A method for preparing a carbon-containing material Ru-based catalyst

Abstract

The application provides a preparation method of a carbon material Ru-based catalyst and application of the carbon material Ru-based catalyst in partial hydrogenation of benzene to cyclohexene. According to the activity test results, the introduction of the carbon material improves the benzene conversion rate and appropriately increases the selectivity of cyclohexene. This is mainly due to the rich functional groups on the surface of the carbon material and the unique electronic effect, which increases the dispersion of the metal Ru and stabilizes the Ru δ+ In the reducing reaction system. The application selects a fixed bed as an evaluation device of the cyclohexene, avoids the problems such as difficult separation of products and catalysts in the traditional autoclave device, is beneficial to continuous production of the cyclohexene and provides certain convenience for subsequent industrial application.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, and specifically relates to the application of a carbon material in a hydrogenation catalyst. Background Technology

[0002] Carbon materials, due to their abundant functional groups, large specific surface area, and easy availability, are often used as supports or additives in the field of catalysts. For example, Zhou et al. [Zhou Y, et al. Nat Catal 2022; 5:1145-1156] loaded single-atom Ru onto N-doped carbon materials using a ball milling method for propane dehydrogenation; Kang et al. [Kang J, et al. Chem 2022; 8:1050-1066] prepared single-atom Ir-modified Co-CNT (Co-carbon nanotube) catalysts using an impregnation method for Fischer-Tropsch synthesis; Cheng et al. [Cheng Y, et al. J Catal 2019; 374:24-35] prepared Mg-modified Fe-based catalysts using graphene as a support for the synthesis of low-carbon olefins from syngas; and Zheng et al. [Zheng J, et al. Science 2022; 376:288-292] prepared C using a urea precipitation method. 60 Promoted Cu-based catalysts are used for the hydrogenation of oxalate to ethylene glycol under normal pressure.

[0003] The partial hydrogenation of benzene to cyclohexene is a typical hydrogenation reaction, commonly used in the industrial production of caprolactam and adipic acid, with cyclohexane as the main byproduct. Thermodynamically, the standard Gibbs free energy for the hydrogenation of benzene to cyclohexene is -23 kJ / mol, while that for cyclohexene formation is -98 kJ / mol. These conditions are thermodynamically unfavorable for cyclohexene formation, thus necessitating the development of suitable catalysts to achieve higher cyclohexene yields under milder conditions. Currently, B [Zhou G, et al. J Catal 2014; 311:393-403] and Cd [Wang W, et al. ChemCatChem 2012; 4:1836-1843] are often added to Ru-based catalysts, polyols are added to the solvent [Sun H, et al. Chem Eur J 2013; 218:415-424], and metal Ru supported in the configuration of hydrotalcite (LDHs) [Song Y, et al. ChemCatChem 2022; 14:1-11] are used to improve the yield of cyclohexene. The catalyst performance evaluation device and industrial production device used are mainly high-pressure reactors. Although connecting several high-pressure reactors in series can solve the problem of continuous production to a certain extent [Sun H, et al. Chin J Catal 2013; 34:1482-1488], there are still disadvantages such as difficulty in separating the catalyst from the product. Therefore, it is necessary to design a catalyst that can meet the requirements of fixed-bed applications to facilitate the continuous industrial production of cyclohexene.

[0004] In the Ru-based catalyst for the partial hydrogenation of benzene to cyclohexene, the roles of Ru in different valence states are not the same. According to literature reports, some positively charged Ru... δ+ Ru plays a significant role in the adsorption of benzene and the desorption of cyclohexene. δ+ The abundant presence of Ru is crucial for improving cyclohexene yield. Therefore, when designing catalysts, ensuring that some positively charged Ru remains is a key consideration. δ+ Achieving stable and abundant cyclohexene production is an important approach to increasing cyclohexene yield. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for preparing a Ru-based catalyst containing carbon and its application in the partial hydrogenation of benzene to cyclohexene. The Ru-based catalyst provided by this invention is suitable for fixed-bed reactors, which can facilitate the continuous production of cyclohexene and has certain industrial application value.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] (1) Prepare mixed metal salt solutions of Li, Zn, and Al salts, and a mixed alkaline solution of NaOH and Na₂CO₃. During solution preparation, ([Zn... 2+ ]+[Li + ]) / [Al 3+ The molar ratio of [Al] is 1.5-3.0. 3+ The number of moles of [CO3] is 2- The molar number of [OH-] is 0.2-1.0 times that of [Li]. + ]+[Zn 2+ ]+[Al 3+ 0.5-3.0 times that of ]

[0008] (2) Under vigorous stirring, the metal salt solution and the alkaline solution are simultaneously added dropwise to water containing carbon material. During the titration, the pH is maintained at 8.0-11.0, and then aged for 12 hours. After aging, it is filtered with deionized water until the filtrate is neutral, and then dried at 70°C for 12 hours. The result is LDHs.

[0009] (3) The LDHs obtained in step (2) are calcined and then loaded with metal Ru and reduced to obtain Ru-LDHs supported on Ru-based catalyst.

[0010] In some preferred embodiments, in step (1) [Li + ] / ([Li + ]+[Zn 2+ The molar ratio of ]) is 0 to 1.

[0011] In some preferred embodiments, in step (1), the Li salt is one or more of LiNO3, CH3COOLi, Li2SO4, and Li(acac), the Zn salt is one or more of Zn(NO3)2, ZnSO4, (CH3COO)2Zn, and Zn(acac)2, and the Al salt is one or more of Al(NO3)3, Al2(SO4)3, and Al(acac)3.

[0012] In some preferred embodiments, the aging temperature in step (2) is 50 to 120°C.

[0013] In some preferred embodiments, the carbon material in step (2) is CNT, graphene, or C 60 It contains one or more of activated carbon, with a doping content of 0.5 to 30.0 wt%.

[0014] In some preferred embodiments, the loading method of the metal in step (3) is one or more of precipitation, KBH4 reduction, and impregnation. Specifically: the precipitation method involves simultaneously adding the metal solution and NaOH solution to the LDHs solution, maintaining the pH at 10.0 during the addition process, and then filtering until the filtrate is neutral; the KBH4 reduction method involves mixing the metal salt solution and LDHs evenly, adding the KBH4 solution, and then filtering until the filtrate is neutral; the impregnation method involves mixing the metal salt solution and LDHs evenly, evaporating to dryness at 80°C, and then calcining at 300-400°C.

[0015] In some preferred embodiments, the loading of metallic Ru in step (3) is 0.1 to 15 wt%.

[0016] This invention provides a method for preparing the Ru-based catalyst doped with carbon materials as described above, and its application in the partial hydrogenation of benzene to cyclohexene.

[0017] The beneficial results of this invention are as follows:

[0018] This invention provides a method for preparing a Ru-based catalyst doped with carbon materials, applied to the partial hydrogenation of benzene to cyclohexene. The abundant hydroxyl and carboxyl functional groups on the surface of the carbon material can improve the dispersion of the metal and also have electronic interactions with metallic Ru, thus stabilizing Ru during the reaction. δ+ This makes it difficult for it to be reduced to Ru in reducing systems. 0 Furthermore, the introduction of carbon materials enhances the hydrogenation capacity of the catalytic system, enabling the carbon-doped Ru-based catalyst to convert benzene to cyclohexene under normal pressure. The decrease in hydrogen pressure significantly reduces the probability of cyclohexene being over-hydrogenated to cyclohexane, thus contributing to an increased cyclohexene yield. Detailed Implementation

[0019] This invention provides a method for preparing a Ru-based catalyst doped with carbon materials, applicable to the partial hydrogenation of benzene to cyclohexene. In this invention, a fixed-bed reactor is used for catalytic performance evaluation, which solves the problem of difficult product-catalyst separation and facilitates continuous production.

[0020] In this invention, unless otherwise specified, the evaluation method for the partial hydrogenation of benzene to cyclohexene is as follows: a measured amount of catalyst is taken and loaded into a fixed-bed reactor. After checking for leaks, the catalyst is injected at a rate of 50 ml / min. -1 Pure hydrogen gas was introduced at a constant flow rate, and reduction was carried out at 300℃ for 2 hours. Then, water and benzene were introduced into the reaction tubes using a high-pressure pump, while pure hydrogen was introduced at a constant flow rate. Once the reaction temperature reached the target temperature, the reaction began, and the reaction time was 48 hours. All products were analyzed offline by gas chromatography.

[0021] In this invention, unless otherwise specified, the reaction conditions for the partial hydrogenation of benzene to cyclohexene are: atmospheric pressure, 150°C, WLHSV = 3.0 h. -1 H2O / benzene = 10 (vol / vol), H2 / benzene = 40 (mol / mol).

[0022] To further illustrate the present invention, detailed descriptions are provided below with reference to embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0023] Example 1

[0024] Weigh out 8.5g Na₂CO₃ and 7.5g NaOH, dissolve them in 1600ml of water to prepare an alkaline solution. Weigh out 15.0g Al(NO₃)₃·9H₂O, 7.5g LiNO₃, and 2.5g Zn(NO₃)₂·6H₂O, dissolve them in 1600ml of water to prepare a liquid metal solution. Simultaneously add the alkaline solution and the liquid metal solution to a solution containing 1.0g C. 60 In 500 ml of water, control the titration rate and stir vigorously at room temperature to maintain the pH of the solution at approximately 9.5. After titration, age the solution at 80°C for 12 hours, then filter and wash until the filtrate is neutral. Dry the resulting precipitate at 80°C overnight to obtain LDHs, which, after calcination at 350°C, become the catalyst support LDO. At this point, [Zn 2+ ] / ([Zn 2+ ]+[Li + The carbon content is 5.0 wt%.

[0025] Weigh 10g of LDO and disperse it in 100ml of water. After stirring evenly, add 2.4g of RuCl3 and stir for 3 hours. Then, slowly add an aqueous solution containing 4.2g of KBH4. After complete reduction, filter until the filtrate is free of Cl ions. Dry at 80℃ overnight. The resulting product is a carbon-doped Ru-based catalyst, abbreviated as Ru-LDO. At this point, the Ru content is 10.5wt%.

[0026] Example 2

[0027] Ru-LDO was prepared according to Example 1, except that the carbon content used in this example was 15.0 wt%.

[0028] Example 3

[0029] Ru-LDO was prepared according to Example 1, except that the carbon content used in this example was 2.5 wt%.

[0030] Example 4

[0031] Ru-LDO was prepared according to Example 1, except that the carbon material used in this example was graphene, with a content of 15.0 wt%.

[0032] Example 5

[0033] Ru-LDO was prepared according to Example 4, except that the carbon material content in this example was 5.0 wt%.

[0034] Example 6

[0035] Ru-LDO was prepared according to Example 4, except that the carbon content used in this example was 2.5 wt%.

[0036] Example 7

[0037] Ru-LDO was prepared according to Example 1, except that the carbon material used in this example was CNT, with a content of 5.0 wt%.

[0038] Example 8

[0039] Ru-LDO was prepared according to Example 1, except that the carbon material used in this example was activated carbon, with a content of 5.0 wt%.

[0040] Example 9

[0041] Ru-LDO was prepared according to Example 1. The difference from Example 1 is that in this example, [Zn] 2+ ] / ([Zn 2+ ]+[Li + ]) = 0.2.

[0042] Example 10

[0043] Ru-LDO was prepared according to Example 1. The difference from Example 1 is that in this example, [Zn] 2+ ] / ([Zn 2+ ]+[Li + ]) = 0.5.

[0044] Example 11

[0045] Ru-LDO was prepared according to Example 1, except that the Ru content in this example was 5.0 wt%.

[0046] Example 12

[0047] Ru-LDO was prepared according to Example 1, except that the Li salt in this example was CH3COOLi.

[0048] Example 13

[0049] Ru-LDO was prepared according to Example 1, except that the Zn salt in this example was ZnSO4.

[0050] Example 14

[0051] Ru-LDO was prepared according to Example 1, except that the Al salt in this example is Al(acac)3.

[0052] Comparative Example 1

[0053] Ru-LDO was prepared according to Example 1, except that no carbon material was added in this example.

[0054] Comparative Example 2

[0055] Ru-LDO was prepared according to Example 9, except that no carbon material was added in this example.

[0056] Comparative Example 3

[0057] Ru-LDO was prepared according to Example 10, except that no carbon material was added in this example.

[0058] The above samples were subjected to benzene partial hydrogenation activity evaluation under the conditions described above, and the catalytic activity test results are listed in Table 1. The results show that the introduction of carbon materials significantly improved the benzene conversion rate and also appropriately increased the cyclohexene selectivity, thereby increasing the cyclohexene yield. This is mainly due to the abundant functional groups on the surface of the carbon materials, which enhance the metal dispersion, coupled with the hydrogen storage properties of the carbon materials themselves, increasing the hydrogen content on the catalyst surface. In addition, the electronic effects of the carbon materials themselves also facilitate the carrying of a partially positively charged Ru... δ+ Its stability allows it to exist stably in reducing reaction systems, while Ru δ+ This process is more conducive to the desorption of cyclohexene, preventing excessive hydrogenation to form cyclohexane during the reaction. Ultimately, this allows the Ru-based catalyst doped with carbon materials to maintain high cyclohexene selectivity even with increased benzene conversion. In the carbon material, C... 60 For best results, add an appropriate amount of Vitamin C. 60 The highest cyclohexene yield can be obtained. This may be related to C. 60 It is related to its excellent electron transfer properties.

[0059] Table 1. Catalytic performance evaluation results of the examples

[0060]

[0061]

[0062] The above description is only a preferred embodiment of the present invention. It should be noted that improvements and modifications made by those skilled in the art without departing from the principle of the present invention should also be considered within the protection scope of the present invention.

Claims

1. A method for preparing a Ru-based catalyst containing carbon materials, characterized in that, Includes the following steps: (1) Prepare mixed metal salt solutions of Li, Zn, and Al salts, and a mixed alkaline solution of NaOH and Na₂CO₃; during the solution preparation process, ([Zn 2+ ]+[Li + ]) / [Al 3+ The molar ratio of [Al] is 1.5-3.

0. 3+ The number of moles of [CO3] is 2- 0.2-1.0 times that of ], [OH - The number of moles of [Li] is + ]+[Zn 2+ ]+[Al 3+ ] 0.5-3.0 times; [Li + ] / ([Li + ]+[Zn 2+ The molar ratio of ]) is 0~1; (2) Under vigorous stirring, a metal salt solution and an alkaline solution are simultaneously added dropwise to water containing carbon materials, namely CNTs, graphene, and C. 60 One or more of the following are used: activated carbon, with a doping content of 0.5 ~ 30.0 wt%. During titration, the pH is maintained at 8.0-11.

0. After aging, the activated carbon is washed with water until neutral and dried to obtain LDHs. (3) The LDHs obtained in step (2) are calcined and then loaded with metal Ru, and then reduced to obtain Ru-based catalyst Ru-LDHs supported on LDHs.

2. The method according to claim 1, characterized in that, In step (1), the Li salt is one or more of LiNO3, CH3COOLi, Li2SO4, and Li(acac), the Zn salt is one or more of Zn(NO3)2, ZnSO4, (CH3COO)2Zn, and Zn(acac)2, and the Al salt is one or more of Al(NO3)3, Al2(SO4)3, and Al(acac)3.

3. The method according to claim 1, characterized in that, The aging temperature in step (2) is 50 ~ 120℃.

4. The method according to claim 1, characterized in that, In step (3), the metal loading method is one or more of precipitation, KBH4 reduction, and impregnation. Specifically: precipitation involves simultaneously adding the metal solution and NaOH solution to the LDHs solution, maintaining the pH at 9.0-10.0 during the addition process, and then filtering until the filtrate is neutral; KBH4 reduction involves mixing the metal salt solution and LDHs evenly, adding the KBH4 solution, and then filtering until the filtrate is neutral; impregnation involves mixing the metal salt solution and LDHs evenly, evaporating to dryness, and then calcining at 300-400℃.

5. The method according to claim 1, characterized in that, In step (3), the loading of metallic Ru is 0.1~15 wt%.

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