A catalyst for hydrogenating carbon dioxide to ethanol, its preparation method and application

Abstract

The present invention discloses a catalyst for hydrogenating carbon dioxide to ethanol, its preparation method and application. The catalyst is composed of an active metal, a promoter and a carrier. The active metal is Cu, Co and Ga. The promoter is a combination of any one of Mn or K and Na. The carrier is a carbon carrier. Calculated by the weight ratio of the catalyst being 100%, the contents of each component are as follows: Cu 10-20%, Co 10-20%, Ga 5-10%, Na 1-3%, Mn or K 1-3%, and the balance is the carrier. The introduction of the carbon carrier in the catalyst of the present invention is beneficial to the dispersion of the active metal. At the same time, the electronic effect of the carbon carrier creates more active site interfaces of the active components. The structural effect and the electronic effect of the carbon carrier promoting metal dispersion play a synergistic role, improving the selectivity of the target product. The preparation method of the catalyst of the present invention is simple, the preparation process is short, and it is environmentally friendly and easy to scale up.

Description

Technical Field

[0001] The present invention belongs to the technical field of ethanol preparation, and particularly relates to a catalyst for catalytic hydrogenation of carbon dioxide to ethanol, a preparation method thereof, and an application thereof. Background Art

[0002] As a carbon resource with rich sources, simple structure, non-toxicity and recyclability, the chemical catalytic conversion of CO2 into chemicals and fuels has multiple significances for solving environmental, resource and economic problems.

[0003] The thermodynamic stability and kinetic inertness of CO2 molecules themselves make their activation difficult, and a large amount of energy input is required for their catalytic conversion. Hydrogen, as a high-energy molecule, is often used for the conversion of CO2 into high-value chemicals. Converting CO2 into alcohols has better atom economy than producing hydrocarbons. Although the hydrogenation of CO2 to methanol has received extensive attention and research in many CO2 hydrogenation processes, ethanol has a higher energy density and is widely used as a clean fuel and chemical raw material. Due to the complexity and uncontrollability of the reaction path, the hydrogenation of CO2 to ethanol is more challenging than that of methanol. By comparing and analyzing different catalysts for the hydrogenation of CO2 to ethanol (Chem. Eng. Sci. 2023, 282, 119226), it is not difficult to find that noble metal catalysts have a low CO2 conversion rate and high catalyst costs, Co-based catalysts have a high methane content in the products of CO2 hydrogenation, and Mo-based catalysts have both low CO2 conversion rate and ethanol selectivity. The Cu-based catalyst for methanol synthesis has been the most widely studied in the hydrogenation of CO2 to alcohols, and its hydrogenation activity and selectivity of the target product are medium, but it also depends on the selection of the carrier and additives.

[0004] In addition to the high stability and difficult activation of CO2 molecules in the hydrogenation of CO2 to ethanol, there are also problems of C-C coupling and C-O insertion after CO2 activation. C-C coupling determines the carbon number distribution, and C-O bond insertion determines the selectivity of alcohol products. Therefore, it will be of great significance to provide a catalyst that can effectively promote CO2 activation, control C-C coupling and C-O insertion, and thus efficiently catalyze the hydrogenation of CO2 to ethanol. Summary of the Invention

[0005] Aiming at the defects of the prior art, the present invention provides a catalyst for catalytic hydrogenation of carbon dioxide to ethanol, a preparation method thereof, and an application thereof. The catalyst does not contain noble metal active components, has low cost, and good catalytic performance.

[0006] A catalyst for hydrogenating carbon dioxide to ethanol, the catalyst is composed of an active metal, a promoter and a support; the active metal is Cu, Co and Ga, the promoter is a combination of any one of Mn or K and Na, and the support is a carbon support; calculated according to the weight ratio of the catalyst being 100%, the contents of each component are as follows: Cu 10-20%, Co 10-20%, Ga 5-10%, Na 1-3%, Mn or K 1-3%, and the balance is the support.

[0007] Preferably, the carbon support is any one of activated carbon, carbon nanotubes or graphene.

[0008] Preferably, the specific surface area of the carbon support is 200-900 m 2 / g.

[0009] More preferably, the specific surface area of the carbon support is 300-890 m 2 / g.

[0010] The preparation method of the catalyst for hydrogenating carbon dioxide to ethanol includes the following steps:

[0011] (1) Add the support to a nitric acid solution, heat and reflux at 70-150 °C for 3-14 h, filter, wash with deionized water until neutral, dry, grind, and obtain the treated support;

[0012] (2) Add the metal salts corresponding to the active metal and the promoter to water or ethanol to obtain a mixed solution of the active metal and the promoter;

[0013] (3) Add the treated support obtained in step (1) to the mixed solution in step (2), perform ultrasonic treatment for 2-5 h, stir to dry at room temperature, then dry, calcine, grind, tablet, form, and sieve through a 20-60 mesh sieve to obtain the catalyst.

[0014] Preferably, the metal salts corresponding to the active metal and the promoter are their corresponding nitrates, chlorides or acetates, and the total concentration of the active metal and the promoter in the mixed solution is 0.2-1 mol / L.

[0015] Preferably, the ratio of the support to the nitric acid solution is 1 g:10-20 mL, and the concentration of the nitric acid solution is 5-10 mol / L.

[0016] Preferably, the drying condition in step (1) is drying at 60-100 °C for 8-12 h; the drying condition in step (3) is drying at 80-120 °C for 7-12 h, and the calcination condition is calcination at 300-450 °C for 3-8 h.

[0017] Preferably, the power of the ultrasonic treatment is 200 - 800 w.

[0018] A method for catalytic hydrogenation of carbon dioxide to ethanol is as follows: The catalyst is loaded into a fixed - bed reactor, and a hydrogen - containing gas is introduced for reduction activation. Then, the temperature is adjusted to 220 - 300 °C, and a mixed gas of CO2 and H2 is switched in, and the pressure is increased to 2 - 5 MPa for reaction; wherein, the catalyst is the catalyst of the present invention.

[0019] Preferably, in the mixed gas of CO2 and H2, the volume ratio of CO2 to H2 is 1:3 - 6, and the space velocity of the mixed gas of CO2 and H2 relative to the catalyst is 3000 - 8000 h -1 ; The conditions for reduction activation are reduction at 250 - 350 °C and normal pressure for 3 - 6 h. Among them, the flow rate of the hydrogen - containing gas is 30 - 100 mL / min, the hydrogen - containing gas is hydrogen, or a mixed gas of hydrogen and a balance gas, and the volume fraction of hydrogen in the mixed gas of hydrogen and the balance gas is 5% ≤ hydrogen < 100%, and the balance gas is nitrogen, helium or argon.

[0020] Advantages of the present invention:

[0021] (1) In the catalyst of the present invention, the introduction of a carbon carrier is beneficial to the dispersion of active metals. At the same time, the electronic effect of the carbon carrier creates more active - site interfaces of active components. The structural effect and electronic effect of the carbon carrier promoting metal dispersion play a synergistic role, jointly promoting C - C bond coupling and C - O bond insertion, and improving the selectivity of target products;

[0022] (2) The preparation method of the catalyst of the present invention is simple, the preparation process is short, and it is environmentally friendly and easy to scale up. Detailed implementation mode

[0023] Example 1

[0024] A catalyst for catalytic hydrogenation of carbon dioxide to ethanol, the catalyst is composed of active metals, promoters and a carrier; the active metals are Cu, Co and Ga, the promoters are Mn and Na, and the carrier is carbon nanotubes with a specific surface area of 300 m 2 / g; Calculated according to 100% of the weight of the catalyst, the contents of each component are as follows: Cu 20%, Co 10%, Ga 10%, Na 1%, Mn 3%, and the carrier 56%.

[0025] The preparation method of the catalyst for catalytic hydrogenation of carbon dioxide to ethanol includes the following steps:

[0026] (1) Add the carrier to a 10 moL / L nitric acid solution at a ratio of 1 g:20 mL, heat under reflux at 150 °C for 8 h, filter, wash with deionized water until neutral, dry at 80 °C for 12 h, and grind to obtain the treated carrier.

[0027] (2) Dissolve copper nitrate, cobalt acetate, gallium chloride, manganese acetate, and sodium nitrate in ethanol to obtain a mixed solution with a total metal ion concentration of 0.2 mol / L.

[0028] (3) Add the treated carrier obtained in step (1) to the mixed solution in step (2), ultrasonically treat at an ultrasonic power of 800 w for 2 h, stir to dry at room temperature, then dry at 120 °C for 8 h, calcine in a muffle furnace at 300 °C for 8 h, grind, tablet, form, and sieve through a 20 - 40 mesh sieve to obtain the catalyst.

[0029] Example 2

[0030] A catalyst for the hydrogenation of carbon dioxide to ethanol, which is composed of active metals, promoters, and a carrier; the active metals are Cu, Co, and Ga, the promoters are K and Na, and the carrier is activated carbon with a specific surface area of 890 m 2 / g; calculated by 100% of the catalyst's weight, the contents of each component are as follows: Cu 20%, Co 20%, Ga 5%, Na 3%, K 3%, and the carrier 49%.

[0031] The preparation method of the catalyst for the hydrogenation of carbon dioxide to ethanol includes the following steps:

[0032] (1) Add the carrier to a 5 moL / L nitric acid solution at a ratio of 1 g:20 mL, heat under reflux at 70 °C for 14 h, filter, wash with deionized water until neutral, dry at 100 °C for 10 h, and grind to obtain the treated carrier.

[0033] (2) Dissolve copper nitrate, cobalt chloride, gallium chloride, potassium acetate, and sodium nitrate in ethanol to obtain a mixed solution with a total metal ion concentration of 0.5 mol / L.

[0034] (3) Add the treated carrier obtained in step (1) to the mixed solution in step (2), ultrasonically treat at an ultrasonic power of 200 w for 5 h, stir to dry at room temperature, then dry at 80 °C for 12 h, calcine in a muffle furnace at 380 °C for 4 h, grind, tablet, form, and sieve through a 40 - 60 mesh sieve to obtain the catalyst.

[0035] Example 3

[0036] A catalyst for hydrogenating carbon dioxide to ethanol, the catalyst being composed of an active metal, a promoter, and a support; the active metal is Cu, Co, and Ga, the promoter is K and Na, and the support is graphene with a specific surface area of 590 m 2 / g; calculated by 100% of the weight ratio of the catalyst, the contents of each component are as follows: Cu 10%, Co 20%, Ga 7%, Na 2%, K 1%, and the support 60%.

[0037] The preparation method of the catalyst for hydrogenating carbon dioxide to ethanol includes the following steps:

[0038] (1) According to the ratio of 1 g:10 mL, add the support to an 8 moL / L nitric acid solution, heat and reflux at 120 °C for 9 h, filter, wash with deionized water until neutral, dry at 100 °C for 10 h, and grind to obtain the treated support;

[0039] (2) Dissolve copper chloride, cobalt nitrate, gallium nitrate, potassium chloride, and sodium chloride in water to obtain a mixed solution with a total metal ion concentration of 1 mol / L;

[0040] (3) Add the treated support obtained in step (1) to the mixed solution in step (2), perform ultrasonic treatment at an ultrasonic power of 600 w for 3 h, stir at room temperature until dry, then dry at 110 °C for 7 h, calcine in a muffle furnace at 450 °C for 3 h, grind, tablet, form, and screen through a 20 - 60 mesh sieve to obtain the catalyst.

[0041] Example 4

[0042] A catalyst for hydrogenating carbon dioxide to ethanol, the catalyst being composed of an active metal, a promoter, and a support; the active metal is Cu, Co, and Ga, the promoter is K and Na, and the support is carbon nanotubes with a specific surface area of 300 m 2 / g; calculated by 100% of the weight ratio of the catalyst, the contents of each component are as follows: Cu 20%, Co 20%, Ga 10%, Na 3%, K 1%, and the support 46%.

[0043] The preparation method of the catalyst for hydrogenating carbon dioxide to ethanol includes the following steps:

[0044] (1) According to the ratio of 1 g:20 mL, add the support to a 10 moL / L nitric acid solution, heat and reflux at 150 °C for 3 h, filter, wash with deionized water until neutral, dry at 60 °C for 8 h, and grind to obtain the treated support;

[0045] (2) Dissolve copper chloride, cobalt chloride, gallium chloride, potassium chloride and sodium nitrate in water to obtain a mixed solution with a total metal ion concentration of 0.4 mol / L;

[0046] (3) Add the treated carrier obtained in step (1) to the mixed solution in step (2), perform ultrasonic treatment for 4 h under an ultrasonic power of 400 w, stir until dry at room temperature, then dry at 100 °C for 12 h, calcine in a muffle furnace at 400 °C for 5 h, grind, tablet, form, and screen through a 40 - 60 mesh sieve to obtain the catalyst.

[0047] Comparative Example 1

[0048] A catalyst for catalytic hydrogenation of carbon dioxide to ethanol, the catalyst consists of an active metal, a promoter and a carrier; the active metal is Cu, Co and Ga, the promoter is Mn, and the carrier is carbon nanotubes with a specific surface area of 300 m 2 / g; calculated according to the weight ratio of the catalyst being 100%, the contents of each component are as follows: Cu 20%, Co 10%, Ga 10%, Mn 3%, carrier 57%.

[0049] The preparation method of the catalyst for catalytic hydrogenation of carbon dioxide to ethanol includes the following steps:

[0050] (1) According to the ratio of 1 g:20 mL, add the carrier to 10 moL / L nitric acid solution, heat and reflux at 150 °C for 8 h, filter, wash with deionized water until neutral, dry at 80 °C for 12 h, and grind to obtain the treated carrier;

[0051] (2) Dissolve copper nitrate, cobalt acetate, gallium chloride and sodium nitrate in ethanol to obtain a mixed solution with a total metal ion concentration of 0.2 mol / L;

[0052] (3) Add the treated carrier obtained in step (1) to the mixed solution in step (2), perform ultrasonic treatment for 2 h under an ultrasonic power of 800 w, stir until dry at room temperature, then dry at 120 °C for 8 h, calcine in a muffle furnace at 300 °C for 8 h, grind, tablet, form, and screen through a 20 - 40 mesh sieve to obtain the catalyst.

[0053] Comparative Example 2

[0054] Use SBA - 15 molecular sieve with a specific surface area of 530 m 2 / g to replace the carbon nanotubes with a specific surface area of 300 m 2 / g, and the others are the same as in Example 1.

[0055] Comparative Example 3

[0056] Use carbon nanotubes with a specific surface area of 69 m2 The carbon black support of / g is used to replace the carbon nanotubes with a specific surface area of 300 m 2 / g, and the others are the same as in Example 1.

[0057] Catalytic performance evaluation

[0058] A method for catalytic hydrogenation of carbon dioxide to ethanol is as follows: The catalyst is filled into a fixed-bed reactor, and a hydrogen-containing gas is introduced for reduction activation. Then, the reaction temperature is adjusted to 220 - 300 °C, and a mixed gas of CO2 and H2 is switched in and the pressure is increased to 2 - 5 MPa for reaction;

[0059] Among them, the catalyst is the catalyst of the present invention;

[0060] In the mixed gas of CO2 and H2, the volume ratio of CO2 to H2 is 1:3 - 6, and the space velocity of the mixed gas of CO2 and H2 relative to the catalyst is 3000 - 8000 h -1 ; The conditions for reduction activation are reduction at 250 - 350 °C and normal pressure for 3 - 6 h. Among them, the flow rate of the hydrogen-containing gas is 30 - 100 mL / min, the hydrogen-containing gas is hydrogen or a mixed gas of hydrogen and a balance gas, and the volume fraction of hydrogen in the mixed gas of hydrogen and the balance gas is 5% ≤ hydrogen < 100%, and the balance gas is nitrogen, helium or argon;

[0061] The specific reaction conditions and results are shown in Table 1;

[0062] Table 1 Reaction conditions and results

[0063]

[0064] As can be seen from Table 1, the catalyst provided by the present invention has high catalytic activity and high selectivity for the target product when catalytically hydrogenating carbon dioxide to ethanol. Compared with Example 1, in Comparative Example 1, when the promoter does not contain metal Na, its catalytic activity is significantly reduced; in Comparative Example 2, when the support is replaced with SBA-15 molecular sieve that cannot produce an electronic effect, even if its specific surface area is increased, the catalytic activity still cannot reach that of Example 1 of the present invention, indicating that the support in the present invention not only plays a structural effect of dispersing active components, but also its electronic effect plays an important role; Comparative Example 3 shows that even if the support is replaced with a similar carbon support carbon black, but when the specific surface area of the support is reduced, its catalytic activity is also significantly reduced, indicating that even if the selected support has an electronic effect, but when its specific surface area is too small, it cannot fully play the structural effect of dispersing active components and cannot produce excellent catalytic activity. Thus, it shows that the carbon support in the present invention can promote the synergistic effect of the structural effect and the electronic effect of metal dispersion, improve the selectivity of the target product, and thus improve the catalytic performance.

Claims

1. A catalyst for catalyzing the hydrogenation of carbon dioxide to ethanol, characterized in that: The catalyst is composed of an active metal, an additive and a carrier; the active metal is Cu, Co and Ga, the additive is a combination of any one of Mn or K and Na, and the carrier is a carbon carrier; based on the weight ratio of the catalyst being 100%, the content of each component is as follows: Cu 10-20%, Co 10-20%, Ga 5-10%, Na 1-3%, Mn or K 1-3%, and the balance is the carrier; The specific surface area of ​​the carbon carrier is 300-890m 2 / g.

2. The catalyst for catalyzing the hydrogenation of carbon dioxide to ethanol according to claim 1, characterized in that: The carbon carrier is any one of activated carbon, carbon nanotubes or graphene.

3. The method for preparing the catalyst for catalytic hydrogenation of carbon dioxide to ethanol according to claim 1, characterized in that: The following steps are involved: (1) adding the carrier to a nitric acid solution, heating and refluxing at 70-150° C. for 3-14 hours, filtering, washing with deionized water until neutral, drying, and grinding to obtain a treated carrier; (2) adding metal salts corresponding to the active metal and the auxiliary agent into water or ethanol to obtain a mixed solution of the active metal and the auxiliary agent; (3) Add the treated carrier obtained in step (1) to the mixed solution of step (2), perform ultrasonic treatment for 2-5 hours, stir until dry at room temperature, and then dry, roast, grind, tablet, shape, and sieve through a 20-60 mesh sieve to obtain the catalyst.

4. The method for preparing a catalyst for catalytic hydrogenation of carbon dioxide to ethanol according to claim 3, characterized in that: The metal salts corresponding to the active metal and the auxiliary agent are their corresponding nitrates, chlorides or acetates, and the total concentration of the active metal and the auxiliary agent in the mixed solution is 0.2-1 mol / L.

5. The method for preparing the catalyst for catalytic hydrogenation of carbon dioxide to ethanol according to claim 4, characterized in that: The ratio of the carrier to the nitric acid solution is 1 g: 10-20 mL, and the concentration of the nitric acid solution is 5-10 mol / L.

6. The method for preparing the catalyst for catalytic hydrogenation of carbon dioxide to ethanol according to claim 5, characterized in that: The drying conditions in step (1) are drying at 60-100°C for 8-12h; the drying conditions in step (3) are drying at 80-120°C for 7-12h, and the calcination conditions are calcination at 300-450°C for 3-8h.

7. The method for preparing the catalyst for catalytic hydrogenation of carbon dioxide to ethanol according to claim 5, characterized in that: The power of the ultrasonic treatment is 200-800w.

8. A method for preparing ethanol by catalytic hydrogenation of carbon dioxide, characterized in that: Specifically, the catalyst is loaded into a fixed bed reactor, hydrogen-containing gas is introduced for reduction activation, then the reaction temperature is adjusted to 220-300°C, a mixed gas of CO2 and H2 is introduced, and the pressure is increased to 2-5MPa for reaction; wherein the catalyst is the catalyst described in claim 1.

9. The method for preparing ethanol by catalytic hydrogenation of carbon dioxide according to claim 8, characterized in that: The volume ratio of CO2 to H2 in the mixed gas of CO2 and H2 is 1:3-6, and the space velocity of the mixed gas of CO2 and H2 relative to the catalyst is 3000-8000h -1 The reduction activation conditions are reduction at 250-350°C and normal pressure for 3-6 hours, wherein the flow rate of the hydrogen-containing gas is 30-100 mL / min, the hydrogen-containing gas is hydrogen, or a mixture of hydrogen and a balance gas, the volume proportion of hydrogen in the mixture of hydrogen and the balance gas is 5%≤hydrogen<100%, and the balance gas is nitrogen, helium or argon.

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