Catalyst capable of regulating and controlling oxygen vacancy concentration, preparation method of catalyst and application of catalyst in oxygen oxidation desulfurization

Abstract

The invention provides a catalyst capable of regulating and controlling oxygen vacancy concentration, a preparation method of the catalyst and application of the catalyst in oxygen oxidation desulfurization, and belongs to the crossing field of nano-catalysis and environmental protection technologies. The preparation method comprises the following steps: firstly, dropwise adding a mixed solution containing ammonium heptamolybdate and ammonium metavanadate into water, heating and stirring, then adding a carrier g-C3N4 to obtain a reaction solution, centrifuging the reaction solution to obtain a solid phase, and carrying out high-temperature calcination on the solid phase; secondly, carrying out high-temperature calcination treatment on the raw materials again under the condition that reducing gas is continuously introduced; and finally, adding a sample into a NaBH4 solution, stirring at room temperature for 1-7 hours, centrifuging, filtering and drying to obtain the Mo-V / g-C3N4 composite material. According to the prepared catalyst, regulation and control over the oxygen vacancy concentration can be achieved through H2 high-temperature calcination reduction and NaBH4 chemical reduction, oxygen oxidation desulfurization reaction can be driven by taking oxygen as an oxidizing agent at the low temperature of 80 DEG C, and 100% conversion of DBT is achieved; and the preparation process is simple, low in cost, easy to separate, green and environment-friendly and can be used for industrial production.

Description

Technical Field

[0001] The present invention belongs to the cross - field of nano - catalysis and environmental protection technology, and relates to a low - temperature and highly efficient oxygen - oxidative desulfurization catalyst and its preparation strategy, in particular to a catalyst with adjustable oxygen vacancy concentration, its preparation method and application in oxygen - oxidative desulfurization. Background Art

[0002] With the development of society and the rapid growth of the economy, people's consumption of fuel is increasing. After fuel combustion, a large amount of sulfur oxides (SO x ) are produced. These sulfur oxides mainly exist in the form of sulfur dioxide (SO2) gas. The excessive emission of SO2 will have a huge impact on society, such as polluting the environment, causing equipment corrosion, forming acid rain, and seriously affecting human health, causing respiratory damage. Oxygen - oxidative desulfurization is a new desulfurization technology that uses oxygen in the air as a green oxidant to efficiently convert sulfur - containing compounds (such as thiophenes) in fuel into sulfonic acid or sulfone products at normal temperature and pressure. Compared with the high - temperature and high - pressure conditions of traditional hydrodesulfurization and the dependence of oxidative desulfurization on dangerous oxidants (such as hydrogen peroxide), this method directly uses oxygen in the air, combining environmental protection, safety and economy, without the need for complex storage and transportation equipment, no harmful by - products and low cost. Its core lies in developing highly efficient catalysts to activate stable oxygen molecules. By designing metal active sites or electron - rich carriers, oxygen is promoted to dissociate into active oxygen species, and sulfur - containing impurities are selectively oxidized without destroying the fuel hydrocarbon structure. Therefore, it is crucial to prepare a catalyst that can activate oxygen under mild conditions.

[0003] Shao (Chemical Engineering Science 284 (2024) 119463) et al. designed a series of MoO3 / La2O2CO3 catalysts with different MoO3 particle sizes through a simple citric acid - assisted hydrothermal strategy, and deeply analyzed the influence of the particle size of MoO3 / La2O2CO3 catalysts on the oxygen - oxidative desulfurization performance. The DBT conversion rate can reach 100% at 130 °C for 2.5 h. Although Mo - based catalysts have good catalytic activity in the field of oxidative desulfurization, the reaction condition of 130 °C will cause the co - oxidation of other components in the fuel, which will not only reduce the octane number of the fuel and affect the quality of the oil product, but also affect the rate of oxidative desulfurization.

[0004] Now, more and more researchers have noticed the importance of oxygen vacancies in oxidative desulfurization with oxygen. Oxygen vacancies can adsorb and activate oxygen, which is of great significance for low-temperature oxidative desulfurization with oxygen. Liu (Ind. Eng. Chem. Res. 2020, 59, 6488-6496) et al. prepared hierarchical hollow Co-Ni-Mo-O mixed metal oxide nanotubes constructed from ultrathin CoMoO4 / NiMoO4 nanosheets using the sacrificial template method. Using O2 in the air as the oxidant, complete aerobic oxidation of various sulfides was achieved at 100 °C, where oxygen vacancies played a key role in the adsorption and activation of oxygen. Although the reaction temperature was reduced to 100 °C, there would still be some co-oxidation of components in the fuel, reducing the quality of the oil product. At the same time, although the catalyst contained oxygen vacancies, its content was not high, and the general law of oxygen vacancies and reaction activity was not deeply explored. Therefore, it is crucial to explore the catalytic activity of catalysts with a high oxygen vacancy concentration.

[0005] Since the activation of oxygen requires giving electrons to oxygen to activate it into reactive oxygen species, the choice of carrier is also particularly important. Graphitic carbon nitride (g-C3N4) has attracted much attention due to its advantages such as two-dimensional layered structure, excellent stability, and simple preparation method (Colloids and Surfaces A 572 (2019) 250-258). Its two-dimensional layered structure provides more active centers during the reaction. At the same time, the π-conjugation in its ring structure can promote the transfer of electrons from the carrier to the active center, which is more conducive to activating oxygen into superoxide radicals. Therefore, based on the above research status, g-C3N4 as a carrier, loaded with metal oxides by different means to form a high oxygen vacancy concentration, not only promotes the adsorption of oxygen but also promotes the activation of oxygen, and has high research value. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, in order to achieve adjustable oxygen vacancy concentration and catalyze oxidative desulfurization with oxygen under mild conditions, the present invention provides a Mo-V / g-C3N4 catalyst with adjustable oxygen vacancy concentration. The prepared heterogeneous catalyst can achieve oxidative desulfurization with oxygen at 80 °C and has good reusability. Moreover, the catalyst prepared by the present invention can realize the regulation and control of the oxygen vacancy concentration through high-temperature calcination reduction with H2 and chemical reduction with NaBH4. At a relatively low temperature of 80 °C, using oxygen as the oxidant can drive the oxidative desulfurization reaction with oxygen and achieve 100% conversion of DBT. And the preparation process is simple, low-cost, easy to separate, environmentally friendly and can be industrially produced.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A preparation method of a catalyst with adjustable oxygen vacancy concentration, comprising the following steps:

[0009] Step (1): Add 10 - 15 g of melamine into a porcelain boat, cover the lid and place it in a tube furnace. Before heating, introduce N₂ for 30 - 60 min to ensure that the tube is filled with N₂. Subsequently, heat it at a heating rate of 3 - 5 °C / min to 500 - 550 °C under continuous N₂ flow, calcine it at 500 - 550 °C for 3 - 6 h, and then cool it to room temperature. Scrape out the large yellow solid and grind it into powder to obtain the support g-C₃N₄.

[0010] Step (2): Drop a mixed solution containing ammonium heptamolybdate and ammonium metavanadate into pure water, raise the temperature to 40 - 70 °C, stir at a speed of 400 - 800 rpm for 20 - 60 min, then continue to add the support g-C₃N₄ into the solution, and then continue to stir for 1 - 3 h until the support is evenly dispersed to obtain a reaction solution. Among them, in the mixed solution, the concentration of ammonium heptamolybdate is 0.01 - 0.1 mol / L, and the concentration of ammonium metavanadate is 0.01 - 0.1 mol / L. The addition amount of pure water and the mixed solution is that for every 10 mL of pure water, 1 - 2 mL of the mixed solution containing ammonium heptamolybdate and ammonium metavanadate is added; the addition amount of the support g-C₃N₄ is that for every 10 mL of pure water, 1 - 5 g of the support is added.

[0011] Step (3): Centrifuge the reaction solution obtained in step (2) in a centrifuge. The obtained solid phase is washed with pure water and then centrifuged at a speed of 8000 - 10000 rpm for 2 - 5 times to remove the liquid phase. The obtained solid phase is dried at 80 - 100 °C for 10 - 12 h.

[0012] Step (4): After cooling the sample dried in step (3) to room temperature, grind it into powder. Place it in a tube furnace and heat it at a heating rate of 3 - 5 °C / min to 300 °C - 450 °C under continuous air flow, and calcine it at the corresponding temperature for 3 - 6 h. Then cool it to room temperature.

[0013] Step (5): Continue to place the sample obtained in step (4) in a tube furnace, introduce reducing gas (5% H₂, 95% N₂) for 30 - 90 min to ensure that the tube is filled with reducing gas. Subsequently, under the condition of continuous introduction of reducing gas, heat it at a heating rate of 3 - 5 °C / min to 300 - 400 °C, and calcine it at the corresponding temperature for 3 - 6 h. Then cool it to room temperature. Through the reducing gas, H₂ combines with the lattice oxygen in the metal oxide at high temperature to generate water vapor and escapes from the surface, resulting in the loss of oxygen atoms from the lattice to produce oxygen vacancies.

[0014] Step (6): Add the sample in step (5) to the NaBH4 solution, stir at room temperature for 1 h to 7 h, and after centrifugation, filtration, and drying, the chemically reduced catalyst can be obtained. By further treatment with the NaBH4 chemical reduction method, a higher concentration of oxygen vacancies can be obtained, and finally, the Mo-V / g-C3N4 composite material can be obtained.

[0015] Furthermore, the concentration of the NaBH4 solution is 0.1 - 0.5 mol / L; the addition amount of the sample and the NaBH4 solution is that for every 50 - 150 mg of the catalyst, 50 mL of the NaBH4 solution is added. The strongly reducing BH4 - Induce the reduction of the valence state of metal cations through electron transfer. To maintain charge balance, adjacent lattice oxygen is removed in the form of hydroxyl or H2O, and finally, a metal oxide with an electron-rich defect state is formed. Its oxygen vacancy concentration can be regulated by the NaBH4 concentration and time.

[0016] A catalyst with adjustable oxygen vacancy concentration is the Mo-V / g-C3N4 composite material obtained by the above preparation method. The Mo-V / g-C3N4 composite material is a sheet structure stacked layer by layer. The active metals are evenly distributed and highly dispersed.

[0017] The application of a catalyst with adjustable oxygen vacancy concentration to the oxidative desulfurization process in a simulated oil system with dibenzothiophene as the desulfurization object. Using Mo-V / g-C3N4 as the oxygen oxidative desulfurization catalyst, deep desulfurization can be achieved at low temperatures. In the described simulated oil system, decalin is used as the solvent, dibenzothiophene is used as the sulfur-containing species, tetradecane is used as the gas-phase internal standard, and oxygen is used as the desulfurization oxidant. The oxidative desulfurization process is carried out under the condition of 70 - 80 °C, the reaction time is 600 min, the conversion rate of benzothiophene can reach more than 95%, and when the reaction temperature is 80 °C, the oxidative desulfurization efficiency can reach 100% in 10 h.

[0018] The innovation points of the present invention are: Selecting g-C3N4 as the carrier, its π-conjugated system can promote the transfer of electrons from the carrier to the active center, which is more conducive to the activation of oxygen. By regulating the oxygen vacancies of the catalyst through the H2 high-temperature calcination reduction in step (5) and the NaBH4 chemical reduction in step (6), a series of catalysts with different oxygen vacancy concentrations are prepared, and the highest oxygen vacancy concentration can reach 54%.

[0019] The beneficial effects of the present invention:

[0020] (1) The Mo-V / g-C3N4 material of the present invention uses g-C3N4 as the carrier, and its special π-conjugated structure can promote electron transfer and accelerate oxygen activation.

[0021] (2) The Mo-V / g-C3N4 of the present invention prepares a series of catalysts with different oxygen vacancy concentrations through high-temperature calcination reduction with H2 and chemical reduction with NaBH4.

[0022] (1) The Mo-V / g-C3N4 of the present invention is a novel catalyst in the field of oxidative desulfurization using oxygen as an oxidant, with simple operation, low cost, environmental friendliness, and mild reaction conditions.

[0023] (2) The present invention uses oxygen as the oxidant in the oxidative desulfurization process, with mild reaction conditions and simple operation. The desulfurization rate can reach 100% under the reaction conditions of 80 °C and 6 h. At the same time, it has excellent reusability and is suitable for large-scale industrial production. Description of the Drawings

[0024] Figure 1 SEM image of the Mo-V / g-C3N4 material prepared in Example 1. Figure 1 (a, b) are the carrier g-C3N4; Figure 1 (c, d) are Mo-V / g-C3N4 after high-temperature calcination reduction with H2; Figure 1 (e, f) are Mo-V / g-C3N4 after high-temperature calcination reduction with H2 and chemical reduction with NaBH4;

[0025] Figure 2 XRD pattern of the Mo-V / g-C3N4 material prepared in Example 1.

[0026] Figure 3 Oxygen oxidative desulfurization reaction result diagram of the Mo-V / g-C3N4 material prepared in Example 1.

[0027] Figure 4 Recycling result diagram of the Mo-V / g-C3N4 material prepared in Example 1. Detailed Embodiments

[0028] The following further describes the present invention in detail in combination with actual embodiments. Of course, the present invention is not limited to the following specific embodiments.

[0029] Example 1

[0030] First step, preparation of the g-C3N4 carrier

[0031] Take 10 g of melamine and place it in a porcelain boat. Spread it flat and cover it, then place it in a tube furnace. Before heating, introduce N2 for 30 min to ensure that the tube is filled with nitrogen. Subsequently, heat it at a heating rate of 5 °C / min to 550 °C under continuous N2 introduction, calcine it at 550 °C for 3 h, and after it cools to room temperature, take out the large yellow solid and grind it into powder.

[0032] Figure 1 Figures a and b are SEM images of the as-prepared supported g-C3N4 material, and the stacked sheet-like structure of the support can be seen.

[0033] In the second step, 1 mL of an ammonium heptamolybdate solution with a concentration of 0.01 mol / L and a mixed solution of ammonium metavanadate with a concentration of 0.01 mol / L were dropped into 10 mL of deionized water. After stirring at 800 rpm for 30 min at 60 °C, the solution turned yellow. Subsequently, 1 g of the prepared g-C3N4 support was added, and the mixture was stirred in a water bath at 60 °C for 2 h.

[0034] In the third step, the mixture was transferred to a 10 mL centrifuge tube and centrifuged at 10000 rpm. After centrifugation, the upper liquid phase was poured off, and deionized water was added to the remaining solid for washing. This washing process was repeated three times, and then the remaining solid was placed in a vacuum drying oven and dried at 80 °C for 12 h.

[0035] In the fourth step, the dried material was ground and added to a porcelain boat, which was then placed in a tubular furnace. Air was introduced, and the temperature was raised to 400 °C at a heating rate of 5 °C / min and calcined at the corresponding temperature for 4 h. After it cooled to room temperature, the above-prepared catalyst was continued to be placed in the tubular furnace, and a reducing gas (5% H2, 95% N2) was introduced for 30 min to ensure that the tube was filled with the reducing gas. Subsequently, under the condition of continuous introduction of the reducing gas, the temperature was raised to 400 °C at a heating rate of 5 °C / min and calcined at the corresponding temperature for 3 h. After it cooled to room temperature.

[0036] In the fifth step, 150 mg of the above catalyst was added to 50 mL (0.25 mol / L) of NaBH4 solution and stirred at room temperature for 7 h. The mixture was transferred to a 10 mL centrifuge tube and centrifuged at 10000 rpm. After centrifugation, the upper liquid phase was poured off, and deionized water was added to the remaining solid for washing. This washing process was repeated three times, and then the remaining solid was placed in a vacuum drying oven and dried at 80 °C for 12 h to obtain Mo-V / g-C3N4 with an oxygen vacancy concentration of 54%.

[0037] Use the material prepared above as the catalyst for oxidative desulfurization with oxygen. Using dibenzothiophene as the sulfur-containing species, prepare a simulated oil containing 500 ppm dibenzothiophene and an internal standard (1 ml of n-tetradecane is made up to 25 ml with decalin as the solvent, and this solution is used as the internal standard). Weigh 30 mg of the catalyst into a 50 mL two-necked flask, add a magnetic stir bar and 20 mL of the 500 ppm simulated oil respectively, then place it in an oil bath, heat up to 80 °C, then introduce oxygen, turn on the circulating cooling water, and react for 10 h. After the reaction is completed, stop introducing oxygen, take out the two-necked flask and cool it in a cold water bath until the temperature of the two-necked flask drops to room temperature. Filter out the catalyst in the reaction system, and detect the content of DBT by GC-FID. It can be calculated that the conversion rate of dibenzothiophene can reach 100% in 6 h.

[0038] Comparative Case 1 (compared with Example 1)

[0039] First step, prepare the g-C3N4 support

[0040] Take 10 g of melamine and put it into a porcelain boat, spread it flat and cover it, then put it into a tube furnace. Before heating, introduce N2 for 30 min to ensure that the tube is filled with nitrogen. Then heat it at a heating rate of 5 °C / min to 550 °C under continuous N2 flow, calcine it at 550 °C for 3 h, and after it cools to room temperature, take out the large yellow solid and grind it into powder.

[0041] Second step, drop 1 mL of ammonium heptamolybdate solution with a concentration of 0.01 mol / L and a mixed solution of ammonium metavanadate with a concentration of 0.01 mol / L into 10 mL of deionized water. After stirring at 800 rpm at 60 °C for 30 min, the solution turns yellow. Then add 1 g of the prepared g-C3N4 support and keep stirring in a water bath at 60 °C for 2 h.

[0042] Third step, transfer the mixed solution to a 10 mL centrifuge tube and centrifuge at 10000 rpm. After centrifugation, pour off the upper liquid phase, add deionized water to the remaining solid for washing. After repeating this washing process three times, place the remaining solid in a vacuum drying oven and dry it at 80 °C for 12 h.

[0043] Step 4: Grind the dried material and add it to a porcelain boat. Place it in a tube furnace, introduce air, and heat it to 400 °C at a heating rate of 5 °C / min, and calcine it at the corresponding temperature for 3 h. After it cools down to room temperature, continue to place the prepared catalyst in the tube furnace, introduce reducing gas (5% H2, 95% N2) for 30 min to ensure that the tube is filled with reducing gas. Subsequently, heat it to 400 °C at a heating rate of 5 °C / min under the condition of continuously introducing reducing gas, and calcine it at the corresponding temperature for 3 h. Wait for it to cool down to room temperature. Obtain Mo-V / g-C3N4 without chemical reduction by NaBH4, and its oxygen vacancy concentration is 30%.

[0044] Figure 1 c and d are SEM images of the Mo-V / g-C3N4 material prepared in Comparative Example 1. The stacked sheet structure of the carrier can still be seen, indicating that high-temperature calcination reduction with H2 will not damage the structure of the carrier.

[0045] Use the above-prepared material as a catalyst for oxidative desulfurization with oxygen. Using dibenzothiophene as the sulfur-containing species, prepare a simulated oil containing 500 ppm dibenzothiophene and an internal standard (1 ml of n-tetradecane is made up to 25 ml with decalin as the solvent, and this solution is used as the internal standard). Weigh 30 mg of the catalyst and place it in a 50 mL two-necked flask. Add a magnetic stirrer and 20 mL of 500 ppm simulated oil respectively, then place it in an oil bath, heat it to 80 °C, then introduce oxygen, turn on the circulating cooling water, and react for 10 h. After the reaction is completed, stop introducing oxygen, take out the two-necked flask and cool it in a cold water bath until the temperature of the two-necked flask drops to room temperature. Filter out the catalyst in the reaction system, and detect the content of DBT by GC-FID. It is calculated that the conversion rate of dibenzothiophene in 6 h is only 72%.

[0046] By performing a ratio analysis of Comparative Example 1 (the conversion rate of dibenzothiophene in 6 h is 100%) and Example 1 (the conversion rate of dibenzothiophene in 6 h is 72%), it can be seen that Comparative Example 1 did not perform the operation in the fifth step of Example 1, that is, it did not perform chemical reduction with NaBH4. After XPS characterization analysis, it is obtained that the oxygen vacancy concentration of Mo-V / g-C3N4 prepared in Comparative Example 1 is only 30%, while the oxygen vacancy concentration of Mo-V / g-C3N4 prepared in Example 1 is as high as 54%. This shows that the chemical reduction with NaBH4 in step (5) of the present invention can form a higher concentration of oxygen vacancies on the basis of high-temperature calcination reduction with H2. The higher the oxygen vacancy concentration, the more favorable it is for the adsorption and activation of oxygen, and the more likely it is to promote the conversion of dibenzothiophene.

[0047] Example 2

[0048] Step 1: Prepare the g-C3N4 support

[0049] Take 10 g of melamine and place it in a porcelain boat. Spread it flat, cover it, and put it into a tube furnace. Before heating, introduce N2 for 30 min to ensure that the tube is filled with nitrogen. Then, heat it at a heating rate of 5 °C / min to 550 °C under continuous N2 flow, calcine it at 550 °C for 3 h, wait for it to cool to room temperature, take out the large yellow solid, and grind it into powder.

[0050] In the second step, drop 1 mL of ammonium heptamolybdate solution with a concentration of 0.01 mol / L and a mixed solution of ammonium metavanadate with a concentration of 0.01 mol / L into 10 mL of deionized water. Stir the solution at 800 rpm for 30 min at 60 °C, and the solution turns yellow. Then add 1 g of the prepared g-C3N4 support and keep stirring in a water bath at 60 °C for 2 h.

[0051] In the third step, transfer the mixed solution to a 10 mL centrifuge tube and centrifuge it at 10000 rpm. After centrifugation, pour off the upper liquid phase, add deionized water to the remaining solid for washing. Repeat this washing process three times, and then place the remaining solid in a vacuum drying oven and dry it at 80 °C for 12 h.

[0052] In the fourth step, grind the dried material and add it to a porcelain boat, put it into a tube furnace, introduce air, and heat it at a heating rate of 5 °C / min to 350 °C, and calcine it at the corresponding temperature for 3 h. Wait for it to cool to room temperature. Then, put the above-prepared catalyst into the tube furnace again, introduce reducing gas (5% H2, 95% N2) for 30 min to ensure that the tube is filled with reducing gas. Then, under the condition of continuous introduction of reducing gas, heat it at a heating rate of 5 °C / min to 350 °C, and calcine it at the corresponding temperature for 3 h. Wait for it to cool to room temperature. Obtain Mo-V / g-C3N4 without chemical reduction by NaBH4, and its oxygen vacancy concentration is 25%.

[0053] Use the above-prepared material as a catalyst for oxidative desulfurization of oxygen. Take dibenzothiophene as the sulfur-containing species, and prepare a simulated oil containing 500 ppm dibenzothiophene and an internal standard (1 ml of n-tetradecane is fixed to 25 ml with decalin as the solvent, and this solution is used as the internal standard). Weigh 30 mg of the catalyst and put it into a 50 mL two-necked flask, add a magnetic stirrer and 20 mL of 500 ppm simulated oil respectively, then place it in an oil bath, heat it to 80 °C, then introduce oxygen, turn on the circulating cooling water, and react for 10 h. After the reaction is over, stop introducing oxygen, take out the two-necked flask and cool it in a cold water bath until the temperature of the two-necked flask drops to room temperature. Filter out the catalyst in the reaction system, and detect the content of DBT by GC-FID. Through calculation, the conversion rate of dibenzothiophene in 10 h can reach 92%.

[0054] Example 3

[0055] The first step is to prepare the g-C3N4 support

[0056] Put 15 g of melamine into a porcelain boat, flatten it and cover it, then place it in a tube furnace. Before heating, introduce N₂ for 60 min to ensure that the tube is filled with nitrogen. Subsequently, heat it at a heating rate of 3 °C / min to 500 °C under continuous N₂ flow, calcine it at 500 °C for 6 h. After it cools down to room temperature, take out the large yellow solid and grind it into powder.

[0057] In the second step, drop 2 mL of a mixed solution of ammonium heptamolybdate solution with a concentration of 0.1 mol / L and ammonium metavanadate with a concentration of 0.1 mol / L into 10 mL of deionized water. Stir the solution at 70 °C and 400 rpm for 30 min, and the solution turns yellow. Then add 5 g of the prepared g-C₃N₄ support and keep stirring in a water bath at 70 °C for 3 h.

[0058] In the third step, transfer the mixed solution to a 10 mL centrifuge tube and centrifuge it at 8000 rpm. After centrifugation, pour off the upper liquid phase, and add deionized water to the remaining solid for washing. Repeat this washing process 5 times, and then place the remaining solid in a vacuum drying oven and dry it at 100 °C for 10 h.

[0059] In the fourth step, grind the dried material and add it to a porcelain boat, then place it in a tube furnace. Introduce air and heat it at a heating rate of 3 °C / min to 300 °C, and calcine it at the corresponding temperature for 6 h. After it cools down to room temperature, put the above-prepared catalyst into the tube furnace again, introduce reducing gas (5% H₂, 95% N₂) for 90 min to ensure that the tube is filled with reducing gas. Subsequently, heat it at a heating rate of 3 °C / min to 300 °C under continuous flow of reducing gas, and calcine it at the corresponding temperature for 6 h. After it cools down to room temperature.

[0060] In the fifth step, take 50 mg of the above catalyst and add it to 50 mL (0.1 mol / L) of NaBH₄ solution, stir it at room temperature for 1 h, transfer the mixed solution to a 10 mL centrifuge tube and centrifuge it at 8000 rpm. After centrifugation, pour off the upper liquid phase, and add deionized water to the remaining solid for washing. Repeat this washing process three times, and then place the remaining solid in a vacuum drying oven and dry it at 100 °C for 10 h to obtain Mo-V / g-C₃N₄ with an oxygen vacancy concentration of 34%.

[0061] Use the material prepared above as the catalyst for oxidative desulfurization with oxygen. Using dibenzothiophene as the sulfur-containing species, prepare a simulated oil containing 500 ppm dibenzothiophene and an internal standard (1 ml of n-tetradecane is made up to 25 ml with decalin as the solvent, and this solution is used as the internal standard). Weigh 30 mg of the catalyst into a 50 mL two-necked flask, add a magnetic stirrer and 20 mL of the 500 ppm simulated oil respectively, then place it in an oil bath, heat it to 80 °C, then introduce oxygen, pass circulating cooling water, and react for 10 h. After the reaction is completed, stop introducing oxygen, take out the two-necked flask and cool it in a cold water bath until the temperature of the two-necked flask drops to room temperature. Filter out the catalyst in the reaction system, and detect the content of DBT by GC-FID. The conversion rate of dibenzothiophene after 10 h can reach 95% through calculation.

[0062] Example 4

[0063] First step, prepare the g-C3N4 support

[0064] Take 12.5 g of melamine and put it into a porcelain boat, spread it flat and cover it, then put it into a tube furnace. Pass N2 for 45 min before heating to ensure that the tube is filled with nitrogen. Then heat it to 500 °C at a heating rate of 4 °C / min under continuous N2 flow, calcine it at 525 °C for 4 h, wait until it cools to room temperature, take out the large yellow solid, and grind it into powder.

[0065] Second step, drop 1.5 mL of ammonium heptamolybdate solution with a concentration of 0.05 mol / L and a mixed solution of ammonium metavanadate with a concentration of 0.05 mol / L into 10 mL of deionized water. After stirring at 600 rpm at 40 °C for 30 min, the solution turns yellow. Then add 3 g of the prepared g-C3N4 support and keep stirring in a water bath at 40 °C for 1 h.

[0066] Third step, transfer the mixed solution to a 10 mL centrifuge tube and centrifuge it at 9000 rpm. After centrifugation, pour off the upper liquid phase, add deionized water to the remaining solid for washing. Repeat this washing process 2 times, and then place the remaining solid in a vacuum drying oven and dry it at 90 °C for 11 h.

[0067] Fourth step, grind the dried material and add it to a porcelain boat, put it into a tube furnace, introduce air and heat it to 350 °C at a heating rate of 4 °C / min, and calcine it at the corresponding temperature for 5 h. Wait until it cools to room temperature, then put the catalyst prepared above into the tube furnace again, introduce reducing gas (5% H2, 95% N2) for 60 min to ensure that the tube is filled with reducing gas. Then heat it to 350 °C at a heating rate of 4 °C / min under continuous introduction of reducing gas, and calcine it at the corresponding temperature for 5 h. Wait until it cools to room temperature.

[0068] Step 5: Add 100 mg of the above catalyst to 50 mL (0.5 mol / L) of NaBH4 solution, stir at room temperature for 3 h, transfer the mixture to a 10 mL centrifuge tube, and centrifuge at 9000 rpm. After centrifugation, pour off the upper liquid phase, and add deionized water to the remaining solid for washing. After repeating this washing process three times, place the remaining solid in a vacuum drying oven and dry at 90 °C for 11 h to obtain Mo-V / g-C3N4 with an oxygen vacancy concentration of 41%.

[0069] Use the material prepared above as a catalyst for oxidative desulfurization of oxygen. Using dibenzothiophene as the sulfur-containing species, prepare a simulated oil containing 500 ppm of dibenzothiophene and an internal standard (1 ml of n-tetradecane is made up to 25 ml with decalin as the solvent, and this solution is used as the internal standard). Weigh 30 mg of the catalyst and place it in a 50 mL two-necked flask, add a magnetic stirrer and 20 mL of 500 ppm simulated oil respectively, then place it in an oil bath, heat up to 80 °C, then introduce oxygen, and pass circulating cooling water, and react for 10 h. After the reaction is completed, stop introducing oxygen, take out the two-necked flask and cool it in a cold water bath until the temperature of the two-necked flask drops to room temperature. Filter out the catalyst in the reaction system, and detect the content of DBT by GC-FID. The conversion rate of dibenzothiophene can reach 97% after 10 h through calculation.

[0070] Example 5

[0071] Step 1: Prepare the g-C3N4 support

[0072] Take 10 g of melamine and put it into a porcelain boat, spread it flat and cover it, and then put it into a tube furnace. Pass N2 for 45 min before heating to ensure that the tube is filled with nitrogen. Then heat it to 500 °C at a heating rate of 4 °C / min under continuous N2 flow, calcine it at 525 °C for 4 h, and after it cools to room temperature, take out the large yellow solid and grind it into powder.

[0073] Step 2: Drop 1.5 mL of ammonium heptamolybdate solution with a concentration of 0.05 mol / L and a mixed solution of ammonium metavanadate with a concentration of 0.05 mol / L into 10 mL of deionized water. After stirring at 600 rpm at 40 °C for 30 min, the solution turns yellow. Then add 3 g of the prepared g-C3N4 support and keep stirring in a water bath at 40 °C for 1 h.

[0074] Step 3: Transfer the mixture to a 10 mL centrifuge tube and centrifuge at 9000 rpm. After centrifugation, pour off the upper liquid phase, and add deionized water to the remaining solid for washing. After repeating this washing process twice, place the remaining solid in a vacuum drying oven and dry at 90 °C for 11 h.

[0075] Step 4: Grind the dried material and add it to a porcelain boat. Place the boat in a tube furnace, introduce air, and heat it to 350 °C at a heating rate of 4 °C / min. Calcinate at the corresponding temperature for 5 h. After it cools down to room temperature, put the prepared catalyst into the tube furnace again, introduce reducing gas (5% H2, 95% N2) for 60 min to ensure that the tube is filled with reducing gas. Then, heat it to 350 °C at a heating rate of 4 °C / min under the condition of continuously introducing reducing gas, and calcinate at the corresponding temperature for 5 h. Wait for it to cool down to room temperature.

[0076] Step 5: Take 100 mg of the above catalyst and add it to 50 mL (0.5 mol / L) of NaBH4 solution. Stir at room temperature for 5 h, transfer the mixture to a 10 mL centrifuge tube, and centrifuge at 9000 rpm. After centrifugation, pour off the upper liquid phase, and add deionized water to the remaining solid for washing. Repeat this washing process three times, and then place the remaining solid in a vacuum drying oven and dry it at 90 °C for 11 h to obtain Mo-V / g-C3N4 with an oxygen vacancy concentration of 47%.

[0077] Use the above-prepared material as a catalyst for oxidative desulfurization of oxygen. Using dibenzothiophene as the sulfur-containing species, prepare a simulated oil containing 500 ppm of dibenzothiophene and an internal standard (1 ml of n-tetradecane is made up to 25 ml with decalin as the solvent, and this solution is used as the internal standard). Weigh 30 mg of the catalyst and put it into a 50 mL two-necked flask, add a magnetic stir bar and 20 mL of 500 ppm simulated oil respectively, then place it in an oil bath, heat it to 80 °C, then introduce oxygen, turn on the circulating cooling water, and react for 10 h. After the reaction is completed, stop introducing oxygen, take out the two-necked flask and cool it in a cold water bath until the temperature of the two-necked flask drops to room temperature. Filter out the catalyst in the reaction system, and detect the content of DBT by GC-FID. The conversion rate of dibenzothiophene can reach 100% after 10 h of calculation.

[0078] Example 6

[0079] The rest of the implementation process is the same as that of Example 1. Transfer the reacted reaction solution to a 10 mL centrifuge tube and centrifuge at 10000 rpm for 10 min. After pouring off the liquid phase, wash the solid phase. Select ethanol as the detergent, add 8 mL of acetone to the remaining solid phase above, ultrasonicate for 6 min, and then centrifuge it. Centrifuge at 10000 rpm for 10 min, take the remaining solid phase after pouring off the acetone washing solution into the oven. Dry it at 100 °C for 3 h, and wait for it to cool to obtain the regenerated catalyst. Apply the regenerated catalyst to low-temperature oxidative desulfurization according to Example 6, and the DBT conversion rate for the second reuse is 98%. After repeating the use 5 times, the DBT conversion rate can still be maintained at about 96%. It can be seen that acetone washing can maintain the excellent reusability of the catalyst. Figure 4It is the result diagram of the reuse of the 6Mo-V / g-C3N4 catalyst in Example 6.

[0080] The above-described embodiments only represent the implementation modes of the present invention, but should not be construed as limiting the scope of the present invention patent. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A preparation method of a catalyst with adjustable oxygen vacancy concentration, characterized in that, The described preparation method includes the following steps: Step (1), preparing the carrier g-C3N4; Step (2), dropping a mixed solution containing ammonium heptamolybdate and ammonium metavanadate into pure water, heating to 40 - 70 °C, stirring, and then continuing to add the carrier g-C3N4 to the solution, and then continuing to stir until the carrier is evenly dispersed to obtain a reaction solution; Step (3), drying the solid phase obtained by centrifuging the reaction solution obtained in step (2) to obtain a sample; Step (4), after cooling the sample dried in step (3) to room temperature, grinding it into powder; putting it into a tubular furnace, and under continuous introduction of air, performing high-temperature calcination, and then cooling to room temperature; Step (5), continuing to put the sample obtained in step (4) into the tubular furnace, introducing a reducing gas and ensuring that the tube is filled with the reducing gas; then performing high-temperature calcination treatment under continuous introduction of the reducing gas; Step (6), adding the sample in step (5) to a NaBH4 solution, stirring at room temperature for 1 h - 7 h, centrifuging, filtering, and drying to obtain the Mo-V / g-C3N4 composite material, which is the catalyst.

2. The preparation method of a catalyst with adjustable oxygen vacancy concentration according to claim 1, characterized in that, The specific process of step (1) is as follows: Under the protection of an inert gas, melamine is subjected to high-temperature calcination to obtain a carrier, where the high-temperature calcination temperature is 500 - 550 °C and the time is 3 - 6 h; In step (1), the inert gas protection is achieved by first introducing N2 into the reaction system and then continuously introducing an N2 flow during the entire high-temperature calcination process.

3. The preparation method of a catalyst with adjustable oxygen vacancy concentration according to claim 1, characterized in that, In step (2): In the mixed solution, the concentration of ammonium heptamolybdate is 0.01 - 0.1 mol / L, and the concentration of ammonium metavanadate is 0.01 - 0.1 mol / L; For every 10 mL of pure water, 1 - 2 mL of the mixed solution containing ammonium heptamolybdate and ammonium metavanadate and 1 - 5 g of the carrier are correspondingly added; The stirring speed is 400 - 800 rpm, and the time is 20 - 60 min; the continuous stirring time is 1 - 3 h.

4. The preparation method of a catalyst with adjustable oxygen vacancy concentration according to claim 1, characterized in that, Step (3) is specifically as follows: The solid phase obtained by centrifuging the reaction solution obtained in step (2) is washed with pure water, and then centrifuged at a speed of 8000 - 10000 rpm for 2 - 5 times to remove the liquid phase, and the obtained solid phase is dried at 80 - 100 °C for 10 - 12 h.

5. The preparation method of a catalyst with adjustable oxygen vacancy concentration according to claim 1, characterized in that, The high-temperature calcination temperature in step (4) is 300 °C - 450 °C, and the time is 3 - 6 h.

6. The preparation method of a catalyst with adjustable oxygen vacancy concentration according to claim 1, characterized in that, In step (5): The high-temperature calcination temperature is 300 °C - 400 °C, and the time is 3 - 6 h; The reducing gas is 5% by volume of H2 and 95% by volume of N2; the reducing gas is introduced for 30 - 90 min to ensure that the tube is filled with the reducing gas.

7. The preparation method of a catalyst with adjustable oxygen vacancy concentration according to claim 1, characterized in that, In step (6): The concentration of the NaBH4 solution is 0.1 - 0.5 mol / L; The addition amount of the sample and the NaBH4 solution is that for every 50 - 150 mg of the catalyst, 50 mL of the NaBH4 solution is correspondingly added.

8. A catalyst with adjustable oxygen vacancy concentration, characterized in that, The catalyst with adjustable oxygen vacancy concentration is the Mo-V / g-C3N4 composite material obtained by using the preparation method described in any one of claims 1 - 7. This Mo-V / g-C3N4 composite material has a layered stacked sheet structure; the active metals are evenly distributed and highly dispersed.

9. Use of a catalyst with adjustable oxygen vacancy concentration as described in claim 8, characterized in that, Apply it to the oxidative desulfurization process in a model oil system with dibenzothiophene as the desulfurization target. Using Mo-V / g-C3N4 as the catalyst for oxidative desulfurization with oxygen, deep desulfurization can be achieved at low temperatures.

10. Use of the catalyst with adjustable oxygen vacancy concentration according to claim 9, characterized in that, In the described model oil system, decalin is used as the solvent, dibenzothiophene is used as the sulfur-containing species, tetradecane is used as the gas-phase internal standard, and oxygen is used as the desulfurization oxidant. The oxidative desulfurization process is carried out under the conditions of 70-80 °C for a reaction time of 600 min. The conversion rate of benzothiophene can reach over 95%, and when the reaction temperature is 80 °C, the oxidative desulfurization efficiency can reach 100% after 10 h.

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