Preparation and application of rare earth MOF-based hindered Lewis acid-base pair for hydrogenation

Abstract

The invention discloses preparation and application of a rare earth MOF (Metal Organic Framework)-based hindered Lewis acid-base pair for hydrogenation, and belongs to a preparation technology of a nano catalytic material. According to the preparation method, in the synthesis process of rare earth MOF, a proper amount of transition metal is introduced to serve as a doping agent, rare earth-transition bimetallic MOFs with adjustable defects and morphology are synthesized, and hindered Lewis acid-base pairs serving as active sites can be effectively used for DCPD hydrogenation. Through heteroatom doping and defect engineering technologies, RE-MOF lattice distortion is induced while a second metal active site is introduced, so that the catalytic performance of the material is improved. RE-X-BTC (wherein X represents a doped transition metal, and BTC represents trimesic acid) shows enhanced Lewis acid-base characteristics and hydrogen adsorption and desorption characteristics, and selective hydrogenation of a substrate is realized by precisely regulating and controlling reaction conditions. The implementation of the invention provides a new way for the application of the porous MOF in the field of hydrogenation catalysis.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of nano-catalytic materials and the application of dicyclopentadiene (DCPD) hydrogenation, and particularly relates to a preparation method of a rare earth MOF-based frustrated Lewis pair for hydrogenation. Background Art

[0002] As a key component in the C5 fraction of petroleum processing, dicyclopentadiene (DCPD) exhibits its application value in multiple fields such as pesticide manufacturing, the rubber industry, and the production of unsaturated resins. In recent years, technological progress has promoted the expansion of DCPD into the fields of new polymer materials and fine chemicals. Among them, endo-tetrahydrodicyclopentadiene (endo-THDCPD) obtained by the hydrogenation conversion of DCPD has attracted much attention as a high-density fuel due to its excellent performance. However, in the field of DCPD hydrogenation technology, the application of traditional noble metals, transition metals, or alloy catalysts faces problems such as high costs (due to large usage amounts) and easy agglomeration and deactivation, which have become the key challenges in the application of DCPD hydrogenation reactions.

[0003] In recent years, metal-organic framework materials (MOFs) have become ideal porous carriers for active components due to their high specific surface area, unique electronic properties, and adjustable structures, effectively improving metal dispersion and atomic utilization. Although many progresses have been made in the research on MOFs, it still relies on the additional loading of noble metals or transition metals and requires high-temperature treatment or the use of strong reducing agents for reduction. The preparation process is cumbersome, and the stability of the materials has become an urgent problem to be solved, especially the frequent occurrence of MOF structure collapse and metal leaching. In addition, the number of active sites of single-metal MOF materials is limited and the thermal stability is insufficient, making it difficult to meet the requirements of the dicyclopentadiene hydrogenation reaction. Traditional homogeneous frustrated Lewis pairs (FLPs) have attracted much attention as new hydrogenation active substances, but their characteristics of non-recyclability and sensitivity to reaction conditions have greatly limited their practical applications. Currently, using the unique porous structure of MOF carriers to encapsulate functional hydrogenation sites (FLPs) provides a new opportunity to significantly reduce the usage amounts of noble metals and transition metals and simultaneously improve the selectivity of hydrogenation reactions. However, the implementation of this innovative strategy faces multiple challenges: First, it is necessary to precisely embed large Lewis acid-base molecules into the pore structure of MOFs. This process not only encounters significant molecular diffusion resistance but also poses extremely strict requirements on the size, shape, and surface properties of MOF pores. In addition, its synthesis steps are complex and cumbersome, and it is extremely difficult to precisely control the material structure, especially the uniform distribution of active sites is difficult to effectively control. These problems together constitute the bottleneck hindering its large-scale industrial production and application.

[0004] In view of this, the development of a MOF catalytic material with both low cost, high DCPD hydrogenation activity and selectivity, and high stability has become an urgent need to promote the efficient research and development of dicyclopentadiene hydrogenation catalytic materials. Summary of the Invention

[0005] To solve the problems existing in the prior art, the present invention provides a simple preparation method for constructing frustrated Lewis pairs in a porous rare earth MOF system. Based on the highly stable rare earth MOF, a heteroatom doping and defect construction strategy is adopted, and transition metals are introduced into the rare earth MOF metal clusters by a solvothermal method to obtain a rare earth-transition bimetallic MOF material with frustrated Lewis acid-base sites and secondary metal sites, which can not only realize the intrinsic MOF catalytic performance for DCPD hydrogenation, but also be produced and applied at low cost and on a large scale.

[0006] The preparation method of the present invention is as follows:

[0007] Dissolve rare earth nitrate and transition metal nitrate in a mixed solvent of N,N-dimethylformamide, ethanol and water, wherein the total molar amount (M) of rare earth nitrate and transition metal nitrate is 2-6 mmol, and the ratio is 10-a:a (1≤a≤5). After stirring and dissolving, add trimesic acid ligand, and the amount of trimesic acid ligand (L) is added to the reaction system according to M:L = 1:4-6, and the molar amount is 0.012-0.04 mol. Continue to stir the mixture to obtain a uniform mixed solution. Pour it into a polytetrafluoroethylene reaction kettle and place it in an oven for high-temperature solvothermal reaction. The obtained product is centrifuged, washed and then dried to obtain a rare earth-transition bimetallic MOFs catalytic material RE-X-BTC, and finally vacuum activation pretreatment is carried out to obtain RE-X-BTC-T.

[0008] Further, the rare earth nitrate is one of lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, praseodymium nitrate hexahydrate, neodymium nitrate hexahydrate, europium nitrate hexahydrate, gadolinium nitrate hexahydrate, dysprosium nitrate hexahydrate, ytterbium nitrate pentahydrate, and yttrium nitrate hexahydrate.

[0009] Further, the transition metal nitrate is one of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, copper nitrate trihydrate, and zinc nitrate hexahydrate.

[0010] Further, the amount of the mixed solvent (V) is added according to M:V = 1:10-15, and the volume ratio of the solvents N,N-dimethylformamide, ethanol and water is 1:1:1.

[0011] Further, the stirring is carried out with a magnetic stirrer for 30-60 min to dissolve the reagents, and the continuous stirring time is 20-30 min.

[0012] Further, the conditions for the high-temperature solvothermal reaction in the reactor are that the heating rate of the oven is 2-10 °C / min, the reaction temperature is 150-180 °C, and it is maintained in the oven for 24-48 h.

[0013] Further, for the washing, the product is first washed with DMF 3-5 times, and then washed with deionized water 8-10 times. The solvent amount used for each washing is 5M mL (2 ≤ M ≤ 6). For the drying, it is dried in an oven at 60-80 °C for 12-24 h.

[0014] Further, the temperature (T) for the vacuum activation pretreatment is 120-200 °C, and the treatment time is 3-12 h.

[0015] The obtained rare-earth-transition bimetallic MOFs catalytic material RE-X-BTC-T is used for the hydrogenation reaction of dicyclopentadiene.

[0016] In the present invention, by regulating the types of rare-earth metals and transition metals, and utilizing the coordination ability and ionic radius difference between rare-earth metals and transition metals, frustrated Lewis acid-base sites and second-metal adsorption sites are constructed in the MOF framework structure, enhancing the effective adsorption and activation of active sites for H2 and the C=C double bond in DCPD, and realizing the hydrogenation catalysis of rare-earth-transition bimetallic MOFs for DCPD.

[0017] In the present invention, by changing the dosages of rare-earth metals and transition metals, the growth kinetic process and defect content of MOFs are effectively regulated, and the localized X-O-RE basic unit is introduced, effectively optimizing the distribution of unsaturated sites and electronic interactions, and showing enhanced Lewis acid-base characteristics and hydrogen adsorption / desorption characteristics. Therefore, the complete conversion of the substrate can be achieved under mild reaction conditions while maintaining good cyclic stability.

[0018] The advantages of the present invention are as follows:

[0019] 1) Compared with the traditional homogeneous catalytic system, constructing a Lewis acid-base pair catalytic system in the porous rare-earth MOF system is relatively simple and stable, and it is easy to regulate the steric hindrance and electronic effects, greatly enhancing the DCPD hydrogenation activity of rare-earth MOFs.

[0020] 2) Regulating the types and dosages of the two metals can effectively regulate the defects and morphologies of the rare-earth-transition bimetallic MOFs catalytic material, and can realize the controllable regulation of the electronic state, acid-base characteristics, and catalytic activity of the active components.

[0021] 3) The catalytic material can be obtained only through a one-step solvothermal method in this preparation method, avoiding the loading process of additional metal elements or homogeneous FLPs. It not only has a simple process, controllable parameters, and a short cycle, but also ingeniously prevents structural damage, achieving a balance between catalytic activity and stability, and is suitable for low-cost and large-scale production of catalysts. Description of the Drawings

[0022] Figure 1 SEM photograph of Nd5-Ni5-BTC obtained in Example 4.

[0023] Figure 2 TEM photograph of Nd5-Ni5-BTC obtained in Example 4.

[0024] Figure 3 XRD pattern of Nd5-Ni5-BTC obtained in Example 4. Detailed Implementation Modes

[0025] The technical solutions of the present invention will be further described below in conjunction with specific implementation modes.

[0026] Example 1

[0027] First, 0.87 g of praseodymium nitrate hexahydrate and 0.58 g of nickel nitrate hexahydrate (molar ratio 5:5) were dissolved in 45 ml of a mixed solvent (N,N-dimethylformamide:ethanol:water = 1:1:1), and stirred with a magnetic stirrer for 30 min. After the reagents were dissolved, 0.024 mol of trimesic acid ligand was added, and the mixture was stirred for another 30 min to obtain a homogeneous mixed solution. Then the solution was poured into a 100 mL polytetrafluoroethylene reaction kettle, and the temperature was raised to 180 °C at a rate of 5 °C / min in an oven and maintained for 30 h. The obtained product was centrifuged and washed, first washed 4 times with DMF, and then washed 9 times with deionized water, with a solvent volume of 20 mL for each washing. After washing, it was dried in a vacuum oven at 80 °C for 12 h to obtain the Pr5-Ni5-BTC sample, without the need to be treated with a strong reducing agent such as sodium borohydride. Vacuum activation can be carried out before the hydrogenation test. Take 50 mg of the sample and activate it in a vacuum oven at 120 °C for 6 h to obtain Pr5-Ni5-BTC-120.

[0028] DCPD hydrogenation performance test: Weigh 0.02 g of the powdered catalyst and add it to a high-pressure hydrogenation reactor. Then add 5 mL of methanol solvent and 200 μL of DCPD substrate. Seal the reactor and repeatedly purge it with H2 three times to remove air. Subsequently, set the H2 reaction pressure of the reactor to 2 MPa, the reaction temperature to 100 °C, the reaction time to 10 h, and the stirring speed to 600 rpm. After the catalytic reaction is completed, centrifuge and separate the catalyst and the solvent. Take the supernatant, dilute it with methanol solvent, and analyze the product composition by GC-MS (gas chromatography-mass spectrometry). For the Pr5-Ni5-BTC sample, its Ni content is only 2.3 wt%, the DCPD conversion rate is 90.6%, the selectivity of the dihydro product DHDCPD is 89.1%, and the selectivity of the tetrahydro product THDCPD is 10.9%. For the Pr5-Ni5-BTC-120 sample, its DCPD conversion rate is 100%, the selectivity of the dihydro product DHDCPD is 88.2%, and the selectivity of the tetrahydro product THDCPD is 11.8%.

[0029] Example 2

[0030] The synthesis steps are the same as those in Example 1, where the metal dosage is adjusted to 1.04 g of praseodymium nitrate hexahydrate and 0.47 g of nickel nitrate hexahydrate (molar ratio 6:4), and the Pr6-Ni4-BTC sample can be obtained. Before the hydrogenation test, vacuum activation can be carried out. Take 50 mg of the sample and activate it in a vacuum oven at 120 °C for 6 h to obtain Pr6-Ni4-BTC-120.

[0031] DCPD hydrogenation performance test: The test steps are the same as those in Example 1. For the Pr6-Ni4-BTC sample, its DCPD conversion rate is 79.8%, the selectivity of the dihydro product DHDCPD is 95.9%, and the selectivity of the tetrahydro product THDCPD is 4.1%. For the Pr6-Ni4-BTC-120 sample, its DCPD conversion rate is 98.5%, the selectivity of the dihydro product DHDCPD is 95.6%, and the selectivity of the tetrahydro product THDCPD is 4.4%.

[0032] Example 3

[0033] The synthesis steps are the same as those in Example 1, where the metal dosage is adjusted to 1.56 g of praseodymium nitrate hexahydrate and 0.12 g of nickel nitrate hexahydrate (molar ratio 9:1), and the Pr9-Ni1-BTC sample can be obtained. Before the hydrogenation test, vacuum activation can be carried out. Take 50 mg of the sample and activate it in a vacuum oven at 120 °C for 6 h to obtain Pr9-Ni1-BTC-120.

[0034] DCPD hydrogenation performance test: The test procedure is the same as that in Example 1. For the Pr9-Ni1-BTC sample, its DCPD conversion rate is 23.7%, the selectivity of the dihydro product DHDCPD is 99.9%, and the selectivity of the tetrahydro product THDCPD is 0.1%. For the Pr9-Ni1-BTC-120 sample, its DCPD conversion rate is 72.5%, the selectivity of the dihydro product DHDCPD is 94.3%, and the selectivity of the tetrahydro product THDCPD is 5.7%.

[0035] Example 4

[0036] The synthesis procedure is the same as that in Example 1, where the metal and its dosage are adjusted to 0.88 g of neodymium nitrate hexahydrate and 0.58 g of nickel nitrate hexahydrate (molar ratio 5:5), and the Nd5-Ni5-BTC sample can be obtained. Vacuum activation can be carried out before the hydrogenation test. Take 50 mg of the sample and activate it in a vacuum oven at 120 °C for 6 h to obtain Nd5-Ni5-BTC-120. Figure 1 It can be seen from the scanning electron microscope (SEM) image that the prepared Nd5-Ni5-BTC is a flower-like morphology formed by the stacking of lamellae, and the size is relatively large, about 30 - 50 μm. Figure 2 It can be seen from the transmission electron microscope (TEM) image that Ni metal is uniformly incorporated into the Nd-BTC framework structure, and no obvious Ni nanoparticles are generated. Figure 3 It can be seen from the XRD pattern of that Nd5-Ni5-BTC has good crystallinity and forms a monoclinic symmetric structure.

[0037] DCPD hydrogenation performance test: The test procedure is the same as that in Example 1. For the Nd5-Ni5-BTC sample, its Ni content is only 0.91 wt%, its DCPD conversion rate is 100%, the selectivity of DHDCPD is 89.7%, and the selectivity of THDCPD is 10.3%. After centrifuging the catalyst, it is centrifugally washed with methanol 3 times and then transferred to a high-pressure hydrogenation reactor. Repeat the above steps. After 5 catalytic cycle tests, the DCPD conversion rate is 100%, the selectivity of DHDCPD is 88.8%, and the selectivity of THDCPD is 11.2%. For the Nd5-Ni5-BTC-120 sample, its DCPD conversion rate is 100%, the selectivity of DHDCPD is 87.1%, and the selectivity of THDCPD is 12.9%.

[0038] Example 5

[0039] The synthesis procedure is the same as that in Example 1, where the metal and its dosage are adjusted to 0.88 g of neodymium nitrate hexahydrate and 0.48 g of copper nitrate trihydrate (molar ratio 5:5), and the Nd5-Cu5-BTC sample can be obtained. Vacuum activation can be carried out before the hydrogenation test. Take 50 mg of the sample and activate it in a vacuum oven at 120 °C for 6 h to obtain Nd5-Cu5-BTC-120.

[0040] Hydrogenation performance test of DCPD: The test procedure is the same as that in Example 1, where the reaction temperature and time are adjusted to 120 °C and 24 h. For the Nd5-Cu5-BTC sample, the DCPD conversion rate is 60.7%, the selectivity of the dihydro product DHDCPD is 93.7%, and the selectivity of the tetrahydro product THDCPD is 6.3%. For the Nd5-Cu5-BTC-120 sample, its DCPD conversion rate is 91.7%, the selectivity of DHDCPD is 93.8%, and the selectivity of THDCPD is 6.2%.

[0041] Example 6

[0042] The synthesis procedure is the same as that in Example 1, where the metal and its dosage are adjusted to 0.89 g of europium nitrate hexahydrate and 0.58 g of nickel nitrate hexahydrate (molar ratio 5:5), and the Eu5-Ni5-BTC sample can be obtained. Vacuum activation can be carried out before the hydrogenation test. Take 50 mg of the sample and activate it in a vacuum oven at 120 °C for 6 h to obtain Eu5-Ni5-BTC-120.

[0043] Hydrogenation performance test of DCPD: The test procedure is the same as that in Example 1. For the Eu5-Ni5-BTC sample, its Ni content is only 0.96 wt%, the DCPD conversion rate is 91.7%, the selectivity of DHDCPD is 93.8%, and the selectivity of THDCPD is 6.2%. For the Eu5-Ni5-BTC-120 sample, its DCPD conversion rate is 100%, the selectivity of DHDCPD is 90.6%, and the selectivity of THDCPD is 10.4%.

[0044] Example 7

[0045] The synthesis procedure is the same as that in Example 1, where the metal and its dosage are adjusted to 0.91 g of dysprosium nitrate hexahydrate and 0.58 g of nickel nitrate hexahydrate (molar ratio 5:5), and the Dy5-Ni5-BTC sample can be obtained. Vacuum activation can be carried out before the hydrogenation test. Take 50 mg of the sample and activate it in a vacuum oven at 120 °C for 6 h to obtain Dy5-Ni5-BTC-120.

[0046] Hydrogenation performance test of DCPD: The test procedure is the same as that in Example 1. For the Dy5-Ni5-BTC sample, its Ni content is only 2.05 wt%, the DCPD conversion rate is 71.2%, the selectivity of DHDCPD is 93.9%, and the selectivity of THDCPD is 6.1%. For the Dy5-Ni5-BTC-120 sample, its DCPD conversion rate is 100%, the selectivity of DHDCPD is 85.2%, and the selectivity of THDCPD is 14.8%.

[0047] The above examples can prove that rare earth-transition bimetallic MOF catalytic materials can utilize their intrinsic Lewis acid-base sites to promote the hydrogenation reaction of DCPD. This not only gets rid of the dependence on precious metals in traditional processes, but also greatly reduces the amount of transition metals used (less than 5 wt%), while cleverly avoiding the cumbersome steps of using easily explosive reducing agents such as sodium borohydride (NaBH4) for reduction treatment. These advantages greatly reduce the production cost and significantly improve the safety during the production process.

[0048] The above are only examples of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modifications, equivalent replacements, improvements, etc. made within the ideas and principles of the present application shall be included within the scope of the claims of the present application.

Claims

1. A method for preparing a rare earth MOF-based hindered Lewis acid-base pair for hydrogenation, characterized in that: Rare earth nitrate and transition metal nitrate are dissolved in a mixed solvent of N,N-dimethylformamide, ethanol and water, wherein the total molar amount M of the rare earth nitrate and the transition metal nitrate is 2~6 mmol, and the ratio is 10-a:a, wherein 1≤a≤5. After stirring and dissolving, trimesic acid ligand is added, and the amount of trimesic acid ligand L is added to the reaction system according to M:L=1:4~6, and the molar amount is 0.012~0.04 mol. The mixture is continuously stirred to obtain a uniform mixed solution, which is poured into a polytetrafluoroethylene reactor and placed in an oven for high-temperature solvent thermal reaction. The obtained product is centrifuged, washed and dried to obtain a rare earth-transition bimetallic MOFs catalytic material RE-X-BTC, and finally vacuum activation pretreatment is performed to obtain RE-X-BTC-T.

2. The preparation method according to claim 1, characterized in that: The rare earth nitrate is one of lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, praseodymium nitrate hexahydrate, neodymium nitrate hexahydrate, europium nitrate hexahydrate, gadolinium nitrate hexahydrate, dysprosium nitrate hexahydrate, ytterbium nitrate pentahydrate and yttrium nitrate hexahydrate.

3. The preparation method according to claim 1, characterized in that: The transition metal nitrate is one of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, copper nitrate trihydrate, and zinc nitrate hexahydrate.

4. The preparation method according to claim 1, characterized in that: The mixed solvent amount V is added according to M:V=1:10-15, wherein the volume ratio of solvent N,N-dimethylformamide, ethanol and water is 1:1:

1.

5. The preparation method according to claim 1, characterized in that: The stirring is carried out by using a magnetic stirrer for 30 to 60 minutes to dissolve the reagent, and the stirring time is continued for 20 to 30 minutes.

6. The preparation method according to claim 1, characterized in that: The conditions for the high-temperature solvent thermal reaction in the reactor are as follows: the heating rate of the oven is 2-10°C / min, the reaction temperature is 150-180°C, and the reaction is maintained in the oven for 24-48 hours.

7. The preparation method according to claim 1, characterized in that: The washing is to wash the product with DMF for 3-5 times, and then with deionized water for 8-10 times, the amount of solvent used for each washing is 5M mL, wherein 2≤M≤6, and the drying is to dry in an oven at 60-80°C for 12-24 h.

8. The preparation method according to claim 1, characterized in that: The temperature T of the vacuum activation pretreatment is 120-200°C, and the treatment time is 3-12 h.

9. The rare earth-transition bimetallic MOFs catalytic material RE-X-BTC-T obtained by the preparation method according to any one of claims 1 to 8 is used for the hydrogenation reaction of dicyclopentadiene.

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