A catalyst for hydrothermal reduction of co2 by glycerol, preparation method and application thereof

Abstract

This invention discloses a catalyst for the hydrothermal reduction of CO2 from glycerol, its preparation method, and its application. The catalyst is a Ru / Al2O3(A) catalyst rich in surface hydroxyl groups, with a Ru content of 0.5wt%–5wt% and an Al content of 50wt%–53wt%. The catalyst exhibits a nanosheet morphology and can withstand the high-temperature and high-pressure water environment during the reaction. Under optimal reaction conditions, the formic acid yield reaches as high as 37.5%, and the lactic acid yield reaches as high as 78.7%. The minimum Ru dosage is only 0.5wt%, which is due to the good distribution of two-dimensional nanosheets on the nanosheets, which is conducive to the full exposure of Ru active sites. In addition, the synergistic effect of Ru and surface hydroxyl groups is the key to maintaining high catalytic performance and effectively reducing the use of alkali additives. Ultimately, a high CO2 conversion rate and high formic acid and lactic acid yields can be achieved at a relatively low reaction temperature, with less dosage and less alkali additives, while the reaction process has good stability.

Description

Technical Field

[0001] This invention belongs to the field of carbon emission reduction and conversion technology, specifically a catalyst for the hydrothermal reduction of CO2 by glycerol, its preparation method and its application. Background Technology

[0002] With the increasing prominence of global energy issues and the global carbon imbalance caused by excessive CO2 emissions, the development of clean hydrogen energy and its application in the production of chemicals through CO2 hydrogenation reduction have attracted widespread attention from scientists worldwide. However, challenges remain, including high production costs of green hydrogen, low conversion rates in CO2 reduction technology, and safety concerns regarding the storage and transportation of gaseous hydrogen. Biomass resources are abundant, environmentally friendly, and aligned with the concept of sustainable development, possessing the potential to replace petrochemical resources. Therefore, the efficient utilization of biomass resources to produce hydrogen and in-situ coupled CO2 reduction to produce high-value chemicals is a highly economically valuable method.

[0003] Formic acid is an important organic chemical raw material with significant economic value and wide applications in fuel cells, pharmaceuticals, and other fields. The production of formic acid through carbon dioxide hydrogenation not only consumes carbon dioxide but also generates considerable economic benefits. Traditionally, the hydrogen source for this process primarily comes from hydrogen produced in the fossil fuel industry. Utilizing renewable glycerol as a hydrogen source can alleviate dependence on fossil fuels and is also inexpensive, clean, and pollution-free. Lactic acid, as an important biomass "platform molecule" proposed by the U.S. Department of Energy (DOE), can be further value-added into high-value chemicals with wide applications in the food, cosmetics, pharmaceuticals, adhesives, coatings, plastics, textile fibers, and carbon fibers industries. However, traditionally, lactic acid is mainly obtained through the fermentation of grain crops, which may lead to a conflict between chemical production and people's livelihoods. Therefore, developing preparation methods based on non-grain biomass raw materials is imperative.

[0004] In summary, considering economic benefits and carbon-negative emission reduction technologies, glycerol, as a byproduct of biodiesel production, can generate hydrogen and lactic acid under catalysis. Glycerol-based CO2 reduction combines biomass conversion technology with carbon dioxide resource utilization technology, making it a promising carbon-negative technology. Compared to direct hydrogenation, glycerol significantly reduces the Gibbs free energy of the CO2 hydrogenation reaction. During biomass dehydrogenation, besides generating hydrogen to reduce carbon dioxide, the biomass itself is further converted to produce other high-value-added chemicals. Therefore, this process achieves the synergistic conversion of biomass and CO2. The two most important steps in the entire process are biomass dehydrogenation and bicarbonate (the form in which carbon dioxide exists in aqueous solution) hydrogenation. However, current hydrothermal reduction of CO2 from glycerol to co-produce lactic acid and formic acid typically requires temperatures above 300°C and the use of excess alkali under hydrothermal conditions. To make the reaction conditions milder, suitable catalysts need to be found. Currently, noble metal catalysts are mostly used in the biomass reduction of carbon dioxide (bicarbonate) reaction, among which Ru-based catalysts have good activity and stability. However, the developed Ru-based catalysts require excessive amounts of precious metals; Ru must constitute more than 5 wt% of the catalyst mass to maintain a conversion rate of around 25%. A concentration below 5 wt% results in a conversion rate of <20%. Furthermore, the hydrothermal environment during the reaction makes the active metal on the catalyst prone to growth and aggregation, leading to deactivation and poor catalyst stability. In addition, the use of excessive alkali (to maintain a formic acid yield of ≥20%, the NaOH / glycerol molar ratio must be no less than 0.25) makes the process unsustainable, hindering its commercial application.

[0005] To address the aforementioned problems, the research direction of this invention is to provide a new catalyst that can achieve a high conversion rate of CO2 and obtain high yields of formic acid and lactic acid at a lower reaction temperature, with less dosage and fewer alkali additives, while also exhibiting good reaction stability. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention provides a catalyst for the hydrothermal reduction of CO2 from glycerol, a preparation method thereof, and its application. When this catalyst is applied to the process of preparing lactic acid and formic acid from CO2 by the hydrothermal reduction of glycerol, a high conversion rate of CO2 can be achieved at a lower reaction temperature, with a smaller dosage and fewer alkali additives, and a higher yield of formic acid and lactic acid can be obtained. At the same time, the reaction process has good stability.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a catalyst for the hydrothermal reduction of CO2 by glycerol, wherein the catalyst is a Ru / Al2O3(A) catalyst rich in surface hydroxyl groups, and the Ru content in the catalyst is 0.5wt% to 5wt%; the Al content is 50wt% to 53wt%.

[0008] The specific steps of the above-mentioned preparation method for the hydrothermal reduction of CO2 catalyst from glycerol are as follows:

[0009] 1) Thoroughly mix and stir the alkaline alumina support with NaOH alkaline solution at 5–35℃, and control the pH value at 8–11;

[0010] 2) In a sealed container, the temperature is controlled at 200-300℃, and the mixture is stirred for 2-8 hours. After cooling to room temperature, it is filtered and washed with deionized water to obtain an Al2O3(A) precursor rich in surface hydroxyl groups.

[0011] 3) Prepare solution A from Ru salt;

[0012] 4) At 5–35°C, the above solution A is mixed and stirred with an Al2O3(A) precursor rich in surface hydroxyl groups for 6–12 hours to form a precipitate.

[0013] 5) Evaporate the precipitate using a rotary evaporator at 50–90°C, and wash it with deionized water;

[0014] 6) The washed Ru / Al2O3(A) precursor was vacuum dried at 80-120℃, calcined at 100-300℃ for 4-24h, and then pressed into tablets and pulverized through a 40-200 mesh sieve to obtain a preliminary catalyst.

[0015] 7) The preliminary catalyst obtained in step 6) is reduced at 200-600°C for 4-12 hours under a 5% H2 / 95% Ar atmosphere to prepare a Ru / Al2O3(A) catalyst rich in surface hydroxyl groups.

[0016] Furthermore, the concentration of Ru in solution A is 0.01 g / ml, and the corresponding volume of solution is taken according to the catalyst with different Ru loading.

[0017] Furthermore, in step 6), the roasting temperature is 100–200℃, and the roasting time is 4–12 hours. These parameters result in better roasting performance.

[0018] Furthermore, in step 7), the reduction temperature is 300–500℃, and the reduction time is 4–8 hours. These parameters result in better reduction performance.

[0019] The above-mentioned catalyst is used in the hydrothermal reduction of CO2 from glycerol to prepare lactic acid and formic acid. The catalyst, glycerol, HCO3- / CO2, and NaOH are added to a reactor in a molar ratio of (0.001–0.01):1:1:0.5, with the water filling rate controlled at 25–60%. The reaction is carried out at 200–400°C under sealed conditions for 15–240 min. The reaction pressure is the sum of the saturated vapor pressure corresponding to the reaction temperature and the pressure of the hydrogen gas produced in the reaction. This process converts CO2 into formic acid and glycerol into lactic acid. The products obtained in this invention are mainly lactic acid and formic acid, with small amounts of pyruvic acid and acetate also produced. A high-purity aqueous solution of lactic acid and formic acid can be obtained by filtration using a 0.15 μm filter membrane.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) This invention does not require the additional introduction of high-purity hydrogen when performing hydrothermal reduction of CO2 with glycerol, which greatly reduces the energy consumption of the reaction and the cost of hydrogen transportation and storage. It is also more efficient and environmentally friendly, achieving negative carbon emission reduction while causing less pollution to the environment.

[0022] (2) The Ru / Al2O3(A) catalyst rich in surface hydroxyl groups prepared in this invention exhibits a nanosheet morphology, which can withstand the high temperature and high pressure water environment during the reaction. Under optimal reaction conditions, the formic acid yield is as high as 37.5%, and the lactic acid yield is as high as 78.7%, which surpasses the best performance reported by existing heterogeneous catalytic systems. At the same time, the amount of noble metal Ru in the catalyst is significantly reduced by 60%, and the minimum amount of Ru is only 0.5 wt%; this is because the two-dimensional nanosheets on the nanosheets are well distributed, which is conducive to the full exposure of Ru active sites. Furthermore, the synergistic effect of Ru and surface hydroxyl groups is the key to maintaining the high catalytic performance of this system.

[0023] (5) The catalyst of this invention exhibits high product selectivity in the hydrothermal reduction of CO2 from glycerol. The main liquid-phase products are formic acid and lactic acid. Under optimal reaction conditions, the formic acid yield reaches 37.5%, and the lactic acid yield reaches 78.7%, making them easy to separate and purify. Furthermore, the nanosheet structure of this catalyst significantly inhibits the aggregation of active Ru nanoparticles, thereby significantly improving catalyst stability. Simultaneously, the abundant hydroxyl groups on the catalyst support surface facilitate CO2 capture and conversion, effectively reducing the use of alkali additives. Ultimately, a high CO2 conversion rate and high formic acid and lactic acid yields can be achieved at a relatively low reaction temperature with minimal alkali additives, while maintaining good reaction stability. Detailed Implementation

[0024] The present invention will be further described below.

[0025] Example 1: Preparation of Cat-1 catalyst

[0026] Alkaline alumina support was thoroughly mixed with NaOH alkaline solution at 25℃, and the pH was controlled at 10. The mixture was stirred for 6 hours at 280℃ in a sealed container. After cooling to room temperature, it was filtered and washed with deionized water to obtain an Al2O3(A) precursor rich in surface hydroxyl groups. 5g of the Al2O3(A) precursor was weighed and placed in a flask. After initial dispersion, it was sonicated for 30 minutes. Then, 100-120ml of water was added and stirred. A 0.01g / ml aqueous solution of RuCl3 was prepared. 25ml of this solution was added dropwise to the flask while stirring using a pipette. The mixture was stirred for 6 hours. The water was evaporated to dryness using a rotary evaporator under vacuum. The evaporation was first carried out at 55-60℃ for 30 minutes, then the temperature was increased to 70-85℃ to accelerate evaporation. After evaporation, the catalyst and the flask were dried in an 80℃ oven. The catalyst was scraped out of the flask using a spatula, ground evenly in a mortar and pestle, and then washed three times with deionized water. The washed Ru / Al2O3(A) was vacuum dried at 80°C, calcined at 200°C for 8 hours, and then ground evenly in a mortar to obtain the catalyst Cat-1.

[0027] Example 2: Preparation of Cat-2 catalyst

[0028] Alkaline alumina support was thoroughly mixed with NaOH alkaline solution at 25℃, and the pH was controlled at 10. The mixture was stirred for 6 hours at 280℃ in a sealed container. After cooling to room temperature, it was filtered and washed with deionized water to obtain an Al2O3(A) precursor rich in surface hydroxyl groups. 5g of the Al2O3(A) precursor was weighed and placed in a flask. After initial dispersion, it was sonicated for 30 minutes. Then, 100-120ml of water was added and stirred. A 0.01g / ml aqueous solution of RuCl3 was prepared. 5ml of this solution was added dropwise to the flask while stirring using a pipette. The mixture was stirred for 6 hours. The water was evaporated to dryness using a rotary evaporator under vacuum. The evaporation was first carried out at 55-60℃ for 30 minutes, then the temperature was increased to 70-85℃ to accelerate evaporation. After evaporation, the catalyst and the flask were dried in an 80℃ oven. The catalyst was scraped out of the flask using a spatula, ground evenly in a mortar and pestle, and then washed three times with deionized water. The washed Ru / Al2O3(A) was vacuum dried at 80°C, calcined at 200°C for 8 hours, and then ground evenly in a mortar to obtain the catalyst Cat-2.

[0029] Example 3: Preparation of Cat-3 catalyst

[0030] Alkaline alumina support was thoroughly mixed with NaOH alkaline solution at 25℃, and the pH was controlled at 10. The mixture was stirred for 6 hours at 280℃ in a sealed container. After cooling to room temperature, it was filtered and washed with deionized water to obtain an Al2O3(A) precursor rich in surface hydroxyl groups. 5g of the Al2O3(A) precursor was weighed and placed in a flask. After initial dispersion, it was sonicated for 30 minutes. Then, 100-120ml of water was added and stirred. A 0.01g / ml aqueous solution of RuCl3 was prepared, and 2.5ml of this solution was added dropwise to the flask while stirring. The mixture was stirred for 6 hours. The water was evaporated to dryness using a rotary evaporator under vacuum. The evaporation was first carried out at 55-60℃ for 30 minutes, then the temperature was increased to 70-85℃ to accelerate evaporation. After evaporation, the catalyst and the flask were dried in an 80℃ oven. The catalyst was scraped out of the flask using a spatula, ground evenly in a mortar and pestle, and then washed three times with deionized water. The washed Ru / Al2O3(A) was vacuum dried at 80°C, calcined at 200°C for 8 hours, and then ground evenly in a mortar to obtain the catalyst Cat-3.

[0031] Example 4: Preparation of Cat-4 catalyst

[0032] Alkaline alumina support was thoroughly mixed with NaOH alkaline solution at 25℃, and the pH was controlled at 10. The mixture was stirred for 6 hours at 280℃ in a sealed container. After cooling to room temperature, it was filtered and washed with deionized water to obtain an Al2O3(A) precursor rich in surface hydroxyl groups. 5g of the Al2O3(A) precursor was weighed and placed in a flask. After initial dispersion, it was sonicated for 30 minutes. Then, 100-120ml of water was added and stirred. A 0.01g / ml aqueous solution of RuCl3 was prepared. 0.5ml of this solution was added dropwise to the flask while stirring using a pipette. The mixture was stirred for 6 hours. The water was evaporated to dryness using a rotary evaporator under vacuum. The evaporation was first carried out at 55-60℃ for 30 minutes, then the temperature was increased to 70-85℃ to accelerate evaporation. After evaporation, the catalyst and the flask were dried in an 80℃ oven. The catalyst was scraped out of the flask using a spatula, ground evenly in a mortar and pestle, and then washed three times with deionized water. The washed Ru / Al2O3(A) was vacuum dried at 80°C, calcined at 200°C for 8 hours, and then ground evenly in a mortar to obtain the catalyst Cat-4.

[0033] Example 5: Preparation of Cat-5 catalyst

[0034] Alkaline alumina support was thoroughly mixed with NaOH alkaline solution at 25℃, and the pH was controlled at 10. The mixture was stirred for 6 hours at 280℃ in a sealed container. After cooling to room temperature, it was filtered and washed with deionized water to obtain an Al2O3(A) precursor rich in surface hydroxyl groups. 5g of the Al2O3(A) precursor was weighed and placed in a flask. After initial dispersion, it was sonicated for 30 minutes. Then, 100-120ml of water was added and stirred. A 0.01g / ml aqueous solution of RuCl3 was prepared. 0.5ml of this solution was added dropwise to the flask while stirring using a pipette. The mixture was stirred for 6 hours. The water was evaporated to dryness using a rotary evaporator under vacuum. The evaporation was first carried out at 55-60℃ for 30 minutes, then the temperature was increased to 70-85℃ to accelerate evaporation. After evaporation, the catalyst and the flask were dried in an 80℃ oven. The catalyst was scraped out of the flask using a spatula, ground evenly in a mortar and pestle, and then washed three times with deionized water. The washed Ru / Al2O3(A) was vacuum dried at 80℃, calcined at 200℃ for 8 hours, and reduced at 200℃ for 4 hours under a 5% H2 / 95% Ar atmosphere. After homogenization in a mortar, the resulting catalyst was designated Cat-5.

[0035] Example 6: Preparation of Cat-6 catalyst

[0036] Alkaline alumina support was thoroughly mixed with NaOH alkaline solution at 25℃, and the pH was controlled at 10. The mixture was stirred for 6 hours at 280℃ in a sealed container. After cooling to room temperature, it was filtered and washed with deionized water to obtain an Al2O3(A) precursor rich in surface hydroxyl groups. 5g of the Al2O3(A) precursor was weighed and placed in a flask. After initial dispersion, it was sonicated for 30 minutes. Then, 100-120ml of water was added and stirred. A 0.01g / ml aqueous solution of RuCl3 was prepared. 0.5ml of this solution was added dropwise to the flask while stirring using a pipette. The mixture was stirred for 6 hours. The water was evaporated to dryness using a rotary evaporator under vacuum. The evaporation was first carried out at 55-60℃ for 30 minutes, then the temperature was increased to 70-85℃ to accelerate evaporation. After evaporation, the catalyst and the flask were dried in an 80℃ oven. The catalyst was scraped out of the flask using a spatula, ground evenly in a mortar and pestle, and then washed three times with deionized water. The washed Ru / Al2O3(A) was vacuum dried at 80℃, calcined at 200℃ for 8 hours, and reduced at 400℃ for 4 hours under a 5% H2 / 95% Ar atmosphere. After homogenization in a mortar, the resulting catalyst was Cat-6.

[0037] Example 7: Preparation of Cat-7 catalyst

[0038] Alkaline alumina support was thoroughly mixed with NaOH alkaline solution at 25℃, and the pH was controlled at 10. The mixture was stirred for 6 hours at 280℃ in a sealed container. After cooling to room temperature, it was filtered and washed with deionized water to obtain an Al2O3(A) precursor rich in surface hydroxyl groups. 5g of the Al2O3(A) precursor was weighed and placed in a flask. After initial dispersion, it was sonicated for 30 minutes. Then, 100-120ml of water was added and stirred. A 0.01g / ml aqueous solution of RuCl3 was prepared. 0.5ml of this solution was added dropwise to the flask while stirring using a pipette. The mixture was stirred for 6 hours. The water was evaporated to dryness using a rotary evaporator under vacuum. The evaporation was first carried out at 55-60℃ for 30 minutes, then the temperature was increased to 70-85℃ to accelerate evaporation. After evaporation, the catalyst and the flask were dried in an 80℃ oven. The catalyst was scraped out of the flask using a spatula, ground evenly in a mortar and pestle, and then washed three times with deionized water. The washed Ru / Al2O3(A) was vacuum dried at 80℃, calcined at 200℃ for 8 hours, and reduced at 600℃ for 4 hours under a 5% H2 / 95% Ar atmosphere. After homogenization in a mortar, the resulting catalyst was designated Cat-7.

[0039] Effect verification:

[0040]

[0041] The catalysts prepared in Examples 1 to 7 were used to prepare lactic acid and formic acid by hydrothermal reduction of CO2 from glycerol under the same conditions. A control group was set up, which was under the same conditions except that it used an existing Ru catalyst. The products were qualitatively analyzed by GC / MS and quantitatively analyzed by HPLC after the reaction. The evaluation results of Catalysts 1 to 7 are shown in Table 1.

[0042] Glycerol (2 mmol), catalyst (20 mg), sodium bicarbonate / CO2 (2 mmol), sodium hydroxide (1 mmol), and a high-temperature stir bar were loaded into an 8 ml high-pressure reactor, achieving a filling rate of 60%. The reactor was sealed and placed in a 280°C heating platform at a pressure equal to the sum of the corresponding saturated vapor pressure and the pressure of the hydrogen gas produced during the reaction. The reaction was allowed to proceed for 3 hours. At the preset reaction time point, the heating device was turned off, and the reactor body was rapidly placed in cold water for quenching to interrupt the reaction. The liquid and gas samples from the reactor were then collected and analyzed using appropriate methods.

[0043] Table 1 Performance of Catalysts Cat1-7

[0044]

[0045] As shown in Table 1, the experimental groups using catalysts from Examples 1 to 7 all exhibited significantly better results than the control group using the existing Ru catalyst in terms of glycerol conversion, lactic acid yield, and formic acid production. Furthermore, the Cat-6 catalyst prepared in Example 6 demonstrated the best performance under the same conditions.

[0046] Test 1: The reaction performance of the Cat-6 catalyst prepared in Example 6 was tested under different temperature conditions:

[0047] Glycerol (2 mmol), Cat-6 catalyst (20 mg), sodium bicarbonate / CO2 (2 mmol), sodium hydroxide (1 mmol), and a high-temperature stir bar were loaded into an 8 ml high-pressure reactor, achieving a filling rate of 60%. The reactor was sealed and placed in a heating platform. The temperature of the heating platform was varied, and the pressure was adjusted to the sum of the corresponding saturated vapor pressure and the pressure of the hydrogen gas produced in the reaction. The reaction was allowed to proceed for 3 hours. At the preset reaction time point, the heating device was turned off, and the reactor body was rapidly placed in cold water for quenching to interrupt the reaction. The liquid and gas samples in the reactor were then collected and analyzed using appropriate methods.

[0048] The product was qualitatively analyzed by GC / MS and quantitatively analyzed by HPLC after the reaction. The results of the evaluation at different temperatures are shown in Table 2.

[0049] Table 2. Reaction performance of Cat-6 catalyst at different temperatures

[0050]

[0051] As shown in Test 1, the Cat-6 catalyst prepared in Example 6 exhibits higher glycerol conversion rate, lactic acid yield, and formic acid yield at a reaction temperature of 230°C than the corresponding data for the existing Ru catalyst at a reaction temperature of 280°C (as shown in Table 1). This demonstrates that when the catalyst prepared in this invention is applied to the hydrothermal reduction of CO2 from glycerol to produce lactic acid and formic acid, it can achieve a higher CO2 conversion rate and obtain higher formic acid and lactic acid yields at a lower reaction temperature, with less dosage and fewer alkali additives.

[0052] Test 2: The reaction performance of the Cat-6 catalyst prepared in Example 6 under different base additive conditions was tested:

[0053] Glycerol (2 mmol), Cat-6 catalyst (20 mg), sodium bicarbonate / CO2 (2 mmol), sodium hydroxide (x mmol), and a high-temperature stir bar were loaded into an 8 ml high-pressure reactor, achieving a filling rate of 60%. The reactor was sealed and placed in a 280°C heating platform at a pressure equal to the sum of the corresponding saturated vapor pressure and the pressure of the hydrogen gas produced during the reaction. The reaction was allowed to proceed for 3 hours. At the preset reaction time point, the heating device was turned off, and the reactor was rapidly placed in cold water for quenching to interrupt the reaction. The liquid and gas samples from the reactor were then collected and analyzed using appropriate methods.

[0054] The product was qualitatively analyzed by GC / MS and quantitatively analyzed by HPLC after the reaction. The evaluation results for different alkali concentrations are shown in Table 3.

[0055] Table 3 Reaction performance of Cat-6 catalyst with different base additives.

[0056]

[0057] Test 2 shows that the Cat-6 catalyst prepared in Example 6 can achieve a high level of glycerol conversion, lactic acid yield, and formic acid yield when the amount of alkali additive is 0.25 mmol. Therefore, it can be shown that when the catalyst prepared in this invention is used in the process of hydrothermal reduction of CO2 by glycerol to produce lactic acid and formic acid, a relatively small amount of alkali additive can be used to achieve a high conversion rate of CO2 and obtain a high yield of formic acid and lactic acid.

[0058] Furthermore, the amount of Ru in the catalysts prepared in each embodiment of the present invention is less than 5 wt%, and the minimum is only 0.5 wt% (i.e., the amount of Ru in the catalysts prepared in Examples 4 to 7 is 0.5 wt%). Moreover, each catalyst can achieve good results in the process of hydrothermal reduction of CO2 from glycerol to prepare lactic acid and formic acid. Therefore, based on the above effect verification and two tests, it can be concluded that when the catalyst prepared by the present invention is applied to the process of hydrothermal reduction of CO2 from glycerol to prepare lactic acid and formic acid, it can achieve a high conversion rate of CO2 and obtain a high yield of formic acid and lactic acid at a lower reaction temperature, with less dosage and less alkaline additive.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A catalyst for the hydrothermal reduction of CO2 from glycerol, characterized in that, The catalyst is a Ru / Al2O3 catalyst rich in surface hydroxyl groups, and the catalyst has a nanosheet morphology; the Ru content in the catalyst is 0.5wt% to 5wt%; the Al content is 50wt% to 53wt%. The specific steps for preparing this catalyst are as follows: 1) Thoroughly mix and stir the alkaline alumina support with NaOH alkaline solution at 5–35℃, and control the pH value at 8–11; 2) In a sealed container, the temperature is controlled at 200-300℃, and the mixture is stirred for 2-8 hours. After cooling to room temperature, the mixture is filtered and washed with deionized water to obtain an Al2O3 precursor rich in surface hydroxyl groups. 3) Prepare solution A from Ru salt; 4) At 5–35°C, the above solution A is mixed and stirred with an Al2O3 precursor rich in surface hydroxyl groups for 6–12 hours to form a precipitate. 5) Evaporate the precipitate using a rotary evaporator at 50–90°C, and wash it with deionized water; 6) The washed Ru / Al2O3 precursor was vacuum dried at 80-120℃, calcined at 100-300℃ for 4-24h, and then pressed into tablets and pulverized through a 40-200 mesh sieve to obtain a preliminary catalyst. 7) The preliminary catalyst obtained in step 6) is reduced at 200-600°C for 4-12 hours under a 5% H2 / 95% Ar atmosphere to prepare a Ru / Al2O3 catalyst rich in surface hydroxyl groups.

2. The catalyst according to claim 1, characterized in that, The concentration of Ru in solution A is 0.01 g / ml.

3. The catalyst according to claim 1, characterized in that, In step 6), the roasting temperature is 100-200℃ and the roasting time is 4-12h.

4. The catalyst according to claim 1, characterized in that, In step 7), the reduction temperature is 300–500℃ and the reduction time is 4–8 hours.

5. An application of the catalyst described in claim 1 in the hydrothermal reduction of CO2 by glycerol to prepare lactic acid and formic acid, wherein the catalyst, glycerol, HCO3- / CO2, and NaOH are added to a reactor in a molar ratio of (0.001-0.01):1:1:0.5, the water filling rate is controlled at 25-60%, and the reaction is carried out at 200-400°C under sealed conditions for 15-240 min. The reaction pressure is the sum of the saturated vapor pressure corresponding to the reaction temperature and the pressure of the hydrogen gas produced by the reaction, thereby converting CO2 into formic acid and glycerol into lactic acid.

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