Molybdenum-based oxide / carbide / GO heterojunction catalyst, preparation method thereof and application of molybdenum-based oxide / carbide / GO heterojunction catalyst in field of fuel oxidation desulfurization

Abstract

The invention relates to the technical field of catalysts, in particular to a molybdenum-based oxide / carbide / GO heterojunction catalyst, a preparation method thereof and application of the molybdenum-based oxide / carbide / GO heterojunction catalyst in the field of fuel oxidation desulfurization. The preparation method comprises the following steps: S1, adding dimethylimidazole and metal salt into a graphene oxide aqueous solution, and stirring for reaction; s2, adding an aniline monomer and an initiator, dropwise adding phosphomolybdic acid as a molybdenum source, and centrifuging, washing and freeze-drying a product after the reaction is finished to obtain a polyaniline modified ZIFs / GO composite precursor adsorbed with the molybdenum source; and S3, performing high-temperature pyrolysis on the composite precursor in a protective atmosphere to obtain the catalyst. The invention provides a mode of constructing a molybdenum-based oxide / carbide heterostructure by enhancing the electron-donating capability and conductivity of a carrier through double-doped electron-donating elements, and develops a catalyst with high catalytic activity and low cost. The catalytic efficiency in the oxidative desulfurization process can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly to a molybdenum-based oxide / carbide / GO heterojunction catalyst, a preparation method thereof, and an application thereof in the field of fuel oxidative desulfurization. Background Art

[0002] Approximately 90% of the world's energy comes from fossil fuels such as coal, oil, and natural gas. With the rapid development of industry, the energy demand has been continuously increasing, resulting in a decreasing annual amount of high-quality fossil fuel resources, and a large number of low-quality fossil fuels have been exploited and used. However, inferior fuels contain a large amount of sulfides, and the combustion of sulfur-containing fuels releases a large amount of harmful gases such as SOx, which not only causes serious environmental pollution, destroys the ecological balance, but also poses a threat to human health. Therefore, in order to meet the dual goals of energy demand and green sustainable development, deep desulfurization of fuel oil has become a hot issue discussed internationally. Although traditional hydrodesulfurization (HDS) technology can effectively remove organic sulfur compounds such as mercaptans and sulfides, it requires a large amount of hydrogen and heat energy when treating aromatic sulfides, significantly increasing the operating cost. Therefore, it is particularly important to develop more environmentally friendly and efficient desulfurization technologies to make up for the deficiencies of HDS. Currently, technologies such as oxidative desulfurization (ODS), adsorption desulfurization, extraction desulfurization, and photocatalytic oxidation have become potential alternative solutions. Among them, ODS technology is considered the most promising green chemical desulfurization method because it can efficiently remove aromatic sulfur compounds under mild conditions with low cost and no hydrogen consumption. In addition, the sole oxidation product of ODS desulfurization - sulfone, can be separated from the system through simple subsequent treatments such as extraction and adsorption, and can be widely used in fields such as medicine and energy through further processing, with high added value.

[0003] It should be noted that the key to ODS technology lies in the development of desulfurization catalysts with high catalytic activity and good reusability. Molybdenum-based oxides (such as MoO2, MoO3, and MoOx) have become a research hotspot for low-cost ODS catalysts due to their adjustable structures, high catalytic activities, and excellent stabilities. However, during the ODS catalytic process, the binding energy of the strong Mo-O bond between the surface of molybdenum-based oxides and the oxidant hydrogen peroxide (H2O2) limits the further improvement of its catalytic efficiency. Summary of the Invention

[0004] The object of the present invention is to propose a molybdenum-based oxide / carbide / GO heterojunction catalyst, a preparation method thereof, and an application thereof in the field of fuel oxidative desulfurization, aiming at the above-mentioned deficiencies of the prior art.

[0005] The first object of the present invention is to provide a preparation method of a molybdenum-based oxide / carbide / GO heterojunction catalyst, comprising the following steps:

[0006] S1. Add dimethylimidazole and metal salt to the graphene oxide aqueous solution and stir to react;

[0007] S2. Then add aniline monomer and initiator to the reaction system of step S1, dropwise add phosphomolybdic acid as the molybdenum source, and after the reaction, centrifuge, wash with water, and freeze-dry the product to obtain a composite precursor of ZIFs / GO modified with polyaniline adsorbed with the molybdenum source;

[0008] S3. Pyrolyze the composite precursor at 700 - 1000 °C under a protective atmosphere to obtain a molybdenum-based oxide / carbide / GO heterojunction composite catalyst.

[0009] Further, the concentration range of the graphene oxide aqueous solution is 1 - 10 mg / mL.

[0010] Further, the metal salt includes any one of nitrates, chlorides, or acetates of zinc, cobalt, nickel, iron, copper, and manganese.

[0011] Further, the molybdenum source includes one or more of phosphomolybdic acid, ammonium molybdate, and sodium molybdate; the initiator is ammonium persulfate.

[0012] Further, the high-temperature pyrolysis means maintaining at 700 - 1000 °C for 2 h under a nitrogen atmosphere.

[0013] Further, the mass ratio of the metal salt, the mass of dimethylimidazole, and the volume of the graphene oxide aqueous solution in S1 is 0.1 - 0.5 g : 0.8 - 8.0 g : 10 ml.

[0014] Further, the volume ratio of the aniline dosage to the volume of the graphene oxide aqueous solution is 0.1 - 0.5 : 10.

[0015] Further, the mass ratio of phosphomolybdic acid to the metal salt is 0.1 - 1.0 : 0.1 - 0.5.

[0016] The second object of the present invention is to provide a molybdenum-based oxide / carbide / GO heterojunction catalyst prepared by the above preparation method.

[0017] The third object of the present invention is to provide an application of the molybdenum-based oxide / carbide / GO heterojunction catalyst as described above in the field of fuel oxidative desulfurization.

[0018] The present invention adopts a simple "one-pot" synthesis method. Dimethylimidazole and a metal source are added to an aqueous solution of graphene oxide (GO) to achieve the mutual combination of metal-organic framework ZIFs and graphene oxide. Subsequently, aniline monomer is added to the reaction system, and polyoxometalate phosphomolybdic acid is dropped as a molybdenum source. After the reaction, a ZIFs / GO composite precursor modified by polyaniline (PANI) adsorbed with the molybdenum source is obtained. Through high-temperature pyrolysis, ZIFs provide an additional metal source and a carbon skeleton, PANI provides a nitrogen source and a carbon source, GO serves as a carrier to form a metal / nitrogen dual-doped carbon carrier, and the polyoxometalate is in-situ converted into a molybdenum oxide / carbide heterojunction in the carbon skeleton, that is, a molybdenum-based oxide / carbide heterojunction composite catalyst uniformly loaded on a carrier with strong electron-donating ability is obtained.

[0019] The molybdenum-based oxide / carbide / GO heterojunction catalyst prepared by the present invention makes full use of the large specific surface area and excellent electron transport characteristics of the 2D graphene (GO) carrier. Electron-rich cobalt (Co) / nitrogen (N) dual-atom-doped carbon is coupled on the GO carrier, which increases the amount of transferable electron carriers in the carrier and optimizes the electron-donating ability of the carrier. In addition, by designing the catalyst structure, a heterostructure of MoO2 and Mo2C is constructed, and in-situ high-dispersion and uniform loading on the carrier are realized, optimizing the contact mode between MoO2 / Mo2C and the carrier, and further improving its surface electronic structure, which can effectively improve the catalytic efficiency in the oxidative desulfurization process and provide a green and efficient solution for the deep desulfurization technology of fuel oil.

[0020] In the present invention, the two-component carbon-modified GO carrier not only makes full use of the 2D large specific surface area and conductivity of GO, but also uses the ZIFs carbon skeleton and in-situ pyrolytic carbonization of aniline to provide a carbon source for the oxide / carbide heterojunction and limit the growth of heterojunction nanoparticles.

[0021] In the present invention, in-situ coupling between the electron-donating carrier and the heterostructure improves the electron transport efficiency, which is beneficial to the electron regulation on the catalyst surface. At the same time, the oxide / carbide heterostructure also exposes abundant active centers, further improving its catalytic activity. Description of the Drawings

[0022] Figure 1 XRD patterns of the products obtained from the precursor in Example 1 at different high-temperature pyrolysis temperatures;

[0023] Figure 2 SEM images of the precursor obtained in Example 1 and MoO2 / Mo2C-CoNC / GO;

[0024] Figure 3 TEM / HRTEM images of MoO2 / Mo2C-CoNC / GO obtained in Example 1;

[0025] Figure 4 Removal effect curve of MoO2 / Mo2C-CoNC / GO in Example 1 at a reaction temperature of 60 °C with n-octane as the simulated oil for 4000 ppm DBT. Detailed implementation manners

[0026] The following are specific embodiments of the present invention and in combination with the accompanying drawings, the technical solutions of the present invention will be further described, but the present invention is not limited to these embodiments.

[0027] The following takes an example to illustrate the preparation of a molybdenum-based oxide / carbide heterojunction catalyst uniformly loaded on a carrier with strong electron-donating ability.

[0028] Example 1:

[0029] (1) Take 10 mL of a 2 mg / mL graphene (GO) aqueous solution and ultrasonicate for 30 min; dissolve 0.2 g of cobalt nitrate hexahydrate in 10 mL of deionized water and ultrasonicate to form a uniform solution A. Then weigh 2 g of dimethylimidazole and dissolve it in 10 mL of deionized water and ultrasonicate to form a uniform solution B.

[0030] (2) Place the ultrasonically treated GO solution in an ice-water bath and add solution A under magnetic stirring. After stirring for 15 min, add solution B dropwise to form a mixed solution. Subsequently, measure 0.2 mL of aniline solution and dissolve it in 20 mL of 1.0 M hydrochloric acid aqueous solution to form solution C, and gradually add it dropwise to the above mixed solution and stir for 5 min.

[0031] (3) Weigh 1.0 g of ammonium persulfate and dissolve it in 10 mL of deionized water, and gradually add it dropwise to the above solution to initiate the polymerization of aniline monomers; at the same time, gradually add 10 mL of an aqueous solution containing 0.6 g of phosphomolybdic acid (phosphomolybdic acid is Keggin-type polyoxometalate H3PMo 12 O 40 ·xH2O, namely PMo 12 ) dropwise into it and stir for 12 h.

[0032] (4) After the reaction, centrifuge, wash with water, and freeze-dry the product to obtain a composite precursor; place the precursor in a tube furnace and pyrolyze it at 900 °C for 2 h under a nitrogen atmosphere to obtain a molybdenum-based oxide / carbide heterojunction composite catalyst MoO2 / Mo2C-CoNC / GO uniformly loaded on a carrier with strong electron-donating ability.

[0033] Example 2:

[0034] (1) Take 10 mL of a 5 mg / mL graphene (GO) aqueous solution and ultrasonicate it for 30 min; dissolve 0.3 g of iron(III) nitrate nonahydrate in 10 mL of deionized water and ultrasonically mix it evenly to form solution A. Then, weigh 4.0 g of 1-methylimidazole and dissolve it in 10 mL of deionized water and ultrasonically mix it evenly to form solution B;

[0035] (2) Place the ultrasonically treated GO solution in an ice-water bath and add solution A under magnetic stirring. After stirring for 15 min, add solution B dropwise to form a mixed solution; Subsequently, measure 0.4 mL of aniline solution and dissolve it in 20 mL of 1.0 M hydrochloric acid aqueous solution to form solution C, and gradually add it dropwise to the above mixed solution and stir for 5 min;

[0036] (3) Weigh 1.0 g of ammonium persulfate and dissolve it in 10 mL of deionized water, and gradually add it dropwise to the above solution to initiate the polymerization of aniline monomers; At the same time, gradually add 10 mL of an aqueous solution containing 1 g of phosphomolybdic acid dropwise thereto and stir for 12 h;

[0037] (4) After the reaction is completed, centrifuge, wash with water, and freeze-dry the product to obtain a composite precursor; Place the precursor in a tube furnace under a nitrogen atmosphere and pyrolyze it at 1000 °C for 2 h to obtain a molybdenum-based oxide / carbide heterojunction composite catalyst MoO2 / Mo2C-FeNC / GO uniformly loaded on a strong electron-donating ability support.

[0038] Example 3:

[0039] (1) Take 10 mL of an 8 mg / mL graphene (GO) aqueous solution and ultrasonicate it for 30 min; dissolve 0.1 g of zinc acetate in 10 mL of deionized water and ultrasonically mix it evenly to form solution A. Then, weigh 1 g of 1-methylimidazole and dissolve it in 10 mL of deionized water and ultrasonically mix it evenly to form solution B;

[0040] (2) Place the ultrasonically treated GO solution in an ice-water bath and add solution A under magnetic stirring. After stirring for 15 min, add solution B dropwise to form a mixed solution; Subsequently, measure 0.1 mL of aniline solution and dissolve it in 20 mL of 1.0 M hydrochloric acid aqueous solution to form solution C, and gradually add it dropwise to the above mixed solution and stir for 5 min;

[0041] (3) Weigh 1.0 g of ammonium persulfate and dissolve it in 10 mL of deionized water, and gradually add it dropwise to the above solution to initiate the polymerization of aniline monomers; At the same time, gradually add 10 mL of an aqueous solution containing 0.2 g of phosphomolybdic acid dropwise thereto and stir for 12 h;

[0042] (4) After the reaction is completed, the product is centrifuged, washed with water, and freeze-dried to obtain a composite precursor; the precursor is pyrolyzed at 700 °C for 2 h in a tubular furnace under a nitrogen atmosphere to obtain a molybdenum-based oxide / carbide heterojunction composite catalyst MoO2 / Mo2C-ZnNC / GO uniformly loaded on a strong electron-donating ability support.

[0043] Example 4:

[0044] (1) Take 10 mL of a 10 mg / mL graphene (GO) aqueous solution and sonicate it for 30 min; dissolve 0.5 g of nickel chloride hexahydrate in 10 mL of deionized water and sonicate it evenly to form solution A, then weigh 6 g of dimethylimidazole and dissolve it in 10 mL of deionized water and sonicate it evenly to form solution B;

[0045] (2) Place the sonicated GO solution in an ice-water bath and add solution A under magnetic stirring. After stirring for 15 min, add solution B dropwise to form a mixed solution; subsequently, measure 0.5 mL of aniline solution and dissolve it in 20 mL of 1.0 M hydrochloric acid aqueous solution to form solution C, and add it dropwise to the above mixed solution and stir for 5 min;

[0046] (3) Weigh 1.0 g of ammonium persulfate and dissolve it in 10 mL of deionized water, and add it dropwise to the above solution to initiate the polymerization of aniline monomers; at the same time, add 10 mL of an aqueous solution containing 1.0 g of phosphomolybdic acid dropwise thereto and stir for 12 h;

[0047] (4) After the reaction is completed, the product is centrifuged, washed with water, and freeze-dried to obtain a composite precursor; the precursor is pyrolyzed at 800 °C for 2 h in a tubular furnace under a nitrogen atmosphere to obtain a molybdenum-based oxide / carbide heterojunction composite catalyst MoO2 / Mo2C-NiNC / GO uniformly loaded on a strong electron-donating ability support.

[0048] Example 5:

[0049] ODS application of the molybdenum-based oxide / carbide heterojunction composite catalyst uniformly loaded on a strong electron-donating ability support:

[0050] Taking Example 1 as an example, for the prepared composite catalyst MoO2 / Mo2C-CoNC / GO, at 60 °C, using n-octane as the simulated oil, acetonitrile phase as the extractant, and 30% H2O2 aqueous solution as the oxidant, react at 60 °C and 500 rpm for 2 - 40 min, and monitor the sulfur content in the simulated oil by HPLC test. Among them, the sulfide can be one of dibenzothiophene (DBT), benzothiophene (BT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT).

[0051] Test the desulfurization effect of the MoO2 / Mo2C-CoNC / GO catalyst prepared in Test Example 1 on 4000 ppm sulfide and plot the desulfurization curve. As Figure 4 shown, the catalyst has a good removal effect on DBT. The removal efficiency at 15 min is as high as 99%, and complete removal can be achieved within 30 min, which has certain commercial value.

[0052] Figure 1 XRD patterns of the products obtained from the precursor in Example 1 at different high-temperature pyrolysis temperatures; it can be seen from the figure that with the increase of the high-temperature pyrolysis temperature, distinct crystal forms gradually form inside the catalyst. At lower temperatures, the crystal form of molybdenum oxide first appears, and with the increase of temperature, the carburization effect gradually strengthens, and the crystal form structure of molybdenum carbide appears in the molybdenum oxide crystal form, forming a heterostructure of molybdenum oxide / molybdenum carbide, indicating that the preparation result of the catalyst meets the expected design.

[0053] Figure 2 SEM images of the precursor obtained in Example 1 and MoO2 / Mo2C-CoNC / GO Figure 2 In a and b, SEM images of the prepared precursor are shown. It can be seen that an obvious polymer layer adheres to the surface of GO, and the surface is rough, indicating the adsorption of heteropolyacid; in addition, from Figure 2 c and d, it can be seen that the MoO2 / Mo2C-CoNC / GO catalyst still maintains a three-dimensional wrinkled structure, but a large number of cubic framework structures are distributed on the surface, indicating that ZIFs have successfully adhered to the surface of GO.

[0054] Figure 3 TEM / HRTEM images of MoO2 / Mo2C-CoNC / GO obtained in Example 1. From Figure 3 a and b in it, it can be seen that ZIFs framework structures adhere to the surface of graphene. Further enlarged images (c, d) show that various crystal forms are formed inside the framework, and various crystal forms also exist on the surface of GO outside the framework. Combining with the XRD results, these lattices can be attributed to MoO2 and Mo2C. In addition, it can be seen that the contact between the two lattices is close, which is beneficial to the electron regulation between different species.

[0055] For those not covered above, the prior art shall apply.

[0056] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are only for illustration purposes and not for limiting the scope of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways for substitution, but will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention should all be included within the protection scope of the present invention.

Claims

1. A method for preparing a molybdenum-based oxide / carbide / GO heterojunction catalyst, characterized in that: The steps include: S1, adding dimethylimidazole and metal salt to the graphene oxide aqueous solution and stirring to react; S2, adding aniline monomer and initiator to the reaction system of step S1, and dropping molybdenum source, after the reaction is completed, centrifuging, washing and freeze-drying the product to obtain a polyaniline-modified ZIFs / GO composite precursor adsorbed with molybdenum source; S3. Pyrolyze the composite precursor at 700-1000° C. under a protective atmosphere to obtain a molybdenum-based oxide / carbide / GO heterojunction composite catalyst.

2. The preparation method according to claim 1, characterized in that: The graphene oxide aqueous solution has a concentration range of 1-10 mg / mL.

3. The preparation method according to claim 1, characterized in that: The metal salt includes any one of nitrate, chloride or acetate of zinc, cobalt, nickel, iron, copper or manganese.

4. The preparation method according to claim 1, characterized in that: The molybdenum source includes one or more of phosphomolybdic acid, ammonium molybdate and sodium molybdate; and the initiator is ammonium persulfate.

5. The preparation method according to claim 1, characterized in that: The high temperature pyrolysis refers to keeping the temperature at 700-1000° C. for 2 hours in a nitrogen atmosphere.

6. The preparation method according to claim 1, characterized in that: The volume ratio of the mass of the metal salt in S1, the mass of dimethylimidazole and the graphene oxide aqueous solution is 0.1-0.5g:0.8-8.0g:10ml.

7. The preparation method according to claim 1, characterized in that: The volume ratio of aniline to graphene oxide aqueous solution is 0.1-0.5:

10.

8. The preparation method according to claim 1, characterized in that: The mass ratio of phosphomolybdic acid to metal salt is 0.1-1.0:0.1-0.

5.

9. A molybdenum-based oxide / carbide / GO heterojunction catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the molybdenum-based oxide / carbide / GO heterojunction catalyst as claimed in claim 9 in the field of fuel oxidation desulfurization.

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