Preparation method of methane dry reforming monatomic catalyst and methane dry reforming method

Abstract

The application discloses a kind of methane dry reforming single-atom catalyst preparation and use method, using two-step annealing method to prepare single-atom catalyst, more oxygen vacancies are formed on CeO2 carrier by the way of plasma modification, keep higher metal coverage, realize the stable metal content far higher than traditional impregnation method, reduce the generation of by-product and carbon deposition, prolong the service life of catalyst.When using the catalyst, the catalyst is added to the discharge area of low-temperature plasma fluidized bed reactor; start high-voltage power supply, so that low-temperature plasma is generated in the discharge area; the catalyst particles in the discharge area are directly contacted with active substances. Under the synergistic action of plasma catalysis, methane and carbon dioxide are activated to produce carbon monoxide and hydrogen, achieving high catalytic performance and energy efficiency. The carbon generated by CH4 dissociation is reduced from the root, and the continuous reaction can reduce the influence of intermediate by-products on hydrogen selectivity and carbon dioxide conversion rate.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, specifically relating to a method for preparing a single-atom catalyst for methane dry reforming and a method for methane dry reforming. Background Technology

[0002] Due to global warming, effective measures are needed to reduce greenhouse gas emissions. Increasing attention is being paid to the reduction and utilization of greenhouse gases. Carbon dioxide and methane, accounting for 76% and 16% respectively, are the main components of greenhouse gases, but they are also abundant and inexpensive carbon sources; methane is also considered a clean energy source for achieving a low-carbon economy. How to achieve the resource utilization of methane and carbon dioxide has attracted considerable attention.

[0003] Dry methane reforming (DRM) has emerged as an effective solution for reducing greenhouse gas emissions. It converts methane and carbon dioxide into syngas, specifically hydrogen and carbon dioxide, and is a crucial component of world-class industrial processes and energy conversion, such as Fischer-Tropsch synthesis (FT), carbonylation, hydroformylation, and the synthesis of fuels and high-value-added chemicals. Therefore, dry methane reforming technology offers unique economic and environmental benefits. Although DRM emerged approximately 30 years ago, its potential to reduce rising greenhouse gas emissions and provide cleaner fossil fuel utilization has sparked renewed interest in related catalytic technologies. Over the past few decades, efforts have been focused on developing and designing new catalysts to improve the conversion rate of methane and carbon dioxide in DRM technology. The core of DRM technology is the catalyst, with metal catalysts being the most commonly used. Metal catalysts can be further divided into noble metal and non-noble metal catalysts. Non-noble metal catalysts exhibit good application potential due to their low cost and high activity. Ni-based catalysts, with their excellent activity in activating CH bonds, high reactivity, abundant reserves, and low price, have become the most promising DRM candidate catalysts. Carbon dioxide and methane are very stable due to their low Gibbs free energies (-394 kJ / mol and -50.7 kJ / mol, respectively). Therefore, activating carbon dioxide and methane requires a large energy supply and a highly active catalyst. Thus, deep cracking of carbon dioxide (DRM) is a strongly endothermic process, typically requiring high temperatures of 400–1000 °C to achieve high yields. However, nickel metal agglomerates and sinters at reforming temperatures above 590 °C, leading to catalyst deactivation. Furthermore, carbon produced by deep cracking of CH4 tends to accumulate on the catalyst surface, covering active sites and causing catalyst deactivation.

[0004] Based on the bottlenecks of the above-mentioned DRM technology, coking and thermal stability can be reduced by preparing single-atom catalysts; DRM can be carried out at room temperature by catalyst-coupled plasma discharge, thereby reducing energy consumption costs and avoiding high-temperature sintering of N catalysts.

[0005] Previous studies have shown that the size of the catalytically active component has a significant impact on carbon deposition. Ni nanoparticles with a diameter of 2 nm or in the 7-10 nm range show a significant reduction in carbon deposition. However, smaller Ni particles typically exhibit poorer thermal stability and are prone to sintering under DRM reaction conditions. Because single-atom catalysts consist of isolated individual metal atoms dispersed on a solid support, they possess uniform active sites and exhibit greater thermal stability and durability than nanoparticle catalysts. Therefore, preparing single-atom catalysts can, to some extent, reduce carbon deposition and increase thermal stability.

[0006] Low-temperature plasma refers to the generation of highly excited-state molecules, atoms, free radicals, active ions, and high-energy electrons at room temperature, promoting thermodynamically unfavorable reactions and enabling catalytic reactions to proceed at low temperatures, effectively solving the problem of catalyst sintering at high temperatures. Simultaneously, the highly active substances generated by plasma induce structural changes and surface faceting of the catalyst, promoting charge deposition and the formation of active sites, thereby activating the metal and reactants, prolonging the contact time between reactants and catalyst, and achieving higher activation and conversion rates. The combination of plasma and catalyst allows the DRM reaction to proceed smoothly at room temperature, lowering the activation barrier, reducing energy consumption, and effectively preventing Ni sintering at high temperatures. Furthermore, the high-energy electrons generated by plasma facilitate the conversion of CH4 into adsorbed CH4(s), fundamentally reducing carbon generated by CH4 ionization. Therefore, constructing a low-temperature plasma-synergistic nickel-based single-atom catalytic system overcomes the problems of catalyst carbon deposition and sintering, achieving a near-1 H2 / CO2 ratio for the efficient activation of methane and carbon dioxide, which is beneficial for carbonyl synthesis and FT synthesis of chemicals. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a single-atom catalyst for dry reforming of methane and a method for dry reforming of methane.

[0008] In a first aspect, the present invention provides a method for preparing a single-atom catalyst for dry reforming of methane, comprising the following steps:

[0009] Step 1: Add powdered CeO2 support to the nickel chloride precursor solution and stir continuously to form an emulsion; perform a first annealing treatment on the resulting emulsion; the temperature of the first annealing treatment is lower than the decomposition temperature of nickel chloride;

[0010] Step 2: The powder obtained in Step 1 is subjected to a second annealing treatment to obtain the Ni / CeO2 single-atom catalyst. The temperature of the second annealing treatment is 400℃~550℃.

[0011] Step 3: The prepared Ni / CeO2 single-atom catalyst is placed in a plasma discharge device for modification.

[0012] Preferably, the annealing temperature for the first annealing process is 220℃~300℃. The annealing temperature for the second annealing process is 500℃.

[0013] Preferably, the product obtained from the first annealing treatment is washed and then subjected to a second annealing treatment.

[0014] Preferably, the plasma discharge device has a discharge power of 4W to 7W, a frequency of 2kHz to 5kHz, a carrier gas atmosphere of 20% H2 / N2, a gas flow rate of 50mL / min to 100mL / min, and a modification treatment time of 20h to 24h.

[0015] Preferably, the Ni single-atom loading of the single-atom catalyst is 10 wt.% to 23 wt.%.

[0016] As a preferred embodiment, the preparation process of the CeO2 support in step one is as follows: Ce(NO3)3 solution is added dropwise to NaOH solution and stirred continuously to form an emulsion; then the obtained emulsion is subjected to hydrothermal treatment to form a precipitate, the obtained precipitate is washed until neutral, dried and then sintered to obtain the CeO2 support.

[0017] Preferably, the hydrothermal treatment temperature is 100°C and the treatment time is 24 hours.

[0018] Preferably, the drying temperature of the drying treatment is 80℃~100℃, and the drying time is 12h~24h. The sintering temperature of the sintering treatment is 500℃~550℃, and the sintering time is 3h~4h.

[0019] Secondly, the present invention provides a method for dry reforming of methane, the process of which is as follows:

[0020] Step 1: Constructing the plasma fluidized bed reactor; The plasma fluidized bed reactor includes a quartz tube, a grounding electrode, a high-voltage electrode, and a high-voltage power supply; The grounding electrode is wound around the outside of the quartz tube; The high-voltage electrode is placed in the center of the inside of the quartz tube; A gas inlet is located at the bottom of the quartz tube, and a gas outlet is located at the top; The gas inlet is used to introduce the reaction gas; The gas outlet is used to output the reaction products; The high-voltage power supply is used to power the plasma fluidized bed reactor. During operation, the grounding electrode and the high-voltage electrode undergo volumetric discharge within the quartz tube to form a discharge zone;

[0021] Step 2: Add the aforementioned methane dry reforming single-atom catalyst to the discharge zone of the low-temperature plasma fluidized bed reactor, and continuously input methane and carbon dioxide into the discharge zone through the gas inlet; the ratio of total gas flow rate to catalyst mass is 12 L·min. -1 ·g -1 ~18L·min-1 ·g -1 The high-voltage power supply is activated, causing the generation of active substances, including excited-state substances and free radicals, within the discharge zone; the voltage is 20kV to 35kV; the catalyst particles in the discharge zone are in direct contact with the active substances. Under the synergistic effect of plasma catalysis, methane and carbon dioxide are activated to produce carbon monoxide and hydrogen.

[0022] Preferably, the discharge zone of the plasma fluidized bed reactor is 20 mm long and the discharge gap is 2.5 mm. The molar ratio of CH4 / CO2 is (1-9):1, and the total gas flow rate is 50 mL / min to 100 mL / min. The grounding electrode is a stainless steel mesh, and the high-voltage electrode is a stainless steel rod.

[0023] Preferably, the inlet ratio of methane to carbon dioxide is 1:1, and the temperature of the low-temperature plasma fluidized bed reactor is 100-150℃.

[0024] The beneficial effects of this invention are:

[0025] 1. This invention uses a two-step annealing method to prepare Ni / CeO2 single-atom catalysts. The first annealing at a lower temperature can remove ligands that have not undergone chemical adsorption on the support, avoiding their aggregation and covering of active sites; it prevents sintering in the subsequent high-temperature second annealing, maximizing the possibility of metal binding with all available coordination sites; it maintains a high metal coverage, achieving a stable metal content far higher than that of the traditional impregnation method.

[0026] 2. This invention promotes the surface interaction between Ni and CeO2 through plasma modification, which helps to form more oxygen vacancies on the CeO2 support, enhances the thermal stability and selectivity of the catalyst, and facilitates the adsorption and activation of methane and carbon dioxide on oxygen vacancies, thereby reducing the generation of by-products and coke deposits and extending the service life of the catalyst.

[0027] 3. This invention utilizes a plasma fluidized bed reactor to achieve high catalytic performance and energy efficiency. On one hand, the high-energy electrons and other active substances generated by the plasma promote thermodynamically unfavorable reactions, allowing the DRM catalytic reaction to proceed smoothly at low temperatures and effectively preventing Ni sintering at high temperatures. On the other hand, the generation of plasma facilitates the conversion of CH4 into adsorbed CH4(s), fundamentally reducing carbon generated by CH4 dissociation. Furthermore, the plasma fluidized bed reactor provides advantages such as a small temperature gradient and uniform gas-solid phase contact, while also exhibiting high heat and mass transfer efficiency, enabling continuous reaction and reducing the impact of intermediate byproducts on hydrogen selectivity and carbon dioxide conversion rate.

[0028] 4. This invention proposes an intelligent control method for methane dry reforming using low-temperature plasma based on artificial neural network numerical simulation. By optimizing multiple process parameter settings, the optimal catalyst can be obtained, achieving high conversion rates of methane and carbon dioxide while significantly reducing the amount of coke generated during the catalytic process. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of the single-atom catalyst in Example 1 of the present invention.

[0030] Figure 2 This is a schematic diagram of the plasma fluidized bed reactor in Embodiment 2 of the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings.

[0032] Example 1

[0033] like Figure 1 As shown, a method for preparing a single-atom catalyst for dry reforming of methane includes the following steps:

[0034] Step 1: Dissolve a certain amount of Ce(NO3)3·6H2O and NaOH separately in deionized water. Slowly add the Ce(NO3)3 solution dropwise to the NaOH solution, stirring continuously for 30–60 min to form an emulsion. Then transfer the emulsion to a 100 mL stainless steel autoclave and hydrothermally treat it at 100 °C for 24 h. After hydrothermal treatment, allow the autoclave to cool naturally, centrifuge the precipitate, and then filter and wash until the filtrate is neutral (pH = 7). Dry the obtained product at 80–100 °C for 12–24 h, and sinter it at 500–550 °C for 3–4 h to obtain a CeO2 support with a nanorod morphology.

[0035] Step 2: Add the prepared CeO2 support to the nickel chloride precursor solution. Mix and stir the precursor solution until it becomes an emulsion, then perform a first annealing treatment at 300℃. The first annealing temperature must be lower than the decomposition temperature of nickel chloride. The decomposition temperature of nickel chloride is 300-310℃, and the temperature of the first annealing treatment should be controlled to be less than or equal to 300℃.

[0036] Step 3: Wash the powder obtained from the first annealing treatment with ultrapure water and ethanol alternately 3 to 5 times, and then perform a second annealing treatment at 500℃ to obtain the Ni / CeO2 single-atom catalyst.

[0037] The nickel single-atom loadings using different precursor solutions and first annealing temperatures are shown in Table 1.

[0038] Table 1

[0039]

[0040]

[0041] As can be seen from Table 1, the nickel single-atom loading is the highest when NiCl2·6H2O is used as the precursor solution and the first annealing temperature is 300℃, which is a significant improvement compared to the traditional single-atom loading being controlled within 5%.

[0042] Step 4: The annealed Ni / CeO2 single-atom catalyst is placed in a plasma discharge device for modification treatment for 20–24 h. This etches the catalyst surface, creating more oxygen vacancies on the CeO2 support and promoting surface interactions of the catalyst. The plasma discharge device has a discharge power of 4–7 W, a frequency of 2–5 kHz, a carrier gas atmosphere of 20% H2 / N2, and a gas flow rate of 50–100 mL / min.

[0043] In this embodiment, the nickel single-atom loading of the single-atom catalyst is 10wt.% to 23wt.%, the discharge power of the plasma discharge device is 4.8W, the frequency is 2.5kHz, and the gas flow rate is 100mL / min.

[0044] Example 2

[0045] like Figure 2 As shown, a method for producing syngas from methane through dry reforming is implemented using the catalyst described in Example 1 in conjunction with a plasma fluidized bed reactor. The plasma fluidized bed reactor is obtained by adding a plasma generator to a fluidized bed reactor, which generates plasma through dielectric barrier discharge. The plasma fluidized bed reactor includes a quartz tube 1, a grounding electrode 2, a high-voltage electrode 3, and a high-voltage power supply 7. The grounding electrode 2 is wound around the outside of the quartz tube 1; the high-voltage electrode 3 is placed at the center inside the quartz tube 1; a gas inlet 5 is provided at the bottom of the quartz tube 1, and a gas outlet 6 is provided at the top; the gas inlet 5 is used to introduce the reaction gas; the gas outlet 6 is used to output the reaction products; and the high-voltage power supply 7 is used to supply power to the plasma fluidized bed reactor. During operation, the grounding electrode 2 and the high-voltage electrode 3 undergo volumetric discharge within the quartz tube 1 to form a discharge zone 4.

[0046] The specific process of using the single-atom catalyst for dry reforming of methane described in Example 1 to produce syngas from dry methane is as follows:

[0047] In the discharge zone 4 of the low-temperature plasma fluidized bed reactor, the methane dry reforming single-atom catalyst from Example 1 is added, and methane and carbon dioxide are continuously fed into the discharge zone 4 through the gas inlet 5. The high-voltage power supply 7 is activated to generate low-temperature plasma in the discharge zone 4. The low-temperature plasma promotes the generation of active substances, including excited-state substances and free radicals, within the discharge zone 4. The catalyst particles in the discharge zone 4 are in direct contact with the active substances. Under the synergistic effect of plasma catalysis, methane and carbon dioxide are activated to produce carbon monoxide and hydrogen. The inlet gas ratio of methane to carbon dioxide is (1–9):1, and the total flow rate is 50–100 mL / min. The reactor temperature can be measured using an infrared thermometer and maintained at approximately 300°C.

[0048] In this embodiment, the discharge zone length of the plasma fluidized bed reactor is 20 mm, and the discharge gap is 2.5 mm. The molar ratio of CH4 / CO2 is 1:1, and the gas flow rate is 100 ml / min. The grounding electrode 2 is a stainless steel mesh, and the high-voltage electrode 3 is a stainless steel rod. The discharge power is 100 W, the discharge frequency is 7.5 kHz, and the nickel atom loading is 16.3 wt%.

[0049] Example 3

[0050] The preparation parameters of the single-atom catalyst described in Example 1 and the intelligent control method of its hydrogen production parameters are as follows:

[0051] A method for optimizing the preparation parameters of a single-atom catalyst using an artificial neural network model includes the following steps:

[0052] The obtained catalysts were placed in DBD (dielectric barrier discharge) plasma reactors and DRM experiments were conducted according to the discharge process parameters of each group. The CO2 conversion rate, H2 / CO yield ratio, hydrogen selectivity and coke mass on the surface of the spent catalyst were recorded during the experiment.

[0053] Step 1: Design and implement multivariate experiments: Multivariate experiments are divided into catalyst preparation experiments and methane dry reforming experiments.

[0054] The catalyst preparation experiment involved repeatedly adjusting the modified discharge power, discharge frequency, carrier gas atmosphere, and carrier gas flow rate during the plasma modification stage of the catalyst preparation process, and detecting the CO2 conversion rate and hydrogen selectivity of the obtained catalyst as the first training set.

[0055] The process of methane dry reforming experiment is as follows: the gas flow rate, DRM discharge power, and catalyst nickel atom loading are adjusted multiple times during the methane dry reforming process, and the H2 / CO yield ratio and the carbon deposit quality on the surface of the spent catalyst are detected as the second training set.

[0056] Step 2: Construct a first backpropagation neural network (BPNN) with four input variables (discharge power, discharge frequency, carrier gas atmosphere, and carrier gas flow rate during plasma modification) and two output variables (CO2 conversion rate and hydrogen selectivity). Train the first BPNN in MATLAB using the corresponding data from the training set. Using the highest value of the two output variables as the expectation, perform a grid search on each input variable to predict the corresponding output variables under different input variables. Select the output variable that best meets the expectation and its corresponding input variable, and prepare the catalyst based on the obtained input variables.

[0057] Step 3: Construct a second BP neural network with three input variables: gas flow rate during dry reforming, DRM discharge power, and catalyst nickel atom loading; and two output variables: H2 / CO yield ratio and coke mass on the spent catalyst surface. Train the second BP neural network in MATLAB using the corresponding data from the training set. Predict the corresponding output variables through grid search, select the output variables that best meet the expectations and the corresponding discharge process parameters, and prepare the catalyst according to the obtained preparation process parameters.

[0058] In this embodiment, the optimal modified discharge power during catalyst preparation is 4.8 W, the discharge frequency is 2.5 kHz, the carrier gas atmosphere is 20% H / N2, and the carrier gas flow rate is 100 mL / min; the optimal total gas flow rate during methane dry reforming is 100 mL / min, the DRM discharge power is 100 W, and the nickel atom loading is 16.3 wt%. The ratio of total gas flow rate to catalyst mass is 12.5 L·min. -1 ·g -1 .

Claims

1. A method for preparing a single-atom catalyst for dry reforming of methane, characterized in that: Includes the following steps: Step 1: Powdered CeO2 support is added to the nickel chloride precursor solution and stirred continuously to form an emulsion; the resulting emulsion is subjected to a first annealing treatment; the temperature of the first annealing treatment is lower than the decomposition temperature of nickel chloride; the annealing temperature of the first annealing treatment is 220℃~300℃. Step 2: The powder obtained in Step 1 is subjected to a second annealing treatment to obtain a Ni / CeO2 single-atom catalyst; the annealing temperature in the second annealing treatment is 500℃; the product obtained in the first annealing treatment is washed and then subjected to a second annealing treatment. Step 3: The prepared Ni / CeO2 single-atom catalyst is placed in a plasma discharge device for modification treatment to obtain a methane dry reforming single-atom catalyst; the discharge power of the plasma discharge device is 4W to 7W, the frequency is 2kHz to 5kHz, the carrier gas atmosphere is 20% H2 / N2, and the gas flow rate is 50mL / min to 100mL / min; the modification treatment time is 20h to 24h; the Ni single-atom loading of the methane dry reforming single-atom catalyst is 10wt.% to 23wt.%.

2. The method for preparing a single-atom catalyst for dry reforming of methane according to claim 1, characterized in that: The preparation process of CeO2 support described in step one is as follows: Ce(NO3)3 solution is added dropwise to NaOH solution and stirred continuously to form an emulsion; then the obtained emulsion is subjected to hydrothermal treatment to form a precipitate, the obtained precipitate is washed until neutral, dried and then sintered to obtain CeO2 support.

3. The method for preparing a single-atom catalyst for dry reforming of methane according to claim 2, characterized in that: The drying temperature for the drying process is 80℃~100℃, and the drying time is 12h~24h; the sintering temperature for the sintering process is 500℃~550℃, and the sintering time is 3h~4h.

4. A method for preparing syngas by dry reforming of methane, characterized in that: Includes the following steps: Step 1: Constructing a plasma fluidized bed reactor; The plasma fluidized bed reactor includes a quartz tube (1), a grounding electrode (2), a high-voltage electrode (3), and a high-voltage power supply (7); The grounding electrode (2) is wound around the outside of the quartz tube (1); The high-voltage electrode (3) is placed in the center of the inside of the quartz tube (1); A gas inlet (5) is provided at the bottom of the quartz tube (1), and a gas outlet (6) is provided at the top; The gas inlet (5) is used to introduce the reaction gas; The gas outlet (6) is used to output the reaction products; The high-voltage power supply (7) is used to supply power to the plasma fluidized bed reactor; During operation, the grounding electrode (2) and the high-voltage electrode (3) form a discharge zone (4) by volume discharge in the quartz tube (1); Step 2: Add the methane dry reforming single-atom catalyst prepared by the method described in claim 1 to the discharge zone of the plasma fluidized bed reactor, and continuously input methane and carbon dioxide into the discharge zone through the gas inlet; the ratio of catalyst mass to total gas flow rate is 12 L·min. -1 ·g -1 ~18 L·min -1 ·g -1 The high-voltage power supply is activated to induce the generation of active substances, including excited-state substances and free radicals, in the discharge zone; the voltage is 20kV to 35kV; the catalyst particles in the discharge zone are in direct contact with the active substances; under the synergistic effect of plasma catalysis, methane and carbon dioxide are activated to produce carbon monoxide and hydrogen.

5. The method for preparing syngas by dry reforming methane according to claim 4, characterized in that: The plasma fluidized bed reactor has a discharge zone length of 20 mm and a discharge gap of 2.5 mm; a molar ratio of CH4 / CO2 = (1~9):1; a total gas flow rate of 50 mL / min~100 mL / min; a grounding electrode made of stainless steel mesh; and a high-voltage electrode made of stainless steel rod.

6. The method for preparing syngas by dry reforming methane according to claim 4, characterized in that: The inlet ratio of methane to carbon dioxide is 1:1, and the temperature of the plasma fluidized bed reactor is 300°C.

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