Preparation of supported catalysts using basic gases and use thereof

Abstract

The present application relates to the technical field of catalyst, and discloses a method for preparing a supported catalyst by using alkaline gas, the supported catalyst and application thereof, which comprises the following steps: (1) contacting a solution containing active component precursor and inorganic alkaline substance with a carrier to obtain a solid-liquid mixture; the active component precursor comprises a noble metal precursor; (2) drying the solid-liquid mixture in the presence of a first alkaline substance to obtain a solid product; (3) then activating the solid product in the presence of a second alkaline substance; wherein the first alkaline substance and the second alkaline substance are independently nitrogen-containing alkaline substances. The catalyst has a low acid amount and a B acid / L acid acid amount ratio, and when used in a propylene epoxidation reaction, can significantly reduce the selectivity of by-products propyl aldehyde and acetone, while obtaining a higher propylene conversion rate and propylene oxide selectivity.

Description

Technical Field

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

[0002] In 1860, Frenchman B. Auschel first synthesized propylene oxide in a laboratory. In 1931, Union Carbide in the United States built the world's first plant to produce propylene oxide using the chlorohydrin process. In the 1960s, Spain and the United States developed the indirect oxidation process. Currently, both methods are used in production, each accounting for 50%, but the latter is showing a trend of catching up.

[0003] Subsequently, researchers developed a direct oxygen oxidation method, which directly oxidizes propylene, hydrogen, and oxygen into propylene oxide in the presence of a catalyst and diluent gas N2. They also conducted research on bifunctional catalysts supported by noble metals. The above reaction process is simple, economical, and environmentally friendly, offering significant advantages over existing processes. However, it also presents significant challenges. For example, the high acid content and high ratio of Brønsted (B) to Lewis (L) acids in the bifunctional catalysts result in high levels of byproducts—propionaldehyde and acetone. Since the boiling points of propionaldehyde and acetone are close to those of propylene oxide, they are difficult to remove from the product, significantly reducing the purity of propylene oxide. Furthermore, the high content of byproducts such as propionaldehyde and acetone increases the amount of adsorbent and extractant required for the separation and purification of byproducts and the main propylene oxide product, increasing the energy consumption of subsequent separation processes (the amount of adsorbent used is reduced through adsorption-desorption). Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of high acid content in existing catalysts and high acid ratio of Brønsted acid to Lewis acid. The existence of the above problems will lead to a high proportion of propionaldehyde and acetone, which are byproducts of acid catalysis, affecting the main reaction and reducing the selectivity of the target product. Therefore, this invention provides a method for preparing a supported catalyst using alkaline gas and the application of the supported catalyst.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a supported catalyst using an alkaline gas, the method comprising the following steps:

[0006] (1) A solid-liquid mixture is obtained by contacting an aqueous solution of an active component precursor, an aqueous solution of an inorganic alkaline substance, and a carrier; the active component precursor includes a noble metal precursor;

[0007] (2) The solid-liquid mixture is then dried in the presence of the first alkaline substance to obtain a solid product.

[0008] (3) The solid product is then activated in the presence of a second alkaline substance;

[0009] The first alkaline substance and the second alkaline substance are each independently nitrogen-containing alkaline substances.

[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 support and an active component supported on the support, wherein the active component comprises a noble metal, the total acidity of the catalyst is less than 0.61 mmol / g, the ratio of Brønsted acid to Lewis acid is less than 1.1, and 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.

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

[0013] The present invention has achieved the following beneficial effects:

[0014] (1) The present invention reduces the amount of acid in the catalyst and the acid ratio of B acid / L acid by drying and activating a solid-liquid mixture containing a support, an active component precursor and an inorganic alkaline substance in the presence of a nitrogen-containing alkaline substance in sequence, thereby increasing the loading of the active component, improving the utilization rate of precious metals and reducing the synthesis cost of the catalyst.

[0015] (2) The catalyst of the present invention has a low acid content and a B acid / L acid ratio. When used in the propylene epoxidation reaction, it can significantly reduce the selectivity of the by-products propionaldehyde and acetone, greatly simplify the separation and purification process of propylene oxide products, reduce the amount of adsorbent and extractant used in the separation process and the energy consumption of product separation; at the same time, it can obtain a high propylene conversion rate and propylene oxide selectivity.

[0016] (3) In a preferred embodiment, the catalyst of the present invention has a high proportion of active components with a particle size of 2-5 nm and a high proportion of reduced active components, which can further reduce the selectivity of by-products propionaldehyde and acetone, and improve the conversion rate of propylene and the selectivity of propylene oxide.

[0017] (4) In preferred embodiment, the catalyst of the present invention can effectively prevent the agglomeration of active components in the catalyst during the catalytic reaction; prevent the conversion rate of raw materials and the selectivity of products from decreasing significantly with the increase of catalytic reaction time; and significantly improve the heat resistance stability of the catalyst. Attached Figure Description

[0018] Figure 1 This is a transmission electron microscope image of the catalyst prepared in Example 1;

[0019] Figure 2 This is a transmission electron microscope (TEM) image of the catalyst prepared in Comparative Example 3. Detailed Implementation

[0020] 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.

[0021] The first aspect of this invention provides a method for preparing a supported catalyst using an alkaline gas, the method comprising the following steps:

[0022] (1) A solid-liquid mixture is obtained by contacting an aqueous solution of an active component precursor, an aqueous solution of an inorganic alkaline substance, and a carrier; the active component precursor includes a noble metal precursor;

[0023] (2) The solid-liquid mixture is then dried in the presence of the first alkaline substance to obtain a solid product.

[0024] (3) The solid product is then activated in the presence of a second alkaline substance;

[0025] The first alkaline substance and the second alkaline substance are each independently nitrogen-containing alkaline substances.

[0026] According to the present invention, preferably, the nitrogen-containing alkaline substance includes ammonia and / or a nitrogen-containing organic amine. The nitrogen-containing organic amine may have 1-5 carbon atoms and 1-3 nitrogen atoms; the nitrogen-containing organic amine may be a dialkylamine and / or an alkyldiamine. More preferably, the nitrogen-containing organic amine includes dimethylamine and / or ethylenediamine.

[0027] According to the present invention, the precious metal may be gold, silver and platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, platinum), and preferably, the active component precursor is an Au precursor.

[0028] According to the present invention, preferably, the carrier comprises at least one of carbon nanotubes, titanium-silicon molecular sieves, silicon-aluminum molecular sieves, all-silicon molecular sieves, phosphorus-aluminum molecular sieves, tin-silicon molecular sieves, carbon black, activated carbon, silicon dioxide, aluminum oxide, cerium oxide, zeolite, resin, cordierite, hydroxyapatite, polymers and alkaline earth metal carbonates; preferably carbon nanotubes and / or titanium-silicon molecular sieves.

[0029] In this invention, the support can be purchased or prepared using existing methods. There are no particular limitations on the performance parameters of the support. The inventors further discovered that, using the same support and the drying method of this invention (controlling the drying rate of the solid-liquid mixture within a specific range), the proportion of active components with a particle size of 2-5 nm in the catalyst can be significantly increased. For example, when using titanium-silicon molecular sieves as a support, compared to conventional drying methods, the drying method of this invention can increase the proportion of active components with a particle size of 2-5 nm. Similarly, the drying method of this invention has similar advantages when used with supports such as carbon nanotubes.

[0030] According to a specific embodiment of the present invention, the preparation method of the carrier may include: removing an aqueous solution containing a silicon source, a titanium source, and an alkali source, followed by hydrothermal crystallization, solid-liquid separation, and calcination in sequence; wherein the molar ratio R1 of the silicon source, titanium source, alkali source, and water is 100:0.002-60:1-200:50-1000; 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 tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate, and tetraethyl or tetrabutyl silicate. The titanium source is at least one of the following: pentyl esters; the titanium source is an organotitanium, 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; the alkali source is an organic alkali, 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 includes at least one of tetrapropyl ammonium hydroxide, tetraethyl ammonium hydroxide, tetrabutyl ammonium hydroxide, and tetrapentyl ammonium hydroxide. In this invention, the molar ratio R1 of the silicon source, titanium source, alkali source, and water can also be 100:0.2-8:50-120:300-600.

[0031] According to a specific embodiment of the present invention, the method for preparing the carrier may include the following steps:

[0032] (1) Preparation of a solution containing silicon, titanium, and alkali sources: Weigh tetraethyl silicate and pour it into a beaker equipped with a magnetic stir bar, 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 20-50 min to mix them evenly. The transparent solution is recorded as A1. Tetrapropylammonium hydroxide is slowly added to A1. It initially becomes turbid and gradually turns into a milky white opaque suspension, which is recorded as A2. Increase the speed of the magnetic stir bar to 600-800 r / min, add a certain amount of distilled water to A2, and continue stirring for 40-100 min. The milky white opaque suspension then turns into a colorless and transparent solution again, which is recorded as A3. The molar ratio R1 of tetraethyl silicate, tetrabutyl titanate, tetrapropylammonium hydroxide, and water is 100:0.1-4:40-120:400-600.

[0033] (2) De-alcoholization treatment: Heat solution A3 to 70-110℃ to distill off the ethanol and butanol produced by the hydrolysis of titanium silica sol. The liquid level of solution A3 in the beaker will drop. At this time, add the same amount of distilled water to keep the liquid level unchanged. After 2-10 hours of alcohol distillation treatment, the liquid level of solution A3 will remain basically stable and no longer drop. The solution at this time is recorded as A4.

[0034] (3) Hydrothermal crystallization: Pour A4 into a high-pressure hydrothermal reactor and heat it to 140-200℃ for hydrothermal crystallization for 10-80h. Then carry out solid-liquid separation, washing, drying and calcination. The calcination conditions include a temperature of 550-650℃ and a time of 4-10h.

[0035] According to the present invention, preferably, the amount of the active component precursor, calculated as metal element, is 0.005-2.5g per 100g of carrier.

[0036] In this invention, the solid-liquid mixture can be obtained by either a deposition-precipitation method or an impregnation method. The deposition-precipitation method involves first mixing an aqueous solution of the active component precursor with a carrier, and then adding an aqueous solution of an inorganic alkaline substance dropwise to obtain the solid-liquid mixture. The impregnation method involves first mixing an aqueous solution of the active component precursor with an aqueous solution of an inorganic alkaline substance to obtain an impregnation solution, and then contacting the impregnation solution with a carrier to obtain the solid-liquid mixture.

[0037] According to the present invention, preferably, the solid-liquid mixture is obtained by first mixing an aqueous solution of an active component precursor with an aqueous solution of an inorganic alkaline substance to obtain a solution containing an active component precursor and an inorganic alkaline substance, and then contacting it with a carrier to obtain a solid-liquid mixture.

[0038] According to the present invention, preferably, the solution containing the active component precursor and the inorganic alkaline substance further includes a dispersant.

[0039] According to the present invention, preferably, the solution containing the active component precursor, dispersant and inorganic alkaline substance is obtained by: mixing the aqueous solution of the active component precursor with the dispersant to obtain solution B1; then adjusting the pH value of solution B1 to 5.5-7.5 using the aqueous solution of inorganic alkaline substance to obtain solution B2; and then aging solution B2 under aging conditions so that the pH value of solution B2 is 7.5-9.8.

[0040] According to the present invention, preferably, the amount of dispersant used is 0.01-1.5g relative to 100g of carrier. In the present invention, the amount of the active component precursor, calculated as metal element, relative to 100g of carrier is 0.01g, 0.1g, 0.3g, 0.5g, 0.7g, 0.9g, 1.1g, 1.3g, 1.5g, or any two of the above ranges; the amount of dispersant used can be 0.01g, 0.05g, 0.5g, 0.1g, 0.5g, 1g, 1.2g, 1.5g, or any two of the above ranges.

[0041] 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.

[0042] According to the present invention, preferably, the concentration of the aqueous solution of the inorganic alkaline substance is 0.005-0.25 mol / L.

[0043] 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.

[0044] 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 1-8 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.

[0045] According to the present invention, the contact method can be any method commonly used in the art to load the active component onto the support, such as impregnation or deposition / precipitation. Whether using impregnation or deposition / precipitation, the method of the present invention can effectively reduce the acid content and the Brønsted acid / Low acid ratio in the catalyst, thereby increasing the loading of the active component. Compared to deposition / precipitation, the method of the present invention achieves better results when using impregnation. More preferably, the contact method includes ultrasonic impregnation and oscillatory impregnation; wherein the ultrasonic impregnation time is 20-80 min; the oscillatory impregnation is performed under light-shielding conditions, and the oscillatory impregnation time is 10-30 h. The oscillation frequency can be 50-1200 r / min; 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 0.06-1.35 g water / (cm³). 2 h·g carrier). In this invention, the drying rate is 0.06 g water / (cm³). 2 h·g carrier), 0.2g 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), 1.1g water / (cm³) 2 h·g carrier), 1.2g water / (cm³) 2 h·g carrier), 1.3g water / (cm³) 2 h·g carrier), 1.35g water / (cm³) 2 The drying rate is 0.5-1 g water / (cm³) (h·g carrier), and more preferably, the range of any two of the above points. 2 h·g carrier); more preferably 0.5-0.6g water / (cm³) 2 h·g carrier).

[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 further discovered that limiting the drying rate of the solid-liquid mixture obtained by contacting a solution containing an active component precursor and an inorganic alkaline substance with a support within the above-mentioned range can not only increase the content of active components with a particle size of 2-5 nm in the catalyst, increase the number of 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 active components with a particle size of 2-5 nm in the catalyst, increase the number of active centers, and improve the catalytic performance of the catalyst. Preferably, the drying conditions include: a temperature of 25-75°C and a relative humidity ≤55%. More preferably, the fluctuation range of the relative humidity during the drying process is ≤5%. The relative humidity can be 55%, 50%, 45%, 35%, 25%, 15%, 10%, 5%, or any combination of the above, for example, 5-20%. The fluctuation range of the relative humidity can be 5%, 4%, 3%, 2%, 1%, 0.5%, or any combination of the above, for example, 2-3%.

[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, under drying conditions, when the first alkaline substance is a gas, the amount of the first alkaline substance used increases the vacuum degree of the drying system by 5-100 kPa after the first alkaline substance is introduced.

[0052] In this invention, before drying, the system is first brought to a low vacuum level, and then a first alkaline substance (gas) is introduced into the system to increase the vacuum level. The amount of the first alkaline substance (gas) is controlled by adjusting the vacuum level before and after the introduction of the first alkaline substance (gas). For example, before introducing the first alkaline substance (gas), the vacuum level of the system is set to 1-50 kPa, and after introducing the first alkaline substance (gas), the vacuum level of the system increases to 6-150 kPa.

[0053] According to the present invention, preferably, under dry conditions, when the first alkaline substance is a liquid, the amount of the first alkaline substance is 0.1-2.5 g relative to each gram of solid-liquid mixture.

[0054] According to the present invention, preferably, the activation conditions include: a temperature of 150-350°C and a time of more than 2 hours, preferably 2.5-10 hours.

[0055] According to the present invention, preferably, under activation conditions, when the second alkaline substance is a gas, the amount of the second alkaline substance used increases the vacuum degree of the drying system by 10-150 kPa after the second alkaline substance is introduced. Similarly, the method of controlling the vacuum degree of the system during the activation process is similar to that during the drying process. For example, before the second alkaline substance (gas) is introduced, the vacuum degree of the system is set to 1-50 kPa, and after the second alkaline substance (gas) is introduced, the vacuum degree of the system increases to 11-200 kPa.

[0056] According to the present invention, preferably, under activation conditions, when the second alkaline substance is a liquid, the amount of the first alkaline substance is 0.1-2.5 g relative to each gram of dried product.

[0057] A second aspect of the present invention provides a supported catalyst prepared by the method described above.

[0058] A third aspect of the present invention provides a supported catalyst comprising a support and an active component supported on the support, wherein the active component comprises a noble metal, the total acidity of the catalyst is less than 0.61 mmol / g, and the acidity ratio of Brønsted acid to Lewis acid (denoted as Brønsted acid / L-acid) is less than 1.1, wherein, 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.

[0059] Preferably, the total acidity of the catalyst is less than 0.52 mmol / g, more preferably 0.3-0.42 mmol / g.

[0060] Preferably, the ratio of the amount of Brønsted acid to L-acid in the catalyst is less than 0.9, more preferably 0.55-0.7.

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

[0062] According to the present invention, preferably, the content of the active component, calculated as metal element, is 0.005-1.25% by weight, more preferably 0.08-0.1% by weight, based on the total weight of the catalyst.

[0063] According to the present invention, preferably, the carrier comprises at least one of carbon nanotubes, titanium-silicon molecular sieves, silicon-aluminum molecular sieves, all-silicon molecular sieves, phosphorus-aluminum molecular sieves, tin-silicon molecular sieves, carbon black, activated carbon, silicon dioxide, aluminum oxide, cerium oxide, zeolite, resin, cordierite, hydroxyapatite, polymers and alkaline earth metal carbonates; preferably carbon nanotubes and / or titanium-silicon molecular sieves.

[0064] According to the present invention, preferably, the ratio of the hydroxyl density Q4 / Q3 of the catalyst is 3-12, wherein 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 the Si MAS NMR spectrum. More preferably, the ratio of the hydroxyl density Q4 / Q3 of the catalyst is 4-7, and even more preferably 4.7-6.5.

[0065] According to the present invention, preferably, within any 100nm × 100nm region on the catalyst, the proportion of noble metal particles with a diameter of 2-5nm to the total number of noble metal particles with a diameter of 1-10nm is greater than 65%. Limiting the proportion of noble metal particles with a diameter of 2-5nm within the above range can further improve the conversion rate of propylene, the selectivity of propylene oxide, and the utilization rate and space-time yield of hydrogen. More preferably, within any 100nm × 100nm region on the catalyst, the proportion of noble metal particles with a diameter of 2-5nm to the total number of noble metal particles with a diameter of 1-10nm is ≥80% (e.g., 80-100%), and more preferably ≥90%.

[0066] 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 is 1:0.1-2, preferably 1:0.1-1.2, and more preferably 1:0.1-0.3. In this invention, the reduced state is represented by zero valence; for example, Au in its reduced state is represented as Au. 0 .

[0067] According to the present invention, preferably, when the noble metal is Au, Au includes reduced Au and oxidized Au, wherein the weight ratio of reduced Au to oxidized Au is 1:0.1-2, preferably 1:0.1-1.2, and more preferably 1:0.1-0.3. More preferably, the oxidized Au includes 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 1:0.15-0.7:0.05-0.45, preferably 1:0.19-0.42:0.06-0.3.

[0068] The fourth aspect of this invention provides the application of the catalyst described above in the preparation of propylene oxide.

[0069] 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.

[0070] According to the present invention, preferably, the flow rate of the propylene is 1-700 mL / min.

[0071] According to the present invention, preferably, the temperature for preparing propylene oxide is 160-225°C.

[0072] 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.

[0073] The present invention will be described in detail below through embodiments. In the following embodiments,

[0074] The method for testing the titanium-silicon molar ratio parameter of molecular sieves is as follows: Inductively coupled plasma optical emission spectroscopy (ICP-OES) is used to test the content of titanium and silicon elements in the molecular sieves, thereby obtaining the overall titanium-silicon ratio;

[0075] 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.

[0076] Preparation Example 1

[0077] This preparation example illustrates the preparation method of titanium-silicon molecular sieves.

[0078] (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 initially becomes turbid and gradually turns into a milky white opaque suspension, which is recorded as A2. Increase the speed of the magnetic stirrer to 600-800 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 100:0.6:75:500.

[0079] (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.

[0080] (3) Hydrothermal crystallization: Pour A4 into a high-pressure hydrothermal reactor and heat to 172℃ for 60 hours of hydrothermal crystallization. After hydrothermal crystallization, allow the reactor to cool naturally to below 40℃, 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, discard the supernatant, and leave the solid material A6. Treat A6 in an oven at 50℃ for 20 hours. At this time, 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, thus obtaining titanium silicon molecular sieve.

[0081] The titanium-silicon molecular sieve obtained in Preparation Example 1 had a titanium-silicon ratio of 0.006:1 and a total specific surface area of ​​438 m². 2 / g, total pore volume is 0.39cm³ 3 / g.

[0082] Example 1

[0083] (1-1) 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. Maintaining a stirring rate of 400 r / min, slowly add 0.1 mol / L KHCO3 aqueous solution to solution B1, with a dropping rate controlled at 1 mL / min, to obtain solution B2, with a pH of 6.68. Continue stirring solution B2 for 3.5 h to obtain impregnation solution with a pH of 8.16.

[0084] (1-2) 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 impregnation in an ultrasonic cleaner and oscillation impregnation on an oscillator at room temperature. The ultrasonic impregnation time was 30 min, and the oscillation impregnation time was 24 h. The oscillation frequency was 100 r / min, and the solid-liquid mixture was shielded from light during the oscillation.

[0085] (2) 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%, maximum relative humidity fluctuation of 3%, vacuum of 2 kPa before drying, followed by ammonia gas introduction to a vacuum of 70 kPa; drying was stopped after reaching constant weight, resulting in blocky solids, which were then ground to a particle size of less than 0.06 mm. The oven settings resulted in a drying rate of 0.562 g water / (cm³). 2 h·g carrier).

[0086] (3) Then the solid ground in step (2) is placed in a vacuum oven for activation. The vacuum degree is 2 kPa before activation begins. Then a mixture of dimethylamine and air (the volume ratio of dimethylamine to air is 1:3) is introduced and the vacuum degree is 70 kPa. Under this atmosphere, the catalyst is activated at 200°C for 2.5 h to obtain the catalyst.

[0087] Example 2-17

[0088] The catalyst was prepared according to the method of Example 1, except that the drying temperature, relative humidity and maximum fluctuation of the drying, drying rate, vacuum degree before drying, activation temperature, and vacuum degree before activation were as shown in Table 1. During the drying process, the vacuum degree was controlled at 70 kPa after the introduction of the first alkaline substance, and during the activation process, the vacuum degree was controlled at 70 kPa after the introduction of the second alkaline substance.

[0089] Table 1

[0090]

[0091] Example 18

[0092] The catalyst was prepared according to the method of Example 1, except that the KHCO3 aqueous solution was replaced with an aqueous solution of NaOH of equal concentration and volume. The pH values ​​of solution B2 and the impregnation solution were 8.20 and 7.06, respectively.

[0093] Example 19

[0094] The catalyst was prepared according to the method of Example 1, except that the dispersant was replaced with an equal amount of ethylenediamine.

[0095] Example 20—Preparation of a catalyst using a precipitation-deposition method

[0096] (1) First, add 5g of the titanium-silicon molecular sieve obtained in Example 1 to a beaker, then add HAuCl4 aqueous solution and ethylene glycol, stir vigorously for 1 hour, and then add KHCO3 aqueous solution to obtain a solid-liquid mixture. The amount of HAuCl4 aqueous solution and ethylene glycol is the same as in step (1) of Example 1, and the dropping rate of KHCO3 aqueous solution is the same as in Example 1.

[0097] (2) The solid-liquid mixture obtained in step (1) is dried and activated, wherein the drying and activation are the same as step (3) of Example 1.

[0098] Example 21

[0099] The catalyst was prepared according to the method of Example 1, except that the ultrasonic impregnation temperature was 80°C and the vibration impregnation temperature was 80°C.

[0100] Example 22

[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 4.0, and solution B2 was stirred for another 3 hours to obtain an impregnation solution with a pH of 6.2.

[0102] Comparative Example 1

[0103] The catalyst was prepared according to the method of 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 2.2.

[0104] Comparative Example 2

[0105] 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.

[0106] Comparative Example 3

[0107] The catalyst was prepared according to the method of Example 20, except that the solid-liquid mixture obtained in step (1) was subjected to solid-liquid separation to obtain a solid, and then the solid was directly activated.

[0108] Comparative Example 4

[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 5

[0111] The catalyst was prepared according to the method of Example 1, except that drying was carried out in an air atmosphere (without ammonia gas) at atmospheric pressure (101 kPa), at a temperature of 100°C, and at a relative humidity of 60%. The drying rate was 1.65 g water / (cm³). 2 h·g carrier).

[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 (2-3 nm) Au nanoparticles. Figure 2 In the catalyst, the particle size of the active component Au is 5-10 nm, and Au agglomerates, resulting in poor dispersibility. In general, the Au nanoparticles in Comparative Example 3 are larger in size, with a larger size difference between each nanoparticle, and the overall dispersion on the TS-1 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 2-5 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 2-5 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]

[0123] (II) Test the performance of the catalysts prepared in the above examples and comparative examples in the preparation of propylene oxide.

[0124] 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.

[0125] 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;

[0126] 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);

[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] Acetone selectivity (S) CH3COCH3 = Amount of acetone in the product / (Amount of C3 product + 2 / 3 of C2 product + 1 / 3 of C1 product);

[0129] 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);

[0130] PO air-time yield = propylene conversion (C C3H6 )*Propylene oxide selectivity (S PO *Airspeed (GHSV).

[0131] Table 3

[0132]

[0133]

[0134] 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 a supported catalyst using alkaline gas, characterized in that, The method includes the following steps: (1) A solid-liquid mixture is obtained by contacting an aqueous solution of an active component precursor, an aqueous solution of an inorganic alkaline substance, and a carrier; the active component precursor includes a noble metal precursor; (2) The solid-liquid mixture is then dried in the presence of the first alkaline substance to obtain a solid product. (3) The solid product is then activated in the presence of a second alkaline substance; The first alkaline substance and the second alkaline substance are each independently nitrogen-containing alkaline substances.

2. The method according to claim 1, wherein, The nitrogen-containing alkaline substance includes ammonia and / or nitrogen-containing organic amines; preferably, the nitrogen-containing organic amines include dimethylamine and / or ethylenediamine.

3. The method according to claim 1 or 2, wherein, The active component precursor is an Au precursor; And / or, the carrier includes at least one of carbon nanotubes, titanium-silicon molecular sieves, silicon-aluminum molecular sieves, all-silicon molecular sieves, phosphorus-aluminum molecular sieves, tin-silicon molecular sieves, carbon black, activated carbon, silicon dioxide, aluminum oxide, cerium oxide, zeolite, resin, cordierite, hydroxyapatite, polymers, and alkaline earth metal carbonates; preferably carbon nanotubes and / or titanium-silicon molecular sieves. And / or, relative to each 100g carrier, the amount of the active component precursor, calculated as metal element, is 0.005-2.5g.

4. The method according to any one of claims 1-3, wherein, The solid-liquid mixture is obtained by first mixing an aqueous solution of the active component precursor with an aqueous solution of an inorganic alkaline substance to obtain a solution containing the active component precursor and the inorganic alkaline substance, and then contacting it with a carrier to obtain a solid-liquid mixture. Preferably, the solution containing the active component precursor and the inorganic alkaline substance further includes a dispersant; More preferably, the solution containing the active component precursor, dispersant and inorganic alkaline substance is obtained by mixing the aqueous solution of the active component precursor with the dispersant to obtain solution B1; then adjusting the pH of solution B1 to 5.5-7.5 with the aqueous solution of inorganic alkaline substance to obtain solution B2; then aging solution B2 under aging conditions so that the pH of solution B2 is 7.5-9.

8. Preferably, the amount of dispersant used is 0.01-1.5g per 100g of carrier.

5. The method according to any one of 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 aqueous solution of the inorganic alkaline substance is 0.005-0.25 mol / L; And / or, the dispersant comprises at least one of ethylenediamine, ethylene glycol, urea, disodium ethylenediaminetetraacetate, bipyridine, glycerol, N,N dimethylformamide, acetone, toluene, tannic acid, and cyclohexane; And / or, the aging time is 1-8 hours.

6. The method according to any one of claims 1-5, wherein, The contact methods include ultrasonic impregnation and vibration impregnation; wherein, ultrasonic impregnation takes 20-80 minutes; vibration impregnation is carried out under light-proof conditions and takes 10-30 hours.

7. The method according to any one of claims 1-6, wherein, The drying conditions are such that the drying rate of the solid-liquid mixture is 0.06-1.35 g water / (cm³). 2 h·g carrier); Preferably, the drying conditions include: a temperature of 25-75°C and a relative humidity of ≤55%. Preferably, the relative humidity fluctuation during the drying process is ≤5%; Preferably, under drying conditions, when the first alkaline substance is a gas, the amount of the first alkaline substance increases the vacuum degree of the drying system by 5-100 kPa after the first alkaline substance is introduced. Preferably, under dry conditions, when the first alkaline substance is a liquid, the amount of the first alkaline substance used is 0.1-2.5g per gram of solid-liquid mixture.

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; Preferably, under activation conditions, when the second alkaline substance is a gas, the amount of the second alkaline substance increases the vacuum degree of the drying system by 10-150 kPa after the second alkaline substance is introduced. Preferably, under activation conditions, when the second alkaline substance is a liquid, the amount of the first alkaline substance is 0.1-2.5g relative to each gram of dried product.

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 support and an active component supported on the support, wherein the active component includes a noble metal, the total acidity of the catalyst is less than 0.61 mmol / g, the acidity ratio of Brønsted acid to Lewis acid is less than 1.1, and 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.

11. The catalyst according to claim 10, wherein, The active component is Au; And / or, based on the total weight of the catalyst, the content of the active component, calculated as metal element, is 0.005-1.25% by weight; And / or, the carrier includes at least one of carbon nanotubes, titanium-silicon molecular sieves, silicon-aluminum molecular sieves, all-silicon molecular sieves, phosphorus-aluminum molecular sieves, tin-silicon molecular sieves, carbon black, activated carbon, silicon dioxide, aluminum oxide, cerium oxide, zeolite, resin, cordierite, hydroxyapatite, polymers, and alkaline earth metal carbonates; preferably carbon nanotubes and / or titanium-silicon molecular sieves. And / or, the ratio of the hydroxyl density Q4 / Q3 of the catalyst is 3-12, where 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; And / or, in any 100nm×100nm region on the catalyst, the proportion of noble metal particles with a diameter of 2-5nm to the total number of noble metal particles with a diameter of 1-10nm is greater than 65%.

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

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