CuO-ZnO-ZrO2-CeO2 core-shell catalyst, preparation method thereof and application of CuO-ZnO-ZrO2-CeO2 core-shell catalyst in preparation of methanol

Abstract

The invention relates to a CuO-ZnO-ZrO2-coated CeO2 core-shell catalyst, a preparation method thereof and an application of the CuO-ZnO-ZrO2-coated CeO2 core-shell catalyst in methanol preparation, the preparation method comprises the following steps: dissolving copper nitrate and zinc nitrate in deionized water to form a mixed solution, then adding a precipitator, and carrying out a hydrothermal reaction to obtain copper-zinc nanoscale dispersed particles; then dispersing the particles in deionized water, adding a zirconium nitrate aqueous solution for hydrothermal reaction, and precipitating zirconium on the outer layers of the particles; and adding a cerium nitrate aqueous solution and a precipitant into the system, carrying out a hydrothermal reaction, and after the reaction is finished, carrying out suction filtration, washing, drying, grinding and calcining to obtain the CuO-ZnO-ZrO2 at CeO2 core-shell catalyst. The application process is as follows: CO2 and H2 are used as raw materials, cyclohexanol is used as a solvent, and under the action of the core-shell catalyst, hydrogenation reaction is performed at 190-210 DEG C to prepare methanol. When the core-shell catalyst is applied to preparation of methanol through hydrogen transfer hydrogenation, excellent catalytic activity and stability and higher methanol selectivity can be shown.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal catalysts, and particularly relates to a CuO-ZnO-ZrO2@CeO2 core-shell catalyst, a preparation method thereof, and an application thereof in the preparation of methanol. Background Art

[0002] With the large-scale combustion of fossil fuels, the emissions of CO2 are increasing year by year. The concentration of CO2 in the atmosphere has rapidly increased from 280 ppm before industrialization to 420 ppm in 2022. It is predicted that by the end of the 21st century, the concentration of CO2 in the atmosphere will reach 700 - 1100 ppm. As a cheap, easily available and environmentally friendly renewable carbon resource, CO2 can be utilized with high value through chemical reactions, which can not only reduce CO2 emissions, but also provide a new green route for the preparation of energy products, chemicals and materials.

[0003] Methanol, also known as hydroxy methane, wood spirit or wood alcohol, is the simplest saturated monohydric alcohol in structure and was first discovered in the dry distillation and cracking of wood. Methanol is a good carrier for storing energy and has a very wide range of uses. First of all, as a basic organic chemical raw material, methanol can be used to produce formaldehyde, acetic acid, dimethyl ether, olefins, aromatic compounds, methyl formate, methylamine, dimethyl carbonate, etc.; secondly, methanol is not only a good organic solvent, but also an excellent clean energy and vehicle fuel. Methyl tert-butyl ether (MTBE) obtained by its reaction with tert-butanol is a high-octane unleaded gasoline additive. At present, the largest downstream of methanol is still mainly methanol-to-olefins, accounting for 50.59%.

[0004] The method of hydrogenating CO2 to methanol is a completely new idea, usually referred to as "methanol economy". The hydrogenation of CO2 to methanol is an exothermic process, and the molecular weight of the carbon-containing molecules decreases. Therefore, thermodynamically, lowering the temperature and increasing the pressure are beneficial to improving the selectivity of methanol. However, CO2 has stable chemical properties and is difficult to activate, so a relatively high temperature is required thermodynamically to promote the conversion of CO2. In addition, during the reaction of hydrogenating CO2 to methanol, the reverse water-gas shift reaction (RWGS) and the CO2 methanation reaction are likely to occur. At the same time, a large amount of water is generated during the reaction process, which inhibits the activity of the catalyst and ultimately leads to catalyst deactivation. Therefore, in the actual application process of the CO2 hydrogenation to methanol technology, there are problems of low CO2 conversion rate and low methanol selectivity. The reaction of hydrogenating CO2 to methanol is as follows: CO2 + 3H2 → CH3OH + H2O, △H 298K = -40.9 kJ / mol.

[0005] The catalyst system for hydrogenating CO2 to methanol is usually a copper-based catalyst improved from the Cu / ZnO / Al2O3 catalyst for synthesizing methanol from syngas. There are also noble metal catalysts, metal oxide catalysts, and some other types of catalysts. In China, it is still in the laboratory small-scale test stage. The operating conditions of the most common Cu / ZnO-based catalysts are usually under relatively high reaction temperatures (>250 °C) and relatively high reaction pressures (H2 + CO2 > 5 MPa). Noble metal-supported catalysts usually have high methanol selectivity, but their high production costs limit their industrial applications. Metal oxide catalysts mainly include In2O3-based catalysts and ZnO-ZrO2 solid solutions, etc. They have good methanol selectivity and stability, and generally require higher reaction temperatures than Cu / ZnO-based catalysts, resulting in high energy consumption. Therefore, developing inexpensive and efficient catalyst systems is of great significance for hydrogenating CO2 to methanol. Summary of the Invention

[0006] The purpose of the present invention is to provide a CuO-ZnO-ZrO2@CeO2 core-shell catalyst, its preparation method, and its application in the preparation of methanol. When the CuO-ZnO-ZrO2@CeO2 core-shell catalyst is applied to hydrogen transfer hydrogenation for preparing methanol, it can exhibit excellent catalytic activity and stability, as well as higher methanol selectivity.

[0007] To achieve the above-mentioned invention purpose, the technical solution adopted by the present invention is:

[0008] A preparation method of a CuO-ZnO-ZrO2@CeO2 core-shell catalyst, comprising the following steps:

[0009] (1) Dissolve copper nitrate and zinc nitrate in deionized water to form a mixed solution, and then drop the mixed solution into a precipitating agent for hydrothermal reaction. After the reaction ends, filter by suction and wash to obtain copper-zinc nanoscale dispersed particles;

[0010] (2) Uniformly disperse the copper-zinc nanoscale dispersed particles in deionized water, add an aqueous solution of zirconium nitrate for hydrothermal reaction, and further precipitate zirconium on the outer layer of the copper-zinc nanoscale dispersed particles;

[0011] (3) Add an aqueous solution of cerium nitrate to the solution system obtained in step (2), then add a precipitating agent for hydrothermal reaction. After the reaction ends, filter by suction, wash, dry, and grind, and then heat up to 400 °C for calcination to obtain a CuO-ZnO-ZrO2@CeO2 core-shell catalyst with a CuO-ZnO core on the inner side, a discontinuous ZrO2 shell in the middle layer, and a continuous porous CeO2 outer shell on the outer layer.

[0012] Preferably, in step (1), the concentrations of copper nitrate and zinc nitrate in the mixed solution are 0.4 mol / L and 0.255 mol / L, respectively; the hydrothermal reaction temperature is 50 °C, and the hydrothermal reaction time is 1 h.

[0013] Preferably, in step (1), the precipitating agent is an aqueous sodium carbonate solution with a mass concentration of 2.12%, and the volume ratio between the precipitating agent and the mixed solution is 5:1.

[0014] Preferably, in step (2), the concentration of the zirconium nitrate aqueous solution is 0.5 mol / L; the hydrothermal reaction temperature is 50 °C, and the hydrothermal reaction time is 2 h.

[0015] Preferably, in step (2), the volume ratio between the zirconium nitrate aqueous solution and deionized water is 1:10.

[0016] Preferably, in step (3), the concentration of the cerium nitrate aqueous solution is 0.5 mol / L, and the volume ratio between the cerium nitrate aqueous solution and the zirconium nitrate aqueous solution is 1:1; the precipitating agent is an aqueous sodium carbonate solution with a mass concentration of 8%; the hydrothermal reaction temperature is 50 °C, and the hydrothermal reaction time is 2 h.

[0017] Preferably, in step (3), the drying temperature is 80 °C, and the drying time is 12 h; the heating rate is 5 °C / min, and the calcination time is 5 h.

[0018] To achieve the object of the invention, the present invention also provides a CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared by the above preparation method.

[0019] To achieve the object of the invention, the present invention also provides an application of the above CuO-ZnO-ZrO2@CeO2 core-shell catalyst in the catalytic low-temperature hydrogen transfer hydrogenation of CO2 to prepare methanol.

[0020] Furthermore, the specific application process is as follows: using CO2 and H2 as raw materials, cyclohexanol as a solvent, under the action of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst described in claim 8, a hydrogenation reaction is carried out at 190 - 210 °C to obtain methanol; the pressure ratio between H2 and CO2 is (1 - 5):1, the dosage of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst is 2.07% of the mass of the used solvent, and the hydrogenation reaction time is 5 - 40 h.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The CuO-ZnO-ZrO2@CeO2 core-shell catalyst provided by the present invention exhibits excellent catalytic activity in the reaction of hydrogenating CO2 to methanol.

[0023] (2) The present invention provides that the reaction conditions of the hydrogen transfer path in the reaction of CO2 hydrogenation to methanol are milder, and higher methanol selectivity can be obtained;

[0024] (3) The CuO-ZnO-ZrO2@CeO2 core-shell catalyst provided by the present invention does not need to be activated during the reaction process, and still maintains high activity during repeated reactions, thus showing excellent stability;

[0025] (4) The preparation method of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst provided by the present invention is simple, the preparation cost is low, and the industrial application prospect is good; the prepared CuO-ZnO-ZrO2@CeO2 core-shell catalyst has a larger pore diameter and more pores on the one hand, which is more conducive to contact with the raw materials and improves its catalytic performance; on the other hand, it also has rich active sites, which promote the adsorption and activation of CO2 and are beneficial to improving the activity of the catalyst. Description of the Drawings

[0026] Figure 1 It is a flow chart of the preparation method of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst;

[0027] Figure 2 It is a scanning electron microscope image of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared in Example 1 of the present invention (a) and the CuO-ZnO-ZrO2@CeO2 core-shell catalyst after 4 cycles of reaction (b);

[0028] Figure 3 It is a transmission electron microscope image (a) and eds images (b-g) of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared in Example 1 of the present invention;

[0029] Figure 4 It is an XRD pattern of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared in Example 1 of the present invention and the CuO-ZnO-ZrO2@CeO2 core-shell catalyst after 4 cycles of reaction;

[0030] Figure 5 The N2 adsorption-desorption curve (a) and pore size distribution map (b) of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared in Example 1 of the present invention;

[0031] Figure 6 It is an H2-TPR spectrum of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared in Example 1 of the present invention;

[0032] Figure 7XPS spectra of Cu 2p (a), Zn 2p (b), Zr 3d (c), Ce 3p (d) and O 1s (e) of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared in Example 1 of the present invention. Detailed implementation mode

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] The raw materials and reagents used in the following examples are all commercially available products with a purity of analytical pure or above, unless otherwise specified.

[0035] Example 1

[0036] As Figure 1 shown, a preparation method of a CuO-ZnO-ZrO2@CeO2 core-shell catalyst includes the following steps:

[0037] (1) Dissolve 0.004 mol of copper nitrate and 0.0026 mol of zinc nitrate in 10 mL of deionized water to form a mixed solution, and then gradually drop the mixed solution into 50 mL of an aqueous solution containing 1.06 g of sodium carbonate, and carry out a hydrothermal reaction at 50 °C (stir for 1 h). After the reaction is completed, filter by suction, wash, and obtain copper-zinc nanoscale dispersed particles;

[0038] (2) Uniformly disperse the copper-zinc nanoscale dispersed particles in 100 mL of deionized water, add 10 mL of an aqueous solution containing 0.005 mol of zirconium nitrate, and carry out a hydrothermal reaction at 50 °C (stir for 2 h) to further precipitate zirconium on the outer layer of the copper-zinc nanoscale dispersed particles;

[0039] (3) Add 10 mL of an aqueous solution containing 0.005 mol of cerium nitrate to the above solution system, then drop 10 mL of an aqueous solution containing 0.80 g of sodium carbonate, and carry out a hydrothermal reaction at 50 °C (stir for 2 h). After the reaction is completed, filter by suction, wash, dry, grind, and calcine in a muffle furnace at 400 °C to obtain a CuO-ZnO-ZrO2@CeO2 core-shell catalyst with a CuO-ZnO core on the inner side, a discontinuous ZrO2 shell in the middle layer, and a continuous and porous CeO2 outer shell on the outer layer.

[0040] From Figure 2 (a) and Figure 2 (b), it can be seen that the catalyst is in a porous flake structure after high-temperature calcination, which is more conducive to contact with the raw materials and improves its catalytic performance. Moreover, after 4 cycles of catalytic reactions, the morphology of the catalyst has not changed, indicating that the catalyst has good stability. From Figure 3 (a), the core-shell structure of the catalyst can be seen. Energy spectrum scanning of the catalyst shows the results as shown in (b)-(g), which also confirms that the catalyst has a core-shell structure. FromFigure 4 It can be seen that the peak value of the catalyst after 4 cycles of reaction corresponds to that before the reaction, which shows that the catalyst has good stability. The catalyst was tested using a N2 physical adsorption and desorption instrument, and the adsorption and desorption isotherms obtained are as follows: Figure 5 As shown in (a), based on the IUPAC classification, the prepared catalyst has a typical type IV adsorption isotherm curve. Figure 5 (b) shows that the average pore size of the catalyst is larger, which is conducive to contact with the raw materials and promotes the reaction. The XPS spectrum of Cu 2p of CuO-ZnO-ZrO2@CeO2 is shown in Figure 2. Figure 7 (a) shows that the high binding energy Cu 2p 3 / 2 The peak (933.0 eV) and satellite peaks are due to the Cu 2+ The presence of species, such as Figure 7 As shown in (b), Zn 2p 3 / 2 peak (1021.4 eV) and Zn 2p 1 / 2 The peak (1044.4 eV) appears because Zn 2+ The presence of species, such as Figure 7 As shown in (c), the catalyst contains Zr 3d 5 / 2 and Zr 3d 3 / 2 There are two peaks. Since zirconium replaces the lattice position of cerium, the binding energy of the former is higher than that of metal Zr and lower than that of ZrO2, such as Figure 7 As shown in (d), the catalyst is Ce 4+ Species mainly and a small amount of Ce 3+ Species, Ce 3+ The speciation may be due to the Zr 4+ or Cu 2+ Replace Ce 4+ Species, among which 882.0, 888.6, and 897.9 eV are attributed to Ce 4+ 3D 5 / 2 , 900.6, 907.2, 916.2 eV are attributed to Ce 4+ 3D 3 / 2 , the peaks represented by 884.6eV and 902.4eV belong to Ce 3+ In Figure 7 As shown in (e), the α peak is the lattice oxygen of the metal oxide, the β peak is the defect oxygen, and the γ peak is the surface hydroxyl group, which can usually promote catalytic activity. Figure 6 It can be seen that the H2-TPR spectra of CuO-ZnO-ZrO2@CeO2 catalysts all contain three reduction peaks, and the low-temperature α peak is attributed to the Cu 2+ The β peak represents copper oxide particles with small crystal size, and the γ peak represents copper oxide particles with large crystal size. The prepared catalyst has excellent reduction performance.

[0041] The CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared in this example was applied to the catalytic low-temperature hydrogen transfer hydrogenation of CO2 to produce methanol. The specific application process was as follows:

[0042] The performance test for catalytic hydrogen transfer to achieve CO2 hydrogenation to produce methanol was carried out in a micro-reactor. After the reactor was thoroughly dried, 9.68 g of cyclohexanol was placed in the reactor with a rotor. First, CO2 was charged into the reactor to 0.75 MPa, and then H2 was charged to 3 MPa. 0.2 g of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared in this example was added, and the CO2 hydrogenation reaction was carried out at 200 °C for 20 h. After the reaction, after the reactor was cooled, the catalyst was separated by a centrifuge. The liquid-phase product mixture was quantitatively analyzed by a gas chromatograph with an FID detector, and the content of each product was determined by the internal standard method. The gas-phase product mixture was quantitatively analyzed by an infrared gas analyzer. The activity data of this catalyst for catalytic hydrogen transfer to achieve CO2 hydrogenation to produce methanol are shown in Table 1 in the appendix.

[0043] Comparative example

[0044] Replace 9.68 g of cyclohexanol in Example 1 with 7.74 g of cyclohexane, and the remaining steps are the same as in Example 1. The activity data of this catalyst for catalytic CO2 hydrogenation to produce methanol are shown in Table 1 in the appendix.

[0045] Example 2

[0046] Replace 200 °C in Example 1 with 190 °C, and the remaining steps are the same as in Example 1. The activity data of the catalyst are shown in Table 1 in the appendix.

[0047] Example 3

[0048] Replace 200 °C in Example 1 with 210 °C, and the remaining steps are the same as in Example 1. The activity data of the catalyst are shown in Table 1 in the appendix.

[0049] Example 4

[0050] Replace 20 h in Example 1 with 5 h, and the remaining steps are the same as in Example 1. The activity data of the catalyst are shown in Table 1 in the appendix.

[0051] Example 5

[0052] Replace 20 h in Example 1 with 10 h, and the remaining steps are the same as in Example 1. The activity data of the catalyst are shown in Table 1 in the appendix.

[0053] Example 6

[0054] Replace 20 h in Example 1 with 40 h, and the remaining steps are the same as in Example 1. The activity data of the catalyst are shown in Table 1 in the appendix.

[0055] Example 7

[0056] Replace the step of filling CO2 to 0.75 MPa in Example 1 with filling CO2 to 0.5 MPa, and the remaining steps are the same as those in Example 1. The activity data of the catalyst are shown in Table 1 in the appendix.

[0057] Example 8

[0058] Replace the step of filling CO2 to 0.75 MPa in Example 1 with filling CO2 to 1 MPa, and the remaining steps are the same as those in Example 1. The activity data of the catalyst are shown in Table 1 in the appendix.

[0059] Example 9

[0060] Replace the step of filling CO2 to 0.75 MPa in Example 1 with filling CO2 to 1.5 MPa, and the remaining steps are the same as those in Example 1. The activity data of the catalyst are shown in Table 1 in the appendix.

[0061] Table 1 Catalytic activity data of each example

[0062]

[0063] The activity of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst for the catalytic hydrogenation of CO2 to methanol was studied in a batch micro-reactor, and its performance is shown in Table 1. Comparing Example 1 with the comparative example, it can be seen that compared with the reaction system where hydrogen transfer does not occur, the reaction path of hydrogen transfer can greatly improve the conversion rate of CO2 and the selectivity of methanol. Comparing Examples 1-3, it can be seen that as the temperature increases, the conversion rate of CO2 gradually increases. Comparing Example 1 with Examples 4-6, it can be seen that as the reaction time extends, the conversion rate of CO2 and the selectivity of methanol gradually increase. When the reaction time extends from 20 h to 40 h, the increasing trend of the conversion rate of CO2 and the selectivity of methanol slows down. Comparing Example 1 with Examples 7-9, it can be seen that the selectivity of methanol increases as the ratio of the pressure of H2 to CO2 increases. In the 4 cycles of Example 1, the conversion rate of CO2 slightly decreases, mainly because part of the catalyst is lost after each use, indicating that the catalyst has excellent stability.

[0064] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a CuO-ZnO-ZrO2@CeO2 core-shell catalyst, characterized in that: The following steps are involved: (1) dissolving copper nitrate and zinc nitrate in deionized water to form a mixed solution, then dropping the mixed solution into a precipitant to perform a hydrothermal reaction, and after the reaction is completed, filtering and washing to obtain copper-zinc nano-scale dispersed particles; (2) uniformly dispersing copper-zinc nano-scale dispersed particles in deionized water, adding zirconium nitrate aqueous solution to carry out hydrothermal reaction, and further precipitating zirconium on the outer layer of the copper-zinc nano-scale dispersed particles; (3) adding an aqueous solution of cerium nitrate to the solution system obtained in step (2), and then adding a precipitant to carry out a hydrothermal reaction. After the reaction is completed, filtering, washing, drying, grinding, and then heating to 400° C. to calcine to obtain a CuO-ZnO-ZrO2@CeO2 core-shell catalyst having a CuO-ZnO core on the inside, a discontinuous ZrO2 shell in the middle layer, and a continuous loose and porous CeO2 shell on the outer layer.

2. The method for preparing a CuO-ZnO-ZrO2@CeO2 core-shell catalyst according to claim 1, characterized in that: In step (1), the concentrations of copper nitrate and zinc nitrate in the mixed solution are 0.4 mol / L and 0.255 mol / L respectively; the hydrothermal reaction temperature is 50° C., and the hydrothermal reaction time is 1 h.

3. A method for preparing a CuO-ZnO-ZrO2@CeO2 core-shell catalyst according to claim 1 or 2, characterized in that: In step (1), the precipitant is a sodium carbonate aqueous solution with a mass concentration of 2.12%, and the volume ratio between the precipitant and the mixed solution is 5:

1.

4. A method for preparing a CuO-ZnO-ZrO2@CeO2 core-shell catalyst according to claim 1 or 2, characterized in that: In step (2), the concentration of the zirconium nitrate aqueous solution is 0.5 mol / L; the hydrothermal reaction temperature is 50° C., and the hydrothermal reaction time is 2 h.

5. The method for preparing a CuO-ZnO-ZrO2@CeO2 core-shell catalyst according to claim 1 or 2, characterized in that: In step (2), the volume ratio between the zirconium nitrate aqueous solution and deionized water is 1:

10.

6. A method for preparing a CuO-ZnO-ZrO2@CeO2 core-shell catalyst according to claim 1 or 2, characterized in that: In step (3), the concentration of the cerium nitrate aqueous solution is 0.5 mol / L, and the volume ratio between the cerium nitrate aqueous solution and the zirconium nitrate aqueous solution is 1:1; the precipitant is an aqueous sodium carbonate solution with a mass concentration of 8%; the hydrothermal reaction temperature is 50° C., and the hydrothermal reaction time is 2 h.

7. A method for preparing a CuO-ZnO-ZrO2@CeO2 core-shell catalyst according to claim 1 or 2, characterized in that: In step (3), the drying temperature is 80° C. and the drying time is 12 h; the heating rate is 5° C. / min and the calcination time is 5 h.

8. A CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst according to claim 8 in catalyzing low-temperature hydrogen transfer hydrogenation of CO2 to produce methanol.

10. The use according to claim 9, characterized in that: The specific application process is: using CO2 and H2 as raw materials and cyclohexanol as solvent, a hydrogenation reaction is carried out at 190-210°C under the action of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst described in claim 8 to produce methanol; the pressure ratio between the H2 and CO2 is (1-5):1, the amount of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst is 2.07% of the mass of the solvent used, and the hydrogenation reaction time is 5-40h.

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