CN115228491B - A highly dispersed rhodium-based catalyst and its preparation method and its application in the production of ethanol from carbon dioxide - Google Patents

Abstract

The application discloses a high-dispersion supported rhodium-based catalyst, a preparation method thereof and application thereof in preparing ethanol from carbon dioxide, and mainly solves the problems of low conversion rate and poor high-carbon alcohol selectivity in a carbon dioxide hydrogenation reaction. The catalyst comprises molybdenum carbide, rhodium element and potassium element, wherein the rhodium element and the potassium element are supported on the molybdenum carbide. According to the application, the second active component rhodium with carbonyl insertion function is introduced into the molybdenum carbide catalyst for generating methanol by hydrogenating carbon dioxide, so that the double-active-center synergistic composite catalyst is formed, and under the modification of alkali metal auxiliary agents, high-selectivity hydrogenation of carbon dioxide to ethanol is realized, and meanwhile, the conversion rate of carbon dioxide is higher.

Description

A highly dispersed rhodium-based catalyst, its preparation method and its application in the production of ethanol from carbon dioxide

Technical Field

The present application relates to a highly dispersed rhodium-based catalyst and a preparation method thereof and application in the hydrogenation of carbon dioxide to produce ethanol, belonging to the field of petrochemical industry.

Background technique

As human society develops rapidly, it consumes a large amount of fossil energy and emits a large amount of greenhouse gases, such as carbon dioxide and methane. This has led to the world facing increasingly severe energy and environmental crises. Carbon dioxide is a cheap, non-toxic gas with a wide range of sources. Its resource utilization and catalytic conversion into fuels with high industrial value such as formic acid, alcohols and even fuel oil can improve the utilization rate of carbon resources on the one hand, and help solve the environmental problem of global warming on the other.

As a high-energy-density fuel, ethanol can not only be used as an automobile fuel additive in current practical applications, but can also completely replace traditional gasoline and use ethanol fuel as the main power source. At the same time, as a common chemical solvent, it is also widely used in cosmetics, medicine, pesticides and other fields. Therefore, converting carbon dioxide into ethanol is one of the most ideal products for realizing the "liquid sunshine" (Joule 2018, 2 (10), 1925–1949) strategy of efficiently utilizing renewable energy (solar energy).

At present, in the catalytic hydrogenation of _CO2 to produce ethanol, homogeneous catalysts generally have relatively high activity and selectivity, but due to the metal complex catalysts (CN 104995161A, US 8912240B2) used in the reaction process, not only are they expensive and have poor stability, but also the difficulty of separation from the product after the reaction is an unavoidable problem. In view of these characteristics of homogeneous catalysis, scientists have been committed to the research of _CO2 efficient hydrogenation heterogeneous catalysts. Among them, modified Fischer-Tropsch catalysts (such as Fe-based, Co-based, etc.) have received extensive attention because of their high carbon chain growth ability. However, directly using CO2 hydrogenation catalysts for _CO2 hydrogenation reaction, there are still many problems, because _CO2 hydrogenation to produce ethanol is not the same as the mechanism of ethanol production from synthesis gas, and there are relatively few catalysts developed for the hydrogenation characteristics of _CO2 . When traditional Fischer-Tropsch modified catalysts are used in CO ₂ hydrogenation reactions, the CO ₂ conversion rate is low and a large amount of low-carbon alkanes are still generated in the hydrogenation products. The liquid alcohol products after the reaction conform to the ASF distribution. In addition to ethanol, the products also contain mixed alcohols such as methanol and propanol, and the degree of carbon chain growth cannot be accurately controlled. At the same time, the effective catalyst starting temperature of Fischer-Tropsch catalysts is generally 300°C or above. Higher reaction temperatures also mean higher energy consumption and more by-products.

In summary, the current homogeneous catalysts for catalytic _CO2 hydrogenation to ethanol have high requirements for reaction equipment, complex process flow, poor stability, and short catalyst life; while heterogeneous catalysts require high reaction temperatures, large process energy consumption, and many by-products, and the catalyst activity is not high, and the ethanol selectivity is low. When the _CO2 conversion rate is greater than 10%, the ethanol selectivity will be less than 40%. Therefore, in order to realize the resource utilization of _CO2 and reduce dependence on fossil energy, it is necessary to develop an efficient heterogeneous catalyst with high activity and high ethanol selectivity for _CO2 conversion under mild conditions.

Summary of the invention

In the process of _CO2 hydrogenation to ethanol, the adsorption and activation of _CO2 and hydrogen are the prerequisites for the reaction to occur. _CO2 , as a non-polar molecule, is highly inert and difficult to activate. Due to its special electron structure, molybdenum carbide has the properties of precious metals, so it has a strong activation ability for both _CO2 and hydrogen. The object of the present invention is to provide a highly active, especially highly selective, _CO2 hydrogenation catalyst for ethanol production based on the characteristics of _CO2 hydrogenation reaction.

The present invention uses molybdenum carbide, which can effectively activate _CO2 and hydrogen, as a carrier, utilizes the ability of precious metal rhodium to dissociate and adsorb _CO2 to form carbonyl species and form initial carbon-carbon bonds, and anchors the precious metal rhodium on the molybdenum carbide carrier, thereby obtaining a new bifunctional catalyst with high activity and good stability in the _CO2 hydrogenation reaction.

The technical problem to be solved by the present invention is to improve the catalyst preparation method in view of the problem that _CO2 is difficult to activate and the selectivity of the hydrogenation product ethanol is not high, further introduce alkali metal potassium, and regulate the ability of the molybdenum carbide carrier to adsorb and activate _CO2 to generate intermediates, thereby improving the selectivity and activity of the catalyst in the carbon dioxide hydrogenation reaction to produce ethanol.

The present invention provides a molybdenum carbide-based hydrogenation catalyst with high catalyst efficiency and a preparation method thereof, the method being simple, easy to control and highly operable. The present invention not only improves the stability of the catalyst and reduces the loading amount of the noble metal rhodium of the catalyst by regulating the loading amount of the noble metal rhodium and combining the stabilizing effect of the molybdenum carbide carrier. The introduction of rhodium plays an important role in the establishment and stability of the bifunctional active center, and the amount of rhodium added will directly affect its hydrogenation properties. The catalyst prepared by the present invention has high reaction activity and high ethanol selectivity, and has great application prospects for _CO2 hydrogenation to ethanol.

According to one aspect of the present application, a supported rhodium-based catalyst is provided, wherein the catalyst comprises molybdenum carbide, a rhodium element, and a potassium element, wherein the rhodium element and the potassium element are supported on the molybdenum carbide.

The rhodium element is an active element;

The potassium element is an auxiliary element;

The rhodium element is loaded on molybdenum carbide in the form of a single substance;

The mass ratio of the rhodium element to the carrier is 0.001:1 to 0.5:1;

The mass ratio of the potassium element to the carrier is 0.001:1 to 0.5:1.

Further optionally, the upper limit of the mass ratio of the rhodium element to the carrier can be independently selected from 0.5:1, 0.4:1, and 0.3:1; the lower limit of the mass ratio of the rhodium element to the carrier can be independently selected from 0.001:1, 0.002:1, and 0.003:1.

Further optionally, the upper limit of the mass ratio of the potassium element to the carrier can be independently selected from 0.5:1, 0.4:1, and 0.3:1; the lower limit of the mass ratio of the potassium element to the carrier can be independently selected from 0.001:1, 0.002:1, and 0.003:1.

According to another aspect of the present application, a method for preparing the supported rhodium-based catalyst is provided, the method comprising at least the following steps:

Step (1) a precursor solution and an aromatic amine compound undergo an organic-inorganic hybrid reaction to prepare a composite;

Step (2) mixing a precursor solution containing potassium element with the composite to prepare a supported rhodium-based catalyst;

Optionally, the method of step (1) is selected from at least one of impregnation, coprecipitation or deposition precipitation;

The method of step (2) is selected from at least one of impregnation, coprecipitation or deposition precipitation.

In step (1), the precursor solution contains a precursor of rhodium element and a precursor of molybdenum element;

Optionally, the precursor of the rhodium element is selected from at least one of rhodium chloride, rhodium nitrate and rhodium sulfate;

The precursor of the molybdenum element is selected from at least one of molybdic acid, paramolybdic acid, molybdate and paramolybdate;

The aromatic amine compound is aniline; the concentration of the aniline is 0.1 to 10 mol/L;

Further optionally, the upper limit of the aniline concentration can be independently selected from 8 mol/L, 8.5 mol/L, 9 mol/L, 9.5 mol/L, 10 mol/L; the lower limit of the aniline concentration can be independently selected from 0.1 mol/L, 0.5 mol/L, 1.0 mol/L, 1.5 mol/L, 2 mol/L.

The precursor containing potassium in step (2) is selected from at least one of potassium chloride, potassium carbonate and potassium nitrate;

The concentration of the potassium element is 0.1-10 mol/L, calculated as potassium ion concentration.

Further optionally, the upper limit of the concentration of the potassium element can be independently selected from 8mol/L, 8.5mol/L, 9mol/L, 9.5mol/L, and 10mol/L; the lower limit of the concentration of the potassium element can be independently selected from 0.5mol/L, 1.0mol/L, 2mol/L, 3mol/L, and 4mol/L.

Optionally, the precursor solution in step (1) includes a solvent and hydrochloric acid;

The solvent is selected from deionized water;

The carbonization reaction is carried out in a stirring manner.

Optionally, in step (2), before the mixing, the step further includes pre-treating the composite;

The pretreatment includes drying and calcining in sequence;

In step (2), after the mixing, a post-treatment process is also included, and the post-treatment process includes stirring, calcining and reducing in sequence.

Optionally, in step (1), the pH value of the precursor solution is 3 to 5;

Further optionally, the pH value of the mixed solution can be independently selected from 3, 4, and 5;

In the step (1), the stirring temperature is 25 to 80° C. and the stirring time is 1 to 12 hours;

Further optionally, the stirring temperature can be independently selected from 25°C, 50°C, 80°C;

Further optionally, the stirring time can be independently selected from 1 h, 6 h, and 12 h.

In the pretreatment of step (2), the drying temperature is 60 to 100° C. and the drying time is 5 to 12 hours;

Further optionally, the drying temperature may be independently selected from 60°C, 80°C, 100°C;

Further optionally, the drying time can be independently selected from 5h, 10h, 12h;

In the pretreatment of step (2), the calcination temperature is 500-800° C. and the calcination time is 3-6 hours;

The calcination heating rate is 2°C/min;

Further optionally, the calcination temperature may be independently selected from 500°C, 600°C, 800°C;

Further optionally, the calcination time can be independently selected from 3h, 4h, 5h, 6h;

In the pretreatment of step (2), the calcination is carried out under an inert atmosphere;

Optionally, in the pretreatment of step (2), the inert atmosphere is an argon atmosphere.

Optionally, in the step (2), in the post-treatment process, the stirring temperature is 25°C to 60°C;

The stirring time is 1 to 12 hours;

Further optionally, the stirring time can be independently selected from 1h, 6h, 12h;

Further optionally, the stirring temperature can be independently selected from 25°C, 30°C, 40°C, 50°C, 60°C;

Optionally, in the step (2), in the post-treatment process, the calcination temperature is 200-500° C.; the calcination time is 3-6 hours; the calcination heating rate is 2° C./min;

Further optionally, the calcination temperature may be independently selected from 200°C, 300°C, 400°C, 500°C;

Further optionally, the calcination time can be independently selected from 3h, 4h, 5h, 6h;

In the post-treatment process, the calcination is carried out under an inert atmosphere;

In the post-treatment process, the inert atmosphere is an argon atmosphere;

In the post-treatment step, the reduction is performed under a hydrogen atmosphere.

Optionally, in the step (2), in the post-treatment process, the reduction temperature is 200 to 400° C.; the reduction time is 1 to 3 hours;

The reduction heating rate is 2°C/min;

Further optionally, the reduction temperature may be independently selected from 200°C, 300°C, 400°C;

Further optionally, the reduction time can be independently selected from 1h, 2h, 3h;

According to another aspect of the present application, a method for preparing ethanol by hydrogenating carbon dioxide is provided, wherein the above-mentioned supported rhodium-based catalyst or the supported rhodium-based catalyst prepared according to the above-mentioned method is mixed with a solvent, and the mixture is contacted and reacted with a mixed gas containing carbon dioxide and hydrogen to prepare ethanol.

Optionally, the method comprises at least the following steps:

The supported rhodium-based catalyst is placed in a reactor, a solvent is added, carbon dioxide is introduced, and after the air inside the reactor is replaced, a mixed gas of carbon dioxide and hydrogen is introduced to reach the reaction pressure; a contact reaction occurs to prepare ethanol;

Optionally, the mass ratio of the supported rhodium-based catalyst to the solvent is 0.01 to 0.1;

Further optionally, the upper limit of the mass ratio of the supported rhodium-based catalyst to the mass ratio of the solvent can be independently selected from 0.06, 0.07, 0.08, 0.09, and 0.1; the lower limit of the mass ratio of the supported rhodium-based catalyst to the mass ratio of the solvent can be independently selected from 0.01, 0.02, 0.03, 0.04, and 0.05.

Optionally, the volume ratio of carbon dioxide to hydrogen is 1:1 to 1:6;

Further optionally, the upper limit of the volume ratio of carbon dioxide to hydrogen can be independently selected from 1:1, 1:1.5, 1:2, 1:2.5, 1:3; the lower limit of the volume ratio of carbon dioxide to hydrogen can be independently selected from 1:4, 1:4.5, 1:5, 1:5.5, 1:6.

Optionally, the reaction temperature is 100-300° C.; the reaction time is 0.5 h to 20 h.

Further optionally, the reaction temperature may be independently selected from 100°C, 200°C, 300°C;

Further optionally, the upper limit of the reaction time can be independently selected from 16h, 17h, 18h, 19h, 20h; the lower limit of the reaction time can be independently selected from 0.5h, 1.5h, 2.5h, 3.5h, 4.5h;

Optionally, the solvent is selected from at least one of water, N,N-dimethylformamide, cyclohexane, dichloromethane, and 1,4-dioxane;

The mass ratio of the supported rhodium-based catalyst to carbon dioxide is 1:10 to 1:1;

Further optionally, the upper limit of the mass ratio of the supported rhodium-based catalyst to carbon dioxide can be independently selected from 1:1, 1:1.5, 1:2, 1:2.5, 1:3; the lower limit of the mass ratio of the supported rhodium-based catalyst to carbon dioxide can be independently selected from 1:8, 1:8.5, 1:9, 1:9.5, 1:10;

The reaction pressure is 0.5-8Mpa;

Further optionally, the upper limit of the reaction pressure can be independently selected from 4.0 MPa, 5.0 MPa, 6.0 MPa, 7.0 MPa, and 8.0 MPa; the lower limit of the reaction pressure can be independently selected from 0.5 MPa, 1.0 MPa, 1.5 MPa, 2.0 MPa, and 2.5 MPa.

Compared with the prior art, this application has the following beneficial effects:

(1) Due to its special electronic structure, molybdenum carbide has the properties of precious metals. Molybdenum carbide can be used as a carrier to effectively adsorb and activate _CO2 and hydrogen at the same time. By introducing the second active component rhodium with carbonyl insertion function into the molybdenum carbide catalyst that has the function of hydrogenating carbon dioxide to produce methanol, the rhodium element is loaded on the molybdenum carbide. By regulating the content and valence state of the metal rhodium, a composite catalyst with dual active centers is formed, which makes the catalyst have good catalytic activity in the carbon dioxide hydrogenation reaction, and achieves high selectivity of carbon dioxide hydrogenation to ethanol while having a high carbon dioxide conversion rate.

(2) The introduction of alkali metal potassium as an auxiliary component further regulates the surface electronic structure of the catalyst. On the one hand, the introduction of alkaline metal promotes the adsorption and activation of acidic _CO2 . On the other hand, it also plays a role in regulating the adsorption and activation of hydrogen by the carrier molybdenum carbide, thereby achieving higher catalytic activity and ethanol selectivity while obtaining higher catalyst stability.

(3) The catalyst has a simple preparation method, high catalytic efficiency, strong operability, and is easy to control, and has broad development space and market application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is an XRD diagram of molybdenum carbide in the catalyst sample prepared in Example 1;

FIG. 2 is an XPS graph of elemental rhodium in the catalyst sample prepared in Example 1.

Detailed ways

The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

In the examples of the present application, the catalyst evaluation, conversion rate and selectivity calculation methods are as follows:

The activity evaluation of the catalyst in the _CO2 hydrogenation to ethanol reaction was carried out in a high-pressure closed reactor. The specific experimental process is as follows:

50 mg of catalyst was placed in a high-pressure sealed reactor and 5 ml of solvent was added. At room temperature, the air in the reactor was replaced with high-purity CO ₂ for three times, and then high-pressure H ₂ (the molar ratio of carbon dioxide, hydrogen, and nitrogen was 1:3:1, with nitrogen as an internal standard) was introduced. The reaction was carried out at 150°C for 10 hours. After the reaction was completed, it was cooled to room temperature, the gas in the reactor was collected with an air bag, and the residual liquid was further centrifuged to take the supernatant. The gas phase product and the liquid phase product were detected and analyzed offline on an Agilent 7890B chromatograph, equipped with two detectors, TCD and FID, and two chromatographic columns, TDX-01 (2.0 m×2 mm) and FFAP (30.0 m×0.32 mm×1 μm), wherein the TDX-01 chromatographic column was used to detect and analyze the gas phase product, and the FFAP chromatographic column was used to detect and analyze CH ₃ OH and CH ₃ CH ₂ OH.

The _CO2 conversion rate is calculated based on the amount of _CO2 reduction, using the following formula:

The products generated by the reaction are mainly CH ₃ OH and CH ₃ CH ₂ OH. The calculation formula for the selectivity of each product is as follows:

In the formula, x(in) (x represents CO ₂ , N ₂ ) represents the concentration of x in the feed gas, and x(out) represents the concentration of x in the liquid product tail gas.

Example 1

Step (1) Weigh 0.04 g of RhCl ₃ ·3H ₂ O and 5.20 g of (NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O respectively, dissolve in 100 ml of deionized water, add aniline, the concentration of aniline is 1 mol/L, and continue stirring. Slowly drop 1 mol/L HCl solution into the above solution, adjust the pH to 4, and then continue stirring in a 50° C. water bath for 6 h; after the reaction is completed, the generated white solid is washed with 400 ml of ethanol, filtered, and dried at 80° C. for 10 h; after drying, the solid is placed in a tube furnace, heated to 600° C. at 2° C./min in an argon atmosphere, and calcined for 5 h to obtain a composite.

Step (2) completely dissolving soluble potassium carbonate in deionized water with a potassium ion concentration of 0.5 mol/L, then adding the above-mentioned complex, stirring at 25° C. for 6 hours, and evaporating to dryness; placing the evaporated solid in a tubular furnace, heating to 400° C. at 2° C./min under an argon atmosphere, and calcining for 4 hours; after cooling to room temperature, heating to 300° C. at 2° C./min under a hydrogen atmosphere, reducing for 2 hours, and finally obtaining a supported rhodium-based catalyst sample.

As can be seen from FIG1 , the carrier is molybdenum carbide crystals, and the molybdenum carbide has a high degree of crystallinity. As can be seen from FIG2 , the rhodium element exists in the catalyst in the form of a single substance.

Embodiments 2 to 23

The method is the same as that in Example 1, except that the process conditions for the preparation are changed respectively, and the product is used for the reaction of hydrogenating carbon dioxide to produce ethanol at 150°C, 5 MPa and 1,4-dioxane. The preparation conditions and evaluation results different from those in Example 1 are detailed in Table 1.

Table 1 Effect of different preparation process conditions on the performance of carbon dioxide hydrogenation to ethanol catalyst

Embodiment 24

Weigh 0.02 g of RhCl ₃ ·3H ₂ O and 5.20 g of (NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O respectively and dissolve them in 100 ml of deionized water. Add aniline to a concentration of 1 mol/L and continue stirring. Slowly drop 1 mol/L HCl solution into the above solution to adjust the pH to 4, and then continue stirring in a water bath at 50°C for 6 hours; after the reaction is completed, the generated white solid is washed with 400 ml of ethanol, filtered, and dried at 80°C for 10 hours; after drying, the solid is placed in a tubular furnace, heated to 600°C at 2°C/min under an argon atmosphere and calcined for 5 hours to obtain a composite; soluble potassium carbonate is completely dissolved in deionized water with a potassium ion concentration of 0.5 mol/L, and then the above composite is added, stirred at 25°C for 6 hours, and evaporated to dryness; the evaporated solid is further placed in a tubular furnace, heated to 400°C at 2°C/min under an argon atmosphere, and calcined for 4 hours; after cooling to room temperature, heated to 300°C at 2°C/min under a hydrogen atmosphere, reduced for 2 hours, and finally a supported rhodium-based catalyst sample is obtained.

Embodiment 25

The preparation steps are the same as those in Example 1, except that the amount of RhCl ₃ ·3H ₂ O added is increased to 0.06 g.

Embodiment 26

The preparation steps are the same as those in Example 1, except that the amount of RhCl ₃ ·3H ₂ O added is increased to 0.08 g.

Embodiment 27

The preparation steps are the same as those in Example 1, except that the potassium ion concentration is 1 mol/L.

Embodiment 28

The preparation steps are the same as those in Example 1, except that the potassium ion concentration is 2 mol/L.

Embodiment 29

The preparation steps are the same as those in Example 1, except that the potassium ion concentration is 4 mol/L.

Embodiment 30

The catalysts prepared in Example 1 and Examples 24, 25 and 26 were used in the reaction of hydrogenating carbon dioxide to produce ethanol at 150°C, 5 MPa and 1,4-dioxane. The performances thereof are listed in Table 2.

Table 2 Effect of different Rh loadings on the performance of CO2 hydrogenation to ethanol catalysts

Table 2 shows that the catalytic activity of CO ₂ hydrogenation is: Example 26> Example 25> Example 24> Example 1; and the selectivity of ethanol is: Example 26< Example 25< Example 24< Example 1. This indicates that the preferred amount of RhCl ₃ ·3H ₂ O added is 0.02-0.04 g. When the amount of RhCl ₃ ·3H ₂ O added is greater than 0.04 g, as the amount of rhodium loading increases, the hydrogenation capacity of the catalyst is enhanced, and the rate of methanol generation is greater than the rate of ethanol generation, so that the selectivity of ethanol decreases as the rhodium content increases.

Embodiment 31:

The catalysts prepared in Example 1 and Examples 27, 28 and 29 were used in the reaction of hydrogenating carbon dioxide to produce ethanol at 150°C, 5 MPa and 1,4-dioxane. The performances thereof are listed in Table 3.

Table 3 Effect of different K loadings on the performance of CO2 hydrogenation to ethanol catalysts

As can be seen from Table 3, the catalytic activity of CO ₂ hydrogenation is: Example 27> Example 1> Example 28> Example 29; the selectivity of ethanol is: Example 27> Example 1> Example 28> Example 29. This shows that the proper increase in the content of potassium metal can not only improve the catalytic activity of CO ₂ hydrogenation, but also improve the selectivity of ethanol. The preferred potassium ion concentration is 0.5-1 mol/L. When the potassium ion concentration is greater than 1 mol/L, the activation conversion of CO ₂ is inhibited, the hydrogenation efficiency is weakened, resulting in reduced activity, and the excessively high potassium content also affects the carbon-carbon coupling process, resulting in reduced selectivity of ethanol.

The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical contents disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims (17)

1. A supported rhodium-based catalyst for preparing ethanol by carbon dioxide hydrogenation is characterized in that,

The catalyst comprises molybdenum carbide, rhodium element and potassium element;

the rhodium element and the potassium element are supported on the molybdenum carbide;

the rhodium element is loaded on molybdenum carbide in a simple substance form;

The mass ratio of rhodium to the carrier is 0.001:1-0.5:1;

the mass ratio of the potassium element to the carrier is 0.001:1-0.5:1;

the preparation method of the supported rhodium-based catalyst at least comprises the following steps:

Step (1): carrying out organic-inorganic hybridization reaction on the precursor solution and an aromatic amine compound to prepare a compound;

step (2): mixing a precursor solution containing potassium element with the compound to prepare a supported rhodium-based catalyst;

in the step (1), the precursor solution contains a precursor of rhodium element and a precursor of molybdenum element;

the aromatic amine compound is aniline; the concentration of the aniline is 0.1-10 mol/L;

The concentration of the potassium element is 0.5-1 mol/L, calculated by the concentration of potassium ions;

the precursor solution in the step (1) comprises a solvent and hydrochloric acid;

step (2), before mixing, further comprising a step of pretreating the composite;

The pretreatment comprises drying and calcination in sequence, wherein the calcination temperature is 500-800 ℃; the calcination time is 3-6 hours;

after mixing, the method further comprises a post-treatment procedure, wherein the post-treatment procedure sequentially comprises stirring, calcining and reducing;

the pH value of the precursor solution is 3-5.

2. A process for the preparation of the supported rhodium-based catalyst of claim 1, said process comprising at least the steps of:

Step (1): carrying out organic-inorganic hybridization reaction on the precursor solution and an aromatic amine compound to prepare a compound;

step (2): mixing a precursor solution containing potassium element with the compound to prepare a supported rhodium-based catalyst;

in the step (1), the precursor solution contains a precursor of rhodium element and a precursor of molybdenum element;

the aromatic amine compound is aniline; the concentration of the aniline is 0.1-10 mol/L;

The concentration of the potassium element is 0.5-1 mol/L, calculated by the concentration of potassium ions;

the precursor solution in the step (1) comprises a solvent and hydrochloric acid;

step (2), before mixing, further comprising a step of pretreating the composite;

the pretreatment comprises drying and calcination in sequence, wherein the calcination temperature is 500-800 ℃, and the calcination time is 3-6 hours;

after mixing, the method further comprises a post-treatment procedure, wherein the post-treatment procedure sequentially comprises stirring, calcining and reducing;

the pH value of the precursor solution is 3-5.

3. The method according to claim 2, wherein,

The precursor of rhodium element is at least one of rhodium chloride, rhodium nitrate and rhodium sulfate; the precursor of molybdenum element is at least one of molybdic acid, paramolybdic acid, molybdate and paramolybdate.

4. The method according to claim 2, wherein,

In the step (2), the precursor of the potassium element is at least one selected from potassium chloride, potassium carbonate and potassium nitrate.

5. The method according to claim 2, wherein,

In step (1), the solvent is selected from deionized water;

the organic-inorganic hybridization reaction adopts a stirring mode.

6. The method according to claim 5, wherein,

In the step (1), the stirring temperature is 25-80 ℃; the stirring time is 1-12 h.

7. The method according to claim 2, wherein,

In the step (2), the pretreatment conditions are as follows: the drying temperature is 60-100 ℃, and the drying time is 5-12 hours; the calcination is performed under inert atmosphere conditions.

8. The method according to claim 7, wherein,

The inactive atmosphere is an argon atmosphere.

9. The method according to claim 2, wherein,

In the step (2), in the post-treatment step, the stirring temperature is 25-60 ℃; stirring time is 1-12 h; the calcination temperature is 200-500 ℃; the calcination time is 3-6 hours; the calcination is performed under inert atmosphere conditions.

10. The method according to claim 9, wherein,

The inactive atmosphere is an argon atmosphere.

11. The method according to claim 2, wherein,

The reduction is carried out under the condition of hydrogen atmosphere; the reduction temperature is 200-400 ℃; the reduction time is 1-3 h.

12. A method for preparing ethanol by hydrogenating carbon dioxide is characterized by comprising the following steps: mixing the supported rhodium-based catalyst according to claim 1 or the supported rhodium-based catalyst prepared by the preparation method according to any one of claims 2-11 with a solvent, and performing contact reaction with a mixed gas containing carbon dioxide and hydrogen to prepare ethanol.

13. Method according to claim 12, characterized in that it comprises at least the following steps:

Placing the supported rhodium-based catalyst into a reaction kettle, adding a solvent, introducing carbon dioxide, replacing air in the reaction kettle, and introducing a mixed gas of carbon dioxide and hydrogen into the reaction kettle to reach the reaction pressure; and (3) carrying out contact reaction to prepare the ethanol.

14. The method of claim 12, wherein the step of determining the position of the probe is performed,

The volume ratio of the carbon dioxide to the hydrogen is 1:1-1:6.

15. The method of claim 12, wherein the step of determining the position of the probe is performed,

The reaction temperature is 100-300 ℃; the reaction time is 0.5 h-20 h.

16. The method of claim 12, wherein the step of determining the position of the probe is performed,

The solvent is at least one selected from water, N-dimethylformamide cyclohexane, dichloromethane and 1,4 dioxane.

17. The method of claim 13, wherein the step of determining the position of the probe is performed,

The reaction pressure is 0.5-8 mpa.