Preparation and application of a nickel-based catalyst based on homogeneous deposition-precipitation method

Abstract

This invention provides a method for preparing and applying a nickel-based catalyst based on homogeneous deposition precipitation. The preparation method includes: preparing precursor solution systems containing magnesium salt and nickel salt respectively; performing a first loading operation based on homogeneous deposition precipitation, mixing the magnesium salt solution with urea and MCM-41 molecular sieve and heating to obtain a catalyst precursor loaded with magnesium; performing a second loading operation based on impregnation, mixing the catalyst precursor with the nickel salt solution, evaporating the solvent, and calcining to obtain a nickel-based catalyst; and performing in-situ pretreatment to activate the metal centers, transforming them into nickel-magnesium composite active centers. This invention utilizes the confinement effect of the MCM-41 molecular sieve channels and the chemical anchoring effect of magnesium to inhibit the high-temperature sintering of nickel metal grains; and improves the catalyst's anti-coking and anti-sintering performance in methane dry reforming reactions by promoting carbon dioxide adsorption and conversion through magnesium species.

Description

Technical Field

[0001] This invention relates to the field of catalyst material preparation technology, specifically to the preparation and application of a nickel-based catalyst based on homogeneous deposition precipitation method. Background Technology

[0002] With the increasing severity of the greenhouse effect, dry reforming of methane, which converts methane and carbon dioxide into syngas, has become an important pathway for the resource utilization of greenhouse gases. The dry reforming reaction can convert two major greenhouse gases into syngas, which can then be used in existing technologies to synthesize chemicals such as alcohols, liquid alkanes, and olefins. Among various dry reforming catalytic systems, nickel-based catalysts have become the core catalytic materials of widespread interest and use due to their high carbon-hydrogen bond dissociation ability and lower cost compared to precious metals.

[0003] In existing methane dry reforming technologies, porous inorganic materials are typically used as catalyst supports. Nickel metal precursors are loaded onto the support surface via impregnation or co-precipitation processes, and then introduced into the reactor for online operation after high-temperature reduction. The support material primarily provides specific surface area to disperse the active metal components, while the nickel metal active centers are responsible for catalyzing the adsorption and dissociation of the mixed gas under medium-to-high temperature reaction conditions. To meet actual conversion efficiency requirements, the aforementioned catalytic reaction system needs to maintain continuous operation for extended periods under high-temperature conditions.

[0004] However, in the sustained high-temperature dry reforming reaction environment, existing supported nickel-based catalysts suffer from a technical defect: rapid degradation of catalytic performance due to sintering of the metal active centers. Catalysts prepared using conventional supports and traditional supported processes exhibit weak bonding between the metal particles and the support surface, with the active components largely exposed on the outer surface of the support. Under high-temperature thermodynamic driving, nickel metal grains are highly susceptible to migration and aggregation, leading to severe sintering deactivation. Furthermore, under these conditions, the metal particles also face the problem of carbon deposition deactivation. Both of these factors constrain the long-term stability of the catalytic system. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing and applying nickel-based catalysts based on homogeneous deposition precipitation, which solves the problems of existing nickel-based catalysts being prone to sintering deactivation due to metal grain migration and aggregation in the high-temperature reaction of methane dry reforming, as well as carbon deposition deactivation due to the formation of coated graphite carbon covering the active sites on the surface, thus causing rapid decline in catalytic performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of the present invention provides a nickel-based catalyst based on homogeneous deposition precipitation method, comprising an MCM-41 molecular sieve support and nickel-magnesium composite active centers deposited inside the pores of the MCM-41 molecular sieve; the nickel-magnesium composite active centers contain a metallic phase that has been reduced and activated by in-situ pretreatment. In this process, magnesium is first loaded into the MCM-41 molecular sieve through a homogeneous deposition precipitation process, while nickel is subsequently loaded into the nickel-magnesium composite active center through an impregnation process.

[0007] This invention achieves the following anti-deactivation effects through specific component composition and loading sequence: Regarding resistance to sintering deactivation, physical confinement and chemical anchoring synergistically suppress grain coarsening and grain ripening caused by atomic migration. The regular honeycomb-like pore structure inside the MCM-41 molecular sieve physically confines the nickel nanoparticles within the pores, limiting overall grain migration. Simultaneously, hydroxyl groups on the MCM-41 molecular sieve surface combine with introduced metal ions to generate anchoring sites. The nickel-magnesium composite system constructed by the stepwise loading process enhances the interaction between metal species and the MCM-41 molecular sieve support, attaching activated nickel particles to specific sites and reducing the risk of sintering deactivation of the catalyst under medium-to-high temperature dry reforming reaction conditions. Regarding resistance to carbon deposition deactivation, the formation of coated graphitic carbon is suppressed by regulating the surface chemical pathways of the reactants. Carbon deposition during methane dry reforming originates from the accumulation of nickel carbide species and the disruption of dynamic equilibrium caused by excessive reaction on the carbon dioxide side. Magnesium introduced through prior homogeneous deposition redirects the allocation of carbon dioxide adsorption sites. Dispersed magnesium species promote the transformation and removal of carbon-containing reaction intermediates, preventing carbon substances from covering the active sites of nickel metal and ensuring the long-term stable operation of the catalytic system.

[0008] A second aspect of this invention provides a method for preparing a nickel-based catalyst based on homogeneous deposition precipitation, comprising the following steps: The preparation of the auxiliary metal precursor solution and the main active metal precursor solution is carried out. Magnesium salt is used to prepare the auxiliary metal precursor solution, and nickel salt is used to prepare the main active metal precursor solution. Implement the additive pre-loading operation based on homogeneous deposition precipitation process: Mix the additive metal precursor solution with precipitant and MCM-41 molecular sieve, initiate the reaction in a heated environment to control the nucleation and growth process of additive metal species on the surface of MCM-41 molecular sieve, and after the reaction is completed, extract, dry and calcinate to obtain catalyst precursor loaded with additive elements. Implement the host active metal loading operation based on impregnation process: Mix the obtained catalyst precursor with the host active metal precursor solution, evaporate the solvent under heating conditions, and after drying and calcination, obtain a nickel-based catalyst with a specific loading order. In-situ pretreatment of nickel-based catalysts to activate metal centers: The obtained nickel-based catalysts are placed in a hydrogen-containing gas stream for programmed temperature rise treatment to reduce the metal oxides to a catalytically active metallic phase, so that the nickel and magnesium deposited in the internal channels of MCM-41 molecular sieves interact and are transformed into nickel-magnesium composite active centers.

[0009] As a further limitation of the preparation method: The magnesium salt used in preparing the auxiliary metal precursor solution includes one or more of magnesium acetate, magnesium chloride, and magnesium sulfate; or, the element used in preparing the auxiliary metal precursor solution may be replaced by one or more of calcium, strontium, lanthanum, and cerium. The nickel salt used in preparing the main active metal precursor solution includes one or more of nickel acetate, nickel chloride, and nickel sulfate; or, the element used in preparing the main active metal precursor solution may be replaced by one or more of iron, cobalt, and copper. The solvent used in preparing the solution includes one or more of water, ethanol, acetonitrile, and acetone.

[0010] In the homogeneous deposition precipitation process, the precipitant is urea added in the range of 0.1 g to 5 g by mass. The reaction conditions are as follows: the temperature of the reaction system is controlled between 50℃ and 95℃, and the pH of the reaction solution is continuously monitored until the pH value reaches the range of 6.5 to 9.0, at which point the reaction is terminated. The calcination operation is carried out at 550℃ for 4 hours. The mass fraction of magnesium loaded in the homogeneous deposition precipitation method is set within the range of 0%-5%. Preferably, the mass fraction of magnesium loaded by the homogeneous deposition precipitation method is 0.5%.

[0011] In the impregnation process, the equivalent parameters of the MCM-41 molecular sieve are calculated by measuring the remaining mass of the catalyst precursor obtained from the calcination operation. Based on these equivalent parameters, the main active metal precursor solution is added to the catalyst precursor in a proportional manner for mixing. The evaporation operation is carried out at a controlled heating temperature between 20°C and 75°C. The calcination operation is performed at 550°C for 4 hours. The mass fraction of nickel loaded in the impregnation method is set within the range of 0%-20%.

[0012] Preferably, the impregnation method loads nickel with a mass fraction of 5%.

[0013] In the in-situ pretreatment, nitrogen gas at a flow rate of 30 mL / min was purged into the reaction tube packed with the nickel-based catalyst. Under nitrogen purging conditions, the temperature was increased to 700 °C at a heating rate of 10 °C / min. After reaching 700 °C, hydrogen gas at a flow rate of 30 mL / min was introduced to maintain the pre-reduction operation for 2 hours. Subsequently, nitrogen gas at a flow rate of 30 mL / min was introduced again for continuous purging for 30 minutes.

[0014] A third aspect of this invention provides the application of a nickel-based catalyst based on homogeneous deposition precipitation in the dry reforming reaction of methane, comprising: The catalytic conversion operation of nickel-based catalyst in methane dry reforming reaction is carried out by: the nickel-based catalyst that has been pretreated in situ is connected to the reaction device, and reaction gas containing methane and carbon dioxide is introduced. By controlling the reaction temperature and gas flow rate, methane and carbon dioxide are converted into syngas at the nickel-magnesium composite active center.

[0015] As a further limitation of the application: The introduced reaction gases include methane, carbon dioxide, and nitrogen, with the flow rates of methane, carbon dioxide, and nitrogen set at 25 ml / min.

[0016] The application process includes online sampling and performance parameter calculation of reaction products. A gas chromatograph with a thermal conductivity detector is used to analyze the mixed gas stream at the outlet of the reaction apparatus online to obtain the content signals of each gas component. The content signals are then converted into the volume fraction of each gas component using a pre-calibrated correction factor. Based on the volume fraction and the calculated total volumetric flow rate of the outlet gas, the corresponding outlet flow rate for each gas species is calculated. Furthermore, based on the ratio of the inlet flow rate to the outlet flow rate for each gas species, the conversion rate of the corresponding reactant and the hydrogen-to-carbon ratio parameter in the product are calculated.

[0017] This invention provides a method for preparing and applying a nickel-based catalyst based on homogeneous deposition precipitation. It offers the following advantages: 1. This invention employs MCM-41 molecular sieve as a support and combines a stepwise loading strategy of introducing magnesium additives in advance and impregnating the main active metal nickel in the later stage. It utilizes the physical confinement effect of the pore structure on the internal nickel nanoparticles to restrict the overall migration of the grains, and enhances the interaction force between the metal and the support interface by using the anchoring points generated by the surface hydroxyl groups and metal ions. This stabilizes the reduced nickel particles and suppresses the sintering phenomenon under the high temperature environment of dry reforming, thereby improving the anti-sintering stability of the catalyst.

[0018] 2. This invention introduces magnesium species into a nickel-based catalyst system through a preliminary homogeneous deposition precipitation process, forming reversible active hydroxyl species on the surface. This redistributes the adsorption sites of carbon dioxide, allowing the aforementioned active hydroxyl species to directly participate in the adsorption and activation steps of carbon dioxide molecules, thereby accelerating the oxidation reaction of carbon species. This promotes the transformation and removal of carbon-containing reaction intermediates that are prone to coking, breaking the dynamic equilibrium caused by excessive carbon dioxide reaction leading to nickel carbide accumulation. It also avoids the coating of graphite carbon covering the nickel active sites, thus improving the catalyst's anti-coking performance.

[0019] 3. This invention introduces an auxiliary agent by using urea as a slow-release precipitant in an aqueous system in conjunction with a homogeneous deposition precipitation process, and introduces the main active metal by combining it with an impregnation process. This avoids the agglomeration of metal precursors caused by local concentration abrupt changes in the traditional direct precipitation method, and guides nickel species to deposit deep into the molecular sieve channels. Under the condition of not relying on expensive atomic layer deposition equipment, the active metal clusters are uniformly dispersed into the interior of the support, which improves the exposure degree of active components on the catalyst surface, and realizes the reduction of catalyst preparation cost and full utilization of materials. Attached Figure Description

[0020] Figure 1 These are stability test diagrams for Embodiment 1 and Comparative Example 1 of the present invention; Figure 2 The XRD pattern of the catalyst in Example 1 of the present invention is shown below. Figure 3 This is a TEM image of the catalyst of Example 1 of the present invention; Figure 4 EDS image of the catalyst of Example 1 of the present invention; Figure 5 This is a condition optimization diagram based on magnesium loading of the present invention. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see the appendix Figure 5 This invention provides a method for preparing and applying a nickel-based catalyst based on homogeneous deposition precipitation. Addressing the deactivation problem of nickel-based catalysts during methane dry reforming, which is prone to carbon deposition and sintering of active components, this embodiment controls the metal deposition order and loading method to establish a nickel-magnesium composite microstructure. The overall preparation, application process, and associated deactivation prevention mechanism are described below.

[0023] S1. Prepare solution systems containing auxiliary precursors and active metal precursors, respectively. In the solution preparation stage, select water or alcohol solvents to dissolve specific metal salt compounds to provide the metal ion source for subsequent deposition and loading operations.

[0024] S2. Implement the additive preloading operation based on homogeneous deposition precipitation process. Mix the additive precursor solution with the precipitant and molecular sieve support, and initiate the reaction in a heated environment. Based on the homogeneous deposition precipitation process, control the slow-release rate of the precipitant in the aqueous system to control the nucleation and growth process of the additive metal species on the surface of the molecular sieve support, avoiding the aggregation of metal precursors caused by local concentration abrupt changes in conventional direct precipitation methods. The aforementioned molecular sieve support is MCM-41 molecular sieve with regularly arranged honeycomb channels; the aforementioned additive precursor is a magnesium salt. The introduced magnesium element is dispersed inside the channels of the MCM-41 molecular sieve, creating a basic induction environment for subsequent loading of active components.

[0025] S3. Implement the main active metal loading operation based on the impregnation process. The catalyst precursor, treated and dried in step S2, is mixed with the main impregnation solution containing the active metal, and the liquid solvent is removed by evaporation under heating conditions. Nickel is selected as the main active metal. Since the dispersed magnesium sites have already adhered to the MCM-41 molecular sieve before step S3, these magnesium sites induce the deposition process of nickel species in the impregnation solution. The pre-introduced magnesium sites guide nickel ions in the impregnation solution into the pores of the MCM-41 molecular sieve for deposition.

[0026] S4. Perform in-situ pretreatment of the nickel-based catalyst to activate the metal centers. The nickel-based catalyst obtained in step S3 is placed in a hydrogen-containing gas stream for programmed temperature rise treatment to reduce the metal oxide into a catalytically active metallic phase. During the reduction process, the nickel and magnesium deposited in the internal channels of the MCM-41 molecular sieve interact to transform into nickel-magnesium composite active centers.

[0027] S5. Implement the catalytic conversion application of nickel-based catalysts in the dry reforming reaction of methane. The pretreated nickel-based catalyst is connected to the reaction apparatus, and reaction gases containing methane and carbon dioxide are introduced. By controlling the reaction temperature and gas flow rate, methane and carbon dioxide are converted into syngas at the nickel-magnesium composite active centers, achieving the resource-based conversion and online analysis and evaluation of greenhouse gases.

[0028] In the stepwise deposition catalytic system constructed in steps S1 to S5 above, the anti-deactivation energy relies on the structural effect generated by the nickel-magnesium composite active center.

[0029] To address the sintering deactivation problem of nickel-based catalysts during use, this embodiment employs a combination of physical confinement and chemical anchoring to suppress the sintering of active metals. The uniquely ordered pore structure of MCM-41 molecular sieve provides physical confinement, limiting the overall migration of nickel nanoparticles within the pores. At the chemical level, the surface of MCM-41 molecular sieve contains hydroxyl groups, which can combine with introduced metal ions to form anchoring sites. The stepwise loading of the nickel-magnesium composite system enhances the interaction between the metal species and the MCM-41 molecular sieve. These interactions attach activated nickel particles to specific sites, reducing the risk of sintering deactivation of nickel-based catalysts under medium-to-high temperature dry reforming reaction conditions.

[0030] To address the carbon buildup problem causing catalyst activity decline and equipment blockage during methane dry reforming, this embodiment suppresses carbon buildup formation by controlling the surface chemical pathways of the reactants. Carbon buildup during the methane dry reforming reaction originates from the accumulation of nickel carbide species due to excessive reaction on the carbon dioxide side. This accumulation disrupts the dynamic equilibrium of nickel carbide species, leading to the formation of graphitic carbon. Within the constructed nickel-magnesium composite active center, the introduction of magnesium redirects the distribution of carbon dioxide adsorption sites, causing the transformation and removal of carbon-containing reaction intermediates. This prevents carbon from covering the nickel metal active sites, ensuring the stable operation of the catalytic system.

[0031] In step S1 above, the specific operation of preparing solution systems containing auxiliary precursors and active metal precursors can be further refined into the following sub-steps: S101. Prepare the auxiliary metal precursor solution. Weigh 0.1 g to 5 g of magnesium nitrate hexahydrate and dilute to 100 mL with solvent to obtain the metal precursor solution. Preferably, the mass of magnesium nitrate hexahydrate used is 11.149 g. The magnesium nitrate hexahydrate used to prepare the aforementioned magnesium nitrate solution can be replaced with other magnesium salts, including magnesium acetate, magnesium chloride, and magnesium sulfate. Furthermore, the aforementioned magnesium nitrate solution can be replaced with a salt solution of one or more elements from Group IIA and Group IIIB. Specifically, the aforementioned Group IIA and Group IIIB elements include magnesium, calcium, strontium, lanthanum, and cerium. Preferably, magnesium is used to prepare the salt solution.

[0032] S102. Prepare the main active metal precursor solution. Weigh 0 to 20 grams of nickel nitrate hexahydrate and dilute to 100 ml with solvent to obtain the nickel nitrate solution used in the subsequent impregnation process. Preferably, the mass of nickel nitrate hexahydrate used is set to 7.921 grams. The nickel nitrate hexahydrate used to prepare the aforementioned nickel nitrate solution can be replaced with other nickel salts, including nickel acetate, nickel chloride, and nickel sulfate. The aforementioned nickel nitrate solution can be replaced with a salt solution of one or more short-period transition metals. The aforementioned short-period transition metals specifically include iron, cobalt, nickel, and copper. Preferably, nickel is used to prepare the salt solution.

[0033] S103. Perform the selection of the precursor solution solvent type. The solvent used to prepare the aforementioned salt solutions includes one or more of water, ethanol, acetonitrile, and acetone. Use the aforementioned solvent to adjust the volume of the aforementioned metal salts to different concentrations. Preferably, deionized water and anhydrous ethanol are used to prepare the solutions. In addition, the metal source can be introduced by skipping the dissolution step and directly adding the undissolved metal salt solid to the subsequent process flow.

[0034] In step S2 above, the additive preloading operation based on homogeneous deposition precipitation process can be further refined into the following sub-steps: S201. Take a volume of the auxiliary metal precursor solution ranging from 0 mL to 30 mL, and dilute it with deionized water to bring the total liquid volume to 37 mL. For the solution used in the homogeneous deposition precipitation loading operation, the solvent type includes an ethanol-water solution with a volume fraction ranging from 0% to 60%.

[0035] S202. Add urea in the range of 0 to 5 grams by mass to the diluted auxiliary metal precursor solution as a precipitant for homogeneous deposition precipitation reaction.

[0036] S203. Add 1.000 g of MCM-41 molecular sieve to the mixed solution. Place the reaction system containing MCM-41 molecular sieve in a heated environment for homogeneous deposition precipitation. Control the temperature of the reaction system between 50℃ and 95℃. Continuously monitor the pH of the reaction solution until the pH value reaches the range of 6.5 to 9.0, at which point the reaction is terminated.

[0037] S204. Filter the mixture after the reaction to obtain a solid filter cake. Wash the solid filter cake and dry it at 80°C. Calcine the dried solid at 550°C for 4 hours to obtain a catalyst precursor loaded with additive elements. Preferably, the mass fraction of magnesium loaded by homogeneous deposition precipitation is set to 0.5%.

[0038] In step S3 above, the implementation of the host active metal loading operation based on the impregnation process can be further refined into the following sub-steps: S301. Take a volume of the main active metal precursor solution ranging from 0 mL to 15 mL, and dilute it with anhydrous ethanol until the total liquid volume reaches 15 mL, then mix thoroughly. For the salt solution used in the impregnation loading operation, the solvent used to prepare the solution includes one or more of water, ethanol, acetonitrile, and acetone. Different solvents are used to prepare salt solutions of different concentrations.

[0039] S302. Calculate the remaining mass of the catalyst precursor obtained from the calcination operation in step S204. Calculate the equivalent mass of the MCM-41 molecular sieve based on the remaining mass of the catalyst precursor. Add the diluted main active metal precursor solution to the catalyst precursor in proportion and mix. Place the mixed system in a heating environment and control the heating temperature within the range of 20℃ to 75℃ to carry out an evaporation operation to remove the solvent.

[0040] S303. The solid product obtained after evaporation to remove the solvent is dried at 80°C. The dried solid product is then calcined at 550°C for 4 hours to obtain a nickel-based catalyst with a specific loading order. Preferably, the mass fraction of nickel element loaded by the impregnation method is set to 5%.

[0041] In step S4 above, the specific operation of in-situ pretreatment of the nickel-based catalyst can be further refined into the following sub-steps: S401. Perform the physical forming and loading operation of the nickel-based catalyst. Compress the prepared nickel-based catalyst powder into a solid tablet. Crush the solid tablet and sieve it to obtain catalyst particles in the range of 40 to 80 mesh. Measure 0.100 g of the catalyst particles and mix them thoroughly with 0.500 g of quartz sand with a particle size in the range of 40 to 80 mesh. Load the mixed solid material into a quartz tube. Connect the quartz tube filled with the solid material to the fixed-bed reaction evaluation device.

[0042] S402. Perform in-situ temperature-programmed pre-reduction of the nickel-based catalyst. Purge the quartz tube with nitrogen gas at a flow rate of 30 mL / min. While purging with nitrogen, raise the temperature inside the quartz tube to 700°C. Purge the quartz tube with hydrogen gas at a flow rate of 30 mL / min. Maintain this hydrogen environment for 2 hours to complete the pre-reduction of the nickel-based catalyst. After the pre-reduction is complete, purge the quartz tube again with nitrogen gas at a flow rate of 30 mL / min for 30 minutes.

[0043] In step S5 above, the application and evaluation of nickel-based catalysts in the dry reforming of methane can be further refined into the following sub-steps: S501. Implement controlled operation of the methane dry reforming catalytic reaction. After the pre-reduction and nitrogen purging operations are completed, raise the temperature inside the quartz tube to the required temperature. Introduce the reaction gases into the quartz tube, including methane, carbon dioxide, and nitrogen. Preferably, the flow rates of methane, carbon dioxide, and nitrogen are set to 25 mL / min.

[0044] S502. Implement online sampling and performance parameter calculation of reaction products. Utilize a gas chromatograph (GC) thermal conductivity detector (TCD) to perform online analysis of the mixed gas stream at the reaction tube outlet. The GCCD outputs the content signals of each gas component. Combined with a pre-calibrated correction factor, the content signals are converted to obtain the volume fraction of each gas component. After data normalization and combined with the total volumetric flow rate of the outlet gas, the outlet flow rate corresponding to each species is obtained. Based on the inlet flow rate values ​​and outlet flow rate calculation results for each gas species, the reactant conversion rate and hydrogen-to-carbon ratio parameter for the corresponding species are calculated. The initial catalytic performance of the nickel-based catalyst in the methane dry reforming reaction is evaluated using the reactant conversion rate and hydrogen-to-carbon ratio parameter.

[0045] S503. Conduct a long-term catalytic stability assessment of the nickel-based catalyst. Replace with fresh nickel-based catalyst and perform loading and pretreatment operations using the same process as in steps S401 to S402. Under specific high-temperature conditions, conduct stability tests by introducing inlet gas with the same space velocity and composition. Continuously acquire methane conversion and carbon dioxide conversion data, and evaluate the anti-coking and anti-sintering performance of the nickel-based catalyst by analyzing the trend of conversion data over time.

[0046] To verify the technical effectiveness of the stepwise deposition strategy for preparing nickel-based catalysts, the following parallel examples and comparative examples were implemented for comparison and illustration. Example

[0047] 0.465 mL of a 0.448 mol / L magnesium nitrate solution, 1.552 g of urea, 1.000 g of MCM-41, and 37 mL of deionized water were mixed and stirred in an oil bath at 85°C for 8 hours. The reaction was stopped when the pH of the reaction solution reached 8.3. The filter cake was filtered and washed, dried at 80°C, and calcined at 550°C for 4 hours to obtain the catalyst precursor. 3.345 mL of a 0.272 mol / L nickel nitrate ethanol solution was diluted to 15 mL. The catalyst precursor was weighed, and the diluted nickel nitrate solution was mixed with the catalyst precursor. The solvent was evaporated in an oil bath at 60°C, dried at 80°C, and calcined at 550°C for 4 hours to obtain the nickel-based catalyst. 0.100 g of 40-80 mesh catalyst particles were mixed with 0.500 g of quartz sand and packed into the catalyst. The catalyst was heated to 700°C under nitrogen purging at 30 mL / min, and pre-reduced with hydrogen at 30 mL / min for 2 hours. Then, methane, carbon dioxide, and nitrogen were introduced at 25 mL / min each. Within 7 hours, the methane conversion rate was between 80.2% and 81.6%, and the carbon dioxide conversion rate was between 81.5% and 83.2%. A fresh nickel-based catalyst was then used, and stability tests were conducted at 800°C. Within 1000 hours, the methane conversion rate was between 93.7% and 94.1%, and the carbon dioxide conversion rate was between 94.3% and 95.6%. Example

[0048] The operating conditions for Example 2 were basically the same as those for Example 1, except that the amount of magnesium nitrate solution used was adjusted to 0.185 mL. The reaction test temperature was raised to 900 °C. Within 7 hours, the methane conversion rate was between 98.4% and 99.2%, and the carbon dioxide conversion rate was between 98.7% and 100.0%. Example

[0049] The operating conditions for Example 3 were basically the same as those for Example 1, except that the amount of magnesium nitrate solution was adjusted to 1.865 mL, the amount of deionized water was adjusted to 35 mL, and the reaction time was extended to 56 hours. The reaction test temperature was lowered to 650°C. Within 7 hours, the methane conversion rate decreased from 54.4% to 49.1%, and the carbon dioxide conversion rate decreased from 57.8% to 53.2%. Example

[0050] The operating conditions for Example 4 were basically the same as those for Example 1, except that the amount of nickel nitrate solution used was adjusted to 1.340 mL. The flow rates of the reaction gases methane, carbon dioxide, and nitrogen were adjusted to 5 mL / min. Within 7 hours, the methane conversion rate decreased from 79.0% to 76.7%, and the carbon dioxide conversion rate remained between 80.7% and 81.2%. Example

[0051] The operating conditions in Example 5 were basically the same as in Example 1, except that the amount of nickel nitrate solution used was adjusted to 10.0 mL. The flow rates of the reaction gases methane, carbon dioxide, and nitrogen were each adjusted to 100 mL / min. Within 7 hours, the methane conversion rate was between 34.9% and 36.7%, and the carbon dioxide conversion rate was between 41.0% and 42.9%. Example

[0052] Example 6 reversed the metal loading order. First, 3.345 mL of nickel nitrate solution, 1.552 g of urea, 1.000 g of MCM-41, and 34 mL of deionized water were added for a homogeneous precipitation reaction for 18 hours, reaching a pH of 7.4. Then, 0.465 mL of magnesium nitrate solution was diluted to 15 mL and mixed with the precursor. Within 7 hours, the methane conversion rate decreased from 71.8% to 57.3%, and the carbon dioxide conversion rate decreased from 73.1% to 58.3%.

[0053] Comparative Example 1: Comparative Example 1 used only homogeneous deposition precipitation to load nickel, without adding magnesium as an auxiliary agent. Nickel nitrate solution, 1.552 g of urea, 1.000 g of MCM-41, and 32 mL of deionized water were added to Comparative Example 1, and the reaction time was 32 hours. The methane conversion rate remained between 79.1% and 80.8% within 7 hours. After replacing the catalyst with fresh one and conducting a 400-hour stability test at 800°C, the methane conversion rate decreased from 92.7% to 80.2%.

[0054] Comparative Example 2: Comparative Example 2 employed a homogeneous coprecipitation method, simultaneously adding magnesium nitrate solution and nickel nitrate solution for a 32-hour homogeneous deposition precipitation reaction. Within 7 hours, the methane conversion rate decreased from 74.4% to 69.9%.

[0055] Comparative Example 3: Comparative Example 3 used a co-impregnation method, where a nickel nitrate solution and a magnesium nitrate solution were mixed and then directly added to an MCM-41 molecular sieve for evaporation loading. Within 7 hours, the methane conversion rate decreased from 57.2% to 44.4%.

[0056] Comparative Example 4: Comparative Example 4 used only homogeneous deposition precipitation to load magnesium, without adding nickel. Within 7 hours, the methane conversion rate ranged from 1.7% to 5.1%.

[0057] The catalyst activity data of each example and each comparative example at the 7th hour of reaction were summarized and compared. As shown in Table 1, the methane conversion rate of Example 1 was 80.3%, the carbon dioxide conversion rate was 82.3%, and the hydrogen-to-carbon ratio was 0.940. The methane conversion rate of Example 2 was 98.6%, the carbon dioxide conversion rate was 99.8%, and the hydrogen-to-carbon ratio was 0.986. The methane conversion rate of Example 3 was 49.1%, the carbon dioxide conversion rate was 53.2%, and the hydrogen-to-carbon ratio was 0.821. The methane conversion rate of Example 4 was 76.7%, the carbon dioxide conversion rate was 80.7%, and the hydrogen-to-carbon ratio was 0.940. The methane conversion rate of Example 5 was 36.7%, the carbon dioxide conversion rate was 41.0%, and the hydrogen-to-carbon ratio was 0.929. The methane conversion rate of Example 6 was 57.3%, the carbon dioxide conversion rate was 58.3%, and the hydrogen-to-carbon ratio was 0.863. The methane conversion rate of Comparative Example 1 was 79.1%, the carbon dioxide conversion rate was 81.6%, and the hydrogen-to-carbon ratio was 0.942. Comparative Example 2 had a methane conversion rate of 69.9%, a carbon dioxide conversion rate of 70.4%, and a hydrogen-to-carbon ratio of 0.906. Comparative Example 3 had a methane conversion rate of 44.4%, a carbon dioxide conversion rate of 44.2%, and a hydrogen-to-carbon ratio of 0.796. Comparative Example 4 had a methane conversion rate of 1.7% and a carbon dioxide conversion rate of 2.6%.

[0058] Table 1 Catalyst activity of each embodiment and comparative example at 7 h methane conversion rate Carbon dioxide conversion rate Hydrogen-to-carbon ratio Example 1 80.3% 82.3% 0.940 Example 2 98.6% 99.8% 0.986 Example 3 49.1% 53.2% 0.821 Example 4 76.7% 80.7% 0.940 Example 5 36.7% 41.0% 0.929 Example 6 57.3% 58.3% 0.863 Comparative Example 1 79.1% 81.6% 0.942 Comparative Example 2 69.9% 70.4% 0.906 Comparative Example 3 44.4% 44.2% 0.796 Comparative Example 4 1.7% 2.6% —— See attached document Figure 1 , Figure 1 This is a stability test diagram of Embodiment 1 and Comparative Example 1 according to an embodiment of the present invention. Figure 1 Online test data were recorded under a high temperature condition of 800℃. Example 1, containing pre-loaded magnesium, maintained a stable conversion rate during a 1000-hour test period. Comparative Example 1, without added magnesium, showed a significant decrease in conversion rate during a 400-hour test period. The comparative data verified that the composite active center constructed by the stepwise loading process possesses anti-coking and anti-sintering properties.

[0059] See attached document Figure 2 , Figure 2 This is an XRD pattern of Embodiment 1 according to an embodiment of the present invention. Figure 2 The phase structure data before and after the pre-reduction operation were recorded. Before pre-reduction, diffraction peaks of nickel oxide phase appeared in the spectrum, and after pre-reduction, diffraction peaks of elemental metallic nickel phase appeared in the spectrum, indicating that the pretreatment operation completed the construction of the reduced metal center.

[0060] See attached document Figure 3 , Figure 3 This is a TEM image of Embodiment 1 according to an embodiment of the present invention; see attached... Figure 4 , Figure 4This is an EDS image of Embodiment 1 according to an embodiment of the present invention. Figure 3 The microscopic distribution of the internal pores and metal particles in the catalyst was recorded, indicating that the metal particles did not exhibit large-scale aggregation. Figure 4 The elemental mapping distribution data show that nickel, magnesium, and silicon are uniformly distributed in the catalyst structure.

[0061] See attached document Figure 5 , Figure 5 This is a conditional optimization diagram based on magnesium loading according to an embodiment of the present invention. Figure 5 The carbon dioxide conversion rate, methane conversion rate, and hydrogen-to-carbon ratio curves were recorded under conditions of varying magnesium additive loading, substitution of alkaline earth metal species, and substitution of rare earth metal species. Figure 5 Data shows that there is a specific ratio window for adding magnesium to achieve control over reaction performance.

[0062] For the physical assembly of the fixed-bed reaction evaluation device, the gas path connection of the gas chromatograph thermal conductivity detector, the data acquisition procedure of the X-ray diffractometer, the imaging operation of the transmission electron microscope, and the elemental calibration of the energy dispersive X-ray spectroscopy, those skilled in the art can use the conventional operation manuals of the relevant instruments to carry out the above-mentioned operational details, which are well known in the art and will not be elaborated here.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A nickel-based catalyst based on a homogeneous deposition precipitation method, characterized in that, It includes an MCM-41 molecular sieve support and nickel-magnesium composite active centers deposited inside the pores of the MCM-41 molecular sieve; the nickel-magnesium composite active centers contain a metallic phase that has been reduced and activated through in-situ pretreatment. In this process, the magnesium element in the nickel-magnesium composite active center is first loaded into the MCM-41 molecular sieve through a homogeneous deposition precipitation process, and the nickel element in the nickel-magnesium composite active center is subsequently loaded through an impregnation process.

2. A method for preparing a nickel-based catalyst based on homogeneous deposition precipitation as described in claim 1, characterized in that, Includes the following steps: Step S1: Prepare the auxiliary metal precursor solution and the main active metal precursor solution, wherein the auxiliary metal precursor solution is prepared using a magnesium salt and the main active metal precursor solution is prepared using a nickel salt. Step S2: Implement the additive pre-loading operation based on homogeneous deposition precipitation process: Mix the additive metal precursor solution with precipitant and MCM-41 molecular sieve, and initiate the reaction in a heating environment to control the nucleation and growth process of additive metal species on the surface of MCM-41 molecular sieve. After the reaction is completed, the catalyst precursor loaded with additive elements is obtained through extraction, drying and calcination. Step S3: Implement the main active metal loading operation based on impregnation process: Mix the catalyst precursor obtained in step S2 with the main active metal precursor solution, evaporate the solvent under heating conditions, and after drying and calcination, obtain a nickel-based catalyst with a specific loading order. Step S4: Perform in-situ pretreatment of the nickel-based catalyst to activate the metal center: Place the nickel-based catalyst obtained in step S3 into a hydrogen-containing gas stream for programmed temperature rise treatment to reduce the metal oxide into a catalytically active metallic phase.

3. The method for preparing a nickel-based catalyst based on homogeneous deposition precipitation according to claim 2, characterized in that, In step S1: The magnesium salt used in preparing the auxiliary metal precursor solution includes one or more of magnesium acetate, magnesium chloride, and magnesium sulfate; or, the element used in preparing the auxiliary metal precursor solution may be replaced with one or more of calcium, strontium, lanthanum, and cerium. The nickel salt used to prepare the main active metal precursor solution includes one or more of nickel acetate, nickel chloride, and nickel sulfate; Alternatively, the element used in preparing the main active metal precursor solution may be replaced with one or more of iron, cobalt, and copper. The solvents used to prepare the solution include one or more of water, ethanol, acetonitrile, and acetone.

4. The method for preparing a nickel-based catalyst based on homogeneous deposition precipitation according to claim 3, characterized in that, In step S2: The precipitant is urea, and the mass of the urea added is in the range of 0 to 5 grams. The reaction conditions for the homogeneous deposition precipitation process are as follows: the temperature of the reaction system is controlled within the range of 50°C to 95°C, and the pH of the reaction solution is continuously monitored until the pH value of the reaction solution reaches the range of 6.5 to 9.0, at which point the reaction is terminated. The calcination conditions are as follows: calcination at 550°C for 4 hours.

5. The method for preparing a nickel-based catalyst based on homogeneous deposition precipitation according to claim 4, characterized in that, In step S3: The main active metal precursor solution is added as follows: the remaining mass of the catalyst precursor obtained from the calcination operation in step S2 is calculated, the equivalent of MCM-41 molecular sieve is calculated based on the remaining mass of the catalyst precursor, and the main active metal precursor solution is added to the catalyst precursor in proportion and mixed. The conditions for evaporating and removing the solvent are: controlling the heating temperature within the range of 20°C to 75°C during the evaporation operation; The calcination conditions are as follows: calcination at 550°C for 4 hours.

6. The method for preparing a nickel-based catalyst based on homogeneous deposition precipitation according to claim 5, characterized in that: In step S2, the mass fraction of magnesium loaded by the homogeneous deposition precipitation method is set to be in the range of 0.2%-2%; In step S3, the mass fraction of nickel element loaded by the impregnation method is set to be in the range of 2%-15%.

7. The method for preparing a nickel-based catalyst based on homogeneous deposition precipitation according to claim 6, characterized in that, In step S4, the in-situ pretreatment operation steps include: Nitrogen gas at a flow rate of 30 mL / min was introduced into the reaction tube containing the nickel-based catalyst for purging. Under nitrogen purging conditions, the temperature was increased to 700°C at a heating rate of 10°C / min. After the temperature reaches 700℃, hydrogen gas is introduced at a flow rate of 30 ml / min, and the pre-reduction operation is completed by maintaining the hydrogen environment for 2 hours. Then, nitrogen gas is introduced again at a flow rate of 30 ml / min for 30 minutes to purge.

8. The application of a nickel-based catalyst based on homogeneous deposition precipitation as described in claim 1 in the dry reforming reaction of methane.

9. The application according to claim 8, characterized in that, The application includes: connecting the nickel-based catalyst that has undergone in-situ pretreatment to the reaction device, introducing reaction gas containing methane and carbon dioxide, and converting methane and carbon dioxide into syngas at the nickel-magnesium composite active center by controlling the reaction temperature and gas flow rate. The reaction gases include methane, carbon dioxide, and nitrogen, with the flow rates of methane, carbon dioxide, and nitrogen set at 25 ml / min.

10. The application according to claim 9, characterized in that, The application also includes online sampling and performance parameter calculation of reaction products: The mixed gas stream at the outlet of the reaction device is analyzed and detected online using a gas chromatograph thermal conductivity detector to obtain the content signal of each gas component; combined with a pre-calibrated correction factor, the content signal is converted into the volume fraction of each gas component. After data normalization and combined with the total volumetric flow rate of the outlet gas, the outlet flow rate of each species was obtained. Based on the inlet flow rate and outlet flow rate of each gas species, the reactant conversion rate and hydrogen-to-carbon ratio of the corresponding species were calculated.

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