Application of reducible ion skeleton in two-site catalysis and photo-thermal catalysis

Abstract

The invention is applicable to the technical field of ion skeletons, and provides application of a reducible ion skeleton in double-site catalysis and photo-thermal catalysis. Two multi-metal oxygen cluster-based ion skeletons AlMo6-V10 and CrMo6-V10 are prepared through a beaker reaction, the prepared ion skeletons are used as heterogeneous catalysts to catalyze a Knoevenagel condensation reaction and a thioether oxidation reaction, and results show that the ion skeletons have enhanced catalytic effects on the two reactions and show a double-site catalytic capability. And by adding SnCl2, [V10O28] < 6-> in the two ion skeletons can be partially reduced, so that the reduced ion skeletons have photothermal conversion capability, and are used as a photothermal agent / catalyst integrated material for efficient selective cycloaddition of alkylene oxide and carbon dioxide. According to the invention, the structure type of the ion skeleton is expanded, uniform distribution of double clusters is realized, in-situ reduction of the ion skeleton is realized for the first time, and the ion skeleton is applied to the field of near-infrared photothermal catalysis.

Description

Technical Field

[0001] The present invention belongs to the technical field of ionic skeletons, and in particular relates to the application of reducible ionic skeletons in dual-site catalysis and photothermal catalysis. Background Art

[0002] Ionic frameworks are a type of ordered porous materials with two-dimensional or three-dimensional periodic structures based on ionic bonds. Compared with the coordination bonds or covalent bonds between the components in metal organic frameworks and covalent organic frameworks with similar structures, the ionic interactions between the components in ionic frameworks are easier to form, making their synthesis conditions relatively mild and generally completed through a beaker reaction. However, despite the rapid development of ionic covalent organic frameworks, there are relatively few reports on ionic frameworks purely based on ionic bonds. This may be mainly because the radius of anions and cations in ionic compounds is usually small, making it difficult to support the formation of a skeleton structure with larger pores. Therefore, when preparing ionic frameworks, it is crucial to choose appropriate building blocks.

[0003] Polyoxometalates are a class of clusters formed by high-valent early transition metal ions through oxygen bridging. They have diverse compositions and structures and are large in size. They are usually negatively charged and are ideal for building blocks of anions in ionic frameworks. By rationally combining polyanions with different numbers and arrangements of alkali metal or alkaline earth metal clusters, ionic frameworks with various structures can be obtained. For example, based on the principle of charge balance between anions and cations, {Na 2} and {Na 4 The clusters can be combined with divalent and tetravalent Anderson-type polyanions through ionic bonds to form a two-dimensional ionic skeleton. In terms of structural characteristics, the ionic skeleton has the characteristics of positive and negative charge separation, which is conducive to its selective adsorption of polar gas molecules or gas molecules with polar bonds, so that it can be used for the separation of different types of gases. For example, the three-dimensional ionic skeleton constructed by the ionic interaction between the Anderson-type polyoxometalate clusters modified by trihydroxy ligands and sodium ions can selectively adsorb ammonia, sulfur dioxide and carbon dioxide, but not hydrogen, nitrogen and methane. Although the ionic skeleton has shown significant advantages in gas adsorption, the development in other fields, such as catalysis, is still relatively lacking, and it is necessary to prepare ionic skeleton catalysts through reasonable design. For this reason, the present invention proposes the application of reducible ionic skeletons in dual-site catalysis and photothermal catalysis. Summary of the invention

[0004] The purpose of the present invention is to provide an application of a reducible ion framework in dual-site catalysis and photothermal catalysis, aiming to solve the problems raised in the above background technology.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] Application of reducible ion skeletons in dual-site catalysis, preparation of AlMo through beaker reaction 6 -V 10 and CrMo 6 -V 10 ion skeletons, and using the prepared ion skeletons as heterogeneous catalysts to catalyze the Knoevenagel condensation reaction and the sulfide oxidation reaction.

[0007] Furthermore, the preparation method of the AlMo 6 -V 10 ion skeleton is as follows:

[0008] Dissolve 0.20 g of Na 6 V 10 O 28 and 0.19 g of Na 3 [Al(OH) 6 Mo 6 O 18 in 5 mL of hydrochloric acid solution, then ultrasonicate for 10 min, filter to obtain an orange solution, and leave the filtrate standing open at room temperature for 3 days to finally obtain orange crystals of AlMo 6 -V 10 .

[0009] Furthermore, the preparation method of the CrMo 6 -V 10 ion skeleton is as follows:

[0010] Dissolve 0.20 g of Na 6 V 10 O 28 and 0.21 g of Na 3 [Cr(OH) 6 Mo 6 O 18 in 5 mL of hydrochloric acid solution, then ultrasonicate for 10 min, filter to obtain an orange solution, and leave the filtrate standing open at room temperature for 3 days to finally obtain orange crystals of CrMo 6 -V 10 .

[0011] Furthermore, the pH of the hydrochloric acid solution is 3.

[0012] Application of reducible ion skeletons in photothermal catalysis, by reducing the AlMo 6 -V 10 and CrMo 6 -V 10 ion skeletons respectively to obtain reduction products r-AlMo 6 -V 10 and r-CrMo 6 -V 10, using the reduction product r-AlMo 6 -V 10 and r-CrMo 6 -V 10 as a photothermal catalyst for the efficient selective cycloaddition of epoxides and carbon dioxide.

[0013] Furthermore, the specific process of the reduction treatment is as follows:

[0014] Dissolve the reducing agent in ethanol, then dropwise add it to the ionic framework crystal and observe the change of color with time; after the reaction is completed, wash the reduced crystal with ethanol 3 times to obtain the final reduction product.

[0015] Furthermore, the reducing agent is oxalic acid, vitamin C or SnCl 2 .

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] Two ionic frameworks based on polyoxometalates were prepared by beaker reaction. In these two structures, the Anderson-type polyanions [Al(OH) 6 Mo 6 O 18 3- and [Cr(OH) 6 Mo 6 O 18 3- are respectively connected with small clusters {Na + formed by alkali metal Na 4 O 18} through terminal oxygen to form a two-dimensional ionic framework. [V 10 O 28 6- clusters are uniformly distributed in the voids of the two-dimensional framework structure as guest molecules and are fixed by double hydrogen bonds with the Anderson-type polyanions to form an ionic framework with uniform distribution of double clusters. Using the prepared ionic framework as a heterogeneous catalyst to catalyze the Knoevenagel condensation reaction and the sulfide oxidation reaction, the experimental results show that the ionic framework has enhanced catalytic effects on both types of reactions and exhibits dual-site catalytic ability. More importantly, by adding SnCl 2 the [V 10 O 28 6- ​​​​Partial reduction is performed to achieve structural transformation from single crystal to single crystal, so that the reduced ionic skeleton has photothermal conversion capability and is used as a photothermal agent / catalyst integrated material for the efficient selective cycloaddition of alkylene oxide and carbon dioxide. The present invention not only realizes the uniform dispersion of double clusters in the ionic skeleton for the first time, but also the two types of clusters in the skeleton can jointly achieve an effective improvement in the catalytic effect. In addition, the present invention realizes the in-situ reduction of the ionic skeleton for the first time and further applies it to the field of near-infrared photothermal catalysis, expanding the application range of the ionic skeleton. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 For AlMo 6 -V 10 Schematic diagram of the structure; (a) AlMo 6 -V 10 Basic building blocks [AlMo 6 (OH) 6 O 18 ] 3- and {Na 4 O 18}Structure diagram, (b) [AlMo 6 (OH) 6 O 18 ] 3- in {Na 4 O 18}, (c) {Na 4 O 18 In the anion [AlMo 6 (OH) 6 O 18 ] 3- The distribution around (d) contains [AlMo 6 (OH) 6 O 18 ] 3- and {Na 4 O 18} ionic skeleton structure, (e) [V 10 O 28 ] 6- In the loading of the ionic framework, the crystallographic water and hydrogen ions in the structure were omitted.

[0019] Figure 2 For AlMo 6 -V 10 Linear {Na 4 O 18} clusters, and the numbers indicate the distances between adjacent sodium ions.

[0020] Figure 3 For AlMo 6 Cluster and V 10The stacking model of clusters in AlMo 6 -V 10 in

[0021] Figure 4 For AlMo 6 -V 10 and CrMo 6 -V 10 The solid infrared spectra; where (a) Na 3 AlMo 6 , Na 6 V 10 , AlMo 6 -V 10 The infrared spectra, (b) Na 3 CrMo 6 , Na 6 V 10 , CrMo 6 -V 10 The infrared spectra.

[0022] Figure 5 For AlMo 6 -V 10 and CrMo 6 -V 10 The thermogravimetric curves; where (a) The thermogravimetric curve of AlMo 6 -V 10 , (b) The thermogravimetric curve of CrMo 6 -V 10 The thermogravimetric curve.

[0023] Figure 6 For AlMo 6 -V 10 and CrMo 6 -V 10 The powder X-ray diffraction patterns before and after soaking in different solvents; where (a) The powder X-ray diffraction patterns of AlMo 6 -V 10 before and after soaking in different solvents, (b) The powder X-ray diffraction patterns of CrMo 6 -V 10 before and after soaking in different solvents.

[0024] Figure 7 For the reaction efficiency of the Knoevenagel condensation reaction using AlMo 6 -V 10 and CrMo 6 -V 10 as catalysts; where (a) The curve of the substrate conversion rate varying with time using AlMo 6 -V 10 as a catalyst, (b) CrMo6 -V 10 Substrate conversion rate curves over time for the catalyst, (c) with AlMo 6 -V 10 and CrMo 6 -V 10 as the catalyst, the substrate conversion rate curves after 3 cycles of recycling.

[0025] Figure 8 For AlMo 6 -V 10 and CrMo 6 -V 10 FT-IR spectra before and after being used as the catalyst for the Knoevenagel condensation reaction; where (a) AlMo 6 -V 10 FT-IR spectra before and after being used as the catalyst for the Knoevenagel condensation reaction, (b) CrMo 6 -V 10 FT-IR spectra before and after being used as the catalyst for the Knoevenagel condensation reaction.

[0026] Figure 9 For AlMo 6 -V 10 and CrMo 6 -V 10 Powder X-ray diffraction patterns before and after being used as the catalyst for the Knoevenagel condensation reaction; where (a) AlMo 6 -V 10 Powder X-ray diffraction patterns before and after being used as the catalyst for the Knoevenagel condensation reaction, (b) CrMo 6 -V 10 Powder X-ray diffraction patterns before and after being used as the catalyst for the Knoevenagel condensation reaction.

[0027] Figure 10 Possible pathways for the Knoevenagel condensation reaction with the ionic framework as the catalyst. Two cluster structures play similar roles, where [V 10 O 28 6- is used as a representative and represented by the polyhedral structure.

[0028] Figure 11 For AlMo 6 -V 10 and CrMo 6 -V 10 Catalytic performance in the thioether oxidation reaction; where (a) Substrate conversion rate curves over time for AlMo 6 -V 10 as the catalyst in the thioether oxidation reaction, (b) CrMo 6 -V 10 ​As the curve of substrate conversion rate of the catalyst varying with time, (c) the substrate conversion rate after 3 - cycle recovery when using AlMo 6 -V 10 and CrMo 6 -V 10 catalysts, (d) the substrate selectivity curve after 3 - cycle recovery when using AlMo 6 -V 10 and CrMo 6 -V 10 catalysts.

[0029] Figure 12 For the infrared spectra of AlMo 6 -V 10 and CrMo 6 -V 10 before and after being used as catalysts for the thioether oxidation reaction; among which (a) the infrared spectra of AlMo 6 -V 10 before and after being used as catalysts for the thioether oxidation reaction, (b) the infrared spectra of CrMo 6 -V 10 before and after being used as catalysts for the thioether oxidation reaction.

[0030] Figure 13 For the powder X - ray diffraction spectra of AlMo 6 -V 10 and CrMo 6 -V 10 before and after being used as catalysts for the thioether oxidation reaction; among which (a) the powder X - ray diffraction spectra of AlMo 6 -V 10 before and after the thioether oxidation reaction, (b) the powder X - ray diffraction spectra of CrMo 6 -V 10 before and after the thioether oxidation reaction.

[0031] Figure 14 For the influence results of different free radicals on the reaction and the possible path of the thioether oxidation reaction by hydrogen peroxide; among which (a) the bar chart of substrate conversion rate when adding benzoquinone and p - phenylenediamine under different catalyst conditions, (b) the possible path of the thioether oxidation reaction by hydrogen peroxide. Two cluster structures play similar roles, and here [V 10 O 28 6- is used as a representative.

[0032] Figure 15 For the optical photos of AlMo 6 -V 10 crystals before and after dropping a reducing agent; among which (a) AlMo 6 -V 10 ​Optical photos of the crystal before and after dropping oxalic acid solution, (b) In AlMo 6 -V 10 Optical photos of the crystal before and after dropping vitamin C solution.

[0033] Figure 16 For AlMo 6 -V 10 In-situ reduction; among which (a) Optical photos of the crystal at different times after dropping SnCl 6 -V 10 solution on the AlMo 2 crystal, (b) Changes in the stacking structures of two clusters in the crystal before and after the reduction reaction, (c) Ultraviolet photoelectron spectroscopy of V in AlMo 6 -V 10 , (d) Ultraviolet photoelectron spectroscopy of Mo in AlMo 6 -V 10 , (e) Ultraviolet photoelectron spectroscopy of V in r-AlMo 6 -V 10 , (f) Ultraviolet photoelectron spectroscopy of Mo in r-AlMo 6 -V 10 in the figure.

[0034] Figure 17 For r-AlMo 6 -V 10 Schematic diagram of the stacking of two cluster structures.

[0035] Figure 18 For r-AlMo 6 -V 10 Schematic diagram of the hydrogen bond between two cluster structures.

[0036] Figure 19 For AlMo 6 -V 10 Infrared spectra before and after the reduction of AlMo 6 -V 10 and thermogravimetric curve of r-AlMo 6 -V 10 ; among which (a) Infrared spectra of AlMo 6 -V 10 before and after the reduction, (b) Thermogravimetric curve of r-AlMo

[0037] Figure 20 For Na 3 AlMo 6 and Na 6 V 10 Optical photos of the crystal before and after being reduced by SnCl 2 ; among which (a) Na 3 AlMo 6The crystal was SnCl 2 Optical photographs before and after reduction, (b) Na 6 V 10 The crystal was SnCl 2 Optical photographs before and after reduction.

[0038] Figure 21 For CrMo 6 -V 10 Infrared spectra before and after reduction and the thermogravimetric curve of r-CrMo 6 -V 10 ; where (a) CrMo 6 -V 10 Infrared spectra before and after reduction, (b) Thermogravimetric curve of r-CrMo 6 -V 10 。

[0039] Figure 22 For V, Mo in CrMo 6 -V 10 , r-CrMo 6 -V 10 Ultraviolet photoelectron spectroscopy diagrams; where (a) V in CrMo 6 -V 10 Ultraviolet photoelectron spectroscopy diagram, (b) Mo in CrMo 6 -V 10 Ultraviolet photoelectron spectroscopy diagram, (c) V in r-CrMo 6 -V 10 Ultraviolet photoelectron spectroscopy diagram, (d) Mo in r-CrMo 6 -V 10 Ultraviolet photoelectron spectroscopy diagram.

[0040] Figure 23 For the photothermal performance and its stability investigation of r-AlMo6-V10 under near-infrared light irradiation; where (a) Local enlarged ultraviolet-visible-infrared spectra of AlMo 6 -V 10 and r-AlMo 6 -V 10 , (b) Temperature change curves in the solution with and without r-AlMo 6 -V 10 under 808 nm near-infrared light irradiation, (c) Temperature change curves of r-AlMo 6 -V 10 experiencing 5 times of near-infrared light irradiation and extinction, (d) Heating and cooling curves of the solution under 808 nm near-infrared light irradiation and turning off. The intensity of the near-infrared laser is 2 W cm –2 .

[0041] Figure 24 is r-CrMo 6 -V 10 's light absorption performance and r-AlMo 6 -V 10 's photothermal conversion efficiency exploration; where (a) CrMo 6 -V 10 and r-CrMo 6 -V 10 's partially enlarged ultraviolet-visible-infrared spectrum; (b) r-AlMo Figure 23 obtained from the cooling curve in (d) of 6 -V 10 's time-–lnθ dependence curve.

[0042] Figure 25 is the exploration of the photothermal performance and its stability of r-CrMo 6 -V 10 ; where (a) temperature change curves of the solution with and without r-CrMo 6 -V 10 under 808 nm near-infrared light irradiation, (b) temperature change curves of r-CrMo 6 -V 10 under 5 cycles of near-infrared light irradiation and extinction; the intensity of the near-infrared laser is 2 W cm –2 .

[0043] Figure 26 is the exploration of the photothermal performance and its quantitative evaluation of r-CrMo 6 -V 10 ; where (a) heating and cooling curves of the solution under 808 nm near-infrared light irradiation and turning off. (b) Time-–lnθ dependence curve obtained from the cooling curve in (a) of Figure 26 ; the intensity of the near-infrared laser is 2 W cm –2 .

[0044] Figure 27 is the catalytic performance and recycling stability of r-AlMo 6 -V 10 and r-CrMo 6 -V 10 in the cycloaddition reaction of epichlorohydrin and carbon dioxide; where (a) substrate conversion rate vs. time curve of r-AlMo 6 -V 10 as a catalyst, (b) substrate conversion rate vs. time curve of r-CrMo 6 -V 10 as a catalyst, (c) with r-AlMo 6 -V 10 and r-CrMo6 -V 10 The conversion rate curve of the substrate recovered after 4 cycles when using the catalyst.

[0045] Figure 28 is r-AlMo 6 -V 10 and r-CrMo 6 -V 10 Investigation of the structural stability of r-AlMo 6 -V 10 Infrared spectra of the catalyst before and after the cycloaddition reaction of epichlorohydrin with carbon dioxide, (b) r-CrMo 6 -V 10 Infrared spectra of the catalyst before and after the cycloaddition reaction of epichlorohydrin with carbon dioxide.

[0046] Figure 29 is r-AlMo 6 -V 10 and r-CrMo 6 -V 10 Investigation of the crystal structure stability of r-AlMo 6 -V 10 Powder X-ray diffraction spectra of the catalyst before and after the cycloaddition reaction of epichlorohydrin with carbon dioxide, (b) r-CrMo 6 -V 10 Powder X-ray diffraction spectra of the catalyst before and after the cycloaddition reaction of epichlorohydrin with carbon dioxide.

[0047] Figure 30 For the possible reaction pathways of the cycloaddition of propylene oxide with carbon dioxide in a system using a reduced ionic framework as the catalyst. Two cluster structures play similar roles, where [V 10 O 28 6- is used as a representative. Detailed implementation manners

[0048] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0049] The following describes the specific implementation of the present invention in detail with reference to specific embodiments.

[0050] The present invention provides a method for preparing a reducible ionic framework, comprising the following steps:

[0051] Na 8 H(V 10 O 28 ​)[Al(OH) 6 Mo 6 O 18 ·30H 2 O(AlMo 6 -V 10 ) Synthesis: Dissolve Na 6 V 10 O 28 (0.20 g, 0.18 mmol) and Na 3 [Al(OH) 6 Mo 6 O 18 (0.19 g, 0.18 mmol) in 5 mL of hydrochloric acid solution with pH 3, then sonicate for 10 min, filter to obtain an orange solution, leave the filtrate standing open at room temperature for 3 days, and finally obtain orange crystals with a yield of 52.1%. Calculated values for elemental analysis: Na 6.87, Al 1.01%, V 19.04, and Mo 21.51%; experimental values: Na 6.41, Al 0.99%, V 19.85, and Mo 21.02%.

[0052] Na 8 H(V 10 O 28 )[Cr(OH) 6 Mo 6 O 18 ·30H 2 O(CrMo 6 -V 10 ) Synthesis: Dissolve Na 6 V 10 O 28 (0.20 g, 0.18 mmol) and Na 3 [Cr(OH) 6 Mo 6 O 18 (0.21 g, 0.18 mmol) in 5 mL of hydrochloric acid solution with pH 3, then sonicate for 10 min, filter to obtain an orange solution, leave the filtrate standing open at room temperature for 3 days, and finally obtain orange crystals with a yield of 45.6%. Calculated values for elemental analysis: Na 6.81%, Cr 1.93%, V 18.86%, and Mo 21.31%; experimental values: Na 6.44%, Cr 1.89%, V 19.01%, and Mo 20.95%.

[0053] Reduction of the ionic framework: Oxalic acid, vitamin C, and SnCl 2Used as reducing agents for the reduction of ionic frameworks respectively. The specific operation method is as follows: Dissolve the reducing agent in ethanol, then dropwise add it to the ionic framework crystals and observe the change of color over time. After the reaction is completed, wash the reduced crystals with ethanol three times to obtain the final reduction product.

[0054] Results and Discussion;

[0055] (1) Structure Characterization;

[0056] The prepared AlMo 6 -V 10 and CrMo 6 -V 10 ionic frameworks are isostructural and both crystallize in the triclinic system, space group. The specific crystallographic information and refinement results are shown in Table 1.

[0057] Table 1 MMo 6 -V 10 (M = Al, Cr) Crystallographic Parameters and Refinement Results

[0058]

[0059]

[0060] a R 1 = Σ||F o |-|F c || / Σ|F o |; b wR 2 = Σ[w(F o 2 -F c 2 ) 2 / Σ[w(F o 2 ) 2 1 / 2 .

[0061] In the two ionic frameworks, except for the different heteroatoms of the Anderson-type polyoxometalate, the rest are the same. Below, AlMo 6 -V 10 is taken as an example for structure description. The AlMo 6 -V 10 ionic framework consists of Na + , the Anderson-type polyanion [AlMo 6 (OH) 6 O 18 3- , the isopolyanion [V 10 O 28 ​​6- and water molecules. As Figure 1 shown in a), the Na in the framework + forms a linear {Na 4 O 18} cluster through the bridging action of water molecules. Between Na1 and Na2 at both ends, and between Na3 and Na4, they exist in the form of a double-bridged dimer, and the distance between Na-Na is respectively and Correspondingly, the adjacent Na2-Na4 distance slightly increases to ( Figure 2 ) through the bridging of a single water molecule between the two dimers. Among the 18 oxygen atoms in the {Na 4 O 18} cluster, 4 come from the Anderson-type cluster, and the remaining 14 are all water molecules, indicating that the hydration of Na + plays an important promoting role in the formation of the Na cluster. As Figure 1 shown in b), Na + is connected to the polyanion through the terminal oxygen. Each {Na 4 O 18} cluster is connected to the surrounding 3 [AlMo 6 (OH) 6 O 18 3- through 4 sites. Correspondingly, each [AlMo 6 (OH) 6 O 18 3- is adjacent to 6 {Na 4 O 18} clusters, 4 of which are connected in a single-site form, and the remaining 2 are suspended on the cluster in a double-site form ([[]] Figure 1 in c). Under the combined action of the above two connection forms, [AlMo 6 (OH) 6 O 18 3- and the {Na 4 O 18} cluster form a two-dimensional ionic framework ([[]] Figure 1 in d), while the V 10 cluster fills the pores in the ionic framework ([[]] Figure 1 in e). As can be seen from Figure 3 , in the ionic framework, [AlMo 6 (OH) 6 O 18 3- and [V 10 O 28 6- ​​​​​​Showing an interval arrangement indicates that the ionic framework has successfully achieved the ordered dispersion of the two clusters.

[0062] In addition to single-crystal X-ray diffraction data, solid-state infrared spectroscopy was also used to characterize the structures of the two ionic frameworks. As Figure 4 shown in a and b, from the comparison diagrams of the two ionic frameworks with Na 3 Al(OH) 6 Mo 6 O 24 (Na 3 AlMo 6 ), Na 3 Cr(OH) 6 Mo 6 O 24 (Na 3 CrMo 6 ), and Na 6 V 10 O 28 (Na 6 V 10 ), it can be seen that the characteristic vibration peaks of the two polyoxometalate clusters are present in the ionic framework. Among them, the peaks located at 1000 - 700 cm -1 can be attributed to the vibrations of Mo=O, V=O, and Mo-O-Mo, V-O-V respectively, while the peaks below 500 cm -1 are attributed to the symmetric and asymmetric stretching vibrations of Al-O and Cr-O. The hydroxyl bending vibration peak at 1650 cm -1 and the hydroxyl stretching vibration peak at around 3500 cm -1 indicate the presence of water molecules in the structure. The valence bond calculation results show that all Mo in the ionic framework is +6 valence, all V is +5 valence, while Al and Cr are +3 valence, and the oxygen on the two anions is not protonated. Therefore, the two clusters carry a total of 9 negative charges. Among them, 8 Na + serve as counter cations, and the remaining charges are balanced by partially protonated crystalline water molecules, which is also consistent with the acidic environment during the reaction process. The two ionic frameworks have similar thermogravimetric curves ( Figure 5 a and b). In the initial stage, as the temperature increases, the crystalline water in the structure gradually loses and remains basically stable after 300 °C. In addition to thermal stability, the solvent stability of the ionic framework was also evaluated. As can be seen from Figure 6 a and b, when the ionic framework is immersed in acetonitrile (CH 3 CN), methanol (CH 3 OH), and ethanol (CH 3 CH 2After one day in the (OH) solvent, the powder X-ray diffraction pattern of the dried sample was basically the same as that before soaking (As-synthesized) and was consistent with the powder X-ray diffraction pattern (Simulated) simulated from single crystal data, indicating that the ionic framework could maintain the structural integrity in these solvents, laying a foundation for subsequent heterogeneous catalysis work.

[0063] (2) Catalytic performance of the ionic framework in the Knoevenagel condensation reaction;

[0064] The prepared ionic framework achieved a uniform arrangement of two clusters and could maintain structural stability in a variety of organic solvents, so it was used as a heterogeneous catalyst to catalyze the Knoevenagel condensation reaction, and benzaldehyde and malononitrile were used as reaction substrates to optimize and explore the catalytic conditions.

[0065]

[0066] As shown in Table 2, when the temperature was raised from room temperature to 60 °C, the conversion rate of the substrate increased significantly, indicating that temperature plays an important role in promoting the reaction. Under the same conditions, when the ratio of catalyst to substrate was tried to be reduced from 0.1% to 0.05%, the conversion rate of the substrate decreased from 97% to 72%, indicating that 0.1% was a more suitable ratio of catalyst to substrate. When the reaction system solvent was changed to solvent-free, acetonitrile or chloroform (CHCl 3 ), the conversion rate of its substrate decreased to varying degrees, indicating that methanol was a more suitable reaction solvent.

[0067] Table 2 Performance of the catalyst in the Knoevenagel condensation reaction under different conditions a

[0068]

[0069] a Reaction conditions: benzaldehyde: 1 mmol, malononitrile: 1 mmol, catalyst: AlMo 6 -V 10 , solvent: 0.2 mL. b The conversion rate was obtained from the NMR analysis results, using naphthalene as the internal standard and calculated based on benzaldehyde.

[0070] According to the results of the optimization study of the catalytic reaction conditions, methanol was selected as the solvent, the ratio of catalyst to substrate was 0.1%, the reaction temperature was 60 °C, and the reaction time was 15 min to evaluate the catalytic effects of each component in the ionic framework.

[0071]

[0072] As shown in Table 3, under the above reaction conditions, the conversion rate of the substrate was only 49% without a catalyst, while 3 AlMo 6 and Na 3 CrMo 6 When Na 6 V 10 When vanadium clusters were used as catalysts, the conversion rate of the reaction reached 77%, indicating that vanadium clusters have a better catalytic effect on this type of reaction. In order to further explore the catalytic performance of these polymetallic oxygen clusters, two ionic frameworks (AlMo 6 -V 10 and CrMo 6 -V 10 ) as catalyst, and studied its effect on the reaction. The results showed that when AlMo 6 -V 10 When CrMo was used as the catalyst, the conversion rate of the substrate increased significantly from 49% to 99%, indicating that the skeleton structure has a strong promoting effect on the reaction. 6 -V 10 When NaO2 was used as a catalyst, the conversion rate of the substrate was also increased to 99%, which also illustrates the importance of the skeleton structure in the catalytic reaction. The improvement of the skeleton structure on the catalytic reaction effect is believed to come from its effective and uniform dispersion of the two polymetallic oxygen clusters, thereby improving the utilization efficiency of the catalyst. In order to prove the significance of the uniform dispersion of polymetallic oxygen clusters in the skeleton structure, corresponding comparative experiments were carried out. 3 AlMo 6 and Na 6 V 10 The physical blending product (named Na 3 AlMo 6 +Na 6 V 10 ) as a catalyst, under the same conditions, the conversion rate of the substrate (85%) was lower than that of the corresponding ion skeleton catalysis. 3 CrMo 6 and Na 6 V 10 The physical blending product (named Na 3 CrMo 6 +Na 6 V 10 ) as a catalyst, under the same conditions, the conversion rate of the substrate (87%) is also lower than that of the corresponding ion framework catalysis. This comparative experiment further proves that the uniform dispersion of the two polymetallic oxygen clusters by the ion framework effectively improves its catalytic efficiency.

[0073] Table 3 Performance of Different Catalysts in Knoevenagel Condensation Reaction a

[0074]

[0075] a Reaction conditions: Benzaldehyde: 1 mmol, Malononitrile: 1 mmol, Catalyst: 10 -3 mmol, CH 3 OH: 0.2 mL, Reaction temperature: 60 °C, Reaction time: 15 min. b The conversion rate was obtained from the NMR analysis results, using naphthalene as the internal standard and calculated based on benzaldehyde.

[0076] From the conversion rates of the substrates under the above various conditions, it can be seen that when using two ionic frameworks (AlMo 6 -V 10 and CrMo 6 -V 10 ) as catalysts, the Knoevenagel condensation reaction shows extremely high reaction efficiency. Therefore, we further studied this reaction process in depth. From the substrate conversion rate-time relationship curves ( Figure 7 a and b), it can be seen that in the initial stage of the reaction (3 min), the conversion rate of the substrate reached a relatively high level, indicating that the substrate has a relatively fast reaction rate. After 3 min, the reaction continued, and the conversion rate of the substrate further increased, but the increase amplitude became smaller, and both reached 99% at 15 min. To further verify the role of the catalyst in the substrate conversion process, the catalyst was removed from the reaction system by hot filtration during the reaction, and the conversion rate of the substrate was continuously monitored. As Figure 7 shown in a, when the catalyst AlMo 6 -V 10 was removed from the reaction system, the conversion rate of the substrate only increased slightly, and the conversion rate at 15 min was 68%, far lower than 99% when the catalyst was present. Similarly, in the system with CrMo 6 -V 10 as the catalyst, after removing the catalyst, the conversion rate of the substrate benzaldehyde at 15 min was about 68%, which was also far lower than the substrate conversion rate of 99% when the catalyst was present ( Figure 7 b). These results all indicate that the ionic framework catalysts used have good promotion effects on the Knoevenagel condensation reaction. To further evaluate the usability of the catalyst, after the reaction was completed, the above two catalysts were extracted from the system by filtration, and after procedures such as washing and drying, they were used for the next catalytic reaction, realizing the recycling of the catalyst. The experimental results show that after 3 cycles of recycling, these two catalysts still maintain a high catalytic efficiency, indicating their good catalytic recyclability (Figure 7 In c). In addition, a catalyst stability evaluation experiment was carried out. The results showed that the infrared spectra of the catalyst before and after the catalytic reaction ( Figure 8 in a and b) and the powder X-ray diffraction spectra ( Figure 9 in a and b) remained basically unchanged, indicating that the catalyst had good stability.

[0077] The above research results show that the two prepared ionic skeletons both have good catalytic effects on the reaction of benzaldehyde and malononitrile, and can obtain high substrate conversion rates, fast reaction rates, and a simple catalyst recycling process.

[0078] To further expand the application scope of the catalyst, while keeping the substrate malononitrile unchanged, different substituents were introduced on benzaldehyde to study their corresponding catalytic effects. As shown in Table 4, when an electron-withdrawing group -Br, -Cl or -NO 2 was introduced at the para-position of benzaldehyde, the conversion rate of the substrate remained basically unchanged, which was similar to the case of introducing -Cl at the ortho-position. On the contrary, when an electron-donating group was introduced into the substrate, whether it was a hydroxyl group, a methoxy group at the para-position, or a methyl group at the ortho-position, it would lead to a significant decrease in the substrate conversion rate. The above results show that the introduction of an electron-donating group reduces the reactivity of the aldehyde group and is not conducive to the occurrence of the Knoevenagel condensation reaction.

[0079] Table 4 Performance of the ionic skeleton catalyst in the Knoevenagel condensation reaction of malononitrile with benzaldehyde bearing different substituents a

[0080]

[0081] a Reaction conditions: malononitrile: 1 mmol, substrate: 1 mmol, catalyst: 10 -3 mmol, CH 3 OH: 0.2 mL, reaction temperature: 60 °C, reaction time: 15 min. b The conversion rate was obtained from the NMR analysis results, using naphthalene as an internal standard and calculated based on the benzaldehyde derivative.

[0082] Based on the reaction process of this reaction in a similar system, taking the reaction of benzaldehyde and malononitrile as an example, the role of the ionic skeleton in the Knoevenagel condensation reaction was analyzed and a possible reaction process was proposed. From the above catalytic performance, it can be seen that both of the two polyoxometalates in the ionic skeleton have an approximate promoting effect on the reaction, and the metal ions in the two cluster structures have similar coordination environments. Therefore, we speculate that the two polyoxometalates in the ionic skeleton act as a dual-site catalyst to promote the occurrence of the reaction. Here, [V 10 O 28 6- ​For example, the description is as follows: Figure 10 ) When the substrate encounters the catalyst in the reaction system, a methylene hydrogen of malononitrile is activated and captured by the terminal oxygen of the polyoxometalate, forming a positively charged transition state. At this time, the negatively charged malononitrile undergoes an addition reaction with benzaldehyde, the carbon-oxygen double bond opens, and the negative charge is transferred to the oxygen atom. Subsequently, the negatively charged addition product combines with the positively charged polyoxometalate to form a hydroxyl-substituted phenylmalononitrile, and then after dehydration, the final product is obtained.

[0083] (3) Catalytic performance of the ionic framework in the oxidation reaction of thioethers;

[0084] To test the potential application of the ionic framework in more reaction types, it was continued to be used as a catalyst in the oxidation reaction of thioethers. The catalytic oxidation reaction conditions were optimized and explored using benzyl mercaptan as the substrate.

[0085]

[0086] As shown in Table 5, in the presence of the catalyst, using acetonitrile as the solvent, the conversion rate of benzyl mercaptan at room temperature is relatively low, and only 40% is converted after 2.5 h. As the temperature is increased to 35 °C and the reaction time is extended to 3 h, the conversion rate of the substrate can be significantly increased to 80%. When the temperature is further increased to 45 °C, the progress of the reaction reaches 97%. Changing the reaction solvent from acetonitrile to ethanol or reducing the amount of the catalyst will cause a significant decrease in the conversion rate of the reaction.

[0087] Table 5 Performance of the catalyst in the oxidation reaction of benzyl mercaptan under different conditions a

[0088]

[0089] a Reaction conditions: benzyl mercaptan: 0.25 mmol, H 2 O 2 : 0.44 mmol, catalyst: AlMo 6 -V 10 , solvent: 0.4 mL; b The conversion rate was obtained from the analysis results of 1H NMR spectrum, using trimethylsilane as the internal standard and calculated according to the amount of benzyl mercaptan added; c Selectivity refers to the proportion of sulfoxide (A) in the product.

[0090] According to the results of the optimization study of the catalytic reaction conditions, hydrogen peroxide was selected as the oxidant, acetonitrile as the solvent, the ratio of the catalyst to the substrate was 0.4%, the reaction temperature was 45 °C, and the reaction time was 3 h. The catalytic effects of each component in the ionic wind were evaluated.

[0091]

[0092] As shown in Table 6, under the above-selected reaction conditions, all catalysts had high selectivity for the sulfoxide product of benzyl methyl sulfide, but there were significant differences in the conversion of the substrate. When no catalyst was present, the conversion of the substrate was only 6%, while for 3 AlMo 6 Na 3 CrMo 6 Na 6 V 10 as catalysts, the conversions of the reaction could reach 66%, 63% and 66% respectively, indicating that these two types of polyoxometalates both had good catalytic effects on the oxidation of sulfides. For the ionic frameworks containing two polyoxometalates, they had better catalytic effects on the reaction. When 6 AlMo 10 -V 6 and 10 CrMo 6 -V 10 were used as catalysts, the conversions of the substrate were increased to 97% and 98% respectively. In contrast, the catalysts prepared by physically mixing two Anderson-type polyoxometalates with

[0093] Table 6 Performance of the oxidation reaction of benzyl methyl sulfide by hydrogen peroxide in the presence of different catalysts a

[0094]

[0095] a Reaction conditions: benzyl methyl sulfide: 0.25 mmol, H 2 O 2 : 0.44 mmol, amount of catalyst: 1 μmol, CH 3 CN: 0.4 mL, reaction temperature: 45 °C, reaction time: 3 h; b The conversion was obtained from the results of 1H NMR analysis, using trimethylsilane as an internal standard and calculated according to the amount of benzyl methyl sulfide added; c The selectivity refers to the proportion of sulfoxide (A) in the products.

[0096] In the reaction of catalytic oxidation of benzyl methyl sulfide by the ionic framework, although the conversion of the substrate reached 97% ( 6 AlMo 10 -V 6 ) and 98% ( 10 CrMo Figure 11It can be seen from a) and b) that the reaction develops rapidly in the initial stage, and a substrate conversion rate close to 80% can be obtained within 0.5 h. Subsequently, the conversion rate gradually increases slowly and approaches the end point of the reaction at 3 h. The catalyst leakage experiment shows that ( Figure 11 in a) and b), during the reaction process, when the catalyst is removed from the system, the conversion of the substrate approaches stagnation, indicating that the catalyst has a decisive promoting effect on the occurrence of the reaction. Since the catalyst is insoluble in the reaction system, the catalyst can be recovered by filtration after the reaction is completed, and can be used for the next cycle reaction after treatment such as washing and drying. The experimental results show that after 3 cycles, the conversion rate ( Figure 11 in c) and the selectivity ( Figure 11 in d) do not show obvious attenuation, indicating that the catalyst has a certain recycling ability. By comparing the infrared spectra ( Figure 12 ) and powder X-ray diffraction spectra ( Figure 13 ) of the catalyst before and after the reaction, it can be known that the catalyst remains stable during the reaction and the framework structure is not damaged.

[0097] In order to expand the application of the ionic framework in the catalytic oxidation of sulfide compounds, the conversion rate and selectivity of the reaction in the presence of different substituents were further studied. As can be seen from Table 7, whether the para position of the benzene ring is an electron-withdrawing group (-Br, -Cl or -NO 2 ), or an electron-donating group (p-methoxy), or when the methyl position is changed to an ethyl group, its influence on the conversion rate and selectivity is not significant. When the methyl position is replaced by a benzene ring, its large steric hindrance may affect the reaction and cause a significant decrease in the conversion rate of the substrate. The above results show that the prepared ionic framework has general applicability for the selective oxidation of sulfides.

[0098] Table 7 Performance of sulfide oxidation reactions with different substituents using an ionic framework as the catalyst a

[0099]

[0100]

[0101] a Reaction conditions: sulfide: 0.25 mmol, H 2 O 2 : 0.44 mmol, catalyst: 1 μmol, CH 3 CN: 0.4 mL, reaction temperature: 45 °C, reaction time: 3 h; b The conversion rate was obtained from the results of 1H NMR analysis, using trimethylsilane as the internal standard and calculated according to the amount of benzyl mercaptan added; c The selectivity refers to the proportion of sulfoxide (A) in the product.

[0102] To enhance the understanding of the reaction process, the method of adding radical scavengers to the reaction system was used to explore the effects of different radicals on the reaction. As can be seen from Figure 14 a, when the radical scavenger p-benzoquinone (p-BQ) was added to the system, regardless of whether the catalyst was the single Na · O 2 - , Na 3 AlMo 6 , Na 3 CrMo 6 , Na 6 V 10 , or the ionic framework AlMo 6 -V 10 and CrMo 6 -V 10 , the conversion rate of the substrate decreased to a certain extent, but the decrease was not significant. This phenomenon indicates that although · O 2 radicals existed in the reaction process, the proportion was not high. When the · OH scavenger diphenylamine (DPA) was added to the reaction system, the conversion rate of thioether decreased significantly under different catalyst environments. This result shows that · OH being captured greatly disrupted the reaction process, thus proving that the catalytic reaction underwent a reaction path of hydroxyl radicals.

[0103] In the thioether oxidation reaction with H 2 O 2 as the oxidant, based on the structures, functional characteristics of the components in the reaction system and the presence of radicals, the following possible reaction paths were proposed. As shown in Figure 14 b, under the action of the ionic framework, H 2 O 2 decomposed to generate active oxygen, which combined with the metal ions in the polyoxometalate and further formed peroxides at the terminal oxygen position of the polyoxometalate. Subsequently, the peroxides contacted the thioether to form sulfoxide, and the polyoxometalate returned to the initial state to complete a cycle. During the activation of H 2 O 2 by the polyoxometalate, both · O 2 - radicals and · OH radicals were generated. By comparing the reaction conditions in the presence of different radical scavengers, the conclusion was drawn that the process of conversion via hydroxyl radicals accounted for a higher proportion.

[0104] (4) In-situ reduction of the ionic framework;

[0105] The prepared ionic framework contains two types of polyanions. Generally speaking, in an unrestricted situation, due to the Anderson-type polyoxometalate having two terminal oxygen atoms, the hexavalent Mo in its structure is not easily reduced; relatively speaking, the pentavalent V in 10 O 28 6- has relatively high activity and is easily partially reduced to tetravalent V in the presence of a reducing agent. To explore the redox behavior of polyanions in a framework-confined environment, different reducing agents were added to observe the changes in the framework. The specific method was to place the ionic framework crystal on a glass slide and then drop a solution containing different reducing agents to observe the changes in the crystal. Taking AlMo 6 -V 10 as an example, when oxalic acid was used as the reducing agent, after 1 h, no obvious change occurred in the crystal ( Figure 15 a), indicating that the reducing ability of oxalic acid was relatively weak and the framework was not reduced. When VC (vitamin C) was used as the reducing agent, a yellow-to-green transition occurred in the crystal after 3 min and it turned green after 1 h ( Figure 15 b), indicating that the crystal was partially reduced and the crystal gradually weathered. When SnCl 2 was used as the reducing agent, the yellow crystal underwent a transition from yellow to green and then gradually to dark green and finally existed in a crystalline form ( Figure 16 a). Compared with oxalic acid and vitamin C, SnCl 2 not only has stronger reducibility, but its smaller molecular size is also conducive to its full contact with polyanions, thus better completing the redox process.

[0106] Compared with before reduction, the quality of the crystal after reduction was slightly worse. After many attempts, perfect crystals could still not be obtained. The results of single crystal analysis could not give all the structural details, but the existence of these two polyanions, [AlMo 6 (OH) 6 O 18 3- and [V 10 O 28 6- , could be clearly distinguished, as well as their positional relationship in the spatial arrangement. As can be seen from Figure 17 , compared with before reduction, [V 10 O 28 6- showed an obvious tilt, resulting in more hydrogen bond interactions between it and the [AlMo 6 (OH) 6 O 18 3- clusters ( Figure 18 ). In addition, the positional relationship between the two cluster structures after reduction also changed significantly. For example,​​​​​Figure 16 As shown in b), before reduction, the first two clusters are arranged alternately horizontally and continuously vertically, while after reduction, the structures of the last two clusters are arranged alternately in both directions. Infrared spectroscopy shows that the characteristic peaks of each component in AlMo 6 -V 10 do not change significantly, indicating that the basic building blocks in the structure still exist after reduction ( Figure 19 as shown in a). [V 10 O 28 6- The ability to achieve torsion in the crystal environment is closely related to its state of existence. In the unreduced state, there is no strong direct ionic bond between [V 10 O 28 6- and Na + . It only acts through a double hydrogen bond with [AlMo 6 (OH) 6 O 18 3- and is thus loaded inside the framework structure. This relatively loose binding mode and interaction method provide available space for its structural transformation in the presence of a reducing agent, and effectively reduce the energy barrier of the reaction, promoting the progress of the reduction reaction.

[0107] To determine the specific location where the reduction reaction occurs in the ionic framework, SnCl 3 was added to separate Na 6 AlMo 6 and Na 10 V 2 . Under similar conditions, as can be seen from Figure 20 a, after adding the reducing agent for 1 h, the crystal of Na 3 AlMo 6 basically does not change, while the color of Na 6 V 10 obviously deepens ( Figure 20 as shown in b), indicating that the location where the reduction reaction occurs in the framework structure is on [V 10 O 28 6- . In addition to qualitative analysis, we also quantitatively characterized the reduction degree of the ionic framework using X-ray photoelectron spectroscopy. As Figure 16 shown in c-f, AlMo 6 -V 10 ​​​​After reduction, all the Mo in the structure remains the same as before the reaction, with a valence of +6, while the characteristic peak of V shows obvious broadening. After peak fitting and calculation, it can be known that about 45% of the pentavalent V is reduced to tetravalent V. Combining with the partial structural information given by X-ray single crystal diffraction, infrared spectroscopy, elemental analysis, X-ray photoelectron spectroscopy, and thermogravimetry ( Figure 19 the result in b), it can be concluded that the molecular formula of the reduced AlMo 6 -V 10 is Na 8 H 5.5 (V Ⅳ 4.5 :V Ⅴ 5.5 O 28 )[Al(OH) 6 Mo 6 O 18 ·20H 2 O (r-AlMo 6 -V 10 ). When SnCl 6 -V 10 is added to CrMo 2 , it shows a reaction phenomenon similar to that of AlMo 6 -V 10 . After characterization analysis ( Figure 21 a and b in, Figure 22 a-d in), its reduced molecular formula is Na 8 H 5.5 (V Ⅳ 4.5 :V Ⅴ 5.5 O 28 )[Cr(OH) 6 Mo 6 O 18 ·17H 2 O (r-CrMo 6 -V 10 ).

[0108] (5) Near-infrared photothermal catalysis of r-AlMo 6 -V 10 and r-CrMo 6 -V 10 ;

[0109] After the ion skeleton is reduced, the color becomes significantly darker, indicating an enhanced light absorption ability. The ion skeleton before and after reduction was characterized by ultraviolet-visible-near-infrared absorption spectroscopy. As Figure 23 a in and Figure 24 a in show, the reduced product r-AlMo 6 -V10 and r-CrMo 6 -V 10 An obvious absorption peak appears between 590 - 1070 nm. As mentioned above, this is due to the partial reduction of V. To further explore the near-infrared photothermal conversion ability of the reduced ionic framework and apply it to liquid-phase near-infrared photothermal catalysts, we further studied its photothermal behavior in solution. As Figure 23 shown in b of -2 , when irradiated with an 808 nm near-infrared laser with a power density of 2 W cm 6 -V 10 dispersion system, the temperature rises rapidly and reaches a maximum value of 83 °C in about 300 s and can remain stable. As a comparison, when there is no r-AlMo 6 -V 10 in the system, under the same illumination conditions, its temperature only rises by about 10 °C. This kind of photothermal performance of the dispersion system is recyclable. After at least 5 cycles, its photothermal conversion ability still remains ( Figure 23 c). According to the heating-cooling curve of the r-AlMo 6 -V 10 dispersion system ( Figure 23 d), the photothermal conversion efficiency of the system can be calculated to be 16.3% ( Figure 24 b). When irradiating the r-CrMo 6 -V 10 dispersion system with near-infrared light, it shows a similar heating process as the r-AlMo 6 -V 10 dispersion system, and remains stable after rapidly heating to 84 °C ( Figure 25 a), and undergoes multiple cycles without obvious attenuation ( Figure 25 b). According to the heating-cooling curve of the r-CrMo 6 -V 10 dispersion system ( Figure 26 a), the photothermal conversion efficiency of the system can be calculated to be 22.2% ( Figure 26 b).

[0110] According to the near-infrared photothermal performance of r-AlMo 6 -V 10 and r-CrMo 6 -V 10 , they were used as photothermal catalysts to accelerate the cycloaddition reaction of epoxides with carbon dioxide, and the conditions of the catalytic reaction were optimized and explored using epichlorohydrin and carbon dioxide as substrates as a model.

[0111]

[0112] As shown in Table 8, when there is no [[CH]] 3 CH 2 CH 2 CH 2 ) 4 N·Br (TBA·Br) in the reaction system or the amount of N·Br (TBA·Br) is relatively small, the progress of the reaction does not exceed 10%. When the amounts of TBA·Br and the catalyst are increased simultaneously and the reaction temperature is raised from 55 °C to 70 °C, the conversion rate of the substrate increases significantly to 80%. Under the condition that the substrate epichlorohydrin is 6.3 mmol and acts as a solvent, when the amount of the catalyst is 10 –3 mmol, TBA·Br is 0.62 mmol, the reaction temperature is 80 °C, and the reaction time is 4 h, the conversion rate of the substrate reaches 99%, which is set as the optimal reaction condition. On this basis, the catalytic ability of each component of the catalyst is evaluated, and the catalytic results at room temperature and an external heating temperature of 80 °C are compared with those of photothermal catalysis.

[0113] Table 8 Catalytic performance of the catalyst for the cycloaddition reaction of epichlorohydrin and carbon dioxide under different conditions a

[0114]

[0115] a Reaction conditions: Epichlorohydrin: 0.5 mL, 6.3 mmol, solvent-free, CO 2 balloon. b The conversion rate is calculated based on the elementary epichlorohydrin and determined by 1H NMR.

[0116] As shown in Table 9, when there is no catalyst, the conversion rate of epichlorohydrin is very low, about 10%, whether at room temperature, under heating or under near-infrared light irradiation. When using Na 3 AlMo 6 and Na 3 CrMo 6 as catalysts, since they have no near-infrared photothermal conversion ability, the increase in the conversion rate of the substrate under light irradiation is limited. At the same time, under external heating conditions, the conversion rate of the substrate is not high, indicating that their catalytic abilities are relatively weak. In contrast, when using the reduced Na 6 V 10 (r-Na 6 V 10 ) as a catalyst, due to its good photothermal conversion ability, the solution temperature can be rapidly increased under near-infrared light irradiation, resulting in a significant increase in the substrate conversion rate to 56%. Under external heating conditions, when using r-Na 6 V 10 as a catalyst, the conversion rate of the substrate can also reach 26%, indicating that compared with the Anderson structure polyanion, r-Na6 V 10 has a stronger catalytic effect. When using the reduced skeletal structure r-AlMo 6 -V 10 and r-CrMo 6 -V 10 as catalysts, their good photothermal conversion ability effectively promotes the reaction. Under near-infrared light irradiation, the conversion rate of epichlorohydrin can reach 99%, showing good catalytic performance. In contrast, by external heating, under the same conditions, the conversion rate of the substrate can only reach about 45%, indicating that near-infrared light has a strong promoting effect on the reaction. Under near-infrared light irradiation conditions, the reason for the significant increase in the substrate conversion rate can be attributed to the integration of the photothermal center and the catalytic center in the reduced ionic skeleton. The heat generated by the photothermal center can directly act on the catalytic center quickly and without loss, thus effectively improving the reaction efficiency. In addition, regardless of the catalyst, when the reaction temperature of the system is at room temperature, the conversion rate of the substrate does not exceed 11%, indicating that temperature plays an irreplaceable role in crossing the energy barrier during the substrate reaction process, which further reveals the advantages of the integration of the photothermal center and the catalytic center.

[0117] Table 9 Catalytic reaction performance of the cycloaddition of epichlorohydrin and carbon dioxide under different reaction conditions a

[0118]

[0119] a Reaction conditions: epichlorohydrin: 6.3 mmol, TBA·Br: 0.62 mmol, catalyst: 1 μmol, CO 2 balloon; "Photothermal" means the reaction is completed under near-infrared light irradiation (808 nm laser, power density 2 W cm -2 ), "External heating at 80 °C" and "Room temperature" mean the reaction is carried out in an oil bath heated to 80 °C or room temperature (about 25 °C), and the reaction time is 4 h. All reactions are carried out in the dark to ensure that the only available light source during the reaction is near-infrared light. The yield is based on epichlorohydrin and is calculated using the results of nuclear magnetic resonance hydrogen spectrum.

[0120] To further enhance the understanding of the reaction process, the change of substrate conversion rate with time was monitored. As Figure 27 shown in a of and b of 27, in the first hour of the reaction, the conversion rate of the substrate rapidly increases to about 50%, and then the conversion rate slowly rises. At 4 h, it approaches the end point of the reaction and reaches 99%. When the reaction proceeds to 1 h, the catalyst is removed from the reaction system by hot filtration. It can be seen that in the subsequent time, the substrate conversion rate hardly changes, indicating that r-AlMo 6 -V 10and r-CrMo 6 -V 10 plays an important role in the progress of the cycloaddition reaction of carbon dioxide. No solvent is used during the reaction process, and the catalyst is also insoluble in the substrate. Therefore, the catalyst can be removed by extraction and used for the next catalytic reaction after treatment. After at least 4 cycles, the conversion rate of the substrate does not change significantly( Figure 27 c) in). The infrared spectra( Figure 28 ) and powder X-ray diffraction spectra( Figure 29 ) of the catalyst before and after the catalytic reaction indicate that the catalyst remains stable during the reaction and the framework structure still exists.

[0121] To expand the application of the reduced ionic framework in near-infrared photothermal catalysis, the influence of substituents on the cycloaddition reaction of carbon dioxide was further investigated. As shown in Table 10, when the electron-withdrawing group Cl at the end of the epoxide was removed, the catalytic ability of the two reduced frameworks for the substrate did not decrease, and the conversion rate could still reach 99%. When the electron-withdrawing group Cl at the end of the epoxide was replaced by a benzene ring, the conversion rate of the substrate decreased slightly. Under the action of the two catalysts, the conversion rates of the substrate were 90% and 93% respectively. It is speculated that the relatively large volume of the benzene ring may hinder the rapid progress of the reaction. To verify this speculation, an oxygen atom was added between the epoxide and the benzene ring. It can be seen that the conversion rate of the reaction increased relative to the substrate substituted by the benzene ring. Under the action of the two catalysts, the conversion rates of the substrate reached 96% and 98% respectively. On the other hand, when the molecule directly combined with cyclohexane was used as the substrate, under the action of the two catalysts, the conversion rates of the substrate decreased significantly to 51% and 53% respectively, further verifying the hindering effect of steric hindrance on the reaction.

[0122] Table 10 Performance of the catalyst in the cycloaddition reaction of epoxides with different substituents and carbon dioxide a

[0123]

[0124] a Reaction conditions: epichlorohydrin: 6.3 mmol, TBA·Br: 0.62 mmol, catalyst: 1 μmol, CO 2 balloon, reaction time: 4 h, the reaction was completed under near-infrared light (808 nm laser, 2 W cm -2 ). b The yield is based on epichlorohydrin and calculated using the results of 1H NMR spectroscopy.

[0125] In the cycloaddition reaction of epoxides and carbon dioxide with an ionic framework as the catalyst, based on the degree of reaction progression in the presence of different components, combined with the structural characteristics of the ionic framework and the reaction mechanisms of similar systems in the literature, the following possible reaction processes are proposed. As Figure 30 shown, the epoxide is activated through the weak connection between the oxygen atom and the metal ions of the polyoxometalate, and thus undergoes ring-opening in the presence of bromide ions, transforming into a bromo-substituted intermediate. In the further reaction, carbon dioxide inserts into this intermediate product to obtain the ring-opened carbonate, and subsequently the bromine leaves to give the final product, cyclic carbonate.

[0126] Conclusion: The ionic bonds between the {Na 4 O 18} clusters formed by sodium ions and the Anderson-type polyanions [AlMo 6 (OH) 6 O 18 3- and [CrMo 6 (OH) 6 O 18 3- construct two isomorphic two-dimensional ionic frameworks. [V 10 O 28 6- is located in the voids of the framework and is stabilized by adjacent Anderson-type clusters through double hydrogen bonds. The ordered distribution of two types of polyoxometalates in the same structure is successfully achieved in the prepared ionic framework, which is beneficial to obtaining higher efficiency in catalytic reactions. Using the ionic framework as the catalyst, its performance in the Knoevenagel condensation reaction and the sulfide oxidation reaction was studied. The results show that the ionic framework has enhanced catalytic conversion ability for the substrates of both types of reactions, showing the characteristics of dual-site catalysis. The catalytic effect of the ionic framework is better than that of the physical mixture of the two polyoxometalates under the same conditions, indicating that the uniformly dispersed polyoxometalates in the ionic framework are more conducive to the conversion of substrates. In the presence of a reducing agent, [V 10 O 28 6- in the ionic framework can be partially reduced to achieve a single-crystal-to-single-crystal structural transformation, and the reduced product has strong absorption in the near-infrared region and has the ability of near-infrared photothermal conversion. The reduced ionic framework serves both as a photothermal agent and as a catalyst for the near-infrared photothermal cycloaddition reaction of propylene oxide and carbon dioxide. The experimental results show that under the action of the photothermal-catalytic integrated reduced ionic framework, the epoxide can be efficiently and selectively converted into the corresponding cyclic carbonate, and the conversion efficiency under photothermal conditions is significantly better than that of the corresponding externally heated reaction efficiency, demonstrating the advantages of near-infrared photothermal catalysis.

[0127] ​​​​The above research results provide new ideas for the construction of ion skeletons based on polyoxometalates and also provide a new method for the co-crystallization of multiple polyoxometalates in the same structure. The coexistence of multiple polyoxometalates provides multiple catalytic sites for the system, enhancing the catalytic ability of the system. Moreover, the reduced polyoxometalates can also endow the system with photothermal conversion ability, thus expanding the application scope of the system. In addition, by utilizing the reducibility of some polyanions and the special chemical environment provided by the framework structure, the single-crystal-to-single-crystal structural transformation is completed within a limited range, expanding the application scope of similar related strategies.

[0128] The above are only the preferred embodiments of the present invention. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent.

Claims

1. Application of a reducible ion framework in dual-site catalysis, characterized in that: Preparation of AlMo6-V by beaker reaction 10 and CrMo6-V 10 The prepared ionic framework is used as a heterogeneous catalyst to catalyze the Nauwengler condensation reaction and thioether oxidation reaction.

2. The use according to claim 1, characterized in that: The AlMo6-V 10 The preparation method of the ionic framework is as follows: 0.20 g Na6V 10 O 28 and 0.19 g Na3[Al(OH)6Mo6O 18 ] was dissolved in 5 mL of hydrochloric acid solution, then ultrasonicated for 10 min, filtered to obtain an orange solution, and the filtrate was left to stand at room temperature for 3 days to finally obtain orange crystals of AlMo6-V 10 .

3. The use according to claim 2, characterized in that: The CrMo6-V 10 The preparation method of the ionic framework is as follows: 0.20 g Na6V 10 O 28 and 0.21 g Na3[Cr(OH)6Mo6O 18 ] was dissolved in 5 mL of hydrochloric acid solution, then ultrasonicated for 10 min, filtered to obtain an orange solution, and the filtrate was left to stand at room temperature for 3 days to finally obtain orange crystals of CrMo6-V 10 .

4. The use according to claim 3, characterized in that: The pH of the hydrochloric acid solution is 3.

5. Application of reducible ion framework in photothermal catalysis, characterized in that: Through AlMo6-V 10 and CrMo6-V 10 The ionic framework was reduced to obtain the reduced products r-AlMo6-V 10 and r-CrMo6-V 10 , using the reduction product r-AlMo6-V 10 and r-CrMo6-V 10 It can be used as a photothermal catalyst for the efficient and selective cycloaddition of alkylene oxides with carbon dioxide.

6. The use according to claim 5, characterized in that: The specific process of the restoration process is as follows: The reducing agent was dissolved in ethanol, then added dropwise onto the ionic framework crystals and the color change over time was observed; after the reaction was completed, the reduced crystals were washed 3 times with ethanol to obtain the final reduction product.

7. The use according to claim 6, characterized in that: The reducing agent is oxalic acid, vitamin C or SnCl2.

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