Low-temperature high-activity carbon dioxide methanation catalyst and preparation method thereof

Abstract

The invention discloses a low-temperature high-activity carbon dioxide methanation catalyst and a preparation method thereof. The catalyst is of a supported structure and is represented by aNi-bMn / ZrO2, Ni is an active component, Mn is a promoter, ZrO2 is a carrier, a is larger than or equal to 5 wt% and smaller than or equal to 75 wt%, and b is larger than or equal to 0 wt% and smaller than or equal to 20 wt%. The catalyst is prepared by a Pechini method and comprises the following steps: mixing a metal salt solution containing nickel, manganese and zirconium with citric acid and ethylene glycol to form sol, drying to form gel, roasting and reducing to obtain the final catalyst. The low-temperature activity of the catalyst is remarkably improved by introducing a proper amount of manganese element, and the catalyst shows high CO2 conversion rate (up to 80%) and high CH4 selectivity (close to 100%) under the conditions of 225 DEG C and 0.1 MPa, and has good long-term stability. The method is simple in process and easy to amplify, and the obtained catalyst is excellent in performance under low-temperature and normal-pressure conditions and has a wide industrial application prospect.

Description

Technical Field

[0001] This invention relates to a low-temperature, highly active carbon dioxide methanation catalyst and its preparation method, belonging to the field of industrial catalysis technology. Technical Background

[0002] With the widespread use of fossil fuels, carbon dioxide emissions have been rising year by year. As one of the most significant greenhouse gases, the greenhouse effect caused by excessive carbon dioxide emissions has received widespread global attention. Therefore, controlling carbon emissions and realizing the resource utilization of captured carbon dioxide has become a research focus. Converting carbon dioxide into methane through hydrogenation not only helps reduce carbon emissions but is also considered an effective way to address energy shortages. This process enables the resource utilization of carbon dioxide and stores "green hydrogen," which is difficult to store on a large scale and over long periods, in the form of methane. The generated CH4 can be directly integrated into existing natural gas pipeline networks, achieving carbon recycling.

[0003] Highly efficient catalysts are the core of carbon dioxide methanation technology. To achieve high CO2 conversion and CH4 selectivity, researchers both domestically and internationally have conducted extensive research. Current studies indicate that noble metals (such as Ru and Rh) and transition metals (such as Ni and Co) perform well in the catalytic hydrogenation of CO2. Although Ni-based catalysts exhibit lower activity at low temperatures compared to Ru and Rh catalysts, their low cost and high methane selectivity make them considered the most promising catalyst system for industrial applications.

[0004] However, Ni-based catalysts still have certain limitations in practical applications: reactions usually need to be carried out at relatively high temperatures, and the active components are prone to agglomeration and surface carbon accumulation, leading to a decrease in activity. Studies have shown that increasing the nickel loading, optimizing the support and promoters, and enhancing the dispersibility of nickel and the metal-support interaction can help improve the low-temperature activity and stability of the catalyst.

[0005] Patent CN 111495378 A discloses a carbon dioxide methanation catalyst, which prepares a Ni-based hydrotalcite precursor supported on a metal oxide by a hydrothermal method, and then obtains a metallic nickel catalyst by calcination under an ammonia atmosphere and reduction with hydrogen.

[0006] Patent CN 107376925 A discloses a carbon dioxide methanation catalyst. The catalyst composition and the percentage of each component in the total mass of the catalyst are as follows: NiO 30%-60%, Al2O3 30%-60%, MgO 2%-10%, Fe2O3 1-10%, La2O3 0.5%-5%, CeO2 0.5%-5%, CaO 1%-10%, and K2O 1%-3%. The catalyst is prepared by urea precipitation to produce a nickel-aluminum hydrotalcite catalyst precursor, followed by the addition of potassium carbonate and calcium aluminate cement for wet grinding and kneading, and then molding into sheets to prepare the finished methanation catalyst.

[0007] Patent CN 116059990 A discloses a carbon dioxide methanation catalyst, comprising: a support, an active component, and an auxiliary agent, wherein the support is an aluminum-calcium composite oxide with a spinel structure, the active component is nickel, and the auxiliary agent is lanthanum oxide. In this document, the catalyst precursor is prepared by co-precipitation, followed by calcination to obtain the catalyst.

[0008] Patent CN 117920232 A discloses a carbon dioxide methanation catalyst. This document introduces a specific trace amount of yttrium and uses a urea precipitation-condensation-reflux method to prepare a nickel-aluminum hydrotalcite precursor, which is then calcined to obtain a nickel-based catalyst with high nickel content and high dispersion.

[0009] However, the catalysts in the aforementioned existing technologies still have shortcomings in terms of preparation processes and performance. For example, the catalyst disclosed in patent CN111495378 A requires calcination in an ammonia atmosphere, making large-scale preparation difficult; the catalyst composition in patent CN 107376925A is relatively complex, with a long preparation process, which is not conducive to industrial-scale production; and patent CN 117920232 A requires a condensation reflux process, which also presents certain difficulties in large-scale preparation. In addition, the catalysts involved in the above patents still have room for further improvement in methanation performance. Therefore, developing a carbon dioxide methanation catalyst with both high activity and stability under normal pressure and low temperature conditions is of significant practical importance. Summary of the Invention

[0010] To address the aforementioned issues, the inventors conducted in-depth research and discovered that introducing an appropriate amount of manganese can significantly improve the low-temperature performance of the catalyst. Furthermore, they employed the Pechini method to prepare a precursor containing nickel, manganese, and zirconium. After calcination and reduction treatment, a nickel-based catalyst with high nickel content and high dispersion was obtained, thereby achieving efficient carbon dioxide methanation under normal pressure and low temperature conditions.

[0011] The specific technical solution is as follows: [1] A carbon dioxide methanation catalyst, which is a supported catalyst, represented as aNi-bMn / ZrO2, wherein Ni is the active component, Mn is the co-catalyst, ZrO2 is the support, and satisfies 5wt%≤a≤75wt% and 0≤b≤20wt%.

[0012] [2] According to the catalyst described in [1], preferably, 10wt%≤a≤60wt%, 0.5wt%≤b≤10wt%; more preferably, 25wt%≤a≤55wt%, 2wt%≤b≤12wt%.

[0013] [3] A method for preparing a carbon dioxide methanation catalyst, comprising the following steps: (1) Prepare an aqueous solution A containing metallic nickel, manganese and zirconium; (2) Weigh out citric acid with a total number of moles of cations similar to those in step (1), dissolve it in deionized water, and obtain solution B; (3) Slowly add solution B to solution A while stirring continuously. Then add ethylene glycol with a similar total number of cations as above and continue stirring to form a mixed solution C. (4) Mixed solution C is heated and stirred in a water bath or oil bath at a temperature of 60~100℃ until a sol is formed; (5) The sol was dried at 105°C to obtain a fluffy gel-like catalyst precursor; (6) After crushing and grinding the precursor from step (5), calcinate it in a muffle furnace at a temperature of 350~600℃ and reduce it in a reducing atmosphere at a temperature of 400~600℃.

[0014] [4] According to the preparation method described in [3], the total molar concentration of nickel, manganese and zirconium in aqueous solution A is 0.01~0.20 mol / L; the number of moles of citric acid is 0.9~1.1 times the total number of moles of nickel, manganese and zirconium, preferably 0.95~1.05 times.

[0015] [5] According to the preparation method described in [3] or [4], in step (1), the nickel salt is selected from one or more of nickel nitrate, nickel chloride, and nickel acetate; the manganese salt and zirconium salt are selected from one or more of the corresponding nitrate, chloride, acetate, or sulfate.

[0016] [6] According to the preparation method described in [3] or [4], steps (1) to (3) are all carried out at 10~40°C.

[0017] [7] According to the preparation method described in [3] or [4], the stirring time in step (3) is 1 to 6 hours; the heating and stirring time in step (4) is 4 to 12 hours; the drying time in step (5) is 8 to 24 hours; the calcination time in step (6) is 1 to 5 hours and the reduction time is 1 to 5 hours.

[0018] [8] According to the preparation method described in [3] or [4], the molar ratio of manganese to zirconium is 0 to 0.8, preferably 0.05 to 0.6.

[0019] [9] The carbon dioxide methanation catalyst obtained by any one of [3] to [8].

[0020]

[10] The carbon dioxide methanation catalyst according to any one of [1], [2] and [9], wherein the carbon dioxide conversion rate is not less than 60% and the methane selectivity is not less than 99% under the conditions of 240°C, 0.1MPa and 36000mL / g / h; preferably, the carbon dioxide conversion rate is not less than 80% and the methane selectivity is not less than 99.5% under the conditions of 225°C, 0.1MPa and 36000mL / g / h.

[0021] Beneficial effects of the present invention Compared with existing technologies, this invention provides a Mn-modified Ni / ZrO2 carbon dioxide methanation catalyst that exhibits high CO2 conversion and high CH4 selectivity under low temperature (225~300℃) and normal pressure (0.1MPa) conditions. Specifically, the preferred catalyst achieves a carbon dioxide conversion of 80% and a methane selectivity of 100% under conditions of 225℃, 0.1MPa, and 36000mL / g / h, and can operate stably for 120 hours without significant deactivation. The catalyst preparation method of this invention is simple and easy to scale up, yielding a nickel-based catalyst with high nickel content (25~55wt%) and good dispersibility, exhibiting excellent catalytic performance and stability under low temperature and normal pressure, and showing significant prospects for industrial application. Detailed Implementation

[0022] The present invention will be described in detail below through some embodiments, but the present invention is not limited to these embodiments.

[0023] Example 1: Preparation of 35Ni / ZrO2 using the Pechini method Weigh 3.472 g of nickel nitrate hexahydrate (Ni(NO3)26H2O) and 2.439 g of zirconium oxynitrate hydrate (ZrO(NO3)2xH2O), and dissolve them in 30 mL of deionized water at 25 °C with stirring until completely dissolved to obtain an aqueous solution A of approximately 0.02 mol / L. Weigh 4.321 g of citric acid, and dissolve it in 30 mL of deionized water at 25 °C with stirring until completely dissolved to obtain solution B. While stirring continuously, slowly add solution B dropwise to solution A, then add 1.25 mL of ethylene glycol dropwise while stirring continuously to obtain mixed solution C. Mixed solution C was heated and stirred in a water bath at 70°C for 8 hours to form a sol. The sol was dried in an oven at 105°C for 12 hours to obtain a fluffy gel-like catalyst precursor. The precursor was crushed and ground, then calcined in a muffle furnace at 450°C for 2 hours, and then reduced in a tube furnace at 500°C for 2 hours under a hydrogen atmosphere to obtain a 35Ni / ZrO2 catalyst.

[0024] Example 2: Preparation of 35Ni-2Mn / ZrO2 using the Pechini method Weigh 3.472 g of nickel nitrate hexahydrate (Ni(NO3)26H2O), 2.365 g of zirconium oxynitrate hydrate (ZrO(NO3)2xH2O), and 0.183 g of manganese nitrate hydrate (Mn(NO3)24H2O). Dissolve them in 30 mL of deionized water at 25 °C with stirring until completely dissolved to obtain an aqueous solution A of approximately 0.02 mol / L metal salt. Weigh 4.4 g of citric acid and dissolve it in 30 mL of deionized water at 25 °C with stirring until completely dissolved to obtain solution B. While stirring continuously, slowly add solution B dropwise to solution A, then add 1.28 mL of ethylene glycol dropwise while stirring continuously to obtain mixed solution C. Mixed solution C was heated and stirred in a water bath at 70°C for 8 hours to form a sol. The sol was dried in an oven at 105°C for 12 hours to obtain a fluffy gel-like catalyst precursor. The precursor was crushed and ground, then calcined in a muffle furnace at 450°C for 2 hours, and then reduced in a tube furnace at 500°C for 2 hours under a hydrogen atmosphere to obtain the 35Ni-2Mn / ZrO2 catalyst.

[0025] Example 3: Preparation of 35Ni-5Mn / ZrO2 using the Pechini method Weigh 3.472 g of nickel nitrate hexahydrate (Ni(NO3)26H2O), 2.252 g of zirconium oxynitrate hydrate (ZrO(NO3)2xH2O), and 0.459 g of manganese nitrate hydrate (Mn(NO3)24H2O). Dissolve them in 30 mL of deionized water at 25 °C with stirring until completely dissolved to obtain an aqueous solution A of approximately 0.02 mol / L metal salt. Weigh 4.517 g of citric acid and dissolve it in 30 mL of deionized water at 25 °C with stirring until completely dissolved to obtain solution B. While stirring continuously, slowly add solution B dropwise to solution A, then add 1.31 mL of ethylene glycol dropwise while stirring continuously to obtain mixed solution C. Mixed solution C was heated and stirred in a water bath at 70°C for 8 hours to form a sol. The sol was dried in an oven at 105°C for 12 hours to obtain a fluffy gel-like catalyst precursor. The precursor was crushed and ground, then calcined in a muffle furnace at 450°C for 2 hours, and then reduced in a tube furnace at 500°C for 2 hours under a hydrogen atmosphere to obtain a 35Ni-5Mn / ZrO2 catalyst.

[0026] Example 4: Preparation of 35Ni-8Mn / ZrO2 using the Pechini method Weigh 3.472 g of nickel nitrate hexahydrate (Ni(NO3)26H2O), 2.13 g of zirconium oxynitrate hydrate (ZrO(NO3)2xH2O), and 0.733 g of manganese nitrate hydrate (Mn(NO3)24H2O). Dissolve them in 30 mL of deionized water at 25 °C with stirring until completely dissolved to obtain an aqueous solution A of approximately 0.02 mol / L. Weigh 4.787 g of citric acid and dissolve it in 30 mL of deionized water at 25 °C with stirring until completely dissolved to obtain solution B. While stirring continuously, slowly add solution B dropwise to solution A, then add 1.39 mL of ethylene glycol dropwise while stirring continuously to obtain a mixed solution C. Mixed solution C was heated and stirred in a water bath at 70°C for 8 hours to form a sol. The sol was dried in an oven at 105°C for 12 hours to obtain a fluffy gel-like catalyst precursor. The precursor was crushed and ground, then calcined in a muffle furnace at 450°C for 2 hours, and then reduced in a tube furnace at 500°C for 2 hours under a hydrogen atmosphere to obtain the 35Ni-8Mn / ZrO2 catalyst.

[0027] Example 1: Preparation of 35Ni-5Mn / ZrO2 by co-impregnation method Weigh 3.472 g of nickel nitrate hexahydrate (Ni(NO3)26H2O) and 0.459 g of manganese nitrate hydrate (Mn(NO3)24H2O), and dissolve them in 30 mL of deionized water at 25 °C with stirring until completely dissolved to obtain an aqueous solution A of approximately 0.02 mol / L metal salt. Weigh 1.2 g of commercial ZrO2 support, and add the ZrO2 support to solution A with continuous stirring to obtain mixture B. Mixture B is heated and stirred in a water bath at 70 °C until it evaporates to dryness; the evaporated solid is placed in an oven and dried at 80 °C for 12 h to obtain a catalyst precursor; the precursor is pulverized and ground, calcined in a muffle furnace at 450 °C for 2 h, and then reduced in a tube furnace at 500 °C for 2 h under a hydrogen atmosphere to obtain the 35Ni-5Mn / ZrO2 catalyst.

[0028] Example 2: Preparation of 35Ni-5Mn / ZrO2 by coprecipitation method Weigh 3.472 g of nickel nitrate hexahydrate (Ni(NO3)26H2O), 2.252 g of zirconium oxynitrate hydrate (ZrO(NO3)2xH2O), and 0.459 g of manganese nitrate hydrate (Mn(NO3)24H2O). Dissolve them in 30 mL of deionized water at 25 °C and stir until completely dissolved to obtain an aqueous solution A of approximately 0.02 mol / L metal salt. Add concentrated ammonia (28%) dropwise to solution A to produce a precipitate. Control the pH of the solution to around 10 and continue stirring for 12 h. Filter the resulting suspension and wash it with deionized water until the washing liquid is neutral. Place the resulting filter cake in an oven and dry it at 80 °C for 12 h to obtain the catalyst precursor. Crush and grind the precursor, calcine it in a muffle furnace at 450 °C for 2 h, and then reduce it in a tube furnace at 500 °C for 2 h under a hydrogen atmosphere to obtain the 35Ni-5Mn / ZrO2 catalyst.

[0029] Catalytic performance evaluation The performance of the catalysts obtained in Examples 1-4 and Comparative Examples 1-2 in the carbon dioxide methanation reaction was evaluated in a fixed-bed quartz tubular reactor.

[0030] 0.1 g of catalyst sample was packed into the reactor. Before the reaction, H2 / N2 (5 / 45 mL / min) was introduced into the reactor, and the temperature was increased to 500℃ at 10℃ / min and maintained for 2 h. Then, the reactor was purged with this atmosphere and cooled to the set reaction temperature (200, 225, 240, 280, 320, 360℃). After reaching the set reaction temperature and stabilizing for 30 min, the reaction gas was introduced. The reaction gas used was H2 / CO2 / N2 (40 / 10 / 10 mL / min), with a space velocity of 36000 mL / g / h and a reaction pressure of 1 atmosphere. After reacting at the set reaction temperature for 30 min, samples were taken and measured. The composition of the reactor outlet gas was analyzed using a gas chromatograph (GC7980plus, Ruihong) equipped with a thermal conductivity detector (TCD). The concentrations of each component (H2, N2, CO, CH4, CO2) were measured, and the CO2 conversion rate and CH4 selectivity were calculated according to the following formula.

[0031]

[0032]

[0033] The quantity in the above formula refers to the number of moles of the corresponding substance.

[0034] The CO2 conversion rates of the catalysts in Examples 1-4 and Comparative Examples 1-2 at different reaction temperatures are listed in Table 1. Since the CH4 selectivity on all catalysts is above 99%, it is not shown in the table here. Table 1. CO2 conversion rate (%) of the catalysts in Examples 1-4 and Comparative Examples 1-2 at different reaction temperatures.

[0035] Table 2. CO2 conversion rate of the catalysts in Examples 1 and 3 at 225°C as a function of reaction time.

[0036] As shown in Table 1, the catalysts prepared by the Pechini method in Examples 1-4 all exhibited high CO2 conversion rates within the temperature range of 240-360℃. Among them, Examples 2-4, by introducing specific trace amounts of manganese, showed significantly higher CO2 conversion rates at low temperatures (240℃) than the catalyst in Example 1 without added manganese. In particular, the catalyst in Example 3 achieved approximately 80% CO2 conversion at a low temperature of 225℃, while maintaining near 100% CH4 selectivity, demonstrating significantly superior performance compared to the other examples.

[0037] Furthermore, as shown in Table 1, under the same catalyst composition, the catalyst of Example 3 prepared by the Pechini method has better CO2 methanation performance than the catalysts prepared by the co-impregnation method (Comparative Example 1) and the co-precipitation method (Comparative Example 2), indicating that this method has a significant advantage in improving catalytic performance.

[0038] The data in Table 2 show that the Ni / ZrO2 catalyst modified with an appropriate amount of Mn (Example 3) can still maintain about 80% CO2 conversion and 100% CH4 selectivity after reacting for 120 hours at 225℃, 0.1 MPa and space velocity of 36000 mL / g / h. Its performance is significantly better than that of the unmodified Ni / ZrO2 catalyst under the same conditions, demonstrating excellent reaction stability.

[0039] In summary, the Ni-based catalyst and its preparation method provided in the embodiments of the present invention have the following beneficial effects: the preparation method is simple, easy to scale up, and can obtain a nickel-based catalyst with high nickel content (25~55 wt%) and good dispersibility. This catalyst exhibits excellent CO2 methanation activity and long-term stability under low temperature and atmospheric pressure conditions, and has significant potential for industrial application.

Claims

1. A carbon dioxide methanation catalyst, characterized in that, It is a supported catalyst, represented as aNi-bMn / ZrO2, where Ni is the active component, Mn is the co-catalyst, and ZrO2 is the support, and satisfies 5wt%≤a≤75wt% and 0≤b≤20wt%.

2. The catalyst according to claim 1, characterized in that, 10wt%≤a≤60wt%, 0.5wt%≤b≤10wt%; preferably, 25wt%≤a≤55wt%, 2wt%≤b≤12wt%.

3. A method for preparing a carbon dioxide methanation catalyst, characterized in that, It includes the following steps: (1) Prepare an aqueous solution A containing metallic nickel, manganese and zirconium; (2) Weigh out citric acid with a total number of moles of cations similar to those in step (1), dissolve it in deionized water, and obtain solution B; (3) Slowly add solution B to solution A while stirring continuously. Then add ethylene glycol with a similar total number of cations as above and continue stirring to form a mixed solution C. (4) Mixed solution C is heated and stirred in a water bath or oil bath at a temperature of 60~100℃ until a sol is formed; (5) The sol was dried at 105°C to obtain a fluffy gel-like catalyst precursor; (6) After crushing and grinding the precursor from step (5), calcinate it in a muffle furnace at a temperature of 350~600℃ and reduce it in a reducing atmosphere at a temperature of 400~600℃.

4. The preparation method according to claim 3, characterized in that, The total molar concentration of nickel, manganese, and zirconium in aqueous solution A is 0.01~0.20 mol / L; the molar amount of citric acid is 0.9~1.1 times the total molar amount of nickel, manganese, and zirconium, preferably 0.95~1.05 times.

5. The preparation method according to claim 3 or 4, characterized in that, In step (1), the nickel salt is selected from one or more of nickel nitrate, nickel chloride, and nickel acetate; the manganese salt and zirconium salt are selected from one or more of the corresponding nitrate, chloride, acetate, or sulfate.

6. The preparation method according to claim 3 or 4, characterized in that, Steps (1) to (3) are all carried out at 10~40℃.

7. The preparation method according to claim 3 or 4, characterized in that, The stirring time in step (3) is 1 to 6 hours; the heating and stirring time in step (4) is 4 to 12 hours; the drying time in step (5) is 8 to 24 hours; the calcination time in step (6) is 1 to 5 hours, and the reduction time is 1 to 5 hours.

8. The preparation method according to claim 3 or 4, characterized in that, The molar ratio of manganese to zirconium is 0 to 0.8, preferably 0.05 to 0.

6.

9. A carbon dioxide methanation catalyst obtained by the preparation method according to any one of claims 3 to 4.

10. The carbon dioxide methanation catalyst according to any one of claims 1, 2, and 9, characterized in that, The carbon dioxide conversion rate is not less than 60% and the methane selectivity is not less than 99% under the conditions of 240℃, 0.1MPa, and 36000mL / g / h; preferably, the carbon dioxide conversion rate is not less than 80% and the methane selectivity is not less than 99.5% under the conditions of 225℃, 0.1MPa, and 36000mL / g / h.

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