Nanometer magnesium oxide material, preparation method and application thereof

Abstract

The application relates to the technical field of catalysts, and discloses a nano magnesium oxide material and a preparation method and application thereof. The nano magnesium oxide material has a porous structure, wherein the particle size of the nano magnesium oxide is 20-200 nm; and the pore size of the porous structure is 5-45 nm. The classical nucleation growth process of the magnesium oxide is directionally adjusted in a weak alkaline nucleation system, and then the nano magnesium oxide with a controllable grain size distribution is obtained. The nano magnesium oxide material has good catalytic activity in the synthesis of propylene carbonate from CO2 and an epoxide under the conditions of no solvent and no auxiliary agent, and the catalyst is not deactivated after multiple uses, and has good stability.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to nano-magnesium oxide materials, their preparation methods, and applications. Background Technology

[0002] CO2 is considered one of the major greenhouse gases contributing to unusual climate change. It is also an abundant, non-toxic, and renewable C1 resource. In recent years, research on converting CO2 into high-value-added chemicals has received widespread attention in order to mitigate the effects of the greenhouse effect. The conversion of CO2 into cyclic carbonates is one of the most promising pathways for CO2 utilization. Propylene carbonate is an important intermediate in chemical production, possessing advantages such as high boiling point, good solubility, and biodegradability. It can be used for the purification of natural gas and synthetic ammonia feedstock, and also as a solvent in the petrochemical and new energy industries. Propylene carbonate is stable and resistant to strong light and high heat, so it can also be used in extremely harsh environments such as satellite and deep-well mining, and is widely used as a wood adhesive in the construction industry.

[0003] The main methods for synthesizing propylene carbonate include the phosgene method, the CO2-propylene glycol / glycerol method, the urea alcoholysis method, the CO2-halogenated alcohol method, the CO2-methanol method, and the CO2-propylene oxide cycloaddition method. The phosgene method, which severely pollutes the environment, has been gradually phased out by the market. When glycerol or diols are used as raw materials, there are numerous byproducts and thermodynamic limitations, resulting in poor atom economy. Urea reacting with diols can also produce propylene carbonate, but its single-pass conversion rate is low and the operating conditions are harsh. The synthesis of propylene carbonate from haloalcohols and CO2 is an important method, but it usually produces byproducts such as halide salts, which corrode equipment. Using propargyl alcohol as a raw material, propylene carbonate can also be produced under suitable catalysts, but its economic efficiency is poor and it is mainly used for laboratory synthesis. The CO2-methanol method is mainly used to produce dimethyl carbonate, with propylene carbonate primarily produced as a co-product; however, it suffers from a long process, low product purity, and high separation energy consumption. The cycloaddition of CO2 and propylene oxide to prepare propylene carbonate is the most widely studied method, with 100% atom economy, high yield of propylene carbonate, and good economic value.

[0004] Currently, homogeneous catalysts such as small organic molecules and ionic liquids, as well as heterogeneous catalysts such as metal oxides, metal Schiff base complexes, and metal-organic frameworks, are widely used in this system. For example, patent application CN115340629A discloses a method for synthesizing cyclic carbonates using a quaternary ammonium salt-type ionic liquid as a catalyst, achieving a 92% yield at 80℃ for 24 hours; however, the catalyst synthesis process is cumbersome and the structure is complex. Patent application CN11432557A discloses a method for synthesizing ethylene carbonate using tetraethylammonium bromide as a catalyst, achieving a 95% conversion rate of ethylene oxide at 130℃ and 3 MPa CO2 pressure; however, the catalyst catalytic conditions are harsh, and the catalyst preparation process is complex. Patent application CN111393402A discloses a... A method for preparing propylene carbonate by cycloaddition of CO2 with epoxides via acid / quaternary ammonium salt composite catalysis, wherein the catalyst is a multi-component homogeneous catalyst, and separation is relatively difficult.

[0005] Compared to homogeneous catalysts, heterogeneous catalysts have advantages such as easily tunable structure and easy separation. However, current heterogeneous catalysts still suffer from problems such as low catalyst activity due to insufficient active sites or decreased catalytic stability due to the loss of active sites during long-term use. Furthermore, metal oxide catalysts face challenges such as difficulty in controlling grain size and pore properties, and poor CO2 activation ability; in particular, large grain size leads to internal diffusion affecting the reaction, resulting in low catalyst activity and slow reaction rates. While traditional methods such as acid-base post-treatment, adding trace elements, and controlling nucleation temperature can adjust the grain size of metal oxides, they also make the synthesis process more cumbersome. This significantly increases the time and economic costs of industrial synthesis, and also causes environmental pollution and large-scale energy consumption. Therefore, finding a metal oxide catalyst with small grain size, high activity, and high stability is an urgent technical problem to be solved. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of large grain size and difficult-to-control pore properties in existing metal oxide catalysts, which lead to low catalyst activity and slow cycloaddition reaction rates. This invention provides a nano-magnesium oxide material, its preparation method, and its application. The nano-magnesium oxide has a small particle size, good pore structure, and excellent catalytic activity. Under solvent-free and additive-free conditions, the nano-magnesium oxide material has good catalytic activity in the synthesis of propylene carbonate from CO2 and epoxides, and the catalyst does not deactivate after multiple uses, exhibiting good stability.

[0007] To achieve the above objectives, the first aspect of the present invention provides a nano-magnesium oxide material having a porous structure, wherein the particle size of the nano-magnesium oxide is 20-200 nm, the pore size of the porous structure is 5-45 nm, and the nano-magnesium oxide has a regular columnar structure.

[0008] Preferably, the particle size of the nano-magnesium oxide is 20-150 nm, and the pore size of the porous structure is 5-35 nm.

[0009] The second aspect of this invention provides a method for preparing nano-magnesium oxide materials, the method comprising the following steps: reacting an alkali source and a magnesium source, and calcining the solid phase in the resulting product;

[0010] The alkali source is selected from one or more of the following: ammonium bicarbonate, urea, ammonia, n-butylamine, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapropylammonium bromide, and tetrabutylammonium bromide.

[0011] The reaction conditions include a temperature of 80-140℃ and a time of 8-12h.

[0012] Preferably, the magnesium source is selected from one or more of magnesium nitrate, magnesium acetate, and magnesium chloride.

[0013] Preferably, the alkali source is used in the form of an aqueous solution, and the concentration of the aqueous solution is 0.1-10 mol / L.

[0014] Preferably, the magnesium source is used in the form of an aqueous solution, and the concentration of the magnesium source aqueous solution is 0.01-5 mol / L.

[0015] Preferably, the molar ratio of the alkali source to the magnesium source, calculated as magnesium element, is 1-30:1, more preferably 2-12:1.

[0016] Preferably, the method further includes: rapidly adding the alkali source solution dropwise into the magnesium source solution under stirring to obtain a mixed solution, and then carrying out a crystallization reaction on the mixed solution.

[0017] Preferably, the pH value of the mixed solution is 7-9.

[0018] Preferably, the calcination conditions include: a heating rate of 1-6℃ / min, a temperature of 600-900℃, and a time of 3-5h.

[0019] A third aspect of the present invention provides the application of the aforementioned nano-magnesium oxide material in the catalytic synthesis of propylene carbonate from CO2 and epoxides.

[0020] The nano-magnesium oxide material of this invention has a small particle size and a good porous structure, which can reduce the influence of internal diffusion on mass and heat transfer, and at the same time improve the CO2 adsorption capacity of the nano-magnesium oxide material, thereby improving the catalytic performance of the catalyst, optimizing the reaction kinetics of the cycloaddition reaction, and increasing the reaction rate; the nano-magnesium oxide catalyst does not deactivate after multiple uses and has good stability.

[0021] In the preparation method of the nano-magnesium oxide material described in this invention, the method is based on the principle of classical crystal nucleation. At high temperature, a weakly alkaline precipitant slowly releases hydroxide ions, thereby regulating the binding rate of hydroxide ions and magnesium ions, coordinating the nucleation rate and growth rate of crystals, and thus controlling the grain size of magnesium oxide. Furthermore, the method can also directionally design magnesium oxide with different grain sizes by changing the type of precipitant, thereby achieving precise control over its crystallinity. The raw materials used in this method can be directly purchased from the market, are inexpensive and readily available; the preparation method does not require the addition of halogenated hydrocarbons, trace elements, or reinforcing phases under harsh atmospheric conditions, significantly reducing the synthesis steps, and the preparation process produces no waste gas emissions, making it green and environmentally friendly. Attached Figure Description

[0022] Figure 1 The XRD pattern of the nano-magnesium oxide prepared in Example 1 is shown.

[0023] Figure 2 The attached diagram shows the nitrogen physical adsorption-desorption spectrum of the nano-magnesium oxide prepared in Example 1;

[0024] Figure 3 This is the pore size distribution map of the nano-magnesium oxide prepared in Example 1;

[0025] Figure 4 This is the SEM image of the nano-magnesium oxide prepared in Example 1. Detailed Implementation

[0026] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0027] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0028] like Figure 1 , Figure 2 and Figure 3 As shown, the nano-magnesium oxide material of the present invention has a porous structure, wherein the particle size of the nano-magnesium oxide is 20-200 nm, preferably 20-150 nm, more preferably 20-100 nm; the pore size of the porous structure is 5-45 nm, preferably 5-35 nm, more preferably 5-30 nm; as shown Figure 4 As shown, the nano-magnesium oxide of this invention has a regular columnar structure. In a preferred embodiment, when the particle size and pore size of the nano-magnesium oxide material are within the above-mentioned preferred range, the catalytic activity of the nano-magnesium oxide material can be significantly improved.

[0029] In this invention, the preparation method of the nano-magnesium oxide material includes the following steps: reacting an alkali source and a magnesium source, and calcining the solid phase in the resulting product;

[0030] The alkali source is selected from one or more of the following: ammonium bicarbonate, urea, ammonia, n-butylamine, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapropylammonium bromide, and tetrabutylammonium bromide.

[0031] The reaction conditions include a temperature of 80-140℃ and a time of 8-12h.

[0032] In a preferred embodiment, the alkali source can be one or more of urea, ammonia, or ammonium bicarbonate, more preferably urea and / or ammonia. In these preferred embodiments, using the aforementioned preferred alkali sources can regulate the grain size of the nano-magnesium oxide material, forming a good porous structure, thereby improving the catalytic activity of the nano-magnesium oxide material.

[0033] In the method described in this invention, the reaction temperature is higher than the crystal growth temperature and lower than the tolerance temperature for precursor decomposition.

[0034] In a preferred embodiment, the reaction conditions may include: a temperature of 100-140°C, more preferably 120-130°C, and a time of 9-12 hours, more preferably 9-11 hours. In these embodiments, limiting the reaction conditions to the above ranges, and especially the preferred ranges, enables the grain nucleation rate to exceed the crystal growth rate, thereby obtaining a nano-magnesium oxide material with smaller grains and a well-developed porous structure, and thus improving the catalytic activity of the nano-magnesium oxide material.

[0035] In the method described in this invention, the reaction can be carried out under oil bath conditions, specifically a static oil bath and / or a dynamic oil bath, preferably a dynamic oil bath.

[0036] In this invention, the magnesium source can be one or more of magnesium nitrate, magnesium acetate, and magnesium chloride, preferably magnesium acetate and / or magnesium chloride. In some embodiments, the magnesium chloride is used as magnesium chloride hexahydrate.

[0037] In a preferred embodiment, the alkali source is used in the form of an aqueous solution, and the concentration of the aqueous solution is 0.1-10 mol / L, preferably 0.1-5 mol / L.

[0038] In a preferred embodiment, the magnesium source is used in the form of an aqueous solution, and the concentration of the magnesium source aqueous solution is 0.01-5 mol / L, preferably 0.1-3 mol / L.

[0039] In a preferred embodiment, the method may further include: rapidly adding the alkali source solution dropwise into the magnesium source solution under stirring to obtain a mixed solution, and then subjecting the mixed solution to a crystallization reaction.

[0040] More preferably, the pH value of the mixed solution is 7-9.

[0041] More preferably, the stirring conditions include a temperature of 110-130°C and a time of 0.2-0.5 h. In these preferred embodiments, preparing the mixed solution using the aforementioned method ensures thorough mixing of the solution without generating amorphous magnesium oxide, thereby improving the catalytic activity of the nano-magnesium oxide material.

[0042] In the method described in this invention, the molar ratio of the alkali source to the magnesium source, based on elemental magnesium, can be 1-30:1, preferably 1-10:1, and more preferably 1-5:1. In some embodiments, when the molar ratio of the alkali source to the magnesium source, based on elemental magnesium, is within the aforementioned preferred range, the catalytic activity of the nano-magnesium oxide material prepared by the method can be further improved.

[0043] In a preferred embodiment, the method may further include: cooling the reaction product to separate the solid and liquid phases, washing and drying the resulting solid phase, and then calcining it.

[0044] More preferably, the cooling can be water cooling or natural cooling; the solid-liquid separation can be vacuum filtration or centrifugal separation, with centrifugal separation being the most preferred; the drying temperature should be lower than the decomposition temperature of the solid phase obtained from the reaction, with 70-90℃ being the most preferred.

[0045] In the method described in this invention, the calcination temperature is higher than the decomposition temperature of the precursor but lower than the tolerance temperature of the magnesium oxide crystal, the calcination time is lower than the tolerance calcination time of the magnesium oxide crystal, and the calcination heating rate is lower than the tolerance heating rate of the magnesium oxide crystal.

[0046] In a preferred embodiment, the calcination conditions may include: a temperature of 600-900℃, more preferably 700-800℃, a time of 3-5 h, more preferably 4-5 h, and a heating rate of 1-6℃ / min, more preferably 2-5℃ / min. In these preferred embodiments, when the calcination conditions are within these preferred ranges, the method can effectively control the decomposition rate of the solid product, and the calcined magnesium oxide nanomaterial has a small particle size and good pore structure, thereby improving the catalytic activity and stability of the magnesium oxide nanomaterial.

[0047] In some embodiments, the process of preparing the nano-magnesium oxide material may include: dissolving a magnesium source and an alkali source in water to obtain a magnesium source solution with a concentration of 0.01-5 mol / L and an alkali source solution with a concentration of 0.1-10 mol / L; then rapidly adding the magnesium source aqueous solution dropwise to the alkali source solution at 110-130°C with stirring to obtain a mixed solution, resulting in a mixed solution C with a pH of approximately 7-9, wherein the molar ratio of the alkali source to the magnesium source is 1-30:1; reacting solution C hydrothermally in an oil bath at 80-140°C for 8-12 hours to obtain a suspension D; centrifuging the suspension D three times after naturally cooling it to room temperature; washing the obtained solid phase with alternating ethanol and water; drying it in an oven at 70-90°C for 10-20 hours; and then calcining it at 600-900°C for 3-5 hours (heating rate of 1-6°C / min). When the preparation method is carried out according to this embodiment, the prepared nano-magnesium oxide material has superior catalytic activity.

[0048] The nano-magnesium oxide material described in this invention can be applied in the catalytic synthesis of propylene carbonate from CO2 and epoxides. In this invention, the nano-magnesium oxide material, as a catalyst, can reduce the influence of internal diffusion on mass and heat transfer. The surface of the nano-magnesium oxide material has abundant unsaturated hydroxyl groups, exhibiting excellent CO2 adsorption capacity, thereby improving the catalytic performance of the catalyst, optimizing the reaction kinetics of the cycloaddition reaction, and increasing the reaction rate. Furthermore, the nano-magnesium oxide material described in this invention does not deactivate after repeated use, demonstrating good stability.

[0049] The following examples further illustrate the nano-magnesium oxide material, its preparation method, and its applications according to the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0050] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0051] Example 1

[0052] (2) Dissolve 15g of magnesium chloride hexahydrate in 100mL of deionized water to obtain solution A (0.74mol / L); dissolve 15g of urea in 100mL of deionized water to obtain solution B (2.5mol / L); add solution B dropwise to solution A to obtain a mixed solution C with a pH of about 8, wherein the molar ratio of the alkali source to the magnesium source is 3.4:1; and perform a hydrothermal reaction of solution C in an oil bath at 120℃ for 10h to obtain suspension D.

[0053] (3) After the suspension D was naturally cooled to room temperature, it was centrifuged 3 times. The resulting solid phase was washed with ethanol and water alternately, and then dried in an oven at 80°C for 12 hours. Then it was calcined at 800°C for 4 hours (heating rate of 5°C / min) to prepare the nano magnesium oxide material, which is designated as Cat-1.

[0054] Example 2

[0055] (1) Dissolve 15g of magnesium acetate in 100mL of deionized water to obtain solution A (1.05mol / L); dissolve 15g of urea in 100mL of deionized water to obtain solution B (2.5mol / L); add solution B dropwise to solution A to obtain a mixed solution C with a pH of about 9, wherein the molar ratio of the alkali source to the magnesium source is 2.4:1; and perform a hydrothermal reaction of solution C in an oil bath at 120℃ for 10h to obtain suspension D.

[0056] (2) After cooling the suspension D to room temperature, centrifuge it three times. Wash the obtained solid phase with ethanol and water alternately, then dry it in an oven at 80°C for 12 hours. Then calcine it at 800°C for 4 hours (heating rate of 5°C / min) to prepare the nano magnesium oxide material, named Cat-2.

[0057] Example 3

[0058] (1) Dissolve 30g of magnesium chloride hexahydrate in 100mL of deionized water to obtain solution A (1.48mol / L); dissolve 30g of ammonia in 100mL of deionized water to obtain solution B, wherein the concentration of ammonia in solution B is 2.14mol / L; add solution B dropwise to solution A to obtain a mixed solution C with a pH of about 8, wherein the molar ratio of the alkali source to the magnesium source is 1.4:1; and perform a hydrothermal reaction of solution C in an oil bath at 120℃ for 10h to obtain suspension D.

[0059] (2) The suspension D was cooled to room temperature and centrifuged 3 times. The resulting solid phase was washed with ethanol and water alternately, dried in an oven at 80°C for 12 hours, and then calcined at 800°C for 4 hours (heating rate of 5°C / min) to prepare the nano magnesium oxide material, named Cat-3.

[0060] Example 4

[0061] (1) Dissolve 15g of magnesium chloride hexahydrate in 100mL of deionized water to obtain solution A (0.74mol / L); dissolve 15g of urea in 100mL of deionized water to obtain solution B (2.5mol / L); add solution B dropwise to solution A to obtain a mixed solution C with a pH of about 7, wherein the molar ratio of the alkali source to the magnesium source is 3.4:1; and perform a hydrothermal reaction of solution C in an oil bath at 120℃ for 10h to obtain suspension D.

[0062] (2) After cooling the suspension D to room temperature, centrifuge it three times. Wash the obtained solid phase with ethanol and water alternately, then dry it in an oven at 80°C for 12 hours. Then calcine it at 700°C for 4 hours (heating rate of 2°C / min) to prepare the nano magnesium oxide material, which is designated as Cat-4.

[0063] Example 5

[0064] (1) Dissolve 15g of magnesium chloride hexahydrate in 100mL of deionized water to obtain solution A (0.74mol / L); dissolve 15g of ammonia in 100mL of deionized water to obtain solution B, wherein the concentration of ammonia in solution B is 2.14mol / L; add solution B dropwise to solution A to obtain a mixed solution C with a pH of about 7, wherein the molar ratio of the alkali source to the magnesium source is 2.9:1; and perform a hydrothermal reaction of solution C in an oil bath at 120℃ for 12h to obtain suspension D.

[0065] (2) After cooling the suspension D to room temperature, centrifuge it three times. Wash the obtained solid phase with ethanol and water alternately, then dry it in an oven at 80°C for 12 hours. Then calcine it at 800°C for 4 hours (heating rate of 5°C / min) to prepare the nano magnesium oxide material, which is named Cat-5.

[0066] Example 6

[0067] (1) Dissolve 15g of magnesium chloride hexahydrate in 100mL of deionized water to obtain solution A (0.74mol / L); dissolve 132g of urea in 100mL of deionized water to obtain solution B (22mol / L); add solution B dropwise to solution A to obtain a mixed solution C with a pH of about 9, wherein the molar ratio of the alkali source to the magnesium source is 30:1; and perform a hydrothermal reaction of solution C in an oil bath at 120℃ for 10h to obtain suspension D.

[0068] (2) After cooling the suspension D to room temperature, centrifuge it three times. Wash the obtained solid phase with ethanol and water alternately, then dry it in an oven at 80°C for 12 hours. Then calcine it at 700°C for 5 hours (heating rate of 5°C / min) to prepare the nano magnesium oxide material, named Cat-6.

[0069] Example 7

[0070] (1) Dissolve 15g of magnesium acetate in 100mL of deionized water to obtain solution A (1.05mol / L); dissolve 15g of urea in 100mL of deionized water to obtain solution B; add solution B (2.5mol / L) dropwise to solution A to obtain a mixed solution C with a pH of about 8, wherein the molar ratio of the alkali source to the magnesium source is 2.4:1; and perform a hydrothermal reaction of solution C in an oil bath at 130℃ for 10h to obtain suspension D.

[0071] (2) After cooling the suspension D to room temperature, centrifuge it three times. Wash the obtained solid phase with ethanol and water alternately, then dry it in an oven at 80°C for 12 hours. Then calcine it at 600°C for 5 hours (heating rate of 6°C / min) to prepare the nano magnesium oxide material, named Cat-7.

[0072] Example 8

[0073] (1) Dissolve 25g of magnesium chloride hexahydrate in 100mL of deionized water to obtain solution A (1.23mol / L); dissolve 15g of urea in 100mL of deionized water to obtain solution B (2.5mol / L); add solution B dropwise to solution A to obtain a mixed solution C with a pH of about 8, wherein the molar ratio of the alkali source to the magnesium source is 2:1; and at 140℃, perform a hydrothermal reaction of solution C in an oil bath for 8 hours to obtain suspension D.

[0074] (2) After cooling the suspension D to room temperature, centrifuge it three times. Wash the obtained solid phase with ethanol and water alternately, dry it in an oven at 80°C for 12 hours, and then calcine it at 900°C for 3 hours (heating rate of 1°C / min) to prepare the nano magnesium oxide material, named Cat-8.

[0075] Example 9

[0076] This embodiment prepares nano-magnesium oxide according to the method of Example 1. The difference is that in step (1), the temperature of the hydrothermal reaction is 80°C, and the nano-magnesium oxide material is prepared, which is designated as Cat-9.

[0077] Example 10

[0078] (1) Dissolve 15g of magnesium chloride hexahydrate in 100mL of deionized water to obtain solution A (0.74mol / L); dissolve 150g of urea in 100mL of deionized water to obtain solution B (25mol / L); add solution B dropwise to solution A to obtain a mixed solution C with a pH of about 9, wherein the molar ratio of the alkali source to the magnesium source is 34:1; and perform a hydrothermal reaction of solution C in an oil bath at 120℃ for 10h to obtain suspension D.

[0079] (2) After cooling the suspension D to room temperature, centrifuge it three times. Wash the obtained solid phase with ethanol and water alternately, then dry it in an oven at 80°C for 12 hours. Then calcine it at 1000°C for 8 hours (heating rate of 5°C / min). The nano magnesium oxide material could not be obtained and was named Cat-10.

[0080] Example 11

[0081] This embodiment is implemented according to the method described in Example 1, except that in step (1), 15g of magnesium chloride hexahydrate and 15g of urea are dissolved in 200mL of deionized water, and the resulting mixed solution is crystallized in an oil bath at 120℃ for 10h to obtain suspension D. The nano-magnesium oxide material, designated Cat-11, is thus prepared.

[0082] Comparative Example 1

[0083] This comparative example was carried out according to the method described in Example 1, except that in step (1), the crystallization temperature was 180°C, and the specific steps are as follows:

[0084] (1) Dissolve 15g of magnesium chloride hexahydrate in 100mL of deionized water to obtain solution A (0.74mol / L); dissolve 15g of urea in 100mL of deionized water to obtain solution B (2.5mol / L); add solution B dropwise to solution A to obtain a mixed solution C with a pH of about 8, wherein the molar ratio of the alkali source to the magnesium source is 3.4:1; and perform a hydrothermal reaction of solution C in an oil bath at 180℃ for 10h to obtain suspension D.

[0085] (2) After cooling the suspension D to room temperature, centrifuge it three times. Wash the obtained solid phase with ethanol and water alternately, then dry it in an oven at 80°C for 12 hours. Then calcine it at 800°C for 12 hours (heating rate of 5°C / min). The nano magnesium oxide material could not be obtained and was designated as D-Cat-1.

[0086] Comparative Example 2

[0087] This comparative example was carried out according to the method described in Example 1, except that in step (1), the alkaline source reagent was sodium hydroxide. The specific steps are as follows:

[0088] (1) Dissolve 15g of magnesium chloride hexahydrate in 100mL of deionized water to obtain solution A (0.74mol / L); dissolve 30g of sodium hydroxide in 100mL of deionized water to obtain solution B (7.5mol / L); add solution B dropwise to solution A to obtain a mixed solution C with a pH of about 13, wherein the molar ratio of the alkali source to the magnesium source is 10:1; and perform a hydrothermal reaction of solution C in an oil bath at 120℃ for 10h to obtain suspension D.

[0089] (2) After cooling the suspension D to room temperature, centrifuge it three times. Wash the obtained solid phase with ethanol and water alternately, then dry it in an oven at 80°C for 12 hours. Then calcine it at 800°C for 12 hours (heating rate is 5°C / min). The nano magnesium oxide material could not be obtained and was designated as D-Cat-2.

[0090] Comparative Example 3

[0091] This comparative example was carried out according to the method described in Example 1, except that in step (1), the crystallization temperature was 40°C. The specific steps are as follows:

[0092] (1) Dissolve 15g of magnesium chloride hexahydrate in 100mL of deionized water to obtain solution A (0.74mol / L); dissolve 15g of urea in 100mL of deionized water to obtain solution B (2.5mol / L); add solution B dropwise to solution A to obtain a mixed solution C with a pH of about 8, wherein the molar ratio of the alkali source to the magnesium source is 3.4:1; and in an oil bath at 40℃ for 12h, obtain suspension D.

[0093] (2) After cooling the suspension D to room temperature, centrifuge it three times. Wash the obtained solid phase with ethanol and water alternately, then dry it in an oven at 80°C for 12 hours. Then calcine it at 800°C for 12 hours (heating rate of 5°C / min). The nano magnesium oxide material could not be obtained and was designated as D-Cat-3.

[0094] Test Example 1

[0095] The nano-magnesium oxide materials prepared in Examples 1-11 and Comparative Examples 1-3 were characterized by SEM, and the SEM characterization was carried out in accordance with the JY / T 0584-2020 standard.

[0096] The nano-magnesium oxide materials prepared in Examples 1-11 and Comparative Examples 1-3 were subjected to nitrogen adsorption-desorption. The nitrogen adsorption characterization was carried out in accordance with GB / T 19587-2017 standard.

[0097] The results are shown in Table 1.

[0098] Table 1

[0099] sample Nano magnesium oxide particle size / nm Nano-magnesium oxide pore size / nm Example 1 20 5 Example 2 35 10 Example 3 40 10 Example 4 49 15 Example 5 34 8 Example 6 72 25 Example 7 56 12 Example 8 45 25 Example 9 26 6 Example 10 51 2 Example 11 176 45 Comparative Example 1 214 50 Comparative Example 2 337 52 Comparative Example 3 279 55

[0100] Test Example 2

[0101] The materials prepared in Examples 1-11 and Comparative Examples 1-3 were used to catalyze the cycloaddition reaction of propylene oxide, wherein the catalytic reaction included the following steps:

[0102] 0.23 g of the nano-magnesium oxide and 4.14 g of propylene oxide were placed in a 50 mL batch reactor and reacted under magnetic stirring. After reacting at 140 °C for 10 h, the solid-liquid mixture was separated by centrifugation, and the resulting liquid was then analyzed by liquid chromatography.

[0103] The results are shown in Table 2.

[0104] Table 2

[0105]

[0106] As can be seen from the results in Tables 1 and 2, by adopting the technical solution of the present invention, the nano-magnesium oxide materials Cat-1 to Cat-11 described in Examples 1-9 all have a grain size of 20-200 nm and a pore size of 5-45 nm. The nano-magnesium oxide described in the present invention exhibits good catalytic activity for the carbon dioxide cycloaddition reaction under solvent-free and additive-free conditions. Moreover, the nano-magnesium oxide materials described in the present invention exhibit higher catalytic activity as the grain size and pore size decrease, and the nano-magnesium oxide materials prepared in Examples 1-9 preferably have even better catalytic activity. In addition, the catalytic activity of the nano-magnesium oxide materials described in the present invention remains basically unchanged after three cycles of use, exhibiting good stability. In contrast, in Comparative Examples 1-3, since the prepared nano-magnesium oxide materials D-Cat-1 to D-Cat-3 have a particle size greater than 200 nm and a pore size greater than 50 nm, their catalytic activity, selectivity, and stability are far inferior to those of the nano-magnesium oxide materials Cat-1 to Cat-11 prepared in Examples 1-11.

[0107] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A nano-magnesium oxide material, characterized in that, The nano-magnesium oxide material has a porous structure, wherein the particle size of the nano-magnesium oxide is 20-200 nm; the pore size of the porous structure is 5-45 nm, and the nano-magnesium oxide has a regular columnar structure.

2. The nano-magnesium oxide material according to claim 1, characterized in that, The nano-magnesium oxide has a particle size of 20-150 nm, and the porous structure has a pore size of 5-35 nm.

3. A method for preparing nano-magnesium oxide materials, characterized in that, The method includes the following steps: reacting an alkali source and a magnesium source, and calcining the solid phase in the resulting product; The alkaline source is selected from one or more of ammonium bicarbonate, urea, ammonia, n-butylamine, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapropylammonium bromide, and tetrabutylammonium bromide. The reaction conditions include a temperature of 80-140℃ and a time of 8-12h.

4. The method according to claim 3, characterized in that, The magnesium source is selected from one or more of magnesium nitrate, magnesium acetate, and magnesium chloride.

5. The method according to claim 3 or 4, characterized in that, The alkali source is used in the form of an aqueous solution, and the concentration of the aqueous solution is 0.1-10 mol / L.

6. The method according to claim 3 or 4, characterized in that, The magnesium source is used in the form of an aqueous solution, and the concentration of the magnesium source aqueous solution is 0.01-5 mol / L.

7. The method according to any one of claims 3-6, characterized in that, The molar ratio of the alkali source to the magnesium source, calculated in terms of magnesium element, is 1-30:1, preferably 2-12:

1.

8. The method according to any one of claims 3-7, characterized in that, The method further includes: rapidly adding the alkaline source solution dropwise into the magnesium source solution under stirring to obtain a mixed solution, and then carrying out a crystallization reaction on the mixed solution; Preferably, the pH value of the mixed solution is 7-9.

9. The method according to any one of claims 3-8, characterized in that, The calcination conditions include: a heating rate of 1-6℃ / min, a temperature of 600-900℃, and a time of 3-5h.

10. The application of the nano-magnesium oxide material according to claim 1 or 2 in the catalytic synthesis of propylene carbonate from CO2 and epoxides.

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