Method for preparing high-defect titanium-based bimetallic organic framework desulfurization catalyst by plasma and application thereof

Abstract

A method for preparing a high-defect titanium-based bimetallic organic framework desulfurization catalyst by plasma and application, N,N-dimethylformamide and acetic acid are mixed, then add trimesic acid and alkaline earth metal salt to obtain a solution. After the solid is completely dissolved, tetraisopropyl titanate is added and high-speed stirring is maintained. The reaction container is sealed and heated, and after the reaction is completed, the sample is filtered, then dried and washed with ethanol and dried. The sample is treated by plasma using inert gas to obtain Ti2M2(μ3-O)2(BTC) x , M=Ca, Sr, Ba, Cd, 4 / 3 The use of inert gas treatment ensures that the material will not chemically react during the treatment process, thereby better utilizing the advantages of defects. The prepared catalyst is used for oxidizing macromolecular sulfur-containing compounds, and its catalytic activity is greatly improved compared to before plasma treatment, and the catalytic performance does not decrease significantly in 5-20 cycle experiments.

Description

Technical Field

[0001] This invention belongs to the field of catalysis for oxidative desulfurization using high-porosity materials, specifically relating to a method and application for plasma preparation of a high-defect titanium-based bimetallic organic framework desulfurization catalyst. Background Technology

[0002] Oxidative desulfurization (ODS) has become a common technology for producing ultra-low sulfur fuels. Compared to hydrodesulfurization (HDS), ODS has the advantage of milder operating conditions, requiring no high temperature, high pressure, or hydrogen. Furthermore, ODS can effectively remove large-molecule sulfur-containing compounds, such as dibenzothiophene (DBT), which are difficult to remove using traditional hydrodesulfurization methods. The corresponding sulfone product (DBTO2) can be easily removed by solvent extraction or adsorption. Therefore, the key step in the ODS process is the oxidation of sulfur-containing compounds.

[0003] Titanium-based metal-organic frameworks (Ti-MOFs) have attracted much attention due to their abundant reserves, low toxicity, significant redox activity, and good photocatalytic activity. These properties make them ideal candidate materials for applications in catalysis, biology, and medicine. Compared to supported catalysts, the metal active centers of metal-organic frameworks are more stable and less prone to loss. However, the complex chemical processes involved in the dissolution of Ti(IV) and its tendency to hydrolyze, leading to the formation of TiO2, pose a significant challenge to the attempt to create new Ti-MOF structures. Currently, there are fewer than one hundred unique Ti-MOFs, a very small fraction compared to the approximately one hundred thousand known metal-organic frameworks. Furthermore, most discovered Ti-MOFs are coordination saturated, thus limiting their full potential.

[0004] Manufacturing defects is an effective means of forming open metal sites and optimizing Zr-MOFs. Against this backdrop, research on defect manufacturing in MOFs is no longer limited to zirconium-based frameworks, especially UiO-66. While UiO-66 has many advantages in defect engineering research, there is still a pressing need to explore other metal-based MOFs. Developing a new type of MOF for defect engineering is crucial for refining the relationship between defects and properties in different systems. However, the chemical properties of MOFs of other metals vary greatly and are highly sensitive to synthesis conditions, posing significant challenges to defect introduction and characterization. Titanium (Ti) possesses low electronegativity and high polarizability, allowing for the formation of diverse titanium clusters during MOF synthesis. Therefore, these clusters lack a clear thermodynamic conformation during synthesis, and even slight changes in synthesis conditions can prevent the formation of the target structure. Furthermore, the Ti precursor is prone to hydrolysis, making the synthesis process highly sensitive. Adding modifiers or additives often leads to synthesis failure, making the introduction of defects from scratch relatively difficult. (See Li, L.; Wang, XS; Liu, TF; Ye, JHTitanium-Based MOF Materials: From Crystal Engineering to Photocatalysis. Small Methods 2020, 4(12), 2000486) Even in the rare cases where defects are introduced through de novo synthesis, the number of defects remains relatively small, and the morphology of the resulting MOFs is often affected. (See Lázaro, IA; Almora-Barrios, N.; Tatay, S.; Martí-Gastaldo, C. Effect of modulator connectivity on promoting defectivity in titanium-organic frameworks. Chem. Sci. 2021, 12(7), 2586-2593.)

[0005] In this invention, we propose a direct method involving plasma-induced defect generation, which can produce high concentrations of defects in titanium-based MOFs under controlled treatment duration and intensity. The catalytic activity of the sample treated with inert gas plasma was significantly enhanced during the oxidation of dibenzothiophene. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings and deficiencies of current technologies by proposing a metal-organic framework material with a high defect rate, which exhibits good stability and catalytic performance.

[0007] The technical solution of the present invention:

[0008] A method for preparing a high-defect titanium-based bimetallic organic framework desulfurization catalyst using plasma, comprising the following steps:

[0009] (1) Add modifier and N,N-dimethylformamide (DMF) to the inner liner of the hydrothermal autoclave reactor and stir to obtain solution I;

[0010] (2) While stirring, add pyromellitic acid (H3BTC) and alkaline earth metal salt to solution I, and obtain solution II after they are completely dissolved;

[0011] (3) Under high-speed stirring, tetraisopropyl titanate was added to solution II to obtain solution III;

[0012] (4) Seal solution III in a high-pressure reactor with a polytetrafluoroethylene liner and place it in an oven for hydrothermal reaction;

[0013] (5) Take out the reaction vessel after step (4) and let it cool naturally to room temperature. Filter out the obtained solid and wash it with ethanol.

[0014] (6) Filter out the solid obtained in step (5) and activate it under vacuum. Then, use the activated sample to perform inert gas plasma treatment and wash the plasma-treated sample with ethanol.

[0015] (7) The metal-organic framework material obtained in step (6) is heated and dried under vacuum to obtain a high-defect titanium-based metal-organic framework material. The treated MOF structure is Ti2M2(μ3-O)2(BTC)x, (M = Ca, Sr, Ba, Cd), where 4 / 3 < x < 8 / 3. When the number of ligands missing reaches 4 / 3, the MOF structure becomes unstable.

[0016] The molar ratio of pyromellitic acid, tetraisopropyl titanate, and alkaline earth metal salt is 1:(0.18-0.22):(0.18-0.22).

[0017] The modifier is one or more of acetic acid and formic acid. The volume ratio between the modifier and DMF is 1:(2-6), and the molar ratio between the modifier and tetraisopropyl titanate is (300-1500):1.

[0018] The metal salt used is one of the following: calcium salt, barium salt, strontium salt, or cadmium salt.

[0019] The hydrothermal reaction temperature is 100℃-150℃, and the reaction time is 48-56h.

[0020] Plasma treatment is carried out in an inert atmosphere, including helium, neon, argon, etc., with a treatment time of 3-9 minutes and a treatment voltage of 20-70kV.

[0021] Vacuum heating drying temperature is 90-150℃, drying time is 10-24h.

[0022] This invention uses an oxidative desulfurization reaction to evaluate the catalytic performance of the prepared catalyst. The specific operation steps are as follows:

[0023] The substrate dibenzothiophene, solvent n-octane, and an internal standard biphenyl with a similar molar amount to dibenzothiophene were added to the reactor. After the solid was completely dissolved in the system, a catalyst and oxidant (cumene hydrogen peroxide, tert-butyl hydrogen peroxide, hydrogen peroxide, oxygen, etc.) were added. After the reaction proceeded for a period of time, the supernatant was taken for quantitative analysis using gas chromatography-mass spectrometry.

[0024] The beneficial effects of this invention are:

[0025] 1. This invention synthesizes bimetallic MOF materials using different alkaline earth metals and titanium sources. By controlling the use of different alkaline earth metal salts, the oxidative desulfurization catalytic performance of the obtained materials can be significantly affected. Different metals in MOFs facilitate electron transfer during the reaction process; therefore, the catalytic activity can be adjusted by doping with different alkaline earth metals. The MOF material with the highest catalytic efficiency has a TOF value that is nearly 20 times higher than that of the MOF material with the lowest catalytic efficiency.

[0026] 2. This invention uses plasma bombardment to create defects in existing Ti-MOFs, avoiding the structural instability of titanium-based MOFs caused by de novo synthesis methods, and also yielding materials with high defect content. This is because inert gases hardly bond with other atoms and always exist in atomic form. Applying inert gases to plasma treatment does not generate free radicals but only ions. This effectively avoids damage to the MOF framework, thus providing the possibility of preparing samples with high defect rates. Compared to samples that have not undergone plasma treatment, the defective titanium-based MOFs lose some ligands, forming new pore sizes and generating more unsaturated metal sites, thus increasing the acidity of the material.

[0027] 3. The oxidative desulfurization efficiency of samples with defects created by plasma treatment is significantly improved. The conversion rate is calculated as follows: after a certain reaction time, the supernatant is taken and analyzed using gas chromatography-mass spectrometry. By comparing the peak area ratio between the internal standard (biphenyl) and the substrate, the conversion rate is calculated as: 1 - (substrate peak area at a certain moment / substrate peak area of ​​the initial sample) / (internal standard peak area at a certain moment / internal standard peak area of ​​the initial sample). Attached Figure Description

[0028] Figure 1XRD images of titanium-based MOFs with different defect contents prepared in Example 3.

[0029] Figure 2 XRD images of titanium-based MOFs with different defect contents prepared in Example 4.

[0030] Figure 3 Nitrogen adsorption isotherm images of the titanium-based MOF with the highest defect content prepared in Example 3 and the original sample.

[0031] Figure 4 The image shown is a scanning transmission electron microscope image of the original sample prepared in Example 3.

[0032] Figure 5 The image is a scanning transmission electron microscope image of the titanium-based MOF with the highest defect content prepared in Example 3.

[0033] Figure 6 The image shows the X-ray photoelectron spectrum of the original sample prepared in Example 3.

[0034] Figure 7 The image shows the X-ray photoelectron spectroscopy of the titanium-based MOF with the highest defect content prepared in Example 3. Detailed Implementation

[0035] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0036] Example 1

[0037] A method for preparing high-defect metal-organic framework catalysts using titanium-based metal-organic frameworks as precursors and by plasma treatment of the titanium-based metal-organic frameworks includes the following steps:

[0038] (1) Add 3.5 ml of acetic acid and 12 ml of N,N-dimethylformamide (DMF) to the inner liner of the hydrothermal autoclave reactor and stir to obtain solution I.

[0039] (2) While stirring, add 125 mg of pyromellitic acid (H3BTC) and 26.8 mg of calcium chloride hexahydrate (CaCl2·6H2O) to solution I. After they are completely dissolved, solution II is obtained.

[0040] (3) Under high-speed stirring, 36 μL of tetraisopropyl titanate was added to solution II to obtain solution III.

[0041] (4) Solution III was sealed in a high-pressure reactor with a polytetrafluoroethylene liner and placed in an oven for hydrothermal reaction at 120°C for 48 hours. The reaction was repeated multiple times to accumulate samples.

[0042] (5) Take out the reaction vessel after the reaction in step (4) and let it cool naturally to room temperature. Filter out the obtained solid and wash it with ethanol.

[0043] (6) The solid obtained in step (5) was filtered out and activated under vacuum at 150°C. 100 mg of the activated sample was then subjected to plasma treatment. The plasma conditions were 50 kV and the treatment time was 5 min. The plasma-treated sample was then washed with ethanol.

[0044] (7) The metal-organic framework material obtained in step (6) is heated and dried under vacuum at 150°C to obtain a titanium-based metal-organic framework material with high defects. The content of each lost ligand accounts for 44.6% of the content of the ligand before treatment. When the sample is used for oxidative desulfurization experiments, its catalytic efficiency is significantly better than that of titanium-based MOFs without plasma treatment.

[0045] Example 2

[0046] Based on Example 1, calcium chloride hexahydrate was replaced with the same amount of strontium chloride hexahydrate to obtain MUV-10(Sr). The remaining treatments were the same as in Example 1.

[0047] Example 3

[0048] Catalytic efficiency of oxidative desulfurization reaction in titanium-based MOF samples treated with plasma at different processing voltages

[0049] Add 1000 ppm of dibenzothiophene, 5 ml of n-octane, and an equal amount of biphenyl as an internal standard to a 10 ml glass bottle. After the solid has completely dissolved in the system, in multiple experiments, add 10 mg of catalyst treated with argon plasma at different voltages for different times, and 8 times the amount of dibenzothiophene in cumene hydrogen peroxide. Figure 1 As shown, the XRD images of all samples after plasma treatment are similar, indicating that the sample structure did not collapse under plasma bombardment. (Comparison) Figure 4 and Figure 5 It can be seen that plasma treatment roughens the crystal surface, which also confirms the loss of ligands. In summary... Figure 6 as well as Figure 7As can be seen, Ti in the plasma-treated sample underwent a new valence state, which is due to ligand deficiency. The reaction was carried out at 80℃ under normal pressure. After 12 hours of reaction, the supernatant was collected and quantitatively analyzed using gas chromatography-mass spectrometry (GC-MS). The analytical results are shown in Table 1. It can be seen that when the treatment time remained constant, the number of missing ligands and the conversion rate of the sample initially increased and then decreased with increasing treatment voltage. Furthermore, the sample treated with argon plasma at 50 kV for 5 minutes showed the best catalytic effect and also had the highest number of missing ligands, meaning it contained the highest content of defects. Moreover, at this point, the defect content of the sample had reached nearly half.

[0050] Table 1: Effects of different treatment voltages on defects and oxidative desulfurization conversion rate of MOF materials

[0051] 0 0 0 52 30 5 0.37 82 40 5 0.39 86 50 5 1.19 95 60 5 0.62 88 70 5 0.64 90

[0052] Example 4

[0053] Catalytic efficiency of oxidative desulfurization reaction in titanium-based MOF samples treated with plasma for different times

[0054] Add 1000 ppm of dibenzothiophene, 5 ml of n-octane, and an equal amount of biphenyl as an internal standard to a 10 ml glass bottle. After the solid has completely dissolved in the system, in multiple experiments, add 10 mg of catalyst treated with 50 kV argon plasma for different times and 8 times the amount of dibenzothiophene in cumene hydrogen peroxide. Figure 2 As shown, the XRD images of all samples after plasma treatment are similar, indicating that the sample structure was not damaged by plasma bombardment. The reaction was carried out at atmospheric pressure and 80℃. After 12 hours of reaction, the supernatant was collected for quantitative analysis using gas chromatography-mass spectrometry (GC-MS). The analytical results are shown in Table 2. It can be seen that when the treatment voltage remains constant, the number of missing ligands and the conversion rate of the samples first increase and then decrease with increasing treatment time. Furthermore, the sample treated with argon plasma at 50 kV for 5 minutes showed the best catalytic effect and also had the highest number of missing ligands, meaning it contained the highest content of defects. Moreover, at this point, the defect content of the sample had reached nearly half.

[0055] Table 2: Effects of different treatment durations on defects and oxidative desulfurization conversion rate of MOF materials

[0056] 0 0 0 52 50 3 0.39 83 50 4 0.41 84 50 5 1.19 95 50 6 0.65 90 50 7 0.45 85 50 9 0.29 80

[0057] Example 5

[0058] Catalytic efficiency of plasma-treated titanium-based MOF samples for oxidative desulfurization reactions on different substrates

[0059] 1000 ppm of a sulfur-containing compound (such as thiophene, benzothiophene, dibenzothiophene, 4,6-dimethyldibenzothiophene), 5 ml of n-octane, and biphenyl (the same amount as the sulfur-containing substrate) were added to a 10 ml glass bottle as an internal standard. After the solid was completely dissolved in the system, 10 mg of catalyst treated with 50 kV argon plasma for 5 minutes and 8 times the amount of dibenzothiophene hydroperoxide were added to the system in multiple experiments. The reaction was carried out at different temperatures under normal pressure. After 12 hours of reaction, the supernatant was taken and quantitatively analyzed by gas chromatography-mass spectrometry. The analytical results are shown in Table 3. It can be seen that when the treatment voltage remains constant, the number of missing ligands and the conversion rate of the sample first increase and then decrease with the increase of treatment time. The sample treated with 50 kV argon plasma for 5 minutes showed the best catalytic effect and also had the highest number of missing ligands, that is, the highest content of defects. Moreover, at this point, the defect content of the sample had reached nearly half.

[0060] Table 3: Oxidation-desulfurization conversion rate of MOF materials treated with plasma at different temperatures

[0061] 50 5 20 33 50 5 40 40 50 5 60 71 50 5 80 95 50 5 100 99

Claims

1. A method for preparing a high-defect titanium-based bimetallic organic framework desulfurization catalyst using plasma, characterized in that, The steps are as follows: (1) Add modifier and N,N-dimethylformamide to the inner liner of the hydrothermal autoclave reactor and stir to obtain solution I; the modifier is acetic acid and / or formic acid, the volume ratio of modifier to N,N-dimethylformamide is 1:(2-6), and the molar ratio of modifier to tetraisopropyl titanate is (300-1500):1; (2) While stirring, add pyromellitic acid and alkaline earth metal salt to solution I, and obtain solution II after they are completely dissolved; (3) Under high-speed stirring, tetraisopropyl titanate was added to solution II to obtain solution III; The molar ratio of the pyromellitic acid, tetraisopropyl titanate, and alkaline earth metal salt is 1:(0.18-0.22):(0.18-0.22); (4) The solution III is sealed in a high-pressure reactor with a polytetrafluoroethylene liner and placed in an oven for hydrothermal reaction; (5) Remove the reaction vessel after step (4) and allow it to cool naturally to room temperature. Filter out the obtained solid and wash it with ethanol. (6) Filter out the solid obtained in step (5) and activate it under vacuum. Then, use the activated sample to perform inert gas plasma treatment and wash the plasma-treated sample with ethanol. (7) The metal-organic framework material obtained in step (6) is heated and dried under vacuum to obtain a high-defect titanium-based metal-organic framework material.

2. The method for preparing a high-defect titanium-based bimetallic organic framework desulfurization catalyst by plasma according to claim 1, characterized in that, The alkaline earth metal salt is one of calcium salt, barium salt, or strontium salt.

3. The method for preparing a high-defect titanium-based bimetallic organic framework desulfurization catalyst by plasma according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 100℃-150℃ for 48-56 hours.

4. The method for preparing a high-defect titanium-based bimetallic organic framework desulfurization catalyst by plasma according to claim 1, characterized in that, The plasma treatment is carried out in an inert atmosphere, including helium, neon, and argon. The plasma treatment time is 3-9 minutes, and the treatment voltage is 20-70 kV.

5. The method for preparing a high-defect titanium-based bimetallic organic framework desulfurization catalyst by plasma according to claim 1, characterized in that, The vacuum heating and drying temperature is 90-150℃, and the drying time is 10-24h.

6. The high-defect titanium-based bimetallic organic framework desulfurization catalyst obtained by the method according to any one of claims 1-5 is used for oxidative desulfurization reactions, characterized in that, The steps are as follows: Dibenzothiophene, n-octane, and biphenyl (an internal standard with a similar amount of dibenzothiophene) are added to the reactor; after the solid is completely dissolved in the system, a high-defect titanium-based bimetallic organic framework desulfurization catalyst and cumene hydrogen peroxide as an oxidant are added to react.

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