Catalyst for olefin epoxidation and its preparation method and application

Abstract

The application belongs to the technical field of catalysts, and discloses an olefin epoxidation catalyst, a preparation method and application thereof, the preparation method comprising the following steps: (1) preparing a silver-containing solution, wherein the silver-containing solution comprises a silver compound precursor, an organic amine, water and an optional additive; (2) fully contacting the silver-containing solution with an alumina carrier, and draining the excess solution on the surface of the carrier to obtain a carrier loaded with the silver-containing solution; (3) treating the carrier loaded with the silver-containing solution in infrared radiation to obtain the catalyst. The olefin epoxidation catalyst prepared by the method has a significantly reduced silver content gradient inside and outside the catalyst, greatly improved activity center dispersity, reduced agglomeration and blockage of nanoparticles, and excellent catalytic performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, more particularly, to a preparation method of a catalyst for olefin epoxidation, a catalyst prepared by the preparation method and application thereof. BACKGROUND

[0002] Alkylene oxide is an important product and intermediate in the petrochemical industry, and is widely used in light industry, chemical industry, medicine, textile and food industries. Among them, ethylene oxide (EO) is an important ethylene derivative product, mainly used for producing ethylene glycol (EG), synthetic detergents, non-ionic surfactants, anti-freezing agents, emulsifiers, ethylene glycol products, etc., and has a wide and important application in many fields such as washing and dyeing, electronics, medicine, pesticides, textiles, automobiles, oil exploitation and refining.

[0003] At present, most of the industrial devices for producing EO in the world adopt ethylene process, that is, ethylene and oxygen are directly epoxidized under the action of silver catalyst to generate EO, and the byproduct is mostly CO2. In the existing research, silver catalyst is currently the only effective catalyst in this process, and is the core of ethylene epoxidation reaction.

[0004] The silver catalyst used in industrial EO / EG devices can be mainly divided into three types: high-activity silver catalyst, high-selectivity silver catalyst and medium-selectivity silver catalyst. Among them, the high-activity silver catalyst has the characteristics of high activity and good stability, and the selectivity is about 80% to 82%, which is more suitable for traditional devices with high CO2 concentration (generally 5% to 10%) at the inlet of the reactor; the high-selectivity silver catalyst has the characteristics of high selectivity, which can generally exceed 88%, but requires a low CO2 concentration at the inlet, generally less than 1%, which is suitable for devices with relatively low space-time yield; the medium-selectivity silver catalyst has the characteristics of activity and selectivity between the above two catalysts, and the selectivity can reach about 85%, and the inlet CO2 concentration is generally required to be below 3%.

[0005] The activity, selectivity and stability of silver catalyst are the main indicators for evaluating the performance of silver catalyst. With the continuous improvement of energy consumption and environmental protection requirements in recent years, new devices or modified devices more and more begin to use high-selectivity or medium-selectivity silver catalysts, which gradually replace the traditional high-activity silver catalysts. In the development of silver catalysts for decades, the modification of silver catalysts mainly focuses on the modification of the carrier and the additive, and the research on the preparation and activation process is relatively less.

[0006] US4833261, US4761394 disclose silver catalysts with the addition of rhenium promoters, which opens the prelude to the study of high-selectivity silver catalysts. CN105233824A discloses a silver catalyst composed of mixed promoters of Na, Cs, Ce, Re, Zr, etc., and an adjusting gas for promoting the stability of the catalyst activity is introduced into the reaction system with the reaction raw materials during the reaction process to improve the stability of the catalyst. CN112206798A discloses a silver catalyst based on a composite carrier composed of α-silicon carbide and α-aluminum oxide.

[0007] In the above patent documents, the modification of the carrier and the promoter is still mainly studied, and the selectivity is improved to a certain extent, but the basic preparation process has not changed, and the traditional preparation and activation process is still used. For the traditional thermal activation process, the inventors found that the rapid contact process of high-temperature gas with the catalyst easily leads to uneven heating of the catalyst, causing differences in the internal and external compositions, which in turn significantly affects the catalytic performance, greatly affecting the comprehensive performance of the silver catalyst, especially the stability, and the process energy consumption is large. Therefore, it is of great significance to develop a more efficient and comprehensive silver catalyst preparation method. SUMMARY

[0008] The purpose of the present application is to solve the problems of uneven heating and limited improvement of the comprehensive performance of the catalyst in the preparation process of the ethylene epoxidation catalyst for preparing ethylene oxide. The inventors of the present application have conducted extensive and in-depth research in the field of nanocatalysts and their preparation processes. The results show that the use of infrared radiation can make the silver catalyst more fully activated under the action of infrared radiation, and the heating of the catalyst is more uniform. Compared with the traditional activation process, the activity component distribution uniformity inside and outside the catalyst is significantly improved, and the prepared catalyst has better comprehensive performance. The silver catalyst obtained in this way has better comprehensive performance when used to catalyze the direct gas-phase oxidation of ethylene to prepare ethylene oxide.

[0009] To achieve the above-mentioned purpose, the first aspect of the present application provides a preparation method of an olefin epoxidation catalyst, which comprises:

[0010] (1) preparing a silver-containing solution, wherein the silver-containing solution comprises a silver compound precursor, an organic amine, water, and optionally a promoter;

[0011] (2) contacting the silver-containing solution with an alumina carrier, and draining the excess solution on the surface of the carrier to obtain a carrier loaded with the silver-containing solution;

[0012] (3) treating the carrier loaded with the silver-containing solution in infrared radiation to obtain a catalyst.

[0013] The second aspect of the present application provides an olefin epoxidation catalyst prepared by the above preparation method.

[0014] The third aspect of the present application provides an application of the above catalyst in direct oxidation of olefin to produce alkylene oxide, preferably in direct oxidation of ethylene to produce ethylene oxide.

[0015] The beneficial technical effects of the present application are as follows:

[0016] The olefin epoxidation catalyst prepared by the method of the present application significantly reduces the silver content gradient inside and outside the catalyst, greatly improves the dispersion of active centers, reduces the agglomeration and blockage of nanoparticles, and has excellent catalytic performance. Compared with the prior art, the activity, selectivity and stability of the catalyst are further improved, the reaction raw materials are saved, the reaction by-products are reduced, and the service life of the catalyst is prolonged.

[0017] The preparation method of the present application greatly improves the preparation efficiency of the catalyst and reduces the energy consumption of the production of the catalyst.

[0018] Other features and advantages of the present application will be described in detail in the following specific embodiments. DETAILED DESCRIPTION

[0019] The preferred embodiments of the present application will be described in more detail below. Although the preferred embodiments of the present application are described below, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein.

[0020] The first aspect of the present application provides a preparation method of an olefin epoxidation catalyst, which comprises:

[0021] (1) preparing a silver-containing solution, wherein the silver-containing solution comprises a silver compound precursor, an organic amine, water, and optionally an auxiliary agent;

[0022] (2) contacting the silver-containing solution with an alumina carrier, and draining the excess solution on the surface of the carrier to obtain a carrier loaded with the silver-containing solution;

[0023] (3) treating the carrier loaded with the silver-containing solution in infrared radiation to obtain a catalyst.

[0024] In order to reduce and fix silver on the surface of the carrier, the above carrier loaded with the silver-containing solution needs to be activated. In the present application, the activation is carried out by infrared radiation. According to the present application, preferably, the infrared radiation is carried out in a furnace or a tunnel device equipped with an infrared radiator, and the infrared radiator is preferably an electric heating infrared radiator.

[0025] The infrared radiation wavelength used in the infrared irradiation is 5-350 μm, preferably 5-300 μm, and further preferably 200-300 μm; the temperature of the material to be irradiated is 150-400 °C, preferably 150-350 °C; and the time of the infrared irradiation is 1-50 min, preferably 2-30 min, and further preferably 2-5 min.

[0026] According to the present application, preferably, the infrared irradiation is carried out in a flowing gaseous atmosphere, which is preferably at least one selected from the group consisting of a stream of air, a stream of nitrogen / oxygen mixture, a stream of helium / oxygen mixture, and a stream of nitrogen / hydrogen mixture, and further preferably a stream of nitrogen / oxygen mixture and / or a stream of helium / oxygen mixture.

[0027] The flow rate of the gaseous atmosphere is 40-500 ml / min, preferably 40-350 ml / min, and further preferably 200-350 ml / min.

[0028] According to the present application, preferably, the silver compound precursor is at least one selected from the group consisting of silver nitrate, silver carbonate, silver oxalate, and silver oxide.

[0029] The organic amine in the present application can be selected from a variety of organic amine compounds as long as it can form a complex with a silver compound. According to the present application, preferably, the organic amine is at least one selected from the group consisting of ethylamine, ethylenediamine, n-propylamine, 1,3-propanediamine, n-butylamine, 1,4-butanediamine, ethanolamine, and propanolamine.

[0030] The auxiliary agent is at least one selected from the group consisting of an alkali metal auxiliary agent, an alkaline earth metal auxiliary agent, a rhenium auxiliary agent, and an optional co-auxiliary agent of rhenium.

[0031] In a preferred embodiment of the present application, the alkali metal auxiliary agent can be one or more of soluble compounds of lithium, sodium, potassium, rubidium, and cesium, such as at least one of sulfate, nitrate, and hydroxide of the above-mentioned alkali metal elements. The alkaline earth metal auxiliary agent can be one or more of soluble compounds of magnesium, calcium, strontium, and barium, such as at least one of sulfate, nitrate, and acetate of the above-mentioned alkaline earth metal elements. The rhenium auxiliary agent can be one or more selected from the group consisting of oxides of rhenium, ammonium rhenate, perrhenic acid, and perrhenate. The co-auxiliary agent of rhenium can be one or more selected from the group consisting of molybdenum compounds, tungsten compounds, chlorine compounds, manganese compounds, nickel compounds, phosphorus compounds, and boron compounds.

[0032] According to the present application, preferably, the amounts of the raw materials are such that the silver content in the catalyst, on an elemental basis, is 5-40 wt%, preferably 10-30 wt%, and the weight content of the promoter in the catalyst, on a metallic basis, is 0-5000 ppm, preferably 100-3500 ppm, with the balance being the alumina support;

[0033] In the promoter, on a metallic basis, the weight content of alkali metal is preferably 10-1500 ppm, further preferably 50-1200 ppm; the weight content of alkaline earth metal is preferably 5-1000 ppm, further preferably 20-800 ppm; the weight content of rhenium metal is preferably 10-1500 ppm, further preferably 20-1000 ppm; and the weight content of the co-promoter of rhenium, on a metallic basis, is preferably 0-1000 ppm, further preferably 10-500 ppm.

[0034] According to the present application, preferably, the sufficient contact is any industrial preparation mode of the supported catalyst, such as impregnation, spraying or coating, preferably impregnation, further preferably reduced-pressure impregnation.

[0035] In a preferred embodiment of the present application, the silver-containing mixed solution is impregnated into the support under a vacuum degree of less than 10 mmHg, the temperature of the mixed solution is preferably controlled to be 0-30℃, and the impregnation time is preferably 10-60 minutes. Then the impregnation solution is drained.

[0036] According to the present application, preferably, the preparation method further comprises:

[0037] (4) The obtained catalyst is subjected to steps (2) and (3) again.

[0038] When it is necessary to increase the silver content in the catalyst, a silver-containing solution with a higher concentration can be prepared, or at least one operation of step (4) is performed according to the above method, i.e. the catalyst obtained after the activation of step (3) is impregnated and activated again, so as to increase the loaded silver content.

[0039] In the present application, the alumina support can be a conventional support in the field of alkylene oxide catalysts. According to the present application, preferably, the alumina support is a shaped porous α-alumina support; and the alumina support preferably has the following characteristics: the crush strength of the alumina support is 20-200 N / particle, preferably 50-100 N / particle; the specific surface area is 0.2-5 m 2 / g, preferably 0.5-2 m 2 / g; the water absorption is 30-80%, preferably 40-60%; and the pore volume is 0.2-1.2 ml / g, preferably 0.5-1.0 ml / g.

[0040] In the present application, the porous α-alumina carrier can be in any form commonly used in the art, such as spherical, ring-shaped or cylindrical.

[0041] The second aspect of the present application provides the catalyst for olefin epoxidation prepared by the above preparation method.

[0042] The catalyst for olefin epoxidation of the present application can directly catalyze the oxidation of olefins to form alkylene oxide, and is particularly suitable for the direct catalytic oxidation of ethylene to form ethylene oxide, and has further improved catalytic performance.

[0043] As described above, the catalyst comprises a porous α-alumina carrier and the following components deposited thereon, based on the total weight of the catalyst:

[0044] i) 5-40 wt%, preferably 10-30 wt% of silver active component in terms of silver element;

[0045] ii) 10-1500 ppm, preferably 50-1200 ppm of alkali metal promoter in terms of alkali metal element;

[0046] iii) 5-1000 ppm, preferably 20-800 ppm of alkaline earth metal promoter in terms of alkaline earth metal element;

[0047] iv) 10-1500 ppm, preferably 20-1000 ppm of rhenium promoter in terms of rhenium atom;

[0048] v) optional co-promoter of rhenium, if present, the weight content of which in terms of metal element is 5-1000 ppm, preferably 10-500 ppm;

[0049] the balance being the carrier.

[0050] The catalyst of the present application can be tested by the following performance test method:

[0051] The catalyst of the present application is tested for activity and selectivity by a laboratory fixed-bed micro-reactor (hereinafter referred to as "micro-reactor") evaluation device. The micro-reactor evaluation device uses a stainless steel reaction tube with an inner diameter of 4 mm, which is placed in a heating jacket. The catalyst is packed in a volume of 1 ml (12-18 mesh), and inert packing is placed at the lower part to make the catalyst bed located in the constant temperature zone of the heating jacket.

[0052] The process conditions for the micro-reactor evaluation of the catalyst of the present application are as follows:

[0053] Reaction gas composition: ethylene 30.0±2.0 mol%, oxygen 7.4±0.2 mol%, carbon dioxide <2.0 mol%, dichloroethane in appropriate amount, the balance being nitrogen balance gas; reaction pressure 2.1 MPa; space velocity 6000 h -1; set the target concentration of ethylene oxide in the reactor outlet tail gas 2.5%.

[0054] The third aspect of the present application provides the use of the above-mentioned catalyst in the direct oxidation of olefins to produce alkylene oxide, preferably in the direct oxidation of ethylene to produce ethylene oxide.

[0055] The present application is further illustrated by the following examples:

[0056] In all the following examples and comparative examples, the carrier used is an industrially produced shaped porous α-alumina carrier having the following characteristics: crushing strength 80 N / particle, specific surface area 1.20 m 2 / g, water absorption 54%, pore volume 0.8 ml / g.

[0057] The infrared radiation furnace used in all the following examples is a furnace equipped with infrared radiators, which are electrically heated infrared radiators.

[0058] In all the following examples and comparative examples, the activity and selectivity of the catalyst are tested by a laboratory fixed-bed micro-reactor (hereinafter referred to as "micro-reactor") evaluation device. The micro-reactor evaluation device uses a stainless steel reaction tube with an inner diameter of 4 mm, which is placed in a heating jacket. The catalyst loading volume is 1 ml (12-18 mesh), and there is inert filler at the lower part to make the catalyst bed located in the constant temperature zone of the heating jacket.

[0059] In the micro-reactor evaluation process conditions of the catalyst, the reaction gas composition is: ethylene 30.0 ± 2.0 mol%, oxygen 7.4 ± 0.2 mol%, carbon dioxide < 2.0 mol%, dichloroethane in appropriate amount, and the balance is nitrogen balance gas; reaction pressure 2.1 MPa; space velocity 6000 h -1 ; set the target concentration of ethylene oxide in the reactor outlet tail gas 2.5%.

[0060] When the above reaction conditions are stabilized, the composition of the inlet and outlet gas of the reactor is continuously determined. After the determination results are corrected for volume shrinkage, the selectivity is calculated according to the following formula:

[0061]

[0062] Where ΔEO is the difference in ethylene oxide concentration between the outlet gas and the inlet gas, and the average of more than 10 sets of test data is taken as the test result for that day.

[0063] The activity of the catalyst is judged by the reaction temperature, the lower the reaction temperature, the higher the activity. The stability of the catalyst is judged by the reaction temperature rise, the smaller the reaction temperature rise during the same evaluation time, the better the stability.

[0064] The relative silver element content of the inner and outer surface of the catalyst is determined by EDX, the lower the ratio R of the silver element content of the outer surface to the inner surface, the smaller the gradient difference of the silver content between the inner and outer surface, and the more uniform the silver dispersion.

[0065] Example 1

[0066] A mixture of 20 g ethylenediamine, 10 g ethanolamine and 41.5 g deionized water was prepared, and after complete dissolution, 28.3 g silver nitrate was slowly added to the mixture while stirring, and the solution temperature was maintained at 0-15℃, so that the silver nitrate was completely dissolved. Then 0.045 g cesium hydroxide, 0.063 g strontium sulfate, 0.054 g peroxymolybdic acid and 0.020 g ammonium molybdate were added to prepare a silver-containing impregnation solution. 10 g of α-alumina carrier was placed in a container, vacuumed to below 10 mmHg, and then the above-mentioned silver-containing impregnation solution was added to immerse the carrier, and after 30 minutes, the excess impregnation solution was drained, so that there was no residual liquid that could drip from the surface. Then the impregnated material was activated in an infrared radiation furnace with flowing air, the infrared radiation wavelength was 280 μm, the gas flow rate was 250 ml / min, the material temperature was controlled at 300℃, and the activation time was 1 minute, to prepare a silver catalyst S1.

[0067] Example 2

[0068] The catalyst was prepared according to the method of Example 1, except that the "activation time of 1 minute" in Example 1 was changed to "activation time of 2 minutes", and the other conditions were the same as in Example 1, to prepare a catalyst S2.

[0069] Example 3

[0070] The catalyst was prepared according to the method of Example 1, except that the "flowing air" in Example 1 was changed to "flowing helium / oxygen mixed gas", and the other conditions were the same as in Example 1, to prepare a catalyst S3.

[0071] Example 4

[0072] A mixture of 20 g ethylenediamine, 10 g ethanolamine and 41.5 g deionized water was prepared. After complete dissolution, 28.3 g silver nitrate was slowly added to the mixture while stirring, and the solution temperature was maintained at 0-15°C to ensure complete dissolution of the silver nitrate. Then 0.056 g cesium hydroxide, 0.063 g strontium sulfate, 0.067 g peroxymolybdic acid and 0.020 g ammonium molybdate were added to prepare a silver-containing impregnation solution. 10 g of α-alumina carrier was placed in a container, and vacuum was applied until the pressure was below 10 mmHg. Then the above-mentioned silver-containing impregnation solution was added to immerse the carrier, and the carrier was kept immersed for 30 minutes. The excess impregnation solution was then drained, and the surface of the carrier was made free of residual liquid that could drip. The impregnated carrier was then activated in an infrared radiation furnace with flowing air, with an infrared radiation wavelength of 280 μm, a gas flow rate of 250 ml / min, and a carrier temperature of 300°C, for 1 minute, to prepare silver catalyst S4.

[0073] Example 5

[0074] A catalyst was prepared according to the method of Example 4, except that the "activation time of 1 minute" in Example 4 was changed to "activation time of 2 minutes", and the other conditions were the same as in Example 4, to prepare catalyst S5.

[0075] Example 6

[0076] A catalyst was prepared according to the method of Example 4, except that the "carrier temperature of 300°C" in Example 4 was changed to "carrier temperature of 320°C", and the other conditions were the same as in Example 4, to prepare catalyst S6.

[0077] Comparative Example 1

[0078] A mixture of 20 g ethylenediamine, 10 g ethanolamine and 41.5 g deionized water was prepared. After complete dissolution, 28.3 g silver nitrate was slowly added to the mixture while stirring, and the solution temperature was maintained at 0-15°C to ensure complete dissolution of the silver nitrate. Then 0.056 g cesium hydroxide, 0.063 g strontium sulfate, 0.067 g peroxymolybdic acid and 0.020 g ammonium molybdate were added to prepare a silver-containing impregnation solution. 10 g of α-alumina carrier was placed in a container, and vacuum was applied until the pressure was below 10 mmHg. Then the above-mentioned silver-containing impregnation solution was added to immerse the carrier, and the carrier was kept immersed for 30 minutes. The excess impregnation solution was then drained, and the surface of the carrier was made free of residual liquid that could drip. The impregnated carrier was then activated in an infrared radiation furnace with flowing air, with an infrared radiation wavelength of 280 μm, a gas flow rate of 250 ml / min, and a carrier temperature of 300°C, for 1 minute, to prepare silver catalyst S4.

[0079] Comparative Example 2

[0080] A catalyst was prepared according to the method of Comparative Example 1, except that the "activation time of 1 minute" in Comparative Example 1 was changed to "activation time of 5 minutes", and the other conditions were the same as in Comparative Example 1, to prepare catalyst DS2.

[0081] Comparative Example 3

[0082] The catalyst was prepared according to the method of Comparative Example 1, except that "temperature 300℃" in Comparative Example 1 was changed to "temperature 320℃", and other conditions were the same as in Comparative Example 1, to obtain catalyst DS3.

[0083] Comparative Example 4

[0084] A mixture of 20 g of ethylenediamine, 10 g of ethanolamine and 41.5 g of deionized water was obtained, and after complete dissolution, 28.3 g of silver nitrate was slowly added to the mixture while stirring, and the solution temperature was maintained at 0-15℃, so that the silver nitrate was completely dissolved. Then 0.056 g of cesium hydroxide, 0.063 g of strontium sulfate, 0.067 g of peroxymolybdate and 0.020 g of ammonium molybdate were added to prepare a silver-containing impregnation solution. 10 g of α-alumina carrier was placed in a container, vacuumed to below 10 mmHg, and then the above-mentioned silver-containing impregnation solution was added to immerse the carrier, and after 30 minutes, the excess impregnation solution was drained, so that there was no residual liquid that could be dripped on the surface. Then activation was carried out in an air stream at a temperature of 300℃ for 5 minutes, to obtain silver catalyst DS4.

[0085] Characterization and Test Example

[0086] The catalysts S1-S6 of Examples 1-6 and the catalysts DS1-DS4 of Comparative Examples 1-4 were characterized for elemental content, and the relative content ratio R of the outside and the inside was calculated, as shown in Table 1 below; and the above-mentioned catalysts were compared and evaluated for two months under the conditions of the gas composition and space velocity of 6000h-1 and the reaction pressure of 2.1 MPa, and the results are shown in Table 1 below. -1

[0087] Table 1: Results of micro-reaction evaluation and characterization of catalysts S1-S6 and comparative catalysts DS1-DS4

[0088] Sample Average selectivity (%) Initial reaction temperature (%) Reaction temperature rise (°C) R Catalyst S1 85.1 220.3 6.2 1.58 Catalyst S2 85.5 219.8 5.7 1.46 Catalyst S3 85.3 220.7 5.8 1.32 Catalyst S4 86.2 221.0 6.3 1.51 Catalyst S5 87.1 220.8 5.9 1.34 Catalyst S6 87.5 221.2 6.0 1.52 Comparative catalyst DS1 83.2 225.0 8.6 3.50 Comparative catalyst DS2 83.8 223.2 8.0 3.28 Comparative catalyst DS3 84.2 223.4 8.2 3.30 Comparative catalyst DS4 84.5 224.7 8.7 3.18

[0089] As can be seen from the above examples, comparative examples and Table 1, the silver catalyst prepared by the infrared irradiation preparation method has significantly improved dispersion of active centers compared with the silver catalyst prepared by the traditional preparation method, and when used for catalyzing the direct gas-phase oxidation of ethylene to prepare ethylene oxide, the activity, reaction selectivity and stability of the catalyst are improved, and the catalytic performance is further improved. In addition, the preparation method of the present application shortens the required time and improves the production efficiency.

[0090] ​Having described various embodiments of the application, it is to be understood that the above description is meant to be illustrative only, and that many modifications and variations of the embodiments are possible without departing from the scope and spirit of the described embodiments. Many modifications and variations of the described embodiments are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims and their equivalents, the described embodiments can be practiced otherwise than as specifically described.

Claims

1. A method for preparing a catalyst for olefin epoxidation, characterized in that, The preparation method includes: (1) Prepare a silver-containing solution, wherein the silver-containing solution comprises a silver compound precursor, an organic amine, water, and optional additives; (2) The silver-containing solution is brought into full contact with the alumina carrier, and the excess solution on the surface of the carrier is drained off to obtain a carrier containing the silver-containing solution; (3) The support containing the silver solution is treated with infrared irradiation to obtain the catalyst; The infrared radiation wavelength selected for the infrared irradiation is 5-350μm; the temperature of the irradiated material is controlled at 150-400℃; and the infrared irradiation time is 1-50 min.

2. The preparation method according to claim 1, wherein, The infrared irradiation is carried out in a furnace or tunnel equipment equipped with an infrared radiator; The infrared radiation wavelength selected for the infrared irradiation is 5-300μm; the temperature of the irradiated material is controlled at 150-350℃; and the infrared irradiation time is 2-30 min.

3. The preparation method according to claim 2, wherein, The infrared radiator is an electrically heated infrared radiator.

4. The preparation method according to claim 2, wherein, The infrared radiation wavelength selected for the infrared irradiation is 200-300μm.

5. The preparation method according to claim 2, wherein, The infrared irradiation time is 2-5 minutes.

6. The preparation method according to claim 1, wherein, The infrared irradiation is carried out in a flowing gaseous atmosphere; The flow rate of the gaseous atmosphere is 40-500 ml / min.

7. The preparation method according to claim 6, wherein, The gaseous atmosphere is selected from at least one of an air flow, a nitrogen / oxygen mixed flow, a helium / oxygen mixed flow, and a nitrogen / hydrogen mixed flow.

8. The preparation method according to claim 7, wherein, The gaseous atmosphere is selected from a nitrogen / oxygen mixed gas flow and / or a helium / oxygen mixed gas flow.

9. The preparation method according to claim 6, wherein, The flow rate of the gaseous atmosphere is 40-350 ml / min.

10. The preparation method according to claim 9, wherein, The flow rate of the gaseous atmosphere is 200-350 ml / min.

11. The preparation method according to claim 1, wherein, The silver compound precursor is selected from at least one of silver nitrate, silver carbonate, silver oxalate, and silver oxide; The organic amine is selected from at least one of ethylamine, ethylenediamine, n-propylamine, 1,3-propanediamine, n-butylamine, 1,4-butanediamine, ethanolamine, and propanolamine; The additive is selected from at least one of alkali metal additives, alkaline earth metal additives, rhenium additives, and optionally rhenium co-additives.

12. The preparation method according to claim 1, wherein, The amount of each raw material used is such that, based on the total weight of the catalyst, the silver content in the catalyst, calculated as an element, is 5-40 wt%; the weight content of the auxiliary agent in the catalyst, calculated as a metal element, is 0-5000 ppm; and the balance is an alumina support.

13. The preparation method according to claim 12, wherein, The amount of each raw material used is such that, based on the total weight of the catalyst, the silver content in the catalyst, calculated as an element, is 10-30 wt%; the weight content of the auxiliary agent in the catalyst, calculated as a metal element, is 100-3500 ppm; and the balance is an alumina support.

14. The preparation method according to claim 12, wherein, The additives, calculated by metal element, contain 10-1500 ppm by weight of alkali metals; 5-1000 ppm by weight of alkaline earth metals; 10-1500 ppm by weight of rhenium metals; and 0-1000 ppm by weight of rhenium co-additives, calculated by metal element.

15. The preparation method according to claim 13, wherein, The additives, calculated by metal element, contain 50-1200 ppm by weight of alkali metals; 20-800 ppm by weight of alkaline earth metals; 20-1000 ppm by weight of rhenium metals; and 10-500 ppm by weight of rhenium co-additives, calculated by metal element.

16. The preparation method according to claim 1, wherein, The full contact refers to immersion, spraying, or coating.

17. The preparation method according to claim 16, wherein, The term "full contact" refers to immersion.

18. The preparation method according to claim 17, wherein, The full contact refers to depressurized impregnation.

19. The preparation method according to claim 1, wherein, The preparation method further includes: (4) Repeat steps (2) and (3) with the obtained catalyst.

20. The preparation method according to claim 1, wherein, The alumina carrier is a shaped porous α-alumina carrier.

21. The preparation method according to claim 1, wherein, The alumina carrier has a crushing strength of 20-200 N / particle and a specific surface area of ​​0.2-5 m². 2 / g; water absorption rate is 30-80%; pore volume is 0.2-1.2ml / g.

22. The preparation method according to claim 21, wherein, The alumina carrier has a crushing strength of 50-100 N / particle and a specific surface area of ​​0.5-2 m². 2 / g; water absorption rate 40-60%; pore volume 0.5-1.0ml / g.

23. A catalyst for olefin epoxidation prepared by any one of claims 1-22.

24. The application of the catalyst according to claim 23 in the direct oxidation of olefins to produce epoxides.

25. The application of the catalyst according to claim 23 in the direct oxidation of ethylene to produce ethylene oxide.

Images