Method for the ambient temperature synthesis of multi-defect co-mn metal oxide catalysts

Abstract

This invention discloses a room-temperature synthesis method for a multi-defect Co-Mn metal oxide catalyst, comprising the following steps: first, a Co-based metal-organic framework (Co-BTC) is synthesized as a precursor using a solvothermal method; then, Mn is incorporated using a mechanical ball milling method, simultaneously increasing surface oxygen vacancies, to obtain a layered Co-Mn metal oxide catalyst. The Co-BTC precursor, prepared using a solvothermal method, is then incorporated with Mn using a mechanical ball milling method to prepare the layered Co-Mn metal oxide catalyst. The metal-organic framework, as a catalyst precursor, can inhibit the aggregation of active components; the mechanochemical method is used for Mn incorporation and the construction of surface oxygen vacancies. The resulting catalyst exhibits a 90% conversion rate at 260℃ and demonstrates good low-temperature catalytic performance for hydrocarbons such as propane.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of inorganic nanocatalytic materials, in particular to a normal temperature synthesis method of a multi-defect Co-Mn metal oxide catalyst. BACKGROUND

[0002] Among the atmospheric pollutants, volatile organic compounds (VOCs) generally have strong chemical stability, biological toxicity, and difficult degradability, etc., and are one of the main components of air pollutants, which has caused serious harm to the ecological environment and human health. Therefore, it is of great significance to study how to economically and efficiently treat VOCs to protect human health and the natural environment. Among the numerous VOCs treatment technologies, thermal catalytic oxidation technology is considered to be the preferred choice for large-scale degradation of VOCs in industry because of its high catalytic efficiency, low energy consumption, green environmental protection (main degradation products are CO2, H2O, etc.), high energy utilization rate, and high universality. Since the price of noble metal catalysts is high, it limits its commercial application, and transition metal elements are often used as active components for VOCs catalytic oxidation due to their wide source and excellent catalytic activity, especially Co and Mn elements, which have good catalytic degradation activity for most VOCs components including propane. However, different preparation methods and post-synthesis modifications will affect the specific surface area, morphology, defect density, etc. of the catalyst, and thus affect the activity of the catalyst. For example, in the preparation of Co-Mn metal oxide catalysts, if high-temperature calcination is used, small particles will aggregate into larger blocks, reducing the exposure opportunity of active sites and affecting the performance of the catalyst, and the specific surface area of the Co-Mn metal oxide catalyst prepared by the existing preparation method needs to be improved. SUMMARY

[0003] Therefore, the purpose of the present application is to provide a normal temperature synthesis method of a multi-defect Co-Mn metal oxide catalyst, which can avoid the aggregation of small particles into larger blocks during high-temperature calcination, increase the exposure opportunity of active sites, make the catalyst preparation process more green and environmentally friendly, and also improve the specific surface area of the Co-Mn metal oxide catalyst.

[0004] The normal temperature synthesis method of the multi-defect Co-Mn metal oxide catalyst of the present application comprises the following steps:

[0005] First, Co-based metal organic framework Co-BTC is synthesized by a solvothermal method as a precursor, and then Mn elements are doped by a mechanical ball milling method to increase surface oxygen vacancies, thereby preparing a Co-Mn metal oxide catalyst with a lamellar structure;

[0006] Further, the method comprises the following steps:

[0007] S1, solvothermal synthesis of precursor Co-BTC: the cobalt salt and H3BTC are dissolved in the solvent respectively, and the above dispersion system is treated by ultrasonic until the solid is completely dissolved, then HCOOH is added to the two solutions respectively, the obtained solution is mixed and reacted, and the purple red crystal is collected, washed and dried to obtain Co-BTC;

[0008] S2, preparation of Co-Mn oxide: corundum balls, Co-BTC, Mn source and NaOH are mixed and added to a ball mill jar, the obtained solid product is washed and dried in vacuum to obtain a Co-Mn oxide catalyst;

[0009] Further, in step S1, the cobalt salt is Co(NO3)2·6H2O, and the solvent is an aqueous solution of N,N-dimethylformamide;

[0010] Further, in step S1, the obtained solution is mixed and incubated at 60-80 DEG C for 65-80 h; the drying temperature is 50-70 DEG C, and the drying time is 15-25 h;

[0011] Further, in step S1, the molar ratio of Co(NO3)2·6H2O, H3BTC and HCOOH is 1:1:2;

[0012] Further, in step S2, the Mn source is potassium permanganate; the drying temperature is 50-70 DEG C, and the drying time is 15-25 h;

[0013] Further, in step S2, the corundum balls are a mixture of corundum balls with a diameter of 1.0 cm and corundum balls with a diameter of 0.5 cm;

[0014] Further, in step S2, the mass ratio of Co-BTC to KMnO4 is 5:1-4.

[0015] The method for synthesizing the multi-defect Co-Mn metal oxide catalyst at room temperature disclosed in the application adopts a solvothermal method to prepare Co metal organic framework (Co-BTC) as a precursor, and uses a mechanical ball milling method to add Mn to prepare a Co-Mn metal oxide catalyst with a sheet structure. The metal organic framework as a catalyst precursor can inhibit the agglomeration of active components; the mechanical chemical method is used to add Mn and construct surface oxygen vacancies, and the conversion rate of the prepared catalyst is 90% at 260 DEG C, which has good low-temperature catalytic effect on hydrocarbons such as propane. The method is simple and green, the catalyst preparation has good reproducibility, can avoid the aggregation of small particles into larger blocks in the high-temperature calcination process, increase the exposure opportunity of active sites, make the catalyst preparation process more green, and also can improve the specific surface area of the Co-Mn metal oxide catalyst, and the highest specific surface area can reach 195.3 m 2 / g.

[0016] Mechanochemistry is essentially a process in which mechanical energy generated by compression, shearing, impact, and stretching promotes physical and chemical transformations. Through collisions, extrusion, shearing, and friction between grinding media and materials, mechanochemistry induces chemical reactions to change the internal structure, crystal phase, and surface properties of materials, thereby promoting material modification or chemical reactions. Mechanochemistry has the advantages of short modification time, high reaction activity, and no corrosion, and is considered a green, sustainable, and easily scalable synthesis technology. Compared with other synthesis technologies, mechanochemistry not only provides the possibility of eliminating the use of a large amount of solvent, but also has the opportunity to achieve synthesis strategies, reactions, and molecules that were previously unavailable in solution. In addition, mechanochemistry can produce unique physical and chemical properties during synthesis, directly modifying or constraining materials.

[0017] Metal organic frameworks (MOFs) materials are coordination polymers formed by connecting metal or metal clusters as nodes through polydentate organic ligands. MOFs are often used as precursors to prepare single-atom catalysts or metal oxide catalysts with dispersed active centers. For example, carbon-based single-atom catalysts derived from MOFs are often used in electrocatalysis due to their excellent performance and stability. In addition, transition metal oxide catalysts derived from MOFs as precursors can inhibit the agglomeration of active sites to some extent, making their catalytic activity better than that of traditional co-precipitation prepared oxide catalysts. With the penetration of defect theory into MOFs materials, metal organic gels, two-dimensional metal organic frameworks, and amorphous metal organic frameworks with coordination defects have more potential application prospects than traditional MOFs with different structural forms. MOFs with a large number of coordination defects have a special structure of short-range order and long-range disorder, which meets the dispersion of metal ions and refines the crystal grains, which also provides feasibility for the preparation of defect-rich Mn-Co metal oxides.

[0018] The application of the Co-Mn oxide catalyst with a multi-defect amorphous structure prepared by the method of the present application: the catalyst is used for catalytic oxidation of propane, the raw gas composition is propane 1 vol%, O2 10 vol%, and 89 vol% N2 as the balance gas, the reaction temperature is increased from room temperature to 500 DEG C, the heating rate is 10 DEG C·min -1 ; the total flow rate of the reaction gas is 100 mL·min -1 , the mass space velocity is 120000 ml g -1 h -1 . BRIEF DESCRIPTION OF DRAWINGS

[0019] The present application will be further described below in conjunction with the drawings and examples:

[0020] Figure 1 X-ray diffraction (XRD) patterns of the Co-Mn metal oxide samples prepared, where Co x Mn 1-x O-1 / 1, Co x Mn 1-x O-1 / 2, Co x Mn 1-x O-1 / 3, Co x Mn 1-x O-1 / 4 correspond to the XRD patterns of the samples of Example 1, Example 2, Example 3, and Example 4, respectively;

[0021] Figure 2 Activity curves of the Co-Mn metal oxide samples prepared for the catalytic oxidation of C3H8, where Co x Mn 1-x O-1 / 1, Co x Mn 1-x O-1 / 2, Co x Mn 1-x O-1 / 3, Co x Mn 1-x O-1 / 4 correspond to the activity curves of the samples of Example 1, Example 2, Example 3, and Example 4, respectively;

[0022] Figure 3 SEM pictures of the Co-Mn metal oxide samples prepared, where Co x Mn 1-x O-1 / 1, Co x Mn 1-x O-1 / 2, Co x Mn 1-x O-1 / 3, Co x Mn 1-x O-1 / 4 correspond to the SEM pictures of the samples of Example 1, Example 2, Example 3, and Example 4, respectively. DETAILED DESCRIPTION

[0023] Example One

[0024] Co(NO3)2-6H2O (2.3520 g, 4 mmol) and H3BTC (1.7152 g, 4 mmol) were dissolved in 160 mL solvent (120 mL DMF, 40 mL H2O) respectively, the above dispersion was treated by ultrasound until the solid was completely dissolved, then 300 μL HCOOH (8 mmol) was added dropwise, shaken uniformly, to obtain a red transparent solution. The solution was transferred to a 250 mL blue screw neck bottle, and incubated at 70 °C for 72 h. The purple-red crystals formed after the reaction was completed were collected by filtration, washed with 30 mL anhydrous ethanol for 3 times, dried at 60 °C for 18 h, to obtain Co-BTC. Twenty-five corundum balls (five with a diameter of 1.0 cm, twenty with a diameter of 0.5 cm), 1.0 g Co-BTC, 0.2 g potassium permanganate and 0.27 g NaOH (+1 mL deionized water) were placed in a zirconia material ball mill tank (50 mL) reactor one by one for ball milling for 30 min, the obtained solid product was washed with DMF for 10 min, washed with anhydrous ethanol and deionized water for two times respectively, and dried in a vacuum oven at 60 °C for 18 h, to obtain a Co-Mn oxide catalyst.

[0025] Example Two

[0026] Co(NO3)2-6H2O (2.3520 g, 4 mmol) and H3BTC (1.7152 g, 4 mmol) were dissolved in 160 mL solvent (120 mL DMF, 40 mL H2O) respectively, the above dispersion was treated by ultrasound until the solid was completely dissolved, then 300 μL HCOOH (8 mmol) was added dropwise, shaken uniformly, to obtain a red transparent solution. The solution was transferred to a 250 mL blue screw neck bottle, and incubated at 70 °C for 72 h. The purple-red crystals formed after the reaction was completed were collected by filtration, washed with 30 mL anhydrous ethanol for 3 times, dried at 60 °C for 18 h, to obtain Co-BTC. Twenty-five corundum balls (five with a diameter of 1.0 cm, twenty with a diameter of 0.5 cm), 1.0 g Co-BTC, 0.2 g potassium permanganate and 0.27 g NaOH (+1 mL deionized water) were placed in a zirconia material ball mill tank (50 mL) reactor one by one for ball milling for 30 min, the obtained solid product was washed with DMF for 10 min, washed with anhydrous ethanol and deionized water for two times respectively, and dried in a vacuum oven at 60 °C for 18 h, to obtain a Co-Mn oxide catalyst.

[0027] Example Three

[0028] Co(NO3)2-6H2O (2.3520 g, 4 mmol) and H3BTC (1.7152 g, 4 mmol) were dissolved in 160 mL solvent (120 mL DMF, 40 mL H2O) respectively, the above dispersion was treated by ultrasound until the solid was completely dissolved, then 300 μL HCOOH (8 mmol) was added dropwise, shaken uniformly, to obtain a red transparent solution. The solution was transferred to a 250 mL blue screw neck bottle, and incubated at 70 °C for 72 h. The purple-red crystals formed after the reaction was completed were collected by filtration, washed with 30 mL anhydrous ethanol for 3 times, dried at 60 °C for 18 h, to obtain Co-BTC. Twenty-five corundum balls (five with a diameter of 1.0 cm, twenty with a diameter of 0.5 cm), 1.0 g Co-BTC, 0.6 g potassium permanganate and 0.27 g NaOH (+1 mL deionized water) were placed in a zirconia material ball mill tank (50 mL) reactor one by one for ball milling for 30 min, the obtained solid product was washed with DMF for 10 min, washed with anhydrous ethanol and deionized water for two times respectively, and dried in a vacuum oven at 60 °C for 18 h, to obtain a Co-Mn oxide catalyst.

[0029] Example Four

[0030] Co(NO3)2-6H2O (2.3520 g, 4 mmol) and H3BTC (1.7152 g, 4 mmol) were dissolved in 160 mL solvent (120 mL DMF, 40 mL H2O) respectively, the above dispersion was treated by ultrasound until the solid was completely dissolved, then 300 μL HCOOH (8 mmol) was added dropwise, shaken uniformly, to obtain a red transparent solution. The solution was transferred to a 250 mL blue screw neck bottle, and incubated at 70 °C for 72 h. The purple-red crystals formed after the reaction was completed were collected by filtration, washed with 30 mL anhydrous ethanol for 3 times, dried at 60 °C for 18 h, to obtain Co-BTC. Twenty-five corundum balls (five with a diameter of 1.0 cm, twenty with a diameter of 0.5 cm), 1.0 g Co-BTC, 0.8 g potassium permanganate and 0.27 g NaOH (+1 mL deionized water) were placed in a zirconia material ball mill tank (50 mL) reactor one by one for ball milling for 30 min, the obtained solid product was washed with DMF for 10 min, washed with anhydrous ethanol and deionized water for two times respectively, and dried in a vacuum oven at 60 °C for 18 h, to obtain a Co-Mn oxide catalyst.

[0031] Example Five

[0032] Co(NO3)2*6H2O (2.3520 g, 4 mmol) and H3BTC (1.7152 g, 4 mmol) were dissolved in 160 mL solvent (120 mL DMF, 40 mL H2O) respectively, the above dispersion was treated by ultrasound until the solid was completely dissolved, then 300 μL HCOOH (8 mmol) was added dropwise, shaken uniformly, to obtain a red transparent solution. The solution was transferred to a 250 mL blue screw neck bottle, and incubated at 60 °C for 80 h. The purple-red crystals formed after the reaction was completed were collected by filtration, washed with 30 mL anhydrous ethanol for 3 times, and dried at 50 °C for 20 h to obtain Co-BTC. Twenty-five corundum balls (five with a diameter of 1.0 cm, twenty with a diameter of 0.5 cm), 1.0 g Co-BTC, 0.3 g potassium permanganate and 0.27 g NaOH (+1 mL deionized water) were placed in a zirconium oxide material ball mill tank (50 mL) reactor one by one for ball milling for 30 min, and the obtained solid product was washed with DMF for 10 min, anhydrous ethanol and deionized water for two times respectively, and dried in a vacuum oven at 50 °C for 20 h to obtain a Co-Mn oxide catalyst.

[0033] Example Six

[0034] Co(NO3)2*6H2O (2.3520 g, 4 mmol) and H3BTC (1.7152 g, 4 mmol) were dissolved in 160 mL solvent (120 mL DMF, 40 mL H2O) respectively, the above dispersion was treated by ultrasound until the solid was completely dissolved, then 300 μL HCOOH (8 mmol) was added dropwise, shaken uniformly, to obtain a red transparent solution. The solution was transferred to a 250 mL blue screw neck bottle, and incubated at 60 °C for 80 h. The purple-red crystals formed after the reaction was completed were collected by filtration, washed with 30 mL anhydrous ethanol for 3 times, and dried at 50 °C for 20 h to obtain Co-BTC. Twenty-five corundum balls (five with a diameter of 1.0 cm, twenty with a diameter of 0.5 cm), 1.0 g Co-BTC, 0.3 g potassium permanganate and 0.27 g NaOH (+1 mL deionized water) were placed in a zirconium oxide material ball mill tank (50 mL) reactor one by one for ball milling for 30 min, and the obtained solid product was washed with DMF for 10 min, anhydrous ethanol and deionized water for two times respectively, and dried in a vacuum oven at 50 °C for 20 h to obtain a Co-Mn oxide catalyst.

[0035] Test Example 1:

[0036] The Co-Mn oxides of Examples 1-4 were respectively tested for x Mn 1-x O-1 / 1, Co x Mn 1-x O-1 / 2, Co x Mn1-x O-1 / 3, Co x Mn 1-x O-1 / 4 samples were tested by XRD, and the results are shown in Figure 1 O-1 / 1, Co x Mn 1-x O-1 / 2, Co x Mn 1-x O-1 / 3, Co x Mn 1-x O-1 / 4, Co x Mn 1- x The O-1 / 4 samples all contain MnCo2O4 spinel structure, and the amount of Mn incorporated will generate a multi-phase mixture containing Co3O4, Mn3O4 and MnCo2O4. With the increase of the amount of KMnO4, the degree of amorphousness of the prepared catalysts is improved, and the shift angle becomes larger, which may be the result of the increase of crystal defects or lattice distortion.

[0037] Test Example 2:

[0038] Co x Mn 1-x O-1 / 1, Co x Mn 1-x O-1 / 2, Co x Mn 1-x O-1 / 3, Co x Mn 1-x O-1 / 4 samples were tested by scanning electron microscopy (SEM), and the results are shown in -1 -1 The C3H8catalytic oxidation activity evaluation test of the O-1 / 4 samples was carried out on a fixed bed reactor system. 50 mg of the sample was mixed with 0.85 g of quartz sand uniformly and placed in a quartz tube reactor. The total flow rate of the reaction mixed gas (89 vol% N2+10 vol% O2+1 vol% C3H8) was 100 mL / min, and the corresponding mass space velocity was 120000 mL·g -1 ·h -1 The reaction temperature was controlled by a thermocouple located inside the catalyst bed. The concentration of C3H8after the mixed gas passed through the catalyst was detected online by a gas detection device.

[0039] Test Example 3:

[0040] Co x Mn 1-x O-1 / 1, Co x Mn 1-x O-1 / 2, Co x Mn 1-x O-1 / 3, Co x Mn 1-x O-1 / 4 samples were tested by scanning electron microscopy (SEM), and the results are shown inFigure 3 The SEM pictures of the samples are shown in the figure. It can be seen from the figure that with the increase of the amount of KMnO4, the catalyst particles tend to be broken in general, when Co:Mn is 1:1, the catalyst presents a hexagon close to the precursor, and the surface is covered with fine particles, when Co:Mn is 1:2, the catalyst presents a large irregular block, when Co:Mn is 1:3 or 1:4, the catalyst presents a small flake-shaped accumulation, and especially when Co:Mn is 1:4, the particles are uniformly distributed, and the particle size distribution is narrow.

[0041] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the present application and not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A room-temperature synthesis method for a multi-defect Co-Mn metal oxide catalyst, characterized in that... : First, a Co-based metal-organic framework Co-BTC was synthesized using a solvothermal method as a precursor. Then, Mn was incorporated by mechanical ball milling to increase surface oxygen vacancies, thus obtaining a layered Co-Mn metal oxide catalyst. Includes the following steps: S1, Solvothermal synthesis of precursor Co-BTC: Cobalt salt and H3BTC are dissolved in solvent and the dispersion is ultrasonically treated until the solid is completely dissolved. Then, HCOOH is added to the two solutions respectively. After the resulting solutions are mixed and reacted, purple-red crystals are collected, washed and dried to obtain Co-BTC. The cobalt salt is Co(NO3)2·6H2O, and the molar ratio of Co(NO3)2·6H2O, H3BTC and HCOOH is 1:1:

2. S2, Preparation of Co-Mn oxide: Corundum balls, Co-BTC, Mn source and NaOH are mixed and added to a ball mill jar for ball milling. The resulting solid product is washed and dried under vacuum to obtain Co-Mn oxide catalyst. The Mn source is potassium permanganate and the mass ratio of Co-BTC to KMnO4 is 5:1-4.

2. The room-temperature synthesis method of the multi-defect Co-Mn metal oxide catalyst according to claim 1, characterized in that: In step S1, the solvent is an aqueous solution of N,N-dimethylformamide.

3. The room-temperature synthesis method of the multi-defect Co-Mn metal oxide catalyst according to claim 1, characterized in that: In step S1, the obtained solution is mixed and kept at 60-80 ℃ for 65-80 h; the drying temperature is 50-70 ℃ and the drying time is 15-25 h.

4. The room-temperature synthesis method of the multi-defect Co-Mn metal oxide catalyst according to claim 1, characterized in that: In step S2, the drying temperature is 50-70 ℃ and the drying time is 15-25 h.

5. The room-temperature synthesis method of the multi-defect Co-Mn metal oxide catalyst according to claim 1, characterized in that: In step S2, the corundum sphere is a mixture of corundum spheres with a diameter of 1.0 cm and corundum spheres with a diameter of 0.5 cm.

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