Preparation of metal copper organic framework material and application thereof in photocatalytic alcohol dehydrogenation to aldehyde

Abstract

The application discloses a kind of preparation of metal copper organic framework material and its application in the photocatalytic alcohol dehydrogenation preparation aldehyde. The application is loaded with metal copper as photocatalyst by metal organic framework (MOF), and alcohol compound is oxidized into corresponding aldehyde by high selectivity by light. The process can occur at room temperature, normal pressure, without oxidant, has more green, environmental protection advantage.

Description

Technical Field

[0001] The present invention belongs to the field of photocatalysis, and in particular relates to the preparation of a metallic copper organic framework material and its application in photocatalytic dehydrogenation of alcohols to produce aldehydes. Background Art

[0002] Formaldehyde is a critical chemical raw material, playing an irreplaceable role in industries such as plastics, coatings, pharmaceuticals, and textiles. With the development of industrialization and urbanization, the demand for formaldehyde and its derivatives continues to grow, driving the research and optimization of formaldehyde production technologies. Currently, formaldehyde is primarily produced using methanol as a raw material. Formaldehyde is produced by catalytic oxidation of methanol in an oxygen atmosphere. Because methanol oxidation is an exothermic reaction, it is typically performed at temperatures above 600°C. Furthermore, formaldehyde is highly susceptible to oxidation, and the reaction is carried out in an oxidizing atmosphere with the presence of O2, which can easily lead to over-oxidation of the formaldehyde, producing byproducts such as formic acid, carbon monoxide, and carbon dioxide. Overall, traditional methods for producing formaldehyde suffer from high energy consumption and numerous byproducts, resulting in high costs and environmental pollution. Therefore, developing a novel method to produce formaldehyde through the oxidation of methanol under mild conditions and without the use of strong oxidants is highly desirable.

[0003] Acetaldehyde is also an important chemical raw material, widely used in industries such as plastics, fragrances, pharmaceuticals, and dyes. With the continuous expansion of industrialization and consumer markets, the demand for acetaldehyde and its derivatives is also growing, driving research and innovation in acetaldehyde production technologies. Currently, acetaldehyde is mainly produced from ethanol via catalytic oxidation under high-temperature conditions. However, the high temperatures required for ethanol oxidation (typically above 300°C) result in high energy consumption. Furthermore, acetaldehyde is easily further oxidized to acetic acid or completely decomposed into carbon dioxide and water, resulting in the formation of numerous byproducts, reducing product selectivity and economics while also increasing the environmental burden. Therefore, developing a novel pathway for ethanol oxidation to acetaldehyde under mild conditions using photocatalytic technology is of great significance. Photocatalytic reactions utilize sunlight or artificial light as their energy source, do not require strong oxidants, and can proceed at room temperature, significantly reducing energy consumption. Furthermore, the design of suitable catalyst systems has the potential to improve acetaldehyde selectivity and reduce byproduct formation.

[0004] In summary, the photocatalytic oxidation of methanol to formaldehyde and ethanol to acetaldehyde not only effectively reduces energy consumption and environmental pollution during the production process, but also significantly improves reaction selectivity and reduces the formation of byproducts. This direct photocatalytic conversion of alcohols to aldehydes is green, efficient, and sustainable, and holds significant research significance and application prospects for modern chemical production. Summary of the Invention

[0005] This invention addresses the high energy consumption, environmental pollution, and use of strong oxidants in traditional industrial aldehyde production. It provides a method for preparing a copper-based organic framework (MOF) and its application in the photocatalytic dehydrogenation of alcohols to aldehydes. This invention utilizes a copper-loaded metal-organic framework (MOF) as a photocatalyst to selectively oxidize alcohols to their corresponding aldehydes under illumination. This process occurs at room temperature and pressure, without the need for oxidants, offering the advantages of being more environmentally friendly.

[0006] The method for preparing the metallic copper organic framework material of the present invention comprises the following steps:

[0007] Step 1: Tetrabutyl titanate and 1,4-benzenedicarboxylic acid are added to a mixed solvent consisting of anhydrous N,N-dimethylformamide (DMF) and anhydrous methanol, and ultrasonically dispersed uniformly; the resulting mixture is placed in a 20 mL high-pressure reactor and heated. After cooling to room temperature, the product is collected by centrifugation and washed three times with anhydrous DMF and anhydrous methanol respectively. The collected solid is dried under vacuum and vacuum activated to obtain MIL-125.

[0008] Step 2: The MIL-125(Ti) obtained in step 1 was uniformly dispersed in methanol by ultrasonication, and the mixture was transferred to a photocatalytic quartz reactor. The reactor was then filled with inert gas, and the reactor was irradiated with a xenon lamp for a period of time. After that, the irradiation was stopped and CuCl2 solutions of different concentrations were injected. After stirring, the mixture was transferred to a centrifuge tube for centrifugal separation, and the product Cu was obtained after drying. X -MIL-125.

[0009] In step 1, the temperature of the heating reaction in the high-pressure reactor is 130° C., the reaction time is 15 h, and the heating rate is 2-8° C. / min.

[0010] In step 2, the reactor was irradiated with a 300 W xenon lamp for 0.5 h, and then the illumination was stopped and CuCl2 solutions of different concentrations were injected. After stirring, the mixture was transferred to a centrifuge tube and centrifuged. After drying, the product Cu X -MIL-125.

[0011] The present invention introduces copper (Cu) with different metal loadings into the metal organic framework material (MIL-125), denoted as Cu x -MIL-125 (x = 0, 0.8, 1.6, 2.0), using MIL-125 to generate an intermediate state with high reducing properties under light conditions to achieve the reduction loading of Cu and avoid the use of reducing reagents.

[0012] Furthermore, the loading of Cu on the MOF material can be controlled by controlling the amount of precursor added, with x=0.8-2.0, preferably x=0.8-1.6.

[0013] The invention discloses an application of the metal copper organic framework material in photocatalytic dehydrogenation of alcohol compounds to produce aldehydes.

[0014] The alcohol compounds include methanol, ethanol and the like.

[0015] The 10 mg Cu X -MIL-125 material (x=0.8-1.6) was placed in 10 mL of anhydrous alcohol compound and ultrasonically dispersed evenly. The mixture was transferred to a photocatalytic quartz reactor, filled with inert gas, and irradiated with a 300 W xenon lamp for 2 h. The gas phase product was detected by gas chromatography, and the liquid phase product was quantitatively detected by nuclear magnetic resonance.

[0016] There are several traditional methods for introducing metals into Ti-MOF: 1. Doping method: During the synthesis of Ti-MOF, the precursors of other metals (such as Zn 2+ 、Fe 3+ 、Cu 2+ 1. The first method is to add metal salts (such as metal salts) to form multi-metal nodes or mixed metal clusters. Since the metal is added during the synthesis stage, the crystal structure of the MOF will be unstable. 2. Impregnation method: The synthesized Ti-MOF is immersed in a solution containing the target metal, and the metal is loaded into the MOF structure through the combination of the metal and the coordination sites in the framework (such as carboxylic acid groups and hydroxyl groups). However, this method will cause uneven distribution of metal ions and the loading capacity is limited. 3. Vapor deposition method: The metal atomic layer is precisely deposited on the surface or inside of the Ti-MOF through chemical vapor deposition technology. Although highly uniform metal distribution can be achieved, the equipment requirements are high and expensive. 4. Reduction method: The Ti-MOF is immersed in a metal salt solution, and then the metal is reduced to nanoparticles loaded on the surface or pores of the MOF through a reducing agent (such as NaBH4) or heat treatment. However, thermal decomposition may destroy the unique pore structure of the MOF, resulting in reduced catalytic activity.

[0017] This catalytic material is created by introducing Cu metal into pre-synthesized MIL-125 (Ti). Unlike doping methods, which introduce metal during the synthesis phase, this method preserves the MOF's overall structure without disrupting its crystallinity. Furthermore, the invention utilizes MIL-125 to generate highly reducing intermediate species upon illumination, exposing unsaturated coordination sites at specific locations. This allows for precise control of the metal anchoring position. Furthermore, the metal anchoring process does not require high-temperature treatment and is inexpensive.

[0018] In addition, the metal copper organic framework material of the present invention can not only smoothly realize the photocatalytic dehydrogenation of methanol to formaldehyde, but also realize the photocatalytic dehydrogenation of ethanol to acetaldehyde. Those skilled in the art know that ethanol is more difficult to dehydrogenate than methanol. On the one hand, from the perspective of thermal catalysis, ethanol is more stable than methanol because the bond energy of the CH bond in ethanol is higher; furthermore, the activation energy of the ethanol dehydrogenation reaction is also higher than that of methanol. On the other hand, from the perspective of photocatalysis, the photocatalytic reaction requires the effective separation and transfer of electron-hole pairs. The smaller molecular size and simple electronic structure of methanol may be more suitable for the energy level matching of the photocatalyst. However, the complex structure of ethanol may lead to a longer electron transfer path or unsatisfactory energy matching, thereby reducing the photocatalytic efficiency.

[0019] The reason why the copper-based organic framework material of the present invention can simultaneously realize the photocatalytic dehydrogenation of methanol and ethanol to formaldehyde and acetaldehyde is:

[0020] First, the conduction band (CB) and valence band (VB) energy structures of the catalysts have sufficient driving force for the dehydrogenation of methanol and ethanol: the conduction band electrons can participate in the reduction reaction (e.g., reducing H + The holes in the valence band have sufficient oxidizing power to effectively extract electrons from methanol and ethanol molecules, initiating the dehydrogenation reaction.

[0021] Secondly, Ti-MOF catalysts generally absorb a wide range of light (including ultraviolet, visible, and even near-infrared light), providing sufficient photogenerated electrons and holes for different reactions. While methanol and ethanol may require different energy, the photocatalyst, through efficient light absorption, can generate sufficient electron-hole pairs to activate both molecules. Furthermore, the rational use of Cu in this invention modifies the catalyst's band gap structure, improving its utilization of visible light.

[0022] Taking ethanol as an example, during the photocatalytic reaction of the metal copper organic framework material of the present invention, light is irradiated to the Ti-based catalyst to generate electron-hole pairs, and at the same time, ethanol is adsorbed on the Cu active site. Then, the photogenerated holes attack the α-CH of ethanol, and ethanol loses an H atom to generate an intermediate ethoxy group adsorbed on the Cu active site. The intermediate ethoxy group further loses the H atom on the hydroxyl group on Cu to generate acetaldehyde, and the two lost protons obtain photogenerated electrons to obtain H2.

[0023] The present invention demonstrates, through cyclic experiments, that the catalyst does not deactivate. First, unlike thermal catalysis, photocatalysis operates under mild conditions, making it less susceptible to thermal aggregation that can damage the catalyst structure. Second, because the metal position can be precisely controlled, the Cu atoms precisely coordinate with the oxygen atoms on the Ti-O clusters to form a stable structure, ensuring a stable catalytic reaction.

[0024] The beneficial effects of the present invention are embodied in:

[0025] 1. The present invention is a metal organic framework material based on MIL-125. This type of material has the characteristics of rich pore size and low density, and has good industrial application prospects.

[0026] 2. The present invention utilizes MIL-125 to generate intermediate species with high reducing ability after light exposure to achieve metal reduction. Unlike the traditional impregnation-reduction method, it does not require the use of reducing agents such as H2.

[0027] 3. The present invention uses light to selectively oxidize alcohols to their corresponding aldehydes. This process occurs at room temperature and atmospheric pressure, without the need for oxidants, making it more environmentally friendly than traditional industrial methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The Cu prepared by introducing metal into the metal organic framework structure of the present invention X -PXRD of MIL-125 catalyst material.

[0029] Figure 2 The Cu prepared by introducing metal into the metal organic framework structure of the present invention X -SEM image of MIL-125 catalyst material.

[0030] Figure 3 The Cu prepared by introducing metal into the metal organic framework structure of the present invention X -MIL-125 catalyst material is used for UV-visible spectroscopic analysis.

[0031] Figure 4 The Cu prepared by introducing metal into the metal organic framework structure of the present invention X - Liquid product selectivity diagram of the MIL-125 catalyst material used in the methanol dehydrogenation to formaldehyde reaction.

[0032] Figure 5 The Cu prepared by introducing metal into the metal organic framework structure of the present invention X - Cycle diagram of the methanol dehydrogenation to formaldehyde reaction using MIL-125 catalyst material.

[0033] Figure 6 The Cu prepared by introducing metal into the metal organic framework structure of the present invention X - Cycle diagram of the MIL-125 catalyst material used in the dehydrogenation of ethanol to acetaldehyde reaction. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further analyzed and explained below through specific embodiments.

[0035] Example 1: Composite material based on the introduction of metal into a metal organic framework structure

[0036] (1) Preparation method

[0037] 1. Preparation of MIL-125

[0038] 0.3 mL of tetrabutyl titanate and 0.6 g of 1,4-benzenedicarboxylic acid were added to 9 mL of anhydrous N,N-dimethylformamide (DMF) and 1.2 mL of anhydrous methanol and ultrasonically dispersed uniformly. The resulting mixture was placed in a 20 mL high-pressure reactor and heated at 130 °C for 15 h. After cooling to room temperature, the product was collected by centrifugation and washed three times with anhydrous DMF and anhydrous methanol respectively. The collected solid was vacuum activated at 120 °C to obtain MIL-125 for use.

[0039] 2. Cu at specific metal anchoring sites X -Preparation of MIL-125 catalyst materials

[0040] Accurately weigh 20 mg of purified MIL-125 material and place it in 10 mL of anhydrous methanol. Ultrasonication is then used to thoroughly disperse the material in the methanol solution to form a uniform mixed solution. During the dispersion process, the sample can be placed in an ice bath to prevent prolonged ultrasonication from heating the solution.

[0041] Next, the evenly dispersed mixture is carefully transferred to a photocatalytic quartz reactor for the photocatalytic reaction. A high-purity inert gas (such as nitrogen or argon) is introduced into the reactor to remove oxygen or other impurities, ensuring a completely inert environment. Subsequently, a 300W xenon lamp is used as a light source to illuminate the mixture in the reactor for 0.5 hours. During this process, the light energy provided by the xenon lamp excites the MIL-125 material, prompting it to produce highly reducing intermediate species, thus preparing for the subsequent introduction of metal ions.

[0042] After the illumination is complete, the light source is turned off and different concentrations of CuCl2 solution are injected into the reaction system according to the experimental design. To ensure that the CuCl2 solution is in full contact with the MIL-125 material, rapid magnetic stirring is performed to allow the copper ions in the solution to be effectively adsorbed into the MIL-125 framework and reduced.

[0043] The mixed solution is then transferred from the reactor to a centrifuge tube and centrifuged using a high-speed centrifuge to ensure complete separation of the solid product and the supernatant. The separated solid product is then washed multiple times with an anhydrous solvent to remove excess copper ions and residual solvent adsorbed on the surface of the material.

[0044] Finally, the separated solid product is dried at low temperature (usually dried in a vacuum drying oven at 60-80°C for several hours) to obtain the target product Cu doped with copper ions. X After drying, the product can be collected and sealed for storage for further photocatalytic performance research or structural characterization analysis.

[0045] (2) Testing

[0046] 1. The obtained Cu with different loadings X -MIL-125 was characterized by PXRD, and the results were as follows Figure 1 As shown. Figure 1 It can be seen that the Cu X -MIL-125 crystal form remains intact, proving that the Cu prepared by the present invention X -MIL-125 material is structurally correct and the crystal structure is not disrupted after anchoring the metal.

[0047] 2. The obtained Cu with different loadings X -MIL-125 was tested for metal loading by ICP, and the results are shown in Table 1. Table 1 shows the Cu prepared by introducing metal into the metal organic framework structure of the present invention. X - ICP results of MIL-125 catalyst material. As shown in Table 1, by adjusting the concentration of different CuCl2 solution precursors, the loading of Cu can be accurately adjusted, which proves that the Cu prepared by the present invention X -MIL-125 material has the characteristics of precise and adjustable metal loading.

[0048]

[0049] 3. The obtained Cu with different loadings X -MIL-125 was characterized by scanning electron microscopy. Figure 2 As shown. Figure 2 It can be seen that the morphology of the MOF of the present invention can still be maintained after the introduction of Cu metal.

[0050] 4. The obtained Cu with different loadings X -MIL-125 was characterized by UV-visible spectrophotometry, and the results were as follows Figure 3 As shown. Figure 3 It can be seen that the material has good potential for solar energy utilization, proving that the Cu prepared by the present invention X -MIL-125 material has the characteristics of being applicable to photocatalytic reactions.

[0051] 5. The obtained Cu with different loadings X -MIL-125 was used to detect the gas phase products of methanol dehydrogenation to formaldehyde by GC and the liquid phase products by NMR or UV-visible spectrophotometry. The results are shown in Table 2. As can be seen from Table 2, under nitrogen atmosphere, different loadings of Cu X Using MIL-125 as the catalyst and methanol or ethanol as the solvent, the reaction was irradiated for 2 hours. The H2 yield was monitored by GC, and the formaldehyde or acetaldehyde yields were measured by NMR or UV-visible spectrophotometry. The results showed: 1. Cu-anchored MIL-125 significantly improved its activity in both the methanol dehydrogenation to formaldehyde and the ethanol dehydrogenation to acetaldehyde reactions compared to the original MIL-125 (Ti). 2. With increasing Cu loading, the reaction activity exhibited a volcano-shaped curve, reaching peak activity at a loading of 1.6%.

[0052] 6. The highest activity Cu 1.6 -MIL-125 was used to detect the yield of aldehyde compounds by NMR or UV-visible spectrophotometry. The results were as follows: Figure 4 As shown. Figure 4 As shown in Figure 2, the catalyst still maintains good activity and selectivity after the cyclic experiment is carried out to the third round. X -MIL-125 material can be recycled as a catalyst for the dehydrogenation of alcohols to produce aldehydes.

[0053] Example 2: Application of the MOF material prepared by the present invention in the dehydrogenation of alcohols to produce aldehydes

[0054] (I) Effect of different Cu loading catalysts

[0055] Method: Take Cu X 10 mg of MIL-125 catalyst material and 10 mL of anhydrous methanol or anhydrous ethanol were added to a 160 mL photocatalytic quartz reactor and irradiated with a 300 W xenon lamp for 2 h. Hydrogen was detected by gas chromatography and formaldehyde by nuclear magnetic resonance. The reaction equation is as follows.

[0056]

[0057] Table 2 is the Cu prepared after introducing metal into the metal organic framework structure of the present invention. X -Product activity of methanol dehydrogenation to formaldehyde reaction using MIL-125 catalyst material.

[0058]

[0059] Table 3 is the Cu prepared after the metal is introduced into the metal organic framework structure of the present invention. X-Product activity of MIL-125 catalyst material in the dehydrogenation of ethanol to acetaldehyde.

[0060]

[0061] The volcano-shaped curve of the reaction activity may be due to the fact that metals generally act as electron traps or facilitate electron-hole separation in photocatalysis. However, if the metal loading is too high, the excess metal sites will become recombination centers for electron-hole pairs, leading to rapid recombination of photogenerated carriers and significantly reducing the photocatalytic performance.

[0062] (2) Recyclability of catalyst

[0063] Catalyst recovery: After the reaction is completed, filter to separate the catalyst from the reaction mixture, filter out, and dry.

[0064] Specific operation of the cycle experiment: take the most active Cu 1.6 -MIL-125 catalyst material 10 mg and anhydrous methanol 10 mL were added into a 160 mL photocatalytic quartz reactor respectively. After irradiation with a 300 W xenon lamp for 2 h, the H2 yield was detected by GC, and the formaldehyde or acetaldehyde yield was detected by nuclear magnetic resonance or UV-visible spectrophotometry.

[0065] like Figure 5 and Figure 6 As shown in the figure, the catalyst still maintains good activity and selectivity after the cyclic experiment is carried out to the third round. X -MIL-125 catalyst material can be recycled as a catalyst for the dehydrogenation of alcohols to produce aldehydes.

Claims

1. A method for preparing a metallic copper organic framework material, characterized in that The steps include: Step 1: Tetrabutyl titanate and 1,4-benzenedicarboxylic acid are added to a mixed solvent consisting of anhydrous N,N-dimethylformamide and anhydrous methanol, and ultrasonically dispersed uniformly; the resulting mixture is placed in an autoclave and heated, cooled to room temperature, and the product is collected by centrifugation and washed with anhydrous DMF and anhydrous methanol, respectively. The collected solid is dried under vacuum and vacuum activated to obtain MIL-125(Ti); Step 2: The MIL-125(Ti) obtained in step 1 was uniformly dispersed in methanol by ultrasonication, and the mixture was transferred to a photocatalytic quartz reactor. The reactor was then filled with inert gas, and the reactor was irradiated with a xenon lamp for a period of time. After that, the irradiation was stopped and CuCl2 solutions of different concentrations were injected. After stirring, the mixture was transferred to a centrifuge tube for centrifugal separation, and the product Cu was obtained after drying. X -MIL-125.

2. The preparation method according to claim 1, wherein: In step 1, the temperature of the heating reaction in the high-pressure reactor is 130° C., the reaction time is 15 h, and the heating rate is 2-8° C. / min.

3. The preparation method according to claim 1, wherein: In step 2, the reactor was irradiated with a 300 W xenon lamp for 0.5 h, then the illumination was stopped and CuCl2 solutions of different concentrations were injected. The Cu loading amount was controlled by controlling the amount of precursor CuCl2 added.

4. The preparation method according to claim 3, wherein: The Cu loading is 0.8%-2.0%.

5. The preparation method according to claim 3, wherein: The Cu loading is 0.8%-1.6%.

6. Use of the metallic copper organic framework material prepared by the preparation method according to any one of claims 1 to 5 in photocatalytic dehydrogenation of alcohol compounds to produce aldehydes.

7. The use according to claim 6, characterized in that: The alcohol compound includes one or more of methanol and ethanol.

8. The use according to claim 6 or 7, characterized in that: The metal copper organic framework material Cu X -MIL-125 is placed in anhydrous alcohol compounds and ultrasonically dispersed evenly. The mixture is transferred to a photocatalytic quartz reactor, inert gas is filled into the reactor, and the reactor is irradiated with a xenon lamp to carry out photocatalytic dehydrogenation reaction.

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