A metal-doped composite catalyst for carbon dioxide hydrogenation to methanol and a preparation method thereof

Abstract

The application discloses a metal-doped composite catalyst for carbon dioxide hydrogenation to methanol and a preparation method thereof. The catalyst comprises copper oxide, zinc oxide and a doped metal; the doped metal is selected from one or more of iron, cobalt, nickel, cerium, indium, aluminum, manganese, chromium and magnesium. The adsorption and activation capacity of the catalyst to CO2 and H2 is controlled by directional introduction of the doped metal elements, the selectivity of the target product methanol is improved, meanwhile, the number of surface active sites is increased by using heteroatoms, and the carbon dioxide conversion rate and the selectivity of methanol are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of catalytic conversion of carbon dioxide, and particularly relates to a metal-doped composite catalyst for carbon dioxide hydrogenation to methanol and a preparation method thereof. BACKGROUND

[0002] With the intensification of energy and environmental crises, clean energy development and carbon neutralization technology have become the focus of current social attention. As an important greenhouse gas, the gradual increase in the concentration of carbon dioxide in the atmosphere leads to global warming, causing a series of climate problems such as sea level rise, ocean current change, and extreme weather, which seriously threatens the sustainable development of human society. Under the background of "carbon peak" and "carbon neutralization", carbon dioxide hydrogenation to basic chemical methanol is considered to be one of the feasible ways to promote carbon dioxide resource utilization and achieve carbon neutralization. However, the high chemical inertness of CO2 and multiple hydrogenation competitive paths make the methanol selectivity and yield low; in addition, there is a problem of low CO2 single-pass conversion rate due to the limitation of thermodynamic equilibrium. The main ways of carbon dioxide reduction currently include photocatalytic reduction, electrocatalytic reduction, thermal catalytic reduction, and coupling of the above technologies. Photocatalytic reduction of carbon dioxide is one of the most ideal ways of carbon utilization, but its efficiency is low and difficult to meet the actual demand, while thermal catalytic conversion of carbon dioxide is one of the most promising paths at present.

[0003] CO2 hydrogenation catalysts mainly include Cu-based catalysts, In-based catalysts and oxide solid solution catalysts, among which Cu-based catalysts have good carbon dioxide catalytic conversion activity and are considered to be the most promising catalysts for industrial application, but they are prone to sintering in the reaction atmosphere, leading to catalyst deactivation, and the selectivity of by-products such as CO and alkanes is high. Therefore, it is urgent to develop a carbon dioxide hydrogenation catalyst for methanol production with high activity, high selectivity and high stability. SUMMARY

[0004] The purpose of the present application is to provide a metal-doped composite catalyst for carbon dioxide hydrogenation to methanol, which comprises copper oxide, zinc oxide and a doping metal.

[0005] According to an embodiment of the present application, the mass fraction of copper oxide is 20-80wt%, the mass fraction of zinc oxide is 10-70wt%, and the mass fraction of the doping metal is 1-10wt%.

[0006] According to an embodiment of the present application, the doping metal is selected from one or more of iron, cobalt, nickel, cerium, indium, aluminum, manganese, chromium and magnesium; preferably one or more of iron, cobalt and nickel.

[0007] According to an embodiment of the present application, the doping metal is introduced in situ during the synthesis of the catalyst.

[0008] The present application aims to provide a preparation method of the above-mentioned catalyst, comprising the following steps:

[0009] S1, uniformly mixing copper salt and zinc salt in a solvent, then adding sodium citrate, and stirring to obtain a mixed solution A;

[0010] Before adding the alkaline solution to adjust the pH, an appropriate amount of sodium citrate is added to adjust the particle size of the catalyst to be more uniform. Due to the special properties of sodium citrate, the addition of sodium citrate here improves the conversion rate of carbon dioxide and the selectivity of methanol. To solve the problem that the acidic citric acid commonly used in the prior art, and the commonly used dispersants and stabilizers such as polyvinylpyrrolidone, polyethylene glycol, and EDTA cannot well adjust the particle size of the catalyst to be more uniform, and more greatly improve the conversion rate of carbon dioxide and the selectivity of methanol.

[0011] S2, preparing an aqueous carbonate solution, slowly adding the aqueous carbonate solution to the mixed solution A, adjusting the pH of the solution to 2.5-4.5, and obtaining a suspension B; preferably, in step S2, the pH of the solution is adjusted to 2.5-3.5;

[0012] By controlling the pH in step S3 to 2.5-4.5, the interaction between the metal oxide and the doped metal can be controlled, and the conversion rate of carbon dioxide can be improved.

[0013] S3, adding a doped metal salt to the suspension B obtained in step S2, continuously adding the aqueous carbonate solution under stirring, and adjusting the pH to 7.5-9.5; preferably, in step S3, the pH is adjusted to 7.5-8.0;

[0014] By directional introduction of the doped metal element, that is, adding the doped metal salt to the suspension of the active metal component, the selectivity of methanol and the conversion rate of CO2 can be improved.

[0015] S4, after sufficient reaction, centrifugation, washing, drying, and calcination to obtain the composite catalyst.

[0016] The centrifugation refers to centrifugal separation of the solid-liquid mixture after sufficient reaction to obtain a solid product.

[0017] According to an embodiment of the present application, in step S1, the copper salt and the zinc salt are selected from one or more of their corresponding nitrate, hydrochloride, sulfate, and acetylacetone salt.

[0018] According to an embodiment of the present application, in step S1, the solvent is selected from one or more of water, methanol, and ethanol.

[0019] According to one embodiment of the present application, in step S1, the total concentration of copper salt and zinc salt is 0.2-2.5 mol / L, and the mass ratio of sodium citrate to copper salt is 1:20-1:10.

[0020] According to one embodiment of the present application, in step S2, the carbonate is one or more of sodium carbonate, potassium carbonate, and ammonium carbonate, and the concentration of the carbonate is 0.1-2.0 mol / L.

[0021] According to one embodiment of the present application, the dropping speed of the carbonate is 1-5 drops per second.

[0022] According to one embodiment of the present application, in step S2, the temperature of the above-mentioned mixed solution A is 20-40℃ when the aqueous solution of carbonate is slowly added.

[0023] According to one embodiment of the present application, in step S3, the doping metal salt is a nitrate or hydrochloride of the doping metal.

[0024] According to one embodiment of the present application, in step S4, the reaction temperature is 40-90℃, and the reaction time is 12-48 hours.

[0025] According to one embodiment of the present application, in step S4, the calcination temperature is 250-300℃, the heating rate is 2-5℃ per minute, and the time is 2-4 hours.

[0026] According to one embodiment of the present application, in step S4, the calcination atmosphere is air.

[0027] Advantages:

[0028] Compared with the prior art, the present application has the following advantages:

[0029] 1. The directional introduction of metal elements for doping controls the adsorption and activation ability of the catalyst to CO2 and H2, improves the selectivity of target products, and increases the number of surface active sites by using heteroatoms to improve the carbon dioxide conversion rate and the selectivity of methanol.

[0030] 2. By regulating the synthesis means, the catalyst particle size is reduced and the metal interface is promoted to form, thereby improving the performance of carbon dioxide catalytic conversion.

[0031] 3. The catalyst of the present application uses non-noble metal raw materials, which is cheap, simple in preparation process, good in repeatability, and easy to scale up production.

[0032] The present application will be further described below in conjunction with the drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0033] ATTACHMENT Figure 1is the X-ray diffraction pattern (XRD) of the metal-doped composite catalyst prepared in Example 1.

[0034] Figure 1 is the X-ray diffraction pattern (XRD) of the metal-doped composite catalyst prepared in Example 1. Figure 2 is the X-ray photoelectron spectroscopy (XPS) of the metal-doped composite catalyst prepared in Example 1. DETAILED DESCRIPTION

[0035] The technical solutions of the present application are further described below according to specific examples. The protection scope of the present application is not limited to the following examples, and these examples are listed only for illustrative purposes and do not limit the present application in any way.

[0036] In the context of the present specification, unless explicitly stated otherwise, any matter or item not mentioned is directly applicable to what is known in the art without any modification. Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solutions or technical ideas thus formed are considered to be part of the original disclosure or original description of the present application and should not be considered as new content that has not been disclosed or anticipated herein, unless the combination is considered to be obviously unreasonable by those skilled in the art.

[0037] Carbon dioxide hydrogenation activity test

[0038] The carbon dioxide catalytic hydrogenation activity test was carried out using a fixed bed microreactor, the feed gas was H2, CO2 and Ar with a volume ratio of 72:24:4, the space velocity was 12000 mL·g -1 ·min -1 The catalyst loading was 0.5 g, and the quartz sand was 4.5 g, the reaction temperature was 240℃, and the sample was analyzed by chromatography equipped with hydrogen flame ion detection and thermal conductivity cell detector.

[0039] Example 1:

[0040] 15 g of copper nitrate and 5 g of zinc nitrate were mixed uniformly in 100 mL of water, then 1.5 g of sodium citrate was added, and after stirring, a mixture was obtained; a 0.5 mol / L aqueous sodium carbonate solution was prepared, and was slowly added to the above mixture at a rate of 2 drops per second at a constant temperature of 40℃, and the pH of the solution was adjusted to 2.5 to obtain a suspension; 0.5 g of nickel nitrate was added, and the pH was adjusted to 8.0 while continuing to add the sodium carbonate solution under stirring; after sufficient reaction at 40℃ for 24 hours, centrifugation, washing, and drying were carried out, the temperature was increased at a rate of 2℃ per minute to 250℃, and the metal-doped composite catalyst was obtained after calcination at 250℃ in an air atmosphere for 2 hours and cooling to room temperature. Figure 1 is the XRD pattern of the metal-doped composite catalyst, and it can be seen that there are obvious copper oxide and zinc oxide crystal phases, while the amount of doped metal is low and no obvious signal is observed. Figure 2The XPS spectrum of the metal-doped composite catalyst shows that Cu and Zn in the sample exist in +2 valence, and the content of the doped metal is low, and no obvious signal is observed.

[0041] As shown in Table 1, in Example 1, at a reaction temperature of 240°C, the carbon dioxide conversion rate is 19.1%, the methanol selectivity is 60.1%, the carbon monoxide selectivity is 39.1%, and the methane selectivity is 0.8%.

[0042] Example 2:

[0043] 15 g of copper nitrate and 5 g of zinc nitrate were uniformly mixed in 100 mL of water, and then 2.0 g of sodium citrate was added. After stirring, a mixture was obtained. A 0.5 mol / L sodium carbonate aqueous solution was prepared, and was slowly added to the above mixture at a speed of 2 drops per second under the condition of constant temperature at 40°C. The pH of the solution was adjusted to 2.5 to obtain a suspension. 0.5 g of cobalt nitrate was added, and the sodium carbonate solution was continuously added under stirring, and the pH was adjusted to 8.0. After fully reacting at 40°C for 24 hours, centrifugation, washing, and drying were performed. The temperature was increased at a rate of 2°C per minute to 250°C, and calcination treatment was performed at 250°C in an air atmosphere for 2 hours. After cooling to room temperature, a metal-doped composite catalyst was obtained. As shown in Table 1, in Example 2, at a reaction temperature of 240°C, the carbon dioxide conversion rate is 18.5%, the methanol selectivity is 66.1%, the carbon monoxide selectivity is 33.1%, and the methane selectivity is 0.8%.

[0044] Example 3:

[0045] 20 g of copper nitrate and 5 g of zinc nitrate were uniformly mixed in 100 mL of water, and then 2.0 g of sodium citrate was added. After stirring, a mixture was obtained. A 0.5 mol / L sodium carbonate aqueous solution was prepared, and was slowly added to the above mixture at a speed of 2 drops per second under the condition of constant temperature at 60°C. The pH of the solution was adjusted to 2.5 to obtain a suspension. 0.5 g of iron nitrate was added, and the sodium carbonate solution was continuously added under stirring, and the pH was adjusted to 8.0. After fully reacting at 40°C for 24 hours, centrifugation, washing, and drying were performed. The temperature was increased at a rate of 2°C per minute to 300°C, and calcination treatment was performed at 300°C in an air atmosphere for 2 hours. After cooling to room temperature, a metal-doped composite catalyst was obtained. As shown in Table 1, in Example 3, at a reaction temperature of 240°C, the carbon dioxide conversion rate is 21.5%, the methanol selectivity is 69.1%, the carbon monoxide selectivity is 30.3%, and the methane selectivity is 0.6%.

[0046] Example 4:

[0047] Example 4: 15 g of copper nitrate and 5 g of zinc nitrate were mixed uniformly in 100 mL of water, then 2.0 g of sodium citrate was added, and after stirring, a mixture was obtained; a 0.5 mol / L aqueous sodium carbonate solution was prepared, and was slowly added to the above mixture at a rate of 2 drops per second at a constant temperature of 50°C, and the pH of the solution was adjusted to 2.5 to obtain a suspension, 1.0 g of ferric nitrate was added, and the sodium carbonate solution was continuously added under stirring, and the pH was adjusted to 8.0; after fully reacting at 60°C for 24 hours, centrifugation, washing, and drying were performed, the temperature was increased at a rate of 2°C per minute to 300°C, and calcination was performed at 300°C in an air atmosphere for 2 hours, and after cooling to room temperature, a metal-doped composite catalyst was obtained. As shown in Table 1, in Example 4, at a reaction temperature of 240°C, the carbon dioxide conversion rate was 20.5%, the methanol selectivity was 71.2%, the carbon monoxide selectivity was 28.3%, and the methane selectivity was 0.5%.

[0048] Example 5:

[0049] 15 g of copper nitrate and 8 g of zinc nitrate were mixed uniformly in 100 mL of water, then 2.0 g of sodium citrate was added, and after stirring, a mixture was obtained; a 1.0 mol / L aqueous sodium carbonate solution was prepared, and was slowly added to the above mixture at a rate of 2 drops per second at a constant temperature of 40°C, and the pH of the solution was adjusted to 3.5 to obtain a suspension, 0.5 g of ferric nitrate was added, and the sodium carbonate solution was continuously added under stirring, and the pH was adjusted to 7.5; after fully reacting at 60°C for 24 hours, centrifugation, washing, and drying were performed, the temperature was increased at a rate of 2°C per minute to 300°C, and calcination was performed at 300°C in an air atmosphere for 2 hours, and after cooling to room temperature, a metal-doped composite catalyst was obtained. As shown in Table 1, in Example 5, at a reaction temperature of 240°C, the carbon dioxide conversion rate was 18.9%, the methanol selectivity was 68.2%, the carbon monoxide selectivity was 31.7%, and the methane selectivity was 0.1%.

[0050] Example 6:

[0051] A mixture of 15 g of copper nitrate and 8 g of zinc nitrate in 100 mL of water was mixed uniformly, and then 2.0 g of sodium citrate was added. After stirring, a mixture was obtained. A 1.0 mol / L aqueous sodium carbonate solution was prepared, and was slowly added to the above mixture at a rate of 2 drops per second at a constant temperature of 60°C. The pH of the solution was adjusted to 3.5, and a suspension was obtained. 0.5 g of cobalt nitrate was added, and the sodium carbonate solution was continuously added under stirring, and the pH was adjusted to 7.5. After sufficient reaction at 60°C for 48 hours, centrifugation, washing, and drying were performed. The temperature was increased at a rate of 2°C per minute to 300°C, and calcination was performed at 300°C in an air atmosphere for 2 hours. After cooling to room temperature, a metal-doped composite catalyst was obtained. As shown in Table 1, in Example 6, at a reaction temperature of 240°C, the carbon dioxide conversion rate was 22.6%, the methanol selectivity was 70.2%, the carbon monoxide selectivity was 29.5%, and the methane selectivity was 0.3%.

[0052] In addition, a comparative experiment was designed to prove that the metal doping synergistic effect plays an important role in improving the carbon dioxide hydrogenation activity and methanol selectivity. The specific scheme is as follows:

[0053] Comparative Example 1

[0054] A mixture of 15 g of copper nitrate and 8 g of zinc nitrate in 100 mL of water was mixed uniformly, and then 2.0 g of sodium citrate was added. After stirring, a mixture was obtained. A 1.0 mol / L aqueous sodium carbonate solution was prepared, and was slowly added to the above mixture at a rate of 2 drops per second at a constant temperature of 40°C. The pH of the solution was adjusted to 7.5. After sufficient reaction at 60°C for 24 hours, centrifugation, washing, and drying were performed. Calcination was performed at 300°C for 2 hours at a temperature increase rate of 2°C per minute. After cooling to room temperature, a copper oxide-zinc oxide composite catalyst without metal doping was obtained. As shown in Table 1, in Comparative Example 1, at a reaction temperature of 240°C, the carbon dioxide conversion rate was 14.1%, the methanol selectivity was 48.2%, the carbon monoxide selectivity was 48.7%, and the methane selectivity was 4.1%.

[0055] Comparative Example 2

[0056] The other conditions were the same as in Example 1, except that no sodium citrate was added. The reaction results are shown in Table 1.

[0057] Comparative Example 3

[0058] Mix 15 g of copper nitrate, 5 g of zinc nitrate and 0.5 g of nickel nitrate in 100 mL of water, then add 1.5 g of sodium citrate, stir to obtain a mixture; prepare a 0.5 mol / L aqueous solution of sodium carbonate, slowly add the above mixture at a rate of 2 drops per second under the condition of constant temperature 50℃, adjust the pH to 8.0; after fully reacting at 40℃ for 24 hours, centrifuge, wash, dry, and calcine at 250℃ in air for 2 hours with a heating rate of 2℃ per minute, and then cool to room temperature to obtain the metal-doped composite catalyst. As shown in Table 1, in Comparative Example 3, the carbon dioxide conversion rate is 10.8%, the methanol selectivity is 45.6%, the carbon monoxide selectivity is 39.6%, and the methane is 14.8% when the reaction temperature is 240℃.

[0059] Comparative Example 4

[0060] Mix 15 g of copper nitrate and 5 g of zinc nitrate in 100 mL of water, then add 1.5 g of sodium citrate, stir to obtain a mixture; prepare a 0.5 mol / L aqueous solution of sodium carbonate, slowly add the above mixture at a rate of 2 drops per second under the condition of constant temperature 40℃, adjust the solution pH to 6.5; weigh 0.5 g of nickel nitrate and add it to the suspension obtained in step S2, continue to add sodium carbonate under stirring, and adjust the pH to 8.0; after fully reacting at 40℃ for 24 hours, centrifuge, wash, dry, and calcine at 250℃ in air for 2 hours with a heating rate of 2℃ per minute, and then cool to room temperature to obtain the metal-doped composite catalyst.

[0061] Comparative Example 5

[0062] The other conditions are the same as in Example 1, except that sodium citrate is replaced by citric acid.

[0063] Comparative Example 6

[0064] The other conditions are the same as in Example 1, except that sodium citrate is replaced by EDTA.

[0065] Comparative Example 7

[0066] The other conditions are the same as in Example 1, except that sodium citrate is replaced by polyvinylpyrrolidone.

[0067] Comparative Example 8

[0068] The other conditions are the same as in Example 1, except that sodium citrate is replaced by polyethylene glycol.

[0069] Table 1 is the test results of the carbon dioxide catalytic reduction performance of the metal-doped composite catalyst.

[0070] Table 1

[0071]

[0072]

Claims

1. A method for preparing a metal-doped composite catalyst for the methanol synthesis from carbon dioxide and hydrogen, characterized in that The catalyst comprises copper oxide, zinc oxide and a doping metal; the doping metal is selected from one or more of iron, cobalt, nickel, cerium, indium, aluminum, manganese, chromium, and magnesium; and the preparation method comprises the following steps: S1, uniformly mixing copper salt and zinc salt in a solvent, then adding sodium citrate, and stirring to obtain a mixed solution A; S2, preparing an aqueous carbonate solution, adding the aqueous carbonate solution to the mixed solution A, adjusting the pH of the solution to 2.5-4.5 to obtain a suspension B; S3, adding a doping metal salt to the suspension B obtained in step S2, continuously adding the aqueous carbonate solution under stirring, and adjusting the pH to 7.5-9.5; S4, after sufficient reaction, centrifuging, washing, drying, and calcining to obtain the composite catalyst.

2. The production method according to claim 1, characterized by, In step S1, the copper salt and zinc salt are selected from one or more of their corresponding nitrate, hydrochloride, sulfate, and acetylacetone salt.

3. The preparation method according to claim 1, characterized in that, In step S1, the solvent is selected from one or more of water, methanol, and ethanol.

4. The method of claim 1, wherein, In step S1, the concentration of the copper salt and zinc salt is independently 0.2-2.5 mol / L, and the mass ratio of sodium citrate to copper salt is 1:20-1:

10.

5. The preparation method according to claim 1, characterized in that, In step S2, the carbonate is one or more of sodium carbonate, potassium carbonate, and ammonium carbonate, and the concentration of the carbonate is 0.1-2.0 mol / L.

6. The method of claim 1, wherein, In step S2, the temperature for adding the aqueous carbonate solution to the mixed solution A is 20-40℃.

7. The preparation method according to claim 1, characterized in that, In step S2, the solution pH is adjusted to 2.5-3.

5.

8. The method of claim 1, wherein, In step S3, the pH is adjusted to 7.5-8.

0.

9. The method of claim 1, wherein, In step S4, the reaction temperature is 40-90℃, and the reaction time is 12-48 hours.

10. The method of claim 9, wherein, In step S4, the reaction temperature is 40-60℃, and the reaction time is 24 hours.

11. A metal-doped composite catalyst for the hydrocarbon of carbon dioxide to methanol, characterized in that, Prepared by the preparation method of any one of claims 1-10.

12. The catalyst of claim 11, wherein, The mass fraction of copper oxide is 20-80 wt%, the mass fraction of zinc oxide is 10-70 wt%, and the mass fraction of the doping metal is 1-10 wt%.

13. The catalyst of claim 11, wherein The doping metal is one or more of iron, cobalt, and nickel. The doping metal is one or more of iron, cobalt, and nickel.

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