Preparation method and application of a copper-based catalyst supported on cerium oxide

Abstract

The present invention relates to a preparation method and application of a cerium oxide (CeO2)-supported copper (Cu)-based catalyst, in which Cu is supported on the CeO2 surface in the form of a combination of Cu single atoms and Cu nanoparticles, a combination of Cu single atoms in mixed valence states, or a combination of Cu mixed oxides. The catalyst can be used to prepare three different high-value-added chemicals and derivatives: cyclic carbonates, oxazolidinones, and α-hydroxyketones, using carbon dioxide (CO2) as a raw material.

Description

Technical Field

[0001] The present invention belongs to the fields of materials, catalysis and chemical industry, and in particular relates to a CeO2-loaded copper-based heterogeneous catalyst, a preparation method and application thereof. Background Art

[0002] CO2 is a non-toxic, inexpensive, readily available, and renewable C1 resource. In recent years, the use of CO2 to produce fine chemicals has attracted widespread attention. The carboxylation and cyclization reactions of CO2 to produce cyclic carbonates, oxazolidinones, and their derivative components are research hotspots. CO2 can react with propargyl alcohol to produce α-methylene cyclic carbonates, a functionalized organic compound widely found in natural products and microorganisms. Its structure contains a highly reactive ester group and an exocyclic carbon-carbon double bond, making it easy to derivatize. It often serves as an intermediate in reaction processes and has high biological activity or synthetic application value. Furthermore, CO2 can also be used to prepare higher-value-added derivatives such as oxazolidinones, α-hydroxyketones, carbamates, and asymmetric carbonates. For example, a three-component derivatization reaction of CO2, propargyl alcohols, and H2O can yield α-hydroxyketone compounds.

[0003] α-Methylene cyclic carbonate is an important organic synthesis intermediate and chemical intermediate. Currently, homogeneous catalysts are often used, such as Ru (Journal of Molecular Catalysis, 1992, 74 (1-3): 97-107), Pd (The Journal of Organic Chemistry, 1986, 51 (26): 5499-5501), Cu (Journal of Organometallic Chemistry, 1997, 545-546: 337-344), Ag (Bulletin of the Chemical Society of Japan, 2011, 84 (7): 698-717 and other series of results), phosphine (The Journal of Organic Chemistry, 2007, 72 (2): 647-649 and other series of results), N-heterocyclic carbene (NHC) (Angewandte Chemie, 2009, 121(23):4258-4261), K2CO3 / crown ether (Journal of Molecular Catalysis A: Chemical, 1999, 139(1):1-9), bicyclic guanidine (Advanced Synthesis & Catalysis, 2011, 353(1):133-146), Ag-NHC complex (Advanced Synthesis & Catalysis, 2013, 355(10):2019-2028), N-heterocyclic olefin / CO2 adduct (Journal of the American Chemical Society, 2013, 135(32):11996–12003) have also been developed for this reaction (ACS Catalysis, 2017, 7(3):2248–2256). In addition, reactions using ionic liquids (ACS Sustainable Chemistry & Engineering, 2019, 7(6): 5614-5619) or electrochemical methods (Tetrahedron, 2010, 66(52): 9981–9985) have also been reported. However, the existing technology still has shortcomings. The widely used ionic liquid catalytic system for homogeneous catalysis is expensive, and the product is difficult to separate from other raw materials and catalysts from the homogeneous mixed system, making purification difficult. Currently, there is a technology that immobilizes ionic liquids on carriers such as covalent organic framework materials (MOFs) (Angew. Chem. Int. Ed. 2022, e202114817), achieving heterogeneity of homogeneous catalysts and facilitating the separation of products and catalysts.However, similar homogeneous catalyst immobilization techniques lead to complex and expensive catalytic material preparation processes, potential loss of catalyst molecules after repeated use, and the need for higher CO₂ pressures and dewatering solvents. Therefore, there is an urgent need to develop low-cost, environmentally friendly preparation methods and heterogeneous (heterogeneous) catalytic technologies to chemically immobilize CO₂ into high-value-added products such as α-methylene cyclic carbonates, oxazolidinones, and α-hydroxyketones.

[0004] α-Hydroxyketones are important structures found in a variety of pharmaceuticals and natural products. The earliest traditional synthetic routes required the use of highly toxic strong acids such as mercury salts and sulfuric acid, which are environmentally polluting and inconsistent with the principles of green chemistry. Subsequently, various strategies for preparing α-hydroxyketones have emerged, including olefin oxidation and ketone reduction with acetyl alcohol hydration. However, these strategies are prone to Meyer-Schuster and Rupe rearrangements, resulting in numerous byproducts, low product purity, and low yield. The development of new chemical reaction catalytic systems and preparation processes is urgently needed.

[0005] Therefore, this patent, through scientific design and optimized step-by-step reduction preparation method, can obtain flaky cerium oxide nanosheets loaded with Cu-based heterogeneous catalysts through aqueous impregnation reduction method combined with subsequent different high-temperature calcination atmosphere treatment means, realize the effective combination of different levels of catalytic active sites such as nanostructure and single atomic structure, and realize the bimolecular synergistic conversion of CO2 and propargyl alcohol and propargylamine to prepare α-methylene cyclic carbonate compounds and oxazolidinone compounds, which can significantly improve the selectivity and universality of the reaction. In addition, this multi-component Cu-based heterogeneous catalyst can catalyze the three-component reaction of CO2, propargyl alcohol, and H2O to generate α-hydroxy ketone compounds in one step, which is an environmentally friendly method for efficiently synthesizing α-hydroxy ketone compounds in a new reaction catalytic system. This patent is for the development of a new type of heterogeneous catalyst and the application of CO2 catalytic conversion technology. Summary of the Invention

[0006] One of the problems to be solved by the present invention is to address the harsh catalytic conditions, long reaction times, and insufficient active sites in the existing synthesis of cyclic carbonates and oxazolidinone compounds using CO2, and the synthesis of α-hydroxyketone compounds using a three-component derivatization reaction of CO2, propargyl alcohol compounds, and H2O. The present invention provides a new catalyst and its synthesis method. To solve the above technical problems, the present invention proposes the following technical solutions:

[0007] One aspect of the present invention relates to a CeO2-loaded Cu-based catalyst, wherein the Cu is loaded on the CeO2 surface in the form of a combination of Cu single atoms in mixed valence states, a combination of Cu single atoms and Cu nanoparticles, or a combination of Cu composite oxides. The catalyst of the present invention has mixed and coexisting multi-component catalytic sites and exhibits multi-molecule activation properties. It can be used to catalyze the reaction of CO2 and propargyl alcohol / amine compounds to generate cyclic carbonate compounds and oxazolidinone compounds. It can also be used to catalyze the three-component reaction of CO2, propargyl alcohol, and H2O to generate α-hydroxy copper, efficiently achieving the chemical fixation of CO2 into three different high-value-added biopharmaceutical and organic chemical products. The metal loaded in the present invention is Cu, which is low-cost and conducive to further improving the catalytic activity of the catalyst.

[0008] In a preferred embodiment of the present invention, the CeO2 has oxygen vacancies. By using CeO2 as a carrier, the present invention provides more oxygen vacancies for metal loading, which helps to improve the catalytic yield.

[0009] In a preferred embodiment of the present invention, the catalyst has a two-dimensional nanosheet structure. The catalyst of the present invention has a large specific surface area and open pores, which facilitate heat transfer, mass transfer, and diffusion. This helps the product quickly leave the reaction site, thereby suppressing side reactions and improving catalytic efficiency.

[0010] In another preferred embodiment of the present invention, the loading amount of the metal is 0.05-10 wt% of the total weight of the catalyst.

[0011] Another object of the present invention is to provide a method for preparing the above-mentioned catalyst; the preparation method comprises the following steps: synthesizing defect-rich CeO2 nanosheets by a hydrothermal method and a two-step calcination in air and H2; dispersing the prepared carrier in an alcohol solution, loading metal Cu under stirring, adding NaBH4 for reduction, and then drying, and then calcining the dried solid.

[0012] In a preferred embodiment of the present invention, the calcination is carried out in an atmosphere of H2 / Ar, air or N2. In order to improve the catalytic performance and induce the formation of multi-component Cu sites, it is preferred to carry out the calcination in a mixed gas atmosphere of H2 / Ar. By reducing H2 calcination, the monovalent single-atom Cu1 sites and the zero-valent nanoparticle Cu n Coexisting Cu1+Cu n / CeO2 catalyst, and the mixed valence single atomic sites coexisting Cu1 / CeO2 catalyst were obtained by calcining in protective atmosphere N2, and the mixed oxide coexisting Cu was obtained by calcining in oxidizing atmosphere Air. x O / CeO2 (x=1,2) catalyst.

[0013] Another aspect of the present invention also relates to the use of the above catalyst in catalyzing the reaction of propargyl alcohol compounds, propargylamine compounds and CO2 to produce cyclic carbonates and oxazolidinone compounds, and their three-component derivatization reaction with H2O to produce α-hydroxy copper.

[0014] In a preferred embodiment of the present invention, the catalyst catalyzes the reaction of propargyl alcohol / amine compound and CO2, comprising the following steps: dispersing the propargyl alcohol / amine compound, the catalyst and the auxiliary agent in a solvent, and reacting under a CO2 atmosphere.

[0015] In a preferred embodiment of the present invention, the reaction is carried out at normal temperature and pressure.

[0016] In a preferred embodiment of the present invention, the catalyst catalyzes the three-component reaction of propargyl alcohol compounds, CO2 and H2O, comprising the following steps: dispersing the propargyl alcohol compounds, H2O, the catalyst and the auxiliary agent in a solvent, and reacting under a CO2 atmosphere.

[0017] In a preferred embodiment of the present invention, the reaction is carried out at 70-90° C. and normal pressure.

[0018] In a preferred embodiment of the present invention, the propargyl alcohol / amine compounds include but are not limited to the following propargyl alcohol / amine molecules with different steric hindrances, electron-pushing groups, and electron-deficient groups, such as: 2-methyl-3-butyn-2-ol, acetylene cyclohexanol, 3-methyl-1-pentyn-3-ol, 3-ethyl-1-pentyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, N-(2-propynyl)aniline, etc.

[0019] In a preferred embodiment of the present invention, the solvent includes but is not limited to polar solvents such as acetonitrile and N,N-dimethylformamide, and the auxiliary agent includes but is not limited to 1,8-diazabicycloundec-7-ene (DBU).

[0020] In a preferred embodiment of the present invention, the catalytic conversion rate of the reaction of the propargyl alcohol / amine compound with CO2 is greater than 99%, and the selectivity of the reaction is greater than 92%. The catalytic conversion rate of the three-component reaction of the propargyl alcohol compound, CO2, and H2O is greater than 99%, and the selectivity is greater than 88%.

[0021] One advantage of the present invention is that the catalyst used is a heterogeneous catalyst, which to some extent solves the problems of high catalyst cost, harsh reaction conditions, and difficulty in catalyst separation and purification in conventional homogeneous reaction systems.

[0022] To achieve the above objectives, the preferred CeO2-loaded Cu-based catalyst with multi-component active sites and the testing technical scheme for the catalytic reaction are as follows:

[0023] a. The cerium salt, morphology directing agent and pH regulator were added to deionized water, mixed evenly and placed in a reactor for hydrothermal synthesis, and a white precipitate was obtained after centrifugation, washing and drying;

[0024] b. The white precipitate obtained in step a was calcined in a muffle furnace to obtain a light yellow two-dimensional flaky cerium oxide support;

[0025] c. The light yellow two-dimensional flaky cerium oxide support obtained in step b was calcined in a 5% H2 / Ar gas mixture to obtain a defect-rich two-dimensional flaky cerium oxide support;

[0026] d. The powdered sample obtained in step c was dispersed in alcohol, a certain amount of copper salt was added for impregnation, and a reducing agent was added according to the proportion of reduction, followed by filtration, washing, and drying to obtain a supported catalyst;

[0027] e. The catalyst obtained in step d was calcined in different atmospheres (5% H2 / Ar, N2, Air) to obtain three oxide-supported catalysts containing multi-component Cu sites.

[0028] Preferably, the cerium salt in step a is one of cerium nitrate and cerium chloride.

[0029] Preferably, the morphology directing agent in step a is one of hexamethylenetetramine, cetyltrimethylammonium chloride and cetyltrimethylammonium bromide.

[0030] Preferably, the pH adjuster in step a is one of glacial acetic acid, dilute hydrochloric acid, and dilute nitric acid.

[0031] Preferably, the alcohol in step c is one of ethanol, methanol and ethylene glycol.

[0032] Preferably, the copper salt in step c is one of copper nitrate, copper chloride and copper acetate.

[0033] Preferably, the reducing substance in step c is one of citric acid, hydrazine hydrate and sodium borohydride.

[0034] Beneficial effects of the present invention:

[0035] This invention utilizes a step-by-step reduction method involving aqueous sodium borohydride wet impregnation and high-temperature calcination in different atmospheres to synthesize a Cu-based metal catalyst with different multi-component active sites on its surface. The varying calcination atmospheres simultaneously adjust the number of oxygen vacancies on the support, thereby regulating the interaction between the support and the metal, achieving synergistic improvements in performance. Furthermore, the reaction substrates are relatively broad, and it is applicable to a variety of propargyl alcohol and propargylamine compounds. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 : Reaction equation for the carboxylation cyclization reaction of propargyl alcohol with carbon dioxide.

[0037] Figure 2 : The three-component reaction equation of propargyl alcohol, CO2 and H2O.

[0038] Figure 3 : Transmission electron microscopy images of the catalytic materials prepared in Examples 1, 2 and 3.

[0039] Figure 4 : Cu1+Cu prepared in Example 1 n Spherical aberration corrected electron microscope image of / CeO2 catalytic material.

[0040] Figure 5 : X-ray diffraction spectra (XRD) of the catalytic materials prepared in Examples 1, 2 and 3.

[0041] Figure 6 : The Cu 2p X-ray photoelectron spectroscopy (XPS) of the catalytic materials prepared in Examples 1, 2 and 3 confirmed the presence of mixed valence components of Cu single atoms and Cu oxides.

[0042] Figure 7 : Transmission electron microscopy image of the CeO2 catalytic material prepared in Comparative Example 1.

[0043] Figure 8 : The product α-methylene cyclic carbonate prepared in Example 4 1 HNMR spectrum.

[0044] Figures 9-13 : The product prepared by expanding the substrate in Example 4 1 HNMR spectrum. DETAILED DESCRIPTION

[0045] To further understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0046] Unless otherwise specified, all reagents involved in the embodiments of the present invention are commercially available products and can be purchased through commercial channels.

[0047] Example 1: Cu1+Cu n Synthesis of / CeO2 catalyst (Cu1 refers to copper single atom, Cu n refers to copper nanoparticles):

[0048] a. Dissolve 325 mg of Ce(NO3)3·6H2O and 736 mg of hexamethylenetetramine in 15 mL of methanol, add 0.6 mL of glacial acetic acid, stir at room temperature, place in a high-temperature reactor, and react at 140°C for 9 h.

[0049] b. The product of step a was centrifuged and washed, and then vacuum dried. The dried powder was first calcined at 500°C in air for 2 h, and then calcined at 350°C in H2 / Ar for 3 h.

[0050] c. The carrier of step b was dissolved in methanol, and copper acetate solution was added dropwise, wherein the Cu loading amount accounted for 5wt% of the carrier weight ratio, and stirred at room temperature for 12h. Sodium borohydride solution with the amount of Cu atoms and the like was slowly added dropwise, stirred at room temperature, filtered and dried in vacuo.

[0051] d. The product in step c was heated to 200 ° C in H2 / Ar atmosphere and maintained for 2 h to obtain Cu1+Cu n / CeO2 catalyst.

[0052] Example 2: Synthesis of Cu1 / CeO2 catalyst:

[0053] a. The early steps are similar to those in Example 1-ac.

[0054] b. The product in step a was heated to 200°C in a N2 atmosphere and maintained for 2 hours to obtain a Cu1 / CeO2 catalyst. Figure 6 From the XPS test results, it can be seen that Cu1 / CeO2 has Cu + and Cu 2+ There are two mixed valence peaks.

[0055] Example 3: Cu x Synthesis of O / CeO2 (x=1,2) catalyst:

[0056] a. The early steps are similar to those in Example 1-ac.

[0057] b. The product in step a was heated to 200 ° C in an air atmosphere and maintained for 2 h to obtain Cu x O / CeO2 (x=1,2) catalyst. The test results show that the divalent Cu atomic ratio is 42.5% and the monovalent Cu atomic ratio is 57.5%.

[0058] The morphology of the catalyst was characterized by transmission electron microscopy, and it was found that the material showed a two-dimensional material CeO2 thin nanohexagonal sheet ( Figure 3 ), the protrusions scattered on the surface all indicate the presence of Cu-based small particles. In addition to the presence of Cu-based particles, there is also the dispersion of metal Cu single atoms, which was verified by spherical aberration electron microscopy ( Figure 4 ). XRD of Examples 1, 2, and 3 confirmed the chemical phase and composition of the catalyst ( Figure 5 The information on the electronic structure and valence state of the elements (including Ce, Cn, and O) on the surface of these catalysts was obtained by XPS. Figure 6 The above results show that Example 1 is the coexistence of Cu single atom sites and nanoparticle sites; Example 2 is the coexistence of Cu single atom mixed valence sites; Example 3 is the coexistence of Cu single atom mixed valence sites; x O(x=1,2) sites coexist.

[0059] Example 4: Cu1+Cu n Catalytic Application of CeO2 in the Reaction of Propargyl Alcohol / Amine with CO2

[0060] 100 mg of the catalyst from Example 1 was weighed and placed in a reactor. 1 mmol of the reactants and 1 mmol of DBU were then added, followed by 3 mL of acetonitrile. After bubbling CO₂ gas through the reactor, a balloon was placed on the upper end of the reactor and inflated to a predetermined volume. The reaction was then allowed to proceed at a temperature of 25°C and a constant stirring rate for 5 hours. After completion of the reaction, a predetermined amount of biphenyl (an internal standard) was added, the reaction solution was removed, and the clear, transparent supernatant was retained. The catalytic performance was tested by gas chromatography and nuclear magnetic resonance, and the yield was calculated. The results are shown in Table 1.

[0061] Table 1

[0062]

[0063]

[0064] [a] Yield represents the yield of the pure product after purification

[0065] Example 5: Catalytic Application of Cu1 / CeO2 in the Reaction of Propargyl Alcohol and CO2

[0066] 100 mg of the catalyst from Example 2 was weighed and placed in a reactor. 1 mmol of the reactants, 2-methyl-3-butyn-2-ol, and 1 mmol of DBU were then added. 3 mL of acetonitrile was then added to the reactor, and the reactor was placed in an ultrasonicator to fully disperse the catalyst in the acetonitrile. After CO2 gas was bubbled through the reactor, a balloon was placed on the upper end of the reactor and inflated to a predetermined volume. The reaction was then carried out at a temperature of 25°C and a constant stirring rate for 5 hours. After the reaction was complete, a certain amount of the internal standard, biphenyl, was added, the reaction solution was removed, and the clear, transparent supernatant was retained. Gas chromatography revealed a reaction conversion of 77.7%, and a selectivity of 78.2% for the target product, α-methylene cyclic carbonate.

[0067] Example 6: Cu x Catalytic Application of O / CeO2 in the Reaction of Propargyl Alcohol and CO2

[0068] 100 mg of the catalyst from Example 3 was weighed and placed in a reactor. 1 mmol of the reactants, 2-methyl-3-butyn-2-ol, and 1 mmol of DBU were then added. 3 mL of acetonitrile was then added to the reactor, and the reactor was placed in an ultrasonicator to fully disperse the catalyst in the acetonitrile. After CO2 gas was bubbled into the reactor, a balloon was placed on the upper end of the reactor and inflated to a predetermined volume. The reaction was then carried out at a temperature of 25°C and a constant stirring rate for 5 hours. After completion of the reaction, a certain amount of the internal standard, biphenyl, was added, the reaction solution was removed, and the clear, transparent supernatant was retained. Gas chromatography revealed a 42% conversion rate and a 33% selectivity for the target product, α-methylene cyclic carbonate.

[0069] The catalytic performance of the three catalysts in the reaction of propargyl alcohol with CO2 is shown in Table 2.

[0070] Table 2

[0071]

[0072]

[0073] The above experimental results show that Cu1+Cu n / CeO2 catalyst had the best results in terms of conversion, selectivity and yield, followed by Cu1 / CeO2 catalyst, and Cu x The catalytic effect of O / CeO2 catalyst is relatively poor, but it can still play a catalytic role.

[0074] Example 7: Cu1+Cu n / CeO2 Catalytic Application in the Three-Component Reaction of Propargyl Alcohol, CO2 and H2O

[0075] 100 mg of the catalyst from Example 1 was weighed and placed in a reactor. 1 mmol of the reactant, 2-methyl-3-butyn-2-ol, 2 mmol of H₂O, and 1 mmol of DBU were then added. 3 mL of acetonitrile was then added to the reactor, and the reactor was placed in an ultrasonicator to fully disperse the catalyst in the acetonitrile. After CO₂ gas was bubbled into the reactor, a balloon was placed on the upper end of the reactor and inflated to a predetermined volume. The reaction was then carried out at a temperature of 80°C and a constant stirring rate for 5 hours. After the reaction was completed, a certain amount of the internal standard, biphenyl, was added, the reaction solution was removed, and the clear, transparent supernatant was retained. Gas chromatography revealed a reaction conversion of 99.7%, and a selectivity of 88.7% for the target product, α-hydroxyketone.

[0076] Example 8: Catalytic Application of Cu1 / CeO2 in the Three-Component Reaction of Propargyl Alcohol, CO2, and H2O

[0077] 100 mg of the catalyst from Example 2 was weighed and placed in a reactor. 1 mmol of the reactant, 2-methyl-3-butyn-2-ol, 2 mmol of H₂O, and 1 mmol of DBU were then added. 3 mL of acetonitrile was then added to the reactor, and the reactor was placed in an ultrasonicator to fully disperse the catalyst in the acetonitrile. After CO₂ gas was bubbled into the reactor, a balloon was placed on the upper end of the reactor and inflated to a predetermined volume. The reaction was then carried out at a temperature of 80°C and a constant stirring rate for 5 hours. After completion of the reaction, a certain amount of the internal standard biphenyl was added, the reaction solution was removed, and the clear, transparent supernatant was retained. Gas chromatography revealed a reaction conversion of 93.5%, and a selectivity of 88.7% for the target product, α-hydroxyketone.

[0078] Example 9: Cu x Catalytic Application of O / CeO2 in the Three-Component Reaction of Propargyl Alcohol, CO2 and H2O

[0079] 100 mg of the catalyst from Example 3 was weighed and placed in a reactor. 1 mmol of the reactant, 2-methyl-3-butyn-2-ol, 2 mmol of H₂O, and 1 mmol of DBU were then added. 3 mL of acetonitrile was then added to the reactor, and the reactor was placed in an ultrasonicator to fully disperse the catalyst in the acetonitrile. After CO₂ gas was bubbled into the reactor, a balloon was placed on the upper end of the reactor and inflated to a predetermined volume. The reaction was then carried out at a temperature of 80°C and a constant stirring rate for 5 hours. After the reaction was completed, a certain amount of the internal standard biphenyl was added, the reaction solution was removed, and the clear, transparent supernatant was retained. Gas chromatography revealed a reaction conversion of 72.7%, and a selectivity of 90.1% for the target product, α-hydroxyketone.

[0080] The catalytic performance of the three catalysts in the three-component reaction of propargyl alcohol, CO2 and H2O is shown in Table 3.

[0081] Table 3

[0082] Example catalyst Conversion rate (%) Selectivity (%) Yield (%) 7 Example 1 99.7 88.7 88.4 8 Example 2 93.5 88.7 82.9 9 Example 3 72.7 90.1 65.5

[0083] The above experimental results show that Cu1+Cu n / CeO2 catalyst had the best results in terms of conversion, selectivity and yield, followed by Cu1 / CeO2 catalyst, and Cu x The catalytic effect of O / CeO2 catalyst is relatively poor, but it can still play a catalytic role.

[0084] Comparative Example 1: Preparation of CeO2 carrier

[0085] a. Dissolve 325 mg of Ce(NO3)3·6H2O and 736 mg of hexamethylenetetramine in 15 mL of methanol, add 0.6 mL of glacial acetic acid, stir, place in a high-temperature reactor, and react at 140°C for 9 h.

[0086] b. The product of step a was centrifuged and washed, and then vacuum dried. The dried powder was first calcined in air at 500°C for 2 h, and then calcined in H2 / Ar at 350°C for 3 h to obtain a CeO2 support.

[0087] The morphology of the catalyst was characterized by transmission electron microscopy, and it was found that the material showed a two-dimensional layered structure ( Figure 7 ).

[0088] Comparative Example 2: Catalytic Application of CeO2 in the Reaction of Propargyl Alcohol and CO2

[0089] 100 mg of the catalyst from Comparative Example 1 was weighed and placed in a reactor. 1 mmol of the reactant 2-methyl-3-butyn-2-ol and 1 mmol of DBU were then added. 3 mL of acetonitrile was then added to the reactor, and the reactor was placed in an ultrasonic machine to fully disperse the catalyst in the acetonitrile. After CO2 gas was bubbled into the reactor, a balloon was placed on the upper end of the reactor and inflated to a certain volume with CO2 gas. The reaction was then carried out at a temperature of 25°C and a constant stirring speed for 5 hours. After the reaction was completed, a certain amount of internal standard biphenyl was added, the reaction solution was removed, and the clear and transparent supernatant was retained. Gas chromatography showed that the reaction conversion was 46.3%, and the selectivity of the target product, α-methylene cyclic carbonate, was 52.8%.

[0090] Comparative Example 3: Catalytic Application of Commercial Cu2O Powder in the Reaction of Propargyl Alcohol and CO2

[0091] 4.4 mg of commercial Cu2O powder was weighed and placed in a reactor. 1 mmol of the reactant, 2-methyl-3-butyn-2-ol, and 1 mmol of DBU were then added. 3 mL of acetonitrile was then added to the reactor, and the catalyst was thoroughly dispersed in the acetonitrile using an ultrasonicator. After bubbling CO2 gas into the reactor, a balloon was placed over the reactor top and inflated to a desired volume. The reaction was then allowed to proceed at 25°C with a constant stirring rate for 5 hours. After the reaction was complete, a predetermined amount of the internal standard, biphenyl, was added, and the reaction solution was removed, retaining the clear, transparent supernatant. Gas chromatography revealed a 9.9% conversion rate and a 65.4% selectivity for the target product, α-methylene cyclic carbonate.

[0092] Comparative Example 4: Catalytic Application of Commercial Cu Powder in the Reaction of Propargyl Alcohol and CO2

[0093] 4.4 mg of commercial Cu powder was weighed and placed in a reactor. 1 mmol of the reactants, 2-methyl-3-butyn-2-ol and 1 mmol of DBU, were then added. 3 mL of acetonitrile was then added to the reactor, and the catalyst was thoroughly dispersed in the acetonitrile using an ultrasonicator. After bubbling CO2 gas into the reactor, a balloon was placed over the reactor top and inflated to a desired volume. The reaction was then allowed to proceed at 25°C with a constant stirring rate for 5 hours. After the reaction was complete, a predetermined amount of the internal standard, biphenyl, was added, and the reaction solution was removed, retaining the clear, transparent supernatant. Gas chromatography revealed a conversion of 79.2%, with a selectivity of 80.9% for the target product, α-methylene cyclic carbonate.

[0094] The catalytic performance of Comparative Examples 2, 3 and 4 in the reaction of propargyl alcohol with CO2 is shown in Table 2.

[0095] The preferred embodiments of the present invention are described above, but they are not intended to limit the present invention. Those skilled in the art may make improvements and changes to the embodiments disclosed herein without departing from the scope and spirit of the present invention.

Claims

1. Application of a CeO2-supported Cu-based catalyst in catalyzing the carboxylation cyclization reaction of propargyl alcohol compounds with carbon dioxide to produce cyclic carbonates, characterized in that: The Cu is loaded on the CeO2 surface in the form of a combination of Cu single atoms and Cu nanoparticles, a combination of Cu single atoms in mixed valence states, or a combination of Cu composite oxides. The amount of catalyst used in the reaction is 5%-8% of the mass of the reactants, the reaction temperature is 20-80°C, the reaction pressure is 0.5-3 atmospheres, and the reaction time is 4-8 hours.

2. The use according to claim 1, characterized in that The propargyl alcohol compound is selected from 2-methyl-3-butyn-2-ol, ethynyl cyclohexanol, 3-methyl-1-pentyn-3-ol, 3-ethyl-1-pentyn-3-ol and / or 3,5-dimethyl-1-hexyn-3-ol.

3. The use according to claim 1 or 2, characterized in that The Cu is loaded on the CeO2 surface in the form of a combination of Cu single atoms and Cu nanoparticles.

4. The use according to claim 1 or 2, characterized in that The loading amount of the metal Cu is 0.05-30 wt% of the total weight of the catalyst.

5. The use according to claim 1 or 2, characterized in that: The loading amount of the metal Cu is 3.0-7.0 wt% of the total weight of the catalyst.

6. The use according to claim 1 or 2, characterized in that The catalyst is a two-dimensional nanosheet structure.

7. The use according to claim 1 or 2, characterized in that The catalyst is prepared by a step-by-step reduction method, which includes reduction by chemical wet impregnation of sodium borohydride in an aqueous phase and high-temperature calcination in different atmospheres, wherein the atmosphere is selected from hydrogen-argon mixed gas, nitrogen or air.

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