Rhodium monatomic / nano-diamond-graphene composite material catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of chemical catalysis, and relates to a rhodium monatomic / nano-diamond-graphene composite material catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: firstly preparing a nano-diamond-graphene composite material as a carrier, then dispersing rhodium on a graphene shell layer on the surface of the carrier in a monatomic form by adopting an impregnation process, and carrying out reduction heat treatment to obtain the rhodium-based nano-diamond-graphene composite material catalyst. The catalyst efficiently dehydrogenates n-butane in mixed feed gas to generate butene, and the use temperature of the catalyst is 450-500 DEG C. Compared with a traditional platinum-tin bimetallic catalyst, the rhodium monatomic / nano-diamond-graphene composite material catalyst disclosed by the invention can realize efficient conversion of n-butane to generate butene under a low-temperature condition, has no pollution to the environment, and is green and environment-friendly.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical catalysis, and relates to a rhodium single atom / nano-diamond-graphene composite material catalyst, a preparation method and application thereof, in particular to a catalyst for an alkane direct dehydrogenation reaction to produce olefins. More specifically, the present application relates to a composite material catalyst taking a nano-diamond-graphene composite material as a carrier and metal rhodium as an active component, a preparation method thereof and application in a n-butane direct dehydrogenation reaction to produce butene. BACKGROUND

[0002] Butene, as a key basic chemical raw material, plays an important role in the modern chemical industry chain. Its main uses include the synthesis of butadiene, methyl ethyl ketone, sec-butyl alcohol, pentanal, isooctene and various butene polymers, and it is an important basic raw material for the production of medicines, fuels, synthetic rubber and adhesives. In the past decade, with the continuous growth of demand for downstream chemical products, especially in the fields of high-performance polymers, fine chemicals and new energy materials, the market demand for butene has shown an increasing trend year by year, and the traditional production process has been difficult to meet the growing market demand. It is worth noting that China still relies partly on imports for basic chemical raw materials such as butene. According to relevant data, the import volume of butene in China in 2024 still reached 36,000 tons. At the same time, there are a large amount of low-carbon alkanes in shale gas, oilfield associated gas and by-products of methanol-to-olefin processes worldwide. These resources are currently mostly used as fuels, and their utilization value has not been fully realized, resulting in waste of carbon resources and environmental burden. Therefore, how to efficiently and selectively convert these low-carbon alkanes into corresponding low-carbon olefins has become one of the key issues for the petrochemical industry to increase economic benefits and sustainable development. Therefore, the development of an efficient n-butane direct dehydrogenation catalyst for butene has great strategic significance and practical demand for realizing the high-value conversion of low-carbon resources, ensuring the safety of the supply chain of key chemical raw materials, and promoting the green upgrading of the petroleum and chemical industry.

[0003] Currently, the catalysts used in the industrial process of n-butane direct dehydrogenation to produce olefins are mainly solid supported catalysts, among which platinum-tin bimetallic catalysts, chromium oxide catalysts and vanadium oxide catalysts are the most widely used. However, these traditional catalyst systems have a significant drawback: their intrinsic catalytic activity at low temperatures is low, which requires the industrial operating temperature to be maintained above 530°C. Such a high reaction temperature not only causes a huge energy consumption in the production process, but also easily leads to deep cracking of alkanes and rapid carbon deposition on the surface of the catalyst, resulting in a decrease in catalyst selectivity and a shortening of service life. Therefore, the development of new dehydrogenation catalysts with high catalytic activity and good stability at relatively low temperatures has become an important development direction in this technical field.

[0004] Single-atom catalysts have shown great potential in the field of heterogeneous catalysis. For noble metal supported catalysts, dispersing and stabilizing noble metals as individual atoms on the support surface can theoretically achieve near 100% utilization of noble metal atoms. This not only greatly improves the utilization efficiency of metal atoms but also modulates their electronic structure and reaction pathways through strong metal-support interactions, thereby enhancing catalytic activity while strengthening their resistance to sintering and carbon deposition. This can significantly improve catalytic efficiency and greatly reduce the amount of noble metal used, which is of great significance for reducing the cost of industrial catalysts. However, the inherent thermodynamic instability caused by the high surface free energy of single-atom catalysts makes the active components prone to sintering and agglomeration during the reaction, leading to a decline in reaction performance. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention, through careful design of the support material, utilizes the interaction between the metal and the support and the spatial obstruction of metal atom aggregation by the support to apply a single-atom rhodium catalyst to the direct dehydrogenation reaction of n-butane, thus developing a high-performance, low-cost, and environmentally friendly catalyst.

[0006] The purpose of this invention is to provide a rhodium single-atom / nanodiamond-graphene composite catalyst, its preparation method, and its application. The rhodium single-atom / nanodiamond-graphene composite catalyst prepared by this invention can be used in the direct dehydrogenation of n-butane to butene, achieving efficient catalysis of the direct dehydrogenation of n-butane to butene at relatively low temperatures.

[0007] To achieve the above-mentioned objectives, the specific technical solution adopted by the present invention is as follows: A rhodium single-atom / nanodiamond-graphene composite catalyst, wherein the catalyst uses metallic rhodium as the active component and nanodiamond-graphene composite material as the support; wherein the rhodium loading in the catalyst is 0.001~0.1%, preferably 0.01~0.1%.

[0008] The nanodiamond-graphene composite material has a core-shell structure, with nanodiamond forming the core and graphene covering the outer shell; the thickness of the graphene shell is 0.6-6 nm; the particle size of the nanodiamond-graphene composite material is 10-600 nm.

[0009] In this catalyst, rhodium is supported on the surface of the nanodiamond-graphene composite support in an atomically dispersed form, and forms stable metal-carbon bonds with carbon atoms at carbon defect sites in the graphene layer.

[0010] A method for preparing a rhodium single-atom / nanodiamond-graphene composite catalyst includes the following steps: (1) Using nanodiamond as raw material, a nanodiamond-graphene composite material carrier is obtained through a high-temperature heat treatment process; (2) The rhodium precursor solution was loaded onto the nanodiamond-graphene composite material carrier obtained in step (1) by impregnation process to obtain the rhodium-based nanodiamond-graphene composite material catalyst precursor. (3) The catalyst precursor obtained in step (2) is placed in a reactor and subjected to reduction heat treatment under a mixed gas of hydrogen and inert gas to finally obtain a rhodium single atom / nanodiamond-graphene composite catalyst.

[0011] Further, the preparation process of the nanodiamond-graphene composite material carrier in step (1) is as follows: the nanodiamond raw material is subjected to high-temperature calcination treatment at 900-1100℃, preferably 1000-1100℃, under an inert atmosphere with a flow rate of 80-150 mL / min for 3-5 hours, preferably 4-5 hours; the nanodiamond raw material has a particle size of 10-600 nm, and the inert atmosphere is one or both of He and Ar.

[0012] Further, the impregnation process described in step (2) is specifically operated as follows: 200 mg of nanodiamond-graphene composite material carrier is weighed into 2-6 mL of anhydrous ethanol, and then the corresponding volume of rhodium nitrate precursor solution is measured into the above solution according to the target loading amount. After ultrasonic treatment for 2-10 min, it is stirred for 12-24 h, and then vacuum dried at 60-100℃ for 10-24 h, and naturally cooled to room temperature; the concentration of the rhodium nitrate precursor solution is 10~20 g / L.

[0013] Further, in the hydrogen and inert gas mixture described in step (3), the volume fraction of hydrogen is 10-30%, and the total flow rate of the mixture is controlled at 20-30 mL / min; the temperature range of the reduction heat treatment is 300-500℃, preferably 400-500℃; the reduction time is 1-3h, preferably 1-2h; after the reduction heat treatment is completed, it is cooled to room temperature under the protection of a pure helium atmosphere with a flow rate of 7-30 mL / min.

[0014] Application of a rhodium single-atom / nanodiamond-graphene composite catalyst in the dehydrogenation reaction of n-butane.

[0015] The n-butane dehydrogenation reaction is carried out in the presence of a catalyst, with a catalyst dosage of 10-50 g and a reaction temperature controlled at 450-500 °C. The gas hourly space velocity is 1000-120000 mL / (g·h), and the gas composition is n-butane, hydrogen, and helium, with a molar ratio of 1:(0.5-5):(40-50).

[0016] Compared with the prior art, the present invention has the following significant advantages and beneficial technical effects: 1. The catalyst of this invention utilizes the abundant carbon defects and functional groups on the surface of the nanodiamond-graphene composite support. Through strong metal-support interactions with rhodium atoms, it achieves high dispersion and stable fixation of rhodium species at the atomic scale. This single-atom dispersion allows the atomic utilization rate of the precious metal rhodium to theoretically reach 100%, significantly reducing the amount of precious metal used in the catalyst. This achieves highly efficient catalysis while saving on catalyst manufacturing costs.

[0017] 2. The catalyst of this invention exhibits excellent catalytic activity at relatively low temperatures (e.g., 480°C). The initial n-butane conversion rate, calculated per unit mass of rhodium, can reach 4.3 mol / (g·h), while the selectivity for the target product, butene, can reach 99.7%, which is superior to the performance of conventional catalysts at similar temperatures.

[0018] 3. The catalyst of this invention can achieve efficient dehydrogenation of n-butane under mild conditions of 450-500℃. This operating temperature is lower than the high temperature range of 530-680℃ required by traditional industrial dehydrogenation equipment, which can significantly reduce the heat input of the reaction process, effectively save energy consumption, and reduce production and operating costs.

[0019] 4. The catalyst of this invention does not contain toxic heavy metals, and the reaction process is mild with few byproducts, meeting the requirements of green environmental protection and clean production. It is environmentally friendly and has no industrial pollution problems.

[0020] 5. Compared with traditional platinum-tin bimetallic catalysts, the rhodium single-atom / nanodiamond-graphene composite catalyst of this invention can achieve efficient conversion of n-butane to butene under low-temperature conditions, and is environmentally friendly and pollution-free. Attached Figure Description

[0021] Figure 1 This is a TEM image of the morphology of the nanodiamond-graphene composite material.

[0022] Figure 2 The image shows a HAADF-STEM image of the rhodium single-atom / nanodiamond-graphene composite catalyst prepared in Example 1.

[0023] Figure 3 This is a schematic diagram showing the stability test results of the catalyst prepared in Example 1 in the long-cycle n-butane dehydrogenation reaction. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below through specific embodiments and application examples, but the scope of protection of the present invention is not limited to the following embodiments.

[0025] Example 1: The catalyst preparation process in this embodiment is as follows: Commercial nanodiamond raw materials with a particle size of 10-100 nm were placed in a tube furnace and calcined at 1100 °C in a high-purity argon atmosphere at a flow rate of 100 mL / min for 4 hours. After calcination, the material was naturally cooled to room temperature to obtain surface-graphitized nanodiamond powder, i.e., nanodiamond-graphene composite material, denoted as ND@G. Figure 1 As shown, multilayer graphene is derived on the surface of nanodiamond, with a shell thickness of 0.6-3 nm.

[0026] Weigh 200 mg of the above-mentioned nanodiamond-graphene composite material and place it in a clean 25 mL beaker. Add 2 mL of anhydrous ethanol to this beaker as a solvent. Calculate the required volume of a 20 g / L rhodium nitrate precursor solution based on the final rhodium loading of 0.02 wt% in the prepared catalyst, and add it to the beaker using a pipette. Sonicate the mixture for 2 minutes to ensure thorough dispersion of the support in the solution. Then, place the beaker on a magnetic stirrer and stir at room temperature for 24 hours under open conditions to allow rhodium ions to be fully adsorbed onto the nanodiamond-graphene composite material. Afterward, transfer the beaker to a vacuum drying oven and dry under vacuum at 60°C for 24 hours. After drying, allow it to cool naturally to room temperature to obtain the rhodium-based nanodiamond-graphene composite catalyst precursor powder.

[0027] The obtained precursor powder was transferred to a quartz tube reactor and placed in a programmed temperature-controlled furnace. A mixed reducing gas consisting of hydrogen and helium (10% hydrogen by volume) was introduced at a total gas flow rate of 20 mL / min. The furnace temperature was increased to 500 °C at a rate of 5 °C / min and maintained at this temperature for 1 hour for reduction. After the reduction process, heating was stopped, and pure helium (flow rate 20 mL / min) was used as the protective atmosphere, allowing the reactor to cool naturally to room temperature in the helium flow. Finally, a rhodium single-atom / nanodiamond-graphene composite catalyst with a rhodium loading of 0.02 wt% was obtained, denoted as 0.02Rh / ND@G. The HAADF-STEM image of this catalyst is shown below. Figure 2 As shown in the figure, rhodium is uniformly dispersed in single-atom form on the surface of the nanodiamond-graphene composite material carrier.

[0028] Application Example 1: This application example is used to evaluate the catalytic performance of the 0.02Rh / ND@G catalyst prepared in Example 1 in the direct dehydrogenation reaction of n-butane.

[0029] The catalytic reaction was carried out in a continuous flow fixed-bed reactor. The specific operation was as follows: A small amount of quartz wool was filled into the middle of a quartz glass reaction tube to support the catalyst. Then, 50 mg of a 0.02Rh / ND@G catalyst sample was accurately weighed and evenly distributed on the quartz wool to form a catalyst bed with a height of approximately 1 cm. The filled reaction tube was installed into the reactor, and the gas lines were connected. High-purity helium (He) was turned on to purge the reaction system for 30 minutes to completely remove air from the pipelines and reactor. After purging, the programmed temperature control system was activated to heat the catalyst bed to the target reaction temperature of 480°C. After the temperature stabilized, the inlet gas was switched to a mixed reaction gas consisting of n-butane, hydrogen, and helium, with the total space velocity (GHSV) controlled at 22500 mL / (g·h). The reaction lasted for 10 hours, during which the composition of the outlet gas of the reactor was quantitatively analyzed using an online gas chromatograph to calculate the conversion rate of n-butane and the selectivity of each product. The specific reaction conditions and average performance data within 10 hours of reaction are summarized in Table 1 below. Figure 3 From Figure 3 As can be seen from this, the catalyst prepared in Example 1 remained stable during the 10-hour n-butane dehydrogenation reaction without significant decrease, demonstrating good stability.

[0030] Table 1. Reaction conditions and results of the butane dehydrogenation reaction catalyzed by the catalyst prepared in Example 1.

[0031] Example 2: The catalyst was prepared according to the method of Example 1, except that the amount of rhodium nitrate solution was adjusted so that the rhodium atom loading was 0.1 wt%. The final catalyst was denoted as 0.1Rh / ND@G.

[0032] Application Example 2: The catalyst performance was tested according to the protocol in Application Example 1, with the only difference being that the catalyst dosage was adjusted to 10 mg and the GHSV was 112500 (ml / g·h). The reaction conditions and results are shown in Table 2. Table 2. Reaction conditions and results of the butane dehydrogenation reaction catalyzed by the catalyst prepared in Example 2.

[0033] Comparative Example 1: The catalyst was prepared according to the method of Example 1, except that the precursors were adjusted to H2PtCl6 and SnCl2 solution, and the amount of chloroplatinic acid with a concentration of 20 g / L and stannous chloride solution with a loading of 0.5 wt% was calculated and used. The resulting catalyst was denoted as 0.5Pt0.5Sn / ND@G.

[0034] Comparative Application Example 1 The catalyst performance was tested according to the scheme in Application Example 1. The reaction conditions and results are shown in Table 3 below: Table 3. Reaction conditions and results of the dehydrogenation of n-butane catalyzed by the catalyst prepared in Comparative Example 1.

[0035] Comparative Example 2: The catalyst was prepared according to the method of Example 1, except that the amount of rhodium nitrate precursor solution was adjusted. The amount of solution was calculated and used according to a loading of 0.3 wt%. The resulting catalyst was denoted as 0.3Rh / ND@G. The active component mainly exists in the form of clusters.

[0036] Comparative Application Example 2 The catalyst performance was tested according to the scheme in Application Example 1. The reaction conditions and results are shown in Table 4 below: Table 4. Reaction conditions and results of the dehydrogenation reaction of n-butane catalyzed by the catalyst prepared in Comparative Example 2.

[0037] By comparing the catalytic reaction results of Application Example 1 and Application Example 2, it can be seen that the Rh / ND@G catalyst prepared in this invention can further improve the n-butane conversion rate under high space velocity reaction conditions compared with the PtSn / ND@G catalyst.

[0038] A comparison of the catalytic reaction results of Application Example 2 and Application Example 2 shows that the single-atom 0.02Rh / ND@G catalyst prepared according to this invention can further improve the conversion rate of n-butane and the yield of butene compared with the 0.3Rh / ND@G cluster catalyst under high space velocity reaction conditions. The isolated electronic structure of the single-atom rhodium catalyst is more conducive to the timely desorption of olefin products, achieving highly selective dehydrogenation of alkanes.

[0039] By using the dehydrogenation catalyst of the present invention, high catalytic activity can be achieved at low noble metal loading and low temperature, while also helping to improve catalyst stability, reduce energy consumption, and lower unit production costs, thus showing good application prospects.

[0040] The above examples are for reference only. Any technical solutions that are similar to or derived from the concept of this patent are within the scope of protection of this invention.

Claims

1. A rhodium single-atom / nanodiamond-graphene composite catalyst, characterized in that: The catalyst uses metallic rhodium as the active component and nanodiamond-graphene composite material as the support; the loading of rhodium in the catalyst is 0.001~0.1%, preferably 0.01~0.1%.

2. The rhodium single-atom / nanodiamond-graphene composite catalyst according to claim 1, characterized in that: The nanodiamond-graphene composite material has a core-shell structure, with nanodiamond forming the core and graphene covering the outer shell; the thickness of the graphene shell is 0.6-6 nm; the particle size of the nanodiamond-graphene composite material is 10-600 nm.

3. The rhodium single-atom / nanodiamond-graphene composite catalyst according to claim 1, characterized in that: In this catalyst, rhodium is supported on the surface of the nanodiamond-graphene composite support in an atomically dispersed form, and forms stable metal-carbon bonds with carbon atoms at carbon defect sites in the graphene layer.

4. A method for preparing a rhodium single-atom / nanodiamond-graphene composite catalyst according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Using nanodiamond as raw material, a nanodiamond-graphene composite material carrier is obtained through a high-temperature heat treatment process; (2) The rhodium precursor solution was loaded onto the nanodiamond-graphene composite material carrier obtained in step (1) by impregnation process to obtain the rhodium-based nanodiamond-graphene composite material catalyst precursor. (3) The catalyst precursor obtained in step (2) is placed in a reactor and subjected to reduction heat treatment under a mixed gas of hydrogen and inert gas to finally obtain a rhodium single atom / nanodiamond-graphene composite catalyst.

5. The preparation method according to claim 4, characterized in that: The preparation process of the nanodiamond-graphene composite material carrier in step (1) is as follows: the nanodiamond raw material is subjected to high-temperature calcination at 900-1100℃, preferably 1000-1100℃, under an inert atmosphere with a flow rate of 80-150 mL / min for 3-5 hours, preferably 4-5 hours; the nanodiamond raw material has a particle size of 10-600 nm, and the inert atmosphere is one or both of He and Ar.

6. The preparation method according to claim 4, characterized in that: The impregnation process described in step (2) is specifically operated as follows: Weigh 200 mg of nanodiamond-graphene composite material carrier into 2-6 mL of anhydrous ethanol, then measure the corresponding volume of rhodium nitrate precursor solution into the above solution according to the target loading amount, sonicate for 2-10 min, stir for 12-24 h, then vacuum dry at 60-100℃ for 10-24 h, and naturally cool to room temperature; the concentration of the rhodium nitrate precursor solution is 10~20 g / L.

7. The preparation method according to claim 4, characterized in that: In step (3), the volume fraction of hydrogen in the mixed gas of hydrogen and inert gas is 10-30%, and the total flow rate of the mixed gas is controlled at 20-30 mL / min; the temperature range of the reduction heat treatment is 300-500℃, preferably 400-500℃; the reduction time is 1-3h, preferably 1-2h; after the reduction heat treatment is completed, it is cooled to room temperature under the protection of pure helium atmosphere with a flow rate of 7-30 mL / min.

8. The application of a rhodium single-atom / nanodiamond-graphene composite catalyst according to any one of claims 1-3 in the dehydrogenation reaction of n-butane.

9. The application according to claim 8, characterized in that: The n-butane dehydrogenation reaction is carried out in the presence of a catalyst, with a catalyst dosage of 10-50 g and a reaction temperature controlled at 450-500 °C. The gas hourly space velocity is 1000-120000 mL / (g·h), and the gas composition is n-butane, hydrogen, and helium, with a molar ratio of 1:(0.5-5):(40-50).

Images