A method for preparing, a product of, and an application of a BN-coated Ni catalyst.

Abstract

This invention provides a method for preparing a BN-coated Ni catalyst, a product thereof, and its application. The method utilizes vapor deposition to deposit BN on the surface of a Ni substrate to prepare a BN-coated Ni catalyst. By leveraging the interaction between Ni and B, the electronic environment of B is adjusted, increasing the reaction activity and lowering the required reaction temperature, thus achieving excellent low-temperature, high-activity, and highly selective propane oxidative dehydrogenation performance. Simultaneously, the foamed nickel possesses excellent pore structure and thermal conductivity, preventing heat accumulation at any single point during the reaction and avoiding localized hot spots on the catalyst. Finally, in addition to surface reactions, the abundant pores of the foamed nickel also provide a site for gas-phase free radical reactions, further enhancing the reaction activity.

Description

Technical Field

[0001] This invention belongs to the field of catalytic chemical technology, specifically relating to a method for preparing a BN-coated Ni catalyst, the product, and its application. Background Technology

[0002] Propylene, the second largest organic olefin chemical after ethylene, is a crucial chemical raw material and polymer monomer, widely used and in high demand in the synthesis of polypropylene, propylene oxide, acrylonitrile, acrylic acid, cumene, butanol, and other products. Currently, propylene is sourced from petroleum-based naphtha cracking and catalytic cracking, Fischer-Tropsch synthesis to olefins, methanol-to-propylene, and propane dehydrogenation. Among these, the propane dehydrogenation route is considered more economically feasible and environmentally friendly, making it a promising and economically competitive propylene production technology.

[0003] Propane dehydrogenation technology is divided into direct dehydrogenation and oxidative dehydrogenation. Oxidative dehydrogenation of propane is an exothermic process, without the constraints of thermodynamic equilibrium, and it is carried out in an oxidizing atmosphere, offering advantages such as no coking, fast reaction rate, and low reaction temperature. In 2016, American scientists Hermans et al. first applied commercially available hexagonal boron nitride (h-BN) and boron nitride nanotubes (BNNTs) as non-metallic catalysts in the propane oxidative dehydrogenation reaction, demonstrating excellent catalytic performance and attracting widespread attention from researchers. Since then, the design of boron-based catalysts, the exploration of their reaction mechanisms and structure-activity relationships, and further improvements in olefin selectivity and yield have become key research focuses.

[0004] Propane oxidative dehydrogenation is an exothermic reaction, which easily leads to the formation of localized hot spots on the catalyst during the reaction. This results in adverse phenomena such as sintering of the active component and increased surface coking, reducing the catalyst's activity. Furthermore, boron-based catalysts exhibit poor low-temperature activity, and reactions at high temperatures not only increase energy consumption but also lead to the production of CO peroxidation products. x The increase in [something] and the decrease in selectivity are problems that urgently need to be addressed. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preparing a boron nitride (BN)-coated Ni catalyst. The method employs a vapor deposition process to deposit boron nitride onto the surface of a Ni substrate, thus preparing a boron nitride-coated nickel catalyst. This catalyst structure utilizes the interaction between Ni and B to adjust the electronic environment of B, increasing the reactivity of boron nitride, lowering the required reaction temperature, and achieving excellent low-temperature, high-activity, and high-selectivity propane oxidative dehydrogenation reaction.

[0006] In addition, the present invention provides an application of the BN-coated Ni catalyst prepared by the above preparation method in the propane oxidative dehydrogenation reaction.

[0007] A method for preparing a BN-coated Ni catalyst, comprising:

[0008] A gas-phase precipitation method was used to deposit nitrogen and boron sources into a reactor containing a Ni substrate. After the deposition reaction was completed, the reaction product was subjected to high-temperature heat treatment to obtain the BN-coated Ni catalyst.

[0009] The above preparation method uses vapor deposition to deposit a boron nitride coating layer on the surface of a Ni substrate. By utilizing the interaction between Ni and B, the electronic environment of B is adjusted, its reactivity is increased, and the required reaction temperature is reduced, thus achieving excellent low-temperature, high-activity, and highly selective propane oxidative dehydrogenation performance.

[0010] Preferably, the Ni substrate is one or more of nickel foam, nickel foil, and nickel particles. Nickel foam is more preferred. Nickel foam has excellent pore structure and thermal conductivity, which can effectively prevent heat accumulation at a single point during the propane oxidative dehydrogenation reaction, avoiding the occurrence of localized hot spots on the catalyst. In addition to surface reactions, the abundant pores of nickel foam also provide a site for gas-phase free radical reactions, increasing reactivity from another perspective.

[0011] Preferably, the volumetric flow rate ratio of the nitrogen source to the boron source is (0.1–10):1. More preferably, it is (1–5):1. Even more preferably, it is (2–4):1.

[0012] Preferably, the deposition reaction temperature is 600–1400°C. More preferably, it is 600–1000°C. Even more preferably, it is 600–750°C to obtain a higher deposition rate.

[0013] Preferably, the deposition reaction time is 0.5 to 5 hours. More preferably, it is 1 to 3 hours.

[0014] Preferably, the residence time of the nitrogen and boron sources during the deposition reaction is 0.01–10 s. More preferably, it is 0.1–0.5 s. Even more preferably, it is 0.13–0.35 s.

[0015] The residence time of nitrogen and boron sources can be controlled by adjusting the total flow rate into the reactor.

[0016] Preferably, the nitrogen source is ammonia.

[0017] Preferably, the boron source is one or more selected from boron chloride, boron bromide, and boron iodide. More preferably, it is boron chloride.

[0018] Preferably, when introducing the boron source, nitrogen or a mixture of nitrogen and hydrogen is used as the carrier gas to introduce the boron source into the reactor.

[0019] Preferably, a coaxial double quartz tube is used to separately introduce the nitrogen source and the boron source into the reactor. More preferably, the distance between the outlet of the coaxial double quartz tube and the Ni substrate is 5–15 mm. To prevent premature reaction of the nitrogen and boron sources while ensuring thorough mixing, and even more preferably, the distance between the outlet of the coaxial double quartz tube and the Ni substrate is 8–12 mm.

[0020] Preferably, before being introduced into the reactor, both the nitrogen source and the boron source (including the carrier gas) are purified to remove impurities.

[0021] To obtain better crystallinity, the high-temperature heat treatment temperature is preferably 1000–1600°C. More preferably, it is 1000–1500°C.

[0022] Preferably, the high-temperature heat treatment time is 1 to 3 hours. More preferably, it is 1.5 to 2.5 hours.

[0023] As a preferred option, after the deposition reaction is complete, other gases are shut off, and only nitrogen is introduced, followed by high-temperature heat treatment of the reaction products.

[0024] As a preferred embodiment, a method for preparing a BN-coated Ni catalyst includes:

[0025] A Ni substrate was placed in a reactor, and nitrogen and boron sources with a set flow rate ratio were introduced into the reactor through a coaxial double quartz tube to carry out a deposition reaction. After the deposition reaction was completed, the reaction product was subjected to high-temperature heat treatment to obtain the BN-coated Ni catalyst.

[0026] A BN-coated Ni catalyst is prepared by any one of the methods described above. This catalyst utilizes the presence of the core Ni to adjust the electronic environment of B in the coating layer, effectively increasing the catalyst's reactivity, lowering the required reaction temperature, and achieving a highly selective and high-conversion propane oxidative dehydrogenation reaction at low temperatures.

[0027] Application of a BN-coated Ni catalyst as described above in the oxidative dehydrogenation reaction of propane.

[0028] As a preferred embodiment, the application includes:

[0029] The prepared BN-coated Ni catalyst was packed into a quartz reaction tube with an inner diameter of 10 mm and installed in a fixed-bed tubular reactor. A mixed gas containing propane, oxygen and nitrogen was introduced to carry out an oxidative dehydrogenation reaction, and the product composition was analyzed online by gas chromatography.

[0030] Preferably, the loading amount of the BN-coated Ni catalyst is 50–150 mg.

[0031] Preferably, the volume ratio of propane, oxygen, and nitrogen is 1:(0.5-3):(1-6). More preferably, it is 1:(1-2):(3-4).

[0032] Preferably, the temperature of the oxidative dehydrogenation reaction is 400–500°C. More preferably, it is 440–460°C.

[0033] Preferably, the space velocity of the mixed gas is 7200-14400 ml / g / h. More preferably, it is 10000-11000 ml / g / h.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] The method for preparing the BN-coated Ni catalyst of this invention adopts the idea of ​​adding metal to change the electronic environment of boron, thereby affecting its chemical performance. BN is deposited on the surface of a Ni substrate using vapor deposition to prepare the BN-coated Ni catalyst. By utilizing the interaction between Ni and B, the electronic environment of B is adjusted, increasing the reaction activity and lowering the required reaction temperature, thus achieving excellent low-temperature, high-activity, and highly selective propane oxidative dehydrogenation performance. Simultaneously, the foamed nickel has a very good pore structure and thermal conductivity, preventing heat accumulation at any single point during the reaction and avoiding localized hot spots on the catalyst. Finally, in addition to surface reactions, the abundant pores of the foamed nickel also provide a site for gas-phase free radical reactions, increasing the reaction activity from another perspective. Attached Figure Description

[0036] Figure 1 X-ray diffraction patterns of BN-coated nickel foam catalysts at different vapor-phase deposition temperatures;

[0037] Figure 2 Scanning electron microscope image of BN-coated nickel foam catalyst. Detailed Implementation

[0038] To further illustrate the present invention, the following describes in detail a method for preparing a BN-coated Ni catalyst provided by the present invention, with reference to specific embodiments.

[0039] Example 1

[0040] Take a piece of foamed Ni with a diameter of approximately 60 mm and a thickness of approximately 10 mm, place it in the deposition zone of the reactor, 10 mm from the outlet of the coaxial double quartz tube, set the deposition temperature to 650℃, and allow NH3 and Q to flow through one of the coaxial double quartz tubes. NH3 =60ml / min, the other route is BCl3+N2+H2, Q BCl3 =20ml / min, Q N2 =120ml / min, Q H2=20ml / min, gas residence time is 0.24s. After deposition for 2h, other gases are turned off, only N2 is introduced, the temperature is raised to 1300℃ for subsequent heat treatment, and the temperature is kept constant for 2h. After the temperature drops to room temperature, the target catalyst, namely BN-coated foamed Ni catalyst, is taken out.

[0041] Figure 2 This is a SEM image of the catalyst prepared in this embodiment. Figure 2 The middle left figure shows that the Ni foam has a very good pore structure, which is conducive to heat diffusion and gas-phase free radical reaction. Figure 2 The middle right figure shows that BN is uniformly deposited on the surface of the foamed Ni, providing a large number of active centers and improving reactivity.

[0042] 90 mg of the prepared catalyst was installed in a fixed-bed tubular reactor (reaction tube inner diameter 10 mm) using a loose-phase packing method. A mixed gas containing propane, oxygen, and nitrogen in a volume ratio of 1:1.5:3.5 was introduced. The oxidative dehydrogenation temperature was 440 °C, and the space velocity of the mixed gas was 10800 L·g⁻¹. -1 ·h -1 The oxidative dehydrogenation reaction was carried out, and the product composition was analyzed online by gas chromatography, revealing a propane conversion rate of 20% and a propylene selectivity of 80%. The analysis results indicate that the BN-coated foamed Ni catalyst prepared in this embodiment exhibits high activity and high selectivity at low temperatures during the propane oxidative dehydrogenation reaction.

[0043] Example 2 (Selection of Deposition Temperature)

[0044] Take a piece of foamed Ni with a diameter of approximately 60 mm and a thickness of approximately 10 mm, and place it in the deposition zone of the reactor, 10 mm from the outlet of the coaxial double quartz tube. The deposition temperatures are set to 600℃, 650℃, 700℃, and 750℃, respectively. One path of the coaxial double quartz tube carries NH3, Q NH3 =60ml / min, the other route is BCl3+N2+H2, Q BCl3 =20ml / min, Q N2 =120ml / min, Q H2 =20ml / min, at which point the gas residence time is 0.24s. After deposition for 2h, other gases are turned off, and only N2 is introduced. The temperature is raised to 1300℃ for subsequent heat treatment, and the temperature is kept constant for 2h. After the temperature drops to room temperature, the target catalyst is taken out, and four BN-coated foamed Ni catalysts at different deposition temperatures are obtained, which are designated as catalysts 1#, 2#, 3# and 4#, respectively.

[0045] Figure 1 The images show a comparison of X-ray diffraction patterns of BN-coated Ni foam catalysts prepared at different deposition temperatures. Figure 1As can be seen, with the increase of deposition temperature, BN crystallinity is better, and the reaction activity is enhanced without burying the catalytic ability of Ni.

[0046] The catalytic performance of the four catalysts prepared above for the oxidative dehydrogenation of propane was tested according to the reaction conditions and methods described in Example 1. The results are shown in Table 1.

[0047] Table 1 Catalytic performance of catalysts with different gas residence times

[0048] catalyst Propane conversion rate / % Propylene selectivity / % 1#(600℃) 30.4 60.2 2#(650℃) 20.7 80.2 3#(700℃) 19.1 79.1 4#(750℃) 16.1 78.5

[0049] Table 1 shows that the propane oxidative dehydrogenation performance first increases and then decreases with increasing deposition temperature. This may be because, within a certain temperature range, as the deposition temperature increases, the crystallinity of BN increases, the BN coating on the surface of the foamed Ni gradually becomes more complete, and the deposition thickness gradually increases, weakening the effect of Ni-induced over-oxidation of propane, thereby enhancing the selectivity of the prepared catalyst and improving the catalytic effect. However, when the deposition temperature is too high, the deposition thickness of BN on the surface of the foamed Ni becomes too large, and the outermost BN coating layer that can contact propane is less affected by the core Ni, affecting the propane conversion rate and reducing the catalytic performance of the catalyst. The catalyst prepared at a deposition temperature of 650℃ exhibits the best overall effect in propane conversion and propylene selectivity in the propane oxidative dehydrogenation reaction, demonstrating the best catalytic effect, and is the optimal deposition temperature.

[0050] Example 3 (Selection of Gas Residence Time)

[0051] A piece of Ni foam with a diameter of approximately 60 mm and a thickness of approximately 10 mm was placed in the deposition zone of the reactor, 10 mm from the outlet of the coaxial double quartz tube. The deposition temperature was set at 650℃. One path of the coaxial double quartz tube carried NH3, and the other carried BCl3+N2+H2, maintaining a flow ratio of NH3 to BCl3 of 3:1. Simultaneously, the total gas flow rate was controlled to achieve gas residence times of 0.13 s, 0.19 s, 0.24 s, 0.30 s, and 0.35 s, respectively. After 2 hours of deposition, all other gases were shut off, and only N2 was introduced. The temperature was raised to 1300℃ for subsequent heat treatment and held at that temperature for 2 hours. After the temperature dropped to room temperature, the target catalyst was removed, and five BN-coated Ni foam catalysts with different gas residence times were prepared, designated as catalysts #5, #6, #7, #8, and #9.

[0052] The catalytic performance of the five catalysts prepared above for the oxidative dehydrogenation of propane was tested according to the reaction conditions and methods described in Example 1. The results are shown in Table 2.

[0053] Table 2 Catalytic performance of catalysts with different gas residence times

[0054] Gas residence time / s Propane conversion rate / % Propylene selectivity / % 5#(0.13s) 38.7 56.8 6#(0.19s) 23.3 70.2 7#(0.24s) 20.7 80.2 8#(0.30s) 17.7 78.8 9#(0.35s) 16.6 78

[0055] As shown in Table 2, the oxidative dehydrogenation performance of propane first increases and then decreases with increasing gas residence time. This may be because, within a certain residence time, the longer the gas residence time, the more complete the BN coating layer on the surface of the foamed Ni, thereby improving the catalytic performance of the catalyst and the selectivity of propylene. However, when the residence time is too long, the thickness of the BN coating layer gradually increases, and the outermost BN coating layer that can contact propane is less affected by the core nickel, resulting in a worsening effect on the propane conversion rate.

[0056] Example 4 (Selection of nitrogen source / boron source volumetric flow rate ratio)

[0057] A piece of foamed Ni with a diameter of approximately 60 mm and a thickness of approximately 10 mm was placed in the deposition zone of the reactor, 10 mm from the outlet of the coaxial double quartz tube. The deposition temperature was set to 650℃. One path of the coaxial double quartz tube carried NH3, and the other carried BCl3+N2+H2. The total gas flow rate was controlled to ensure a gas residence time of 0.24 s. The flow ratios of NH3 and BCl3 were set to 1:1, 2:1, 3:1, 4:1, and 5:1, respectively. After deposition for 2 hours, all other gases were shut off, and only N2 was introduced. The temperature was raised to 1300℃ for subsequent heat treatment and held at that temperature for 2 hours. After the temperature dropped to room temperature, the target catalyst was removed, yielding five BN-coated foamed Ni catalysts with different nitrogen and boron source volume flow ratios, designated as catalysts 10#, 11#, 12#, 13#, and 14#.

[0058] The catalytic performance of the five catalysts prepared above for the oxidative dehydrogenation of propane was tested according to the reaction conditions and methods described in Example 1. The results are shown in Table 3.

[0059] Table 3 Catalytic performance of catalysts with different nitrogen and boron source volume flow ratios

[0060] Gas residence time / s Propane conversion rate / % Propylene selectivity / % 10#(1：1) 17.1 78.3 11#(2：1) 18.9 79.1 12#(3：1) 20.7 80.2 13#(4：1) 18.6 79.6 14#(5：1) 17.2 78.8

[0061] As shown in Table 3, the propane oxidative dehydrogenation performance first increases and then decreases with the increase of the NH3:BCl3 flow ratio. This may be because the BN morphology formed at the optimal gas ratio is the best, and the proportion of active sites is the highest. The greater the deviation from this optimal gas ratio, the more likely it is to form some rough BN large particles or defects that are not conducive to the reaction, thus reducing the catalytic performance of the catalyst.

[0062] Example 5

[0063] Take a Ni foil with a diameter of approximately 60 mm and a thickness of approximately 10 mm, place it in the deposition zone of the reactor, 10 mm from the outlet of the coaxial double quartz tube, set the deposition temperature to 650℃, and allow NH3 and Q to flow through one of the coaxial double quartz tubes. NH3=60ml / min, the other route is BCl3+N2+H2, Q BCl3 =20ml / min, Q N2 =120ml / min, Q H2 =20 ml / min, gas residence time is 0.24 s. After deposition for 2 h, other gases are turned off, only N2 is introduced, the temperature is raised to 1300℃ for subsequent heat treatment, and the temperature is kept constant for 2 h. After the temperature drops to room temperature, the target catalyst is taken out to obtain BN-coated Ni foil catalyst.

[0064] 90 mg of the prepared catalyst was installed in a fixed-bed tubular reactor using a loosely packed configuration. A mixed gas containing propane, oxygen, and nitrogen in a volume ratio of 1:1.5:3.5 was introduced. The oxidative dehydrogenation temperature was 440 °C, and the space velocity of the mixed gas was 10800 L·g⁻¹. -1 ·h -1 The product composition was analyzed by online gas chromatography after undergoing an oxidative dehydrogenation reaction, yielding a propane conversion rate of 21% and a propylene selectivity of 78%.

[0065] Example 6 (Changing the Ni substrate and deposition temperature)

[0066] Take a Ni foil with a diameter of approximately 60 mm and a thickness of approximately 10 mm, place it in the deposition zone of the reactor, 10 mm from the outlet of the coaxial double quartz tube, set the deposition temperature to 600℃, and allow NH3 and Q to flow through one of the coaxial double quartz tubes. NH3 =60ml / min, the other route is BCl3+N2+H2, Q BCl3 =20ml / min, Q N2 =120ml / min, Q H2 =20ml / min, at which point the gas residence time is 0.24s. After deposition for 2h, other gases are turned off, and only N2 is introduced. The temperature is raised to 1300℃ for subsequent heat treatment, and the temperature is kept constant for 2h. After the temperature drops to room temperature, the target catalyst is taken out, and the BN-coated Ni foil catalyst is obtained.

[0067] 90 mg of the prepared catalyst was installed in a fixed-bed tubular reactor using a loosely packed configuration. A mixed gas containing propane, oxygen, and nitrogen in a volume ratio of 1:1.5:3.5 was introduced. The oxidative dehydrogenation temperature was 440 °C, and the space velocity of the mixed gas was 10800 L·g⁻¹. -1 ·h -1 The product composition was analyzed online by gas chromatography after undergoing an oxidative dehydrogenation reaction.

[0068] At a temperature of 440°C, the catalyst achieved a propane conversion of 28.9% and a propylene selectivity of 62%.

Claims

1. The application of a BN-coated Ni catalyst in the oxidative dehydrogenation reaction of propane, characterized in that, The preparation method of the BN-coated Ni catalyst includes: A gas-phase precipitation method was used to deposit nitrogen and boron sources into a reactor containing a Ni substrate. After the deposition reaction was completed, the reaction product was subjected to high-temperature heat treatment to obtain the BN-coated Ni catalyst. The Ni substrate is nickel foam.

2. The application of the BN-coated Ni catalyst according to claim 1 in the oxidative dehydrogenation reaction of propane, characterized in that, The volumetric flow rate ratio of nitrogen source to boron source is (0.1~10):

1.

3. The application of the BN-coated Ni catalyst according to claim 1 in the oxidative dehydrogenation reaction of propane, characterized in that, The deposition reaction is carried out at a temperature of 600~1400℃ for a time of 0.5~5h.

4. The application of the BN-coated Ni catalyst according to claim 1 in the oxidative dehydrogenation reaction of propane, characterized in that, During the deposition reaction, the residence time of the nitrogen and boron sources is 0.01~10s.

5. The application of the BN-coated Ni catalyst according to claim 1 in the oxidative dehydrogenation reaction of propane, characterized in that, The nitrogen source is ammonia. The boron source is one or more of boron chloride, boron bromide, and boron iodide.

6. The application of the BN-coated Ni catalyst according to claim 1 in the oxidative dehydrogenation reaction of propane, characterized in that, The high-temperature heat treatment temperature is 1000~1600℃.

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