Preparation method and application of methane dry reforming catalyst

Abstract

The invention belongs to the field of chemistry, and provides a preparation method of a catalyst for methane dry reforming, which comprises the following steps: preparing a 3D-Ti-Ce-O carrier, and loading Ni, Fe and Nb active metals on the 3D-Ti-Ce-O carrier to obtain a Ni-Fe-Nb / 3D-Ti-Ce-O catalyst. The invention further provides a methane dry reforming reaction, CH4 and CO2 are mixed according to the volume ratio of 1: 1 and then serve as raw material gas, the raw material gas is input into an inner cavity of a quartz tube from a gas inlet and outlet to make contact with a catalyst, and then a reaction is conducted under the plasma discharge effect, so that CO and H2 are generated. The Ni-Fe-Nb / 3D-Ti-Ce-O catalyst provided by the invention is relatively high in methane and carbon dioxide conversion rate and long-term stability in DBD (Dibenzodiazepine).

Description

Technical Field

[0001] The invention belongs to the field of chemistry, and in particular relates to a supported catalyst, a preparation method and application of the catalyst in a methane dry reforming reaction under dielectric barrier discharge conditions. Background Art

[0002] The bond energy of methane molecules is extremely high, and the methane-to-carbon dioxide reforming (DRM) reaction is a highly endothermic reaction process that requires high temperature conditions to occur, and is accompanied by side reactions such as methane cracking and CO disproportionation. The application of plasma technology can input high-quality energy into the reaction system to activate the reactants, generate free radicals, ions, electrons and other active substances in the system, so that the reaction can proceed under mild conditions. Dielectric barrier discharge (DBD) is a commonly used plasma technology that has been proven to achieve methane dry reforming reactions at atmospheric pressure and near room temperature.

[0003] Adding a catalyst to DBD can further improve the conversion rate and selectivity of the reaction. Most of the catalysts used in current research are active metal-supported catalysts. Commonly used metals include Fe, Cu, Pt, Ni, Au, etc., and carriers include Al2O3, MgO, SiO2, ZrO2, etc. During the reaction, problems such as changes in the catalyst structure and deactivation may occur. Therefore, the development of a highly active and stable catalyst is very important for the development of DBD in methane dry reforming.

[0004] For example, patent CN114733528A discloses a method for preparing a nickel / cerium oxide catalyst, which uses a precipitation method to prepare a basic cerium carbonate precursor and an impregnation method to load Ni to obtain a Ni / CeO2 catalyst, thereby improving the reaction conversion rate. However, after loading Ni, the catalyst carrier undergoes obvious aggregation; patent CN116393158A discloses a method for preparing a catalyst for producing synthesis gas by dry reforming of methane and its application, wherein Ni and Ce are loaded on MCM-41 by an impregnation method, and then a Ni-Ce / MCM-41 catalyst is obtained by radio frequency plasma treatment, thereby enhancing the interaction between the active component, the additive, and the carrier. Summary of the invention

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

[0006] In order to solve the above problems, the present invention provides a method for preparing a catalyst for methane dry reforming: preparing a 3D-Ti-Ce-O carrier, and loading Ni, Fe, and Nb active metals on the 3D-Ti-Ce-O carrier to obtain a Ni-Fe-Nb / 3D-Ti-Ce-O catalyst.

[0007] As an improvement of the preparation method of the catalyst for methane dry reforming of the present invention, the method comprises 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, and then precipitate (filter after precipitation);

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

[0010] 2) The precipitate obtained in step 1) is first frozen in a liquid nitrogen environment (-196° C.), and then vacuum freeze-dried, ground, and calcined in sequence to obtain a 3D-Ti-Ce-O carrier (3D-Ti-Ce-O scaffold carrier);

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

[0012] 3) Weigh 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 carrier obtained in step 2) is immersed in a metal salt solution;

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

[0015] Note: The amount of water in the metal salt solution only needs to ensure that the nickel salt, iron salt and niobium salt can be completely dissolved;

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

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

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

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

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

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

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

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

[0024] The nickel salt is nickel nitrate, nickel chloride or nickel sulfate, the iron salt is iron nitrate, iron chloride or iron sulfate, and the niobium salt is niobium oxalate.

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

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

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

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

[0029] Then the temperature is raised to the calcination temperature at a rate of 10±0.5°C / min for calcination.

[0030] As a further improvement of the method for preparing the catalyst for dry reforming of methane of the present invention, the drying temperature of step 4) is 120±20° C. and the drying time is 12 to 48 hours.

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

[0032] The present invention also provides a methane dry reforming reaction, which is carried out in a coaxial cylindrical dielectric barrier discharge reactor. The reactor includes a quartz tube and a stainless steel rod sleeved in the quartz tube. A quartz jacket is arranged in the middle position of the outer wall of the quartz tube, and the catalyst is located in the plasma discharge area. The catalyst is a catalyst for methane dry reforming prepared by any of the above methods. CH4 and CO2 are mixed in a volume ratio of 1:1 and then input as raw gas from the gas inlet and outlet into the inner cavity of the quartz tube to contact with the catalyst, and then react under the action of plasma discharge to generate CO and H2.

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

[0034] The above-mentioned methane dry reforming reaction is specifically catalyzed in a coaxial DBD reactor, and circulating water is introduced into the reactor to keep the reaction at a constant temperature.

[0035] The beneficial effects of the present invention are as follows: the prepared carrier is a 3D structured support composed of Ti-Ce composite oxide nanorods under rapid low temperature treatment, has abundant grain boundaries, a large specific surface area, and can provide more active sites; the nickel-based catalyst is low in price and has an activity comparable to that of precious metal catalysts in the methane dry reforming reaction, and at the same time, Fe and Nb with high thermodynamic stability are introduced to improve the catalytic activity of the catalyst; the redox electrons to Ce 4+ / Ce 3+ The oxygen storage capacity and high concentration of active oxygen species can inhibit carbon deposition and improve the stability of the catalyst. The Ni-Fe-Nb / 3D-Ti-Ce-O catalyst provided by the present invention exhibits high methane and carbon dioxide conversion rates and long-term stability in DBD. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0037] Figure 1 Schematic diagram of a coaxial cylindrical dielectric barrier discharge reactor. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with specific embodiments. The examples are only used to explain the present invention, but the protection scope 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) 0.2 mol (about 68 mL) of tetrabutyl titanate and 0.2 mol (about 86.8 g) of solid cerium nitrate hexahydrate were dissolved in 300 mL of ethanol under stirring at 50° C. to obtain solution A;

[0041] (2) Continue to drip ammonia water into solution A at a rate of 5 mL / min under stirring until the pH of solution A is adjusted to 9-10, at which time a yellow precipitate (Ti-Ce oxide) is produced, which is then filtered;

[0042] The stirring rate of the whole process is 600±100r / min.

[0043] (3) The solid obtained by filtration in step (1) was placed in liquid nitrogen at -196°C for freezing treatment for 30 minutes; then placed in a vacuum freeze dryer for treatment at -60°C for 48 hours; ground into powder (passed through a 40-60 mesh sieve), placed in a muffle furnace for calcination, heated to 200°C at a rate of 10°C / min, and calcined for 3 hours to obtain a 3D-Ti-Ce-O carrier;

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

[0045] Nickel nitrate hexahydrate, ferric nitrate nonahydrate and niobium oxalate are dissolved in deionized water to obtain solution B; the amount of deionized water used is only required to ensure that nickel nitrate hexahydrate, ferric nitrate nonahydrate and niobium oxalate can be dissolved.

[0046] Weigh the 3D-Ti-Ce-O support and place it in solution B for 4 h;

[0047] (5) Filter the impregnated solution obtained in step (3) by suction, and dry the solid obtained by filtration in an oven at 120° C. for 12 h;

[0048] (6) The dried solid was ground into particles of 20-40 mesh, placed in a muffle furnace, heated to 600°C at a rate of 10°C / min, and then calcined for 4 hours to obtain a Ni-Fe-Nb / 3D-Ti-Ce-O catalyst that can be used for methane dry reforming.

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

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

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

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

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

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

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

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

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

[0058] Comparative Example 1-2, relative to Example 1, the use of "86.8 g of solid cerium nitrate hexahydrate" in step (1) is eliminated, and in the subsequent steps, "86.8 g of solid cerium nitrate hexahydrate" is dissolved in deionized water 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 are the same as in Example 1. The rest is the same as in Example 1.

[0059] Comparative Example 2: Compared with Example 1, the use of "iron nitrate nonahydrate" in step (3) is eliminated, and the rest is the same as Example 1.

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

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

[0062] Experiment 1: Evaluation of Catalysts

[0063] Evaluation of the catalytic activity and stability of the catalysts in a coaxial cylindrical dielectric barrier discharge reactor ( Figure 1). The reactor body includes a stainless steel rod set in a quartz tube, the stainless steel rod coincides with the axis of the quartz tube, both ends of the stainless steel rod are located outside the inner cavity of the quartz tube, and a sealing insulating fastener is set at the fracture of the quartz tube to seal the two;

[0064] The stainless steel rod is 30cm long, 6mm in diameter, and made of 022Cr 17 Ni 12 Mo2 stainless steel; the quartz tube has a wall thickness of 2 mm, an outer diameter of 18 mm, and a length of 22 cm; a gas inlet and outlet are provided on the sealing insulating fastener, and the gas inlet and outlet are connected to the inner cavity of the quartz tube.

[0065] A quartz jacket is set in the middle of the outer wall of the quartz tube, with a length of 8 cm and a thickness of 0.1 mm; a quartz branch pipe is set 1 cm away from both ends of the quartz jacket as a circulating water inlet and outlet, that is, the quartz branch pipe as the circulating water inlet and outlet is connected to the circulating water channel in the quartz jacket. The quartz branch pipe as the circulating water inlet and outlet is 2 mm thick and 2 cm long.

[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 area.

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

[0068] The discharge gap is 4 mm and the discharge length is 8 cm. Circulating water is passed through the quartz jacket and the water temperature is 30°C.

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

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

[0071] The reaction formula 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] From the above experiments, it can be seen that the catalyst provided by the present invention for methane dry reforming under dielectric barrier discharge plasma conditions can catalyze methane dry reforming reaction at room temperature and pressure, and has high activity and long-term stability (at least up to 5 hours).

[0078] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for preparing a catalyst for dry reforming of methane, characterized in that: A 3D-Ti-Ce-O carrier is prepared, and active metals Ni, Fe and Nb are loaded on the 3D-Ti-Ce-O carrier to obtain a Ni-Fe-Nb / 3D-Ti-Ce-O catalyst.

2. The method for preparing a catalyst for dry reforming of methane according to claim 1, characterized in that The steps include: 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:cerium salt=1:(1±0.05); 2) Freezing the precipitate obtained in step 1) in a liquid nitrogen environment, and then performing vacuum freeze drying, grinding, and calcining in sequence to obtain a 3D-Ti-Ce-O carrier; The calcination temperature is 200±20°C and the calcination time is 3±0.5h; 3) Weigh soluble nickel salt, iron salt and niobium salt and dissolve them in water to obtain a metal salt solution; The 3D-Ti-Ce-O carrier obtained in step 2) is immersed in a metal salt solution; The Ni in the nickel salt is 5-20wt% of the weight of the 3D-Ti-Ce-O carrier, the Fe in the iron salt is 1-10wt% of the weight of the 3D-Ti-Ce-O carrier, and the Nb in the niobium salt is 0.5-5wt% of the weight of the 3D-Ti-Ce-O carrier; 4) Filter the product obtained in step 3) by suction, and dry the filter cake obtained by suction filtration to obtain a dried solid; 5) After the solid is dried in step 4), it is ground and then placed in a muffle furnace for calcination at a temperature of 600±50° C. for a time of 3 to 8 hours to obtain a Ni-Fe-Nb / 3D-Ti-Ce-O catalyst.

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

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

5. The method for preparing a catalyst for dry reforming of methane according to any one of claims 2 to 4, characterized in that In step 3): The immersion time is 4 to 8 hours; The nickel salt is nickel nitrate, nickel chloride or nickel sulfate, the iron salt is iron nitrate, iron chloride or iron sulfate, and the niobium salt is niobium oxalate.

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

7. The method for preparing a catalyst for dry reforming of methane according to any one of claims 2 to 6, characterized in that: The drying temperature of step 4) is 120±20° C., and the drying time is 12 to 48 hours.

8. The method for preparing a catalyst for dry reforming of methane according to claim 7, characterized in that In the step 5), grinding is performed at room temperature until the powder passes through a 20-40 mesh sieve; and then the powder is heated to the calcination temperature at a rate of 10±0.5°C / min for calcination.

9. A methane dry reforming reaction is carried out in a coaxial cylindrical dielectric barrier discharge reactor, the reactor comprising a quartz tube and a stainless steel rod sleeved in the quartz tube, a quartz jacket is arranged in the middle of the outer wall of the quartz tube, and the catalyst is located in the plasma discharge region; characterized in that: The catalyst is a catalyst for methane dry reforming prepared by any method as claimed in claims 1 to 8, wherein CH4 and CO2 are mixed in a volume ratio of 1:1 and input into the inner cavity of a quartz tube from a gas inlet and outlet as raw gas, and after contacting with the catalyst, react under the action of plasma discharge to generate CO and H2.

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