.

[0031] As a further improvement to the preparation method of the catalyst for dry reforming of methane of the present invention, in step 5): grinding is performed at room temperature until it passes through a sieve of 20 to 40 mesh; and then calcination is performed by heating to the calcination temperature at a rate of 10 ± 0.5 °C / min.

[0032] This invention also provides a methane dry reforming reaction, carried out in a coaxial cylindrical dielectric barrier discharge reactor. The reactor includes a quartz tube and a stainless steel rod fitted inside the quartz tube. A quartz jacket is set at the middle position of the outer wall of the quartz tube, and the catalyst is located in the plasma discharge region. The catalyst is a methane dry reforming catalyst prepared by any of the above methods. CH4 and CO2 are mixed at a volume ratio of 1:1 and then used as raw gas. The mixture is introduced into the inner cavity of the quartz tube through the gas inlet and outlet and comes into contact with the catalyst. The reaction takes place under the action of plasma discharge to generate CO and H2.

[0033] The reaction is CH4 + CO2 → 2CO + 2H2; the products are discharged from the gas outlet. The products (CO and H2) are analyzed using an online gas chromatograph equipped with a flame ionization detector (FID) and a thermal conductivity detector (TCD).

[0034] The aforementioned dry reforming reaction of methane is specifically catalyzed in a coaxial DBD reactor, with circulating water introduced into the reactor to maintain the reaction at a constant temperature.

[0035] The beneficial effects of this invention are as follows: the prepared support is a 3D scaffold composed of Ti-Ce composite oxide nanorods under rapid low-temperature treatment, possessing abundant grain boundaries and a large specific surface area, thus providing more active sites; the nickel-based catalyst is inexpensive and exhibits activity comparable to noble metal catalysts in the dry reforming reaction of methane; simultaneously, the introduction of Fe and thermodynamically stable Nb enhances the catalytic activity of the catalyst; the redox electron pair Ce... 4+ / Ce 3+ The high oxygen storage capacity and high concentration of active oxygen species can inhibit carbon deposition and improve catalyst stability. The Ni-Fe-Nb / 3D-Ti-Ce-O catalyst provided by this invention exhibits high methane and carbon dioxide conversion rates and long-term stability in DBD. Attached Figure Description

[0036] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0037] Figure 1 This is a schematic diagram of a coaxial cylindrical dielectric barrier discharge reactor. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments. The examples given are only for explaining the present invention, but the scope of protection of the present invention is not limited thereto:

[0039] Example 1: A method for preparing a catalyst for dry reforming of methane, comprising the following steps:

[0040] (1) Take 0.2 mol (about 68 mL) of tetrabutyl titanate and 0.2 mol (about 86.8 g) of cerium nitrate hexahydrate solid, stir and dissolve in 300 mL of ethanol at 50 °C to obtain solution A;

[0041] (2) Continue to add ammonia water dropwise to solution A at a rate of 5 mL / min under stirring until the pH of solution A is adjusted to 9-10. At this point, a yellow precipitate (Ti-Ce oxide) is produced, and then the solution is filtered.

[0042] The stirring rate throughout the process was 600±100 r / min.

[0043] (3) The solid obtained by filtration in step (1) is placed in liquid nitrogen at -196℃ for 30 min; then placed in a vacuum freeze dryer at -60℃ for 48 h; after being ground into powder (passed through a 40-60 mesh sieve), it is placed in a muffle furnace for calcination. The temperature is increased to 200℃ at a rate of 10℃ / min and then calcined for 3 h to obtain 3D-Ti-Ce-O support.

[0044] (4) The Ni in nickel nitrate hexahydrate is set to 5 wt% of the weight of the 3D-Ti-Ce-O support, the Fe in ferric nitrate nonahydrate is set to 1 wt% of the weight of the 3D-Ti-Ce-O support, and the Nb in niobium oxalate is set to 0.5 wt% of the weight of the 3D-Ti-Ce-O support.

[0045] Dissolve nickel nitrate hexahydrate, ferric nitrate nonahydrate, and niobium oxalate in deionized water to obtain solution B; the amount of deionized water only needs to be sufficient to dissolve nickel nitrate hexahydrate, ferric nitrate nonahydrate, and niobium oxalate.

[0046] Weigh out a 3D-Ti-Ce-O support and place it in solution B, then immerse it for 4 hours;

[0047] (5) The solution obtained in step (3) is filtered by vacuum filtration, and the solid obtained by vacuum filtration is dried in an oven at 120°C for 12 hours.

[0048] (6) Grind the dried solid into particles of 20-40 mesh, put it into a muffle furnace, heat it to 600℃ at a rate of 10℃ / min and calcine it for 4h to obtain a Ni-Fe-Nb / 3D-Ti-Ce-O catalyst that can be used for dry reforming of methane.

[0049] Example 2: Compared with Example 1, the weight ratio of Ni to 3D-Ti-Ce-O support in nickel nitrate hexahydrate in step (3) was changed from "5wt%" to "10wt%", and the rest was the same as in Example 1.

[0050] Example 3: Compared with Example 1, the weight ratio of Ni to 3D-Ti-Ce-O support in nickel nitrate hexahydrate in step (3) was changed from "5wt%" to "15wt%", and the rest was the same as in Example 1.

[0051] Example 4: Compared with Example 1, the weight ratio of Fe to 3D-Ti-Ce-O carrier in ferric nitrate nonahydrate in step (3) was changed from "1wt%" to "3wt%", and the rest was the same as in Example 1.

[0052] Example 5: Compared with Example 1, the weight ratio of Fe to 3D-Ti-Ce-O carrier in ferric nitrate nonahydrate in step (3) was changed from "1wt%" to "5wt%", and the rest was the same as in Example 1.

[0053] Example 6: Compared with Example 1, the weight ratio of Fe to 3D-Ti-Ce-O carrier in ferric nitrate nonahydrate in step (3) was changed from "1wt%" to "8wt%", and the rest was the same as in Example 1.

[0054] Example 7: Compared with Example 1, the weight ratio of Nb in niobium oxalate to 3D-Ti-Ce-O support in step (3) was changed from "0.5wt%" to "1wt%", and the rest was the same as in Example 1.

[0055] Example 8: Compared with Example 1, the weight ratio of Nb to 3D-Ti-Ce-O support in niobium oxalate in step (3) was changed from "0.5wt%" to "3wt%", and the rest was the same as in Example 1.

[0056] Example 9: Compared with Example 1, the weight ratio of Nb to 3D-Ti-Ce-O support in niobium oxalate in step (3) was changed from "0.5wt%" to "5wt%", and the rest was the same as in Example 1.

[0057] Comparative Example 1-1: Compared to Example 1, the use of "86.8g of cerium nitrate hexahydrate solid" in step (1) is omitted. In this case, the precipitate obtained in step (1) is an oxide of Ti. The rest is the same as in Example 1.

[0058] Comparative Examples 1-2: Compared to Example 1, the use of "86.8g of cerium nitrate hexahydrate solid" in step (1) was omitted. In subsequent steps, "86.8g of cerium nitrate hexahydrate solid" was dissolved in deionized water along with nickel nitrate hexahydrate, ferric nitrate nonahydrate, and niobium oxalate to obtain solution B. The amounts of nickel nitrate hexahydrate, ferric nitrate nonahydrate, and niobium oxalate were the same as in Example 1. The rest was the same as in Example 1.

[0059] Comparative Example 2: Compared to Example 1, the use of "ferric nitrate nonahydrate" in step (3) was omitted, and the rest was the same as in Example 1.

[0060] Comparative Example 3: Compared to Example 1, the use of "niobium oxalate" in step (3) was omitted, and the rest was the same as in Example 1.

[0061] Comparative Example 4: Compared to Example 1, the freezing treatment in liquid nitrogen in step (3) is omitted. That is, the solid obtained by filtration in step (1) is directly placed into a vacuum freeze dryer for processing. The rest is the same as in Example 1.

[0062] Experiment 1: Evaluation of Catalysts

[0063] The catalytic activity and stability of the catalyst were evaluated in a coaxial cylindrical dielectric barrier discharge reactor. Figure 1The reactor body consists of a stainless steel rod housed inside a quartz tube. The stainless steel rod coincides with the axis of the quartz tube, with both ends of the stainless steel rod located outside the inner cavity of the quartz tube. Sealing and insulating fasteners are installed at the break points of the quartz tube to seal both parts.

[0064] The stainless steel bar is 30cm long and 6mm in diameter, and is made of 022Cr steel. 17 Ni 12 Mo2 stainless steel; quartz tube with a wall thickness of 2mm, an outer diameter of 18mm, and a length of 22cm; the sealing and insulating fasteners are equipped with gas inlets and outlets, which are connected to the inner cavity of the quartz tube.

[0065] A quartz jacket, 8cm long and 0.1mm thick, is installed in the middle of the outer wall of the quartz tube. Quartz branch pipes, serving as circulating water inlets and outlets, are installed 1cm from both ends of the quartz jacket. These branch pipes are connected to the circulating water channels inside the quartz jacket. The thickness of these branch pipes is 2mm and the length is 2cm.

[0066] The high-voltage power supply is connected to one end of the stainless steel rod, and the ground wire is connected to the quartz jacket. The area covered by the quartz jacket is the plasma discharge region.

[0067] The catalyst is placed in the cavity formed by the inner surface of the quartz tube and the outer surface of the stainless steel rod, and is directly opposite the quartz jacket, that is, the catalyst is located in the plasma discharge region.

[0068] The discharge gap is 4mm and the discharge length is 8cm; the quartz jacket is filled with circulating water at a temperature of 30℃.

[0069] Powered by a high-voltage AC power supply at a frequency of 3kHz, with a plasma power of 45W, the discharge signal was collected by a digital oscilloscope.

[0070] The experiment was conducted at ambient temperature and pressure. CH4 and CO2 were mixed in a 1:1 volume ratio and introduced as the raw gas into the inner cavity of a quartz tube through the gas inlet and outlet. After contacting the catalyst, the reaction was carried out under the action of plasma discharge at a total flow rate of 100 mL / min. The reaction products were discharged from the gas outlet. The results were measured at 1 h, 3 h, and 5 h after the start of the reaction. The products (CO and H2) were analyzed using an online gas chromatograph equipped with a flame ionization detector (FID) and a thermal conductivity detector (TCD).

[0071] The reaction is CH4 + CO2 → 2CO + 2H2

[0072] CH4 conversion rate:

[0073] CO2 conversion rate:

[0074] The test results are shown in Table 1 below:

[0075] Table 1

[0076]

[0077] The above experiments show that the catalyst provided by this invention for methane dry reforming under dielectric barrier discharge plasma conditions can catalyze the methane dry reforming reaction at room temperature and pressure, and has high activity and long-term stability (at least 5 hours).

[0078] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for dry reforming methane, carried out in a coaxial cylindrical dielectric barrier discharge reactor, the reactor comprising a quartz tube and a stainless steel rod fitted inside the quartz tube, a quartz jacket disposed at the middle position of the outer wall of the quartz tube, and a catalyst located within the plasma discharge region; characterized in that: The catalyst is a catalyst for dry reforming of methane. CH4 and CO2 are mixed in a volume ratio of 1:1 and then used as raw gas. The mixture is introduced into the inner cavity of the quartz tube through the gas inlet and outlet and comes into contact with the catalyst. The reaction takes place under the action of plasma discharge to generate CO and H2. The preparation method of the catalyst for dry reforming of methane includes the following steps: 1) Dissolve tetrabutyl titanate and cerium salt in ethanol to form a system, add alkaline substances until the pH of the system is 9-10, thereby precipitating; The molar ratio of tetrabutyl titanate to cerium salt is 1:(1±0.05); 2) The precipitate obtained in step 1) is first frozen in a liquid nitrogen environment, and then subjected to vacuum freeze drying, grinding and calcination in sequence to obtain a 3D-Ti-Ce-O support; The calcination temperature is 200±20℃, and the calcination time is 3±0.5h; 3) Weigh out soluble nickel salt, iron salt and niobium salt and dissolve them in water to obtain a metal salt solution; The 3D-Ti-Ce-O support obtained in step 2) was immersed in a metal salt solution; The Ni content in the nickel salt is 5–20 wt% of the weight of the 3D-Ti-Ce-O support, the Fe content in the iron salt is 1–10 wt% of the weight of the 3D-Ti-Ce-O support, and the Nb content in the niobium salt is 0.5–5 wt% of the weight of the 3D-Ti-Ce-O support. 4) Filter the product obtained in step 3), and dry the filter cake to obtain a dried solid. 5) After the solid dried in step 4) is ground, it is placed in a muffle furnace for calcination at a temperature of 600±50℃ for 3 to 8 hours to obtain the Ni-Fe-Nb / 3D-Ti-Ce-O catalyst.

2. The reaction method for dry reforming of methane according to claim 1, characterized in that... The cerium salt in step 1) is cerium nitrate or cerium chloride.

3. The reaction method for dry reforming of methane according to claim 2, characterized in that... In step 1): The alkaline substance is ammonia water, ammonium chloride aqueous solution, or sodium hydroxide aqueous solution; For every 0.2 mol of tetrabutyl titanate, use 300±50 mL of ethanol.

4. The reaction method for dry reforming of methane according to any one of claims 1 to 3, characterized in that... In step 3): The soaking time is 4 to 8 hours; Nickel salts are nickel nitrate, nickel chloride, or nickel sulfate; iron salts are ferric nitrate, ferric chloride, or ferric sulfate; and niobium salts are niobium oxalate.

5. The reaction method for dry reforming of methane according to claim 4, characterized in that... In step 2): Freezing time in liquid nitrogen environment is 30 min to 1 h; The vacuum freeze-drying temperature was -60±10℃, and the time was 48±2h; Grind at room temperature until it passes through a 40-60 mesh sieve; Then, the temperature is increased to the calcination temperature at a rate of 10±0.5℃ / min for calcination.

6. The reaction method for dry reforming of methane according to claim 5, characterized in that: The drying temperature in step 4) is 120±20℃, and the drying time is 12~48h.

7. The reaction method for dry reforming of methane according to claim 6, characterized in that... In step 5), grinding is performed at room temperature until the material passes through a sieve of 20-40 mesh; then the temperature is increased to the calcination temperature at a rate of 10±0.5℃ / min for calcination.

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