P-bn rod catalyst for propane oxidative dehydrogenation and preparation method and application thereof

Abstract

The application discloses a P-BN rod-shaped catalyst for propane oxidative dehydrogenation and a preparation method and application thereof, and belongs to the technical field of catalyst preparation and application. The catalyst is prepared by an in-situ self-assembly and high-temperature pyrolysis two-step method, and takes melamine as a nitrogen source, boric acid as a boron source and red phosphorus as a phosphorus source. The obtained P-BN rod-shaped catalyst is used for propane oxidative dehydrogenation reaction under the condition of normal pressure and 520 DEG C, and corresponding unsaturated olefins can be prepared with high selectivity. The catalyst prepared by the application has the characteristics of rod-shaped structure, high olefin selectivity and long catalytic life, and the synthesis method of the catalyst is simple, raw materials are cheap and easy to obtain, pollution-free, and has the prospect of industrial application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalyst preparation and application, and particularly relates to a P-BN rod-shaped catalyst for propane oxidative dehydrogenation and a preparation method and application thereof. BACKGROUND

[0002] Propylene is an important component of the petrochemical industry, and the downstream product polypropylene accounts for more than half of the world's propylene demand. Among different propylene production strategies, propane oxidative dehydrogenation to propylene is considered to be a promising method due to its favorable thermodynamics and minimal coke formation. However, a major challenge of propane oxidative dehydrogenation is to improve the selectivity and yield of propylene, as it has a tendency to over-oxidize, leading to the formation of byproduct carbon dioxide. With the growing concern about the "carbon peak", designing a new generation of sustainable nanocatalysts has become a core basic scientific problem in this field.

[0003] Boron-based non-metallic materials represented by hexagonal boron nitride have been widely reported to have selectivity to olefins and inhibit the formation of byproducts (Science, 2016: 354, 1570-1573). Compared with traditional metal or metal oxide systems, the unique behavior of oxygen activation into active surface and gaseous radicals rather than lattice oxygen is considered to be the main reason for the excellent performance of boron-based catalysts (Science, 2016: 354, 1570-1573). However, due to the complex preparation process and unsatisfactory catalytic activity, the application of boron nitride in alkane activation is still far from advanced level. In recent years, people have noticed the inhomogeneous nature of the B-N bond in hexagonal boron nitride, and have been committed to adjusting the material surface properties by heteroatom doping (Catal. Sci. Technol., 2018: 8, 5900-5905), thereby adjusting the electronic distribution (ChemCatChem, 2019, 11: 3730-3744) and energy gap (Appl. Catal., B: 2019, 256, 117827). However, the hexagonal boron nitride synthesized by chemical vapor deposition and mechanical exfoliation reported so far still has problems of high preparation cost, low product yield, and catalytic activity in propane oxidative dehydrogenation reaction still needs to be improved.

[0004] The difficulty in solving the above problems lies in selecting a suitable, simple and highly reproducible preparation method, and introducing more catalytically active sites by doping heteroatoms. Therefore, in view of the problems existing in the prior art, the present application is committed to developing a P-BN catalyst with novel and stable structure which is easy to prepare, starting from the hydrogen bond self-assembly between molecules. It is found from the review of the current research literature in this field that the preparation method of the P-BN catalyst reported in this study has not been reported so far. SUMMARY

[0005] In view of the above existing problems, the present application aims to provide a P-BN rod-shaped catalyst for propane oxidative dehydrogenation and its preparation method and application. The prepared P-BN catalyst is a non-metallic catalyst, the preparation method is simple, the raw materials are cheap and easy to obtain, and the catalyst has a novel rod-shaped structure, and shows high selectivity and stability when used for propane oxidative dehydrogenation.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A preparation method of a P-BN rod-shaped catalyst for propane oxidative dehydrogenation comprises the following steps:

[0008] (1) Melamine, boric acid and red phosphorus are placed in a planetary ball mill for ball milling, and physical methods are used to mix them uniformly;

[0009] (2) The uniformly mixed powder in step (1) is washed, filtered and dried to obtain a precursor;

[0010] (3) The precursor obtained in step (2) is carbonized at a high temperature under a nitrogen atmosphere at a certain heating rate, and then naturally cooled to room temperature, and ground to obtain the P-BN rod-shaped catalyst.

[0011] In the above step (1), the amount of melamine added is 0.02 mol, the amount of boric acid added is 0.04 mol, and the amount of red phosphorus added is 0.01 mol; the ball milling conditions are room temperature, the rotation speed is 500 r / min, and the ball milling time is 1 h.

[0012] In the above step (2), the washing solvent is deionized water and ethanol, the washing times are 3-4 times, and the drying time is 12 h.

[0013] In the above step (3), the heating rate is 10 ℃ / min, the high-temperature carbonization temperature is 1150 ℃, and the carbonization time is 2 h.

[0014] The P-BN rod-shaped catalyst prepared by the above method is used for propane oxidative dehydrogenation to prepare corresponding unsaturated hydrocarbons. When the catalyst is used for the above oxidative dehydrogenation reaction, it has high olefin selectivity, long catalytic life, and no pollution. The use conditions of the P-BN rod-shaped catalyst are as follows: the reaction temperature is 520 ℃, the flow ratio of the reaction gas is C3H8:O2:He=6:3:11, and the total flow rate of the reaction gas is 20 mL / min.

[0015] When the boron nitride catalyst of the present application is used for oxidative dehydrogenation reaction, the olefin selectivity of the catalyst can still reach 90% when the propane conversion rate exceeds 20%, and this process can achieve high olefin selectivity at high propane conversion rate.

[0016] Compared with the prior art, the P-BN catalyst prepared by the synthetic method has the advantages that the synthetic method is simple, the raw materials are cheap and easy to obtain, the prepared P-BN catalyst is a metal-free catalyst and is pollution-free, the structure is novel, the P-BN catalyst has rich pore structures, can provide more potential reaction sites and diffusion channels, and is beneficial to mass transfer and surface and radical reactions. When the P-BN catalyst is used as a catalyst for the oxidative dehydrogenation reaction of propane, the P-BN catalyst has good catalytic activity and high-temperature stability. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A scanning electron microscope (SEM) image of the P-BN rod-shaped catalyst prepared in Example 1.

[0018] Figure 2 An X-ray powder diffraction (XRD) image of the P-BN rod-shaped catalyst prepared in Example 1.

[0019] Figure 3 A Fourier transform infrared spectroscopy (FT-IR) image of the P-BN rod-shaped catalyst prepared in Example 1.

[0020] Figure 4 A nitrogen adsorption-desorption curve and a pore size distribution graph of the P-BN rod-shaped catalyst prepared in Example 1.

[0021] Figure 5 An SEM image of the BN prepared in Comparative Example 1.

[0022] Figure 6 A catalytic performance graph of the P-BN rod-shaped catalyst prepared in Example 1 in the oxidative dehydrogenation reaction of propane.

[0023] Figure 7 A catalytic product distribution graph of the P-BN rod-shaped catalyst prepared in Example 1 in the oxidative dehydrogenation reaction of propane. DETAILED DESCRIPTION

[0024] The following examples are used to further illustrate the present application, so as to better illustrate the content of the present application.

[0025] Example 1:

[0026] 0.02 mol of melamine, 0.04 mol of boric acid and 0.01 mol of red phosphorus were placed in a planetary ball mill and ball milled at a rotation speed of 500 r / min for 1 h to mix them uniformly; the well-mixed powder was washed for 3-4 times, filtered and dried for 12 h to obtain a precursor; the obtained precursor was heated to 1150℃ at a heating rate of 10℃ / min under a nitrogen atmosphere, and reacted for 2 h; after natural cooling to room temperature, the phosphorus-doped boron nitride catalyst was obtained by grinding. The catalyst was named as P-BN catalyst.

[0027] Comparative Example 1:

[0028] 0.02 mol of melamine and 0.04 mol of boric acid were placed in a planetary ball mill and ball-milled at 500 r / min for 1 h to ensure uniform mixing. The thoroughly mixed powder was washed 3-4 times, filtered, and dried for 12 h to obtain the precursor. The obtained precursor was heated to 1150 °C under a nitrogen atmosphere at a heating rate of 10 °C / min and reacted for 2 h. After naturally cooling to room temperature, it was ground to obtain boron nitride material, which was used as a sample for morphological comparison and named BN material.

[0029] The morphology and structure of the P-BN catalyst were characterized using scanning electron microscopy (SEM). Figure 1 As shown, the material has an adhesive rod-like structure.

[0030] The crystal structure of the P-BN catalyst was studied using X-ray powder diffraction (XRD). Figure 2 As shown, all samples exhibit two broad diffraction peaks near 26.7° and 42.6°, which belong to the (002) and (100) crystal planes of the h-BN structure, respectively.

[0031] The surface functional groups of the P-BN catalyst were studied using Fourier transform infrared spectroscopy (FT-IR). Figure 3 As shown, 3200cm -1 The broad peak at 1402 cm⁻¹ is attributed to the vibration of the stretched -NH₂ group. -1 and 799cm -1 The two wavebands at this point correspond to the in-plane transverse tensile vibration of the BNB and the out-of-plane bending vibration of the BNB, respectively. 900cm -1 The peak value at 1693cm is caused by the BO vibration. -1 and 3409cm -1 The characteristic peaks at 1029 cm⁻¹ belong to the bending and stretching vibrations of the -OH group, respectively. Furthermore, the P-BN catalyst exhibits [a certain characteristic] at 1029 cm⁻¹. -1 and 1177cm -1 Characteristic peaks caused by P=O and PN stretching vibrations appeared at the [value]. The presence of these two peaks confirms that phosphorus is incorporated into the h-BN structure, indicating the successful preparation of the P-BN catalyst.

[0032] Through N2 physical adsorption-desorption test, such as Figure 4 As shown in (a), the adsorption-desorption isotherms obtained by the test are all typical type IV, and obvious type H3 hysteresis loops are produced, indicating that mesoporous structures exist in all of them. Figure 4 The pore size distribution diagram in (b) further confirms that all prepared catalysts possess micro-mesoporous structures. The calculated specific surface area and pore structure parameters of the samples are shown in Table 1, indicating that the specific surface area of ​​the P-BN catalyst is 10.80 m². 2 / g.

[0033] Table 1 Specific surface area and pore structure parameters of the porous carbon material prepared by the specific implementation method

[0034]

[0035] The morphology and structure of BN and P-BN were characterized by scanning electron microscopy, respectively. From the SEM images of BN, it can be seen that the morphology is blocky structure, while the morphology of P-BN is stick structure. Figure 5 The SEM images of BN show that the morphology is blocky structure, while the morphology of P-BN is stick structure. Figure 1 The SEM images of P-BN in Example 1 show that the morphology is stick structure. The above results show that the introduction of phosphorus can affect the formation of stick morphology.

[0036] The P-BN catalyst prepared in Example 1 was tested for catalytic performance in the propane oxidative dehydrogenation reaction. The reaction was carried out on a single-stage temperature-controlled heating furnace device under normal pressure reaction, and the material was loaded in a quartz tube reactor for testing. The specific conditions are as follows:

[0037] Chromatographic analysis conditions: both chromatographic columns use high-purity N2 as chromatographic carrier gas, FID flow pressure is 0.04 MPa, TCD flow pressure is 0.2 MPa; hydrogen flow pressure of FID1 and FID2 is 0.035 MPa and 0.03 MPa, respectively; air flow pressure is 0.03 MPa. Injector: 150℃, FID detector: 150℃, TCD detector: 150℃, conversion furnace: 330℃. Column oven temperature rising conditions: the initial temperature is 70℃, which is kept for 14 min, then the temperature is raised to 150℃ at a rate of 20℃ / min and kept for 5 min to remove residual components in the chromatographic column.

[0038] Loading: first, 30mg of quartz wool was laid in a quartz tube reactor with an inner diameter of 6mm, a wall thickness of 2mm and a length of 360mm, then 200mg of P-BN catalyst prepared in Example 1 with a size of 20-40 mesh was loaded into the quartz tube reactor, and finally a layer of 30mg of quartz wool was laid on the upper part of the material.

[0039] Catalytic performance evaluation: the reaction gas with a flow ratio of C3H8:O2:He=6:3:11 was set for reaction, the total flow rate of the reaction gas was 20mL / min, and the reaction temperature was 520℃.

[0040] As shown in the catalytic performance of P-BN catalyst in the propane oxidative dehydrogenation reaction, the P-BN catalyst exhibited good performance in the preparation of propylene by propane oxidative dehydrogenation. When the propane conversion rate exceeded 20%, the olefin selectivity on the catalyst could still reach 90%, and high olefin selectivity could be achieved at high propane conversion rate. Figure 6 As shown in the catalytic performance of P-BN catalyst in the propane oxidative dehydrogenation reaction, the P-BN catalyst exhibited good performance in the preparation of propylene by propane oxidative dehydrogenation. When the propane conversion rate exceeded 20%, the olefin selectivity on the catalyst could still reach 90%, and high olefin selectivity could be achieved at high propane conversion rate.

[0041] Figure 7 ​The catalytic product distribution of P-BN catalyst in propane oxidative dehydrogenation reaction can be seen from the figure, CO X The product selectivity is less than 8.0%, and the selectivity of CO2 is only 0.34%, and almost no carbon dioxide is produced by over-oxidation. It shows that the P-BN catalyst can effectively inhibit the deep cracking of propylene, thereby ensuring high olefin selectivity and catalytic activity.

[0042] In summary, the P-BN catalyst prepared in the application has the characteristics of high olefin selectivity and long catalytic life by introducing phosphorus to form a novel rod-like structure. The synthesis method of the catalyst is simple, the raw materials are cheap and easy to obtain, pollution-free, and has the prospect of industrial application.

[0043] The above-described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the protection scope of the application.

Claims

1. A method for preparing a P-BN stick catalyst for the oxidative dehydrogenation of propane, characterized by: The method comprises the following steps: (1) mixing melamine, boric acid and red phosphorus, ball milling to make them uniformly mixed; (2) washing, filtering and drying the uniformly mixed powder in step (1) to obtain a precursor; (3) high-temperature carbonizing the precursor in step (2) under a nitrogen atmosphere, naturally cooling to room temperature, and grinding to obtain the P-BN rod-shaped catalyst; The molar ratio of melamine, boric acid and red phosphorus in step (1) is 2:4:1; The ball milling temperature in step (1) is room temperature, the rotating speed is 500 r / min, and the time is 1 h; The heating rate in step (3) is 10 ℃ / min, the high-temperature carbonizing temperature is 1150 ℃, and the high-temperature carbonizing time is 2 h.

2. The method of claim 1, wherein: The washing solvent in step (2) is deionized water and ethanol, the washing times are 3-4 times, and the drying time is 12 h.

3. A P-BN rod-shaped catalyst for propane oxidative dehydrogenation, which is prepared by the method according to any one of claims 1-2.

4. Use of a P-BN rod catalyst for the oxidative dehydrogenation of propane, prepared according to the process of any one of claims 1-2, characterized by: The P-BN rod-shaped catalyst is applied to the preparation of corresponding unsaturated hydrocarbons by propane oxidative dehydrogenation; the use conditions of the P-BN rod-shaped catalyst are as follows: the reaction temperature is 520 ℃, the flow ratio of the reaction gas is C3H8:O2:He=6:3:11, and the total flow rate of the reaction gas is 20 mL / min.

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