Catalyst as well as preparation method and application thereof

Abstract

The invention provides a catalyst and a preparation method and application thereof.The catalyst comprises a core, a first coating layer and a second coating layer, the first coating layer is located on at least part of the surface of the core, and the second coating layer is located on at least part of the surface of the core and at least part of the surface of the first coating layer or located on at least part of the surface of the core. The second coating layer is located on at least part of the surface of the first coating layer; the core comprises silicon dioxide, the first coating layer comprises a silicon-titanium molecular sieve layer, the second coating layer comprises a silicon dioxide shell layer with communicating holes, and the communicating holes are communicated with the outside; and the silicon-titanium ratio of the silicon-titanium molecular sieve layer is 10-800. The catalyst not only can effectively inhibit the occurrence of side reactions, but also can effectively improve the yield and selectivity of epoxidation products.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, and relates to a catalyst, in particular to a catalyst and a preparation method and application thereof. BACKGROUND

[0002] A new round of energy revolution strategic concept proposed in the Energy Development Plan of China requires promoting the comprehensive utilization of high value-added products downstream of fossil energy, opening up the industry upgrading through refining integration, and becoming the leading direction of China's petrochemical industry. Therefore, taking the integration of refining, olefins and aromatics has positive significance for improving product added value and making up for the huge gap in domestic basic chemical raw materials.

[0003] Currently, based on the catalytic cracking of olefins, the downstream high-quality preparation of high-end chemicals is the core of the current refining integration field. Because the olefin molecule contains a carbon-carbon double bond, it can usually undergo selective oxidation reaction to form an epoxide compound, and further initiate the formation of a bifunctional compound. In the olefin epoxidation reaction, a catalyst is usually required, and the catalyst can be divided into homogeneous catalysts and heterogeneous catalysts according to the existing phase state; among them, the homogeneous catalysts generally include polyoxometalates, metal porphyrin metal organic complexes, and the heterogeneous catalysts include metal organic framework materials (MOFs), supported metal catalysts, and zeolite molecular sieves, etc.

[0004] Patent CN101091921A discloses a preparation method of a propylene epoxidation catalyst. By using a shaped silicon oxide as a carrier, then loading titanium in an organic solvent, and then treating with water vapor and organosilicon, the problem of easy generation of extra-framework titanium species in the preparation process of titanium silicalite is solved, the effective utilization rate of peroxide compounds is improved, and the catalytic epoxidation performance is good.

[0005] Patent CN110316740A discloses a hollow core-shell structure titanium silicalite catalyst and a preparation method thereof. The molecular sieve takes TS-1 molecular sieve as the core and Silicalite-1 molecular sieve as the shell, and uses a silicon source, an organic amine template agent and a hollow titanium silicalite as raw materials to hydrothermally synthesize and prepare a hollow core-shell structure titanium silicalite catalyst. The obtained hollow core-shell structure titanium silicalite catalyst has stable crystal structure, high-activity six-coordinated titanium active centers, controllable composition, excellent catalytic performance in oxidation reactions such as olefin epoxidation and ketone / aldehyde ammoxidation with H2O2 as the oxidant; and the preparation method has simple steps, convenient operation and is easy to be applied in industrialization.

[0006] Patent CN109264739A discloses a kind of multi-stage pore nano titanium silicon molecular sieve synthesis method without additional mesoporous template, compared with mesoporous titanium silicon molecular sieve in prior art, it does not need additional mesoporous template, and mesoporous structure is formed by kirkendall growth effect, and the mesoporous pore size is mainly 2.8-4.5nm.The preparation method is simple, high yield and low preparation cost.

[0007] However, most of the above catalysts include silicon-titanium molecular sieves, but the acid sites Si-OH in titanium-silicon molecular sieves interact with the epoxy compounds generated in the olefin epoxidation reaction, causing ring-opening reactions to generate oxygen-containing substances, and as the reaction continues, the oxygen-containing substances will undergo oligomerization reactions and generate carbonaceous substances that deactivate the catalyst, reducing the reactivity of the catalyst.

[0008] Therefore, it is necessary to improve the catalyst to effectively inhibit the occurrence of side reactions and effectively improve the yield and selectivity of the epoxidation product. SUMMARY

[0009] To overcome the above-mentioned defects, the present application provides a catalyst that not only effectively inhibits the occurrence of side reactions but also effectively improves the yield and selectivity of the epoxidation product.

[0010] The present application also provides a method for preparing a catalyst, which can effectively inhibit the side reactions between the epoxidation product and the acid sites, improve the activity of the catalyst, and effectively improve the yield and selectivity of the epoxidation product when used in the selective oxidation of olefins.

[0011] The present application also provides a method for selectively oxidizing olefins, which can effectively improve the yield and selectivity of the epoxidation product when the above-mentioned catalyst or the catalyst prepared by the above-mentioned method is used in the selective oxidation of olefins.

[0012] The present application provides a catalyst comprising a core, a first coating layer, and a second coating layer, the first coating layer being located on at least part of the surface of the core, the second coating layer being located on at least part of the surface of the core and at least part of the surface of the first coating layer, or the second coating layer being located on at least part of the surface of the first coating layer.

[0013] The core comprises silicon dioxide, the first coating layer comprises a silicon-titanium molecular sieve layer, and the second coating layer comprises a silicon dioxide shell layer with connected pores that are in communication with the outside.

[0014] The silicon-titanium ratio of the silicon-titanium molecular sieve layer is 10-800.

[0015] Furthermore, the thickness of the first coating layer is 40nm-100nm, and / or the thickness of the second coating layer is 50nm-100nm.

[0016] Furthermore, the catalyst has a specific surface area of ​​100 m². 3 / g-450m 3 / g.

[0017] This invention also provides a method for preparing a catalyst, comprising the following steps:

[0018] 1) A silicon source is added dropwise to an aqueous solution of a template agent at a rate of 0.04-0.06 mL / s to obtain a first solution; a mixed solution of a titanium source and isopropanol is added dropwise to the first solution at a rate of 0.05 mL / 8-10 s, and the mixture is stirred evenly at room temperature to obtain a second solution; silicon dioxide seeds are added to the second solution, and the mixture is stirred evenly at room temperature, followed by aging and crystallization treatments. The product obtained after crystallization treatment is washed, dried, and calcined to obtain the first product.

[0019] The silicon source is SiO2, the titanium source is TiO2, and the molar ratio of the silicon source, template agent, titanium source and water is 1:(0.1-0.8):(0.00125-0.1):(30-80); the calcination temperature is 500℃-600℃, and the calcination time is 5h-8h.

[0020] 2) The first product, ethanol, ammonia, diethyl ether, and silicon source were sequentially added to an aqueous solution of hexadecyltrimethylammonium bromide. After mixing evenly at room temperature, a second product was obtained. The second product was then washed, dried, and calcined sequentially to obtain the catalyst.

[0021] The silicon source is SiO2, and the molar ratio of silicon source to hexadecyltrimethylammonium bromide is 1:(0.1-1); the calcination temperature is 500℃-600℃, and the calcination time is 5h-8h.

[0022] Furthermore, in step 1), the mass ratio of the silicon dioxide seed crystal to the silicon source is 1:(5-20).

[0023] Furthermore, in step 1), the temperature during the aging process is 60℃-90℃, and the time is 80min-240min.

[0024] And / or, the crystallization treatment is performed at a temperature of 130℃-190℃ for a time of 60h-100h;

[0025] And / or, the drying temperature is 70℃-90℃.

[0026] Furthermore, in step 2), the mass ratio of the first product to the silicon source is 1:(0.5-10).

[0027] Furthermore, in step 2), the volume ratio of the ethanol to the ammonia is 1:(0.02-1);

[0028] And / or, the drying temperature is 70℃-90℃.

[0029] Furthermore, the silicon source includes tetraethyl orthosilicate and / or silica sol;

[0030] And / or, the titanium source includes at least one of tetrabutyl titanate, tetraethyl titanate, tetraisopropyl titanate, titanium trichloride, and titanium tetrachloride;

[0031] And / or, the template agent includes at least one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetraethylammonium bromide.

[0032] The present invention also provides a method for selective oxidation of olefins, wherein the catalyst described in any one of the above claims, or the catalyst prepared by the method described in any one of the above claims, is used in the selective oxidation reaction of olefins.

[0033] This invention enables the catalyst to include a core, a first coating layer, and a second coating layer, wherein the first coating layer is located on at least a portion of the surface of the core, and the second coating layer is located on at least a portion of the surface of the core and at least a portion of the surface of the first coating layer, or the second coating layer is located on at least a portion of the surface of the first coating layer, and the core includes silicon dioxide, the first coating layer includes a silicon-titanium molecular sieve layer, and the second coating layer includes a silicon dioxide shell layer with interconnected pores that are connected to the outside. This not only effectively suppresses side reactions but also enables the catalyst to achieve a high yield and selectivity of epoxidation products in the selective oxidation of olefins. Attached Figure Description

[0034] Figure 1 This is a TEM image of the first product in Embodiment 1 of the present invention;

[0035] Figure 2 This is a TEM image of the catalyst in Example 1 of the present invention;

[0036] Figure 3 The UV-Vis spectrum of the catalyst in Example 1 of this invention;

[0037] Figure 4 The XRD pattern of the catalyst in Example 1 of this invention is shown below.

[0038] Figure 5 This is the N2 isothermal physical adsorption-desorption spectrum of the catalyst in Example 1 of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0040] The first aspect of the present invention provides a catalyst comprising a core, a first coating layer and a second coating layer, wherein the first coating layer is located on at least a portion of the surface of the core, and the second coating layer is located on at least a portion of the surface of the core and at least a portion of the surface of the first coating layer, or the second coating layer is located on at least a portion of the surface of the first coating layer.

[0041] The core comprises silicon dioxide, the first coating layer comprises a silicon-titanium molecular sieve layer, and the second coating layer comprises a silicon dioxide shell layer with interconnecting pores that are connected to the outside.

[0042] The silicon-to-titanium ratio of the silicon-to-titanium molecular sieve layer is 10-800.

[0043] The catalyst of this invention has a special structure, specifically comprising a core and a first coating layer of silicon-titanium molecular sieve located on at least a portion of the surface of the core, and a second coating layer of silica located on the surface of the first coating layer away from the core. The first coating layer of silicon-titanium molecular sieve has a silicon-to-titanium ratio of 10-800, providing sufficient reactive sites. The second coating layer has interconnecting pores that connect to the outside of the silicon-titanium molecular sieve layer, exhibiting good channel permeability and a "dendritic" structure. This ensures high diffusion performance in the selective oxidation of olefins, allowing reactant molecules to fully contact and react with the titanium sites. Simultaneously, the "dendritic" silica shell effectively covers acidic sites, inhibiting side reactions between epoxidation products and acidic sites, preventing acid-catalyzed ring-opening reactions, significantly reducing the content of oxygen-containing substances, and effectively inhibiting the formation of carbon deposits that could deactivate the catalyst, thereby improving the catalyst's reactivity and increasing the yield and productivity of the epoxidation products.

[0044] In one specific embodiment, the thickness of the first coating layer is 40 nm to 100 nm. Within this range, the catalyst has a large number of titanium active sites, which ensures that reactant molecules can diffuse smoothly to the active sites, thereby improving the catalyst's reactivity.

[0045] In one specific embodiment, the thickness of the second coating layer is 50 nm to 100 nm. Within this range, the acidic sites in the first coating layer can be effectively covered, and the reactant molecules can diffuse well, increasing the probability of contact with the active sites of titanium, thereby giving the catalyst higher reactivity and effectively improving the yield and productivity of the epoxidation product.

[0046] In one specific embodiment, the catalyst has a specific surface area of ​​100 m². 3 / g-450m 3 / g. Within this range, the catalyst has a higher specific surface area, which increases the contact area between the catalyst and reactant molecules, further improving the diffusion effect and thus giving the catalyst higher activity.

[0047] A second aspect of the present invention provides a method for preparing the catalyst of the first aspect, comprising the following steps:

[0048] 1) A silicon source is added dropwise to an aqueous solution of a template agent at a rate of 0.04-0.06 mL / s to obtain a first solution; a mixed solution of a titanium source and isopropanol is added dropwise to the first solution at a rate of 0.05 mL / 8-10 s, and the mixture is stirred evenly at room temperature to obtain a second solution; silicon dioxide seeds are added to the second solution, and the mixture is stirred evenly at room temperature, followed by aging and crystallization treatments. The product obtained after crystallization treatment is washed, dried, and calcined to obtain the first product.

[0049] The silicon source is SiO2, the titanium source is TiO2, and the molar ratio of silicon source, template agent, titanium source and water is 1:(0.1-0.8):(0.00125-0.1):(30-80); the calcination temperature is 500℃-600℃, and the calcination time is 5h-8h.

[0050] 2) The first product, ethanol, ammonia, diethyl ether, and silicon source were sequentially added to an aqueous solution of hexadecyltrimethylammonium bromide. After mixing evenly at room temperature, the second product was obtained. The second product was then washed, dried, and calcined sequentially to obtain the catalyst.

[0051] The silicon source is SiO2, and the molar ratio of silicon source to hexadecyltrimethylammonium bromide is 1:(0.1-1); the calcination temperature is 500℃-600℃, and the calcination time is 5h-8h.

[0052] Specifically, in step 1), firstly, the template agent is dissolved in deionized water and mixed evenly at room temperature to obtain an aqueous solution of the template agent; the silicon source is added to the aqueous solution of the template agent at a dropping rate of 0.04-0.06 mL / s and mixed evenly at room temperature to obtain a first solution; secondly, a mixed solution of titanium source and isopropanol (IPA) is added to the aforementioned first solution at a dropping rate of 0.05 mL / 8-10 s and mixed evenly at room temperature to obtain a second solution; in the second solution, the molar ratio of silicon source (calculated as SiO2), template agent, titanium source (calculated as TiO2) and water is 1:(0.1-0.8):(0.00125-0.1):(30-80); finally, silicon dioxide seeds are added to the aforementioned second solution and mixed evenly at room temperature, followed by aging treatment and crystallization treatment in sequence. The crystallized product is washed, dried, and calcined at a calcination temperature of 500℃-600℃ for a holding time of 5h-8h to obtain the first product.

[0053] In this invention, the silicon source refers to a water-soluble or water-soluble silicon-containing compound; the titanium source refers to a water-soluble or water-soluble titanium-containing compound. As long as it contains the target element (Si, Ti), it is within the scope of this invention.

[0054] This invention does not specifically limit the types and sources of template agents, silicon sources, and titanium sources; products prepared using commercially available products or conventional preparation methods well known to those skilled in the art are acceptable.

[0055] The present invention does not specifically limit the mixing method; for example, mixing can be carried out by stirring.

[0056] The present invention does not specify the mixing time; for example, the mixing time is 20-40 minutes.

[0057] The ratio of titanium source to isopropanol (IPA) and the mass ratio of silicon dioxide seed crystal to silicon source are not specifically limited in this invention.

[0058] This invention does not specify the drying temperature and time; it is sufficient to evaporate the moisture from the washed product.

[0059] The present invention does not specifically limit the method of aging treatment. For example, the reaction system that needs to be aged can be heated to remove alcohol, treated at a certain temperature for a period of time, and deionized water is continuously added during the treatment to ensure that the total volume of the reaction system remains unchanged, so as to carry out the aging treatment.

[0060] This invention does not specify the temperature and time for the aging process.

[0061] The present invention does not specifically limit the method of crystallization treatment. For example, the crystallization treatment can be carried out by pouring the reaction system to be crystallized into the polytetrafluoroethylene liner of the crystallization kettle and crystallizing it at a certain temperature for a period of time.

[0062] This invention does not specify the temperature and time for the crystallization process.

[0063] This invention does not specifically limit the preparation method of silicon dioxide seeds. For example, they can be prepared by methods including the following:

[0064] The template agent and deionized water were mixed and stirred at room temperature until the mixture became clear, resulting in an aqueous solution of the template agent. A silicon source was added to the aqueous solution of the template agent at a dropping rate of 0.04-0.06 mL / s and stirred rapidly until the reaction system became clear. The molar ratio of silicon source (as SiO2), template agent and water was 1:(0.1-0.8):(10-80). Then, aging and crystallization treatments were performed. The crystallized product was washed, dried and calcined to obtain silicon dioxide seed crystals.

[0065] The present invention does not specifically limit the type of template agent, which can be the same as the template agent in step 1).

[0066] The present invention does not specify the stirring speed after adding the silicon source to the template agent aqueous solution, and it can be consistent with the dropping speed of the silicon source in step 1).

[0067] The present invention does not specifically limit the drying temperature and time, and they can be consistent with the drying temperature and time in step 1).

[0068] The present invention does not specifically limit the roasting temperature and holding time, and they can be consistent with the roasting temperature and roasting time in step 1).

[0069] The present invention does not specifically limit the aging treatment, crystallization treatment and drying conditions in the preparation process of silicon dioxide seeds. They can be consistent with the aging treatment, crystallization treatment and drying conditions in step 1) above, and will not be elaborated here.

[0070] In step 2), hexadecyltrimethylammonium bromide is dissolved in deionized water and mixed evenly at room temperature to obtain an aqueous solution of hexadecyltrimethylammonium bromide. The first product, ethanol, and ammonia are added sequentially to the aforementioned aqueous solution of hexadecyltrimethylammonium bromide and mixed evenly at room temperature. Then, diethyl ether is added and mixed evenly at room temperature. Finally, a silicon source is added, with a molar ratio of silicon source (calculated as SiO2) to hexadecyltrimethylammonium bromide of 1:(0.1-1). After mixing evenly at room temperature, a second product is obtained. The second product is then washed, dried, and calcined sequentially at a calcination temperature of 500℃-600℃ for 5h-8h to obtain the catalyst.

[0071] The limitations on the silicon source in this invention are the same as those described above, and will not be repeated here.

[0072] The present invention does not specifically limit the source of hexadecyltrimethylammonium bromide; any commercially available product or product prepared by conventional methods well known to those skilled in the art is acceptable.

[0073] The present invention does not specifically limit the mass ratio of the first product to the silicon source or the volume ratio of ethanol to ammonia.

[0074] This invention does not impose specific limitations on the amount of diethyl ether used, or the ratio of silicon source to ethanol or ammonia.

[0075] The present invention does not specify the mixing time; for example, the mixing time is 20-40 minutes.

[0076] The present invention does not specifically limit the drying temperature and time, or the heating rate during the calcination process. For example, the heating rate is 1℃ / min-10℃ / min, and further, the heating rate is 4℃ / min-6℃ / min.

[0077] The catalyst preparation method of this invention first involves generating a silicon-titanium molecular sieve layer on the surface of silicon dioxide seed crystals, and then generating a dendritic silicon dioxide shell layer with interconnected pores on the surface of the silicon-titanium molecular sieve layer. By controlling the silicon-titanium ratio in the silicon-titanium molecular sieve, it is possible to ensure that reactant molecules can diffuse through the interconnected pores to the silicon-titanium molecular sieve layer in the selective oxidation of olefins and react fully. Moreover, the dendritic silicon dioxide shell layer can effectively cover acidic sites, suppress side reactions between epoxidation products and acidic sites, thereby reducing the impact of carbon deposits on catalyst activity and significantly improving the yield and productivity of epoxidation products.

[0078] In one specific embodiment, in step 1), the mass ratio of silicon dioxide seed crystals to silicon source is 1:(5-20). When the mass ratio of silicon dioxide seed crystals to silicon source is within the aforementioned range, it helps to ensure that the thickness of the first coating layer in the catalyst is between 40 nm and 100 nm, thereby increasing the active sites of titanium in the catalyst and helping the reactant molecules to have higher diffusion performance in the selective oxidation reaction of olefins, effectively improving the reaction activity of the catalyst, and thus increasing the yield and productivity of the epoxidation product.

[0079] In one specific embodiment, in step 1), the aging treatment temperature is 60℃-90℃, and the time is 80min-240min. Further, the aging treatment temperature is 80℃. Within this range, the formation of titanium oligomers can be effectively avoided, further enhancing the catalyst activity.

[0080] In one specific embodiment, in step 1), the crystallization treatment temperature is 130℃-190℃, and the time is 60h-100h. Further, the crystallization treatment temperature is 170℃. Within this range, the formation of impurity crystals during the crystallization process can be avoided, ensuring the purity of the silicon-titanium molecular sieve.

[0081] In one specific embodiment, in step 1), the drying temperature is 70℃-90℃.

[0082] In one specific embodiment, in step 2), the mass ratio of the first product to the silicon source is 1:(0.5-10). For example, the mass ratio can be 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10. When the mass ratio of the first product to the silicon source is within the aforementioned range, it helps to ensure that the thickness of the second coating layer in the catalyst is between 50 nm and 100 nm, thereby effectively covering the acidic sites in the silicon-titanium molecular sieve and further improving the diffusion performance of reactant molecules during the reaction process, thus effectively improving the yield and productivity of the epoxidation product.

[0083] In one specific embodiment, the volume ratio of ethanol to ammonia is 1:(0.02-1). Further, the volume ratio of ethanol to ammonia is 1:(0.02-0.05).

[0084] In one specific embodiment, the drying temperature is 70°C-90°C. The drying temperature should be lower than the decomposition temperature of hexadecyltrimethylammonium bromide. When the drying temperature is within the aforementioned range, the decomposition of hexadecyltrimethylammonium bromide, which would lead to the collapse of the crystal structure, can be avoided.

[0085] In one specific embodiment, the silicon source includes tetraethyl orthosilicate and / or silica sol;

[0086] And / or, the titanium source includes at least one of tetrabutyl titanate, tetraethyl titanate, tetraisopropyl titanate, titanium trichloride, and titanium tetrachloride;

[0087] And / or, the template agent includes at least one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetraethylammonium bromide.

[0088] When the aforementioned three types of compounds are mixtures of various specific compounds, the present invention does not impose excessive restrictions on the proportions between the various specific compounds.

[0089] Furthermore, the above-mentioned template agent can also be used in combination with at least one of n-butylamine, ethylenediamine, tetrabutylammonium hydroxide, and tetrabutylammonium bromide.

[0090] When the template agent is mixed with at least one of n-butylamine, ethylenediamine, tetrabutylammonium hydroxide, and tetrabutylammonium bromide, the present invention does not impose a specific limit on the mixing ratio.

[0091] A third aspect of this invention provides a method for selective oxidation of olefins, in which the catalyst of the first aspect, or the catalyst prepared by the method of the second aspect, is used in the selective oxidation reaction of olefins. Since the aforementioned catalyst comprises a core and a first coating layer of silicon-titanium molecular sieve located on at least a portion of the surface of the core, and a second coating layer of silica shell located on the surface of the first coating layer away from the core, and the silicon-titanium ratio in the silicon-titanium molecular sieve is 10-800, using this catalyst in the selective oxidation reaction of olefins can not only effectively suppress side reactions but also achieve high yields and selectivity of epoxidation products.

[0092] The catalyst of the present invention will be described in detail below through specific embodiments.

[0093] Example 1

[0094] 1) Preparation of silica seed crystals: 24 mL of tetrapropylammonium hydroxide (TPAOH, 35 wt%) and 28 mL of deionized water were mixed and stirred at room temperature for 30 min until clear. Then, 23 mL of tetraethyl orthosilicate (TEOS) was added to the aforementioned TPAOH aqueous solution at a dropping rate of 0.05 mL / s and stirred rapidly for 1 h until the solution was clear. The molar ratio of silicon source (calculated as SiO2), template agent and water was 1:0.39:23.5. The reaction system was heated to 80 °C and aged for 120 min, with deionized water continuously added to maintain a constant volume of the reaction system. The aged reaction system was poured into the polytetrafluoroethylene liner of a crystallization kettle and crystallized at 170 °C for 72 h. After crystallization, the crystallization kettle was removed and cooled to room temperature. The resulting product was then washed, centrifuged, dried at 90 °C for 12 h, and calcined at 550 °C for 6 h to obtain silica seed crystals.

[0095] 2) Dissolve 3g of n-butylamine and 5mL of tetrapropylammonium hydroxide (TPAOH, 35wt%) in 17mL of deionized water and stir at room temperature for 30min. Add 10g of silica sol (30wt% SiO2) to the aforementioned aqueous solution of n-butylamine and TPAOH at a dropping rate of 0.05mL / s and stir at room temperature for 1h to obtain the first solution. Mix 0.4g of tetrabutyl titanate (TBOT) with 20mL of isopropanol (IPA) and stir for 30min to obtain a mixed solution of TBOT and IPA. Add the mixed solution of TBOT and IPA dropwise to the first solution at a rate of 0.05mL / 9s and stir thoroughly for 3h to obtain the second solution. The reaction mixture was prepared in the following manner: a liquid containing silicon source, template agent, titanium source, and water in a molar ratio of 1:0.172:0.024:30.2; 1 g of silicon dioxide seed crystals were added to the second solution and stirred at room temperature for 30 min; the reaction system was heated to 80 °C and aged for 120 min, during which deionized water was continuously added to maintain a constant volume of the reaction system; the aged reaction system was poured into a polytetrafluoroethylene liner of a crystallization vessel and crystallized at 170 °C for 72 h; after crystallization, the crystallization vessel was removed and cooled to room temperature, and the crystallized product was then washed, centrifuged, dried at 90 °C for 12 h, and calcined at 550 °C for 6 h to obtain the first product;

[0096] 3) Add 1.5 g of hexadecyltrimethylammonium bromide (CTAB) to 210 mL of deionized water and stir at room temperature for 15 min to obtain an aqueous CTAB solution; add 1.0 g of the first product to the aforementioned aqueous CTAB solution, then add 60 mL of ethanol and 2.4 mL of ammonia water, stir at room temperature for 15 min, then add 30 mL of diethyl ether, and sonicate at 25 °C for 20 min, then add 1.5 mL of tetraethyl orthosilicate (TEOS) dropwise, and continue stirring at 25 °C for 6 h to obtain the second product; wherein the molar ratio of silicon source to hexadecyltrimethylammonium bromide is 1:0.61; wash the second product, centrifuge, dry at 80 °C for 10 h, and calcine at 550 °C for 6 h to obtain the catalyst of this embodiment.

[0097] Example 2

[0098] The catalyst preparation method in this embodiment is basically the same as that in Example 1, except that in step 1), the tetrapropylammonium hydroxide (TPAOH, 35wt%) is adjusted to 7mL, the deionized water is adjusted to 18mL, the TEOS is adjusted to 28mL, and the dropping rate of tetraethyl orthosilicate (TEOS) is adjusted to 0.04mL / s; then the molar ratio of silicon source (calculated as SiO2), template agent and water is 1:0.1:10.

[0099] The aging temperature was adjusted to 70℃ and the time to 90 min; the crystallization temperature was adjusted to 130℃ and the time to 100 h; the calcination temperature was adjusted to 500℃ and the time to 7 h.

[0100] In step 2), the dropping rate of tetraethyl orthosilicate (TEOS) is adjusted to 0.04 mL / s, the amount of tetrapropylammonium hydroxide (TPAOH) is adjusted to 8 mL, the amount of deionized water is adjusted to 30 mL, and the amount of 10 g silica sol is adjusted to 12 mL of TEOS; the amount of tetrabutyl titanate (TBOT) is adjusted to 0.3 g; and the dropping rate of the mixed solution of TBOT and IPA is adjusted to 0.05 mL / 8 s; wherein, the molar ratio of silicon source, template agent, titanium source and water is 1:0.261:0.017:37;

[0101] The silicon dioxide seed crystals were adjusted to 0.7g; the aging temperature was adjusted to 70℃ and the time to 90min; the crystallization temperature was adjusted to 130℃ and the time to 100h; and the calcination temperature was adjusted to 500℃ and the time to 7h.

[0102] In step 3), the cetyltrimethylammonium bromide (CTAB) is adjusted to 3.25 g, the first product is adjusted to 3.72 g, the ammonia solution is adjusted to 30 mL, and the TEOS solution is adjusted to 2 mL; then the molar ratio of silicon source to cetyltrimethylammonium bromide is 1:1.

[0103] Adjust the drying temperature to 90℃ and the time to 12h; adjust the roasting temperature to 500℃ and the roasting time to 7h.

[0104] Example 3

[0105] The preparation method of the catalyst in this embodiment is basically the same as that in Example 1, except that in step 1), the tetrapropylammonium hydroxide (TPAOH, 35wt%) is adjusted to 12mL, the deionized water is adjusted to 31mL, the TEOS is adjusted to 6mL, and the dropping rate of tetraethyl orthosilicate (TEOS) is adjusted to 0.06mL / s; then the molar ratio of silicon source (calculated as SiO2), template agent and water is 1:0.77:80.

[0106] The aging treatment temperature was adjusted to 90℃ and the time was adjusted to 150 min; the crystallization treatment temperature was adjusted to 180℃ and the time was adjusted to 96 h; the drying temperature was adjusted to 80℃ and the time was adjusted to 14 h; the calcination temperature was adjusted to 600℃ and the time was adjusted to 5 h.

[0107] In step 2), the deionized water is adjusted to 29 mL; the silica sol (30 wt% SiO2) is adjusted to 5 g; the tetrabutyl titanate (TBOT) is adjusted to 0.85 g; the dropping rate of tetraethyl orthosilicate (TEOS) is adjusted to 0.06 mL / s; and the dropping rate of the mixed solution of TBOT and IPA is adjusted to 0.05 mL / 10 s. The molar ratio of silicon source, template agent, titanium source and water is then 1:0.34:0.1:79.2.

[0108] Adjust the silicon dioxide seed crystal to 1g; adjust the aging treatment temperature to 90℃ and the time to 150min; adjust the crystallization treatment temperature to 180℃ and the time to 96h; adjust the calcination temperature to 600℃ and the time to 5h.

[0109] In step 3), TEOS is adjusted to 5.4 mL; the molar ratio of silicon source to hexadecyltrimethylammonium bromide is 1:0.17; ammonia is adjusted to 60 mL; drying temperature is adjusted to 90℃ and time is adjusted to 16 h; calcination temperature is adjusted to 600℃ and time is adjusted to 5 h.

[0110] Example 4

[0111] The preparation method of the catalyst in this embodiment is basically the same as that in Example 1. The difference is that in step 1), the aging treatment temperature is adjusted to 60°C and the time is adjusted to 240 min; the crystallization treatment temperature is adjusted to 150°C and the time is adjusted to 84 h; the drying temperature is adjusted to 70°C and the time is adjusted to 16 h; and the calcination time is adjusted to 8 h.

[0112] In step 2), the tetrapropylammonium hydroxide (TPAOH) is adjusted to 3 mL; the deionized water is adjusted to 41 mL; and the tetrabutyl titanate (TBOT) is adjusted to 0.2 g. Then the molar ratio of silicon source, template agent, titanium source and water is 1:0.1:0.012:55.4.

[0113] The silicon dioxide seed crystal was adjusted to 0.5g; the aging treatment temperature was adjusted to 60℃ and the time was adjusted to 240min; the crystallization treatment temperature was adjusted to 150℃ and the time was adjusted to 84h; the calcination time was adjusted to 8h.

[0114] In step 3), the cetyltrimethylammonium bromide (CTAB) is adjusted to 9g; TEOS is adjusted to 10.5mL; and ethanol is adjusted to 50mL; then the molar ratio of silicon source to cetyltrimethylammonium bromide is 1:0.53; the drying temperature is adjusted to 90℃ and the time is adjusted to 16h; and the calcination time is adjusted to 8h.

[0115] Example 5

[0116] The catalyst preparation method in this embodiment is basically the same as that in Example 1, except that in step 1), TPAOH is adjusted to 26 mL; the molar ratio of silicon source, template agent, and water is 1:0.43:24.2; the aging treatment temperature is adjusted to 85℃ and the time is adjusted to 80 min; the crystallization treatment temperature is adjusted to 160℃ and the time is adjusted to 96 h; the drying temperature is adjusted to 80℃ and the time is adjusted to 10 h; and the calcination temperature is adjusted to 600℃.

[0117] In step 2), the amount of tetrapropylammonium hydroxide (TPAOH) is adjusted to 23 mL, and the amount of deionized water is adjusted to 23 mL; the amount of tetrabutyl titanate (TBOT) is adjusted to 0.8 g; then the molar ratio of silicon source, template agent, titanium source and water is 1:0.8:0.047:50.

[0118] The dropping rate of the TBOT and IPA mixed solution was adjusted to 0.05 mL / 8 s; the aging treatment temperature was adjusted to 85 °C and the time was adjusted to 80 min; the silica seed crystals were adjusted to 0.8 g; the crystallization treatment temperature was adjusted to 160 °C and the time was adjusted to 96 h; and the calcination temperature was adjusted to 600 °C.

[0119] In step 3), adjust the ammonia water to 1.2 mL and the TEOS to 1 mL; then the molar ratio of silicon source to hexadecyltrimethylammonium bromide is 1:0.61; adjust the drying temperature to 80℃ and the time to 10 h. Adjust the calcination temperature to 600℃.

[0120] Example 6

[0121] The preparation method of the catalyst in this embodiment is basically the same as that in Example 1. The difference is that in step 1), TPAOH is adjusted to 28 mL, deionized water is adjusted to 40 mL, and TEOS is adjusted to 26 mL; then the molar ratio of silicon source (calculated as SiO2), template agent and water is 1:0.41:27.7.

[0122] The aging treatment temperature was adjusted to 90℃ and the time to 90 min; the crystallization treatment temperature was adjusted to 190℃ and the time to 60 h; the drying temperature was adjusted to 70℃ and the time to 16 h; and the calcination temperature was adjusted to 500℃ and the time to 8 h.

[0123] In step 2), the tetrapropylammonium hydroxide (TPAOH) is adjusted to 12 mL, the deionized water is adjusted to 21 mL, and the tetrabutyl titanate (TBOT) is adjusted to 0.022 g; then the molar ratio of silicon source, template agent, titanium source and water is 1:0.41:0.00129:40.

[0124] The dropping rate of the TBOT and IPA mixed solution was adjusted to 0.05 mL / 10 s; the silica seed crystals were adjusted to 0.8 g; the aging treatment temperature was adjusted to 90 °C and the time to 90 min; the crystallization treatment temperature was adjusted to 190 °C and the time to 60 h; the drying temperature was adjusted to 70 °C and the time to 16 h; and the calcination temperature was adjusted to 500 °C and the time to 8 h.

[0125] In step 3), the ammonia water is adjusted to 3 mL and the TEOS is adjusted to 2 mL; the molar ratio of silicon source to hexadecyltrimethylammonium bromide is 1:0.46; the drying temperature is adjusted to 75℃ and the time is adjusted to 14 h; the calcination temperature is adjusted to 500℃ and the time is adjusted to 8 h.

[0126] Example 7

[0127] The preparation method of the catalyst in this embodiment is basically the same as that in Example 1. The difference is that in step 2), the silicon dioxide seed crystal is adjusted to 0.4g, so the mass ratio of the seed crystal to the silicon source is 1:25.

[0128] Example 8

[0129] The catalyst preparation method in this embodiment is basically the same as that in Example 2. The difference is that in steps 1) and 2), the aging treatment temperature is adjusted to 50°C and the time is adjusted to 60 min.

[0130] Example 9

[0131] The preparation method of the catalyst in this embodiment is basically the same as that in Example 3, except that in steps 1) and 2), the crystallization temperature is adjusted to 120°C and the time is adjusted to 50h.

[0132] Example 10

[0133] The preparation method of the catalyst in this embodiment is basically the same as that in Example 5. The difference is that in step 3), the first product is adjusted to 2.5g, so the mass ratio of the first product to the silicon source is 1:0.37.

[0134] Example 11

[0135] The preparation method of the catalyst in this embodiment is basically the same as that in Example 6. The difference is that in step 3), the ammonia water is adjusted to 0.9 mL, so the volume ratio of ethanol to ammonia water is 1:0.015.

[0136] Comparative Example 1

[0137] The preparation method of the catalyst in this comparative example is basically the same as that in Example 1, except that the silica seed crystals are not coated, i.e. steps 2) and 3) are not included, thus obtaining the catalyst of this comparative example.

[0138] Comparative Example 2

[0139] The preparation method of the catalyst in this comparative example is basically the same as that in Example 1. The difference is that only the first coating layer, the silicon-titanium molecular sieve layer, is coated on the silicon dioxide seed crystals, i.e., step 3 is not included, to obtain the catalyst of this comparative example.

[0140] Comparative Example 3

[0141] The preparation method of the catalyst in this comparative example is basically the same as that in Example 1. The difference is that the catalyst in this comparative example is a traditional catalyst, that is, it only includes step 2), to obtain the catalyst of this comparative example.

[0142] Comparative Example 4

[0143] The preparation method of the catalyst in this comparative example is basically the same as that in Example 1. The difference is that in step 2), the tetrabutyl titanate (TBOT) is adjusted to 2.4g; then the molar ratio of silicon source, template agent, titanium source and water is 1:0.172:0.141:30.2.

[0144] Comparative Example 5

[0145] The preparation method of the catalyst in this comparative example is basically the same as that in Example 1. The difference is that in step 3), the cetyltrimethylammonium bromide is adjusted to 0.5g and TEOS is adjusted to 4mL; then the molar ratio of silicon source to cetyltrimethylammonium bromide is 1:0.08.

[0146] Test case

[0147] 1. The first product from Example 1 and the catalyst were subjected to TEM testing. The test results are as follows: Figure 1 and Figure 2 As shown.

[0148] Figure 1 This is a TEM image of the first product in Example 1, by... Figure 1 As can be seen, a coating layer is uniformly covered on the surface of the silicon dioxide core. This coating layer is a silicon-titanium molecular sieve layer. Figure 2 The TEM image of the catalyst in Example 1 is shown below. Figure 2 It is known that there is a "dendritic" shell on the surface of the catalyst, which can not only effectively cover the acidic sites, but also ensure that the reactant molecules can reach the silicon-titanium molecular sieve layer smoothly for full reaction in the selective oxidation of olefins. While effectively suppressing side reactions, it can also improve the yield and selectivity of epoxidation products.

[0149] 2. The catalyst in Example 1 was subjected to UV-Vis spectroscopy and XRD tests. The test results are shown in [Figure 1]. Figure 3 and Figure 4.

[0150] Figure 3 The UV-Vis spectrum of the catalyst in Example 1 is shown below. Figure 3 It is known that the catalyst in Example 1 does not have non-framework titanium nanoparticles around 330 nm. Non-framework titanium nanoparticles can cause ring opening of epoxides and reduce the selectivity of epoxidation products. Therefore, the catalyst of the present invention can effectively improve the selectivity of epoxidation products in the selective oxidation reaction of olefins.

[0151] Figure 4 The XRD pattern of the catalyst in Example 1 is shown below. Figure 4 As can be seen, the XRD pattern of the catalyst in Example 1 shows typical MFI framework structure characteristics, proving the successful synthesis of silicon-titanium molecular sieve.

[0152] 3. Nitrogen adsorption-desorption tests were performed on the catalyst in Example 1 above. The test results are shown in [Figure Number]. Figure 5 ; Figure 5 The N2 isothermal physisorption-desorption spectrum of the catalyst in Example 1 is shown below. Figure 5 It can be seen that the adsorption isotherm in the spectrum conforms to the IV, H4 type hysteresis loop, indicating that the catalyst in Example 1 has a mixed micro-mesoporous pore structure.

[0153] 4. ICP testing was performed on the catalysts in the above examples and comparative examples to obtain the silicon-to-titanium ratio of the silicon-titanium molecular sieve layers. The test results are shown in Table 1. Simultaneously, the catalysts in the above examples and comparative examples were used in the epoxidation reaction of 1-hexene, including the following steps:

[0154] 20 mL of acetonitrile solvent, 0.2 g of the above catalyst, 2 g of NH4Cl, 1.2 g of 1-hexene, and 1.2 g of hydrogen peroxide (H2O2, 30 wt%) were added to a reaction vessel. The reactor was sealed, and the reaction time was set to 3 h, the reaction temperature to 60 °C, and the rotation speed to 600 r / min. After the reaction was completed, the reaction vessel was immediately cooled to room temperature with ice water. The reaction product was removed, poured into a transparent sample bottle, and anhydrous sodium sulfate was added. The bottle was shaken thoroughly to remove water. The supernatant was then collected after standing. The supernatant was stirred and mixed thoroughly. 1 mL of the sample was then transferred to a chromatographic bottle for analysis, yielding the product. The molar amount of hexane produced and the molar amount of unreacted 1-hexene can be used to calculate the molar amount of 1-hexene consumed in the production of hexane based on the chemical reaction equation. The yield of hexane (%) is calculated as: molar amount of 1-hexene consumed in the production of hexane / (total molar amount of 1-hexene added - molar amount of unreacted 1-hexene) × 100%. The yield of hexane (%) is calculated as: molar amount of 1-hexene consumed in the production of hexane / total molar amount of 1-hexene added × 100%. The calculation results are shown in Table 1. The evaluation of the liquid-phase epoxidation of 1-hexene was carried out in a 50 mL micro reactor equipped with magnetic stirring.

[0155] Table 1

[0156]

[0157]

[0158] As shown in Table 1:

[0159] The catalysts in Examples 1-11 achieve high hexane oxide yields and selectivity in the 1-hexene epoxidation reaction, with high hydrogen peroxide utilization. The catalyst in Example 2 achieves a hexane oxide yield of up to 60.5%, a selectivity of 99.7%, and a hydrogen peroxide utilization rate of 97.8%, significantly higher than Comparative Examples 1-5. The catalyst in Comparative Example 5 exhibits poor performance, possibly due to an insufficient molar ratio of silicon source to hexadecyltrimethylammonium bromide (1:0.08). This insufficient amount of hexadecyltrimethylammonium bromide prevents the formation of sufficient interconnected pores in the second coating layer, reducing the specific surface area and hindering the diffusion of reactant molecules to the active sites. Consequently, the hexane oxide yield, selectivity, and hydrogen peroxide utilization rate decrease sharply. Therefore, the catalysts of this invention not only effectively suppress side reactions but also significantly improve the yield and selectivity of the epoxidation products.

[0160] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A catalyst, characterized in that, The catalyst includes a core, a first coating layer, and a second coating layer. The first coating layer is located on at least a portion of the surface of the core, and the second coating layer is located on at least a portion of the surface of the core and at least a portion of the surface of the first coating layer, or the second coating layer is located on at least a portion of the surface of the first coating layer. The core comprises silicon dioxide, the first coating layer comprises a silicon-titanium molecular sieve layer, and the second coating layer comprises a silicon dioxide shell layer with interconnecting pores that are connected to the outside. The silicon-to-titanium ratio of the silicon-to-titanium molecular sieve layer is 10-800.

2. The catalyst according to claim 1, characterized in that, The thickness of the first coating layer is 40nm-100nm, and / or the thickness of the second coating layer is 50nm-100nm.

3. The catalyst according to claim 1 or 2, characterized in that, The catalyst has a specific surface area of ​​100 m². 3 / g-450m 3 / g.

4. A method for preparing the catalyst according to any one of claims 1-3, characterized in that, Includes the following steps: 1) The silicon source was added dropwise to the aqueous solution of the template agent at a rate of 0.04-0.06 mL / s to obtain the first solution; A mixture of titanium source and isopropanol was added dropwise to the first solution at a rate of 0.05 mL / 8-10 s. After mixing thoroughly at room temperature, a second solution was obtained. Add silica seeds to the second solution, mix evenly at room temperature, and then perform aging and crystallization treatments in sequence. The product obtained after crystallization treatment is washed, dried, and calcined in sequence to obtain the first product. The silicon source is SiO2, the titanium source is TiO2, and the molar ratio of the silicon source, template agent, titanium source and water is 1:(0.1-0.8):(0.00125-0.1):(30-80); the calcination temperature is 500℃-600℃, and the calcination time is 5h-8h. 2) The first product, ethanol, ammonia, diethyl ether, and silicon source were sequentially added to an aqueous solution of hexadecyltrimethylammonium bromide. After mixing evenly at room temperature, a second product was obtained. The second product was then washed, dried, and calcined sequentially to obtain the catalyst. The silicon source is SiO2, and the molar ratio of silicon source to hexadecyltrimethylammonium bromide is 1:(0.1-1); the calcination temperature is 500℃-600℃, and the calcination time is 5h-8h.

5. The method for preparing the catalyst according to claim 4, characterized in that, In step 1), the mass ratio of the silicon dioxide seed crystal to the silicon source is 1:(5-20).

6. The method for preparing the catalyst according to claim 4 or 5, characterized in that, In step 1), the temperature during the aging process is 60℃-90℃, and the time is 80min-240min; And / or, the crystallization treatment is performed at a temperature of 130℃-190℃ for a time of 60h-100h; And / or, the drying temperature is 70℃-90℃.

7. The method for preparing the catalyst according to any one of claims 4-6, characterized in that, In step 2), the mass ratio of the first product to the silicon source is 1:(0.5-10).

8. The method for preparing the catalyst according to any one of claims 4-7, characterized in that, In step 2), the volume ratio of ethanol to ammonia is 1:(0.02-1); And / or, the drying temperature is 70℃-90℃.

9. The method for preparing the catalyst according to any one of claims 4-8, characterized in that, The silicon source includes tetraethyl orthosilicate and / or silica sol; And / or, the titanium source includes at least one of tetrabutyl titanate, tetraethyl titanate, tetraisopropyl titanate, titanium trichloride, and titanium tetrachloride; And / or, the template agent includes at least one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetraethylammonium bromide.

10. A method for selective oxidation of olefins, characterized in that, The catalyst according to any one of claims 1-3, or the catalyst prepared by the method of any one of claims 4-9, is used in the selective oxidation reaction of olefins.

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