Modified ets-10 molecular sieve, preparation method and catalyst for preparing aromatic aldehyde by methyl-substituted aromatic oxidation and application

Abstract

The application discloses a modified ETS-10 molecular sieve, a preparation method, a catalyst for preparing aromatic aldehyde through methyl-substituted aromatic hydrocarbon oxidation and application of the catalyst. The modified ETS-10 molecular sieve comprises silicon dioxide and metal oxides; the metal comprises titanium, vanadium and alkali metal. The application takes the modified ETS-10 molecular sieve obtained through hydrothermal synthesis as a carrier, and loads active components Ni / Pd / Pt / Mo / Mn / Cr, so that the basicity and oxidation reaction performance of the catalyst are improved, the adsorption performance to reactants is enhanced, and the yield of aromatic aldehyde is improved. The obtained catalyst can be used in the reaction for preparing corresponding aromatic aldehyde from methyl-substituted aromatic hydrocarbon, and has great industrial application potential.

Description

Technical Field

[0001] This invention relates to the field of aromatic side-chain oxidation technology, specifically to a modified ETS-10 molecular sieve, its preparation method, and a catalyst for the oxidation of methyl-substituted aromatics to prepare aromatic aldehydes, as well as their applications. Background Technology

[0002] Aromatic hydrocarbon side-chain oxidation reactions generally refer to the oxidation of side chains connected to an aromatic ring and containing α-H, resulting in the formation of corresponding aromatic acids, alcohols, aldehydes, ketones, acid anhydrides, and other oxygen-containing functional groups. Aromatic hydrocarbon oxidation products and their derivatives are important fine chemical intermediates, widely used in pharmaceuticals, pesticides, fragrances, dyes, and polymer materials industries, possessing high economic value. Aromatic aldehydes, in particular, are compounds where an aldehyde group is connected to an aromatic ring. As important organic synthesis intermediates, aromatic aldehydes play a crucial role in pharmaceuticals, petrochemicals, and dyes, and have broad market prospects.

[0003] Selective oxidation of methyl aromatic hydrocarbon side chains is challenging due to the strong CH bond energy and low molecular polarity, making substrate activation difficult. Furthermore, the reaction rarely stops at the aldehyde formation step, easily leading to deep oxidation to benzoic acid, thus reducing the selectivity of benzaldehyde. However, benzaldehyde products have higher industrial value. Compared to oxidation reactions where the oxidation depth cannot be controlled, chemical methods offer a cost advantage in raw materials. Therefore, the traditional method for synthesizing benzaldehyde is the methyl aromatic hydrocarbon halogenation hydrolysis method, which involves chlorination and saponification of the methyl group to produce benzaldehyde. This method is not only environmentally polluting but also results in low benzaldehyde yields and the presence of halide ions in the product, limiting its application. In contrast, gas-phase oxidation uses air directly as an oxygen source, resulting in high product purity, low equipment investment, and continuous production. However, the high reactivity of gas-phase oxidation leads to low yields of the corresponding aromatic aldehydes. Liquid-phase oxidation, on the other hand, offers milder reaction conditions, no deep oxidation products, and high selectivity for aromatic aldehydes, giving it certain advantages. The oxygen source for liquid-phase oxidation reactions can be air, oxygen, or hydrogen peroxide. Among them, air and oxygen have relatively low conversion rates, while hydrogen peroxide has a significantly high conversion rate. However, hydrogen peroxide may also undergo hydroxylation reactions with benzene rings to generate phenolic byproducts. Therefore, finding a suitable catalyst to improve the selectivity of the target product is particularly important. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a modified ETS-10 molecular sieve, its preparation method, a catalyst for the oxidation of methyl-substituted aromatic hydrocarbons to prepare aromatic aldehydes, and its application. This invention aims to develop a highly active reaction method for the oxidation of methyl-substituted aromatic hydrocarbons to prepare corresponding aromatic aldehydes. The method of this invention features a simple preparation process, higher reactivity, easier catalyst separation, reusability, and a higher yield of aromatic aldehydes.

[0005] One objective of this invention is to provide a modified ETS-10 molecular sieve comprising silicon dioxide and metal oxides, wherein the metals include titanium, vanadium and alkali metals.

[0006] In a preferred embodiment of the present invention,

[0007] The metal oxides include titanium dioxide, vanadium pentoxide, sodium oxide (Na2O), and potassium oxide (K2O).

[0008] In a preferred embodiment of the present invention,

[0009] Based on 100 wt% of the modified ETS-10 molecular sieve, the silica content is 60-80 wt%, preferably 65-75 wt%; and / or, the titanium dioxide content is 10-30 wt%, preferably 10-20 wt%; and / or, the vanadium pentoxide content is 0.1-10%, preferably 0.5-5%; and / or, the total sodium oxide and potassium oxide content is 2-20 wt%, preferably 2-10 wt%.

[0010] In a preferred embodiment of the present invention,

[0011] The modified ETS-10 molecular sieve has a specific surface area of ​​200–350 m². 2 ·g -1 Preferably 280–320m 2 ·g -1 Among them, the specific surface area of ​​micropores is 180–310 m². 2 ·g -1 Preferably 200–310m 2 ·g -1 .

[0012] The second objective of this invention is to provide a method for preparing a modified ETS-10 molecular sieve, which is one of the objectives of this invention, including the step of hydrothermal synthesis of components including a titanium source, a vanadium source, a silicon source, sodium hydroxide and KF·2H2O to obtain the modified ETS-10 molecular sieve.

[0013] In a preferred embodiment of the present invention,

[0014] The method includes:

[0015] 1) Mix the silicon source with sodium hydroxide and water until homogeneous to obtain a silicon source solution;

[0016] 2) Disperse and dissolve the titanium source and vanadium source together in water to obtain a vanadium-titanium source solution;

[0017] 3) Mix the vanadium-titanium source solution from step 2) with the silicon source solution from step 1) to obtain the sol precursor;

[0018] 4) Add KF·2H2O to the sol precursor and age it to obtain a crystallized precursor;

[0019] 5) The modified ETS-10 molecular sieve is obtained by crystallizing the crystallization precursor.

[0020] In a preferred embodiment of the present invention,

[0021] In step 1),

[0022] The silicon source is selected from at least one of tetraethyl orthosilicate, silica sol, water glass, and sodium silicate.

[0023] In a preferred embodiment of the present invention,

[0024] In step 2),

[0025] The titanium source is selected from at least one of titanium sulfate, titanium oxysulfate, titanium tetrachloride, titanium trichloride, and tetrabutyl titanate; and / or,

[0026] The vanadium source is selected from at least one of ammonium metavanadate (NH4VO3), alum sulfate, vanadium oxysulfate, and vanadium oxalate.

[0027] In a preferred embodiment of the present invention,

[0028] In step 4),

[0029] The aging time is 1 to 24 hours.

[0030] In a preferred embodiment of the present invention,

[0031] In step 5),

[0032] The crystallization temperature is 150–230°C, preferably 200–230°C, and the crystallization time is 8–36 hours, preferably 20–36 hours; and / or,

[0033] The crystallization process further includes washing and drying steps; preferably, the drying temperature is 80-150°C, and / or the drying time is 4-48 hours.

[0034] In the preparation method described above,

[0035] The amounts of silicon source, vanadium source, titanium source, sodium hydroxide, and KF·2H2O added are calculated according to the ratio of silicon dioxide:titanium dioxide:vanadium pentoxide:sodium oxide:potassium fluoride:water in the crystallization precursor, preferably (3-6):1:(0.05-0.5):(4-8):(0.8-2):(150-300).

[0036] In step 2), the ratio of water to the total mass of vanadium and titanium sources is 5 to 15:1, and the total amount of water used in steps 1) and 2) is the total amount of water required for calculation.

[0037] The preferred method for preparing the modified ETS-10 molecular sieve of the present invention includes the following steps:

[0038] (1) Under stirring, the silicon source and NaOH are dispersed and dissolved in water to obtain a silicon source solution;

[0039] (2) Under stirring, the titanium source and the vanadium source are dispersed and dissolved together in water to obtain a vanadium-titanium source solution;

[0040] (3) Under stirring, the vanadium-titanium source solution and the silicon source solution are mixed to obtain a sol precursor;

[0041] (4) Add KF·2H2O as a mineralizing agent to the sol precursor and age it to obtain a crystallized precursor;

[0042] (5) The crystallization precursor is transferred into a hydrothermal reactor and crystallized under heating and autogenous pressure. The crystallized product is filtered and washed until the pH of the filtrate is 7. The product is then dried to obtain the modified ETS-10 molecular sieve.

[0043] A third objective of this invention is to provide a catalyst for the oxidation of methyl-substituted aromatic hydrocarbons to prepare aromatic aldehydes, comprising a support and an active component, wherein the support is a modified ETS-10 molecular sieve as described in one objective of this invention or a modified ETS-10 molecular sieve obtained by the preparation method described in another objective of this invention.

[0044] In a preferred embodiment of the present invention,

[0045] The active component is a transition metal or its oxide, preferably selected from at least one of Mo, Mn, Cr, Ni, Pd, and Pt (Pd and Pt are in metallic form, the others are in oxide form).

[0046] The loading of the active component is 0.3-8% of the total mass of the catalyst, preferably 0.4-5%, and more preferably 0.8-4%.

[0047] The fourth objective of this invention is to provide a method for preparing a catalyst for the oxidation of methyl-substituted aromatic hydrocarbons to aromatic aldehydes, as described in the third objective of this invention. The method includes loading the salt corresponding to the active component onto the modified ETS-10 molecular sieve using an impregnation method, followed by drying and calcination to obtain the catalyst.

[0048] In a preferred embodiment of the present invention,

[0049] The drying temperature is 80–150°C, and the drying time is 4–48 h; and / or the calcination temperature is 450–650°C, and the calcination time is 1–8 h.

[0050] The catalyst for the oxidation of methyl-substituted aromatic hydrocarbons to the corresponding aromatic aldehydes is preferably prepared using the following steps:

[0051] (1) Dissolve the salt corresponding to the active component in the dispersion solvent, with the amount of solvent corresponding to the total pore volume of the carrier, to prepare a uniform solution;

[0052] (2) The solution obtained in step (1) is added dropwise to the modified ETS-10 molecular sieve for equal volume impregnation. The resulting catalyst precursor is dried and calcined to obtain the catalyst.

[0053] The fifth objective of this invention is to provide a method for preparing aromatic aldehydes by oxidizing methyl-substituted aromatic hydrocarbons, using the catalyst for preparing aromatic aldehydes by oxidizing methyl-substituted aromatic hydrocarbons according to the third objective of this invention or the catalyst for preparing aromatic aldehydes by oxidizing methyl-substituted aromatic hydrocarbons obtained by the preparation method according to the fourth objective of this invention.

[0054] In a preferred embodiment of the present invention,

[0055] The step of reacting methyl-substituted aromatic hydrocarbons with hydrogen peroxide in the presence of a solvent and the catalyst, using hydrogen peroxide as an oxygen source; preferably,

[0056] The solvent is at least one selected from water, acetonitrile, acetone, N-methylpyrrolidone (NMP), and N,N-dimethylformamide (DMF); and / or,

[0057] The methyl-substituted aromatic hydrocarbon is at least one selected from toluene, o-xylene, p-xylene, m-xylene, p-tert-butyltoluene, o-chlorotoluene, and p-chlorotoluene; and / or

[0058] The volume ratio of the methyl-substituted aromatic hydrocarbon to the solvent is 1:3 to 10; and / or, the volume ratio of the hydrogen peroxide to the methyl-substituted aromatic hydrocarbon is 1 to 5:1; and / or, the amount of the catalyst used per 10 mL of the methyl-substituted aromatic hydrocarbon is 0.1 to 0.5 g; and / or,

[0059] The reaction temperature is 80–120°C, the reaction time is 4–24 h, and the reaction pressure is 0.1–2 MPa.

[0060] The method for preparing aromatic aldehydes by oxidation of methyl-substituted aromatic hydrocarbons preferably uses a stirred tank as the reactor.

[0061] Molecular sieves possess a range of advantages, including large specific surface area, high selectivity, tunable framework elements, and structural stability. ETS-10, with its large twelve-membered ring micropores (0.49 × 0.76 nm), is well-suited for reactions involving benzene rings. Furthermore, ETS-10 molecular sieves exhibit strong ion exchange performance, which can be further enhanced by doping with various elements. Due to the unique nature of methyl aromatic hydrocarbon oxidation, the reaction is highly sensitive to the state of active sites in the catalyst, as well as the catalyst's acidity and adsorption properties. Therefore, this invention employs a V-framework-doped K,Na-V-ETS-10 molecular sieve to further improve the reaction performance of methyl aromatic hydrocarbon oxidation to aromatic aldehydes.

[0062] This invention primarily addresses the problems of poor reaction performance, high separation costs, and lack of recyclability associated with homogeneous catalysts used in existing technologies. It employs a heterogeneous basic catalyst with higher reactivity, easier separation, and reusability for the oxidation of methyl-substituted aromatic hydrocarbons to prepare corresponding aromatic aldehydes, thereby improving the yield of aromatic aldehydes. This catalyst is applicable to the direct oxidation of various methyl aromatic hydrocarbons to aromatic aldehydes. A supported catalyst is prepared by using K,Na-V-ETS-10 molecular sieve obtained through hydrothermal synthesis as a support and loading it with active components Ni / Pd / Pt / Mo / Mn / Cr. This improves the basicity and oxidation reaction performance of the catalyst, while also enhancing its adsorption properties for reactants, thus increasing the yield of aromatic aldehydes. The resulting catalyst can be used for the preparation of corresponding aromatic aldehydes from methyl-substituted aromatic hydrocarbons, demonstrating significant potential for industrial application. Detailed Implementation

[0063] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0064] All raw materials used in the examples are conventional commercially available raw materials.

[0065] In this invention, the XRF method test uses an S8 Tiger X-ray fluorescence spectrometer (XRF) manufactured by Bruker GmbH, Germany, to analyze the molecular sieves at a wavelength of 1000 nm and a focal length of 1 nm.

[0066] In this invention, the specific surface area of ​​the molecular sieve was measured using a Micromeritics TriStar 3000 physical adsorption instrument and calculated using the BET method.

[0067] In this embodiment of the invention, the aromatic hydrocarbon conversion rate and aromatic aldehyde yield are defined as follows:

[0068]

[0069]

[0070] The methyl aromatic hydrocarbon oxidation reaction in the embodiments and comparative examples of the present invention was carried out in a 100mL batch reactor. Methyl aromatic hydrocarbon raw material, solvent, hydrogen peroxide and catalyst powder were added to the reactor, and stirring and heating were turned on to start the reaction. The reaction pressure was 0.1-2MPa.

[0071] Example 1

[0072] Catalyst preparation:

[0073] 1. Carrier preparation

[0074] (1) The feed ratio is SiO2:TiO2:V2O5:Na2O:KF:H2O=6:1:0.2:4.2:1.6:250. The corresponding contents of water glass, vanadium oxysulfate, TiCl4, NaOH, and KF·2H2O are calculated according to this ratio as raw materials.

[0075] (2) Gel preparation in a beaker: Mix a portion of water (the total amount of water used in steps (2) and (3) is the total amount of water required in step (1), water glass and NaOH thoroughly under stirring to obtain a silicon source solution;

[0076] (3) Disperse and dissolve vanadium sulfate and TiCl4 together in water according to the total mass ratio of water to vanadium sulfate and TiCl4 of 10:1 to obtain vanadium-titanium source solution;

[0077] (4) The above vanadium-titanium source solution and the above silicon source solution are mixed and stirred to form a semi-transparent gel (i.e., sol precursor);

[0078] (5) Add the amount of KF·2H2O calculated in step (1) to the sol precursor as a mineralizing agent, stir and age for 1 hour to obtain a crystallized precursor;

[0079] (6) The crystallization precursor was transferred into a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 210°C for 32 hours. The mixture was then filtered, washed, and dried at 110°C for 12 hours to obtain K,Na-V-ETS-10 molecular sieve (i.e., modified ETS-10 molecular sieve).

[0080] The synthesized K,Na-V-ETS-10 molecular sieve had a SiO2 content of 76.8%, a TiO2 content of 14.5%, a Na2O content of 4.1%, a K2O content of 1.7%, and a V2O5 content of 2.9% (determined by XRF method). The specific surface area of ​​the K,Na-V-ETS-10 molecular sieve was measured using a physical adsorption analyzer and calculated using the BET method, yielding a specific surface area of ​​317.2 m². 2 ·g -1 The specific surface area of ​​the micropores is 301.7 m². 2 ·g -1 .

[0081] 2. Loading of active components

[0082] Take 3g of the dried K,Na-V-ETS-10 molecular sieve and place it in a crucible. According to the principle that Cr2O3 accounts for 2.5% of the total mass of the catalyst, weigh out the corresponding mass of chromium nitrate and dissolve it in water to obtain an impregnation solution. Then, drop the impregnation solution into the molecular sieve powder and impregnate it with equal volume. The catalyst precursor obtained by impregnation is dried at 110℃ for 8h and then calcined at 500℃ for 4h to obtain a catalyst for the oxidation of methyl-substituted aromatic hydrocarbons to prepare aromatic aldehydes.

[0083] Reaction performance evaluation:

[0084] The catalyst dosage was 0.3 g. 10 mL of toluene was mixed with 75 mL of acetonitrile solvent, with a H₂O₂:R ratio (R being toluene) of 2:1 (volume ratio). The reaction pressure was 0.9 MPa, the reaction temperature was 110 °C, and the reaction time was 6 h. The toluene conversion rate was determined to be 25.5%, and the benzaldehyde yield was 16.7%. The catalyst can be directly recovered after filtration.

[0085] Example 2

[0086] Catalyst preparation:

[0087] 1. Carrier preparation

[0088] The support (K,Na-V-ETS-10 molecular sieve) prepared in Example 1 was used.

[0089] 2. Loading of active components

[0090] Take 3g of the dried K,Na-V-ETS-10 molecular sieve and place it in a crucible. According to the principle that Pd accounts for 0.6% of the total mass of the catalyst, weigh the corresponding mass of Pd(NH3)2Cl2 and dissolve it in water to obtain an impregnation solution. Then, drop the impregnation solution into the molecular sieve powder and impregnate it with equal volume. The catalyst precursor obtained by impregnation is dried at 110℃ for 8h and then calcined at 500℃ for 4h to obtain a catalyst for the oxidation of methyl-substituted aromatic hydrocarbons to prepare aromatic aldehydes.

[0091] Reaction performance evaluation:

[0092] The catalyst dosage was 0.3 g. 10 mL of toluene was mixed with 75 mL of acetonitrile solvent, with a H₂O₂:R ratio (R being toluene) of 2:1 (volume ratio). The reaction temperature was 110 °C, the reaction pressure was 1.2 MPa, and the reaction time was 6 h. The toluene conversion rate was determined to be 30.5%, and the benzaldehyde yield was 21.1%. The catalyst can be directly recovered after filtration.

[0093] Example 3

[0094] Catalyst preparation:

[0095] 1. Carrier preparation

[0096] The support (K,Na-V-ETS-10 molecular sieve) prepared in Example 1 was used.

[0097] 2. Loading of active components

[0098] Take 3g of the dried K,Na-V-ETS-10 molecular sieve and place it in a crucible. According to the ratio of Pd to 0.6% of the total catalyst mass and Cr2O3 to 2.5% of the total catalyst mass, weigh out the corresponding mass of Pd(NH3)2Cl2 and chromium nitrate and dissolve them in water to obtain an impregnation solution. Then, drop the impregnation solution into the molecular sieve powder and impregnate it with equal volume. The catalyst precursor obtained by impregnation is dried at 110℃ for 8h and then calcined at 500℃ for 4h to obtain a catalyst for the oxidation of methyl-substituted aromatic hydrocarbons to prepare aromatic aldehydes.

[0099] Reaction performance evaluation:

[0100] The catalyst dosage was 0.3 g. 10 mL of toluene was mixed with 75 mL of acetonitrile solvent, with a H₂O₂:R ratio (R being toluene) of 2:1 (volume ratio). The reaction temperature was 110 °C, the reaction pressure was 1.0 MPa, and the reaction time was 6 h. The toluene conversion rate was determined to be 35.6%, and the benzaldehyde yield was 26.4%. The catalyst can be directly recovered after filtration.

[0101] Example 4

[0102] Catalyst preparation:

[0103] 1. Carrier preparation

[0104] (1) The feed ratio is SiO2:TiO2:V2O5:Na2O:KF:H2O=6:1:0.4:4.2:1.6:250. The corresponding contents of water glass, vanadium oxysulfate, TiCl4, NaOH, and KF·2H2O are calculated according to this ratio as raw materials.

[0105] (2) Prepare gel in a 250mL beaker: Mix some water (the total amount of water used in steps (2) and (3) is the total amount of water required in step (1)), water glass and NaOH thoroughly under stirring to obtain a silicon source solution;

[0106] (3) Disperse and dissolve vanadium sulfate and TiCl4 together in water according to the total mass ratio of water to vanadium sulfate and TiCl4 of 10:1 to obtain vanadium-titanium source solution;

[0107] (4) The above vanadium-titanium source solution and the above silicon source solution are mixed and stirred to form a semi-transparent gel (i.e., sol precursor);

[0108] (5) Add the amount of KF·2H2O calculated in step (1) to the sol precursor as a mineralizing agent, stir and age for 1 hour to obtain a crystallized precursor;

[0109] (6) The crystallization precursor was transferred into a hydrothermal reactor with a polytetrafluoroethylene liner, crystallized at 220°C for 32 hours, filtered, washed, and dried at 90°C for 36 hours to obtain K,Na-V-ETS-10 molecular sieve (i.e. modified ETS-10 molecular sieve).

[0110] The synthesized K,Na-V-ETS-10 molecular sieve had a SiO2 content of 77.0%, a TiO2 content of 13.4%, a Na2O content of 3.6%, a K2O content of 1.5%, and a V2O5 content of 4.5% (determined by XRF method). The specific surface area of ​​the K,Na-V-ETS-10 molecular sieve was measured using a physical adsorption analyzer and calculated using the BET method, yielding a specific surface area of ​​299.7 m². 2 ·g -1 The specific surface area of ​​the micropores is 273.5 m². 2 ·g -1 .

[0111] 2. Loading of active components

[0112] Take 3g of the dried K,Na-V-ETS-10 molecular sieve and place it in a crucible. According to the ratio of Pd to 0.6% of the total catalyst mass and MnO2 to 3% of the total catalyst mass, weigh out the corresponding mass of Pd(NH3)2Cl2 and manganese nitrate and dissolve them in water to obtain an impregnation solution. Then, drop the impregnation solution into the molecular sieve powder and impregnate it with equal volume. The catalyst precursor obtained by impregnation is dried at 100℃ for 6h and then calcined at 480℃ for 4h to obtain a catalyst for the oxidation of methyl-substituted aromatic hydrocarbons to prepare aromatic aldehydes.

[0113] Reaction performance evaluation:

[0114] The catalyst dosage was 0.3 g. 10 mL of o-xylene was mixed with 75 mL of acetonitrile solvent, with a H₂O₂:R ratio (R being o-xylene) of 2:1 (volume ratio). The reaction temperature was 120 °C, the reaction pressure was 0.6 MPa, and the reaction time was 6 h. The o-xylene conversion rate was determined to be 22.4%, and the o-phthalaldehyde yield was 17.1%. The catalyst can be directly recovered after filtration.

[0115] Example 5

[0116] Catalyst preparation:

[0117] 1. Carrier preparation

[0118] (1) The feed ratio is SiO2:TiO2:V2O5:Na2O:KF:H2O=6:1:0.3:4.2:1.6:250. The corresponding contents of water glass, vanadium oxysulfate, TiCl4, NaOH, and KF·2H2O are calculated according to this ratio as raw materials.

[0119] (2) Prepare gel in a 250mL beaker: Mix some water (the total amount of water used in steps (2) and (3) is the total amount of water required in step (1)), water glass and NaOH thoroughly under stirring to obtain a silicon source solution;

[0120] (3) Disperse and dissolve vanadium sulfate and TiCl4 together in water according to the total mass ratio of water to vanadium sulfate and TiCl4 of 10:1 to obtain vanadium-titanium source solution;

[0121] (4) The above vanadium-titanium source solution and the above silicon source solution are mixed and stirred to form a semi-transparent gel (i.e., sol precursor);

[0122] (5) Add the amount of KF·2H2O calculated in step (1) to the sol precursor as a mineralizing agent, stir and age for 1 hour to obtain a crystallized precursor;

[0123] (6) The crystallization precursor was transferred into a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 220°C for 28 hours. The mixture was then filtered, washed, and dried at 135°C for 10 hours to obtain K,Na-V-ETS-10 molecular sieve (i.e. modified ETS-10 molecular sieve).

[0124] The synthesized K,Na-V-ETS-10 molecular sieve had a SiO2 content of 73.7%, a TiO2 content of 16.8%, a Na2O content of 3.7%, a K2O content of 1.6%, and a V2O5 content of 4.2% (determined by XRF method). The specific surface area of ​​the K,Na-V-ETS-10 molecular sieve was measured using a physical adsorption analyzer and calculated using the BET method, yielding a specific surface area of ​​309.3 m². 2 ·g -1 The microporous specific surface area is 292.4 m². 2 ·g -1 .

[0125] 2. Loading of active components

[0126] Take 3g of the dried K,Na-V-ETS-10 molecular sieve and place it in a crucible. According to the principle that Pd accounts for 0.6% of the total mass of the catalyst, weigh out the corresponding mass of Pd(NH3)2Cl2 and dissolve it in water to obtain an impregnation solution. Then, drop the impregnation solution into the molecular sieve powder and impregnate it with equal volume. The catalyst precursor obtained by impregnation is dried at 100℃ for 6h and then calcined at 480℃ for 4h to obtain a catalyst for the oxidation of methyl-substituted aromatic hydrocarbons to prepare aromatic aldehydes.

[0127] Reaction performance evaluation:

[0128] The catalyst dosage was 0.3 g. 10 mL of p-chlorotoluene was mixed with 75 mL of acetonitrile solvent, with a H₂O₂:R ratio (R being p-chlorotoluene) of 2:1 (volume ratio). The reaction temperature was 120 °C, the reaction pressure was 1.1 MPa, and the reaction time was 6 h. The conversion rate of p-chlorotoluene was determined to be 25.8%, and the yield of p-chlorobenzaldehyde was 17.3%. The catalyst can be directly recovered after filtration.

[0129] Example 6

[0130] Catalyst preparation:

[0131] 1. Carrier preparation

[0132] The support (K,Na-V-ETS-10 molecular sieve) prepared in Example 5 was used.

[0133] 2. Loading of active components

[0134] Take 3g of the dried K,Na-V-ETS-10 molecular sieve and place it in a crucible. According to the ratio of Pd to 0.6% of the total catalyst mass and Cr2O3 to 3% of the total catalyst mass, weigh Pd(NH3)2Cl2 and chromium nitrate and dissolve them in water to obtain an impregnation solution. Then, drop the impregnation solution into the molecular sieve powder and impregnate it with equal volume. The catalyst precursor obtained by impregnation is dried at 100℃ for 6h and then calcined at 480℃ for 4h to obtain a catalyst for the oxidation of methyl-substituted aromatic hydrocarbons to prepare aromatic aldehydes.

[0135] Reaction performance evaluation:

[0136] The catalyst dosage was 0.3 g. 10 mL of p-tert-butyltoluene was mixed with 75 mL of acetonitrile solvent at a H₂O₂:R (R being p-tert-butyltoluene) ratio of 2:1 (volume ratio). The reaction temperature was 120 °C, the reaction pressure was 1.2 MPa, and the reaction time was 6 h. The conversion rate of p-tert-butyltoluene was determined to be 26.4%, and the yield of p-tert-butylbenzaldehyde was 17.7%. The catalyst can be directly recovered after filtration.

[0137] Example 7

[0138] Catalyst preparation:

[0139] 1. Carrier preparation

[0140] (1) The feed ratio is SiO2:TiO2:V2O5:Na2O:KF:H2O=7:1:0.5:4.5:1.8:300. The corresponding contents of water glass, vanadium oxysulfate, TiCl4, NaOH, and KF·2H2O are calculated according to this ratio as raw materials.

[0141] (2) Prepare gel in a 250mL beaker: Mix some water (and the total amount of water used in steps (2) and (3) is the total amount of water required in step (1)), water glass and NaOH thoroughly under stirring to obtain a silicon source solution;

[0142] (3) Disperse and dissolve vanadium sulfate and TiCl4 together in water according to the total mass ratio of water to vanadium sulfate and TiCl4 of 10:1 to obtain vanadium-titanium source solution;

[0143] (4) The above vanadium-titanium source solution and the above silicon source solution are mixed and stirred to form a semi-transparent gel (i.e., sol precursor);

[0144] (5) Add the amount of KF·2H2O calculated in step (1) to the sol precursor as a mineralizing agent, stir and age for 18 hours to obtain a crystallized precursor;

[0145] (6) The crystallization precursor was transferred into a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 220°C for 28 hours. The mixture was then filtered, washed, and dried at 100°C for 10 hours to obtain K,Na-V-ETS-10 molecular sieve (i.e., modified ETS-10 molecular sieve).

[0146] The synthesized K,Na-V-ETS-10 molecular sieve had a SiO2 content of 73.6%, a TiO2 content of 17.3%, a Na2O content of 5.0%, a K2O content of 2.2%, and a V2O5 content of 1.9% (determined by XRF method). The specific surface area of ​​the K,Na-V-ETS-10 molecular sieve was measured using a physical adsorption analyzer and calculated using the BET method, yielding a specific surface area of ​​296.7 m². 2 ·g -1 The microporous specific surface area is 268.9 m². 2 ·g -1 .

[0147] 2. Loading of active components

[0148] Take 3g of the dried K,Na-V-ETS-10 molecular sieve and place it in a crucible. According to the principle that Pd accounts for 0.6% of the total mass of the catalyst, weigh out the corresponding mass of Pd(NH3)2Cl2 and dissolve it in water to obtain an impregnation solution. Then, drop the impregnation solution into the molecular sieve powder and impregnate it with equal volume. The catalyst precursor obtained by impregnation is dried at 100℃ for 6h and then calcined at 480℃ for 4h to obtain a catalyst for the oxidation of methyl-substituted aromatic hydrocarbons to prepare aromatic aldehydes.

[0149] Reaction performance evaluation:

[0150] The catalyst dosage was 0.3 g. 10 mL of toluene was mixed with 75 mL of acetonitrile solvent, with a H₂O₂:R ratio (R being toluene) of 2:1 (volume ratio). The reaction pressure was 0.9 MPa, the reaction temperature was 110 °C, and the reaction time was 6 h. The toluene conversion rate was determined to be 24.0%, and the benzaldehyde yield was 15.2%. The catalyst can be directly recovered after filtration.

[0151] Comparative Example 1

[0152] Catalyst preparation:

[0153] 1. Carrier preparation

[0154] Anatase TiO2 was used as the support.

[0155] 2. Loading of active components

[0156] Take 3g of dried anatase TiO2 powder and place it in a crucible. According to the ratio of Pd to 0.6% of the total catalyst mass and Cr2O3 to 3% of the total catalyst mass, weigh Pd(NH3)2Cl2 and chromium nitrate and dissolve them in water to obtain an impregnation solution. Then, drop the impregnation solution into the molecular sieve powder and impregnate it with equal volume. The catalyst precursor obtained by impregnation is dried at 100℃ for 6h and then calcined at 480℃ for 4h to obtain the catalyst.

[0157] Reaction performance evaluation:

[0158] The catalyst dosage was 0.3 g. 10 mL of p-tert-butyltoluene was mixed with 75 mL of acetonitrile solvent, with a H2O2:R ratio (R being p-tert-butyltoluene) of 2:1 (volume ratio). The reaction temperature was 120 °C, the reaction pressure was 1.2 MPa, and the reaction time was 6 h. The conversion rate of p-tert-butyltoluene was determined to be 9.5%, and the yield of p-tert-butylbenzaldehyde was 6.1%.

[0159] Comparative Example 2

[0160] Catalyst preparation:

[0161] 1. Carrier preparation

[0162] The carrier prepared in Example 5 was used.

[0163] 2. Loading of active components

[0164] 3g of dried K,Na-V-ETS-10 molecular sieve was placed in a crucible. Pd (NH3)2Cl2 and ferric nitrate were dissolved in water to obtain an impregnation solution, with Pd accounting for 0.6% of the total catalyst mass and Fe2O3 accounting for 3%. This impregnation solution was then dripped into the molecular sieve powder for equal-volume impregnation. The resulting catalyst precursor was dried at 100℃ for 6 hours, followed by calcination at 480℃ for 4 hours to obtain the catalyst.

[0165] Reaction performance evaluation:

[0166] The catalyst dosage was 0.3 g. 10 mL of p-tert-butyltoluene was mixed with 75 mL of acetonitrile solvent, with a H2O2:R ratio (R being p-tert-butyltoluene) of 2:1 (volume ratio). The reaction temperature was 120 °C, the reaction pressure was 1.2 MPa, and the reaction time was 6 h. The conversion rate of p-tert-butyltoluene was determined to be 20.8%, the yield of p-tert-butylbenzaldehyde was 5.9%, and the p-cresol product was found to be relatively obvious, with a yield of 3.7%.

[0167] Comparative Example 3

[0168] Catalyst preparation:

[0169] 1. Carrier preparation

[0170] (1) The feeding ratio is SiO2:TiO2:Na2O:KF:H2O=6:1:4.2:1.6:250. The corresponding contents of water glass, TiCl4, NaOH, and KF·2H2O are calculated according to this ratio as raw materials.

[0171] (2) Gel preparation in a beaker: Mix a portion of water (the total amount of water used in steps (2) and (3) is the total amount of water required in step (1), water glass and NaOH thoroughly under stirring to obtain a silicon source solution;

[0172] (3) Dissolve TiCl4 in water at a total mass ratio of 10:1 to obtain a titanium source solution;

[0173] (4) Mix the above titanium source solution with the above silicon source solution and stir to form a semi-transparent gel (i.e., sol precursor);

[0174] (5) Add the amount of KF·2H2O calculated in step (1) to the sol precursor as a mineralizing agent, stir and age for 1 hour to obtain a crystallized precursor;

[0175] (6) The crystallization precursor was transferred into a hydrothermal reactor with a polytetrafluoroethylene liner, crystallized at 210°C for 32 hours, filtered, washed, and dried at 110°C for 12 hours to obtain K,Na-ETS-10 molecular sieve.

[0176] The synthesized K,Na-ETS-10 molecular sieve has a SiO2 content of 77.9%, a TiO2 content of 15.8%, a Na2O content of 4.4%, and a K2O content of 1.9%. The specific surface area of ​​the K,Na-ETS-10 molecular sieve, measured by a physical adsorption analyzer and calculated using the BET method, is 313.5 m². 2 ·g -， The specific surface area of ​​the micropores is 296.7 m². 2 ·g -1 .

[0177] 2. Loading of active components

[0178] Take 3g of the dried K,Na-ETS-10 molecular sieve and place it in a crucible. Weigh out the corresponding mass of chromium nitrate and V2O5 + oxalic acid particles (molar ratio 1:2) according to the total mass of Cr2O3 and V2O5. Dissolve them in water to obtain an impregnation solution. Then, drop the impregnation solution into the molecular sieve powder and impregnate it with equal volume. The catalyst precursor obtained by impregnation is dried at 110℃ for 8h and then calcined at 500℃ for 4h to obtain a catalyst for the oxidation of methyl-substituted aromatic hydrocarbons to prepare aromatic aldehydes.

[0179] Reaction performance evaluation:

[0180] The catalyst dosage was 0.3 g. 10 mL of toluene was mixed with 75 mL of acetonitrile solvent, with a H₂O₂:R ratio (R being toluene) of 2:1 (volume ratio). The reaction pressure was 0.9 MPa, the reaction temperature was 110 °C, and the reaction time was 6 h. The toluene conversion rate was determined to be 18.2%, and the benzaldehyde yield was 12.5%. The catalyst can be directly recovered after filtration.

[0181] Comparative Example 4

[0182] Using cobalt acetate catalyst, 40 mL of p-tert-butyltoluene was mixed with 280 mL of acetonitrile solvent and added to the reactor at a catalyst-to-liquid mass ratio of 1:500. The volume ratio of H2O2:R (where R is p-tert-butyltoluene) was 2:1. The reaction system was heated to 120 °C, the reaction pressure was 1.2 MPa, and the reaction time was 6 h. The conversion rate of p-tert-butyltoluene was determined to be 28.7%, and the yield of p-tert-butylbenzaldehyde was 17.6%. The catalyst needs to be obtained after removing the solvent and product by distillation or other methods.

[0183] As can be seen from Example 6 and Comparative Example 1, the catalysts obtained by using existing supports to load the transition metal active components of the present invention exhibit significantly lower conversion rates for methyl-substituted aromatics and lower selectivity for aromatic aldehydes compared to the present invention. As can be seen from Example 6 and Comparative Example 2, the catalysts obtained by using other metal active components or a composite loading of other metal active components with the transition metal active components of the present invention also exhibit significantly lower selectivity for aromatic aldehydes compared to the present invention, and tend to yield p-cresol products. As can be seen from Example 1 and Comparative Example 3, compared to loading V onto K,Na-ETS-10 molecular sieves, the present invention, using a V-framework-doped K,Na-V-ETS-10 molecular sieve, significantly improves both the conversion rate for methyl-substituted aromatics and the selectivity for aromatic aldehydes, thus better enhancing the reaction performance for the oxidation of methyl-substituted aromatics to aromatic aldehydes. As can be seen from Example 6 and Comparative Example 4, compared to commonly used complexed Co organometallic catalysts in the prior art, the catalyst of the present invention also exhibits higher conversion rates for methyl-substituted aromatics and higher selectivity for aromatic aldehydes, and is easier to separate and recover.

[0184] As can be seen from Examples 1-7, the catalyst prepared by the present invention using modified ETS-10 molecular sieve obtained by hydrothermal synthesis as a support and loading active components Ni / Pd / Pt / Mo / Mn / Cr has a high conversion rate for methyl-substituted aromatic hydrocarbons and selectivity for aromatic aldehydes, and is easier to separate and recycle.

Claims

1. A catalyst for the oxidation of methyl-substituted aromatic hydrocarbons to prepare aromatic aldehydes, comprising a support and an active component, wherein the support is a modified ETS-10 molecular sieve; the modified ETS-10 molecular sieve contains silica and a metal oxide; the metal includes titanium, vanadium, and alkali metals; the active component is a transition metal or its oxide; the transition metal is selected from at least one of Mo, Mn, Cr, Ni, Pd, and Pt; the method for preparing the modified ETS-10 molecular sieve includes a step of hydrothermal synthesis of components including a titanium source, a vanadium source, a silicon source, sodium hydroxide, and KF·2H2O to obtain the modified ETS-10 molecular sieve.

2. The catalyst according to claim 1, characterized in that: The metal oxides include titanium dioxide, vanadium pentoxide, sodium oxide, and potassium oxide.

3. The catalyst according to claim 2, characterized in that: Based on the weight of the modified ETS-10 molecular sieve as 100wt%, the content of silicon dioxide is 60-80wt%; and / or the content of titanium dioxide is 10-30wt%; and / or the content of vanadium pentoxide is 0.1-10wt%; and / or the total content of sodium oxide and potassium oxide is 2-20wt%.

4. The catalyst according to claim 3, characterized in that: Based on the weight of the modified ETS-10 molecular sieve as 100wt%, the content of silicon dioxide is 65-75wt%; and / or, the content of titanium dioxide is 10-20wt%; and / or, the content of vanadium pentoxide is 0.5-5wt%; and / or, the total content of sodium oxide and potassium oxide is 2-10wt%.

5. The catalyst according to claim 1, characterized in that: The modified ETS-10 molecular sieve has a specific surface area of ​​200~350 m². 2 ·g -1 Among them, the specific surface area of ​​micropores is 180~310m². 2 ·g -1 .

6. The catalyst according to claim 5, characterized in that: The modified ETS-10 molecular sieve has a specific surface area of ​​280~320 m². 2 ·g -1 Among them, the specific surface area of ​​micropores is 200~310m². 2 ·g -1 .

7. The catalyst according to claim 1, characterized in that: The preparation method includes: 1) Mix the silicon source with sodium hydroxide and water until homogeneous to obtain a silicon source solution; 2) Disperse and dissolve the titanium source and vanadium source together in water to obtain a vanadium-titanium source solution; 3) Mix the vanadium-titanium source solution from step 2) with the silicon source solution from step 1) to obtain the sol precursor; 4) Add KF·2H2O to the sol precursor and age it to obtain a crystallized precursor; 5) The modified ETS-10 molecular sieve is obtained by crystallizing the crystallization precursor.

8. The catalyst according to claim 7, characterized in that: In step 1), The silicon source is selected from at least one of tetraethyl orthosilicate, silica sol, water glass, and sodium silicate.

9. The catalyst according to claim 7, characterized in that: In step 2), The titanium source is selected from at least one of titanium sulfate, titanium oxysulfate, titanium tetrachloride, titanium trichloride, and tetrabutyl titanate; and / or, The vanadium source is selected from at least one of ammonium metavanadate, alum sulfate, vanadium oxysulfate, and vanadium oxyoxalate.

10. The catalyst according to claim 7, characterized in that: In step 4), The aging time is 1 to 24 hours.

11. The catalyst according to claim 7, characterized in that: In step 5), The crystallization temperature is 150~230℃, and the crystallization time is 8~36 h; and / or, The crystallization process also includes washing and drying steps.

12. The catalyst according to claim 11, characterized in that: The drying temperature is 80~150℃, and / or the drying time is 4~48 h.

13. The catalyst according to claim 7, characterized in that: The amounts of silicon source, vanadium source, titanium source, sodium hydroxide, and KF·2H2O added are calculated according to the ratio of silicon dioxide: titanium dioxide: vanadium pentoxide: sodium oxide: potassium fluoride: water = (2~8):1:(0.05~1):(3~9):(0.8~3):(100~500) in the crystallization precursor.

14. The catalyst according to claim 13, characterized in that: The amounts of silicon source, vanadium source, titanium source, sodium hydroxide, and KF·2H2O added are calculated according to the ratio of silicon dioxide: titanium dioxide: vanadium pentoxide: sodium oxide: potassium fluoride: water = (3~6):1:(0.05~0.5):(4~8):(0.8~2):(150~300) in the crystallization precursor.

15. The catalyst according to claim 14, characterized in that: In step 2), the ratio of water to the total mass of vanadium and titanium sources is 5 to 15:1, and the total amount of water used in steps 1) and 2) is the total amount of water required for the calculation.

16. The catalyst according to claim 1, characterized in that: The loading of the active component is 0.3 to 8% of the total mass of the catalyst.

17. The catalyst according to claim 16, characterized in that: The loading of the active component is 0.4 to 5% of the total mass of the catalyst.

18. The catalyst according to claim 17, characterized in that: The loading of the active component is 0.8 to 4% of the total mass of the catalyst.

19. A method for preparing a catalyst according to any one of claims 1-18, comprising the steps of loading a soluble salt corresponding to the active component onto the modified ETS-10 molecular sieve by impregnation, followed by drying and calcination to obtain the catalyst.

20. The preparation method according to claim 19, characterized in that: The drying temperature is 80~150℃ and the drying time is 4~48 h; and / or the calcination temperature is 450~650℃ and the calcination time is 1~8 h.

21. A method for preparing aromatic aldehydes by oxidation of methyl-substituted aromatic hydrocarbons, using the catalyst described in any one of claims 1-18 or the catalyst obtained by the preparation method described in any one of claims 19-20.

22. The method as described in claim 21, characterized in that The method includes: The step of reacting methyl-substituted aromatic hydrocarbons with hydrogen peroxide in the presence of a solvent and the catalyst, using hydrogen peroxide as an oxygen source.

23. The method as described in claim 22, characterized in that: The solvent is at least one selected from water, acetonitrile, acetone, N-methylpyrrolidone, and N,N-dimethylformamide; and / or, The methyl-substituted aromatic hydrocarbon is at least one selected from toluene, o-xylene, p-xylene, m-xylene, p-tert-butyltoluene, o-chlorotoluene, and p-chlorotoluene; and / or The reaction temperature is 80~120℃, the reaction time is 4~24 h, and the reaction pressure is 0.1~2 MPa.

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