Preparation method and application of alpha-Ga2O3 catalyst for preparing methanol through carbon dioxide hydrogenation

Abstract

The invention provides a preparation method and application of an alpha-Ga2O3 catalyst for preparing methanol through carbon dioxide hydrogenation, and the preparation method comprises the following steps: S1, dissolving Ga (NO3) 3 solid in deionized water to obtain a Ga (NO3) 3 solution with the concentration range of 0.05-0.2 mol / L; s2, dropwise adding ammonia water with the concentration of 1-3 mol / L into the Ga (NO3) 3 solution for precipitation to obtain turbid liquid with the pH value range of 8-12; s3, putting the turbid liquid into a hydrothermal kettle, putting the hydrothermal kettle into a blast oven, setting the temperature to be 50-100 DEG C, carrying out continuous hydrothermal synthesis for 12-30 hours to obtain a hydrothermal turbid liquid, and carrying out suction filtration, washing and drying treatment on the turbid liquid to obtain a product GaOOH; and S4, putting the reaction product GaOOH into a muffle furnace, heating to 560-640 DEG C at a set heating rate, and roasting for 2-6 hours at a high temperature to obtain the alpha-Ga2O3 catalyst. The catalyst prepared by the preparation method disclosed by the invention has the effects of relatively high methanol generation activity and stability.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to an α-Ga 2 O 3 catalyst for hydrogenating carbon dioxide to methanol, a preparation method thereof, and an application thereof. Background Art

[0002] The rapid development of modern society has promoted the prosperous development of industries such as electricity, transportation, and commodity manufacturing. However, behind this is the large-scale use of fossil fuels - coal, oil, and natural gas, which has also led to huge environmental disasters, that is, a large amount of CO 2 is released into the atmosphere during power generation, manufacturing production, and internal combustion engine combustion. The rapidly increasing CO 2 concentration in the atmosphere has simultaneously refreshed the rate of increase in the global average temperature, not only disrupting the natural balance but also bringing huge risks to human society. Against this background, countries around the world have signed the Paris Agreement to achieve the goal of "carbon neutrality" and achieve a dynamic balance between emissions and consumption of CO 2 To efficiently achieve this goal, it is not only necessary to develop new energy sources such as nuclear energy, solar energy, and wind energy as alternatives, but also to apply new technologies to capture and utilize CO 2 in the atmosphere. In 2005, Nobel laureate George A. Olah et al. proposed to capture CO 2 and synthesize methanol with higher economic value from "green hydrogen" prepared from renewable energy as a potential substitute for hydrocarbon fuels. As a fuel with high energy density, the calorific value of methanol combustion reaches 1111 kJ / kg. Utilizing CO 2 and H 2 to synthesize methanol has broad application prospects and economic value.

[0003] Currently, the mainstream catalyst system for thermally catalytic methanol synthesis from CO 2 is Cu-based catalysts. The Cu / ZnO synthesized by Witoon et al. (Witoon et al. Fuel Processing Technology. 2013, 116: 72-78.) can reach a CO 2 conversion rate of 5% and a methanol selectivity of 98% under the conditions of 3 MPa and 280 °C. However, Cu / ZnO-based catalysts still have huge defects. Due to the presence of water in the reaction process, the Cu-based catalysts will be poisoned, thereby reducing the catalytic activity in the reaction. Enhancing the stability and anti-poisoning ability of Cu / ZnO catalysts to improve their durability and efficiency in industrial applications remains the focus of the development of Cu-based catalysts.

[0004] Another developed catalyst for hydrogenating CO 2 to methanol is In 2O 3 Catalyst. Different from the Cu / ZnO-based catalyst, In 2 O 3 -based catalyst has good methanol selectivity and hardly produces by-products during the reaction. At 5 MPa and 300 °C, the CO 2 conversion rate can still reach 8%-10%. Wang et al. (Wang et al. Journal of Materials Chemistry A. 2023, 11: 26804-26811) synthesized Pt@In 2 O 3 catalyst, which can reach a methanol space-time yield of 29 mmol·g -1 ·h -1 and a methanol selectivity of 73% under 3 MPa conditions. Ye et al. (Ye et al. ACS Catalysis. 2013, 3: 1296-1306) used simulation calculation methods to point out that the surface defects of In 2 O 3 played an important role in improving methanol activity. However, In 2 O 3 -based catalysts also have some disadvantages, such as low single-pass conversion rate of CO 2 ; poor stability during the reaction, and the activity is easy to decrease during long-term catalytic reactions; and the high price of In makes In 2 O 3 also have a relatively high application cost.

[0005] Similar to In 2 O 3 , Ga 2 O 3 shows certain catalytic performance in the catalytic reaction of CO 2 hydrogenation to methanol. However, the difference is that Ga 2 O 3 generally acts as a carrier and promoter in the catalyst to accelerate the reaction. Li et al. (Li et al. Journal of Catalysis. 2016, 343: 157-167.) added Ga to the CuZn nanoalloy to induce the construction of a ZnO-Ga 2 O 4 electronic heterojunction to promote charge transfer. When the introduction amount of Ga reaches 5 mol%, the methanol yield of Cu / ZnO is increased from 7.5% to 11.5% of Cu / ZnO-5Ga. At the same time, Ga 2 O 3As an excellent semiconductor material, loading noble metals as a carrier can also greatly improve the selectivity of methanol. Manrique et al. (Manrique et al. Catalysis Science & Technology. 2020, 10: 6644-6658.) loaded Pd onto Ga 2 O 3 to construct bimetallic Pd-Ga active sites with strong interactions, significantly improving the selectivity and space-time yield of methanol. However, there has been no reported research on directly catalyzing the hydrogenation of COto methanol using Ga 2 O 3 2 alone as a catalyst. Compared with Cu-based catalysts, Ga 2 O 3 has higher stability; compared with In 2 O 3 , Ga 2 O 3 is cheaper, and Ga 2 O 3 is not easily reduced in a reducing atmosphere, enhancing its stability. Therefore, developing an efficient Ga 2 catalyst for the hydrogenation of CO 2 O 3 to methanol has important theoretical significance and economic value. Summary of the Invention

[0006] Aiming at the deficiencies of the existing technology, the object of the present invention is to provide a preparation method and application of an α-Ga 2 O 3 catalyst for the hydrogenation of carbon dioxide to methanol, which has the advantages of high methanol formation activity and stability.

[0007] The above object of the present invention is achieved through the following technical solutions: A preparation method of an α-Ga 2 O 3 catalyst for the hydrogenation of carbon dioxide to methanol, comprising the following steps:

[0008] S1. Dissolve solid Ga(NO 3 ) 3 in deionized water to obtain a Ga(NO 3 ) 3 solution with a concentration range of 0.05-0.2 mol / L;

[0009] S2. Dropwise add ammonia water with a concentration of 1-3 mol / L to the Ga(NO 3 ) 3 solution for precipitation, and obtain a suspension with a pH value range of 8-12;

[0010] S3. Load the suspension into a hydrothermal autoclave, place it in a forced-air oven, set the temperature to 50°C - 100°C, and carry out hydrothermal synthesis for 12 - 30 h to obtain the hydrothermally treated suspension. Then, subject the suspension to suction filtration, washing, and drying to obtain the product GaOOH;

[0011] S4. Place the reaction product GaOOH in a muffle furnace, heat it to 560°C - 640°C at a set heating rate, and perform high-temperature calcination for 2 - 6 h to obtain α-Ga 2 O 3 catalyst.

[0012] Preferably, in step S1, the concentration range of the obtained Ga(NO 3 ) 3 solution is 0.08 - 0.12 mol / L.

[0013] Preferably, in step S2, when gradually adding ammonia water with a concentration of 1.2 - 1.8 mol / L to the Ga(NO 3 ) 3 solution for precipitation, control the molar ratio of Ga(NO 3 ) 3 / NH 3 to be 0.08 - 0.18.

[0014] Furthermore, it is characterized in that the concentration of the ammonia water is 1.5 mol / L.

[0015] Preferably, in step S3, the hydrothermal reaction temperature range is 55°C - 80°C.

[0016] Preferably, in step S3, the specific filtration steps are as follows: Wash the hydrothermally formed white precipitate alternately with deionized water and absolute ethanol. Specifically, wash it three times with 300 ml - 500 ml of deionized water; and wash it three times alternately with 100 ml - 200 ml of absolute ethanol.

[0017] Preferably, in step S3, the specific drying steps are as follows: Place the washed precipitate in a forced-air oven for drying, set the drying temperature range to 50 - 100°C, and the drying time range to 5 - 8 h.

[0018] Preferably, in step S4, the set heating rate is 0.5 - 3°C / min.

[0019] Preferably, in step S4, the high-temperature calcination temperature range is: 580°C - 610°C.

[0020] The present invention also discloses the application of the Ga 2 O 3 catalyst prepared according to the above preparation method in the hydrogenation of carbon dioxide to methanol.

[0021] In summary, the present invention includes at least one of the following beneficial technical effects: the present invention utilizes Ga(NO 3 ) 3 A Ga synthesized with ammonia 2 O 3 Catalysts for catalytic CO 2 In the hydrogenation reaction to produce methanol, it has a higher methanol production activity and stability. 2 O 3 The catalyst preparation method is simple and inexpensive. 2 The highest methanol selectivity of 80% was obtained when the conversion rate was 3.9%, and after 100h of reaction, CO 2 The decrease in conversion rate and methanol selectivity was very small, no more than 3%, which was better than most Cu-based catalysts and In 2 O 3 Based catalyst, it is fully demonstrated that the Ga 2 O 3 It is a CO with great potential 2 Hydrogenation catalyst for methanol. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the α-Ga in Example 1 of the present invention and Comparative Example 3 2 O 3 Sample catalytic CO 2 Schematic diagram of the change of methanol selectivity with reaction temperature in the hydrogenation reaction to methanol;

[0023] Figure 2 is the α-Ga in Example 1 of the present invention and Comparative Example 3 2 O 3 Sample catalytic CO 2 CO in the hydrogenation to methanol reaction 2 Schematic diagram of the change of conversion rate with reaction temperature;

[0024] Figure 3 is the α-Ga in Example 1 of the present invention 2 O 3 X-ray diffraction (XRD) patterns of the samples. DETAILED DESCRIPTION

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the following will clearly and completely describe the technical solutions of the embodiments of this application in conjunction with the accompanying drawings of the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, rather than all of them. Based on the described embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

[0026] Example 1:

[0027] First, weigh out 1.406 g of Ga(NO 3 ) 3 ·xH 2 O and put it into a beaker, then pour 55 ml of deionized water and dissolve it under magnetic stirring. At the same time, prepare a 1.5 M ammonia water solution, and dropwise add the 1.5 M ammonia water solution drop by drop under magnetic stirring until the pH of the suspension is 10. Then transfer the suspension into a hydrothermal reactor and carry out a hydrothermal reaction at 60 °C for 18 h. Wash the white precipitate alternately with 400 ml of deionized water and 150 ml of absolute ethanol three times until it is neutral. Subsequently, dry it in a blast drying oven at 60 °C for 5 h to collect the white powder. Put the white powder into a muffle furnace and heat it to 600 °C at a heating rate of 1 °C / min and calcine it for 3 h. The sample name is α-Ga 2 O 3 -10-60-600.

[0028] Example 2:

[0029] First, weigh out 1.406 g of Ga(NO 3 ) 3 ·xH 2 O and put it into a beaker, then pour 55 ml of deionized water and dissolve it under magnetic stirring. At the same time, prepare a 1.5 M ammonia water solution, and dropwise add the 1.5 M ammonia water solution drop by drop under magnetic stirring until the pH of the suspension is 8. Then transfer the suspension into a hydrothermal reactor and carry out a hydrothermal reaction at 60 °C for 18 h. Wash the white precipitate alternately with 400 ml of deionized water and 150 ml of absolute ethanol three times until it is neutral. Subsequently, dry it in a blast drying oven at 60 °C for 5 h to collect the white powder. Put the white powder into a muffle furnace and heat it to 600 °C at a heating rate of 1 °C / min and calcine it for 3 h. The sample name is α-Ga 2 O 3 -8-60-600.

[0030] Example 3:

[0031] First, weigh out Ga(NO 3 ) 3 ·xH 2Weigh out 1.406 g of Ga(NO₃)₃·xH₂O and place it in a beaker. Pour in 55 ml of deionized water and dissolve it under magnetic stirring. Meanwhile, prepare a 1.5 M ammonia aqueous solution and gradually add the 1.5 M ammonia aqueous solution drop by drop under magnetic stirring until the pH of the suspension is 12. Then transfer the suspension to a hydrothermal reactor and carry out hydrothermal reaction at 60 °C for 18 h. Wash the white precipitate alternately with 400 ml of deionized water and 150 ml of absolute ethanol for 3 times until it is neutral. Subsequently, dry it in a forced-air oven at 60 °C for 5 h to collect the white powder. Put the white powder into a muffle furnace and calcine it at a heating rate of 1 °C / min to 600 °C for 3 h. The sample name is α-Ga 2 O 3 -12 - 60 - 600.

[0032] Example 4:

[0033] First, weigh out 1.406 g of Ga(NO 3 ) 3 ·xH 2 O and place it in a beaker. Pour in 55 ml of deionized water and dissolve it under magnetic stirring. Meanwhile, prepare a 1.5 M ammonia aqueous solution and gradually add the 1.5 M ammonia aqueous solution drop by drop under magnetic stirring until the pH of the suspension is 10. Then transfer the suspension to a hydrothermal reactor and carry out hydrothermal reaction at 60 °C for 18 h. Wash the white precipitate alternately with 400 ml of deionized water and 150 ml of absolute ethanol for 3 times until it is neutral. Subsequently, dry it in a forced-air oven at 60 °C for 5 h to collect the white powder. Put the white powder into a muffle furnace and calcine it at a heating rate of 1 °C / min to 560 °C for 3 h. The sample name is α-Ga 2 O 3 -10 - 60 - 560.

[0034] Example 5:

[0035] First, weigh out 1.406 g of Ga(NO 3 ) 3 ·xH 2 O and place it in a beaker. Pour in 55 ml of deionized water and dissolve it under magnetic stirring. Meanwhile, prepare a 1.5 M ammonia aqueous solution and gradually add the 1.5 M ammonia aqueous solution drop by drop under magnetic stirring until the pH of the suspension is 10. Then transfer the suspension to a hydrothermal reactor and carry out hydrothermal reaction at 60 °C for 18 h. Wash the white precipitate alternately with 400 ml of deionized water and 150 ml of absolute ethanol for 3 times until it is neutral. Subsequently, dry it in a forced-air oven at 60 °C for 5 h to collect the white powder. Put the white powder into a muffle furnace and calcine it at a heating rate of 1 °C / min to 640 °C for 3 h. The sample name is α-Ga 2 O 3 -10 - 60 - 640.

[0036] Comparative Example 1:

[0037] First, weigh out 1.406 g of Ga(NO 3 ) 3 ·xH 2 O and put it into a beaker. Pour 55 ml of deionized water into the beaker and dissolve it under magnetic stirring. At the same time, prepare a 1.5 M ammonia aqueous solution, and gradually add the 1.5 M ammonia aqueous solution dropwise under magnetic stirring until the pH of the suspension is 7. Then transfer the suspension into a hydrothermal autoclave and carry out hydrothermal reaction at 60 °C for 18 h. Wash the white precipitate alternately with 400 ml of deionized water and 150 ml of absolute ethanol for 3 times until it is neutral. Subsequently, dry it in a blast drying oven at 60 °C for 5 h to collect the white powder. Put the white powder into a muffle furnace and calcine it at a heating rate of 1 °C / min to 600 °C for 3 h. The sample name is α-Ga 2 O 3 -7-60-600.

[0038] Comparative Example 2:

[0039] First, weigh out 1.406 g of Ga(NO 3 ) 3 ·xH 2 O and put it into a beaker. Pour 55 ml of deionized water into the beaker and dissolve it under magnetic stirring. At the same time, prepare a 1.5 M ammonia aqueous solution, and gradually add the 1.5 M ammonia aqueous solution dropwise under magnetic stirring until the pH of the suspension is 13. Then transfer the suspension into a hydrothermal autoclave and carry out hydrothermal reaction at 60 °C for 18 h. Wash the white precipitate alternately with 400 ml of deionized water and 150 ml of absolute ethanol for 3 times until it is neutral. Subsequently, dry it in a blast drying oven at 60 °C for 5 h to collect the white powder. Put the white powder into a muffle furnace and calcine it at a heating rate of 1 °C / min to 600 °C for 3 h. The sample name is α-Ga 2 O 3 -13-60-600.

[0040] Comparative Example 3:

[0041] First, weigh out 1.406 g of Ga(NO 3 ) 3 ·xH 2 O and put it into a beaker. Pour 55 ml of deionized water into the beaker and dissolve it under magnetic stirring. At the same time, prepare a 1.5 M ammonia aqueous solution, and gradually add the 1.5 M ammonia aqueous solution dropwise under magnetic stirring until the pH of the suspension is 10. Then transfer the suspension into a hydrothermal autoclave and carry out hydrothermal reaction at 60 °C for 18 h. Wash the white precipitate alternately with 400 ml of deionized water and 150 ml of absolute ethanol for 3 times until it is neutral. Subsequently, dry it in a blast drying oven at 60 °C for 5 h to collect the white powder. Put the white powder into a muffle furnace and calcine it at a heating rate of 1 °C / min to 540 °C for 3 h. The sample name is α-Ga 2 O 3-10 - 60 - 540。

[0042] Comparative Example 4:

[0043] First, weigh out 1.406 g of Ga(NO 3 ) 3 ·xH 2 O and put it into a beaker, then pour 55 ml of deionized water and dissolve it under magnetic stirring. At the same time, prepare a 1.5 M ammonia aqueous solution, and dropwise add the 1.5 M ammonia aqueous solution drop by drop under magnetic stirring until the pH of the suspension is 10. Then transfer the suspension into a hydrothermal autoclave and carry out a hydrothermal reaction at 60 °C for 18 h. Wash the white precipitate alternately with 400 ml of deionized water and 150 ml of absolute ethanol for 3 times until it is neutral. Subsequently, dry it in a blast drying oven at 60 °C for 5 h to collect the white powder. Put the white powder into a muffle furnace and calcine it at a heating rate of 1 °C / min to 660 °C for 3 h. The sample name is α-Ga 2 O 3 -10 - 60 - 660。

[0044] Comparative Example 5:

[0045] First, weigh out 1.406 g of Ga(NO 3 ) 3 ·xH 2 O and put it into a beaker, then pour 55 ml of deionized water and dissolve it under magnetic stirring. At the same time, prepare a 1.5 M ammonia aqueous solution, and dropwise add the 1.5 M ammonia aqueous solution drop by drop under magnetic stirring until the pH of the suspension is 10. Then transfer the suspension into a hydrothermal autoclave and carry out a hydrothermal reaction at 40 °C for 18 h. Wash the white precipitate alternately with 400 ml of deionized water and 150 ml of absolute ethanol for 3 times until it is neutral. Subsequently, dry it in a blast drying oven at 60 °C for 5 h to collect the white powder. Put the white powder into a muffle furnace and calcine it at a heating rate of 1 °C / min to 600 °C for 3 h. The sample name is α-Ga 2 O 3 -10 - 40 - 600。

[0046] Comparative Example 6:

[0047] First, weigh out 1.406 g of Ga(NO 3 ) 3 ·xH 2Weigh out 1.406 g of O and place it in a beaker. Pour 55 ml of deionized water into it and dissolve it under magnetic stirring. At the same time, prepare a 1.5 M ammonia aqueous solution, and slowly add the 1.5 M ammonia aqueous solution drop by drop under magnetic stirring until the pH of the suspension is 10. Then transfer the suspension into a hydrothermal reactor and carry out hydrothermal reaction at 110 °C for 18 h. Wash the white precipitate alternately with 400 ml of deionized water and 150 ml of absolute ethanol for 3 times until it is neutral. Subsequently, dry it in a blast drying oven at 60 °C for 5 h to collect the white powder. Put the white powder into a muffle furnace and calcine it at a heating rate of 1 °C / min to 600 °C for 3 h. The sample name is α-Ga 2 O 3 -10 - 110 - 600.

[0048] Application example:

[0049] Apply the catalysts prepared in Examples 1 - 5 and Comparative Examples 1 - 6 to the reaction of hydrogenation of carbon dioxide to methanol. The specific steps are as follows:

[0050] Select 0.1 g of the catalysts prepared in Examples 1 - 5 and Comparative Examples 1 - 6 with a mesh size of 40 - 80, mix them with 0.1 g of quartz sand respectively, and load them into a quartz tube. Before starting the reaction, introduce high-purity H with a flow rate of 15 mL / min under atmospheric pressure 2 Pretreat the catalyst, raise the temperature to 280 °C at a heating rate of 3 °C / min and reduce it for 1 h, then cool it to 250 °C under H 2 atmosphere, and introduce the mixed raw material gas (H 2 / CO 2 = 3 / 1, molar ratio) into the fixed-bed reactor, adjust the reactor pressure to reach 3 MPa, and keep the space velocity at 12000 mL·h -1 ·g cat -1 , and keep the reaction time at each reaction temperature point for 1 h. Among them, the temperature range for catalyst activity evaluation is from 250 °C to 400 °C, and the heating rate is 30 °C / h.

[0051] When the catalysts prepared in Examples 1 - 5 and Comparative Examples 1 - 6 are applied to the reaction of hydrogenation of carbon dioxide to methanol, and the reaction temperature is 340 °C, the experimental data of CO 2 conversion rate, methanol selectivity and methanol space-time yield are shown in Table 1.

[0052] Table 1 CO -1 ·g cat -1 conversion rate, methanol selectivity and methanol space-time yield of each example and comparative example sample under the operating conditions of 3 MPa, 340 °C, 12000 mL·h 2 conversion rate, methanol selectivity and methanol space-time yield

[0053]

[0054]

[0055] Table 2 CO conversion rate, methanol selectivity of samples in each example and comparative example, and CO conversion rate and methanol selectivity after continuous reaction for 100 h under the operating conditions of 3 MPa, 340 °C, and 12,000 mL·h -1 ·g cat -1 after reacting for 1 h 2 and the CO conversion rate and methanol selectivity after continuous reaction for 100 h 2

[0056]

[0057]

[0058] In summary:

[0059] In Example 1, a Ga catalyst synthesized from Ga(NO 3 ) 3 and ammonia water was used in the catalytic hydrogenation of CO to methanol reaction. At the same time, a fixed bed was used to evaluate the catalyst samples. The evaluation results showed that the Ga 2 O 3 sample obtained by hydrothermal treatment at pH = 10 and 60 °C for 18 h and finally calcined at 600 °C for 3 h showed the highest catalytic activity. The evaluation results showed that when the reaction temperature was 340 °C, the CO 2 conversion rate and methanol selectivity of the α-Ga 2 O 3 catalyst were 3.90% and 80.0% respectively, and the methanol space-time yield reached the maximum of 0.134 g 2 O 3 2 ·h MeOH ·g -1 ·g cat -1 .

[0060] As can be seen from Table 1, within the range of the examples, as the pH value increased, the CO 2 conversion rate gradually increased, and the methanol selectivity decreased slightly. The higher the pH value, the smaller the particle size of α-Ga 2 O 3 , which was beneficial to the conversion of CO 2 . As the calcination temperature and hydrothermal temperature increased, the CO 2 conversion rate gradually decreased, and the methanol selectivity gradually increased. The increase in the calcination temperature and hydrothermal temperature made the particle size of α-Ga 2 O 3 ​​has a more perfect crystal phase structure, higher crystallinity, and more uniform active sites, improving methanol selectivity. However, for α-Ga 2 O 3 , the specific surface area will become smaller, resulting in a decrease in the conversion rate of CO 2 . The stability test in Table 2 also shows that Example 1 has the highest stability. After reacting for 100 h, the decrease in the conversion rate of CO 2 and methanol selectivity does not exceed 3%. In the other examples, the decrease in methanol production activity does not exceed 6%, indicating that by controlling appropriate synthesis conditions, α-Ga 2 O 3 not only has high methanol production activity, but also the catalyst hardly deactivates after reacting for 100 h.

[0061] In Comparative Examples 1 and 2, when the pH of the suspension is not within the preferred range of 8-12, compared with Examples 1-3, the conversion rate of CO 2 and methanol selectivity show a significant decrease, far lower than the example samples, and the methanol space-time yield does not exceed 0.1 g MeOH ·h -1 ·g cat -1 . Similarly, for Comparative Examples 3-6, when the calcination temperature and hydrothermal temperature deviate from the example range, the conversion rate of CO 2 and methanol selectivity are significantly lower than those of the examples, and the space-time yield of methanol is also low, all not exceeding 0.1 g MeOH ·h -1 ·g cat -1 . This is because too low a pH value or too low a temperature is not conducive to the formation of the α-crystal phase of the Ga 2 O 3 sample, reducing the active centers for methanol production and resulting in low methanol selectivity and CO 2 conversion rate; too high a pH value is also not conducive to the formation of the α-crystal phase of the Ga 2 O 3 sample; too high calcination temperature and hydrothermal temperature result in an increase in the particle size of the Ga 2 O 3 sample and a decrease in the specific surface area, leading to a decrease in the conversion rate of CO 2 .

[0062] In Table 2, it can be seen that after reacting for 100 h, the inactivation rate of all Comparative Examples 1-6 is significantly faster than that of the examples, and the conversion rate of CO 2 and methanol selectivity have decreased by 10%, indicating that the formation of the α-crystal phase and particle size are the key factors for methanol production. The examples have high stability in the CO 2 hydrogenation to methanol reaction, while the comparative examples have poor stability.

[0063] In summary, the sample of Example 1 exhibited the highest CO 2 catalytic hydrogenation to methanol ability and showed extremely high stability in the 100-h continuous reaction stability test.

[0064] Figure 1 and Figure 2 are schematic diagrams showing the variation rules of methanol selectivity and CO 2 conversion rate with increasing temperature in Example 1 and Comparative Example 3. By analyzing the broken line representing Example 1 in Figure 1 , it can be obtained that when the temperature is 250 °C, the methanol selectivity is only 53.5%, and as the temperature rises to 310 °C, the methanol selectivity reaches an extreme value of 82.0%. When the temperature continues to rise, the methanol selectivity begins to decrease. By analyzing the broken line representing Example 1 in Figure 2 , it can be obtained that the CO 2 conversion rate continuously increases with increasing temperature. At low temperatures, the CO 2 conversion rate is only 0.03%, but when the temperature rises to 400 °C, the CO 2 conversion rate reaches 7.7%.

[0065] In addition, by analyzing the broken line representing Comparative Example 3 in Figure 1 , it can be obtained that its variation rule is basically the same as that in Example 1, but the overall methanol selectivity of the catalyst prepared in Comparative Example 3 is significantly lower than that of the catalyst prepared in Example 1. By analyzing the broken line representing Comparative Example 3 in Figure 2 , it can be obtained that its variation rule is basically the same as that in Example 1. When the temperature is in the range of 310 - 400 °C, the CO 2 conversion rate of the catalyst prepared in Comparative Example 3 is slightly lower than that of the catalyst prepared in Example 1.

[0066] The gallium oxide sample of Example 1 synthesized in this experiment was characterized by XRD, and the results are as Figure 3 shown. Obvious high-intensity diffraction peaks exist at positions of 34.7° and 35.5°, representing the (104) crystal plane and (110) crystal plane of the α-Ga 2 O 3 sample.

[0067] The above are all preferred embodiments of this application. The protection scope of this application is not limited accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of this application should be covered within the protection scope of this application.

Claims

1. A method for preparing an α-Ga2O3 catalyst for hydrogenating carbon dioxide to methanol, characterized in that: The steps include: S1. dissolving Ga(NO3)3 solid in deionized water to obtain a Ga(NO3)3 solution with a concentration range of 0.05-0.2 mol / L; S2. Add 1-3 mol / L ammonia water dropwise to the Ga(NO3)3 solution for precipitation, and obtain a suspension with a pH value ranging from 8 to 12; S3, the suspension is charged into a hydrothermal kettle, placed in a blast oven at 50°C-100°C and continued for hydrothermal synthesis for 12-30h to obtain a hydrothermal suspension, and the suspension is filtered, washed, and dried to obtain the product GaOOH; S4. Place the reaction product GaOOH in a muffle furnace, heat it to 560°C-640°C at a set heating rate, and calcine it at high temperature for 2-6 hours to obtain an α-Ga2O3 catalyst.

2. The method for preparing an α-Ga2O3 catalyst for producing methanol by hydrogenation of carbon dioxide according to claim 1, characterized in that: In step S1, the concentration range of the Ga(NO3)3 solution is 0.08-0.12 mol / L.

3. The method for preparing an α-Ga2O3 catalyst for producing methanol by hydrogenation of carbon dioxide according to claim 1, characterized in that: In the step S2, when ammonia water with a concentration of 1.2-1.8 mol / L is added dropwise to the Ga(NO3)3 solution for precipitation, the molar ratio of the amount of Ga(NO3)3 / NH3 is controlled to be 0.08-0.

18.

4. The method for preparing an α-Ga2O3 catalyst for producing methanol by hydrogenation of carbon dioxide according to claim 1 or 3, characterized in that: The concentration of the ammonia water is 1.5 mol / L.

5. The method for preparing an α-Ga2O3 catalyst for producing methanol by hydrogenation of carbon dioxide according to claim 1, characterized in that: In step S3, the hydrothermal reaction temperature ranges from 55°C to 80°C.

6. The method for preparing an α-Ga2O3 catalyst for preparing methanol by hydrogenation of carbon dioxide according to claim 1, characterized in that: In step S3, the specific steps of filtering are as follows: the white precipitate after hydrothermal treatment is washed alternately with deionized water and anhydrous ethanol, wherein 300ml-500ml of deionized water is used for washing three times; and 100ml-200ml of anhydrous ethanol is used for washing three times.

7. The method for preparing an α-Ga2O3 catalyst for producing methanol by hydrogenation of carbon dioxide according to claim 1, characterized in that: In step S3, the specific steps of drying are as follows: the precipitate obtained after washing is placed in a blast oven for drying, and the drying temperature is set in the range of 50-100° C. and the drying time is set in the range of 5-8 hours.

8. The method for preparing an α-Ga2O3 catalyst for preparing methanol by hydrogenation of carbon dioxide according to claim 1, characterized in that: In step S4, the heating rate is set to 0.5-3°C / min.

9. The method for preparing an α-Ga2O3 catalyst for preparing methanol by hydrogenation of carbon dioxide according to claim 1, characterized in that: In the step S4, the temperature range of high temperature calcination is: 580°C-610°C.

10. Use of the Ga2O3 catalyst prepared by the preparation method according to any one of claims 1 to 9 in synthesizing methanol by hydrogenation of carbon dioxide.

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