Oxygen-enriched defect MgAl-MMO as well as preparation method and application thereof

Abstract

The invention relates to the technical field of plastic degradable materials, in particular to oxygen-enriched defect MgA < 1->-MMO and a preparation method and application thereof.The oxygen-enriched defect MgA < 1->-MMO is MgA < 1-x > formed by uniformly dispersing an active component MgO on Al < 2 > O < 3 >, and x is the roasting temperature; the preparation method comprises the following steps: S1, preparing an MgAl-LDHs precursor by adopting a coprecipitation method; s2, preparing MgAl-MMO rich in oxygen deficiency by adopting a topological transformation method; specifically, a synthesized MgA l-LDHs precursor is placed in a porcelain boat, roasted at the temperature of 400-700 DEG C and then cooled to the room temperature, and MgAl-MMO rich in oxygen defects is obtained. The MgAl-500 constructed by the invention shows good catalytic activity in ethylene glycol hydrolysis of PET, and can completely degrade PET under the conditions of 200 DEG C and 40 min, and the yield of the monomer BHET is 90%.

Description

Technical Field

[0001] The invention relates to the technical field of plastic degradation materials, and in particular to an oxygen-rich defect MgAl-MMO and a preparation method and application thereof. Background Art

[0002] Plastic is a kind of polymer material composed of long-chain organic molecules. It has the advantages of strong practicality, low cost and stable chemical properties, so it is widely used in daily life. By 2050, it is estimated that the amount of plastic waste in nature will reach 1.2 billion tons, of which more than 80% will be directly discarded or landfilled. Due to the chemical inertness of plastic, its natural degradation may take hundreds of years. The large accumulation of plastic waste in nature will cause serious harm to the environment and human life. For example, the production of plastic products not only requires a large amount of resource consumption but also produces a large amount of carbon dioxide to form a greenhouse effect, while discarded plastic waste in urban streets, tourist attractions and even the ocean will cause serious visual pollution. In addition, plastic waste in the soil not only hinders the sustainable use of land, but also destroys the nutrients and water absorbed by crops. More importantly, discarded plastics in the ocean threaten the survival of aquatic animals and then invade the human food chain. Therefore, it is urgent to take a series of measures to recycle or degrade plastics and realize the recycling of discarded plastics.

[0003] PET material, namely polyethylene terephthalate, is one of the most important varieties of thermoplastic polyester. Because it can provide excellent oxygen, carbon dioxide and moisture barriers, it is widely used in the packaging industry, especially disposable packaging (i.e. plastic packaging, water bottles, soft drinks and food containers). PET glycolysis refers to the process of using ethylene glycol as a solvent to decompose PET (polyethylene terephthalate) into monomer diethylene terephthalate (BHET) through a chemical reaction. This method has mild reaction conditions, high activity and high selectivity, and the solvent ethylene glycol used has the advantages of low vapor pressure and low toxicity. It is the most widely used chemical recycling method for waste PET. There are two reaction mechanisms of PET glycolysis. The first is to activate ethylene glycol, the catalyst forms hydrogen bonds with ethylene glycol, or the catalyst deprotonates ethylene glycol to form active nucleophilic species EG. – , which as a nucleophile can more easily attack the carbonyl carbon in PET; the second is to activate the ester group, the catalyst activates the carbonyl oxygen in PET, thereby increasing the electropositivity of the carbonyl carbon in PET.

[0004] Heterogeneous metal oxides and supported metal catalysts prepared by traditional co-precipitation and impregnation methods have problems such as active species being embedded, uneven dispersion of active sites, and unstable active site structure, which will lead to reduced activity and stability of the catalyst during the reaction. The main layer of hydrotalcite has highly ordered and uniformly arranged metal elements, and its composition and proportion are adjustable. It has structural characteristics with topological transition characteristics, and its topological transition properties can be used to prepare heterogeneous metal oxides and supported metal catalysts. The highly active sites exposed by heterogeneous metal oxides can improve catalytic activity. Therefore, constructing heterogeneous metal oxides with exposed highly active sites through the LDHs topological transition strategy is an effective means to improve catalyst activity. Summary of the invention

[0005] In order to solve the above problems, the present invention provides an oxygen-rich defect MgAl-MMO and a preparation method and application thereof.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] The invention discloses an oxygen-defect MgAl-MMO, wherein the oxygen-defect MgAl-MMO is MgAl-x with uniformly dispersed active sites. Specifically, the active component MgO is uniformly dispersed on Al2O3, and x is the calcination temperature. When preparing the oxygen-defect MgAl-MMO, MgAl-LDHs is used as a precursor and is prepared by a topological transformation method using its unique topological transformation properties.

[0008] The present invention also provides a method for preparing the above-mentioned oxygen-rich defect MgAl-MMO, comprising the following steps:

[0009] S1. Prepare MgAl-LDHs precursor by co-precipitation method; specifically:

[0010] Take 15-20 mL of 1M Mg(NO3)2·6H2O and 5-10 mL of 1M Al(NO3)3·9H2O, mix them, and obtain solution A;

[0011] Add 10-20 mL of 1M NaOH and 10-20 mL of 1M Na2CO3 mixed solution into a 100 mL three-necked flask to obtain solution B;

[0012] At 80°C, solution A was added dropwise to solution B, the dripping speed of the peristaltic pump was controlled to be 14 rpm, and a magnetic stirrer was used to stir during the dropping process;

[0013] After the dropwise addition was completed, the obtained precipitate was washed with deionized water until it was neutral, and finally washed once with anhydrous ethanol, and the product was dried in an oven at 60° C. for later use.

[0014] S2, preparing oxygen-rich defect MgAl-MMO by topological transformation method;

[0015] The synthesized MgAl-LDHs was placed in a porcelain boat, heated to 400°C, 500°C, 600°C, and 700°C at a heating rate of 2°C / min, and then calcined for 3 hours, and then cooled to room temperature to obtain MgAl-x rich in oxygen defects, where x represents different calcination temperatures, x=400, 500, 600, and 700. In the present invention, the number of oxygen defects can be controlled by changing the calcination temperature, and the number of oxygen defects first increases and then decreases as the calcination temperature increases.

[0016] The oxygen-deficient MgAl-MMO of the present invention can be applied to glycolysis of PET. The oxygen defects in the oxygen-deficient MgAl-MMO can activate O2 in the air to generate active oxygen species O - , reactive oxygen species O - Further activation of EG to EG - , E.G. - As a nucleophile, it is easier to attack the carbonyl carbon in PET, breaking the CO bond in the carbonyl group, thereby depolymerizing PET into monomer BHET.

[0017] In the present invention, MgAl-500 calcined at 500° C. has the most oxygen defects. When used, the volume ratio of PET / EG (ethylene glycol) is 1:10, the amount of MgAl-500 is 15 mg, the degradation temperature is 200° C., and the degradation time is 40 min.

[0018] The present invention has the following beneficial effects:

[0019] In the above scheme, the number of oxygen defects in MgAl-x can be controlled by changing the calcination temperature, and the oxygen defects can activate O2 in the air to produce active oxygen species O - , reactive oxygen species O - Further activation of EG to EG - ,EG - As a nucleophile, it is easier to attack the carbonyl carbon in PET, breaking the CO bond in the carbonyl group, thereby depolymerizing PET into monomer BHET.

[0020] In the above scheme, the constructed MgAl-500 exhibits good catalytic activity in glycolysis of PET. The experimental results show that MgAl-500 can completely degrade PET under the conditions of 200°C and 40min, and the yield of its monomer BHET is 90%. The material is applied to the degradation of commercial waste PET, and has a good degradation effect on commercial waste PET of different sizes. The experiment of expanding the size of commercial waste PET <2nm by 7 times has also achieved a BHET yield of 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the synthesis of MgA lx;

[0022] Figure 2 For the structural characterization of MgA lx;

[0023] Figure 3 Characterization of oxygen defects in MgAlx;

[0024] Figure 4 The catalytic performance test results of MgA lx. DETAILED DESCRIPTION

[0025] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0026] 1. Preparation of MgAl-LDHs Precursor

[0027] MgAl-LDHs precursor was prepared by coprecipitation. Specifically, 15 mL of 1M Mg(NO3)2·6H2O and 5 mL of 1M Al(NO3)3·9H2O were taken, and the two salt solutions were mixed to obtain solution A. A mixed solution of 20 mL of 1M NaOH and 20 mL of 1M Na2CO3 was added to a 100 mL three-necked flask to obtain solution B. Solution A was added dropwise to solution B at 80°C using a peristaltic pump, and the dripping speed of the peristaltic pump was controlled to 14 rpm. A magnetic stirrer was used to stir during the dripping process. After the dripping was completed, the obtained precipitate was washed with deionized water until it was neutral, and finally washed once with anhydrous ethanol. The product was dried in an oven at 60°C for later use.

[0028] 2. Preparation of oxygen-deficient MgAl-MMO

[0029] Oxygen-defective MgAl-MMO was prepared by a topological transformation method. Specifically, the synthesized MgAl-LDHs were placed in a porcelain boat, heated from room temperature to 400°C, 500°C, 600°C, and 700°C at a heating rate of 2°C / min, and then calcined for 3 hours, and then cooled to room temperature to obtain MgAl-MMO rich in oxygen defects. The obtained samples were labeled as: MgAlx (x represents different calcination temperatures, x = 400, 500, 600, 700).

[0030] pass Figure 2(a) The TG-DTA curve of MgAl-LDHs shows that MgAl-LDHs loses hydroxyl groups and water molecules on the layer before 200°C, loses interlayer anions and collapses the hydrotalcite layer at 200°C to 400°C. Figure 2 (b) XRD shows that when the calcination temperature is 400 °C, MgAl-LDH is completely transformed into mixed oxides, which is consistent with the conclusion of TG-DTA data.

[0031] 27 Al solid NMR and EPR prove the existence of oxygen vacancies in MgAl-x, and O 1s XPS proves that MgAl-500 has the most oxygen vacancies. The binding energy of O 1s first increases and then decreases with the increase of calcination temperature, while the binding energy of Mg 2p and Al 2p orbitals first decreases and then increases, indicating that with the increase of calcination temperature, electrons are transferred from Mg and Al atoms to O atoms.

[0032] Catalytic performance display

[0033] The oxygen-defective MgAl-x was applied to the degradation of waste PET. The specific experimental conditions were: PET: 0.5g, EG: 5mL, Cat (MgAl-400, MgAl-500, MgAl-600, MgAl-700): 15mg, reaction temperature: 200℃, reaction time: 40min. The results are as follows Figure 4 As shown in the figure, MgAl-500 has the best catalytic performance, and the yield of BHET can reach 90%. Then the reaction conditions of MgAl-500 glycolysis of PET were optimized. Figure 4 b It can be concluded that the optimal calcination temperature is 500℃. Figure 4 cd can be concluded that the optimal feed ratio is PET / EG=1:10 (g / mL), Figure 4 ef can be concluded that the optimal reaction conditions are 200℃, 40min. Based on this, the optimal reaction conditions can be obtained as follows: PET / EG=1:10, 15mg Cat(MgAl-500), 200℃, 40min. Finally, MgAl-500 was applied to the degradation of waste PET of different sizes. It was found that with the decrease of the size of waste PET flakes, the yield of BHET gradually increased. The experiment of PET flakes with a size of less than 2nm was expanded by 7 times, and its BHET yield also reached 80%.

[0034] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. An oxygen-rich defect MgAl-MMO, characterized in that: The oxygen-rich defect MgAl-MMO is MgAl-x in which the active component MgO is uniformly dispersed on Al2O3, and x is the calcination temperature. During the preparation, MgAl-LDHs is used as a precursor and a topological transformation method is adopted.

2. The method for preparing an oxygen-rich defective MgAl-MMO according to claim 1, characterized in that: The steps include: S1. Preparing MgAl-LDHs precursor by co-precipitation method; S2, preparing oxygen-rich defect MgAl-MMO by topological transformation method; The synthesized MgAl-LDHs precursor is placed in a porcelain boat, calcined at 400-700°C, and then cooled to room temperature to obtain MgAl-MMO rich in oxygen defects.

3. The method for preparing an oxygen-rich defective MgAl-MMO according to claim 2, characterized in that: The step S1 specifically includes the following steps: Take 15-20 mL of 1M Mg(NO3)2·6H2O and 5-10 mL of 1M Al(NO3)3·9H2O, mix them, and obtain solution A; Add 10-20 mL of 1M NaOH and 10-20 mL of 1M Na2CO3 mixed solution into a 100 mL three-necked flask to obtain solution B; At 80°C, solution A was added dropwise to solution B, the dripping speed of the peristaltic pump was controlled to be 14 rpm, and a magnetic stirrer was used to stir during the dropping process; After the dropwise addition was completed, the obtained precipitate was washed with deionized water until it was neutral, and finally washed once with anhydrous ethanol, and the product was dried in an oven at 60° C. for later use.

4. The method for preparing an oxygen-rich defective MgAl-MMO according to claim 2, characterized in that: In the step S2, the synthesized MgAl-LDHs is placed in a porcelain boat, heated to 400°C, 500°C, 600°C, and 700°C at a heating rate of 2°C / min, and then calcined for 3 hours, and then cooled to room temperature to obtain MgAl-x rich in oxygen defects, where x represents different calcination temperatures, x=400, 500, 600, and 700.

5. Use of the oxygen-defective MgAl-MMO as claimed in claim 1 in glycolysis of PET.

6. The use according to claim 5, characterized in that: The oxygen-defective MgAl-MMO is MgAl-500.

7. The use according to claim 6, characterized in that: When used, the volume ratio of PET / EG is 1:10, the amount of MgAl-500 is 15 mg, the degradation temperature is 200°C, and the degradation time is 40 min.

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