Catalyst for hydrothermal reduction of CO2 by glycerol, preparation method and application thereof

Abstract

The invention discloses a catalyst for hydrothermal reduction of CO2 by glycerol, a preparation method and application of the catalyst, the catalyst is a Ru / Al2O3 (A) catalyst rich in surface hydroxyl, and the content of Ru in the catalyst is 0.5-5 wt%; the content of Al is 50 wt%-53 wt%; the catalyst is in a nanosheet shape and can bear a high-temperature and high-pressure water environment in the reaction process, the yield of formic acid reaches up to 37.5% under the optimal reaction condition, and the yield of lactic acid reaches up to 78.7%; the lowest dosage of Ru is only 0.5 wt%; the two-dimensional nanosheets on the nanosheets are well distributed, so that the Ru active sites can be fully exposed. In addition, the synergistic effect of Ru and surface hydroxyl is the key for maintaining the high catalytic performance of the system and effectively reducing the use of alkali additives. And finally, at a low reaction temperature, under the conditions of a small use amount and a small amount of an alkali additive, a high CO2 conversion rate can be realized, high formic acid and lactic acid yields can be obtained, and the stability of the reaction process is good.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon emission reduction and conversion, and specifically relates to a catalyst for hydrothermally reducing CO with glycerol, a preparation method thereof, and an application thereof. 2 Background Art

[0002] With the increasing prominence of global energy problems and the global carbon imbalance caused by excessive emissions of CO, the development of clean energy hydrogen and its application in the hydrogenation reduction of CO to chemicals have attracted extensive attention from scientists around the world. However, there are still problems such as high preparation cost of green hydrogen, low conversion rate of CO reduction technology, and safety of gaseous hydrogen storage and transportation. Biomass resources are rich in sources, green and environmentally friendly, in line with the concept of sustainable development, and have the potential to replace petrochemical resources. Therefore, efficiently utilizing biomass resources to produce hydrogen and in-situ coupling CO reduction to produce high-value chemicals is a method with great economic value. 2 Formic acid is an important organic chemical raw material with significant economic value and is widely used in fuel cells, the pharmaceutical field, etc. Hydrogenating carbon dioxide to formic acid can not only consume carbon dioxide but also create considerable economic benefits. The hydrogen source in traditional carbon dioxide hydrogenation to formic acid mainly comes from hydrogen produced by the fossil industry. Using renewable glycerol as a hydrogen source can not only alleviate the dependence on fossil energy but also be cheap, clean, and pollution-free. Lactic acid, as an important biomass "platform molecule" proposed by the US Department of Energy (DOE), can be further value-added and converted into high-value-added chemicals and has a wide range of applications in industries such as food, cosmetics, medicine, adhesives, coatings, plastics, textile fibers, and carbon fibers. Traditionally, lactic acid in industry is mainly obtained by fermenting food crops, which may lead to conflicts between chemical production and the "rice bowls" of the people. Therefore, it is also imperative to develop a preparation method based on non-food biomass raw materials. 2 In summary, from the perspectives of economic benefits and negative carbon emission reduction technology, since glycerol, as a by-product in the production process of biodiesel, can generate hydrogen and lactic acid under the action of a catalyst, glycerol reduction of CO 2 combines biomass conversion technology and carbon dioxide resource utilization technology and is a promising carbon-negative technology. Compared with the direct hydrogenation method, glycerol can significantly reduce the Gibbs free energy of the CO 2 hydrogenation reaction. During the dehydrogenation process of biomass, in addition to generating hydrogen to reduce carbon dioxide, the biomass itself will be further transformed to generate other high-value-added chemicals. Therefore, this process realizes the conversion of biomass and CO

[0003]

[0004] 2 2 2 ​​​​​For the co - conversion, the two most important steps in the whole process are biomass dehydrogenation and hydrogenation of bicarbonate (the form of carbon dioxide in aqueous solution). However, currently in the hydrothermal reduction of CO by glycerol 2 In the process of co - producing lactic acid and formic acid, the reaction usually requires a temperature higher than 300 °C and the use of excessive alkali under hydrothermal conditions. In order to make the reaction conditions milder, it is necessary to find a suitable catalyst for the reaction. Currently, in the reaction of biomass reducing carbon dioxide (bicarbonate), mostly noble - metal - type catalysts are used. Among them, Ru - based catalysts have good activity and stability. However, the noble - metal dosage of the developed Ru - based catalysts is too high. The Ru content in the catalyst needs to be greater than 5 wt% to maintain a conversion rate of about 25%. If it is lower than 5 wt%, the conversion rate will be < 20%. Moreover, in the reaction process, the hydrothermal environment makes the active metal of the catalyst easy to grow and agglomerate, resulting in deactivation, and the catalyst stability is poor. In addition, the use of excessive alkali (to maintain a formic acid yield of ≥ 20%, the molar ratio of NaOH / glycerol is not less than 0.25) also makes this process unsustainable and hinders its commercial application.

[0005] Regarding the above problems, how to provide a new catalyst that can achieve a high conversion rate of CO at a lower reaction temperature, with less dosage and fewer alkali additives, and can obtain a high yield of formic acid and lactic acid, while having good stability in the reaction process, is the research direction required by the present invention. 2 Higher conversion rate, and can obtain a higher yield of formic acid and lactic acid, while the reaction process has good stability, is the research direction required by the present invention. Summary of the Invention

[0006] In view of the problems existing in the above - mentioned prior art, the present invention provides a catalyst for the hydrothermal reduction of CO by glycerol, 2 its preparation method and its application. When the catalyst is applied to the process of preparing lactic acid and formic acid by the hydrothermal reduction of CO by glycerol, 2 it can achieve a high conversion rate of CO at a lower reaction temperature, with less dosage and fewer alkali additives, 2 and can obtain a high yield of formic acid and lactic acid, while the reaction process has good stability.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a catalyst for the hydrothermal reduction of CO by glycerol, 2 the catalyst is a Ru / Al 2 O 3 (A) catalyst rich in surface hydroxyl groups, and the Ru content in the catalyst is 0.5 wt% - 5 wt%; the Al content is 50 wt% - 53 wt%.

[0008] The preparation method of the above - mentioned catalyst for the hydrothermal reduction of CO by glycerol, 2 the specific steps are as follows: 1) Mix the basic alumina support and the NaOH alkaline solution thoroughly and stir at 5 - 35 °C, and control the pH value at 8 - 11; 2) Control the temperature at 200 - 300 °C in a closed container, stir for 2 - 8 hours, and after cooling to room temperature, filter and wash with deionized water to obtain an Al 2 O 3 (A) precursor rich in surface hydroxyl groups; 3) Prepare solution A by dissolving the Ru salt; 4) At 5 - 35 °C, mix and stir the above solution A with the Al 2 O 3 (A) precursor rich in surface hydroxyl groups for 6 - 12 hours to form a precipitation solution; 5) Evaporate to obtain a precipitate at 50 - 90 °C using a rotary evaporator and wash with deionized water; 6) Vacuum dry the washed Ru / Al 2 O 3 (A) precursor at 80 - 120 °C, calcine at 100 - 300 °C for 4 - 24 h, and then perform tabletting, crushing, and sieving through a 40 - 200 mesh sieve to obtain a preliminary catalyst; 7) Reduce the preliminary catalyst obtained in step 6) in a 5% H 2 / 95% Ar atmosphere at 200 - 600 °C for 4 - 12 hours to prepare a Ru / Al 2 O 3 (A) catalyst rich in surface hydroxyl groups.

[0009] Furthermore, the concentration of Ru in solution A is 0.01 g / ml, and corresponding volumes of the solution are taken respectively according to the synthesis of catalysts with different Ru loadings.

[0010] Furthermore, in step 6), the calcination temperature is 100 - 200 °C and the calcination time is 4 - 12 h. The calcination effect is better under this parameter.

[0011] Furthermore, in step 7), the reduction temperature is 300 - 500 °C and the reduction time is 4 - 8 h. The reduction effect is better under this parameter.

[0012] The application of the above catalyst in the hydrothermal reduction of glycerol with CO 2 to prepare lactic acid and formic acid. Add the catalyst, glycerol, HCO 3 - / CO 2 , and NaOH into the reactor in a molar ratio of (0.001 - 0.01):1:1:0.5, control the water filling rate at 25 - 60%, and react 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 hydrogen pressure generated by the reaction, so as to be able to convert CO2 Glycerol is converted into formic acid, and glycerol is converted into lactic acid. The products obtained in the present invention are mainly lactic acid and formic acid, and at the same time, a small amount of pyruvic acid and acetate are generated; an aqueous solution of lactic acid and formic acid with high purity can be obtained by filtration; the filtration is specifically carried out using a 0.15um filter membrane.

[0013] Compared with the prior art, the present invention has the following advantages: (1) When the present invention performs hydrothermal reduction of CO with glycerol 2 no additional high-purity hydrogen needs to be introduced, which greatly reduces the reaction energy consumption and the cost during the transportation and storage of hydrogen, and is more efficient, green and environmentally friendly, causing little pollution to the environment while achieving negative carbon emission reduction.

[0014] (2) The Ru / Al rich in surface hydroxyl groups prepared in the present invention 2 O 3 (A) The catalyst exhibits a nanosheet morphology, which can withstand the high-temperature and high-pressure aqueous environment during the reaction. Under the 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 exceeds the best performance reported in the existing heterogeneous catalytic systems. At the same time, the noble metal Ru dosage of the catalyst is significantly reduced by 60%, and the lowest Ru dosage is only 0.5wt%; this is because the two-dimensional nanosheets on the nanosheets are well distributed, which is conducive to the full exposure of the Ru active sites. And the synergistic effect of the presence of Ru and surface hydroxyl groups is the key to maintaining the high catalytic performance of this system.

[0015] (5) The product selectivity of the catalyst for hydrothermal reduction of CO with glycerol in the present invention 2 is high. The main components of the liquid-phase products are formic acid and lactic acid. Under the 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 is easy to separate and purify; and because the nanosheet structure of the catalyst can significantly inhibit the aggregation of active Ru nanoparticles, the stability of the catalyst is significantly improved. At the same time, the rich hydroxyl groups on the surface of the catalyst support are beneficial to the capture and conversion of CO 2 , effectively reducing the use of alkali additives. Finally, at a lower reaction temperature, with less dosage and less alkali additives, a higher conversion rate of CO 2 can be achieved, and higher yields of formic acid and lactic acid can be obtained, and the reaction process has good stability. Detailed implementation manners

[0016] The present invention will be further described below.

[0017] Example 1: Preparation of Cat-1 catalyst At 25 °C, the basic alumina support was thoroughly mixed and stirred with the NaOH alkaline solution, and the pH value was controlled at 10. In a closed container, the temperature was controlled at 280 °C, and it was stirred for 6 hours. After cooling to room temperature, it was filtered and washed with deionized water to obtain Al rich in surface hydroxyl groups 2 O 3 (A) precursor; Weigh 5 g of Al 2 O 3 (A) The precursor was placed in an eggplant-shaped flask. After preliminary dispersion, it was sonicated for 30 min, taken out, 100 - 120 ml of water was added and stirred. RuCl 3 was prepared into an aqueous solution of 0.01 g / ml. Take 25 ml of the solution, and while stirring, use a pipette to drop the Ru-containing solution into the eggplant-shaped flask. Stir for 6 h, use a rotary evaporator to evaporate the water to dryness under vacuum. First, rotate and evaporate at 55 - 60 °C for 30 min, then raise the temperature to 70 - 85 °C to accelerate evaporation. After evaporation to dryness, the catalyst together with the eggplant-shaped flask was dried in an oven at 80 °C. Use a spatula to scrape out the catalyst in the eggplant-shaped flask, grind it evenly in a mortar, and wash it three times with deionized water. The washed Ru / Al 2 O 3 (A) was vacuum dried at 80 °C and calcined at 200 °C for 8 h. After grinding evenly in a mortar, the obtained catalyst was Cat-1.

[0018] Example 2: Preparation of Cat-2 catalyst At 25 °C, the basic alumina support was thoroughly mixed and stirred with the NaOH alkaline solution, and the pH value was controlled at 10. In a closed container, the temperature was controlled at 280 °C, and it was stirred for 6 hours. After cooling to room temperature, it was filtered and washed with deionized water to obtain Al rich in surface hydroxyl groups 2 O 3 (A) precursor; Weigh 5 g of Al 2 O 3 (A) The precursor was placed in an eggplant-shaped flask. After preliminary dispersion, it was sonicated for 30 min, taken out, 100 - 120 ml of water was added and stirred. RuCl 3 was prepared into an aqueous solution of 0.01 g / ml. Take 5 ml of the solution, and while stirring, use a pipette to drop the Ru-containing solution into the eggplant-shaped flask. Stir for 6 h, use a rotary evaporator to evaporate the water to dryness under vacuum. First, rotate and evaporate at 55 - 60 °C for 30 min, then raise the temperature to 70 - 85 °C to accelerate evaporation. After evaporation to dryness, the catalyst together with the eggplant-shaped flask was dried in an oven at 80 °C. Use a spatula to scrape out the catalyst in the eggplant-shaped flask, grind it evenly in a mortar, and wash it three times with deionized water. The washed Ru / Al 2 O 3 (A) was vacuum dried at 80 °C and calcined at 200 °C for 8 h. After grinding evenly in a mortar, the obtained catalyst was Cat-2.

[0019] Example 3: Preparation of Cat-3 Catalyst At 25°C, the basic alumina support was thoroughly mixed and stirred with the NaOH alkaline solution, and the pH value was controlled at 10. The temperature was controlled at 280°C in a closed container, and stirred for 6 hours. After cooling to room temperature, it was filtered and washed with deionized water to obtain Al rich in surface hydroxyl groups 2 O 3 (A) Precursors; Weigh 5 g of Al 2 O 3 (A) The precursor was placed in an eggplant-shaped flask. After preliminary dispersion, it was sonicated for 30 min, taken out, 100 - 120 ml of water was added and stirred. RuCl 3 was prepared into an aqueous solution of 0.01 g / ml. Take 2.5 ml of the solution, and while stirring, use a pipette to drop the Ru-containing solution into the eggplant-shaped flask. Stir for 6 h. Using a rotary evaporator, the water was evaporated to dryness under vacuum. First, it was rotary evaporated at 55 - 60°C for 30 min and then heated to 70 - 85°C to accelerate evaporation. After evaporation to dryness, the catalyst together with the eggplant-shaped flask was dried in an oven at 80°C. Use a spatula to scrape out the catalyst in the eggplant-shaped flask, grind it evenly in a mortar, and wash it three times with deionized water. The washed Ru / Al 2 O 3 (A) was vacuum dried at 80°C and calcined at 200°C for 8 h. After grinding evenly in a mortar, the obtained catalyst was Cat-3

[0020] Example 4: Preparation of Cat-4 Catalyst At 25°C, the basic alumina support was thoroughly mixed and stirred with the NaOH alkaline solution, and the pH value was controlled at 10. The temperature was controlled at 280°C in a closed container, and stirred for 6 hours. After cooling to room temperature, it was filtered and washed with deionized water to obtain Al rich in surface hydroxyl groups 2 O 3 (A) Precursors; Weigh 5 g of Al 2 O 3 (A) The precursor was placed in an eggplant-shaped flask. After preliminary dispersion, it was sonicated for 30 min, taken out, 100 - 120 ml of water was added and stirred. RuCl 3 was prepared into an aqueous solution of 0.01 g / ml. Take 0.5 ml of the solution, and while stirring, use a pipette to drop the Ru-containing solution into the eggplant-shaped flask. Stir for 6 h. Using a rotary evaporator, the water was evaporated to dryness under vacuum. First, it was rotary evaporated at 55 - 60°C for 30 min and then heated to 70 - 85°C to accelerate evaporation. After evaporation to dryness, the catalyst together with the eggplant-shaped flask was dried in an oven at 80°C. Use a spatula to scrape out the catalyst in the eggplant-shaped flask, grind it evenly in a mortar, and wash it three times with deionized water. The washed Ru / Al 2 O 3 (A) was vacuum dried at 80°C and calcined at 200°C for 8 h. After grinding evenly in a mortar, the obtained catalyst was Cat-4

[0021] Example 5: Preparation of Cat-5 Catalyst At 25 °C, the basic alumina support was thoroughly mixed and stirred with the NaOH alkaline solution, and the pH value was controlled at 10. The temperature was controlled at 280 °C in a closed container, and stirred for 6 hours. After cooling to room temperature, it was filtered and washed with deionized water to obtain Al rich in surface hydroxyl groups 2 O 3 (A) precursor; Weigh 5 g of Al 2 O 3 (A) The precursor was placed in an eggplant-shaped flask. After preliminary dispersion, it was sonicated for 30 min, taken out, 100 - 120 ml of water was added and stirred. RuCl 3 was made into an aqueous solution of 0.01 g / ml. Take 0.5 ml of the solution, and while stirring, use a pipette to drop the Ru-containing solution into the eggplant-shaped flask. Stir for 6 h, use a rotary evaporator to evaporate the water under vacuum. First, evaporate at 55 - 60 °C for 30 min, then raise the temperature to 70 - 85 °C to accelerate evaporation. After evaporation, the catalyst together with the eggplant-shaped flask was dried in an oven at 80 °C. Use a spatula to scrape out the catalyst in the eggplant-shaped flask, grind it evenly in a mortar, and wash it three times with deionized water. The washed Ru / Al 2 O 3 (A) was dried under vacuum at 80 °C, calcined at 200 °C for 8 h, and reduced at 200 °C for 4 h in a 5% H 2 / 95% Ar atmosphere. After grinding evenly in a mortar, the obtained catalyst was Cat-5

[0022] Example 6: Preparation of Cat-6 Catalyst At 25 °C, the basic alumina support was thoroughly mixed and stirred with the NaOH alkaline solution, and the pH value was controlled at 10. The temperature was controlled at 280 °C in a closed container, and stirred for 6 hours. After cooling to room temperature, it was filtered and washed with deionized water to obtain Al rich in surface hydroxyl groups 2 O 3 (A) precursor; Weigh 5 g of Al 2 O 3 (A) The precursor was placed in an eggplant-shaped flask. After preliminary dispersion, it was sonicated for 30 min, taken out, 100 - 120 ml of water was added and stirred. RuCl 3 was made into an aqueous solution of 0.01 g / ml. Take 0.5 ml of the solution, and while stirring, use a pipette to drop the Ru-containing solution into the eggplant-shaped flask. Stir for 6 h, use a rotary evaporator to evaporate the water under vacuum. First, evaporate at 55 - 60 °C for 30 min, then raise the temperature to 70 - 85 °C to accelerate evaporation. After evaporation, the catalyst together with the eggplant-shaped flask was dried in an oven at 80 °C. Use a spatula to scrape out the catalyst in the eggplant-shaped flask, grind it evenly in a mortar, and wash it three times with deionized water. The washed Ru / Al 2O 3 (A) Vacuum drying at 80 °C, calcining at 200 °C for 8 h, and reducing in 5% H 2 / 95% Ar atmosphere at 400 °C for 4 hours. After grinding evenly with a mortar, the obtained catalyst is Cat-6.

[0023] Example 7: Preparation of Cat-7 catalyst At 25 °C, the basic alumina support is fully mixed and stirred with the NaOH alkaline solution, and the pH value is controlled at 10. The temperature is controlled at 280 °C in a closed container, and stirred for 6 hours. After cooling to room temperature, it is filtered and washed with deionized water to obtain Al rich in surface hydroxyl groups 2 O 3 (A) precursor; Weigh 5 g of Al 2 O 3 (A) The precursor is placed in an eggplant-shaped flask. After preliminary dispersion, it is ultrasonicated for 30 min, taken out, 100 - 120 ml of water is added and stirred. RuCl 3 is prepared into an aqueous solution of 0.01 g / ml. Take 0.5 ml of the solution, and while stirring, use a pipette to drop the Ru-containing solution into the eggplant-shaped flask. Stir for 6 h, use a rotary evaporator to evaporate the water under vacuum. First, rotary evaporate at 55 - 60 °C for 30 min, then raise the temperature to 70 - 85 °C to accelerate evaporation. After evaporation, the catalyst together with the eggplant-shaped flask is dried in an oven at 80 °C. Use a spatula to scrape out the catalyst in the eggplant-shaped flask, grind it evenly with a mortar, and wash it three times with deionized water. The washed Ru / Al 2 O 3 (A) Vacuum drying at 80 °C, calcining at 200 °C for 8 h, and reducing in 5% H 2 / 95% Ar atmosphere at 600 °C for 4 hours. After grinding evenly with a mortar, the obtained catalyst is Cat-7.

[0024] Effect verification: The catalysts prepared in Examples 1 to 7 are all used to hydrothermally reduce CO from glycerol under the following same conditions 2 to prepare lactic acid and formic acid; and a control group is set up. The conditions of the control group are the same, except that an existing Ru catalyst is used; after the reaction, the products are qualitatively analyzed by GC / MS and quantitatively analyzed by HPLC. The evaluation results of Cat1 - 7 catalysts are shown in Table 1.

[0025] Glycerol (2 mmol), catalyst (20 mg), sodium bicarbonate / CO 2(2 mmol), sodium hydroxide (1 mmol), and a high-temperature magnetic stir bar were placed into an 8-ml autoclave to achieve a filling rate of 60%. The autoclave was sealed and placed in a heating block at 280 °C. The pressure was the sum of the corresponding saturated vapor pressure and the hydrogen pressure generated by the reaction. The reaction was carried out for 3 h. When the preset reaction time point was reached, the heating device was turned off, and the autoclave body was quickly placed in cold water for rapid quenching to interrupt the reaction in time. The liquid and gas samples in the autoclave were further collected and analyzed by appropriate methods.

[0026] Table 1 Performance Table of Cat1 - 7 Catalysts As can be seen from Table 1, in each experimental group using the catalysts of Examples 1 to 7, the glycerol conversion rate, lactic acid yield, and formic acid yield were significantly better than those of the control group using the existing Ru catalyst. Among them, the Cat-6 catalyst prepared in Example 6 had the best effect under the same conditions.

[0027] Test 1: The reaction performance of the Cat-6 catalyst prepared in Example 6 was tested under different temperature conditions: Glycerol (2 mmol), catalyst Cat-6 (20 mg), sodium bicarbonate / CO 2 (2 mmol), sodium hydroxide (1 mmol), and a high-temperature magnetic stir bar were placed into an 8-ml autoclave to achieve a filling rate of 60%. The autoclave was sealed and placed in a heating block. The temperature of the heating block was changed. The pressure was the sum of the corresponding saturated vapor pressure and the hydrogen pressure generated by the reaction. The reaction was carried out for 3 h. When the preset reaction time point was reached, the heating device was turned off, and the autoclave body was quickly placed in cold water for rapid quenching to interrupt the reaction in time. The liquid and gas samples in the autoclave were further collected and analyzed by appropriate methods.

[0028] After the reaction, the products were qualitatively analyzed by GC / MS and quantitatively analyzed by HPLC. The evaluation results at different temperatures are shown in Table 2.

[0029] Table 2 Reaction Performance of Cat-6 Catalyst at Different Temperatures From Test 1, it can be obtained that when the reaction temperature of the Cat-6 catalyst prepared in Example 6 was 230 °C, its glycerol conversion rate, lactic acid yield, and formic acid yield were all higher than the corresponding data of the existing Ru catalyst at a reaction temperature of 280 °C (as shown in Table 1). Therefore, it can be shown that the catalyst prepared by the present invention can be applied to the hydrothermal reduction of CO 2 in the process of preparing lactic acid and formic acid, and can achieve a higher conversion rate of CO at a lower reaction temperature, with less dosage and less alkali additive, and can obtain higher yields of formic acid and lactic acid. 2 ​

[0030] Test 2: The reaction performance of the Cat-6 catalyst prepared in Example 6 was tested under different alkali additives: Glycerol (2 mmol), catalyst Cat-6 (20 mg), sodium bicarbonate / CO 2 (2 mmol), sodium hydroxide (x mmol), and a high-temperature magnetic stir bar were loaded into an 8-ml autoclave to achieve a filling rate of 60%. The autoclave was sealed and placed in a heating block at 280 °C. The pressure was the sum of the corresponding saturated vapor pressure and the hydrogen pressure generated by the reaction. The reaction was carried out for 3 h. At the preset reaction time point, the heating device was turned off, and the autoclave body was quickly placed in cold water for quenching to interrupt the reaction in time. The liquid and gas samples in the autoclave were further collected and analyzed by appropriate methods.

[0031] After the reaction, the products were qualitatively analyzed by GC / MS and quantitatively analyzed by HPLC. The evaluation results at different alkali concentrations are shown in Table 3.

[0032] Table 3 Reaction performance of Cat-6 catalyst under different alkali additives From Test 2, it can be seen that when the amount of alkali additive used in the Cat-6 catalyst prepared in Example 6 is 0.25 mmol, its glycerol conversion rate, lactic acid yield, and formic acid yield can reach relatively high levels. Therefore, it can be shown that the catalyst prepared by the present invention can be applied to the hydrothermal reduction of glycerol with CO 2 In the process of preparing lactic acid and formic acid, with less alkali additive, the high conversion rate of CO 2 can be achieved, and relatively high yields of formic acid and lactic acid can be obtained.

[0033] In addition, the amount of Ru in the catalysts prepared in each example of the present invention is less than 5 wt%, and the minimum is only 0.5 wt% (i.e., the Ru content in the catalysts prepared in Examples 4 to 7 is 0.5 wt%); and each catalyst can achieve good results in the process of hydrothermal reduction of glycerol with CO 2 In the process of preparing lactic acid and formic acid. Therefore, based on the above effect verification and the two tests, it can be concluded that the catalyst prepared by the present invention can be applied to the hydrothermal reduction of glycerol with CO 2 In the process of preparing lactic acid and formic acid, at a relatively low reaction temperature, with less amount and less alkali additive, the high conversion rate of CO 2 can be achieved, and relatively high yields of formic acid and lactic acid can be obtained.

[0034] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A catalyst for the hydrothermal reduction of CO2 by glycerol, characterized in that: 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%.

2. A method for preparing a catalyst for hydrothermal reduction of CO2 by glycerol according to claim 1, characterized in that: The specific steps are: 1) Fully mix and stir the basic alumina support and the NaOH alkaline solution at 5-35°C, and control the pH value to be between 8 and 11; 2) Control the temperature at 200-300° C. in a sealed container, stir for 2-8 hours, cool to room temperature, filter, and wash with deionized water to obtain an Al2O3 (A) precursor rich in surface hydroxyl groups; 3) Prepare solution A with Ru salt; 4) Mixing the above-mentioned solution A with the Al2O3 (A) precursor rich in surface hydroxyl groups at 5-35° C. and stirring for 6-12 hours to form a precipitate; 5) Evaporate the precipitate using a rotary evaporator at 50-90°C and wash with deionized water; 6) The washed Ru / Al2O3(A) precursor is vacuum dried at 80-120°C, calcined at 100-300°C for 4-24h, and then tableted and crushed through a 40-200 mesh sieve to obtain a preliminary catalyst; 7) The preliminary catalyst obtained in step 6) is reduced in a 5% H2 / 95% Ar atmosphere at 200-600°C for 4-12 hours to prepare a Ru / Al2O3 (A) catalyst rich in surface hydroxyl groups.

3. The preparation method according to claim 2, characterized in that: The concentration of Ru in the solution A is 0.01 g / ml.

4. The preparation method according to claim 2, characterized in that: In the step 6), the calcination temperature is 100-200° C. and the calcination time is 4-12 hours.

5. The preparation method according to claim 2, characterized in that: In the step 7), the reduction temperature is 300-500° C. and the reduction time is 4-8 hours.

6. An application of the catalyst described in claim 1 in the hydrothermal reduction of CO2 with 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 to be 25-60%, and the reaction is carried out at 200-400°C under sealed conditions for 15-240 minutes. The reaction pressure is the sum of the saturated vapor pressure corresponding to the reaction temperature and the hydrogen pressure generated by the reaction, thereby converting CO2 into formic acid and glycerol into lactic acid.

Images