A catalyst for the dehydrogenation of perhydro-N-propylcarbazole, its preparation method and application

Abstract

This invention provides a catalyst for the dehydrogenation of perhydro-N-propylcarbazole and its preparation method. The method uses 3-aminopropyltrimethoxysilane (APTMS) as the nitrogen source, grafts a high density of amino functional groups onto the surface of a SiO2 support, and loads palladium ions onto the modified SiO2 support, achieving the dual effects of support surface modification and metal nanoparticle loading. The catalyst prepared by this invention has broad application potential and is suitable for perhydro-N-propylcarbazole dehydrogenation reaction systems, significantly improving catalyst activity and selectivity. The amino-modified catalyst exhibits significantly enhanced adsorption capacity for reactants, improved reaction selectivity, and significantly enhanced catalytic activity. The catalyst preparation method provided by this invention is simple and efficient, offering an innovative research path for developing highly selective, highly active, and low-noble-metal-loading Pd-based dehydrogenation catalysts, with broad prospects for promotion and application.

Description

Technical Field

[0001] This invention belongs to the field of dehydrogenation reaction catalyst technology, specifically relating to a perhydro-N-propylcarbazole dehydrogenation reaction catalyst and its preparation method, as well as the application of the above-mentioned perhydro-N-propylcarbazole dehydrogenation reaction catalyst. Background Technology

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

[0003] In recent years, SiO2, with its excellent structure, has been extensively studied. This type of material possesses tunable porosity and a large specific surface area, exhibiting superior performance in adsorption and heterogeneous catalysis. However, the interaction between SiO2 and active metals is weak, which is detrimental to the dispersion of active components and may reduce catalyst stability. Modifying the surface of SiO2 can significantly improve its performance. For example, introducing amine functional groups into the SiO2 surface not only modulates the surface acidity and basicity of the catalyst but also introduces specific active sites, providing strong support for achieving diversity in catalytic reactions.

[0004] Existing research indicates that nitrogen-containing compounds such as melamine and bipyridine are widely used for surface modification of SiO2 supports. However, these modification methods have several inherent limitations: Melamine binds to the support surface primarily through hydrogen bonding and physical adsorption, resulting in relatively weak interactions and insufficient stability of the modified layer. Furthermore, melamine molecules are prone to self-aggregation, forming large crystals and causing uneven distribution of the nitrogen source on the support surface. More importantly, melamine may generate various byproducts during heat treatment, which can adversely affect subsequent catalytic reactions. While bipyridine nitrogen sources bind to the support through coordination, the bond strength remains insufficient. In addition, the high cost of bipyridine compounds significantly limits their prospects for large-scale industrial application.

[0005] Therefore, providing a dehydrogenation catalyst with low noble metal loading, high stability, and high catalytic activity is an urgent technical problem to be solved. Summary of the Invention

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

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

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

[0009] One of the technical solutions adopted to achieve the objective of this invention is: to provide a method for preparing a catalyst for the dehydrogenation reaction of perhydro-N-propylcarbazole, comprising the following steps:

[0010] S1. The template agent and acid are mixed and added to the silicon source for hydrothermal reaction. The product is dried, the template agent is removed and washed to obtain a porous SiO2 support.

[0011] S2. The porous SiO2 support and 3-aminopropyltrimethoxysilane (APTMS) were mixed in a solvent at a mass ratio of (1-4):1 and stirred. The product was washed and dried to obtain an amino functional group modified SiO2 support.

[0012] S3. Palladium ions are loaded onto an amino-functionalized SiO2 support to obtain a catalyst precursor;

[0013] S4. The catalyst precursor is placed in a reducing atmosphere and calcined at 150-450℃ for 3-8 hours to obtain the perhydroN-propylcarbazole dehydrogenation catalyst.

[0014] The overall concept of this invention is as follows:

[0015] The catalyst preparation method provided by this invention involves first grafting a high density of amine functional groups onto the surface of a SiO2 support, and then loading palladium ions onto the modified SiO2 support, thereby achieving the dual effects of support surface modification and metal nanoparticle loading. The nitrogen-containing functional groups play a dual role in the catalytic reaction through their unique electronic structure: on the one hand, the lone pair electrons of the nitrogen-containing functional groups form coordination bonds with the N-propylcarbazole molecule, guiding the removal of hydrogen at specific positions on the molecule; on the other hand, electron transfer occurs between the amine group and palladium (Pd), enhancing the Pd content. 0 The increased electron cloud density enhances the d-π feedback interaction between Pd and the benzene ring structure in the intermediate. This synergistic effect not only improves the selectivity of the reaction but also optimizes the overall activity of the catalyst.

[0016] This invention introduces nitrogen-containing functional groups using 3-aminopropyltrimethoxysilane (APTMS) as a nitrogen source. Compared to melamine, APTMS not only exhibits significantly improved stability by being firmly anchored to the SiO2 surface through Si-O-Si covalent bonds, but also avoids the problems of uneven N-source distribution and byproduct formation caused by self-aggregation leading to large crystals. Compared to bipyridine, which is bound by coordination bonds, APTMS forms more stable covalent bonds and offers better cost-effectiveness, making it more suitable for widespread promotion and application.

[0017] Furthermore, in the above preparation method, the amount of APTMS added and the calcination reduction temperature are two important factors determining the catalytic performance:

[0018] Numerous experimental results show that insufficient APTMS addition weakens the metal-support interaction, reduces the electron cloud density around Pd0, and ultimately decreases the number of active sites on the catalyst. Conversely, excessive APTMS addition causes pore blockage in the catalyst, leading to a decrease in specific surface area and metal agglomeration, significantly affecting the catalytic effect. In this invention, controlling the mass ratio of porous SiO2 support to APTMS at (1-4):1 allows the support to maintain a large specific surface area and ensures good Pd dispersion.

[0019] Regarding calcination reduction temperature, a suitable calcination reduction temperature can enhance the interaction between metallic Pd and the support, improve the dispersion of Pd, and promote electron transfer between amine groups and Pd. These synergistic effects improve the Pd... 0 The increased electron cloud density enhances the density of acidic sites on the catalyst surface and the adsorption stability for hydrogen species, thereby improving the adsorption capacity for the reactant perhydro-N-propylcarbazole (12H-NPCZ). However, it is important to note that excessively high reduction temperatures can damage the amine structure in the catalyst, leading to a significant decrease in catalytic performance. In this invention, controlling the calcination reduction temperature to 150-450℃ and the calcination reduction time to 3-8 hours can effectively improve the catalytic performance of the product.

[0020] Preferably, in the above preparation method, when the mass ratio of porous SiO2 support to APTMS is controlled at (2-3):1, the calcination temperature is 150-300℃, and the calcination time is 3-8h, the obtained catalyst has better catalytic performance and can significantly improve the hydrogen release and conversion rate.

[0021] Further, in step S1, the molar ratio of the template agent, acid, and silicon source is 1:(20-40):(50-70); the acid is selected from hydrochloric acid, nitric acid, and phosphoric acid. Preferably, the acid is hydrochloric acid, the template agent is P123 template agent, and the silicon source is tetraethyl orthosilicate.

[0022] Furthermore, in step S1, the hydrothermal reaction temperature is 50-70℃ and the time is 12-36h.

[0023] In step S1 of this invention, the preparation of porous SiO2 templates under hydrothermal conditions not only fully utilizes the structure-directing effect of the template agent but also accelerates the reaction kinetics process and promotes the ordered assembly of molecules. This combined method can significantly improve the crystallinity and purity of the product, resulting in a more regular crystal structure. Simultaneously, due to the increased solubility of reactants and accelerated molecular motion under hydrothermal conditions, the reaction rate is enhanced, which is beneficial for forming a more uniform product structure. Furthermore, hydrothermal conditions can enhance the assembly behavior of the template agent, enabling precise control over the pore size, shape, and distribution of the product. The resulting materials typically exhibit a denser packing structure and stronger chemical bonding, thus demonstrating excellent mechanical properties and thermal stability.

[0024] Further, in step S2, the solvent includes one of toluene, tetrahydrofuran, and ethanol; the stirring temperature is 70-90℃, 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℃ to obtain an amino-functionalized SiO2 support in the form of a white powder.

[0025] Furthermore, in step S3, the palladium salt providing palladium ions includes one or more combinations of palladium nitrate, palladium chloride, and chloropalladium acid.

[0026] Further, in step S3, the loading method includes: dissolving the palladium salt and the amino functional group modified SiO2 support in a mixed solution of ethanol and water at a palladium loading of no more than 1 wt.%, and then washing and drying the product.

[0027] Preferably, in step S3, palladium salt is first added to concentrated ammonia water, and a complex is obtained by ultrasonic treatment. Then, it is mixed with SiO2 support modified with amine functional groups to improve the dispersion effect of Pd on the support.

[0028] Furthermore, in step S4, the reducing atmosphere is a mixture of hydrogen and argon, wherein the volume percentage of hydrogen in the mixture is 10%-30%.

[0029] Furthermore, in step S4, the heating rate of the calcination treatment is 5-10℃ / min.

[0030] The second objective of this invention is achieved by providing a perhydro-N-propylcarbazole dehydrogenation catalyst, prepared by the method described in one objective of this invention; wherein the loading of the noble metal Pd in ​​the perhydro-N-propylcarbazole dehydrogenation catalyst is not higher than 1 wt.%. Preferably, the palladium loading is 0.9 wt.%-1 wt.%.

[0031] The third objective of this invention is achieved by providing an application of the perhydro-N-propylcarbazole dehydrogenation catalyst according to the second objective of this invention, wherein the dehydrogenation reaction temperature is 180-185°C. Preferably, the dehydrogenation reaction temperature is 180°C.

[0032] Furthermore, in the aforementioned application, the stirring speed is 200-500 rpm, and the reaction time is 3 h. Preferably, the mass ratio of the perhydro-N-propylcarbazole dehydrogenation catalyst to perhydro-N-propylcarbazole (12H-NPCZ) is 1:5.

[0033] Furthermore, the perhydro-N-propylcarbazole dehydrogenation catalyst provided by this invention is also applicable to the dehydrogenation reaction of organic liquid hydrogen storage materials such as dimethylindole, dibenzyltoluene, and perhydro-N-ethylcarbazole.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] (1) The perhydro-N-propylcarbazole dehydrogenation catalyst and its preparation method provided by this invention involve dual modification of the SiO2 support by surface grafting of high-density amine functional groups and Pd metal nanoparticle support. The nitrogen-containing functional groups play a dual role in the catalytic reaction through their unique electronic structure: on the one hand, the lone pair electrons of the nitrogen-containing functional groups form coordination bonds with the N-propylcarbazole molecule, guiding the removal of hydrogen at specific positions on the molecule; on the other hand, electron transfer occurs between the amine group and palladium (Pd), enhancing the Pd content. 0 The increased electron cloud density enhances the d-π feedback interaction between Pd and the benzene ring structure in the intermediate. This synergistic effect not only improves the selectivity of the reaction but also optimizes the overall activity of the catalyst.

[0036] (2) In the catalyst prepared by the present invention, the loading of the noble metal Pd is not higher than 1 wt.%. When this catalyst is applied to the dehydrogenation reaction of perhydro-N-propylcarbazole, 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 excellent cycling performance, and still maintains a high hydrogen release and conversion rate after 10 cycles. Attached Figure Description

[0037] Figure 1 This is a diagram of the perhydroN-propylcarbazole dehydrogenation reaction apparatus used in the performance testing of this invention.

[0038] Figure 2 The graph shows the cycle stability test results of the catalyst prepared in Example 1 of this invention.

[0039] Among them, 1-sampling port; 2-reaction raw material; 3-catalyst; 4-oil bath; 5-serpentine condenser. Detailed Implementation

[0040] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0042] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0043] The main parameters and experimental conditions involved in the various embodiments and comparative examples of the present invention are shown in Table 1 below.

[0044] Table 1

[0045]

[0046] Example 1

[0047] This embodiment provides a method for preparing a catalyst for the dehydrogenation reaction of perhydro-N-propylcarbazole, including the following steps:

[0048] Step 1: P123 template agent and hydrochloric acid are mixed evenly and then tetraethyl orthosilicate is added. The molar ratio of P123 template agent, hydrochloric acid and tetraethyl orthosilicate is 1:30:60. Then the mixture is transferred to a hydrothermal reactor and hydrothermally reacted at 60°C for 24 hours. The product is dried, the template agent is removed and washed to obtain a porous SiO2 support.

[0049] Step 2: 3.0 g SiO2 was dispersed in anhydrous toluene solution containing 1.5 g APTMS and stirred at 80 °C for 6 h. Then, the mixture was washed and filtered with toluene and ethanol, and dried under vacuum at 40 °C to obtain a white powder product, namely the amino functional group modified SiO2 support (N / SiO2).

[0050] Step 3: Using PdCl2 as a Pd metal precursor, weigh 0.050 g of PdCl2 and place it in a beaker, add 10 ml of concentrated ammonia, sonicate, add 3 g of N / SiO2, dissolve in a mixed solution of ethanol and water, and dry to obtain the catalyst precursor.

[0051] Step 4: The precursor was calcined and reduced to 300℃ for 3 h under a 10% H2 / Ar atmosphere at a heating rate of 5℃ / min to obtain the perhydro-N-propylcarbazole dehydrogenation catalyst.

[0052] Example 2

[0053] The difference between this embodiment and Example 1 is that the calcination temperature in step 4 is adjusted to 150°C, while the other steps and operating conditions remain unchanged, to obtain a perhydroN-propylcarbazole dehydrogenation catalyst.

[0054] Example 3

[0055] The difference between this embodiment and Example 1 is that the calcination time in step 4 is adjusted to 5 hours, while the other steps and operating conditions remain unchanged, thus obtaining a perhydroN-propylcarbazole dehydrogenation catalyst.

[0056] Example 4

[0057] The difference between this embodiment and Example 1 is that the calcination time in step 4 is adjusted to 8 hours, while the other steps and operating conditions remain unchanged, to obtain a perhydroN-propylcarbazole dehydrogenation catalyst.

[0058] Example 5

[0059] The difference between this embodiment and Example 1 is that the amount of APTMS in step 2 is adjusted to 1g, while the other steps and operating conditions remain unchanged, to obtain a perhydroN-propylcarbazole dehydrogenation catalyst.

[0060] Example 6

[0061] The difference between this embodiment and Example 1 is that the amount of APTMS in step 2 is adjusted to 0.75g, the calcination temperature in step 4 is adjusted to 150℃, and the other steps and operating conditions remain unchanged, thus obtaining a perhydroN-propylcarbazole dehydrogenation catalyst.

[0062] Example 7

[0063] The difference between this embodiment and Example 6 is that the heating rate in step 4 is adjusted to 8°C / min, while the other steps and operating conditions remain unchanged, thus obtaining a perhydroN-propylcarbazole dehydrogenation catalyst.

[0064] Example 8

[0065] The difference between this embodiment and Example 6 is that the heating rate in step 4 is adjusted to 10℃ / min, while the other steps and operating conditions remain unchanged, thus obtaining a perhydroN-propylcarbazole dehydrogenation catalyst.

[0066] Example 9

[0067] The difference between this embodiment and Example 1 is that the amount of APTMS in step 2 is adjusted to 3g, the calcination temperature in step 4 is adjusted to 150℃, and the other steps and operating conditions remain unchanged, thus obtaining a perhydroN-propylcarbazole dehydrogenation catalyst.

[0068] Example 10

[0069] The difference between this embodiment and Example 1 is that the calcination temperature in step 4 is adjusted to 450°C, while the other steps and operating conditions remain unchanged, to obtain a perhydroN-propylcarbazole dehydrogenation catalyst.

[0070] Example 11

[0071] The difference between this embodiment and Example 6 is that the palladium salt in step 3 is adjusted to 0.070g of chloropalladium acid, while the other steps and operating conditions remain unchanged, to obtain a perhydroN-propylcarbazole dehydrogenation catalyst.

[0072] Example 12

[0073] The difference between this embodiment and Example 6 is that the palladium salt in step 3 is adjusted to 0.065g palladium nitrate, while the other steps and operating conditions remain unchanged, to obtain the perhydroN-propylcarbazole dehydrogenation catalyst.

[0074] Comparative Example

[0075] The difference between this comparative example and Example 6 is that APTMS is not added in the catalyst preparation steps, while the remaining steps and operating conditions remain unchanged, and the catalyst is obtained.

[0076] Application performance testing

[0077] (a) Catalytic performance test of dehydrogenation reaction

[0078] The dehydrogenation reaction of perhydro-N-propylcarbazole (12H-NPCZ) was carried out under atmospheric pressure, and the reaction apparatus was as follows: Figure 1 As shown. 0.2 g of the catalyst prepared in each example and comparative example, along with 3 g of 1,3,5-trimethylbenzene and 1 g of 12H-NPCZ, were weighed and added to a two-necked flask. The apparatus temperature was then set to the specified temperature of 180°C. After the temperature stabilized, the stirring speed was set to 200 r / min, and the dehydrogenation reaction timer was started. During the reaction, liquid samples were collected at predetermined time intervals, and in-situ analysis was performed using an Agilent GC 7890B gas chromatograph to evaluate the catalyst's catalytic dehydrogenation activity through product component analysis.

[0079] The catalytic performance of the catalysts prepared in each example and comparative example in the dehydrogenation reaction of perhydro-N-propylcarbazole within 180 min is shown in Table 2.

[0080] Table 2

[0081]

[0082] As can be seen from the above table,

[0083] Compared with the comparative example without APTMS, the catalysts prepared in Examples 1-12 of this invention have better hydrogen release effects, and the amount of hydrogen released and the conversion rate are improved to varying degrees.

[0084] Furthermore, through systematic analysis of the hydrogen release and conversion rate data of Examples 1-12, it can be determined that calcination temperature and the amount of amine functional group grafting are the two key factors affecting catalyst performance. The test results of Examples 1-5 show that when the calcination reduction temperature is 150-300℃, the calcination time is 3-8h, and the mass ratio of porous SiO2 support to APTMS is controlled at (2-3):1, the catalyst exhibits better hydrogen release performance within 180℃, with a hydrogen release amount greater than 5 wt.% and a conversion rate greater than 90%. Further, compared to Examples 2-5, Example 1, by controlling the mass ratio of porous SiO2 support to APTMS at 2:1, the calcination reduction temperature at 300℃, and the calcination time at 3h, produces a catalyst with the best hydrogen release performance, achieving complete hydrogen release within 180℃ and 180min, with a conversion rate of 100%.

[0085] (ii) Cyclic stability test

[0086] The catalyst prepared in Example 1 was subjected to cycle stability testing. Cycle stability and dehydrogenation reaction catalytic performance testing were conducted under the same conditions. After each dehydrogenation reaction, the catalyst was washed, filtered, and dried before the next cycle experiment. The cycle stability test results of this catalyst are as follows: Figure 2 As shown.

[0087] Depend on Figure 2 As can be seen, the catalyst prepared by this invention has excellent cycle stability. After three cycles, the catalyst still maintains complete catalytic activity, achieving a hydrogen release of 5.43 wt.% and a hydrogen release rate of 100%. Even after 10 cycles, the catalyst still exhibits good catalytic performance, with the hydrogen release maintained at 5 wt.% and the hydrogen release rate reaching 92.08%.

[0088] The above are merely 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 recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. Use of a catalyst for dehydrogenation of perhydro-N-propylcarbazole, characterized in that, In the application, the mass ratio of the perhydro-N-propylcarbazole dehydrogenation catalyst to perhydro-N-propylcarbazole is 1:5, the dehydrogenation temperature is 180°C, and the time is 3h; The preparation method of the perhydro-N-propylcarbazole dehydrogenation catalyst comprises the following steps: S1, mixing the template agent with the acid and then adding the silicon source, carrying out hydrothermal reaction, drying the product, removing the template agent and washing to obtain the porous SiO2 carrier; S2, mixing the porous SiO2 carrier and 3-aminopropyltrimethoxysilane in a mass ratio of (2-3):1 in a solvent, stirring treatment, and drying the product to obtain the amine group functional group modified SiO2 carrier; S3, loading palladium ions on the amine group functional group modified SiO2 carrier to obtain a catalyst precursor; S4, placing the catalyst precursor in a reducing atmosphere, calcining at 150-300°C for 3-8h to obtain the perhydro-N-propylcarbazole dehydrogenation catalyst; in the perhydro-N-propylcarbazole dehydrogenation catalyst, the loading amount of noble metal Pd is 0.9wt.%-1.0wt.%.

2. Use according to claim 1, characterized in that, In step S1, the molar ratio of the template agent, 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 agent is a P123 template agent, and the silicon source is tetraethyl orthosilicate.

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

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

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

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

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

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

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