Cobalt-aluminum composite oxide and preparation method and application thereof

Abstract

The invention provides a cobalt-aluminum composite oxide and a preparation method and application thereof, and belongs to the technical field of catalyst preparation. When the cobalt-aluminum composite oxide provided by the invention is used in the process of preparing methane through CO2 hydrogenation, Co and Al are both active components, and the two components cannot be absent. A metal Co < 0 > site is used for dissociating hydrogen, and Al is an important electron and structural aid, can adjust the relative proportion of Co < 0 > and Co < delta + > (such as Co < 2 + >), and forms a rich metal Co < 0 >-cobalt-aluminum composite oxide (cobalt is Co < 2 + >) interface for adsorption and activation of CO2. The cobalt-aluminum composite oxide provided by the invention shows excellent CO2 methanation reaction performance as a catalyst. The preparation method provided by the invention is simple to operate, low in cost, free of secondary pollution and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and in particular relates to a cobalt-aluminum composite oxide and a preparation method and application thereof. Background Art

[0002] CO2 is an important C1 chemical platform compound. By reacting with hydrogen produced from renewable energy, CO2 can be converted into high-value-added chemicals such as methane, light olefins, aromatics, and liquefied petroleum gas. The implementation of this process not only effectively reduces the CO2 content in the atmosphere and mitigates the greenhouse effect, but also develops an alternative non-petroleum route for producing clean fuels. It plays an important role in accelerating the adjustment of the energy structure, guiding new technological innovations, and promoting the development of green technology industries. Among them, methane is not only the main component of natural gas and can be directly used as a fuel, but it is also an important carrier of hydrogen energy. Compared with the synthesis of methanol, light olefins, and aromatics, CO2 hydrogenation to methane has a higher reaction rate and target product selectivity, and the reaction conditions are relatively mild, making it easy to scale up industrially.

[0003] Precious metal catalysts (such as Rh, Ru and Pd) have shown high catalytic activity in the process of CO2 hydrogenation to methane; however, the high price of these catalytic systems has greatly increased the cost of catalyst preparation, restricting their industrial application. Ni-based catalysts are also widely used in CO2 methanation processes and have shown high CO2 conversion rates and methane selectivity. However, Ni-based catalysts are prone to sintering and agglomeration during the reaction, resulting in rapid deactivation of the catalyst. For example, Mn-modified Ni / bentonite catalysts at 300 ° C, 3600 mL / (g cat Under the conditions of 100 °C (100 °F / 100 °C) and 100 °F (100 °C / 100 °C), the CO2 conversion rate dropped significantly after 140 h of reaction. Furthermore, Ni-based catalysts have a high activation temperature, often requiring temperatures of 350°C or higher to effectively activate CO2 and H2. For example, the CO2 conversion rate of a Ni / TiO2 catalyst at 300°C was approximately 12%, but increasing the reaction temperature to 350°C increased the CO2 conversion rate to approximately 46%. In contrast, Co-based catalysts exhibit higher low-temperature CO2 methanation activity and better catalytic stability.

[0004] Despite this, existing Co-based catalysts still suffer from low reaction activity and methane yield. Summary of the Invention

[0005] In view of this, the present invention aims to provide a cobalt-aluminum composite oxide, a preparation method thereof, and its application. The cobalt-aluminum composite oxide provided by the present invention, when used as a catalyst in CO2 hydrogenation to methane, has the advantages of high CO2 conversion, high methane selectivity and yield, a short reaction induction period, and high catalytic stability.

[0006] In order to achieve the above object, the present invention provides the following solutions:

[0007] The present invention provides a method for preparing a cobalt-aluminum composite oxide, comprising the following steps:

[0008] A water-soluble cobalt salt, a water-soluble aluminum salt, water, and a precipitant are mixed to perform a precipitation reaction to obtain a cobalt-aluminum composite oxide precursor; the molar ratio of cobalt ions in the water-soluble cobalt salt to aluminum ions in the water-soluble aluminum salt is (0.2-0.6):(0.005-0.6); and the ratio of the total molar amount of metal ions in the water-soluble cobalt salt and the water-soluble aluminum salt to the molar amount of the precipitant is 1:(2-7.5);

[0009] The cobalt-aluminum composite oxide precursor is calcined to obtain the cobalt-aluminum composite oxide.

[0010] Preferably, the water-soluble cobalt salt includes one or more of cobalt nitrate, cobalt chloride and cobalt sulfate; the water-soluble aluminum salt includes one or more of aluminum nitrate, aluminum chloride and aluminum sulfate.

[0011] Preferably, the precipitant includes one or more of water-soluble carbonates, water-soluble bicarbonates and water-soluble hydroxides.

[0012] Preferably, the precipitation reaction temperature is 60-90° C. and the time is 2-10 h.

[0013] Preferably, the calcination temperature is 300-750° C. and the calcination time is 3-10 hours.

[0014] The present invention provides a cobalt-aluminum composite oxide prepared by the preparation method described in the above scheme, the chemical formula of which is Co a Al b O c ; Among them, the ratio of a and b is (0.44~90):1, the ratio of (a+b) and c is (4.55~7.5):(6~10.5); the valence of Co is +(8 / 3).

[0015] The present invention provides the use of the cobalt-aluminum composite oxide described in the above scheme as a catalyst in the hydrogenation of carbon dioxide to methane.

[0016] Preferably, the method for producing methane by hydrogenating carbon dioxide comprises the following steps:

[0017] activating the cobalt-aluminum composite oxide to obtain an activated cobalt-aluminum composite oxide;

[0018] The activated cobalt-aluminum composite oxide catalyzes a mixed gas containing CO2 and H2 to undergo a catalytic hydrogenation reaction to obtain methane.

[0019] Preferably, the activation includes reducing the cobalt-aluminum composite oxide and performing pretreatment thereof. The activation temperature is 300-500°C, the time is 1-4 hours, and the atmosphere is a hydrogen atmosphere. The catalytic hydrogenation reaction temperature is 260-400°C, the pressure of the mixed gas is 0.1-5 MPa, and the time is 15-5000 hours.

[0020] Preferably, the volume ratio of H2 and CO2 is (1-8):1; the reaction space velocity of the mixed gas is 800-400000 mL / (h·g).

[0021] The present invention provides a method for preparing a cobalt-aluminum composite oxide, comprising the following steps: mixing a water-soluble cobalt salt, a water-soluble aluminum salt, water and a precipitant, performing a precipitation reaction, and obtaining a cobalt-aluminum composite oxide precursor; the molar ratio of cobalt ions in the water-soluble cobalt salt to aluminum ions in the water-soluble aluminum salt is (0.2-0.6):(0.005-0.6); the ratio of the total molar amount of metal ions in the water-soluble cobalt salt and the water-soluble aluminum salt to the molar amount of the precipitant is 1:(2-7.5); and calcining the cobalt-aluminum composite oxide precursor to obtain the cobalt-aluminum composite oxide. When the cobalt-aluminum composite oxide provided by the present invention is used in the process of CO2 hydrogenation to produce methane, Co and Al are both active components, and neither component is indispensable; the metal Co 0 (Before catalyzing CO2 hydrogenation to produce methane, the cobalt-aluminum composite oxide needs to be reduced to obtain Co 0 ) sites are used to dissociate hydrogen, while Al is an important electronic and structural additive that can regulate the Co 0 and Co δ+ (For example, Co 2+ , which is also obtained by reducing the cobalt-aluminum composite oxide before the catalytic reaction. 2+ ) and formed a rich metallic cobalt (Co 0 )-Cobalt aluminum composite oxide (cobalt is Co 2 + ) interface for CO2 adsorption and activation. The cobalt-aluminum composite oxide provided by the present invention exhibits excellent CO2 methanation reaction performance as a catalyst. The preparation method provided by the present invention is simple to operate, low-cost, and has no secondary pollution, making it suitable for large-scale industrial production.

[0022] The present invention provides the use of the cobalt-aluminum composite oxide described in the above scheme as a catalyst in the hydrogenation of carbon dioxide to methane. The cobalt-aluminum composite oxide provided by the present invention has a rich metal cobalt-cobalt-aluminum composite oxide interface in the process of CO2 hydrogenation to methane, which effectively promotes the activation of H2 and CO2. The results of the embodiment show that under the conditions of 350°C and 1MPa, the cobalt-aluminum composite oxide provided by the present invention is used as a catalyst. In the process of CO2 hydrogenation to methane, the CO2 conversion rate and methane selectivity reach 94.7% and 99.9% respectively, and the methane yield reaches 94.6%. Moreover, the catalyst can operate stably for more than 3500 hours without obvious deactivation, showing important industrial application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 The XRD spectrum of the cobalt-aluminum composite oxide obtained in Example 1;

[0025] Figure 2 TEM image of the cobalt-aluminum composite oxide prepared in Example 1;

[0026] Figure 3 This is a graph showing the change in CO2 conversion, methane selectivity and methane yield over reaction time in the CO2 hydrogenation to methane reaction of the cobalt-aluminum composite oxide obtained in Example 1. DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing a cobalt-aluminum composite oxide, comprising the following steps:

[0028] A water-soluble cobalt salt, a water-soluble aluminum salt, water, and a precipitant are mixed to perform a precipitation reaction to obtain a cobalt-aluminum composite oxide precursor; the molar ratio of cobalt ions in the water-soluble cobalt salt to aluminum ions in the water-soluble aluminum salt is (0.2-0.6):(0.005-0.6); and the ratio of the total molar amount of metal ions in the water-soluble cobalt salt and the water-soluble aluminum salt to the molar amount of the precipitant is 1:(2-7.5);

[0029] The cobalt-aluminum composite oxide precursor is calcined to obtain the cobalt-aluminum composite oxide.

[0030] Unless otherwise specified, the raw materials and equipment used in the present invention are all commercially available products.

[0031] The invention mixes water-soluble cobalt salt, water-soluble aluminum salt, water and a precipitant, performs precipitation reaction and obtains a cobalt-aluminum composite oxide precursor.

[0032] In the present invention, the mixing preferably includes:

[0033] A water-soluble cobalt salt, a water-soluble aluminum salt and first water are first mixed to obtain a composite metal ion salt solution;

[0034] performing a second mixing of the precipitant and the second water to obtain a precipitant solution;

[0035] The composite metal ion salt solution and the precipitant solution are mixed for the third time.

[0036] In the present invention, the water-soluble cobalt salt preferably includes one or more of cobalt nitrate, cobalt chloride and cobalt sulfate, more preferably cobalt nitrate; the water-soluble aluminum salt preferably includes one or more of aluminum nitrate, aluminum chloride and aluminum sulfate, more preferably aluminum nitrate.

[0037] In the present invention, the precipitant preferably includes one or more of a water-soluble carbonate, a water-soluble bicarbonate and a water-soluble hydroxide, more preferably a water-soluble carbonate. In the present invention, the water-soluble carbonate preferably includes one or more of ammonium carbonate, sodium carbonate and potassium carbonate, more preferably ammonium carbonate. In the present invention, the water-soluble hydroxide preferably includes sodium hydroxide and / or potassium hydroxide, more preferably sodium hydroxide. In the present invention, the water-soluble bicarbonate preferably includes sodium bicarbonate. In the present invention, when the precipitant includes two or more, the present invention has no special limitation on the mass ratio of each precipitant, and they can be added in any proportion.

[0038] In the present invention, when the precipitant is a water-soluble carbonate, the cobalt-aluminum composite oxide precursors are cobalt carbonate and aluminum carbonate; when the precipitant is a water-soluble bicarbonate, the cobalt-aluminum composite oxide precursors are cobalt bicarbonate and aluminum bicarbonate; when the precipitant is a hydroxide, the cobalt-aluminum composite oxide precursors are cobalt hydroxide and aluminum hydroxide.

[0039] The present invention has no special requirements for the first mixing, the second mixing and the third mixing. It is sufficient to fully dissolve and uniformly mix the water-soluble cobalt salt, the water-soluble aluminum salt and the precipitant using methods well known in the art.

[0040] In the present invention, the concentration of cobalt ions in the composite metal ion salt solution is preferably 0.2 to 0.6 mol / L. In embodiments of the present invention, it can be specifically 0.2 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L or 0.6 mol / L. The concentration of aluminum ions in the composite metal ion salt solution is preferably 0.005 to 0.6 mol / L. In embodiments of the present invention, it can be specifically 0.005 mol / L, 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.5 mol / L or 0.6 mol / L. In the present invention, the molar ratio of cobalt ions in the water-soluble cobalt salt to aluminum ions in the water-soluble aluminum salt is (0.2-0.6):(0.005-0.6). In embodiments of the present invention, the molar ratio can be 0.2:0.005, 0.2:0.6, 0.4:0.1, 0.45:0.005, 0.45:0.05, 0.45:0.3, 0.45:0.1, 0.6:0.005 or 1:1.

[0041] In the present invention, the concentration of the precipitant solution is preferably 0.9 to 6.75 mol / L. In embodiments of the present invention, it can be 0.9 mol / L, 1 mol / L, 2.40 mol / L, 2.42 mol / L, 2.48 mol / L, 3 mol / L, 4.9 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, 6.5 mol / L or 6.75 mol / L. In the present invention, the volume ratio of the composite metal ion salt solution to the precipitant solution is preferably 1:1.

[0042] In the present invention, the ratio of the total molar amount of metal ions in the composite metal ion salt solution to the molar amount of the precipitant is 1:(2-7.5). In embodiments of the present invention, it can be 1:2, 1:4.36, 1:4.4, 1:4.96, 1:5, 1:5.45, 1:6, 1:6.53, 1:7 or 1:7.5. The present invention controls the ratio of the total molar amount of metal ions in the composite metal ion salt solution to the molar amount of the precipitant within the above range, which can not only ensure sufficient precipitation of metal ions, but also improve the utilization efficiency of raw materials.

[0043] In the present invention, the precipitation reaction temperature is preferably 60-90°C, and in embodiments of the present invention, it can be 60°C, 70°C, 80°C, or 90°C. The precipitation reaction time is 2-10 hours, and in embodiments of the present invention, it can be 2 hours, 4 hours, 6 hours, 8 hours, or 10 hours. In the present invention, the precipitation reaction is preferably carried out under normal pressure. Controlling the precipitation reaction temperature between 60-90°C in the present invention can better promote the formation of cobalt and aluminum precipitates.

[0044] After the precipitation reaction is completed, the reaction solution is preferably filtered, and the obtained solid is sequentially washed with water, centrifuged and dried. In the present application, the water washing preferably uses deionized water, and the number of washing times is preferably 1-10, more preferably 2-8; the drying temperature is preferably 80-150°C, and in the examples of the present application, it can be specifically 80°C, 90°C, 100°C, 110°C, 120°C, 140°C or 150°C; and the drying time is preferably 3-15h, and in the examples of the present application, it can be specifically 3h, 4h, 5h, 6h, 8h, 10h, 12h, 14h or 15h.

[0045] After obtaining the cobalt-aluminum composite oxide, the cobalt-aluminum composite oxide precursor is calcined to obtain the cobalt-aluminum composite oxide.

[0046] In the present application, the calcination temperature is preferably 300-750°C, and in the examples of the present application, it can be specifically 300°C, 400°C, 500°C, 600°C, 700°C or 750°C; the calcination time is preferably 3-10h, and in the examples of the present application, it can be specifically 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h. In the present application, the calcination atmosphere is preferably air atmosphere. Controlling the calcination temperature to 300-750°C can promote the generation of cobalt-aluminum composite oxide and prevent phase separation caused by excessively high calcination temperature.

[0047] After the calcination is completed, the obtained oxide is preferably sequentially tabletted, crushed and sieved. The present application does not have special limitations on the tabletted, crushed and sieved operations, and the tabletted, crushed and sieved operations well known to those skilled in the art can be adopted to obtain a cobalt-aluminum composite oxide with a particle size of 10-80 mesh.

[0048] When the cobalt-aluminum composite oxide provided by the present application is used in the process of CO2 hydrogenation to produce methane, Co and Al are both active components, and neither component can be absent; the metal Co 0 (reduction of the cobalt-aluminum composite oxide is required before catalyzing CO2 hydrogenation to produce methane, and Co 0 sites are used to dissociate hydrogen, and Al is an important electron and structural promoter, which can adjust the relative proportion of Co 0 and Co δ+ (such as Co 2+ , and Co 2+ is obtained by reducing the cobalt-aluminum composite oxide before the catalytic reaction); and a rich cobalt (Co 0 )-cobalt-aluminum composite oxide interface (cobalt is Co 2+) for CO2 adsorption and activation. The cobalt-aluminum composite oxide provided by the present application exhibits excellent CO2 methanation reaction performance as a catalyst. The preparation method provided by the present application is simple to operate, low in cost, free of secondary pollution, and suitable for large-scale industrial production.

[0049] The present application provides a cobalt-aluminum composite oxide prepared by the preparation method described in the above scheme, and the chemical formula is Co a Al b O c , the ratio of a and b is (0.44-90):1, the ratio of (a+b) and c is (4.55-7.5):(6-10.5), and the valence of Co is + (8 / 3).

[0050] In the present application, a, b and c are the molar ratios of Co, Al and O atoms, and the total valence of the cobalt-aluminum composite oxide is zero, the valence of Al is +3, and the valence of oxygen is -2. In the present application, the ratio of a and b is (0.44-90):1, and in the embodiments of the present application, it can be specifically 0.44:1, 1:1, 0.45:0.3, 0.45:0.1, 5:1, 0.45:0.05, 10:1, 15:1, 20:1, 30:1, 40:1, 80:1 or 90:1. In the present application, when the cobalt content is too low, the content of metal Co 0 formed during the reduction process is too low, which is not conducive to the activation of hydrogen dissociation; and when the cobalt content is too high, too much metal Co 0 is generated, which seriously agglomerates, resulting in a decrease in the cobalt-aluminum composite oxide and being not conducive to CO2 adsorption. Therefore, the ratio of a and b is controlled to be (0.44-90):1, which is conducive to the activation of hydrogen dissociation and can ensure the effective adsorption of CO2.

[0051] In the present application, the ratio of (a+b) and c is (4.55-7.5):(6-10.5), and in the embodiments of the present application, it can be specifically 5.5:7.5, 5:6.75, 7.5:10.5 or 4.55:6.075.

[0052] In the present application, the particle size of the cobalt-aluminum composite oxide is preferably 10-80 mesh, more preferably 20-60 mesh, and further preferably 20-40 mesh. By controlling the particle size of the cobalt-aluminum composite oxide within the above range, the raw materials H2 and CO2 can be ensured to fully contact the cobalt-aluminum composite oxide, and the mechanical strength of the cobalt-aluminum composite oxide can be improved, which is conducive to promoting the CO2 hydrogenation to methane.

[0053] The present application provides the application of the cobalt-aluminum composite oxide described in the above scheme as a catalyst in the carbon dioxide hydrogenation to methane.

[0054] In the present invention, the method for producing methane by hydrogenating carbon dioxide preferably comprises the following steps:

[0055] activating the cobalt-aluminum composite oxide to obtain an activated cobalt-aluminum composite oxide;

[0056] The activated cobalt-aluminum composite oxide catalyzes a mixed gas containing CO2 and H2 to undergo a catalytic hydrogenation reaction to obtain methane.

[0057] In the present invention, the activation preferably includes performing a reduction pretreatment on the cobalt-aluminum composite oxide. In the present invention, the activation temperature is preferably 300-500°C, and in embodiments of the present invention, specifically 300°C, 400°C, 450°C, or 500°C; the activation time is preferably 1-4 hours, and in embodiments of the present invention, specifically 1 hour, 2 hours, 3 hours, or 4 hours; and the activation atmosphere preferably includes a hydrogen atmosphere.

[0058] The present invention can promote the partial metal Co 0 The generation of metal cobalt-cobalt aluminum composite oxide interface not only improves the hydrogen dissociation activity, but also promotes CO2 adsorption, which is beneficial to the production of methane.

[0059] In the present invention, the temperature of the catalytic hydrogenation reaction is preferably 260-400°C. In embodiments of the present invention, it can be specifically 260°C, 300°C, 350°C or 400°C. The pressure of the mixed gas is preferably 0.1-5 MPa. In embodiments of the present invention, it can be specifically 0.1 MPa, 0.5 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa or 5 MPa. The reaction time is preferably 15-5000 h. In embodiments of the present invention, it can be specifically 15 h, 20 h, 100 h, 200 h, 500 h, 1000 h, 2000 h, 3000 h, 4000 h or 5000 h.

[0060] In the present invention, the volume ratio of H2 and CO2 is preferably (1 to 8):1. In embodiments of the present invention, it can be 1:1, 2:1, 3:1, 4:1, 6:1 or 8:1. The reaction space velocity of the mixed gas is preferably 800 to 400,000 mL / (h·g). In embodiments of the present invention, it can be 800 mL / (h·g), 1,000 mL / (h·g), 2,000 mL / (h·g), 10,000 mL / (h·g), 12,000 mL / (h·g), 20,000 mL / (h·g), 24,000 mL / (h·g), 50,000 mL / (h·g), 100,000 mL / (h·g), 200,000 mL / (h·g), or 400,000 mL / (h·g).

[0061] The cobalt-aluminum composite oxide provided by the present invention has a rich metallic cobalt-cobalt-aluminum composite oxide interface during CO2 hydrogenation to methane, effectively promoting the activation of H2 and CO2. Experimental results show that at 350°C and 1 MPa, the cobalt-aluminum composite oxide provided by the present invention, as a catalyst, achieves a CO2 conversion rate and methane selectivity of 94.7% and 99.9%, respectively, and a methane yield of 94.6%. Furthermore, the catalyst can operate stably for over 3500 hours without significant deactivation, demonstrating significant potential for industrial applications.

[0062] In addition, the cobalt-aluminum composite oxide prepared by the present invention is reduced before catalyzing CO2 hydrogenation to produce methane to form a unique metal cobalt (Co 0 )-Cobalt aluminum composite oxide (cobalt is Co 2+ ) interface structure, in which metallic cobalt is used to dissociate H2 to form active H species, while cobalt-aluminum composite oxide is used for CO2 adsorption. The close contact between the two forms a metallic cobalt-cobalt-aluminum composite oxide interface structure, which promotes the rapid hydrogenation of active H* and adsorbed CO2, which is beneficial to methane production.

[0063] To further illustrate the present invention, a cobalt-aluminum composite oxide provided by the present invention, its preparation method and application are described in detail below with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0064] Example 1

[0065] 130.97 g of cobalt nitrate hexahydrate and 37.51 g of aluminum nitrate nonahydrate were dissolved in 1000 mL of deionized water to obtain a Co-Al composite metal ion salt solution (the concentration of cobalt ions was 0.45 mol / L and the concentration of aluminum ions was 0.1 mol / L).

[0066] 288.27 g of ammonium carbonate was dissolved in 1000 mL of deionized water to obtain an ammonium carbonate solution with a concentration of 3 mol / L.

[0067] The ammonium carbonate solution and the Co-Al composite metal ion salt solution were mixed and subjected to a precipitation reaction at normal pressure and a 70°C water bath for 4 hours. After the precipitation reaction, the reaction solution was filtered, and the resulting solid was washed three times with deionized water. After centrifugation, the resulting solid was transferred to an oven and dried at 100°C for 10 hours to obtain a cobalt-aluminum composite oxide precursor.

[0068] The cobalt-aluminum composite oxide precursor was transferred into a muffle furnace and calcined at 400°C in an air atmosphere for 6 hours. After tableting, crushing and screening, a cobalt-aluminum composite oxide (Co) with a particle size of 20 to 40 mesh was obtained.4.5 AlO 7.5 )。

[0069] Example 2

[0070] 130.97 g of cobalt nitrate hexahydrate and 18.76 g of aluminum nitrate nonahydrate were dissolved in 1000 mL of deionized water to obtain a Co-Al composite metal ion salt solution (the concentration of cobalt ions was 0.45 mol / L, and the concentration of aluminum ions was 0.05 mol / L).

[0071] 238.28 g of ammonium carbonate was dissolved in 1000 mL of deionized water to obtain an ammonium carbonate solution with a concentration of 2.48 mol / L.

[0072] The ammonium carbonate solution and the Co-Al composite metal ion salt solution were mixed, and a precipitation reaction was performed under normal pressure and in a 70°C water bath for 4 h. After the precipitation reaction, the reaction solution was filtered, the obtained solid was washed with deionized water for 3 times, and after centrifugation, the obtained solid material was transferred to an oven for drying treatment at 100°C for 10 h to obtain a cobalt-aluminum composite oxide precursor.

[0073] The cobalt-aluminum composite oxide precursor was transferred into a muffle furnace, and calcination treatment was performed at 400°C in an air atmosphere for 6 h. After tabletting, crushing and sieving, a cobalt-aluminum composite oxide (Co 4.5 Al 0.5 O 6.75 )。

[0074] Example 3

[0075] 130.97 g of cobalt nitrate hexahydrate and 112.56 g of aluminum nitrate nonahydrate were dissolved in 1000 mL of deionized water to obtain a Co-Al composite metal ion salt solution (the concentration of cobalt ions was 0.45 mol / L, and the concentration of aluminum ions was 0.3 mol / L).

[0076] 470.84 g of ammonium carbonate was dissolved in 1000 mL of deionized water to obtain an ammonium carbonate solution with a concentration of 4.90 mol / L.

[0077] The ammonium carbonate solution and the Co-Al composite metal ion salt solution were mixed, and a precipitation reaction was performed under normal pressure and in a 70°C water bath for 4 h. After the precipitation reaction, the reaction solution was filtered, the obtained solid was washed with deionized water for 3 times, and after centrifugation, the obtained solid material was transferred to an oven for drying treatment at 100°C for 10 h to obtain a cobalt-aluminum composite oxide precursor.

[0078] The cobalt-aluminum composite oxide precursor was transferred into a muffle furnace and calcined at 400°C in an air atmosphere for 6 hours. After tableting, crushing and screening, a cobalt-aluminum composite oxide (Co) with a particle size of 20 to 40 mesh was obtained. 4.5 Al3O 10.5 ).

[0079] Example 4

[0080] 130.97 g of cobalt nitrate hexahydrate and 1.88 g of aluminum nitrate nonahydrate were dissolved in 1000 mL of deionized water to obtain a Co-Al composite metal ion salt solution (the concentration of cobalt ions was 0.45 mol / L and the concentration of aluminum ions was 0.005 mol / L).

[0081] 179.71 g of ammonium carbonate was dissolved in 1000 mL of deionized water to obtain an ammonium carbonate solution with a concentration of 1.87 mol / L.

[0082] The ammonium carbonate solution and the Co-Al composite metal ion salt solution were mixed and subjected to a precipitation reaction at normal pressure and a 70°C water bath for 4 hours. After the precipitation reaction, the reaction solution was filtered, and the resulting solid was washed three times with deionized water. After centrifugation, the resulting solid was transferred to an oven and dried at 100°C for 10 hours to obtain a cobalt-aluminum composite oxide precursor.

[0083] The cobalt-aluminum composite oxide precursor was transferred into a muffle furnace and calcined at 400°C in an air atmosphere for 6 hours. After tableting, crushing and screening, a cobalt-aluminum composite oxide (Co) with a particle size of 20 to 40 mesh was obtained. 4.5 Al 0.05 O 6.075 ).

[0084] Example 5

[0085] 130.97 g of cobalt nitrate hexahydrate and 37.51 g of aluminum nitrate nonahydrate were dissolved in 1000 mL of deionized water to obtain a Co-Al composite metal ion salt solution (the concentration of cobalt ions was 0.45 mol / L and the concentration of aluminum ions was 0.1 mol / L).

[0086] 335.06 g of potassium carbonate was dissolved in 1000 mL of deionized water to obtain a potassium carbonate solution with a concentration of 2.42 mol / L.

[0087] The potassium carbonate solution and the Co-Al composite metal ion salt solution were mixed and subjected to a precipitation reaction at normal pressure and a 70°C water bath for 4 hours. After the precipitation reaction, the reaction solution was filtered, and the resulting solid was washed three times with deionized water. After centrifugation, the resulting solid was transferred to an oven and dried at 100°C for 10 hours to obtain a cobalt-aluminum composite oxide precursor.

[0088] The Co-Al composite oxide precursor was transferred into a muffle furnace, calcined at 400°C in air for 6h, and after tabletting, crushing and sieving, a Co-Al composite oxide (Co 4.5 AlO 7.5 ) with a particle size of 20-40 mesh was obtained.

[0089] Example 6

[0090] 130.97g of cobalt nitrate hexahydrate and 37.51g of aluminum nitrate nonahydrate were dissolved in 1000mL of deionized water to obtain a Co-Al composite metal ion salt solution (the concentration of cobalt ions was 0.45mol / L, and the concentration of aluminum ions was 0.1mol / L).

[0091] 256.5g of sodium carbonate was dissolved in 1000mL of deionized water to obtain a sodium carbonate solution with a concentration of 2.42mol / L.

[0092] The sodium carbonate solution and the Co-Al composite metal ion salt solution were mixed, and a precipitation reaction was carried out at normal pressure and in a 70°C water bath for 4h. After the precipitation reaction, the reaction liquid was filtered, the obtained solid was washed with deionized water for 3 times, and after centrifugation, the obtained solid material was transferred into an oven and dried at 100°C for 10h to obtain a Co-Al composite oxide precursor;

[0093] The Co-Al composite oxide precursor was transferred into a muffle furnace, calcined at 400°C in air for 6h, and after tabletting, crushing and sieving, a Co-Al composite oxide (Co 4.5 AlO 7.5 ) with a particle size of 20-40 mesh was obtained.

[0094] Example 7

[0095] 130.97g of cobalt nitrate hexahydrate and 37.51g of aluminum nitrate nonahydrate were dissolved in 1000mL of deionized water to obtain a Co-Al composite metal ion salt solution (the concentration of cobalt ions was 0.45mol / L, and the concentration of aluminum ions was 0.1mol / L).

[0096] 201.62g of sodium bicarbonate was dissolved in 1000mL of deionized water to obtain a sodium bicarbonate solution with a concentration of 2.40mol / L.

[0097] The sodium bicarbonate solution and the Co-Al composite metal ion salt solution were mixed and subjected to a precipitation reaction at normal pressure and a 70°C water bath for 4 hours. After the precipitation reaction, the reaction solution was filtered, and the resulting solid was washed three times with deionized water. After centrifugation, the resulting solid was transferred to an oven and dried at 100°C for 10 hours to obtain a cobalt-aluminum composite oxide precursor.

[0098] The cobalt-aluminum composite oxide precursor was transferred into a muffle furnace and calcined at 400°C in an air atmosphere for 6 hours. After tableting, crushing and screening, a cobalt-aluminum composite oxide (Co) with a particle size of 20 to 40 mesh was obtained. 4.5 AlO 7.5 ).

[0099] Example 8

[0100] 130.97 g of cobalt nitrate hexahydrate and 37.51 g of aluminum nitrate nonahydrate were dissolved in 1000 mL of deionized water to obtain a Co-Al composite metal ion salt solution (the concentration of cobalt ions was 0.45 mol / L and the concentration of aluminum ions was 0.1 mol / L).

[0101] 96.00 g of sodium hydroxide was dissolved in 1000 mL of deionized water to obtain a sodium hydroxide solution with a concentration of 2.40 mol / L.

[0102] The sodium hydroxide solution and the Co-Al composite metal ion salt solution were mixed and subjected to a precipitation reaction at normal pressure and a 70°C water bath for 4 hours. After the precipitation reaction, the reaction solution was filtered, and the resulting solid was washed three times with deionized water. After centrifugation, the resulting solid was transferred to an oven and dried at 100°C for 10 hours to obtain a cobalt-aluminum composite oxide precursor.

[0103] The cobalt-aluminum composite oxide precursor was transferred into a muffle furnace and calcined at 400°C in an air atmosphere for 6 hours. After tableting, crushing and screening, a cobalt-aluminum composite oxide (Co) with a particle size of 20 to 40 mesh was obtained. 4.5 AlO 7.5 ).

[0104] Comparative Example 1

[0105] 130.97 g of cobalt nitrate hexahydrate was dissolved in 1000 ml of deionized water to obtain a Co metal ion salt solution (the concentration of cobalt ions was 0.45 mol / L).

[0106] 235.42 g of ammonium carbonate was dissolved in 1000 ml of deionized water to obtain an ammonium carbonate solution with a concentration of 2.45 mol / L.

[0107] The ammonium carbonate solution and the Co metal ion salt solution were mixed and subjected to a precipitation reaction at normal pressure and 70°C in a water bath for 4 hours. After the precipitation reaction, the reaction solution was filtered, and the resulting solid was washed three times with deionized water. After centrifugation, the resulting solid was transferred to an oven and dried at 100°C for 10 hours to obtain a cobalt oxide precursor.

[0108] The cobalt oxide is transferred into a muffle furnace and calcined at 400° C. in an air atmosphere for 6 hours. After tableting, crushing and sieving, cobalt oxide (Co 3 O 4 ) with a particle size of 20 to 40 meshes is obtained.

[0109] Comparative Example 2

[0110] 168.81 g of aluminum nitrate nonahydrate was dissolved in 1000 ml of deionized water to obtain an Al metal ion salt solution (the concentration of aluminum ions was 0.45 mol / L).

[0111] 235.42 g of ammonium carbonate was dissolved in 1000 ml of deionized water to obtain an ammonium carbonate solution with a concentration of 2.45 mol / L.

[0112] The ammonium carbonate solution and the Co metal ion salt solution were mixed and subjected to a precipitation reaction at normal pressure and 70°C in a water bath for 4 hours. After the precipitation reaction, the reaction solution was filtered, and the resulting solid was washed three times with deionized water. After centrifugation, the resulting solid was transferred to an oven and dried at 100°C for 10 hours to obtain an aluminum oxide precursor.

[0113] The aluminum oxide precursor is transferred into a muffle furnace and calcined at 400° C. in an air atmosphere for 6 hours. After tableting, crushing and screening, aluminum oxide (Al 2 O 3 ) with a particle size of 20 to 40 meshes is obtained.

[0114] Comparative Example 3

[0115] 130.97 g of cobalt nitrate hexahydrate and 18.76 g of aluminum nitrate nonahydrate were dissolved in 1000 mL of deionized water to obtain a Co-Al composite metal ion salt solution (the concentration of cobalt ions was 0.45 mol / L and the concentration of aluminum ions was 0.05 mol / L).

[0116] 360.00 g of sodium hydroxide was added to the Co-Al composite metal ion salt solution, and the mixture was stirred uniformly to obtain a composite solution.

[0117] The composite solution was transferred into a reaction kettle with a polytetrafluoroethylene liner, and then hydrothermal reaction was carried out at 100°C (not normal pressure) for 24 h. After the hydrothermal reaction, the reaction solution was filtered, the obtained solid was washed with deionized water for 3 times, and then the obtained solid was transferred into an oven and dried at 100°C for 10 h. Subsequently, the dried solid was transferred into a muffle furnace, calcined at 400°C in air for 6 h, and then pressed, crushed and sieved to obtain cobalt-aluminum composite oxide (Co 4.5 Al 0.5 O 6.75 )(HT-1).

[0118] Comparative Example 4

[0119] 130.97 g of cobalt nitrate hexahydrate and 37.51 g of aluminum nitrate nonahydrate were dissolved in 1000 mL of deionized water to obtain a Co-Al composite metal ion salt solution (the concentration of cobalt ions was 0.45 mol / L, and the concentration of aluminum ions was 0.1 mol / L).

[0120] 360.00 g of sodium hydroxide was added to the Co-Al composite metal ion salt solution, and a composite solution was obtained after stirring uniformly.

[0121] The composite solution was transferred into a reaction kettle with a polytetrafluoroethylene liner, and then hydrothermal reaction was carried out at 100°C (not normal pressure) for 24 h. After the hydrothermal reaction, the reaction solution was filtered, the obtained solid was washed with deionized water for 3 times, and then the obtained solid was transferred into an oven and dried at 100°C for 10 h. Subsequently, the dried solid was transferred into a muffle furnace, calcined at 400°C in air for 6 h, and then pressed, crushed and sieved to obtain cobalt-aluminum composite oxide (Co 4.5 AlO 7.5 )(HT-2).

[0122] Application Example 1

[0123] The oxides prepared in Examples 1-8 and Comparative Examples 1-4 were used as catalysts for catalytic performance test.

[0124] The oxides prepared in Examples 1-8 and Comparative Examples 1-4 were reduced at 400°C in a hydrogen atmosphere for 2 h to obtain reduced catalysts. CO2-H2 mixed gas (H2:CO2 volume ratio = 4:1) was introduced into a reactor containing the reduced catalysts, and catalytic hydrogenation reaction was carried out to obtain methane, and the catalytic reaction time was 30 h.

[0125] The catalytic performance results of the oxides prepared in Examples 1 to 8 and Comparative Examples 1 to 4 under different catalytic hydrogenation reaction conditions are shown in Table 1.

[0126] Table 1 Catalytic performance of oxides prepared in Examples 1 to 8 and Comparative Examples 1 to 4

[0127]

[0128] As shown in Table 1, the cobalt-aluminum composite oxide prepared by the present invention has a CO conversion rate of 84.7-94.7%, a methane (CH4) selectivity of 98.7-99.9%, and a methane yield of 78.7-94.6% in the CO2 hydrogenation to methane reaction process. However, under the same reaction conditions, the CO2 conversion rate of the cobalt oxide (Comparative Example 1) and aluminum oxide (Comparative Example 2) catalysts alone is only 30.2% and 1.7%, and the methane selectivity and yield are reduced to 97.3% and 29.4% for Comparative Example 1 and 3.4% and 0.06% for Comparative Example 2, respectively. In addition, the cobalt aluminum composite oxides (HT-1 and HT-2) prepared by the hydrothermal method (Comparative Examples 3 and 4) have CO2 conversion, methane selectivity, and methane yield of Comparative Example 3: 79.2%, 91.1%, and 72.2% under the same CO2 hydrogenation to methane reaction conditions; Comparative Example 4: 53.2%, 69.9%, and 37.2%, respectively, which are also lower than those of the cobalt aluminum composite oxide catalyst prepared by the present invention. These results indicate that the cobalt aluminum composite oxide catalyst prepared by the present invention has superior catalytic performance in CO2 hydrogenation to CH4.

[0129] Stability testing

[0130] The reaction stability of the cobalt-aluminum composite oxide catalyst prepared in Example 1 of the present invention was tested. The pretreatment conditions were: reduction treatment at 400°C in a hydrogen atmosphere for 2 hours to obtain a reduced catalyst; the reaction conditions were: reaction temperature of 350°C, pressure of 1 MPa, and CO2-H2 mixed gas space velocity of 12 L / (h·g). The catalytic performance of the cobalt-aluminum composite oxide catalyst changes with reaction time as shown in the figure below. Figure 3 shown.

[0131] from Figure 3 The cobalt-aluminum composite oxide catalyst prepared in the present invention exhibits high catalytic activity, high methane selectivity and yield, and high catalytic stability in the CO2 hydrogenation to methane process. After 3500 hours of reaction, the cobalt-aluminum composite oxide catalyst showed no significant deactivation, with CO2 conversion, methane selectivity, and methane yield maintained at 85.2%, 99.5%, and 84.8%, respectively.

[0132] Structural characterization

[0133] Figure 1The XRD spectrum of the cobalt-aluminum composite oxide obtained in Example 1 is shown in FIG. Figure 1 It can be seen that the prepared cobalt-aluminum composite oxide exhibits the diffraction peak of cobalt oxide, while aluminum oxide is amorphous.

[0134] Figure 2 TEM image of the cobalt-aluminum composite oxide prepared in Example 1. Figure 2 It can be seen that the prepared cobalt-aluminum composite oxide exhibits a nanoparticle stacking morphology.

[0135] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a cobalt-aluminum composite oxide, characterized in that: The following steps are involved: A water-soluble cobalt salt, a water-soluble aluminum salt, water, and a precipitant are mixed to perform a precipitation reaction to obtain a cobalt-aluminum composite oxide precursor; the molar ratio of cobalt ions in the water-soluble cobalt salt to aluminum ions in the water-soluble aluminum salt is (0.2-0.6):(0.005-0.6); and the ratio of the total molar amount of metal ions in the water-soluble cobalt salt and the water-soluble aluminum salt to the molar amount of the precipitant is 1:(2-7.5); The cobalt-aluminum composite oxide precursor is calcined to obtain the cobalt-aluminum composite oxide.

2. The preparation method according to claim 1, characterized in that The water-soluble cobalt salt includes one or more of cobalt nitrate, cobalt chloride and cobalt sulfate; the water-soluble aluminum salt includes one or more of aluminum nitrate, aluminum chloride and aluminum sulfate.

3. The preparation method according to claim 1, characterized in that The precipitant includes one or more of water-soluble carbonates, water-soluble bicarbonates and water-soluble hydroxides.

4. The preparation method according to claim 1 or 3, characterized in that The temperature of the precipitation reaction is 60-90° C., and the time is 2-10 hours.

5. The preparation method according to claim 1, characterized in that The calcination temperature is 300-750° C., and the calcination time is 3-10 hours.

6. The cobalt-aluminum composite oxide prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The chemical formula is Co a Al b O c ; Among them, the ratio of a and b is (0.44~90):1, the ratio of (a+b) and c is (4.55~7.5):(6~10.5); the valence of Co is +(8 / 3).

7. Use of the cobalt-aluminum composite oxide according to claim 6 as a catalyst in the hydrogenation of carbon dioxide to methane.

8. The use according to claim 7, characterized in that The method for preparing methane by hydrogenating carbon dioxide comprises the following steps: activating the cobalt-aluminum composite oxide to obtain an activated cobalt-aluminum composite oxide; The activated cobalt-aluminum composite oxide catalyzes a mixed gas containing CO2 and H2 to undergo a catalytic hydrogenation reaction to obtain methane.

9. The use according to claim 8, characterized in that The activation includes reducing the cobalt-aluminum composite oxide and performing pretreatment. The activation temperature is 300-500°C, the time is 1-4 hours, and the atmosphere is hydrogen. The catalytic hydrogenation reaction temperature is 260-400°C, the pressure of the mixed gas is 0.1-5 MPa, and the time is 15-5000 hours.

10. The use according to claim 8, characterized in that The volume ratio of H2 and CO2 is (1-8):1; the reaction space velocity of the mixed gas is 800-400000 mL / (h·g).

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