Preparation method of MOF-derived TiO2 loaded Ni-O-Ni dimer catalyst

Abstract

The invention discloses a preparation method of an MOF-derived TiO2 loaded Ni-O-Ni dimer catalyst, and relates to a preparation method of a catalyst for photocatalytic glycerol reforming to prepare synthesis gas. In order to solve the problem of low efficiency of photocatalytic conversion of biomass glycerol into synthesis gas, the method comprises the following steps: adding a nickel ion solution into a suspension of MIL-125 powder, stirring, separating to prepare a precursor, and performing high-temperature treatment to obtain the O-Ni2 / TiO2 photocatalyst. The MOF-derived TiO2 scaffold has a highly porous structure, and supports highly exposed active sites of Ni-O-Ni dimers connected by oxygen bridges, and the Ni-O-Ni sites adjust the local electronic structure of the Ni sites. The O-Ni2 / TiO2 is used for glycerol reforming, the average precipitation rates of H2 and CO are 2542.6 and 361.7 [mu] mol g <-1 > h <-1 >, the selectivity is 96.1%, and the catalyst can be applied to the field of synthesis gas preparation through glycerol reforming.

Description

Technical Field

[0001] The present invention relates to a preparation method of a catalyst for photocatalytic reforming of glycerol to syngas. Background Art

[0002] Biomass resources are renewable energy and carbon carriers generated by photosynthesis using solar energy, carbon dioxide, and water. The selective catalytic conversion of biomass-derived chemicals (such as glycerol) into high-value-added products has attracted extensive attention because it ensures the sustainable supply of energy and chemicals. The industrial processes for such conversion usually require high temperature and high pressure, which have negative impacts on energy consumption and the environment. In this context, solar-driven photocatalytic technology, characterized by mild reaction conditions and the ability to convert biomass without consuming large amounts of fossil energy, contributes to the sustainable utilization of biomass. Therefore, the use of photocatalytic technology to efficiently and highly selectively convert biomass-derived glycerol into syngas provides a promising solution to the problem of energy shortage. In the Chinese patent "A Method for Preparing Acetol and Syngas by Photocatalytic Conversion of Glycerol" with the application number 202310542317.7, using glycerol as a substrate, under visible light irradiation, Mn-doped CdS (Mn / CdS) as a photocatalyst, glycerol undergoes photocatalytic dehydration to obtain the liquid-phase product acetol and the gas-phase product syngas (H2 + CO). The product selectivity is high, but this catalyst has the disadvantage of a low evolution rate of H2 and CO. Summary of the Invention

[0003] The object of the present invention is to solve the problem of low conversion efficiency of photocatalytic biomass glycerol, and to provide a preparation method of a MOF-derived TiO2-supported Ni-O-Ni dimer catalyst, which is a MOF-derived TiO2-supported oxygen-bridged Ni-O-Ni site catalyst (O-Ni2 / TiO2).

[0004] The preparation method of the MOF-derived TiO2-supported Ni-O-Ni dimer catalyst of the present invention is carried out according to the following steps:

[0005] First, terephthalic acid is added to N,N-dimethylformamide, stirred and dissolved, then methanol is added, and stirring is continued for 15 - 25 minutes; then tetrabutyl titanate is added, and stirring is continued for 30 - 50 minutes to obtain a mixed solution; then the obtained mixed solution is transferred to a high-pressure reaction kettle and maintained at a temperature of 140 - 160 °C for 15 - 18 hours; after cooling to room temperature, filtration is carried out, and the solid phase is washed clean with N,N-dimethylformamide and methanol and dried under vacuum to obtain MIL-125 powder;

[0006] II. Dissolve NiCl2·6H2O in deionized water to obtain solution A; dissolve oxalic acid in deionized water to obtain solution B; add solution B dropwise to solution A under continuous stirring, and continue stirring for 1.5 - 2.5 hours after the addition is complete to obtain solution C;

[0007] III. Add MIL-125 powder to methanol and disperse it evenly with ultrasonic waves to obtain a MIL-125 suspension; then add solution C dropwise to the MIL-125 suspension, continue stirring for 3.5 - 4.5 hours after the addition is complete, and then perform centrifugal separation. Wash the solid phase with ethanol until clean to obtain a precursor;

[0008] IV. Place the precursor in a high-temperature furnace and heat it to 400 - 600 °C at a rate of 2 - 5 °C / min and hold for 3.5 - 4.5 hours to obtain a MOF-derived TiO2-supported Ni-O-Ni dimer catalyst, denoted as O-Ni2 / TiO2.

[0009] Furthermore, in step I, the mass ratio of terephthalic acid to the volume of N,N-dimethylformamide is 1 g:(15 - 20) mL.

[0010] Furthermore, in step I, the mass ratio of terephthalic acid, the volume of methanol, and the volume of tetrabutyl titanate is 1 g:(1.5 - 2.5):(0.2 - 0.3).

[0011] Furthermore, the mass ratio of NiCl2·6H2O to oxalic acid described in step II is (3 - 5):1.

[0012] Furthermore, the mass ratio of the MIL-125 powder to the volume of methanol described in step III is 1 g:(20 - 100) mL.

[0013] Furthermore, the mass ratio of the MIL-125 powder to the molar amount of Ni in solution C described in step III is 1 g:0.1 - 0.2 mmol.

[0014] The photocatalytic reforming of glycerol to syngas involves complex catalytic reactions with multiple reactants, intermediates, and products. The MOF-derived TiO2-supported oxygen-bridged Ni-O-Ni dual-atom site photocatalyst of the present invention has two atoms interacting with intermediates at each active site. This dual-metal atom-dispersed catalyst has an easily adjustable electronic structure and stronger interaction with the catalytic support. The synergistic effect between metal atoms can change the adsorption mode of key intermediates, lower the activation energy, and optimize the reaction pathway, thus significantly improving the catalytic efficiency and selectivity. At the same time, the high specific surface area, porous structure, and rich functional groups of MOF are conducive to the formation of a stable Ni-O-Ni structure after calcination. MOF-derived TiO2 has an increased specific surface area, allowing more active sites to be exposed. This unique dual-atom catalyst can achieve efficient electron-hole separation and exhibits excellent photocatalytic activity and selectivity in the conversion of glycerol to syngas.

[0015] The O-Ni2 / TiO2 material prepared in the present invention. By regulating the Ni loading amount and reaction conditions, the structure of the catalyst is precisely controlled. The prepared O-Ni2 / TiO2 photocatalyst has a unique Ni-O-Ni dimer catalytic site, effectively enhancing the electron transfer efficiency, reducing the recombination of photogenerated electrons and holes, and improving the overall efficiency of the catalytic reaction. The O-Ni2 / TiO2 material of the present invention uses a low-energy LED as a light source and can significantly increase the reaction rate of glycerol reforming to H2 and CO without high-temperature and high-pressure conditions. Under single-wavelength ultraviolet irradiation at 365 nm, the average evolution rates of H2 and CO reach 2542.6 and 361.7 μmol g -1 h -1 , respectively. The selectivity of the gaseous target product syngas is as high as 96.1%. The yields of H2 and CO are 17.2 and 14.9 times that of TiO2, respectively, demonstrating excellent photocatalytic performance and also having excellent stability and reusability.

[0016] The preparation method of the composite material of the present invention has a simple synthesis method, convenient operation, low cost, less equipment investment, low energy consumption and environmental pollution, is conducive to large-scale production, and conforms to the concepts of sustainable development and green chemistry. It can be used in the field of photocatalytic glycerol conversion. Description of the Drawings

[0017] Figure 1 XRD patterns of MIL-125 and Ni / MIL-125 prepared in Steps 1 and 3 of Example 1;

[0018] Figure 2 SEM images of MIL-125 and Ni / MIL-125 prepared in Steps 1 and 3 of Example 1;

[0019] Figure 3 SEM image of O-Ni2 / TiO2 prepared in Step 4 of Example 1;

[0020] Figure 4 TEM image of O-Ni2 / TiO2 prepared in Step 4 of Example 1;

[0021] Figure 5 Performance graph of photocatalytic glycerol reforming to syngas over O-Ni2 / TiO2 prepared in Step 4 of Example 1;

[0022] Figure 6 Comparison graph of photocatalytic glycerol reforming to syngas over O-Ni2 / TiO2 prepared in Step 4 of Example 1 with others;

[0023] Figure 7 Stability test graph of photocatalytic glycerol reforming to syngas over O-Ni2 / TiO2 prepared in Step 4 of Example 1. Figure 8 Stability test graph of photocatalytic glycerol reforming to syngas over the O-Ni2 / TiO2 catalyst prepared in Example 1. Detailed implementation manners

[0024] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] Example 1: The preparation method of the MOF-derived TiO2-supported Ni-O-Ni dimer catalyst in this example is carried out according to the following steps:

[0026] I. Add 1.5 g of terephthalic acid to 27 mL of N,N-dimethylformamide, stir at a speed of 500 revolutions per minute for 15 minutes, then add 3 mL of methanol, and continue to stir for 20 minutes; then add 0.75 mL of tetrabutyl titanate, and continue to stir at a speed of 500 revolutions per minute for 40 minutes to obtain a mixed solution; then transfer the obtained mixed solution to a 50 mL autoclave and maintain it at a temperature of 150 °C for 16 hours; after cooling to room temperature, filter, wash the solid phase twice with N,N-dimethylformamide and methanol respectively, and dry it in a vacuum drying oven for 12 hours to obtain MIL-125 powder;

[0027] II. Dissolve 20 mg of NiCl2·6H2O in 20 mL of deionized water to obtain solution A; dissolve 5 mg of oxalic acid in 20 mL of deionized water to obtain solution B; drop solution B into solution A under continuous stirring, and continue to stir for 2 hours after dropping to obtain solution C;

[0028] III. Add 0.5 g of MIL-125 powder into 50 mL of methanol, disperse it evenly by ultrasonic wave to obtain a MIL-125 suspension; then drop Solution C into the MIL-125 suspension, stir for another 4 hours after dropping, then centrifuge and wash the solid phase with ethanol to obtain a precursor, denoted as Ni2 / MIL-125;

[0029] IV. Place the precursor in a high-temperature furnace, heat it up to 450 °C at a rate of 2 °C / min and hold for 4 hours to obtain a MOF-derived TiO2-supported Ni-O-Ni dimer catalyst, denoted as O-Ni2 / TiO2.

[0030] The XRD patterns of MIL-125 prepared in Step 1 and Ni2 / MIL-125 prepared in Step 3 of Example 1 are as Figure 1 shown. It can be seen from Figure 1 that the addition of the Ni component does not change the crystal structure of MIL-125 itself.

[0031] The SEM images of MIL-125 and Ni2 / MIL-125 prepared in Steps 1 and 3 of Example 1 are as Figure 2 shown. a is MIL-125 and b is Ni2 / MIL-125. It can be seen from Figure 2 that the addition of the Ni component does not change the morphology of MIL-125 itself. Both MIL-125 and Ni2 / MIL-125 are in the shape of round cakes.

[0032] The SEM image of O-Ni2 / TiO2 prepared in Step 4 of this Example 1 is as Figure 3 shown. It can be seen from Figure 3 that after calcination, O-Ni2 / TiO2 retains the original round cake shape of Ni2 / MIL-125, but the size is reduced, which is caused by the loss of ligands during the calcination process.

[0033] The TEM image of O-Ni2 / TiO2 prepared in Step 4 of this Example 1 is as Figure 4 shown. It can be seen through TEM that O-Ni2 / TiO2 is in the shape of a round cake assembled by small particles.

[0034] In O-Ni2 / TiO2 prepared in Step 4 of this Example 1, there are Ni-O-Ni double atomic sites bridged by oxygen, as Figure 5 and shown in Table 1. Through synchrotron radiation fitting analysis, the existence of Ni-O-Ni double atomic sites is further determined.

[0035] Table 1 Synchrotron radiation display Figure 5 The fitting results

[0036]

[0037] Comparative Example 1: This comparative example is to prepare a Ni / TiO₂ catalyst. The specific method is carried out according to the following steps:

[0038] I. Add 1.5 g of terephthalic acid to 27 mL of N,N-dimethylformamide, stir at a speed of 500 revolutions per minute for 15 minutes, then add 3 mL of methanol, and continue to stir for 20 minutes. Then, add 0.75 mL of tetrabutyl titanate, stir at a speed of 500 revolutions per minute for 40 minutes to obtain a mixed solution; transfer the obtained mixed solution to a 50 mL high-pressure reaction kettle, and maintain it at 150 °C for 16 hours; after cooling to room temperature, filter, wash the solid phase twice with N,N-dimethylformamide and methanol respectively, and then dry it in a vacuum drying oven for 12 hours to obtain MIL-125 powder;

[0039] II. Dissolve 20 mg of NiCl₂·6H₂O in 20 mL of deionized water to prepare solution A; disperse 0.5 g of MIL-125 powder in 50 mL of methanol by ultrasonic wave until it is uniformly dispersed to obtain a MIL-125 methanol suspension; then slowly drop solution A into the MIL-125 methanol suspension, stir for another 4 hours, and then perform centrifugal separation. Wash the solid phase twice with ethanol to obtain a precursor;

[0040] III. Place the precursor in a high-temperature furnace, heat it to 450 °C at a rate of 2 °C / min and maintain it for 4 hours to obtain the catalyst Ni / TiO₂.

[0041] Comparative Example 2: This example is to prepare a TiO₂ catalyst. The specific method is carried out according to the following steps:

[0042] I. Add 1.5 g of terephthalic acid to 27 mL of N,N-dimethylformamide, stir at a speed of 500 revolutions per minute for 15 minutes, then add 3 mL of methanol, and stir for another 20 minutes. Then, add 0.75 mL of tetrabutyl titanate, and stir at a speed of 500 revolutions per minute for another 40 minutes. Transfer the obtained solution to a 50 mL high-pressure reaction kettle, and maintain it at 150 °C for 16 hours. After cooling to room temperature, filter, wash the solid phase twice with N,N-dimethylformamide and methanol respectively, and then dry it in a vacuum drying oven for 12 hours to obtain MIL-125 powder;

[0043] II. Place the MIL-125 powder in a high-temperature furnace, heat it to 450 °C at a rate of 2 °C / min and maintain it for 4 hours to obtain the catalyst TiO₂.

[0044] The O-Ni2 / TiO2 prepared in Example 1, the Ni / TiO2 prepared in Comparative Example 1, and the TiO2 prepared in Comparative Example 2 were used as photocatalysts for the photocatalytic glycerol reforming experiment. The specific process was as follows: A 30W LED lamp was used as the light source, and the photocatalytic glycerol reforming experiment was carried out in a 50 mL quartz reactor. 20 mg of the catalyst dispersion was added to 19 mL of deionized water, and 1 mL of glycerol was added; then the mixture was bubbled with Ar for 30 minutes and then exposed to light while maintaining Ar; subsequently, the yields of H2 and CO were measured by gas chromatography and the yields were calculated.

[0045] The performance graph of the O-Ni2 / TiO2 prepared in Example 1 for photocatalytic glycerol reforming to syngas is as Figure 6 shown. From Figure 6 it can be seen that O-Ni2 / TiO2 can continuously produce H2 and CO under continuous light illumination.

[0046] The comparison graph of the yields of the O-Ni2 / TiO2 prepared in Example 1, the Ni / TiO2 prepared in Comparative Example 1, and the TiO2 prepared in Comparative Example 2 for photocatalytic glycerol reforming to syngas is as Figure 7 shown. From Figure 7 it can be seen that the yields of H2 and CO of O-Ni2 / TiO2 are higher than those of TiO2 and Ni / TiO2. This is because the special Ni-O-Ni dimer in the catalyst enhances the adsorption ability of glycerol during the photocatalytic process, effectively inhibits the recombination of photo-generated electrons and holes, and increases the availability of active sites on the catalyst, which improves the photocatalytic performance. Under the irradiation of a single-wavelength ultraviolet light of 365 nm, the average evolution rates of H2 and CO of the O-Ni2 / TiO2 prepared in Example 1 reached 2542.6 and 361.7 μmol g -1 h -1 respectively, and the selectivity of the gas target product syngas was as high as 96.1%. The yields of H2 and CO were 17.2 and 14.9 times those of TiO2 respectively. In Example 1, oxalic acid chelation was used to form an oxygen-bridged diatomic Ni-O-Ni (O-Ni2 / TiO2) in MOF-derived TiO2 to regulate the local electronic structure of atomically dispersed Ni sites. Among them, the MOF-derived TiO2 support provides a highly porous structure to support the highly exposed active sites of Ni-O-Ni dimers connected by oxygen bridges. The Ni-O-Ni sites regulate the local electronic structure of the Ni sites and promote the adsorption and activation of reactant molecules. Thus, the O-Ni2 / TiO2 photocatalyst exhibits strong photocatalytic activity and selectivity in the glycerol reforming reaction.

[0047] The stability test of photocatalytic reforming of glycerol to syngas was carried out using the O-Ni2 / TiO2 catalyst prepared in Example 1. After the catalytic reaction, the catalyst was centrifuged at a high speed of 10,000 revolutions per minute for 5 minutes, then rinsed with ethanol and the catalyst was collected. The O-Ni2 / TiO2 obtained after drying in a vacuum drying oven was used for the cyclic stability test of photocatalytic reforming of glycerol to syngas. As Figure 8 shown, from Figure 8 it can be seen that O-Ni2 / TiO2 still maintained a high H2 and CO yield under 8 consecutive cycles.

[0048] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the 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 method for preparing a MOF-derived TiO2-supported Ni-O-Ni dimer catalyst, characterized in that The method proceeds as follows:

1. Add terephthalic acid to N,N-dimethylformamide, stir to dissolve, then add methanol, and continue stirring for 15 to 25 minutes; then add tetrabutyl titanate, and continue stirring for 30 to 50 minutes to obtain a mixed solution; then transfer the obtained mixed solution to a high-pressure reactor and keep it at a temperature of 140 to 160°C for 15 to 18 hours; after cooling to room temperature, filter, wash the solid phase with N,N-dimethylformamide and methanol, and vacuum dry to obtain MIL-125 powder; 2. Dissolve NiCl2·6H2O in deionized water to obtain solution A; dissolve oxalic acid in deionized water to obtain solution B; add solution B dropwise to solution A under continuous stirring, and continue stirring for 1.5 to 2.5 hours after the addition is complete to obtain solution C; 3. Add MIL-125 powder into methanol and disperse it evenly with ultrasound to obtain MIL-125 suspension; then drop solution C into the MIL-125 suspension, stir for 3.5 to 4.5 hours after the dropwise addition, and then centrifuge and wash the solid phase with ethanol to obtain a precursor; Fourth, the precursor is placed in a high temperature furnace, and the temperature is increased to 400-600°C at a rate of 2-5°C / min and maintained for 3.5-4.5 hours to obtain a MOF-derived TiO2-loaded Ni-O-Ni dimer catalyst, which is recorded as O-Ni2 / TiO2.

2. The method for preparing a MOF-derived TiO2-supported Ni-O-Ni dimer catalyst according to claim 1, characterized in that: In step 1, the ratio of the mass of terephthalic acid to the volume of N,N-dimethylformamide is 1 g:(15-20) mL.

3. The method for preparing a MOF-derived TiO2-supported Ni-O-Ni dimer catalyst according to claim 1 or 2, characterized in that: In step 1, the ratio of the mass of terephthalic acid, the volume of methanol, and the volume of tetrabutyl titanate is 1 g: (1.5-2.5): (0.2-0.3).

4. The method for preparing a MOF-derived TiO2-supported Ni-O-Ni dimer catalyst according to claim 1 or 2, characterized in that: The mass ratio of NiCl2·6H2O to oxalic acid in step 2 is (3-5):

1.

5. The method for preparing a MOF-derived TiO2-supported Ni-O-Ni dimer catalyst according to claim 1 or 2, characterized in that: The ratio of the mass of the MIL-125 powder described in step 3 to the volume of methanol is 1 g: (20-100) mL.

6. The method for preparing a MOF-derived TiO2-supported Ni-O-Ni dimer catalyst according to claim 1 or 2, characterized in that: The ratio of the mass of the MIL-125 powder described in step 3 to the molar number of Ni in solution C is 1 g: 0.1-0.2 mmol.

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