Ni-a-il catalyst, preparation method and application

Abstract

The application discloses a Ni-A-IL catalyst, a preparation method and application. The ring addition reaction of CO2 and epoxide to form cyclic carbonate is the most sustainable method of chemical carbon fixation. Although various hybrid catalysts have been developed for this coupling reaction, they are still affected by the loss of ionic liquid and poor stability. The application prepares a Ni-based monomer aerogel (Ni-A catalyst) with rich hydroxyl groups, then the imidazole-based IL is grafted onto the Ni-A catalyst through a dealcoholization condensation reaction, and after vacuum drying treatment, the Ni-A-IL catalyst is prepared. The Ni-A-IL realizes a propylene carbonate (PC) yield of 98.7% and a PO conversion rate of 98.7%. In addition, the Ni-A-IL shows excellent stability, and the PC yield can still be maintained at 97.8% after seven cycles.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a Ni-A-IL catalyst, its preparation method, and its application. Background Technology

[0002] As a renewable and abundant C1 resource, CO2 has been converted into value-added chemicals over the past decade. Using CO2 as a feedstock in chemical production helps alleviate environmental and energy supply issues. Among various conversion attempts, the cycloaddition of CO2 with epoxides to form cyclic carbonates has received particular attention due to its 100% atom economy and valuable products. In this coupling reaction, specially functionalized ionic liquids (ILs) exhibit high thermal and chemical stability as the primary catalysts, especially imidazole-based ILs. Generally, imidazole-based ILs have high solubility for CO2, thus maximizing the adsorption affinity of CO2 within them. More importantly, imidazole-based ILs can form hydrogen bonds with oxygen atoms in epoxides, promoting the ring-opening step and significantly enhancing the activity of the cycloaddition reaction. In this respect, ILs are currently considered the dominant catalysts and are used for the industrial-scale synthesis of cyclic carbonates. However, the separation of the driving product from the ILs requires high energy consumption, and complex processes are needed to purify the homogeneous catalyst. Therefore, there is an urgent need to develop efficient and reusable heterogeneous catalysts to achieve high catalytic activity and convenient separation of products from the reaction system.

[0003] Numerous studies have focused on developing highly efficient heterogeneous catalysts for the simultaneous activation of CO2 and epoxides, achieving significant progress. Metal-organic frameworks (MOFs) with abundant coordination-unsaturated metal nodes can act as Lewis acids to activate epoxides. For example, Carlos et al. synthesized titanium-based MOFs in which coordination-unsaturated titanium acts as a hard acid to adsorb propylene oxide (PO), followed by nucleophilic I-anions attacking the β-carbon atom of PO for ring-opening. Furthermore, charge rearrangement induced by interactions between single atoms and the support can enhance the affinity of intermediate species at the active site. This behavior significantly lowers the activation energy of the ring-opening reaction. For instance, Li et al. found that charge redistribution between Ir single atoms and the WO3 support facilitates the adsorption of styrene oxide and Br-anions onto the W and Ir sites, respectively. This process promotes the ring-opening step of styrene oxide, thereby improving catalytic conversion efficiency.

[0004] Over the past few decades, researchers have immobilized ionic liquids (ILs) on various support materials, such as organic polymers, inorganic functional materials, biopolymers, and porous silica. As expected, these catalysts have exhibited catalytic activity comparable to ILs. However, they are still plagued by the significant loss of ILs and poor stability. It has been definitively demonstrated that immobilized ILs occur through the direct reaction of siloxanes with hydroxyl groups on the surface of a solid substrate. Therefore, it is naturally understood that the concentration of hydroxyl groups on the solid substrate surface is a crucial controlling factor for grafting efficiency. Summary of the Invention

[0005] The cycloaddition reaction of CO2 with epoxides to form cyclic carbonates is the most sustainable method for chemical carbon fixation. Although various hybrid catalysts have been developed for this coupling reaction, they are still affected by ionic liquid loss and poor stability. To address the problems of the prior art, this invention provides a Ni-A-IL catalyst, its preparation method, and its applications. This invention uses a hydroxyl-rich Ni-based monomer aerogel (Ni-A) as a solid support and grafts an imidazole-based IL onto the aerogel surface (Ni-A-IL) via a dealcoholization condensation reaction. The resulting Ni-A-IL exhibits excellent performance for the cycloaddition reactions of CO2 and PO under mild conditions without the need for additional auxiliary catalysts or solvents.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for preparing a Ni-A-IL catalyst includes the following steps:

[0008] (1) Ni-A catalyst was prepared by using polyacrylic acid (PAA) as a template to induce the formation of Ni-based hydrogel and then supercritical drying.

[0009] (2) The imidazole-based IL was grafted onto the Ni-A catalyst by a dealcoholization condensation reaction, and the Ni-A-IL catalyst was obtained after vacuum drying.

[0010] Furthermore, the preparation method of the Ni-A catalyst in step (1) is as follows:

[0011] Step a: Dissolve acrylic acid in deionized water, then add K2S2O8 initiator to carry out polymerization reaction to obtain polyacrylic acid hydrogel;

[0012] Step b: Add nickel salt to ethanol, stir, pour into polyacrylic acid hydrogel, then add propylene oxide (PO) to obtain wet gel, wash and dry to obtain Ni-A catalyst.

[0013] Further, in step a, 0.5 ml of acrylic acid is dissolved in 2.5 ml of deionized water, and then 25 mg of K2S2O8 initiator is added to start the polymerization reaction.

[0014] Furthermore, the polymerization reaction in step a is carried out at a temperature of 60°C for 2 hours.

[0015] Further, in step b, 10 ml of ethanol containing 0.594 g of NiCl2·6H2O is poured into the polyacrylic acid hydrogel prepared in step a. After stirring for 5-20 min, the hydrogel dissolves in the ethanol solution. Then, 3 ml of propylene oxide (PO) is added. After 2 hours, a laurel green gel is formed. The gel is allowed to stand at room temperature for 24 hours. Subsequently, the gel is immersed in an ethanol bath and washed for 3 days. Finally, the solvent in the wet gel is replaced with CO2 in a supercritical drying device for 2-3 days to obtain the laurel green aerogel, i.e., the Ni-A catalyst.

[0016] Furthermore, the preparation method of the Ni-A-IL catalyst in step (2) is as follows: 1-methylimidazolium and (3-chloropropyl)trimethoxysilane are dissolved in acetonitrile and refluxed under N2 protection. After the reaction is completed, Ni-A catalyst is added to continue the reaction. The resulting aerogel is washed and dried to obtain the Ni-A-IL catalyst.

[0017] Further, in step (2), 2.72 g of 1-methylimidazole and 8 mL of (3-chloropropyl)trimethoxysilane were dissolved in 50 mL of acetonitrile and refluxed at 85 °C for 12 hours under N2 protection. After the reaction was completed, 3.5 g of Ni-A catalyst was added and the reaction was continued for 12 hours. The resulting aerogel was washed three times with acetonitrile. Finally, the grafted aerogel was vacuum dried at 40 °C to obtain the Ni-A-IL catalyst.

[0018] The present invention also provides the application of the Ni-A-IL catalyst prepared by the above preparation method in the cycloaddition reaction of CO2 with epoxide, specifically: 3 ml of PO and 50 mg of catalyst are placed in a stainless steel autoclave, CO2 is introduced into the autoclave at a certain pressure, the reaction equipment is heated to a specified temperature and maintained for a certain time, after the reaction is completed, the reaction vessel is placed in ice water to cool, then the pressure is slowly reduced, the catalyst is collected after washing with acetonitrile, and the collected liquid is centrifuged in an 8000 rpm centrifuge for 5 min.

[0019] As a preferred embodiment of the present invention, in the cycloaddition reaction of CO2 and epoxide catalyzed by Ni-A-IL catalyst, the CO2 pressure is 1 MPa, the reaction temperature is 120°C, and the reaction time is 2 hours.

[0020] The beneficial effects of this invention are as follows: This invention uses a hydroxyl-rich Ni-based monomer aerogel (Ni-A) as a solid support and grafts an imidazole-based IL onto the aerogel surface via a dealcoholization condensation reaction (Ni-A-IL). The resulting Ni-A-IL exhibits excellent performance in the cycloaddition reactions of CO2 and PO under mild conditions without the need for additional auxiliary catalysts or solvents, with a propylene carbonate (PC) yield as high as 98.7% and a PO conversion rate of 98.7%. This catalyst also exhibits excellent stability due to the three strong Si-O bonds preventing IL loss; after seven cycles, the PC yield remains at 97.8%. Attached Figure Description

[0021] Figure 1 The diagram shows the catalyst synthesis process, where (a) is the Ni-A catalyst and (b) is the Ni-A-IL catalyst.

[0022] Figure 2 Photograph of the Ni-A-IL catalyst.

[0023] Figure 3 The images are SEM images of the catalysts, (a) for Ni-A and (b) for Ni-A-IL.

[0024] Figure 4 The images show magnified HAADF-STEM images and corresponding EDX elemental distribution images of Ni-A-IL. Figure 5 The DRIFT spectra of Ni-A and Ni-A-IL are shown.

[0025] Figure 6 To obtain the XPS spectra of the samples. (a) Ni 2p, (b) O 1s, (c) C 1s and (d) Cl 2p XPS spectra of Ni-A and Ni-A-IL. (e) Ni-A-IL N 1s and (f) Si 2p XPS spectra.

[0026] Figure 7 The conversion of PO and the yield of PC on Ni-A,IL and Ni-A-IL were determined. Reaction conditions: 3 mL PO, 50 mg catalyst, CO2 pressure: 1 MPa, 120 °C, 2 h.

[0027] Figure 8 The effects of different parameters on the conversion of PO and the yield of PC catalyzed by Ni-A-IL were investigated. (a) Effect of reaction time. Reaction conditions: 3 mL PO, 50 mg catalyst, CO2 pressure: 1 MPa. (b) Effect of reaction temperature. Reaction conditions: 3 mL PO, 50 mg catalyst, CO2 pressure: 1 MPa, 2 h. (c) Effect of pressure. Reaction conditions: 3 mL PO, 50 mg catalyst, 120 °C, 2 h.

[0028] Figure 9 Repeat experiments were conducted for the Ni-A-IL catalyzed cycloaddition of CO2 and PO. Reaction conditions: 3 mL PO, 50 mg catalyst, CO2 pressure: 1 MPa, 120 °C, 2 h.

[0029] Figure 10 In-situ DRIFT spectra of Ni-A and Ni-A-IL after treatment with PO and CO2. (a) PO treatment; (b) CO2 treatment.

[0030] Figure 11 The in-situ DRIFT spectra of the cycloaddition reaction of CO2 and PO catalyzed by Ni-A-IL are shown at a reaction temperature of 120℃ and different reaction times.

[0031] Figure 12 This is a schematic diagram of the mechanism of the Ni-A-IL catalytic cycloaddition reaction of CO2 and PO.

[0032] Figure 13 XPS measurement spectra of Ni-A and Ni-A-IL.

[0033] Figure 14 The effect of catalyst quality on the cycloaddition reaction of CO2 and PO catalyzed by Ni-A-IL. Reaction conditions: 3 ml PO, CO2; pressure: 1 MPa, 120 °C, 2 h.

[0034] Figure 15 The image shows the 1H NMR spectrum collected after the reaction catalyzed by Ni-A-IL catalyst. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above-described invention.

[0036] Example 1

[0037] The preparation method of the Ni-A-IL catalyst in this embodiment is as follows:

[0038] (1) The formation of Ni-based hydrogels was induced using polyacrylic acid (PAA) as a template, and a Ni-A catalyst was prepared after supercritical drying. The specific steps are as follows: First, 0.5 mL of acrylic acid was dissolved in 2.5 mL of deionized water. Then, 25 mg of K2S2O8 initiator was added to start the polymerization reaction. The reaction was carried out at 60 °C for 2 hours to obtain polyacrylic acid hydrogel. Then, 10 mL of ethanol containing 0.594 g of NiCl2·6H2O was poured into the hydrogel. After stirring for several minutes, the hydrogel dissolved in the ethanol solution. 3 mL of propylene oxide (PO) was added to the solution, and after 2 hours, a laurel green gel was formed. The wet gel was allowed to stand at room temperature for 24 hours. Then, the gel was immersed in an ethanol bath for 3 days for cleaning. Finally, the solvent in the wet gel was replaced with CO2 in a supercritical drying device for 2-3 days to obtain a laurel green aerogel.

[0039] (2) An imidazole-based IL was grafted onto Ni-A via a dealcoholization condensation reaction. After vacuum drying, a Ni-A-IL catalyst was prepared. The specific steps are as follows: 2.72 g of 1-methylimidazolium and 8 mL of (3-chloropropyl)trimethoxysilane were dissolved in 50 mL of acetonitrile. The mixed solution was refluxed at 85 °C. More importantly, N2 was injected into a single-necked flask for protection. After reacting for 12 hours, 3.5 g of Ni-A was added to the flask. The reaction was continued for another 12 hours, and the resulting aerogel was washed three times with acetonitrile. Finally, the grafted aerogel was vacuum dried at 40 °C to synthesize the Ni-A-IL catalyst.

[0040] The Ni-A catalyst was prepared by a template method (see...). Figure 1 a). In this process, the obtained polyacrylic acid (PAA) was used as a template to induce the formation of Ni-based hydrogels. After supercritical drying, the Ni-A catalyst was synthesized.

[0041] The synthesis process of Ni-A-IL catalyst is as follows: Figure 1 As shown in b. First, 1-methylimidazole and (3-chloropropyl)trimethoxysilane were mixed and refluxed under nitrogen protection for 12 hours. After the reaction, an imidazole-based IL was obtained. Second, the imidazole-based IL was grafted onto Ni-A via a dealcoholization condensation reaction. After vacuum drying, the Ni-A-IL catalyst was prepared.

[0042] 1. Ni-A-IL can be easily placed on dandelions, demonstrating its ultra-lightweight properties (see...). Figure 2 BET testing confirmed that both Ni-A and Ni-A-IL possess porous structures. Table 1 shows that after the surface grafting reaction, the specific surface area increased from 83.38 m² / s². 2 / g decreased to 1.51m 2 / g, pore size increased from 1.93nm to 2.07nm. Meanwhile, Ni-A ( Figure 3 a) and Ni-A-IL ( Figure 3 The scanning electron microscope (SEM) images in b) clearly show that the aerogel consists of spherical nanoparticles that aggregate to form a porous network. The average diameter of the nanoparticles in Ni-A-IL (approximately 2 μm) is significantly larger than that of Ni-A (approximately 30 nm). Based on high-angle dark-field scanning transmission electron microscopy (HAADF-STEM) images, Ni-A-IL exhibits a porous microstructure (see...). Figure 4 STEM energy-dispersive X-ray (EDX) elemental distribution mapping images show that Ni, O, C, Si, N, and Cl elements are uniformly distributed in the Ni-A-IL catalyst. EDX results indicate that IL is uniformly grafted onto the aerogel.

[0043] Table 1. BET specific surface area and pore diameter of different catalysts

[0044] catalyst <![CDATA[BET specific surface area (m 2 / g) pore diameter (nm)]]> Ni-A 83.3819 1.9319 Ni-A-IL 1.5107 2.0727

[0045] 2. The functional groups on the aerogel surface were determined using the DRIFT technique. The specific method is as follows:

[0046] In-situ DRIFT experiments were conducted in a high-pressure chamber using a Fourier transform infrared spectrometer and a liquid nitrogen detector. After sample treatment, background spectra were obtained after treatment with 1 bar nitrogen at a rate of 30 sccm for 30 minutes. For PO treatment, 1 bar nitrogen was passed into a PO solution at 120°C at a rate of 30 sccm for 30 minutes, followed by treatment at a rate of 20 sccm for 15 minutes. For CO2 treatment, 1 bar CO2 was passed into the sample at 120°C at a rate of 30 sccm for 30 minutes, followed by treatment at a rate of 20 sccm for 15 minutes. For both PO and CO2 treatment, 1 bar CO2 was passed through the PO solution at a rate of 30 sccm for 30 minutes, followed by treatment at a rate of 20 sccm for 15 minutes. The chamber was then heated to 120°C. Each curve was acquired every 5 minutes for a total of 0.5 hours.

[0047] exist Figure 5 In the middle, Ni-A shows 3200-3600 cm⁻¹ -1 The broad peaks in the region, corresponding to the stretching vibrations of -OH, indicate the abundance of hydroxyl groups on the Ni-A surface. In contrast, the DRIFT curve of Ni-A-IL shows several new peaks (3300-3500 cm⁻¹). -1 The strong signal within the range is attributed to NH vibration. Located at 1723 cm⁻¹. -1 1549cm -1 1433cm-1 The three typical peaks at the position are correlated with the extension frequency of the imidazole ring. DRIFT data indicate the presence of imidazole-based ILs on the Ni-A-IL surface. Table 2 shows the functional group information of the Ni-A and Ni-A-IL surfaces. Furthermore, the Si content of Ni-A-IL was determined by inductively coupled plasma (ICP-P) to determine the amount of grafted ILs in the aerogel. The measured Si content was 10.3 wt%, therefore the amount of IL was 3.7 mmol g. -1 Based on the above characterization, it can be seen that the present invention successfully grafts IL onto the surface of aerogel.

[0048] Table 2. Functional groups on the surface of Ni-A and Ni-A-IL catalysts

[0049]

[0050] 3. This invention further investigated the electronic structure of the sample using X-ray photoelectron spectroscopy (XPS). The XPS investigation spectrum of Ni-A-IL confirmed the presence of Ni, O, C, Si, N, and Cl elements (see...). Figure 13 Notably, the elemental composition is consistent with the EDX results. The Ni 2p spectrum shows two characteristic peaks at 855.7 eV and 873.6 eV, corresponding to Ni 2p³ / 2 and Ni 2p¹ / 2, respectively, revealing that Ni has a valence state of +2 (…). Figure 6 a). In Figure 6 In b, the O1s spectrum of Ni-A shows a strong signal at 531.7 eV, which can be attributed to the Ni-O bond. Another peak is located at 533.4 eV, associated with the C=O bond. The O1s spectrum of Ni-A-IL, however, shows only one peak at 532.3 eV, which can be attributed to the Si-O bond. In the C1s region, both Ni-A and Ni-A-IL show two identical peaks, located at 284.8 eV and 288.3 eV respectively, corresponding to the CH and C=O bonds. Figure 6 c). Furthermore, in the C1s spectrum of Ni-A-IL, a new signal centered at 286.3 eV was identified as a C=N bond in the imidazole ring. The Cl2p spectrum of Ni-A showed two spin-orbit splitting peaks at 198.5 eV and 200.3 eV, corresponding to Cl2p3 / 2 and Cl2p1 / 2, respectively, which can be attributed to bonding with the metal ( Figure 6 d). After the grafting reaction, the Cl 2p spectrum showed significant differences. In the Ni-A-IL Cl 2p spectrum, a new peak appeared at 201.7 eV, while the peak at 200.2 eV was enhanced due to the binding of the Cl- anion with the ionic liquid cation. For the N1s spectrum, two distinct peaks from the imidazole ring appeared ( Figure 6e). The peak at 400.6 eV was assigned to pyrrole nitrogen. Another peak at 399.2 eV was attributed to pyridine nitrogen. In the Si 2s region, the dominant peak is located at 102.6 eV and is associated with the Si-O bond (e). Figure 6 f). The above results also indicate that IL was successfully grafted onto the aerogel surface.

[0051] Example 2

[0052] Application of the Ni-A-IL catalyst prepared in Example 1 in the CO2 cycloaddition reaction:

[0053] In a typical catalytic cycloaddition reaction, 3 ml of propylene oxide (PO) and 50 mg of catalyst were placed in a stainless steel autoclave. Then, CO2 was introduced into the autoclave at varying pressures. The reaction apparatus was heated to a specified temperature and maintained for a certain time. After the reaction was complete, the autoclave was cooled in ice water. Subsequently, the pressure was slowly reduced, and the catalyst was collected after washing with acetonitrile. The specific reaction conditions were: PO: 3 ml (41 mmol), Cat.: 50 mg, pressure 1 MPa, reaction temperature 120 °C, reaction time 2 h.

[0054] After the reaction was completed, the collected liquid was centrifuged at 8000 rpm for 5 min. The conversion of PO and the yield of propylene carbonate (PC) generated in the reaction were determined by gas chromatography (GC) with a flame ionization detector. 1-Dodecanol was used as an internal standard, and qualitative analysis was performed by 1H NMR.

[0055] This invention investigated the catalytic performance of Ni-A, IL (i.e., the imidazole-based IL prepared in the synthesis of Ni-A-IL), and Ni-A-IL. The amounts of Ni-A, IL, and Ni-A-IL were all 50 mg. The products were measured by gas chromatography and 1H nuclear magnetic resonance (NMR) analysis. After reacting at 120 °C and 1 MPa CO2 for 2 hours, the yield of Ni-A was only 27.8% (…). Figure 7 In contrast, IL and Ni-A-IL showed a significant improvement in activity. When 50 mg of IL was added, the yield of PC reached 90.3%. The cycloaddition reaction of the Ni-A-IL catalyst achieved a PC yield of 98.7% and a PO conversion of 98.7%. The appropriate pore size and volume of Ni-A-IL facilitated the diffusion of reactants to the active sites. Figure 8 In section b, the effect of temperature on PC yield and PO conversion was measured within a temperature range of 60 to 130 °C. As the temperature increased to 120 °C, both yield and conversion gradually increased. No significant improvement in catalytic performance was observed above 120 °C. Therefore, 120 °C was selected as the optimal reaction temperature. Similarly, with increasing pressure, both yield and conversion increased, reaching their maximum values ​​at 1 MPa. Figure 8 c). Figure 8 The results showed that conversion and yield increased with increasing reaction time, then stabilized at 2 hours. Therefore, subsequent tests used 2 hours as the optimal reaction time to systematically study the catalyst quality. Figure 14 A sharp increase in catalytic performance was observed by increasing the catalyst mass from 30 to 50 mg. No significant changes were observed when the catalyst mass exceeded 50 mg.

[0056] To assess the reusability of the Ni-A-IL catalyst, regeneration experiments were conducted. After each experiment, the catalyst was centrifuged and washed three times with methanol, then dried in a vacuum oven. After seven runs, no significant decrease in PO conversion and PC yield was observed, and the catalytic performance remained at 97.8%. Figure 9 Three strong Si-O bonds in Ni-A-IL firmly anchor the IL to the aerogel and effectively prevent the loss of active species. Therefore, the resulting Ni-A-IL exhibits high stability and reusability. Furthermore, no byproducts were detected in any of the tests. Figure 15 ).

[0057] This invention investigates the cycloaddition reaction mechanism of CO2 and PO using diffuse reflectance infrared Fourier transform spectroscopy (DRIFT).

[0058] The cycloaddition reaction mechanism of propylene oxide (PO) with carbon dioxide was investigated using in-situ DRIFT (differential infrared transmission spectroscopy). Background spectra were obtained after introducing 1 bar of N2 at 120 °C for approximately 30 minutes. To introduce PO into the reaction chamber, the PO solution was bubbled with 1 bar of N2 for 20 minutes to remove oxygen.

[0059] exist Figure 10 In a, 2998 and 1410cm -1 The peaks at these locations are caused by the tensile and deformation vibrations of CH. (1410, 1257, 1127, 1033, 965, 832 cm⁻¹) -1 The peak at 667 cm⁻¹ was attributed to the COC framework vibration of PO. Ni-A, with its abundant surface -OH groups, can form hydrogen bonds with PO. Simultaneously, the protons of the imidazole cations in Ni-A-IL can also form hydrogen bonds with PO. Therefore, both Ni-A and Ni-A-IL exhibit strong adsorption capacity for PO. After 30 minutes of 1 bar CO₂ introduction, Ni-A-IL showed a strong peak at 667 cm⁻¹. -1 The new peak at that point corresponds to the bending vibration of CO2. Figure 10(b) The spectrum of Ni-A showed only a weak signal. This phenomenon indicates that Ni-A-IL has a stronger CO2 adsorption and activation capacity than Ni-A.

[0060] exist Figure 11 In this process, CO2 was bubbled into a PO solution at a pressure of 1 bar for 30 minutes to achieve CO2 saturation. In-situ DRIFT measurements were then performed, and this was considered the curve at 0 minutes (the first test, where no reaction occurred, is labeled as the 0-minute test curve). The reaction chamber was then sealed and heated to 120°C. One curve was acquired every 5 minutes. After 5 minutes of reaction, a new strong signal appeared at 1794 cm⁻¹, attributed to the stretching vibration of C=O in PC. The intensity of this peak continuously increased with increasing reaction time. Meanwhile, at 1177 cm⁻¹... -1 A weak peak also appeared at 2298, 1410, 1118, 1029, 956, and 832 cm⁻¹, caused by the stretching vibration of CO in PC. Conversely, with increasing reaction time, the peaks of PO at 2298, 1410, 1118, 1029, 956, and 832 cm⁻¹ increased. -1 The peak at 770 cm⁻¹ was significantly weakened. These results indicate that PO was consumed and PC was synthesized. When the temperature was increased to 120℃, the peak at 770 cm⁻¹ was significantly weakened. -1 The peak at which the C-Cl bond is attributed is formed through Cl- nucleophilic attack on PO. Further extending the reaction time to 30 minutes slightly weakens this peak. Increasing the temperature from room temperature to 120℃ enhances the CO2 bending vibration peak, indicating that CO2 is well activated at 120℃.

[0061] Based on the above results, Figure 12 A proposed reaction mechanism is described. The first step of the cycloaddition reaction is the activation of the PO ring. The proton of the imidazole ring forms a hydrogen bond with the oxygen atom in the PO molecule. Then, the nucleophile Cl- attacks the less sterically hindered β-carbon atom of PO, causing the PO ring to open. Subsequently, the formed alkoxy anion again acts as a nucleophile to attack the CO2 activated by tertiary ammonium in the IL. Finally, the intermediate is eliminated along with Cl- through inner ring merging to convert to PC. The catalyst is regenerated and placed into a new round of catalytic reaction.

[0062] In summary, this invention provides a highly active Ni-A-IL catalyst for the CO2 cycloaddition reaction. The Ni-A-IL catalyst, due to the presence of three strong Si-O bonds, firmly immobilizes the ionic liquid onto the aerogel and effectively prevents the loss of active species. Therefore, the Ni-A-IL catalyst obtained by this invention not only achieves high activity for the cycloaddition of CO2 and PO but also exhibits excellent stability. In-situ DRIFT measurements show that the ionic liquid immobilized on the aerogel can effectively activate CO2 and PO. The Cl- ions in Ni-A-IL attack PO via nucleophilic attack without the need for additional halide ions. This invention not only provides a simple route for designing functional catalysts with practical application potential but also provides useful insights into the cycloaddition mechanism of CO2 and propylene oxide.

[0063] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A process for the preparation of a Ni-A-IL catalyst, characterized in that The preparation method comprises the following steps: (1) using polyacrylic acid PAA as a template to induce the formation of Ni-based hydrogel, and preparing Ni-A after supercritical drying treatment; (2) grafting an imidazole-based ionic liquid IL onto the Ni-A through a dealcoholization condensation reaction, and preparing the Ni-A-IL catalyst after vacuum drying treatment.

2. The process for the preparation of a Ni-A-IL catalyst according to claim 1, characterized in that, The preparation method of the Ni-A in the step (1) is as follows: Step a: dissolving acrylic acid in deionized water, and then adding a K2S2O8 initiator to initiate a polymerization reaction to obtain a polyacrylic acid hydrogel; Step b: adding a nickel salt into ethanol, stirring, and then pouring the mixture into the polyacrylic acid hydrogel, and then adding propylene oxide PO to obtain a wet gel, and then cleaning and drying to obtain the Ni-A.

3. The process for the preparation of a Ni-A-IL catalyst according to claim 2, characterized in that, 0.5 ml of acrylic acid is dissolved in 2.5 ml of deionized water, and then 25 mg of a K2S2O8 initiator is added to initiate a polymerization reaction.

4. The process for the preparation of Ni-A-IL catalyst as claimed in claim 2, wherein, The polymerization reaction is carried out at a temperature of 60 DEG C for 2 hours.

5. The process for the preparation of Ni-A-IL catalyst as claimed in claim 2, wherein, In the step b, 10 ml of ethanol containing 0.594 g of NiCl2 6H2O is poured into the polyacrylic acid hydrogel prepared in the step a, and after stirring for 5-20 min, the hydrogel is dissolved in the ethanol solution, and then 3 ml of propylene oxide PO is added, and after 2 hours, a laurel green gel is formed, and the gel is left to stand at room temperature for 24 hours, and then the gel is immersed in an ethanol bath for cleaning for 3 days; finally, the solvent in the wet gel is replaced with CO2 in a supercritical drying device for 2-3 days to obtain a laurel green aerogel, namely the Ni-A.

6. The method of preparing a Ni-A-IL catalyst according to claim 1, characterized by, The preparation method of the Ni-A-IL catalyst in the step (2) is as follows: 1-methylimidazole and (3-chloropropyl)trimethoxysilane are dissolved in acetonitrile, and a reflux reaction is carried out under N2 protection, and after the reaction is completed, the Ni-A is added for continuous reaction, and the obtained aerogel is washed and dried to obtain the Ni-A-IL catalyst.

7. The process for the preparation of a Ni-A-IL catalyst according to claim 6, characterized in that, 2.72 g of 1-methylimidazole and 8 ml of (3-chloropropyl)trimethoxysilane are dissolved in 50 ml of acetonitrile, and a reflux reaction is carried out at 85 DEG C for 12 hours under N2 protection, and after the reaction is completed, 3.5 g of the Ni-A is added for continuous reaction for 12 hours, the obtained aerogel is washed with acetonitrile for three times, and finally, the grafted aerogel is vacuum dried at 40 DEG C to obtain the Ni-A-IL catalyst.

8. Application of the Ni-A-IL catalyst prepared by the preparation method in any one of claims 1-7 in a CO2 and epoxide cycloaddition reaction.

9. Use according to claim 8, characterized in that: 3 ml of PO and 50 mg of the catalyst are placed in a stainless steel autoclave, CO2 is filled into the autoclave to a certain pressure, the reaction equipment is heated to a specified temperature and kept for a certain time, after the reaction is completed, the reaction autoclave is cooled in ice water, and then the pressure is slowly reduced, and the catalyst is collected after being washed with acetonitrile, and the collected liquid is centrifuged in a centrifuge at 8000 rpm for 5 min.

10. Use according to claim 9, characterized in that: The CO2 pressure is 1 MPa, the reaction temperature is 120 DEG C, and the reaction time is 2 hours.

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