Preparation method and application of core-shell type nano oxide boron-carbon-nitrogen-oxygen catalyst for oxidative dehydrogenation of propane

Abstract

The invention provides a preparation method and application of a core-shell nano oxide boron-carbon-nitrogen-oxygen catalyst for oxidative dehydrogenation of propane, the catalyst takes tetrafluoroborate ionic liquid as a boron source, and a carbon-nitrogen source (cyanamide or a polymer thereof) and a commercially available nano oxide (including but not limited to silicon oxide, aluminum oxide and zirconium oxide) are added into an aqueous solution of the tetrafluoroborate ionic liquid; and uniformly stirring and mixing at a constant temperature in a sealed manner, evaporating water, drying, and finally heating to 550 DEG C in an air atmosphere in a programmed manner for pyrolysis to obtain the core-shell type oxide coated BCNO catalyst. The optimized SiO2 (at) BCNO (the mass percentage of B is 7.5 wt%) has excellent propane oxidative dehydrogenation catalytic activity and propylene selectivity under an oxygen-enriched condition, and is good in stability. The process is easy to control, the universality is high, the pyrolysis temperature is low, special atmosphere protection is not needed, and large-scale preparation is facilitated.

Description

Technical Field

[0001] The invention belongs to the field of chemical industry catalysis and relates to a core-shell nano oxide @ boron carbon nitrogen oxide (BCNO) catalyst for propane oxidative dehydrogenation and a preparation method thereof. Background Art

[0002] Propylene is the basic raw material for the three major synthetic materials (plastics, rubber, and chemical fibers). At present, the main propylene production processes include petroleum byproduct steam cracking, fluidized catalytic cracking, coal or methanol to olefins, and direct dehydrogenation of propane. The shale gas revolution has led to a rapid increase in propane production and has also promoted the rapid development of propane dehydrogenation technology. However, the direct dehydrogenation process of propane has high energy consumption and the catalyst is prone to carbon deposition. Propane oxidative dehydrogenation is a thermodynamically spontaneous reaction with the advantages of low operating temperature and less carbon deposition. It is an ideal alternative process for the direct dehydrogenation process of propane. Metal oxide catalysts generally have the disadvantage that high-temperature propane or propylene is easily deeply oxidized to carbon oxides. In recent years, boron-based catalysts represented by h-BN have been favored by researchers due to their ultra-high olefin selectivity (Science, 2016, 354, 1570; Chem. Commun., 2024,60, 7535).

[0003] Studies have shown that the appropriate amount of carbon doping in h-BN can significantly affect the electronic microenvironment of h-BN and improve its propane oxidative dehydrogenation performance (Appl. Catal. A, 2021, 628, 118402; Angew. Chem. Int. Ed. 2023, 62,e202307470; Sci. China Chem., 2023, 66, 2389). However, the BCN catalyst used in the preparation process requires inert gas or ammonia protection during pyrolysis, and the pyrolysis temperature is as high as 900-1200 °C, which is harsh and energy-intensive. At the same time, BCN catalysts often have an induction period in the process of propane oxidative dehydrogenation, resulting in unstable initial catalytic performance; and the catalyst has poor oxygen tolerance, the feed gas can only be an oxygen-poor atmosphere, and the long-term working stability of the catalyst is also limited. Therefore, it is challenging to innovate the catalyst preparation method or process, reduce the energy consumption of the preparation process, and obtain a new BCN-type propane oxidative dehydrogenation catalyst with stable catalytic performance under oxygen-rich conditions. This is also the only way for such catalysts to move towards industrial application. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a method for preparing a core-shell nano oxide@boron carbon nitrogen oxygen catalyst for propane oxidative dehydrogenation.

[0005] The technical solution adopted by the present invention is: A method for preparing a core-shell nano oxide @ boron carbon nitrogen oxygen catalyst for propane oxidative dehydrogenation comprises the following steps: Step 1: dissolve tetrafluoroborate ionic liquid in deionized water, add cyanamide or its polymer, stir in a sealed oil bath at 90 °C for 0.5 h, then add commercially available nano oxide, continue to stir in a sealed oil bath at 90 °C for 0.5 h, then evaporate the solvent water at 90 °C until it becomes viscous, and dry in an oven at 80 °C overnight; Step 2: Grind the solid obtained in step 1 and pyrolyze it at 550 °C in an air atmosphere of a muffle furnace, wherein the heating rate is 1 °C / min, 100 °C is maintained for 1 h, 350 °C is maintained for 2 h, and 550 °C is maintained for 2 h, to obtain a nano oxide @ boron carbon nitrogen oxide (BCNO) catalyst.

[0006] The tetrafluoroborate ionic liquid is one of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-methyl-3-octylimidazolium tetrafluoroborate or 1-butyl-4-methylpyridinium tetrafluoroborate; preferably 1-ethyl-3-methylimidazolium tetrafluoroborate.

[0007] Wherein, the cyanamide or its polymer is one of cyanamide, dicyandiamide, melamine, cyanuric acid or methylguanamine; preferably melamine.

[0008] In step 1, the molar ratio of B to N in the raw material is 0.025-0.10:1, preferably 0.05:1.

[0009] In step 1, the commercially available nano-oxide includes but is not limited to at least one of SiO2, Al2O3 or ZrO2, and no pretreatment is required.

[0010] In step 1, the mass ratio of tetrafluoroborate to oxide is 0.5 to 2:1, preferably 1:1.

[0011] The catalyst obtained by the above preparation method of the present invention has an irregular core-shell structure, with boron carbon nitrogen oxide (BCNO) as the shell layer and commercially available nano oxide as the core, preferably SiO2, and the mass percentage of B element is 3.4~23.4 wt%, preferably 7.5wt%.

[0012] The core-shell nano oxide @ BCNO catalyst of the present invention is used in the oxidative dehydrogenation reaction of propane under oxygen-rich conditions.

[0013] The application method of the core-shell nano oxide @ BCNO catalyst in the propane oxidative dehydrogenation reaction under oxygen-rich conditions is as follows: 100 mg of the core-shell nano oxide @ BCNO catalyst is placed in a quartz tube reactor, and a mixed gas of propane (C3H8), oxygen (O2) and nitrogen (N2) is introduced, wherein the volume ratio of C3H8:O2:N2 is 1:2:7, the total flow rate is 40 mL / min, and the reaction temperature is 400-540 ° C. After isothermal reaction for 30 min, gas chromatography is used to collect data and detect the product composition and content, and the detection temperature interval is 20 ° C.

[0014] The beneficial effects of the present invention are: Compared with the existing BCN catalyst preparation technology for propane oxidative dehydrogenation, the core-shell nano oxide @BCNO catalyst of the present invention has the following advantages: 1. The present invention adopts a core-shell design, with inexpensive and readily available commercial nano-oxides as the core, which significantly reduces the use of boron source and nitrogen source. At the same time, BCNO is used as the shell, which improves the utilization rate of boron source and nitrogen source and increases the dispersion and exposure of BO catalytic active components.

[0015] 2. The pyrolysis is carried out in a muffle furnace in an air atmosphere, without the need for special inert gas or ammonia atmosphere, and the pyrolysis temperature is reduced to 550 °C. The operation process is simple, the energy consumption is reduced, and it is easy to mass produce. At the same time, the BO catalytic active component is generated in situ during the pyrolysis process in the air atmosphere, so that the catalyst does not need to be activated before use.

[0016] 3. Commercially available nano oxides are used as the core to effectively improve the stability of the shell BCNO catalyst, oxygen tolerance and the anti-loss performance of the BO active components under oxygen-rich reaction conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a SEM image of the SiO2@BCNO-2 catalyst prepared in Example 1-2; Figure 2 This is a test chart of the catalytic reaction life of the SiO2@BCNO-2 catalyst prepared in Example 1-2. DETAILED DESCRIPTION

[0018] The present invention is described in detail with reference to the following specific embodiments and the accompanying drawings; it should be understood that the following embodiments are only intended to illustrate the technical solutions of the present invention and are not intended to limit the scope of the present invention in any way. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

[0019] The ionic liquid used in the present invention is one of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-methyl-3-octylimidazolium tetrafluoroborate or 1-butyl-4-methylpyridinium tetrafluoroborate, preferably 1-ethyl-3-methylimidazolium tetrafluoroborate.

[0020] The carbon and nitrogen source used in the present invention is one of cyanamide, dicyandiamide, melamine, cyanuric acid and methylguanamine, preferably melamine.

[0021] The commercially available nano-oxides used in the present invention include but are not limited to at least one of SiO2, Al2O3 or ZrO2, and no pretreatment is required.

[0022] Unless otherwise specified, the instruments and reagents described in this example can be obtained from commercial sources.

[0023] In the examples, propane conversion rate (%) = 100 × (amount of propane substance before reaction / amount of propane substance after reaction) / amount of propane substance before reaction.

[0024] Product selectivity (%) = 100 × the amount of the corresponding product substance / (the amount of propane substance before the reaction / the amount of propane substance after the reaction) Example 1-1 The preparation process of the core-shell SiO2@BCNO-1 catalyst described in this embodiment is as follows: Take 2.2 g of 1-ethyl-3-methylimidazolium tetrafluoroborate and dissolve it in 30 mL of deionized water, stir it in a closed oil bath at 90 °C, add 5.0 g of melamine, and stir it in a closed state for 0.5 h; weigh 4.4 g of commercially available nano-SiO2 and add it to the above solution, stir it in a closed state at 90 °C for 0.5 h, then stir it in an open state at 90 °C to evaporate the solvent water until it becomes viscous, and dry it in an oven at 80 °C overnight. After solid grinding, put it in a muffle furnace, and heat it to 550 °C in an air atmosphere (heating rate 1 °C / min, 100 °C for 1 h, 350 °C for 2 h, and 550 °C for 2 h) by pyrolysis to obtain SiO2@BCNO-1 catalyst, in which the mass percentage of B is determined by inductively coupled plasma mass spectrometry to be 3.4 wt%, and the molar ratio of each element on the catalyst surface is determined by X-ray photoelectron spectroscopy, as shown in Table 1.

[0025] Example 1-2 The preparation process of the core-shell SiO2@BCNO-2 catalyst described in this embodiment is as follows: Take 4.4 g of 1-ethyl-3-methylimidazolium tetrafluoroborate and dissolve it in 60 mL of deionized water, stir it in a closed oil bath at 90 °C, add 10 g of melamine, and stir it in a closed oil bath for 0.5 h; weigh 4.4 g of commercially available nano-SiO2 and add it to the above solution, stir it in a closed oil bath at 90 °C for 0.5 h, then stir it in an open air bath at 90 °C to evaporate the solvent water until it becomes viscous, and dry it in an oven at 80 °C overnight. After the solid is ground, put it in a muffle furnace, and heat it to 550 °C in an air atmosphere (heating rate 1 °C / min, 100 °C for 1 h, 350 °C for 2 h, and 550 °C for 2 h) for pyrolysis to obtain SiO2@BCNO-2 catalyst, such as Figure 1 As shown in the SEM image of the SiO2@BCNO-2 catalyst prepared in Example 1, the mass percentage of B was determined to be 7.5 wt% using an inductively coupled plasma mass spectrometer, and the molar ratio of each element on the catalyst surface was determined using X-ray photoelectron spectroscopy, see Table 1.

[0026] Examples 1-3 The preparation process of the core-shell SiO2@BCNO-3 catalyst described in this embodiment is as follows: Take 8.8 g of 1-ethyl-3-methylimidazolium tetrafluoroborate and dissolve it in 120 mL of deionized water, stir it in a closed oil bath at 90 °C, add 20 g of melamine, and stir it in a closed state for 0.5 h; weigh 4.4 g of commercially available nano-SiO2 and add it to the above solution, stir it in a closed state at 90 °C for 0.5 h, then stir it in an open state at 90 °C to evaporate the solvent water until it becomes viscous, and dry it in an oven at 80 °C overnight. After solid grinding, put it in a muffle furnace, and heat it to 550 °C in an air atmosphere (heating rate 1 °C / min, 100 °C for 1 h, 350 °C for 2 h, 550 °C for 2 h) for pyrolysis to obtain SiO2@BCNO-3 catalyst. The mass percentage of B was determined by inductively coupled plasma mass spectrometry to be 23.4 wt%, and the molar ratio of each element on the catalyst surface was determined by X-ray photoelectron spectroscopy, as shown in Table 1.

[0027] Table 1. Atomic percentage of each element on the surface of the catalyst prepared for Examples 1-1 to 1-3 Examples 1-4 The preparation process of the core-shell Al2O3@BCNO catalyst described in this embodiment is as follows: Take 4.4 g of 1-ethyl-3-methylimidazolium tetrafluoroborate and dissolve it in 60 mL of deionized water, stir it in a closed oil bath at 90 °C, add 10 g of melamine, and stir it in a closed oil bath for 0.5 h; weigh 4.4 g of commercially available nano-Al2O3 and add it to the above solution, stir it in a closed oil bath at 90 °C for 0.5 h, then stir it in an open oil bath at 90 °C to evaporate the solvent water until it becomes viscous, and dry it in an oven at 80 °C overnight. After the solid is ground, it is placed in a muffle furnace and programmed to heat up to 550 °C in an air atmosphere (heating rate 1 °C / min, 100 °C for 1 h, 350 °C for 2 h, and 550 °C for 2 h) for pyrolysis to obtain the Al2O3@BCNO catalyst, in which the mass percentage of B is 8.1 wt% as determined by inductively coupled plasma mass spectrometry.

[0028] Examples 1-5 The preparation process of the core-shell ZrO2@BCNO catalyst described in this embodiment is as follows: Take 4.4 g of 1-ethyl-3-methylimidazolium tetrafluoroborate and dissolve it in 60 mL of deionized water, stir it in a closed oil bath at 90 °C, add 10 g of melamine, and stir it in a closed oil bath for 0.5 h; weigh 4.4 g of commercially available nano ZrO2 and add it to the above solution, stir it in a closed oil bath at 90 °C for 0.5 h, then stir it in an open oil bath at 90 °C to evaporate the solvent water until it becomes viscous, and dry it in an oven at 80 °C overnight. After the solid is ground, put it in a muffle furnace, and heat it to 550 °C in an air atmosphere (heating rate 1 °C / min, 100 °C for 1 h, 350 °C for 2 h, and 550 °C for 2 h) for pyrolysis to obtain ZrO2@BCNO catalyst, in which the mass percentage of B is 7.3 wt% as determined by inductively coupled plasma mass spectrometry.

[0029] Application Example 2-1 The core-shell SiO2@BCNO-1 catalyst prepared in Example 1-1 was used to catalyze the propane oxidative dehydrogenation reaction under oxygen-rich conditions, and the specific steps were as follows: 100 mg of the core-shell SiO2@BCNO-1 catalyst prepared in Example 1-1 was weighed and placed in a quartz tube reactor, and a mixed gas of C3H8, O2 and N2 was introduced, wherein the volume ratio of C3H8:O2:N2 was 1:2:7, the total flow rate was 40 mL / min, and the reaction temperature was 400-540 °C. After isothermal reaction for 30 min, data was collected and product composition and content were detected by gas chromatography, and the detection temperature was 20 °C. At 500 °C, the C3H8 conversion rate was 13.3%, the propylene selectivity was 81.8%, and the ethylene selectivity was 8.4%.

[0030] Application Example 2-2 The core-shell SiO2@BCNO-2 catalyst prepared in Example 1-2 was used to catalyze the propane oxidative dehydrogenation reaction under oxygen-rich conditions, and the specific steps were as follows: 100 mg of the core-shell SiO2@BCNO-2 catalyst prepared in Example 1-2 was weighed and placed in a quartz tube reactor, and a mixed gas of C3H8, O2 and N2 was introduced, wherein the volume ratio of C3H8:O2:N2 was 1:2:7, the total flow rate was 40 mL / min, and the reaction temperature was 400-540 °C. After isothermal reaction for 30 min, data was collected by gas chromatography and the product composition and content were detected, and the detection temperature was 20 °C. At 500 °C, the C3H8 conversion rate was 25.1%, the propylene selectivity was 77.5%, and the ethylene selectivity was 9.5%; the catalyst performance did not change significantly after continuous reaction for 40 h under this condition (see Figure 2 , catalytic reaction life test diagram of SiO2@BCNO-2 (B mass percentage is 7.5 wt%) catalyst prepared in Example 1-2 (reaction temperature 500 °C)).

[0031] Application Example 2-3 The core-shell SiO2@BCNO-3 catalyst prepared in Example 1-3 was used to catalyze the propane oxidative dehydrogenation reaction under oxygen-rich conditions, and the specific steps were as follows: 100 mg of the core-shell SiO2@BCNO-3 catalyst prepared in Example 1-3 was weighed and placed in a quartz tube reactor, and a mixed gas of C3H8, O2 and N2 was introduced, wherein the volume ratio of C3H8:O2:N2 was 1:2:7, the total flow rate was 40 mL / min, and the reaction temperature was 400-540 °C. After isothermal reaction for 30 min, data was collected by gas chromatography and the product composition and content were detected, and the detection temperature interval was 20 °C. At 500 °C, the C3H8 conversion rate was 6.6%, the propylene selectivity was 91.1%, and the ethylene selectivity was 5.0%.

[0032] Application Example 2-4 The core-shell Al2O3@BCNO catalyst prepared in Example 1-4 was used to catalyze the propane oxidative dehydrogenation reaction under oxygen-rich conditions, and the specific steps were as follows: 100 mg of the core-shell Al2O3@BCNO catalyst prepared in Example 1-4 was weighed and placed in a quartz tube reactor, and a mixed gas of C3H8, O2 and N2 was introduced, wherein the volume ratio of C3H8:O2:N2 was 1:2:7, the total flow rate was 40 mL / min, and the reaction temperature was 400-540 °C. After isothermal reaction for 30 min, data was collected by gas chromatography and the product composition and content were detected, and the detection temperature was 20 °C. At 500 °C, the C3H8 conversion rate was 32.1%, the propylene selectivity was 65.0%, and the ethylene selectivity was 12.5%.

[0033] Embodiment 2-5 In this example, the core-shell ZrO2@BCNO catalyst prepared in Examples 1-5 is used to catalyze the propane oxidative dehydrogenation reaction under oxygen-rich conditions, and the specific steps are as follows: 100 mg of the core-shell ZrO2@BCNO catalyst prepared in Example 1-5 was weighed and placed in a quartz tube reactor, and a mixed gas of C3H8, O2 and N2 was introduced, wherein the volume ratio of C3H8:O2:N2 was 1:2:7, the total flow rate was 40 mL / min, and the reaction temperature was 400-540 °C. After isothermal reaction for 30 min, data was collected by gas chromatography and the product composition and content were detected, and the detection temperature was 20 °C. At 500 °C, the C3H8 conversion rate was 5.6%, the propylene selectivity was 90.8%, and the ethylene selectivity was 5.1%.

Claims

1. A method for preparing a core-shell nano oxide @ boron carbon nitrogen oxygen catalyst for propane oxidative dehydrogenation, characterized in that: The following steps are involved: Step 1: dissolve tetrafluoroborate ionic liquid in deionized water, add cyanamide or its polymer, stir in a sealed oil bath at 90 °C for 0.5 h, then add commercially available nano oxide, continue to stir in a sealed oil bath at 90 °C for 0.5 h, then evaporate the solvent water at 90 °C until it becomes viscous, and dry in an oven at 80 °C overnight; Step 2: Grind the solid obtained in step 1 and pyrolyze it at 550 °C in an air atmosphere of a muffle furnace, wherein the heating rate is 1 °C / min, 100 °C is maintained for 1 h, 350 °C is maintained for 2 h, and 550 °C is maintained for 2 h, to obtain a nano-oxide @ boron carbon nitrogen oxide (BCNO) catalyst.

2. The preparation method according to claim 1, characterized in that: The tetrafluoroborate ionic liquid is one of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-methyl-3-octylimidazolium tetrafluoroborate or 1-butyl-4-methylpyridinium tetrafluoroborate.

3. The preparation method according to claim 1 or 2, characterized in that: The cyanamide or its polymer is one of cyanamide, dicyandiamide, melamine, cyanuric acid or methylguanamine.

4. The preparation method according to claim 3, characterized in that: The molar ratio of B to N in the raw material is 0.025~0.10:

1.

5. The preparation method according to claim 4, characterized in that: The molar ratio of B to N in the raw material is 0.05:

1.

6. The preparation method according to claim 1, 2, 4 or 5, characterized in that: The commercially available nano-oxide includes but is not limited to at least one of SiO2, Al2O3 or ZrO2, and does not require pretreatment.

7. The preparation method according to claim 6, characterized in that: The mass ratio of tetrafluoroborate to oxide is 0.5 to 2:

1.

8. The preparation method according to claim 7, characterized in that: The mass ratio of tetrafluoroborate to oxide is 1:

1.

9. A catalyst prepared according to the method of claim 1, 2, 4, 5 or 8, characterized in that: It is an irregular core-shell structure, with boron, carbon, nitrogen and oxygen as the shell and commercially available nano oxides as the core, and the mass percentage of B element is 3.4~23.4 wt%.

10. Use of the core-shell nano oxide @ BCNO catalyst according to claim 9 in propane oxidative dehydrogenation reaction under oxygen-rich conditions.

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