Carbon-based catalysts, their preparation methods and applications, and dehydrogenation methods for methylcyclohexane

Abstract

This invention relates to the field of chemical hydrogen storage, and discloses a carbon-based catalyst, its preparation method and application, and a method for the dehydrogenation of methylcyclohexane. The catalyst comprises nitrogen (N), carbon (C), hydrogen (H), and platinum nanoparticles; the catalyst has the following properties: "Pt x C y N z H a The schematic chemical composition of the catalyst is shown in the figure, where z:a = 1.5~5; z:x = 5~50; z:y < 0.016; in the catalyst, nitrogen atoms are covalently bonded to at least two carbon atoms; nitrogen atoms are covalently bonded to hydrogen atoms; the carbon tetrachloride adsorption value (CTC) of the catalyst is ≥80%; in the XRD spectrum of the catalyst, the A of the Pt(111), (200), (220), (222) crystal plane diffraction peaks of the platinum nanoparticles is ≥85%, and A = (Pt(111) peak area) / (peak area of ​​Pt(111) + peak area of ​​Pt(200) + peak area of ​​Pt(220) + peak area of ​​Pt(222))) × 100%. This catalyst has good catalytic activity and low hydrogenolysis activity, making it particularly suitable for dehydrogenation reactions, such as the dehydrogenation reaction of alkyl-substituted cycloalkanes. It can effectively control the hydrogenolysis reaction during the dehydrogenation process and reduce the generation of by-products. It is especially suitable for the application of methylcyclohexane dehydrogenation reaction. After the dehydrogenation reaction, the conversion rate of methylcyclohexane is high, and the methane content in the product is <0.3wt%.

Description

Technical Field

[0001] This invention relates to a carbon-based catalyst, its preparation method and application, and a method for the dehydrogenation of methylcyclohexane. Background Technology

[0002] Hydrogen energy is a widely available, clean, carbon-free secondary energy source with diverse applications, making it one of the most promising clean energy sources. Currently, the bottleneck for large-scale hydrogen energy application lies in its efficient and safe utilization. Organic liquid hydrogen storage technology utilizes chemical reactions to store hydrogen within an organic molecular framework, achieving ambient temperature and pressure storage and transportation of hydrogen, effectively addressing a key challenge in the hydrogen energy industry. Consequently, numerous teams in Germany, Japan, and China have conducted in-depth research and explored industrial applications of this technology.

[0003] During the dehydrogenation of hydrogen from the organic molecular skeleton, side reactions such as isomerization, hydrogenolysis, and disproportionation also occur simultaneously, with hydrogenolysis accounting for the largest proportion of these side reactions. The hydrogenolysis reaction during the dehydrogenation of methylcyclohexane involves the hydrogenolysis of toluene into benzene and methane. The methane produced increases the difficulty and cost of subsequent hydrogen purification, while hydrogenolysis also causes the loss of hydrogen storage medium. Therefore, it is essential to effectively control the hydrogenolysis reaction during dehydrogenation, control methane formation and hydrogen storage medium loss, and improve the overall techno-economic efficiency. Atsushi Nakano et al. (AppliedCatalysis A, General 2017, 543, 75-81) modified a Pt / Al2O3 catalyst with Mn, demonstrating that Mn covers low-coordination-number Pt sites in the catalyst, reducing the catalyst's hydrogenolysis activity and the methane content in the products. Chiyoda Corporation reported a process for modifying the support with sulfur (International Journal of Hydrogen Energy, 2006, 31, 1348-1356) that reduced the methane content in the product. While using a second element to cover the hydrogenolysis active sites can effectively reduce the methane content in the product, an inappropriate amount of the second element can also lead to a decline in catalyst activity. Summary of the Invention

[0004] The purpose of this invention is to provide a carbon-based catalyst, its preparation method, and its application. This catalyst has high dehydrogenation activity and low hydrogenolysis activity, and is particularly suitable for dehydrogenation reactions such as the dehydrogenation reaction of alkyl-substituted cycloalkanes. It can effectively control the hydrogenolysis reaction in the dehydrogenation process, reduce the generation of methane, and improve the economic efficiency of subsequent hydrogen purification.

[0005] According to a first aspect of the present invention, a carbon-based catalyst is provided, the catalyst comprising nitrogen (N), carbon (C), hydrogen (H), and platinum nanoparticles; said catalyst having the following formula: "Ptx C y N z H a The schematic chemical composition of the catalyst is given by z:a = 1.5~5; z:x = 5~50; z:y < 0.016; in the catalyst, nitrogen atoms are covalently bonded to at least two carbon atoms; nitrogen atoms are covalently bonded to hydrogen atoms; the carbon tetrachloride adsorption value (CTC) of the catalyst is ≥80%; in the XRD spectrum of the catalyst, the A of the diffraction peaks of the Pt(111), (200), (220), (222) crystal planes of the platinum nanoparticles is ≥85%, and A = (Pt(111) peak area / (Pt(111) peak area + Pt(200) peak area + Pt(220) peak area + Pt(222) peak area)) × 100%.

[0006] According to a second aspect of the present invention, the present invention provides a method for preparing the catalyst of the present invention, wherein the method comprises: (1) contacting a carbon-based support with an ammonia source to dope the support with nitrogen to obtain a solid rich in CN chemical bonds; (2) The solid is impregnated with an impregnation solution containing platinum ions; the solid and liquid are separated, and then dried, reduced in a reducing atmosphere, and annealed in an inert atmosphere.

[0007] According to a third aspect of the invention, the invention provides the application of the catalyst of the invention in a dehydrogenation reaction.

[0008] According to a fourth aspect of the present invention, the present invention provides a method for dehydrogenating methylcyclohexane, the method comprising: subjecting methylcyclohexane to a dehydrogenation reaction in the presence of the catalyst described in the present invention.

[0009] The catalyst of this invention has a high proportion of (111) crystal planes in the supported platinum nanoparticles, with A≥85%.

[0010] The catalyst of this invention has good catalytic activity and low hydrogenolysis activity, making it particularly suitable for use in dehydrogenation reactions, especially for the dehydrogenation of alkyl-substituted cycloalkanes. It can effectively control the hydrogenolysis reaction during the dehydrogenation process, reduce the generation of by-products, and improve the economic efficiency of the entire dehydrogenation technology. Attached Figure Description

[0011] Figure 1 This is the XRD curve of the carbon-based catalyst sample prepared in Example 1 of this invention. Detailed Implementation

[0012] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0013] This invention provides a carbon-based catalyst comprising nitrogen (N), carbon (C), hydrogen (H), and platinum nanoparticles; the catalyst has the following properties: "Pt x C y N z H a The schematic chemical composition of the catalyst is given by z:a = 1.5~5; z:x = 5~50; z:y < 0.016; in the catalyst, nitrogen atoms are covalently bonded to at least two carbon atoms; nitrogen atoms are covalently bonded to hydrogen atoms; the carbon tetrachloride adsorption value (CTC) of the catalyst is ≥80%; in the XRD spectrum of the catalyst, the A of the diffraction peaks of the Pt(111), (200), (220), (222) crystal planes of the platinum nanoparticles is ≥85%, and A = (Pt(111) peak area / (Pt(111) peak area + Pt(200) peak area + Pt(220) peak area + Pt(222) peak area)) × 100%.

[0014] The carbon-based catalyst provided by this invention has good catalytic activity and low hydrogenolysis activity, making it particularly suitable for the dehydrogenation of alkyl-substituted cycloalkanes, especially for the dehydrogenation reaction of methylcyclohexane. After the dehydrogenation reaction, the conversion rate of methylcyclohexane is high, and the methane content in the product is <0.3wt%.

[0015] According to a preferred embodiment of the present invention, the carbon tetrachloride adsorption value (CTC) of the catalyst is 90-120%.

[0016] According to a preferred embodiment of the present invention, in the XRD pattern of the catalyst, the ratio of the Pt(111) peak area to the Pt(220) peak area is ≥15; and the ratio of the Pt(111) peak area to the Pt(222) peak area is ≥20. The catalyst of the present invention that satisfies the foregoing characteristics has superior performance.

[0017] According to a preferred embodiment of the present invention, the particle size of the platinum nanoparticles in the catalyst is 10-20 nm. The catalyst of the present invention, satisfying the foregoing characteristics, exhibits superior performance.

[0018] Catalysts that meet the aforementioned requirements can achieve the purpose of this invention, and there are no special requirements for their specific structure, etc. According to one embodiment of this invention, the N and C elements in the catalyst are provided by a nitrogen-containing carbon-based support, and the platinum nanoparticles are loaded on the nitrogen-containing carbon-based support.

[0019] In this invention, the range of carbon-based supports that can be selected in the catalyst is relatively wide. This is an illustrative example, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the carbon-based support is selected from one or more of graphene, carbon nanotubes, and activated carbon. In the embodiments of the invention, activated carbon is used as the carbon-based support to illustrate the advantages of the invention, but it does not limit the scope of the invention.

[0020] In this invention, there are no special requirements for the content of each element in the nitrogen-containing carbon-based support of the catalyst. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the content of N in the nitrogen-containing carbon-based support is 0.1-2 wt%. The aforementioned technical solution has the advantage of enhancing the interaction between the support and platinum nanoparticles.

[0021] According to a preferred embodiment of the present invention, in the catalyst of the present invention, the number of N atoms covalently bonded to three C atoms accounts for 43%-67% of the total number of N atoms. The molecular sieve of the present invention, satisfying the foregoing requirements, possesses both high dehydrogenation activity and low hydrogenolysis activity.

[0022] According to a preferred embodiment of the present invention, the platinum nanoparticles in the catalyst exist in the form of elemental matter; the a content of the platinum nanoparticles is preferably 85-95%, more preferably 90%-94%.

[0023] In this invention, the composition of the catalyst can be selected from a wide range. This is an illustrative example, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the platinum content, based on the total weight of the catalyst, is 0.1 wt%-1.5 wt%, preferably 0.2 wt%-0.9 wt%, for example, 0.3 wt%, 0.4 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, etc. In this embodiment of the invention, a platinum content of 0.5 wt% is used to illustrate the advantages of the invention.

[0024] According to a preferred embodiment of the present invention, the nitrogen content, based on the total weight of the catalyst, is 0.5 wt%-1.7 wt%, preferably 0.7 wt%-1.3 wt%, for example 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, etc.

[0025] In this invention, there are no special requirements for the preparation method of the catalyst. According to one embodiment of the present invention, the present invention provides a method for preparing the catalyst of the present invention, wherein the method includes: (1) The carbon-based support is brought into contact with an ammonia source to dope the support with nitrogen, resulting in a solid rich in CN chemical bonds; (2) The solid is impregnated with an impregnation solution containing platinum ions; the solid and liquid are separated, and then dried, reduced in a reducing atmosphere, and annealed in an inert atmosphere.

[0026] In this invention, the catalyst preparation process employs a two-stage heat treatment process. First, the dried catalyst precursor is placed in a reducing atmosphere to form elemental platinum, followed by annealing. The initial reduction converts the platinum compound into elemental platinum, which has better thermal stability, avoiding the aggregation of platinum elements caused by direct high-temperature reduction, which would form uncontrollable large-sized platinum nanoparticles and reduce catalyst activity. The subsequent annealing enhances the mobility of platinum atoms, allowing the platinum nanoparticles to fuse within a controllable range, resulting in a slight increase in size (the clear Pt crystal diffraction peaks observed in the catalyst obtained in Example 1 also demonstrate the high-temperature fusion phenomenon of the nanoparticles). The highly active crystal faces (crystal faces with hydrogenolysis activity) formed by the nanoparticles during the reduction stage gradually disappear, and the area ratio of the (111) crystal face diffraction peaks of the platinum nanoparticles also increases accordingly.

[0027] In this invention, there are no special requirements for the type of ammonia source in step (1). The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the ammonia source is selected from liquid ammonia and / or a mixture of ammonia and an inert gas, preferably a mixture of ammonia and an inert gas.

[0028] According to a preferred embodiment of the present invention, the concentration of ammonia in the mixed gas is 5-20 vol%, for example, 5 vol%, 8 vol%, 10 vol%, 15 vol%, 18 vol%, 20 vol%, etc. During the contact process between the carbon-based support and ammonia, ammonia reacts with the carbon-based support to form CN chemical bonds. When N forms covalent bonds with at least two C atoms simultaneously, the structure is relatively stable; when it forms covalent bonds with three C atoms simultaneously, the group stability is optimal, and the anchoring effect of N on the metal nanoparticles is also strongest. Therefore, controlling the connection mode of N and C on the support is crucial for the subsequent catalyst treatment. However, the connection mode of N and C is closely related to the physical quantity "ammonia flow rate / support mass". If the "ammonia flow rate / support mass" is too low, the N element content of the support is low, and N is mainly connected with one C; if the "ammonia flow rate / support mass" is too high, the carbon skeleton of the support is destroyed, and N mainly forms covalent bonds with two C atoms. In the product, the proportion of N connected with three C atoms is relatively low. At the same time, the ammonia content in the treatment gas also affects the connection mode of N and C. The inventors of this invention, through extensive experimental research, concluded that when the concentration of ammonia in the treated gas is 5-20 vol%, and the ammonia flow rate / carrier mass is 5-30 mL·min... -1 ·g -1 At that time, the N atoms connected to the three C atoms in the resulting carrier have an appropriate proportion.

[0029] According to a preferred embodiment of the present invention, the inert gas in the mixed gas is preferably one or more of argon, nitrogen and helium. Argon is used as an example in the embodiments of the present invention to illustrate the advantages of the present invention, but this does not limit the scope of the present invention.

[0030] In this invention, the contact conditions between the carbon-based support and the ammonia source can be selected over a wide range. For this invention, the preferred conditions include: the ammonia source flow rate (ammonia meter) / support mass being 5-30 mL / min. -1 ·g -1 For example, 5 mL·min -1 ·g -1 10 mL·min -1 ·g -1 15 mL·min -1 ·g -1 20 mL·min -1 ·g -1 25 mL·min -1 ·g -1 30 mL·min -1 ·g -1 wait.

[0031] In this invention, the temperature conditions for contact between the carbon-based carrier and the ammonia source can be selected over a wide range. For this invention, the preferred contact temperature is 800-1000℃, such as 810℃, 860℃, 910℃, 950℃, 990℃, 1000℃, etc.

[0032] In this invention, the contact time between the carbon-based carrier and the ammonia source can be selected within a wide range, and is specifically determined based on factors such as temperature, for example, the contact time is 4-8 hours.

[0033] In this invention, there are no special requirements for the contact method between the carbon-based carrier and the ammonia source, as long as sufficient contact is achieved. Generally, contact is achieved through a tubular furnace, which is well known to those skilled in the art, and will not be described in detail here.

[0034] In this invention, the reduction temperature T1 in step (2) can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, T1 is 300-400℃, for example, 300℃, 320℃, 350℃, 370℃, 390℃, etc.

[0035] In this invention, there are no special requirements for the reduction method in step (2). It is generally carried out in a reducing gas. According to a preferred embodiment of this invention, the reducing gas is a hydrogen-containing gas, preferably a mixture of hydrogen and an inert gas, for example, a mixture with a hydrogen content of 70-100 vol%.

[0036] In this invention, there are no special requirements for the restoration time, as long as the restoration effect is achieved. According to a preferred embodiment of this invention, the restoration time is 4-5 hours.

[0037] In this invention, the aforementioned technical solutions can all achieve the purpose of this invention. In step (2), the annealing conditions can be adjusted as needed. For this invention, the preferred annealing conditions in step (2) include: annealing temperature T2 = T1 + (50~100)℃, preferably T2 is 420-470℃, for example, 420℃, 430℃, 440℃, 450℃, 460℃, etc., and the annealing is carried out in an annealing gas, which is an inert gas. The aforementioned technical solutions have the advantage of increasing the proportion of (111) crystal plane content in catalyst nanoparticles.

[0038] In this invention, the catalyst preparation process employs a two-stage heat treatment process. First, the dried catalyst precursor is reduced in a reducing atmosphere at temperature T1 to form elemental platinum. Then, it is annealed at a higher temperature (T1 + (50~100) °C) under an inert atmosphere. The initial reduction at a lower temperature converts the platinum compound into elemental platinum, which has better thermal stability, avoiding the aggregation of platinum elements caused by direct high-temperature reduction, which would form uncontrollable large-sized platinum nanoparticles and reduce the catalyst activity. Subsequently, annealing at a slightly higher temperature under an inert atmosphere gives the platinum atoms stronger mobility, allowing the platinum nanoparticles to fuse together within a controllable range, resulting in a slight increase in size (the clear Pt crystal diffraction peaks observed in the catalyst obtained in Example 1 also prove the high-temperature fusion phenomenon of nanoparticles). The highly active crystal planes (crystal planes with hydrogenolysis activity) formed by the nanoparticles during the reduction stage gradually disappear, and the proportion of the diffraction peak area of ​​the (111) crystal plane of the platinum nanoparticles also increases accordingly.

[0039] According to a preferred embodiment of the present invention, the inert gas is one or more of argon, helium and nitrogen.

[0040] In this invention, there are no special requirements for the annealing time, as long as the desired annealing effect is achieved. According to a preferred embodiment of this invention, the annealing time is 1-3 hours.

[0041] In this invention, the purpose of this invention can be achieved by using the aforementioned preparation methods. In step (2), the range of types of impregnation solutions containing platinum ions is relatively wide. The following is an illustrative description, but it does not limit the scope of this invention. Preferably, the impregnation solution containing platinum ions is one or more of chloroplatinic acid aqueous solution, dichlorotetraaminoplatinum aqueous solution, and tetraammine nitrate platinum aqueous solution.

[0042] In this invention, there are no special requirements for the solid-liquid ratio in the immersion contact. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the solid-liquid ratio in the immersion contact is 0.5-1.5, for example, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, etc.

[0043] In this invention, the concentration of platinum ions in the impregnation solution can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the concentration of platinum ions in the impregnation solution is 10-40 mg / mL, for example, 15 mg / mL, 18 mg / mL, 20 mg / mL, 23 mg / mL, 25 mg / mL, 28 mg / mL, 30 mg / mL, 32 mg / mL, 35 mg / mL, etc.

[0044] In this invention, there are no special requirements for the conditions of immersion contact in step (2). The following is an illustrative description, but it does not limit the scope of the invention. For this invention, the preferred conditions for immersion contact include: a temperature of 25-40°C, preferably 30-40°C. The time is determined according to the temperature, etc., and is generally 3-4 hours.

[0045] According to a preferred embodiment of the present invention, the pH value is adjusted to 3.5-5.5 during the immersion contact process, more preferably 3.5-4.5.

[0046] In this invention, there are no special requirements for the method used to achieve the target pH value in step (2). According to a preferred embodiment of this invention, the pH value is adjusted by adding an acidic solution.

[0047] In this invention, there are no special requirements for the type of acidic solution. According to a preferred embodiment of the invention, the acidic solution is selected from one or more of hydrochloric acid, acetic acid, citric acid and nitric acid.

[0048] In this invention, there are no special requirements for the solid-liquid separation method in step (2), such as by filtration.

[0049] In this invention, the solid obtained from solid-liquid separation is dried to obtain the precursor of the catalyst of this invention. This invention has no special requirements for the drying temperature, for example, the drying temperature is 80-120℃.

[0050] In this invention, there are no special requirements for the drying time; generally, it is best to achieve the desired drying effect. According to a preferred embodiment of this invention, the drying time is 4-8 hours.

[0051] In this invention, the catalyst prepared by the preparation method provided by this invention has a platinum nanoparticle (111) crystal plane ratio of ≥85%, which effectively inhibits the hydrogenolysis activity of the catalyst. When the catalyst prepared by the preparation method of this invention is used to carry out the dehydrogenation reaction of alkyl-substituted cycloalkanes, the methane content in the product is <0.3wt%.

[0052] The catalyst of the present invention is particularly suitable for use in dehydrogenation reactions. The present invention provides the application of the catalyst of the present invention in the dehydrogenation of alkyl-substituted cycloalkanes; preferably, the application step includes: carrying out a dehydrogenation reaction of alkyl-substituted cycloalkanes in the presence of the catalyst of the present invention.

[0053] In this invention, there are no special requirements for the chain length of the alkyl group in the alkyl-substituted cycloalkanes. According to a preferred embodiment of this invention, the alkyl group is a C1-C3 alkyl group.

[0054] In this invention, there are no special requirements for the chain length of the cycloalkanes in the alkyl-substituted cycloalkanes. According to a preferred embodiment of this invention, the cycloalkanes are C3-C9 cycloalkanes.

[0055] According to a preferred embodiment of the present invention, the alkyl-substituted cycloalkane is one or more selected from methylcyclohexane, ethylcyclohexane, 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane, and 1,4-dimethylcyclohexane. The advantages of the present invention are illustrated by dehydrogenation of methylcyclohexane in the examples.

[0056] According to a preferred embodiment of the present invention, the alkyl-substituted cycloalkane is methylcyclohexane.

[0057] In this invention, the temperature range for the dehydrogenation reaction of methylcyclohexane is relatively wide. For this invention, the temperature is 350-470℃, for example, 360℃, 380℃, 410℃, 430℃, 450℃, 460℃, etc. In this embodiment of the invention, 460℃ is used as an example to illustrate the advantages of the invention, but this does not limit the scope of the invention.

[0058] In this invention, the mass hourly space velocity (MHSV) for the methylcyclohexane dehydrogenation reaction can be selected over a wide range; for this invention, the MHSV is 1-10 h⁻¹. -1 For example, 3h -1 5h -1 7h -1 8h -1 9h -1 In this embodiment of the invention, 8h is used. -1 The advantages of the present invention are illustrated by way of example, but are not limited thereto.

[0059] The catalyst of this invention can effectively control the generation of byproducts in the dehydrogenation reaction of methylcyclohexane. According to this invention, after the dehydrogenation reaction, the methane content in the product after 72 hours of reaction is <0.3wt%.

[0060] In this invention, the dehydrogenation reaction is generally carried out in a reaction tube, which is well known to those skilled in the art, and will not be described in detail here.

[0061] The present invention will be described in detail below through embodiments.

[0062] In the following embodiments, The crystal structure of the catalyst was analyzed using a D / Max-2400X XRD from Rigaku Corporation, Japan. The XRD was performed with Cu target Kα radiation, X-ray wavelength 0.154 nm, tube voltage 40 kV, tube current 100 mA, and scan rate 6° / min. The area of ​​each diffraction peak was calculated by integration using peak fitting software, and the Pt content in the sample was tested using ICP. XPS was used to analyze the bonding mode of N and C atoms and the content of corresponding nitrogen species in the catalyst; The carbon tetrachloride adsorption capacity (CTC) of the catalyst was determined according to GB / T 12496.5-1999.

[0063] The particle size of Pt nanoparticles was calculated using XRD curves combined with the Scherrer equation.

[0064] The methane content in the products of the dehydrogenation of methylcyclohexane to produce hydrogen was detected using an Agilent 7890B gas chromatograph.

[0065] The activated carbon is a commercially available product from Tianjin Carbon Membrane Environmental Technology Co., Ltd., with the brand name CC1500-1840.

[0066] In the following embodiments of the present invention, XPS analysis of the connection mode of N and C atoms and the corresponding nitrogen species content revealed that in all samples, nitrogen atoms were covalently connected to at least two carbon atoms; nitrogen atoms were covalently connected to hydrogen atoms.

[0067] In the following embodiments of the present invention, the catalyst has Pt x C y N z H a The schematic chemical composition of the z:a, z:x, and z:y is summarized in Table 1.

[0068] Example 1 30 g of activated carbon support was placed in a tube furnace, and an ammonia / argon mixture with an ammonia concentration of 10 vol% was introduced. The ammonia flow rate (measured as ammonia) / support mass was 30 mL·min. -1 ·g -1 The mixture was contacted at 800℃ for 6 hours to obtain a solid. 20 g of the obtained solid was placed in 20 mL of an aqueous solution of chloroplatinic acid (20 mg / mL), and hydrochloric acid was added to adjust the pH to 4. The solution was then allowed to stand at 30℃ for 4 hours. Subsequently, it was filtered and dried at 100℃ for 6 hours to obtain precursor A. Precursor A was reduced at 350℃ in a hydrogen / argon mixture with a hydrogen content of 90 vol% for 4 hours. It was then annealed at 420℃ in an argon atmosphere for 2 hours.

[0069] In the catalyst, N and C atoms are connected by covalent bonds. XPS was used to analyze the bonding mode of N and C atoms and the corresponding nitrogen species content. ICP was used to determine the platinum content in the catalyst, and elemental analysis was used to determine the nitrogen content. XRD was used to characterize the crystal structure of the catalyst, and the results are as follows: Figure 1As shown, the catalyst exhibits diffraction peaks at 2Theta of 40° and 46°, corresponding to the (111), (200), (220), and (222) crystal plane diffraction of Pt, respectively. The area of ​​each diffraction peak can be calculated using peak fitting software, thereby calculating the proportion of the (111) crystal plane diffraction peak. The Pt element content, nitrogen element content, and nitrogen species content in the catalyst are listed in Table 1. The CTC value of the catalyst is 97%.

[0070] Dehydrogenation of methylcyclohexane to produce hydrogen: In a reaction tube, the catalyst and methylcyclohexane were reacted under a hydrogen atmosphere. The catalyst loading was 1 g, the reaction temperature was 460 °C, and the mass hourly space velocity (WHSV) of methylcyclohexane was 8 h⁻¹. -1 The product after 72 hours of reaction was subjected to full component analysis to obtain the methane content and methylcyclohexane conversion rate. The results are summarized in Table 1.

[0071] Example 2 30 g of activated carbon support was placed in a tube furnace, and an ammonia / argon mixture with an ammonia concentration of 20 vol% was introduced. The ammonia flow rate (as ammonia) / support mass was 10 mL·min. -1 ·g -1 The mixture was contacted at 800℃ for 4 hours to obtain a solid. 15 g of the obtained solid was placed in 26 ml of a 10 mg / mL aqueous solution of dichlorotetraaminoplatinum, and acetic acid was added to adjust the pH to 4.5. The solution was then allowed to stand at 35℃ for 3 hours. Subsequently, it was filtered and dried at 90℃ for 8 hours to obtain precursor A. Precursor A was reduced at 320℃ in a hydrogen / argon mixture with a hydrogen content of 99 vol% for 5 hours. It was then annealed at 420℃ in a helium atmosphere for 3 hours.

[0072] In the catalyst, N and C atoms are connected by covalent bonds. XPS was used to analyze the bonding mode of N and C atoms and the corresponding nitrogen species content. ICP was used to determine the platinum content in the catalyst, and elemental analysis was used to determine the nitrogen content. XRD was used to characterize the crystal structure of the catalyst. The Pt, nitrogen, and nitrogen species contents in the catalyst are listed in Table 1. The CTC value of the catalyst is 111%.

[0073] Dehydrogenation of methylcyclohexane to produce hydrogen: In a reaction tube, the catalyst and methylcyclohexane were reacted under a hydrogen atmosphere. The catalyst loading was 1 g, the reaction temperature was 460 °C, and the mass hourly space velocity (WHSV) of methylcyclohexane was 8 h⁻¹. -1 The product after 72 hours of reaction was subjected to full component analysis to obtain the methane content and methylcyclohexane conversion rate. The results are summarized in Table 1.

[0074] Example 3 30 g of activated carbon support was placed in a tube furnace, and an ammonia / argon mixture with an ammonia concentration of 5 vol% was introduced. The ammonia flow rate (measured as ammonia) / support mass was 5 mL·min. -1 ·g -1 The mixture was contacted at 1000℃ for 4 hours to obtain a solid. 15 g of the solid was placed in 30 mL of an aqueous solution of platinum tetraamminenitrate (13 mg / mL), and nitric acid was added to adjust the pH to 5.5. The solution was then allowed to stand at 35℃ for 3 hours. Subsequently, it was filtered and dried at 90℃ for 8 hours to obtain precursor A. Precursor A was reduced at 400℃ in a hydrogen / argon mixture (70 vol%) for 5 hours. It was then annealed at 470℃ in a helium atmosphere for 1 hour.

[0075] In the catalyst, N and C atoms are connected by covalent bonds. XPS was used to analyze the bonding mode of N and C atoms and the corresponding nitrogen species content. ICP was used to determine the platinum content in the catalyst, and elemental analysis was used to determine the nitrogen content. XRD was used to characterize the crystal structure of the catalyst. The Pt, nitrogen, and nitrogen species contents in the catalyst are listed in Table 1. The CTC value of the catalyst is 90%.

[0076] Dehydrogenation of methylcyclohexane to produce hydrogen: In a reaction tube, the catalyst and methylcyclohexane were reacted under a hydrogen atmosphere. The catalyst loading was 1 g, the reaction temperature was 460 °C, and the mass hourly space velocity (WHSV) of methylcyclohexane was 8 h⁻¹. -1 The product after 72 hours of reaction was subjected to full component analysis to obtain the methane content and methylcyclohexane conversion rate. The results are summarized in Table 1.

[0077] Example 4 The method and steps are the same as in Example 1, except that the reduction temperature is 380°C and the annealing temperature is 480°C. The catalyst CTC value is 100%.

[0078] Example 5 The method steps are the same as in Example 1, except that no acid is added to adjust the pH. The catalyst CTC value is 96%.

[0079] Example 6 The method and steps were the same as in Example 1, except that the pH value was adjusted to 2 after acid treatment. The catalyst CTC value was 94%.

[0080] Example 7 30 g of activated carbon carrier was placed in a tube furnace, and an ammonia / helium mixture with an ammonia concentration of 16 vol% was introduced. The ammonia flow rate (as ammonia) / carrier mass was 18 mL·min. -1 ·g -1The mixture was contacted at 910℃ for 4 hours to obtain a solid. 20 g of the obtained solid was placed in 17 mL of an aqueous solution with a concentration of 25 mg / mL chloroplatinic acid, and hydrochloric acid was added to adjust the pH to 3.7. The solution was then allowed to stand at 32℃ for 4 hours. Subsequently, it was filtered and dried at 110℃ for 5 hours to obtain precursor A. Precursor A was reduced with hydrogen at 330℃ for 3 hours, followed by annealing at 430℃ in an argon atmosphere for 2 hours.

[0081] In the catalyst, N and C atoms are connected by covalent bonds. XPS was used to analyze the bonding mode of N and C atoms and the corresponding nitrogen species content. ICP was used to determine the platinum content in the catalyst, and elemental analysis was used to determine the nitrogen content. XRD was used to characterize the crystal structure of the catalyst. The Pt, nitrogen, and nitrogen species contents in the catalyst are listed in Table 1. The CTC value of the catalyst is 112%.

[0082] Dehydrogenation of methylcyclohexane to produce hydrogen: In a reaction tube, the catalyst and methylcyclohexane were reacted under a hydrogen atmosphere. The catalyst loading was 1 g, the reaction temperature was 460 °C, and the mass hourly space velocity (WHSV) of methylcyclohexane was 8 h⁻¹. -1 The product after 72 hours of reaction was subjected to full component analysis to obtain the methane content and methylcyclohexane conversion rate. The results are summarized in Table 1.

[0083] Example 8 30 g of activated carbon support was placed in a tube furnace, and an ammonia / helium mixture with an ammonia concentration of 20 vol% was introduced. The ammonia flow rate (as ammonia) / support mass was 25 mL·min. -1 ·g -1 The mixture was contacted at 950℃ for 4 hours to obtain a solid. 20 g of the obtained solid was placed in 37 mL of an aqueous solution of chloroplatinic acid with a concentration of 35 mg / mL. Nitric acid was added to adjust the pH of the solution to 3.5, and the mixture was allowed to stand at 25℃ for 4 hours. Subsequently, it was filtered and dried at 120℃ for 4 hours to obtain precursor A. Precursor A was reduced with hydrogen at 350℃ for 4 hours, followed by annealing at 400℃ under a nitrogen atmosphere for 2 hours.

[0084] In the catalyst, N and C atoms are connected by covalent bonds. XPS was used to analyze the bonding mode of N and C atoms and the corresponding nitrogen species content. ICP was used to determine the platinum content in the catalyst, and elemental analysis was used to determine the nitrogen content. XRD was used to characterize the crystal structure of the catalyst. The Pt, nitrogen, and nitrogen species contents in the catalyst are listed in Table 1. The CTC value of the catalyst is 118%.

[0085] Dehydrogenation of methylcyclohexane to produce hydrogen: In a reaction tube, the catalyst and methylcyclohexane were reacted under a hydrogen atmosphere. The catalyst loading was 1 g, the reaction temperature was 460 °C, and the mass hourly space velocity (WHSV) of methylcyclohexane was 8 h⁻¹. -1 The product after 72 hours of reaction was subjected to full component analysis to obtain the methane content and methylcyclohexane conversion rate. The results are summarized in Table 1.

[0086] Comparative Example 1 The method and steps were followed in Example 1, except that the activated carbon support did not undergo an ammonia treatment stage. The results are shown in Table 1. The catalyst CTC value was 78%.

[0087] Comparative Example 2 The method steps of Example 1 were followed, except that the catalyst precursor did not undergo an annealing treatment stage. The results are shown in Table 1. The catalyst CTC value was 85%.

[0088] Table 1

[0089] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A carbon-based catalyst, characterized in that, The catalyst comprises nitrogen (N), carbon (C), hydrogen (H), and platinum nanoparticles; the catalyst has the following properties: Pt x C y N z H a The schematic chemical composition of z:a = 1.5~5; z:x = 5~50; z:y < 0.016; In the catalyst, nitrogen atoms are covalently bonded to at least two carbon atoms; nitrogen atoms are covalently bonded to hydrogen atoms. The catalyst has a carbon tetrachloride adsorption value (CTC) of ≥80%; In the XRD spectrum of the catalyst, the A of the Pt(111), (200), (220), (222) crystal plane diffraction peaks of the platinum nanoparticles is ≥85%, and A = (Pt(111) peak area / (Pt(111) peak area + Pt(200) peak area + Pt(220) peak area + Pt(222) peak area)) × 100%.

2. The catalyst according to claim 1, wherein, The catalyst has a carbon tetrachloride adsorption value (CTC) of 90-120%; and / or In the XRD pattern of the catalyst, the ratio of Pt(111) peak area to Pt(220) peak area is ≥15; the ratio of Pt(111) peak area to Pt(222) peak area is ≥20; and / or The particle size of the platinum nanoparticles in the catalyst is 10-20 nm.

3. The catalyst according to claim 1 or 2, wherein, The nitrogen and carbon elements in the catalyst are provided by a nitrogen-containing carbon-based support, and the platinum nanoparticles are loaded on the nitrogen-containing carbon-based support. Preferably, the carbon-based support is selected from one or more of graphene, carbon nanotubes, and activated carbon; Preferably, the nitrogen content in the nitrogen-containing carbon-based support is 0.1-2 wt%; Preferably, the number of N atoms covalently bonded to the three C atoms accounts for 43%-67% of the total number of N atoms.

4. The catalyst according to any one of claims 1-3, wherein, The platinum nanoparticles in the catalyst exist in elemental form; and / or The a a content of platinum nanoparticles is 85%-95%, preferably 90%-94%; and / or The platinum content, based on the total weight of the catalyst, is 0.1 wt%-1.5 wt%, preferably 0.2 wt%-0.9 wt%; and / or The nitrogen content of the catalyst is 0.5 wt%-1.7 wt%, preferably 0.7 wt%-1.3 wt%, based on the total weight of the catalyst.

5. A method for preparing the catalyst according to any one of claims 1-4, characterized in that, The method includes: (1) The carbon-based support is brought into contact with an ammonia source to dope the support with nitrogen, resulting in a solid rich in CN chemical bonds; (2) The solid is impregnated with an impregnation solution containing platinum ions; the solid and liquid are separated, and then dried, reduced in a reducing atmosphere, and annealed in an inert atmosphere.

6. The preparation method according to claim 5, wherein, In step (1), The ammonia source is selected from liquid ammonia and / or a mixture of ammonia and an inert gas, preferably a mixture of ammonia and an inert gas; more preferably, the concentration of ammonia in the mixture is 5-20 vol%, and the inert gas is one or more of argon, nitrogen and helium. and / or Contact conditions include: ammonia source flow rate (ammonia meter) / carrier mass of 5-30 mL / min. -1 ·g -1 ; and / or temperature 800-1000℃; and / or time 4-8h.

7. The preparation method according to claim 5 or 6, wherein, In step (2), The reduction temperature is T1, the annealing temperature is T2, T2 = T1 + (50~100)℃, preferably T2 is 420-470℃; and / or The reduction conditions include a reduction temperature T1 of 300-400℃.

8. The preparation method according to any one of claims 5-7, wherein, In step (2), The impregnation solution containing platinum ions is selected from one or more of the following: aqueous solution of chloroplatinic acid, aqueous solution of dichlorotetraaminoplatinum, and aqueous solution of tetraamminenitrate platinum. and / or Conditions for immersion contact include: The solid-liquid mass ratio is 0.5-1.5; and / or The platinum ion concentration in the impregnation solution is 10-40 mg / mL; and / or The temperature is 25-40℃, preferably 30-40℃; and / or pH value is 3.5-5.5; and / or The pH value is adjusted to the target value using an acidic solution during the immersion contact process; preferably, the acidic solution is selected from one or more of hydrochloric acid, acetic acid, citric acid and nitric acid.

9. The use of the catalyst according to any one of claims 1-4 in dehydrogenation reactions, more preferably in the dehydrogenation of alkyl-substituted cycloalkanes; Preferably, in the alkyl-substituted cycloalkanes, the alkyl group is a C1-C3 alkyl group, and the cycloalkanes are C3-C9 cycloalkanes; More preferably, the alkyl-substituted cycloalkanes are selected from one or more of methylcyclohexane, ethylcyclohexane, 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane, and 1,4-dimethylcyclohexane.

10. A method for dehydrogenating methylcyclohexane, characterized in that, The method comprises: carrying out a dehydrogenation reaction of methylcyclohexane in the presence of the catalyst described in any one of claims 1-4; Preferably, the conditions for the dehydrogenation reaction include: The temperature is 350-470℃; and / or the mass hourly space velocity of methylcyclohexane is 1-10 h⁻¹. -1 ; Preferably, after the dehydrogenation reaction, the methane content in the product is <0.3wt%.

Images