Defective manganese-based catalyst as well as preparation method and application thereof in catalytic oxidation of ethylene

Abstract

The invention provides a defective manganese-based catalyst, the phase composition of the defective manganese-based catalyst comprises beta-MnO2, Mn2O3 and Mn5O8, and the molar ratio of Mn < 3 + > to Mn < 4 + > is (8-12): 1. The invention also provides a preparation method and application of the defective manganese-based catalyst. The defective manganese-based catalyst provided by the invention has excellent catalytic activity, does not need to use noble metal or transition metal as an active component, has a very excellent effect in the aspect of catalytic oxidation of ethylene, and can be used as a novel and efficient ethylene degradation catalyst. The preparation method provided by the invention is simple and convenient in process, low in cost, high in operability and high in safety, so that the preparation method has good industrial practicability and is suitable for large-scale production and application.

Description

Technical Field

[0001] The invention relates to the field of industrial catalysis, and in particular to a defective manganese-based catalyst and a preparation method thereof, and also to application of the defective manganese-based catalyst in catalytic oxidation of ethylene. Background Art

[0002] The catalysts commonly used in the chemical industry are mainly precious metal catalysts and transition metal catalysts. Although precious metal catalysts have excellent performance, they are expensive, have poor thermal stability and are easily poisoned, which limits their industrial development. Therefore, low-cost, high-stability transition metal oxide catalysts have gained more favor among researchers. Among the many transition metal oxide catalysts, manganese oxide catalysts (MnO x ) Because it has a variety of variable valences (+2, +3, +4, +7) and good electron transfer ability, it can undergo rapid redox reactions and exhibit excellent catalytic activity. The catalytic activity of manganese oxide catalysts is closely related to multiple factors such as their structure, morphology, surface chemical state, and synergistic effects among multiple components.

[0003] Since manganese has a variety of variable valence states, it can form a variety of oxides such as Mn2O3, Mn3O4, MnO2 and MnO. Manganese oxide catalysts with different valence states will show different catalytic activities under specific conditions.

[0004] Kim et al. (Applied Catalysis B: Environmental, 2010, 98(3-4): 180-185) found that the presence of easily reducible Mn 3+ -O bond, Mn2O3 catalyst has good oxygen mobility, thus showing better catalytic activity than MnO2 and Mn3O4. Wang et al. (Reaction Kinetics, Mechanisms and Catalysis, 2016, 118 (2): 605-619) compared the catalytic performance of MnO2 and mixed oxides of Mn2O3 and Mn5O8 and found that MnO2 catalyst showed better toluene catalytic performance due to its better low-temperature reducibility and higher surface adsorbed oxygen content.

[0005] Chinese patent CN 104923281A (Nano manganese oxide molecular sieve for efficient removal of nitrogen oxides at room temperature and its preparation method) discloses a nano manganese oxide molecular sieve catalyst for efficient removal of nitrogen oxides at room temperature, and also discloses that the nano manganese oxide molecular sieve has surface oxygen vacancies, which can be used as catalytic active sites to enhance catalytic performance, and by doping alkaline earth metal ions, the alkalinity of the nano manganese oxide molecular sieve is enhanced, thereby also enhancing the adsorption and storage capacity of acidic nitrogen oxides. Chinese patent CN 112156778A (A manganese oxide-loaded noble metal single atom formaldehyde oxidation catalyst and its preparation method and application) discloses a manganese oxide-loaded noble metal single atom formaldehyde oxidation catalyst, which loads noble metal single atoms on the surface of manganese oxide, and utilizes the characteristics of manganese species with multiple valence states, rich pore structure, and more defect sites to achieve uniform and stable placement of noble metal single atoms, thereby obtaining better catalytic activity and stability. Chinese patent CN 112156779A (A manganese oxide-supported noble metal single-atom VOC oxidation catalyst, its preparation method and application) discloses a manganese oxide-supported noble metal single-atom VOC oxidation catalyst, wherein the noble metal used is at least two of platinum, ruthenium, palladium and gold. The catalyst uses active manganese oxide as an active carrier, which can supplement the noble metal active center and improve the catalyst reaction activity.

[0006] In summary, although manganese oxides have good catalytic properties, most of them need to be used in combination with other active ingredients, which is costly and has a complicated preparation process, which is not conducive to large-scale application. Summary of the invention

[0007] In order to make up for the deficiencies in the prior art, an object of the present invention is to provide a defective manganese-based catalyst which has excellent catalytic performance and can be used alone for the catalytic oxidation of ethylene.

[0008] Another object of the present invention is to provide a method for preparing the defective manganese-based catalyst.

[0009] Another object of the present invention is to provide application of the defective manganese-based catalyst.

[0010] The first aspect of the present invention provides a defective manganese-based catalyst, the phase composition of which includes β-MnO2, Mn2O3 and Mn5O8, wherein Mn 3+ / Mn 4+ The molar ratio is 8 to 12:1.

[0011] The defective manganese-based catalyst provided by the present invention has a specific phase composition, including β-MnO2, Mn2O3 and Mn5O8, and Mn 3+ / Mn 4+It also has a specific molar ratio range, which can form more defect sites in the catalyst and change the microscopic morphology of the catalyst. By adjusting the species and defect sites of manganese oxides, the catalytic performance of defective manganese-based catalysts can be significantly improved, thereby achieving the purpose of catalyzing ethylene degradation alone without introducing transition metals or precious metal elements as active components.

[0012] In some preferred embodiments, the phase composition of the defective manganese-based catalyst may include, by mole, 70-80% of β-MnO2, 10-20% of Mn2O3, and 5-10% of Mn5O8.

[0013] In some preferred embodiments, the microscopic morphology of the defective manganese-based catalyst can be a rod-shaped (e.g., a rod-shaped) having an average diameter of 5 to 15 nm (e.g., about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, or any combination of diameter intervals). Figure 4 In some more preferred embodiments, the microscopic morphology of the defective manganese-based catalyst may be a rod-like shape with an average diameter of 5 to 10 nm.

[0014] In some preferred embodiments, the specific surface area of ​​the defective manganese-based catalyst may be 100 to 200 m 2 / g (for example, about 100 m 2 / g, about 110m 2 / g, about 120m 2 / g, about 130m 2 / g, about 140m 2 / g, about 150m 2 / g, about 160m 2 / g, about 170m 2 / g, about 180m 2 / g, about 190m 2 / g, about 200m 2 / g or any combination of specific surface area intervals). In some more preferred embodiments, the specific surface area of ​​the defective manganese-based catalyst may be 140 to 200 m 2 / g.

[0015] In some preferred embodiments, the average pore size of the defective manganese-based catalyst may be 5 to 20 nm (e.g., about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 15 nm, about 18 nm, about 20 nm, or any combination of pore size intervals). In some more preferred embodiments, the average pore size of the defective manganese-based catalyst may be 5 to 10 nm.

[0016] The second aspect of the present invention provides a method for preparing a defective manganese-based catalyst according to any one of the above technical solutions, comprising the following steps:

[0017] S1: Evenly dispersing potassium permanganate, a dispersant and a divalent manganese salt in water to obtain a dispersed solution, wherein the molar ratio of the potassium permanganate to the divalent manganese salt is 2:3-5;

[0018] S2: subjecting the dispersed solution to a hydrothermal reaction at 120-160° C. for 12-18 hours to obtain a hydrothermal material; and

[0019] S3: separating the solid matter from the hydrothermal material, washing, drying and calcining to obtain the defective manganese-based catalyst.

[0020] In the preparation method provided by the present invention, the Mn 2+ and Mn 7+ and the conditions of the hydrothermal reaction, thereby obtaining the defective manganese-based catalyst having a specific phase composition and a specific microscopic morphology as described in the present invention.

[0021] In the preparation method provided by the present invention, the divalent manganese salt may be a common divalent manganese water-soluble salt in the art. In some preferred embodiments, the divalent manganese salt may be selected from one or more of manganese sulfate, manganese nitrate, manganese acetate or a hydrate thereof, wherein the hydrate of the divalent manganese salt may be a hydrate containing any amount of crystal water.

[0022] In the preparation method provided by the present invention, the dispersant can be selected from one or more of polyethylene glycol (PEG), triblock copolymer P123 (full name: polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, molecular formula: PEO-PPO-PEO), polyvinyl pyrrolidone (PVP), and cetyltrimethylammonium bromide (CTAB). In some preferred embodiments, the amount of the dispersant used can be 10 to 20 times the amount of the potassium permanganate used by mass.

[0023] In the preparation method provided by the present invention, the step S1 may further include the following steps:

[0024] S101: dissolving the potassium permanganate in water at 20-50° C. to obtain a potassium permanganate aqueous solution;

[0025] S102: adding the dispersant to the potassium permanganate aqueous solution, stirring at 80-100° C. for 1-5 hours to obtain a mixed solution; and

[0026] S103: adding the divalent manganese salt to the mixed solution, stirring at 80-100° C. for 1-5 hours to obtain the dispersed solution.

[0027] In the preparation method provided by the present invention, in step S101, the mass percentage concentration of the potassium permanganate aqueous solution can be 0.8-3% (for example, about 0.8%, about 1.0%, about 1.2%, about 1.5%, about 1.8%, about 2.0%, about 2.2%, about 2.5%, about 2.8%, about 3.0% or any combination of mass percentage intervals). In some preferred embodiments, the mass percentage concentration of the potassium permanganate aqueous solution can be 1.5-2%.

[0028] In the preparation method provided by the present invention, in step S3, the separated solid matter can be washed 2 to 4 times with deionized water, and the washing temperature can be room temperature (ie, 25° C.).

[0029] In the preparation method provided by the present invention, in step S3, the drying temperature of the drying can be 80-120° C., and the drying time can be 10-20 hours. In some preferred embodiments, the drying temperature of the drying can be 90-110° C., and the drying time can be 10-15 hours.

[0030] In the preparation method provided by the present invention, in the step S3, the calcination temperature can be 400-600°C, and the calcination time can be 3-8 hours. In some preferred embodiments, the calcination temperature can be 480-520°C, and the calcination time can be 4-6 hours.

[0031] In the preparation method provided by the present invention, in step S3, the heating rate during calcination can be 3-8°C / min, for example, 5°C / min.

[0032] In the preparation method provided by the present invention, the desired material can be obtained through a separation step, such as separating solid matter from a hydrothermal material, and the separation method can be a common method in the art, including but not limited to natural sedimentation, (normal pressure or vacuum) filtration, centrifugation, etc.

[0033] The third aspect of the present invention provides the use of the defective manganese-based catalyst described in any one of the above technical solutions or the defective manganese-based catalyst prepared by the preparation method described in any one of the above technical solutions in catalytic oxidation of ethylene.

[0034] The defective manganese-based catalyst provided by the present invention utilizes the characteristics of manganese oxide species diversity, mixed valence states, controllable morphology, and more defect sites, and can effectively achieve the adsorption, activation and oxidation of ethylene gas, thereby achieving efficient catalytic oxidation of ethylene without the presence of other active components (especially transition metals or precious metals), thereby achieving the degradation and removal of ethylene.

[0035] The defective manganese-based catalyst provided by the present invention has excellent catalytic activity. When used for catalytic oxidation of ethylene, the conversion rate of ethylene can reach 50% at 110°C, the conversion rate of ethylene can reach 90% at 180°C, and the CO2 selectivity can reach more than 99%.

[0036] The technical solution provided by the present invention has the following advantages:

[0037] (1) The defective manganese-based catalyst provided by the present invention has the characteristics of diverse manganese oxide species, mixed valence states, controllable morphology, and a large number of defect sites, and thus has excellent catalytic activity. In addition, no precious metal or transition metal is required as an active component, which greatly reduces the manufacturing cost of the catalyst.

[0038] (2) The defective manganese-based catalyst provided by the present invention has an excellent effect in the catalytic oxidation of ethylene, and can therefore be used as a new and efficient ethylene degradation catalyst, which is beneficial to the degradation and removal of ethylene and VOCs containing ethylene, and provides a new idea for the prevention and control of ethylene pollution. It is green and environmentally friendly and has very important economic value and social significance.

[0039] (3) The preparation method provided by the present invention utilizes cheap and readily available potassium permanganate and divalent manganese salt as raw materials, and controls the ratio of manganese ions with different valence states and the conditions of the hydrothermal reaction to obtain the defective manganese-based catalyst of the present invention. The process is simple, the cost is low, the operability is strong and the safety is high, so it has good industrial applicability and is suitable for large-scale production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is an appearance diagram of the defective manganese-based catalyst prepared in Example 3;

[0041] Figure 2 The X-ray powder diffraction (XRD) pattern of the defective manganese-based catalyst prepared in Example 3;

[0042] Figure 3 It is a nitrogen adsorption-desorption isotherm diagram of the defective manganese-based catalyst prepared in Example 3;

[0043] Figure 4 This is a SEM image of the defective manganese-based catalyst prepared in Example 3;

[0044] Figure 5This is the XPS spectrum of Mn2p of the defective manganese-based catalyst prepared in Example 3. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments.

[0046] Unless otherwise specified, the raw materials or reagents used in the examples and comparative examples of the present invention are commercially available products.

[0047] The percentages used in the embodiments and comparative examples of the present invention are all mass percentages unless otherwise specified.

[0048] Example 1

[0049] 2g of potassium permanganate powder was dissolved in 100mL of deionized water at 50°C, and 40g of dispersant PEG400 was added to the above solution. The resulting mixed solution was heated to 80°C and stirred for 2h. Then, 7.97g of manganese nitrate tetrahydrate was added to the above mixed solution and stirred at 80°C for 2h. After that, the above mixture was placed in a polytetrafluoroethylene hydrothermal reactor and hydrothermally reacted at 160°C for 18h. Then, the mixture after the above hydrothermal reaction was centrifuged, and the solid obtained after separation was washed with deionized water, washed at room temperature, and washed 3 times. Finally, it was dried at 100°C for 12h, calcined at 500°C for 5h, and the heating rate was 5°C / min to obtain the defective manganese-based catalyst 1.

[0050] The main phase composition of defective manganese-based catalyst 1 includes: β-MnO2, Mn2O3 and Mn5O8. The phase composition obtained by semi-quantitative XRD includes (by mole): β-MnO2 about 70.3%, Mn2O3 about 19.8% and Mn5O8 about 9.9%. 3+ / Mn 4+ The molar ratio is 12:1.

[0051] The catalyst is rod-shaped with an average diameter of 8.3 nm and a specific surface area of ​​145.3 m 2 / g, and the average pore size is 6.2nm.

[0052] Example 2

[0053] Dissolve 2g of potassium permanganate powder in 100mL of deionized water at 20°C, and then add 20g of dispersant CTAB to the above solution. Heat the resulting mixed solution to 100°C and stir for 2h. Then, add 4.4g of manganese acetate to the above mixed solution and stir at 100°C for 2h. After that, place the above mixture in a hydrothermal reactor of polytetrafluoroethylene and hydrothermally react at 140°C for 14h. Next, centrifuge the above hydrothermal mixture, wash the solid obtained after separation with deionized water, wash it at room temperature, and wash it 3 times. Finally, dry it at 100°C for 12h, calcine it at 500°C for 5h, and the heating rate is 5°C / min to obtain defective manganese-based catalyst 2.

[0054] The main phase composition of defective manganese-based catalyst 2 includes: β-MnO2, Mn2O3 and Mn5O8. The phase composition obtained by semi-quantitative XRD includes (by mole): β-MnO2 about 78.3%, Mn2O3 about 12.5% ​​and Mn5O8 about 9.2%. 3+ / Mn 4+ The molar ratio is 10:1.

[0055] The catalyst is rod-shaped with an average diameter of 5.2 nm and a specific surface area of ​​168.4 m 2 / g, and the average pore size is 8.6nm.

[0056] Example 3

[0057] Dissolve 2g of potassium permanganate powder in 100mL of deionized water at 30°C, and then add 30g of dispersant P123 (molecular weight 332.48) to the above solution. Heat the obtained mixed solution to 90°C and stir for 2h. Then, add 2.88g of manganese sulfate monohydrate to the above mixed solution and stir at 100°C for 2h. After that, place the above mixture in a polytetrafluoroethylene hydrothermal reactor and react hydrothermally at 120°C for 12h. Next, centrifuge the mixture after the hydrothermal reaction, wash the solid obtained after separation with deionized water, wash it at room temperature, and wash it 3 times. Finally, dry it at 100°C for 12h, calcine it at 500°C for 5h, and the heating rate is 5°C / min to obtain a defective manganese-based catalyst 3, which has an appearance as shown below. Figure 1 shown.

[0058] like Figure 2 As shown, the main phase composition of defective manganese-based catalyst 3 includes: β-MnO2, Mn2O3 and Mn5O8. The phase composition obtained by XRD semi-quantitative analysis includes (by mole): β-MnO2 about 77%, Mn2O3 about 14% and Mn5O8 about 9%. Figure 5 As shown, the Mn 3+ / Mn 4+ The molar ratio is 8:1.

[0059] like Figure 3 and Figure 4 As shown in Figure 2, the catalyst is rod-shaped with an average diameter of 7.6 nm and a specific surface area of ​​187.8 m 2 / g, and the average pore size is 5.1nm.

[0060] Comparative Example 1

[0061] Dissolve 2g of potassium permanganate powder in 10mL of deionized water at 30°C, and then add 30g of dispersant P123 to the above solution. Heat the resulting mixed solution to 90°C and stir for 2h. Then, add 2.2g of manganese acetate (molecular weight 173.03) to the above mixed solution and stir at 100°C for 2h. After that, place the above mixture in a polytetrafluoroethylene hydrothermal reactor and perform a hydrothermal reaction at 120°C for 12h. Next, centrifuge the mixture after the hydrothermal reaction, wash the solid obtained after separation with deionized water, wash it at room temperature, and wash it 3 times. Finally, dry it at 100°C for 12h, calcine it at 500°C for 5h, and the heating rate is 5°C / min to obtain manganese-based catalyst 4.

[0062] The main phase composition of manganese-based catalyst 4 is β-MnO2, all of which is tetravalent manganese. The catalyst morphology is flaky, with a specific surface area of ​​127.8 m 2 / g, and the average pore size is 5.1nm.

[0063] Comparative Example 2

[0064] Commercially available potassium permanganate powder was dried at 100°C for 12 h and calcined at 500°C for 5 h at a heating rate of 5°C / min to obtain manganese-based catalyst 5.

[0065] The main phase composition of manganese-based catalyst 5 is β-MnO2, all of which is tetravalent manganese. The catalyst morphology is spherical, with a specific surface area of ​​87.8 m 2 / g, and the average pore size is 3.4nm.

[0066] Comparative Example 3

[0067] Commercially available Mn2O3 (Sigma-Aldrich, CAS 1317-34-6) was used as the catalyst.

[0068] Test Case

[0069] The catalysts prepared in Examples 1-3 and Comparative Examples 1-3 were pelletized (40-60 mesh) and tested for their catalytic activity in catalyzing ethylene oxidation. -1, ethylene concentration is 700ppm, carrier gas is N2. The ethylene conversion rate is calculated by the inlet and outlet ethylene concentration of the test device (American MKS MultiGas 6030 Fourier transform infrared gas analyzer), and the temperature T90 corresponding to the ethylene conversion rate reaching 90% is tested by program heating at a heating rate of 5°C / min.

[0070] Table 1

[0071]

[0072] It can be seen from the results in Table 1 that the defective manganese-based catalyst provided by the present invention has excellent catalytic activity in the catalytic oxidation of ethylene, and does not require the use of precious metals or transition metals as active components. Therefore, it can be used as a new and efficient ethylene degradation catalyst with strong industrial applicability.

[0073] The catalyst prepared in Comparative Example 1 did not control the Mn 2+ and Mn 7+ The ratio of is within a specific range, so the phase is single and the catalytic effect is poor. The catalysts of Comparative Examples 2 and 3 are also manganese oxides composed of a single phase, so it is difficult to achieve a good catalytic effect.

[0074] Unless otherwise defined, the terms used in the present invention have the meanings commonly understood by those skilled in the art.

[0075] The embodiments described in the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Those skilled in the art may make various other substitutions, changes and improvements within the scope of the present invention. Therefore, the present invention is not limited to the above embodiments, but is only limited by the claims.

Claims

1. A defective manganese-based catalyst, characterized in that: The phase composition of the defective manganese-based catalyst includes β-MnO2, Mn2O3 and Mn5O8, wherein Mn 3+ / Mn 4+ The molar ratio is 8 to 12:

1.

2. The defective manganese-based catalyst according to claim 1, characterized in that The phase composition of the defective manganese-based catalyst comprises, by mole, 70-80% of β-MnO2, 10-20% of Mn2O3 and 5-10% of Mn5O8.

3. The defective manganese-based catalyst according to claim 1 or 2, characterized in that The microstructure of the defective manganese-based catalyst is rod-shaped with an average diameter of 5 to 15 nm; and / or The specific surface area of ​​the defective manganese-based catalyst is 100 to 200 m 2 / g; and / or The average pore diameter of the defective manganese-based catalyst is 5 to 20 nm.

4. The method for preparing the defective manganese-based catalyst according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1: Evenly dispersing potassium permanganate, a dispersant and a divalent manganese salt in water to obtain a dispersed solution, wherein the molar ratio of the potassium permanganate to the divalent manganese salt is 2:3-5; S2: subjecting the dispersed solution to a hydrothermal reaction at 120-160° C. for 12-18 hours to obtain a hydrothermal material; and S3: separating the solid matter from the hydrothermal material, washing, drying and calcining to obtain the defective manganese-based catalyst.

5. The preparation method according to claim 4, characterized in that: The divalent manganese salt is selected from one or more of manganese sulfate, manganese nitrate, manganese acetate or hydrates thereof.

6. The preparation method according to claim 4 or 5, characterized in that: The dispersant is selected from one or more of polyethylene glycol (PEG), triblock copolymer P123, polyvinyl pyrrolidone (PVP), and cetyltrimethylammonium bromide (CTAB); and / or The amount of the dispersant used is 10 to 20 times the amount of the potassium permanganate used by mass.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The step S1 further comprises the following steps: S101: dissolving the potassium permanganate in water at 20-50° C. to obtain a potassium permanganate aqueous solution; S102: adding the dispersant to the potassium permanganate aqueous solution, stirring at 80-100° C. for 1-5 hours to obtain a mixed solution; and S103: adding the divalent manganese salt to the mixed solution, stirring at 80-100° C. for 1-5 hours to obtain the dispersed solution.

8. The preparation method according to any one of claims 4 to 7, characterized in that: In the step S3, the drying temperature is 80-120° C. and the drying time is 10-20 hours.

9. The preparation method according to any one of claims 4 to 8, characterized in that: In the step S3, the calcination temperature is 400-600° C., and the calcination time is 3-8 hours.

10. Use of the defective manganese-based catalyst according to any one of claims 1 to 3 or the defective manganese-based catalyst prepared by the preparation method according to any one of claims 4 to 9 in catalytic oxidation of ethylene.

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