Preparation method and application of catalyst containing vacancy cluster ultrathin CeO2 nanosheet
By preparing ultra-thin CeO2 nanosheet catalysts containing vacancy clusters, the problem of low yield of DMC in synthesis of CO2 and CH3OH is solved, and the coordinated activation and efficient catalysis of CO2 and CH3OH are achieved, and environmentally friendly characteristics are achieved.
Patent Information
- Application Number
- CN202510232112.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-28
- Publication Date
- 2025-06-20
AI Technical Summary
In the prior art, the yield of synthesis of dimethyl carbonate (DMC) between CO2 and CH3OH is low, mainly due to the "inertness" of CO2 molecules themselves, which leads to difficulty in activation.
Using the preparation method of ultra-thin CeO2 nanosheet catalyst containing vacancy clusters, ultra-thin CeO2 nanosheets were formed during Ce-MOF synthesis by adjusting the ratio of ligand to surfactant, and the catalyst rich in O-Ce-O vacancy clusters was obtained by calcining under an air atmosphere.
The activity and yield of DMC synthesized by CO2 and CH3OH is significantly improved, and the coordinated activation of CO2 and CH3OH is achieved. The catalytic process is environmentally friendly and does not produce harmful by-products.
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Figure CN120169341A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of catalyst preparation, and in particular relates to a preparation method and application of an ultra-thin CeO2 nanosheet catalyst containing vacancy clusters. Background Art
[0002] In the context of global climate change, excessive emissions of carbon dioxide (CO2) have become a serious environmental problem, leading to a series of hazards such as greenhouse effect, glacier melting and extreme climate phenomena. Therefore, the use of CO2 to synthesize high-value-added chemicals has become an important way to achieve dual carbon goals and energy transformation. Dimethyl carbonate (DMC) is a widely used chemical raw material due to its characteristics of safe and convenient use, environmental protection, low toxicity, and excellent performance. It is known as the "new cornerstone" of today's organic synthesis. Therefore, the use of CO2 to synthesize DMC demonstrates competitive advantages in the CO2 conversion path.
[0003] The synthesis of DMC from CO2 and CH3OH is a multi-molecule cooperative reaction: one molecule of CH3OH dissociates to form a CH3O* group that reacts with the CO2 free radical to form methyl carbonate (CH3OCOO*); then, CH3OCOO* decomposes to form the key intermediate CH3OCO*, which couples with another molecule of CH3O* group to form DMC. However, the "inertness" of the CO2 molecule itself (C=O bond 750 kJ / mol) is the main reason for the low yield of DMC. Ce on the surface of CeO2 3+ With Ce 4+ The mutual exchange makes the catalyst surface rich in oxygen vacancies, which can effectively activate CO2 molecules. Studies have shown that compared with CO2, CH3O* species are more easily adsorbed on the oxygen vacancies on the CeO2 surface, resulting in competitive activation of CO2 and CH3OH at oxygen vacancies. Therefore, constructing multiple active sites at adjacent positions becomes the key to achieving synergistic activation of CO2 and CH3OH to increase the yield of DMC. Summary of the invention
[0004] The purpose of the present invention is to provide a preparation method and application of an ultrathin CeO2 nanosheet catalyst containing vacancy clusters. The ultrathin CeO2 nanosheet catalyst containing vacancy clusters has a significant effect on the activity of catalyzing CO2 / CH3OH to prepare dimethyl carbonate, providing a new research idea for the preparation of efficient cerium-based catalysts and the synthesis of dimethyl carbonate.
[0005] The present invention adopts the following technical solution: A method for preparing an ultra-thin CeO2 nanosheet catalyst containing vacancy clusters comprises the following steps: S1, cerium nitrate hexahydrate and pyromellitic acid were dissolved in equal volumes of deionized water and stirred for 0.5-2 h to form solution A and solution B; S2. Dissolve polyvinylpyrrolidone in deionized water and stir for 0.5 - 1 h to form solution C; S3. Take equal volumes of solution A and solution B and mix them. Carry out a reflux reaction under a constant temperature condition of 50 °C; simultaneously, dropwise add an equal volume of solution C at a rate of 30 drops per minute, and continue refluxing for 1 h to form a milky white suspension D; S4. Centrifuge and collect the white suspension D, and wash it 3 times with deionized water and anhydrous ethanol respectively. Finally, dry it in an oven at 100 °C for 12 h to obtain the Ce-MOFs precursor; S5. Put the Ce-MOFs precursor into a crucible and calcine it in an air atmosphere. After the calcination is completed, take out the crucible and cool it to room temperature, and then collect the product, namely, a catalyst containing vacancy cluster ultrathin CeO2 nanosheets is prepared.
[0006] Further, the molar ratio of cerium nitrate hexahydrate to pyromellitic acid in S1 is 1:1, and the volume of deionized water is 50 - 200 mL.
[0007] Further, the molar ratio of pyromellitic acid to polyvinylpyrrolidone is 1:1 - 1:5.
[0008] Further, the volume of deionized water in S2 is 50 - 200 mL.
[0009] Further, the volumes of solution A, solution B, and solution C in S3 are all 20 - 200 mL.
[0010] Further, the calcination temperature in S5 is 500 °C and the calcination time is 5 h.
[0011] A catalyst containing vacancy cluster ultrathin CeO2 nanosheets is applied to catalyze the synthesis of DMC from CO2 / CH3OH under different temperature conditions.
[0012] The principle of the present invention is as follows: The present invention uses cerium nitrate as the cerium source, pyromellitic acid as the ligand, and polyvinylpyrrolidone (PVP) as the surfactant. During the synthesis of Ce-MOF, PVP plays a dispersing role to obtain ultrathin Ce-MOF, and ultrathin CeO2 nanosheets are obtained by calcination in an air atmosphere. Theoretical calculation results show that reducing the thickness of CeO2 contributes to the formation of O-Ce-O vacancy clusters. According to the results of aberration-corrected scanning electron microscopy, it is confirmed that the ultrathin CeO2 prepared by the present invention contains O-Ce-O vacancy clusters.
[0013] The vacancy clusters of the present invention exist in the form of an O-Ce-O structure. The main feature of this preparation method is that by adjusting the ratio of the ligand to the surfactant within the range of 1:1 - 1:5, a catalyst containing vacancy cluster ultrathin CeO2 nanosheets can be prepared, and the content of vacancy clusters in the CeO2 nanosheets increases with the increase of the proportion of the surfactant.
[0014] The beneficial effects of the present invention are as follows: 1. The preparation method of the vacancy-cluster-containing ultrathin CeO2 nanosheets in the present invention is simple and easy to control, and it has excellent performance in catalyzing the synthesis of DMC from CO2 / CH3OH. The reaction process is environmentally friendly and does not produce harmful by-products. 2. Compared with CeO2 containing oxygen vacancies, the introduction of rich vacancy clusters constructs multi-active sites at adjacent positions on the CeO2 surface, realizing the synergistic activation of CO2 and CH3OH. 3. Preparing vacancy-cluster-containing ultrathin CeO2 nanosheets and applying them to the field of catalyzing the synthesis of DMC from CO2 can not only provide new methods and new applications for the preparation of highly active Ce-based materials, but also have potential application value for solving the energy crisis and environmental green governance. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Figure 1 X-ray diffraction (XRD) patterns of the CeO2 catalysts prepared in Examples 1-3 of the present invention; Figure 2 SEM images of the CeO2 catalyst prepared in Example 1 of the present invention; Figure 3 SEM images of the CeO2 catalyst prepared in Example 2 of the present invention; Figure 4 SEM images of the CeO2 catalyst prepared in Example 3 of the present invention; Figure 5 DMC yield diagrams of the CeO2 catalysts prepared in Examples 1-3 of the present invention; Figure 6 AC-TEM images of the CeO2 catalyst prepared in Example 2 of the present invention; Figure 7 Existence forms (theoretical calculation) of vacancy clusters in the CeO2 catalysts in Examples 1-3 of the present invention; Figure 8 Electron paramagnetic resonance diagrams (ERP) of the CeO2 catalysts prepared in Examples 1-3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION
[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.
[0017] Example 1 Cerium nitrate hexahydrate was used as the cerium source, pyromellitic acid was used as the ligand, deionized water was used as the solvent, and polyvinylpyrrolidone was used as the surfactant.
[0018] 1) Cerium(III) nitrate hexahydrate and pyromellitic acid (molar ratio 1:1) were separately dissolved in deionized water of equal volume (50 mL), and stirred for 0.5 h to form solutions A and B. Polyvinylpyrrolidone (ligand to surfactant molar ratio 1:1) was dissolved in 50 mL of deionized water with a volume fraction, and stirred for 0.5 h to form solution C. Equal volumes of 50 mL of solutions A and B were taken and mixed, and a reflux reaction was carried out under a constant temperature condition of 50 °C. At the same time, an equal volume of solution C was added dropwise at a rate of 30 drops per minute, and reflux was continued for 1 h to form a milky white suspension D. Centrifugation was carried out for collection, and it was washed 3 times with deionized water and absolute ethanol respectively. Finally, it was dried in an oven at 100 °C for 12 h to obtain the Ce-MOFs precursor; 2) 0.1 g of the Ce-MOFs precursor was weighed and placed in a crucible. It was calcined at 500 °C for 5 h in an air atmosphere. The crucible was taken out and cooled to room temperature, and then the product was collected, that is, the ultrathin CeO2 nanosheet catalyst containing vacancy clusters was prepared, denoted as CeO2-1.
[0019] The above-prepared ultrathin CeO2 nanosheet catalyst containing vacancy clusters was used for the performance test of catalyzing CO2 / CH3OH to prepare DMC (catalyst: 0.1 g, initial pressure of CO2: 2 MPa, CH3OH: 35 mL). The selectivity of the liquid-phase product DMC was 100%. At different temperature conditions (120 °C, 140 °C, 160 °C), the yields of DMC were 7.2, 18.3, and 12.6 mmol / g respectively.
[0020] Example 2 Cerium(III) nitrate hexahydrate was used as the cerium source, pyromellitic acid as the ligand, deionized water as the solvent, and polyvinylpyrrolidone as the surfactant.
[0021] 1) Cerium(III) nitrate hexahydrate and pyromellitic acid (molar ratio 1:1) were separately dissolved in deionized water of equal volume (100 mL), and stirred for 1 h to form solutions A and B. Polyvinylpyrrolidone (ligand to surfactant molar ratio 1:3) was dissolved in 100 mL of deionized water with a volume fraction, and stirred for 0.8 h to form solution C. Equal volumes of 100 mL of solutions A and B were taken and mixed, and a reflux reaction was carried out under a constant temperature condition of 50 °C. At the same time, 100 mL of solution C was added dropwise at a rate of 30 drops per minute, and reflux was continued for 1 h to form a milky white suspension D. Centrifugation was carried out for collection, and it was washed 3 times with deionized water and absolute ethanol respectively. Finally, it was dried in an oven at 100 °C for 12 h to obtain the Ce-MOFs precursor; 2) Weigh 0.3 g of the Ce-MOFs precursor and put it into a crucible. Under an air atmosphere, calcine it at 500 °C for 5 h. Take out the crucible and cool it to room temperature, then collect the product, obtaining the catalyst of ultrathin CeO2 nanosheets containing vacancy clusters, denoted as CeO2-3.
[0022] The above-prepared catalyst of ultrathin CeO2 nanosheets containing vacancy clusters was used for the performance test of catalyzing CO2 / CH3OH to prepare DMC (catalyst: 0.1 g, initial pressure of CO2: 2 MPa, CH3OH: 35 mL). The selectivity of the liquid-phase product DMC was 100%. At different temperature conditions (120 °C, 140 °C, 160 °C), the yields of DMC were 10.8, 31.2, and 24.8 mmol / g respectively.
[0023] Example 3 Cerium nitrate hexahydrate was used as the cerium source, pyromellitic acid was used as the ligand, deionized water was used as the solvent, and polyvinylpyrrolidone was used as the surfactant.
[0024] 1) Cerium nitrate hexahydrate and pyromellitic acid (molar ratio 1:1) were respectively dissolved in equal volumes (200 mL) of deionized water and stirred for 2 h to form solutions A and B; polyvinylpyrrolidone (molar ratio of ligand to surfactant 1:5) was dissolved in 200 mL of deionized water with a volume fraction and stirred for 1 h to form solution C. Take equal volumes of 200 mL of solutions A and B and mix them, and carry out a reflux reaction under the condition of constant temperature at 50 °C; at the same time, dropwise add 200 mL of solution C at a rate of 30 drops per minute, and continue to reflux for 1 h to form a milky white suspension D. Carry out centrifugal separation and collection, and wash it 3 times with deionized water and absolute ethanol respectively. Finally, dry it in an oven at 100 °C for 12 h to obtain the Ce-MOFs precursor; 2) Weigh 0.5 g of the Ce-MOFs precursor and put it into a crucible. Under an air atmosphere, calcine it at 500 °C for 5 h. Take out the crucible and cool it to room temperature, then collect the product, obtaining the catalyst of ultrathin CeO2 nanosheets containing vacancy clusters, denoted as CeO2-5.
[0025] The above-prepared catalyst of ultrathin CeO2 nanosheets containing vacancy clusters was used for the performance test of catalyzing CO2 / CH3OH to prepare DMC (catalyst: 0.1 g, initial pressure of CO2: 2 MPa, CH3OH: 35 mL). The selectivity of the liquid-phase product DMC was 100%. At different temperature conditions (120 °C, 140 °C, 160 °C), the yields of DMC were 10.3, 31.8, and 25.6 mmol / g respectively.
[0026] All the pharmaceutical reagents used in the above examples are of analytical grade.
[0027] From Figure 1It can be seen that high-purity CeO2 nanosheet catalysts can be prepared by changing the ratio of the ligand to the surfactant.
[0028] It can be seen from Figures 2 to 4 that increasing the amount of the surfactant causes the CeO2 to gradually transform from multi-layer nanosheets to ultra-thin nanosheets.
[0029] It can be seen from Figure 6 that the catalyst prepared in Example 2 has cerium vacancies.
[0030] It can be seen from Figure 7 the theoretical calculation results that the formation energy is the lowest in the form of an O-Ce-O structure on the CeO2 surface, indicating that it is most likely to exist as an O-Ce-O vacancy cluster on the CeO2 surface, and reducing the thickness of CeO2 helps to form an O-Ce-O vacancy cluster.
[0031] It can be seen from Figure 8 that changing the ratio of the ligand to the surfactant can obtain ultra-thin CeO2 containing O-Ce-O vacancy clusters with different concentrations.
[0032] Matters not covered in this invention are well-known technologies. Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for preparing an ultrathin CeO2 nanosheet catalyst containing vacancy clusters, characterized in that: The steps include: S1, cerium nitrate hexahydrate and pyromellitic acid were dissolved in equal volumes of deionized water and stirred for 0.5-2 h to form solution A and solution B; S2, dissolving polyvinyl pyrrolidone in deionized water and stirring for 0.5-1 h to form solution C; S3, taking equal volumes of solution A and solution B, mixing them, and performing reflux reaction at a constant temperature of 50°C; at the same time, adding an equal volume of solution C at a rate of 30 drops / min, and continuing to reflux for 1 h to form a milky white suspension D; S4, the white suspension D was collected by centrifugation, washed with deionized water and anhydrous ethanol for three times respectively, and finally dried in an oven at 100°C for 12 h to obtain a Ce-MOFs precursor; S5. Put the Ce-MOFs precursor into a crucible and calcine it in an air atmosphere. After the calcination is completed, take out the crucible and cool it to room temperature, then collect the product to obtain an ultra-thin CeO2 nanosheet catalyst containing vacancy clusters.
2. The method for preparing an ultrathin CeO2 nanosheet catalyst containing vacancy clusters according to claim 1, characterized in that: The molar ratio of cerium nitrate hexahydrate to pyromellitic acid in S1 is 1:1, and the volume of deionized water is 50-200 mL.
3. The method for preparing an ultrathin CeO2 nanosheet catalyst containing vacancy clusters according to claim 1, characterized in that: The molar ratio of pyromellitic acid to polyvinyl pyrrolidone is 1:1-1:
5.
4. The method for preparing an ultrathin CeO2 nanosheet catalyst containing vacancy clusters according to claim 1, characterized in that: The volume of the deionized water in S2 is 50-200 mL.
5. The method for preparing an ultrathin CeO2 nanosheet catalyst containing vacancy clusters according to claim 1, characterized in that: The volumes of solution A, solution B and solution C in S3 are all 20-200 mL.
6. The method for preparing an ultrathin CeO2 nanosheet catalyst containing vacancy clusters according to claim 1, characterized in that: The calcination temperature in S5 is 500° C. and the calcination time is 5 h.
7. An ultrathin CeO2 nanosheet catalyst containing vacancy clusters prepared by the preparation method described in claim 1 is used to catalyze CO2 / CH3OH to synthesize DMC under different temperature conditions.
Citation Information
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