A method for recycling an aluminum-based spent catalyst carrier to prepare a carbon dioxide hydrogenation methanation catalyst

Abstract

The application discloses a method for preparing a carbon dioxide hydrogenation methanation catalyst by recycling an aluminum-based waste catalyst carrier, and belongs to the field of catalyst preparation technology. The method comprises the following steps: (1) mixing and roasting the aluminum-based waste catalyst and sodium hydroxide to obtain a sodium calcination product; (2) adding a weak alkaline solution to perform leaching treatment to obtain a sodium metaaluminate leaching solution; (3) adding an acidic solution drop by drop to adjust the pH value to alkaline, and then performing aging, separation and drying to obtain an alumina precursor; (4) calcining the alumina precursor to obtain mesoporous alumina; (5) adding the mesoporous alumina into a metal salt solution to sequentially perform ultrasonic treatment and impregnation treatment, and then performing drying and calcination on a catalyst precursor; the metal salt solution contains a first metal Ni; and (6) heating the catalyst precursor under a hydrogen gas flow to perform reduction to obtain the carbon dioxide hydrogenation methanation catalyst. The application realizes efficient recycling of the aluminum-based waste catalyst, and has the advantages of green environmental protection, high recycling efficiency and good catalytic performance of the recycled product.

Description

Technical Field

[0001] This invention relates to the field of aluminum-based waste catalyst regeneration technology, and in particular to a method for preparing carbon dioxide hydrogenation methanation catalyst by reusing aluminum-based waste catalyst recycling carrier. Background Technology

[0002] Aluminum-based catalysts occupy a crucial position in the petrochemical industry. They are indispensable catalytic materials in petrochemical production processes, widely used in key stages such as catalytic cracking, hydrocracking, polymerization, and isomerization. The high thermal stability, mechanical strength, and unique catalytic properties of aluminum-based catalysts make them key factors in improving petrochemical production efficiency and product quality. Furthermore, aluminum-based catalysts are increasingly used in environmental protection, such as in waste gas and wastewater treatment, effectively reducing pollutant emissions and significantly improving environmental quality. Therefore, aluminum-based catalysts are not only an important driving force for technological progress in the petrochemical industry but also an indispensable key material for promoting green chemistry and sustainable development. The recycling of spent aluminum-based catalysts has significant environmental and resource utilization value. Besides the active metal, Al₂O₃, as a carrier, is the most abundant component of aluminum-based catalysts. Recovering aluminum from spent aluminum-based catalysts is not only technically feasible but also has high economic value. In addition, catalysts adsorb harmful substances such as arsenic, sulfur, chlorine, and nickel carbonyl during use. If these spent catalysts are not properly treated, they will cause serious environmental pollution. Therefore, the recycling of aluminum-based waste catalysts can not only reduce environmental pollution, but also effectively alleviate the current situation of resource shortage, and has significant economic benefits and environmental significance.

[0003] Carbon dioxide hydrogenation methanation catalysts hold immense significance in the field of carbon sequestration. Firstly, this technology provides a pathway to convert the greenhouse gas carbon dioxide into valuable energy products, playing a positive role in mitigating global climate change. Under the action of the catalyst, CO2 reacts with hydrogen to produce methane, effectively reducing CO2 emissions and producing a clean energy source. Research progress on CO2 methanation catalysts shows that by optimizing the catalyst's structure and composition, low-temperature and efficient CO2 conversion can be achieved. This not only improves CO2 utilization but also significantly reduces energy consumption, possessing significant practical implications. Furthermore, this technology contributes to the development of carbon capture, utilization, and storage (CCUS) technologies, providing technical support for achieving carbon neutrality. Therefore, carbon dioxide hydrogenation methanation catalysts play a crucial role in carbon sequestration and energy conversion, having a profound impact on promoting environmental protection and achieving sustainable energy development.

[0004] Current research on the recycling and reuse of aluminum-based catalysts mainly focuses on the recovery of precious metals. However, the chemicals used in these recycling methods, such as aqua regia, are highly corrosive, and the treatment of leachate and secondary pollution issues are not considered. Although Al₂O₃ is a commonly used support for carbon dioxide hydrogenation methanation catalysts, the specific surface area and pore size distribution of Al₂O₃ supports prepared by different methods vary, as do the dispersion and stability of active metals on the support surface. Consequently, their catalytic activities for carbon dioxide hydrogenation methanation also differ. Therefore, how to recycle and reuse aluminum-based catalysts to prepare highly active carbon dioxide hydrogenation methanation catalysts remains a pressing technical problem that needs to be solved. Summary of the Invention

[0005] Based on the above, and addressing the problems of incomplete metal resource recovery, highly corrosive waste acid during the recovery process, large quantities of recycled acid, and failure to utilize the recovered products for high-value purposes in existing processes, this invention provides a method for reusing an aluminum-based waste catalyst support to prepare a carbon dioxide hydrogenation methanation catalyst. The method involves recovering the aluminum-based waste catalyst, preparing a high-purity mesoporous alumina material for the support using sodium aluminate as an intermediate product, and then using this material to prepare a regenerated carbon dioxide hydrogenation methanation catalyst. The entire process significantly reduces the amount of strong acid used. On one hand, the process of this invention achieves green and efficient leaching of metallic aluminum; on the other hand, the carbon-fixing catalyst prepared in this invention exhibits excellent catalytic performance, realizing the resource utilization of the recovered products. This invention has the advantages of simple process, strong operability, cost savings, and environmental friendliness.

[0006] In a first aspect, the present invention provides a method for preparing a carbon dioxide hydrogenation methanation catalyst by reusing an aluminum-based waste catalyst recovery support, comprising the following steps: (1) The aluminum-based waste catalyst was mixed with sodium hydroxide and calcined to obtain the sodium-calcined product; (2) Add a weak alkaline solution to the sodium-calcined product for leaching treatment to obtain sodium aluminate leachate; (3) The sodium aluminate leaching solution is added dropwise into an acidic solution to adjust the pH value to alkaline. After aging, separation and drying, the alumina precursor is obtained. (4) The alumina precursor is calcined to obtain mesoporous alumina; (5) The mesoporous alumina is added to a metal salt solution and subjected to ultrasonic treatment and impregnation treatment in sequence, followed by drying and calcination to obtain a catalyst precursor; the metal in the metal salt solution includes the first metal Ni; (6) The catalyst precursor is reduced by heating under a hydrogen gas flow to obtain the carbon dioxide hydrogenation methanation catalyst.

[0007] In the above-mentioned method for recycling and reusing aluminum-based waste catalyst carriers to prepare carbon dioxide hydrogenation methanation catalysts, further, the aluminum-based waste catalyst contains ≥98% alumina by mass; even further, the aluminum-based waste catalyst is an Fe-doped Pt-Sn / Al2O3 waste catalyst, comprising alumina, platinum dioxide, ferric oxide, and tin oxide; as an example, the aluminum-based waste catalyst is an Fe-doped Pt-Sn / Al2O3 waste catalyst used in light oil catalytic reforming processes, wherein the alumina by mass is 98%, the active component platinum dioxide by mass is 0.35%, the ferric oxide by mass is 0.19%, and the tin oxide by mass is 0.18%. In this invention, after sodium roasting and leaching, the aluminum element is converted into easily soluble sodium aluminate, which is entirely present in the leachate, while other metal elements remain primarily in the insoluble leaching residue.

[0008] In the above-mentioned method for recycling and reusing aluminum-based waste catalyst carriers to prepare carbon dioxide hydrogenation methanation catalysts, the method further includes, before step (1): calcining the aluminum-based waste catalyst at 500°C for 2 hours to remove carbon, followed by ball milling to obtain waste catalyst powder. This pretreatment removes residual oil and coke from the surface of the waste catalyst. The calcination is specifically carried out in a muffle furnace.

[0009] In the above-mentioned method for recycling and reusing aluminum-based waste catalyst carriers to prepare carbon dioxide hydrogenation methanation catalysts, further, in step (1), the mass ratio of the aluminum-based waste catalyst to sodium hydroxide is 1:(0.8-1.5), such as 1:1.2, the calcination temperature is 300-500℃, and the calcination time is 1-2.5h, such as calcination at 450℃ for 2h. As an example, the calcination of the aluminum-based waste catalyst and sodium hydroxide is carried out under aerobic conditions.

[0010] In the above-mentioned method for preparing carbon dioxide hydrogenation methanation catalyst by recycling and reusing aluminum-based waste catalyst carrier, further, in step (2), the weakly alkaline solution is a NaOH solution with a pH of 7.0 to 9.5 (e.g., pH=8.5), the liquid-to-solid ratio in the leaching treatment step is (20 to 30) mL:1g (e.g., 20 mL:1g), and the temperature is 25 to 65℃, e.g., 35℃; In step (3), the acidic solution is an inorganic acid, including nitric acid, such as a 0.1 mol / L nitric acid solution; the dropping rate is 2 mL / min; and adjusting the pH value to alkaline means adjusting the pH to 10. In step (4), the roasting temperature is 400-600℃, preferably 450℃, and the time is 1-2h.

[0011] In the above-mentioned method for preparing carbon dioxide hydrogenation methanation catalyst by recycling aluminum-based waste catalyst carrier, further, based on the mass of the carbon dioxide hydrogenation methanation catalyst, the Ni loading is 10% to 25%, preferably 15% to 25%, more preferably 20% to 25%, and even more preferably 20%.

[0012] Furthermore, the metal in the metal salt solution also includes a second metal, which is any one of Mn, Mo, Co, V, and Ce; preferably, based on the mass of the carbon dioxide hydrogenation methanation catalyst, the loading of the second metal is 0.5% to 3%, more preferably 1% to 3%; more preferably, the second metal is V, and based on the mass of the carbon dioxide hydrogenation methanation catalyst, the loading of Ni is 20% and the loading of V is 1%.

[0013] In the above-mentioned method for preparing carbon dioxide hydrogenation methanation catalyst by recycling aluminum-based waste catalyst carrier, in step (5), the ultrasonic treatment step has a temperature of 15-35℃ (e.g., room temperature 20-25℃) and a time of 30-60min (e.g., 60min). In step (5), the temperature in the impregnation treatment step is 15-35℃ (e.g., room temperature 20-25℃), and the time is 10-18h (e.g., 12h). In step (5), the roasting temperature is 300–500°C, such as 500°C, and the time is 2–6 hours, such as 4 hours. The roasting is specifically carried out in a muffle furnace. In step (6), the reduction temperature is 500-700℃ and the time is 1-2h. If the reduction is carried out at 500℃ for 1h, the metallic Ni will exist stably in the form of NiO. Therefore, the reduction step is usually carried out before the catalytic reaction. Specifically, the catalyst can be placed in a fixed bed and reduced under a hydrogen gas flow. After reduction, the temperature is lowered and the reaction gas is introduced to carry out the catalytic reaction.

[0014] In a second aspect, the present invention provides a carbon dioxide hydrogenation methanation catalyst prepared by the method described in any of the preceding claims.

[0015] Thirdly, the present invention provides a method for producing methane by hydrogenation of carbon dioxide, comprising the following steps: A mixture of carbon dioxide, hydrogen, and a balance gas is reacted with the carbon dioxide hydrogenation methanation catalyst described above to produce methane.

[0016] In the above-mentioned method for producing methane by carbon dioxide hydrogenation, as an example, the size of the carbon dioxide hydrogenation methanation catalyst is 30-50 μm; The volume ratio of carbon dioxide to hydrogen is 1:4; The carbon dioxide in the mixture has a volume fraction of 16%. The balancing gas is nitrogen. The reaction temperature is 200–700°C, such as 300°C; The reaction was carried out at atmospheric pressure. The reaction space velocity of the carbon dioxide hydrogenation methanation catalyst is 4000–4500 h⁻¹. -1 For example, the gas space velocity is 4248 h⁻¹ -1 The spacetime velocity refers to the velocity of the reactant gas passing through each m³ per unit time, with units of m. 3 catalyst / h), i.e., h -1 .

[0017] The present invention has the following beneficial effects: (1) The method for preparing carbon-fixing catalysts by recycling aluminum-based waste catalyst carriers provided by the present invention is simple, efficient, green and environmentally friendly. It can achieve efficient recovery of Al components in waste catalysts. The prepared mesoporous alumina samples have high purity, large specific surface area and strong stability, which fully meet the requirements as catalyst carrier materials.

[0018] (2) The carbon dioxide hydrogenation methanation catalyst prepared by the method of recycling the aluminum-based waste catalyst carrier provided by the present invention has good catalytic performance and realizes the resource utilization of Al in the aluminum-based waste catalyst. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the method for preparing carbon dioxide hydrogenation methanation catalyst by recycling and reusing aluminum-based waste catalyst carriers according to the present invention.

[0020] Figure 2 XRD characterization of the Ni-V / Al2O3 catalyst precursor synthesized in Example 9 of this invention.

[0021] Figure 3 This is a SEM characterization of the Ni-V / Al2O3 catalyst precursor synthesized in Example 9 of the present invention.

[0022] Figure 4 This is a performance test of the Ni-V / Al2O3 catalyst synthesized in Example 9 of the present invention. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0024] The calculation formulas in the following examples are as follows: (1) Carbon dioxide conversion rate

[0025] (2) Methane yield

[0026] Among them, C CO2 Y CH4 These represent the conversion rate of carbon dioxide and the yield of methane, respectively.

[0027] Unless otherwise specified, the methods used in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0028] The aluminum-based waste catalyst in the following examples is a Fe-doped Pt-Sn / Al2O3 waste catalyst used in the catalytic reforming process of light oil. It contains, by mass percentage, 98% alumina, 0.35% platinum dioxide (the active ingredient), and trace amounts of other elements such as 0.19% ferric oxide and 0.18% tin oxide.

[0029] Example 1 This embodiment provides a method for reusing an aluminum-based waste catalyst recovery support to prepare a 5% Ni / Al2O3 catalyst for carbon dioxide hydrogenation methanation, such as... Figure 1 As shown, the specific steps are as follows: (1) Take 10g of aluminum-based waste catalyst and place it in a ceramic boat. Place it in a muffle furnace and calcine at 500℃ for 2h. After cooling to room temperature, take out the sample.

[0030] (2) Take 5g of the sample obtained in step (1) and grind it thoroughly in a mortar for 0.5h. After grinding, pass the sample through a 100-mesh sieve for later use.

[0031] (3) Take 2g of sample from step (2) and mix it with 2.4g of sodium hydroxide. Grind it thoroughly in a mortar. Place the mixed sample in a porcelain boat and calcine it in a muffle furnace at 450℃ for 2 hours to obtain the calcined mixed sample.

[0032] (4) Dilute the NaOH solution to pH=8.5 to obtain a weakly alkaline solution. Add 40mL of the weakly alkaline solution to 2g of the calcined mixed sample obtained in step (3), place it in a constant temperature water bath at 35℃ and stir to leach. After filtration, obtain a sodium aluminate solution. ICP analysis of the leachate composition showed that the only metal elements were Al and Na, with almost no other metal impurities.

[0033] (5) The sodium aluminate solution obtained in step (4) is added dropwise to a 0.1 mol / L nitric acid solution at a flow rate of 2 mL / min using a peristaltic pump. After adjusting the pH to 10, the alumina precursor is obtained by aging, filtration, washing and drying.

[0034] (6) The alumina precursor was placed in a muffle furnace and calcined at 500°C for 2 hours to obtain a mesoporous alumina sample.

[0035] (7) Add 1.24g of nickel nitrate hexahydrate to 10mL of deionized water and place it on a magnetic stirrer for thorough stirring.

[0036] (8) Weigh 5g of the recovered mesoporous alumina sample and slowly add it to the mixed solution that is being stirred. Continue stirring the mixed sample for 30 minutes to ensure uniform mixing. Transfer the stirred mixed sample to a CNC ultrasonic cleaner and perform ultrasonic treatment for 60 minutes. Then place the sample at room temperature for 12 hours to soak.

[0037] (9) Place the impregnated sample in an electric heating drying oven and dry for 18 hours. After thorough drying, grind the resulting block sample into powder using a mortar and pestle.

[0038] (10) The powdered sample was placed in a muffle furnace and calcined at 500°C for 4 hours to obtain the catalyst precursor; (11) 0.5 g of catalyst precursor was reduced for 1 h under H2 gas flow at 500 ℃. After the reduction was completed, the temperature was lowered to 200 ℃ to obtain a 5% Ni / Al2O3 catalyst sample.

[0039] Example 2 This embodiment provides a method for preparing 10%Ni / Al2O3 carbon dioxide hydrogenation methanation catalyst by recycling aluminum-based waste catalyst carrier. The specific steps are similar to those used in Example 1. The only difference is that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 2.48g of nickel nitrate hexahydrate.

[0040] Example 3 This embodiment provides a method for preparing a 15%Ni / Al2O3 carbon dioxide hydrogenation methanation catalyst by recycling an aluminum-based waste catalyst carrier. The specific steps are similar to those used in Example 1, except that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 3.72g of nickel nitrate hexahydrate.

[0041] Example 4 This embodiment provides a method for preparing a 20%Ni / Al2O3 catalyst for carbon dioxide hydrogenation methanation by recycling an aluminum-based waste catalyst carrier. The specific steps are similar to those used in Example 1, except that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 4.96g of nickel nitrate hexahydrate.

[0042] Example 5 This embodiment provides a method for preparing 25%Ni / Al2O3 carbon dioxide hydrogenation methanation catalyst by recycling aluminum-based waste catalyst carrier. The specific steps are similar to those used in Example 1. The only difference is that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 6.19g of nickel nitrate hexahydrate.

[0043] Example 6 This embodiment provides a method for preparing a 20%Ni-1%Mn / Al2O3 catalyst for carbon dioxide hydrogenation methanation by reusing an aluminum-based waste catalyst recycling carrier. The specific steps are similar to those used in Example 1, except that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 4.96g of nickel nitrate hexahydrate, and 0.23g of manganese nitrate tetrahydrate is added.

[0044] Example 7 This embodiment provides a method for preparing a 20%Ni-1%Mo / Al2O3 catalyst for carbon dioxide hydrogenation methanation by recycling an aluminum-based waste catalyst carrier. The specific steps are similar to those used in Example 1. The only difference is that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 4.96g of nickel nitrate hexahydrate, and 0.10g of ammonium heptahydrate is added.

[0045] Example 8 This embodiment provides a method for preparing a 20%Ni-1%Co / Al2O3 catalyst for carbon dioxide hydrogenation methanation by reusing an aluminum-based waste catalyst recycling carrier. The specific steps are similar to those used in Example 1, except that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 4.96g of nickel nitrate hexahydrate, and 0.25g of cobalt nitrate hexahydrate is added.

[0046] Example 9 This embodiment provides a method for preparing a 20%Ni-1%V / Al2O3 catalyst for carbon dioxide hydrogenation methanation by recycling an aluminum-based waste catalyst carrier. The specific steps are similar to those used in Example 1. The only difference is that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 4.96g of nickel nitrate hexahydrate, and 0.12g of ammonium metavanadate is added.

[0047] Example 10 This embodiment provides a method for preparing a 20%Ni-0.5%V / Al2O3 catalyst for carbon dioxide hydrogenation methanation by reusing an aluminum-based waste catalyst recycling carrier. The specific steps are similar to those used in Example 1, except that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 4.96g of nickel nitrate hexahydrate, and 0.06g of ammonium metavanadate is added.

[0048] Example 11 This embodiment provides a method for preparing a 20%Ni-2%V / Al2O3 catalyst for carbon dioxide hydrogenation methanation by reusing an aluminum-based waste catalyst recycling carrier. The specific steps are similar to those used in Example 1, except that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 4.96g of nickel nitrate hexahydrate, and 0.24g of ammonium metavanadate is added.

[0049] Example 12 This embodiment provides a method for preparing a 20%Ni-3%V / Al2O3 catalyst for carbon dioxide hydrogenation methanation by recycling an aluminum-based waste catalyst carrier. The specific steps are similar to those used in Example 1. The only difference is that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 4.96g of nickel nitrate hexahydrate, and 0.36g of ammonium metavanadate is added.

[0050] Example 13 This embodiment provides a method for preparing a 20%Ni-1%Ce / Al2O3 catalyst for carbon dioxide hydrogenation methanation by reusing an aluminum-based waste catalyst recycling carrier. The specific steps are similar to those used in Example 1, except that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 4.96g of nickel nitrate hexahydrate, and 0.16g of cerium nitrate hexahydrate is added.

[0051] Example 14 This embodiment provides a method for preparing a 20%Ni-1%Ce / Al2O3 catalyst for carbon dioxide hydrogenation methanation by reusing an aluminum-based waste catalyst recycling carrier. The specific steps are similar to those used in Example 1, except that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 4.96g of nickel nitrate hexahydrate, and 0.32g of cerium nitrate hexahydrate is added.

[0052] Example 15 This embodiment provides a method for preparing a 20%Ni-1%Ce / Al2O3 catalyst for carbon dioxide hydrogenation methanation by reusing an aluminum-based waste catalyst recycling carrier. The specific steps are similar to those used in Example 1, except that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 4.96g of nickel nitrate hexahydrate, and 0.48g of cerium nitrate hexahydrate is added.

[0053] Example 16 This embodiment provides a method for preparing a 20%Ni-1%Ce / Al2O3 catalyst for carbon dioxide hydrogenation methanation by reusing an aluminum-based waste catalyst recycling carrier. The specific steps are similar to those used in Example 1, except that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 4.96g of nickel nitrate hexahydrate, and 0.16g of ruthenium nitrate is added.

[0054] Example 17 This embodiment provides a method for preparing a 20%Ni-1%Ce / Al2O3 catalyst for carbon dioxide hydrogenation methanation by reusing an aluminum-based waste catalyst recycling carrier. The specific steps are similar to those used in Example 1, except that in step (7), 1.24g of nickel nitrate hexahydrate is replaced with 4.96g of nickel nitrate hexahydrate, and 0.16g of lanthanum nitrate hexahydrate is added.

[0055] Comparative Example 1 Similar to the method used in Example 4, except that steps (1)-(4) are omitted, and the obtained sodium aluminate solution is replaced with a directly prepared sodium aluminate solution. The concentration of sodium aluminate is the same as in Example 4, and steps (5)-(10) are the same as in Example 4.

[0056] Comparative Example 2 Similar to the method used in Example 9, except that steps (1)-(4) are omitted, and the obtained sodium aluminate solution is replaced with a directly prepared sodium aluminate solution. The concentration of sodium aluminate is the same as in Example 1, and steps (5)-(10) are the same as in Example 9.

[0057] Performance testing I. Alumina Performance Testing The performance parameters of the mesoporous alumina sample prepared in step (6) of Example 4 and the alumina sample prepared in Comparative Example 1 were tested, and the results are shown in Table 1.

[0058] Table 1. Comparison of Alumina Properties

[0059] As shown in Table 1, although the alumina samples prepared from different raw materials have the same purity, the alumina prepared from the recovered sodium aluminate of this invention has a much higher specific surface area, pore size, and porosity than the alumina prepared from pure sodium aluminate. This demonstrates that the mesoporous alumina samples prepared by this invention have high purity, large specific surface area, and strong stability, making them more suitable as catalyst support materials.

[0060] II. Relevant Characterization The XRD and SEM characterization results of the precursor of the 20%Ni-1%V / Al2O3 catalyst for carbon dioxide hydrogenation methanation prepared in step (10) of Example 9 are shown in [reference needed]. Figure 2-3 .Depend on Figure 2 Middle characteristic peaks and Figure 3 It can be seen that metallic Ni is uniformly loaded on the surface of the carrier in the form of NiO, and therefore is converted into Ni in the subsequent reduction step (11).

[0061] III. Catalytic Performance The catalytic activity of the catalysts prepared in the above examples and comparative examples was evaluated using the following steps: A layer of catalyst particles with a specific size (30-50 μm) was placed in the center of the reactor, and a thermocouple was inserted into the bottom of the catalyst bed to adjust the heating temperature. A feed stream containing hydrogen and carbon dioxide (50 mL / min) was introduced into the reactor at a molar ratio of 4:1, with nitrogen as the equilibrium gas (carbon dioxide volume fraction in the mixed gas was 16%), and a gas space velocity (GHSV) of 4200 h⁻¹. −1 The reaction was carried out in the temperature range of 200–700 °C, and the product stream was analyzed using an online gas chromatograph.

[0062] The Ni-V / Al2O3 catalyst synthesized in Example 9 exhibits the following CO2 conversion and CH4 yield at 200–700 °C: Figure 4 As shown. Under normal pressure, the reaction temperature was 300℃ and the gas hourly space velocity was 4248 h⁻¹. -1 The experimental results are shown in Table 2.

[0063] Table 2. Catalyst Activity Evaluation Results

[0064] As shown in Table 2, the catalyst sample in Example 1, with a Ni loading of 5 wt%, achieved a carbon dioxide conversion rate of 37.0% and a methane yield of 37.0%, exhibiting poor catalytic performance. The catalyst sample in Example 2, with a Ni loading of 10 wt%, achieved a carbon dioxide conversion rate of 84.5% and a methane yield of 84.5%, exhibiting good catalytic performance. The catalyst sample in Example 3, with a Ni loading of 15%, achieved a carbon dioxide conversion rate of 88.3% and a methane yield of 88.3%, exhibiting good catalytic performance. The catalyst sample in Example 4, with a Ni loading of 20%, achieved a carbon dioxide conversion rate of 90.6% and a methane yield of 90.5%, exhibiting the best catalytic activity. Further increasing the Ni loading in Example 5 did not significantly change the catalytic activity. With further addition of doped metals, when the Ni loading is 20wt% and 1% V metal is added for modification, the carbon dioxide conversion rate is 93.0% and the methane yield is 93.0% at a reaction temperature of 300℃. All carbon dioxide is converted into methane with almost no other byproducts generated, and the catalytic activity reaches its maximum, showing good low-temperature catalytic performance.

[0065] The comparison between Example 4 and Comparative Example 1 shows that the carbon dioxide conversion rate and methane yield of Example 4 are both higher than those of Comparative Example 1. This is because the mesoporous alumina prepared by the method of the present invention from recovered aluminum-based waste catalyst has a higher specific surface area and stronger stability, resulting in higher catalytic activity of the prepared catalyst, consistent with the results in Table 2. Similarly, in the comparison between Example 9 and Comparative Example 2, the carbon dioxide conversion rate and methane yield of Example 9 are both higher than those of Comparative Example 2. The method of the present invention not only realizes the resource utilization of Al in aluminum-based waste catalyst, but also the prepared catalyst exhibits excellent catalytic performance for the hydrogenation and methanation of carbon dioxide.

[0066] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including modifications made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A method for producing methane by hydrogenation of carbon dioxide, characterized in that, Includes the following steps: A mixture of carbon dioxide, hydrogen, and equilibrium gas is reacted with a carbon dioxide hydrogenation methanation catalyst to produce methane. The reaction temperature is 300℃; The reaction was carried out at atmospheric pressure. The preparation method of the carbon dioxide hydrogenation methanation catalyst includes the following steps: (1) The aluminum-based waste catalyst was mixed with sodium hydroxide and calcined to obtain the sodium-calcined product; (2) Add a weak alkaline solution to the sodium-calcined product for leaching treatment to obtain sodium aluminate leachate; (3) The sodium aluminate leaching solution is added dropwise into an acidic solution to adjust the pH value to alkaline. After aging, separation and drying, the alumina precursor is obtained. (4) The alumina precursor is calcined to obtain mesoporous alumina; (5) The mesoporous alumina is added to a metal salt solution and subjected to ultrasonic treatment and impregnation treatment in sequence, followed by drying and calcination to obtain a catalyst precursor; the metal in the metal salt solution includes the first metal Ni; (6) The catalyst precursor is reduced by heating under a hydrogen gas flow to obtain the carbon dioxide hydrogenation methanation catalyst; Based on the mass of the carbon dioxide hydrogenation methanation catalyst, the Ni loading is 10% to 25%.

2. The method for producing methane by carbon dioxide hydrogenation according to claim 1, characterized in that: The preparation method of the carbon dioxide hydrogenation methanation catalyst further includes, before step (1): calcining the aluminum-based waste catalyst at 500°C for 2 hours to remove carbon, followed by ball milling to obtain waste catalyst powder; and / or, In step (1), the mass ratio of the aluminum-based waste catalyst to sodium hydroxide is 1:(0.8-1.5), the calcination temperature is 300-500℃, and the calcination time is 1-2.5h.

3. The method for producing methane by hydrogenation of carbon dioxide according to any one of claims 1-2, characterized in that: In step (2), the weakly alkaline solution is a NaOH solution with a pH of 7.0–9.5, the liquid-to-solid ratio in the leaching treatment step is (20–30) mL:1 g, and the temperature is 25–65 °C; and / or, In step (3), adjusting the pH value to alkaline means adjusting the pH to 10; and / or, In step (4), the roasting temperature is 400-600℃ and the time is 1-2h.

4. The method for producing methane by hydrogenation of carbon dioxide according to any one of claims 1-2, characterized in that: Based on the mass of the carbon dioxide hydrogenation methanation catalyst, the Ni loading is 15% to 25%.

5. The method for producing methane by carbon dioxide hydrogenation according to claim 4, characterized in that: Based on the mass of the carbon dioxide hydrogenation methanation catalyst, the Ni loading is 20% to 25%.

6. The method for producing methane by carbon dioxide hydrogenation according to claim 5, characterized in that: Based on the mass of the carbon dioxide hydrogenation methanation catalyst, the Ni loading is 20%.

7. The method for producing methane by hydrogenation of carbon dioxide according to claim 4, characterized in that: The metal salt solution also includes a second metal, which is any one of Mn, Mo, Co, V, and Ce.

8. The method for producing methane by hydrogenation of carbon dioxide according to claim 7, characterized in that: Based on the mass of the carbon dioxide hydrogenation methanation catalyst, the loading of the second metal is 0.5% to 3%.

9. The method for producing methane by carbon dioxide hydrogenation according to claim 8, characterized in that: Based on the mass of the carbon dioxide hydrogenation methanation catalyst, the loading of the second metal is 1% to 3%.

10. The method for producing methane by carbon dioxide hydrogenation according to claim 7, characterized in that: The second metal is V, and based on the mass of the carbon dioxide hydrogenation methanation catalyst, the loading of Ni is 20% and the loading of V is 1%.

11. The method for producing methane by hydrogenation of carbon dioxide according to any one of claims 1-2, characterized in that: In step (5), the ultrasonic treatment step is performed at a temperature of 15–35°C for 30–60 min; and / or, In step (5), the impregnation treatment step is carried out at a temperature of 15–35°C for 10–18 hours; and / or, In step (5), the calcination temperature is 300–500°C, and the time is 2–6 hours; and / or, In step (6), the reduction temperature is 500-700℃ and the time is 1-2h.

12. The method for producing methane by hydrogenation of carbon dioxide according to claim 1, characterized in that: The volume ratio of carbon dioxide to hydrogen is 1:4; The carbon dioxide in the mixture has a volume fraction of 16%. The balancing gas is nitrogen. The reaction space velocity of the carbon dioxide hydrogenation methanation catalyst is 4000–4500 h⁻¹. -1 .

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