Catalyst for synthesizing methanol through carbon dioxide hydrogenation as well as preparation and application of catalyst

Abstract

The invention relates to a catalyst for synthesizing methanol through carbon dioxide hydrogenation as well as preparation and application of the catalyst. The preparation method of the catalyst comprises the following steps: dissolving Cu (NO3) 2.3 H2O, Zn (NO3) 2.6 H2O, Ce (NO3) 3.6 H2O and Fe (NO3) 3.9 H2O in water to obtain a mixed solution, fully stirring the mixed solution, adding citric acid, stirring the solution to a sol state at a preheating temperature, foaming and gelling to obtain a reaction product, and drying and calcining the reaction product to obtain the catalyst for synthesizing methanol through carbon dioxide hydrogenation. The catalyst prepared by the scheme provided by the invention is prepared by adopting a sol-gel method, and the CZCe catalyst is modified by taking Fe as an auxiliary agent, so that higher specific surface area and dispersity are realized, more active sites are provided for reaction, and the catalytic performance of the catalyst is improved. The prepared catalyst is used for synthesizing methanol through carbon dioxide hydrogenation, and has higher methanol selectivity, space time yield and stability.

Description

Technical Field

[0001] The present application relates to the technical field of carbon dioxide hydrogenation utilization, and in particular to a catalyst for synthesizing methanol by hydrogenation of carbon dioxide, and its preparation and application. Background Art

[0002] Methanol has attracted widespread attention due to its significant demand, ease of storage and transportation, and abundance of raw materials. Methanol has been widely used in the chemical and energy industries. As a key organic feedstock, it is commonly converted into light olefins, high-octane gasoline, methyl halides / ethers / esters, and other high-value-added chemicals. Furthermore, due to its higher octane rating and lower air pollution compared to traditional petroleum, methanol is considered a promising additive or alternative to gasoline-based liquid fuels. However, to meet the ever-increasing energy demand, the overexploitation of traditional fossil energy sources has led to the industrial use of large amounts of fossil fuels and other carbon-containing fuels, resulting in significant carbon dioxide emissions and accelerating global warming. Therefore, the production of methanol from captured carbon dioxide and renewable hydrogen has attracted considerable attention due to its potential to reduce dependence on fossil fuels and the harmful environmental impacts of their carbon dioxide. A key step in achieving this goal is the development of efficient methanol synthesis catalysts with excellent selectivity and stability.

[0003] Currently, methanol is usually produced by catalyzing carbon monoxide using a Cu / ZnO / Al2O3 catalyst under certain pressure (5 ~ 10 MPa) and temperature (200 ~ 300 ℃). However, under carbon dioxide hydrogenation conditions, this catalyst will undergo a reverse water gas shift (RWGS) side reaction and accelerate the sintering of the Cu catalyst, resulting in low methanol selectivity and poor stability in the hydrogenation reaction.

[0004] Therefore, there is an urgent need to develop a new and efficient catalyst with high methanol selectivity and good stability for the hydrogenation of carbon dioxide to methanol, so as to improve the methanol selectivity, space-time yield and stability. Summary of the Invention

[0005] In order to solve or partially solve the problems existing in the related art, the present application provides a catalyst for synthesizing methanol by hydrogenation of carbon dioxide and its preparation and application. The catalyst for synthesizing methanol by hydrogenation of carbon dioxide can solve the problems of poor stability, low product selectivity and low methanol space-time yield of existing catalysts under carbon dioxide hydrogenation conditions.

[0006] The present application provides a method for preparing a catalyst for synthesizing methanol by hydrogenating carbon dioxide, comprising the following steps: 1) Dissolve Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Ce(NO3)3·6H2O and Fe(NO3)3·9H2O in water to obtain a mixed solution, wherein the molar ratio of Cu, Zn, Ce and Fe is 6:3(1-x):1:3x, x is 10 mol%, 30 mol% or 50 mol%; the atomic proportion of Cu is 60 atom%; 2) The mixed solution in step 1) is fully stirred and then citric acid is added. The solution is stirred at a preheated temperature until it reaches a sol state and then foamed into a gel to obtain a reaction product. The reaction product is dried and calcined to obtain a catalyst for synthesizing methanol from carbon dioxide hydrogenation.

[0007] Optionally, Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Ce(NO3)3·6H2O and Fe(NO3)3·9H2O are dissolved in water to obtain a mixed solution, wherein the molar ratio of Cu, Zn, Ce and Fe is 6:3(1-x):1:3x, and x is 10 mol%.

[0008] Optionally, the total metal cation concentration in the mixed solution is 1 mol / L; and the molar ratio of citric acid to total metal cations is 1:1.2.

[0009] Optionally, the preheating temperature is 80-85°C.

[0010] Optionally, the temperature during the foaming of the gel is 120°C and the drying time is 12 to 20 hours.

[0011] Optionally, the calcination temperature is 400°C, the heating rate is 5°C / min, and the calcination time is 4 h.

[0012] The present application also provides a catalyst for synthesizing methanol by hydrogenating carbon dioxide, which is prepared using the above-mentioned preparation method.

[0013] The present application also provides an application of a catalyst in the synthesis of methanol by hydrogenation of carbon dioxide. The catalyst is placed in a fixed-bed reactor connected in series with a gas chromatograph, and a reducing gas is introduced. The catalyst is reduced at 300°C for 3 to 4 hours. Then, a reaction gas is introduced, and the synthesis of methanol by hydrogenation of carbon dioxide is carried out at 250°C and 3 MPa.

[0014] Optionally, the reducing gas is a mixture of hydrogen and nitrogen, with a molar ratio of hydrogen to nitrogen being 5:95.

[0015] Optionally, the reaction gas is a mixture of carbon dioxide, hydrogen and nitrogen, the molar ratio of carbon dioxide, hydrogen and nitrogen is 23:69:8, and the space velocity of the reaction gas is 11000 ~ 12000 mL·g cat-1 ·h −1 .

[0016] Beneficial effects

[0017] (1) The present application uses Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Ce(NO3)3·6H2O and Fe(NO3)3·9H2O as raw materials and citric acid as a complexing agent, and adopts a sol-gel method to prepare a catalyst, thereby inhibiting the growth of particle size and improving the dispersibility of the particles; the catalyst utilizes ZnO to maintain the specific surface area of ​​copper and prevent copper particles from sintering, and utilizes CeO2 to have unique catalytic properties due to oxygen vacancies and variable oxidation states, synergistically promoting the hydrogenation of carbon dioxide to synthesize methanol; at the same time, an appropriate amount of Fe is added to promote the dispersion of Cu and Zn, forming abundant active sites, thereby improving the catalytic performance of the catalyst.

[0018] (2) The present application prepares a catalyst for the hydrogenation of carbon dioxide to methanol by adjusting the molar ratio of Cu, Zn, Ce and Fe in the raw materials so that the particles are evenly dispersed; the appropriate ratio of Cu and Zn enables a synergistic effect between Cu and Zn, and ZnO can maintain the specific surface area of ​​copper, prevent the sintering of copper particles, and form more Cu-ZnO through the synergistic effect between Cu and Zn. x Active sites promote CO2 hydrogenation. The selection of a quaternary catalyst containing Cu, Zn, Ce, and Fe can improve methanol selectivity and have good stability. It has higher methanol selectivity and space-time yield while using simple raw materials and simplifying the process.

[0019] (3) The raw materials of this application are widely available, the process is simple, and it has the advantages of being easy to control and environmentally friendly. In addition, the resulting catalyst achieves a higher specific surface area and dispersion, has higher methanol selectivity, space-time yield and stability, and realizes efficient resource utilization of carbon dioxide, providing a new alternative for industrial methanol synthesis catalysts.

[0020] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and other objects, features and advantages of the present application will become more apparent through a more detailed description of exemplary embodiments of the present application in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the present application.

[0022] Figure 1 This is a scanning electron microscope image of a catalyst for synthesizing methanol from carbon dioxide hydrogenation prepared as shown in Comparative Example 1 of the present application; Figure 2This is a scanning electron microscope image of a catalyst for synthesizing methanol from carbon dioxide hydrogenation prepared as shown in Example 1 of the present application; Figure 3 This is an XRD characterization result diagram of a catalyst for synthesizing methanol from carbon dioxide hydrogenation prepared as shown in Examples 1-3 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0023] The following describes embodiments of the present application in more detail with reference to the accompanying drawings. Although the accompanying drawings illustrate embodiments of the present application, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. Rather, these embodiments are provided to make the present application more thorough and complete, and to fully convey the scope of the present application to those skilled in the art.

[0024] The method for preparing the catalyst in the present application is a sol-gel method, which requires ensuring that the metal ion concentration is 1 mol / L. At the same time, citric acid is added, and the molar ratio of metal ions to citric acid is 1:1.2. Based on this, the molar ratio of Cu and Zn is fixed, the amount of citric acid must be certain, the metal ion concentration must be certain, and the water to be added must require the sum of the molar ratios of Cu, Zn, Ce, and Fe to be constant. The molar ratio of Cu, Zn, Ce, and Fe is 6:3(1-x):1:3x, where x represents different Fe doping amounts x=0mol%, 10mol%, 30mol%, and 50mol%.

[0025] The present application provides a preparation method for a catalyst for synthesizing methanol by hydrogenating carbon dioxide. The method comprises the following steps: weighing Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Ce(NO3)3·6H2O, and Fe(NO3)3·9H2O nitrates, dissolving them in deionized water, stirring them thoroughly, adding citric acid, transferring the solution to an oil bath, stirring it to a sol state, and rapidly transferring it to a foaming gel in a blast drying oven. Finally, the dried and evenly ground reaction product is calcined in a muffle furnace to obtain a catalyst.

[0026] Among them, the fixed Cu atom accounted for 60atom%, and the molar ratio of Cu / Zn / Ce / Fe was 6:3(1-x):1:3x (x=0, 10, 30, 50mol%); the required amount of M nitrate (M=Cu, Zn, Ce, Fe) was dissolved in deionized water (total metal cation concentration 1mol / L) according to the corresponding metal molar ratio.

[0027] Wherein, citric acid is added according to the molar ratio of metal ions to complexing agents, wherein n 总离子 :n 柠檬酸 =1:1.2.

[0028] The sol was carried out in an oil bath, and the temperature of the oil bath was 80 ~ 85 ℃.

[0029] Among them, the foaming gel was carried out in a blast drying oven at a temperature of 120 °C and a drying time of 12 to 20 h.

[0030] The calcination was carried out in a muffle furnace at a temperature of 400 °C and a calcination time of 4 h.

[0031] The above catalyst can be used for the synthesis of methanol by hydrogenation of carbon dioxide. The specific reaction process includes: The catalyst was placed in a fixed-bed reactor connected in series with a gas chromatograph, and a reducing gas was introduced to reduce the catalyst at 300°C for 3 to 4 hours. Then, the reaction gas was introduced to carry out a carbon dioxide hydrogenation to methanol reaction at 250°C and 3 MPa.

[0032] The reducing gas is a mixture of hydrogen and nitrogen, and the molar ratio of hydrogen to nitrogen is 5:95.

[0033] The reaction gas is a mixture of carbon dioxide, hydrogen and nitrogen, the molar ratio of carbon dioxide, hydrogen and nitrogen is 23:69:8, and the space velocity of the reaction gas is 11000 ~ 12000 mL·g cat -1 ·h −1 .

[0034] This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the content.

[0035] Example 1

[0036] A catalyst for synthesizing methanol by hydrogenation of carbon dioxide, the preparation method of which comprises the following steps: The molar ratio of Cu, Zn, Ce and Fe is 6:3(1-x):1:3x. When x is 10 mol%, the molar ratio of Cu / Zn / Ce / Fe is 6:2.7:1:0.3. 2.899 g Cu(NO3)2·3H2O, 1.606 g Zn(NO3)2·6H2O, 0.868 g Ce(NO3)3·6H2O and 0.243 g Fe(NO3)3·9H2O nitrates were weighed and dissolved in deionized water to obtain a mixed solution (total metal cation concentration 1 mol / L). After sufficient stirring at room temperature, the mixture was heated according to the molar ratio of metal ions to complexing agents. 总离子 :n 柠檬酸=1:1.2, 5.044 g of citric acid monohydrate was added, and the solution was transferred to an oil bath preheated to 80°C. After stirring until a sol state occurred, the solution was quickly transferred to a 120°C forced air drying oven to form a foaming gel and dried overnight for 12 hours. Finally, the dried and uniformly ground sample was calcined in a muffle furnace at 400°C for 4 hours at a heating rate of 5°C / min. The resulting catalyst was designated Fe10-CZCe.

[0037] Example 2

[0038] A catalyst for synthesizing methanol by hydrogenation of carbon dioxide, the preparation method of which comprises the following steps: The molar ratio of Cu, Zn, Ce and Fe is 6:3(1-x):1:3x. When x is 30 mol%, the molar ratio of Cu / Zn / Ce / Fe is 6:2.1:1:0.9. 2.899 g Cu(NO3)2·3H2O, 1.249 g Zn(NO3)2·6H2O, 0.868 g Ce(NO3)3·6H2O and 0.727 g Fe(NO3)3·9H2O nitrates were weighed and dissolved in deionized water to obtain a mixed solution (total metal cation concentration 1 mol / L). After sufficient stirring at room temperature, the mixture was heated according to the molar ratio of metal ions to complexing agents. 总离子 :n 柠檬酸 =1:1.2, 5.044 g of citric acid monohydrate was added, and the solution was transferred to an oil bath preheated to 80°C. After stirring until a sol state occurred, it was quickly transferred to a 120°C forced air drying oven to form a foaming gel and dried overnight for 12 hours. Finally, the dried and uniformly ground sample was calcined in a muffle furnace at 400°C for 4 hours at a heating rate of 5°C / min. The resulting catalyst was designated Fe30-CZCe.

[0039] Example 3

[0040] A catalyst for synthesizing methanol by hydrogenation of carbon dioxide, the preparation method of which comprises the following steps: The molar ratio of Cu, Zn, Ce and Fe is 6:3(1-x):1:3x. When x is 50 mol%, the molar ratio of Cu / Zn / Ce / Fe is 6:1.5:1:1.5. 2.899 g Cu(NO3)2·3H2O, 0.892 g Zn(NO3)2·6H2O, 0.868 g Ce(NO3)3·6H2O and 1.212 g Fe(NO3)3·9H2O nitrates were weighed and dissolved in deionized water to obtain a mixed solution (total metal cation concentration 1 mol / L). After sufficient stirring at room temperature, the mixture was heated according to the molar ratio of metal ions to complexing agents. 总离子 :n 柠檬酸=1:1.2, 5.044 g of citric acid monohydrate was added, and the solution was transferred to an oil bath preheated to 80°C. After stirring until a sol state, it was quickly transferred to a 120°C forced air drying oven to form a foaming gel and dried overnight for 12 hours. Finally, the dried and uniformly ground sample was calcined in a muffle furnace at 400°C for 4 hours at a heating rate of 5°C / min. The resulting catalyst was designated Fe50-CZCe.

[0041] The difference between Comparative Example 1 and Example 1 is that the catalyst prepared in Comparative Example 1 does not contain any Fe element as an auxiliary agent.

[0042] The specific steps are as follows: the molar ratio of Cu / Zn / Ce / Fe is 6:3:1:0, 2.899 g Cu(NO3)2·3H2O, 1.785 g Zn(NO3)2·6H2O, 0.868 g Ce(NO3)3·6H2O, and 0 g Fe(NO3)3·9H2O nitrates are weighed and dissolved in deionized water to obtain a mixed solution (total metal cation concentration is 1 mol / L), and after sufficient stirring at room temperature, the molar ratio of metal ions to complexing agents is n. 总离子 :n 柠檬酸 =1:1.2, 5.044 g of citric acid monohydrate was added, and the solution was transferred to an oil bath preheated to 80°C. After stirring until a sol state occurred, the solution was quickly transferred to a 120°C forced air drying oven to form a foaming gel and dried overnight for 12 hours. Finally, the dried and uniformly ground sample was calcined in a muffle furnace at 400°C for 4 hours at a heating rate of 5°C / min. The resulting catalyst was designated FeO-CZCe.

[0043] Comparative Example 1: The surface morphology of the catalyst prepared without adding any Fe element as a promoter is compared with that of the catalyst prepared in Example 1 ( Figure 1 、 Figure 2 ), after adding an appropriate amount of Fe-modified CZCe catalyst, the dispersion of the catalyst particles becomes better and the surface becomes more porous, which is more conducive to the contact and adsorption of active centers with carbon dioxide, and is more conducive to improving the catalytic performance of the catalyst.

[0044] Example 4

[0045] This example is used to evaluate the catalytic performance of the catalysts in Examples 1-3 and Comparative Example 1 in the reaction of synthesizing methanol from carbon dioxide hydrogenation. The specific process is as follows: 500 mg of catalyst was placed in a fixed-bed reactor connected in series with a gas chromatograph, and the reducing gas was introduced. The catalyst was reduced at 300°C for 4 hours. Then, the reaction gas was introduced, and the carbon dioxide hydrogenation to methanol reaction was carried out at 250°C and 3 MPa. After the reactor stabilized for 4 hours, data was collected and carbon monoxide, carbon dioxide gas products, and methanol liquid products were analyzed using a gas chromatograph equipped with TCD and FID. The carbon dioxide conversion rate, methanol selectivity, carbon monoxide selectivity, and methanol space-time yield were expressed as 、 、 、 express.

[0046] The reducing gas is a mixture of hydrogen and nitrogen, with a molar ratio of hydrogen to nitrogen of 5:95; the reaction gas is a mixture of carbon dioxide, hydrogen and nitrogen, with a molar ratio of carbon dioxide, hydrogen and nitrogen of 23:69:8, and the space velocity of the reaction gas is 12000 mL·g cat -1 ·h −1 The evaluation of catalyst activity is shown in Table 1.

[0047] Table 1 Evaluation results of catalyst activity

[0048] As can be seen from Table 1, by adding an appropriate amount of Fe-modified CZCe catalyst, wherein the molar ratio of Cu / Zn / Ce / Fe in Example 1 is 6:2.7:1:0.3, the catalytic performance of the prepared catalyst Fe10-CZCe is significantly improved, with a carbon dioxide conversion rate of 14.5%, a methanol selectivity of 81.5%, a carbon monoxide selectivity of 18.5%, and a methanol space-time yield of 204.9 g·kg cat -1 ·h -1 .

[0049] from Figure 3 It can be seen from the XRD characterization results that the proportion of Zn in Cu / Zn gradually decreases, and the Cu-ZnO formed between Cu and Zn x The number of active sites also gradually decreases, and the catalytic performance of the catalyst should gradually decrease, but the final catalytic performance trend is to increase first and then decrease, which is due to the doping of Fe in Example 1. Figure 1 and Figure 2 The SEM morphology characterization shows that the Fe-doped catalyst in Example 1 is better than the Cu-ZnO without Fe doping. x For the catalyst of Comparative Example 1 with the most active sites, the particles are more evenly dispersed, which further illustrates that although Cu-ZnO xThe number of active sites decreases, but the incorporation of Fe makes up for this shortcoming, making the particles evenly dispersed and enhancing the anti-sintering and catalytic performance.

[0050] The embodiments of the present application have been described above. The above description is illustrative and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or improvements to the technology in the market, or to enable other persons skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing a catalyst for synthesizing methanol by hydrogenation of carbon dioxide, characterized in that: The following steps are involved: 1) Dissolve Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Ce(NO3)3·6H2O and Fe(NO3)3·9H2O in water to obtain a mixed solution, wherein the molar ratio of Cu, Zn, Ce and Fe is 6:3(1-x):1:3x, x is 10 mol%, 30 mol% or 50 mol%; the atomic proportion of Cu is 60 atom%; 2) The mixed solution in step 1) is fully stirred and then citric acid is added. The solution is stirred at a preheated temperature until it reaches a sol state and then foamed into a gel to obtain a reaction product. The reaction product is dried and calcined to obtain a catalyst for synthesizing methanol from carbon dioxide hydrogenation.

2. The preparation method according to claim 1, characterized in that Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Ce(NO3)3·6H2O and Fe(NO3)3·9H2O were dissolved in water to obtain a mixed solution, wherein the molar ratio of Cu, Zn, Ce and Fe was 6:3(1-x):1:3x, and x was 10 mol%.

3. The preparation method according to claim 1, characterized in that The total metal cation concentration in the mixed solution is 1 mol / L; the molar ratio of the citric acid to the total metal cations is 1:1.

2.

4. The preparation method according to claim 1, characterized in that The preheating temperature is 80-85°C.

5. The preparation method according to claim 1, characterized in that The temperature of the foaming gel is 120° C. and the drying time is 12 to 20 hours.

6. The preparation method according to claim 1, characterized in that The calcination temperature is 400° C., the heating rate is 5° C. / min, and the calcination time is 4 h.

7. A catalyst for synthesizing methanol by hydrogenation of carbon dioxide, characterized in that: The product is prepared by the preparation method according to any one of claims 1 to 6.

8. Use of a catalyst in the synthesis of methanol by hydrogenation of carbon dioxide, characterized in that: The catalyst is placed in a fixed-bed reactor connected in series with a gas chromatograph, and reducing gas is introduced to reduce the catalyst at 300° C. for 3 to 4 hours. Then, reaction gas is introduced to carry out carbon dioxide hydrogenation to methanol synthesis reaction at 250° C. and 3 MPa.

9. The use according to claim 8, characterized in that The reducing gas is a mixture of hydrogen and nitrogen, and the molar ratio of hydrogen to nitrogen is 5:

95.

10. The use according to claim 8, characterized in that The reaction gas is a mixture of carbon dioxide, hydrogen and nitrogen, the molar ratio of carbon dioxide, hydrogen and nitrogen is 23:69:8, and the space velocity of the reaction gas is 11000~12000mL·g cat -1 ·h −1 .

Images