Pyridine oxidation catalyst and preparation method thereof, and preparation method of pyridine-N-oxide

Abstract

The invention provides a pyridine oxidation catalyst, 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 with an inorganic acid solution to obtain a solution A, and mixing the solution A with a Dawson type heteropolyacid precursor to obtain a solution B; performing first reaction on the solution B to obtain an intermediate product; the intermediate product, a transition metal source and an optional carrier are subjected to a second reaction, and the pyridine oxidation catalyst is obtained; 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. According to the present invention, by using the heteropoly acid (WD structure), through transition metal ion complexing, the oxidation reduction site and the acid site of the obtained catalyst are reinforced so as to achieve the purpose of improving the pyridine compound N oxidation synthesis efficiency and the product purity; therefore, efficient application and technical effects of a low-cost and environment-friendly catalytic system in preparation of 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 oxidizing agent 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 oxidizing agent 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 oxidizing agent 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 oxidizing agent 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 oxidizing agent is 5g / min~10g / min; and / or, the compound solution uses acetonitrile and / or toluene as a solvent.

[0017] By applying the technical solution of this invention, heteropolyacids (WD structure) are used to enhance the redox sites and acidic sites of the obtained catalyst through transition metal ion complexation, thereby improving the N oxidation synthesis efficiency and product purity of pyridine compounds. This achieves the efficient application and technical effect of a low-cost, environmentally friendly catalytic system in the preparation of pyridine N-oxides. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0019] As described in the background section, existing catalysts suffer from the problem of being unable to efficiently catalyze the oxidation of pyridine compounds and obtain pyridine-N-oxides with high purity. To address this technical problem, a first aspect of the present invention provides a method for preparing 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 heteropolyacid precursor to obtain solution B; step S2, subjecting solution B to a first reaction to obtain an intermediate product; and step S3, subjecting the intermediate product, a transition metal source, and an optional support to a second reaction to obtain the pyridine oxidation catalyst; wherein the transition metal source is selected from one or more of Mn, Zn, Fe, Co, Cu, and Ni sources.

[0020] Heteropolyanions or polyoxometalates are a class of compounds with the general formula [XM] y O y ] m− Metal oxide clusters, where X represents a heteroatom and M represents a 4d or 5d transition metal ion. They exhibit rich structural diversity and have various applications in catalysis, materials science, medicine, and biology. The Wells–Dawson type [X2M] cluster used in this invention... 18 O 62 ] (16−2n)−The heteropolyacid structure (M / X ratio = 9) allows its WD structure to be controllably "opened," generating "vacancy" species. These vacancies can be intercalated with various other metal ions (such as V, Mn, Fe, Co, Cu, Zn transition metals, and even lanthanides), thereby precisely customizing its redox and acidic sites. Based on this, this invention adds divalent transition metal ions to the Dawson-type heteropolyacid, achieving functional customization and unique "liquid-like" behavior through "vacancy-substitution" chemistry, resulting in highly efficient bulk catalytic activity and reversible multi-electron redox characteristics. The resulting pyridine oxidation catalyst achieves superior catalytic oxidation under mild conditions. Specifically, in the preparation process provided by this invention: in step S1, the molybdenum source is mixed with an inorganic acid solution to form solution A, preparing a basic intermediate product containing a Mo-OW framework for the next reaction. The introduction of molybdenum not only enhances the redox activity of the catalyst but also modulates its acidic sites, which is crucial for the subsequent intercalation of transition metal ions. The presence of the inorganic acid solution facilitates the dissolution and reaction of molybdenum ions. The resulting solution A is then mixed with a Dawson-type heteropolyacid precursor to generate solution B. The structural characteristics of the Dawson-type heteropolyacid precursor, such as its high symmetry and tunable acidity, provide a favorable microenvironment for the formation of the intermediate product and a stable structural basis for subsequent transition metal ion doping. In step S2, the first reaction promotes the uniform distribution and strong binding of molybdenum ions in the heteropolyacid framework, forming a highly stable intermediate product rich in active sites. The resulting intermediate product not only retains the structural advantages of the Dawson-type heteropolyacid but also enhances its affinity for transition metal ions through molybdenum ion intercalation, creating favorable conditions for subsequent transition metal doping. In step S3, the intermediate product, the transition metal source, and an optional support undergo a second reaction to ultimately generate a pyridine oxidation catalyst. Complexation and doping with transition metal sources (Mn, Zn, Fe, Co, Cu, and Ni) not only increased the redox sites of the obtained catalyst, but also optimized its adaptability to different pyridine derivatives, ultimately significantly enhancing the oxidation activity of the obtained catalyst for the N atom of the pyridine ring, while maintaining its stability under mild reaction conditions.

[0021] In summary, this invention is based on a Dawson-type cage-like anion with a unique structure containing gaps and vacancies, and doped with transition metal ions. During this process, the transition metal ions first coordinate to the "gap" in the Dawson-type anion structure of the intermediate product, and then coordinate with the oxygen atoms surrounding the "gap," ultimately forming a large, complex, structurally stable, and highly catalytically active double-cage "sandwich" structure bridged by the transition metal. Based on this unique structure, highly efficient catalytic oxidation of pyridine can be achieved.

[0022] In step S1, the preferred 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 concentration range of 1 ± 0.1 M can significantly improve the dissolution efficiency of molybdenum ions, promoting more uniform mixing with the Dawson-type heteropolyacid precursor and more effectively forming a highly ordered intermediate product. The preferred weight ratio of the molybdenum source to the inorganic acid solution optimizes the relative concentrations of the reactants, ensuring sufficient dissolution of the molybdenum source while reducing the damage to the heteropolyacid structure caused by excess inorganic acid, resulting in higher integrity and stability of the obtained catalytic active sites. In practical applications, to form a more structurally stable intermediate product, thereby promoting more effective complexation of subsequent transition metal ions into the structure and obtaining a pyridine oxidation catalyst with superior catalytic performance, the preferred molybdenum source is selected from one or more of sodium molybdate, sodium phosphomolybdate, ammonium phosphomolybdate, and ammonium molybdate.

[0023] To obtain a pyridine oxidation catalyst with higher catalytic activity and a more stable structure, the chemical formula of the Dawson-type heteropolyacid precursor is further optimized to be Na. 12 P2W 18-n O 56 The preferred chemical formula for the intermediate product is [H6P2W]. 18- n Mo n O 62 The molar ratio of the Dawson-type heteropolyacid precursor to the molar ratio of Mo in the molybdenum source is preferably 1:(3~7.5). This is to promote more uniform insertion of Mo ions into the heteropolyacid framework, forming catalytic sites with higher activity and stability, thereby further improving the efficiency of the resulting catalyst in oxidizing N atoms on the pyridine ring. Simultaneously, this preferred molar ratio can also more effectively reduce over-acidification of the catalyst active sites caused by excess Mo ions, thus achieving higher selectivity in the oxidation of pyridine compounds.

[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 The structure of ·24H2O is more stable, and the subsequent complexation and doping of transition metal elements in it can be more uniform and stable, thus enabling the preparation of pyridine oxidation catalysts with higher catalytic activity and longer service life.

[0025] In step S2, the preferred reaction time for the first reaction is 2-3 hours, and the first reaction is carried out at 40-50°C. This facilitates more effective bonding between the Mo element and the heteropolyacid groups in the heteropolyacid framework, forming a more stable composite structure. This provides a more ideal microenvironment for the doping of transition metal ions, ultimately resulting in a pyridine oxidation catalyst with a more stable structure and stronger activity and selectivity. Furthermore, to promote a more uniform distribution of molybdenum ions in the heteropolyacid structure and thus more efficiently form intermediates rich in redox sites, the first reaction is preferably carried out under stirring.

[0026] Furthermore, step S2 includes: 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 acidic solution is recrystallized to obtain an intermediate product. This preferred embodiment, on the one hand, removes impurities that may be generated during the reaction, and on the other hand, further promotes the structural recombination of the intermediate product, improves its purity and crystallinity, which is beneficial for the more uniform incorporation and more effective binding of subsequent transition metal ions, ultimately forming a pyridine oxidation catalyst with higher oxidation activity and selectivity. In practical applications, the acidic solution is selected from one or more of hydrochloric acid solution, nitric acid solution, and sulfuric acid solution. To reduce the introduction of impurities and thus further improve the purity and activity of the obtained pyridine oxidation catalyst, hydrochloric acid solution is more preferred.

[0027] In step S3, the preferred molar ratio of intermediate product to transition metal source is 1:(1.5~2.5) to facilitate more complete and uniform incorporation of transition metal ions into the heteropolyacid framework, forming sites with higher oxidation catalytic activity. This also better balances the electronic structure of the final catalyst, further improving its catalytic efficiency and selectivity for the oxidation of N in pyridine compounds. The preferred reaction time for the second reaction is 8h~10h, and the second reaction is carried out at 80℃~120℃. This is to promote a more complete combination of transition metal ions and the intermediate product heteropolyacid framework, resulting in a more stable catalyst structure, reducing irreversible structural changes and damage, and ultimately leading to higher activity and stability of the obtained catalyst in the pyridine oxidation reaction.

[0028] In several typical embodiments, step S3 includes: dissolving the intermediate product in water to obtain a first solution; mixing the first solution, the transition metal source, and an optional support for 0.5 h to 1 h to obtain a second solution; subjecting the second solution to a second reaction to obtain a reaction solution; and evaporating the reaction solution at 60 °C to 70 °C and 0.06 MPa to 0.08 MPa to remove water and obtain a pyridine oxidation catalyst. In the preferred embodiment described above, first dissolving the intermediate product in water to form a first solution not only helps to achieve a more uniform dispersion of transition metal ions but also promotes a more complete combination of the transition metal and the heteropolyacid framework. Subsequently, the mixing time of 0.5 h to 1 h allows for more complete contact between the transition metal ions and the support, resulting in more uniform adsorption and embedding of the metal ions on the support surface. Finally, evaporation treatment at 60℃~70℃ and 0.06MPa~0.08MPa can remove moisture more gently, reducing the potential damage to the catalyst structure caused by high temperature or high pressure. This ultimately significantly improves the purity and structural integrity of the obtained pyridine oxidation catalyst, enhancing its performance in the catalytic reaction. In practical applications, the transition metal source is preferably added in the form of a metal salt. 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 nitrates and / or chlorides.

[0029] When the resulting pyridine oxidation catalyst includes a support, the preferred weight ratio of the transition metal source to the support is 1:(15~45). This allows for more precise optimization of the distribution of transition metal active sites on the selected support, achieving a better balance between the oxidation activity and stability of the resulting catalyst, and further improving its stability under continuous or batch reaction conditions. In practical applications, the preferred support is selected from one or more of SiO2, TiO2, MCM-41, Al2O3, and ZrO2 supports. To expose more active sites and significantly enhance the catalytic activity of the resulting pyridine oxidation catalyst, in practical applications, a specific surface area of ​​260 m² for the SiO2 support is further preferred. 2 / g~290m 2 / g; and / or, the specific surface area of ​​the TiO2 support is 40m². 2 / g~70m 2 / g; and / or, the specific surface area of ​​the MCM-41 carrier is 700m². 2 / g~800m 2 / g; and / or, the specific surface area of ​​the Al2O3 support is 70m². 2 / g~90m 2 / g; and / or, the specific surface area of ​​the ZrO2 support is 40m². 2 / g~50m 2 / g.

[0030] A second aspect of the present invention provides a pyridine oxidation catalyst, which is prepared by the above-described method for preparing pyridine oxidation catalysts, and optionally includes a support. The pyridine oxidation catalyst obtained by the above preparation method possesses a unique structure formed by a "vacancy-substitution" chemistry of Dawson-type heteropolyacids and divalent transition metal ions, thus significantly enhancing its catalytic activity. The obtained pyridine oxidation catalyst can achieve highly efficient and selective oxidation catalysis of pyridine compounds in both homogeneous and heterogeneous reactions.

[0031] It should be noted that due to the complex molecular and electronic structures formed and changed during the preparation process, and the limitations of coordination chemistry and existing testing and characterization methods, it is difficult to perform a comprehensive quantitative characterization of the complex molecular and electronic structures of the obtained pyridine oxidation catalyst. However, performance test results have already shown that the pyridine oxidation catalyst obtained in this invention exhibits superior catalytic activity when catalyzing the oxidation of organic compounds containing pyridine rings.

[0032] A third aspect of this invention provides a method for preparing pyridine-N-oxides, wherein a pyridine compound is reacted with an oxidant in the presence of the aforementioned pyridine oxidation catalyst to obtain pyridine-N-oxides. The pyridine oxidation catalyst obtained by this invention, due to the presence of a special Dawson-type heteropolyacid and a transition metal doped and complexed therein, can effectively activate the pyridine ring and form highly active free radicals when used as a catalyst for the catalytic oxidation of pyridine compounds, thereby efficiently oxidizing the N atom on the pyridine ring to generate high-purity pyridine-N-oxides.

[0033] For the aforementioned pyridine oxidation catalyst, to better protect its metal active sites and promote its catalytic oxidation function, the oxidation reaction is preferably carried out at 75℃~80℃, thereby catalyzing the yield of products with higher purity. In practical applications, the oxidant is selected from one or more of hydrogen peroxide, tert-butyl hydroperoxide, peroxyacetone, and peroxyacid (specifically mCPBA / trifluoroperacetic acid). To minimize the energy of the reaction system, reduce potential catalyst structural degradation at high temperatures, and reduce the excessive consumption of hydrogen peroxide, thereby further improving the purity of the oxidation product and the catalyst's lifespan, a hydrogen peroxide concentration of 30%~35% by mass is further preferred as the oxidant.

[0034] To avoid ambiguity, the term "pyridine compounds" in this invention refers to compounds, especially organic compounds, whose molecular structure contains a pyridine ring. Pyridine-N-oxides are reaction products of the oxidation of organic compounds containing a pyridine ring, in which the nitrogen atom of the pyridine ring is connected to an oxygen atom via a coordinate bond. A reaction route diagram for the oxidation of pyridine compounds with an oxidizing agent to obtain pyridine-N-oxides can be found here:

[0035]

[0036] The structural formulas in the above reaction route diagram are merely examples. R can be aliphatic hydrocarbons, halogenated hydrocarbons, or oxygen-containing hydrocarbon groups. The structures applicable to the catalysts provided by this invention are not limited to these, as long as the structure contains a pyridine ring.

[0037] When the pyridine oxidation catalyst does not include a support, i.e., when the oxidation reaction is a homogeneous reaction, the preferred method for preparing pyridine-N-oxides includes: adding a pyridine compound, a pyridine oxidation catalyst, and an oxidant to an organic solvent, followed by a homogeneous oxidation reaction to obtain pyridine-N-oxides. In this homogeneous reaction, the preferred 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 time is 2h~3h; and / or, the organic solvent is acetonitrile and / or toluene. These preferred reaction conditions, combined with the characteristics of a homogeneous reaction, not only more effectively promote sufficient contact between the active sites of the catalyst and the pyridine compound and the oxidant, promoting the efficient decomposition of the oxidant and generating pyridine-N-oxides with higher selectivity, but also effectively simplify the post-reaction processing.

[0038] When the pyridine oxidation catalyst includes a support, i.e., when the oxidation reaction is a heterogeneous reaction, the preferred method for preparing pyridine-N-oxide includes: loading the pyridine oxidation catalyst into a reactor, and introducing a pyridine compound and an oxidant into the reactor, followed by a heterogeneous oxidation reaction to obtain pyridine-N-oxide. In this heterogeneous reaction, the pyridine compound is preferably 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 one or more of acetonitrile and / or toluene as a solvent. The above-mentioned preferred heterogeneous reaction conditions fully utilize the physical stabilizing effect of the support on the catalyst, as well as the adsorption and diffusion advantages provided by its high specific surface area. Under these conditions, the concentration gradient between the substrate to be oxidized and the catalyst and oxidant is further optimized, thereby significantly improving the selectivity and efficiency of the catalytic oxidation reaction. In practical applications, the reactors used for the above heterogeneous reactions can be fixed-bed reactors, moving-bed reactors, and micro-packed-bed reactors, etc.

[0039] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in this application. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention.

[0040] Example 1

[0041] A method for preparing a pyridine oxidation catalyst:

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

[0043] (1-2) Place mixture A in a four-necked flask and add 9.7 g of Dawson-type heteropolyacid precursor Na. 12 P2W 15 O 56 The resulting mixture B was obtained. In this process, the molar ratio of the Dawson-type heteropolyacid precursor to the molar ratio of Mo in the molybdenum source was 1:3.

[0044] (2-1) After stirring the mixture B at 50°C for 2 hours, filter to obtain the crude product precipitate.

[0045] (2-2) The crude product precipitate was dissolved by heating in hydrochloric acid solution with pH=2, and then recrystallized after cooling to obtain [H6P2W].15 Mo3O 62 ]·24H2O, which is the intermediate product.

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

[0047] (3-2) The resulting reaction liquid system was slowly evaporated to obtain crystals. The evaporation temperature was 60℃ and the vacuum degree was 0.06MPa. This material is the pyridine oxidation catalyst, which is denoted as WDZn in this example.

[0048] Example 2

[0049] A method for preparing a pyridine oxidation catalyst:

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

[0051] (1-2) Place mixture A in a four-necked flask and add 7.8 g of Dawson-type heteropolyacid precursor Na. 12 P2W 15 O 56 The resulting mixture B was obtained. In this process, the molar ratio of the Dawson-type heteropolyacid precursor to the molar ratio of Mo in the molybdenum source was 1:7.5.

[0052] (2-1) After stirring the mixture B at 50°C for 2 hours, filter to obtain the crude product precipitate.

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

[0054] (3-1) Take 10g of the obtained intermediate product [H6P2W] 12 Mo6O 62[H₆P₂W₂]₄H₂O was dissolved in water to obtain a first solution. At room temperature (25±2℃), 1.45g of Zn(NO₃)₂·6H₂O salt solid and 50g of SiO₂ were added, and the mixture was stirred for 0.5h to obtain a second solution. The second solution was kept at 120℃ in a high-pressure reactor for 8h to obtain a homogeneous reaction solution. During this process, [H₆P₂W₂]₄H₂O was dissolved in water to obtain a first solution. 15 Mo3O 62 The molar ratio of 24H2O to the transition metal zinc source is 1:2, and the weight ratio of the transition metal source to the support is 1:34.5.

[0055] (3-2) The resulting reaction liquid system was slowly evaporated to obtain crystals. The evaporation temperature was 60℃ and the vacuum degree was 0.06MPa. This material is the pyridine oxidation catalyst, which is denoted as WDZn-SiO2 in this example.

[0056] Example 3

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

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

[0059] Example 4

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

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

[0062] (1-2) Place mixture A in a four-necked flask and add 9.7 g of Dawson-type heteropolyacid precursor Na. 12 P2W 15 O 56 The resulting mixture B was obtained. In this process, the molar ratio of the Dawson-type heteropolyacid precursor to the molar ratio of Mo in the molybdenum source was 1:3.

[0063] (2-1) After stirring the mixture B at 50°C for 2 hours, filter to obtain the crude product precipitate.

[0064] (2-2) The crude product precipitate was dissolved by heating in hydrochloric acid solution with pH=3, and then recrystallized after cooling to obtain [H6P2W]. 15 Mo3O 62 ]·24H2O, which is the intermediate product.

[0065] (3-1) Take 10g of the obtained intermediate product [H6P2W] 15 Mo3O 62 [H₂·24H₂O] 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, and the mixture was stirred for 0.5 h to obtain a second solution. The second solution was kept at 80℃ in a high-pressure reactor for 10 h to obtain a homogeneous reaction solution. During this process, [H₆P₂W₂] 15 Mo3O 62 The molar ratio of 24H2O to the transition metal nickel source is 1:2, and the weight ratio of the transition metal source to the support is 1:43.1.

[0066] (3-2) The resulting reaction liquid system was slowly evaporated to obtain crystals. The evaporation temperature was 70℃ and the vacuum degree was 0.08MPa. This material is the pyridine oxidation catalyst, which is referred to as WDNi-TiO2 in this example.

[0067] Example 5

[0068] A method for preparing a pyridine oxidation catalyst:

[0069] The only 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, denoted as WDFe.

[0070] Example 6

[0071] A method for preparing a pyridine oxidation catalyst:

[0072] The only 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, denoted as WDCo.

[0073] Example 7

[0074] A method for preparing a pyridine oxidation catalyst:

[0075] The only 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, denoted as WDCo-SiO2.

[0076] Example 8

[0077] A method for preparing a pyridine oxidation catalyst:

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

[0079] Example 9

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

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

[0082] Example 10

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

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

[0085] (1-2) Place mixture A in a four-necked flask and add 9.7 g of Dawson-type heteropolyacid precursor Na. 12 P2W 15 O 56 The resulting mixture B was obtained. In this process, the molar ratio of the Dawson-type heteropolyacid precursor to the molar ratio of Mo in the molybdenum source was 1:3.

[0086] (2-1) After stirring the mixture B at 40°C for 3 hours, filter to obtain the crude product precipitate.

[0087] (2-2) The crude product precipitate was dissolved by heating in hydrochloric acid solution at pH 2.5, and then recrystallized after cooling to obtain [H6P2W]. 15 Mo3O 62 ]·24H2O, which is the intermediate product.

[0088] (3-1) Take 10g of the obtained intermediate product [H6P2W] 15 Mo3O 62 [H₆P₂W₂]₄H₂O was dissolved in water to obtain a first solution. At room temperature (25±2℃), 1.18 g of Cu(NO₃)₂·3H₂O salt solid and 20 g of ZrO₂ were added, and the mixture was stirred for 0.5 h to obtain a second solution. The second solution was kept at 80℃ in a high-pressure reactor for 10 h to obtain a homogeneous reaction solution. During this process, [H₆P₂W₂]₄H₂O was dissolved in water to obtain a first solution. 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 support is 1:16.9.

[0089] (3-2) The resulting reaction liquid system was slowly evaporated to obtain crystals. The evaporation temperature was 70℃ and the vacuum degree was 0.08MPa. This material is the pyridine oxidation catalyst, which is denoted as WDCu-ZrO2 in this example.

[0090] Example 11

[0091] A method for preparing a pyridine oxidation catalyst:

[0092] The only difference between this embodiment and Example 10 is that in step (3-1), an equal weight of Al2O3 is used instead of ZrO2 as the support to prepare a pyridine oxidation catalyst, denoted as WDZn-Al2O3.

[0093] Example 12

[0094] A method for preparing a pyridine oxidation catalyst:

[0095] The only difference between this embodiment and Example 1 is that in step (3-1), an equimolar amount of Mn(NO3)2·4H2O is used instead of Zn(NO3)2·6H2O to prepare a pyridine oxidation catalyst, denoted as WDMn.

[0096] Example 13

[0097] A method for preparing a pyridine oxidation catalyst:

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

[0099] (1-2) Place mixture A in a four-necked flask and add 9.7 g of Dawson-type heteropolyacid precursor Na. 12 P2W 15 O 56 The resulting mixture B was obtained. In this process, the molar ratio of the Dawson-type heteropolyacid precursor to the molar ratio of Mo in the molybdenum source was 1:4.3.

[0100] (2-1) After stirring the mixture B at 50°C for 2 hours, filter to obtain the crude product precipitate.

[0101] (2-2) The crude product precipitate was dissolved by heating in hydrochloric acid solution with pH=3, and then recrystallized after cooling to obtain [H6P2W]. 14 Mo4O 62]·24H2O, which is the intermediate product.

[0102] (3-1) Take 10g of the obtained intermediate product [H6P2W] 14 Mo4O 62 [H₆P₂W₂]₄H₂O was dissolved in water to obtain a first solution. At room temperature (25±2℃), 1.2g of NiCl₂·6H₂O salt solid and 50g of ZrO₂ were added, and the mixture was stirred for 0.5h to obtain a second solution. The second solution was kept at 80℃ in a high-pressure reactor for 10h to obtain a homogeneous reaction solution. During this process, [H₆P₂W₂]₄H₂O was dissolved in water to obtain a first solution. 14 Mo4O 62 The molar ratio of 24H2O to the transition metal nickel source is 1:2, and the weight ratio of the transition metal source to the support is 1:42.

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

[0104] Example 14

[0105] A method for preparing a pyridine oxidation catalyst:

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

[0107] Example 15

[0108] A method for preparing a pyridine oxidation catalyst:

[0109] The only difference between this embodiment and Embodiment 1 is that the Dawson-type heteropolyacid precursor Na is changed in steps (1-2). 12 P2W 15 O 56 The amount of molars used was adjusted so that the ratio of the molar amount of Dawson-type heteropolyacid precursor to the molar amount of Mo in the molybdenum source was changed to 2.5:1.

[0110] Example 16

[0111] A method for preparing a pyridine oxidation catalyst:

[0112] The only difference between this embodiment and Embodiment 1 is that in step (2-1), the reaction holding temperature is changed to 35°C and the stirring reaction time is changed to 4 hours.

[0113] Example 17

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

[0115] The only difference between this embodiment and Embodiment 1 is that in step (2-1), the reaction holding temperature is changed to 55°C and the stirring reaction time is changed to 1 hour.

[0116] Example 18

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

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

[0119] Example 19

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

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

[0122] Example 20

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

[0124] The only difference between this embodiment and Embodiment 1 is that in step (3-1), the heat preservation temperature of the high-pressure reactor is changed to 70°C and the reaction time is changed to 12h.

[0125] Example 21

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

[0127] The only difference between this embodiment and Embodiment 1 is that in step (3-1), the heat preservation temperature of the high-pressure reactor is changed to 130°C and the reaction time is changed to 6 hours.

[0128] Comparative Example 1

[0129] This comparative example uses the existing WO3 / TiO2 catalyst directly as the obtained catalyst sample, and its preparation method refers to CN 104974088A.

[0130] Comparative Example 2

[0131] A method for preparing a pyridine oxidation catalyst:

[0132] The only difference between this comparative example and Example 1 is that no molybdenum source was added in step (1-1).

[0133] Comparative Example 3

[0134] A method for preparing a pyridine oxidation catalyst:

[0135] The only difference between this comparative example and Example 1 is that, in steps (1-2), an equimolar amount of the heteropolyacid Keggin structure Na3PMo was used. 12 O 40 Replaces Dawson-type heteropolyacid precursor Na 12 P2W 15 O 56 .

[0136] Comparative Example 4

[0137] A method for preparing a pyridine oxidation catalyst:

[0138] The only difference between this comparative example and Example 1 is that, in steps (1-2), equimolar amounts of H3[P(W3O] are used. 10 )4]·H2O replaces Dawson-type heteropolyacid precursor Na 12 P2W 15 O 56 .

[0139] Application Example 1

[0140] A method for preparing pyridine-N-oxide:

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

[0142] Application Example 2

[0143] A method for preparing pyridine-N-oxide:

[0144] This application example uses the pyridine oxidation catalyst WDZn-SiO2 containing a support obtained in Example 2 as the catalyst sample. 40g of the tableted WDZn-SiO2 catalyst obtained in Example 2 was placed in a fixed bed, and at 75°C, a 0.5M acetonitrile solution of the pyridine compound to be oxidized was fed at a rate of 0.5g / min, and 35% hydrogen peroxide was fed at a rate of 10mL / min. The reaction purity was determined using liquid chromatography.

[0145] Application Example 3

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

[0147] This application example uses the pyridine oxidation catalyst WDNi obtained in Example 3, which does not contain a support, as the catalyst sample. The structure of the pyridine compound to be oxidized is changed, while the other reaction conditions remain the same as in Application Example 1.

[0148] Application Example 4

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

[0150] This application example uses the pyridine oxidation catalyst WDNi-TiO2 containing a support obtained in Example 4 as the catalyst sample. 40g of the tableted WDNi-TiO2 catalyst obtained in Example 4 was placed in a fixed bed, and a 0.5M toluene solution of the pyridine compound to be oxidized was introduced at a feed rate of 1g / min at 80°C, followed by 35% hydrogen peroxide at a feed rate of 5mL / min. The reaction purity was determined using liquid chromatography.

[0151] Application Example 5

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

[0153] This application example uses the pyridine oxidation catalyst WDFe obtained in Example 5, which does not contain a support, as the catalyst sample. The structure of the pyridine compound to be oxidized is changed, while the other reaction conditions remain the same as in Application Example 1.

[0154] Application Example 6

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

[0156] This application example uses the pyridine oxidation catalyst WDCo obtained in Example 6, which does not contain a support, as the catalyst sample. The structure of the pyridine compound to be oxidized is changed, while the other reaction conditions remain the same as in Application Example 1.

[0157] Application Example 7

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

[0159] This application example uses the pyridine oxidation catalyst WDCo-SiO2 with a support obtained in Example 7 as the catalyst sample. 40g of the tableted WDCo-SiO2 catalyst obtained in Example 7 was placed in a fixed bed, and at 80°C, a 0.5M acetonitrile solution of the pyridine compound to be oxidized was fed at a rate of 0.5g / min, and 30% hydrogen peroxide was fed at a rate of 5mL / min. The reaction purity was determined using liquid chromatography.

[0160] Application Example 8

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

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

[0163] Application Example 9

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

[0165] This application example uses the pyridine oxidation catalyst WDCu obtained in Example 9, which does not contain a support, as the catalyst sample. The structure of the pyridine compound to be oxidized is changed, while the other reaction conditions remain the same as in Application Example 1.

[0166] Application Example 10

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

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

[0169] Application Example 11

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

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

[0172] Application Example 12

[0173] A method for preparing 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. The structure of the pyridine compound to be oxidized is changed, while the other reaction conditions remain the same as in Application Example 1.

[0175] Application Example 13

[0176] A method for preparing pyridine-N-oxide:

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

[0178] Application Example 14

[0179] A method for preparing 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. The structure of the pyridine compound to be oxidized is changed, while the other reaction conditions remain the same as in Application Example 1.

[0181] Application Example 15

[0182] A method for preparing pyridine-N-oxide:

[0183] This application example uses the pyridine oxidation catalyst without a support obtained in Example 14 as the catalyst sample. The structure of the pyridine compound to be oxidized and the reaction conditions are consistent with those in Application Example 1.

[0184] Application Example 16

[0185] A method for preparing pyridine-N-oxide:

[0186] This application example uses the pyridine oxidation catalyst without a support obtained in Example 15 as the catalyst sample. The structure of the pyridine compound to be oxidized and the reaction conditions are consistent with those in Application Example 1.

[0187] Application Example 17

[0188] A method for preparing pyridine-N-oxide:

[0189] This application example uses the pyridine oxidation catalyst without a support obtained in Example 16 as the catalyst sample. The structure of the pyridine compound to be oxidized and the reaction conditions are consistent with those in Application Example 1.

[0190] Application Example 18

[0191] A method for preparing pyridine-N-oxide:

[0192] This application example uses the pyridine oxidation catalyst without a support obtained in Example 17 as the catalyst sample. The structure of the pyridine compound to be oxidized and the reaction conditions are consistent with those in Application Example 1.

[0193] Application Example 19

[0194] A method for preparing pyridine-N-oxide:

[0195] This application example uses the pyridine oxidation catalyst without a support obtained in Example 18 as the catalyst sample. The structure of the pyridine compound to be oxidized and the reaction conditions are consistent with those in Application Example 1.

[0196] Application Example 20

[0197] A method for preparing pyridine-N-oxide:

[0198] This application example uses the pyridine oxidation catalyst without a support obtained in Example 19 as the catalyst sample. The structure of the pyridine compound to be oxidized and the reaction conditions are consistent with those in Application Example 1.

[0199] Application Example 21

[0200] A method for preparing pyridine-N-oxide:

[0201] This application example uses the pyridine oxidation catalyst without a support obtained in Example 20 as the catalyst sample. The structure of the pyridine compound to be oxidized and the reaction conditions are consistent with those in Application Example 1.

[0202] Application Example 22

[0203] A method for preparing pyridine-N-oxide:

[0204] This application example uses the pyridine oxidation catalyst without a support obtained in Example 21 as the catalyst sample. The structure of the pyridine compound to be oxidized and the reaction conditions are consistent with those in Application Example 1.

[0205] Application Example 23

[0206] A method for preparing pyridine-N-oxide:

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

[0208] Application Example 24

[0209] A method for preparing pyridine-N-oxide:

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

[0211] Application Comparative Example 1

[0212] The comparative example used the pyridine oxidation catalyst without support obtained in Comparative Example 1 as the catalyst sample. The structure of the pyridine compound to be oxidized and the reaction conditions were consistent with those in Application Example 1.

[0213] Application Comparative Example 2

[0214] The comparative example used the pyridine oxidation catalyst without a support obtained in Comparative Example 2 as the catalyst sample. The structure of the pyridine compound to be oxidized and the reaction conditions were consistent with those in Application Example 1.

[0215] Application Comparative Example 3

[0216] The comparative example used the pyridine oxidation catalyst without a support obtained in Comparative Example 3 as the catalyst sample. The structure of the pyridine compound to be oxidized and the reaction conditions were consistent with those in Application Example 1.

[0217] Application Comparative Example 4

[0218] The comparative example used the pyridine oxidation catalyst without support obtained in Comparative Example 4 as the catalyst sample. The structure of the pyridine compound to be oxidized and the reaction conditions were consistent with those in Application Example 1.

[0219] In the above application examples and comparative examples, the structural formulas of the pyridine compounds to be oxidized, the structural formulas of the pyridine-N-oxide products obtained by oxidation, and the purity of the products are all shown in Table 1.

[0220] Table 1

[0221]

[0222]

[0223]

[0224] As can be seen from the above description, compared with the comparative examples, the embodiments of the present invention have achieved the preparation of a pyridine oxidation catalyst with high catalytic activity. The obtained pyridine oxidation catalyst can simultaneously achieve efficient and highly selective oxidation catalysis of pyridine compounds in both homogeneous and heterogeneous reactions, ultimately yielding the oxidation product pyridine-N-oxide with high purity.

[0225] Specifically, comparing Application Examples 15 and 16 with Application Examples 1 to 14 reveals that, during the preparation of the pyridine oxidation catalyst (i.e., in Examples 14 and 15), by optimizing the molar ratio of the Dawson-type heteropolyacid precursor to the molar amount of Mo in the molybdenum source, Mo ions can be more uniformly embedded in the heteropolyacid framework, forming catalytic sites with higher activity and stability, thereby further improving the efficiency of the obtained catalyst in oxidizing N atoms on the pyridine ring. Simultaneously, optimizing the molar ratio of the Dawson-type heteropolyacid precursor to the molar amount of Mo in the molybdenum source can also more effectively reduce the over-acidification of the catalyst active sites caused by excess Mo ions, thereby achieving higher selectivity in the oxidation of pyridine compounds.

[0226] Comparing Application Examples 17 and 18 with Application Examples 1 to 14, it can be seen that in the process of preparing the pyridine oxidation catalyst (i.e., in Examples 16 and 17), by optimizing the conditions of the first reaction in step S2, it is possible to promote a more effective combination between the Mo element in the heteropolyacid framework and the heteropolyacid groups, forming a more stable composite structure, thereby providing a more ideal microenvironment for the doping of transition metal ions, and finally obtaining a pyridine oxidation catalyst with a more stable structure and stronger activity and selectivity.

[0227] Comparing Application Examples 19 and 20 with Application Examples 1 to 14, it can be seen that in the process of preparing pyridine oxidation catalysts (i.e., in Examples 18 and 19), by optimizing the amount of transition metal source and, consequently, the molar ratio of intermediate product to transition metal source, transition metal ions can be more fully and uniformly incorporated into the heteropolyacid framework, forming sites with higher oxidation catalytic activity. At the same time, the electronic structure of the final catalyst is better balanced, further improving its catalytic efficiency and selectivity for the oxidation of N in pyridine compounds.

[0228] Comparing Application Examples 21 and 22 with Application Examples 1 to 14, it can be seen that in the process of preparing the pyridine oxidation catalyst (i.e., in Examples 20 and 21), by optimizing the conditions of the second reaction in step S3, the combination of transition metal ions and intermediate heteropolyacid framework can be improved, the resulting catalyst structure is more stable, irreversible structural changes and damage are reduced, and ultimately the obtained catalyst exhibits higher activity and stability in the pyridine oxidation reaction.

[0229] Comparing Application Examples 23 and 24 with Application Examples 1 to 14, it can be seen that in the application of the pyridine oxidation catalyst, i.e. the preparation of pyridine-N-oxide, the pyridine oxidation catalyst obtained by the present invention can better protect the metal active sites on the obtained pyridine oxidation catalyst by optimizing the temperature conditions of the oxidation reaction, so as to better exert its catalytic oxidation function and thereby catalyze the production of products with higher purity.

[0230] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0231] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

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, and solution A is mixed with a Dawson-type heteropolyacid precursor to obtain solution B; In step S2, solution B undergoes a first reaction to obtain an intermediate product; In step S3, the intermediate product, the transition metal source, and the optional support undergo a second reaction to obtain the pyridine oxidation catalyst. The transition metal source is selected from one or more of Mn source, Zn source, Fe source, Co source, Cu source and Ni source.

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; The chemical formula of the Dawson-type heteropolyacid 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, where n is 3~6.

3. The method for preparing the pyridine oxidation catalyst according to claim 1, characterized in that, In step S2, the reaction time of the first reaction is 2h to 3h, and the first reaction is carried out at 40℃ to 50℃.

4. The method for preparing the pyridine oxidation catalyst according to any one of claims 1 to 3, characterized in that, Step S2 includes: the solution B undergoes the 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 acidic solution is recrystallized to obtain the intermediate product.

5. The method for preparing the pyridine oxidation catalyst according to any one of claims 1 to 3, characterized in that, 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℃.

6. The method for preparing the pyridine oxidation catalyst according to any one of claims 1 to 3, characterized in that, In step S3, the weight ratio of the transition metal source to the support is 1:(15~45); and / or, the support is selected from one or more of SiO2 support, TiO2 support, MCM-41 support, Al2O3 support and ZrO2 support.

7. A pyridine oxidation catalyst, characterized in that, The pyridine oxidation catalyst is prepared by the method for preparing the pyridine oxidation catalyst according to any one of claims 1 to 6, and the pyridine oxidation catalyst may optionally include the support.

8. 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 7 to obtain the pyridine-N-oxide; the oxidation reaction is carried out at 75°C to 80°C.

9. The method for preparing pyridine-N-oxide according to claim 8, 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.

10. The method for preparing pyridine-N-oxide according to claim 8, 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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