Application of a polypyrrole-coated defective molybdenum trioxide catalyst

Abstract

The present invention belongs to the technical field of composite catalytic material preparation and relates to a polypyrrole-coated defective molybdenum trioxide catalyst for use in oxidative desulfurization. A method for preparing the catalyst is also disclosed, comprising uniformly dispersing molybdenum powder in n-butanol, slowly adding hydrogen peroxide with continuous stirring, and adding pyrrole when the reaction solution turns bright yellow and transparent. Stirring is continued at room temperature overnight. The solution is placed in an autoclave and subjected to a hydrothermal reaction at 100-160°C for 12-20 hours. After cooling to room temperature, the reaction is centrifuged, and the precipitate is washed with deionized water and anhydrous ethanol, respectively. The resulting precursor is collected and vacuum dried to obtain the catalyst. Using molybdenum powder and pyrrole as raw materials, the present invention employs a one-step hydrothermal synthesis method to produce a polypyrrole-coated defective molybdenum trioxide catalyst with abundant surface oxygen vacancies. This catalyst enhances light absorption efficiency and photothermal conversion efficiency, thereby improving photocatalytic oxidative desulfurization performance. The prepared composite catalyst exhibits advantages such as good selectivity, high stability, and a stable structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite catalytic material preparation, relates to extraction-coupled photocatalytic oxidation desulfurization, and particularly relates to the application of a polypyrrole-coated defective molybdenum trioxide catalyst. Background Art

[0002] In recent years, with the popularization of automobiles, the demand for automotive fuel (gasoline, diesel) has continued to increase, and the sulfur oxides (SO x Air pollution caused by fuel oil (including diesel and diesel) is also increasingly threatening the natural environment and human health. Reducing the content of sulfur compounds in fuel is an important approach to addressing these issues. Dibenzothiophene (DBT) sulfur compounds in fuel are difficult to hydrogenate due to their low reactivity, often requiring greater energy and hydrogen consumption. Therefore, it is necessary to develop a green, efficient, and cost-effective auxiliary desulfurization process for DBT sulfides. This process can achieve low or no sulfur in fuel while minimizing energy consumption during the desulfurization process.

[0003] Extraction-coupled photocatalytic oxidation desulfurization technology combines the advantages of extraction desulfurization and photocatalytic oxidation desulfurization. While using the extractant to promote mass transfer and facilitate the separation of the oil phase and products after the reaction, the photocatalyst with excellent light response performance efficiently oxidizes DBT and its derivatives under the action of the oxidant and converts them into high-value-added organic semiconductor sulfone substances. In addition, compared with catalytic reactions at high temperatures, photocatalytic desulfurization conditions are milder, more economical, and less environmentally burdensome. It has attracted increasing attention from researchers in recent years. However, during the photocatalytic process, the low utilization rate of visible light by the reaction system is the main reason limiting its industrial application. Therefore, developing a photocatalyst with good light response ability and efficient utilization of visible light is the key to improving the efficiency of photocatalytic desulfurization.

[0004] Defective molybdenum oxide (MoO 3-x ) has a rich carrier concentration due to its surface oxygen vacancies and often has excellent photothermal conversion effect due to its good absorption of near-infrared band under natural light. However, despite its strong response and excitation ability to natural light, MoO alone 3-x The rapid recombination of photogenerated electron-hole pairs within the material significantly reduces its redox ability as a photocatalyst. Therefore, it is necessary to combine it with other semiconductor materials to inhibit the recombination of photogenerated electron-hole pairs. Polypyrrole, as an organic semiconductor, has excellent electron-transferring capabilities and can be used as a modifier to manipulate the material's electronic structure. Currently, there are few reports on the application of molybdenum oxide-composite polypyrrole catalysts in photocatalytic oxidative desulfurization. Summary of the Invention

[0005] In order to solve the deficiencies in the above technologies, the present invention aims to adopt a one-step hydrothermal method to utilize molybdenum peroxide species generated by hydrogen peroxide and molybdenum powder to in situ polymerize pyrrole to form a polypyrrole-coated defective molybdenum trioxide composite catalyst.

[0006] Technical Solution

[0007] A preparation method of a polypyrrole-coated defective molybdenum trioxide composite catalyst comprises: adding molybdenum powder to n-butanol and dispersing the mixture uniformly; slowly adding hydrogen peroxide with continuous stirring; adding pyrrole when the reaction solution becomes bright yellow, clear and transparent; and continuously stirring at room temperature overnight; then placing the solution in a high-pressure reactor and performing a hydrothermal reaction at 100-160° C. for 12-20 hours; after the reactants are cooled to room temperature, centrifuging and separating the precipitate, washing the precipitate three times with deionized water and anhydrous ethanol respectively, and collecting the obtained precursor and vacuum drying it to obtain the catalyst.

[0008] In the preferred disclosed embodiment of the present invention, the concentration of hydrogen peroxide is 30 wt %.

[0009] In the preferred disclosed examples of the present invention, the solid-liquid ratio of molybdenum powder, hydrogen peroxide, and n-butanol is 0.15-0.3 g: 2-5 mL: 10-30 mL, preferably 0.20 g: 3 mL: 24 mL.

[0010] In a preferred disclosed embodiment of the present invention, the stirring time of molybdenum powder and hydrogen peroxide in n-butanol is 0.3 to 1 hour, preferably 0.5 hour.

[0011] In the preferred disclosed examples of the present invention, the volume ratio of pyrrole to n-butanol is 62.5 μL, 125 μL, 250 μL: 10-30 mL, preferably 125 μL: 24 mL.

[0012] In a preferred embodiment of the present invention, after adding pyrrole, the mixture is fully stirred for 6 to 24 hours, preferably 12 hours.

[0013] In a preferred disclosed example of the present invention, the hydrothermal reaction temperature is 140° C. and the reaction time is 16 h.

[0014] In a preferred embodiment of the present invention, the precursor is vacuum dried at a temperature of 60 to 100° C. for 8 to 24 hours, preferably at 80° C. for 12 hours.

[0015] The obtained products were designated as MP-n (n = 1, 2, 3, representing the catalysts synthesized when the amount of pyrrole added was 62.5 μL, 125 μL, and 250 μL, respectively).

[0016] The control group was pure MoO prepared according to the above steps without adding pyrrole. 3-x .

[0017] The polypyrrole-coated defective molybdenum oxide catalyst prepared by the method of the present invention is polypyrrole coated on MoO 3-x A "quasi-core-shell structure" is formed on the surface to stabilize the active center of molybdenum oxide. At the same time, elements such as C, N, Mo, and O are evenly distributed on the surface of the catalyst.

[0018] Another object of the present invention is to disclose the application of the prepared polypyrrole-coated defective molybdenum oxide catalyst in the field of extraction-coupled photocatalytic oxidation desulfurization technology, especially the ultra-deep oxidation removal of DBT in fuel using hydrogen peroxide (30wt% H2O2) as an oxidant and acetonitrile as an extractant.

[0019] The present invention regulates the amount of pyrrole added during the reaction, thereby changing the concentration of oxygen vacancies formed by lattice distortion of molybdenum oxide during the reaction. The prepared polypyrrole-coated defective molybdenum oxide has excellent photothermal conversion and demonstrates good performance in the efficient conversion of DBT to DBTO2. The prepared catalyst exhibits good cyclic stability and high selectivity for DBT, and also has good removal efficiency for DBT derivatives (4-MDBT and 4,6-DMDBT), showing promising industrial application prospects. The addition of polypyrrole effectively regulates the electronic structure while creating abundant surface oxygen vacancies, improving the catalyst's photoresponsiveness, enhancing its photothermal conversion efficiency, and promoting the desulfurization reaction system's utilization of visible light. Furthermore, the modification of the defective molybdenum trioxide effectively suppresses the recombination of photogenerated electron-hole pairs, endowing it with excellent hydrogen peroxide activation capabilities, thus ensuring its application in extractive-coupled photocatalytic oxidation desulfurization.

[0020] In photocatalytic reactions, problems such as the catalyst's weak ability to respond to light and the low utilization rate of light sources limit its catalytic performance and industrial application. In order to solve the above problems, the present invention introduces polypyrrole and defective molybdenum trioxide to form oxygen vacancies by manufacturing the molybdenum oxide lattice distortion, and determines the optimal oxygen vacancy concentration by the amount of precursor pyrrole introduced, thereby bringing abundant free carriers to the catalyst surface. When the surface free electron vibration is consistent with the incident light photon vibration under illumination, a strong resonance between the two can be caused, thereby maximizing the absorption of the incident light energy to achieve photothermal conversion. The synthesized polypyrrole-coated defective molybdenum trioxide catalyst has good light response ability, can efficiently activate hydrogen peroxide, and shows good selectivity for dibenzothiophene sulfur-containing compounds. In addition, the mass transfer effect of the reaction system is enhanced by adding an extractant to the reaction system. Due to the difference in polarity between the solvents, the DBT molecules are first extracted into the acetonitrile-catalyst phase, and then the photocatalytic oxidation reaction is carried out in the acetonitrile-catalyst phase. The reaction product DBTO2 is retained in the acetonitrile phase due to its strong polarity. While achieving sulfur-free fuel, it is also beneficial to the recovery and utilization of high-value-added sulfone substances, greatly increasing the green economic benefits of the reaction process.

[0021] The present invention uses detection technologies such as wide-angle X-ray powder diffraction (XRD), high-magnification transmission electron microscopy (HRTEM), ultraviolet-visible-near-infrared diffuse reflectance spectroscopy (UV-Vis-NIR DRS), electron paramagnetic resonance (EPR) and infrared thermal imaging (IR) to analyze the crystal structure and morphology of the catalyst.

[0022] A model oil was prepared using DBT as the sulfur-containing substrate, H₂O₂ as the oxidant, and acetonitrile as the extractant. The resulting catalyst was used for extractive-coupled photocatalytic oxidative desulfurization of the model oil. DBT in the model oil after the reaction was detected using gas chromatography (GC). The change in residual sulfur content in the model oil was calculated based on the peak area, evaluating the catalyst's performance in DBT removal.

[0023] The formula for calculating the desulfurization rate is: ; Where C0 represents the initial sulfur content of the model oil, C t It represents the residual sulfur content of the model oil within the reaction time t (min), in ppm.

[0024] Beneficial effects

[0025] The present invention utilizes a simple synthesis process. Using molybdenum powder and pyrrole as raw materials, a hydrothermal method is employed to synthesize a polypyrrole-coated defective molybdenum trioxide catalyst with abundant surface oxygen vacancies in a single step. This catalyst enhances light absorption efficiency and photothermal conversion, improving photocatalytic oxidative desulfurization performance. The composite catalyst prepared in this invention exhibits excellent selectivity, high stability, and a stable structure. Under mild conditions, using H₂O₂ as the oxidant and acetonitrile as the extractant, it can completely remove the sulfur-containing compound DBT within 60 minutes (desulfurization rate: 100%). BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 TEM, HRTEM, EDS and Mapping images of MP-2 catalyst;

[0027] Figure 2 UV-Vis-NIR spectra of different catalysts;

[0028] Figure 3 IR spectrum of MP-2 catalyst;

[0029] Figure 4 XPS O 1s fine spectra of different catalysts;

[0030] Figure 5 . Photocatalytic oxidation removal performance of DBT by different catalysts. DETAILED DESCRIPTION

[0031] The present invention is described in detail below with reference to the following examples so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following examples.

[0032] Example 1

[0033] A method for preparing a polypyrrole-coated defective molybdenum trioxide catalyst comprises: measuring 24 mL of n-butanol and placing it in a beaker, weighing 0.2 g of molybdenum powder and uniformly dispersing it in the n-butanol solution, slowly adding 3 mL of 30 wt% hydrogen peroxide dropwise with continuous stirring, and adding 62.5 μL of pyrrole dropwise when the reaction solution becomes bright yellow, clear, and transparent, and continuously stirring at room temperature for 12 hours; charging the stirred solution into a high-pressure reactor and performing a hydrothermal reaction at 140° C. for 16 hours; after the reactants are cooled to room temperature, separating the precipitate by centrifugation and washing it three times with deionized water and anhydrous ethanol, respectively; collecting the precipitate and vacuum drying it at 80° C. for 12 hours to obtain a final catalyst, and the resulting product is recorded as MP-1.

[0034] Example 2

[0035] A method for preparing a polypyrrole-coated defective molybdenum trioxide catalyst comprises the following steps: measuring 24 mL of n-butanol and placing it in a beaker, weighing 0.2 g of molybdenum powder and uniformly dispersing it in the n-butanol solution, slowly dropwise adding 3 mL of 30 wt% hydrogen peroxide and continuously stirring; when the reaction solution turns bright yellow, clear and transparent, dropwise adding 125 μL of pyrrole; and continuously stirring at room temperature for 12 hours; charging the stirred solution into an autoclave, carrying out a hydrothermal reaction at 140° C. for 16 hours; after the reactants are cooled to room temperature, separating the precipitate by centrifugation and washing it three times with deionized water and anhydrous ethanol, respectively; collecting the precipitate and vacuum drying it at 80° C. for 12 hours to obtain a final catalyst, the product being recorded as MP-2.

[0036] Example 3

[0037] A method for preparing a polypyrrole-coated defective molybdenum trioxide catalyst comprises the following steps: measuring 24 mL of n-butanol into a beaker, weighing 0.2 g of molybdenum powder and uniformly dispersing it in the n-butanol solution, slowly dropping 3 mL of 30 wt% hydrogen peroxide and continuously stirring, dropping 250 μL of pyrrole when the reaction solution becomes bright yellow, clear, and transparent, and continuously stirring at room temperature for 12 hours; charging the stirred solution into a high-pressure reactor, performing a hydrothermal reaction at 140° C. for 16 hours, and after the reactants are cooled to room temperature, centrifuging and separating the precipitate, washing it three times with deionized water and anhydrous ethanol, respectively, collecting the precipitate, and vacuum drying it at 80° C. for 12 hours to obtain a final catalyst. The resulting product is recorded as MP-3.

[0038] For comparison, pure defective molybdenum oxide was prepared according to the above steps without adding pyrrole as a control experiment.

[0039] from Figure 1 The TEM image in Figure 2 shows that polypyrrole polymerizes in situ on the defective molybdenum oxide surface to form a quasi-core-shell structure, indicating the successful synthesis of the polypyrrole-coated defective molybdenum trioxide catalyst. HRTEM reveals that the lattice fringes of the molybdenum oxide (110) crystal plane are distorted and dislocated, which is conducive to the formation of oxygen vacancies. Mapping analysis shows that elements such as Mo, O, C, and N are uniformly dispersed in the catalyst. When the amount of pyrrole added is 125 μL, the photocatalytic oxidation desulfurization performance of the prepared catalyst is the best.

[0040] from Figure 2 It can be seen from the UV-Vis-NIR spectrum in the figure that the prepared catalyst has good light response ability in the entire spectrum band, especially showing better light absorption in the visible light and near-infrared light bands, which is conducive to the improvement of the photothermal conversion effect of the catalyst.

[0041] Figure 3Infrared thermal imaging of the catalyst beautifully demonstrates the photothermal conversion process. Under visible light, the temperature rise rate of the reaction solution after adding the MP-2 catalyst is significantly higher than that of the blank sample, further demonstrating the good photothermal conversion efficiency of the prepared catalyst.

[0042] Figure 4 XPS analysis of the catalysts was performed, and the O 1s fine spectra were analyzed to determine the oxygen vacancy concentrations of the catalysts with varying amounts of pyrrole. The figure shows that the oxygen vacancy concentration initially increases and then decreases with increasing pyrrole dosage, which determines the change in free carrier concentration on the surface of the prepared catalysts. Desulfurization performance tests also show a positive correlation between oxygen vacancy concentration and desulfurization performance.

[0043] Example 4

[0044] The extraction-coupled photocatalytic oxidation desulfurization applications of polypyrrole-coated defective molybdenum trioxide catalysts include:

[0045] The polypyrrole-coated defective molybdenum trioxide catalysts obtained in Examples 1-3 were used to remove the aromatic sulfide DBT from a model oil by extractive-coupled photocatalytic oxidation. The experimental conditions were as follows: 0.03 g of catalyst was added to 10 mL of a model oil containing 200 ppm DBT and 5 mL of acetonitrile, and the reaction was stirred in a water bath at 25°C. After stirring in the dark for 30 minutes to reach extraction equilibrium, 19 μL of hydrogen peroxide (O / S = 3:1) was added, and a visible light source was turned on for timing. Samples were collected every 15 minutes and analyzed by gas chromatography (GC). The reaction was terminated after 60 minutes. The DBT removal efficacy of catalysts with varying pyrrole loading was determined.

[0046] from Figure 5 It can be seen that under the same reaction conditions, the order of DBT removal by different composite catalysts is: MP-2 > MP-1 > MP-3, among which MP-2 (pyrrole addition amount is 125μL) has the best performance and can completely remove DBT within 60min (desulfurization rate is 100%).

[0047] Example 5

[0048] A preparation method for a polypyrrole-coated defective molybdenum trioxide catalyst comprises the following steps: measuring 10 mL of n-butanol and placing it in a beaker, weighing 0.15 g of molybdenum powder and uniformly dispersing it in the n-butanol solution for 0.3 h, slowly dropwise adding 2 mL of 30 wt% hydrogen peroxide and continuously stirring, and dropwise adding 62.5 μL of pyrrole when the reaction solution becomes bright yellow, clear, and transparent, and continuously stirring at room temperature for 6 h; charging the stirred solution into an autoclave, performing a hydrothermal reaction at 100° C. for 12 h, and after the reactants are cooled to room temperature, centrifugally separating a precipitate and washing it three times with deionized water and anhydrous ethanol, respectively; collecting the precipitate and vacuum drying it at 60° C. for 8 h to obtain a final catalyst.

[0049] Example 6

[0050] A preparation method for a polypyrrole-coated defective molybdenum trioxide catalyst comprises the following steps: measuring 30 mL of n-butanol and placing it in a beaker, weighing 0.3 g of molybdenum powder and uniformly dispersing it in the n-butanol solution for 1 hour, slowly dropwise adding 5 mL of 30 wt% hydrogen peroxide and continuously stirring, dropwise adding 250 μL of pyrrole when the reaction solution becomes bright yellow, clear and transparent, and continuously stirring at room temperature for 24 hours; charging the stirred solution into a high-pressure reactor, carrying out a hydrothermal reaction at 160° C. for 20 hours, and after the reactants are cooled to room temperature, centrifugally separating a precipitate and washing it three times with deionized water and anhydrous ethanol, respectively; collecting the precipitate and vacuum drying it at 100° C. for 24 hours to obtain a final catalyst.

[0051] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the description of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An application of a polypyrrole-coated defective molybdenum trioxide composite catalyst, characterized in that: It is applied to the field of extraction-coupled photocatalytic oxidation desulfurization technology, wherein the polypyrrole-coated defective molybdenum trioxide composite catalyst has a preparation method comprising: adding molybdenum powder to n-butanol and dispersing it evenly, slowly adding hydrogen peroxide and continuously stirring, adding pyrrole when the reaction solution turns bright yellow, clear and transparent, and continuously stirring at room temperature overnight; then charging the solution into a high-pressure reactor for hydrothermal reaction at 100-160°C for 12-20 hours, cooling the reactants to room temperature, centrifuging and separating the precipitate and washing them three times with deionized water and anhydrous ethanol respectively, collecting the obtained precursor and vacuum drying it.

2. The use of the polypyrrole-coated defective molybdenum trioxide composite catalyst according to claim 1, characterized in that: The extraction-coupled photocatalytic oxidation desulfurization method uses 30 wt% hydrogen peroxide as an oxidant and acetonitrile as an extractant to oxidize and desulfurize DBT in fuel.

3. The use of the polypyrrole-coated defective molybdenum trioxide composite catalyst according to claim 1, characterized in that: The concentration of hydrogen peroxide is 30wt%.

4. The use of the polypyrrole-coated defective molybdenum trioxide composite catalyst according to claim 1, characterized in that: The solid-liquid ratio of molybdenum powder, hydrogen peroxide, and n-butanol is 0.15-0.3g: 2-5mL: 10-30mL.

5. The use of the polypyrrole-coated defective molybdenum trioxide composite catalyst according to claim 4, characterized in that: The solid-liquid ratio of the molybdenum powder, hydrogen peroxide, and n-butanol is 0.20 g: 3 mL: 24 mL.

6. The use of the polypyrrole-coated defective molybdenum trioxide composite catalyst according to claim 1, characterized in that: The molybdenum powder and hydrogen peroxide are stirred in n-butanol for 0.3 to 1 hour.

7. The use of the polypyrrole-coated defective molybdenum trioxide composite catalyst according to claim 6, characterized in that: The molybdenum powder and hydrogen peroxide were stirred in n-butanol for 0.5 h.

8. The use of the polypyrrole-coated defective molybdenum trioxide composite catalyst according to claim 1, characterized in that: The volume ratio of pyrrole to n-butanol was 62.5 μL, 125 μL, and 250 μL: 10 to 30 mL.

9. The use of the polypyrrole-coated defective molybdenum trioxide composite catalyst according to claim 8, characterized in that: The volume ratio of the pyrrole to n-butanol was 125 μL: 24 mL.

10. The use of the polypyrrole-coated defective molybdenum trioxide composite catalyst according to claim 1, characterized in that: The hydrothermal reaction temperature is 140° C., and the reaction time is 16 h.

11. The use of the polypyrrole-coated defective molybdenum trioxide composite catalyst according to claim 1, characterized in that: The precursor is vacuum dried at a temperature of 60 to 100° C. for 8 to 24 hours.

12. The use of the polypyrrole-coated defective molybdenum trioxide composite catalyst according to claim 11, characterized in that: The precursor is vacuum dried at a temperature of 80° C. for 12 h.

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