Preparation method and application of defective metal organic framework material

Abstract

The invention belongs to the technical field of new materials and catalysis, and relates to a preparation method and application of a defective metal organic framework material, and the preparation method comprises the following steps: firstly, mixing a cerium source, a zirconium source, an organic dibasic acid ligand and an acidic regulator, carrying out solvothermal reaction, then mixing a reaction product with an acidic solution, and carrying out heating reaction, thereby obtaining the defective metal organic framework material. The defect type metal organic framework material is obtained; the obtained defect type metal organic framework material can be used for catalyzing a reaction for preparing dimethyl ether through methanol gas phase dehydration. Compared with the prior art, the defect type metal organic framework prepared by the invention has adjustable defect content and pore structure, so that the accurate regulation and control of catalytic activity can be realized; defective sites with Lewis acidity can be used as active centers of the reaction, so that the activity of the catalyst is greatly improved, and a mesoporous structure in a sample can promote mass transfer and diffusion of a reaction substrate and a product, so that the accessibility and the utilization rate of the active sites are improved.

Description

Technical Field

[0001] The present invention belongs to the fields of new materials and catalytic technologies, and relates to a preparation method of a defective metal-organic framework material and its application in the methanol dehydration to dimethyl ether reaction. Background Art

[0002] Dimethyl ether (DME) is a non-toxic and harmless organic compound with excellent combustibility, and its calorific value of combustion is 28,840 kJ / kg. At the same time, no harmful gases such as nitrogen oxides and sulfides are generated after the combustion of DME. Therefore, it is expected to be used as a green and environmentally friendly new energy to replace liquefied petroleum gas (LPG) and vehicle diesel fuel.

[0003] The dimethyl ether produced industrially is mainly obtained through the methanol gas-phase dehydration reaction. The core of this technology lies in the development of high-performance heterogeneous acid catalysts. Currently, the manufacturers of DME at home and abroad mainly include the French United Rhein Lignite Fuel Company, DuPont Company in the United States, DEA Company in Germany, AkzoNobel Company in the Netherlands, Shandong Jiutai Technology Company, Ningxia Coal Industry Group, Zhongyuan Dahua Group, etc. The technologies for producing DME by these companies are mainly the methanol gas-phase dehydration method, and the most commonly used catalyst is γ-Al 2 O 3 and other metal oxides. As commonly used industrial catalysts, metal oxides have the advantages of high stability, high activity, simple preparation, and low cost. However, their surface chemical structure is relatively complex, the active sites are diverse and disorderly distributed, which brings great challenges to the targeted regulation of catalyst performance and the in-depth understanding of the catalytic mechanism. Therefore, the synthesis of metal oxide catalysts with a uniform surface structure and easy to regulate has also become a research hotspot and difficulty in the current catalytic field.

[0004] Metal-organic frameworks (MOFs) are a class of emerging organic-inorganic hybrid materials, and the inorganic building units in their structures are usually metal oxide clusters with sub-nanometer sizes. Compared with traditional metal oxides, the oxide clusters in MOFs have significant advantages such as dispersed order, clear structure, and easy regulation. These characteristics enable the performance of MOFs in catalytic reactions to be precisely regulated, and are also conducive to the in-depth exploration of catalytic mechanisms. However, due to the relatively high coordination saturation and fewer exposed metal sites in traditional MOF materials, their catalytic activities are usually limited. The catalytic performance of MOF materials can be effectively improved by introducing defect sites. Chinese Patent Application CN113559936A discloses a defective UiO-66 photocatalytic material and its preparation method. By adding carboxylic acid as a regulator during the preparation of zirconium-based MOFs, defective UiO-66 is prepared, effectively improving the catalytic performance of traditional UiO-66 photocatalysts. However, the defect content in the samples prepared by this method is relatively low, and the distribution of defect sites cannot be precisely regulated. In recent years, some researchers have begun to pay attention to the application of defective MOFs in the gas-phase dehydration of methanol to DME. However, the existing research work is still in its infancy, mainly focusing on the identification of catalytic sites and the study of catalyst stability. Therefore, to address the deficiencies of existing research, it is of great practical significance to develop a high-performance defective MOF catalyst with controllable structure based on a bimetallic MOF precursor for the gas-phase dehydration of methanol to DME. Summary of the Invention

[0005] The purpose of the present invention is to provide a defective metal-organic framework material, its preparation method and application. By post-treatment with an acidic solution, some building units in the MOF can be selectively removed, thereby precisely regulating the defect sites, pore structure and catalytic activity of methanol dehydration in the material, effectively solving the problems of difficult structure regulation, unclear active sites and low catalytic performance of existing methanol dehydration catalysts.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The first aspect of the present invention provides a preparation method of a defective metal-organic framework material, including:

[0008] S1: Mix a cerium source, a zirconium source, an organic dibasic acid ligand, and an acidic regulator, and perform a solvothermal reaction to obtain a mixed-metal MOF precursor;

[0009] S2: Mix the mixed-metal MOF precursor and an acidic solution, and perform a heating reaction to obtain a defective metal-organic framework material.

[0010] The present invention uses a MOF composed of bimetals as a precursor, and selectively removes some building units through post-treatment with an acidic solution to achieve precise regulation of defect sites, pore structures, and methanol dehydration catalytic performance. The obtained MOF is one of UiO-66 and UiO-67, where the molar ratio of Ce to the total metal usage is 10% to 90%, preferably 20% to 80%.

[0011] The defect content of the MOF material is 0.5 to 3 per inorganic node on average.

[0012] Further, in step S1, the cerium source is selected from at least one of cerium chloride, cerium nitrate, or ammonium cerium nitrate, and the zirconium source is selected from at least one of zirconium chloride, zirconium oxychloride, or zirconium oxynitrate.

[0013] Further, in step S1, the organic dibasic acid ligand is terephthalic acid or 4,4'-biphenyldicarboxylic acid, the total molar amount of the cerium source and the zirconium source to the molar amount of the organic dibasic acid ligand is 0.5 to 2:1, and the concentration of the organic dibasic acid ligand in the reaction solvent is 0.027 to 0.27 mol / L.

[0014] Further, in step S1, the acidic regulator is formic acid or acetic acid, and the molar amount of the acidic regulator to the total molar amount of the cerium source and the zirconium source is 0.1 to 60:1.

[0015] Further, in step S1, the reaction temperature of the solvothermal reaction is 60 to 120 °C, and the reaction time is 0.25 to 12 h.

[0016] As a preferred technical solution, after the solvothermal reaction, the solid product is separated, washed, and activated to obtain a mixed-metal MOF precursor.

[0017] Further, in step S2, in the acidic solution, the solute is selected from one of hydrochloric acid, formic acid, acetic acid, or trifluoroacetic acid, the solvent is N,N-dimethylformamide or water, and the concentration is 1 to 8 mol / L.

[0018] Further, in step S2, the mass-volume ratio of the mixed-metal MOF precursor to the acidic solution is 2 to 20 mg:1 mL.

[0019] Further, in step S2, in the heating reaction, the reaction temperature is 60 to 120 °C, and the reaction time is 6 to 24 h.

[0020] As a preferred technical solution, after the heating reaction, the solid product is separated, washed, and activated to obtain a defective metal-organic framework material.

[0021] The second aspect of the present invention provides an application of a defective metal-organic framework material, including using the defective metal-organic framework material as a catalyst for the reaction of methanol gas-phase dehydration to dimethyl ether.

[0022] Further, the reaction conditions for the reaction of methanol gas-phase dehydration to dimethyl ether include:

[0023] Methanol is introduced into a fixed-bed reactor by the bubbling method, the carrier gas is nitrogen, and the carrier gas flow rate is 5-20 mL / min;

[0024] The methanol partial pressure is 20-350 mbar;

[0025] The catalytic reaction temperature is 180-350 °C, preferably 220-280 °C;

[0026] The catalyst dosage is 20-300 mg, preferably 100-250 mg.

[0027] Compared with the prior art, the present invention has the following characteristics:

[0028] 1) The defective metal-organic framework created by the present invention has adjustable defect content and pore structure, so as to realize precise regulation of catalytic activity; the defect sites with Lewis acidity can serve as the active centers of the reaction, thus greatly improving the catalyst activity, and the mesoporous structure in the sample can also promote the mass transfer and diffusion of reaction substrates and products, thereby improving the accessibility and utilization rate of active sites;

[0029] 2) The defective metal-organic framework catalyst created by the present invention achieves a methanol conversion rate of ≥90% and a dimethyl ether selectivity of ≥99% in the reaction of methanol gas-phase dehydration to dimethyl ether. This catalyst also has excellent stability, and the catalytic activity does not decrease significantly after continuous reaction on a fixed bed for 24 h. Description of the Drawings

[0030] Figure 1 For the conversion rate of methanol in the methanol dehydration reaction catalyzed by the defective UiO-66 in Example 1. Detailed Embodiments

[0031] The present invention will be described in detail below with reference to the drawings and specific embodiments. The following embodiments are implemented on the premise of the above technical solutions of the present invention, and the detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0032] Example 1

[0033] A defective metal-organic framework material, the preparation method of which includes the following steps:

[0034] Step 1: Add 0.255g terephthalic acid, 2mL formic acid and 7.2mL DMF into a 25mL polytetrafluoroethylene hydrothermal reactor, stir until well mixed, then add 0.96mL cerium ammonium nitrate aqueous solution (0.533mmol / mL) and 1.44mL zirconium oxynitrate aqueous solution (0.533mmol / mL). Seal the hydrothermal reactor and place it in a 100℃ oven for reaction for 30min. After the reaction is completed and cooled to room temperature naturally, collect the solid product by centrifugation, wash it three times with DMF, wash it six times with acetone, and then vacuum dry it at 80℃. The obtained sample is recorded as Ce / Zr-UiO-66-40%.

[0035] Step 2: Weigh 100 mg of the prepared Ce / Zr-UiO-66-40% and 20 mL of formic acid DMF solution (5.3 mol / L) into a polytetrafluoroethylene hydrothermal autoclave. After being fully mixed, seal the hydrothermal autoclave and place it in a 100°C oven for 12 hours. After the treatment is completed and naturally cooled to room temperature, the solid product is collected by centrifugation, washed three times with DMF and six times with acetone, and then vacuum dried at 80°C. The obtained sample is recorded as D-UiO-66-40%-FA.

[0036] The defect content of D-UiO-66-40%-FA was measured to be 1.9 on each inorganic node on average by H NMR spectroscopy and thermogravimetric analysis, and the Ce molar content in D-UiO-66-40%-FA was reduced to 6% by inductively coupled plasma spectroscopy.

[0037] 250 mg of the above catalyst was loaded into a fixed bed reactor, and a catalytic test was performed under the conditions of a reaction temperature of 300°C, a nitrogen carrier gas flow rate of 10 mL / min, and a methanol partial pressure of 40 mbar. After 4 hours of reaction, the catalyst activity tended to be stable, and the methanol conversion rate was maintained at about 91%. After 24 hours of reaction, there was no significant decrease in the catalytic activity.

[0038] Example 2

[0039] A defective metal organic framework material, the preparation method of which comprises the following steps:

[0040] Step 1: Add 0.255g terephthalic acid, 2mL formic acid and 7.2mL DMF into a 25mL polytetrafluoroethylene hydrothermal reactor, stir until well mixed, then add 0.96mL cerium ammonium nitrate aqueous solution (0.533mmol / mL) and 1.44mL zirconium oxynitrate aqueous solution (0.533mmol / mL). Seal the hydrothermal reactor and place it in a 100℃ oven for reaction for 30min. After the reaction is completed and cooled to room temperature naturally, collect the solid product by centrifugation, wash it three times with DMF, wash it six times with acetone, and then vacuum dry it at 80℃. The obtained sample is recorded as Ce / Zr-UiO-66-40%.

[0041] Step 2: Weigh 100 mg Ce / Zr-UiO-66-40% and 20 mL acetic acid DMF solution (3.5 mol / L) into a polytetrafluoroethylene hydrothermal autoclave. After sufficient mixing, seal the hydrothermal autoclave and place it in a 120°C oven for 12 hours. After the treatment is completed and naturally cooled to room temperature, the solid product is collected by centrifugation, washed three times with DMF and six times with acetone, and then vacuum dried at 80°C. The obtained sample is recorded as D-UiO-66-40%-AA.

[0042] The defect content of D-UiO-66-40%-AA was measured to be 1.5 on each inorganic node on average by H NMR spectroscopy and thermogravimetric analysis, and the Ce molar content in D-UiO-66-40%-AA was reduced to 13% by inductively coupled plasma spectroscopy.

[0043] 250 mg of the above catalyst was loaded into a fixed bed reactor, and a catalytic test was carried out under the conditions of a reaction temperature of 250°C, a nitrogen carrier gas flow rate of 10 mL / min, and a methanol partial pressure of 40 mbar. After 5 hours of reaction, the catalyst activity tended to be stable, and the methanol conversion rate was maintained at about 57%. After 16 hours of reaction, the catalyst began to slowly deactivate.

[0044] Example 3

[0045] A defective metal organic framework material, the preparation method of which comprises the following steps:

[0046] Step 1: Add 0.255g terephthalic acid, 2mL formic acid and 7.2mL DMF into a 25mL polytetrafluoroethylene hydrothermal reactor, stir until well mixed, then add 0.96mL cerium ammonium nitrate aqueous solution (0.533mmol / mL) and 1.44mL zirconium oxynitrate aqueous solution (0.533mmol / mL). Seal the hydrothermal reactor and place it in a 100℃ oven for reaction for 30min. After the reaction is completed and cooled to room temperature naturally, collect the solid product by centrifugation, wash it three times with DMF, wash it six times with acetone, and then vacuum dry it at 80℃. The obtained sample is recorded as Ce / Zr-UiO-66-40%.

[0047] Step 2: Weigh 100 mg Ce / Zr-UiO-66-40% and 20 mL hydrochloric acid aqueous solution (4 mol / L) into a polytetrafluoroethylene hydrothermal autoclave. After sufficient mixing, seal the autoclave and place it in a 100°C oven for 6 hours. After the treatment is completed and cooled to room temperature naturally, the solid product is collected by centrifugation, washed three times with DMF and six times with acetone, and then dried in vacuum at 80°C. The obtained sample is recorded as D-UiO-66-40%-HCl.

[0048] The defect content of D-UiO-66-40%-HCl was measured by thermogravimetric analysis to be 2.3 on average per inorganic node, and the Ce molar content in D-UiO-66-40%-HCl was reduced to 1% by inductively coupled plasma spectroscopy.

[0049] 250 mg of the above catalyst was loaded into a fixed bed reactor, and a catalytic test was carried out under the conditions of a reaction temperature of 300°C, a nitrogen carrier gas flow rate of 10 mL / min, and a methanol partial pressure of 40 mbar. After 8 hours of reaction, the catalyst activity tended to be stable, and the methanol conversion rate was maintained at about 82%. After 24 hours of reaction, there was no obvious decrease in catalytic activity.

[0050] Example 4

[0051] A defective metal organic framework material, the preparation method of which comprises the following steps:

[0052] Step 1: Add 0.255g terephthalic acid, 2mL formic acid and 7.2mL DMF into a 25mL polytetrafluoroethylene hydrothermal reactor, stir until well mixed, then add 1.44mL cerium ammonium nitrate aqueous solution (0.533mmol / mL) and 0.96mL zirconium oxynitrate aqueous solution (0.533mmol / mL). Seal the hydrothermal reactor and place it in a 100℃ oven for reaction for 30min. After the reaction is completed and cooled to room temperature naturally, collect the solid product by centrifugation, wash it three times with DMF, wash it six times with acetone, and then vacuum dry it at 80℃. The obtained sample is recorded as Ce / Zr-UiO-66-60%.

[0053] Step 2: Weigh 100 mg of Ce / Zr-UiO-66-60% and 20 mL of trifluoroacetic acid DMF solution (5 mol / L), and place them into the inner liner of a polytetrafluoroethylene hydrothermal autoclave. After thorough mixing, seal the hydrothermal autoclave and place it in an oven at 120 °C for 6 h. After the treatment is completed and it cools naturally to room temperature, collect the solid product by centrifugation. Wash it three times with DMF and six times with acetone, and then dry it under vacuum at 80 °C. The obtained sample is denoted as D-UiO-66-60%-TFA.

[0054] The defect content of D-UiO-66-60%-TFA measured by thermogravimetric analysis is 2.5 per inorganic node on average, and the Ce molar content in D-UiO-66-40%-HCl measured by inductively coupled plasma spectroscopy is reduced to 3%.

[0055] Load 250 mg of the above catalyst into a fixed-bed reactor, and conduct catalytic tests under the conditions of a reaction temperature of 250 °C, a nitrogen carrier gas flow rate of 10 mL / min, and a methanol partial pressure of 40 mbar. After reacting for 5 h, the catalyst activity tends to be stable, and the methanol conversion rate is maintained at about 69%. After reacting for 12 h, the catalyst begins to slowly deactivate.

[0056] Example 5

[0057] A defective metal-organic framework material, and its preparation method includes the following steps:

[0058] Step 1: Mix 46.6 mg of anhydrous zirconium chloride, 32.6 mg of cerium nitrate hexahydrate, 96.8 mg of 4,4'-biphenyldicarboxylic acid, 0.38 mL of acetic acid, and 15 mL of DMF. After the solids are completely dissolved, transfer the above solution to the inner liner of a 25 mL polytetrafluoroethylene hydrothermal autoclave. Seal the hydrothermal autoclave and place it in an oven at 120 °C for 24 h. After the reaction is completed and it cools naturally to room temperature, collect the solid product by centrifugation. Wash it three times with DMF and six times with acetone, and then dry it under vacuum at 80 °C. The obtained sample is denoted as Ce / Zr-UiO-67-30%.

[0059] Step 2: Weigh 100 mg of Ce / Zr-UiO-67-30% and 20 mL of formic acid DMF solution (5.3 mol / L), and place them into the inner liner of a polytetrafluoroethylene hydrothermal autoclave. After thorough mixing, seal the hydrothermal autoclave and place it in an oven at 100 °C for 6 h. After the treatment is completed and it cools naturally to room temperature, collect the solid product by centrifugation. Wash it three times with DMF and six times with acetone, and then dry it under vacuum at 80 °C. The obtained sample is denoted as D-UiO-67-30%-FA.

[0060] The defect content of D-UiO-67-30%-FA was measured to be 1.6 on each inorganic node on average by H NMR spectroscopy and thermogravimetric analysis, and the Ce molar content in D-UiO-67-30%-FA was reduced to 4% by inductively coupled plasma spectroscopy.

[0061] 250 mg of the above catalyst was loaded into a fixed bed reactor, and a catalytic test was performed under the conditions of a reaction temperature of 300°C, a nitrogen carrier gas flow rate of 10 mL / min, and a methanol partial pressure of 40 mbar. After 3 hours of reaction, the catalyst activity reached a peak, with a methanol conversion of 84%, and then the catalyst rapidly deactivated.

[0062] Example 6

[0063] A defective metal organic framework material, the preparation method of which comprises the following steps:

[0064] Step 1: Mix 46.6 mg of anhydrous zirconium chloride, 32.6 mg of cerium nitrate hexahydrate, 96.8 mg of 4,4'-biphenyldicarboxylic acid, 0.38 mL of acetic acid and 15 mL of DMF. After the solid is fully dissolved, transfer the above solution to a 25 mL polytetrafluoroethylene hydrothermal kettle. Seal the hydrothermal kettle and place it in a 120 ° C oven to react for 24 hours. After the reaction is completed and naturally cooled to room temperature, collect the solid product by centrifugation, wash it three times with DMF, wash it six times with acetone, and then vacuum dry it at 80 ° C. The obtained sample is recorded as Ce / Zr-UiO-67-30%.

[0065] Step 2: Weigh 100 mg Ce / Zr-UiO-67-30% and 20 mL acetic acid DMF solution (3.5 mol / L) into a polytetrafluoroethylene hydrothermal autoclave. After sufficient mixing, seal the hydrothermal autoclave and place it in a 120°C oven for 6 hours. After the treatment is completed and naturally cooled to room temperature, the solid product is collected by centrifugation, washed three times with DMF and six times with acetone, and then vacuum dried at 80°C. The obtained sample is recorded as D-UiO-67-30%-AA.

[0066] The defect content of D-UiO-67-30%-AA was measured to be 1.4 on each inorganic node by hydrogen nuclear magnetic resonance spectroscopy and thermogravimetric analysis, and the molar content of Ce in D-UiO-67-30%-AA was reduced to 7% by inductively coupled plasma spectroscopy.

[0067] 250 mg of the above catalyst was loaded into a fixed bed reactor, and a catalytic test was performed under the conditions of a reaction temperature of 250°C, a nitrogen carrier gas flow rate of 10 mL / min, and a methanol partial pressure of 40 mbar. After 2.5 hours of reaction, the catalyst activity reached a peak, with a methanol conversion of 50%, and then the catalyst rapidly deactivated.

[0068] Example 7

[0069] A defective metal organic framework material, the preparation method of which comprises the following steps:

[0070] Step 1: Mix 46.6 mg of anhydrous zirconium chloride, 16.3 mg of cerium nitrate hexahydrate, 96.8 mg of 4,4'-biphenyldicarboxylic acid, 0.38 mL of acetic acid and 15 mL of DMF. After the solid is fully dissolved, transfer the above solution to a 25 mL polytetrafluoroethylene hydrothermal kettle. Seal the hydrothermal kettle and place it in a 120 ° C oven to react for 24 hours. After the reaction is completed and naturally cooled to room temperature, collect the solid product by centrifugation, wash it three times with DMF, wash it six times with acetone, and then vacuum dry it at 80 ° C. The obtained sample is recorded as Ce / Zr-UiO-67-20%.

[0071] Step 2: Weigh 100 mg Ce / Zr-UiO-67-20% and 20 mL hydrochloric acid aqueous solution (3 mol / L) into a polytetrafluoroethylene hydrothermal autoclave. After sufficient mixing, seal the autoclave and place it in a 100°C oven for 6 hours. After the treatment is completed and cooled to room temperature naturally, the solid product is collected by centrifugation, washed three times with DMF and six times with acetone, and then dried in vacuum at 80°C. The obtained sample is recorded as D-UiO-67-20%-HCl.

[0072] The defect content of D-UiO-67-20%-HCl was measured to be 2.0 on each inorganic node on average by thermogravimetric analysis, and the Ce molar content in D-UiO-67-20%-HCl was reduced to 1% by inductively coupled plasma spectroscopy.

[0073] 250 mg of the above catalyst was loaded into a fixed bed reactor and catalytic testing was performed under the conditions of reaction temperature of 300°C, nitrogen carrier gas flow rate of 10 mL / min, and methanol partial pressure of 40 mbar. After 4 hours of reaction, the catalyst activity reached a peak, with methanol conversion of 75%, and then the catalyst rapidly deactivated.

[0074] Example 8

[0075] A defective metal organic framework material, the preparation method of which comprises the following steps:

[0076] Step 1: Mix 46.6 mg of anhydrous zirconium chloride, 16.3 mg of cerium nitrate hexahydrate, 96.8 mg of 4,4'-biphenyldicarboxylic acid, 0.38 mL of acetic acid, and 15 mL of DMF. After the solids are fully dissolved, transfer the above solution to the inner liner of a 25 mL Teflon hydrothermal autoclave. Seal the autoclave and place it in an oven at 120 °C for 24 h. After the reaction is completed and cooled naturally to room temperature, collect the solid product by centrifugation, wash it three times with DMF and six times with acetone, and then dry it under vacuum at 80 °C. The obtained sample is denoted as Ce / Zr-UiO-67-20%.

[0077] Step 2: Weigh 100 mg of Ce / Zr-UiO-67-20% and 20 mL of a trifluoroacetic acid DMF solution (3 mol / L) and put them into the inner liner of a Teflon hydrothermal autoclave. After thorough mixing, seal the autoclave and place it in an oven at 120 °C for 6 h. After the treatment is completed and cooled naturally to room temperature, collect the solid product by centrifugation, wash it three times with DMF and six times with acetone, and then dry it under vacuum at 80 °C. The obtained sample is denoted as D-UiO-67-20%-TFA.

[0078] The defect content of D-UiO-67-20%-TFA measured by thermogravimetric analysis is 1.7 per inorganic node on average, and the Ce molar content in D-UiO-67-20%-TFA measured by inductively coupled plasma spectroscopy is reduced to 2%.

[0079] Load 250 mg of the above catalyst into a fixed-bed reactor and carry out catalytic tests under the conditions of a reaction temperature of 250 °C, a nitrogen carrier gas flow rate of 10 mL / min, and a methanol partial pressure of 40 mbar. The catalyst activity reaches a peak after 3 h of reaction, and the methanol conversion is 56%. Subsequently, the catalyst quickly deactivates.

[0080] Comparative Example 1

[0081] A defective metal-organic framework material, the preparation method of which is different from that of Example 1 only in that: the dosage of ammonium cerium nitrate aqueous solution (0.533 mmol / mL) is changed to 0.48 mL, and the dosage of zirconyl nitrate aqueous solution (0.533 mmol / mL) is changed to 2.02 mL. The obtained precursor is denoted as Ce / Zr-UiO-66-20%, and the obtained final catalyst is denoted as D-UiO-66-20%-FA.

[0082] The defect content of D-UiO-66-20%-FA measured by nuclear magnetic resonance hydrogen spectrum and thermogravimetric analysis is 1.4 per inorganic node on average, and the Ce content in D-UiO-66-20%-FA measured by inductively coupled plasma spectroscopy is reduced to 3%.

[0083] 250 mg of the above catalyst was charged into a fixed-bed reactor, and catalytic tests were carried out under the conditions of a reaction temperature of 300 °C, a carrier gas flow rate of 10 mL / min, and a methanol partial pressure of 40 mbar. After 3 h of reaction, the catalyst activity tended to be stable, and the methanol conversion rate was maintained at about 80%. After 24 h of reaction, the catalytic activity did not decrease significantly.

[0084] Comparative Example 2

[0085] A defective metal-organic framework material, the preparation method of which is different from that of Example 1 only in that: after Ce / Zr-UiO-66-40% is prepared, no secondary acid treatment is required.

[0086] The defect content of Ce / Zr-UiO-66-40% was measured by 1H NMR and thermogravimetric analysis to be 0.9 per inorganic node on average.

[0087] 250 mg of the above catalyst was charged into a fixed-bed reactor, and catalytic tests were carried out under the conditions of a reaction temperature of 250 °C, a nitrogen carrier gas flow rate of 10 mL / min, and a methanol partial pressure of 40 mbar. After 2 h of reaction, the catalyst activity reached a peak, and the methanol conversion was 42%. Subsequently, the catalyst was slowly deactivated.

[0088] The preparation conditions of the samples in each example are shown in Table 1. The precursors selected are UiO-66 and UiO-67, and the acids selected for post-treatment include formic acid, acetic acid, hydrochloric acid, and trifluoroacetic acid. Since the chemical stability of UiO-67 is weaker than that of UiO-66, the post-treatment conditions of UiO-67 are milder than those of UiO-66. For the same precursor, the reaction conditions are milder when using a stronger acid solution for post-treatment.

[0089] Table 1 Preparation conditions of the samples in each example

[0090]

[0091]

[0092] The defect content and catalytic performance of the samples of each embodiment are shown in Table 2. Generally speaking, the catalytic activity increases with the increase of the defect content and reaction temperature. However, the catalyst in Example 3 has a higher defect content than that in Example 1, while the methanol conversion rate is lower. This is because the catalyst in Example 3 is prepared by post-treatment with hydrochloric acid, so the defect sites are occupied by Cl ions. Compared with the formate in Example 1, Cl ions are more difficult to be exposed during the reaction process, resulting in fewer active sites that can participate in the reaction during the reaction process, thus leading to a lower methanol conversion rate. For UiO-66 and UiO-67 with similar defect contents, the catalytic activity of UiO-66 is generally higher than that of UiO-67, because UiO-66 has higher chemical stability and can maintain a stable structure during the reaction process, while UiO-67 will decompose during the reaction process, resulting in a decrease in activity. The results of Comparative Example 1 show that regulating the content of Ce in the precursor can regulate the defect content of the final catalyst, thereby realizing the regulation of catalytic activity. The results of Comparative Example 2 show that the MOF after treatment with an acidic solution has a higher defect content and catalytic activity than the untreated MOF, reflecting the superiority of this preparation method.

[0093] Table 2 Defect content and catalytic performance of the samples of each embodiment

[0094]

[0095]

[0096] Figure 1 is the conversion rate of methanol in the methanol dehydration reaction catalyzed by defective UiO-66 in Example 1. Within the first 4 h of the reaction, the catalyst activity increases rapidly, because at the initial state, the defect sites of UiO-66 are occupied by formate, and during the reaction, these formates will react with methanol to form methyl formate and be discharged, so that more defect sites can be exposed during the reaction process. The catalyst activity reaches the peak at about 4 h of the reaction, indicating that all defect sites have participated in the reaction. During the subsequent reaction process, the catalyst activity basically remains unchanged, indicating that the structure of defective UiO-66 can be maintained stable under this reaction condition.

[0097] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. Obviously, those who are familiar with the technology in this field can easily make various modifications to these embodiments and apply the general principles described here to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A preparation method of a defective metal-organic framework material, characterized in that, comprising: S1: Mixing a cerium source, a zirconium source, an organic dibasic acid ligand, and an acidic regulator, and performing a solvothermal reaction to obtain a mixed-metal MOF precursor; S2: Mixing the mixed-metal MOF precursor and an acidic solution, and performing a heating reaction to obtain a defective metal-organic framework material.

2. The preparation method of the defective metal-organic framework material according to claim 1, characterized in that, in step S1, the cerium source is selected from at least one of cerium chloride, cerium nitrate or ammonium cerium nitrate, and the zirconium source is selected from at least one of zirconium chloride, zirconyl chloride or zirconyl nitrate.

3. The preparation method of the defective metal-organic framework material according to claim 1, characterized in that, in step S1, the organic dibasic acid ligand is terephthalic acid or 4,4'-biphenyldicarboxylic acid, and the ratio of the total molar amount of the cerium source and the zirconium source to the molar amount of the organic dibasic acid ligand is 0.5-2:1, and the concentration of the organic dibasic acid ligand in the reaction solvent is 0.027-0.27 mol / L.

4. The preparation method of the defective metal-organic framework material according to claim 1, characterized in that, in step S1, the acidic regulator is formic acid or acetic acid, and the ratio of the molar amount of the acidic regulator to the total molar amount of the cerium source and the zirconium source is 0.1-60:

1.

5. The preparation method of the defective metal-organic framework material according to claim 1, characterized in that, in step S1, in the solvothermal reaction, the reaction solvent is N,N-dimethylformamide, the reaction temperature is 60-120 °C, and the reaction time is 0.25-12 h.

6. The preparation method of the defective metal-organic framework material according to claim 1, characterized in that, in step S2, in the acidic solution, the solute is selected from one of hydrochloric acid, formic acid, acetic acid or trifluoroacetic acid, the solvent is N,N-dimethylformamide or water, and the concentration is 1-8 mol / L.

7. The preparation method of the defective metal-organic framework material according to claim 1, characterized in that, in step S2, the mass-volume ratio of the mixed-metal MOF precursor to the acidic solution is 2-20 mg:1 mL.

8. The preparation method of the defective metal-organic framework material according to claim 1, characterized in that, in step S2, in the heating reaction, the reaction temperature is 60-120 °C, and the reaction time is 6-24 h.

9. An application of a defective metal-organic framework material prepared by the method according to any one of claims 1 to 8, characterized in that, the defective metal-organic framework material is used as a catalyst for the reaction of methanol gas-phase dehydration to dimethyl ether.

10. The application of the defective metal-organic framework material according to claim 9, characterized in that, the reaction conditions of the reaction of methanol gas-phase dehydration to dimethyl ether include: the methanol partial pressure is 20-350 mbar; the catalytic reaction temperature is 180-350 °C; the catalyst dosage is 20-300 mg.

Images