A method for preparing a palladium-supported triazine-based molecular heterojunction and its use in the catalytic dehydrogenation of dipentene

Abstract

This invention discloses a method for preparing palladium-supported triazine-based molecular heterojunction materials, comprising: mixing at least two aromatic nitrile compounds, then grinding and mixing them uniformly with a metal halide salt, calcining them in a tube furnace, washing, purifying, and drying to obtain the triazine-based molecular heterojunction material; wherein the aromatic nitrile compounds are at least two of terephthalonitrile, terephthalic acid acetonitrile, or 4,4'-dicyanobiphenyl; mixing the triazine-based molecular heterojunction material and palladium chloride-hydrochloric acid solution uniformly, heating under reflux, cooling to room temperature, adjusting the pH to alkaline with sodium hydroxide solution, adding sodium borohydride solution for reduction reaction, and after the reaction is completed, washing and drying to obtain the palladium-supported triazine-based molecular heterojunction material. Applying this catalyst to the catalytic dehydrogenation of dipentene to p-cymene can yield high-yield and high-purity p-cymene products, which is of great significance for catalyst development and the high-value utilization of biomass.

Description

Technical Field

[0001] This invention relates to the preparation of a palladium-supported triazine molecular heterojunction and its use in the catalytic dehydrogenation of dipentene, belonging to the fields of catalyst preparation and the technology of dipentene dehydrogenation to prepare cymenes. Background Technology

[0002] Industrial dipentenes are mainly composed of a mixture of double-bonded isomers of monocyclic monoterpenes and are byproducts of the industrial production of camphor or terpineol. The p-cymene prepared by the dehydrogenation reaction of industrial dipentenes is a high-value-added fine chemical product with broad application prospects in medicine, agriculture, chemical engineering, and materials.

[0003] Currently, nickel-based catalysts, such as Raney nickel and nickel formate, are the main catalysts used for the catalytic dehydrogenation of dipentene to p-cymenes. Compared with liquid-phase dehydrogenation, gas-phase dehydrogenation is more effective, but it has drawbacks such as higher reaction temperature, poorer safety, higher equipment requirements leading to higher production costs, and difficulty in separating byproducts (Applied Catalysis A, 1999, 188(1-2):287; Applied Catalysis A, 1997, 158(1-2):145; Forest Products Chemistry and Industry, 1993, 13(4):305). Therefore, the study of liquid-phase dehydrogenation reactions with mild reaction conditions, high safety, and simple operation has become a research focus for many researchers in recent years, especially the development of catalysts.

[0004] Noble metal catalysts (such as palladium, platinum, and rhodium) exhibit high catalytic activity in the dehydrogenation of aromatic compounds, and the reaction conditions are mild. Selecting suitable supports to immobilize noble metal catalysts and heterogeneously apply them to the dehydrogenation reaction of dipentene is expected to improve the yield of cymenes and refine reaction conditions, which is of great significance for promoting the development of deep processing of turpentine in my country.

[0005] Covalent triazine frameworks (CTFs) are covalent organic framework materials composed of aromatic NC=N triazine ring units and aromatic structural units connected by covalent bonds. CTFs possess nitrogen-rich properties, organic conjugated structures, and good stability, making them promising catalyst supports in heterogeneous catalysis (Macromolecular Rapid Communications, 2015, 36(20):1799). However, most CTFs suffer from high exciton binding energies and weak electron transport capabilities (Nano Today, 2021, 39:101183; Solar RRL, 2021, 5(6):2000541), making them unsuitable for the catalytic dehydrogenation of dipentene to p-cymene.

[0006] To date, there have been no reports on the application of palladium-supported triazine-based molecular heterojunctions as catalysts for the dehydrogenation of dipentene to p-cymene. Therefore, this invention utilizes at least two aromatic nitrile monomers with low cost, similar structures, and electron-donating and electron-withdrawing capabilities, respectively, to synthesize triazine-based molecular heterojunctions via molten salt method and copolymerization. A palladium-supported triazine-based molecular heterojunction catalyst is then prepared via chemical reduction and further applied to the catalytic dehydrogenation of dipentene to p-cymene. The palladium-supported triazine-based molecular heterojunction catalyst prepared by the method of this invention exhibits high activity, high selectivity, easy product separation, and easy catalyst recovery and recycling, meeting the needs of green chemistry and sustainable development. It is of great significance for catalyst development and the high-value utilization of biomass. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing palladium-supported triazine molecular heterojunctions and their use in the catalytic dehydrogenation of dipentene to p-cymene.

[0008] To solve the above-mentioned technical problems, one of the technical solutions adopted by the present invention is as follows:

[0009] A method for preparing a palladium-supported triazine-based molecular heterojunction material includes the following steps:

[0010] 1) Grind and mix at least two aromatic nitrile compounds with a metal halide salt until homogeneous, calcine in a tube furnace, wash, purify, and dry to obtain a triazine-based molecular heterojunction material; wherein the aromatic nitrile compounds are at least two of terephthalonitrile, terephthalic acid nitrile, or 4,4'-dicyanobiphenyl; and the metal halide salt is one or more of zinc chloride, lithium chloride, sodium chloride, potassium chloride, lithium bromide, potassium bromide, sodium bromide, and their mixed eutectic salts;

[0011] 2) Mix the triazine-based molecular heterojunction material and palladium chloride-hydrochloric acid solution evenly, heat to reflux, cool to room temperature, adjust the pH to alkaline with sodium hydroxide solution, add sodium borohydride solution to carry out reduction reaction, wash and dry after the reaction is completed to obtain palladium-supported triazine-based molecular heterojunction material.

[0012] The palladium-supported triazine-based molecular heterojunction material prepared above mainly contains palladium, carbon, and nitrogen elements. Its structure includes triazine ring donor-acceptor units and palladium, and its morphology is nanosheets modified with nanoparticles.

[0013] The room temperature range in this application includes temperatures from 0 to 40°C.

[0014] The inventors discovered that nitrogen in the triazine-based molecular heterostructure framework can improve the catalytic performance of supported palladium nanoparticles in the following ways: 1) The triazine-based molecular heterostructure possesses nitrogen-rich microheterocyclic rings and a donor-acceptor structure, and its nitrogen sites (triazine nitrogen and piperazine nitrogen) can provide anchoring sites for the metal, allowing the metal nanoparticles to be uniformly dispersed and anchored on the support, thus precisely controlling the size of the metal nanoparticles; 2) The negative charge exhibited by the nitrogen sites can increase the electron density of the metal particles, allowing the metal to maintain high catalytic performance. Therefore, loading palladium nanoparticles onto the triazine-based molecular heterostructure can enable the catalyst to achieve good catalytic effect and stability.

[0015] To further ensure catalytic performance, the mixture of aromatic nitrile compounds is preferably a mixture of terephthalonitrile and terephthalic acid nitrile, more preferably a mixture with a molar ratio of terephthalonitrile to terephthalic acid nitrile of 0.04:(7-8.5). The metal halide salt is preferably a mixture of sodium chloride, potassium chloride, and zinc chloride, more preferably a mixture with a molar ratio of sodium chloride, potassium chloride, and zinc chloride of (1.5-2):(1.5-2):(5-6).

[0016] During preparation, in step 1), the mass ratio of terephthalonitrile to the alkali metal is 1:(0.5-5); the calcination temperature is 150-400℃, and the calcination time is 4-24h.

[0017] To improve product purity and thus enhance catalytic effect, the washing method is as follows: the calcined material is ground into powder, water is added, and the mixture is stirred at 50–100℃ for 1–24 hours. After filtration, the resulting solid is dispersed in a 0.5–2.0 mol / L hydrochloric acid solution and stirred for 1–24 hours. After filtration, the resulting solid is washed with water until neutral to obtain the crude product. The purification and drying method is as follows: the crude product is wrapped in qualitative filter paper and placed in a Soxhlet extractor. It is extracted with methanol as solvent in an oil bath at 90–95℃ for 18–24 hours, followed by Soxhlet extraction with dichloromethane as solvent at 65–70℃ for 18–24 hours. The product is then dried in a vacuum drying oven at 60–70℃ for 8–12 hours to obtain the triazine-based molecular heterojunction material.

[0018] To further ensure the catalytic effect, in step 2) above, the concentration of palladium chloride in the hydrochloric acid-palladium chloride solution is 0.5-200 mmol / L, the concentration of hydrochloric acid is 0.1-2 mol / L, the concentration of sodium hydroxide solution is 0.1-3 mol / L, and the concentration of sodium borohydride solution is 0.05-1 mol / L. The reflux temperature is 70-90℃, and the time is 6-24 h; after reflux, the pH is adjusted to 9-12 with sodium hydroxide solution.

[0019] The theoretical palladium loading is 0.1-10 wt%, preferably 3-7 wt%, and more preferably 5 wt%, where the aforementioned loading is relative to the mass of the triazine molecular heterojunction.

[0020] The second technical solution provided by this invention is as follows:

[0021] The palladium-supported triazine molecular heterojunction material prepared above was used as a catalyst in the catalytic dehydrogenation of dipentene to prepare cymene.

[0022] The method for preparing p-cymene by catalytic dehydrogenation of dipentene is as follows: Palladium-supported triazine molecular heterojunction material and industrial dipentene are stirred and mixed, and heated to react under an inert atmosphere. After the reaction is completed, the mixture is centrifuged and the supernatant is collected to obtain the p-cymene product.

[0023] To ensure the conversion rate of dipentene and the yield of cymene, the preferred mass ratio of catalyst to industrial dipentene is (0.01-0.1):1, the reaction temperature is 160-240℃, the argon pressure is -0.1-10MPa, and the reaction time is 1-10h.

[0024] Further optimization was performed, with the mass ratio of palladium-supported triazine-based molecular heterojunction material to industrial dipentene being 0.02:1, the theoretical palladium loading being 5wt%, the reaction temperature being 220℃, the inert atmosphere being argon gas at a pressure of 0.1MPa, and the reaction time being 6h.

[0025] The palladium-supported triazine-based molecular heterojunction material obtained in this application can be recycled. The specific recycling method is as follows: after the catalytic reaction is completed, centrifugation is performed. The supernatant is the p-cymene product, while the precipitate is the palladium-supported triazine-based molecular heterojunction material. The obtained precipitate is washed with water and then with ethanol, and then vacuum dried at 50-60°C. It can then be recycled as a catalyst for the catalytic dehydrogenation of dipentene to prepare p-cymene.

[0026] The catalytic effect of the palladium-supported triazine-based molecular heterojunction material is almost unaffected after recycling, so it can be repeatedly recycled.

[0027] Any techniques not mentioned in this invention are based on existing technologies.

[0028] The beneficial effects of this invention are as follows:

[0029] 1) The palladium-supported triazine-based molecular heterojunction material provided by the present invention mainly contains palladium, carbon, and nitrogen, and contains methylene, triazine ring units and palladium in its structure, and has the morphology of nanoparticle-modified nanosheets.

[0030] 2) The palladium-supported triazine-based molecular heterojunction catalyst provided by this invention has high catalytic activity and high selectivity in the catalytic dehydrogenation of dipentene to prepare cymene, with the content of cymene in the product reaching 95.90% and the conversion rate of dipentene approaching 100%.

[0031] 3) The palladium-supported triazine-based molecular heterojunction material prepared by this invention can be recycled and reused. The recycling method is simple and easy to operate, and the catalytic effect is almost unaffected after recycling. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a scanning electron microscope image of 5% Pd / M-CTF prepared in Example 1 of the present invention;

[0034] Figure 2 This is a transmission electron microscope image of 5% Pd / M-CTF prepared in Example 1 of the present invention;

[0035] Figure 3 This is a high-resolution transmission electron microscope image of 5% Pd / M-CTF prepared in Example 1 of the present invention;

[0036] Figure 4 The transmission electron microscopy (TEM) spectrum of 5% Pd / M-CTF prepared in Example 1 of this invention;

[0037] Figure 5 This is a transmission electron microscopy (TEM) elemental distribution map of the 5% Pd / M-CTF prepared in Example 1 of this invention.

[0038] Figure 6 The X-ray powder diffraction pattern of 5% Pd / M-CTF prepared in Example 1 of this invention;

[0039] Figure 7 The Fourier transform infrared spectrum of 5% Pd / M-CTF prepared in Example 1 of this invention;

[0040] Figure 8 The X-ray photoelectron spectrum of 5% Pd / M-CTF prepared in Example 1 of this invention; Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The technical features designed in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0042] In the description of this invention, it should be noted that all terms used in this invention (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and should not be construed as limiting the invention; it should be further understood that the terms used in this invention should be understood to have the same meaning as those in the context of this specification and in the relevant field, and should not be understood in an idealized or overly formal sense, except as expressly defined in this invention.

[0043] In this embodiment, the microstructure of the sample was observed using a JSM-7610F Plus scanning electron microscope (SEM) from NJE (Japan); the microstructure and elemental distribution of the sample were obtained using a Talos F200X field emission transmission electron microscope (FET) from Thermo Fisher Scientific (USA); the composition and crystal structure information of the catalyst were obtained using a Smartlab X-ray powder diffractometer from Rigaku Corporation (Japan); the chemical composition and functional group structure information of the catalyst were obtained using a Nicolet Is50 infrared spectrometer from Thermo Fisher Scientific (USA); and the microstructure was analyzed using a K-Alpha spectrometer from Thermo Fisher Scientific (USA). + X-ray photoelectron spectroscopy was used to identify the elemental composition, elemental content, and chemical state of the material surface; the contents of dipentene series components and para-cymene in the product were obtained using an Agilent Technologies Intuvo 9000-7000D2 triple quadrupole gas chromatography-mass spectrometry system.

[0044] The conversion rate of dipentene and the selectivity of the dehydrogenation product for cymene were calculated according to Equations (1) and (2), respectively.

[0045] Conversion rate of dipentene / % = (M D1 -M D2 ) / M D1 ×100(1)

[0046] Selectivity for cymene / % = M O / (M D1 -M D2 )×100(2)

[0047] In the formula, M D1 Indicates the relative mass fraction of dipentene in the raw material; M D2 Indicates the relative mass fraction of dipentene in the reaction product; M O This indicates the relative mass fraction of cymene in the reaction products.

[0048] In the examples, the room temperature was 15–25°C. Unless otherwise specified, the stirring speed was 150 r / min.

[0049] Example 1

[0050] a) Preparation of palladium-supported triazine-based molecular heterojunction materials (5% Pd / M-CTF):

[0051] Terephthalonitrile (0.007 g, 0.04 mmol), terephthalonitrile (1 g, 7.80 mmol), sodium chloride (0.11 g, 1.88 mmol), potassium chloride (0.14 g, 1.88 mmol), and zinc chloride (0.75 g, 5.50 mmol) were uniformly mixed in a quartz mortar (50 mL) to obtain a mixed powder. The mixed powder was calcined at 300 °C for 6 hours in a tube furnace under a nitrogen atmosphere, and then allowed to cool naturally to room temperature. It was then ground into powder and washed as follows: the powder was first added to 300 mL of water and stirred at 80 °C for 12 hours, and then collected by vacuum filtration. The solid was then redispersed in 300 mL of 1.0 mol / L hydrochloric acid solution and stirred for 12 hours. The mixture was then washed 8 times with water until neutral and the crude product was collected. The crude product was purified as follows: the crude product was wrapped in qualitative filter paper and placed in a Soxhlet extractor. It was extracted with methanol as solvent under oil bath heating at 95℃ for 24 h, followed by Soxhlet extraction with dichloromethane as solvent at 70℃ for 24 h. Then it was dried in a vacuum drying oven at 70℃ for 12 h to obtain a yellow triazine-based molecular heterojunction material powder.

[0052] Then, 0.15 g of triazine-based molecular heterojunction material powder was weighed, and 12.5 mg of PdCl2, 2 mL of 2 mol / L hydrochloric acid (HCl mass concentration of 0.73 wt%), and 18 mL of water were added. After ultrasonic-assisted dispersion for 30 min, the mixture was stirred and heated under reflux at 80 °C for 8 h. The solution was then cooled to room temperature, and 1 mol / L NaOH solution was added to adjust the pH to 10. 2 mL of 0.1 mol / L NaBH4 solution was slowly added (12 drops / min). After the addition was complete, the reaction was continued to be stirred at room temperature for 2 h. The mixture was filtered and separated. The precipitate was washed with water until the filtrate was neutral and dried under vacuum at 60 °C to constant weight to obtain 5% Pd / M-CTF, in which the theoretical loading of Pd was 5 wt%.

[0053] The scanning electron microscope image of the 5% Pd / M-CTF prepared in Example 1 is shown below. Figure 1 As shown in the figure, Pd / M-CTF exhibits a porous nanosheet morphology.

[0054] The transmission electron microscope image of the 5% Pd / M-CTF prepared in Example 1 is shown below. Figure 2 As shown in the figure, palladium nanoparticles are uniformly dispersed on the nanosheets of the triazine-based molecular heterostructure.

[0055] The high-resolution transmission electron microscope image of the 5% Pd / M-CTF prepared in Example 1 is shown below. Figure 3 As shown. The locations of the palladium nanoparticles are marked with white circles. The size of the palladium nanoparticles is approximately 4-7 nm. The palladium nanoparticles have distinct lattice fringes with a lattice spacing of 0.228 nm, corresponding to the Pd(111) crystal plane.

[0056] The transmission electron microscopy (TEM) spectrum of the 5% Pd / M-CTF prepared in Example 1 is shown below. Figure 4 As shown. 5% Pd / M-CTF mainly contains C, N, and Pd elements.

[0057] The transmission electron microscopy elemental distribution of the 5% Pd / M-CTF prepared in Example 1 is shown in the figure below. Figure 5 As shown, C, N, and Pd elements are uniformly distributed in the 5% Pd / M-CTF sample, indicating that Pd nanoparticles are uniformly dispersed on M-CTF nanosheets.

[0058] The X-ray powder diffraction pattern of the 5% Pd / M-CTF prepared in Example 1 is as follows. Figure 6 As shown in the figure, the diffraction peaks of 5% Pd / M-CTF and M-CTF at 2θ = 7.6°, 14.4°, 15.4°, and 26.6° correspond to the following values, respectively. The {0002} crystal plane exhibits two broad characteristic peaks at 14.4° and 26.6°, representing the in-plane long-range molecular order of the triazine-based molecular heterojunction polymer network and the interlayer stacking of the π-conjugated aromatic structure, respectively. Simultaneously, the peaks at 2θ = 39.8° and 46.0° in the 5% Pd / M-CTF sample correspond to the (111) and (200) planes of Pd (standard spectrum JCPDF:88-2335), respectively, providing evidence for the formation of Pd nanoparticles. Furthermore, no obvious diffraction peaks for KCl, LiCl, and ZnCl2 were observed, indicating that KCl, LiCl, and ZnCl2 were completely removed during the water washing process.

[0059] The Fourier transform infrared spectrum of the 5% Pd / M-CTF prepared in Example 1 is shown below. Figure 7 As shown. 800-1800cm -1The absorption within the range is the characteristic absorption of the benzene ring and triazine ring, with the 1347 cm⁻¹ being the highest. -1 and 1512cm -1 The presence of a stretching mode of the CN bond in the triazine ring indicates that the two aromatic nitrile precursors were successfully polymerized at a relatively low synthesis temperature of 300℃. (2234cm) -1 The peak is attributed to the unreacted cyano group at the M-CTF terminus. (At 2889 cm⁻¹) -1 The presence of an absorption band corresponding to the methylene symmetric stretching vibration indicates successful polymerization of terephthalonitrile and terephthalocyanine monomers, proving the existence of a triazine molecular heterostructure. Compared to M-CTF, the position of the absorption peak in Pd / M-CTF did not change significantly, indicating that the loading of palladium nanoparticles does not affect the bulk structure of the CTF material.

[0060] The X-ray photoelectron spectrum of the 5% Pd / M-CTF prepared in Example 1 is as follows: Figure 8 As shown, the main constituent elements of Pd / M-CTF are palladium, carbon, and nitrogen. The Pd 3d spectrum consists of two asymmetric peaks assigned to the core energy levels of Pd 3d5 / 2 and Pd 3d3 / 2, which can be fitted using two bimodal peaks. The peaks near 335.4 eV and 340.3 eV are attributed to zero-valent palladium Pd. 0 The peaks near 337.5 eV and 342.9 eV correspond to divalent palladium Pd. 2+ The oxygen peak originates from the adsorption of oxygen and water from the air. In the C 1s spectrum, 284.8 eV corresponds to the sp peak on the benzene ring. 2 The binding energies of the hybrid C=C and methylene CH bonds are shown, with 286.8 eV corresponding to the binding NC=N bonds on the triazine ring. The N 1s spectrum shows that all samples contain two sets of peaks at 398.9 eV and 399.8 eV, corresponding to the sp bonds on the triazine ring, respectively. 2 The structure contains hybrid nitrogen (CN=C) and a terminal C≡N group. The presence of a cyano group is consistent with the infrared spectroscopy results. Furthermore, no elemental peaks were found for the three salts NaCl, KCl, and ZnCl₂, indicating that the salts can be removed by washing with water and acid.

[0061] b) Catalytic dehydrogenation of dipentene to prepare cymenes:

[0062] The catalyst and industrial dipentene (its composition is shown in Table 1) were mixed and stirred. Argon gas was introduced, followed by vacuuming to remove internal air, to carry out the catalytic dehydrogenation of dipentene to prepare cymene. The reaction conditions were: 5% Pd / M-CTF catalyst, 0.1 g catalyst mass, 5 g industrial dipentene mass, temperature 220℃, argon pressure 0.1 MPa, and reaction time 6 h. After the reaction, the mixture was centrifuged, and the supernatant was diluted 100 times with methanol and analyzed using gas chromatography-mass spectrometry. The dipentene conversion rate, selectivity for cymene, and content are shown in Table 3.

[0063] Example 2

[0064] The catalyst synthesis steps were the same as in Example 1, except that the amount of PdCl2 added was 1.3 mg, yielding 0.5% Pd / M-CTF. The conditions for the catalytic dehydrogenation of dipentene were: catalyst of 0.5% Pd / M-CTF (the theoretical Pd loading was 0.5 wt%), catalyst mass of 0.1 g, industrial dipentene mass of 5 g, temperature of 220 °C, argon pressure of 0.1 MPa, and reaction time of 6 h. The dehydrogenation process followed the steps in Example 1. The dipentene conversion, selectivity for cymene, and content are shown in Table 3.

[0065] Example 3

[0066] The catalyst synthesis steps were the same as in Example 1, except that the amount of PdCl2 added was 2.5 mg, yielding 1% Pd / M-CTF. The conditions for the catalytic dehydrogenation of dipentene were: catalyst of 1% Pd / M-CTF (the theoretical Pd loading was 1 wt%), catalyst mass of 0.1 g, industrial dipentene mass of 5 g, temperature of 220 °C, argon pressure of 0.1 MPa, and reaction time of 6 h. The dehydrogenation process followed the steps in Example 1. The dipentene conversion, selectivity for umbelliferous hydrocarbons, and content are shown in Table 3.

[0067] Example 4

[0068] The catalyst synthesis steps were the same as in Example 1, except that the amount of PdCl2 added was 7.5 mg, yielding 3% Pd / M-CTF g. The catalytic dehydrogenation reaction conditions for dipentene were: catalyst of 3% Pd / M-CTF (the theoretical Pd loading was 3 wt%), catalyst mass of 0.1 g, industrial dipentene mass of 5 g, temperature of 220 °C, pressure of 0.1 MPa, and reaction time of 6 h. The dehydrogenation process followed that in Example 1. The dipentene conversion, selectivity for umbelliferous hydrocarbons, and content are shown in Table 3.

[0069] Example 5

[0070] The catalyst synthesis steps were the same as in Example 1, except that the amount of PdCl2 added was 17.5 mg, yielding 7% Pd / M-CTF. The conditions for the catalytic dehydrogenation of dipentene were: catalyst of 7% Pd / M-CTF (the theoretical Pd loading was 7 wt%), catalyst mass of 0.1 g, industrial dipentene mass of 5 g, temperature of 220 °C, pressure of 0.1 MPa, and reaction time of 6 h. The dehydrogenation process followed that in Example 1. The dipentene conversion, selectivity for cymene, and content are shown in Table 3.

[0071] Example 6

[0072] The 5% Pd / M-CTF from the reaction in Example 1 was recovered as follows: The precipitate was centrifuged (8000 rpm for 5 minutes), washed sequentially with water and ethanol, and then vacuum dried at 60°C to obtain 5% Pd / M-CTF-1 for reuse once. The obtained 5% Pd / M-CTF-1 was used for the catalytic dehydrogenation of dipentene. The reaction conditions were: 5% Pd / M-CTF-1 catalyst (0.1 g), 5 g industrial dipentene, temperature 220°C, argon pressure 0.1 MPa, and reaction time 6 h. The dehydrogenation process followed that in Example 1. The dipentene conversion rate, selectivity for cymene, and content are shown in Table 3.

[0073] Example 7

[0074] The 5% Pd / M-CTF-1 obtained after the reaction in Example 6 was recovered as follows: The precipitate was centrifuged (at 8000 rpm for 5 minutes), washed sequentially with water and ethanol, and then vacuum dried at 60°C to obtain 5% Pd / M-CTF-2, which could be reused twice. The aforementioned 5% Pd / M-CTF-2 was used for the catalytic dehydrogenation of dipentene. The reaction conditions were: 5% Pd / M-CTF-2 catalyst (0.1 g), 5 g industrial dipentene, temperature 220°C, argon pressure 0.1 MPa, and reaction time 6 h. The dehydrogenation process was the same as in Example 1. The dipentene conversion rate, selectivity for cymene, and content are shown in Table 3.

[0075] Example 8

[0076] The 5% Pd / M-CTF-2 obtained after the reaction in Example 7 was recovered as follows: The precipitate was centrifuged (at 8000 rpm for 5 minutes), washed sequentially with water and ethanol, and then vacuum dried at 60°C to obtain 5% Pd / M-CTF-3, which could be reused three times. The obtained 5% Pd / M-CTF-3 was then used for the catalytic dehydrogenation of dipentene. The reaction conditions were: 5% Pd / M-CTF-3 catalyst (0.1 g), 5 g industrial dipentene, temperature 220°C, argon pressure 0.1 MPa, and reaction time 6 h. The dehydrogenation process was the same as in Example 1. The dipentene conversion rate, selectivity for cymene, and content are shown in Table 3.

[0077] Example 9

[0078] The catalyst synthesis steps were the same as in Example 1, except that the temperature in the dipentene catalytic dehydrogenation reaction was 160°C. The catalyst was 5% Pd / M-CTF, and the dehydrogenation process was as described in Example 1. The dipentene conversion, selectivity to cymenes, and content are shown in Table 3.

[0079] Example 10

[0080] The catalyst synthesis steps were the same as in Example 1, except that the temperature in the dipentene catalytic dehydrogenation reaction was 180°C. The catalyst was 5% Pd / M-CTF, and the dehydrogenation process was as described in Example 1. The dipentene conversion, selectivity to cymenes, and content are shown in Table 3.

[0081] Example 11

[0082] The catalyst synthesis steps were the same as in Example 1, except that the temperature in the dipentene catalytic dehydrogenation reaction was 200°C. The catalyst was 5% Pd / M-CTF, and the dehydrogenation process was as described in Example 1. The dipentene conversion, selectivity to cymenes, and content are shown in Table 3.

[0083] Example 12

[0084] The catalyst synthesis steps were the same as in Example 1, except that the temperature in the dipentene catalytic dehydrogenation reaction was 240°C. The catalyst was 5% Pd / M-CTF, and the dehydrogenation process was as described in Example 1. The dipentene conversion, selectivity to cymenes, and content are shown in Table 3.

[0085] Comparative Example 1

[0086] The synthesis steps of the triazine-based molecular heterojunction material powder (M-CTF) were the same as in Example 1. The experimental steps for removing the supported palladium were also described. The conditions for the catalytic dehydrogenation reaction of dipentene were: catalyst was M-CTF, catalyst mass was 0.1 g, industrial dipentene mass was 5 g, temperature was 220 °C, argon pressure was 0.1 MPa, reaction time was 6 h, and the dehydrogenation process was as described in Example 1. The dipentene conversion rate and the selectivity and content for umbelliferous hydrocarbons are shown in Table 3.

[0087] Comparative Example 2

[0088] The catalytic dehydrogenation reaction conditions for dipentene were as follows: the catalyst was commercial palladium on carbon (10% Pd / C, containing 55% water, purchased from Bidex Pharmaceuticals), with a catalyst mass of 0.1 g, and the industrial dipentene mass was 5 g; the temperature was 220 °C, the argon pressure was 0.1 MPa, and the reaction time was 6 h. The dehydrogenation process followed the procedure described in Example 1. The dipentene conversion, selectivity for cymene, and content are shown in Table 3.

[0089] Comparative Example 3

[0090] The commercial 10% Pd / C from the reaction in Comparative Example 1 was recovered as follows: The precipitate was centrifuged (at 8000 rpm for 10 minutes), washed sequentially with water and ethanol, and then vacuum dried at 60°C to obtain 10% Pd / C-1 for reuse once. The catalytic dehydrogenation reaction conditions for dipentene were: catalyst 10% Pd / C-1, catalyst mass 0.1 g, industrial dipentene mass 5 g, temperature 220°C, argon pressure 0.1 MPa, reaction time 6 h, and the dehydrogenation process was as described in Example 1. The dipentene conversion, selectivity for umbelliferous hydrocarbons, and content are shown in Table 3.

[0091] Comparative Example 4

[0092] The commercial 10% Pd / C-1 from the reaction in Comparative Example 3 was recovered as follows: The precipitate was centrifuged (at 8000 rpm for 10 minutes), washed sequentially with water and ethanol, and then vacuum dried at 60°C to obtain 10% Pd / C-2 that could be reused twice. The catalytic dehydrogenation reaction conditions for dipentene were: catalyst 10% Pd / C-2, catalyst mass 0.1 g, industrial dipentene mass 5 g, temperature 220°C, argon pressure 0.1 MPa, reaction time 6 h, and the dehydrogenation process was as described in Example 1. The dipentene conversion rate, selectivity for umbelliferous hydrocarbons, and content are shown in Table 3.

[0093] Comparative Example 5

[0094] The commercial 10% Pd / C-2 from the reaction in Comparative Example 4 was recovered as follows: The precipitate was centrifuged (8000 rpm for 10 minutes), washed sequentially with water and ethanol, and then vacuum dried at 60°C to obtain 10% Pd / C-3 that could be reused twice. The catalytic dehydrogenation reaction conditions for dipentene were: catalyst 10% Pd / C-3, catalyst mass 0.1 g, industrial dipentene mass 5 g, temperature 220°C, argon pressure 0.1 MPa, reaction time 6 h, and the dehydrogenation process was as described in Example 1. The dipentene conversion, selectivity for umbelliferous hydrocarbons, and content are shown in Table 3.

[0095] Comparative Example 6

[0096] The catalytic dehydrogenation reaction conditions for dipentene were as follows: the catalyst was H-ZSM-5 molecular sieve (Si / Al = 30), the catalyst mass was 0.1 g, the industrial dipentene mass was 5 g, the temperature was 220℃, the argon pressure was 0.1 MPa, the reaction time was 6 h, and the dehydrogenation process was as described in Example 1. The dipentene conversion rate, selectivity for umbelliferous hydrocarbons, and content are shown in Table 3.

[0097] Comparative Example 7

[0098] The catalytic dehydrogenation reaction conditions for dipentene were as follows: the catalyst was commercial Raney Ni (purchased from Ron Pharmaceuticals), with a catalyst mass of 0.1 g, and the industrial dipentene mass was 5 g; the temperature was 220 °C; the argon pressure was 0.1 MPa; and the reaction time was 6 h. The dehydrogenation process was as described in Example 1. The dipentene conversion, selectivity for cymenes, and content are shown in Table 3.

[0099] Comparative Example 8

[0100] The catalytic dehydrogenation reaction conditions for dipentene were as follows: the catalyst was a mixture of commercial palladium on carbon and Raney nickel (mixed at a mass ratio of 1:1), with a catalyst mass of 0.1 g and an industrial dipentene mass of 5 g; the temperature was 220 °C; the argon pressure was 0.1 MPa; and the reaction time was 6 h. The dehydrogenation process was as described in Example 1. The dipentene conversion rate, selectivity for umbelliferous hydrocarbons, and content are shown in Table 1.

[0101] Comparative Example 9

[0102] The catalytic dehydrogenation reaction conditions for dipentene were as follows: no catalyst was added, only heating was performed, the catalyst mass was 0.1 g, the industrial dipentene mass was 5 g, the temperature was 220℃, the argon pressure was 0.1 MPa, and the reaction time was 6 h. The dehydrogenation process was as described in Example 1. The dipentene conversion rate, selectivity to cymene, and content are shown in Table 1.

[0103] Table 1. Gas chromatography-mass spectrometry analysis results of the industrial dipentene feedstock used in each example.

[0104]

[0105] Table 1 shows the gas chromatography-mass spectrometry analysis results of the industrial dipentene raw materials used in each example. The sum of the mass fractions of the four components belonging to the dipentene series in the industrial dipentene raw materials—α-terpinene, limonene, γ-terpinene, and isoterpinene—was 89.38%.

[0106] Table 2. Gas chromatography-mass spectrometry analysis results of the industrial dipentene dehydrogenation products obtained in Example 1.

[0107]

[0108] Table 2 shows the gas chromatography-mass spectrometry analysis results of the industrial dipentene dehydrogenation products obtained in Example 1 above. Under conditions of 220°C, the dehydrogenation products of p-cymene in the 5% Pd / M-CTF-catalyzed dipentene dehydrogenation reaction mainly contained 95.90% p-cymene, essentially reaching the theoretical value, and also contained small amounts of cis or trans-p-cymene. Alkane 4.10%.

[0109] Table 3. Dipentene conversion rate, selectivity to cymene, and content in each example.

[0110]

[0111]

[0112]

[0113] Table 3 shows the dipentene conversion, selectivity for cymene, and content of the catalysts in the embodiments and comparative examples of the present invention. First, the effect of Pd loading on the catalytic activity of Pd / M-CTF was investigated. As shown in Examples 1-5, among samples with different Pd loadings, 5% Pd / M-CTF exhibited the best catalytic effect on the dehydrogenation of dipentene to cymene. The dipentene dehydrogenation product catalyzed by 5% Pd / M-CTF had the highest cymene content (reaching 95.90%), with a dipentene conversion close to 100% and a cymene selectivity of 95.90%. Reducing the Pd loading to 0.5% or increasing it to 7% both decreased the cymene content in the product. As shown in Comparative Example 1, the catalytic effect of the M-CTF support was poor when no palladium was supported.

[0114] Secondly, the stability of the Pd / M-CTF catalyst was investigated. As shown in Examples 6-8, the 5% Pd / M-CTF sample after reaction was recovered and reused three times. No significant decrease in the content of cymene in the product was observed. The catalyst from Example 8 was further recovered and reused until the 20th time, and the content of cymene in the product (greater than 95.5%) still showed almost no decrease, demonstrating the good catalytic activity stability of the Pd / M-CTF catalyst. As shown in Comparative Examples 2-5, when a commercially available palladium on carbon that had been reused three times was used as the catalyst, the decrease in the content of cymene in the product was more significant.

[0115] Furthermore, the effect of different reaction temperatures on the catalytic activity of 5% Pd / M-CTF was investigated. As shown in Examples 1 and 9-12, when the reaction temperature was 160℃, the conversion rate (96.25%) and selectivity (77.05%) of the dipentene dehydrogenation catalyzed by 5% Pd / M-CTF were relatively low, with the content of cymene in the product being only 80.05%. When the reaction temperature increased from 160℃ to 220℃, the content of cymene in the dipentene dehydrogenation catalyzed by 5% Pd / M-CTF also increased. This is because the dehydrogenation of dipentene to prepare cymene is an endothermic reaction with a significant thermal effect; increasing the reaction temperature within a suitable temperature range is beneficial for the formation of cymene. In the comparative experiments at different reaction temperatures, 5% Pd / M-CTF exhibited the best catalytic effect at 220℃. However, when the temperature exceeds 220°C, such as when it is set to 240°C, the content of p-cymene in the product of the 5% Pd / M-CTF catalytic product decreases slightly. Therefore, this application preferably uses 220°C as the reaction temperature for the dehydrogenation of dipentene to prepare p-cymene.

[0116] Finally, the catalytic activities of different types of catalysts were compared. Comparative Examples 1-8 show that the catalytic performance of 5% Pd / M-CTF is higher than that of unsupported palladium triazine molecular heterojunction M-CTF, commercial 10% Pd / C, H-ZSM-5 molecular sieve (Si / Al = 30), Raney Ni, and a mixture of commercial Pd / C and Raney Ni (mixed at a mass ratio of 1:1). Comparative Example 9 shows that when no catalyst is added and heating is only performed at 220℃ for 6 hours, the content of cymene in the product is very low (44.72%), indicating that the catalyst plays an important promoting role in the dehydrogenation reaction of dipentene.

[0117] The above examples and comparative examples fully demonstrate that palladium-supported triazine-based molecular heterojunction catalysts have good catalytic effects and stability in the dehydrogenation of dipentene to prepare cymenes.

[0118] It should be noted that some parameters or commonly used reagents in the above embodiments or comparative examples are specific or preferred embodiments under the concept of the present invention, and not limitations thereof; those skilled in the art can make adaptive adjustments within the concept and protection scope of the present invention. Furthermore, unless otherwise specified, the raw materials used can also be commercially available products in the art, or prepared by conventional methods in the art.

[0119] Furthermore, those skilled in the art should understand that although many problems exist in the prior art, each embodiment or technical solution of the present invention can be improved in only one or a few aspects, without necessarily solving all the technical problems listed in the prior art or the background art simultaneously. Those skilled in the art should understand that any content not mentioned in a claim should not be construed as a limitation on that claim.

[0120] Although terms such as terephthalonitrile, terephthalic acid nitrile, and alkali metal salts are frequently used herein, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of the invention; interpreting them as any additional limitation would be contrary to the spirit of the invention.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. Use of a palladium loaded triazine-based molecular hetero-junction material, characterized in that: Application of the catalyst in preparation of p-cymene by catalytic dehydrogenation of dipentene The mass ratio of the palladium-loaded triazine-based molecular hetero-junction material to industrial dipentene (0.01-0.1):1, the reaction temperature is 160-220℃, and the reaction time is 1-6h. The preparation method of the palladium-loaded triazine-based molecular hetero-junction material comprises the following steps: 1) at least two aromatic nitrile compounds are uniformly mixed with a metal halide salt, calcination is performed in a tube furnace, and washing, purification, and drying are performed to obtain the triazine-based molecular hetero-junction material; wherein the aromatic nitrile compound is a mixture of terephthalonitrile and p-xylylene cyanide; the metal halide salt is a mixture of sodium chloride, potassium chloride, and zinc chloride with a molar ratio of (1.5-2):(1.5-2):(5-6); the calcination temperature is 150-300℃, and the calcination time is 4-6h; 2) the triazine-based molecular hetero-junction material and a palladium chloride-hydrochloric acid solution are uniformly mixed, heated to reflux, then cooled to room temperature, adjusted to alkaline by a sodium hydroxide solution, reduced by a sodium borohydride solution, washed and dried after the reaction to obtain the palladium-loaded triazine-based molecular hetero-junction material, and the theoretical loading of palladium is 0.1-10 wt% relative to the mass of the triazine-based molecular hetero-junction.

2. Use according to claim 1, characterized in that: In step 1), the mass ratio of the aromatic nitrile compound to the metal halide salt is 1:(0.5-5); the washing method is that the calcined material is ground into powder, stirred in water at a temperature of 50-100℃ for 1-24h, filtered, the obtained solid material is dispersed in a hydrochloric acid solution with a concentration of 0.5-2.0 mol / L and stirred for 1-24h, then filtered, and the obtained solid material is washed with water to neutral to obtain a crude product; the purification and drying method is that the crude product is wrapped with qualitative filter paper and placed in a Soxhlet extractor, heated in an oil bath at 90-95℃, Soxhlet extracted with methanol as the solvent for 18-24h, then Soxhlet extracted with dichloromethane as the solvent at 65-70℃ for 18-24h, and dried in a vacuum drying box at 60-70℃ for 8-12h to obtain the triazine-based molecular hetero-junction material.

3. Use according to claim 1 or 2, characterized in that: In step 1), the aromatic nitrile compound is a mixture of terephthalonitrile and p-xylylene cyanide with a molar ratio of 0.04:(7-8.5).

4. Use according to claim 1 or 2, characterized in that: In step 2), the concentration of palladium chloride in the palladium chloride-hydrochloric acid solution is 0.5-200 mmol / L, and the concentration of hydrochloric acid is 0.1-2 mol / L; the concentration of the sodium hydroxide solution is 0.1-3 mol / L, the concentration of the sodium borohydride solution is 0.05-1 mol / L, the mass-volume ratio of the triazine-based molecular hetero-junction material to the sodium borohydride solution is 1g:(1-100)mL, the reduction reaction temperature is room temperature, and the time is 1-2h; the heating reflux temperature is 70-90℃, and the time is 6-24h; after heating reflux, the pH is adjusted to 9-12 by the sodium hydroxide solution.

5. Use according to claim 1 or 2, characterized in that: The method for preparing p-cymene by catalytic dehydrogenation of dipentene is as follows: a palladium loaded triazine-based molecular heterojunction material and industrial dipentene are stirred and mixed, the mixture is heated for reaction under protection of inert atmosphere, after the reaction is completed, centrifugal separation is performed, the supernatant is taken, and p-cymene product is obtained.

6. Use according to claim 5, characterized in that: After centrifugal separation, the obtained precipitate is sequentially subjected to water washing and ethanol washing, and then vacuum drying is performed at 50-60 DEG C, to obtain the palladium loaded triazine-based molecular heterojunction material, which is recycled for preparing p-cymene by catalytic dehydrogenation of dipentene, and the foregoing steps are recycled and repeated.

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