Titanium silicalite molecular sieve as well as preparation method and application thereof

Abstract

The invention provides a titanium silicalite molecular sieve as well as a preparation method and application thereof. The framework of the titanium silicalite molecular sieve comprises a Ti-O-Si framework and a Ti-O-W framework. By introducing W, the activation efficiency of an acid center on an inert C-H bond in cycloalkane is expected to be enhanced, invalid consumption of H2O2 in the reaction process in the catalytic oxidation process of cycloalkane is reduced, and the yield of a target product is increased. Compared with the prior art, the titanium silicalite molecular sieve doped with tungsten atoms is adopted to catalyze cycloalkane, so that the activity of the catalyst and the effective utilization rate of hydrogen peroxide can be improved, the generation of byproducts can be reduced, the stability of the catalyst can be improved, the service life of the catalyst can be prolonged, and the production cost and environmental pollution can be reduced. By means of the improvement, the process is more suitable for industrial application and has high economic benefits and environmental protection value.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and in particular relates to a titanium silicon molecular sieve and a preparation method and application thereof. Background Art

[0002] TS-1 titanium silicalite exhibits excellent catalytic oxidation performance under mild conditions, particularly high selectivity in oxidation reactions involving H2O2. Its highly dispersed titanium active centers enable it to catalyze oxidation reactions at lower temperatures, thereby reducing the occurrence of side reactions. Compared to traditional catalysts, TS-1 titanium silicalite can effectively reduce energy consumption, exhibits strong resistance to deactivation, and can be reused through simple regeneration after the reaction.

[0003] However, the practical application of titanium silicalite in the oxidation of cycloalkanes to prepare corresponding alcohols and ketones still faces some key challenges. First, cycloalkanes are highly stable alkane molecules with high C-H bond energies, so the requirements for active centers in catalytic reactions are high. Although TS-1 titanium silicalite has excellent catalytic performance, its efficiency in catalyzing cycloalkane oxidation reactions is still constrained by its low reaction rate and selectivity. Secondly, TS-1 titanium silicalite may experience problems such as reduced activity or pore blockage during long-term reactions, affecting the service life and stability of the catalyst. Summary of the Invention

[0004] In view of this, the present invention aims to provide a titanium silicate molecular sieve and its preparation method and application. The titanium silicate molecular sieve has excellent ability to catalyze the oxidation of cycloalkanes to produce cyclic alcohols and cyclic ketones, and has high stability and long life.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a titanium silicon molecular sieve, the framework of which includes a Ti-O-Si framework and a Ti-OW framework.

[0007] Preferably, the molar ratio of Si atoms to tungsten atoms in the titanium silicon molecular sieve body is (25-35):1.

[0008] In a second aspect, the present invention provides a method for preparing titanium silicate molecular sieve, comprising the following steps:

[0009] S1: mixing a silicon source, a titanium source, a tungsten source and a crystallization regulator to obtain a precursor solution;

[0010] S2: crystallizing the precursor solution, separating and obtaining a solid product after the crystallization is completed, and calcining the solid product to obtain a titanium silicon molecular sieve.

[0011] Preferably, the tungsten source is selected from any one or more of ammonium metatungstate, ammonium tungstate or tungstic acid.

[0012] Preferably, the silicon source is selected from tetraethyl orthosilicate.

[0013] Preferably, the titanium source is selected from tetrabutyl titanate.

[0014] Preferably, the crystallization regulator is selected from any one or more of ammonium carbonate, ammonium bicarbonate or carbonamide.

[0015] Preferably, the molar ratio of the silicon source to the tungsten source and the crystallization regulator is 1:(0.02-0.06):(0.04-0.2).

[0016] Preferably, the molar ratio of the silicon source to the titanium source is (20-40):1.

[0017] Preferably, the crystallization temperature is 160-180° C., and the crystallization time is 48-96 hours.

[0018] Preferably, the calcination atmosphere includes air, the calcination temperature is 500-600° C., the heating rate is 2-3° C. / min, and the calcination time is 2-10 h.

[0019] In a third aspect, the present invention provides a catalyst for cycloalkane oxidation reaction, which includes the titanium silicalite prepared according to the above technical solution.

[0020] In a fourth aspect, the present invention provides a method for catalytic oxidation of cycloalkanes, comprising the following steps:

[0021] Cycloalkane is used as a reactant and reacts in the presence of an oxidant and the above-mentioned catalyst to obtain cyclic alcohol and cyclic ketone.

[0022] Preferably, the oxidizing agent is hydrogen peroxide.

[0023] Preferably, the molar ratio of the oxidant to the cycloalkane is 1:(1-3).

[0024] Preferably, the added amount of the catalyst is 3 to 9 wt% of the mass of the cycloalkane.

[0025] Preferably, the reaction temperature is 50-70° C., and the reaction time is 0.5-6 h.

[0026] Preferably, the total selectivity of the cyclic alcohol and cyclic ketone is above 90%.

[0027] Preferably, the conversion rate of the cycloalkanes is above 30%.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention provides a titanium silicon molecular sieve doped with tungsten (W) atoms, wherein the doped tungsten atoms have variable valence states and strong redox properties, and the acidity of the titanium silicon molecular sieve skeleton or surface can be appropriately regulated to increase the adsorption and activation capabilities of substrate molecules. The present invention can replace part of the Si atoms by introducing W, which is expected to enhance the activation efficiency of the acid center for the inert C-H bonds in cycloalkanes, and reduce the ineffective consumption of H2O2 in the reaction process during the catalytic oxidation of cycloalkanes, thereby improving the yield of the target product. In addition, in the process of W-doped modified titanium silicon molecular sieves, tungsten interacts with the Ti-O-Si structure on the skeleton or surface of the titanium silicon molecular sieve, which can not only change the electronic environment around the Ti species, making the Ti site easier to generate and stabilize active oxygen species (such as Ti-OOH, etc.), but also provide electron transfer or synergistic catalytic support for the Ti site.

[0030] Compared to existing technologies, this invention utilizes a tungsten-doped titanium silicon molecular sieve to catalyze the reaction of cycloalkanes. This not only improves catalyst activity and the effective utilization of hydrogen peroxide, while reducing byproduct formation, but also enhances catalyst stability and lifespan, reducing production costs and environmental pollution. This improvement makes the process more suitable for industrial applications, offering both high economic benefits and environmental value.

[0031] According to tests, when cyclopentane or cyclohexane is catalyzed by the titanium silicon molecular sieve doped with tungsten atoms provided by the present invention, the total selectivity of cyclopentanol (hexanol) and cyclopentanone (hexanone) is above 90%, the conversion rate of cyclopentanone (hexane) is above 30%, and the effective utilization rate of hydrogen peroxide is above 70%. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] In view of the problems in the prior art that a single titanium silicate molecular sieve has a low effective reaction rate and low product selectivity in the catalytic oxidation reaction of cycloalkanes, the present invention provides a tungsten-doped titanium silicate molecular sieve, which includes a titanium silicate molecular sieve framework and tungsten atoms doped in the titanium silicate molecular sieve framework, that is, the framework of the titanium silicate molecular sieve includes a Ti-O-Si framework and a Ti-OW framework.

[0034] It should be noted that the doping of W into the framework of the titanium silicate molecular sieve in the present invention is not a conventional method, but is determined after screening and optimization. This is verified by comparing the following examples of the present invention with comparative examples 4 and 5.

[0035] In the present invention, the molar ratio of Si atoms to tungsten atoms in the titanium silicon molecular sieve is (25-35):1, such as 25:1, 26:1, 27:1, 28:1, 29:1, 30:1, 31:1, 32:1, 33:1, 34:1 or 35:1.

[0036] The present invention also provides a method for preparing the titanium silicate molecular sieve, comprising the following steps:

[0037] S1: mixing a silicon source, a titanium source, a tungsten source and a crystallization regulator to obtain a precursor solution;

[0038] S2: crystallizing the precursor solution, separating and obtaining a solid product after the crystallization is completed, and calcining the solid product to obtain a titanium silicon molecular sieve.

[0039] First, a silicon source, a titanium source, a tungsten source and a crystallization regulator are mixed to obtain a precursor solution.

[0040] In some embodiments of the present invention, it is preferred to prepare the silicon source solution, the titanium source solution, and the tungsten source solution before preparing the precursor solution.

[0041] In the present invention, the silicon source is selected from tetraethyl orthosilicate, and the silicon source solution is prepared according to the following method: tetrapropylammonium hydroxide is added to a round-bottom flask and magnetically stirred, and a certain amount of tetraethyl orthosilicate is added to the above solution with stirring, at a drop rate of 2 to 5 seconds per drop, preferably 3 seconds per drop, at room temperature at 300 to 800 rpm, preferably 500 rpm, for 20 to 80 minutes, preferably 30 minutes, until a clear solution is obtained to obtain a silicon source solution. The mass fraction of the tetrapropylammonium hydroxide solution is 20 to 25%, and the molar ratio of tetraethyl orthosilicate to tetrapropylammonium hydroxide is 1:(0.2 to 0.6), preferably 1:0.4.

[0042] In the present invention, the titanium source is selected from tetrabutyl titanate, and the titanium source solution is prepared according to the following method: take an alcohol reagent, such as n-propanol, isopropanol, n-butanol or tert-butanol, preferably isopropanol, into a beaker, weigh a certain amount of tetrabutyl titanate and slowly add it dropwise to the isopropanol at a dropping speed of 2 to 6 seconds per drop, preferably 4 seconds per drop. The mixed solution is placed in an ultrasonic instrument and ultrasonicated at room temperature for 20 to 80 minutes, preferably 30 minutes, until the solution is clarified to obtain a titanium source solution. Wherein, the molar ratio of the silicon source to the titanium source is (20 to 40):1, preferably 30:1, and the molar ratio of the titanium source to the alcohol reagent is 1:(40 to 60), preferably 1:50.

[0043] The room temperature mentioned above refers to a temperature of "10 to 30°C", preferably "15 to 25°C".

[0044] In the present invention, the tungsten source is selected from any one or more of ammonium metatungstate, ammonium tungstate, or tungstic acid; and the crystallization modifier is selected from any one or more of ammonium carbonate, ammonium bicarbonate, or carbonamide. The tungsten source solution is prepared as follows: desalted water is added to a beaker in an amount equal to the volume difference between the desalted water before and after the alcohol is removed, the crystallization modifier is dissolved in the desalted water, and the tungsten source is then added to the desalted water containing the crystallization modifier and dissolved under ultrasound to obtain a tungsten source solution. The molar ratio of the silicon source to the tungsten source and the crystallization modifier is 1:(0.02-0.06):(0.04-0.2), preferably 1:(0.03-0.04):(0.09-0.14), and more preferably 1:0.033:0.11.

[0045] The volume difference before and after the alcohol removal, that is, the volume of alcohol to be removed = the volume of the added alcohol reagent + the volume of the alcohol generated by hydrolysis of the silicon source + the volume of butanol generated by the titanium source.

[0046] In the present invention, it is preferred to add an alkaline crystallization regulator to the tungsten source solution, which can provide a uniform and stable alkaline aqueous phase, reduce the concentration of tungsten, and avoid precipitation caused by excessive local concentration. At the same time, the crystallization regulator can react with [WO4] through electrostatic hydrogen bonds. 2- 、Ti(OH)6 2- A weak coordination complex is formed, thereby anchoring Ti and W at adjacent sites during the nucleation process and increasing the content of Ti-OW framework fragments.

[0047] In some embodiments of the present invention, after obtaining the above-mentioned silicon source solution, titanium source solution, and tungsten source solution, the silicon source solution is preferably placed in an ice-water bath, and the titanium source solution is added dropwise to the silicon source using a constant pressure separatory funnel at a drop rate of 2 to 8 seconds per drop, preferably 4 to 5 seconds per drop, and the dropwise addition process is controlled to be carried out at 0°C. After the dropwise addition, stirring is performed for 20 to 80 minutes, preferably 30 minutes to form a clear mixed solution. Subsequently, the temperature is raised to 80 to 90°C to remove alcohol for 60 to 90 minutes, and the tungsten source solution containing a crystallization regulator is added to the mixed solution at a dropwise addition rate of 2 to 6 seconds per drop, preferably 3 seconds per drop. After the dropwise addition, stirring is performed for 20 to 80 minutes, preferably 30 minutes to form a clear mixed solution to obtain a precursor solution.

[0048] After obtaining the precursor solution, according to the present invention, the precursor solution is crystallized, and after the crystallization is completed, a solid product is separated and calcined to obtain the titanium silicon molecular sieve. Preferably, after the solid product is separated, the solid product is preferably washed and dried before calcining.

[0049] In some embodiments of the present invention, the precursor solution is placed in a polytetrafluoroethylene liner, sealed in a stainless steel hydrothermal crystallization kettle, and statically crystallized in an oven at a certain temperature. After the crystallization is completed, the catalyst powder is separated by high-speed centrifugation at 4000 rpm using a centrifuge, washed with desalted water 2 to 3 times, and placed in an oven to dry at 80 to 100 ° C for 12 to 20 hours. The dried raw powder is ground and placed in a muffle furnace and calcined under an air atmosphere to obtain titanium silicon molecular sieve. The crystallization temperature is 160 to 180 ° C, preferably 165 to 175 ° C; the crystallization time is 48 to 96 hours, preferably 60 to 72 hours; the calcination temperature is 500 to 600 ° C, preferably 520 to 550 ° C; the heating rate is 2 to 3 ° C / min, preferably 2.5 to 3 ° C / min; the calcination time is 2 to 10 hours, preferably 4 to 8 hours.

[0050] The preparation method provided by the present invention has simple steps, is easy to implement, and is conducive to large-scale production or industrial production.

[0051] The present invention also provides a catalyst for cycloalkane oxidation reaction, comprising the titanium silicon molecular sieve involved in the above technical solution.

[0052] The present invention also provides a method for catalytic oxidation of cycloalkanes, comprising the following steps:

[0053] Cycloalkane is used as a reactant and reacts in the presence of an oxidant and the above-mentioned catalyst to obtain a cyclic alcohol or a cyclic ketone.

[0054] In the present invention, the oxidant is hydrogen peroxide. Specifically, the oxidant is an aqueous hydrogen peroxide solution with a concentration of 20 to 50 wt%, preferably 20 to 30 wt%. The molar ratio of the oxidant to the cycloalkane is preferably 1:(1 to 3), more preferably 1:2. The amount of the catalyst added is 3 to 9% wt% of the mass of the cycloalkane, and can be 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt% or 9 wt%, preferably 7 wt%.

[0055] In the present invention, the reaction temperature is 50-70° C., preferably 55-60° C., and the reaction time is 0.5-6 h, preferably 4-6 h.

[0056] In experimental research, the present invention used titanium silicalite doped with tungsten atoms to catalyze the oxidation of cyclopentane or cyclohexane. The results showed that the total selectivity of cyclopentanol (hexanol) and cyclopentanone (hexanone) was above 90%, the conversion rate of cyclopentanone was above 30%, and the effective utilization rate of hydrogen peroxide was above 70%. In addition, compared with titanium silicalite doped with other metal atoms, the activity of tungsten-doped titanium silicalite in catalyzing the oxidation of cycloalkanes was significantly improved, and the utilization rate of hydrogen peroxide was also improved, indicating that the addition of tungsten can enhance the catalytic ability of titanium silicalite in catalyzing the reaction of cycloalkanes to the corresponding alcohols and ketones.

[0057] In summary, the present invention provides a tungsten-doped titanium silicon molecular sieve to improve its catalytic oxidation ability in a hydrogen peroxide system. In the present invention, the tungsten-doped titanium silicon molecular sieve can significantly improve its Lewis acidity while maintaining good stability and catalytic efficiency. In this system, tungsten doping can produce a synergistic effect with the Ti-O-Si skeleton, enhance the generation efficiency of active oxygen species, and effectively inhibit the non-productive decomposition of hydrogen peroxide, thereby improving the utilization rate of H2O2. In addition, the stability of the molecular sieve in the catalytic reaction is significantly enhanced, and it can still maintain high catalytic activity after multiple cycles of use, further improving the reaction rate and selectivity of the hydrogen peroxide oxidation system.

[0058] In order to further illustrate the present invention, the following examples are provided for detailed description. The experimental raw materials used in the following examples of the present invention are all commonly available commercial products.

[0059] Example 1

[0060] (1) 25 wt% of tetrapropylammonium hydroxide was added to a round-bottom flask and stirred magnetically. 6 g of tetraethyl orthosilicate was added to the above solution and stirred. The molar ratio of tetrapropylammonium hydroxide to tetraethyl orthosilicate was 0.2:1. The drop rate was 3 s / drop. The solution was stirred at 500 rpm for 30 min at room temperature until the solution became clear, thereby obtaining a silicon source solution.

[0061] (2) Isopropyl alcohol was placed in a beaker, and tetrabutyl titanate was slowly added dropwise to the isopropyl alcohol. The molar ratio of isopropyl alcohol to tetrabutyl titanate was 40:1, and the molar ratio of tetrabutyl titanate to ethyl orthosilicate was 1:30. The addition rate was 4 s / drop. The mixed solution was sonicated in an ultrasonicator at room temperature for 30 min until the solution became clear, thereby obtaining a titanium source solution.

[0062] (3) Desalted water is added to a beaker. The amount of desalted water added is the volume difference before and after alcohol removal. Ammonium carbonate is dissolved in the desalted water. Then, ammonium tungstate is added to the ammonium carbonate aqueous solution and dissolved under ultrasound to obtain a tungsten source solution.

[0063] (4) The silicon source solution was placed in an ice-water bath, and the titanium source solution was added dropwise to the silicon source using a constant pressure separatory funnel at a rate of 5 s / drop. The addition process was controlled at 0°C, and the mixture was stirred for 30 minutes to form a clear solution. The temperature was then raised to 90°C to remove the alcohol for 60 minutes, and the tungsten source solution was added to the mixed solution at a rate of 3 s / drop. The mixture was stirred for 30 minutes to form a clear mixed solution to obtain a precursor solution.

[0064] (5) The precursor solution was placed in a polytetrafluoroethylene liner, sealed in a stainless steel hydrothermal crystallization kettle, and statically crystallized in an oven at 170°C for 48 hours. After the crystallization, the catalyst powder was separated by high-speed centrifugation at 4000 rpm using a centrifuge, washed three times with desalted water, and dried in an oven at 100°C for 12 hours. The dried powder was ground and calcined in a muffle furnace at 550°C for 8 hours in an air atmosphere at a heating rate of 3°C / min to obtain WTS-1 molecular sieve 1.

[0065] Example 2

[0066] (1) 22.5 wt% of tetrapropylammonium hydroxide was added to a round-bottom flask and stirred with magnetic stirring. 6 g of tetraethyl orthosilicate was added to the above solution and stirred. The molar ratio of tetrapropylammonium hydroxide to tetraethyl orthosilicate was 0.6:1. The drop rate was 3 s / drop. The solution was stirred at 500 rpm for 30 min at room temperature until the solution was clarified to obtain a silicon source solution.

[0067] (2) Isopropyl alcohol was placed in a beaker, and tetrabutyl titanate was slowly added dropwise to the isopropyl alcohol. The molar ratio of isopropyl alcohol to tetrabutyl titanate was 50:1, and the molar ratio of tetrabutyl titanate to ethyl orthosilicate was 1:20. The addition rate was 4 s / drop. The mixed solution was sonicated in an ultrasonicator at room temperature for 30 min until the solution became clear, thereby obtaining a titanium source solution.

[0068] (3) Desalted water is added to a beaker. The amount of desalted water added is the volume difference before and after the alcohol is removed. Carbonamide is dissolved in the desalted water. Tungsten-containing acid is then added to the carbonamide aqueous solution and dissolved under ultrasound to obtain a tungsten source solution.

[0069] (4) The silicon source solution was placed in an ice-water bath, and the titanium source solution was added dropwise to the silicon source using a constant pressure separatory funnel at a rate of 5 s / drop. The addition process was controlled at 0°C, and the mixture was stirred for 30 minutes to form a clear solution. The temperature was then raised to 90°C to remove the alcohol for 60 minutes, and the tungsten source solution was added to the mixed solution at a rate of 3 s / drop. The mixture was stirred for 30 minutes to form a clear mixed solution to obtain a precursor solution.

[0070] (5) The precursor solution was placed in a polytetrafluoroethylene liner, sealed in a stainless steel hydrothermal crystallization kettle, and statically crystallized in an oven at 160°C for 72 hours. After the crystallization, the catalyst powder was separated by high-speed centrifugation at 4000 rpm using a centrifuge, washed three times with desalted water, and dried in an oven at 100°C for 12 hours. The dried powder was ground and calcined in a muffle furnace at 600°C for 10 hours in an air atmosphere at a heating rate of 2°C / min to obtain WTS-1 molecular sieve 2.

[0071] Example 3

[0072] 20 wt% of tetrapropylammonium hydroxide was added to a round-bottom flask and stirred magnetically. 6 g of tetraethyl orthosilicate was added to the above solution and stirred. The molar ratio of tetrapropylammonium hydroxide to tetraethyl orthosilicate was 0.4:1. The dropwise addition rate was 3 s / drop. The mixture was stirred at 500 rpm at room temperature for 30 min until the solution was clarified to obtain a silicon source solution.

[0073] Pour isopropyl alcohol into a beaker and slowly add tetrabutyl titanate dropwise into the isopropyl alcohol. The molar ratio of isopropyl alcohol to tetrabutyl titanate is 60:1, and the molar ratio of tetrabutyl titanate to ethyl orthosilicate is 1:40. Add at a rate of 4 seconds per drop. Place the mixed solution in an ultrasonicator and sonicate at room temperature for 30 minutes until the solution becomes clear, thereby obtaining a titanium source solution.

[0074] Desalted water is added to a beaker. The amount of desalted water added is the volume difference before and after alcohol removal. Ammonium bicarbonate is dissolved in the desalted water. Tungstic acid is then added to the ammonium bicarbonate aqueous solution and dissolved under ultrasound to obtain a tungsten source solution.

[0075] The silicon source solution was placed in an ice-water bath. The titanium source solution was added dropwise to the silicon source using a constant pressure separatory funnel at a rate of 5 seconds per drop. The addition process was controlled at 0°C. After the addition, the solution was stirred for 30 minutes to form a clear solution. The temperature was then raised to 90°C to remove the alcohol for 60 minutes. The tungsten source solution was added to the mixed solution at a rate of 3 seconds per drop. After the addition, the solution was stirred for 30 minutes to form a clear mixed solution to obtain a precursor solution.

[0076] The precursor solution was placed in a polytetrafluoroethylene-lined container, sealed in a stainless steel hydrothermal crystallization kettle, and statically crystallized in an oven at 180°C for 96 hours. After crystallization, the catalyst powder was separated by high-speed centrifugation at 4000 rpm, washed three times with desalted water, and dried in an oven at 100°C for 12 hours. The dried powder was ground and calcined in a muffle furnace at 550°C in air for 4 hours at a heating rate of 2.5°C / min to obtain WTS-1 molecular sieve 3.

[0077] Example 4

[0078] 20 wt% of tetrapropylammonium hydroxide was added to a round-bottom flask and stirred magnetically. 6 g of tetraethyl orthosilicate was added to the above solution and stirred. The molar ratio of tetrapropylammonium hydroxide to tetraethyl orthosilicate was 0.4:1. The dropwise addition rate was 3 s / drop. The mixture was stirred at 500 rpm at room temperature for 30 min until the solution was clarified to obtain a silicon source solution.

[0079] Pour isopropyl alcohol into a beaker and slowly add tetrabutyl titanate dropwise into the isopropyl alcohol. The molar ratio of isopropyl alcohol to tetrabutyl titanate is 40:1, and the molar ratio of tetrabutyl titanate to ethyl orthosilicate is 1:30. Add at a rate of 4 seconds per drop. Place the mixed solution in an ultrasonicator and sonicate at room temperature for 30 minutes until the solution becomes clear, thereby obtaining a titanium source solution.

[0080] Add desalted water into a beaker. The amount of desalted water added is the volume difference before and after alcohol removal. Dissolve ammonium bicarbonate in the desalted water. Then add tungstic acid to the ammonium metatungstate aqueous solution and dissolve it under ultrasound to obtain a tungsten source solution.

[0081] The silicon source solution was placed in an ice-water bath. The titanium source solution was added dropwise to the silicon source using a constant pressure separatory funnel at a rate of 5 seconds per drop. The addition process was controlled at 0°C. After the addition, the solution was stirred for 30 minutes to form a clear solution. The temperature was then raised to 90°C to remove the alcohol for 60 minutes. The tungsten source solution was added to the mixed solution at a rate of 3 seconds per drop. After the addition, the solution was stirred for 30 minutes to form a clear mixed solution to obtain a precursor solution.

[0082] The precursor solution was placed in a polytetrafluoroethylene-lined container, sealed in a stainless steel hydrothermal crystallization kettle, and statically crystallized in an oven at 180°C for 48 hours. After crystallization, the catalyst powder was separated by high-speed centrifugation at 4000 rpm, washed three times with desalted water, and dried in an oven at 100°C for 12 hours. The dried powder was ground and calcined in a muffle furnace at 550°C for 2 hours in an air atmosphere at a heating rate of 3°C / min to obtain WTS-1 molecular sieve 4.

[0083] Example 5

[0084] 25 wt% of tetrapropylammonium hydroxide was added to a round-bottom flask and stirred magnetically. 6 g of tetraethyl orthosilicate was added to the above solution and stirred. The molar ratio of tetrapropylammonium hydroxide to tetraethyl orthosilicate was 0.2:1. The dropwise addition rate was 3 s / drop. The mixture was stirred at 500 rpm at room temperature for 30 min until the solution was clarified to obtain a silicon source solution.

[0085] Pour isopropyl alcohol into a beaker and slowly add tetrabutyl titanate dropwise into the isopropyl alcohol. The molar ratio of isopropyl alcohol to tetrabutyl titanate is 40:1, and the molar ratio of tetrabutyl titanate to ethyl orthosilicate is 1:25. Add at a rate of 4 seconds per drop. Place the mixed solution in an ultrasonicator and sonicate at room temperature for 30 minutes until the solution becomes clear, thereby obtaining a titanium source solution.

[0086] Desalted water is added to a beaker. The amount of desalted water added is the volume difference before and after alcohol removal. Ammonium carbonate is dissolved in the desalted water. Then, ammonium metatungstate is added to the ammonium carbonate aqueous solution and dissolved under ultrasound to obtain a tungsten source solution.

[0087] The silicon source solution was placed in an ice-water bath. The titanium source solution was added dropwise to the silicon source using a constant pressure separatory funnel at a rate of 5 seconds per drop. The addition process was controlled at 0°C. After the addition, the solution was stirred for 30 minutes to form a clear solution. The temperature was then raised to 90°C to remove the alcohol for 60 minutes. The tungsten source solution was added to the mixed solution at a rate of 3 seconds per drop. After the addition, the solution was stirred for 30 minutes to form a clear mixed solution to obtain a precursor solution.

[0088] The precursor solution was placed in a polytetrafluoroethylene-lined container, sealed in a stainless steel hydrothermal crystallization kettle, and statically crystallized in an oven at 160°C for 48 hours. After crystallization, the catalyst powder was separated by high-speed centrifugation at 4000 rpm, washed three times with desalted water, and dried in an oven at 100°C for 12 hours. The dried powder was ground and calcined in a muffle furnace at 500°C in air for 4 hours at a heating rate of 3°C / min to obtain WTS-1 molecular sieve 5.

[0089] Comparative Example 1

[0090] This comparative example provides a method for preparing titanium silicate molecular sieve, which differs from Example 1 only in that no ammonium tungstate is added to obtain Catalyst 1.

[0091] Comparative Example 2

[0092] This comparative example provides a method for preparing titanium silicate molecular sieve, which differs from Example 2 only in that tetrabutyl titanate is not added to obtain Catalyst 2.

[0093] Comparative Example 3

[0094] This comparative example provides a method for preparing titanium silicate molecular sieve, which differs from Example 3 only in that tetrabutyl titanate and tungstic acid are not added to obtain Catalyst 3.

[0095] Comparative Example 4

[0096] This comparative example provides a method for preparing titanium silicate molecular sieve, which differs from Example 4 only in that tungstic acid is replaced by ammonium molybdate to obtain Catalyst 4.

[0097] Comparative Example 5

[0098] This comparative example provides a method for preparing titanium silicate molecular sieve, which differs from Example 3 only in that ammonium metatungstate is replaced by ammonium metavanadate to obtain Catalyst 5.

[0099] Performance Testing

[0100] The catalyst samples prepared in the above examples and comparative examples were tested according to the following steps:

[0101] 22.6 g of 30 wt% hydrogen peroxide and 0.4 mol of cyclopentane or cyclohexane were added to a 100 mL reactor, followed by the addition of 1.0 g of catalyst and the start of the stirrer. The reaction was allowed to proceed at 60°C for 5 h. The product distribution was determined on an Agilent 7890A chromatograph. The results are shown in Table 1 (for cyclopentane) and Table 2 (for cyclohexane).

[0102] in,

[0103]

[0104] m oil _Ketone%: mass percentage of ketone in oil phase;

[0105] m oil _Alcohol%: the mass percentage of alcohol in the oil phase;

[0106] m oil : Oil phase quality;

[0107] m water _Ketone%: mass percentage of ketone in the aqueous phase;

[0108] m water _Alcohol%: the mass percentage of alcohol in the aqueous phase;

[0109] m water %: mass of aqueous phase.

[0110] Table 1

[0111]

[0112] Table 2

[0113]

[0114] It can be seen from the data in Table 1 and Table 2 that the tungsten-doped titanium silicate prepared by the method of the present invention has high catalytic activity. When used in the cyclopentane oxidation reaction and the cyclohexane oxidation reaction, the conversion rate reaches more than 30%; the total selectivity of cyclopentanol ketone and cyclohexanol ketone reaches more than 90%; its effective utilization rate of hydrogen peroxide reaches more than 70%, and compared with the comparative example, it is found that the activity of the tungsten-doped titanium silicate is significantly improved and the utilization rate of hydrogen peroxide is improved, indicating that the addition of tungsten can enhance the catalytic ability of the titanium silicate in catalyzing the reaction of cyclopentane and cyclohexane to prepare the corresponding alcohol ketones.

[0115] Stability test:

[0116] The titanium silicate catalysts prepared in Example 1 and Comparative Example 1 were selected for stability testing. After the reaction, the used catalysts were recovered and a small amount of fresh agent (i.e., unreacted titanium silicate catalyst) was added to maintain a consistent amount of added catalyst. The conversion rate of the reactants and the selectivity of the products during the reaction were analyzed to determine the cyclic stability of the catalyst.

[0117] Table 3

[0118]

[0119]

[0120] By conducting stability tests on titanium silicate molecular sieve catalysts modified with W element and titanium silicate molecular sieves not modified with W element, it was found that the titanium silicate molecular sieve modified with W element still showed good stability after 4 cycles of reaction. Although the conversion rate and selectivity decreased to a certain extent in the later stage of the reaction, the overall change was small, indicating that the catalyst has good long-term activity retention ability and reaction selectivity.

[0121] The above description of the disclosed embodiments will enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A titanium silicon molecular sieve, characterized in that Its skeleton includes Ti-O-Si skeleton and Ti-OW skeleton.

2. The titanium silicon molecular sieve according to claim 1, characterized in that The molar ratio of Si atoms to W atoms in the titanium silicon molecular sieve is (25-35):

1.

3. A method for preparing titanium silicon molecular sieve according to claim 1 or 2, characterized in that: The following steps are involved: S1: mixing a silicon source, a titanium source, a tungsten source and a crystallization regulator to obtain a precursor solution; S2: crystallizing the precursor solution, separating and obtaining a solid product after the crystallization is completed, and calcining the solid product to obtain a titanium silicon molecular sieve.

4. The preparation method according to claim 3, characterized in that The tungsten source is selected from any one or more of ammonium metatungstate, ammonium tungstate or tungstic acid; The silicon source is selected from tetraethyl orthosilicate; The titanium source is selected from tetrabutyl titanate; The crystallization regulator is selected from any one or more of ammonium carbonate, ammonium bicarbonate or carbonamide.

5. The preparation method according to claim 3 or 4, characterized in that The molar ratio of the silicon source to the tungsten source and the crystallization regulator is 1:(0.02-0.06):(0.04-0.2); The molar ratio of the silicon source to the titanium source is (20-40):

1.

6. The preparation method according to any one of claims 3 to 5, characterized in that The crystallization temperature is 160-180° C., and the crystallization time is 48-96 hours; The calcination atmosphere includes air, the calcination temperature is 500-600° C., the heating rate is 2-3° C. / min, and the calcination time is 2-10 hours.

7. A catalyst for cycloalkane oxidation reaction, characterized in that: The invention comprises the titanium silicate molecular sieve according to claim 1 or 2 or the titanium silicate molecular sieve prepared by the preparation method according to any one of claims 3 to 6.

8. A method for catalytic oxidation of cycloalkanes, characterized in that: The following steps are involved: Cycloalkane is used as a reactant and reacted in the presence of an oxidant and the catalyst according to claim 7 to obtain cyclic alcohol and cyclic ketone.

9. The method according to claim 8, characterized in that The oxidant is hydrogen peroxide; The molar ratio of the oxidant to the cycloalkane is 1:(1-3); The amount of the catalyst added is 3 to 9% of the mass of cyclopentane; The reaction temperature is 50-70° C. and the reaction time is 0.5-6 h.

10. The method according to claim 8 or 9, characterized in that The total selectivity of the cyclic alcohol and cyclic ketone is above 90%; The conversion rate of the cycloalkane is above 30%.

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