CN119633853A - A photocatalyst and its preparation method and application - Google Patents

Abstract

The present invention discloses a photocatalyst and a preparation method and application thereof, and relates to the field of catalysts. The photocatalyst is prepared by a hydrothermal-calcination-photodeposition method, and comprises nanoflowers composed of ultra-thin nanosheets of indium zinc sulfide and iridium metal atoms loaded on their surfaces. The catalyst can be applied to free radical photocatalytic alkylation reactions, especially indole C-2 alkylation reactions, greatly improving the yield and selectivity of the reaction. The photocatalyst also has the advantages of less addition of precious metals, high stability, and the ability to catalyze reactions under visible light, and has broad application prospects in the field of organic synthesis.

Description

Photocatalyst, and preparation method and application thereof

Technical Field

The invention relates to the field of catalysts, in particular to a photocatalyst, a preparation method and application thereof.

Background

In the field of fine chemical synthesis, alkylation reactions are used to prepare various intermediates and end products for pharmaceuticals, pesticides, fragrances, dyes, etc. By precisely controlling the alkylation reaction, compounds having specific structures and functionalities can be synthesized to meet specific application requirements. The development of alkylation technology not only helps to increase the efficiency of chemical production, but also helps to reduce environmental impact. The alkylation process with good selectivity and few byproducts can reduce the generation of wastes and promote the effective utilization and recycling of resources.

The traditional alkylation reaction needs extremely high reaction temperature, has larger energy consumption and has weak selectivity to alkyl substitution sites. The photocatalytic alkylation reaction can be performed at room temperature, is clean and energy-saving, has high atom utilization rate, can have good substitution site selectivity according to the selection of the catalyst, and can be compatible with various substitution guiding functional groups due to the mild conditions.

The main types of existing alkylation photocatalysts mainly comprise three main types of metal oxides, composite metal oxides and metal complexes. The metal oxide such as TiO ₂, znO, siO ₂ and the like has good chemical stability and catalytic performance, but has a narrow band gap, usually only can absorb ultraviolet light and has low illumination energy efficiency, the composite metal oxide such as a composite of TiO ₂ and Nb ₂O₅ can widen the light response range by adjusting the composite proportion, enhances the catalytic activity under visible light, but has complex composite process and relatively high cost, and the metal complex such as Ru, pd, rh and the like has higher catalytic activity under visible light, better selectivity, but generally has higher price and insufficient stability, thereby limiting the large-scale application of the complex.

The nano material has extremely large specific surface area and special light absorption property, and is very suitable for serving as a catalyst in photochemical reaction. The Chinese patent publication No. CN113145152A discloses a visible light catalytic one-pot multidirectional chemical selectivity N-alkylation method, wherein the photocatalyst is MXene (transition metal carbon/nitride two-dimensional nano-plate) material dispersed with 3% of metal nano-particles, and the metal nano-particles can be a plurality of platinum, iridium and the like. The catalyst has excellent catalytic activity and selectivity in the presence of an alkaline additive, but the catalyst material has more noble metals, is complex to prepare, requires alkaline conditions in specific application, only solves the problem of N-alkylation, and has no great help to the problem of selective alkylation on aromatic carbon.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a photocatalyst, and a preparation method and application thereof. The photocatalyst comprises indium zinc sulfide nanoflower and iridium metal atoms loaded on the surface of the indium zinc sulfide nanoflower, has high stability, good catalytic performance and wider photoresponse range, and has low content of noble metal, so that the yield and selectivity of free radical type photocatalytic alkylation reaction on some unsaturated carbon can be effectively improved.

The invention aims to provide a photocatalyst which comprises nanoflower composed of indium zinc sulfide (ZnIn ₂S₄) ultrathin nanosheets and iridium metal atoms loaded on the surfaces of the nanoflower.

Another object of the present invention is to provide a method for preparing the above photocatalyst, comprising the steps of:

(1) Weighing zinc salt, indium salt and sulfur source, stirring in a solvent until the zinc salt, the indium salt and the sulfur source are completely dissolved, then carrying out hydrothermal reaction, cooling, filtering, washing filter residues, and drying to obtain a catalyst carrier;

(2) Calcining the catalyst carrier in an inert atmosphere;

(3) And uniformly mixing the calcined catalyst carrier with an iridium ion reagent in water, carrying out photodecomposition reduction after degassing, centrifuging, and drying the obtained precipitate to obtain the photocatalyst.

It is a final object of the present invention to provide the use of the above-described photocatalyst in a free radical photocatalytic alkylation reaction.

The technical scheme of the invention has the following beneficial effects:

1. according to the photocatalyst, the nano flower is used for supporting iridium metal atoms, the required noble metal amount is small, the contact area is large, the catalytic effect is good, the target reaction can reach more than 90% at maximum only by adding 0.05-0.1 mol% of the catalyst with the iridium metal atom loading of 0.3-0.7wt%, the transition metal atom adding amount is 1-3 orders of magnitude lower than that in the prior art, and the cost is low and the efficiency is high.

2. According to the photocatalyst disclosed by the invention, the iridium metal atoms are supported by the nanoflowers, so that the dispersibility of the iridium atoms is improved, the maximum absorption wavelength of the iridium atoms is shifted into a visible light region, the light response range is improved, and the energy consumption of the photocatalytic reaction is reduced.

3. In the preparation method of the photocatalyst, the catalyst carrier is calcined at a high temperature of 200-300 ℃, so that the prepared photocatalyst has high stability, does not generate harmful substances when being applied to exothermic reaction, and is environment-friendly and durable.

4. The photocatalyst is applied to the photocatalytic alkylation reaction of indole compounds, can effectively solve the problem of C-2 selectivity under the condition that an N-1 site has no guide group, reduces the generation of C-3 alkylation products, and has the highest C-2 alkylation yield of 92%.

Drawings

FIG. 1 is a scanning electron microscope image of alkylated photocatalyst particles according to example 1 of the present invention.

Fig. 2 is a transmission electron microscope image of alkylated photocatalyst particles according to example 1 of the present invention, wherein iridium metal atoms are in the red circle.

FIG. 3 is an X-ray diffraction pattern of the catalyst support and alkylated photocatalyst particles of example 1 of the present invention, as well as standard diffraction data for ZnIn ₂S₄.

FIG. 4 is a graph of the test cycle of the alkylation photocatalytic of example 3 of the present invention, wherein each cycle is 8h.

Detailed Description

The present invention will be further described with reference to the following examples and drawings, in order to make the technical means, the creation characteristics, the achievement of the objects and the effects of the present invention easy to understand. It is obvious that the described examples are only some embodiments of the present invention and are illustrative of the technical solution of the present invention and not limiting.

The invention provides a photocatalyst, which comprises nanoflower composed of indium zinc sulfide (ZnIn ₂S₄) ultrathin nanosheets and iridium metal atoms loaded on the surfaces of the nanoflower.

Further, the diameter of the nanoflower is 7-10 mu m.

Further, the loading of the iridium metal atoms is 0.3-0.7wt%. Preferably, the loading amount of the iridium metal atoms is 0.5wt%.

The invention also provides a preparation method of the photocatalyst, which comprises the following steps:

(1) Weighing zinc salt, indium salt and sulfur source, stirring in a solvent until the zinc salt, the indium salt and the sulfur source are completely dissolved, then carrying out hydrothermal reaction, cooling, filtering, washing filter residues, and drying to obtain a catalyst carrier;

(2) Calcining the catalyst carrier in an inert atmosphere;

(3) And uniformly mixing the calcined catalyst carrier with an iridium ion reagent in water, carrying out photodecomposition reduction after degassing, centrifuging, and drying the obtained precipitate to obtain the photocatalyst.

Further, the molar ratio of zinc salt to indium salt to sulfur source is 1:1.5-2:4-5 based on zinc, indium and sulfur. Preferably, the molar ratio of zinc salt, indium salt and sulfur source is 1:2:4.5.

Thioacetamide is one of the common vulcanizing agents in the laboratory, has moderate reaction activity, is milder than the strong vulcanizing agents such as Na ₂ S and the like, is convenient for controlling the reaction rate, and obtains the nanostructure with proper size. The proportion of the substrate is based on the molar ratio of indium zinc sulfide (ZnIn ₂S₄), namely 1:2:4, and a slight excess of sulfur is used on the basis of the molar ratio to ensure the complete reaction of metal elements, and optionally, the use amount of indium can be slightly reduced under the condition of not damaging the integral morphology structure of the catalyst carrier so as to save the cost.

Further, the zinc salt is preferably zinc chloride, the indium salt is preferably indium chloride tetrahydrate, the sulfur source is preferably thioacetamide, and the solvent is ethylene glycol and/or water.

Further, the hydrothermal reaction is carried out for 10-12 hours at 120-160 ℃, and the filter residue is washed and dried by deionized water and absolute ethyl alcohol and then dried for 8-12 hours at 60 ℃. Preferably, the hydrothermal reaction is carried out in a polytetrafluoroethylene-lined vessel.

Further, the calcination treatment is carried out for 6-8 hours at 200-300 ℃, and the inert atmosphere is a nitrogen atmosphere.

The alkylation reaction is generally exothermic, the exothermic heat of the reaction is generally 100-150 kJ/mol, the catalyst can not generate toxic and harmful substances at a higher temperature, and therefore, the catalyst carrier needs to be calcined to remove decomposable impurities and harmful substances, and the mechanical property and the adsorption activity of the catalyst carrier can be improved. Because sulfides are easily oxidized at high temperature, normal pressure nitrogen is needed to be used as a protective gas, and the structure of the catalyst carrier nanoflower is prevented from being damaged.

Further, the iridium ion reagent is iridium chloride or sodium hexachloroiridate, and the photo-deposition reduction is carried out for 1-3 hours. Specifically, the iridium chloride is iridium trichloride and hydrate thereof, and the sodium hexachloroiridate is sodium hexachloroiridium (III) and hydrate thereof.

Among relatively stable trivalent and tetravalent iridium compounds, the iridium ion reagent selects a trivalent iridium compound with weaker oxidability, is favorable for photo-deposition reduction, and has less influence on sulfide catalyst carriers with certain reducibility.

The photo-deposition reduction is to reduce the iridium with high valence state in the iridium ion reagent into iridium atoms and uniformly deposit the iridium atoms on the nanoflower. The method for degassing the liquid nitrogen includes freezing the solution into solid by liquid nitrogen, vacuumizing the container for a period of time, introducing inert gas, and finally heating the solid to melt the solid into the solution.

The invention finally provides application of the photocatalyst in free radical type photocatalytic alkylation reaction, wherein the addition amount of the photocatalyst is 0.05-0.1 mol%, and preferably, the addition amount of the photocatalyst is 0.08mol%.

Specifically, the invention provides application of the photocatalyst in the photocatalytic alkylation reaction of indole compounds, in particular to application in the selective alkylation reaction of indole C-2:

Wherein R ₁ is selected from hydrogen or methyl, R ₂ is selected from hydrogen, alkyl or alkoxy, R ₃ is selected from hydrogen, ester or diethoxyphosphonyl, and R ₄ is selected from methyl, ethyl or phenyl. Wherein, the condition for higher C-2 alkylation yield is that the substituent of the diazonium compound is hydrogen or electron-withdrawing group, and the substituent alkyl on the indole benzene ring is hydrogen or electron-donating group at 4-position.

As the nucleophilic property of the indole C-3 position is stronger, the general electrophilic substitution alkylation method has higher selectivity to the C-3 alkylation product, and guide groups are required to be pre-installed at the N-1 and C-3 positions in order to obtain the C-2 alkylation product. The radical substitution method allows selective C-2 alkylation of indoles without directing groups due to the higher stability of benzylic radical intermediates formed during the C-2 substitution.

The present invention will be specifically described with reference to examples. The experimental methods, if not specified, are conventional methods, and the reagents and materials, if not specified, are commercially available.

Preparation example 1

(1) Weighing 4mmol of zinc chloride, 8mmol of indium chloride tetrahydrate and 18mmol of thioacetamide, adding into a mixed solution of 120mL of ethylene glycol and 120mL of deionized water, stirring for 20min, transferring into a reaction kettle of polytetrafluoroethylene lining material, performing hydrothermal reaction for 10h at 140 ℃, cooling the reaction liquid to room temperature, filtering to collect precipitate, washing 3 times with deionized water, washing 3 times with absolute ethyl alcohol, and drying the precipitate at 60 ℃ for 8h to obtain the catalyst carrier.

(4) Placing the catalyst carrier into a calcination bin, continuously introducing nitrogen, keeping the pressure in the bin consistent with the external atmospheric pressure, and calcining the catalyst carrier at 300 ℃ for 6 hours;

(5) The calcined catalyst carrier (4 mmol) is completely dispersed into deionized water in a quartz photoreactor, 22.1mg of sodium hexachloroiridium (III) hydrate (Na ₃IrCl₆·H₂ O) is added for stirring and dissolution, the mixture is subjected to photodecomposition reduction for 2 hours after degassing, centrifugal separation is carried out, and the obtained precipitate is naturally dried in an oven to obtain the photocatalyst 1, wherein the iridium nanoparticle load is 0.5wt%.

The photocatalyst (0.5 wt% Ir-ZnIn ₂S₄) obtained in example 1 was analyzed by a Scanning Electron Microscope (SEM) to obtain a scanning electron micrograph, and as shown in FIG. 1, the indium zinc sulfide ultrathin nanosheet structure and spherical nanoflower formed by stacking thereof can be seen.

The photocatalyst (0.5 wt% Ir-ZnIn ₂S₄) obtained in example 1 was analyzed by Transmission Electron Microscopy (TEM) to obtain a transmission electron micrograph, as shown in FIG. 2, in which the uniformly dispersed iridium metal atoms on the lower left portion of the indium zinc sulfide ultra-thin nano-sheet can be seen at a larger magnification than that of the SEM photograph.

The catalyst support and alkylated photocatalyst particles obtained in example 1 were subjected to an X-ray powder diffraction test, the results of which are shown in fig. 3. It can be seen that both the catalyst support and the alkylation catalyst particles showed a major diffraction peak of indium zinc sulfide (ZnIn ₂S₄), while a trace amount of iridium of 0.5% did not have any significant effect on the crystal structure, indicating that the structural properties of the catalyst support were maintained after supporting the iridium metal atom.

Preparation example 2

The photocatalyst preparation method in this example is the only difference from the photocatalyst preparation example 1 in that the raw material amount of the catalyst carrier is 4mmol of zinc chloride, 6mmol of indium chloride tetrahydrate and 16mmol of thioacetamide, and the photocatalyst 2 is prepared.

Preparation example 3

The only difference between the preparation method of the photocatalyst in this example and the preparation example 1 is that the photocatalyst 3 is prepared by reacting for 12 hours under the hydrothermal reaction condition of 120 ℃.

Preparation example 4

The only difference between the preparation method of the photocatalyst in this example and the preparation example 1 is that the photocatalyst 4 is prepared by reacting for 10 hours under the hydrothermal reaction condition of 160 ℃.

Preparation example 5

The photocatalyst preparation method in this example is unique from that of preparation example 1 in that the photocatalyst 5 is prepared by calcination at 200 ℃ for 8 hours.

Preparation example 6

The only difference between the preparation method of the photocatalyst in this example and the preparation example 1 is that the addition amount of sodium hexachloroiridium (III) hydrate is 31.0mg, and the photocatalyst 6 in which the iridium metal atom loading amount is 0.7wt% is prepared.

Preparation example 7

The only difference between the preparation method of the photocatalyst in this example and that of preparation example 1 is that the addition amount of sodium hexachloroiridium (III) hydrate is 13.3mg, and the photocatalyst 7 in which the iridium metal atom loading amount is 0.3wt% is prepared.

The alkylated photocatalyst particles obtained in this example were subjected to an alkylated photocatalytic cycle test, four cycles were tested with 8h as one cycle, and the results are shown in fig. 4. It can be seen that the catalyst particles can still maintain their high catalytic activity in continuous catalytic experiments with the least catalyst addition in the scope of the present invention, which indicates that the alkylated photocatalyst particles of the present invention have strong stability and are convenient for recycling.

The following uses the photocatalyst obtained in each preparation example of the present invention to implement its application in the photocatalytic selective alkylation of indole C-2.

Application example 1

This example selects photocatalyst 1 from preparation example 1, and applies it to the following indole C-2 alkylation reaction:

The reaction was carried out in a specially constructed photo-reactor consisting of a cooling block and LED board connected to a constant current (0.7A) power supply. The experimental procedure was as follows:

4mmol (4 equiv) of N-methylindole, 1mmol (1 equiv) of ethyl diazoacetate and 0.8 mu mol (0.08 mol% based on 1equiv reaction) of the photocatalyst 1 obtained in preparation example 1 are dispersed into a mixed solvent (volume ratio 10:1) of 10mL of methanol and 1mL of water, continuously stirred uniformly, degassed for 30min, and subjected to photocatalytic alkylation reaction under a 3W visible light LED lamp, wherein the reaction temperature is controlled at 28 ℃ through a cooling block in the reaction process. The product was analyzed by Gas Chromatography (GC) using argon as carrier gas, and the yield of the target molecule was calculated to be 92%.

Application example 2

The only difference between this example and application example 1 is that the photocatalyst 1 was added in an amount of 1.0. Mu. Mol (0.1 mol%) and the yield of the target molecule was 89%.

Application example 3

The only difference between this example and application example 1 is that the photocatalyst 1 was added in an amount of 0.5. Mu. Mol (0.05 mol%) and the yield of the target molecule was 79%.

Application example 4

The only difference between this example and application example 1 is that the amounts of methanol and water are 10.0mL and 0.2mL (volume ratio 50:1), respectively, and the target molecule yield is 75%.

Application example 5

The only difference between this example and application example 1 is that the amounts of methanol and water are 7.0mL and 3.5mL (volume ratio 2:1), respectively, and the yield of target molecule is 77%.

Application example 6

The only difference between this example and application example 1 is that the reaction was carried out using the photocatalyst 2 obtained in preparation example 2, with a target molecule yield of 90%.

Application example 7

The only difference between this example and application example 1 was that the reaction was carried out using the photocatalyst 3 obtained in preparation example 3, and the yield of the target molecule was 87%.

Application example 8

The only difference between this example and application example 1 was that the reaction was carried out using the photocatalyst 4 obtained in preparation example 4, and the yield of the target molecule was 85%.

Application example 9

The only difference between this example and application example 1 is that the reaction was carried out using the photocatalyst 5 obtained in preparation example 5, and the yield of the target molecule was 81%.

Application example 10

The only difference between this example and application example 1 was that the reaction was carried out using the photocatalyst 6 obtained in preparation example 6, and the yield of the target molecule was 82%.

Application example 11

The only difference between this example and application example 1 is that the reaction was carried out using the photocatalyst 7 obtained in preparation example 7, with a target molecule yield of 73%.

Application example 12

The only difference between this example and application example 1 is that the photocatalyst 1 used was calcined at 150℃for 20min before feeding, with a target molecular yield of 91%.

Application example 13

The only difference between this example and application example 1 is that the reaction used is as follows, with a yield of 93% of the target molecule.

Application example 14

The only difference between this example and application example 1 is that the reaction used is as follows, with a yield of 74% of the target molecule.

Comparative example 1 was used

The only difference between this example and application example 1 is that no photocatalyst was added and the yield of target molecule was 0.

Comparative example 2 was used

The only difference between this example and application example 1 is that no LED illumination is performed and the target molecule yield is 0.

Comparative example 3 was used

The only difference between this example and application example 1 is that the photocatalyst 1 was replaced with the same mass of the catalyst support not supporting iridium metal atoms obtained in preparation example 1, and the target molecular yield was 0.

Table 1 effect of alkylation conditions on yield of target molecules for reaction 1:

As can be seen from the experimental results summarized in Table 1, the catalyst and the light irradiation are necessary for the alkylation reaction to occur, and under the conditions of the examples, the yield of the target molecule (3-substituted product) is more than 75%, wherein the yield of the target molecule can reach 92% with the application example 1 as the optimal.

Table 2 effect of catalyst preparation method on target molecule yield of reaction 1:

From the experimental results summarized in Table 2, it can be seen that the photocatalyst preparation conditions described in preparation example 1 are optimal preparation conditions within the scope of the present invention. The hydrothermal reaction time in the preparation process is prolonged, the crystallinity and the grain diameter of the material can be improved, a uniform microstructure is formed, agglomeration can be caused due to overlong time, the dispersibility is influenced, the hydrothermal reaction temperature is increased, the reaction rate is accelerated, the morphology evolution is promoted, the formation of a nano structure is facilitated, the coarsening of grains is easily caused due to overhigh temperature, the performance is damaged, and the proper preparation conditions are favorable for forming high-activity sites, so that the balance between the performance and the stability of the photocatalyst is realized.

The iridium nano particles in the photocatalyst have great contribution to the selectivity and yield of indole C-2 alkylation reaction. In contrast to this, the present invention provides,The study by Ciszewski et al indicated that the same reaction as in application example 1 was carried out with a rubidium complex catalyst under the same conditions, and the yield of the target molecule was 68-76% which was far lower than in the preferred embodiment of the present invention.

It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above description will be apparent to those of ordinary skill in the art, and it is intended that all such variations or modifications be considered within the scope of the present invention.

Claims (10)

1. A photocatalyst, characterized in that it comprises nanoflowers composed of ultra-thin indium zinc sulfide nanosheets and iridium metal atoms loaded on the surface thereof. 2 . The photocatalyst according to claim 1 , wherein the diameter of the nanoflower is 7 to 10 μm. 3. The photocatalyst according to claim 1 is characterized in that the loading amount of the iridium metal atoms on the surface of the nanoflower is 0.3-0.7 wt%; preferably, the loading amount of the iridium metal atoms on the surface of the nanoflower is 0.5 wt%. 4. A method for preparing a photocatalyst according to any one of claims 1 to 3, characterized in that it comprises the following steps: Weighing zinc salt, indium salt and sulfur source, stirring in a solvent until completely dissolved, then performing a hydrothermal reaction, cooling and filtering, washing and drying the filter residue to obtain a catalyst carrier; The catalyst carrier is calcined in an inert atmosphere; The calcined catalyst carrier and the iridium ion reagent are mixed uniformly in water, degassed, and subjected to photo-deposition reduction, centrifuged, and the obtained precipitate is dried to obtain the photocatalyst. 5. The method for preparing a photocatalyst according to claim 4, characterized in that, based on zinc, indium and sulfur elements, the molar ratio of the zinc salt, indium salt and sulfur source is 1:1.5 to 2:4 to 5; preferably, the molar ratio of the zinc salt, indium salt and sulfur source is 1:2:4.5. 6. The method for preparing a photocatalyst according to claim 5, characterized in that the zinc salt is zinc chloride; the indium salt is indium chloride tetrahydrate; the sulfur source is thioacetamide; and the solvent is ethylene glycol and/or water. 7. The method for preparing a photocatalyst according to claim 4 is characterized in that the conditions for the hydrothermal reaction are to react at 120-160°C for 10-12 hours; the filter residue is washed and dried with deionized water and anhydrous ethanol, and then dried at 60°C for 8-12 hours; preferably, the hydrothermal reaction is carried out in a container lined with polytetrafluoroethylene. 8 . The method for preparing a photocatalyst according to claim 4 , wherein the calcination treatment condition is calcination at 200 to 300° C. for 6 to 8 hours; and the inert atmosphere is a nitrogen atmosphere. 9 . The method for preparing a photocatalyst according to claim 4 , wherein the iridium ion reagent is iridium chloride or sodium hexachloroiridate; and the photodeposition reduction is performed for 1 to 3 hours. 10. Use of the photocatalyst according to any one of claims 1 to 3 in a photocatalytic alkylation reaction, characterized in that the added amount of the photocatalyst is 0.05-0.1 mol%; preferably, the added amount of the photocatalyst is 0.08 mol%.