Preparation method and application of catalyst for preparing olefin through hydrogenation of carbon dioxide

Abstract

The invention relates to the technical field of catalysts, and discloses a preparation method and application of a catalyst for preparing olefin through carbon dioxide hydrogenation. The preparation method comprises the following steps: fully dipping graphite in a mixed solution of dodecane and hexadecane, and taking out to obtain a catalyst carrier; and loading the Fe element and the Mg element into the catalyst carrier by adopting a method of co-precipitating and then roasting to obtain the catalyst for preparing olefin by hydrogenation of carbon dioxide. The catalyst prepared by the preparation method has high stability when being used in a reaction for preparing olefin through hydrogenation of carbon dioxide, can maintain high catalytic activity after long-term use, and has high olefin selectivity at the same time.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a preparation method and application of a carbon dioxide hydrogenation olefin catalyst. BACKGROUND

[0002] With the development of economy and the extensive use of fossil fuels, the concentration of CO2 in the atmosphere has risen sharply, leading to environmental problems such as global climate change, glacier melting and ocean acidification. Reducing carbon emissions has become a global focus. CO2 hydrogenation to olefins is a clean energy technology that uses renewable H2 and recycled CO2 to produce olefins, which not only has economic benefits, but also can alleviate environmental problems.

[0003] Fe-based catalysts are currently a research hotspot for CO2 hydrogenation to olefins due to their environmental friendliness, low cost, and high activity and stability. However, existing Fe-based catalysts face the following problems: low CO2 conversion rate; insufficient olefin selectivity, with a small proportion of product olefins in total hydrocarbons; poor catalyst stability, with Fe being easily oxidized during the reaction, leading to slow deactivation of the catalyst.

[0004] Patent CN104437504A discloses a catalyst for efficient conversion of CO2 to low-carbon olefins, which improves the CO2 conversion rate and low-carbon olefin selectivity by doping transition metal elements in the Fe-based catalyst, but cannot solve the problem of poor catalyst stability due to the easy oxidation of Fe during the reaction. SUMMARY

[0005] To solve the technical problem of poor stability of existing Fe-based catalysts, the present application provides a preparation method and application of a carbon dioxide hydrogenation olefin catalyst. The catalyst obtained by the preparation method of the present application has high stability when used in carbon dioxide hydrogenation to olefins, can maintain high catalytic activity after long-term use, and also has high olefin selectivity.

[0006] The specific technical solutions of the present application are as follows: In a first aspect, the present application provides a preparation method of a carbon dioxide hydrogenation olefin catalyst, comprising the following steps: S1: graphite is fully immersed in a mixture of dodecane and hexadecane and then taken out to obtain a catalyst carrier; S2: Fe and Mg elements are loaded into the catalyst carrier by a co-precipitation and calcination method to obtain a carbon dioxide hydrogenation olefin catalyst.

[0007] The graphite is modified by dodecane and hexadecane, and the obtained hydrophobic graphite is used as a catalyst carrier, which can produce the following effects: when the graphite is immersed in a mixed solution of dodecane and hexadecane, the dodecane can quickly fill the small pores on the surface of the graphite, promote the adhesion of the hexadecane, and then the hexadecane is further attached to the surface of the graphite, which is conducive to the formation of a dense hydrophobic layer. In the subsequent calcination process, the dodecane and hexadecane are partially decomposed, and the alkyl groups are still retained on the graphite to form a hydrophobic layer. Through the above-mentioned way, the dodecane and hexadecane cooperate with each other, which can improve the hydrophobicity of the catalyst to a greater extent. When the catalyst is used in the reaction of carbon dioxide hydrogenation to olefin, the hydrophobicity of the catalyst can help to reduce the contact between the active sites in the catalyst and the water produced in the reaction, thereby alleviating the problem of oxidation deactivation of the active sites and improving the stability of the catalyst.

[0008] In addition, by adding Mg element to the iron-based catalyst, more low-coordination Fe atoms can be generated in the catalyst, thereby improving the catalytic activity of the catalyst. At the same time, the addition of Mg element can also change the electron cloud density of Fe atoms, make the reaction more inclined to the reaction path of generating olefins, and reduce the difficulty of loading Fe element on the hydrophobic graphite.

[0009] Preferably, in step S1, the mass ratio of dodecane to hexadecane is 1:1-3.

[0010] Within the above ratio range, dodecane and hexadecane can better cooperate to improve the hydrophobicity of the catalyst, and further make the catalyst have better stability, which can maintain high catalytic activity after long-term use.

[0011] Preferably, before step S2, the catalyst carrier is mixed with a nitrogen source, ball milled at 400-700 r / min for 180-250 min, and then calcined at 300-350 DEG C for 3.5-4.5 h in an inert atmosphere.

[0012] Through the above-mentioned way, nitrogen atom doping and more vacancy defects can be formed in the catalyst carrier, thereby providing more loading sites for Fe element and Mg element, improving the loading amount and stability of Fe element and Mg element in the catalyst, and thereby giving the catalyst higher catalytic activity and stability. In addition, nitrogen atom doping also helps to improve the adsorption capacity of the catalyst for the reaction intermediate CO, and promotes the carbon dioxide hydrogenation to olefins reaction.

[0013] Further, the mass ratio of the catalyst carrier to the nitrogen source is 1:0.3-0.6.

[0014] Further, the nitrogen source is urea.

[0015] Further, the ball milling process is carried out by using a planetary ball mill.

[0016] As preferred, in step S1, the method of sufficient impregnation is: after stirring and mixing uniformly, continue stirring at 220-260℃ for 4-24h.

[0017] As preferred, in step S2, while loading Fe element and Mg element into the catalyst carrier, Na element is doped into the catalyst carrier by impregnation and calcination method.

[0018] As preferred, the specific process of step S2 comprises: S2.1: drop the solution containing Fe 3+ and Mg 2+ and the alkaline solution into the catalyst carrier dispersion, after precipitation reaction, separate the product; S2.2: grind the product of step S2.1, disperse into the solution containing Na + , and remove the solvent; S2.3: calcine the product of step S2.2 at 300-350℃ in inert atmosphere for 4-5h, to obtain the carbon dioxide to olefin hydrogenation catalyst.

[0019] Further, in step S2.1, the molar ratio of Fe 3+ and Mg 2+ is 1:0.5-1.0, the mass ratio of the catalyst carrier and Fe 3+ is 1:0.2-0.4; in step S2.2, the mass ratio of the product of step S2.1 and Na + is 1:0.01-0.05.

[0020] Further, in step S2.1, the alkaline solution is sodium acetate solution or sodium carbonate solution.

[0021] Further, in step S2.1, during the precipitation reaction, the pH is controlled at 8.0-12.0, the temperature is 60-80℃, and the time is 0.5-1h.

[0022] In the second aspect, the application provides an application of a catalyst in carbon dioxide to olefin hydrogenation reaction, wherein the catalyst is prepared by the above preparation method.

[0023] Compared with the prior art, the application has the following advantages: (1) The application uses dodecane and hexadecane to modify graphite, and the dodecane and hexadecane cooperate with each other, which can improve the hydrophobicity of the catalyst to a greater extent, and further improve the stability of the catalyst. (2) The application can reduce the difficulty of loading Fe element on hydrophobic graphite by introducing Mg element in the Fe-based catalyst, form more low-coordination Fe atoms, thereby improving the catalytic activity, and change the electron cloud density of Fe atoms, thereby improving the olefin selectivity. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the CO2 conversion rate curve of the CO2 hydrogenation reaction using the catalyst in Example 2.

[0025] Figure 2 is the CO2 conversion rate curve of the CO2 hydrogenation reaction using the catalyst in Comparative Example 1. DETAILED DESCRIPTION

[0026] The application will be further described below with reference to examples.

[0027] A preparation method of a carbon dioxide hydrogenation to olefin catalyst, comprising the following steps: S1: graphite is fully immersed in a mixture of dodecane and hexadecane, and then taken out to obtain a catalyst carrier; S2: Fe element and Mg element are loaded into the catalyst carrier by a co-precipitation and calcination method to obtain a carbon dioxide hydrogenation to olefin catalyst.

[0028] In some embodiments, in step S1, the mass ratio of dodecane to hexadecane is 1:1-3.

[0029] In some embodiments, before step S2, the catalyst carrier is mixed with a nitrogen source, ball milled at 400-700 r / min for 180-250 min, and then calcined at 300-350°C for 3.5-4.5 h in an inert atmosphere. Optionally or preferably: the mass ratio of the catalyst carrier to the nitrogen source is 1:0.3-0.6; the nitrogen source is urea; and the ball milling process is performed using a planetary ball mill.

[0030] In some embodiments, in step S1, the method of fully immersing is: after stirring and mixing uniformly, continue to stir at 220-260°C for 4-24 h.

[0031] In some embodiments, in step S2, while loading Fe element and Mg element into the catalyst carrier, Na element is doped in the catalyst carrier by an impregnation and calcination method.

[0032] In some embodiments, the specific process of step S2 comprises: S2.1: Fe 3+ and Mg 2+The solution and the alkaline solution are added dropwise into the catalyst carrier dispersion liquid, a precipitation reaction is carried out, and then the product is separated; In this step, optionally or preferably, the molar ratio of Fe 3+ and Mg 2+ is 1:0.5-1.0, the mass ratio of the catalyst carrier and Fe 3+ is 1:0.2-0.4, the alkaline solution is a sodium acetate solution or a sodium carbonate solution, and in the precipitation reaction, the pH is controlled to be 8.0-12.0, the temperature is 60-80℃, and the time is 0.5-1h; S2.2: The product of step S2.1 is ground and then dispersed into a solution containing Na + , and the solvent is removed; In this step, optionally or preferably, the mass ratio of the product of step S2.1 and Na + is 1:0.01-0.05; S2.3: The product of step S2.2 is calcined at 300-350℃ in an inert atmosphere for 4-5h to obtain a carbon dioxide hydrogenation to olefin catalyst.

[0033] In a second aspect, the application provides a catalyst for use in a carbon dioxide hydrogenation to olefin reaction, wherein the catalyst is prepared by the above method.

[0034] The application will be described in detail below with reference to specific examples. It should be understood that these examples are only used to illustrate the application and not to limit the scope of the application. Any changes and advantages that can be thought of by those skilled in the art without departing from the spirit and scope of the application are included in the application, and the appended claims and any equivalents thereof are the protection scope of the application.

[0035] Example 1 A carbon dioxide hydrogenation to olefin catalyst is prepared by the following steps: S1: Mix dodecane and hexadecane at a mass ratio of 1:2 to obtain an organic solvent. Disperse 20g of graphite in 40g of the organic solvent, mix well by stirring, and then stir at 220℃ for 8h. Filter and wash the precipitate to obtain hydrophobic graphite.

[0036] S2: Take 10g of urea as a nitrogen doping source and mix with 20g of hydrophobic graphite. Put the obtained mixture into a planetary ball mill and ball mill at a speed of 400r / min for 3h. After ball milling, calcine at 300℃ for 4h to obtain a catalyst carrier.

[0037] S3: 16.11 g of iron nitrate nonahydrate and 10.24 g of magnesium nitrate hexahydrate were weighed and dissolved in deionized water to prepare solution A with a total concentration of 1.0 mol / L of iron nitrate and magnesium nitrate. Sodium carbonate was used as a precipitant, which was dissolved in deionized water to prepare solution B with a concentration of 1.0 mol / L. 6.46 g of catalyst carrier was mixed with 100 mL of deionized water to form a suspension, obtaining dispersion C. Solution A and solution B were added to dispersion C by using the parallel flow dropping method to carry out the coprecipitation reaction. During the reaction, the dropping speed of solution A and solution B was controlled to control pH = 8, and the temperature was controlled at 60°C. The coprecipitation reaction time was 30 min. After the precipitation was completed, it was placed for 2 h, and then filtered for 5 times. The product was dried at 120°C to obtain the catalyst precursor.

[0038] S4: The catalyst precursor was ground into powder. 0.046 g of sodium carbonate was dissolved in 5 mL of deionized water, and after being mixed thoroughly, it was added dropwise to 1 g of catalyst precursor powder. After ultrasonic treatment for 2 h, it was dried at 120°C, and then calcined at 350°C for 4 h before cooling to room temperature. The product after calcination was pressed into a tablet at 10 MPa, broken, and sieved to obtain particles with a size of 40-60 mesh to obtain a carbon dioxide hydrogenation to olefin catalyst.

[0039] Example 2 A carbon dioxide hydrogenation to olefin catalyst was prepared by the following steps: S1: 20 g of graphite was dispersed in 40 g of organic solvent obtained by mixing dodecane and hexadecane at a mass ratio of 1:2, and then stirred at 220°C for 8 h. The precipitate was filtered and washed to obtain hydrophobic graphite.

[0040] S2: 10 g of urea was mixed with 20 g of hydrophobic graphite as a nitrogen doping source. The mixture was placed in a planetary ball mill and ball milled at a speed of 400 r / min for 3 h. After ball milling, it was calcined at 300°C for 4 h to obtain a catalyst carrier.

[0041] S3: 16.11 g of iron nitrate nonahydrate and 5.12 g of magnesium nitrate hexahydrate were weighed and dissolved in deionized water to prepare solution A with a total concentration of 1.0 mol / L of iron nitrate and magnesium nitrate. Sodium carbonate was used as a precipitant, which was dissolved in deionized water to prepare solution B with a concentration of 1.0 mol / L. 6.464 g of catalyst carrier was mixed with 100 mL of deionized water to form a suspension, obtaining dispersion C. Solution A and solution B were added to dispersion C by using the parallel flow dropping method to carry out the coprecipitation reaction. During the reaction, the dropping speed of solution A and solution B was controlled to control pH = 8, and the temperature was controlled at 60°C. The coprecipitation reaction time was 30 min. After the precipitation was completed, it was placed for 2 h, and then filtered for 5 times. The product was dried at 120°C to obtain the catalyst precursor.

[0042] S4: The catalyst precursor was ground into powder. 0.046 g of sodium carbonate was dissolved in 5 mL of deionized water, and after being mixed thoroughly, it was added dropwise to 1 g of the catalyst precursor powder. After being ultrasonically treated for 2 h, it was dried at 120°C, and then calcined at 350°C for 4 h before being cooled to room temperature. The product after calcination was pressed into a tablet at 10 MPa, broken, and sieved to obtain particles with a size of 40-60 mesh, thereby obtaining a carbon dioxide hydrogenation to olefin catalyst.

[0043] Example 3 A carbon dioxide hydrogenation to olefin catalyst was prepared by the following steps: S1: Dodecane and hexadecane were mixed in a mass ratio of 1:2 to obtain an organic solvent. 20 g of graphite was dispersed in 40 g of the organic solvent, mixed uniformly by stirring, and then stirred at 220°C for 8 h. The precipitate was filtered and washed to obtain hydrophobic graphite.

[0044] S2: 10 g of urea was used as a nitrogen doping source and mixed with 20 g of the hydrophobic graphite. The mixture was placed in a planetary ball mill and ball milled at a speed of 400 r / min for 3 h. After ball milling, calcination was performed at 300°C for 4 h to obtain a catalyst carrier.

[0045] S3: 16.11 g of iron nitrate nonahydrate and 5.12 g of magnesium nitrate hexahydrate were dissolved in deionized water to prepare a solution A with a total concentration of 1.0 mol / L of iron nitrate and magnesium nitrate. Sodium carbonate was used as a precipitant, dissolved in deionized water, and prepared into a solution B with a concentration of 1.0 mol / L. The catalyst carrier 9.696 g was mixed with 100 mL of deionized water to form a suspension to obtain a dispersion C. Solution A and solution B were added to dispersion C by a parallel flow method, and a coprecipitation reaction was performed. During the reaction, the pH was controlled at 8 by controlling the dropping speed of solution A and solution B, and the temperature was controlled at 60°C. The coprecipitation reaction time was 30 min. After the precipitation was completed, it was left to stand for 2 h, and then filtered 5 times. Drying was performed at 120°C to obtain a catalyst precursor.

[0046] S4: The catalyst precursor was ground into powder. 0.046 g of sodium carbonate was dissolved in 5 mL of deionized water, and after being mixed thoroughly, it was added dropwise to 1 g of the catalyst precursor powder. After being ultrasonically treated for 2 h, it was dried at 120°C, and then calcined at 350°C for 4 h before being cooled to room temperature. The product after calcination was pressed into a tablet at 10 MPa, broken, and sieved to obtain particles with a size of 40-60 mesh, thereby obtaining a carbon dioxide hydrogenation to olefin catalyst.

[0047] Example 4 A carbon dioxide hydrogenation to olefin catalyst was prepared by the following steps: S1: Mix dodecane and hexadecane at a mass ratio of 1:2 to obtain an organic solvent. Disperse 20 g of graphite in 40 g of the organic solvent, mix uniformly under stirring, then stir at 220℃ for 8 h, filter and wash the precipitate to obtain hydrophobic graphite.

[0048] S2: Take 10 g of urea as a nitrogen doping source, mix with 20 g of hydrophobic graphite, and place the obtained mixture in a planetary ball mill to ball mill at a speed of 400 r / min for 3 h. After the ball milling is completed, calcine at 300℃ for 4 h to obtain a catalyst carrier.

[0049] S3: Weigh 16.11 g of iron nitrate nonahydrate and 10.24 g of magnesium nitrate hexahydrate, dissolve them in deionized water to prepare solution A with a total concentration of 1.0 mol / L of iron nitrate and magnesium nitrate. Dissolve sodium carbonate as a precipitant in deionized water to prepare solution B with a concentration of 1.0 mol / L. Mix 9.696 g of the catalyst carrier with 100 mL of deionized water to form a suspension to obtain dispersion C. Using the parallel flow dropping method, drop solution A and solution B into dispersion C to carry out coprecipitation reaction, control the dropping speed of solution A and solution B to control pH = 8 during the reaction, and control the temperature at 60℃, the coprecipitation reaction time is 30 min. After the precipitation is completed, stand for 2 h, suction filter 5 times, and dry at 120℃ to obtain a catalyst precursor.

[0050] S4: Grind the catalyst precursor into powder. Take 0.046 g of sodium carbonate, dissolve it in 5 mL of deionized water, mix thoroughly, then drop it into 1 g of catalyst precursor powder, ultrasonic for 2 h, then dry at 120℃, then calcine at 350℃ for 4 h and then cool to room temperature. Take the product after calcination, press into a tablet under 10 MPa, break and sieve out the particles with a size of 40-60 mesh to obtain a carbon dioxide hydrogenation to olefin catalyst.

[0051] Example 5 A carbon dioxide hydrogenation to olefin catalyst was prepared by the following steps: S1: Mix dodecane and hexadecane at a mass ratio of 1:1 to obtain an organic solvent. Disperse 20 g of graphite in 40 g of the organic solvent, mix uniformly under stirring, then stir at 220℃ for 8 h, filter and wash the precipitate to obtain hydrophobic graphite.

[0052] S2: Take 10 g of urea as a nitrogen doping source, mix with 20 g of hydrophobic graphite, and place the obtained mixture in a planetary ball mill to ball mill at a speed of 400 r / min for 3 h. After the ball milling is completed, calcine at 300℃ for 4 h to obtain a catalyst carrier.

[0053] S3: 16.11 g of iron nitrate nonahydrate and 10.24 g of magnesium nitrate hexahydrate were weighed and dissolved in deionized water to prepare solution A with a total concentration of 1.0 mol / L of iron nitrate and magnesium nitrate. Sodium carbonate was used as a precipitant, which was dissolved in deionized water to prepare solution B with a concentration of 1.0 mol / L. 6.46 g of catalyst carrier was mixed with 100 mL of deionized water to form a suspension, obtaining dispersion C. Solution A and solution B were added to dispersion C by the method of parallel flow dropwise addition to carry out coprecipitation reaction. During the reaction, the pH value was controlled at 8 by controlling the dropwise addition speed of solution A and solution B, and the temperature was controlled at 60°C. The coprecipitation reaction time was 30 min. After the precipitation was completed, it was placed for 2 h, and then filtered for 5 times. The catalyst precursor was obtained by drying at 120°C.

[0054] S4: The catalyst precursor was ground into powder. 0.046 g of sodium carbonate was dissolved in 5 mL of deionized water, and after being mixed thoroughly, it was added dropwise to 1 g of catalyst precursor powder. After ultrasonic treatment for 2 h, it was dried at 120°C, and then calcined at 350°C for 4 h before cooling to room temperature. The product after calcination was pressed into a tablet under 10 MPa, broken, and sieved to obtain particles with a size of 40-60 mesh, thereby obtaining a carbon dioxide hydrogenation to olefin catalyst.

[0055] Example 6 A carbon dioxide hydrogenation to olefin catalyst was prepared by the following steps: S1: 20 g of graphite was dispersed in 40 g of organic solvent obtained by mixing dodecane and hexadecane at a mass ratio of 1:3, and then stirred at 220°C for 8 h. The precipitate was filtered and washed to obtain hydrophobic graphite.

[0056] S2: 10 g of urea was mixed with 20 g of hydrophobic graphite as a nitrogen doping source. The mixture was placed in a planetary ball mill and ball milled at a speed of 400 r / min for 3 h. After ball milling, calcination was performed at 300°C for 4 h to obtain a catalyst carrier.

[0057] S3: 16.11 g of iron nitrate nonahydrate and 10.24 g of magnesium nitrate hexahydrate were weighed and dissolved in deionized water to prepare solution A with a total concentration of 1.0 mol / L of iron nitrate and magnesium nitrate. Sodium carbonate was used as a precipitant, which was dissolved in deionized water to prepare solution B with a concentration of 1.0 mol / L. 6.46 g of catalyst carrier was mixed with 100 mL of deionized water to form a suspension, obtaining dispersion C. Solution A and solution B were added to dispersion C by the method of parallel flow dropwise addition to carry out coprecipitation reaction. During the reaction, the pH value was controlled at 8 by controlling the dropwise addition speed of solution A and solution B, and the temperature was controlled at 60°C. The coprecipitation reaction time was 30 min. After the precipitation was completed, it was placed for 2 h, and then filtered for 5 times. The catalyst precursor was obtained by drying at 120°C.

[0058] S4: The catalyst precursor was ground into powder. 0.046 g of sodium carbonate was dissolved in 5 mL of deionized water, and after being mixed thoroughly, it was added dropwise to 1 g of the catalyst precursor powder. After being ultrasonically treated for 2 h, it was dried at 120°C, and then calcined at 350°C for 4 h before being cooled to room temperature. The product after calcination was pressed into a tablet at 10 MPa, broken, and sieved to obtain particles of 40-60 mesh, thereby obtaining a carbon dioxide hydrogenation to olefin catalyst.

[0059] Example 7 A carbon dioxide hydrogenation to olefin catalyst was prepared by the following steps: S1: 20 g of graphite was dispersed in 40 g of an organic solvent prepared by mixing dodecane and hexadecane at a mass ratio of 1:2, and the mixture was stirred thoroughly and uniformly, and then stirred at 220°C for 8 h. The precipitate was filtered and washed to obtain a catalyst carrier.

[0060] S2: 16.11 g of iron nitrate nonahydrate and 5.12 g of magnesium nitrate hexahydrate were dissolved in deionized water to prepare a solution A with a total concentration of 1.0 mol / L of iron nitrate and magnesium nitrate. Sodium carbonate was used as a precipitant, which was dissolved in deionized water to prepare a solution B with a concentration of 1.0 mol / L. 6.464 g of the catalyst carrier was mixed with 100 mL of deionized water to obtain a dispersion C. Solution A and solution B were added dropwise to dispersion C by the parallel flow method to perform a coprecipitation reaction. During the reaction, the dropping speed of solution A and solution B was controlled to maintain a pH of 8, and the temperature was controlled at 60°C. The coprecipitation reaction time was 30 min. After the precipitation was completed, it was allowed to stand for 2 h, and then filtered 5 times. The product was dried at 120°C to obtain a catalyst precursor.

[0061] S3: The catalyst precursor was ground into powder. 0.046 g of sodium carbonate was dissolved in 5 mL of deionized water, and after being mixed thoroughly, it was added dropwise to 1 g of the catalyst precursor powder. After being ultrasonically treated for 2 h, it was dried at 120°C, and then calcined at 350°C for 4 h before being cooled to room temperature. The product after calcination was pressed into a tablet at 10 MPa, broken, and sieved to obtain particles of 40-60 mesh, thereby obtaining a carbon dioxide hydrogenation to olefin catalyst.

[0062] Comparative Example 1 A carbon dioxide hydrogenation to olefin catalyst was prepared by the following steps: S1: 10 g of urea was mixed with 20 g of graphite as a nitrogen doping source, and the mixture was placed in a planetary ball mill and ball milled at a speed of 400 r / min for 3 h. After ball milling, the mixture was calcined at 300°C for 4 h to obtain a catalyst carrier.

[0063] S2: 16.11 g of iron nitrate nonahydrate and 5.12 g of magnesium nitrate hexahydrate were weighed and dissolved in deionized water to prepare solution A with a total concentration of 1.0 mol / L of iron nitrate and magnesium nitrate. Sodium carbonate was used as a precipitant, which was dissolved in deionized water to prepare solution B with a concentration of 1.0 mol / L. 6.464 g of catalyst carrier was mixed with 100 mL of deionized water to form a suspension, obtaining dispersion C. Solution A and solution B were added to dispersion C by using the parallel flow dropping method to carry out the coprecipitation reaction. During the reaction, the dropping speed of solution A and solution B was controlled to control pH = 8, and the temperature was controlled at 60°C. The coprecipitation reaction time was 30 min. After the precipitation was completed, it was placed for 2 h, and then filtered 5 times. The product was dried at 120°C to obtain the catalyst precursor.

[0064] S3: The catalyst precursor was ground into powder. 0.046 g of sodium carbonate was dissolved in 5 mL of deionized water, and then added dropwise to 1 g of catalyst precursor powder. After ultrasonic treatment for 2 h, the product was dried at 120°C, and then calcined at 350°C for 4 h. The product after calcination was pressed into a tablet under a pressure of 10 MPa, crushed, and sieved to obtain particles with a size of 40-60 mesh, thereby obtaining a carbon dioxide hydrogenation to olefin catalyst.

[0065] Comparative Example 2 A carbon dioxide hydrogenation to olefin catalyst was prepared by the following steps: S1: 20 g of graphite was dispersed in 40 g of dodecane, and then mixed uniformly by stirring. After that, the mixture was stirred at 220°C for 8 h. The precipitate was filtered and washed to obtain hydrophobic graphite.

[0066] S2: 10 g of urea was mixed with 20 g of hydrophobic graphite as a nitrogen doping source. The mixture was placed in a planetary ball mill and ball milled at a speed of 400 r / min for 3 h. After ball milling, the mixture was calcined at 300°C for 4 h to obtain a catalyst carrier.

[0067] S3: 16.11 g of iron nitrate nonahydrate and 10.24 g of magnesium nitrate hexahydrate were weighed and dissolved in deionized water to prepare solution A with a total concentration of 1.0 mol / L of iron nitrate and magnesium nitrate. Sodium carbonate was used as a precipitant, which was dissolved in deionized water to prepare solution B with a concentration of 1.0 mol / L. 6.46 g of catalyst carrier was mixed with 100 mL of deionized water to form a suspension, obtaining dispersion C. Solution A and solution B were added to dispersion C by using the parallel flow dropping method to carry out the coprecipitation reaction. During the reaction, the dropping speed of solution A and solution B was controlled to control pH = 8, and the temperature was controlled at 60°C. The coprecipitation reaction time was 30 min. After the precipitation was completed, it was placed for 2 h, and then filtered 5 times. The product was dried at 120°C to obtain the catalyst precursor.

[0068] S4: The catalyst precursor was ground into powder. 0.046 g of sodium carbonate was dissolved in 5 mL of deionized water, and after being mixed thoroughly, it was added dropwise to 1 g of the catalyst precursor powder. After being ultrasonically treated for 2 h, it was dried at 120°C, and then calcined at 350°C for 4 h before being cooled to room temperature. The product after calcination was pressed into a tablet at 10 MPa, broken, and sieved to obtain particles of 40-60 mesh, thereby obtaining a carbon dioxide hydrogenation to olefin catalyst.

[0069] Comparative Example 3 A carbon dioxide hydrogenation to olefin catalyst was prepared by the following steps: S1: 20 g of graphite was dispersed in 40 g of hexadecane, and after being mixed uniformly by stirring, it was stirred at 220°C for 8 h. The precipitate was filtered and washed, thereby obtaining hydrophobic graphite.

[0070] S2: 10 g of urea was mixed with 20 g of the hydrophobic graphite, and the mixture was placed in a planetary ball mill and ball milled at a speed of 400 r / min for 3 h. After the ball milling was completed, it was calcined at 300°C for 4 h, thereby obtaining a catalyst carrier.

[0071] S3: 16.11 g of iron nitrate nonahydrate and 10.24 g of magnesium nitrate hexahydrate were dissolved in deionized water to prepare a solution A with a total concentration of 1.0 mol / L of iron nitrate and magnesium nitrate. Sodium carbonate was used as a precipitant, and it was dissolved in deionized water to prepare a solution B with a concentration of 1.0 mol / L. 6.46 g of the catalyst carrier was mixed with 100 mL of deionized water to form a suspension, thereby obtaining a dispersion C. Solution A and solution B were added dropwise to the dispersion C in a parallel flow manner to perform a coprecipitation reaction. During the reaction, the dropping speed of solution A and solution B was controlled to control the pH to be 8, and the temperature was controlled to be 60°C. The coprecipitation reaction time was 30 min. After the precipitation was completed, it was left to stand for 2 h, and then it was suction filtered 5 times. The product was dried at 120°C, thereby obtaining a catalyst precursor.

[0072] S4: The catalyst precursor was ground into powder. 0.046 g of sodium carbonate was dissolved in 5 mL of deionized water, and after being mixed thoroughly, it was added dropwise to 1 g of the catalyst precursor powder. After being ultrasonically treated for 2 h, it was dried at 120°C, and then calcined at 350°C for 4 h before being cooled to room temperature. The product after calcination was pressed into a tablet at 10 MPa, broken, and sieved to obtain particles of 40-60 mesh, thereby obtaining a carbon dioxide hydrogenation to olefin catalyst.

[0073] Comparative Example 4 A carbon dioxide hydrogenation to olefin catalyst was prepared by the following steps: S1: 12-dodecanes and hexadecane were mixed in a mass ratio of 1:0.5 to obtain an organic solvent. 20 g of graphite was dispersed in 40 g of the organic solvent, mixed uniformly by stirring, and then stirred at 220℃ for 8 h. The precipitate was filtered and washed to obtain hydrophobic graphite.

[0074] S2: 10 g of urea was taken as a nitrogen doping source and mixed with 20 g of the hydrophobic graphite. The mixture was placed in a planetary ball mill and ball milled at a speed of 400 r / min for 3 h. After the ball milling was completed, the catalyst carrier was obtained by calcining at 300℃ for 4 h.

[0075] S3: 16.11 g of iron nitrate nonahydrate and 10.24 g of magnesium nitrate hexahydrate were dissolved in deionized water to prepare a solution A with a total concentration of 1.0 mol / L of iron nitrate and magnesium nitrate. Sodium carbonate was used as a precipitant and dissolved in deionized water to prepare a solution B with a concentration of 1.0 mol / L. 6.46 g of the catalyst carrier was mixed with 100 mL of deionized water to form a suspension C. Solution A and solution B were added to the dispersion C by the method of parallel flow dropwise addition, and a coprecipitation reaction was carried out. During the reaction, the pH was controlled at 8 by controlling the dropwise addition speed of solution A and solution B, and the temperature was controlled at 60℃. The coprecipitation reaction time was 30 min. After the precipitation was completed, it was placed for 2 h, and then filtered for 5 times. The precipitate was dried at 120℃ to obtain a catalyst precursor.

[0076] S4: The catalyst precursor was ground into powder. 0.046 g of sodium carbonate was dissolved in 5 mL of deionized water, and then added dropwise to 1 g of the catalyst precursor powder. After ultrasonic treatment for 2 h, the mixture was dried at 120℃, and then calcined at 350℃ for 4 h. The product after calcination was pressed into a tablet at 10 MPa, and then broken and sieved to obtain particles with a size of 40-60 mesh. A carbon dioxide hydrogenation to olefin catalyst was obtained.

[0077] Comparative Example 5 A carbon dioxide hydrogenation to olefin catalyst was prepared by the following steps: S1: 12-dodecanes and hexadecane were mixed in a mass ratio of 1:0.5 to obtain an organic solvent. 20 g of graphite was dispersed in 40 g of the organic solvent, mixed uniformly by stirring, and then stirred at 220℃ for 8 h. The precipitate was filtered and washed to obtain hydrophobic graphite.

[0078] S2: 10 g of urea was taken as a nitrogen doping source and mixed with 20 g of the hydrophobic graphite. The mixture was placed in a planetary ball mill and ball milled at a speed of 400 r / min for 3 h. After the ball milling was completed, the catalyst carrier was obtained by calcining at 300℃ for 4 h.

[0079] S3: Weigh 16.11 g of iron nitrate nonahydrate and 10.24 g of magnesium nitrate hexahydrate, and dissolve them in deionized water to prepare solution A with a total concentration of 1.0 mol / L of iron nitrate and magnesium nitrate. Dissolve sodium carbonate in deionized water to prepare solution B with a concentration of 1.0 mol / L. Mix 6.46 g of catalyst carrier with 100 mL of deionized water to form a suspension, and obtain dispersion C. Using the parallel flow dropping method, drop solution A and solution B into dispersion C to perform coprecipitation reaction. During the reaction, control the dropping speed of solution A and solution B to control pH = 8, and control the temperature at 60°C. The coprecipitation reaction time is 30 min. After the precipitation is completed, stand for 2 h, and perform suction filtration for 5 times. Dry at 120°C to obtain the catalyst precursor.

[0080] S4: Grind the catalyst precursor into powder. Take 0.046 g of sodium carbonate, dissolve it in 5 mL of deionized water, and mix thoroughly. Then, drop it into 1 g of catalyst precursor powder. After ultrasonic treatment for 2 h, dry at 120°C. Then, calcine at 350°C for 4 h, and then cool to room temperature. Take the product after calcination, press it into a tablet under 10 MPa, break it, and sieve out the particles with a size of 40-60 mesh to obtain the catalyst for hydrogenation of carbon dioxide to olefins.

[0081] Application Example Take the catalyst prepared according to the method in each of the examples and the comparative examples, and use it to catalyze the reaction of hydrogenation of carbon dioxide to olefins. The specific process is as follows: Before the reaction of hydrogenation of carbon dioxide to olefins, first, load the catalyst into a fixed bed reactor, check the air tightness, and then heat it to 350°C at a rate of 5°C / min. Pass hydrogen gas at a flow rate of 20-30 mL / min to reduce it for 5 h. Then, cool it naturally in the hydrogen stream. During the reaction, pass the mixed gas of H2 / CO2 with a volume ratio of 3:1 at a flow rate of 30 mL / min, and heat it to 300°C at a rate of 5°C / min. During the heating, analyze the product every 30 min by gas chromatography. After the reaction, first, stop heating, pass the mixed gas to cool, and finally, close the valve to disassemble the device to handle the product and the catalyst. The measured initial CO2 conversion rate, initial olefin selectivity, and deactivation time (the time when the CO2 conversion rate is reduced by 10% compared with the initial time) are shown in Table 1. When the catalysts of Example 2 and Comparative Example 1 are used, the changes of CO2 conversion rate with the continuous use time of the catalysts are shown in Figure 1 and Figure 2 .

[0082] Table 1: Catalyst performance test results From the catalyst performance test results in Table 1, it can be seen that: (1) The catalyst stability of Example 2 is higher than that of Comparative Example 1. The reason is that, compared with Comparative Example 1, the graphite is hydrophobically modified by dodecane and hexadecane in Example 2, which can give the catalyst better hydrophobicity, reduce the contact between active sites in the catalyst and water produced in the CO2 hydrogenation reaction, alleviate the problem of oxidation deactivation of active sites, and thus improve the catalyst stability.

[0083] (2) The catalyst stability of Examples 1, 5 and 6 is higher than that of Comparative Examples 2-5. It shows that a synergistic effect can be produced between dodecane and hexadecane, and the catalyst stability can be improved to a greater extent when the two are used together, and the ratio between them will affect the catalyst stability. When the mass ratio between dodecane and hexadecane is 1:1-3, the catalyst can have higher stability. The reason is that, when the graphite is immersed in the mixture of dodecane and hexadecane, dodecane can quickly fill the small pores on the surface of the graphite, promoting the adhesion of hexadecane, and then hexadecane is further attached to the surface of the graphite, which is conducive to the formation of a dense hydrophobic layer. In the subsequent calcination process, dodecane and hexadecane are partially decomposed, and the alkyl groups remain on the graphite to form a hydrophobic layer. In this way, dodecane and hexadecane can cooperate with each other to improve the hydrophobicity of the catalyst to a greater extent.

[0084] (3) Compared with Example 7, the CO2 conversion rate and olefin selectivity of Example 2 are higher. The reason is that, compared with Example 7, Example 2 can form nitrogen atom doping and more vacancy defects in the catalyst support, thereby providing more loading sites for Fe and Mg elements, improving the loading amount and stability of Fe and Mg elements in the catalyst, and thus giving the catalyst higher catalytic activity and stability; in addition, nitrogen atom doping also helps to improve the adsorption capacity of the catalyst for the reaction intermediate CO, promoting the carbon dioxide hydrogenation to olefins reaction.

[0085] (4) Compared with Example 2, Example 1 increases the loading amount of Mg element, and compared with Example 4, it increases the loading amount of Mg element and Fe element. From the catalyst performance detection results, the catalyst stability of Example 1 is lower than that of Examples 2 and 4. The reason may be that: the excessive Mg covers part of the exposed sites of active metals (such as Fe); excessive Mg occupies the dispersion sites of Fe, leading to Fe agglomeration; excessive Mg leads to intensified side reactions (carbon deposition / sintering), resulting in reduced catalyst activity.

[0086] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The raw materials and equipment used in the present application are conventional raw materials and equipment in the art unless otherwise specified, which can be obtained from conventional commercial channels; the methods used in the present application are conventional methods in the art unless otherwise specified.

[0087] The above is only the preferred embodiment of the present application, and does not limit the present application. Any simple modification, change and equivalent transformation of the above embodiment according to the technical essence of the present application still belongs to the protection scope of the technical solution of the present application.

Claims

1. A method for preparing a catalyst for the hydrogenation of carbon dioxide to olefins, characterized in that, Includes the following steps: S1: After thoroughly impregnating graphite in a mixture of dodecane and hexadecane, the graphite is removed to obtain a catalyst support; S2: Fe and Mg elements are loaded onto the catalyst support by co-precipitation followed by calcination to obtain a catalyst for the hydrogenation of carbon dioxide to olefins.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of dodecane to hexadecane is 1:1 to 3.

3. The preparation method according to claim 1, characterized in that, Before step S2, the catalyst support is mixed with the nitrogen source and then ball-milled at 400~700 r / min for 180~250 min, and then calcined at 300~350℃ for 3.5~4.5 h in an inert atmosphere.

4. The preparation method according to claim 3, characterized in that, The mass ratio of the catalyst support to the nitrogen source is 1:0.3~0.

6.

5. The preparation method according to claim 1 or 2, characterized in that, In step S1, the method for thorough impregnation is as follows: after stirring and mixing evenly, continue stirring at 220~260℃ for 4~24h.

6. The preparation method according to claim 1, characterized in that, In step S2, while loading Fe and Mg elements into the catalyst support, Na elements are doped into the catalyst support using an impregnation-calcination method.

7. The preparation method according to claim 6, characterized in that, The specific process of step S2 includes: S2.1: Containing Fe 3+ and Mg 2+ The solution and alkaline solution were added dropwise to the catalyst support dispersion, and after precipitation reaction, the product was separated. S2.2: After grinding the product from step S2.1, disperse it in a container containing Na. + In the solution, remove the solvent; S2.3: The product of step S2.2 is calcined at 300~350℃ for 4~5h in an inert atmosphere to obtain a catalyst for the hydrogenation of carbon dioxide to olefins.

8. The preparation method according to claim 7, characterized in that, In step S2.1, the Fe 3+ and Mg 2+ The molar ratio of the catalyst support and Fe is 1:0.5~1.

0. 3+ The mass ratio is 1:0.2~0.4; In step S2.2, the product of step S2.1 and Na + The mass ratio is 1:0.01~0.

05.

9. The preparation method according to claim 7, characterized in that, In step S2.1, during the precipitation reaction, the pH is controlled at 8.0~12.0, the temperature at 60~80℃, and the time at 0.5~1h.

10. The application of a catalyst in the hydrogenation of carbon dioxide to olefins, characterized in that, The catalyst is prepared by the preparation method described in any one of claims 1 to 9.

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