Preparation method of cobaltosic oxide catalyst and application of cobaltosic oxide catalyst in degradation of VOCs (Volatile Organic Compounds) by electromagnetic induction heating

Abstract

The invention discloses a preparation method of a cobaltosic oxide catalyst and application of the cobaltosic oxide catalyst in degradation of VOCs (Volatile Organic Compounds) through electromagnetic induction heating. The catalyst is prepared by carrying out hydrothermal reaction on cobalt salt and an alkaline reagent and carrying out high-temperature calcination on the obtained product. The Co3O4 catalysts with different particle sizes can be prepared by regulating and controlling the molar ratio of the cobalt salt to the alkaline reagent. Due to the intrinsic magnetism of Co3O4, eddy current can be generated in an alternating magnetic field, so that heat is generated, directional heating of catalytic sites is achieved, heat loss is reduced, the energy utilization rate is increased, and meanwhile, due to the influence of Lorentz force in the magnetic field on the electron migration capability, the electron mobility is improved. Therefore, the catalytic oxidation performance of the catalyst on VOCs and the water vapor resistance under the humid working condition are remarkably improved. The Co3O4 catalyst has the advantages of high efficiency, water vapor resistance and energy consumption reduction, is suitable for high-efficiency purification of VOCs in industrial flue gas, and has a good application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of oxidative decomposition of volatile organic compounds, and relates to a preparation method and application of a cobalt tetroxide catalyst, and specifically to a preparation method of a cobalt tetroxide catalyst and its application in the degradation of VOCs by electromagnetic induction heating. Background Art

[0002] In addition to being an important precursor to ozone pollution and particulate matter pollution, most VOCs themselves are seriously harmful. Long-term exposure to a VOC environment will damage human health.

[0003] Strengthening VOC control is one of the current measures to improve my country's ambient air quality. Catalytic oxidation is the most commonly used method for VOC control. Compared with other gaseous pollutant control methods, catalytic oxidation can oxidize and decompose VOCs into harmless CO2 and H2O at lower temperatures (200-600°C). Therefore, it is considered one of the most effective methods for addressing air pollution. However, in current industrial applications, traditional thermal catalytic oxidation methods require high temperatures to achieve the required degradation of pollutants, resulting in significant energy losses, which further restricts the application of catalytic oxidation methods. Summary of the Invention

[0004] In order to improve the above technical problems, the present invention provides a preparation method and application of a catalyst for catalytic oxidation of volatile organic compounds based on electromagnetic induction heating. The catalyst of the present invention can simultaneously achieve the dual functional goals of efficiently responding to electromagnetic induction heat generation and efficiently degrading volatile organic pollutants.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0006] A method for preparing Co3O4 comprises subjecting a cobalt salt and an alkaline reagent to a hydrothermal reaction, and calcining the obtained product at a high temperature to obtain Co3O4.

[0007] According to an embodiment of the present invention, the reaction molar ratio of the cobalt salt to the alkaline reagent is 1:4 to 1:12, exemplified by 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, and 1:12.

[0008] According to an embodiment of the present invention, the hydrothermal reaction is carried out in a solvent system. For example, a cobalt salt and an alkaline reagent are dissolved in water to form a mixed solution. Preferably, the concentration of the cobalt salt in the mixed solution is 0.05 to 0.2 mol / L, exemplified by 0.1 mol / L.

[0009] In one embodiment of the present invention, the concentration of the alkaline agent is 4-12 times the concentration of the cobalt salt, for example, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, or 12 times.

[0010] According to an embodiment of the present invention, the preparation method further comprises stirring the mixed solution. For example, the stirring time may be 1 to 6 hours, exemplified by 1 hour, 2 hours, 3 hours, 4 hours, and 6 hours.

[0011] According to an embodiment of the present invention, the cobalt salt is Co(NO3)2·6H2O.

[0012] According to an embodiment of the present invention, the alkaline agent is urea, NaOH or Na2CO3.

[0013] According to an embodiment of the present invention, the temperature of the hydrothermal reaction is 80-120°C, exemplified by 80°C, 100°C, and 120°C; the time of the hydrothermal reaction is 24-72h, exemplified by 24h, 48h, 60h, and 72h.

[0014] According to an embodiment of the present invention, the preparation method further comprises a process of performing solid-liquid separation on the reaction system to obtain a reaction product after the hydrothermal reaction is completed. For example, the solid-liquid separation can be performed by means known in the art, such as filtration.

[0015] According to an embodiment of the present invention, the preparation method further comprises washing the reaction product obtained by solid-liquid separation. For example, the washing solvent may be water or ethanol.

[0016] According to an embodiment of the present invention, the preparation method further comprises drying the washed reaction product. For example, the drying temperature is 60-100°C, exemplified by 60°C, 70°C, 80°C, and 100°C. Furthermore, the drying time is 12-24 hours, exemplified by 12 hours, 15 hours, 18 hours, 20 hours, and 24 hours.

[0017] According to an embodiment of the present invention, the high temperature calcination adopts a two-stage calcination process, the temperature of the first stage calcination is 200-400°C, exemplified by 200°C, 300°C, and 400°C; the time of the first stage calcination is 1-3h, exemplified by 1h, 2h, and 3h.

[0018] The temperature of the secondary calcination is 500-600°C, exemplified by 500°C, 550°C, and 600°C; the time of the secondary calcination is 1-3h, exemplified by 1h, 2h, and 3h; the heating rate of the secondary calcination is 1-10°C / min, exemplified by 5°C / min.

[0019] According to an embodiment of the present invention, the preparation method of Co3O4 includes dissolving a cobalt salt and an alkaline reagent in water, stirring and mixing, and then conducting a hydrothermal reaction; filtering the solid material obtained by the hydrothermal reaction, washing it, drying it, and calcining it at high temperature to obtain Co3O4.

[0020] In the present invention, Co3O4 catalysts with different particle sizes and morphologies can be prepared by adjusting the stoichiometric ratio of the cobalt salt and the alkaline reagent, the solvent thermal reaction temperature and the calcination temperature.

[0021] The present invention also provides Co3O4 prepared by the above preparation method.

[0022] According to an embodiment of the present invention, the Co3O4 is in a granular form.

[0023] Preferably, the grain size of the Co3O4 is 25 to 100 nm, exemplified by 28.3 nm, 50.4 nm, and 87.2 nm.

[0024] According to an embodiment of the present invention, the specific surface area of the Co3O4 is 15 to 25 m 3 / g, exemplified by 15.812m 3 / g, 18.315m 3 / g, 22.391m 3 / g.

[0025] The present invention also provides the use of the aforementioned Co₃O₄ as a catalyst. Preferably, the catalyst is used as a catalyst for the catalytic oxidation of volatile organic compounds (VOCs), and more preferably as a catalyst for the catalytic oxidation degradation of VOCs by electromagnetic induction heating. Exemplarily, the catalyst is used as a catalyst for the catalytic oxidation degradation of toluene by electromagnetic induction heating.

[0026] The present invention also provides a method for catalytic oxidation of volatile organic compounds (VOCs), comprising contacting the above-mentioned Co3O4 with volatile organic compounds (VOCs), and heating to cause a catalytic oxidation reaction.

[0027] According to an embodiment of the present invention, the concentration of volatile organic compounds (VOCs) is 200-2000 ppm, exemplarily 1000 ppm.

[0028] According to an embodiment of the present invention, the heating method is electromagnetic induction heating. Preferably, the temperature range of the electromagnetic induction heating is 30-320°C, exemplified by 30°C, 50°C, 100°C, 130°C, 150°C, 170°C, 190°C, 210°C, 230°C, 250°C, 260°C, 270°C, 300°C, and 320°C.

[0029] According to an embodiment of the present invention, in the catalytic oxidation reaction of volatile organic compounds (VOCs), the amount of Co3O4 material used is 100 to 300 mg, and exemplarily 216 mg.

[0030] According to an embodiment of the present invention, the reaction space velocity in the catalytic oxidation reaction is 20,000 to 60,000 mL / g·h, exemplified by 20,000 mL / g·h.

[0031] According to an embodiment of the present invention, the water vapor content in the catalytic oxidation reaction is 1-10 vol.%, exemplified by 1 vol.%, 3 vol.%, 5 vol.%, 7 vol.%, and 10 vol.%.

[0032] Beneficial effects of the present invention:

[0033] (1) The electromagnetic induction heating method can directly act on the catalyst itself to achieve directional heating of the catalytic site, thereby avoiding the heat loss caused by the traditional resistance furnace heating and heat transfer process. The catalytic oxidation reaction is essentially a process of electron transfer between different substances. The catalyst and external energy supply play an accelerating role in the reaction. The energy supply of the electromagnetic field is a new energy supply method for the current catalytic field. It is different from the external energy transfer of traditional thermal catalysis. It can achieve accurate and stable energy supply to the catalytic material to efficiently utilize energy. At the same time, in theory, the moving electrons will be deflected by the Lorentz force in the magnetic field. The change in the electron motion state will inevitably have a direct impact on the reaction process and play a certain role in the degradation of pollutants. In recent years, cobalt tetroxide has been widely used in the fields of metallurgy, energy storage and catalysis as an important industrial material. At the same time, cobalt tetroxide has good electromagnetic induction heating performance. In view of this, the present invention designs a dual-functional cobalt tetroxide Co3O4 catalyst that can simultaneously realize electromagnetic induction heating and catalytic oxidation functions, which is conducive to promoting the healthy development of catalytic oxidation reactions and is of great significance for further improving the air quality of urban and rural residents, reducing ozone pollution, and preventing the continued deterioration of the greenhouse effect.

[0034] (2) Compared with the existing catalyst preparation methods, the present invention is conducive to enriching the particle size and morphology of the Co3O4 catalyst by controlling the alkaline reagent precipitation, solvent thermal reaction and high-temperature calcination conditions, and the Co3O4 of the present invention can further improve the catalytic performance under the electromagnetic field.

[0035] (3) The Co3O4 catalyst prepared by the method of the present invention can be used for the low-temperature catalytic oxidation of common volatile organic compounds under electromagnetic induction heating. Compared with other catalysts with larger particle sizes, the small-particle Co3O4 catalyst of the present invention has a larger specific surface area and electromagnetic field responsiveness. Based on the intrinsic magnetism of Co3O4, eddy currents can be generated in the alternating magnetic field, thereby generating heat to achieve directional heating of the catalytic site, thereby reducing heat loss and improving energy utilization. At the same time, due to the influence of the Lorentz force on the electron migration ability in the magnetic field, the catalytic oxidation performance of the catalyst for VOCs and the resistance to water vapor under humid working conditions are significantly improved, showing better catalytic oxidation performance. The Co3O4 catalyst of the present invention has the advantages of high efficiency, water vapor resistance, and energy saving. It can be used for the efficient purification of VOCs in industrial flue gas and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 These are SEM test images of the catalysts prepared in Examples 1, 2, and 3 of the present invention.

[0037] Figure 2 1 is the XRD pattern of the catalysts prepared in Examples 1, 2 and 3 of the present invention.

[0038] Figure 3 It is a physical adsorption data diagram of the catalysts prepared in Examples 1, 2, and 3 of the present invention.

[0039] Figure 4 The graph shows the toluene conversion activity test results of the catalysts prepared in Examples 1, 2, and 3 of the present invention and the commercial catalyst Co3O4 (commercial Co3O4, analytically pure ≥99.9%, purchased from Aladdin).

[0040] Figure 5 The graph shows the carbon dioxide yield test results of the catalysts prepared in Examples 1, 2, and 3 of the present invention and a commercial catalyst Co3O4 (commercial Co3O4, analytically pure ≥99.9%, purchased from Aladdin).

[0041] Figure 6 This is a graph showing the water vapor stability test results of the catalyst prepared in Example 1 of the present invention in catalytic oxidation of toluene at 210° C. under electromagnetic induction heating.

[0042] Figure 7 This is a graph showing the water vapor stability test results of the catalyst prepared in Example 1 of the present invention during catalytic oxidation of toluene at 260° C. in a resistance furnace.

[0043] Figure 8 This is a test result chart of the energy consumption required to reach the target temperature of the catalyst prepared in Example 1 of the present invention by electromagnetic induction heating and resistance furnace heating. DETAILED DESCRIPTION

[0044] The technical solutions of the present invention will be described in further detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection that the present invention is intended to protect.

[0045] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0046] Example 1

[0047] The preparation method of the catalyst Co3O4-1 comprises the following steps:

[0048] (1) Weigh 2.91 g of Co(NO3)2·6H2O and 2.42 g of urea and dissolve them in 100 mL of deionized water;

[0049] (2) stirring the mixture obtained in step (1) at room temperature for 2 h;

[0050] (3) The mixed solution obtained in step (2) was transferred to a 200 mL autoclave and subjected to hydrothermal reaction at 80° C. for 24 h;

[0051] (4) Filter the product obtained in step (3), wash with water, wash with ethanol, and dry at 100°C for 12 hours;

[0052] (5) The product after drying in step (4) was calcined at 300°C for 2 h in an air atmosphere and then heated to 550°C for 2 h at a heating rate of 5°C / min. The obtained product was named Co3O4-1.

[0053] Example 2

[0054] The preparation method of the catalyst Co3O4-2 comprises the following steps:

[0055] (1) Weigh 2.91 g of Co(NO3)2·6H2O and 4.84 g of urea and dissolve them in 100 mL of deionized water;

[0056] (2) stirring the mixture obtained in step (1) at room temperature for 2 h;

[0057] (3) The mixed solution obtained in step (2) was transferred to a 200 mL autoclave and subjected to hydrothermal reaction at 80° C. for 24 h;

[0058] (4) Filter the product obtained in step (3), wash with water, wash with ethanol, and dry at 100°C for 12 hours;

[0059] (5) The product after drying in step (4) was calcined at 300°C for 2 h in an air atmosphere and then heated to 550°C for 2 h at a heating rate of 5°C / min. The obtained product was named Co3O4-2.

[0060] Example 3

[0061] The preparation method of the catalyst Co3O4-3 comprises the following steps:

[0062] (1) Weigh 2.91 g of Co(NO3)2·6H2O and 7.26 g of urea and dissolve them in 100 mL of deionized water;

[0063] (2) stirring the mixture obtained in step (1) at room temperature for 2 h;

[0064] (3) The mixed solution obtained in step (2) was transferred to a 200 mL autoclave and subjected to hydrothermal reaction at 80° C. for 24 h;

[0065] (4) Filter the product obtained in step (3), wash with water, wash with ethanol, and dry at 100°C for 12 hours;

[0066] (5) The product after drying in step (4) was calcined at 300°C for 2 h in an air atmosphere and then heated to 550°C for 2 h at a heating rate of 5°C / min. The obtained product was named Co3O4-3.

[0067] Figure 1 The SEM test images of the catalysts prepared in Examples 1, 2, and 3 show that the Co3O4 prepared in the present invention is in a uniform granular shape.

[0068] Figure 2 The XRD patterns of the catalysts prepared in Examples 1, 2, and 3 are shown. As can be seen from the figures, Co₃O₄-1, Co₃O₄-2, and Co₃O₄-3 exhibit the same characteristic peaks, indicating the same crystalline structure. As shown in Table 1, the average crystal particle sizes of the catalysts prepared in Examples 1, 2, and 3, calculated using the Scherrer equation, are 28.3 nm, 50.4 nm, and 87.2 nm, respectively.

[0069] Scherrer formula: D = (K*λ) / (β*cosθ), where K is a constant, set to 1; λ is the X-ray wavelength; β is the half-width at half-maximum of the diffraction peak; and θ is the diffraction angle. For this calculation, the characteristic peak was chosen to be 2θ = 36.8°.

[0070] Table 1

[0071]

[0072] Figure 3This is a physical adsorption data diagram of the catalysts prepared in Examples 1, 2, and 3 of the present invention. It can be seen from the figure that Co3O4-1, Co3O4-2, and Co3O4-3 all show typical type IV isotherms with H3-type hysteresis loop characteristics. Their specific surface area results are shown in Table 1 above, among which Co3O4-1 prepared in Example 1 has the largest specific surface area.

[0073] 216 mg of each of the catalysts prepared in Examples 1, 2, and 3 and a commercial Co3O4 sample (purchased from Aladdin) were weighed, with a particle size of 40-60 mesh, a toluene concentration of 1000 ppm, and a reaction space velocity of 20,000 mL / g·h. The samples were tested for activity using resistance furnace heating and electromagnetic induction heating.

[0074] in:

[0075] Toluene conversion rate = (toluene concentration at outlet / toluene concentration at inlet) * 100%.

[0076] CO2 yield = (outlet CO2 concentration / (7*inlet toluene concentration)*100%).

[0077] Note: Toluene concentration and CO2 concentration were detected by gas chromatography.

[0078] Figure 4 The toluene conversion activity test results of the catalysts prepared in Examples 1, 2, and 3 and commercial Co3O4 (purchased from Aladdin) are shown in the figure. As can be seen from the figure, Co3O4-1, Co3O4-2, and Co3O4-3 have excellent activity under resistance furnace heating catalytic conditions (T 90 258℃, 263℃, 257℃ respectively), and are more active than commercial Co3O4 (T 90 292℃); Under electromagnetic induction heating conditions, the activity of Co3O4-1, Co3O4-2, and Co3O4-3 samples increased to varying degrees (T 90 208°C, 233°C, and 251°C, respectively). The Co3O4-1 prepared in Example 1 exhibited stronger electromagnetic field response and thus superior activity. The commercial Co3O4 material, however, did not exhibit the reaction-promoting phenomenon of electromagnetic induction heating and exhibited lower activity.

[0079] Figure 5The following is a graph showing the carbon dioxide yield test results for the catalysts prepared in Examples 1, 2, and 3 of the present invention and commercial Co3O4 (purchased from Aladdin). As can be seen from the graph, Co3O4-1, Co3O4-2, and Co3O4-3 prepared in the present invention can all achieve stable mineralization of toluene to convert it into CO2 under both electromagnetic induction heating and resistance furnace heating conditions. Furthermore, at a temperature where the toluene conversion rate reaches 90%, the toluene-toluene-to-CO2 yields of Co3O4-1, Co3O4-2, and Co3O4-3 are 87.56%, 86.39%, and 83.51%, respectively. However, even under resistance furnace conditions, the commercial Co3O4 material still lacks the ability to stably mineralize toluene before the complete conversion temperature. Its CO2 yield at a temperature where the toluene conversion rate reaches 90% is only 54.55%.

[0080] 216 mg of the Co3O4-1 catalyst sample prepared in Example 1 and a catalyst with a particle size of 40-60 mesh were weighed, the toluene concentration was 1000 ppm, the reaction space velocity was 20000 mL / g·h, and the water vapor content was 0 vol.%, 3 vol.%, and 5 vol.%. Figure 6 This is a graph showing the water vapor stability test results of the catalyst prepared in Example 1 of the present invention in catalytic oxidation of toluene at 210° C. under electromagnetic induction heating. Figure 7 The figure is a test result of the water vapor stability of the catalyst prepared in Example 1 of the present invention when catalytically oxidizing toluene at 260°C in a resistance furnace. Figure 6 and Figure 7 As can be seen in the results, under the same test conditions (maintained at the complete conversion temperature), when water vapor was introduced into the reaction atmosphere at water vapor contents of 3% and 5%, respectively, the activity of the Co3O4 catalyst prepared by the present invention decreased significantly (to approximately 46%) under resistance furnace heating, resulting in deactivation. However, under electromagnetic induction heating, the Co3O4 catalyst prepared by the present invention did not deactivate. This demonstrates that the Co3O4 catalyst prepared by the present invention has good water vapor resistance under electromagnetic induction heating.

[0081] Figure 8 This figure shows the energy consumption required to reach the target temperature of the Co₃O₄-1 catalyst prepared in Example 1 of the present invention using electromagnetic induction heating and resistance furnace heating. (Test conditions: 100 mg of sample was heated from room temperature (30°C) to 150°C, 200°C, and 250°C, respectively, in a reaction atmosphere (1000 ppm toluene, 60 mL / min flow rate). Energy consumption was measured using an energy meter.) The figure shows that electromagnetic induction heating has higher energy utilization than resistance furnace heating, thus achieving energy savings.

[0082] Note: The initial heating temperature of the test is 30°C, and the energy saving ratio = (1-electromagnetic induction heating energy consumption / resistance furnace heating energy consumption) * 100%.

[0083] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for preparing Co3O4, characterized in that: The method comprises subjecting a cobalt salt to a hydrothermal reaction with an alkaline reagent, and calcining the obtained product at a high temperature to obtain Co3O4.

2. The preparation method according to claim 1, wherein The reaction molar ratio of the cobalt salt to the alkaline reagent is 1:4 to 1:

12.

3. The preparation method according to claim 1 or 2, wherein The hydrothermal reaction is carried out in a solvent system. For example, a cobalt salt and an alkaline reagent are dissolved in water to obtain a mixed solution. Preferably, in the mixed solution, the concentration of the cobalt salt is 0.05 to 0.2 mol / L. Preferably, the concentration of the alkaline agent is 4-12 times the concentration of the cobalt salt. Preferably, the preparation method further comprises stirring the mixed solution. For example, the stirring time may be 1 to 6 hours.

4. The preparation method according to any one of claims 1 to 3, wherein The cobalt salt is Co(NO3)2·6H2O. Preferably, the alkaline reagent is urea, NaOH or Na2CO3. Preferably, the temperature of the hydrothermal reaction is 80-120° C.; the time of the hydrothermal reaction is 24-72 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that The high temperature calcination adopts a two-stage calcination process, the temperature of the first stage calcination is 200-400°C; the time of the first stage calcination is 1-3 hours; The temperature of the secondary calcination is 500-600° C.; the time of the secondary calcination is 1-3 hours; and the heating rate of the secondary calcination is 1-10° C. / min.

6. The preparation method according to any one of claims 1 to 5, characterized in that The preparation method of Co3O4 comprises dissolving a cobalt salt and an alkaline reagent in water, stirring and mixing, and then performing a hydrothermal reaction; filtering the solid matter obtained by the hydrothermal reaction, washing it, drying it, and calcining it at a high temperature to obtain Co3O4.

7. Co3O4 prepared by the preparation method according to any one of claims 1 to 6. Preferably, the Co3O4 is in granular form. Preferably, the grain size of the Co3O4 is 25-100 nm. Preferably, the specific surface area of the Co3O4 is 15 to 25 m 3 / g.

8. Use of the Co3O4 according to claim 7 as a catalyst. Preferably, the catalyst is used for the catalytic oxidation of volatile organic compounds (VOCs), more preferably for the catalytic oxidation degradation of VOCs by electromagnetic induction heating. Exemplarily, the catalyst is used for the catalytic oxidation degradation of toluene by electromagnetic induction heating.

9. A method for catalytic oxidation of volatile organic compounds (VOCs), characterized in that: The method comprises contacting the Co3O4 described in claim 7 with volatile organic compounds (VOCs), and heating the mixture to cause a catalytic oxidation reaction.

10. The method according to claim 9, wherein The concentration of the volatile organic compounds (VOCs) is 200 to 2000 ppm. Preferably, the heating method is electromagnetic induction heating. Preferably, the temperature range of the electromagnetic induction heating is 30-320°C. Preferably, in the catalytic oxidation reaction of volatile organic compounds (VOCs), the amount of Co3O4 material used is 100 to 300 mg. Preferably, the reaction space velocity in the catalytic oxidation reaction is 20,000 to 60,000 mL / g·h.

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