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

Abstract

The application relates to a CuO-ZnO-ZrO2@CeO2 core-shell catalyst and a preparation method and application thereof in preparing methanol. The preparation method is as follows: copper nitrate and zinc nitrate are dissolved in deionized water to form a mixed solution, a precipitant is added, and hydrothermal reaction is carried out to obtain copper-zinc nanoscale dispersed particles; then the particles are dispersed in deionized water, a zirconium nitrate aqueous solution is added, and hydrothermal reaction is carried out to precipitate zirconium on the outer layer of the particles; then a cerium nitrate aqueous solution and a precipitant are added to the system, and hydrothermal reaction is carried out; after the reaction, the system is subjected to filtration, washing, drying, grinding and calcination to obtain the CuO-ZnO-ZrO2@CeO2 core-shell catalyst. In the application process, CO2 and H2 are used as raw materials, cyclohexanol is used as a solvent, hydrogenation reaction is carried out under the action of the core-shell catalyst at 190-210 DEG C, and methanol is prepared. The core-shell catalyst can be applied to hydrogen transfer hydrogenation for preparing methanol, and can exhibit excellent catalytic activity and stability and higher methanol selectivity.

Description

Technical Field

[0001] This invention belongs to the field of thermal catalyst technology, specifically relating to a CuO-ZnO-ZrO2@CeO2 core-shell catalyst, its preparation method, and its application in methanol preparation. Background Technology

[0002] With the large-scale burning of fossil fuels, CO2 emissions are increasing year by year. As a cheap, readily available, and environmentally friendly renewable carbon resource, CO2 can be utilized at a high value through chemical reactions, which can not only reduce CO2 emissions but also provide new green routes for the preparation of energy products, chemicals, and materials.

[0003] Methanol, also known as hydroxymethane, wood alcohol, or wood spirit, is the simplest saturated monohydric alcohol, first discovered through the dry distillation and cracking of wood. Methanol is an excellent energy carrier with a wide range of applications. First, as a basic organic chemical raw material, methanol can be used to produce formaldehyde, acetic acid, dimethyl ether, olefins, aromatic compounds, methyl formate, methylamine, and dimethyl carbonate, among others. Second, methanol is not only a good organic solvent but also a high-performance clean energy source and automotive fuel. Its reaction with tert-butanol to obtain methyl tert-butyl ether (MTBE) is a high-octane unleaded gasoline additive. Currently, the largest downstream application of methanol remains methanol-to-olefins, accounting for 50.59%.

[0004] The CO2 hydrogenation to methanol process is a novel approach, often referred to as "methanol economy." CO2 hydrogenation to methanol is an exothermic process, reducing the molecular weight of carbon-containing molecules. Therefore, thermodynamically, lowering the temperature and increasing the pressure is beneficial for improving methanol selectivity. However, CO2 is chemically stable and difficult to activate, so a relatively high temperature is required thermodynamically to promote CO2 conversion. Furthermore, the CO2 hydrogenation to methanol reaction is prone to reverse water-gas reaction (RWGS) and CO2 methanation, and the reaction also produces a large amount of water, inhibiting catalyst activity and ultimately leading to catalyst deactivation. Therefore, CO2 hydrogenation to methanol technology suffers from low CO2 conversion and low methanol selectivity in practical applications. The CO2 hydrogenation to methanol reaction is as follows: CO2 + 3H2 → CH3OH + H2O, ΔH 298K = -40.9 kJ / mol.

[0005] Catalyst systems for CO2 hydrogenation to methanol are typically copper-based catalysts modified from Cu / ZnO / Al2O3 catalysts used in syngas-to-methanol production. Other types of catalysts include noble metal catalysts, metal oxide catalysts, and some others. Domestically, this is still in the laboratory-scale testing stage. The most common Cu / ZnO catalysts typically operate at high reaction temperatures (>250℃) and high reaction pressures (H2+CO2>5MPa). Noble metal-supported catalysts generally exhibit high methanol selectivity, but their high production costs limit their industrial application. Metal oxide catalysts, mainly In2O3 catalysts and ZnO-ZrO2 solid solutions, offer good methanol selectivity and stability, but generally require higher reaction temperatures and consume more energy than Cu / ZnO catalysts. Therefore, developing inexpensive and efficient catalyst systems is of great significance for CO2 hydrogenation to methanol. Summary of the Invention

[0006] The purpose of this invention is to provide a CuO-ZnO-ZrO2@CeO2 core-shell catalyst, its preparation method, and its application in methanol production. The CuO-ZnO-ZrO2@CeO2 core-shell catalyst exhibits excellent catalytic activity and stability, as well as higher methanol selectivity, when applied to the hydrogen transfer hydrogenation process for methanol production.

[0007] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0008] A method for preparing a CuO-ZnO-ZrO2@CeO2 core-shell catalyst includes the following steps:

[0009] (1) Copper nitrate and zinc nitrate were dissolved in deionized water to form a mixed solution. Then the mixed solution was added dropwise to a precipitant for a hydrothermal reaction. After the reaction was completed, the solution was filtered and washed to obtain copper-zinc nano-sized dispersed particles.

[0010] (2) Copper-zinc nano-scale dispersed particles are uniformly dispersed in deionized water, and zirconium nitrate aqueous solution is added to carry out hydrothermal reaction, and zirconium is further precipitated on the outer layer of copper-zinc nano-scale dispersed particles.

[0011] (3) Add cerium nitrate aqueous solution to the solution system obtained in step (2), then add precipitant for hydrothermal reaction. After the reaction is completed, filter, wash, dry, grind, and then calcine at 400℃ to obtain CuO-ZnO-ZrO2@CeO2 core-shell catalyst with CuO-ZnO core on the inner side, discontinuous ZrO2 shell in the middle layer, and continuous loose and porous CeO2 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℃ and the hydrothermal reaction time is 1 h.

[0013] Preferably, 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.

[0014] Preferably, in step (2), the concentration of the zirconium nitrate aqueous solution is 0.5 mol / L; the hydrothermal reaction temperature is 50℃; 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, the volume ratio between the cerium nitrate aqueous solution and the zirconium nitrate aqueous solution is 1:1; the precipitant is an 8% sodium carbonate aqueous solution; the hydrothermal reaction temperature is 50℃, and the hydrothermal reaction time is 2h.

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

[0018] To achieve the purpose 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 purpose of the invention, the present invention also provides the application of the above-mentioned 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 and cyclohexanol as solvent, methanol is produced by hydrogenation reaction at 190-210℃ under the action of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst described in claim 8; the pressure ratio between H2 and CO2 is (1-5):1, the amount of 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.

[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 CO2 hydrogenation to methanol reaction;

[0023] (2) The present invention provides a hydrogen transfer pathway with milder reaction conditions in the CO2 hydrogenation to methanol reaction, which can obtain higher methanol selectivity;

[0024] (3) The CuO-ZnO-ZrO2@CeO2 core-shell catalyst provided by the present invention does not require activation during the reaction process and maintains high activity even after repeated reactions, thus exhibiting excellent stability;

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

[0026] Figure 1 Flowchart of the preparation method of CuO-ZnO-ZrO2@CeO2 core-shell catalyst;

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

[0028] Figure 3 Transmission electron microscope (a) and EDS image (bg) of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared in Example 1 of this invention;

[0029] Figure 4 The XRD patterns of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared in Example 1 of this invention and the CuO-ZnO-ZrO2@CeO2 core-shell catalyst after 4 cycles are shown.

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

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

[0032] Figure 7XPS spectra of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared in Example 1 of this invention: Cu 2p(a), Zn 2p(b), Zr 3d(c), Ce 3p(d) and O1s(e). Detailed Implementation

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

[0034] Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available products with a purity of analytical grade or higher.

[0035] Example 1

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

[0037] (1) Dissolve 0.004 mol copper nitrate and 0.0026 mol zinc nitrate in 10 mL of deionized water to form a mixed solution. Then, gradually add the mixed solution dropwise to 50 mL of an aqueous solution containing 1.06 g sodium carbonate. Place the solution in a hydrothermal reaction at 50 °C (stir for 1 h). After the reaction is complete, filter and wash to obtain copper-zinc nano-scale dispersed particles.

[0038] (2) Copper-zinc nano-sized dispersed particles were uniformly dispersed in 100 mL of deionized water, and 10 mL of aqueous solution containing 0.005 mol zirconium nitrate was added. The mixture was placed at 50 °C for hydrothermal reaction (stirred for 2 h) to further precipitate zirconium on the outer layer of copper-zinc nano-sized dispersed particles.

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

[0040] from Figure 2 (a) and Figure 2 As shown in (b), the catalyst exhibits a porous, plate-like structure after high-temperature calcination, which facilitates contact with the raw materials and improves its catalytic performance. Furthermore, the morphology of the catalyst remained unchanged after four catalytic cycles, indicating good stability. Figure 3 As shown in (a), the core-shell structure of the catalyst is evident. Energy dispersive spectroscopy (EDS) scans of the catalyst, as shown in (b)-(g), also confirm the core-shell structure. Figure 4 As can be seen, the peak value of the catalyst after four cycles corresponds to that before the reaction, indicating good catalyst stability. The catalyst was tested using an N2 physical adsorption-desorption analyzer, and the resulting adsorption-desorption isotherms are shown below. Figure 5 As shown in (a), based on the IUPAC classification, the prepared catalyst exhibits a typical type IV adsorption isotherm, as indicated by the pore size distribution. Figure 5 (b) From this perspective, the catalyst has a relatively large average pore size, which is beneficial for contact with the raw materials and promotes the reaction. The XPS spectrum of Cu 2p in CuO-ZnO-ZrO2@CeO2 is shown below. Figure 7 As shown in (a), the high binding energy Cu 2p 3 / 2 The appearance of the peak (933.0 eV) and satellite peaks is due to Cu 2+ The existence 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) is due to Zn 2+ The existence of species, such as Figure 7 As shown in (c), the catalyst contains Zr 3d 5 / 2 and Zr 3d 3 / 2 The two peaks are due to zirconium replacing cerium's lattice positions; the binding energy of zirconium is higher than that of metallic Zr but lower than that of ZrO2. Figure 7 As shown in (d), the catalyst uses Ce 4+ Species-based and a small amount of Ce 3+ Species, Ce 3+ Speciation may be due to Zr 4+ Or Cu 2+ Replace Ce 4+ Species-dependent, with 882.0, 888.6, and 897.9 eV attributed to Ce. 4+ 3D 5 / 2 900.6, 907.2, and 916.2 eV belong to Ce 4+ 3D 3 / 2 The peaks represented by 884.6 eV and 902.4 eV belong to Ce. 3+ In, such as Figure 7 As shown in (e), the α peak represents lattice oxygen in the metal oxide, the β peak represents defect oxygen, and the γ peak represents surface hydroxyl groups. Surface hydroxyl groups can typically promote catalytic activity. Figure 6 As can be seen, the H2-TPR spectra of the CuO-ZnO-ZrO2@CeO2 catalyst all contain three reduction peaks, with the α peak at low temperature attributed to Cu in the solid solution. 2+ The reduction of the β peak indicates small-sized copper oxide particles, while the γ peak indicates large-sized copper oxide particles. The prepared catalyst exhibits excellent reduction performance.

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

[0042] Performance testing of the catalyst for catalytic hydrogen transfer to achieve CO2 hydrogenation for methanol production was conducted in a microreactor. After the reactor was thoroughly dried, 9.68 g of cyclohexanol was placed in the reactor equipped with a rotor. CO2 was first introduced to 0.75 MPa, followed by H2 to 3 MPa. Then, 0.2 g of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst prepared in this example was added. The CO2 hydrogenation reaction was carried out at 200 °C for 20 h. After the reaction, the catalyst was separated by centrifugation after the reactor cooled. The liquid phase product mixture was quantitatively analyzed using a gas chromatograph equipped with an FID detector, and the content of each product was determined using the internal standard method. The gas phase product mixture was quantitatively analyzed using an infrared gas analyzer. The activity data of this catalyst for catalytic hydrogen transfer to achieve CO2 hydrogenation for methanol production are shown in Appendix Table 1.

[0043] Comparative Example

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

[0045] Example 2

[0046] Replace 200℃ in Example 1 with 190℃, and follow the same steps as in Example 1. Catalyst activity data are shown in Appendix Table 1.

[0047] Example 3

[0048] Replace 200℃ in Example 1 with 210℃, and follow the same steps as in Example 1. Catalyst activity data are shown in Appendix Table 1.

[0049] Example 4

[0050] Replace 20h in Example 1 with 5h, and follow the same steps as in Example 1. Catalyst activity data are shown in Appendix Table 1.

[0051] Example 5

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

[0053] Example 6

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

[0055] Example 7

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

[0057] Example 8

[0058] Replace the CO2 charging to 0.75 MPa in Example 1 with CO2 charging to 1 MPa, and the remaining steps are the same as in Example 1. The catalyst activity data are shown in Appendix Table 1.

[0059] Example 9

[0060] The CO2 charging to 0.75 MPa in Example 1 was replaced with CO2 charging to 1.5 MPa, and the remaining steps were the same as in Example 1. The catalyst activity data are shown in Appendix Table 1.

[0061] Table 1 Catalytic activity data for each embodiment

[0062]

[0063] The activity of a CuO-ZnO-ZrO2@CeO2 core-shell catalyst for the catalytic hydrogenation of CO2 to methanol was studied in a batch microreactor, and its performance is shown in Table 1. Comparing Example 1 and the comparative example, it is evident that the hydrogen transfer reaction pathway significantly improves the CO2 conversion rate and methanol selectivity compared to the reaction system without hydrogen transfer. Comparing Examples 1-3, it is shown that the CO2 conversion rate gradually increases with increasing temperature. Comparing Examples 1 and Examples 4-6, it is evident that the CO2 conversion rate and methanol selectivity gradually increase with increasing reaction time; however, the increasing trend of CO2 conversion rate and methanol selectivity slows down when the reaction time is extended from 20 h to 40 h. Comparing Examples 1 and Examples 7-9, it is evident that the methanol selectivity increases with increasing H2 to CO2 pressure ratio. In Example 1, the CO2 conversion rate decreased slightly after four cycles, mainly due to partial catalyst loss after each use, indicating that the catalyst has excellent stability.

[0064] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a CuO-ZnO-ZrO2@CeO2core-shell catalyst, characterized in that, The method comprises the following steps: (1) dissolving copper nitrate and zinc nitrate in deionized water to form a mixed solution, then adding the mixed solution into a precipitant to perform a hydrothermal reaction, and after the reaction, performing suction filtration and washing to obtain copper-zinc nanoscale dispersed particles; (2) uniformly dispersing the copper-zinc nanoscale dispersed particles in deionized water, adding a zirconium nitrate aqueous solution to perform a hydrothermal reaction, and further precipitating zirconium on the outer layer of the copper-zinc nanoscale dispersed particles; (3) adding a cerium nitrate aqueous solution into the solution system obtained in step (2), then adding a precipitant to perform a hydrothermal reaction, and after the reaction, performing suction filtration, washing, drying, grinding, and then calcining at 400 DEG C to obtain a CuO-ZnO-ZrO2@CeO2 core-shell catalyst with a CuO-ZnO core, a discontinuous ZrO2 shell in the middle layer, and a continuous loose porous CeO2 outer shell on the outer layer.

2. The preparation method of the CuO-ZnO-ZrO2@CeO2core-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 DEG C, and the hydrothermal reaction time is 1 h.

3. The preparation method of the CuO-ZnO-ZrO2@CeO2core-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. The preparation method of the CuO-ZnO-ZrO2@CeO2core-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 DEG C, and the hydrothermal reaction time is 2 h.

5. The preparation method of the CuO-ZnO-ZrO2@CeO2core-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. The preparation method of the CuO-ZnO-ZrO2@CeO2core-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, the volume ratio between the cerium nitrate aqueous solution and the zirconium nitrate aqueous solution is 1:1; the precipitant is a sodium carbonate aqueous solution with a mass concentration of 8%; the hydrothermal reaction temperature is 50 DEG C, and the hydrothermal reaction time is 2 h.

7. The preparation method of the CuO-ZnO-ZrO2@CeO2core-shell catalyst according to claim 1 or 2, characterized in that, In step (3), the drying temperature is 80 DEG C, the drying time is 12 h; the heating rate is 5 DEG C / min, and the calcining time is 5 h.

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

9. Application of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst in claim 8 in catalyzing the preparation of methanol through CO2 low-temperature hydrogen transfer hydrogenation.

10. Use according to claim 9, characterized in that, The specific application process is as follows: taking CO2 and H2 as raw materials, cyclohexanol as a solvent, and under the action of the CuO-ZnO-ZrO2@CeO2 core-shell catalyst in claim 8, hydrogenation reaction is performed at 190-210 DEG C to prepare methanol; the pressure ratio between 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 5-40 h.

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