A method for preparing Mn3O4 and its application in the cycloaddition reaction of CO2 with propylene oxide

Abstract

This invention relates to a method for preparing a Mn3O4 catalyst and its application in the cycloaddition reaction of CO2 with propylene oxide, belonging to the field of catalyst preparation and application technology. The preparation method is as follows: a strong alkaline solution is continuously added dropwise to a manganese salt solution to adjust the pH of the mixed solution to alkaline, resulting in a precursor suspension. This suspension is placed in a hydrothermal reactor, heated and kept at a homogeneous temperature, and after cooling, filtered, washed, dried, and ground to obtain the target catalyst. Under reaction conditions of 3 MPa CO2 pressure, 100–140 °C, and 1 h of catalysis, this Mn3O4 catalyst achieves a conversion rate of 10%–50% for propylene oxide and a selectivity for propylene carbonate exceeding 99%. This preparation method is simple, has low production costs, and a high yield. It is highly selective for catalyzing the conversion of propylene oxide and CO2 to propylene carbonate and can be recycled four times, demonstrating broad industrial application prospects.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a method for preparing a manganese tetroxide catalyst and its application in the preparation of propylene carbonate in the cycloaddition reaction of CO2 and propylene oxide. Background Technology

[0002] Propylene carbonate possesses excellent biodegradability, solubility, and physical properties such as high polarity and high boiling point, making it widely used in polymer industries, electronics industries, textiles, dyes, and chemical reagents. Currently, the industrial process involves the addition reaction of propylene oxide with CO2 under certain pressure, followed by vacuum distillation to produce propylene carbonate. However, these production conditions are quite demanding; therefore, the development of highly efficient catalysts for the cycloaddition reaction of CO2 with epoxides has been a major focus.

[0003] In early studies, the preparation of propylene carbonate from propylene oxide and CO2 mainly utilized homogeneous catalysts, such as ionic liquids, alkali metal salts, and organic bases. These catalysts commonly used halogen-containing catalysts such as potassium iodide. However, homogeneous catalysts have inherent drawbacks, including complex product separation from catalyst and solvent steps, high catalyst recovery costs, and environmental pollution caused by the use of halogen additives. Therefore, heterogeneous catalysis has become another research hotspot for this reaction system, and heterogeneous catalytic systems such as supported ionic liquids, MOF materials, and porous materials have been successively developed. To date, heterogeneous catalysts such as metal oxides and functionalized molecular sieve materials have shown promising industrial application prospects.

[0004] Focusing on the scale-up of the preparation process, the raw material cost and the cyclic stability of the catalyst during mass production are key issues that need to be considered. Metal oxide catalysts, on the other hand, have inexpensive raw materials, are easy to mass-produce, and exhibit good cyclic stability, catalytic activity, and selectivity, making them highly promising for industrial applications. Furthermore, the cycloaddition reaction of CO2 with propylene oxide to produce propylene carbonate via metal oxide catalysts is a green, economical, and efficient process route, and this reaction also boasts advantages such as good product quality, high yield, and catalyst recyclability. Currently, the main metal oxide catalysts used in the cycloaddition reaction of CO2 with propylene oxide are MgO, SnO2, CeO2, La2O3, ZrO2, ZnO, Al2O3, and composite metal oxides. For example, YANO et al. first reported the cycloaddition reaction of CO2 and epoxides catalyzed by MgO as the active component, opening a new chapter in oxide-catalyzed CO cycloaddition reactions. SAENGSAEN et al. prepared a series of SnO2 catalysts via a simple hydrothermal synthesis method. Under atmospheric pressure and in a non-pure CO2 atmosphere (containing 20% ​​methane by volume, based on the volume of CO2), they achieved an epoxide conversion rate of 84%. GAO et al. successfully prepared CeO2 catalysts in three morphologies: cubic, octahedral, and nanorod. Through comprehensive DFT calculations on the (111, 0110), and (100) crystal planes, they found that the CeO2 nano-octahedron, dominated by the (111) plane, had the lowest activation energy, thus exhibiting the highest product yield. Regarding composite metal oxides, to investigate the effect of alkaline earth metal-modified Zn-Al composite oxides on the cycloaddition reaction of CO2 and epoxides to form cyclic carbonates, DAI et al. prepared Zn-M-Al (M=Mg, Ca, Sr, or Ba) composite oxides. Studies have found that alkaline earth metal-modified Zn-Al composite oxides possess both acid and basic sites, and certain characteristics of the basic sites are related to the catalyst activity. Among them, Zn-Mg-Al composite oxides exhibit better catalytic performance due to the presence of more basic sites and moderate basicity. TAMBE et al. prepared La-Zr composite oxides via combustion for catalyzing the cycloaddition reaction of CO2 and epoxides, achieving a 90% conversion of epoxides and 100% selectivity for propylene carbonate. CO2 temperature-programmed desorption (CO2-TPD) and NH3 temperature-programmed desorption (NH3-TPD) results indicate that the incorporation of La introduces strong basic sites, and the simultaneous presence of strong basic and weak acidic sites is more conducive to the cycloaddition reaction of CO2 and epoxides.

[0005] Among metal oxides, manganese oxides are low in preparation cost, highly active, and exhibit diverse crystal structures. Different crystal structures of manganese oxides have different surface microstructures and chemical compositions, resulting in varying catalytic performances. Manganese tetroxide, in particular, has attracted widespread attention in the field of CO2 catalytic conversion due to its unique structure with abundant Lewis acid-base active sites on its surface and its high activity for CO2 catalytic conversion.

[0006] In summary, the cycloaddition reaction of CO2 and propylene oxide to prepare cyclic carbonates is an efficient and applicable method. Therefore, it is of great significance to develop simple, green, low-cost, and highly active metal oxide catalysts for catalyzing the cycloaddition reaction of CO2 and propylene oxide to prepare propylene carbonate. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies for preparing propylene carbonate via the cycloaddition reaction of CO2 and propylene oxide, the present invention aims to provide a method for preparing a Mn3O4 catalyst. This method is simple, inexpensive, yields a high product, and exhibits high selectivity for propylene carbonate, thus possessing significant economic and practical value.

[0008] To achieve the above objectives, the present invention adopts the following technical solution.

[0009] This invention provides a method for preparing a Mn3O4 catalyst, the specific steps of which are as follows: (1) Weigh out MnCl2·4H2O and place it in a beaker. Add distilled water to completely dissolve MnCl2·4H2O in the distilled water to obtain a pink MnCl2·4H2O solution. (2) Weigh out a strong base and place it in a beaker. Add distilled water to completely dissolve the strong base in the distilled water to obtain a strong base solution. (3) Add the strong alkali solution dropwise to the MnCl2·4H2O solution to adjust the pH of the mixed solution to 10~14 to obtain the precursor suspension; (4) The obtained precursor suspension was placed in a 100 mL polytetrafluoroethylene liner, the liner was placed in a 100 mL hydrothermal reactor, and the hydrothermal reactor was placed in a homogeneous reactor for heating and heat preservation. (5) After the reaction is complete, the hydrothermal reactor is taken out and cooled. The suspension is then filtered, washed, dried and ground to obtain a brownish-yellow Mn3O4 catalyst.

[0010] Preferably, in step (1), the manganese salt is one of MnCl2·4H2O, MnCO3, MnSO4·H2O, and MnNO3.

[0011] Preferably, in step (2), the strong base is either NaOH or KOH.

[0012] Preferably, in step (1), the concentration of the prepared manganese salt solution is 0.5 mol / L.

[0013] Preferably, in step (2), the concentration of the prepared strong alkali solution is 1.5~2.5 mol / L.

[0014] Preferably, in step (3), the pH of the mixed solution is adjusted to 12.

[0015] Preferably, in step (4), the heating temperature in the homogeneous reactor is 170~190 ℃ and the holding time is 18 h~30 h.

[0016] Preferably, in step (5), the specific surface area of ​​the obtained Mn3O4 catalyst is 90~100 m². 2 g -1 The average pore size is 23~24 nm.

[0017] Another object of the present invention is to provide a Mn3O4 catalyst prepared by the above preparation method.

[0018] Another object of the present invention is to provide the application of the Mn3O4 catalyst obtained by the preparation method in the preparation of propylene carbonate in the cycloaddition reaction of CO2 and propylene oxide. Under the reaction conditions of 3 MPa CO2 pressure, 100~140 °C and 1 h of catalysis, the Mn3O4 catalyst achieves a conversion rate of 10%~50% for propylene oxide and a selectivity for propylene carbonate of more than 99%.

[0019] By employing the above-described technology, the beneficial effects of the present invention compared to the prior art are as follows: 1. This invention uses a hydrothermal method to prepare manganese tetroxide. The raw materials used are inexpensive and the production cost is low, thus it has broad prospects for industrial production.

[0020] 2. The manganese tetroxide catalyst prepared by this invention has good performance in catalyzing the cycloaddition reaction of CO2 and propylene oxide to prepare propylene carbonate. Under the reaction conditions of CO2 pressure 3 MPa, temperature 100-140 ℃, reaction time 1 h, catalyst 400 mg, and propylene oxide 14.52 g, the Mn3O4 catalyst achieves a conversion rate of 10-50% for propylene oxide and a selectivity of over 99% for propylene carbonate. When the reaction time is 16 h, the conversion rate of propylene oxide can reach 100%, which has the advantage of high yield. The selectivity for propylene carbonate is over 99%, and it can be recycled four times, showing broad prospects for industrial application. Attached Figure Description

[0021] Figure 1 The XRD pattern of the Mn3O4 catalyst prepared by the method of the present invention; Figure 2 Scanning electron microscope image of the Mn3O4 catalyst prepared by the method of the present invention; Figure 3 Transmission electron microscopy image of the Mn3O4 catalyst prepared by the method of the present invention; Figure 4 The attached diagram shows the N2 adsorption and desorption of the Mn3O4 catalyst prepared by the method of this invention. Figure 5 The time history diagram of the Mn3O4 catalyst prepared by the method of the present invention; Figure 6 The figure shows the stability performance of the Mn3O4 catalyst prepared by the method of this invention. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with specific embodiments, but the scope of protection of the present invention is not limited thereto. Although the steps in the present invention are arranged with reference numerals, they are not intended to limit the order of the steps. Unless the order of the steps is explicitly stated or the execution of a certain step requires other steps as a basis, the relative order of the steps can be adjusted. Unless otherwise specified, the chemical reagents and materials in the present invention are all purchased from the market or synthesized from raw materials purchased from the market.

[0023] Example 1: Preparation of Mn3O4 (1) Weigh 5.94 g of MnCl2·4H2O and place it in a beaker. Use a graduated cylinder to measure 60 mL of distilled water and place it in the beaker so that MnCl2·4H2O is completely dissolved in the distilled water. A pink solution of MnCl2·4H2O with a concentration of 0.5 mol / L can be obtained. (2) Weigh 4 g of NaOH and place it in a beaker. Use a graduated cylinder to measure 50 mL of distilled water and place it in the beaker. Dissolve the NaOH completely in the distilled water to obtain a NaOH solution with a concentration of 2 mol / L. (3) NaOH solution was gradually added dropwise to MnCl2·4H2O solution, and the pH value of the mixed solution was adjusted to 12 to obtain the precursor suspension; (4) Place the precursor suspension in a 100 mL polytetrafluoroethylene liner, place the liner in a 100 mL hydrothermal reactor, and finally place the hydrothermal reactor in a homogeneous reactor. Finally, heat the homogeneous reactor to 180 °C and keep it at that temperature for 24 h. (5) After the reaction is complete, the hydrothermal reactor is taken out and cooled. The suspension inside is filtered, washed, dried and ground to obtain the brownish-yellow Mn3O4 catalyst.

[0024] The specific surface area of ​​Mn3O4 was characterized to be 96 m². 2 g -1 The average pore size is 24 nm.

[0025] The performance tests of the Mn3O4 catalyst prepared in Example 1 are as follows: Weigh 400 mg of catalyst into a high-pressure reactor, then weigh (14.52 g) of propylene oxide and 20 mL of N,N-dimethylformamide and mix them evenly. Transfer the mixture into the high-pressure reactor, seal the reactor, and place it in a magnetically heated stirrer. First, introduce 1 MPa of CO2 to check the airtightness of the high-pressure reactor. If there is no CO2 leakage, release the CO2 from the reactor. Repeat the filling and emptying process three times to ensure that there is no air in the reactor. Finally, fill the reactor with gas to give it a certain pressure.

[0026] Adjust the magnetic spindle speed to 500 rpm and start timing when the reactor temperature reaches 120 ℃. After 1 h of reaction, remove the reactor and allow it to cool to room temperature. Then, place the high-pressure reactor in an ice-water bath to lower its temperature to below 5 ℃. Open the gas valve of the high-pressure reactor to vent CO2 until the pressure reaches 0 MPa. Finally, open the high-pressure reactor and remove the reaction solution. Extract and filter the reaction solution using a filter needle. Then, use a gas chromatography micro-injection needle to draw 0.4 μl of the filtrate and perform component analysis using gas chromatography. The gas chromatography H2 flow rate was set to 50–80 mL / min, air flow rate to 200–300 mL / min, carrier gas flow rate to 3–5 mL / min, injection temperature to 280.0 ℃, column furnace initial temperature to 60 ℃ for 6 min, then increase the temperature at 25 ℃ / min to 220 ℃ for 10 min, and FID temperature to 280.0 ℃.

[0027] After the chromatographic peaks are obtained, the conversion rate of propylene oxide is calculated by the peak area, thus obtaining the selectivity of the catalyst for propylene carbonate.

[0028] Under the reaction conditions of CO2 pressure of 3 MPa, temperature of 120 ℃, reaction time of 1 h, Mn3O4 400 mg, N,N-dimethylformamide 20 mL and propylene oxide 14.52 g, the catalyst achieved a propylene oxide conversion rate of 20%, and a propylene oxide conversion rate of 100% at a reaction time of 16 h, with a propylene carbonate selectivity of over 99%.

[0029] In subsequent embodiments, the performance testing of the prepared Mn3O4 catalyst was conducted using the testing methods described in Example 1.

[0030] Example 2: Preparation of Mn3O4 Compared with Example 1, the difference in Example 2 is that in step (3), the pH value of the mixed solution is adjusted to 10 to obtain the precursor suspension.

[0031] Under the reaction conditions of CO2 pressure of 3 MPa, temperature of 120 ℃, reaction time of 1 h, Mn3O4 400 mg, N,N-dimethylformamide 20 mL and propylene oxide 14.52 g, the catalyst achieved a conversion rate of 10% for propylene oxide and a selectivity of over 99% for propylene carbonate.

[0032] Example 3: Preparation of Mn3O4 Compared with Example 1, the difference in Example 3 is that in step (3), the pH value of the mixed solution is adjusted to 14 to obtain the precursor suspension.

[0033] Under the reaction conditions of CO2 pressure of 3 MPa, temperature of 120 ℃, reaction time of 1 h, Mn3O4 400 mg, N,N-dimethylformamide 20 mL and propylene oxide 14.52 g, the catalyst achieved a conversion rate of propylene oxide of 13% and a selectivity of propylene carbonate of over 99%.

[0034] Comparative Example 1 Compared with Example 1, the difference in Example 3 is that the pH value of the mixed solution was adjusted to 9 in step (3), and no precursor suspension was obtained.

[0035] Example 4: Preparation of Mn3O4 Compared with Example 1, the difference of Example 4 is that in step (4), the hydrothermal reactor is placed in the homogeneous reactor, and the homogeneous reactor is heated to 170 °C and kept at that temperature for 24 h.

[0036] Under the reaction conditions of CO2 pressure of 3 MPa, temperature of 120 ℃, reaction time of 1 h, Mn3O4 400 mg, N,N-dimethylformamide 20 mL and propylene oxide 14.52 g, the catalyst achieved a conversion rate of 18% for propylene oxide and a selectivity of over 99% for propylene carbonate.

[0037] Example 5: Preparation of Mn3O4 Compared with Example 1, the difference in Example 5 is that in step (4), the hydrothermal reactor is placed in the homogeneous reactor, and the homogeneous reactor is heated to 190 °C and kept at that temperature for 24 h.

[0038] Under the reaction conditions of CO2 pressure of 3 MPa, temperature of 120 ℃, reaction time of 1 h, Mn3O4 400 mg, N,N-dimethylformamide 20 mL and propylene oxide 14.52 g, the catalyst achieved a conversion rate of propylene oxide of 17% and a selectivity of propylene carbonate of over 99%.

[0039] Example 6: Preparation of Mn3O4 Compared with Example 1, the difference of Example 6 is that in step (4), the hydrothermal reactor is placed in the homogeneous reactor, and the homogeneous reactor is heated to 180 °C and kept at that temperature for 18 h.

[0040] Under the reaction conditions of CO2 pressure of 3 MPa, temperature of 120 ℃, reaction time of 1 h, Mn3O4 400 mg, N,N-dimethylformamide 20 mL and propylene oxide 14.52 g, the catalyst achieved a conversion rate of propylene oxide of 19% and a selectivity of propylene carbonate of over 99%.

[0041] Example 7: Preparation of Mn3O4 Compared with Example 1, the difference of Example 7 is that in step (4), the hydrothermal reactor is placed in the homogeneous reactor, and the homogeneous reactor is heated to 180 °C and kept at that temperature for 30 h.

[0042] Under the reaction conditions of CO2 pressure of 3 MPa, temperature of 120 ℃, reaction time of 1 h, Mn3O4 400 mg, N,N-dimethylformamide 20 mL and propylene oxide 14.52 g, the catalyst achieved a conversion rate of propylene oxide of 19% and a selectivity of propylene carbonate of over 99%.

[0043] Example 8: Preparation of Mn3O4 Compared with Example 1, the difference in Example 8 is that in step (2), 3 g of NaOH is weighed and placed in a beaker, and 50 mL of distilled water is measured with a graduated cylinder and placed in the beaker to completely dissolve the NaOH in the distilled water to obtain a 1.5 mol / L NaOH solution.

[0044] Under the reaction conditions of CO2 pressure of 3 MPa, temperature of 120 ℃, reaction time of 1 h, Mn3O4 400 mg, N,N-dimethylformamide 20 mL and propylene oxide 14.52 g, the catalyst achieved a conversion rate of propylene oxide of 20% and a selectivity of propylene carbonate of over 99%.

[0045] Example 9: Preparation of Mn3O4 Compared with Example 1, the difference in Example 9 is that in step (2), 5 g of NaOH is weighed and placed in a beaker, and 50 mL of distillate is measured and placed in the beaker to completely dissolve the NaOH in the distillate, so as to obtain a 2.5 mol / L NaOH solution.

[0046] Under the reaction conditions of CO2 pressure of 3 MPa, temperature of 120 ℃, reaction time of 1 h, Mn3O4 400 mg, N,N-dimethylformamide 20 mL and propylene oxide 14.52 g, the catalyst achieved a conversion rate of propylene oxide of 20% and a selectivity of propylene carbonate of over 99%.

[0047] Example 10: Reaction temperature was 100 °C Compared with Example 1, the difference in Example 10 is that the performance test conditions of the Mn3O4 catalyst are as follows: under the reaction conditions of CO2 pressure of 3 MPa, temperature of 100 ℃, reaction of 1 h, 400 mg of Mn3O4, 20 mL of N,N-dimethylformamide and 14.52 g of propylene oxide, the catalyst achieves a conversion rate of 10% for propylene oxide and a selectivity of over 99% for propylene carbonate.

[0048] Example 11: Reaction temperature was 140 °C Compared with Example 1, the difference in Example 11 is that the performance test conditions of the Mn3O4 catalyst are as follows: under the reaction conditions of CO2 pressure of 3 MPa, temperature of 140 ℃, reaction of 1 h, 400 mg of Mn3O4, 20 mL of N,N-dimethylformamide and 14.52 g of propylene oxide, the catalyst achieves a conversion rate of 50% for propylene oxide and a selectivity of over 99% for propylene carbonate.

[0049] Example 12: CO2 reaction pressure is 1.5 MPa Compared with Example 1, the difference in Example 12 is that the performance test conditions of the Mn3O4 catalyst are as follows: under the reaction conditions of CO2 pressure of 1.5 MPa, temperature of 120 ℃, reaction time of 1 h, 400 mg of Mn3O4, 20 mL of N,N-dimethylformamide and 14.52 g of propylene oxide, the catalyst achieves a conversion rate of 20% for propylene oxide and a selectivity of over 99% for propylene carbonate.

[0050] Example 13: CO2 reaction pressure is 5 MPa Compared with Example 1, the difference in Example 13 is that the performance test conditions of the Mn3O4 catalyst are as follows: under the reaction conditions of CO2 pressure of 5 MPa, temperature of 120 ℃, reaction of 1 h, 400 mg of Mn3O4, 20 mL of N,N-dimethylformamide and 14.52 g of propylene oxide, the catalyst achieves a conversion rate of 20% for propylene oxide and a selectivity of over 99% for propylene carbonate.

[0051] Example 14: The mass of propylene oxide was 11.62 g. Compared with Example 1, the difference in Example 14 is that the performance test conditions of the Mn3O4 catalyst are as follows: under the reaction conditions of CO2 pressure of 3 MPa, temperature of 120 ℃, reaction of 1 h, 400 mg of Mn3O4, 20 mL of N,N-dimethylformamide and 11.62 g of propylene oxide, the catalyst achieves a conversion rate of 18% for propylene oxide and a selectivity of over 99% for propylene carbonate.

[0052] Example 15: The mass of propylene oxide was 17.42 g. Compared with Example 1, the difference in Example 15 is that the performance test conditions of the Mn3O4 catalyst are as follows: under the reaction conditions of CO2 pressure of 3 MPa, temperature of 120 ℃, reaction of 1 h, 400 mg of Mn3O4, 20 mL of N,N-dimethylformamide and 17.42 g of propylene oxide, the catalyst achieves a conversion rate of 18% for propylene oxide and a selectivity of over 99% for propylene carbonate.

[0053] Example 16 Compared with Example 1, the difference in Example 16 is that the strong alkali solution prepared in step (2) is a KOH solution.

[0054] Under the reaction conditions of CO2 pressure of 3 MPa, temperature of 120 ℃, reaction time of 1 h, 400 mg Mn3O4, 20 mL N,N-dimethylformamide, and 14.52 g propylene oxide, the catalyst achieved a conversion rate of 20% for propylene oxide and a selectivity of over 99% for propylene carbonate.

[0055] Example 17 Compared with Example 1, the difference in Example 17 is that the manganese salts in step (1) are MnCO3, MnSO4·H2O and MnNO3, respectively, to prepare Mn3O4 catalyst.

[0056] Under the reaction conditions of CO2 pressure of 3 MPa, temperature of 120 ℃, reaction time of 1 h, 400 mg Mn3O4, 20 mL N,N-dimethylformamide, and 14.52 g propylene oxide, the catalyst achieved conversion rates of propylene oxide of 18.9%, 19.9%, and 17.3%, respectively, and a selectivity of over 99% for propylene carbonate.

[0057] The XRD pattern of the Mn3O4 catalyst prepared in Example 1 of this invention shows that there are six diffraction peaks at approximately 2θ = 18.00°, 28.88°, 32.31°, 36.08° and 59.84°, corresponding to the six crystal planes (101), (112), (103), (211) and (224).

[0058] Figure 2 The image shows a scanning electron microscope (SEM) image of the Mn3O4 catalyst. As can be seen from the image, the prepared Mn3O4 is composed of square, identical, and uniform nanoparticles.

[0059] Figure 3 This is a transmission electron microscope (TEM) image of the Mn3O4 catalyst prepared in Example 1 of this invention. As can be seen from the image, consistent with the SEM results, the prepared Mn3O4 exhibits a square and uniform particle composition.

[0060] Figure 4 This is a graph showing the N2 adsorption and desorption of the Mn3O4 catalyst prepared in Example 1 of this invention. The characteristic hysteresis loop in the graph indicates that the Mn3O4 catalyst has a distinct mesoporous structure. Calculations show that the specific surface area of ​​Mn3O4 is 96 m². 2 ·g -1 .

[0061] Figure 5 The time history diagram of the Mn3O4 catalyst prepared in Example 1 of this invention shows that the conversion rates of propylene oxide were 0%, 9%, 20%, 37%, 63%, 86%, and 100.0% at reaction times of 0 h, 0.5 h, 1 h, 2 h, 4 h, 8 h, and 16 h, respectively, and the selectivity of propylene carbonate remained above 99%. This indicates that the Mn3O4 catalyst has high catalytic activity.

[0062] Figure 6 The figure shows the stability performance of the Mn3O4 catalyst prepared in Example 1 of this invention. As can be seen from the figure, the conversion rate of propylene oxide is 20%, 19%, 19% and 19% respectively when the catalyst is cyclic for the first, second, third and fourth times. The selectivity of propylene carbonate is maintained above 99% in all cases. It can be concluded that the Mn3O4 catalyst has high stability.

[0063] In addition, the catalytic stability of the Mn3O4 catalyst prepared in Example 1 of this invention to propylene oxide was tested under the same reaction conditions, and the experimental performance is shown in Table 1.

[0064] Table 1. Results of catalyst stability experiments

[0065] Table 1 Reaction conditions: 14.52 g propylene oxide, 0.4 g Mn3O4, reaction temperature 120 ℃, carbon dioxide pressure 3 MPa, 20 mL N,N-dimethylformamide, reaction time 1 h.

[0066] The data analysis in Table 1 shows the experimental performance of the Mn3O4 catalyst in catalytic stability against propylene oxide under the same reaction conditions. It can be concluded that the Mn3O4 catalyst has high stability after being recycled four times.

[0067] The catalytic performance of Mn3O4 catalyst on propylene oxide under different temperature reaction conditions can be seen from Examples 1, 10 and 11, as shown in Table 2.

[0068] Table 2 Effect of different reaction temperatures on the catalytic performance of the catalyst

[0069] Table 2 Reaction conditions: 14.52 g propylene oxide, 0.4 g Mn3O4, reaction temperature 100-140 ℃, carbon dioxide pressure 3 MPa, 20 mL N,N-dimethylformamide, reaction time 1 h.

[0070] The data analysis in Table 2 shows the catalytic performance of Mn3O4 catalyst on propylene oxide at different reaction temperatures. It can be concluded that, under the same reaction conditions, the conversion rate of Mn3O4 catalyst on propylene oxide increases with increasing reaction temperature, but the selectivity of propylene carbonate remains high.

[0071] Through data analysis of Examples 1, 12, and 13, the catalytic performance of Mn3O4 catalyst on propylene oxide under different pressure conditions was studied. It can be concluded that under different pressure conditions, the effect of Mn3O4 catalyst on the conversion rate of propylene oxide and the selectivity of propylene carbonate is small, but the catalytic performance is the best at 3 MPa.

[0072] Through data analysis of Examples 1, 14, and 15, the catalytic performance of Mn3O4 catalyst on propylene oxide under different concentrations of propylene oxide was studied. It was found that under different reactant concentrations, both excessively high and low concentrations of propylene oxide would affect the conversion rate of propylene oxide by the catalyst, but would not affect the selectivity of propylene carbonate.

[0073] As can be seen from Examples 1-9 and Comparative Example 1, the type of manganese salt and the type of strong alkali solution have little effect on the catalytic performance of Mn3O4 catalyst. However, the concentration of strong alkali solution, hydrothermal reaction temperature and time, and pH value of mixed solution have a certain impact on the performance of Mn3O4 catalyst. In this invention, the Mn3O4 catalyst with the best catalytic performance was obtained by using a strong alkali solution concentration of 2.5 mol / L, a precursor suspension pH value of 7, and hydrothermal reaction at 180℃ for 24 h.

[0074] The above description is only a partial embodiment of the present invention and is not intended to limit the present invention. Any equivalent changes and modifications made based on the content of this invention are within the protection scope of this invention.

Claims

1. The application of a Mn3O4 catalyst in the cycloaddition reaction of CO2 with propylene oxide to prepare propylene carbonate, characterized in that, Under reaction conditions of 3 MPa CO2 pressure, 100~140 ℃ and 1 h catalysis, the Mn3O4 catalyst achieved a conversion rate of 10%~50% for propylene oxide and a selectivity of over 99% for propylene carbonate. The preparation steps of this Mn3O4 catalyst are as follows: (1) Weigh out MnCl2·4H2O and place it in a beaker. Add distilled water to completely dissolve MnCl2·4H2O in the distilled water to obtain a pink MnCl2 solution. (2) Weigh out a strong base and place it in a beaker. Add distilled water to completely dissolve the strong base in the distilled water to obtain a strong base solution. (3) Add the strong alkali solution dropwise to the MnCl2 solution continuously, adjust the pH of the mixed solution to 10-14, and obtain the precursor suspension; (4) The obtained precursor suspension was placed in a 100 mL polytetrafluoroethylene liner, the liner was placed in a 100 mL hydrothermal reactor, and the hydrothermal reactor was placed in a homogeneous reactor for heating and heat preservation. (5) After the reaction is complete, the hydrothermal reactor is taken out and cooled. The suspension is then filtered, washed, dried and ground to obtain a brownish-yellow Mn3O4 catalyst.

2. The application according to claim 1, characterized in that, In step (2), the strong base is either NaOH or KOH.

3. The application according to claim 1, characterized in that, In step (1), the concentration of the prepared manganese salt solution is 0.5 mol / L.

4. The application according to claim 1, characterized in that, In step (2), the concentration of the prepared strong alkali solution is 1.5~2.5 mol / L.

5. The application according to claim 1, characterized in that, In step (3), the pH of the mixed solution is adjusted to 12.

6. The application according to claim 1, characterized in that, In step (4), the heating temperature in the homogeneous reactor is 170~190 ℃, and the holding time is 18 h~30 h.

7. The application according to claim 1, characterized in that, In step (5), the specific surface area of ​​the obtained Mn3O4 catalyst is 90~100 m². 2 ·g -1 The average pore size is 23~24 nm.

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