A highly stable and highly active methanation catalyst for synthesis gas and a method for preparing the same

Abstract

This application relates to the technical field of catalyst preparation, specifically disclosing a highly stable and active methanation catalyst for syngas and its preparation method. The method includes the following steps: dissolving nickel and manganese salts in water to obtain solution A; mixing lanthanum carbonate tetrahydrate or lanthanum and cerium carbonate, polyethylene glycol 400, and water uniformly to obtain mixture B; uniformly dispersing composite powder and calcium salt in water, adding mixture B, adjusting pH, heating, aging, simultaneously adding solution A and carbonate solution, dynamically adjusting pH, aging, solid-liquid separation, washing, and drying to obtain a pre-supported body; sequentially impregnating the pre-supported body with potassium salt solutions of increasing concentration, drying, calcining, and cooling to obtain a catalyst precursor; uniformly kneading the catalyst precursor, binder, release agent, and water, followed by molding, curing, drying, reduction, and passivation to obtain the final catalyst. The catalyst prepared in this application exhibits excellent CO and CO2 conversion rates and CH4 selectivity.

Description

Technical Field

[0001] This application relates to the technical field of catalyst preparation, and more specifically, to a highly stable and highly active methanation catalyst for syngas and a method for preparing the same. Background Technology

[0002] The synthetic ammonia industry is a fundamental industry of the national economy, mainly used in fertilizers, chemicals, and other fields. Its production process generates tail gas containing CO and CO2. Direct emission of this tail gas not only wastes resources but also impacts the environment. If it enters subsequent process systems, even low levels of CO and CO2 can poison the catalysts in later stages of ammonia synthesis and reduce product purity. Therefore, it is essential to purify and remove these gases.

[0003] Currently, technologies for treating CO and CO2 in ammonia synthesis tail gas have significant limitations. Traditional adsorption methods require frequent adsorbent regeneration, resulting in complex operations and unstable efficiency. While low-temperature shift conversion can convert some CO, its effectiveness for low-concentration components is limited, failing to meet the demands of deep purification. Conventional high-temperature methanation technology, on the other hand, is primarily designed for high-concentration CO. x The system design results in high operating temperatures and high energy consumption, and it is not suitable for the low CO content in the ammonia tail gas, which can easily lead to waste of catalyst activity or insufficient reaction efficiency.

[0004] Patent application CN109261218A discloses a methanation catalyst, which, by weight, mainly consists of 35-45 parts of active component NiO, and 3-5 parts of oxide promoter La2O3, 8-15 parts of MgO, 30-40 parts of Al2O3, 1-2 parts of K2O, 1-3 parts of SiO2, and 0.3-0.8 parts of CaO. Among them, MgO and Al2O3 form a MgAl2O4 spinel support structure, and K2O, SiO2, CaO, and some Al2O3 exist in a potassium nepheline structure. The catalyst preparation process specifically includes the following steps: (B1) Ni(NO3)2 and La(NO3)3 solutions are prepared into a nitrate mixture, and then MgAl2O4 spinel is added, along with pre-prepared potassium nepheline powder; after stirring evenly, the temperature is raised to 60~80℃, and then neutralized with alkali solution; (B2) after neutralization, the mixture is thermally aged at 70~80℃ for 30~90 min; then spray-dried until the moisture content of the material is less than 5%; finally, it is calcined at 550~650℃ for 2~4 h to obtain a powdered methanation catalyst; (B3) 1%~2% of graphite by mass is added to the powdered catalyst obtained in step (B2) and mixed evenly, and then pressed into a black cylinder or Raschig ring to obtain the methanation catalyst.

[0005] In this scheme, although the basic component is stabilized by introducing pre-synthesized potassium nepheline, it is mixed with MgAl2O4 spinel by dry mixing. Due to the mismatch between their crystal structures and thermal expansion coefficients, weak interfacial bonding is formed. Under temperature shock, thermal stress concentration becomes the origin of microcracks, directly leading to catalyst particle pulverization. In addition, the basic sites of potassium nepheline are firmly locked in their own crystal lattice and cannot form effective synergy with the Ni active sites dispersed on the spinel due to spatial isolation, ultimately resulting in a decrease in catalytic performance. Summary of the Invention

[0006] To improve the catalytic performance and mechanical strength of existing methanation catalysts, especially their catalytic performance in low-concentration CO and CO2 syngas, this application provides a highly stable and highly active methanation catalyst for syngas and its preparation method.

[0007] In a first aspect, this application provides a method for preparing a highly stable and highly active methanation catalyst for syngas, employing the following technical solution:

[0008] A method for preparing a highly stable and highly active methanation catalyst for syngas includes the following steps:

[0009] S1: Dissolve 0.8~1.0 mol of nickel salt and 0.1~0.2 mol of manganese salt in water to obtain solution A;

[0010] S2: Mix 0.05~0.1 mol of lanthanum carbonate tetrahydrate or lanthanum cerium carbonate, 0.1~0.3 g of polyethylene glycol 400 and water evenly to obtain mixture B;

[0011] S3: Disperse 500-700g of composite powder and 0.1-0.3mol of calcium salt evenly in water, add mixed solution B, adjust the pH to 4.8-5.2, heat to 55-65℃, age, simultaneously add solution A and carbonate solution, dynamically adjust the pH to 7.8-8.2, after addition, age, separate solid and liquid, wash, dry, and obtain pre-loaded body;

[0012] S4: The pre-supported material is impregnated sequentially with potassium salt solutions of increasing concentration, with each impregnation time being 20-30 minutes. After drying, calcination, and cooling, the catalyst precursor is obtained.

[0013] S5: The catalyst precursor, binder, release agent and water are kneaded evenly, and then formed, cured, dried, reduced and passivated to obtain a highly stable and highly active methanation catalyst; the composite powder includes γ-Al2O3 and β-Al2O3.

[0014] In this scheme, by precisely controlling the sequential reaction environment of weak acid and weak base, while ensuring the integrity of the composite powder carrier structure, the efficient and uniform loading of multiple active centers is effectively achieved through the synergistic mechanism of rare earth slow dissolution guidance and directional precipitation of active components. Specifically, firstly, calcium ions are used to pre-modify the composite powder support, which forms a stable compound during subsequent calcination, mainly enhancing the framework structure and optimizing the surface properties of the support. Then, with the assistance of a soft template made of polyethylene glycol, the slow-release dissolution of lanthanum carbonate or lanthanum-cerium carbonate is triggered in a weakly acidic environment, allowing large-radius lanthanum / cerium ions to preferentially anchor on the support surface, forming uniformly distributed nucleation sites. Subsequently, in the alkaline co-precipitation stage, these pre-positioned lanthanum / cerium ions effectively guide the uniform precipitation and growth of nickel and manganese ions around them, significantly suppressing segregation caused by differences in ionic radii, constructing a structurally uniform and tightly interacting composite active phase, significantly improving the catalyst's reactivity and thermal stability. Finally, an alkaline shell is constructed by impregnating the outer layer with potassium ions, selectively neutralizing strong acid sites on the surface, effectively inhibiting coke formation while maintaining high methanation activity, thus endowing the catalyst with excellent durability.

[0015] Preferably, the mass ratio of γ-Al2O3 to β-Al2O3 is (7~9):(1~3).

[0016] Preferably, the molar concentration of the carbonate is 1.5~2.0 mol / L.

[0017] Preferably, the mass ratio of the catalyst precursor, binder, release agent and water is 1:(0.08~0.12):(0.015~0.025):(0.15~0.25).

[0018] Preferably, in step S3, the aging time is 40-60 minutes and the aging time is 90-110 minutes.

[0019] Preferably, step S4 specifically involves: mixing a potassium salt solution with a molar concentration of 0.05~0.1mol / L with the pre-supported medium evenly, impregnating for 20~30min without solid-liquid separation, then adding a potassium salt solution with a molar concentration of 0.15~0.3mol / L, continuing impregnation for 20~30min, drying, calcining, and cooling to obtain the catalyst precursor.

[0020] Preferably, in step S4, the liquid-solid ratio of the potassium salt solution with a molar concentration of 0.05~0.1mol / L, the potassium salt solution with a molar concentration of 0.15~0.3mol / L, and the preloaded body is (0.6~0.8)mL:(0.6~0.8)mL:1g.

[0021] In this scheme, a low-concentration potassium salt solution is first used to occupy the strong adsorption sites on the outer surface of the carrier and in the macropores, forming a preliminary and uniform potassium distribution. Subsequently, the high-concentration potassium salt solution can enter and fill the secondary channels more smoothly, effectively avoiding the accumulation and blockage of potassium ions at the pore openings caused by the initial rapid adsorption during a single impregnation.

[0022] Preferably, the binder is pure calcium aluminate cement.

[0023] Preferably, the curing is high-pressure steam curing, with a temperature of 170~180℃, a pressure of 0.8~1.0MPa, and a time of 8~12h.

[0024] In this scheme, pure calcium aluminate cement is fully hydrated under high temperature and high pressure steam environment, generating a large number of well-crystallized and high-strength hydration products. These hydration products intertwine into a dense network structure inside the catalyst particles, further improving the catalyst's impact resistance.

[0025] Preferably, the calcination temperature is 550~620℃ and the time is 2~6h.

[0026] Preferably, the reduction and passivation are performed as follows: in a mixture of hydrogen and nitrogen, at 540~560℃ for 4~6 hours, reduction is carried out, then nitrogen is introduced to cool to 80~90℃, and then the mixture of nitrogen and air or oxygen is switched to perform passivation treatment, while controlling the temperature not to exceed 100℃.

[0027] Preferably, in the mixture of hydrogen and nitrogen, the volume ratio of hydrogen to nitrogen is (25~35):(65~75).

[0028] Preferably, in the mixture of nitrogen and air or oxygen, the volume ratio of nitrogen to oxygen or air is (98~99):(1~2).

[0029] Preferably, the composite powder further includes mesoporous SiO2.

[0030] In this scheme, by further introducing mesoporous SiO2, the pore structure of the catalyst is optimized, providing an efficient mass transfer channel.

[0031] Preferably, the total mass ratio of γ-Al2O3 and β-Al2O3 to the mass ratio of mesoporous SiO2 is 1:(0.15~0.3).

[0032] Preferably, in step S4, the potassium salt solution further contains cobalt salt or copper salt, wherein the molar concentration of cobalt salt or copper salt in the potassium salt solution is 0.01~0.03 mol / L.

[0033] In this scheme, trace amounts of cobalt or copper are introduced into the potassium salt solution. In an alkaline environment, they can act as auxiliary active centers, changing the activation pathway of CO molecules and forming a synergistic effect with the main active center Ni. This significantly improves the ignition activity and reaction rate of the catalyst at low temperatures, making it particularly suitable for low-concentration conditions.

[0034] Secondly, this application provides a highly stable and highly active methanation catalyst for syngas prepared by the above-described preparation method.

[0035] In this scheme, the catalyst uses γ-Al₂O₃ and β-Al₂O₃ composite oxides as the support framework. The introduced calcium component, after calcination, forms calcium aluminate and other reinforcing phases, constituting the internal reinforcing framework of the catalyst, thus endowing it with excellent mechanical strength. Within this reinforced framework, the lanthanum component is pre-released and pre-anchored in a weakly acidic environment, guiding the formation of relatively dispersed and thermally stable nickel and manganese active phases, ensuring the catalytic efficiency and anti-sintering ability of the catalyst core. The outer layer successfully constructs an alkaline functional shell composed of potassium (and optionally cobalt or copper) species. This shell effectively neutralizes strong acid sites on the support surface, thereby significantly inhibiting coke formation and synergistically enhancing the catalyst's reactivity under low-temperature conditions.

[0036] In summary, this application has the following beneficial effects:

[0037] 1. This application employs calcium ion pre-modified composite powder, which, after subsequent calcination, generates uniformly distributed calcium-containing compounds within the support framework. This not only enhances the mechanical strength of the catalyst but also provides an optimized surface environment for subsequent loading. Subsequently, pre-acidification triggers the dynamic slow-release dissolution of lanthanum tetrahydrate or lanthanum / cerium carbonate, allowing large-radius lanthanum / cerium ions to preferentially anchor on the support surface. These pre-anchored ions act as nucleation centers, effectively guiding the highly uniform mixing and precipitation of nickel and manganese active ions, thereby constructing a highly dispersed, strongly interacting, anti-sintering active phase, significantly improving the intrinsic activity and thermal stability of the catalyst. Finally, by impregnating the outermost layer with potassium nitrate to construct an alkaline shell, the catalyst's resistance to coking is selectively neutralized at strong acid sites, significantly enhancing its long-term stability.

[0038] 2. In terms of raw material selection, this application uses lanthanum carbonate tetrahydrate or lanthanum carbonate cerium carbonate, which are more chemically stable and have relatively lower costs, as precursors. This not only has economic advantages, but more importantly, it provides the necessary conditions for realizing the key "dynamic slow-release dissolution" mechanism, thereby further improving the overall cost-effectiveness of the preparation process while ensuring high performance. Attached Figure Description

[0039] Figure 1 SEM image of the highly stable and highly active methanation catalyst in Example 1 of this application;

[0040] Figure 2 SEM image of the highly stable and highly active methanation catalyst in Example 4 of this application. Detailed Implementation

[0041] The present application will be further described in detail below with reference to the embodiments.

[0042] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0043] In the following embodiments:

[0044] γ-Al₂O₃ has a particle size of 20~75μm and a specific surface area ≥280m². 2 / g, with an average pore size of 5~8nm; β-Al2O3 particle size of 20~75μm, and a specific surface area of ​​50~100m². 2 / g; Mesoporous SiO2 particle size 20~75μm, specific surface area ≥400m² 2 / g, with a pore size of 5~10nm.

[0045] Example 1

[0046] The method for preparing a highly stable and highly active methanation catalyst for syngas in this embodiment includes the following steps:

[0047] S1: Add 0.9 mol of nickel nitrate hexahydrate and 0.15 mol of manganese nitrate tetrahydrate to 500 mL of deionized water and stir at 200 r / min until completely dissolved to obtain solution A;

[0048] S2: Add 0.07 mol of lanthanum carbonate tetrahydrate and 0.2 g of polyethylene glycol 400 to 200 mL of deionized water, and stir at 800 r / min for 30 min to obtain mixture B;

[0049] S3: Add 600g of composite powder, 0.2mol of calcium acetate monohydrate, and 2000mL of deionized water to a reaction vessel. Stir and mix at 800r / min for 40min. Slowly add mixture B, and simultaneously adjust the pH to 5.0 with 5% nitric acid. After the addition is complete, adjust the stirring speed to 200r / min and continue stirring and mixing for 15min. Raise the temperature to 60℃ and age for 45min. Adjust the stirring speed to 500r / min and maintain the temperature. Slowly add solution A, and simultaneously add sodium carbonate solution with a molar concentration of 1.5mol / L. Dynamically adjust the pH to 8.0. After the addition is complete, age for 100min, filter, wash twice with 70℃ deionized water, wash once with anhydrous ethanol, and dry in a 110℃ forced-air drying oven to constant weight to obtain the pre-loaded body.

[0050] S4: Add the pre-supported material to the reactor, first add a potassium nitrate solution with a molar concentration of 0.05 mol / L, stir and mix at 200 r / min for 25 min, then add a potassium nitrate solution with a molar concentration of 0.15 mol / L, stir and mix at 200 r / min for 25 min. The liquid-solid ratio of potassium nitrate solution to pre-supported material is 0.7 mL: 1 g each time. Dry in a 110℃ forced-air drying oven to constant weight, transfer to a sintering furnace, heat to 580℃ at 3℃ / min, calcine for 4 h, and cool to room temperature with the furnace to obtain the catalyst precursor;

[0051] S5: The catalyst precursor, pure calcium aluminate cement, graphite, and deionized water were kneaded evenly in a mass ratio of 1:0.1:0.02:0.2, pre-pressed and granulated. The shaped particles were transferred to a high-pressure autoclave and cured at 170℃ and 0.8MPa saturated steam pressure for 10 hours, then dried at 110℃ for 4 hours. The mixture was then packed into a fixed-bed reactor and heated to 550℃ in a hydrogen and nitrogen mixture with a volume ratio of 30:70. The mixture was reduced for 5 hours at a rate of 3℃ / min. The reactor was then purged with high-purity nitrogen and cooled to 80℃. A mixture of compressed air and nitrogen was continuously introduced at a volume ratio of 1:99, and the bed temperature was controlled to not exceed 100℃. After the bed temperature stabilized, the proportion of compressed air in the mixture was slowly increased to ensure that its volume fraction was not higher than 2%. The mixture was then passivated for 4 hours to obtain a highly stable and highly active methanation catalyst.

[0052] The composite powder includes γ-Al2O3 and β-Al2O3, with a mass ratio of γ-Al2O3 to β-Al2O3 of 8:2. Before use, the powder is stirred and mixed evenly, and then dried at 110℃ for 2 hours.

[0053] Example 2

[0054] The method for preparing a highly stable and highly active methanation catalyst for syngas in this embodiment includes the following steps:

[0055] S1: Add 0.8 mol of nickel nitrate hexahydrate and 0.1 mol of manganese nitrate tetrahydrate to 500 mL of deionized water and stir at 200 r / min until completely dissolved to obtain solution A;

[0056] S2: Add 0.05 mol of lanthanum carbonate tetrahydrate and 0.1 g of polyethylene glycol 400 to 200 mL of deionized water, and stir at 800 r / min for 30 min to obtain mixture B;

[0057] S3: Add 500g of composite powder, 0.1mol of calcium acetate monohydrate, and 2000mL of deionized water to a reaction vessel. Stir and mix at 800r / min for 40min. Slowly add mixture B, and simultaneously adjust the pH to 5.2 with 5% nitric acid. After the addition is complete, adjust the stirring speed to 200r / min and continue stirring and mixing for 15min. Raise the temperature to 60℃ and age for 40min. Adjust the stirring speed to 500r / min and maintain the temperature. Slowly add solution A, and simultaneously add sodium carbonate solution with a molar concentration of 1.5mol / L. Dynamically adjust the pH to 7.8. After the addition is complete, age for 90min. Filter, wash twice with 70℃ deionized water, then wash once with anhydrous ethanol. Dry in a 110℃ forced-air drying oven to constant weight to obtain the pre-loaded body.

[0058] S4: The pre-supported material was added to the reactor. First, a potassium nitrate solution with a molar concentration of 0.05 mol / L was added, and the mixture was stirred and impregnated at a speed of 200 r / min for 20 min. Then, a potassium nitrate solution with a molar concentration of 0.15 mol / L was added, and the mixture was stirred and impregnated at a speed of 200 r / min for 20 min. The liquid-solid ratio of the potassium nitrate solution to the pre-supported material was 0.8 mL: 1 g each time. The mixture was dried in a forced-air drying oven at 110 °C until constant weight was achieved. The mixture was then transferred to a sintering furnace and heated to 550 °C at a speed of 3 °C / min for 6 h. The mixture was then cooled to room temperature in the furnace to obtain the catalyst precursor.

[0059] S5: The catalyst precursor, pure calcium aluminate cement, graphite, and deionized water were kneaded evenly in a mass ratio of 1:0.08:0.015:0.15, pre-pressed and granulated. The shaped particles were transferred to a high-pressure autoclave and cured at 180℃ and 1.0MPa saturated steam pressure for 8 hours, then dried at 110℃ for 4 hours. The mixture was then packed into a fixed-bed reactor and heated to 540℃ in a hydrogen and nitrogen mixture with a volume ratio of 25:75. The mixture was reduced for 6 hours at a rate of 3℃ / min. The reactor was then purged with high-purity nitrogen and cooled to 90℃. A mixture of compressed air and nitrogen was continuously introduced at a volume ratio of 1:99, and the bed temperature was controlled to not exceed 100℃. After the bed temperature stabilized, the proportion of compressed air in the mixture was slowly increased to ensure that its volume fraction was not higher than 2%. The mixture was then passivated for 4 hours, unloaded, sieved, and packaged to obtain a highly stable and highly active methanation catalyst.

[0060] The composite powder includes γ-Al2O3 and β-Al2O3, with a mass ratio of γ-Al2O3 to β-Al2O3 of 9:1. Before use, the powder is stirred and mixed evenly, and then dried at 110℃ for 2 hours.

[0061] Example 3

[0062] The method for preparing a highly stable and highly active methanation catalyst for syngas in this embodiment includes the following steps:

[0063] S1: Add 1.0 mol of nickel nitrate hexahydrate and 0.2 mol of manganese nitrate tetrahydrate to 500 mL of deionized water and stir at 200 r / min until completely dissolved to obtain solution A;

[0064] S2: Add 0.1 mol of lanthanum carbonate tetrahydrate and 0.3 g of polyethylene glycol 400 to 200 mL of deionized water, and stir at 800 r / min for 30 min to obtain mixture B;

[0065] S3: Add 700g of composite powder, 0.3mol of calcium acetate monohydrate, and 2000mL of deionized water to a reaction vessel. Stir and mix at 800r / min for 50min. Slowly add mixture B, and simultaneously adjust the pH to 4.8 with 5% nitric acid. After the addition is complete, adjust the stirring speed to 200r / min and continue stirring and mixing for 15min. Heat to 60℃ and age for 60min. Adjust the stirring speed to 500r / min and maintain the temperature. Slowly add solution A, and simultaneously add sodium carbonate solution with a molar concentration of 2.0mol / L. Dynamically adjust the pH to 8.2. After the addition is complete, age for 110min. Filter, wash twice with 70℃ deionized water, then wash once with anhydrous ethanol. Dry in a 110℃ forced-air drying oven to constant weight to obtain the pre-loaded body.

[0066] S4: Add the pre-supported material to the reactor, first add a potassium nitrate solution with a molar concentration of 0.1 mol / L, stir and mix at 200 r / min for 30 min, then add a potassium nitrate solution with a molar concentration of 0.3 mol / L, stir and mix at 200 r / min for 30 min. The liquid-solid ratio of potassium nitrate solution to pre-supported material is 0.6 mL: 1 g each time. Dry in a 110℃ forced-air drying oven until constant weight, transfer to a sintering furnace, heat to 620℃ at 3℃ / min, calcine for 2 h, and cool to room temperature with the furnace to obtain the catalyst precursor;

[0067] S5: The catalyst precursor, pure calcium aluminate cement, graphite, and deionized water were kneaded evenly in a mass ratio of 1:0.12:0.025:0.25, pre-pressed and granulated. The shaped particles were transferred to a high-pressure autoclave and cured at 170℃ and 0.8MPa saturated steam pressure for 12 hours, then dried at 110℃ for 4 hours. The mixture was then packed into a fixed-bed reactor and heated to 560℃ in a hydrogen and nitrogen mixture with a volume ratio of 35:65. The mixture was reduced for 4 hours at a rate of 3℃ / min. The reactor was then purged with high-purity nitrogen and cooled to 80℃. A mixture of oxygen and nitrogen was continuously introduced at a volume ratio of 1:99, and the bed temperature was controlled to not exceed 100℃. After the bed temperature stabilized, the proportion of oxygen in the mixture was slowly increased to ensure that its volume fraction was not higher than 2%. The mixture was then passivated for 4 hours to obtain a highly stable and highly active methanation catalyst.

[0068] The composite powder includes γ-Al2O3 and β-Al2O3, with a mass ratio of γ-Al2O3 to β-Al2O3 of 7:3. Before use, the powder is stirred and mixed evenly, and then dried at 110℃ for 2 hours.

[0069] Example 4

[0070] The method for preparing a highly stable and highly active methanation catalyst for syngas in this embodiment includes the following steps:

[0071] S1: Add 0.9 mol of nickel nitrate hexahydrate and 0.15 mol of manganese nitrate tetrahydrate to 500 mL of deionized water and stir at 200 r / min until completely dissolved to obtain solution A;

[0072] S2: Add 0.07 mol of lanthanum cerium carbonate and 0.2 g of polyethylene glycol 400 to 200 mL of deionized water, and stir at 800 r / min for 30 min to obtain mixture B;

[0073] S3: Add 600g of composite powder, 0.2mol of calcium acetate monohydrate, and 2000mL of deionized water to a reaction vessel. Stir and mix at 800r / min for 40min. Slowly add mixture B, and simultaneously adjust the pH to 5.0 with 5% nitric acid. After the addition is complete, adjust the stirring speed to 200r / min and continue stirring and mixing for 15min. Raise the temperature to 60℃ and age for 45min. Adjust the stirring speed to 500r / min and maintain the temperature. Slowly add solution A, and simultaneously add sodium carbonate solution with a molar concentration of 2mol / L. Dynamically adjust the pH to 8.0. After the addition is complete, age for 100min, filter, wash twice with 70℃ deionized water, wash once with anhydrous ethanol, and dry in a 110℃ forced-air drying oven to constant weight to obtain the pre-loaded body.

[0074] S4: The pre-supported material was added to the reactor. First, a potassium nitrate solution with a molar concentration of 0.1 mol / L was added, and the mixture was stirred and impregnated at 200 r / min for 30 min. Then, a potassium nitrate solution with a molar concentration of 0.3 mol / L was added, and the mixture was stirred and impregnated at 200 r / min for 30 min. The liquid-solid ratio of the potassium nitrate solution to the pre-supported material was 0.6 mL: 1 g each time. The mixture was dried in a 110℃ forced-air drying oven until constant weight was achieved. The mixture was then transferred to a sintering furnace and heated to 600℃ at 3℃ / min for 3.5 h. The mixture was then cooled to room temperature in the furnace to obtain the catalyst precursor.

[0075] S5: The catalyst precursor, pure calcium aluminate cement, graphite, and deionized water were kneaded evenly in a mass ratio of 1:0.1:0.02:0.2, pre-pressed and granulated. The shaped particles were transferred to a high-pressure autoclave and cured at 170℃ and 0.8MPa saturated steam pressure for 10 hours, then dried at 110℃ for 4 hours. The mixture was then packed into a fixed-bed reactor and heated to 550℃ at a volume ratio of 30:70 for 5 hours in a hydrogen and nitrogen mixture. The mixture was then purged with high-purity nitrogen and cooled to 80℃. A mixture of oxygen and nitrogen was continuously introduced at a volume ratio of 1:99, and the bed temperature was controlled to not exceed 100℃. After the bed temperature stabilized, the proportion of oxygen in the mixture was slowly increased to ensure that its volume fraction was not higher than 2%. The mixture was then passivated for 4 hours to obtain a highly stable and highly active methanation catalyst.

[0076] The composite powder includes γ-Al2O3 and β-Al2O3, with a mass ratio of γ-Al2O3 to β-Al2O3 of 8:2. Before use, the powder is stirred and mixed evenly, and then dried at 110℃ for 2 hours.

[0077] Example 5

[0078] The difference between this embodiment and embodiment 4 is that:

[0079] The composite powder includes γ-Al2O3, β-Al2O3 and mesoporous SiO2, with a mass ratio of γ-Al2O3, β-Al2O3 and mesoporous SiO2 of 8:2:1.5.

[0080] The rest is the same as in Example 4.

[0081] Example 6

[0082] The difference between this embodiment and embodiment 4 is that:

[0083] The composite powder includes γ-Al2O3, β-Al2O3 and mesoporous SiO2, with a mass ratio of γ-Al2O3, β-Al2O3 and mesoporous SiO2 of 8:2:3.

[0084] The rest is the same as in Example 4.

[0085] Example 7

[0086] The difference between this embodiment and embodiment 6 is that:

[0087] S4: The pre-supported material was added to the reactor. First, a potassium nitrate solution containing copper nitrate was added, with a molar concentration of 0.1 mol / L for potassium nitrate and 0.01 mol / L for copper nitrate. The mixture was stirred and impregnated at 200 r / min for 30 min. Then, a potassium nitrate solution containing copper nitrate was added, with a molar concentration of 0.3 mol / L for potassium nitrate and 0.03 mol / L for copper nitrate. The mixture was stirred and impregnated at 200 r / min for 30 min. The liquid-solid ratio of the potassium nitrate solution containing copper nitrate to the pre-supported material was 0.6 mL: 1 g each time. The mixture was dried in a 110℃ forced-air drying oven until constant weight, then transferred to a sintering furnace. The temperature was increased to 600℃ at 3℃ / min, and calcined for 3.5 h. The mixture was then cooled to room temperature in the furnace to obtain the catalyst precursor.

[0088] The rest is the same as in Example 6.

[0089] Example 8

[0090] The difference between this embodiment and embodiment 6 is that:

[0091] S4: The pre-supported material was added to the reactor. First, a potassium nitrate solution containing cobalt nitrate was added, with a molar concentration of potassium nitrate of 0.1 mol / L and a molar concentration of cobalt nitrate of 0.01 mol / L. The mixture was stirred and impregnated at 200 r / min for 30 min. Then, a potassium nitrate solution containing cobalt nitrate was added, with a molar concentration of potassium nitrate of 0.3 mol / L and a molar concentration of cobalt nitrate of 0.03 mol / L. The mixture was stirred and impregnated at 200 r / min for 30 min. The liquid-solid ratio of the potassium nitrate solution containing cobalt nitrate to the pre-supported material was 0.6 mL: 1 g each time. The mixture was dried in a 110℃ forced-air drying oven until constant weight, then transferred to a sintering furnace. The temperature was increased to 600℃ at 3℃ / min, and calcined for 3.5 h. The mixture was then cooled to room temperature in the furnace to obtain the catalyst precursor.

[0092] The rest is the same as in Example 6.

[0093] Comparative Example 1

[0094] The comparative method for preparing a highly stable and active methanation catalyst for syngas includes the following steps:

[0095] S1: Add 0.9 mol of nickel nitrate hexahydrate and 0.15 mol of manganese nitrate tetrahydrate to 500 mL of deionized water and stir at 200 r / min until completely dissolved to obtain solution A;

[0096] S2: Add 0.07 mol of lanthanum nitrate hexahydrate and 0.2 g of polyethylene glycol 400 to 200 mL of deionized water, and stir and mix at 800 r / min for 30 min to obtain solution B;

[0097] S3: Add 600g of composite powder, 0.2mol of calcium acetate monohydrate, and 2000mL of deionized water to a reaction vessel. Stir and mix at 800r / min for 40min. Slowly add solution B. After the addition is complete, adjust the speed to 200r / min and continue stirring and mixing for 15min. Raise the temperature to 60℃ and age for 45min. Adjust the speed to 500r / min and maintain the temperature. Slowly add solution A dropwise, and simultaneously add sodium carbonate solution with a molar concentration of 1.5mol / L. Dynamically adjust the pH to 8.0. After the addition is complete, age for 100min. Filter, wash twice with deionized water at 70℃, then wash once with anhydrous ethanol. Dry in a 110℃ forced-air drying oven to constant weight to obtain the pre-loaded body.

[0098] S4: Add the pre-supported material to the reactor, first add a potassium nitrate solution with a molar concentration of 0.05 mol / L, stir and mix at 200 r / min for 25 min, then add a potassium nitrate solution with a molar concentration of 0.15 mol / L, stir and mix at 200 r / min for 25 min. The liquid-solid ratio of potassium nitrate solution to pre-supported material is 0.7 mL: 1 g each time. Dry in a 110℃ forced-air drying oven to constant weight, transfer to a sintering furnace, heat to 580℃ at 3℃ / min, calcine for 4 h, and cool to room temperature with the furnace to obtain the catalyst precursor;

[0099] S5: The catalyst precursor, pure calcium aluminate cement, graphite, and deionized water were kneaded evenly in a mass ratio of 1:0.1:0.02:0.2, pre-pressed and granulated. The shaped particles were transferred to a high-pressure autoclave and cured at 170℃ and 0.8MPa saturated steam pressure for 10 hours, then dried at 110℃ for 4 hours. The mixture was then packed into a fixed-bed reactor and heated to 550℃ in a hydrogen and nitrogen mixture with a volume ratio of 30:70. The mixture was reduced for 5 hours at a rate of 3℃ / min. The reactor was then purged with high-purity nitrogen and cooled to 80℃. A mixture of compressed air and nitrogen was continuously introduced at a volume ratio of 1:99, and the bed temperature was controlled to not exceed 100℃. After the bed temperature stabilized, the proportion of compressed air in the mixture was slowly increased to ensure that its volume fraction was not higher than 2%. The mixture was then passivated for 4 hours to obtain a highly stable and highly active methanation catalyst.

[0100] The composite powder includes γ-Al2O3 and β-Al2O3, with a mass ratio of γ-Al2O3 to β-Al2O3 of 8:2. Before use, the powder is stirred and mixed evenly, and then dried at 110℃ for 2 hours.

[0101] Comparative Example 2

[0102] The difference between this comparative example and Example 1 is as follows:

[0103] S4: Add the pre-supported material to the reactor, add potassium nitrate solution with a molar concentration of 0.1 mol / L, stir and mix at 200 r / min for 50 min, the liquid-solid ratio of potassium nitrate solution to pre-supported material is 1.4 mL: 1 g, dry in a 110℃ forced-air drying oven to constant weight, transfer to a sintering furnace, heat to 580℃ at 3℃ / min, calcine for 4 h, cool to room temperature with the furnace to obtain the catalyst precursor;

[0104] Everything else is the same as in Example 1.

[0105] Comparative Example 3

[0106] The difference between this comparative example and Example 1 is as follows:

[0107] S3: Add 600g of composite powder and 2000mL of deionized water to a reaction vessel and stir at 800r / min for 40min. Slowly add mixture B and simultaneously adjust the pH to 5.0 with 5% nitric acid. After addition, adjust the stirring speed to 200r / min and continue stirring for 15min. Heat to 60℃ and age for 45min. Adjust the stirring speed to 500r / min and maintain the temperature. Slowly add solution A and simultaneously add sodium carbonate solution with a molar concentration of 1.5mol / L. Dynamically adjust the pH to 8.0. After addition, age for 100min, filter, wash twice with 70℃ deionized water, wash once with anhydrous ethanol, and dry in a 110℃ forced-air drying oven to constant weight to obtain the pre-loaded body.

[0108] Everything else is the same as in Example 1.

[0109] Comparative Example 4

[0110] The difference between this comparative example and Example 1 is as follows:

[0111] S5: The catalyst precursor, aluminum sol (based on solid content), graphite, and deionized water were kneaded evenly in a mass ratio of 1:0.1:0.02:0.2, pre-pressed and granulated. The shaped particles were transferred to an autoclave and cured at 170℃ and 0.8MPa saturated vapor pressure for 10 hours, then dried at 110℃ for 4 hours. The mixture was then packed into a fixed-bed reactor and heated to 550℃ in a hydrogen and nitrogen mixture with a volume ratio of 30:70. The mixture was reduced for 5 hours at a rate of 3℃ / min. The reactor was then purged with high-purity nitrogen and cooled to 80℃. A mixture of compressed air and nitrogen was continuously introduced at a volume ratio of 1:99, and the bed temperature was controlled to not exceed 100℃. After the bed temperature stabilized, the proportion of compressed air in the mixture was slowly increased to ensure that its volume fraction was not higher than 2%. The mixture was then passivated for 4 hours to obtain a highly stable and highly active methanation catalyst.

[0112] Everything else is the same as in Example 1.

[0113] Performance testing

[0114] The composition of the feed gas is as follows: CO: 0.91 vol%, CO2: 18.51 vol%, H2: 55.20 vol%, N2: 22.63 vol%, CH4: 1.45 vol%, H2S: 10 ppmv, and the remainder is inert gases such as Ar.

[0115] Test Procedure: The highly stable and active methanation catalysts prepared in Examples 1-8 and Comparative Examples 1-4 were mixed with quartz sand at a volume ratio of 1:1 and then packed into a small fixed-bed reactor. Nitrogen gas was first introduced at a rate of 50 mL / min, and the temperature was increased to 550°C at a rate of 3°C / min. Then, the reducing gas (a mixture of hydrogen and nitrogen at a volume ratio of 30:70) was introduced, and reduction was carried out for 3 hours. After the reduction was completed, the reactor was adjusted to the target operating conditions: temperature of 280°C and pressure of 1.5 MPa. Then, the feed gas was introduced, and the flow rate was adjusted to a space velocity of 5000 h⁻¹. -1 After 12 hours of stable operation, the composition of the outlet gas was detected by an online gas chromatograph. The number of samples was no less than 3, and the average value was taken as the initial activity (including CO conversion rate, CO2 conversion rate, CH4 selectivity and outlet CO concentration). After 500 hours of continuous operation, the amount of catalyst coking and the crushing strength retention rate were detected. The test results are shown in Table 1.

[0116] Table 1 Performance testing of the highly stable and active methanation catalysts prepared in Examples 1-8 and Comparative Examples 1-4

[0117]

[0118] The performance test data in Table 1 shows that:

[0119] Comparative Example 1 used lanthanum nitrate instead of lanthanum carbonate, resulting in significantly lower CO2 conversion rate and outlet CO concentration, as well as poor resistance to coking. Comparative Example 2 used a one-step impregnation method with potassium nitrate, which led to a decrease in CO2 conversion rate and resistance to coking. Comparative Example 3 did not introduce calcium acetate monohydrate, and although the initial CO conversion rate was high, it showed severe coking and a decrease in mechanical strength during long-term operation. Comparative Example 4 used aluminum sol as a binder, which had little effect on the initial conversion rate and selectivity, but reduced the retention rate of mechanical strength.

[0120] In comparison, Examples 1-8 not only achieved near-complete CO conversion and deep purification, but also obtained excellent CO2 conversion rate, CH4 selectivity, and mechanical strength retention. Specifically, Example 4 used lanthanum cerium carbonate instead of lanthanum carbonate, maintaining deep CO purification (outlet <5 ppm) while improving CO2 conversion rate and anti-coking performance compared to Examples 1-3. Examples 5-6 further introduced mesoporous SiO2 to construct a composite support, significantly reducing coking and improving mechanical strength retention while increasing CO2 conversion rate due to the optimized pore structure. Examples 7-8, by introducing cobalt / copper additives, increased CO2 conversion rate to over 88% on the basis of a mesoporous support while maintaining excellent anti-coking performance.

[0121] Combination Figures 1-2 It can be seen that the SEM of the highly stable and active methanation catalyst in Example 1 basically shows a relatively loose small particle agglomeration structure, while the SEM of the highly stable and active methanation catalyst in Example 4 shows finer particles and a more regular pore distribution. This optimized mesoscopic morphology is usually an external manifestation of highly dispersed active components and strong interaction between the active phase and the support. This structural optimization is consistent with the performance results of higher CO2 conversion and lower carbon deposition measured in Example 4, jointly indicating that the lanthanum-cerium carbonate composite promoter can effectively promote the formation of a more advantageous catalyst structure in the system of this invention, thereby achieving higher activity and stability.

[0122] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a highly stable and highly active methanation catalyst for synthesis gas, characterized by, It comprises the following steps: S1: dissolve 0.8-1.0 mol of nickel salt and 0.1-0.2 mol of manganese salt in water to obtain solution A; S2: uniformly mix 0.05-0.1 mol of lanthanum carbonate tetrahydrate or lanthanum cerium carbonate, 0.1-0.3 g of polyethylene glycol 400 and water to obtain mixture B; S3: uniformly disperse 500-700 g of composite powder and 0.1-0.3 mol of calcium salt in water, add mixture B, adjust pH to 4.8-5.2, heat to 55-65℃, age, synchronously add solution A and carbonate solution, dynamically adjust pH to 7.8-8.2, after completion of addition, age, solid-liquid separation, washing, drying to obtain pre-loaded body; S4: sequentially immerse the pre-loaded body in potassium salt solutions with increasing concentrations, each time for 20-30 min, dry, calcine, cool to obtain catalyst precursor; S5: uniformly knead the catalyst precursor, binder, release agent and water, shape, curing, drying, reduction and passivation to obtain high-stability high-activity methanation catalyst; the composite powder comprises γ-Al2O3 and β-Al2O3.

2. The method for preparing a high-stable high-activity methanation catalyst for synthesis gas according to claim 1, characterized by, The mass ratio of the γ-Al2O3 and β-Al2O3 is (7-9):(1-3).

3. The method for preparing a high-stable high-activity methanation catalyst for synthesis gas according to claim 1, characterized by, Step S4 specifically comprises: uniformly mixing the pre-loaded body with a potassium salt solution with a molar concentration of 0.05-0.1 mol / L, immersing for 20-30 min, without solid-liquid separation, then adding a potassium salt solution with a molar concentration of 0.15-0.3 mol / L, continuing to immerse for 20-30 min, drying, calcining, cooling to obtain catalyst precursor.

4. The method for preparing a high-stable and high-activity methanation catalyst for synthesis gas according to claim 1, characterized by, The binder is pure calcium aluminate cement.

5. The method for preparing a high-stable high-activity methanation catalyst for synthesis gas according to claim 1, characterized by, The curing is high-pressure steam curing, with a temperature of 170-180℃, a pressure of 0.8-1.0 MPa and a time of 8-12 h.

6. The method for preparing a high-stable high-activity methanation catalyst for synthesis gas according to claim 1, characterized by, The reduction and passivation comprises: reducing at 540-560℃ for 4-6 h in a mixed gas of hydrogen and nitrogen, then cooling to 80-90℃ by passing nitrogen, then switching to a mixed gas of nitrogen and air or oxygen for passivation treatment, and controlling the temperature to be not higher than 100℃.

7. The method for preparing a high-stable high-activity methanation catalyst for synthesis gas according to claim 1, characterized by, The composite powder further comprises mesoporous SiO2.

8. The method for preparing a highly stable and highly active methanation catalyst for synthesis gas according to claim 7, characterized by, The mass ratio of the total mass of the γ-Al2O3 and β-Al2O3 to the mass of the mesoporous SiO2 is 1:(0.15-0.3).

9. The method for preparing a high-stable high-activity methanation catalyst for synthesis gas according to claim 1, characterized by, In step S4, the potassium salt solution further comprises cobalt salt or copper salt, and the molar concentration of the cobalt salt or copper salt in the potassium salt solution is 0.01-0.03 mol / L.

10. A high-stability high-activity methanation catalyst prepared by the method for preparing a high-stability high-activity methanation catalyst for synthesis gas according to any one of claims 1-9.

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