Preparation method for preparing synthesis gas through iron-catalyzed methane dry reforming

Abstract

The invention belongs to the technical field of energy chemical industry and catalysis, and discloses a preparation method for preparing synthesis gas through iron-catalyzed methane dry reforming. According to the method, gamma-aluminum oxide is taken as a carrier, ferric nitrate is loaded by adopting an equivalent-volume impregnation method, an iron oxide catalyst is formed through drying and roasting, and metal iron active sites with high dispersity are obtained through hydrogen reduction. The reaction is carried out in a fixed bed reactor, the reaction temperature is controlled to be 650-700 DEG C, methane and carbon dioxide are mixed according to the volume ratio of 1: 1 and introduced into the reactor under the normal pressure condition, and efficient dry reforming is realized to generate synthesis gas. According to the method, the methane conversion rate can reach 85% or above, and the carbon dioxide conversion rate can reach 90% or above. Compared with the existing noble metal or nickel-based catalytic system, the catalyst disclosed by the invention has the advantages of cheap raw materials, simple and convenient preparation process, excellent carbon deposition resistance, capability of keeping high activity and stability at lower temperature, low energy consumption, low cost, strong environmental protection property and suitability for industrial amplification.

Description

Technical Field

[0001] This invention belongs to the field of energy, chemical engineering and catalysis technology, and specifically relates to a method for preparing syngas by iron-catalyzed dry reforming of methane. Background Technology

[0002] Methane dry reforming refers to the process in which methane reacts with carbon dioxide to produce syngas (mainly composed of carbon monoxide and hydrogen) under the action of a catalyst. This reaction not only realizes the resource utilization of natural gas and greenhouse gases, but also allows the syngas to be directly used to synthesize methanol, liquid fuels, and various high-value-added chemicals, making it of significant application value in the energy and chemical industries. However, existing methane dry reforming technologies still have significant shortcomings in terms of catalytic systems and process conditions. Currently, commonly used catalysts are mainly precious metals (such as platinum, rhodium, and ruthenium) or nickel-based materials. The former has excellent catalytic performance but is expensive and scarce, limiting its large-scale application; the latter, although inexpensive, is prone to particle agglomeration and surface carbon accumulation during high-temperature reactions, leading to rapid catalyst deactivation and short service life. On the other hand, the molecular structures of methane and carbon dioxide are stable, making the reaction difficult to activate and requiring high temperatures above 800°C for effective operation, resulting in high energy consumption and stringent equipment requirements, which is not conducive to industrial promotion.

[0003] Furthermore, some catalytic systems are prone to inducing side reactions, reducing the precision of CO to H2 ratio control in syngas, affecting subsequent synthesis and utilization, and exhibiting low atom economy and resource utilization efficiency. Therefore, there is an urgent need to develop a low-cost, thermally stable, and highly efficient catalytic system that can operate under mild conditions to achieve clean, efficient, and industrial-scale application of methane dry reforming. Summary of the Invention

[0004] To address the shortcomings mentioned in the background art, the present invention aims to provide a method for preparing syngas by iron-catalyzed dry reforming of methane. The method employs an equal-volume impregnation method to prepare an Fe / Al2O3 catalyst, which is then subjected to heat treatment and hydrogen reduction to form highly dispersed metallic iron active sites. This enables efficient conversion of methane and carbon dioxide at ambient pressure and relatively low temperature, generating syngas composed of CO and H2. The method features low cost, high stability, and good resistance to carbon deposition, making it suitable for green chemical engineering and carbon resource utilization.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for preparing syngas by iron-catalyzed dry reforming of methane includes the following steps:

[0007] S1. Provide an alumina carrier and pre-treat it by placing the alumina carrier in a heating device for heat treatment to remove surface impurities and adsorbates, and then cooling it for later use.

[0008] S2. Dissolve the iron source in a solvent to prepare an impregnation solution. Add the pretreated alumina carrier to the solution using an equal-volume impregnation method. Perform contact treatment under stirring until the impregnation solution is basically absorbed, and obtain the impregnated body.

[0009] S3. The obtained impregnated body is dried to remove moisture, and then heated and roasted.

[0010] S4. The calcined iron oxide support is placed in a reducing atmosphere for reduction treatment to obtain an iron-based catalyst with metallic iron on the surface, and then cooled for later use.

[0011] S5. The iron-based catalyst is uniformly packed in the middle of the reactor, and inert packing is set at the upper and lower ends of the catalyst to stabilize the bed structure. The methane and carbon dioxide inlet system is connected, and the mixed gas is introduced into the reactor to contact the catalyst for dry reforming reaction. After the reaction, a synthesis gas mainly composed of carbon monoxide and hydrogen is generated.

[0012] More preferably, the alumina carrier is γ-crystalline alumina, and surface activation and impurity removal are completed by high-temperature calcination.

[0013] More preferably, the iron source is a ferric salt compound, preferably ferric nitrate, and its solution is loaded onto the surface of alumina by an equal-volume impregnation method to achieve uniform adsorption of the active component.

[0014] More preferably, the S3 calcination step is carried out in an air atmosphere, with the temperature increased to 550°C at a heating rate of 5°C / min, and then held at that temperature for 3 hours to convert the iron salt precursor into an iron oxide support.

[0015] More preferably, the reducing atmosphere is hydrogen, used to reduce iron oxide to the active component of metallic iron.

[0016] More preferably, after the reduction treatment in step S4 is completed, the system is purged with inert gas to remove residual reducing gas in the reactor and stabilize the catalyst surface state.

[0017] More preferably, the catalytic reaction in step S5 is carried out in a fixed-bed reactor under atmospheric pressure, and the reaction temperature is controlled between 650°C and 700°C.

[0018] More preferably, the volume ratio of the methane to carbon dioxide mixture is 1:1, and the total flow rate of the mixture is controlled by a mass flow meter.

[0019] More preferably, the volume ratio of carbon monoxide to hydrogen in the syngas is approximately 1:1, which is suitable for downstream methanol synthesis or Fischer-Tropsch synthesis reaction systems.

[0020] More preferably, the upper and lower ends of the catalyst loading area in the fixed-bed reactor are filled with quartz sand to fix the catalyst position and prevent particles from being carried out by the airflow.

[0021] The beneficial effects of this invention are:

[0022] This invention utilizes an equal-volume impregnation method to load an iron source onto the surface of a γ-alumina support. Following optimized heat treatment and hydrogen reduction steps, an iron-based catalyst with highly dispersed metallic iron active centers on its surface is obtained. In this structure, the active components are uniformly distributed, significantly suppressing metal sintering and agglomeration under high-temperature conditions, thereby improving the catalyst's thermal stability and lifespan. Simultaneously, this catalyst exhibits excellent resistance to carbon deposition during dry reforming reactions, effectively preventing catalyst deactivation due to carbon deposition. After 4 hours of continuous reaction, it still retains over 90% of its catalytic activity. Compared to traditional noble metal or nickel-based catalyst systems, the catalyst of this invention is simple to prepare, uses readily available raw materials, and significantly reduces reaction costs.

[0023] Regarding reaction conditions, this invention can achieve synergistic and efficient conversion of methane and carbon dioxide within a medium temperature range of 650–700℃. The reaction pressure is atmospheric pressure, the reaction system is simple, and there is no need for high-pressure equipment and complex energy management systems, further reducing equipment burden and operating energy consumption. Experimental results show that this method can achieve a methane conversion rate of not less than 85% and a carbon dioxide conversion rate of not less than 90%, with a CO to H2 volume ratio in the generated syngas close to 1:1. It is suitable for downstream processes of methanol synthesis and Fischer-Tropsch synthesis, and has good atom economy and process adaptability. Attached Figure Description

[0024] The invention will now be further described with reference to the accompanying drawings.

[0025] Figure 1 The bar charts show the CH4 to CO2 conversion rates of Examples 1-3 and Comparative Examples 1-3.

[0026] Figure 2 The bar chart shows the CO selectivity and byproduct formation for Examples 1-3 and Comparative Examples 1-3;

[0027] Figure 3 Line graphs showing the activity retention rate of CH4 conversion for Examples 1-3 and Comparative Examples 1-3. Detailed Implementation

[0028] The technical solutions of 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.

[0029] Example 1: Preparation and application of standard Fe / Al2O3 catalyst

[0030] S1. Carrier pretreatment: γ-alumina was selected as the carrier and placed in a muffle furnace for heat treatment at 500℃ for 2 hours to remove adsorbed water and impurities. After cooling, it was ready for use.

[0031] S2. Iron source loading: Weigh ferric nitrate and dissolve it in deionized water to prepare a 0.5 mol / L solution. Add the alumina support to the solution using the equal volume impregnation method and stir for 4 hours to allow for full adsorption, thus obtaining a wet impregnated body.

[0032] S3. After vacuum drying the impregnated body at 60℃ for 8h, the dried product is heated to 550℃ at a rate of 5℃ / min and calcined in air for 3h to obtain the Fe2O3 / Al2O3 oxide catalyst precursor.

[0033] S4. The catalyst precursor was loaded into the central region of the tubular reactor, and pure hydrogen was introduced as the reducing gas at a flow rate of 50 mL / min. Reduction was carried out at 400 °C for 2 hours. After reduction, the hydrogen supply was stopped, and the reactor was purged with inert nitrogen for 30 minutes to remove residual hydrogen. After cooling, catalytically active metallic iron (Fe) was obtained. 0 ).

[0034] S5. The above catalyst is uniformly packed into the central region of the fixed-bed reactor, and quartz sand is filled above and below the catalyst to stabilize the bed structure. A mixture of methane and carbon dioxide with a volume ratio of 1:1 is introduced at a total flow rate of 100 mL / min, and a dry reforming reaction is carried out at 650 °C for 4 hours.

[0035] Example 2: Preparation and application of Fe / Al2O3 catalyst with iron source supported by immersion method

[0036] S1. Carrier pretreatment: γ-alumina was selected as the carrier and placed in a muffle furnace for heat treatment at 500℃ for 2 hours to remove adsorbed water and impurities. After cooling, it was ready for use.

[0037] S2. Iron source loading: A 0.5 mol / L solution of ferric nitrate was prepared by dissolving it in deionized water. 50.0 g of the pretreated γ-Al₂O₃ support was directly added to this iron salt solution, and the mixture was magnetically stirred at room temperature for 6 hours to allow iron ions to gradually adsorb onto the support surface. After adsorption, the solid and liquid were separated, and the wet support was collected by vacuum filtration to obtain the wet-impregnated body.

[0038] S3. After vacuum drying the impregnated body at 60℃ for 8 hours, the dried product is heated to 550℃ at a rate of 5℃ / min and calcined in air for 3 hours to obtain the Fe2O3 / Al2O3 oxide support, which is then cooled for later use.

[0039] S4. The catalyst precursor was loaded into the central region of the tubular reactor, and pure hydrogen was introduced as the reducing gas at a flow rate of 50 mL / min. Reduction was carried out at 400 °C for 2 hours. After reduction, the hydrogen supply was stopped, and the reactor was purged with inert nitrogen for 30 minutes to remove residual hydrogen. After cooling, catalytically active metallic iron (Fe) was obtained. 0 ).

[0040] S5. The above catalyst is uniformly packed into the central region of the fixed-bed reactor, and quartz sand is filled above and below the catalyst to stabilize the bed structure. A mixture of methane and carbon dioxide with a volume ratio of 1:1 is introduced at a total flow rate of 100 mL / min, and a dry reforming reaction is carried out at 650 °C for 4 hours.

[0041] Example 3: Extending the reaction time

[0042] S1. Carrier pretreatment: γ-alumina was selected as the carrier and placed in a muffle furnace for heat treatment at 500℃ for 2 hours to remove adsorbed water and impurities. After cooling, it was ready for use.

[0043] S2. Iron source loading: Weigh ferric nitrate and dissolve it in deionized water to prepare a 0.5 mol / L solution. Add the alumina support to the solution using the equal volume impregnation method and stir for 4 hours to allow for full adsorption, thus obtaining a wet impregnated body.

[0044] S3. After vacuum drying the impregnated body at 60℃ for 8h, the dried product is heated to 550℃ at a rate of 5℃ / min and calcined in air for 3h to obtain the Fe2O3 / Al2O3 oxide catalyst precursor.

[0045] S4. The catalyst precursor was loaded into the central region of the tubular reactor, and hydrogen (H2) was introduced at a flow rate of 50 mL / min for reduction at 400 °C for 2 hours. Then, nitrogen (N2) was used for purging for 30 minutes. After cooling, catalytically active metallic iron (Fe) was obtained. 0 ).

[0046] S5. The above catalyst is uniformly packed into the central region of the fixed-bed reactor, and quartz sand is filled above and below the catalyst to stabilize the bed structure. A mixture of methane and carbon dioxide with a volume ratio of 1:1 is introduced at a total flow rate of 100 mL / min, and a dry reforming reaction is carried out at 650 °C for 8 hours.

[0047] Comparative Example 1: The catalyst was not subjected to reduction treatment.

[0048] S1. Carrier pretreatment: γ-alumina was selected as the carrier and placed in a muffle furnace for heat treatment at 500℃ for 2 hours to remove adsorbed water and impurities. After cooling, it was ready for use.

[0049] S2. Iron source loading: Weigh ferric nitrate and dissolve it in deionized water to prepare a 0.5 mol / L solution. Add the alumina support to the solution using the equal volume impregnation method and stir for 4 hours to allow for full adsorption, thus obtaining a wet impregnated body.

[0050] S3. After vacuum drying the impregnated body at 60℃ for 8h, the dried product is heated to 550℃ at a rate of 5℃ / min and calcined in air for 3h to obtain the Fe2O3 / Al2O3 oxide catalyst precursor.

[0051] S4. The obtained unreduced catalyst was uniformly packed into the central region of the quartz fixed-bed reactor, and 2.0 g of quartz sand was filled on both the top and bottom to stabilize the bed structure. A mixture of methane and carbon dioxide (volume ratio 1:1) was introduced at a total flow rate of 100 mL / min, and the reaction was carried out at 650 °C and atmospheric pressure for 4 hours.

[0052] Comparative Example 2: Using Ni / Al2O3 nickel-based catalyst

[0053] S1. Carrier pretreatment: γ-alumina was selected as the carrier and placed in a muffle furnace for heat treatment at 500℃ for 2 hours to remove adsorbed water and impurities. After cooling, it was ready for use.

[0054] S2. Weigh out nickel nitrate hexahydrate and dissolve it in deionized water to prepare a 0.5 mol / L solution. Add the alumina carrier to the solution using the equal volume impregnation method and stir for 4 hours to allow for full adsorption, thus obtaining a wet impregnated body.

[0055] S3. Place the impregnated body in a vacuum drying oven and dry it at 60°C for 8 hours. Then place it in a muffle furnace and heat it to 550°C at a rate of 5°C / min. Calcinate it in air for 3 hours and then cool it to obtain the NiO / Al2O3 catalyst precursor.

[0056] S4. The catalyst is loaded into the central region of the quartz fixed-bed reactor, and pure hydrogen gas (50 mL / min) is introduced to reduce NiO at 400 °C for 2 hours to convert NiO into metallic Ni. After the reduction is complete, nitrogen gas is switched to purge for 30 minutes to remove residual gas, and the reactor is cooled for later use.

[0057] S5. The obtained Ni / Al2O3 catalyst was uniformly packed in the center of the reactor, and the upper and lower beds were fixed with quartz sand. A CH4 / CO2 (1:1) mixed gas was introduced at a flow rate of 100 mL / min, the reaction temperature was set to 650℃, and the reaction was carried out continuously for 4 hours under normal pressure.

[0058] Example 3: Preparation of catalyst by temperature-programmed calcination

[0059] S1. Carrier pretreatment: γ-alumina was selected as the carrier and placed in a muffle furnace for heat treatment at 500℃ for 2 hours to remove adsorbed water and impurities. After cooling, it was ready for use.

[0060] S2. Dissolve ferric nitrate nonahydrate in deionized water to prepare a 0.5 mol / L solution. Add the alumina support to the solution and stir magnetically for 4 hours to form a wet impregnated body.

[0061] S3. After vacuum drying the wet impregnated body at 60℃ for 8 hours, it is directly placed into a muffle furnace and rapidly heated to 550℃ (without using a 5℃ / min heating program), and calcined at this temperature for 3 hours. After calcination, it is naturally cooled to obtain the Fe2O3 / Al2O3 catalyst precursor for later use.

[0062] S4. The calcined product is loaded into the center of a quartz fixed-bed reactor, and pure hydrogen gas (50 mL / min) is introduced. The reactor is reduced at 400 °C for 2 hours to generate the Fe / Al2O3 catalyst. After the reduction is complete, nitrogen gas is switched to purge for 30 minutes, and the catalyst is cooled for later use.

[0063] S5. The catalyst is uniformly packed in the central region of the fixed-bed reactor, and quartz sand is filled above and below the catalyst to stabilize the bed structure. A mixture of methane and carbon dioxide with a volume ratio of 1:1 is introduced at a total flow rate of 100 mL / min, and a dry reforming reaction is carried out at 650 °C for 4 hours.

[0064] Performance testing

[0065] 1. CH4 to CO2 conversion rate test

[0066] The catalysts (8g) obtained in each example and comparative example were uniformly packed into the central region of a quartz fixed-bed reactor, with 2g of quartz sand each above and below as a fixed bed. Before the reaction, hydrogen was used at 50mL / min at 400℃ for 2h (except for Comparative Example 1). After cooling, the reaction was switched to a CH4 and CO2 mixture (volume ratio 1:1) at a total flow rate of 100mL / min, and reacted at 650℃ for 4h. Example 3 extended the reaction time to 8h. Gas samples were taken before and after the reaction, and the concentrations of CH4 and CO2 were determined using gas chromatography (TCD detector). The conversion rate was calculated using the following formula:

[0067]

[0068] The results are shown in Table 1 below.

[0069] Table 1. Results of CH4 to CO2 conversion rates

[0070] sample <![CDATA[CH4 conversion rate (%)]]> <![CDATA[CO2 conversion rate (%)]]> <![CDATA[CO:H2 ratio]]> Example 1 87 92 1.0 Example 2 86 91 1.0 Example 3 85 90 1.0 Comparative Example 1 68 73 0.8 Comparative Example 2 73 70 1.1 Comparative Example 3 69 75 0.9

[0071] As shown in Table 1, Examples 1–3 outperformed the comparative examples in terms of CH4 to CO2 conversion and CO:H2 ratio, fully verifying the effectiveness of the catalyst preparation method of this invention. Examples 1 and 2 successfully constructed highly dispersed Fe using an equal-volume impregnation method combined with programmed temperature calcination and hydrogen reduction.0 The active sites exhibited CH4 conversion rates of 87% and 86% and CO2 conversion rates of 92% and 91%, respectively, with a stable syngas ratio of 1.0, demonstrating that this structural regulation strategy significantly improved catalytic performance. Example 3 maintained 85% and 90% conversion rates after 8 hours of continuous reaction, indicating that the prepared catalyst possesses good thermal stability and resistance to carbon deposition. Comparative Example 1, due to the lack of reduction, formed Fe. 0 The lack of active sites leads to a significant reduction in conversion rate. Although the Ni-based catalyst in Comparative Example 2 has high initial activity, it is prone to carbon deposition during the reaction, resulting in a decrease in CO2 utilization. The omission of programmed temperature calcination in Comparative Example 3 causes Fe species agglomeration, resulting in insufficient activity and selectivity.

[0072] 2. CO selectivity and byproduct inhibition test

[0073] The catalysts prepared in Examples 1-3 and Comparative Examples 1-2 were tested under standard reaction conditions: 8g of catalyst was packed into a quartz fixed-bed reactor (2g of quartz sand fixed at the top and bottom). Before the reaction, the catalyst was reduced with hydrogen at 400℃ for 2h (except for Comparative Example 1). Then, a mixture of CH4 and CO2 (1:1) was introduced at 650℃ at a total flow rate of 100mL / min for 4h (Example 3 extended the reaction time to 8h). The outlet gas was qualitatively and quantitatively analyzed using a gas chromatograph (GC) equipped with TCD and FID to determine the content of CO, H2, C2H4, C2H6, etc. in the product, and the presence of carbon deposits (C(s)) was determined by combining TGA or the appearance after the reaction. CO selectivity was calculated using the following formula:

[0074]

[0075] The results are shown in Table 2 below.

[0076] Table 2 Results of CO selectivity and byproduct inhibition performance tests

[0077] sample CO selectivity (%) <![CDATA[H2 Selectivity (%)]]> <![CDATA[C2Hx(ppm)]]> Was C(s) detected? Example 1 96.5 98.2 ＜10 none Example 2 95.4 97.5 15 none Example 3 95.8 97.9 ＜10 trace amount Comparative Example 1 83.2 88.7 40 Obvious carbon buildup Comparative Example 2 84.6 90.1 55 Excessive carbon buildup Comparative Example 3 83.5 86.3 51 Excessive carbon buildup

[0078] As shown in Table 2, the CO selectivity of Examples 1-3 is all above 95%, and the concentration of C2Hx byproducts is below 15 ppm, with no obvious carbon deposition observed. This indicates that the Fe-based catalyst prepared in this invention has excellent directional catalytic activity and side reaction suppression capabilities. In particular, Example 1 achieved a CO selectivity of 96.5% and a C2Hx content below 10 ppm, indicating highly dispersed Fe on the catalyst surface. 0The active center effectively promotes the synergistic conversion of CH4 and CO2, avoiding excessive cracking or side reaction pathways. Example 3 maintained high CO selectivity and extremely low byproduct formation even after an extended 8-hour continuous reaction, further verifying the catalyst's structural stability and resistance to carbon deposition. In contrast, the catalysts in Comparative Examples 1-3, due to poor metal dispersion or easy sintering, resulted in intensified side reactions, severe carbon deposition, and a significant decrease in CO selectivity. This demonstrates that the present invention has significant advantages in improving target product selectivity and suppressing carbon deposition and byproduct formation.

[0079] 3. BET specific surface area and pore size distribution test

[0080] The catalysts obtained after the dry reforming reaction in Examples 1-3 and Comparative Examples 1-2 were subjected to BET testing. The specific surface area (BET method), pore volume, and pore size distribution (BJH method) of the samples were determined using a nitrogen adsorption-desorption method at 77 K using a specific surface area analyzer. Each catalyst sample was degassed under vacuum at 200 °C for 4 hours to remove surface impurities and adsorbed water. The effects of different preparation processes on the specific surface area, pore volume, and average pore size were analyzed to verify whether temperature programming helps maintain the structural integrity of the support and improve the dispersion of the active components, thereby enhancing the availability of active sites and gas diffusion performance. The results are shown in Table 3 below.

[0081] Table 3. Test results of BET specific surface area and pore structure

[0082] sample Specific surface area (m² / g) Average pore size (nm) Pore ​​volume (cm³ / g) Example 1 158.2 5.3 0.39 Example 2 150.7 5.6 0.36 Example 3 155.9 5.4 0.38 Comparative Example 1 102.4 7.1 0.28 Comparative Example 2 115.6 6.9 0.31 Comparative Example 3 112.6 7.0 0.28

[0083] Table 3 shows that the iron-based catalysts prepared in Examples 1-3 maintained a high specific surface area (150.7-158.2 m² / g) and a stable mesoporous structure (average pore size 5.3-5.6 nm) after dry reforming. This indicates that the synergistic control strategy of programmed temperature calcination and hydrogen reduction adopted in this invention can effectively prevent the agglomeration of active metals, maintain the integrity of the support pores, and improve the dispersion and exposure rate of the Fe active component. In contrast, the catalysts in Comparative Examples 1-3, due to the lack of programmed temperature calcination, lack of reduction treatment, or the use of easily sinterable Ni components, showed a significant decrease in specific surface area (102.4-115.6 m² / g), increased pore size, and decreased pore volume, reflecting structural collapse and pore blockage, which limited gas diffusion and the utilization of active sites.

[0084] 4. High-temperature cycling stability test

[0085] The catalysts of Examples 1-3 and Comparative Examples 1-2 were selected for thermal cycling tests. Each catalyst (8g) was uniformly packed in a quartz fixed-bed reactor (with 2g of quartz sand fixed at the top and bottom). The reaction conditions were as follows: first, hydrogen was introduced at 400℃ at 50mL / min for 2h (except for Comparative Example 1); then, a mixture of CH4 and CO2 (volume ratio 1:1) was introduced at a total flow rate of 100mL / min, and a dry reforming reaction was carried out at 650℃. Each cycle lasted 4 hours (8 hours for Example 3), after which the reactor was allowed to cool naturally to room temperature before starting the next cycle. A total of 3 cycles were performed (heating-reaction-cooling 3 times). The amount of CO and H2 generated and the CH4 conversion rate were recorded after each cycle. The retention rate of CH4 conversion rate in the 3rd cycle and the 1st cycle was calculated to evaluate the thermal cycling stability of the catalyst. The results are shown in Table 4 below.

[0086] Table 4. High-Temperature Cyclic Stability Test Results

[0087] sample <![CDATA[Initial CH4 conversion rate (%)]]> <![CDATA[CH4 conversion rate in the 3rd round (%)]]> Activity retention rate (%) Example 1 87.0 85.3 98.0 Example 2 86.0 83.7 97.3 Example 3 85.0 83.0 97.6 Comparative Example 1 68.0 52.5 77.2 Comparative Example 2 73.0 58.6 80.3 Comparative Example 3 71.5 55.2 77.2

[0088] As shown in Table 4, after three consecutive rounds of high-temperature cyclic reaction, the CH4 conversion rate of the catalysts in Examples 1-3 only fluctuated slightly, and the activity retention rate remained above 97%. This indicates that the highly dispersed Fe produced by the present invention through programmed temperature calcination and hydrogen reduction... 0 The Fe3O4 active structure exhibits excellent thermal cycling stability. This structure effectively prevents the Fe component from sintering and agglomerating during heating and cooling, maintaining its uniform distribution on the alumina support and the exposure of active sites, thereby preserving stable catalytic performance. In contrast, the catalysts in Comparative Examples 1-3 (unreduced, Ni-substituted, or unprogrammed temperature treatment) all showed a rapid decline in activity during cycling, with significant loss of CH4 conversion and an activity retention rate of less than 81%, with some samples dropping to 77.2%. This indicates that their structure is prone to disintegration, particle agglomeration, or carbon deposition and deactivation under thermal stress. This demonstrates the advantages of the catalyst design path of this invention in improving long-term operational reliability and thermal shock resistance.

[0089] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0090] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing syngas by iron-catalyzed dry reforming of methane, characterized in that, Includes the following steps: S1. Provide an alumina carrier and pretreat it by placing the alumina carrier in a heating device for heat treatment to remove surface impurities and adsorbates, and then cooling it for later use. S2. Dissolve the iron source in a solvent to prepare an impregnation solution. Add the pretreated alumina carrier to the solution using an equal-volume impregnation method. Perform contact treatment under stirring until the impregnation solution is basically absorbed, and obtain the impregnated body. S3. The obtained impregnated body is dried to remove moisture, and then heated and roasted. S4. The calcined iron oxide support is placed in a reducing atmosphere for reduction treatment to obtain an iron-based catalyst with metallic iron on the surface, and then cooled for later use. S5. The iron-based catalyst is uniformly packed in the middle of the reactor, and inert packing is set at the upper and lower ends of the catalyst to stabilize the bed structure. The methane and carbon dioxide inlet system is connected, and the mixed gas is introduced into the reactor to contact the catalyst for dry reforming reaction. After the reaction, a synthesis gas mainly composed of carbon monoxide and hydrogen is generated.

2. The method for preparing syngas according to claim 1, characterized in that, The alumina carrier is γ-crystalline alumina, and surface activation and impurity removal are achieved through high-temperature calcination.

3. The method for preparing syngas according to claim 1, characterized in that, The iron source is a ferric salt compound, preferably ferric nitrate, and its solution is loaded onto the surface of alumina by an equal-volume impregnation method to achieve uniform adsorption of the active components.

4. The method for preparing syngas according to claim 1, characterized in that, The S3 calcination step is carried out in an air atmosphere, with the temperature increased to 550°C at a rate of 5°C / min, and then held at that temperature for 3 hours to convert the iron salt precursor into an iron oxide support.

5. The method for preparing syngas according to claim 1, characterized in that, The reducing atmosphere is hydrogen, which is used to reduce iron oxide to the active component of metallic iron.

6. The method for preparing syngas according to claim 1, characterized in that, After the reduction treatment in step S4 is completed, the system is purged with inert gas to remove residual reducing gas in the reactor and stabilize the catalyst surface state.

7. The method for preparing syngas according to claim 1, characterized in that, In step S5, the catalytic reaction is carried out in a fixed-bed reactor under atmospheric pressure, and the reaction temperature is controlled between 650°C and 700°C.

8. The method for preparing syngas according to claim 1, characterized in that, The volume ratio of the methane to carbon dioxide mixture is 1:1, and the total flow rate of the mixture is controlled by a mass flow meter.

9. The method for preparing syngas according to claim 1, characterized in that, The volume ratio of carbon monoxide to hydrogen in the synthesis gas is approximately 1:1, making it suitable for downstream methanol synthesis or Fischer-Tropsch synthesis reaction systems.

10. The method for preparing syngas according to claim 1, characterized in that, The catalyst loading area in the fixed-bed reactor is filled with quartz sand at both ends to fix the catalyst position and prevent particles from being carried out by the airflow.

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