Pyridine oxidation catalyst, process for the preparation thereof, process for the preparation of pyridine-n-oxides

Abstract

The application provides a pyridine oxidation catalyst and a preparation method thereof, and a preparation method of pyridine-N-oxide. The preparation method of the pyridine oxidation catalyst comprises the following steps: mixing a molybdenum source and an inorganic acid solution to obtain solution A, mixing the solution A and a Dawson type heteropoly acid precursor to obtain solution B; the solution B is subjected to a first reaction to obtain an intermediate product; the intermediate product, a transition metal source and an optional carrier are subjected to a second reaction to obtain the pyridine oxidation catalyst; the transition metal source is selected from one or more of a Mn source, a Zn source, an Fe source, a Co source, a Cu source and a Ni source. The application utilizes the heteropoly acid (WD structure), and through complexation of the transition metal ion, the obtained catalyst is strengthened in the redox sites and the acid sites, so that the purpose of improving the N-oxidation synthesis efficiency of the pyridine compound and the product purity is achieved, and the efficient application and technical effect of the low-cost and environment-friendly catalytic system in the preparation of the pyridine N-oxide are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of organic synthesis, in particular, to a pyridine oxidation catalyst and a preparation method thereof, and a preparation method of pyridine-N-oxide. BACKGROUND

[0002] Pyridine and its derivatives are of great interest due to their unique chemical properties and wide industrial applications, especially in the pharmaceutical, pesticide and fine chemical industries, where they often exist as important intermediates. Pyridine N-oxide, as a member of the pyridine family, has a nitrogen-oxygen group in its structure, which endows the compound with excellent functional group directing properties and reactivity in subsequent reactions, making it an extremely attractive synthetic target. However, current techniques for preparing pyridine N-oxide face a series of challenges, limiting its large-scale production and wide application.

[0003] In the prior art, patent application (Synthesis method of 4-chloro-3-methoxy-2-methyl pyridine-N-oxide, CN107129466 A) uses 20%~30% phosphotungstic acid solution and 4-chloro-3-methoxy-2-methyl pyridine; temperature 85~90℃, drop hydrogen peroxide, and incubate at 83~88℃ for 5~10 hours to obtain 4-chloro-3-methoxy-2-methyl pyridine-N-oxide. Patent application (Method for large-scale preparation of pyridine N-oxide under mild conditions, CN118724805 A) uses copper acetate as catalyst and tetrahydrofuran as solvent to oxidize pyridine to pyridine N-oxide under the condition of 65℃. It is found that the yield of pyridine N-oxide gradually decreases with the increase of substrate steric hindrance, and the yield shows obvious substrate dependence. Patent application (Method for synthesizing 3-cyanopyridine N-oxide in an electric field assisted oxidation tank based on noble metal nanomesh cloth, CN118480788 A) constructs an auxiliary electric field with copper rods or copper plates as negative electrodes and noble metal nanomesh cloth as positive electrodes; constructs an oxidation tank with copper rods or copper plates and noble metal nanomesh cloth fixed at both ends of the inner wall of the oxidation tank. Patent application (High-efficiency and heterogeneous catalytic preparation method of pyridine N-oxide, CN104974088 A) discloses a high-efficiency and heterogeneous catalytic preparation method of pyridine N-oxide. Single-substituted or multi-substituted pyridine or pyridine derivative is selected as the initial raw material, tungsten-loaded titanium dioxide (WO3 / TiO2) is used as the catalyst, and hydrogen peroxide is used as the oxidant to prepare the final product in room temperature aqueous solution.

[0004] In the prior art, the oxidation of pyridine compounds is mostly dependent on high-cost oxidants such as peroxyacetic acid, hydrogen peroxide combined with acetic anhydride or phthalic anhydride, and meta-chloroperbenzoic acid, which not only increases the production cost, but also raises concerns about the safety of transportation and storage. Secondly, although the electrochemical oxidation method theoretically provides an environmentally friendly alternative, the selection and optimization of electrode materials are difficult, and the complex reaction conditions make it difficult to achieve the stability and economy of industrialization. Thirdly, the existing solid-supported catalysts, such as metal oxide-based catalysts, although solve the problem of difficulty in recycling homogeneous catalysts to some extent, still have the defects of low catalytic activity and limited substrate selectivity, which cannot meet the demand of high yield and wide spectrum of applicability.

[0005] Therefore, it is urgent to develop a new catalyst system for the oxidation of pyridine compounds to achieve the synthesis of pyridine-N-oxide with high purity. SUMMARY

[0006] The main purpose of the present application is to provide a pyridine oxidation catalyst and its preparation method, and a preparation method of pyridine-N-oxide, to solve the problem that the catalyst in the prior art cannot efficiently catalyze the oxidation of pyridine compounds and prepare pyridine-N-oxide with high purity.

[0007] To achieve the above purpose, the first aspect of the present application provides a preparation method of a pyridine oxidation catalyst, comprising: step S1, mixing a molybdenum source with an inorganic acid solution to obtain solution A, and mixing solution A with a Dawson-type heteropoly acid precursor to obtain solution B; step S2, solution B is subjected to a first reaction to obtain an intermediate product; step S3, the intermediate product, a transition metal source, and an optional carrier are subjected to a second reaction to obtain the pyridine oxidation catalyst; the transition metal source is selected from one or more of a Mn source, a Zn source, an Fe source, a Co source, a Cu source, and a Ni source.

[0008] Further, in step S1, the molybdenum source is selected from one or more of sodium molybdate, sodium phosphomolybdate, ammonium phosphomolybdate, and ammonium molybdate; the molar concentration of the inorganic acid solution is 1±0.1M; the weight ratio of the molybdenum source to the inorganic acid solution is 1:(50-140); the ratio of the molar amount of the Dawson-type heteropoly acid precursor to the molar amount of Mo element in the molybdenum source is 1:(3-7.5); the inorganic acid is selected from one or more of hydrochloric acid, nitric acid, and sulfuric acid; the chemical formula of the Dawson-type heteropoly acid precursor is Na 12 P2W 18-n O 56 , the chemical formula of the intermediate product is [H6P2W 18-n Mo n O 62 ]·24H2O, wherein n is 3-6.

[0009] Further, in step S2, the reaction time of the first reaction is 2h~3h, and the first reaction is carried out at 40℃~50℃.

[0010] Further, step S2 comprises: solution B is subjected to the first reaction to obtain a crude product; the crude product is dissolved in an acid solution with a pH of 2~3 to obtain a mixed acid solution; and the mixed acid solution is subjected to recrystallization to obtain an intermediate product.

[0011] Further, in step S3, the molar ratio of the intermediate product to the transition metal source is 1:(1.5~2.5); and / or, the reaction time of the second reaction is 8h~10h, and the second reaction is carried out at 80℃~120℃.

[0012] Further, in step S3, the weight ratio of the transition metal source to the carrier is 1:(15~45); and / or, the carrier is selected from one or more of SiO2 carrier, TiO2 carrier, MCM-41 carrier, Al2O3 carrier and ZrO2 carrier.

[0013] The second aspect of the present application provides a pyridine oxidation catalyst, which is prepared by the preparation method of the pyridine oxidation catalyst described above, and the pyridine oxidation catalyst optionally comprises a carrier.

[0014] The third aspect of the present application provides a preparation method of pyridine-N-oxide, which comprises: subjecting a pyridine compound to an oxidation reaction with an oxidant in the presence of the pyridine oxidation catalyst described above to obtain pyridine-N-oxide; and the oxidation reaction is carried out at 75℃~80℃.

[0015] Further, when the pyridine oxidation catalyst does not comprise a carrier, the preparation method of pyridine-N-oxide comprises: adding the pyridine compound, the pyridine oxidation catalyst and the oxidant into an organic solvent to obtain pyridine-N-oxide through a homogeneous oxidation reaction; the weight ratio of the pyridine compound, the pyridine oxidation catalyst and the oxidant is (8~12):1:(12~18); and / or, the time of the homogeneous oxidation reaction is 2h~3h; and / or, the organic solvent is acetonitrile and / or toluene.

[0016] Further, when the pyridine oxidation catalyst comprises a carrier, the preparation method of pyridine-N-oxide comprises: loading the pyridine oxidation catalyst in a reactor, and feeding a pyridine compound and an oxidant into the reactor to obtain pyridine-N-oxide through a heterogeneous oxidation reaction; the pyridine compound is fed in the form of a compound solution with a molar concentration of 0.5±0.01M, and the feeding speed of the compound solution is 0.5g / min~1.0g / min; and / or, the feeding speed of the oxidant is 5g / min~10g / min; and / or, the compound solution uses acetonitrile and / or toluene as a solvent.

[0017] The application of the technical solution of the present application utilizes heteropoly acid (WD structure), and through transition metal ion complexation, the obtained catalyst is strengthened in redox sites and acid sites, the purpose of improving the synthesis efficiency and product purity of pyridine N-oxidation is achieved, and thus the efficient application and technical effect of a low-cost and environmentally friendly catalytic system in the preparation of pyridine N-oxide are realized. DETAILED DESCRIPTION

[0018] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments.

[0019] As described in the background, the catalysts in the prior art cannot efficiently catalyze the oxidation of pyridine compounds, and pyridine-N-oxide cannot be prepared with high purity. In order to solve the above technical problems, the first aspect of the present application provides a preparation method of a pyridine oxidation catalyst, comprising: step S1, mixing a molybdenum source with an inorganic acid solution to obtain solution A, and mixing solution A with a Dawson-type heteropoly acid precursor to obtain solution B; step S2, solution B is subjected to a first reaction to obtain an intermediate product; step S3, the intermediate product, a transition metal source, and an optional carrier are subjected to a second reaction to obtain a pyridine oxidation catalyst; the transition metal source is selected from one or more of a Mn source, a Zn source, a Fe source, a Co source, a Cu source, and a Ni source.

[0020] Heteropoly anions or polyoxometalates are a class of metal oxide clusters with the general formula [XM y O y ] m− where X represents a heteroatom and M represents a 4d or 5d transition metal ion. They have rich structural diversity and various applications in the fields of catalysis, materials science, medicine, and biology. Among them, the Wells-Dawson type [X2M 18 O 62 ] (16−2n)−The WD structure of the heteropoly acid structure with an M / X ratio of 9 can be controllably "opened" to generate a "defect" species, and the defects can be embedded with various other metal ions (such as V, Mn, Fe, Co, Cu, Zn transition metals, and even lanthanide elements), so as to accurately customize the redox and acidic sites. On this basis, the present application adds divalent transition metal ions to the Dawson-type heteropoly acid, realizes the function customization, unique "pseudo-liquid phase" behavior through "defect-substitution" chemistry, realizes the high-efficiency bulk phase catalytic ability, and the reversible multi-electron redox characteristics. The pyridine oxidation catalyst obtained can realize excellent catalytic oxidation under mild conditions. In the above preparation process provided by the present application, specifically: in step S1, the molybdenum source is mixed with the inorganic acid solution to form solution A, which prepares the intermediate product containing the Mo-O-W skeleton for the next reaction. The introduction of molybdenum elements not only enhances the redox activity of the catalyst, but also adjusts the acidic sites of the catalyst, which is crucial for the subsequent embedding of transition metal ions. The presence of the inorganic acid solution helps the dissolution and reaction of the molybdenum ions. Then the obtained solution A is mixed with the Dawson-type heteropoly acid precursor to generate solution B. The structural characteristics of the Dawson-type heteropoly acid precursor, such as high symmetry and controllable acid strength, provide a good microenvironment for the formation of the intermediate product, and also provide a stable structural basis for the subsequent doping of transition metal ions. In step S2, the first reaction promotes the uniform distribution and firm combination of molybdenum ions in the heteropoly acid skeleton, forming an intermediate product with high stability and rich active sites. The obtained intermediate product not only retains the structural advantages of the Dawson-type heteropoly acid, but also enhances the affinity for transition metal ions through the embedding of molybdenum ions, creating favorable conditions for the subsequent doping of transition metals. In step S3, the intermediate product, the transition metal source, and the optional carrier are finally generated into the pyridine oxidation catalyst through the second reaction. The complexation and doping of the transition metal source (Mn source, Zn source, Fe source, Co source, Cu source, and Ni source) not only increases the redox sites of the obtained catalyst, but also optimizes its adaptability to different pyridine derivatives, finally significantly enhances the oxidation activity of the obtained catalyst to the pyridine ring N atom, while maintaining its stability under mild reaction conditions.

[0021] In general, the present application is based on the Dawson-type cage anion with special structure and defects, and the transition metal ions are doped therein. In this process, the transition metal ions are first coordinated to the "defects" in the Dawson-type anion structure of the intermediate product, and are coordinated to the oxygen atoms around the "defects", and finally form a double-cage "sandwich type" structure bridged by transition metals, which is large and complex, stable in structure and significantly catalytically active. Based on the special structure, efficient catalytic oxidation of pyridine can be realized.

[0022] In step S1, the molar concentration of the inorganic acid solution is preferably 1±0.1M; the weight ratio of the molybdenum source to the inorganic acid solution is 1:(50-140). The concentration range of 1±0.1M can more greatly improve the dissolution efficiency of molybdenum ions, promote more uniform mixing of the molybdenum ions and the Dawson-type heteropoly acid precursor, and more effectively form a highly ordered intermediate product. The weight ratio of the molybdenum source to the inorganic acid solution is preferably as above, which correspondingly optimizes the relative concentrations between the reactants, reduces the damage of excess inorganic acid to the structure of the heteropoly acid under the condition of promoting the sufficient dissolution of the molybdenum source, and promotes the obtained catalytically active sites to have higher integrity and stability. In actual applications, in order to form a more stable intermediate product, thereby promoting the subsequent transition metal ions to be more effectively complexed into the structure, and obtaining a pyridine oxidation catalyst with more superior catalytic performance, the molybdenum source is preferably selected from one or more of sodium molybdate, sodium phosphomolybdate, ammonium phosphomolybdate, and ammonium molybdate.

[0023] In order to obtain a pyridine oxidation catalyst with higher catalytic activity and more stable structure, it is further preferred that the chemical formula of the Dawson-type heteropoly acid precursor is Na 12 P2W 18-n O 56 , and the chemical formula of the intermediate product is preferably [H6P2W 18- n Mo n O 62 ]·24H2O, wherein n is 3-6. The ratio of the molar amount of the Dawson-type heteropoly acid precursor to the molar amount of Mo element in the molybdenum source is preferably 1:(3-7.5), which is to promote the Mo ions to be more uniformly embedded in the heteropoly acid framework to form catalytic sites with higher activity and stability, thereby further improving the efficiency of the obtained catalyst for the oxidation of N atoms on the pyridine ring. At the same time, the above-mentioned molar ratio can also more effectively reduce the excessive acidification of the catalytic active sites caused by excessive Mo ions, thereby realizing the higher selective oxidation of pyridine compounds by the catalyst.

[0024] In several typical embodiments, the chemical formula of the intermediate product is preferably [H6P2W 15 Mo3O 62 ]·24H2O, [H6P2W 14 Mo4O 62 ]·24H2O, or [H6P2W 12 Mo6O 62 ]·24H2O, which has a more stable structure, and the subsequent complex doping of transition metal elements in it can be more uniform and stable, thereby being able to prepare a pyridine oxidation catalyst with higher catalytic activity and longer service life.

[0025] In step S2, the reaction time of the first reaction is preferably 2-3 hours, and the first reaction is carried out at 40-50°C, so as to promote more effective combination between Mo elements in the heteropoly acid skeleton and the heteropoly acid groups, form a more stable complex structure, and further provide a more ideal microenvironment for the doping of transition metal ions, so as to obtain a pyridine oxidation catalyst with more stable structure, higher activity and selectivity. In order to promote more uniform distribution of molybdenum ions in the heteropoly acid structure, and further more efficiently form an intermediate product rich in redox sites, the first reaction is preferably carried out under stirring.

[0026] Further, step S2 comprises: obtaining a crude product by solution B through the first reaction; dissolving the crude product in an acid solution with pH of 2-3 to obtain a mixed acid solution; and obtaining an intermediate product by recrystallization of the mixed acid solution. The above preferred scheme, on the one hand, removes impurities that may be produced in the reaction, and on the other hand, further promotes structural reorganization of the intermediate product, improves its purity and crystallinity, and is conducive to more uniform incorporation and more effective combination of subsequent transition metal ions, and finally forms a pyridine oxidation catalyst with higher oxidation activity and selectivity. In practical applications, the acid solution is selected from one or more of hydrochloric acid solution, nitric acid solution and sulfuric acid solution. In order to reduce the introduction of impurities, and further improve the purity and activity of the obtained pyridine oxidation catalyst, the acid solution is more preferably a hydrochloric acid solution.

[0027] In step S3, the molar ratio of the intermediate product to the transition metal source is preferably 1: (1.5-2.5), so as to promote more sufficient and uniform incorporation of transition metal ions into the heteropoly acid skeleton, form a site with higher oxidation catalytic activity, and also better balance the electronic structure of the finally obtained catalyst, further improve its catalytic efficiency and selectivity for N-oxidation of pyridine compounds. The reaction time of the second reaction is preferably 8-10 hours, and the second reaction is carried out at 80-120°C, so as to promote more perfect combination of transition metal ions and the intermediate product heteropoly acid skeleton, form a more stable catalyst structure, reduce irreversible structural changes and damage, and finally promote the obtained catalyst to exhibit higher activity and stability in pyridine oxidation reaction.

[0028] In several typical embodiments, step S3 comprises: dissolving the intermediate product in water to obtain a first solution, mixing the first solution, the transition metal source and the optional carrier for 0.5h-1h to obtain a second solution; subjecting the second solution to a second reaction to obtain a reaction liquid; and subjecting the reaction liquid to evaporation treatment at 60℃-70℃ and 0.06MPa-0.08MPa to remove water and obtain the pyridine oxidation catalyst. In the above preferred scheme, first dissolving the intermediate product in water to form the first solution not only helps the transition metal ions to be more uniformly dispersed, but also promotes the transition metal to be more fully combined with the heteropoly acid framework. Subsequently, the mixing time of 0.5h-1h can promote the transition metal ions to be more fully contacted with the carrier, so that the metal ions are more uniformly adsorbed and embedded on the surface of the carrier. Finally, the evaporation treatment at 60℃-70℃ and 0.06MPa-0.08MPa can more gently remove the water, reduce the potential damage to the structure of the catalyst caused by high temperature or high pressure, and ultimately more significantly improve the purity and structural integrity of the obtained pyridine oxidation catalyst, thereby strengthening its performance in the catalytic reaction. In practical applications, the transition metal source is preferably added in the form of a metal salt. In order to further reduce the introduction of impurities and improve the purity and corresponding catalytic activity of the obtained catalyst, the transition metal source is preferably added in the form of a nitrate salt and / or a chloride salt.

[0029] When the obtained pyridine oxidation catalyst includes a carrier, the weight ratio of the transition metal source to the carrier is preferably 1:(15-45), so as to more accurately optimize the distribution of the transition metal active sites on the optional carrier, achieve a better balance between the oxidation activity and stability of the obtained catalyst, and further improve the stability of the catalyst under continuous or intermittent reaction conditions. In practical applications, the carrier is preferably selected from one or more of SiO2 carrier, TiO2 carrier, MCM-41 carrier, Al2O3 carrier and ZrO2 carrier. In order to expose more active sites and more significantly improve the catalytic activity of the obtained pyridine oxidation catalyst, in practical applications, the specific surface area of the SiO2 carrier can be further preferably 260m 2 / g-290m 2 / g; and / or, the specific surface area of the TiO2 carrier is 40m 2 / g-70m 2 / g; and / or, the specific surface area of the MCM-41 carrier is 700m 2 / g-800m 2 / g; and / or, the specific surface area of the Al2O3 carrier is 70m 2 / g-90m 2 / g; and / or, the specific surface area of the ZrO2 carrier is 40m 2 / g-50m 2 / g.

[0030] The second aspect of the present application provides a pyridine oxidation catalyst, which is prepared by the above-mentioned method for preparing a pyridine oxidation catalyst, and optionally comprises a carrier. Based on the pyridine oxidation catalyst prepared by the above-mentioned method, a special structure formed by Dawson-type heteropoly acid and divalent transition metal ions through "vacancy-substitution" chemistry exists, so that the catalytic activity is significantly improved. The obtained pyridine oxidation catalyst can realize efficient and selective oxidation catalysis of pyridine compounds in both homogeneous and heterogeneous reactions.

[0031] It should be particularly pointed out that, due to the formation and change of complex molecular structure and electronic structure in the preparation process, and due to the limitation of the particularity of coordination chemistry field and the existing test characterization means, it is difficult to comprehensively quantitatively characterize the complex molecular and electronic structure of the obtained pyridine oxidation catalyst. However, the performance test results have shown that the obtained pyridine oxidation catalyst has more superior catalytic activity in catalyzing the oxidation of organic matter containing a pyridine ring.

[0032] The third aspect of the present application provides a method for preparing pyridine-N-oxide, which oxidizes pyridine compounds and oxidizing agents under the action of the above-mentioned pyridine oxidation catalyst to obtain pyridine-N-oxide. The obtained pyridine oxidation catalyst contains a special Dawson-type heteropoly acid and a transition metal doped and complexed therein, so that when it is used as a catalyst to catalyze the oxidation of pyridine compounds, it can effectively activate the pyridine ring, form a highly active free radical, and then efficiently oxidize the N atom on the pyridine ring to generate high-purity pyridine-N-oxide.

[0033] In order to better protect the metal active sites on the above-mentioned pyridine oxidation catalyst and make it better play the catalytic oxidation function, the oxidation reaction is preferably carried out at 75°C~80°C, and the purity of the product obtained by catalysis is higher. In actual application, the oxidizing agent is selected from one or more of hydrogen peroxide, tert-butyl hydroperoxide, peroxide acetone and peroxide acid (specifically, mCPBA / trifluoroperacetic acid). In order to minimize the energy of the reaction system, reduce the possible degradation of the catalyst structure and the excessive consumption of hydrogen peroxide at high temperature, and further improve the purity of the oxidation product and the service life of the catalyst, it is further preferred that the oxidizing agent is hydrogen peroxide with a mass concentration of 30%~35%.

[0034] In order to avoid ambiguity, the pyridine compound mentioned in the present application means a compound containing a pyridine ring in the molecular structure, especially an organic compound. The pyridine-N-oxide is a reaction product of the organic compound containing a pyridine ring in the molecular structure after oxidation, and the nitrogen atom of the pyridine ring in the structure is connected to an oxygen atom through a coordination bond. The reaction route diagram of the pyridine compound and the oxidant to obtain the pyridine-N-oxide can be seen in:

[0035]

[0036] The structural formula in the above reaction route diagram is only an example, and the R in the formula can be an aliphatic hydrocarbon, a halogenated hydrocarbon and an oxygen-containing hydrocarbon group. The structure of the catalyst provided by the present application is not limited to this, and any structure containing a pyridine ring can be used.

[0037] When the pyridine oxidation catalyst does not include a carrier, that is, when the oxidation reaction is a homogeneous reaction, the preparation method of the pyridine-N-oxide preferably includes: adding the pyridine compound, the pyridine oxidation catalyst and the oxidant into an organic solvent, and obtaining the pyridine-N-oxide through the homogeneous oxidation reaction. In the homogeneous reaction process, the weight ratio of the pyridine compound, the pyridine oxidation catalyst and the oxidant is preferably (8-12):1:(12-18); and / or, the time of the homogeneous oxidation reaction is 2h-3h; and / or, the organic solvent is acetonitrile and / or toluene. The above preferred reaction conditions, combined with the characteristics of the homogeneous reaction, not only can more effectively promote the active sites of the catalyst to fully contact with the pyridine compound and the oxidant, promote the efficient decomposition of the oxidant, and generate the pyridine-N-oxide with higher selectivity, but also can effectively simplify the process of post-reaction treatment.

[0038] When the pyridine oxidation catalyst includes a carrier, i.e. when the oxidation reaction is a heterogeneous reaction, the preparation method of pyridine-N-oxide preferably includes: loading the pyridine oxidation catalyst in a reactor, and feeding the pyridine compound and the oxidant into the reactor to obtain the pyridine-N-oxide through the heterogeneous oxidation reaction. In the heterogeneous reaction process, the pyridine compound is preferably fed in the form of a compound solution with a molar concentration of 0.5±0.01M, and the feeding speed of the compound solution is 0.5g / min-1.0g / min; and / or, the feeding speed of the oxidant is 5g / min-10g / min; and / or, the compound solution uses one or more of acetonitrile and / or toluene as the solvent. The above-mentioned preferred heterogeneous reaction conditions make full use of the physical stabilization of the carrier to the catalyst, and the adsorption and diffusion advantages provided by the high specific surface area of the carrier. Under the above-mentioned conditions, the concentration gradient between the oxidation substrate and the catalyst and the oxidant is further optimized, thereby more significantly improving the selectivity and efficiency of the catalytic oxidation reaction. In practical applications, the reactor used in the above-mentioned heterogeneous reaction can be a fixed bed reactor, a moving bed reactor, a micro-packed bed reactor, etc.

[0039] The application will be further described in conjunction with specific examples, which should not be construed as limiting the scope of the application. Unless otherwise defined, all the professional terms used herein have the same meaning as generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific examples and are not intended to limit the protection scope of the application.

[0040] Example 1

[0041] A preparation method of a pyridine oxidation catalyst:

[0042] (1-1) 150g of 1M hydrochloric acid solution and 1.5g of sodium molybdate (i.e. the weight ratio of the molybdenum source to the hydrochloric acid solution is 1:100) were respectively dissolved in 250mL of purified water to obtain a mixed solution A.

[0043] (1-2) The mixed solution A was placed in a four-necked flask, and 9.7g of Dawson-type heteropoly acid precursor Na 12 P2W 15 O 56 to obtain a mixed solution B. In this process, the molar ratio of the Dawson-type heteropoly acid precursor to the molar amount of Mo element in the molybdenum source is 1:3.

[0044] (2-1) The mixed solution B was kept at 50°C for 2h and then filtered to obtain a crude product precipitate.

[0045] (2-2) The obtained crude product precipitate was dissolved in a hydrochloric acid solution with pH=2 and then recrystallized by cooling to obtain [H6P2W15 Mo3O 62 ]·24H2O, which is an intermediate product.

[0046] (3-1) 10 g of the obtained intermediate product [H6P2W 15 Mo3O 62 ]·24H2O was dissolved in water to obtain a first solution. At room temperature (25±2°C), 1.45 g of Zn(NO3)2·6H2O salt solid (i.e. the molar ratio of [H6P2W 15 Mo3O 62 ]·24H2O to the transition metal zinc source is 1:2) was added thereto, and mixed and stirred for 0.5 h to obtain a second solution. The second solution was kept at 120°C in a high-pressure reaction kettle, and the reaction time was 8 h to obtain a homogeneous system reaction liquid.

[0047] (3-2) The obtained reaction liquid system was subjected to slow evaporation to obtain crystals, the evaporation temperature was 60°C, and the vacuum degree was 0.06 MPa. The material, i.e. a pyridine oxidation catalyst, is denoted as WDZn in this embodiment.

[0048] Example 2

[0049] A preparation method of a pyridine oxidation catalyst:

[0050] (1-1) 150 g of 1M hydrochloric acid solution and 3.0 g of sodium molybdate (i.e. the weight ratio of the molybdenum source to the hydrochloric acid solution is 1:50) were respectively dissolved in 250 mL of purified water to obtain a mixed solution A.

[0051] (1-2) The mixed solution A was placed in a four-necked flask, and 7.8 g of Dawson-type heteropoly acid precursor Na 12 P2W 15 O 56 was added thereto to obtain a mixed solution B. In this process, the molar ratio of the Dawson-type heteropoly acid precursor to the molar amount of Mo element in the molybdenum source is 1:7.5.

[0052] (2-1) The mixed solution B was kept at 50°C and stirred for 2 h, and then a crude product precipitate was obtained by filtration.

[0053] (2-2) The obtained crude product precipitate was dissolved by heating in a hydrochloric acid solution with pH=2, and then recrystallized by cooling to obtain [H6P2W 12 Mo6O 62 ]·24H2O, which is an intermediate product.

[0054] (3-1) 10 g of the obtained intermediate product [H6P2W 12 Mo6O 62]·24H2O was dissolved in water to obtain a first solution. At room temperature (25±2°C), 1.45 g of Zn(NO3)2·6H2O salt solid and 50 g of SiO2 were added to the first solution, and mixed and stirred for 0.5 h to obtain a second solution. The second solution was kept at 120°C in a high-pressure reaction kettle, and the reaction time was 8 h to obtain a homogeneous system reaction liquid. In this process, [H6P2W 15 Mo3O 62 The molar ratio of Zn(NO3)2·6H2O to the transition metal zinc source was 1:2, and the weight ratio of the transition metal source to the carrier was 1:34.5.

[0055] (3-2) The obtained reaction liquid system was obtained by slow evaporation, and the evaporation temperature was 60°C and the vacuum degree was 0.06 MPa. The material, i.e., the pyridine oxidation catalyst, is denoted as WDZn-SiO2 in this embodiment.

[0056] Example 3

[0057] A method for preparing a pyridine oxidation catalyst:

[0058] The difference between this embodiment and Example 1 is that in step (3-1), equimolar NiCl2·6H2O is used instead of Zn(NO3)2·6H2O to prepare a pyridine oxidation catalyst, which is denoted as WDNi.

[0059] Example 4

[0060] A method for preparing a pyridine oxidation catalyst:

[0061] (1-1) 150 g of 1M hydrochloric acid solution and 1.29 g of ammonium molybdate (i.e., the weight ratio of the molybdenum source to the hydrochloric acid solution was 1:116.3) were respectively dissolved in 250 mL of purified water to obtain a mixed solution A.

[0062] (1-2) The mixed solution A was placed in a four-necked flask, and 9.7 g of Dawson-type heteropoly acid precursor Na 12 P2W 15 O 56 was added to obtain a mixed solution B. In this process, the molar ratio of the Dawson-type heteropoly acid precursor to the Mo element in the molybdenum source was 1:3.

[0063] (2-1) The mixed solution B was kept at 50°C and stirred for 2 h, and then a crude product precipitate was obtained by filtration.

[0064] (2-2) The obtained crude product precipitate was dissolved by heating in a hydrochloric acid solution with a pH of 3, and then recrystallized by cooling to obtain [H6P2W 15 Mo3O 62 ]·24H2O, i.e., an intermediate product.

[0065] (3-1) 10 g of the obtained intermediate product [H6P2W 15 Mo3O 62 ]·24H2O was dissolved in water to obtain a first solution. At room temperature (25±2℃), 1.16 g of NiCl2·6H2O salt solid and 50 g of TiO2 were added to the first solution, and mixed and stirred for 0.5 h to obtain a second solution. The second solution was kept at 80℃ in a high-pressure reaction kettle, and the reaction time was 10 h to obtain a homogeneous system reaction liquid. In this process, the molar ratio of [H6P2W 15 Mo3O 62 ]·24H2O to the transition metal nickel source was 1:2, and the weight ratio of the transition metal source to the carrier was 1:43.1.

[0066] (3-2) The obtained reaction liquid system was slowly evaporated to obtain crystals, the evaporation temperature was 70℃, and the vacuum degree was 0.08 MPa. The material, i.e., a pyridine oxidation catalyst, is denoted as WDNi-TiO2 in this embodiment.

[0067] Example 5

[0068] A method for preparing a pyridine oxidation catalyst comprises the following steps:

[0069] The difference between this embodiment and Example 1 is that in step (3-1), an equimolar amount of Fe(NO3)3·9H2O is used instead of Zn(NO3)2·6H2O to prepare a pyridine oxidation catalyst, which is denoted as WDFe.

[0070] Example 6

[0071] A method for preparing a pyridine oxidation catalyst comprises the following steps:

[0072] The difference between this embodiment and Example 1 is that in step (3-1), an equimolar amount of Co(NO3)2·6H2O is used instead of Zn(NO3)2·6H2O to prepare a pyridine oxidation catalyst, which is denoted as WDCo.

[0073] Example 7

[0074] A method for preparing a pyridine oxidation catalyst comprises the following steps:

[0075] The difference between this embodiment and Example 2 is that in step (3-1), an equimolar amount of Co(NO3)2·6H2O is used instead of Zn(NO3)2·6H2O to prepare a pyridine oxidation catalyst, which is denoted as WDCo-SiO2.

[0076] Example 8

[0077] A method for preparing a pyridine oxidation catalyst comprises the following steps:

[0078] The difference between this embodiment and embodiment 2 is that MCM-41 is used instead of SiO2 as the carrier in step (3-1) to prepare a pyridine oxidation catalyst, which is denoted as WDZn-MCM-41.

[0079] Embodiment 9

[0080] A method for preparing a pyridine oxidation catalyst:

[0081] The difference between this embodiment and embodiment 1 is that Cu(NO3)2·3H2O is used instead of Zn(NO3)2·6H2O in step (3-1) to prepare a pyridine oxidation catalyst, which is denoted as WDCu.

[0082] Embodiment 10

[0083] A method for preparing a pyridine oxidation catalyst:

[0084] (1-1) 150 g of 1M hydrochloric acid solution and 1.14 g of sodium phosphomolybdate (i.e. the weight ratio of the molybdenum source to the hydrochloric acid solution is 1:131.5) were respectively dissolved in 250 mL of purified water to obtain a mixed solution A.

[0085] (1-2) The mixed solution A was placed in a four-necked flask, and 9.7 g of Dawson-type heteropoly acid precursor Na 12 P2W 15 O 56 was added to obtain a mixed solution B. In this process, the molar ratio of the Dawson-type heteropoly acid precursor to the Mo element in the molybdenum source is 1:3.

[0086] (2-1) The mixed solution B was incubated at 40°C for 3 h and then filtered to obtain a crude product precipitate.

[0087] (2-2) The obtained crude product precipitate was dissolved by heating in a hydrochloric acid solution with pH=2.5, and then recrystallized by cooling to obtain [H6P2W 15 Mo3O 62 ]·24H2O, i.e. an intermediate product.

[0088] (3-1) 10 g of the obtained intermediate product [H6P2W 15 Mo3O 62 ]·24H2O was dissolved in water to obtain a first solution. At room temperature (25±2°C), 1.18 g of Cu(NO3)2·3H2O salt solid and 20 g of ZrO2 were added to the first solution, and mixed and stirred for 0.5 h to obtain a second solution. The second solution was incubated at 80°C in a high-pressure reaction kettle for 10 h to obtain a homogeneous system reaction liquid. In this process, [H6P2W 15 Mo3O62 The molar ratio of 24H2O to the transition metal copper source is 1:2, and the weight ratio of the transition metal source to the carrier is 1:16.9.

[0089] (3-2) The obtained reaction liquid system is subjected to slow evaporation to obtain crystals, the evaporation temperature is 70°C, and the vacuum degree is 0.08 MPa. The material, i.e. the pyridine oxidation catalyst, is recorded as WDCu-ZrO2 in this embodiment.

[0090] Example 11

[0091] A method for preparing a pyridine oxidation catalyst comprises the following steps:

[0092] The difference between this embodiment and Example 10 is that equal weights of Al2O3 are used instead of ZrO2 as the carrier in step (3-1) to prepare a pyridine oxidation catalyst, which is recorded as WDZn-Al2O3.

[0093] Example 12

[0094] A method for preparing a pyridine oxidation catalyst comprises the following steps:

[0095] The difference between this embodiment and Example 1 is that equal molar amounts of Mn(NO3)2·4H2O are used instead of Zn(NO3)2·6H2O in step (3-1) to prepare a pyridine oxidation catalyst, which is recorded as WDMn.

[0096] Example 13

[0097] A method for preparing a pyridine oxidation catalyst comprises the following steps:

[0098] (1-1) 150 g of 1M hydrochloric acid solution and 1.8 g of ammonium molybdate (i.e. the weight ratio of the molybdenum source to the hydrochloric acid solution is 1:83) are respectively dissolved in 250 mL of purified water to obtain a mixed solution A.

[0099] (1-2) The mixed solution A is placed in a four-necked flask, and 9.7 g of Dawson-type heteropoly acid precursor Na 12 P2W 15 O 56 to obtain a mixed solution B. In this process, the molar ratio of the Dawson-type heteropoly acid precursor to the molar amount of Mo element in the molybdenum source is 1:4.3.

[0100] (2-1) The mixed solution B is stirred at 50°C for 2 h, and then a crude product precipitate is obtained by filtration.

[0101] (2-2) The obtained crude product precipitate is heated and dissolved in a hydrochloric acid solution with a pH of 3, and then recrystallized by cooling to obtain [H6P2W 14 Mo4O 62]·24H2O, which is an intermediate product.

[0102] (3-1) 10 g of the obtained intermediate product [H6P2W 14 Mo4O 62 ]·24H2O was dissolved in water to obtain a first solution. At room temperature (25±2℃), 1.2 g of NiCl2·6H2O salt solid and 50 g of ZrO2 were added to the first solution, and mixed and stirred for 0.5 h to obtain a second solution. The second solution was kept at 80℃ in a high-pressure reaction kettle, and the reaction time was 10 h to obtain a homogeneous system reaction liquid. In this process, the molar ratio of [H6P2W 14 Mo4O 62 ]·24H2O to the transition metal nickel source was 1:2, and the weight ratio of the transition metal source to the carrier was 1:42.

[0103] (3-2) The obtained reaction liquid system was slowly evaporated to obtain crystals, the evaporation temperature was 70℃, and the vacuum degree was 0.08 MPa. The material, which is a pyridine oxidation catalyst, is denoted as WDNi-ZrO2 in this embodiment.

[0104] Embodiment 14

[0105] A method for preparing a pyridine oxidation catalyst comprises the following steps:

[0106] The difference between this embodiment and Embodiment 1 is only that in step (1-2), the amount of the Dawson-type heteropoly acid precursor Na 12 P2W 15 O 56 is changed so that the molar ratio of the Dawson-type heteropoly acid precursor to the Mo element in the molybdenum source is changed to 1:10.

[0107] Embodiment 15

[0108] A method for preparing a pyridine oxidation catalyst comprises the following steps:

[0109] The difference between this embodiment and Embodiment 1 is only that in step (1-2), the amount of the Dawson-type heteropoly acid precursor Na 12 P2W 15 O 56 is changed so that the molar ratio of the Dawson-type heteropoly acid precursor to the Mo element in the molybdenum source is changed to 2.5:1.

[0110] Embodiment 16

[0111] A method for preparing a pyridine oxidation catalyst comprises the following steps:

[0112] The difference between this example and Example 1 is that in step (2-1), the reaction temperature is changed to 35°C, and the stirring time is changed to 4 h.

[0113] Example 17

[0114] A method for producing a pyridine oxidation catalyst:

[0115] The difference between this example and Example 1 is that in step (2-1), the reaction temperature is changed to 55°C, and the stirring time is changed to 1 h.

[0116] Example 18

[0117] A method for producing a pyridine oxidation catalyst:

[0118] The difference between this example and Example 1 is that in step (3-1), the amount of the transition metal source is changed so that the molar ratio of [H6P2W 15 Mo3O 62 ]·24H2O to the transition metal source is changed to 1:4.

[0119] Example 19

[0120] A method for producing a pyridine oxidation catalyst:

[0121] The difference between this example and Example 1 is that in step (3-1), the amount of the transition metal source is changed so that the molar ratio of [H6P2W 15 Mo3O 62 ]·24H2O to the transition metal source is changed to 1:1.

[0122] Example 20

[0123] A method for producing a pyridine oxidation catalyst:

[0124] The difference between this example and Example 1 is that in step (3-1), the reaction temperature of the autoclave is changed to 70°C, and the reaction time is changed to 12 h.

[0125] Example 21

[0126] A method for producing a pyridine oxidation catalyst:

[0127] The difference between this example and Example 1 is that in step (3-1), the reaction temperature of the autoclave is changed to 130°C, and the reaction time is changed to 6 h.

[0128] Comparative Example 1

[0129] This comparative example directly uses the existing WO3 / TiO2catalyst as the obtained catalyst sample, and the preparation method thereof refers to CN 104974088A.

[0130] Comparative Example 2

[0131] A preparation method of a pyridine oxidation catalyst:

[0132] This comparative example differs from Example 1 only in that in step (1-1), no molybdenum source is added.

[0133] Comparative Example 3

[0134] A preparation method of a pyridine oxidation catalyst:

[0135] This comparative example differs from Example 1 only in that in step (1-2), an equimolar amount of heteropoly acid Keggin structure Na3PMo 12 O 40 is used instead of Dawson-type heteropoly acid precursor Na 12 P2W 15 O 56 .

[0136] Comparative Example 4

[0137] A preparation method of a pyridine oxidation catalyst:

[0138] This comparative example differs from Example 1 only in that in step (1-2), an equimolar amount of H3[P(W3O 10 )4]·H2O is used instead of Dawson-type heteropoly acid precursor Na 12 P2W 15 O 56 .

[0139] Application Example 1

[0140] A preparation method of pyridine-N-oxide:

[0141] This application example uses the pyridine oxidation catalyst WDZn obtained in Example 1, which does not contain a carrier, as the catalyst sample. 1g of pyridine compound to be oxidized and 0.1g of the catalyst sample are simultaneously added to 12g of acetonitrile solution, and 1.5g of 30% hydrogen peroxide is added dropwise at 80°C. After incubation for 2-3h, the sample is tested for purity by liquid chromatography.

[0142] Application Example 2

[0143] A preparation method of pyridine-N-oxide:

[0144] The application example uses the pyridine oxidation catalyst WDZn-SiO2 containing a carrier obtained in Example 2 as a catalyst sample. After the 40 g of the WDZn-SiO2 catalyst obtained in Example 2 after tabletting is put into a fixed bed, a 0.5 M acetonitrile solution of the pyridine compound to be oxidized is passed in at a feed rate of 0.5 g / min and 35% hydrogen peroxide is passed in at a feed rate of 10 mL / min at 75°C, and the reaction purity result is tested by liquid phase.

[0145] Application Example 3

[0146] A method for preparing a pyridine-N-oxide:

[0147] The application example uses the pyridine oxidation catalyst WDNi obtained in Example 3 not containing a carrier as a catalyst sample, changes the structure of the pyridine compound to be oxidized, and the rest of the reaction conditions remain the same as in Application Example 1.

[0148] Application Example 4

[0149] A method for preparing a pyridine-N-oxide:

[0150] The application example uses the pyridine oxidation catalyst WDNi-TiO2 containing a carrier obtained in Example 4 as a catalyst sample. After the 40 g of the WDNi-TiO2 catalyst obtained in Example 4 after tabletting is put into a fixed bed, a 0.5 M toluene solution of the pyridine compound to be oxidized is passed in at a feed rate of 1 g / min and 35% hydrogen peroxide is passed in at a feed rate of 5 mL / min at 80°C, and the reaction purity result is tested by liquid phase.

[0151] Application Example 5

[0152] A method for preparing a pyridine-N-oxide:

[0153] The application example uses the pyridine oxidation catalyst WDFe obtained in Example 5 not containing a carrier as a catalyst sample, changes the structure of the pyridine compound to be oxidized, and the rest of the reaction conditions remain the same as in Application Example 1.

[0154] Application Example 6

[0155] A method for preparing a pyridine-N-oxide:

[0156] The application example uses the pyridine oxidation catalyst WDCo obtained in Example 6 not containing a carrier as a catalyst sample, changes the structure of the pyridine compound to be oxidized, and the rest of the reaction conditions remain the same as in Application Example 1.

[0157] Application Example 7

[0158] A method for preparing a pyridine-N-oxide:

[0159] This application example uses the pyridine oxidation catalyst WDCo-SiO2 containing a carrier obtained in Example 7 as a catalyst sample. After the WDCo-SiO2 catalyst obtained in Example 7, 40 g after tabletting, was placed in a fixed bed, a 0.5 M acetonitrile solution of a pyridine compound to be oxidized was passed at a feed rate of 0.5 g / min and 30% hydrogen peroxide was passed at a feed rate of 5 mL / min at 80°C, and the reaction purity was measured by liquid chromatography.

[0160] Application Example 8

[0161] A method for preparing a pyridine-N-oxide:

[0162] This application example uses the pyridine oxidation catalyst WDZn-MCM-41 containing a carrier obtained in Example 8 as a catalyst sample, changes the structure of the pyridine compound to be oxidized, and the rest of the reaction conditions are the same as in Application Example 2.

[0163] Application Example 9

[0164] A method for preparing a pyridine-N-oxide:

[0165] This application example uses the pyridine oxidation catalyst WDCu obtained in Example 9, which does not contain a carrier, as a catalyst sample, changes the structure of the pyridine compound to be oxidized, and the rest of the reaction conditions are the same as in Application Example 1.

[0166] Application Example 10

[0167] A method for preparing a pyridine-N-oxide:

[0168] This application example uses the pyridine oxidation catalyst WDCu-ZrO2 containing a carrier obtained in Example 10 as a catalyst sample, changes the structure of the pyridine compound to be oxidized, and the rest of the reaction conditions are the same as in Application Example 2.

[0169] Application Example 11

[0170] A method for preparing a pyridine-N-oxide:

[0171] This application example uses the pyridine oxidation catalyst WDCu-Al2O3 containing a carrier obtained in Example 11 as a catalyst sample, changes the structure of the pyridine compound to be oxidized, and the rest of the reaction conditions are the same as in Application Example 2.

[0172] Application Example 12

[0173] A method for preparing a pyridine-N-oxide:

[0174] This application example uses the pyridine oxidation catalyst WDMn obtained in Example 12, which does not contain a support, as the catalyst sample, changes the structure of the pyridine compound to be oxidized, and the rest of the reaction conditions are the same as in Application Example 1.

[0175] Application Example 13

[0176] A method for producing a pyridine-N-oxide:

[0177] This application example uses the pyridine oxidation catalyst WDNi-ZrO2 obtained in Example 13, which contains a support, as the catalyst sample, changes the structure of the pyridine compound to be oxidized, and the rest of the reaction conditions are the same as in Application Example 2.

[0178] Application Example 14

[0179] A method for producing a pyridine-N-oxide:

[0180] This application example uses the pyridine oxidation catalyst WDZn obtained in Example 1, which does not contain a support, as the catalyst sample, changes the structure of the pyridine compound to be oxidized, and the rest of the reaction conditions are the same as in Application Example 1.

[0181] Application Example 15

[0182] A method for producing a pyridine-N-oxide:

[0183] This application example uses the pyridine oxidation catalyst obtained in Example 14, which does not contain a support, as the catalyst sample, the structure of the pyridine compound to be oxidized, and each of the reaction conditions are the same as in Application Example 1.

[0184] Application Example 16

[0185] A method for producing a pyridine-N-oxide:

[0186] This application example uses the pyridine oxidation catalyst obtained in Example 15, which does not contain a support, as the catalyst sample, the structure of the pyridine compound to be oxidized, and each of the reaction conditions are the same as in Application Example 1.

[0187] Application Example 17

[0188] A method for producing a pyridine-N-oxide:

[0189] This application example uses the pyridine oxidation catalyst obtained in Example 16, which does not contain a support, as the catalyst sample, the structure of the pyridine compound to be oxidized, and each of the reaction conditions are the same as in Application Example 1.

[0190] Application Example 18

[0191] A method for producing a pyridine-N-oxide:

[0192] This application example used the pyridine oxidation catalyst obtained in Example 18, which did not contain a support, as the catalyst sample, and the structure of the pyridine compound to be oxidized and the reaction conditions were the same as in Application Example 1.

[0193] Application Example 19

[0194] A method for producing a pyridine-N-oxide:

[0195] This application example used the pyridine oxidation catalyst obtained in Example 18, which did not contain a support, as the catalyst sample, and the structure of the pyridine compound to be oxidized and the reaction conditions were the same as in Application Example 1.

[0196] Application Example 20

[0197] A method for producing a pyridine-N-oxide:

[0198] This application example used the pyridine oxidation catalyst obtained in Example 18, which did not contain a support, as the catalyst sample, and the structure of the pyridine compound to be oxidized and the reaction conditions were the same as in Application Example 1.

[0199] Application Example 21

[0200] A method for producing a pyridine-N-oxide:

[0201] This application example used the pyridine oxidation catalyst obtained in Example 18, which did not contain a support, as the catalyst sample, and the structure of the pyridine compound to be oxidized and the reaction conditions were the same as in Application Example 1.

[0202] Application Example 22

[0203] A method for producing a pyridine-N-oxide:

[0204] This application example used the pyridine oxidation catalyst obtained in Example 18, which did not contain a support, as the catalyst sample, and the structure of the pyridine compound to be oxidized and the reaction conditions were the same as in Application Example 1.

[0205] Application Example 23

[0206] A method for producing a pyridine-N-oxide:

[0207] This application example uses the pyridine oxidation catalyst WDZn obtained in Example 1, which does not contain a carrier, as the catalyst sample. The structure of the pyridine compound to be oxidized is the same as in Application Example 1, and the temperature condition of the oxidation reaction is changed from 80°C to 65°C.

[0208] Application Example 24

[0209] A method for producing a pyridine-N-oxide:

[0210] This application example uses the pyridine oxidation catalyst WDZn obtained in Example 1, which does not contain a carrier, as the catalyst sample. The structure of the pyridine compound to be oxidized is the same as in Application Example 1, and the temperature condition of the oxidation reaction is changed from 80°C to 85°C.

[0211] Application Comparative Example 1

[0212] This application comparative example uses the pyridine oxidation catalyst obtained in Comparative Example 1, which does not contain a carrier, as the catalyst sample, and the structure of the pyridine compound to be oxidized and the reaction conditions are the same as in Application Example 1.

[0213] Application Comparative Example 2

[0214] This application comparative example uses the pyridine oxidation catalyst obtained in Comparative Example 2, which does not contain a carrier, as the catalyst sample, and the structure of the pyridine compound to be oxidized and the reaction conditions are the same as in Application Example 1.

[0215] Application Comparative Example 3

[0216] This application comparative example uses the pyridine oxidation catalyst obtained in Comparative Example 3, which does not contain a carrier, as the catalyst sample, and the structure of the pyridine compound to be oxidized and the reaction conditions are the same as in Application Example 1.

[0217] Application Comparative Example 4

[0218] This application comparative example uses the pyridine oxidation catalyst obtained in Comparative Example 4, which does not contain a carrier, as the catalyst sample, and the structure of the pyridine compound to be oxidized and the reaction conditions are the same as in Application Example 1.

[0219] In each of the above application examples and application comparative examples, the structural formula of the pyridine compound to be oxidized, the structural formula of the pyridine-N-oxide product obtained by oxidation, and the product purity are shown in Table 1.

[0220] Table 1

[0221]

[0222]

[0223]

[0224] From the above description, it can be seen that, compared with the respective comparative examples, the above-mentioned embodiments of the present application achieve the preparation of a pyridine oxidation catalyst with high catalytic activity. The obtained pyridine oxidation catalyst can simultaneously achieve efficient and selective oxidation catalysis of pyridine compounds in both homogeneous and heterogeneous reactions, and ultimately obtain the oxidation product pyridine-N-oxide with high purity.

[0225] Specifically, as can be seen by comparing application examples 15 and 16 with application examples 1 to 14, in the process of preparing the pyridine oxidation catalyst (i.e. in example 14 and example 15), by preferably selecting the ratio of the molar amount of the Dawson-type heteropoly acid precursor to the molar amount of Mo element in the molybdenum source, the Mo ions can be more uniformly embedded in the heteropoly acid framework, forming catalytic sites with higher activity and stability, thereby further improving the efficiency of the obtained catalyst in oxidizing the N atom on the pyridine ring. At the same time, the preferred ratio of the molar amount of the Dawson-type heteropoly acid precursor to the molar amount of Mo element in the molybdenum source can also more effectively reduce the excessive acidification of the active sites of the catalyst caused by excessive Mo ions, thereby achieving higher selectivity of the catalyst in oxidizing pyridine compounds.

[0226] As can be seen by comparing application examples 17 and 18 with application examples 1 to 14, in the process of preparing the pyridine oxidation catalyst (i.e. in example 16 and example 17), by preferably selecting the conditions of the first reaction in step S2, more effective binding between the Mo element in the heteropoly acid framework and the heteropoly acid group can be promoted, forming a more stable composite structure, thereby providing a more ideal microenvironment for the doping of transition metal ions, and ultimately obtaining a pyridine oxidation catalyst with more stable structure, higher activity and selectivity.

[0227] As can be seen by comparing application examples 19 and 20 with application examples 1 to 14, in the process of preparing the pyridine oxidation catalyst (i.e. in example 18 and example 19), by preferably selecting the amount of transition metal source and further preferably selecting the molar ratio of the intermediate product to the transition metal source, the transition metal ions can be more fully and uniformly doped into the heteropoly acid framework, forming sites with higher oxidation catalytic activity, and also better balancing the electronic structure of the final obtained catalyst, further improving its catalytic efficiency and selectivity in N-oxidation of pyridine compounds.

[0228] Comparing the application examples 21 and 22 with the application examples 1 to 14, it can be seen that, in the process of preparing the pyridine oxidation catalyst (i.e. in the examples 20 and 21), by optimizing the conditions of the second reaction in the step S3, the combination of the transition metal ions with the intermediate product heteropoly acid skeleton can be made more perfect, the structure of the formed catalyst is more stable, the irreversible structural changes and damages are reduced, and finally the obtained catalyst can exhibit higher activity and stability in the pyridine oxidation reaction.

[0229] Comparing the application examples 23 and 24 with the application examples 1 to 14, it can be seen that, in the application process of the pyridine oxidation catalyst, i.e. in the process of preparing the pyridine-N-oxide, based on the obtained pyridine oxidation catalyst of the present application, by optimizing the temperature conditions of the oxidation reaction, the metal active sites on the obtained pyridine oxidation catalyst can be better protected, so that the catalytic oxidation function can be better exerted, and thus the product with higher purity can be obtained.

[0230] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and do not necessarily refer to a specific order or sequence. It should be understood that the terms thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than that described herein.

[0231] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a pyridine oxidation catalyst, characterized in that, include: Step S1: The molybdenum source is mixed with an inorganic acid solution to obtain solution A. Solution A is then mixed with a Dawson-type heteropolyacid precursor to obtain solution B. The chemical formula of the Dawson-type heteropolyacid precursor is Na. 12 P2W 18-n O 56 where n is 3 to 6; Step S2: Solution B undergoes a first reaction to obtain a crude product; the crude product is dissolved in an acidic solution with a pH of 2-3 to obtain a mixed acidic solution. The mixed acid solution was recrystallized to obtain the intermediate product; the reaction time of the first reaction was 2-3 hours, and the first reaction was carried out at 40-50°C; the chemical formula of the intermediate product was [H6P2W]. 18-n Mo n O 62 ·24H2O, where n is 3~6; Step S3: The intermediate product, transition metal source, and optional support undergo a second reaction to obtain the pyridine oxidation catalyst; the transition metal source is selected from one or more of Mn, Zn, Fe, Co, Cu, and Ni sources; the support is selected from one or more of SiO2 support, TiO2 support, MCM-41 support, Al2O3 support, and ZrO2 support; the reaction time of the second reaction is 8h~10h, and the second reaction is carried out at 80℃~120℃; the molar ratio of the intermediate product to the transition metal source is 1:(1.5~2.5); the weight ratio of the transition metal source to the support is 1:(15~45).

2. The method for preparing the pyridine oxidation catalyst according to claim 1, characterized in that, In step S1 The molybdenum source is selected from one or more of sodium molybdate, sodium phosphomolybdate, ammonium phosphomolybdate, and ammonium molybdate. The molar concentration of the inorganic acid solution is 1 ± 0.1 M; The weight ratio of the molybdenum source to the inorganic acid solution is 1:(50~140). The molar ratio of the Dawson-type heteropolyacid precursor to the molar ratio of Mo in the molybdenum source is 1:(3~7.5). The inorganic acid is selected from one or more of hydrochloric acid, nitric acid, and sulfuric acid.

3. A pyridine oxidation catalyst, characterized in that, The pyridine oxidation catalyst is prepared by the method for preparing the pyridine oxidation catalyst according to claim 1 or 2, and the pyridine oxidation catalyst may optionally include the support.

4. A method for preparing pyridine-N-oxide, characterized in that, The pyridine compound is oxidized with an oxidant under the action of the pyridine oxidation catalyst according to claim 3 to obtain the pyridine-N-oxide; the oxidation reaction is carried out at 75°C to 80°C.

5. The method for preparing pyridine-N-oxide according to claim 4, characterized in that, When the pyridine oxidation catalyst does not include the support, the method for preparing the pyridine-N-oxide includes: adding the pyridine compound, the pyridine oxidation catalyst and the oxidant to an organic solvent, and then subjecting the reaction to a homogeneous oxidation reaction to obtain the pyridine-N-oxide; The weight ratio of the pyridine compound, the pyridine oxidation catalyst, and the oxidant is (8~12):1:(12~18). And / or, the homogeneous oxidation reaction takes 2 to 3 hours; And / or, the organic solvent is acetonitrile and / or toluene.

6. The method for preparing pyridine-N-oxide according to claim 4, characterized in that, When the pyridine oxidation catalyst includes the support, the method for preparing the pyridine-N-oxide includes: loading the pyridine oxidation catalyst into a reactor, and introducing the pyridine compound and the oxidant into the reactor, and obtaining the pyridine-N-oxide through a heterogeneous oxidation reaction; The pyridine compound is introduced in the form of a compound solution with a molar concentration of 0.5 ± 0.01 M, and the feed rate of the compound solution is 0.5 g / min to 1.0 g / min; And / or, the feed rate of the oxidant is 5 g / min to 10 g / min; And / or, the compound solution uses acetonitrile and / or toluene as a solvent.

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