Method for preparing supported catalyst by microwave method and supported catalyst and use thereof

Abstract

The application relates to the technical field of catalysts, and discloses a method for preparing a supported catalyst by using a microwave method, the supported catalyst and application of the supported catalyst, the method comprises the following steps: (1) mixing a solution containing an active component precursor and a dispersant to obtain a solution B1; adjusting the pH value of the solution B1 to 3.8-8.5 by using a solution containing inorganic alkaline substances to obtain a solution B2; then aging the solution B2 to obtain an impregnation solution with a pH value of 6-10; (2) impregnating the impregnation solution prepared in the step (1) and a titanium-silicon molecular sieve under first microwave conditions; and then drying and activating the solid-liquid mixture obtained through impregnation. The method disclosed by the application can not only increase the proportion of the number of noble metals with a particle size of 2-6 nm in the catalyst, but also reduce the acid amount ratio of B acid and L acid in the catalyst. The catalyst disclosed by the application can improve the conversion rate of propylene and the selectivity of propylene oxide.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a method for preparing supported catalysts using a microwave method, and supported catalysts and their applications. Background Technology

[0002] Propylene oxide is a chemical with a huge global production and consumption volume. It can be used to produce intermediate chemicals such as polyethers, propylene glycol, isopropanolamine, and allyl alcohol, which in turn generate unsaturated polymer resins, polyurethanes, surfactants, and other chemicals. Propylene oxide is widely used in the food, textile, pharmaceutical, and chemical industries.

[0003] Currently, the main industrial methods for producing propylene oxide include the chlorohydrin process, the co-oxidation process, and the direct oxidation (HPPO) process. The chlorohydrin process's main drawbacks are the use of toxic chlorine gas, severe equipment corrosion, and the generation of large amounts of chlorine-containing wastewater that pollutes the environment, failing to meet the requirements of green chemistry and clean production. Therefore, with increasingly stringent environmental protection requirements, this process will eventually be phased out. While the co-oxidation process overcomes the environmental pollution and equipment corrosion of the chlorohydrin process, making it a relatively cleaner production process, its disadvantages include high requirements for raw material quality, a longer process time, larger investment scale, and profitability heavily influenced by the price of co-products.

[0004] Another relatively novel process is the HPPO method, a direct oxidation method using titanium silicate molecular sieves as catalysts and hydrogen peroxide as oxidant. The HPPO method produces only propylene oxide and water, exhibiting high product selectivity, few byproducts, and a simple, pollution-free process. However, this method suffers from problems such as short catalyst lifetime, high energy consumption, large solvent volume, and low H2O2 utilization. In recent years, the direct oxidation of propylene to propylene oxide has attracted increasing attention due to its simple reaction process. However, the low propylene conversion rate and low propylene oxide selectivity of this method remain to be addressed.

[0005] Meanwhile, existing propylene oxide catalysts have poor thermal stability, and most chemical reactions are exothermic. As the reaction time increases, the active components in the catalyst are prone to agglomeration, which seriously affects the catalytic performance of the catalyst. This not only affects the production efficiency of the plant, but may even lead to catalyst deactivation, forcing the plant to shut down and frequently replace the catalyst, which greatly increases the plant's production costs. Summary of the Invention

[0006] The purpose of this invention is to overcome the problem of poor thermal stability of catalysts in the prior art, and to provide a method for preparing supported catalysts using a microwave method, as well as the supported catalysts and their applications.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a supported catalyst using a microwave method, the method comprising the following steps:

[0008] (1) A solution containing an active component precursor is mixed with a dispersant to obtain solution B1; then, a solution containing an inorganic alkaline substance is used to adjust the pH of solution B1 to 3.8-8.5 to obtain solution B2; then, solution B2 is aged to obtain an impregnation solution with a pH of 6-10; wherein, the active component precursor is a noble metal precursor;

[0009] (2) The impregnation solution prepared in step (1) is impregnated with titanium silicon molecular sieve under the first microwave condition; then the solid-liquid mixture obtained by impregnation is dried and activated.

[0010] A second aspect of the present invention provides a supported catalyst prepared by the method described above.

[0011] A third aspect of the present invention provides a supported catalyst comprising a titanium-silicon molecular sieve and an active component supported on the titanium-silicon molecular sieve, wherein the active component comprises noble metals, and in any 100 nm × 100 nm region on the catalyst, the proportion of noble metal particles with a diameter of 2-6 nm to the total number of noble metal particles with a diameter of 1-10 nm is greater than 60%; the acid ratio of Brønsted acid to Lewis acid in the catalyst is 0.1-0.9.

[0012] The fourth aspect of this invention provides the application of the catalyst described above in the preparation of propylene oxide.

[0013] Through the above technical solution, the present invention achieves the following beneficial effects:

[0014] (1) The impregnation solution is prepared by the method of the present invention and impregnated under microwave conditions. Then the solid-liquid mixture obtained by impregnation is dried and activated. This not only increases the proportion of noble metals with a particle size of 2-6 nm in the catalyst, but also reduces the acid ratio of Brønsted acid to Lewis acid in the catalyst.

[0015] (2) The preferred method of the present invention can further increase the content of active components, the content of reduced active components and the hydroxyl density in the catalyst.

[0016] (3) The catalyst of the present invention has good heat resistance and stability. When used in the gas-phase epoxidation reaction of propylene, it can improve the conversion rate of propylene, the selectivity of propylene oxide and the space-time yield, and improve the service life of the catalyst, reduce the frequency of factory shutdown to replace the catalyst, and reduce the production cost of the factory. Attached Figure Description

[0017] Figure 1This is a transmission electron microscope image of the catalyst prepared in Example 1;

[0018] Figure 2 This is a transmission electron microscope (TEM) image of the catalyst prepared in Comparative Example 3. Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] The first aspect of this invention provides a method for preparing a supported catalyst using a microwave method, the method comprising the following steps:

[0021] (1) A solution containing an active component precursor is mixed with a dispersant to obtain solution B1; the pH of solution B1 is then adjusted to 3.8-8.5 (preferably 4.5-7) using a solution containing an inorganic alkaline substance to obtain solution B2; solution B2 is then aged to obtain an impregnation solution with a pH of 6-10 (preferably 6.5-8.5); wherein the active component precursor is a noble metal precursor;

[0022] (2) The impregnation solution prepared in step (1) is impregnated with titanium silicon molecular sieve under the first microwave condition; then the solid-liquid mixture obtained by impregnation is dried and activated.

[0023] In this invention, the pH value of solution B2 can be 3.8, 4, 5, 6, 7, 8, 8.5, or any range consisting of any two of the above values. The pH value of the impregnation solution can be 6, 7, 8, 9, 10, or any range consisting of any two of the above values.

[0024] According to the present invention, the impregnation method can be a commonly used impregnation method in the art, such as equal volume impregnation, excessive impregnation, etc., preferably, the impregnation method is excessive impregnation. More preferably, the first microwave conditions include: power of 10-70 kHz, temperature of 20-70°C (preferably 30-50°C), and time of 10-80 min.

[0025] According to the present invention, the active component in the active component precursor can be gold, silver, or platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, platinum). Preferably, the active component precursor includes an Au precursor and / or a Pd precursor; more preferably, it is an Au precursor. The active component precursor can be any substance capable of providing a noble metal element to the catalyst, such as a noble metal, a salt of a noble metal, or an oxide of a noble metal. The Au precursor can be at least one of HAuCl4, AuCl3, and Au(NO3)3; the Pd precursor can be at least one of Pd(NO3)2, PdCl2, and PdSO4.

[0026] According to the present invention, preferably, the concentration of the active component precursor solution, calculated as metal element, is 0.1-5 g / L.

[0027] According to the present invention, the dispersant is a ligand that has a weak complexing interaction with Au, wherein the cumulative stability constant of the complex formed by the ligand and Au is <2. Preferably, the dispersant comprises at least one selected from ethylenediamine, ethylene glycol, urea, disodium ethylenediaminetetraacetate, bipyridine, glycerol, N,N dimethylformamide, acetone, toluene, tannic acid, and cyclohexane.

[0028] According to the present invention, preferably, the amount of the active component precursor, calculated as metal element, is 0.005-1.5g per 100g of titanium silicate molecular sieve, and the amount of the dispersant is 0.002-0.8g. In this invention, the amount of the active component precursor, calculated as metal element, is 0.005g, 0.05g, 0.1g, 0.3g, 0.5g, 0.7g, 0.9g, 1.1g, 1.3g, 1.5g, or any two of the above values, relative to 100g of carrier; the amount of the dispersant can be 0.002g, 0.05g, 0.08g, 0.1g, 0.3g, 0.4g, 0.5g, 0.6g, 0.7g, 0.8g, or any two of the above values.

[0029] According to the present invention, preferably, the inorganic alkaline substance is selected from at least one of alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates, and ammonia water; preferably at least one of Na2CO3, K2CO3, Cs2CO3, NaHCO3, and KHCO3. The inventors of the present invention have further discovered that when a weak acid salt of an alkali metal is used as the alkaline substance, the particle size of the active component in the catalyst can be further reduced.

[0030] According to the present invention, preferably, the concentration of the inorganic alkaline substance solution is 0.0025-0.5 mol / L.

[0031] According to the present invention, the aging can be carried out using aging methods commonly used in catalyst preparation processes, as long as the components in the solution containing the active component precursor, dispersant, and alkaline substance are fully mixed and reacted. The aging temperature is not particularly limited and is typically carried out at room temperature. The aging time is sufficient to ensure that the pH value of solution B2 meets the aforementioned range; preferably, the aging time is 0.5-6 hours. In this invention, the room temperature is approximately 20°C. The aging can be carried out with stirring or by standing; typically, the aging is carried out with stirring.

[0032] According to the present invention, preferably, the titanium-silicon molar ratio of the titanium-silicon molecular sieve is 0.0001-0.1:1. The titanium-silicon molar ratio of the titanium-silicon molecular sieve can be 0.0001:1, 0.001:1, 0.005:1, 0.0056:1, 0.006:1, 0.01:1, 0.1:1, or any two of the above ranges.

[0033] According to the present invention, preferably, the total specific surface area of ​​the titanium-silicon molecular sieve is 180-650 m². 2 / g (for example, it can be 180m) 2 / g、280m 2 / g、380m 2 / g、450m 2 / g、480m 2 / g、530m 2 / g、580m 2 / g、650m 2 / g, and the range formed by any two of the above points, preferably 500-650m. 2 / g), the specific surface area of ​​the mesopores is 20-180m². 2 / g (for example, it can be 20m) 2 / g, 50m 2 / g、80m 2 / g, 100m 2 / g, 140m 2 / g, 160m 2 / g、170m 2 / g、180m 2 / g, and the range formed by any two of the above points), the specific surface area of ​​the micropores is 150-470m². 2 / g (for example, it can be 150m) 2 / g、200m 2 / g、280m 2 / g、300m 2 / g、320m 2 / g, 350m 2 / g、380m2 / g、450m 2 / g、470m 2 / g, and the range formed by any two of the above points).

[0034] According to the present invention, preferably, the total pore volume of the titanium-silicon molecular sieve is 0.2-0.75 cm³. 3 / g (for example, 0.2cm) 3 / g, 0.3cm 3 / g, 0.4cm 3 / g, 0.41cm 3 / g, 0.42cm 3 / g, 0.43cm 3 / g, 0.44cm 3 / g, 0.45cm 3 / g, 0.5cm 3 / g, 0.7cm 3 / g, and the range formed by any two of the above points), the pore volume of the mesopores is 0.15-0.45cm³. 3 / g (for example, 0.15cm) 3 / g, 0.2cm 3 / g, 0.25cm 3 / g, 0.26cm 3 / g, 0.27cm 3 / g, 0.28cm 3 / g, 0.3cm 3 / g, 0.4cm 3 / g, 0.45cm 3 / g, and the range formed by any two of the above points), the pore volume of the micropores is 0.1-0.3cm. 3 / g (for example, 0.1cm) 3 / g, 0.15cm 3 / g, 0.15cm 3 / g, 0.16cm 3 / g, 0.17cm 3 / g, 0.18cm 3 / g, 0.2cm 3 / g, 0.3cm 3 / g, and the range formed by any two of the above points).

[0035] According to the present invention, preferably, the average pore size of the titanium-silicon molecular sieve is 0.4-8.8 nm.

[0036] According to the present invention, preferably, the crystallinity of the titanium-silicon molecular sieve is 80-95% (e.g., 80%, 85%, 90%, 95%, and any two of the above), more preferably 90-95%.

[0037] According to the present invention, preferably, the total acid content of the titanium silicate molecular sieve is 0.01-3.5 mmol / g (e.g., 0.01 mmol / g, 0.1 mmol / g, 0.2 mmol / g, 0.3 mmol / g, 0.4 mmol / g, 0.42 mmol / g, 0.45 mmol / g, 0.5 mmol / g, 1 mmol / g, 2 mmol / g, 3 mmol / g, 3.5 mmol / g, and any two of the above ranges), and the Brønsted acid content is 0.0025-2.5 mmol / g (e.g., 0.0025 mmol / g, ...). The acid content of 0.1 mmol / g, 0.13 mmol / g, 0.15 mmol / g, 0.18 mmol / g, 0.2 mmol / g, 0.3 mmol / g, 0.4 mmol / g, 0.5 mmol / g, 1 mmol / g, 2 mmol / g, 2.5 mmol / g, and any two of the above ranges), and the acid ratio of Brønsted acid to Lewis acid is 0.25-2.25 (e.g., 0.25, 0.35, 0.45, 0.5, 0.55, 0.58, 0.65, 1, 1.5, 2, 2.25, and any two of the above ranges).

[0038] According to the present invention, preferably, the preparation method of the titanium-silicon molecular sieve includes: hydrothermal crystallization of an aqueous solution containing a silicon source, a titanium source and an alkali source under a second microwave condition; and then obtaining the titanium-silicon molecular sieve through solid-liquid separation and calcination.

[0039] According to the present invention, preferably, the molar ratio R1 of silicon source, titanium source, alkali source and water is 100:0.001-40:0.5-180:30-900, more preferably 100:0.1-10:20-120:100-800; wherein, the silicon source is calculated as SiO2 and the titanium source is calculated as TiO2. In the present invention, the molar ratio R1 of silicon source, titanium source, alkali source and water can also be 100:0.1-1:60-90:500-700.

[0040] According to the present invention, preferably, the silicon source is organosilicon, more preferably an alkyl silicate, more preferably, the alkyl group in the alkyl silicate is a C1-C6 alkyl group, and even more preferably, the silicon source includes at least one of tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate, and tetrapentyl silicate.

[0041] According to the present invention, preferably, the titanium source is an organotitanium, more preferably an alkyl titanate, more preferably, the alkyl group in the alkyl titanate is a C1-C6 alkyl group, and even more preferably, the titanium source includes at least one of tetrabutyl titanate, tetrapropyl titanate, tetraethyl titanate, and tetrapentyl titanate.

[0042] According to the present invention, preferably, the alkali source is an organic ammonium, more preferably an alkyl ammonium hydroxide, more preferably, the alkyl group in the alkyl ammonium hydroxide is a C1-C6 alkyl group, and even more preferably, the alkali source is at least one of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and tetrapentylammonium hydroxide.

[0043] According to the present invention, preferably, the second microwave conditions include: a power of 50-150 kHz (e.g., 50 kHz, 80 kHz, 100 kHz, 110 kHz, 120 kHz, 130 kHz, 140 kHz, 150 kHz, and any two of the above), a temperature of 100-180°C (e.g., 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, and any two of the above), and a time of 6-18 h (e.g., 6 h, 7 h, 8 h, 9 h, 10 h, 15 h, 18 h, and any two of the above). In the present invention, the pressure of the second microwave can be the autogenous pressure of the reaction system or an externally applied pressure. The pressure of the second microwave can be 500-900 kPa.

[0044] According to the present invention, preferably, the calcination conditions include: a temperature of 500-650°C and a time of 4-10 hours.

[0045] According to the present invention, preferably, the method further includes pre-impregnation under ultrasonic conditions before impregnation under the first microwave conditions, wherein the pre-impregnation time is 0.25-2 hours. The ultrasonic frequency can be a commonly used ultrasonic frequency in the art, such as 25 kHz-100 kHz.

[0046] According to the present invention, preferably, the drying conditions are such that the drying rate of the solid-liquid mixture is 0.03-1.05 g water / (cm³). 2 h·g carrier). In this invention, the drying rate is 0.03 g water / (cm³). 2 h·g carrier), 0.2g water / (cm³) 2 h·g carrier), 0.25g water / (cm³) 2 h·g carrier), 0.3g water / (cm³) 2 h·g carrier), 0.4g water / (cm³) 2 h·g carrier), 0.5g water / (cm³)2 h·g carrier), 0.6g water / (cm³) 2 h·g carrier), 0.7g water / (cm³) 2 h·g carrier), 0.8g water / (cm³) 2 h·g carrier), 0.9g water / (cm³) 2 h·g carrier), 1g water / (cm) 2 h·g carrier), 1.05g water / (cm³) 2 h·g carrier), and the range consisting of any two of the above points.

[0047] In this invention, the drying rate refers to the evaporation rate of water in a solid-liquid mixture, that is, the weight of water that evaporates from the solid-liquid mixture per unit time and unit area of ​​container, relative to a unit weight of carrier. The method for testing the drying rate is as follows: the mass of the carrier in the solid-liquid mixture is denoted as M; the solid-liquid mixture is placed in a glass petri dish with a bottom area of ​​S (in cm²). 2 Weigh the glass petri dish containing the solid-liquid mixture before drying, and record the mass as M1 (g). Then, dry the glass petri dish containing the solid-liquid mixture under a certain temperature and humidity environment until constant weight is reached. Stop drying at this point. Record the drying time as T (h). Weigh the glass petri dish containing the solid after drying, and record the mass as M2 (g). The drying rate of the solid-liquid mixture is calculated using the formula: (M1-M2) / (S×T×M).

[0048] The inventors of this invention have discovered that limiting the drying rate of a solid-liquid mixture obtained by contacting a solution containing an active component precursor and an inorganic alkaline substance with a support within the aforementioned range can not only increase the content of small-particle-size active components in the catalyst, increase active centers, and improve the catalytic performance of the catalyst, but also improve the utilization rate of raw materials, especially the utilization rate of precious metals, and reduce the production cost of the catalyst.

[0049] According to the present invention, the drying rate can be controlled by adjusting the drying temperature and the relative humidity of the drying environment. The inventors further discovered that drying at lower temperatures and lower relative humidity can further increase the content of small-particle-size active components in the catalyst, increase active centers, and improve the catalytic performance of the catalyst. Preferably, the drying conditions include: a temperature of 30-70°C and a relative humidity ≤60%. In this invention, drying is carried out at atmospheric pressure. The relative humidity can be 55%, 50%, 45%, 35%, 25%, 15%, 10%, 5%, or any combination of the above, for example, 5-20%.

[0050] In this invention, the relative humidity is measured using a thermo-hygrometer (model: Alarm-Hygrometer testo 608-H2). Specifically, in this system, relative humidity refers to the ratio of the partial pressure of water vapor in the air to the saturated vapor pressure at the same temperature during the drying process of the solid-liquid mixture.

[0051] According to the present invention, preferably, the fluctuation range of relative humidity during the drying process is ≤5%. The fluctuation range of relative humidity can be 5%, 4%, 3%, 2%, 1%, 0.5%, or a range consisting of any two of the above points, for example, 3-5%.

[0052] According to the present invention, preferably, the activation conditions include: a temperature of 150-350°C and a time greater than 2 hours, preferably 2.5-10 hours. The activation atmosphere can be an inert atmosphere or an oxygen-containing atmosphere, wherein the inert atmosphere can be provided by at least one of nitrogen, argon, helium, and neon, preferably nitrogen. The oxygen-containing atmosphere can be an air atmosphere.

[0053] A second aspect of the present invention provides a supported catalyst prepared by the method described above.

[0054] A third aspect of this invention provides a supported catalyst comprising a titanium-silicon molecular sieve and an active component supported on the titanium-silicon molecular sieve. The active component includes noble metals, and within any 100 nm × 100 nm region on the catalyst, the proportion of noble metal particles with a diameter of 2-6 nm to the total number of noble metal particles with a diameter of 1-10 nm is greater than 60%. The ratio of Brønsted acid (B acid) to Lewis acid (L acid) in the catalyst is 0.1-0.9. In the pyridine infrared spectrum, at 1540 cm⁻¹... -1 The integral area of ​​the characteristic peak at that point is the acidity of Brønsted acid, 1450 cm⁻¹. -1 The integral area of ​​the characteristic peak at that location is the amount of L acid.

[0055] According to the present invention, preferably, in any 100nm×100nm region on the catalyst, the proportion of noble metal particles with a diameter of 2-6nm to the total number of noble metal particles with a diameter of 1-10nm is 70-100%, more preferably 80-95%.

[0056] According to the present invention, preferably, the total acidity of the catalyst is 0.005-3 mmol / g, more preferably 0.4-0.65 mmol / g.

[0057] According to the present invention, preferably, the amount of Brønsted acid in the catalyst is 0.1-0.3 mmol / g, more preferably 0.12-0.21 mmol / g.

[0058] According to the present invention, preferably, the ratio of Brønsted acid to Lewis acid in the catalyst is 0.4-0.72.

[0059] According to the present invention, the valence state of the precious metal may include a reduced state and an oxidized state, wherein the weight ratio of the reduced state to the oxidized state may be 1:0.15-3, preferably 1:0.1-1.3. In this invention, the reduced state is represented by zero valence; for example, Au in its reduced state is represented as Au. 0 .

[0060] According to the present invention, preferably, when the noble metal is Au, Au comprises reduced Au and oxidized Au, wherein the weight ratio of reduced Au to oxidized Au is 1:0.15-3, preferably 1:0.1-1.3. More preferably, oxidized Au comprises Au 1+ and Au 3 + More preferably, the valence state of Au includes Au 0 Au 1+ and Au 3+ More preferably, Au 0 Au 1+ Au 3+ The weight ratio is 1:0.1-0.8:0.05-0.6, preferably 1:0.15-0.45:0.08-0.32.

[0061] According to the present invention, the precious metal may be gold, silver and platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, platinum), preferably, the precious metal is Au and / or Pd; more preferably, the active component is Au.

[0062] According to the present invention, preferably, the content of the active component, calculated as metal element, is 0.0075-1.5% by weight, based on the total weight of the catalyst.

[0063] According to the present invention, preferably, the ratio of the hydroxyl density Q4 / Q3 of the catalyst is 1.5-11, more preferably 3-6, and even more preferably 5-6, wherein Q4 / Q3 represents the hydroxyl density of the catalyst. 29 The ratio of peak areas of the peaks with chemical shifts near -113 ppm and -103 ppm in the Si MAS NMR spectrum.

[0064] The fourth aspect of this invention provides the application of the catalyst described above in the preparation of propylene oxide.

[0065] According to the present invention, preferably, the raw material gas used in the preparation of propylene oxide includes propylene, hydrogen and oxygen, and preferably, the volume ratio of propylene, hydrogen and oxygen is 1:0.1-5:0.1-2.

[0066] According to the present invention, preferably, the flow rate of the propylene is 1-700 mL / min.

[0067] According to the present invention, preferably, the temperature for preparing propylene oxide is 160-225°C.

[0068] Typically, heat treatment of catalysts at high temperatures accelerates the aggregation of active components. In this invention, to verify the heat resistance stability of the catalyst, it is heat-treated before the preparation of propylene oxide. The heat treatment conditions may include: a temperature of 250-370°C, a pressure of 0.2-0.6 MPa, and a time of 1-20 hours.

[0069] The present invention will be described in detail below through embodiments. In the following embodiments,

[0070] The method for testing the silicon-titanium molar ratio in molecular sieves is as follows: the content of titanium and silicon elements in molecular sieves is tested by combining inductively coupled plasma optical emission spectroscopy (ICP-OES) to obtain the overall silicon-titanium ratio of the molecular sieve.

[0071] The pore structure and specific surface area of ​​the molecular sieve were tested using a nitrogen physical adsorption instrument. The specific surface area of ​​the molecular sieve was analyzed using the BET (Brunauer-Emmett-Teller) method, and the pore size distribution was calculated using the BJH (Barrett-Joiner-Halenda) model.

[0072] The method for testing the crystallinity of molecular sieves is as follows: using a JCPDS standard card as the standard sample (whose crystallinity is known, denoted as X). s The XRD diffraction peaks of its crystalline phase in the 2θ = 5-35° range were measured, and several characteristic peaks were obtained, denoted as P. S1 -P Sn Its corresponding peak height is H S1 -H Sn The sum of the peak heights is denoted as ΣH. Si The full width at half maximum (FWHM) at 2θ = 24.5° is denoted as W. S XRD analysis revealed a characteristic peak at the position corresponding to the characteristic peak of S-1 in the molecular sieve being tested; this peak is denoted as P. i1 -P in Its corresponding peak height is H i1 -H in The sum of the peak heights is denoted as ΣH. ii The full width at half maximum (FWHM) at 2θ = 24.5° is denoted as W. i Crystallinity X of the molecular sieve sample to be tested i The calculation formula is as follows:

[0073] X i=X s *(W i *ΣH ii / (W S *ΣH Si )).

[0074] The method for testing the acidity of molecular sieves is as follows: pyridine infrared spectroscopy is used. The sample is placed in a vacuum cell and pretreated for 1 hour at 500℃ and a vacuum of 0.001 Pa. The temperature is then lowered to 200℃, and pyridine vapor is allowed to flow for 30 minutes. Excess unadsorbed pyridine vapor is then degassed at 200℃. Subsequently, the temperature is lowered to 100℃, and the desorption peak of pyridine at the corresponding acidic sites is collected. The peak value at 1540 cm⁻¹ in the corresponding spectrum is [missing value]. -1 The peak at 1450 cm⁻¹ is designated as the characteristic peak of Brønsted acid. -1 The peak is denoted as the L acid characteristic peak. Based on the spectrum, the amount of Brønsted acid and L acid is calculated by integrating the peak areas, and the ratio of Brønsted acid to L acid is obtained. The total acid amount is calculated as: Total acid amount = Brønsted acid amount + L acid amount.

[0075] Preparation Example 1

[0076] This preparation example illustrates the preparation method of titanium-silicon molecular sieves.

[0077] (1) Preparation of a solution containing silicon, titanium, and alkali sources: Weigh tetraethyl silicate and pour it into a beaker equipped with a magnetic stirrer, and keep stirring vigorously; then add tetrabutyl titanate dropwise to the beaker containing tetraethyl silicate, and keep stirring at a rate of 400-600 r / min for 30 min to mix them evenly. The transparent solution is recorded as A1. Add tetrapropylammonium hydroxide solution (the concentration of tetrapropylammonium hydroxide in the tetrapropylammonium hydroxide solution is 25% by weight) slowly to A1. It starts to become turbid and gradually turns into a milky white opaque suspension, which is recorded as A2. Increase the speed of the magnetic stirrer to 600 r / min, add a certain amount of distilled water to A2, and continue stirring for 60 min. The milky white opaque suspension turns into a colorless and transparent solution again, which is recorded as A3. In the mixture A3, the molar ratio R1 of tetraethyl silicate, tetrabutyl titanate, tetrapropylammonium hydroxide and water is 100:0.55:80:650.

[0078] (2) De-alcoholization treatment: The solution A3 is heated to 80℃ to distill off the ethanol and butanol produced by the hydrolysis of the titanium silica sol. The liquid level of solution A3 in the beaker drops. At this time, the same amount of distilled water is added to maintain the liquid level. After 4-8 hours of alcohol distillation treatment, the liquid level of solution A3 basically remains stable and no longer drops. The solution at this time is recorded as A4.

[0079] (3) Hydrothermal crystallization: Pour A4 into a microwave hydrothermal synthesizer, heat to 120℃, and perform microwave-assisted hydrothermal crystallization for 6 hours at a pressure of 700 kPa and a power of 120 kHz. After hydrothermal crystallization, allow the hydrothermal reactor to cool naturally to below 30℃, open the reactor, and remove the milky white suspension material, which is recorded as A5. Centrifuge A5 in a high-speed centrifuge, discard the supernatant, and leave the solid material, which is recorded as A6. Wash A6 with distilled water and repeat the centrifugation process 3-4 times until the pH of the supernatant is <8. Discard the supernatant, leaving the solid material A6. Treat A6 in an oven at 50℃ for 20 hours. At this point, the free water on A6 is basically removed, and A6 appears as irregular clumps, which is recorded as A7. Grind and pulverize A7, then calcine at 550℃ for more than 6 hours to remove the crystallization water and the template agent titanium silicon molecular sieve, obtaining titanium silicon molecular sieve.

[0080] The titanium-silicon molecular sieve obtained in Preparation Example 1 had a titanium-silicon ratio of 0.0055:1 and a total specific surface area of ​​513 m². 2 / g, the specific surface area of ​​the mesopores is 185m². 2 / g, the specific surface area of ​​the micropores is 328m². 2 / g; Total pore volume is 0.44cm³ 3 / g, the pore volume of the mesoporous structure is 0.28cm³. 3 / g, the pore volume of the micropores is 0.16cm³. 3 / g, with an average pore size of 1.25nm and a crystallinity of 95%; the total acidity of the titanium-silicon molecular sieve is 0.401mmol / g, the Brønsted acid content is 0.132mmol / g, and the ratio of Brønsted acid to Lewis acid is 0.49.

[0081] Preparation Example 2

[0082] The titanium-silicon molecular sieve was prepared according to the method of Preparation Example 1. The difference is that in step (3), a microwave hydrothermal synthesizer was not used in the hydrothermal crystallization process. Instead, a conventional high-pressure hydrothermal reactor was used for hydrothermal crystallization. The conditions for hydrothermal crystallization included: a temperature of 180°C, a pressure of 1500 kPa, and a time of 48 h.

[0083] The titanium-silicon molecular sieve obtained in Preparation Example 2 had a titanium-silicon ratio of 0.0053:1 and a total specific surface area of ​​467 m². 2 / g, the specific surface area of ​​the mesopores is 176m². 2 / g, the specific surface area of ​​the micropores is 291m². 2 / g; Total pore volume is 0.42cm³ 3 / g, the pore volume of the mesoporous structure is 0.26cm³. 3 / g, the pore volume of the micropores is 0.16cm³. 3 / g, with an average pore size of 1.37nm and a crystallinity of 88%; the total acidity of the titanium silicate molecular sieve is 0.453mmol / g, the Brønsted acid content is 0.164mmol / g, and the acidity ratio of Brønsted acid to Lewis acid is 0.57.

[0084] Example 1

[0085] (1) Preparation of impregnation solution containing active component precursor, dispersant and alkaline substance: Take 17.24 mL of HAuCl4 aqueous solution (the concentration of Au in HAuCl4 aqueous solution is 0.29 g / L), then add 0.033 g of ethylene glycol to HAuCl4 aqueous solution, and stir at a stirring rate of 400 r / min for 30 min to obtain solution B1. Keep the stirring rate of 400 r / min, and slowly add 0.1 mol / L KHCO3 aqueous solution to solution B1, with the dropping rate controlled at 1 mL / min, to obtain solution B2, the pH value of solution B2 is 6.73. Then continue to stir solution B2 for 3.5 h to obtain impregnation solution, the pH value of impregnation solution is 8.21.

[0086] (2) Impregnation of the carrier with impregnation solution: Take 5g of the titanium-silicon molecular sieve (TS-1) obtained in Example 1 and place it in a container with a bottom area of ​​80cm². 2 The impregnation solution prepared in step (1) was slowly injected into the glass petri dish, with the drop rate controlled at 2 mL / min. The resulting solid-liquid mixture was then subjected to ultrasonic pre-impregnation in an ultrasonic cleaner and microwave impregnation in a hydrothermal microwave synthesizer at room temperature. The ultrasonic impregnation time was 30 min, the microwave impregnation temperature was 30 °C, the microwave impregnation time was 20 min, and the microwave impregnation frequency was 20 kHz.

[0087] (3) Drying and activation: The shaken solid-liquid mixture was placed in a constant temperature and humidity oven with forced air for drying. The oven settings were: temperature 30℃, relative humidity 15%, and maximum relative humidity fluctuation of 3%. Drying was stopped after reaching constant weight, resulting in a blocky solid. The blocky solid was then ground to a particle size of less than 0.06 mm and activated in a muffle furnace at 200℃ for 2.5 h in air atmosphere to obtain the catalyst. The constant temperature and humidity oven settings resulted in a drying rate of 0.28 g water / (cm³). 2 h·g carrier).

[0088] Example 2-19

[0089] The catalyst was prepared according to the method of Example 1, except that the microwave impregnation temperature, time, and frequency, drying temperature, relative humidity and maximum fluctuation of drying, and drying rate are shown in Table 1.

[0090] Table 1

[0091]

[0092]

[0093] Note: " / " indicates that it is the same as in Example 1.

[0094] Example 20

[0095] The catalyst was prepared according to the method of Example 1, except that the KHCO3 aqueous solution was replaced with an equal concentration and volume of KOH aqueous solution. The pH values ​​of solution B2 and the impregnation solution were 8.21 and 7.09, respectively.

[0096] Example 21

[0097] The catalyst was prepared according to the method of Example 1, except that the dispersant was replaced with an equal amount of ethylenediamine.

[0098] Example 22

[0099] The catalyst was prepared according to the method of Example 1, except that the microwave impregnation temperature was 90°C.

[0100] Example 23

[0101] The catalyst was prepared according to the method in Example 1, except that the amount of KHCO3 aqueous solution used was increased so that the pH of solution B2 was 4.06. Solution B2 was then stirred for another 3 hours to obtain an impregnation solution with a pH of 6.17.

[0102] Example 24

[0103] The catalyst was prepared according to the method of Example 1, except that the titanium-silicon molecular sieve was replaced with the titanium-silicon molecular sieve of Preparation Example 2.

[0104] Comparative Example 1

[0105] The catalyst was prepared according to the method in Example 1, except that no KHCO3 aqueous solution was added to adjust the pH of solution B1, and the pH of the resulting impregnation solution was 2.35.

[0106] Comparative Example 2

[0107] The catalyst was prepared according to the method of Example 1, except that the solid-liquid mixture obtained in step (2) was separated into solid and liquid to obtain a solid, and then the solid was directly activated.

[0108] Comparative Example 3

[0109] The catalyst was prepared according to the method in Example 1, except that the KHCO3 aqueous solution was replaced with an aqueous solution of urea of ​​the same concentration.

[0110] Comparative Example 4

[0111] The catalyst was prepared according to the method of Comparative Example 1, except that step (2) did not include the microwave impregnation step.

[0112] Test case

[0113] (I) The catalysts prepared in the above examples and comparative examples were characterized by parameters, and the test results are shown in Table 2.

[0114] Transmission electron microscopy (TEM) images of the catalysts prepared in Example 1 and Comparative Example 3 are shown below. Figure 1 and Figure 2 As shown in the figure, it can be seen that... Figure 1 The catalyst has a high content of Au, which is evenly distributed, has a uniform size, and has a high proportion of small-diameter (2-6nm) Au nanoparticles. Figure 2 In the catalyst, the particle size of the active component Au is 5-10 nm, and Au agglomerates. In general, the Au nanoparticles in Comparative Example 3 are larger in size, the size difference between each nanoparticle is also large, and the overall dispersion on the support is very uneven, with obvious agglomeration.

[0115] The method for testing the content of the active component Au is: inductively coupled plasma optical emission spectroscopy (ICP-OES) to test the Au element content in the catalytic material.

[0116] The method for testing the ratio of Au particles with a diameter of 2-6 nm to the total number of noble metal particles with a diameter of 1-10 nm in the catalyst is as follows: TEM electron microscopy is used to measure and count the total number of Au particles with a diameter of 1-10 nm in any 100 nm × 100 nm region, denoted as N1; at the same time, the number of Au particles with a diameter of 2-6 nm in the same region is counted and denoted as N2; then the ratio of N2 / N1 is calculated.

[0117] The method for determining the form of Au in the catalyst is X-ray photoelectron spectroscopy (XPS). Based on the different electron binding energies of Au in different valence states, Au is obtained after peak separation. 3+ Au 1+ and Au 0 Au exists in different valence states and has a relative size.

[0118] The hydroxyl density of the catalyst was tested using silicon nuclear magnetic resonance (NMR) on a VARIAN VNMRS 400WB NMR spectrometer. The single-pulse method was employed, with (CH3)3Si(CH2)3SO3Na as the chemical shift reference, and a rotation rate of 3 kHz and a cycle delay of 60 s, at a frequency of 79.43 MHz. 29 Si MAS nuclear magnetic resonance spectroscopy measurements. The peak areas near -113 ppm and -103 ppm in the corresponding spectra represent the relative contents of the silicon framework structures Q4:Si(OSi)4 and Q3:Si(OSi)3OH in the molecular sieve, respectively. The ratio Q4 / Q3 represents the relative content of silanol groups in the molecular sieve. The larger the Q4 / Q3 ratio, the lower the hydroxyl content.

[0119] The acidity of the catalyst was tested using pyridine infrared spectroscopy. The sample was placed in a vacuum cell and pretreated for 1 hour at 500℃ and 0.001 Pa. The temperature was then lowered to 200℃, and pyridine vapor was allowed to flow for 30 minutes. Excess unadsorbed pyridine vapor was then degassed at 200℃. Subsequently, the temperature was lowered to 100℃, and the desorption peak of pyridine at the corresponding acidic sites was collected. The peak value at 1540 cm⁻¹ in the corresponding spectrum was obtained. -1 The peak at 1450 cm⁻¹ is designated as the characteristic peak of Brønsted acid. -1 The peak is denoted as the L acid characteristic peak. Based on the spectrum, the amount of Brønsted acid and L acid is calculated by integrating the peak areas, and the ratio of Brønsted acid to L acid is obtained. The total acid amount is calculated as: Total acid amount = Brønsted acid amount + L acid amount.

[0120] Table 2

[0121]

[0122] (II) Test the performance of the catalysts prepared in the above examples and comparative examples in the preparation of propylene oxide.

[0123] Weigh 0.1 g of catalyst and load it into the middle of a fixed-bed reactor, with both ends of the catalyst filled with quartz sand. Then, purge the reactor with nitrogen gas at a flow rate of 14 ml / min. Set the temperature program to increase from room temperature to 350°C at a rate of 1°C / min, and set the reaction pressure to 0.5 MPa. Perform heat treatment on the catalyst for 10 hours. Then, cool the reactor to 170°C, set the reaction pressure to 0.1 MPa, and introduce gases in a volume ratio of propylene, hydrogen, oxygen, and nitrogen of 1:1:1:7 to begin the direct propylene gas-phase epoxidation reaction. The propylene flow rate is set to 2 ml / min. The gaseous components such as hydrogen, oxygen, nitrogen, carbon monoxide, carbon dioxide, and methane in the reaction process were analyzed using an Agilent 7890B gas chromatograph equipped with a TCD detector. Organic compounds such as propylene, propane, propionaldehyde, acrolein, acetone, acetaldehyde, and propylene oxide were analyzed using an Agilent 7890B gas chromatograph equipped with an FID detector. Based on the detection results, the propylene conversion rate, propylene oxide selectivity, propionaldehyde selectivity, and acetone selectivity were calculated. The test results for propylene conversion rate, propylene oxide selectivity, propane selectivity, and acrolein selectivity after 15 hours of reaction are shown in Table 3.

[0124] propylene conversion (C) C3H6 = (Amount of C3 product + 2 / 3 amount of C2 product + 1 / 3 amount of C1 product) / Amount of propylene in the feed gas;

[0125] propylene oxide selectivity (S PO = Amount of propylene oxide in the product / (Amount of C3 product + 2 / 3 of C2 product + 1 / 3 of C1 product);

[0126] Propane selectivity (S) C3H8 = Amount of propane in the product / (Amount of C3 product + 2 / 3 of C2 product + 1 / 3 of C1 product);

[0127] Propionaldehyde selectivity (S) CH3CH2CHO = Amount of propionaldehyde in the product / (Amount of C3 product + 2 / 3 Amount of C2 product + 1 / 3 Amount of C1 product);

[0128] Hydrogen utilization rate (Y) H2 = Amount of propylene oxide in the product / (Amount of hydrogen in the feed gas - Amount of hydrogen in the product);

[0129] PO air-time yield = propylene conversion (C C3H6 )*Propylene oxide selectivity (S PO *Airspeed (GHSV).

[0130] Table 3

[0131]

[0132]

[0133] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing supported catalysts using a microwave method, characterized in that, The method includes the following steps: (1) A solution containing an active component precursor is mixed with a dispersant to obtain solution B1; then the pH of solution B1 is adjusted to 3.8-8.5 using a solution containing an inorganic alkaline substance to obtain solution B2; then solution B2 is aged to obtain an impregnation solution with a pH of 6-10; wherein, the active component precursor is a noble metal precursor; (2) The impregnation solution prepared in step (1) is impregnated with titanium silicon molecular sieve under the first microwave condition; then the solid-liquid mixture obtained by impregnation is dried and activated.

2. The method according to claim 1, wherein, The first microwave conditions include: power of 10-70 kHz, temperature of 20-70 °C, and time of 10-80 min.

3. The method according to claim 1 or 2, wherein, The active component precursor is an Au precursor; And / or, the concentration of the active component precursor solution, calculated as metal element, is 0.1-5 g / L; And / or, the dispersant comprises at least one selected from ethylenediamine, ethylene glycol, urea, disodium ethylenediaminetetraacetate, bipyridine, glycerol, N,N dimethylformamide, acetone, toluene, tannic acid, and cyclohexane; And / or, relative to every 100g of titanium silicate molecular sieve, the amount of the active component precursor, calculated as metal element, is 0.005-1.5g, and the amount of dispersant is 0.002-0.8g.

4. The method according to claims 1-3, wherein, The inorganic alkaline substance is selected from at least one of alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates, and ammonia water; preferably at least one of Na2CO3, K2CO3, Cs2CO3, NaHCO3, and KHCO3. And / or, the concentration of the inorganic alkaline solution is 0.0025-0.5 mol / L; And / or, the aging time is 0.5-6 hours.

5. The method according to any one of claims 1-4, wherein, The titanium-silicon molecular sieve has a titanium-silicon molar ratio of 0.0001-0.1:1 and a total specific surface area of ​​180-650 m². 2 / g, the specific surface area of ​​mesopores is 20-180m² 2 / g, the specific surface area of ​​the micropores is 150-470m². 2 / g, total pore volume is 0.2-0.75cm³ 3 / g, the pore volume of the mesoporous tissue is 0.15-0.45cm³. 3 / g, the pore volume of the micropores is 0.1-0.3cm³. 3 / g, with an average pore size of 0.4-8.8nm and a crystallinity of 80-95%; And / or, the total acid content of the titanium silicate molecular sieve is 0.01-3.5 mmol / g, the Brønsted acid content is 0.0025-2.5 mmol / g, and the acid content ratio of Brønsted acid to Lewis acid is 0.25-2.25; Preferably, the preparation method of the titanium-silicon molecular sieve includes: hydrothermal crystallization of an aqueous solution containing a silicon source, a titanium source, and an alkali source under a second microwave condition; followed by solid-liquid separation and calcination to obtain the titanium-silicon molecular sieve; More preferably, the molar ratio of silicon source, titanium source, alkali source and water, R1, is 100:0.001-40:0.5-180:30-900, preferably 100:0.1-10:20-120:100-800; wherein the silicon source is SiO2 and the titanium source is TiO2. More preferably, the silicon source is organosilicon, preferably an alkyl silicate, more preferably, the alkyl group in the alkyl silicate is a C1-C6 alkyl group, and even more preferably, the silicon source includes at least one of tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate, and tetrapentyl silicate. More preferably, the titanium source is organic titanium, preferably an alkyl titanate, more preferably, the alkyl group in the alkyl titanate is a C1-C6 alkyl group, and even more preferably, the titanium source includes at least one of tetrabutyl titanate, tetrapropyl titanate, tetraethyl titanate, and tetrapentyl titanate. More preferably, the alkali source is an organic ammonium, preferably an alkyl ammonium hydroxide, more preferably, the alkyl group in the alkyl ammonium hydroxide is a C1-C6 alkyl group, and even more preferably, the alkali source is at least one of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and tetrapentylammonium hydroxide; More preferably, the second microwave conditions include: a power of 50-150 kHz, a temperature of 100-180 °C, and a time of 6-18 h; More preferably, the calcination conditions include: a temperature of 500-650°C and a time of 4-10 hours.

6. The method according to any one of claims 1-5, wherein, The method further includes pre-impregnation under ultrasonic conditions before impregnation under the first microwave conditions, wherein the pre-impregnation time is 0.25-2 hours.

7. The method according to claims 1-6, wherein, The drying conditions are such that the drying rate of the solid-liquid mixture is 0.03-1.05 g water / (cm³). 2 h·g carrier); Preferably, the drying conditions include: a temperature of 30-70°C and a relative humidity of ≤60%. Preferably, the relative humidity fluctuation during the drying process is ≤5%.

8. The method according to any one of claims 1-7, wherein, The activation conditions include: a temperature of 150-350℃ and a time of more than 2 hours, preferably 2.5-10 hours.

9. The supported catalyst prepared by the method according to any one of claims 1-8.

10. A supported catalyst, characterized in that, The catalyst comprises a titanium-silicon molecular sieve and an active component supported on the titanium-silicon molecular sieve. The active component includes noble metals. In any 100 nm × 100 nm region on the catalyst, the proportion of noble metal particles with a diameter of 2-6 nm to the total number of noble metal particles with a diameter of 1-10 nm is greater than 60%. The acid ratio of Brønsted acid to Lewis acid in the catalyst is 0.1-0.

9.

11. The catalyst according to claim 10, wherein, The active component is Au; And / or, the content of the active component, based on the total weight of the catalyst and calculated as metal elements, is 0.0075-1.5% by weight; And / or, the total acidity of the catalyst is 0.005-3 mmol / g; And / or, the ratio of the hydroxyl density Q4 / Q3 of the catalyst is 1.5-11, where Q4 / Q3 represents the hydroxyl density of the catalyst. 29 The ratio of peak areas of peaks with chemical shifts near -113 ppm and -103 ppm in SiMAS NMR spectra.

12. The use of the catalyst according to any one of claims 9-11 in the preparation of propylene oxide.

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