Modified FAU type zeolite catalyst for efficiently catalyzing CO2 to prepare methane at low temperature as well as preparation method and application of modified FAU type zeolite catalyst

Abstract

The invention provides a modified FAU type zeolite catalyst for efficiently catalyzing CO2 to prepare methane at low temperature and a preparation method and application of the modified FAU type zeolite catalyst, and relates to the technical field of CO2 methanation catalyst.Firstly, a silicon source, an aluminum source, a sodium source and FAU type zeolite seed crystals are mixed and then stirred at the constant temperature to form gel, and dynamic crystallization is conducted along with temperature rise of a system; after the crystallization is finished, washing, drying and roasting to obtain the FAU type zeolite molecular sieve synthesized by the seed method in one step; adding a metal M compound and a nitrogen-containing compound into the synthesized FAU type zeolite molecular sieve for doping modification to obtain a catalyst precursor; finally, the catalyst precursor is subjected to roasting reduction and passivation, and the modified FAU type zeolite catalyst is obtained. The FAU type zeolite molecular sieve is synthesized in one step through a seed method, the crystallization time is remarkably shortened, the production efficiency is improved, and the product reproducibility is good; and the synthesized FAU type zeolite molecular sieve is modified, and the low-temperature activity and CH4 selectivity of the catalyst are remarkably improved through the synergistic effect of elements M and N.

Description

Technical Field

[0001] This invention belongs to the field of CO2 methanation catalyst preparation technology, specifically relating to a modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2 to methane production, its preparation method, and its application in CO2 methanation. Background Technology

[0002] With the acceleration of global industrialization and the massive consumption of fossil fuels, the concentration of carbon dioxide (CO2) in the atmosphere has continued to rise, from 280 ppm before the Industrial Revolution to over 420 ppm currently, triggering a series of environmental problems such as global warming and frequent extreme weather events. Against this backdrop, countries have introduced policies to promote the research and application of low-carbon technologies. CO2 capture and utilization (CCU) technology is considered one of the key pathways to achieving carbon neutrality. Carbon utilization technologies that convert CO2 into high-value-added chemicals or fuels (such as methane, methanol, and synthetic fuels) can reduce greenhouse gas emissions and alleviate the energy crisis, possessing significant environmental and economic value. Among these technologies, methane (CH4) is a clean and efficient energy carrier that can be directly used in existing natural gas pipeline networks, and its reaction process has high atom economy, making it one of the most promising CO2 conversion technologies.

[0003] CO2 methanation is a typical exothermic reaction. Low temperatures favor the reaction towards the product side, increasing the CO2 equilibrium conversion rate. However, CO2 molecules have high chemical stability, and their activation process requires high energy input. Therefore, the actual reaction usually needs to be carried out under the action of a catalyst. Currently, the main industrial carbon dioxide capture technologies are chemical absorption and physical adsorption. FAU-type molecular sieves, with their unique structure, occupy an important position in physical adsorption. FAU-type molecular sieves are microporous materials, belonging to the octahedral zeolite class, including X-type and Y-type with different silica-alumina ratios. Their framework is mainly composed of aluminosilicates, with secondary structures of double six-membered rings and β-cages. The β-cages are connected by double six-membered rings to form a three-dimensional open framework structure.

[0004] Catalysts prepared using transition metals such as Ni, Co, and Fe as active components are inexpensive and exhibit high catalytic activity, making them the most studied catalyst systems. FAU-type zeolite molecular sieves (including X-type and Y-type) demonstrate great potential in catalysis due to their unique three-dimensional twelve-membered ring pore structure, high specific surface area, tunable Si / Al ratio, and abundant surface hydroxyl groups. However, in existing technologies, the synthesis methods for CO2 methanation catalysts based on FAU-type zeolites mostly employ traditional hydrothermal methods, resulting in crystallization times of 24–72 hours, low production efficiency, and poor product reproducibility. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing a modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2 to methane production, which has short crystallization time, high production efficiency, and good product reproducibility.

[0006] A modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic production of methane from CO2 is also provided.

[0007] It is also necessary to provide a modified FAU-type zeolite catalyst for the low-temperature, high-efficiency catalytic production of methane from CO2, and its application in CO2 methanation.

[0008] The technical solution adopted by this invention to solve its technical problem is:

[0009] A method for preparing a modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2 to methane production involves a one-step synthesis of FAU-type zeolite molecular sieves via a seed method, followed by doping and modification of the synthesized FAU-type zeolite molecular sieves with metal and non-metal elements, and calcination and reduction to obtain the modified FAU-type zeolite catalyst. This method leverages the synergistic effect among multiple elements to enhance the catalyst's low-temperature activity and CH4 selectivity. The specific steps include:

[0010] Synthesis of FAU-type zeolite molecular sieve: Silicon source, aluminum source, sodium source and FAU-type zeolite seed crystal are mixed and stirred at constant temperature to form a gel. Then, the system is dynamically crystallized as the temperature rises. After crystallization, the mixture is washed, dried and calcined to obtain FAU-type zeolite molecular sieve synthesized in one step by seed method, which shortens the crystallization time and provides a doping interface for doping elements.

[0011] Doping modification: Metal M compound and nitrogen-containing compound are added to the synthesized FAU type zeolite molecular sieve for doping modification to obtain catalyst precursor, so as to improve the dispersibility of metal active component and CO2 adsorption and activation ability at low temperature; wherein metal M compound refers to one compound containing a metal element or two compounds containing metal elements, and the metal elements of the two metal elements are different.

[0012] Modified FAU-type zeolite catalyst: The modified FAU-type zeolite catalyst is obtained by calcining, reducing and passivating the catalyst precursor.

[0013] Preferably, in the doping modification step, the metal M compound is a nitrate, chloride, or acetylacetonate of the corresponding metal, and the nitrogen-containing compound is urea, ethylenediamine, or melamine.

[0014] Preferably, the doping modification step specifically comprises: Step 1: dispersing FAU-type zeolite molecular sieve in deionized water to obtain a mixed solution containing FAU-type zeolite molecular sieve;

[0015] Step 2: Add metal M compound and nitrogen-containing compound to the mixed solution containing FAU type zeolite molecular sieve and perform ultrasonic impregnation to dope modification, thereby obtaining a modified mixed solution;

[0016] Step 3: Evaporate the modified mixed solution to dryness to obtain the catalyst precursor.

[0017] Preferably, in step one, the mass ratio of the FAU-type zeolite molecular sieve, the metal M compound, and the nitrogen-containing compound is 1:0.5-2:0.2-0.6.

[0018] Preferably, the ultrasonic impregnation time in step two is 2 to 6 hours, and the temperature for evaporation to dryness in step three is 60 ℃ to 90 ℃.

[0019] Preferably, in the synthesis of the FAU-type zeolite molecular sieve, the silicon source is tetraethyl orthosilicate, the aluminum source is sodium aluminate, the sodium source is sodium hydroxide, the FAU-type zeolite seed crystal accounts for 0.5-3% of the total mass of the system, and the particle size of the FAU-type zeolite seed crystal is 50-200 nm.

[0020] Preferably, in the synthesis of the FAU-type zeolite molecular sieve, the gel formation requires stirring at 60–80°C for 2–4 hours, and the dynamic crystallization requires crystallization at 80–120°C at 50–100 rpm for 8–24 hours.

[0021] Preferably, in the modified FAU-type zeolite catalyst, the passivation atmosphere is 1%–20% O2 / N2, and the passivation time is 4–6 h.

[0022] A modified FAU-type zeolite catalyst is prepared by the above-described method for preparing a modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2 to methane production.

[0023] The catalyst prepared by the method described above for preparing a modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2 to methane conversion is applied in CO2 methanation, wherein the reaction temperature of CO2 methanation is below 250 °C.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The present invention provides a method for preparing a modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2-to-methane production. First, a silicon source, an aluminum source, a sodium source, and FAU-type zeolite seed crystals are mixed. Then, the mixture is stirred at a constant temperature to form a gel, followed by dynamic crystallization as the system temperature increases. After crystallization, the mixture is washed, dried, and calcined to obtain a one-step FAU-type zeolite molecular sieve synthesized via a seed method. Next, a metal M compound and a nitrogen-containing compound are added to the synthesized FAU-type zeolite molecular sieve for doping modification, yielding a catalyst precursor. The metal M compound refers to one compound containing a metal element or two compounds containing different metal elements. Finally, the catalyst precursor is calcined, reduced, and passivated to obtain the modified FAU-type zeolite catalyst. This invention synthesizes FAU-type zeolite molecular sieves in one step via a seed method, significantly shortening crystallization time, improving production efficiency, and exhibiting good product reproducibility. Furthermore, the synthesized FAU-type zeolite molecular sieves are modified by single or double doping with metal M, altering the metal dispersion within the zeolite molecular sieve to provide more active sites for CO2 hydrogenation and significantly enhancing the catalyst's hydrogenation capacity. Simultaneously, the introduction of nitrogen (N) can regulate the electronic properties of the catalyst surface, increasing the number of basic sites and promoting CO2 adsorption and activation. Therefore, the synergistic effect of metal M and non-metal N significantly improves the catalyst's low-temperature activity and CH4 selectivity. Attached Figure Description

[0026] Figure 1 Scanning electron microscope image of the catalyst prepared for Example 6. Detailed Implementation

[0027] The technical solutions and effects of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] This application provides a method for preparing a modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2 to methane production. The method involves a one-step synthesis of FAU-type zeolite molecular sieves via a seed method, followed by doping and modification of the synthesized FAU-type zeolite molecular sieves with metal and non-metal elements, and then calcination and reduction to obtain the modified FAU-type zeolite catalyst. This method utilizes the synergistic effect among multiple elements to enhance the catalyst's low-temperature activity and CH4 selectivity. The specific steps include:

[0029] Synthesis of FAU-type zeolite molecular sieve: Silicon source, aluminum source, sodium source and FAU-type zeolite seed crystal are mixed and stirred at constant temperature to form a gel. Then, the system is dynamically crystallized as the temperature rises. After crystallization, the mixture is washed, dried and calcined to obtain FAU-type zeolite molecular sieve synthesized in one step by seed method, which shortens the crystallization time and provides a doping interface for doping elements.

[0030] In an optional embodiment, in the synthesis of the FAU-type zeolite molecular sieve, the silicon source is tetraethyl orthosilicate, the aluminum source is sodium aluminate, and the sodium source is sodium hydroxide. Inexpensive sodium, aluminum, and silicon oxides are used as raw materials, resulting in low raw material costs and a simple and controllable synthesis process. The FAU-type zeolite seed crystals account for 0.5-3% of the total mass of the system (specifically, this proportion refers to the mass of the FAU-type zeolite seed crystals relative to the total mass of the silicon, aluminum, sodium, and FAU-type zeolite seed crystal formation system). The particle size of the FAU-type zeolite seed crystals is 50-200 nm. The molar ratio of the sodium, aluminum, and silicon sources is (1.0-2.5):1:(5.0-12.0).

[0031] In one optional embodiment, in the synthesis of the FAU-type zeolite molecular sieve, the gel formation requires stirring at 60-80°C for 2-4 hours, and the dynamic crystallization requires crystallization at 80-120°C at 50-100 rpm for 8-24 hours, in order to form an interface capable of doping elements and provide sites for doping elements.

[0032] In one optional embodiment, after crystallization, the product is first washed with deionized water until neutral, then placed in a vacuum drying oven at 80-100 °C for 12-24 h, and finally calcined in air at a temperature of 550-600 °C for 5-8 h to obtain FAU type zeolite molecular sieve.

[0033] In the synthesis of the FAU-type zeolite molecular sieve, each synthesis step needs to be strictly controlled according to the above parameters to ensure the pore structure of the FAU-type zeolite molecular sieve prepared by the one-step seed method, and the molar ratio of Si to Al elements is 2.0-5.0. Otherwise, it will affect the subsequent doping effect of metal M and non-metal N elements and the catalytic performance.

[0034] The support material has a significant impact on catalyst performance. An ideal support should possess high specific surface area, suitable pore structure, good thermal stability, and strong interaction with the active component. Currently, commonly used supports include traditional oxides such as Al2O3, SiO2, and TiO2, as well as novel porous materials such as molecular sieves, carbon materials, and metal-organic frameworks (MOFs). Among them, FAU-type zeolite molecular sieves (including X-type and Y-type) have shown great potential in the field of catalysis due to their unique three-dimensional twelve-membered ring pore structure, high specific surface area, tunable Si / Al ratio, and abundant surface hydroxyl groups. Therefore, this molecular sieve is selected as the support.

[0035] Doping modification: Metal M compound and nitrogen-containing compound are added to the synthesized FAU type zeolite molecular sieve for doping modification to obtain catalyst precursor, so as to improve the dispersibility of metal active component and CO2 adsorption and activation ability at low temperature; wherein metal M compound refers to one compound containing a metal element or two compounds containing metal elements, and the metal elements of the two metal elements are different.

[0036] In one optional embodiment, step one: dispersing FAU-type zeolite molecular sieve in deionized water and ultrasonically treating it for 20-35 minutes to obtain a mixed solution containing FAU-type zeolite molecular sieve.

[0037] Step 2: Add metal M compound and nitrogen-containing compound to the mixed solution containing FAU type zeolite molecular sieve and perform ultrasonic impregnation to dope modification, thereby obtaining a modified mixed solution;

[0038] In one optional embodiment, the mass ratio of the FAU-type zeolite molecular sieve, the metal M compound, and the nitrogen-containing compound is 1:0.5-2:0.2-0.6.

[0039] In one optional embodiment, the metal M compound is a nitrate, chloride, or acetylacetonate of the corresponding metal. All of these are soluble salts, which makes it easier for the metal element to be incorporated into the FAU-type zeolite molecular sieve during the doping modification process and facilitates the dispersion of the metal element. The nitrogen-containing compound is urea, ethylenediamine, or melamine. These substances have good solubility, which is conducive to the incorporation of N element into the FAU-type zeolite molecular sieve and results in a better doping effect.

[0040] Preferably, the metal element of the M compound is one or more of Co and Ru.

[0041] Step 3: Evaporate the modified mixed solution to dryness to obtain the catalyst precursor.

[0042] In one optional embodiment, the ultrasonic impregnation time in step two is 2 to 6 hours, and the temperature for evaporation to dryness in step three is 60 ℃ to 90 ℃.

[0043] Modified FAU-type zeolite catalyst: The modified FAU-type zeolite catalyst is obtained by calcining, reducing and passivating the catalyst precursor.

[0044] In one optional embodiment, the calcination atmosphere is nitrogen, the heating rate is 2-5 °C / min, the calcination temperature is 400-600 °C, and the calcination time is 3-6 h, in order to remove impurities introduced during the doping process.

[0045] In one optional embodiment, the reducing atmosphere is 10%–99.9% H2, the heating rate is 1–3 °C / min, the reduction temperature is 300–500 °C, and the reduction time is 2–4 h, so as to reduce the valence state of the metal element to 0 valence, making it active.

[0046] Specifically, the reducing atmosphere is 10% to 99.9% H2, which refers to the proportion of H2 in the entire reducing atmosphere.

[0047] In one optional embodiment, the passivation atmosphere in the modified FAU-type zeolite catalyst is 1%–20% O2 / N2, and the passivation time is 4–6 h, so as to form a protective layer on the surface of the prepared catalyst and prevent the catalyst from spontaneously combusting at room temperature due to its high activity.

[0048] Specifically, the passivation atmosphere is 1% to 20% O2 / N2, meaning that the reducing atmosphere consists of O2 and N2, with O2 accounting for 1% to 20% of the total O2 and N2 atmosphere.

[0049] A modified FAU-type zeolite catalyst is prepared by the above-described method for preparing a modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2 to methane production.

[0050] The catalyst prepared by the modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2 to methane production as described above is applied in CO2 methanation, wherein the CO2 methanation reaction temperature is below 250 °C. A preferred CO2 methanation reaction temperature is 200 °C–250 °C.

[0051] By modifying the FAU-type zeolite molecular sieve support, single or double doping of metal M and nitrogen (N) are achieved in the catalyst. Doping with metal M alters the metal dispersion on the catalyst surface, providing abundant active sites for CO2 hydrogenation and significantly improving the catalyst's hydrogenation capacity. Simultaneously, the introduction of nitrogen can precisely control the electronic properties of the catalyst surface, increasing the number of basic sites and promoting CO2 adsorption and activation. This invention, through single or double doping of metal M and nitrogen doping, alters the metal dispersion and the number of basic sites on the catalyst surface, thereby coordinating hydrogenation capacity and CO2 adsorption capacity. The synergistic effect of these two factors significantly improves the catalyst's low-temperature activity and CH4 selectivity.

[0052] The following specific examples illustrate a crystal pulling method for improving the production efficiency of lightly boron-doped perfect crystals.

[0053] Example 1:

[0054] Synthesis of FAU-type zeolite molecular sieve: 10.2 g of tetraethyl orthosilicate, 4.1 g of sodium aluminate, and 2.5 g of sodium hydroxide were mixed in 70 mL of deionized water in an Erlenmeyer flask. Then, 0.2 g of FAU-type zeolite seed crystals (100 nm in diameter) were added, and the mixture was stirred at 70 °C for 3 h to form a gel. The system was then heated to 100 °C and dynamically crystallized at 80 rpm for 16 h. After crystallization, the product was washed with deionized water until neutral, then dried in a vacuum drying oven at 80 °C for 24 h, and finally calcined at 550 °C in air for 7 h to obtain the FAU-type zeolite molecular sieve.

[0055] Doping modification: Take 5 g of the above molecular sieve and disperse it in 50 mL of deionized water, and sonicate for 30 min; then add 2.9 g of nickel nitrate and 1.2 g of urea, and continue to sonicate for 4 h; then transfer the mixture to a water bath and stir and evaporate to dryness at 80 ℃ to obtain the Ni / FAU precursor.

[0056] Modified FAU-type zeolite catalyst: The precursor was placed in a tube furnace and calcined at 500 °C for 4 h in a nitrogen atmosphere at a rate of 3 °C / min. After calcination, the temperature was switched to hydrogen atmosphere and reduced at 400 °C for 3 h at a rate of 2 °C / min. After reduction, the temperature was cooled to room temperature. Then, passivation treatment was performed in a 1% O2 / N2 atmosphere to obtain the modified FAU-type zeolite catalyst Ni / FAU.

[0057] Example 2:

[0058] The only difference from Example 1 is that in the doping modification, the metal M compound is 4.0 g of ferric nitrate, the urea content is the same as in Example 1, and the other steps are the same as in Example 1, thus obtaining the modified FAU type zeolite catalyst Fe / FAU.

[0059] Example 3:

[0060] The only difference from Example 1 is that in the doping modification, the metal M compound is 2.9 g of cobalt nitrate, the urea content is the same as in Example 1, and the other steps are the same as in Example 1, thus obtaining the modified FAU type zeolite catalyst Co / FAU.

[0061] Example 4:

[0062] The only difference from Example 1 is that in the doping modification, the metal M compound is 2.6 g of ruthenium chloride, the urea content is the same as in Example 1, and the other steps are the same as in Example 1, thus obtaining the modified FAU type zeolite catalyst Ru / FAU.

[0063] Example 5:

[0064] The only difference from Example 1 is that in the doping modification, the metal M compound is 2.3 g nickel nitrate and 0.5 g ruthenium chloride, and the nitrogen-containing compound is 2.5 g melamine. After ultrasonic impregnation for 5 h, the mixture is transferred to a water bath and stirred and evaporated to dryness at 90 °C to obtain the NiRu / FAU precursor.

[0065] The other steps are the same as in Example 1, and the modified FAU-type zeolite catalyst NiRu / FAU is obtained.

[0066] Example 6:

[0067] The only difference from Example 1 is that in the doping modification, the metal M compound is 2.3 g cobalt nitrate and 0.5 g ruthenium chloride, and the nitrogen-containing compound is 1.2 g ethylenediamine. After ultrasonic impregnation for 3 h, the mixture is transferred to a water bath and stirred and evaporated to dryness at 90 °C to obtain the CoRu / FAU precursor.

[0068] The other steps are the same as in Example 1, and the modified FAU-type zeolite catalyst CoRu / FAU is obtained.

[0069] Scanning electron microscopy was used to examine the modified FAU-type zeolite catalyst CoRu / FAU, such as... Figure 1 As shown.

[0070] Comparative Example 1:

[0071] FAU type zeolite molecular sieves were purchased from Shanghai Zeolite Molecular Sieve Co., Ltd., as comparative catalyst 1.

[0072] Comparative Example 2:

[0073] Take the FAU-type zeolite molecular sieve from Comparative Example 1, and use the doping modification step and the FAU-type zeolite catalyst modification step of Example 3 to prepare Comparative Catalyst 2.

[0074] The catalysts prepared in Examples 1-6 and Comparative Examples 1-2 were subjected to catalyst performance testing and characterization:

[0075] When evaluating the performance of the catalyst, in order to ensure that the catalyst particles are uniform in size and do not clog the reaction tube, the catalysts prepared in Examples 1 to 6 of the present invention should all be made into catalyst particles of 40 to 60 mesh.

[0076] The catalysts prepared in Examples 1-6 and Comparative Examples 1-2 were evaluated in a micro-stationary reactor. The process conditions were: 0.5-1 g of 40-60 mesh catalyst, reaction temperature 150-300 °C, reaction pressure 0.1-2 MPa, feed gas H2 / CO2 = 4, and space velocity 10000-20000 mL·h. -1 ·g -1 .

[0077] Specifically, the catalysts prepared in Examples 1-6 and Comparative Examples 1-2 were evaluated in a fixed-bed reactor. The specific operating steps are as follows: 0.5 g of catalyst was weighed and loaded into the isothermal zone in the middle of the reaction tube. The feed gas H2 / CO2 ratio was 4, the temperature was 200℃, the pressure was atmospheric pressure, and the space velocity (GHSV) was 10000 mL·h. -1 ·g -1 After reaching a stable state, samples were taken for analysis at 1-hour intervals. Gas chromatography was used to perform quantitative and qualitative analysis of the feed gas and products. The CO2 conversion rate and CH4 selectivity were calculated using the methane correlation method described in "Determination of H2, N2, CO, CO2 and C1-C8 Hydrocarbons in Coal-Based Fischer-Tropsch Synthesis Tail Gas by Gas Chromatography". Specific results are shown in Table 1.

[0078] Table 1. Catalysts prepared in Examples 1-6 and Comparative Examples 1-2 under ambient pressure, 200 °C, and 10000 mL·h -1 ·g -1 Catalytic activity experimental data

[0079] The catalysts prepared in Examples 3, 4, and 6 were selected to carry out the CO2 to methane reaction at different catalytic temperatures, and the CO2 conversion rate and CH4 selectivity are shown in Tables 2, 3, and 4.

[0080] Table 2 shows the catalysts prepared in Example 3 under normal pressure and at 10000 mL·h. -1 ·g -1 Reaction performance at different temperatures

[0081] Table 3 shows the catalysts prepared in Example 4 under normal pressure and at 10000 mL·h. -1 ·g -1 Reaction performance at different temperatures

[0082] Table 4. Catalysts prepared in Example 6 under normal pressure and at 10000 mL·h -1 ·g -1 Reaction performance at different temperatures

[0083] Table 1 shows that the catalyst operates at atmospheric pressure, 200 °C, and 10000 mL·h. -1 ·g -1Under the given reaction conditions, the CO2 conversion rate of Examples 1-6 was above 45%, and the CH4 selectivity remained above 97.5%, with the CO2 conversion rate reaching above 76% at higher temperatures (Examples 3 and 4). The catalyst with some dual-doped optimized formulations (Example 6) achieved a CO2 conversion rate of 80.1% under the same conditions, and maintained a CH4 selectivity of over 98.7% within the 150–300 °C range (Table 4). Especially above 200 °C, the conversion rate remained stable at over 80% (Table 4), fully demonstrating its excellent low-temperature catalytic performance and wide temperature adaptability. This indicates that the doping of Co and Ru metals can better alter the metal dispersion on the catalyst surface, resulting in optimal dispersion of the doped metal active components. Furthermore, CoRu / FAU provides abundant active sites for CO2 hydrogenation, significantly enhancing the catalyst's hydrogenation capacity. Simultaneously, the introduction of N element can regulate the electronic properties of the catalyst surface, increase the number of basic sites, and promote CO2 adsorption and activation. CoRu / FAU exhibits the strongest synergistic effect between hydrogenation and CO2 adsorption capabilities, achieving high CO2 conversion and CH4 selectivity at low temperatures (200 °C). This is attributed to Ru's excellent low-temperature catalytic activity and resistance to carbon deposition. Meanwhile, as a transition metal, Co's d-electron configuration results in high selectivity for methane formation and reduces the likelihood of side reactions.

[0084] As can be seen from Table 1, the CO2 conversion rate of Comparative Example 1 was only 11%, and the CH4 selectivity was 90%. The CO2 conversion rate of Comparative Example 2 was only 31%, and the CH4 selectivity was 95%. These results are far from those of the FAU-type zeolite molecular sieve prepared in this invention. This indicates that direct doping modification of FAU-type zeolite molecular sieves using existing technologies cannot uniformly incorporate the doping elements. Only a very small portion can be incorporated, resulting in very low CO2 conversion rate and CH4 selectivity.

[0085] As shown in Table 2, the catalyst of Example 6 (CoRu / FAU) under normal pressure and at 10000 mL·h -1 ·g -1Under the given conditions, the conversion rate rapidly increased from 10.0% to 80.1% in the low-temperature range (150–200 °C), indicating that increased temperature promoted the reaction. This is because increased temperature accelerated the kinetic processes of "H2 dissociation" and "CO2 adsorption activation," rapidly enhancing the synergistic effect. In the medium-high temperature range (200–300 °C), the conversion rate stabilized at around 80.5%, no longer increasing significantly. This indicates that a high CO2 conversion rate can be achieved at around 200 °C, without the need for higher temperatures, demonstrating the advantages of low-temperature methanation. Furthermore, as the temperature increased from 150 °C to 200 °C and above, the CH4 selectivity increased from 98.7% to 99.1% and remained stable. This shows that increased temperature not only accelerates the reaction but also further suppresses side reactions, achieving optimal methane selectivity. Therefore, by modifying the reaction with single or double doping of metals M and N, the synergy between "hydrogenation capacity" and "CO2 adsorption activation capacity" can be controlled, thereby achieving high conversion rates and high selectivity in low-temperature CO2 methanation.

[0086] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for preparing a modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2-to-methane production, characterized in that, FAU-type zeolite molecular sieves were synthesized in one step via a seed method. The synthesized FAU-type zeolite molecular sieves were then modified by doping with metal and non-metal elements, followed by calcination and reduction to obtain modified FAU-type zeolite catalysts. The aim was to utilize the synergistic effect among multiple elements to improve the catalyst's low-temperature activity and CH4 selectivity. The specific steps included are as follows: Synthesis of FAU-type zeolite molecular sieve: Silicon source, aluminum source, sodium source and FAU-type zeolite seed crystal are mixed and stirred at constant temperature to form a gel. Then, the system is dynamically crystallized as the temperature rises. After crystallization, the mixture is washed, dried and calcined to obtain FAU-type zeolite molecular sieve synthesized in one step by seed method, which shortens the crystallization time and provides a doping interface for doping elements. Doping modification: Metal M compound and nitrogen-containing compound are added to the synthesized FAU type zeolite molecular sieve for doping modification to obtain catalyst precursor, so as to improve the dispersibility of metal active component and CO2 adsorption and activation ability at low temperature; wherein metal M compound refers to one compound containing a metal element or two compounds containing metal elements, and the metal elements of the two metal elements are different. Modified FAU-type zeolite catalyst: The modified FAU-type zeolite catalyst is obtained by calcining, reducing and passivating the catalyst precursor.

2. The preparation method of the modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2-to-methane production as described in claim 1, characterized in that, In the doping modification step, the metal M compound is a nitrate, chloride, or acetylacetonate of the corresponding metal, and the nitrogen-containing compound is urea, ethylenediamine, or melamine.

3. The preparation method of the modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2-to-methane production as described in claim 2, characterized in that, The doping modification step is as follows: Step 1: Disperse FAU type zeolite molecular sieve in deionized water to obtain a mixed solution containing FAU type zeolite molecular sieve. Step 2: Add metal M compound and nitrogen-containing compound to the mixed solution containing FAU type zeolite molecular sieve and perform ultrasonic impregnation to dope modification, thereby obtaining a modified mixed solution; Step 3: Evaporate the modified mixed solution to dryness to obtain the catalyst precursor.

4. The preparation method of the modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2-to-methane production as described in claim 3, characterized in that, In step one, the mass ratio of the FAU-type zeolite molecular sieve, the metal M compound, and the nitrogen-containing compound is 1:0.5-2:0.2-0.

6.

5. The preparation method of the modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2-to-methane production as described in claim 3, characterized in that, The ultrasonic impregnation time in step two is 2 to 6 hours, and the temperature for evaporation to dryness in step three is 60 ℃ to 90 ℃.

6. The preparation method of the modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2-to-methane production as described in claim 1, characterized in that, In the synthesis of the FAU-type zeolite molecular sieve, the silicon source is tetraethyl orthosilicate, the aluminum source is sodium aluminate, the sodium source is sodium hydroxide, the FAU-type zeolite seed crystal accounts for 0.5-3% of the total mass of the system, the particle size of the FAU-type zeolite seed crystal is 50-200 nm, and the molar ratio of the sodium source, aluminum source and silicon source is (1.0-2.5):1:(5.0-12.0).

7. The preparation method of the modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2-to-methane production as described in claim 6, characterized in that, In the synthesis of the FAU-type zeolite molecular sieve, the gel formation requires stirring at 60–80°C for 2–4 hours, and the dynamic crystallization requires crystallization at 80–120°C at 50–100 rpm for 8–24 hours.

8. The method for preparing the modified FAU-type zeolite catalyst for low-temperature, high-efficiency catalytic CO2-to-methane production as described in claim 6, characterized in that, In the modified FAU-type zeolite catalyst, the passivation atmosphere is 1%–20% O2 / N2, and the passivation time is 4–6 h.

9. A modified FAU-type zeolite catalyst, characterized in that, It is prepared by the method for preparing the modified FAU-type zeolite catalyst for low-temperature high-efficiency catalytic CO2 to methane as described in any one of claims 1-8.

10. The application of the catalyst prepared by the method for preparing the modified FAU-type zeolite catalyst for low-temperature high-efficiency catalytic CO2 to methane as described in any one of claims 1-8 in CO2 methanation, wherein the reaction temperature of CO2 methanation is below 250 °C.

Images