Low-temperature ethylene oxidation catalyst for enhancing oxygen vacancy as well as preparation method and application of low-temperature ethylene oxidation catalyst

Abstract

The invention belongs to the technical field of chemical catalysts, and particularly discloses a low-temperature ethylene oxidation catalyst for enhancing oxygen vacancies and a preparation method and application thereof, and the preparation method comprises the following steps: S1, adding platinum particles into a solvent according to a certain proportion, dispersing and dissolving to obtain a platinum metal precursor solution; s2, dipping a titanium dioxide carrier into the platinum metal precursor solution obtained in S1 according to a certain proportion, uniformly stirring, and then drying and roasting to obtain a platinum-loaded titanium dioxide carrier; and S3, generating oxygen vacancies on the surface of the titanium dioxide carrier obtained in S2 through an oxygen vacancy pretreatment method to obtain the Pt / TiO catalyst. According to the low-temperature ethylene oxidation catalyst for enhancing the oxygen vacancy as well as the preparation method and the application, a Pt / TiO catalyst for efficiently and stably oxidizing ethylene is realized by introducing an oxygen vacancy mechanism, and the problems of insufficient activity, high humidity sensitivity and poor long-term stability of the existing low-temperature ethylene oxidation catalyst are solved.

Description

Technical Field

[0001] The invention relates to the technical field of chemical catalysts, and in particular to a low-temperature ethylene oxidation catalyst for enhancing oxygen vacancies, a preparation method and an application thereof. Background Art

[0002] The preservation measures adopted during the picking, transportation, storage and sales of fruits and vegetables are important guarantees for them to be served fresh. Ethylene is a typical volatile organic gas (V℃s gas) and is one of the important products of biosynthesis in higher plants. It ultimately promotes the ripening and aging of fruits and vegetables under the conduction of ethylene receptors. When ethylene is released from fruits into the environment to form exogenous ethylene, the exogenous ethylene will catalyze other fruits, especially respiratory climacteric fruits and vegetables, to produce a large amount of ethylene, thereby greatly accelerating the ripening and aging of fruits and vegetables. In addition, if improper transportation causes fruits and vegetables to be bumped, their epidermal damage will increase the release of exogenous ethylene, further accelerating the aging of fruits and vegetables. Therefore, exogenous ethylene elimination technology is the key to reducing the loss rate of fruits and vegetables and improving the level of fruit and vegetable preservation.

[0003] Exogenous ethylene elimination technologies are divided into two categories: physical and chemical elimination. Physical elimination mainly relies on the adsorption of ethylene by activated carbon, molecular sieves or other porous materials. However, adsorption materials are not suitable for large-scale applications due to the need for regular replacement and difficulty in handling. Chemical elimination mainly uses oxidation reactions to achieve efficient conversion of ethylene, which can be divided into direct oxidation of chemical reagents and catalytic oxidation technologies represented by photocatalysis, thermal catalysis and plasma catalysis. Among them, precious metal catalysts can efficiently catalyze the oxidation of ethylene at room temperature or even lower temperatures because the reaction conditions are mild and no additional energy is required.

[0004] In the prior art, supported oxide catalysts have high ethylene oxidation activity. Under specific temperature conditions, when the oxide catalyst is supported on a substrate with a specific pore structure, ethylene can be completely oxidized to carbon dioxide and water. Under 0°C conditions, the oxide-supported catalyst achieved an ethylene conversion rate of 76% and had good reaction stability. However, the reaction activity and long-term stability of the catalyst at lower temperatures are still limited.

[0005] Porous substrate catalysts (such as oxide-supported porous catalysts) are used for the oxidation of low-concentration ethylene. Under low humidity conditions, such catalysts can achieve nearly 100% ethylene conversion at 0°C. However, the stability of such catalysts is poor, especially under high humidity or continuous reaction conditions, and they can only maintain activity for a short time, which is difficult to meet the needs of practical industrial applications.

[0006] Molecular sieve catalysts (such as ZSM-5, Beta and Y molecular sieves) are widely used in low-temperature ethylene oxidation. This type of catalyst can completely oxidize ethylene into carbon dioxide and water at room temperature, but its stability is limited and can only maintain a reaction time of about 20 hours. In addition, some studies have attempted to improve the durability of molecular sieve catalysts by doping with rare earth metals or other additives. Although the anti-deactivation ability has been improved to a certain extent, there is still a problem of long-term activity decay.

[0007] In addition, by modifying molecular sieves and introducing special additives (such as rare earth elements and precious metals), efficient modified molecular sieve catalysts for low-temperature ethylene oxidation are prepared, and their main features include: (1) ZSM-5 catalysts can still maintain an ethylene conversion rate of 95% after 500-1000 hours of reaction, but their catalytic activity and stability at lower temperatures (such as 0°C) are relatively poor.

[0008] (2) Catalysts based on Beta molecular sieves loaded with precious metals (such as palladium and platinum) exhibit efficient ethylene oxidation ability in the low temperature range of -30°C to 0°C, and have high moisture resistance stability, and can maintain excellent catalytic activity even in high humidity environments.

[0009] However, there are still problems with the long-term stability of these modified molecular sieve catalysts under extreme humidity conditions and their adaptability to complex industrial conditions. Summary of the invention

[0010] The purpose of the present invention is to provide a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies, a preparation method and an application thereof, and to achieve a Pt / TiO2 catalyst for efficient and stable ethylene oxidation by introducing an oxygen vacancy mechanism, thereby solving the problems of insufficient activity, strong humidity sensitivity and poor long-term stability of existing low-temperature ethylene oxidation catalysts.

[0011] To achieve the above object, the present invention provides a method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies, comprising the following steps: S1. Adding platinum particles into a solvent in a certain proportion, dispersing and dissolving them to obtain a platinum metal precursor solution; S2, immersing the titanium dioxide carrier in the platinum metal precursor solution obtained in S1 according to a certain ratio, stirring evenly, drying and calcining to obtain a platinum-loaded titanium dioxide carrier; S3. Generate oxygen vacancies on the surface of the titanium dioxide support obtained in S2 by an oxygen vacancy pretreatment method to obtain a Pt / TiO2 catalyst.

[0012] Preferably, in S1, the platinum content of the platinum metal precursor solution is 0.5% to 3%, calculated by mass fraction; The platinum metal precursor solution is one or more of platinum nitrate solution, tetraammine platinum nitrate, and solid platinum nitrate.

[0013] Preferably, in S2, the titanium dioxide carrier is a hydrophilic anatase or rutile phase nanoparticle with a specific surface area of ​​5 to 120 m 2 / g; The volume ratio of the platinum metal precursor solution to the titanium dioxide support is at least 1; The drying and calcining treatment is specifically as follows: firstly, drying treatment is performed at a drying temperature of 60°C to 120°C for 6 to 12 hours; then, the temperature is increased from room temperature to 500°C to 600°C at a rate of 2°C / min to 10°C / min, and the temperature is kept at 5 to 10 hours.

[0014] Preferably, in S3, the oxygen vacancy pretreatment method is one or more of a high temperature reduction method, a plasma treatment method, an alkali treatment method, and the use of TiO2 with different crystal planes.

[0015] Preferably, the high temperature reduction method is specifically: The titanium dioxide carrier obtained in S2 is placed in a reaction vessel and treated at 200°C~600°C and H2 atmosphere for 1~5 hours.

[0016] Preferably, the plasma treatment method is specifically: The titanium dioxide carrier obtained by S2 is placed in a plasma reactor and treated for 1 to 5 hours under an Ar / H2 mixed gas atmosphere and a power of 50 W to 150 W.

[0017] Preferably, the alkali treatment method is specifically: The titanium dioxide carrier is treated with an alkali metal and S2, and is impregnated with a NaCl or KCl aqueous solution and calcined at 500° C. The alkali metal is one or more of K and Na.

[0018] Preferably, the titanium dioxide carrier uses TiO2 with different crystal faces, specifically: The hydrothermal synthesis method is adopted to prepare one or both of TiO2 with 001 crystal plane or 100 crystal plane.

[0019] To achieve the above objectives, the present invention also provides a low-temperature ethylene oxidation Pt / TiO2 catalyst with enhanced oxygen vacancies.

[0020] To achieve the above objectives, the present invention also provides an application of a low-temperature ethylene oxidation Pt / TiO2 catalyst with enhanced oxygen vacancies in the catalytic oxidation of ethylene in a low-temperature, humid gas environment and in the purification of ethylene in industrial exhaust gas and in-vehicle air.

[0021] Therefore, the present invention adopts the above-mentioned low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies, preparation method and application, and the beneficial effects are as follows: (1) The present invention introduces high-concentration oxygen vacancies on the TiO2 surface through the introduction of oxygen vacancy mechanism and optimization of preparation process through pretreatment process (high-temperature reduction or plasma treatment). On the one hand, oxygen vacancies can activate water molecules to generate highly active -OH groups. The -OH groups generated by oxygen vacancies react with ethylene intermediates (such as formaldehyde) to quickly generate CO2 and H2O, avoid the accumulation of by-products, improve reaction efficiency and catalytic stability, and provide additional reaction paths for ethylene oxidation. On the other hand, the interaction between Pt and TiO2 (electron transfer ability) is enhanced, which significantly improves the oxidation performance in low temperature environment. Under room temperature to 0°C conditions, the ethylene conversion rate can reach 100%, and long-term operation (such as more than 100 hours) will not be deactivated and the performance will not be significantly degraded, which significantly extends the service life of the catalyst, solves the problems of insufficient activity and poor long-term stability of existing low-temperature ethylene oxidation catalysts, and provides a new solution for industrial low-temperature V℃s oxidation.

[0022] (2) The present invention effectively avoids the inhibitory effect of humidity on catalytic activity by allowing the highly active -OH group to participate in the oxidation reaction. In a high humidity environment (25%-50% humidity), the catalyst can still maintain excellent activity and stability, thus solving the problem of high humidity sensitivity of existing low-temperature ethylene oxidation catalysts and providing a possibility for VOCs control in high humidity environments.

[0023] (3) The Pt / TiO2 catalyst prepared by the present invention has wide applicability and can be used for ethylene catalytic oxidation reaction in low-temperature, humid gas environment, improving the adaptability of fruit and vegetable preservation to complex conditions to meet more demanding application requirements. In addition, it is also suitable for the purification and treatment of volatile organic compounds (such as ethylene) in industrial exhaust gas or indoor air in high-humidity environment.

[0024] (4) The Pt / TiO2 catalyst prepared by the present invention is green and environmentally friendly. It utilizes moisture in the environment to generate active hydroxyl groups (-OH), avoids excessive dependence on external oxidants, and has the advantages of energy saving and environmental protection. In addition, the reaction products are CO2 and H2O, and there is no accumulation of by-products, thus avoiding secondary pollution.

[0025] (5) The present invention adopts an impregnation method combined with a high-temperature reduction or plasma treatment method to prepare a Pt / TiO2 catalyst. The process is simple and easy, the cost is controllable, and it is suitable for large-scale industrial production. In addition, the amount of Pt / TiO2 catalyst used is small, the energy consumption is low, and the performance is stable during long-term use, which can significantly reduce industrial operating costs and improve economic benefits.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is an electron microscope morphology diagram of a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies, a preparation method, and an application example 1 of the present invention; Figure 2 This is a diagram of ethylene conversion in Example 3 of a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies and a preparation method and application thereof; Figure 3 This is a diagram of ethylene conversion in Example 4 of a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies and a preparation method and application thereof of the present invention; Figure 4 This is an XPS analysis chart of a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies, a preparation method, and an application example of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0029] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0030] Embodiment 1 A method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies comprises the following steps: S1. Weigh 0.04 g Pt(NO3)2 and 5 ml deionized water in a beaker, disperse and dissolve to obtain a platinum metal precursor solution with a platinum content of 0.5%.

[0031] S2. Immerse 5 g of the titanium dioxide carrier in the platinum metal precursor solution obtained in S1, stir evenly, dry in an oven at 80° C. for 12 h, and calcine in a muffle furnace at 500° C. for 5 h to obtain a platinum-loaded titanium dioxide carrier.

[0032] S3. Place the titanium dioxide carrier obtained in S2 in a reaction vessel, and treat it at 200° C. in a H 2 atmosphere for 1 hour to obtain a Pt / TiO 2 catalyst with oxygen vacancies generated on the surface.

[0033] Embodiment 2 A method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies comprises the following steps: S1. Weigh 0.12 g Pt(NO3)2 and 5 ml deionized water in a beaker, disperse and dissolve to obtain a platinum metal precursor solution with a platinum content of 1.5%.

[0034] S2. Immerse 5 g of the titanium dioxide carrier in the platinum metal precursor solution obtained in S1, stir evenly, dry in an oven at 120° C. for 6 h, and calcine in a muffle furnace at 600° C. for 3 h to obtain a platinum-loaded titanium dioxide carrier.

[0035] S3. The titanium dioxide carrier obtained in S2 is placed in a plasma reactor, and treated for 5 hours at a power of 150 W and a 50 ml H2 / Ar mixed gas atmosphere to obtain a Pt / TiO2 catalyst with oxygen vacancies generated on the surface.

[0036] Embodiment 3 A method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies comprises the following steps: S1. Weigh 0.2 g Pt(NO3)2 and 5 ml deionized water in a beaker, disperse and dissolve to obtain a platinum metal precursor solution with a platinum content of 2.5%.

[0037] S2. Immerse 5 g of the titanium dioxide carrier in the platinum metal precursor solution obtained in S1, stir evenly, dry in an oven at 100° C. for 12 h, and calcine in a muffle furnace at 600° C. for 3 h to obtain a platinum-loaded titanium dioxide carrier.

[0038] S3. The titanium dioxide carrier obtained in S2 was immersed in a KCl aqueous solution with a K concentration of 0.2%, calcined at 500°C, and then placed in a reactor and treated at 200°C in a H2 atmosphere for 1 hour to obtain a Pt / TiO2 catalyst with oxygen vacancies generated on the surface.

[0039] Embodiment 4 A method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies comprises the following steps: S1. Weigh 0.15 g of tetraammine platinum nitrate and 10 ml of deionized water in a beaker and disperse and dissolve to obtain a platinum metal precursor solution containing 1.5% platinum. S2. Immerse 5 g of a titanium dioxide carrier having a 001 crystal face in the platinum metal precursor solution obtained in S1, stir evenly, and then dry in an oven at 90° C. for 3 h to obtain a platinum-loaded titanium dioxide carrier.

[0040] S3. The titanium dioxide carrier obtained in S2 is placed in a reactor and reduced in a H2 atmosphere at 200°C for 3 hours to obtain a Pt / TiO2 catalyst with oxygen vacancies generated on the surface.

[0041] Embodiment 5 A method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies comprises the following steps: S1. Weigh 0.2g of platinum nitrate and 5ml of deionized water in a beaker, and disperse and dissolve to obtain a platinum metal precursor solution containing 2% platinum. S2. Immerse 5 g of a titanium dioxide carrier having a 001 crystal face in the platinum metal precursor solution obtained in S1, stir evenly, and then dry in an oven at 90° C. for 3 h to obtain a platinum-loaded titanium dioxide carrier.

[0042] S3. The titanium dioxide carrier obtained in S2 is placed in a reactor and reduced in a H2 atmosphere at 400°C for 1 h to obtain a Pt / TiO2 catalyst with oxygen vacancies generated on the surface.

[0043] Experimental Testing The Pt / TiO2 catalyst prepared in Example 1 was used for structural analysis, and the Pt / TiO2 catalysts prepared in Examples 1 to 5 were used for XPS analysis. Figure 1 As shown, the surface of TiO2 carrier is loaded with Pt. Figure 4 It can be seen that Pt particles are dispersed on the TiO2 carrier and oxygen vacancies are generated on the surface.

[0044] 0.5 g of the Pt / TiO2 catalyst prepared in Example 3 was used to carry out the ethylene catalytic oxidation test. Experimental conditions: hydrogen reduction sample at 200°C, 0°C, 50 ppm ethylene, 21% O2, and Ar as the balance gas. Figure 2 As shown, the ethylene conversion rate reached 100%.

[0045] 0.5 g of the Pt / TiO2 catalyst prepared in Example 4 was used to carry out an ethylene catalytic oxidation test. Experimental conditions: 1°C, 50% relative humidity, 50 ppm ethylene, 21% O2, and Ar as the balance gas. Figure 3 As shown, the ethylene conversion rate reached 80%.

[0046] The Pt / TiO2 catalysts prepared in Examples 1 and 3 and the existing catalysts were used to carry out respiratory climacteric fruit and vegetable preservation tests.

[0047] The specific test method is: The specific test conditions and results are shown in Table 1.

[0048] Table 1 Test conditions and results statistics

[0049] As shown in Table 1, the Pt / TiO2 catalyst prepared by Examples 1 to 3 is compared with the existing catalyst. Under the conditions of (temperature and humidity conditions) 0-3°C and 10-50% relative humidity, the catalytic oxidation performance of the Pt / TiO2 catalyst for trace ethylene has been greatly improved. When the amount of the Pt / TiO2 catalyst is 1g and it lasts for 15 days, it can ensure that there is no ethylene in the closed space. It shows that under the conditions of room temperature to 3°C, the ethylene conversion rate can reach 100%, and it will not be deactivated in long-term operation. In a high humidity environment (25% humidity), the catalyst can still maintain excellent activity and stability.

[0050] Therefore, the present invention adopts the above-mentioned low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies, preparation method and application, and realizes a Pt / TiO2 catalyst for efficient and stable ethylene oxidation by introducing an oxygen vacancy mechanism, thereby solving the problems of insufficient activity, strong humidity sensitivity and poor long-term stability of existing low-temperature ethylene oxidation catalysts.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies, characterized in that: The following steps are involved: S1. Adding platinum particles into a solvent in a certain proportion, dispersing and dissolving them to obtain a platinum metal precursor solution; S2, immersing the titanium dioxide carrier in the platinum metal precursor solution obtained in S1 according to a certain ratio, stirring evenly, drying and calcining to obtain a platinum-loaded titanium dioxide carrier; S3. Generate oxygen vacancies on the surface of the titanium dioxide support obtained in S2 by an oxygen vacancy pretreatment method to obtain a Pt / TiO2 catalyst.

2. The method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies according to claim 1, characterized in that: In S1, the platinum content of the platinum metal precursor solution is 0.5% to 3%, calculated by mass fraction; The platinum metal precursor solution is one or more of platinum nitrate solution, tetraammine platinum nitrate, and solid platinum nitrate.

3. The method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies according to claim 1, characterized in that: In S2, the titanium dioxide carrier is a hydrophilic anatase or rutile phase nanoparticle with a specific surface area of ​​5 to 120 m 2 / g; The volume ratio of the platinum metal precursor solution to the titanium dioxide support is at least 1; The drying and calcining treatment is specifically as follows: firstly, drying treatment is performed at a drying temperature of 60°C to 120°C for 6 to 12 hours; then, the temperature is increased from room temperature to 500°C to 600°C at a rate of 2°C / min to 10°C / min, and the temperature is kept at 5 to 10 hours.

4. The method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies according to claim 1, characterized in that: In S3, the oxygen vacancy pretreatment method is one of a high temperature reduction method, a plasma treatment method, and an alkali treatment method.

5. The method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies according to claim 4, characterized in that: The high temperature reduction method is specifically: The titanium dioxide carrier obtained in S2 is placed in a reaction vessel and treated at 200°C~600°C and H2 atmosphere for 1~5 hours.

6. The method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies according to claim 4, characterized in that: The plasma treatment method is specifically: The titanium dioxide carrier obtained by S2 is placed in a plasma reactor and treated for 1 to 5 hours under an Ar / H2 mixed gas atmosphere and a power of 50 W to 150 W.

7. The method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies according to claim 4, characterized in that: The alkali treatment method is specifically: The titanium dioxide carrier is treated with an alkali metal and S2, and is impregnated with a NaCl or KCl aqueous solution and calcined at 500° C. The alkali metal is one or more of K and Na.

8. The method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies according to claim 3, characterized in that: The titanium dioxide carrier adopts different crystal faces of TiO2, specifically: The hydrothermal synthesis method is adopted to prepare one or both of TiO2 with 001 crystal plane or 100 crystal plane.

9. A Pt / TiO2 catalyst prepared by the method for preparing a low-temperature ethylene oxidation catalyst with enhanced oxygen vacancies according to any one of claims 1 to 8.

10. An application of the low-temperature ethylene oxidation Pt / TiO2 catalyst with enhanced oxygen vacancies as claimed in claim 9 in the catalytic oxidation of ethylene in a low-temperature, humid gas environment and in the purification of ethylene in industrial exhaust gas and in-vehicle air.

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