PerhydroN-propyl carbazole dehydrogenation reaction catalyst and preparation method and application thereof

Abstract

The invention provides an all-hydrogen N-propyl carbazole dehydrogenation reaction catalyst and a preparation method thereof, the preparation method takes 3-aminopropyltrimethoxysilane (APTMS) as a nitrogen source, high-density amino functional groups are grafted on the surface of a SiO2 carrier, and palladium ions are loaded on the modified SiO2 carrier to realize dual effects of carrier surface modification and metal nanoparticle loading. The catalyst prepared by the invention has wide application potential, is suitable for a perhydrogen N-propyl carbazole dehydrogenation reaction system, and can significantly improve the activity and selectivity of the catalyst. The adsorption capacity of the surface of the amido-modified catalyst to reactants is remarkably enhanced, the reaction selectivity is improved, and the catalytic activity is also remarkably improved. The preparation method of the catalyst provided by the invention is simple and efficient, provides an innovative research path for developing a Pd-based dehydrogenation catalyst with high selectivity, high activity and low noble metal loading capacity, and has wide popularization and application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of dehydrogenation reaction catalysts, and specifically relates to a perhydro N-propylcarbazole dehydrogenation reaction catalyst and a preparation method thereof, and also relates to the application of the perhydro N-propylcarbazole dehydrogenation reaction catalyst. Background Art

[0002] In the dehydrogenation reaction system, noble metals such as Pd and Pt are widely used due to their excellent dehydrogenation performance. However, due to their high production cost and easy poisoning and deactivation due to exposure to certain impurities, the feasibility of large-scale application of noble metal catalysts in LOHCs is limited. Therefore, the development of low-noble-metal-loading, low-cost and highly active dehydrogenation catalysts is crucial to the development of organic liquid hydrogen storage technology.

[0003] In recent years, SiO2 with excellent structure has been widely studied. This kind of material has adjustable porosity and large specific surface area, and has shown excellent performance in the field of adsorption and heterogeneous catalysis. However, the interaction between SiO2 material and active metal is weak, which is not conducive to the dispersion of active components, which may reduce the stability of the catalyst. By modifying the surface of SiO2, its performance can be significantly improved. For example, the introduction of amine functional groups on the surface of SiO2 not only adjusts the acidity and alkalinity of the catalyst surface, but also introduces specific active sites, which provides strong support for achieving diversity in catalytic reactions.

[0004] Existing studies have shown that nitrogen-containing compounds such as melamine and bipyridine are widely used for surface modification of SiO2 carriers. However, these modification methods have several inherent limitations: as for melamine, it is mainly combined with the carrier surface through hydrogen bonding and physical adsorption, and this interaction force is relatively weak, resulting in insufficient stability of the modified layer. In addition, melamine molecules are prone to self-aggregation to form large-sized crystals, resulting in uneven distribution of nitrogen sources on the carrier surface. More importantly, melamine may produce various by-products during the heat treatment process, and the presence of these by-products will have an adverse effect on the subsequent catalytic reaction. For bipyridine nitrogen sources, although they are combined with the carrier through coordination, the bonding strength is still insufficient. In addition, the high cost of bipyridine compounds has largely limited their promotion prospects in industrial-scale applications.

[0005] Based on this, providing a dehydrogenation catalyst with low noble metal loading, high stability and high catalytic activity is a technical problem that needs to be solved urgently. Summary of the invention

[0006] One of the purposes of the present invention is to provide a method for preparing a catalyst for the dehydrogenation reaction of perhydro N-propylcarbazole with low noble metal loading, high stability and high catalytic activity.

[0007] The second object of the present invention is to provide a perhydro N-propylcarbazole dehydrogenation catalyst with low noble metal loading, high stability and high catalytic activity.

[0008] The third object of the present invention is to provide an application of a catalyst for the dehydrogenation reaction of perhydro N-propylcarbazole.

[0009] The technical solution adopted by the present invention to achieve one of the purposes is: to provide a method for preparing a catalyst for the dehydrogenation reaction of perhydro N-propylcarbazole, comprising the following steps: S1, mixing the template agent with the acid and adding them to the silicon source to carry out a hydrothermal reaction, drying the product, removing the template agent and washing to obtain a porous SiO2 carrier; S2, mixing the porous SiO2 carrier and 3-aminopropyltrimethoxysilane (APTMS) in a solvent at a mass ratio of (1-4):1, stirring the mixture, washing and drying the product, and obtaining an amine functional group-modified SiO2 carrier; S3, loading palladium ions on a SiO2 carrier modified with an amine functional group to obtain a catalyst precursor; S4. The catalyst precursor is placed in a reducing atmosphere and calcined at 150-450° C. for 3-8 hours to obtain a perhydro-N-propylcarbazole dehydrogenation reaction catalyst.

[0010] The general idea of ​​the present invention is as follows: The preparation method of the catalyst provided by the present invention first grafts high-density amine functional groups on the surface of the SiO2 carrier, and then loads palladium ions onto the modified SiO2 carrier, thereby achieving the dual effects of carrier surface modification and metal nanoparticle loading. Among them, the nitrogen-containing functional group plays a dual role in the catalytic reaction through its unique electronic structure: on the one hand, the lone pair of electrons of the nitrogen-containing functional group forms a coordination bond with the N-propylcarbazole molecule, guiding the removal of hydrogen at a specific position of the molecule; on the other hand, electron transfer occurs between the amine group and palladium (Pd), increasing the Pd 0 The surrounding electron cloud density enhances the d-π feedback between Pd and the benzene ring structure in the intermediate product. This synergistic effect not only improves the selectivity of the reaction, but also optimizes the overall activity of the catalyst.

[0011] The present invention uses 3-aminopropyltrimethoxysilane (APTMS) as a nitrogen source to introduce nitrogen-containing functional groups. Compared with melamine, APTMS can not only be firmly anchored on the SiO2 surface through Si-O-Si covalent bonds, significantly improving stability, but also APTMS does not have the problem of self-polymerization to form larger crystals, resulting in uneven distribution of N sources and generation of by-products. Compared with bipyridine bonded by coordination bonds, APTMS is more stable in forming covalent bonds, and APTMS has better cost performance, which is more conducive to promotion and application.

[0012] Furthermore, in the above preparation method, the amount of APTMS added and the calcination reduction temperature are two important factors that determine the catalytic performance: A large number of experimental results show that when the amount of APTMS added is insufficient, the metal-carrier interaction will be weakened, while reducing the electron cloud density around Pd0, and ultimately reducing the number of active sites of the catalyst. On the contrary, excessive addition of APTMS will cause the catalyst pores to be blocked, resulting in a reduction in specific surface area and metal agglomeration, which significantly affects the catalytic effect. In the present invention, the mass ratio of the porous SiO2 carrier to APTMS is controlled to be (1-4):1, so that the carrier can maintain a larger specific surface area and ensure good dispersion of Pd.

[0013] As for the calcination reduction temperature, the appropriate calcination reduction temperature can enhance the interaction between metal Pd and the support, improve the dispersion of Pd, and promote the electron transfer between amine groups and Pd. These synergistic effects enhance the Pd 0 The surrounding electron cloud density enhances the density of acid sites on the catalyst surface and the adsorption stability of hydrogen species, thereby improving the adsorption capacity of the reactant perhydro N-propylcarbazole (12H-NPCZ). However, it should be noted that too high a reduction temperature will destroy the amine structure in the catalyst, resulting in a significant decrease in catalytic performance. In the present invention, the calcination reduction temperature is controlled to be 150-450°C, and the calcination reduction time is 3-8h, which can effectively improve the catalytic performance of the product.

[0014] Preferably, in the above preparation method, when the mass ratio of the porous SiO2 carrier to APTMS is controlled to be (2-3):1, the calcination temperature is 150-300°C, and the calcination time is 3-8h, the prepared catalyst has better catalytic performance and can significantly improve the hydrogen release and conversion rate.

[0015] Furthermore, in step S1, the molar ratio of the template, the acid, and the silicon source is 1:(20-40):(50-70); the acid is selected from one of hydrochloric acid, nitric acid, and phosphoric acid. Preferably, the acid is hydrochloric acid, the template is P123 template, and the silicon source is tetraethyl orthosilicate.

[0016] Furthermore, in step S1, the temperature of the hydrothermal reaction is 50-70°C and the time is 12-36h.

[0017] In step S1 of the present invention, a porous SiO2 template is prepared under a hydrothermal environment, which can not only give full play to the structural guidance effect of the template, but also utilize the hydrothermal conditions to accelerate the reaction kinetics process and promote the orderly assembly of molecules. This combined method can significantly improve the crystallinity and purity of the product and obtain a more regular crystal structure; at the same time, due to the increased solubility of the reactants under hydrothermal conditions, the molecular motion is accelerated, and the reaction rate is improved, which is conducive to the formation of a more uniform product structure. In addition, the hydrothermal conditions can also enhance the assembly behavior of the template, realize the precise control of the product pore size, shape and distribution, and the formed material usually has a tighter stacking structure and stronger chemical bonding, thereby showing excellent mechanical properties and thermal stability.

[0018] Furthermore, in step S2, the solvent includes one of toluene, tetrahydrofuran and ethanol; the stirring temperature is 70-90°C and the time is 4-8h. Preferably, the product of step S2 is washed with toluene and ethanol, filtered, and vacuum dried at 30-50°C to obtain an amine functional group-modified SiO2 carrier in the form of a white powder.

[0019] Furthermore, in step S3, the palladium salt providing palladium ions includes a combination of one or more of palladium nitrate, palladium chloride, and chloropalladic acid.

[0020] Furthermore, in step S3, the loading method includes: dissolving the palladium salt and the SiO2 carrier modified with the amino functional group in a mixed solution of ethanol and water at a ratio of palladium loading not higher than 1wt.%, and then washing and drying the product.

[0021] Preferably, in step S3, the palladium salt is first added to concentrated ammonia water, subjected to ultrasonic treatment to obtain a complex, and then mixed with an amine functional group-modified SiO2 carrier to improve the dispersion effect of Pd on the carrier.

[0022] Furthermore, in step S4, the reducing atmosphere is a mixed gas of hydrogen and argon, in which the volume percentage of hydrogen is 10%-30%.

[0023] Furthermore, in step S4, the heating rate of the calcination treatment is 5-10°C / min.

[0024] The technical solution adopted by the present invention to achieve the second purpose is: to provide a perhydro N-propylcarbazole dehydrogenation reaction catalyst, which is prepared by the preparation method according to one of the purposes of the present invention; in the perhydro N-propylcarbazole dehydrogenation reaction catalyst, the loading amount of the precious metal Pd is not higher than 1wt.%. Preferably, the loading amount of palladium is 0.9wt.%-1wt.%.

[0025] The technical solution adopted by the present invention to achieve the third purpose is: to provide an application of the catalyst for dehydrogenation of perhydro N-propylcarbazole according to the second purpose of the present invention, wherein the temperature of the dehydrogenation reaction is 180-185° C. Preferably, the temperature of the dehydrogenation reaction is 180° C.

[0026] Furthermore, in the application, the stirring speed is 200-500 rpm and the reaction time is 3 hours. Preferably, the mass ratio of the perhydro-N-propylcarbazole dehydrogenation reaction catalyst to perhydro-N-propylcarbazole (12H-NPCZ) is 1:5.

[0027] Furthermore, the perhydro N-propylcarbazole dehydrogenation reaction catalyst provided by the present invention is also suitable for the dehydrogenation reaction of organic liquid hydrogen storage materials such as dimethyl indole, dibenzyltoluene, and perhydronitroethylcarbazole.

[0028] Compared with the prior art, the present invention has the following beneficial effects: (1) The catalyst for the dehydrogenation of perhydro N-propylcarbazole and its preparation method provided by the present invention double-modifies the SiO2 carrier by grafting high-density amine functional groups on the surface and loading Pd metal nanoparticles. The nitrogen-containing functional group plays a dual role in the catalytic reaction through its unique electronic structure: on the one hand, the lone pair of electrons of the nitrogen-containing functional group forms a coordination bond with the N-propylcarbazole molecule, guiding the removal of hydrogen at a specific position of the molecule; on the other hand, electron transfer occurs between the amine group and palladium (Pd), increasing the Pd 0 The surrounding electron cloud density enhances the d-π feedback between Pd and the benzene ring structure in the intermediate product. This synergistic effect not only improves the selectivity of the reaction, but also optimizes the overall activity of the catalyst.

[0029] (2) In the catalyst prepared by the present invention, the loading amount of the precious metal Pd is not higher than 1wt.%. The catalyst is applied to the dehydrogenation reaction of perhydro-N-propylcarbazole, and complete dehydrogenation can be achieved within 3 hours at a reaction temperature of 180°C. In addition, the catalyst provided by the present invention has very excellent cycle performance, and still maintains a high hydrogen release amount and conversion rate after 10 cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a diagram of a perhydro N-propylcarbazole dehydrogenation reaction device used in the application performance test of the present invention; Figure 2 This is a graph showing the cyclic stability test results of the catalyst prepared in Example 1 of the present invention; Among them, 1-sampling port; 2-reaction raw materials; 3-catalyst; 4-oil bath pot; 5-serpentine condenser. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0032] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0033] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0034] The main parameters and experimental conditions involved in the embodiments and comparative examples of the present invention are shown in Table 1 below.

[0035] Table 1

[0036] Example 1 This embodiment provides a method for preparing a catalyst for the dehydrogenation reaction of perhydro N-propylcarbazole, comprising the following steps: Step 1: Mix the P123 template and hydrochloric acid evenly and then add tetraethyl orthosilicate, wherein the molar ratio of the P123 template, hydrochloric acid and tetraethyl orthosilicate is 1:30:60; then transfer to a hydrothermal reactor and perform hydrothermal reaction at 60°C for 24 hours. The product is dried, the template is removed and washed to obtain a porous SiO2 carrier.

[0037] Step 2: 3.0 g SiO2 was dispersed in an anhydrous toluene solution containing 1.5 g APTMS and stirred at 80 °C for 6 h. Then it was washed with toluene and ethanol, filtered, and dried in vacuum at 40 °C to obtain a white powder product, namely, an amine-functional group-modified SiO2 support (N / SiO2).

[0038] Step 3: Use PdCl2 as the Pd metal precursor, weigh 0.050 g PdCl2 and place it in a beaker, add 10 ml concentrated ammonia water, add 3 g N / SiO2 after ultrasonic treatment, dissolve it in a mixed solution of ethanol and water, and dry it to obtain the catalyst precursor.

[0039] Step 4: The precursor was calcined and reduced at 300°C in a 10% H2 / Ar atmosphere at a heating rate of 5°C / min for 3 h to obtain a perhydro-N-propylcarbazole dehydrogenation reaction catalyst.

[0040] Example 2 The difference between this embodiment and embodiment 1 is that the calcination temperature in step 4 is adjusted to 150° C., and the other steps and operating conditions remain unchanged to obtain a perhydro-N-propylcarbazole dehydrogenation reaction catalyst.

[0041] Example 3 The difference between this embodiment and embodiment 1 is that the calcination time in step 4 is adjusted to 5 hours, and the other steps and operating conditions remain unchanged to obtain a perhydro-N-propylcarbazole dehydrogenation reaction catalyst.

[0042] Example 4 The difference between this embodiment and embodiment 1 is that the calcination time in step 4 is adjusted to 8 hours, and the other steps and operating conditions remain unchanged to obtain a perhydro-N-propylcarbazole dehydrogenation reaction catalyst.

[0043] Example 5 The difference between this embodiment and embodiment 1 is that the amount of APTMS in step 2 is adjusted to 1 g, and the other steps and operating conditions remain unchanged to obtain a perhydro-N-propylcarbazole dehydrogenation reaction catalyst.

[0044] Example 6 The difference between this embodiment and embodiment 1 is that the amount of APTMS in step 2 is adjusted to 0.75 g, the calcination temperature in step 4 is adjusted to 150° C., and the remaining steps and operating conditions remain unchanged to obtain a perhydro-N-propylcarbazole dehydrogenation reaction catalyst.

[0045] Example 7 The difference between this embodiment and embodiment 6 is that the heating rate in step 4 is adjusted to 8° C. / min, and the other steps and operating conditions remain unchanged to obtain a perhydro-N-propylcarbazole dehydrogenation reaction catalyst.

[0046] Example 8 The difference between this embodiment and embodiment 6 is that the heating rate in step 4 is adjusted to 10° C. / min, and the other steps and operating conditions remain unchanged to obtain a perhydro-N-propylcarbazole dehydrogenation reaction catalyst.

[0047] Example 9 The difference between this embodiment and embodiment 1 is that the amount of APTMS in step 2 is adjusted to 3 g, the calcination temperature in step 4 is adjusted to 150° C., and the other steps and operating conditions remain unchanged to obtain a perhydro-N-propylcarbazole dehydrogenation reaction catalyst.

[0048] Example 10 The difference between this embodiment and embodiment 1 is that the calcination temperature in step 4 is adjusted to 450° C., and the other steps and operating conditions remain unchanged to obtain a perhydro-N-propylcarbazole dehydrogenation reaction catalyst.

[0049] Embodiment 11 The difference between this embodiment and embodiment 6 is that the palladium salt in step 3 is adjusted to 0.070 g of chloropalladic acid, and the other steps and operating conditions remain unchanged to obtain a perhydro N-propylcarbazole dehydrogenation reaction catalyst.

[0050] Example 12 The difference between this embodiment and embodiment 6 is that the palladium salt in step 3 is adjusted to 0.065 g of palladium nitrate, and the other steps and operating conditions remain unchanged to obtain a perhydro N-propylcarbazole dehydrogenation reaction catalyst.

[0051] Comparative Example The difference between this comparative example and Example 6 is that APTMS is not added in the catalyst preparation step, and the remaining steps and operating conditions remain unchanged to obtain the catalyst.

[0052] Application performance testing 1. Dehydrogenation reaction catalytic performance test The dehydrogenation reaction of perhydro N-propylcarbazole (12H-NPCZ) is carried out under normal pressure. The reaction apparatus is as follows: Figure 1 As shown. Weigh 0.2 g of the catalyst prepared in each embodiment and comparative example, 3 g of 1,3,5-trimethylbenzene and 1 g of 12H-NPCZ and add them to a two-necked flask. Then set the device temperature to a specified temperature of 180°C, set the stirring speed to 200 r / min after the temperature stabilizes, and start the dehydrogenation reaction timing. During the reaction, liquid samples were collected at predetermined time intervals, and in-situ detection and analysis were performed using an AgilentGC 7890B gas chromatograph, and product component analysis was performed to evaluate the catalytic dehydrogenation activity of the catalyst.

[0053] The catalytic performance of the catalysts prepared in the examples and comparative examples in the dehydrogenation reaction of perhydro-N-propylcarbazole within 180 min is shown in Table 2.

[0054] Table 2

[0055] As can be seen from the above table, Compared with the comparative example without adding APTMS, the catalysts prepared in Examples 1-12 of the present invention have better hydrogen release effect, and the hydrogen release amount and conversion rate are improved to varying degrees.

[0056] In addition, by systematically analyzing the hydrogen release and conversion rate data of Examples 1-12, it can be determined that the calcination temperature and the amount of amino functional group grafting are the two key factors affecting the performance of the catalyst. The test results of Examples 1-5 show that when the calcination reduction temperature is 150-300°C, the calcination time is 3-8h, and the mass ratio of the porous SiO2 carrier to the APTMS addition is controlled to (2-3): 1, the catalyst can show a better hydrogen release effect within 180°C, the hydrogen release is greater than 5wt.%, and the conversion rate is greater than 90%. Further, relative to Examples 2-5, Example 1 controls the mass ratio of the porous SiO2 carrier to APTMS to 2: 1, the calcination reduction temperature is 300°C and the calcination time is 3h, and the prepared catalyst has the best hydrogen release effect, achieving complete hydrogen release at 180°C and within 180min, and the conversion rate is 100%.

[0057] (II) Cyclic stability test The catalyst prepared in Example 1 was subjected to a cycle stability test. The cycle stability and dehydrogenation catalytic performance tests were conducted under the same conditions. After each dehydrogenation reaction, the catalyst was washed, filtered, and dried before the next cycle test. The cycle stability performance test results of the catalyst are shown in FIG. Figure 2 shown.

[0058] Depend on Figure 2 It can be seen that the catalyst prepared by the present invention has very excellent cycle stability. After three cycle tests, the catalyst still maintains complete catalytic activity, achieving a hydrogen release amount of 5.43 wt.% and a hydrogen release rate of 100%. Even after 10 cycles, the catalyst still exhibits good catalytic performance, with a hydrogen release amount maintained at 5 wt.% and a hydrogen release rate of 92.08%.

[0059] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a catalyst for the dehydrogenation reaction of perhydro N-propylcarbazole, characterized in that: The following steps are involved: S1, mixing the template agent with the acid and adding them to the silicon source to carry out a hydrothermal reaction, drying the product, removing the template agent and washing to obtain a porous SiO2 carrier; S2, mixing the porous SiO2 carrier and 3-aminopropyltrimethoxysilane in a solvent at a mass ratio of (1-4):1, stirring the mixture, washing and drying the product, and obtaining an amine functional group-modified SiO2 carrier; S3, loading palladium ions on an amine functional group-modified SiO2 carrier to obtain a catalyst precursor; S4. The catalyst precursor is placed in a reducing atmosphere and calcined at 150-450° C. for 3-8 hours to obtain a perhydro-N-propylcarbazole dehydrogenation reaction catalyst.

2. The preparation method according to claim 1, characterized in that: In step S1, the molar ratio of the template, the acid, and the silicon source is 1:(20-40):(50-70); the acid is selected from one of hydrochloric acid, nitric acid, and phosphoric acid; the template is P123 template, and the silicon source is tetraethyl orthosilicate.

3. The preparation method according to claim 1, characterized in that: In step S1, the temperature of the hydrothermal reaction is 50-70° C. and the time is 12-36 hours.

4. The preparation method according to claim 1, characterized in that: In step S2, the solvent includes one of toluene, tetrahydrofuran and ethanol; the stirring temperature is 70-90°C and the time is 4-8h.

5. The preparation method according to claim 1, characterized in that: In step S3, the palladium salt providing palladium ions includes a combination of one or more of palladium nitrate, palladium chloride, and chloropalladic acid.

6. The preparation method according to claim 1, characterized in that: In step S3, the loading method includes: dissolving the palladium salt and the SiO2 carrier modified with the amino functional group in a mixed solution of ethanol and water at a ratio of palladium loading not higher than 1wt.%, and then washing and drying the product.

7. The preparation method according to claim 1, characterized in that: In step S4, the reducing atmosphere is a mixed gas of hydrogen and argon, in which the volume percentage of hydrogen is 10%-30%.

8. The preparation method according to claim 1, characterized in that: In step S4, the heating rate of the calcination treatment is 5-10°C / min.

9. A catalyst for the dehydrogenation of perhydro N-propylcarbazole, characterized in that: Prepared by the preparation method according to any one of claims 1-8; in the perhydro N-propylcarbazole dehydrogenation reaction catalyst, the loading amount of the precious metal Pd is not higher than 1wt.%.

10. Use of the catalyst for dehydrogenation of perhydro N-propylcarbazole according to claim 9, characterized in that: In the application, the temperature of the dehydrogenation reaction is 180-185°C.

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