Method for preparing second metal modified beta-Mo2C

Abstract

The invention belongs to the technical field of catalytic material synthesis, and particularly relates to a method for preparing second metal modified beta-Mo2C, which comprises the following steps: placing a precursor in a plasma generator, introducing gaseous hydrocarbon as a carbon source into the plasma generator, simultaneously introducing hydrogen as a reducing gas, controlling the gas flow to be 100-200mL / min, controlling the volume ratio of C to H2 to be 1: 12-1: 2, and controlling the reaction temperature to be 20-30 DEG C; under the reduction carbonization action of the reaction gas, beta-Mo2C is generated; the precursor is a mixture of molybdenum salt and second metal salt, and the second metal is loaded on the beta-Mo2C in a simple substance form. The method has the advantages that the method is convenient to operate, a heat source is avoided, the prepared M-Mo2C material is uniform in granularity, low in surface carbon content and good in catalytic performance, and abundant active sites and diffusion environments are provided.

Description

Technical Field

[0001] This invention belongs to the field of catalytic material synthesis technology, and particularly relates to a method for preparing second metal modified β-Mo2C. Background Technology

[0002] The electronic band structure of β-Mo₂C is highly similar to that of platinum group metals, giving it adsorption and activation capabilities approaching those of noble metals in catalytic reactions. Therefore, it is often considered a promising new type of catalyst to replace noble metals and is widely used in reactions such as methane dry reforming, photoelectrocatalysis, dehydrogenation, and hydrorefining. However, β-Mo₂C has strong oxyphilic properties and will be oxidized and deactivated in hydrodeoxygenation reactions. Therefore, a second metal component with strong hydrogenation properties needs to be introduced to delay oxidative deactivation. The traditional method for preparing second metal-modified β-Mo₂C is mainly temperature-programmed reduction carbonization. This method requires strict process control; heating rates exceeding 2°C / min lead to incomplete carbonization and significantly reduced catalytic activity. Furthermore, excessively low carbonization temperatures (such as below a reasonable threshold, generally above 700°C) result in a product containing a large amount of inactive intermediates, and the second metal component agglomerates, resulting in low dispersion and affecting the catalytic activity of the material. This method also requires high energy consumption and has a long preparation cycle.

[0003] Therefore, how to efficiently prepare second-metal-modified β-Mo2C with high dispersion under simple and mild conditions remains an unsolved problem. The core principle of cold plasma preparation of second-metal-modified β-Mo2C is to utilize high-energy particles generated by non-equilibrium discharge to achieve directional reduction carbonization and structural control of the metal precursor at near room temperature. This enables rapid nucleation of metal nanoparticles with precise control of the average particle size at the nanometer scale, effectively suppressing aggregation. The introduced second component is highly dispersed, exposing more active sites. Furthermore, high-energy electron bombardment induces the formation of oxygen vacancies on the material surface, enhancing the adsorption and activation capacity of the reactants. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a method for efficiently preparing second metal-modified β-Mo2C using plasma under mild conditions. Through plasma technology, the reduction and carbonization of the molybdenum-based precursor can be completed in one step under near-room temperature reaction conditions, promoting the reduction of the second metal oxide to a metallic element and uniformly loading it onto the β-Mo2C surface, thereby increasing the number of active sites on the material surface. The method is simple to operate and has high processing efficiency.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing second metal-modified β-Mo2C involves placing a precursor in a plasma generator, introducing gaseous hydrocarbons as a carbon source and hydrogen as a reducing gas, with the gas flow rate controlled at 100-200 mL / min, wherein the volume ratio of C to H2 is 1:12 to 1:2. Under the reducing carbonization effect of the reaction gas, β-Mo2C is generated. The precursor is a mixture of molybdenum salt and a second metal salt, with the second metal attached to the β-Mo2C in elemental form.

[0006] Preparation of the precursor: Ammonium molybdate aqueous solution and second metal salt aqueous solution are mixed, the mass ratio of the second metal to Mo is (0.1~0.4) / 1, and after stirring evenly, the mixture is dried and calcined into powder.

[0007] The hydrocarbons mentioned are one or more of methane, ethane, and ethylene.

[0008] The plasma generator has an input power of 40W or more and a reaction time of 3 hours or more.

[0009] The plasma generator first increases the input voltage of the power supply in a stepwise manner at a rate of 5~10V / min. When the input power reaches 5~15W, it stays for 5~10min to remove water. Then, the input power is gradually increased to the reaction power. After the reaction power is reached, the reaction time is started.

[0010] The plasma generator includes a gas delivery pipeline, a plasma generating unit, and a plasma controller. The gas delivery pipeline is a stainless steel pipe. One end of the gas delivery pipeline is connected to several gas cylinders via a four-way connector, and the other end of the gas delivery pipeline is connected to the T-shaped quartz tube of the plasma generating unit. The plasma generating unit includes a plastic slip ring, a T-shaped quartz tube, a cylindrical quartz tube, and a stainless steel electrode rod. The T-shaped quartz tube and the cylindrical quartz tube are connected by the plastic slip ring. A stainless steel electrode rod, secured with a rubber stopper, is inserted into the center of the top of the T-shaped quartz tube. The stainless steel electrode rod is positioned at the center of the cylindrical quartz tube and is connected to the positive electrode of the plasma controller. The outer wall of the cylindrical quartz tube is covered with aluminum foil and secured by winding wires. The aluminum foil is connected to the negative electrode of the plasma controller. Inside the cylindrical quartz tube covered with aluminum foil, there is a catalyst precursor bed. The stainless steel electrode rod passes through the catalyst precursor bed. The bottom of the cylindrical quartz tube is connected to a rubber tube.

[0011] The plasma controller is a DC power supply.

[0012] Taking methane as a carbon source, the specific reaction process is as follows: MoO3 + H* → MoO2 MoO2+H*+CH x*→β-Mo2C (0≤x<4) MO+H*→M Among them, H* and CH x *Represents high-energy reactive particles generated by hydrogen and methane under plasma. MO represents the second metal oxide, and M represents the introduced second metal.

[0013] The reaction mechanism is as follows: Under CH4 and H2 plasma conditions, MoO3 particles are exposed to the plasma region, and a large number of free electrons attach to the surface of the MoO3 particles to form a shell, making the particles electronegative. During the high-energy electron dynamic collision adsorption and desorption process on the surface of MoO3 particles, energy is transferred to the MoO3 particles, causing the Mo-O bonds to be stretched and twisted until they finally break, promoting the reduction of MoO3. At the same time, the negative electric field generated by the plasma free electron flow produces a Coulomb force effect on the negative electric field of the shell, forming a repulsive force between the shells of different particles, promoting uniform particle dispersion. Under low input power, the energy generated by the applied electric field is insufficient to reduce MoO3 to MoO2. As the input power increases, the electric field in the plasma reactor strengthens, and under the action of hydrogen active species (H*), MoO3 is reduced to MoO2. Under high input power, MoO2 undergoes reductive carburizing under the combined action of H* and CHx* to obtain β-Mo2C.

[0014] The particle size of the prepared second metal-modified β-Mo2C is 1–15 nm.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention employs plasma technology, utilizing plasma from methane and hydrogen to conduct the reaction at near-room temperature, achieving the reduction and carbonization of the molybdenum-based precursor in one step. This results in fine M-Mo2C particles with low surface carbon content and a large number of surface active sites, significantly enhancing the catalytic performance of the prepared M-Mo2C. Furthermore, the Coulomb repulsion force generated by the plasma electric field ensures thorough particle dispersion, forming a product with uniform particle size. The low-temperature reaction inhibits deep hydrocarbon cracking, reduces carbon deposition, and maintains a clean material surface.

[0016] The method of this invention is easy to operate, avoids the use of heat sources, and produces M-Mo2C materials with uniform particle size, low surface carbon content, good catalytic performance, and provides abundant active sites and diffusion environment. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a plasma generator.

[0018] Figure 1In the middle, 1. Gas cylinder, 2. Pressure reducing gauge, 3. Four-way valve, 4. Stainless steel tube, 5. T-shaped quartz tube, 6. Stainless steel electrode rod, 7. Insulated wire, 8. Rubber stopper, 9. Plastic slip ring, 10. Insulating cotton, 11. Aluminum foil, 12. Cylindrical quartz tube, 13. Grounding electrode, 14. Rubber tube, 15. DC power supply, 16. Catalyst precursor bed.

[0019] Figure 2 This is the XRD pattern of β-Mo2C prepared with nickel as the second metal.

[0020] Figure 3 This is the XRD pattern of β-Mo2C prepared with iron as the second metal.

[0021] Figure 4 This is the XRD pattern of β-Mo2C prepared with copper as the second metal. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0023] See Figure 1 The plasma generator used in the method for preparing second metal-modified β-Mo2C includes a gas delivery pipe, a plasma generator, and a plasma controller. The gas delivery pipe is a stainless steel pipe with a four-way valve at the gas input end. The stainless steel pipe 4 is connected to a gas cylinder 1 via the four-way valve, and the other end of the stainless steel pipe 4 is connected to a T-shaped quartz tube 5. A pressure reducing gauge 2 is connected to the gas cylinder 1. The plasma generator includes a plastic slip ring 9, a T-shaped quartz tube 5, a cylindrical quartz tube 12, and a stainless steel electrode rod 6. The plastic slip ring 9 connects the T-shaped quartz tube 5 and the cylindrical quartz tube 12. A stainless steel electrode rod 6, fixed with a rubber stopper 8, is inserted into the middle of the top of the T-shaped quartz tube 5. The stainless steel electrode rod 6 is located at the center of the cylindrical quartz tube 12 and is connected to the positive electrode of the plasma controller via an insulated wire 7. The outer wall of the cylindrical quartz tube 12 is covered with aluminum foil 11 and wound with insulated wire 7, which is then connected to the negative electrode of the plasma controller. The aluminum foil 11 is wrapped with insulating cotton 10 and connected to the grounding electrode 13. A cylindrical quartz tube 12 covering the area of ​​the aluminum foil 11 is filled to form a catalyst precursor bed 16. A stainless steel electrode rod 6 passes through the catalyst precursor bed 16. A rubber tube 14 is connected to the bottom of the cylindrical quartz tube 12 to exhaust the reaction gas. The plasma controller is powered by a DC power supply 15.

[0024] The specific preparation method for second metal-modified β-Mo2C is as follows: A certain amount of ammonium molybdate is dissolved in water and stirred evenly. Then, an appropriate amount of a second metal salt aqueous solution is added dropwise, wherein the mass ratio of the second metal to Mo is (0.1~0.4) / 1, preferably 1:1. After stirring evenly, the solution is dried and calcined to obtain the precursor. Then, the precursor is ground, pressed into tablets, and sieved to obtain 20~40 mesh particles, which are then filled into a cylindrical quartz tube 12 (the middle part of the aluminum foil 11), so that the stainless steel electrode rod 6 passes through the catalyst precursor bed 16. The lower end of the precursor bed 16 is sealed with quartz wool to prevent the precursor from falling off. Since the plasma operation is under high voltage electric field conditions, safety precautions must be taken. Before starting the device, it is necessary to check whether the transformer "zero point" is zero, and at the same time, the discharge frequency should be controlled at about 10kHz. Before the reduction and carbonization reaction, the air in the pipeline needs to be replaced with 100 mL / min of Ar gas, and the airtightness of the device needs to be checked with soapy water. Then, the methane and hydrogen necessary for carbonization and reduction are introduced into the plasma generator, with the total gas flow rate controlled at 100~200 mL / min, and the volume flow ratio of hydrogen to methane controlled at 1:12~1:2. The input voltage is adjusted by the plasma controller to control the input power. The input current increases with the increase of the input voltage, thereby increasing the discharge intensity, increasing the number of discharge channels, and enhancing the energy and density of active species. As a result, the reduction and carbonization capacity of the system increases with the increase of the input power. The input voltage of the power supply is increased at a rate of 5-10V / min. When the input power reaches 5-15W, it needs to be held for 5-10 minutes to remove water (generated by oxide reduction). The water vapor is carried away by the reaction gas introduced into the device and discharged from the device along with the gas through rubber tube 14. Then, the input power is gradually increased to over 40W, at which point timing begins and is maintained for at least 3 hours. During this process, the reaction gas is broken down, thereby generating plasma, which initiates reduction and carbonization reactions in the plasma reactor. After the reaction is completed, the four-way valve 3 is switched to close the input of the reduction and carbonization gas, and the passivation gas (0.5% O2 / Ar (volume ratio) mixture) is introduced. After passivation for 2 hours, the device is disassembled and the prepared catalyst is removed.

[0025] The present invention provides a carbon source, methane, a reducing gas, hydrogen, and a precursor to react to generate a second metal-modified M-Mo2C.

[0026] Example 1: Ni was selected as the second metal introduced, nickel nitrate hexahydrate was chosen as the nickel salt, hydrogen was used as the reducing gas, and methane was used as the carbon source. Following the specific implementation steps, 1g of ammonium molybdate tetrahydrate was dissolved in distilled water. 2.2g (Ni / Mo=0.1), 4.4g (Ni / Mo=0.2), and 8.8g (Ni / Mo=0.4) of nickel nitrate hexahydrate were dissolved in distilled water and added dropwise to the ammonium molybdate solution. After drying for 12 hours, the mixture was calcined at 500℃ for 3 hours. The hydrogen flow rate was controlled at 120mL / min, the methane flow rate at 20mL / min, the dehydration power at 12W, and the dehydration time at 5 minutes. The voltage increase rate was controlled at 8V / min, the required input power for the reaction was 42W, and the reaction time was 4 hours. XRD phase analysis of the prepared product was performed, and the results are shown in the appendix. Figure 2 Appendix Figure 2 In the diffraction pattern, the peaks at 2θ = 34.3°, 37.9°, 39.4°, 52.1°, 61.5°, 69.6°, 74.6°, and 75.5° are characteristic peaks of β-Mo₂C. The particle size of the prepared β-Mo₂C can be calculated to be 8.0–9.0 nm using the Scherrer equation. This preparation process is convenient and rapid (reducing the heating and cooling time of traditional methods) and requires a low reaction temperature.

[0027] Example 2: Fe was selected as the introduced second metal, ferric nitrate hexahydrate was chosen as the iron salt, hydrogen was used as the reducing gas, and methane was used as the carbon source. Following the specific implementation steps, 1g of ammonium molybdate tetrahydrate was dissolved in distilled water. 2.3g (Fe / Mo=0.1), 4.5g (Fe / Mo=0.2), and 9.0g (Fe / Mo=0.4) of ferric nitrate hexahydrate were dissolved in distilled water and added dropwise to the ammonium molybdate solution. After drying for 12 hours, the mixture was calcined at 500℃ for 3 hours. The hydrogen flow rate was controlled at 100mL / min, the methane flow rate at 15mL / min, the dehydration power at 15W, and the dehydration time at 6 minutes. The voltage increase rate was controlled at 5V / min, the required input power for the reaction was 45W, and the reaction time was 4 hours. XRD phase analysis of the prepared product was performed, and the results are shown in the appendix. Figure 3 Appendix Figure 3 In the diffraction pattern, the peaks at 2θ = 34.3°, 37.9°, 39.4°, 52.1°, 61.5°, 69.6°, 74.6°, and 75.5° are characteristic peaks of β-Mo₂C. The particle size of the prepared β-Mo₂C can be calculated to be 9.0–10.0 nm using the Scherrer equation. This preparation process is convenient and rapid (reducing the heating and cooling time of traditional methods) and requires a low reaction temperature.

[0028] Example 3: Cu was selected as the introduced second metal, copper nitrate hexahydrate was chosen, hydrogen was used as the reducing gas, and methane was used as the carbon source. The mixture was fed into an apparatus for preparing second metal-modified β-Mo₂C for reduction and carbonization reactions. Following the specific implementation steps, 1 g of ammonium molybdate tetrahydrate was dissolved in distilled water. 2.3 g (Cu / Mo=0.1), 4.6 g (Cu / Mo=0.2), and 9.2 g (Cu / Mo=0.4) of copper nitrate hexahydrate were dissolved in distilled water and added dropwise to the ammonium molybdate solution. After drying for 12 h, the mixture was calcined at 500 °C for 3 h. The hydrogen flow rate was controlled at 120 mL / min, the methane flow rate at 30 mL / min, the dehydration power at 10 W, and the dehydration time at 8 min. The voltage ramp rate was controlled at 5 V / min, the required input power for the reaction was 41 W, and the reaction time was 4 h. XRD phase analysis of the prepared product was performed, and the results are shown in the appendix. Figure 4 Appendix Figure 4 In the diffraction pattern, the peaks at 2θ = 34.3°, 37.9°, 39.4°, 52.1°, 61.5°, 69.6°, 74.6°, and 75.5° are characteristic peaks of β-Mo₂C. The particle size of the prepared β-Mo₂C can be calculated to be 6.0–8.0 nm using the Scherrer equation. This preparation process is convenient and rapid (reducing the heating and cooling time of traditional methods) and requires a low reaction temperature.

Claims

1. A method for preparing second metal-modified β-Mo2C, characterized in that, The precursor is placed in a plasma generator, in which gaseous hydrocarbons are introduced as a carbon source and hydrogen as a reducing gas. The gas flow rate is controlled at 100-200 mL / min, and the volume ratio of C to H2 is 1:12 to 1:

2. Under the reducing carbonization effect of the reaction gas, β-Mo2C is generated. The precursor is a mixture of molybdenum salt and a second metal salt, with the second metal attached to β-Mo2C in elemental form.

2. The method for preparing second metal-modified β-Mo2C according to claim 1, characterized in that, Preparation of the precursor: Ammonium molybdate aqueous solution and second metal salt aqueous solution are mixed, the mass ratio of the second metal to Mo is (0.1~0.4) / 1, and after stirring evenly, the mixture is dried and calcined into powder.

3. The method for preparing second metal-modified β-Mo2C according to claim 1, characterized in that, The hydrocarbons mentioned are one or more of methane, ethane, and ethylene.

4. The method for preparing second metal-modified β-Mo2C according to claim 1, characterized in that, The plasma generator has an input power of 40W or more and a reaction time of 3 hours or more.

5. The method for preparing second metal-modified β-Mo2C according to claim 4, characterized in that, The plasma generator first increases the input voltage of the power supply in a stepwise manner at a rate of 5~10V / min. When the input power reaches 5~15W, it stays for 5~10min to remove water. Then, the input power is gradually increased to the reaction power. After the reaction power is reached, the reaction time is started.

6. The method for preparing second metal-modified β-Mo2C according to claim 1, characterized in that, The plasma generator includes a gas delivery pipeline, a plasma generating unit, and a plasma controller. The gas delivery pipeline is a stainless steel pipe. One end of the gas delivery pipeline is connected to several gas cylinders via a four-way connector, and the other end of the gas delivery pipeline is connected to the T-shaped quartz tube of the plasma generating unit. The plasma generating unit includes a plastic slip ring, a T-shaped quartz tube, a cylindrical quartz tube, and a stainless steel electrode rod. The T-shaped quartz tube and the cylindrical quartz tube are connected by the plastic slip ring. A stainless steel electrode rod, secured with a rubber stopper, is inserted into the center of the top of the T-shaped quartz tube. The stainless steel electrode rod is positioned at the center of the cylindrical quartz tube and is connected to the positive electrode of the plasma controller. The outer wall of the cylindrical quartz tube is covered with aluminum foil and secured by winding wires. The aluminum foil is connected to the negative electrode of the plasma controller. Inside the cylindrical quartz tube covered with aluminum foil, there is a catalyst precursor bed. The stainless steel electrode rod passes through the catalyst precursor bed. The bottom of the cylindrical quartz tube is connected to a rubber tube.

7. The method for preparing second metal-modified β-Mo2C according to claim 6, characterized in that, The plasma controller is a DC power supply.

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