A Zn and Fe-containing crystal, its preparation method, and its application in the catalytic synthesis of dimethyl carbonate.

Abstract

This application discloses a Zn and Fe-containing crystal, its preparation method, and its applications. The chemical formula of the Zn and Fe-containing crystal is Zn3(cpb)2[Fe(CN)6]2·nH2O; wherein the ligand cpb is 1-(3-carboxyphenyl)-4,4'-bipyridine vizimonium salt. The Zn and Fe-containing crystal provided in this application exhibits thermochromic properties, and the crystalline catalyst stimulated by heating can effectively catalyze the direct synthesis of dimethyl carbonate from CO2 and methanol, showing a significant performance improvement compared to crystals without heating stimulation.

Description

Technical Field

[0001] This invention relates to a crystal containing Zn and Fe, its preparation method and application, and belongs to the field of catalysts. Background Technology

[0002] Dimethyl carbonate (DMC) is a green chemical widely used in the production of polycarbonate and as a solvent for lithium batteries and high-end coatings. Its potential applications include gasoline and diesel additives. The main production technologies include the phosgene process, transesterification, CO esterification, and methanol oxidative carbonylation. The phosgene process has been phased out due to the highly toxic phosgene as a raw material. The transesterification process has high production costs due to the generation of equivalent byproducts (propylene glycol or ethylene glycol). The CO esterification and methanol oxidative carbonylation methods are currently the development directions. From a carbon emission reduction perspective, the direct synthesis of DMC using CO2 and methanol offers the best atom economy and application prospects.

[0003] For the direct synthesis of dimethyl carbonate from CO2 and methanol, various types of catalysts have been developed, including CeO2, ZrO2, heteropoly acids, and metal-organic frameworks (MOFs). However, their catalytic performance is still not high enough, and further development of novel catalysts with well-defined structures and excellent performance is needed. Summary of the Invention

[0004] According to the first aspect of this application, a crystal containing Zn and Fe is provided.

[0005] A crystal containing Zn and Fe, said crystal having the following chemical formula:

[0006] Zn3(cpb)2[Fe(CN)6]2·nH2O;

[0007] The ligand cpb is 1-(3-carboxyphenyl)-4,4'-bipyridine vizigonium salt.

[0008] Optionally, the structure of the crystal is as follows:

[0009] Cyanide ions and viologen ligands bridge Zn and Fe metal ions to form a three-dimensional porous structure with one-dimensional pores filled with guest molecules.

[0010] Specifically, the cpb ligand has two free ends, one provided by the N in the terminal pyridine ring and the other provided by the carboxylate group. These two free ends are connected to two Zn ions respectively, thereby forming a closed two-dimensional organic layer structure.

[0011] One type of Zn ion has a four-coordinate trigonal pyramidal structure, with its coordinating atoms being a carboxyl oxygen atom from one viologen ligand and three cyano nitrogen atoms. The other type of Zn ion has a six-coordinate octahedral structure, with its coordinating atoms being nitrogen atoms from two different viologen ligands and four cyano nitrogen atoms.

[0012] The organic layers extend into a three-dimensional framework via ferricyanide bridging.

[0013] Optionally, the crystal belongs to the monoclinic crystal system, space group P21 / c.

[0014] Optionally, the crystallographic data of the crystal are:

[0015] α=90°, β=92.2~93.5°, γ=90°; Z = 2.

[0016] Specifically, the crystallographic data of the crystal are as follows:

[0017] α=90(3)°, β=92.789(4)-93.159(4)°, γ=90(3)°; Z = 2.

[0018] According to a second aspect of this application, a method for preparing the crystal described above is provided.

[0019] A method for preparing the crystal described above includes at least the following steps:

[0020] a) Obtain the ligand cpb;

[0021] b) The raw material containing ligand cpb, Zn source, K3[Fe(CN)6] and water is placed in a sealed container and crystallized to obtain the crystal.

[0022] Optionally, in step b), the Zn source is selected from at least one of zinc nitrate and zinc chloride.

[0023] Optionally, the molar ratio of the ligand cpb, Zn source, and K3[Fe(CN)6] is 1-4:1-2:1-2.

[0024] Optionally, the crystallization conditions are: crystallization at room temperature for 5 to 10 days.

[0025] Specifically, the crystallization conditions are: crystallization at room temperature for one week.

[0026] In step a), obtaining the ligand cpb is known, as is modified from known methods (see Helvetica Chimica Acta, 2005, 88, 3200).

[0027] Specifically, in step (a), the preparation method of ligand CPB can be any suitable method in the prior art, and this application does not impose strict limitations. First, dinitrochlorobenzene and 4,4'-bipyridine are added to a 100 mL round-bottom flask in a 1:1 ratio, along with approximately 20–40 mL of acetone. The mixture is refluxed at 60 °C for one day. After filtration, the resulting solid powder is washed three times with diethyl ether to obtain an intermediate. Then, the obtained intermediate and m-aminophenyl acid are added to a 100 mL round-bottom flask in a 1:1.5 ratio, along with approximately 20–40 mL of ethanol. The mixture is refluxed at 90 °C for one day. After cooling, an appropriate amount of triethylamine is added and stirred until a pale yellow precipitate forms. After filtration, the resulting solid powder is washed three times with diethyl ether to obtain ligand CPB.

[0028] Optionally, in step b), the crystal is obtained by a diffusion method using a large beaker nested within a smaller beaker.

[0029] Specifically, in step b), the ligand cpb, the Zn source, and K3Fe(CN)6 are dissolved in a small amount of water. Two beakers of different volumes are filled with water, with the smaller beaker nested inside the larger beaker. Using a syringe, the aqueous solutions of the cpb ligand and the Zn source are injected into the smaller beaker, while the aqueous solution of K3Fe(CN)6 is injected into the larger beaker. The water level in the larger beaker is approximately 1 cm higher than that in the smaller beaker. The beakers are then covered with plastic wrap and left to stand for one week to allow crystals to grow.

[0030] According to a third aspect of this application, a crystalline catalyst is provided.

[0031] A crystalline catalyst, wherein the crystalline catalyst is obtained by heating and stimulating a crystal containing Zn and Fe;

[0032] The Zn and Fe-containing crystals are selected from the crystals described above.

[0033] Optionally, the heating temperature is 140–180°C.

[0034] The Zn and Fe-containing crystals, when heated, yield a thermochromic crystalline catalyst. It can be in bulk form or as a crystalline powder.

[0035] According to a fourth aspect of this application, an application of the above-described crystalline catalyst is provided.

[0036] The above-described crystalline catalyst is used in the direct synthesis of dimethyl carbonate from CO2 and methanol, wherein the reaction conditions are as follows:

[0037] The reaction pressure is 3–7 MPa, the reaction temperature is 120–180 °C, and the reaction time is 1–5 hours.

[0038] Under reaction pressures of 3–7 MPa and reaction temperatures of 120–180 °C, CO2 and methanol come into contact with the crystalline catalyst and are efficiently converted into dimethyl carbonate.

[0039] The beneficial effects that this application can produce include:

[0040] 1) The crystalline catalyst provided in this application efficiently catalyzes the reaction of CO2 and methanol to produce dimethyl carbonate under conditions of 5 MPa and 180 °C, with a dimethyl carbonate yield of 16.8 mmol / g. cat. .

[0041] 2) The method for preparing Zn and Fe crystals provided in this application has a controlled synthesis process and can obtain high-quality single crystals. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the three-dimensional structure of crystal PMOF-2A;

[0043] Figure 2 The structural diagrams are shown for crystalline PMOF-2A and crystalline catalyst PMOF-2B obtained after heating stimulation.

[0044] Figure 3 Powder X-ray diffraction patterns of PMOF-2A and PMOF-2B. Detailed Implementation

[0045] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0046] Example 1: Synthesis of ligand cpb

[0047] Synthesis process: First, dinitrochlorobenzene and 4,4'-bipyridine were added to a 100 mL round-bottom flask in a 1:1 ratio, along with approximately 30 mL of acetone. The mixture was refluxed at 60 °C for one day. After filtration, the resulting solid powder was washed three times with diethyl ether to obtain an intermediate. Then, the obtained intermediate and m-aminophenyl acid were added to a 100 mL round-bottom flask in a 1:1.5 ratio, along with approximately 30 mL of ethanol. The mixture was refluxed at 90 °C for one day. After cooling, an appropriate amount of triethylamine was added and stirred until a pale yellow precipitate formed. After filtration, the resulting solid powder was washed three times with diethyl ether to obtain the ligand cpb.

[0048] Example 2 Preparation of crystalline catalyst

[0049] Zinc nitrate hexahydrate (297 mg), cpb ligand (456 mg), and potassium ferricyanide (329 mg) were dissolved in water respectively. Then, water was added to two beakers of different volumes, with the smaller beaker nested inside the larger beaker. The aqueous solutions of cpb ligand and Zn source were injected into the smaller beaker using a syringe, while the aqueous solution of K3Fe(CN)6 was injected into the larger beaker. The water level in the larger beaker was approximately 1 cm higher than that in the smaller beaker. The beakers were then covered with plastic wrap and allowed to stand for one week to crystallize, yielding crystals with the chemical formula Zn3(cpb)2[Fe(CN)6]2·nH2O, denoted as PMOF-2A.

[0050] PMOF-2B was obtained by heating PMOF-2A at 160℃.

[0051] Structural characterization of the sample in Example 3

[0052] X-ray powder diffraction (XRD) phase analysis of the ground PMOF-2A and PMOF-2B crystals was performed on a Rigaku MiniFlex II X-ray diffractometer with a Cu target and a Kα radiation source (λ = 0.154184 nm). The results showed that the samples prepared in Example 2 were high-purity and highly crystalline.

[0053] X-ray single-crystal diffraction of PMOF-2A and PMOF-2B crystals was performed on a Mercury CCD single-crystal diffractometer with a Mo target, a Kα radiation source (λ = 0.07107 nm), and a test temperature of 293 K. The structures were analyzed using Shelxtl97. The theoretical XRD diffraction patterns obtained by importing the single-crystal diffraction structure data (cif file) into Mercury 3.5 software were compared with the experimentally measured XRD diffraction patterns. Figure 3 As shown, the XRD diffraction pattern obtained by fitting single-crystal data is highly consistent with the experimentally measured XRD diffraction pattern, proving that the obtained sample is a high-purity and high-crystallinity sample.

[0054] X-ray powder diffraction and single-crystal diffraction results show that:

[0055] Both PMOF-2A and PMOF-2B crystals belong to the monoclinic crystal system, space group P21 / c. They form a three-dimensional framework structure with triple overlap, where metal Zn ions are bridged by two ligands. This structure contains one-dimensional pores filled with guest molecules. Figure 1This is a schematic diagram of the three-dimensional structure of crystal PMOF-2A. The cpb ligand has two free ends: one provided by the N atom in the terminal pyridine ring, and the other by the carboxylate ion. These two free ends are connected to two Zn ions, forming a closed two-dimensional organic layer structure. One Zn ion has a four-coordinate trigonal pyramidal structure, with one carboxyl oxygen atom and three cyano nitrogen atoms from the viologen ligand as its coordinating atoms. The other Zn ion has a six-coordinate octahedral structure, with two nitrogen atoms from two different viologen ligands and four cyano nitrogen atoms as its coordinating atoms. The organic layer extends into a three-dimensional framework through ferricyanide bridging.

[0056] Among them, the specific structures of PMOF-2A and PMOF-2B are as follows: Figure 2 As shown.

[0057] Specifically, the unit cell parameters of PMOF-2A are: α=90(3)°, β=93.159(4)°, γ=90(3)°; Z = 2. Specifically, the unit cell parameters of PMOF-2B are: α=90(3)°, β=92.789(4)°, γ=90(3)°; Z = 2.

[0058] Example 4: Application of crystalline catalysts in the catalytic synthesis of dimethyl carbonate from CO2 and methanol.

[0059] The direct synthesis of dimethyl carbonate from CO2 and methanol was carried out in a high-pressure reactor with stirring and heating. 20 mg of the above-mentioned crystalline catalyst PMOF-2A or PMOF-2B was placed in the reactor, along with 5 mL of methanol, and the reactor was closed. Before the reaction, the reactor inlet valve was opened to introduce a certain amount of CO2, the inlet valve was closed, and the outlet valve was opened to release the gas from the reactor to replace the air. This step was repeated three times. Finally, CO2 was introduced until the pressure inside the reactor reached 3–7 MPa. Heating was started, and the temperature was raised to 120–180 °C, with stirring for 1–5 hours. After the reaction, the reactor was allowed to cool to room temperature, the pressure was released, and the reaction solution was removed. The catalyst and reaction solution were separated by centrifugation. The upper layer of the reaction solution was taken and quantitatively analyzed by gas chromatography to calculate the dimethyl carbonate yield. The performance results of the crystalline catalyst are shown in Table 1.

[0060] Table 1. Performance of crystalline catalysts in the direct synthesis of dimethyl carbonate from CO2 and methanol.

[0061] Reaction conditions PMOF-2A PMOF-2B Pressure, temperature, time <![CDATA[Yield (mmol / g cat. )]]> <![CDATA[Yield (mmol / g cat. )]]> 3MPa, 140℃, 3 hours 0.9 6.6 3MPa, 160℃, 3 hours 7.5 8.9 5MPa, 120℃, 1 hour 0.4 10.5 5MPa, 120℃, 3 hours 0.6 12.6 5MPa, 140℃, 3 hours 1.7 13.1 5MPa, 160℃, 3 hours 12.2 13.7 5MPa, 160℃, 5 hours 14.5 16.2 5MPa, 180℃, 3 hours 16.1 16.8 7MPa, 140℃, 3 hours 2.2 15.4 7MPa, 160℃, 3 hours 15.2 16.7

[0062] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A crystal containing Zn and Fe, characterized in that, The raw material containing ligand cpb, Zn source, K3[Fe(CN)6] and water was placed in a sealed container and crystallized to obtain crystals containing Zn3(cpb)2[Fe(CN)6]2; Among them, the ligand cpb is 1-(3-carboxyphenyl)-4,4'-bipyridine vizimonium salt; The structure of the crystal is as follows: Cyanide and viologen ligands bridge Zn and Fe metal ions to form a three-dimensional porous structure with one-dimensional pores filled with guest molecules. The cpb ligand has two free ends, one provided by the N in the terminal pyridine ring and the other by the carboxylate group. These two free ends are connected to two Zn ions respectively, thus forming a closed two-dimensional organic layer structure. One type of Zn ion has a four-coordinate trigonal pyramidal structure, with its coordinating atoms being a carboxyl oxygen atom from one viologen ligand and three cyano nitrogen atoms. The other type of Zn ion has a six-coordinate octahedral structure, with its coordinating atoms being nitrogen atoms from two different viologen ligands and four cyano nitrogen atoms. The organic layers extend into a three-dimensional framework via ferricyanide bridging; The unit cell parameters of the crystal are: a=16.8723(8)Å, b=7.4686(3)Å, c=23.9586(13)Å; α=90(3)°, β=93.159(4)°, γ=90(3)°; V=3014.5(2)Å3, Z=2.

2. A method for preparing the crystal according to claim 1, characterized in that, At least the following steps are included: a) Obtain the ligand cpb; b) The raw material containing ligand cpb, Zn source, K3[Fe(CN)6] and water was placed in a sealed container and crystallized to obtain crystals containing Zn3(cpb)2[Fe(CN)6]2.

3. The method according to claim 2, characterized in that, In step b), the Zn source is selected from at least one of zinc nitrate and zinc chloride.

4. The method according to claim 2, characterized in that, The molar ratio of the ligand cpb, Zn source, and K3[Fe(CN)6] is 1~4:1~2:1~2.

5. The method according to claim 2, characterized in that, The crystallization conditions are: crystallization at room temperature for 5 to 10 days.

6. A crystalline catalyst, characterized in that, The crystalline catalyst was obtained by stimulating Zn and Fe crystals with heating at 160°C. The unit cell parameters of the crystalline catalyst are: a = 16.8934(8) Å, b = 7.3960(4) Å, c = 23.7427(12) Å; α = 90(3)°, β = 92.789(4)°, γ = 90(3)°; V = 2963.0(3) Å 3 Z=2; The Zn and Fe-containing crystals are selected from the crystals described in claim 1.

7. The application of the crystal according to claim 1 or the crystalline catalyst according to claim 6 in the direct synthesis of dimethyl carbonate from CO2 and methanol, characterized in that, The conditions for the reaction are: The reaction pressure is 3~7MPa, the reaction temperature is 120~180℃, and the reaction time is 1~5 hours.

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