A method for preparing two-dimensional porous Co3O4 / CeO2 nanosheets and its application

Abstract

This invention provides a method for preparing two-dimensional porous Co3O4 / CeO2 nanosheets and their applications. The method uses Co(NO3)2·6H2O and Ce(NO3)3·6H2O as raw materials, urea as a precipitant, water as a solvent, and D-glucose as a reducing agent, and obtains two-dimensional porous Co3O4 / CeO2 nanosheets through a hydrothermal reaction. The Co3O4 / CeO2 nanosheets prepared by this invention have high crystallinity, high purity, and good reproducibility. The synergistic effect between Co and Ce can significantly improve the Co-C nanosheets. 3+ / Co 2+ The higher proportion of Co doping reveals a richer array of active sites, thereby enhancing the low-temperature thermocatalytic oxidation and decomposition performance of toluene, making it a promising toluene oxidation catalyst. Adjusting the Co doping amount can effectively improve the specific surface area and pore structure of the nanosheets, exposing more coordinated unsaturated metal atoms.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and relates to two-dimensional catalysts, specifically to a method for preparing two-dimensional porous Co3O4 / CeO2 nanosheets and their application. Background Technology

[0002] Two-dimensional materials possess excellent physicochemical properties such as high specific surface area and abundant unsaturated atoms on the surface, leading to their wide application in chemical engineering, functional materials, and biomedicine. Currently, two-dimensional porous nanomaterials, due to their unique pore structure and combined high specific surface area, high porosity, and high adsorption capacity, have significant application value in the emerging energy-related field of photothermal catalysis. For example, transition metal-based two-dimensional porous nanomaterials have begun to show promise in the thermocatalytic oxidation and decomposition of organic pollutants such as toluene. However, existing synthesis methods are cumbersome, produce low-purity products with poor reproducibility, and the intrinsic thermocatalytic oxidation activity of these two-dimensional nanomaterials for toluene remains low. Therefore, to improve the efficiency of thermocatalytic oxidation and decomposition of toluene and to combine the advantages of two-dimensional porous nanomaterials, it is crucial to prepare two-dimensional porous nanosheets with high specific surface area, abundant surface active sites, and excellent catalytic activity. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing two-dimensional porous Co3O4 / CeO2 nanosheets, thereby solving the technical problem that the abundance of active centers in nanosheets prepared by existing methods needs to be further improved.

[0004] Another objective of this invention is to provide an application of Co3O4 / CeO2 nanosheets to address the technical problem that the low-temperature catalytic performance of existing catalysts for the catalytic oxidation of toluene needs further improvement.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for preparing two-dimensional porous Co3O4 / CeO2 nanosheets is disclosed. The method uses Co(NO3)2·6H2O and Ce(NO3)3·6H2O as raw materials, urea as a precipitant, water as a solvent, and D-glucose as a reducing agent to obtain two-dimensional porous Co3O4 / CeO2 nanosheets through hydrothermal reaction.

[0007] The present invention also has the following technical features:

[0008] Specifically, the method includes the following steps:

[0009] Step 1: Under room temperature and stirring conditions, D-glucose, Co(NO3)2·6H2O and Ce(NO3)3·6H2O are dissolved in water, then urea is added and stirring is continued to obtain the precursor solution.

[0010] Step 2: The precursor solution obtained in Step 1 is placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene. After hydrothermal reaction at 140–200℃ for 16–24 h, the supernatant is discarded. The lower precipitate is washed alternately by centrifugation with deionized water and anhydrous ethanol, dried at 60–80℃, ground, and then calcined in a tube furnace at 350–550℃ for 2–5 h. The calcination temperature is increased at a rate of 1℃ / min to obtain two-dimensional porous Co3O4 / CeO2 nanosheets.

[0011] Preferably, the molar ratio of the total amount of Co(NO3)2·6H2O and Ce(NO3)3·6H2O to urea is 1:50 to 3:10.

[0012] Preferably, the molar ratio of Co(NO3)2·6H2O to Ce(NO3)3·6H2O is 1:2 to 16:1.

[0013] The two-dimensional porous Co3O4 / CeO2 nanosheets prepared by the method described above are used as a catalyst for the thermocatalytic oxidative decomposition of toluene.

[0014] Specifically, 0.1 g of two-dimensional porous Co3O4 / CeO2 nanosheet catalyst was placed in a quartz tube reactor with a diameter of 10 mm. The reactant feed consisted of toluene with a mass concentration of 1000 ppm, 20% O2 and 80% N2 as balance gases. The total gas flow rate was controlled at 60 mL / min, the space velocity was 36000 mL / (g·h), and the reaction temperature was 50–370 °C. Toluene was thermally catalytically oxidized and decomposed to produce CO2 and H2O.

[0015] Compared with the prior art, the present invention has the following technical effects:

[0016] (I) The Co3O4 / CeO2 nanosheets prepared by the method of the present invention have high crystallinity, and the synergistic effect between Co and Ce can significantly improve the crystallinity of Co. 3+ / Co 2+ The higher proportion of active sites indicates a richer range of active sites, thereby improving the low-temperature thermocatalytic oxidation and decomposition performance of toluene, making it a promising toluene oxidation catalyst.

[0017] (II) The nanosheets prepared by the method of the present invention have a two-dimensional structure. By adjusting the amount of Co doping, the specific surface area and pore structure of the Co3O4 / CeO2 porous nanosheets can be effectively improved, exposing more coordinated unsaturated metal atoms. The active components are highly dispersed, avoiding the interaction between nanoparticles and their aggregation covering their active sites.

[0018] (III) The preparation method of the present invention can prepare two-dimensional porous Co3O4 / CeO2 nanosheets with uniform size distribution, thinness, large surface area, abundant pores and multi-component synergistic effect, which provides broad application prospects for nano Co3O4 / CeO2 in various fields.

[0019] (IV) The preparation method of the present invention uses urea as a precipitant, water as a solvent, and D-glucose as a reducing agent to prepare regular mesoporous Co3O4 / CeO2 nanosheets in one step hydrothermal method. The production process is simple, the preparation time is short, the cost is low, the yield is high, the reproducibility is strong, and it can be produced on a large scale continuously.

[0020] (V) The preparation method of the present invention uses water as a solvent, which avoids the pollution of the environment by organic solvents.

[0021] (VI) Compared with single-component Co3O4 and CeO2 catalysts, the mesoporous Co3O4 / CeO2 nanosheets prepared in this invention exhibit abundant active centers due to their porous structure. The toluene catalytic performance of Co3O4 / CeO2 nanosheets is significantly better than that of single-component catalysts, and they also possess excellent low-temperature reduction properties. Attached Figure Description

[0022] Figure 1 This is the X-ray diffraction (XRD) pattern of the two-dimensional porous Co3O4 / CeO2 nanosheets prepared in Example 1.

[0023] Figure 2 This is a scanning electron microscope (SEM) image of the two-dimensional porous Co3O4 / CeO2 nanosheets prepared in Example 1.

[0024] Figure 3 yes Figure 2 A magnified view of a portion of the image.

[0025] Figure 4 This is a scanning electron microscope (SEM) image of the two-dimensional porous Co3O4 / CeO2 nanosheets prepared in Example 2.

[0026] Figure 5 This is a scanning electron microscope (SEM) image of the two-dimensional porous Co3O4 / CeO2 nanosheets prepared in Example 3.

[0027] Figure 6The graph shows the thermocatalytic toluene oxidation performance of the two-dimensional porous Co3O4 / CeO2 nanosheets prepared in Example 1 and the single-component Co3O4 and CeO2 catalysts.

[0028] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0029] It should be noted that, unless otherwise specified, all raw materials used in this invention are those known in the prior art.

[0030] Toluene, as a typical volatile organic compound, is highly toxic to human health and has carcinogenic, mutagenic, and teratogenic effects. Therefore, the development of highly efficient thermocatalytic oxidative decomposition catalysts for toluene has become a research hotspot in recent years. Platinum (Pt) and palladium (Pd) catalysts exhibit high catalytic activity for toluene, but their practical application is limited by their scarcity, high cost, and susceptibility to deactivation and poisoning. Currently, there are two main strategies for developing highly efficient non-precious metal-based catalysts for toluene removal: one is to improve the intrinsic activity of the catalyst by adjusting the active components, and the other is to construct catalysts with unique structures.

[0031] In the thermocatalytic oxidative decomposition of toluene, Co-based transition metal oxides (CoO4) exhibit good activity, low cost, and non-toxicity, showing broad development prospects. Among them, Co3O4 two-dimensional nanomaterials have shown improved catalytic performance. However, these single-component Co-based nanocatalysts still suffer from low activity and poor stability, prompting us to explore more advanced and efficient catalysts for the thermocatalytic oxidative decomposition of toluene. Currently, research shows that preparing multi-component nanostructures and utilizing the synergistic effect between components to improve the thermocatalytic oxidative decomposition performance of Co-based nanocatalysts for toluene has become a research hotspot. CeO2 possesses oxygen vacancies and excellent oxygen storage capacity; the synergistic effect between Co3O4 and CeO2 can significantly improve the performance of CoO4 in the thermocatalytic oxidative decomposition of toluene. 3+ / Co 2+ The proportion of active centers is increased to enhance the low-temperature thermocatalytic oxidation and decomposition of toluene by improving the catalyst's performance. However, there are few reports on two-dimensional porous Co3O4 / CeO2 nanomaterials. Therefore, it is necessary and urgent to prepare two-dimensional porous Co3O4 / CeO2 nanosheets with large surface area, abundant pores, and multi-component synergistic effects.

[0032] This invention provides a method for preparing two-dimensional porous Co3O4 / CeO2 nanosheets. The method uses Co(NO3)2·6H2O and Ce(NO3)3·6H2O as raw materials, urea as a precipitant, water as a solvent, and D-glucose as a reducing agent to obtain two-dimensional porous Co3O4 / CeO2 nanosheets through a hydrothermal reaction.

[0033] In this invention, the two-dimensional porous Co3O4 / CeO2 nanosheet catalyst is used in the thermocatalytic oxidation and decomposition of toluene. During the reaction, the catalytic activity is measured at different temperatures by adjusting the temperature controller. Each temperature is maintained for one hour, and then the activity is detected. The tail gas is analyzed using a gas chromatograph. The toluene conversion rate is obtained by the following formula:

[0034]

[0035] In the formula: X[ toluene [toluene] represents the toluene conversion rate. in and [toluene] out These represent the inlet and outlet concentrations of toluene, respectively. (T) 50 To evaluate the low-temperature activity of the catalyst, T 90 The high-temperature activity of the catalyst was evaluated at the temperatures corresponding to a toluene conversion rate of 50% and 90%.

[0036] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0037] Example 1:

[0038] This embodiment provides a method for preparing two-dimensional porous Co3O4 / CeO2 nanosheets, which includes the following steps:

[0039] Step 1: Dissolve 0.015 mol D-glucose, 0.02 mol Co(NO3)2·6H2O and 0.01 mol Ce(NO3)3·6H2O in 60 ml of ultrapure water, then add 0.1 mol urea and continue stirring for 30 min to obtain the precursor solution.

[0040] Step 2: The precursor solution was placed in a 100 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and allowed to stand at 180 °C for 20 h. After the hydrothermal reaction, the supernatant was discarded, and the lower precipitate was washed alternately by centrifugation with deionized water and ethanol, dried at 70 °C for 12 h, ground, and calcined in a tube furnace at 500 °C for 3 h (programmed temperature increase of 1 °C / min) to obtain a mesoporous nanosheet structure of Co3O4 / CeO2 (Co / Ce = 2:1).

[0041] Depend on Figure 1 It can be seen that the product obtained is a Co3O4 / CeO2 bimetallic oxide.

[0042] Depend on Figure 2 It is evident that the obtained product has a mesoporous nanosheet structure.

[0043] Depend on Figure 3As can be seen, the magnified morphology of the Co3O4 / CeO2 nanosheets shows that the nanosheets are highly dispersed and have a porous surface.

[0044] Example 2:

[0045] This embodiment provides a method for preparing two-dimensional porous Co3O4 / CeO2 nanosheets, which includes the following steps:

[0046] Step 1: Dissolve 0.015 mol D-glucose, 0.01 mol Co(NO3)2·6H2O and 0.02 mol Ce(NO3)3·6H2O in 60 ml of ultrapure water, then add 0.1 mol urea and continue stirring for 30 min to obtain the precursor solution.

[0047] Step 2: The precursor solution was placed in a 100 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and allowed to stand at 180 °C for 20 h. After the hydrothermal reaction, the supernatant was discarded, and the lower precipitate was washed alternately by centrifugation with deionized water and ethanol, dried at 70 °C for 12 h, ground, and calcined in a tube furnace at 500 °C for 3 h (programmed temperature increase of 1 °C / min) to obtain a mesoporous nanosheet structure of Co3O4 / CeO2 (Co / Ce = 1:2).

[0048] Depend on Figure 4 It is evident that the obtained product has a mesoporous nanosheet structure.

[0049] Example 3:

[0050] This embodiment provides a method for preparing two-dimensional porous Co3O4 / CeO2 nanosheets, which includes the following steps:

[0051] Step 1: Dissolve 0.015 mol D-glucose, 0.024 mol Co(NO3)2·6H2O and 0.006 mol Ce(NO3)3·6H2O in 60 ml of ultrapure water, then add 0.1 mol urea and continue stirring for 30 min to obtain the precursor solution.

[0052] Step 2: The precursor solution was placed in a 100 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and allowed to stand at 180 °C for 20 h. After the hydrothermal reaction, the supernatant was discarded, and the lower precipitate was washed alternately by centrifugation with deionized water and ethanol, dried at 70 °C for 12 h, ground, and calcined in a tube furnace at 500 °C for 3 h (programmed temperature increase of 1 °C / min) to obtain a mesoporous nanosheet structure of Co3O4 / CeO2 (Co / Ce = 4:1).

[0053] Depend on Figure 5 It is evident that the obtained product has a mesoporous nanosheet structure.

[0054] Example 4:

[0055] This embodiment illustrates the application of the catalyst in the thermocatalytic oxidative decomposition of toluene.

[0056] In this embodiment, the two-dimensional porous Co3O4 / CeO2 nanosheet catalyst was prepared using the preparation method in Example 1; and a single-component Co3O4 catalyst and a single-component CeO2 catalyst were used as controls.

[0057] Specifically, 0.1 g of catalyst was placed in a quartz tube reactor with a diameter of 10 mm. The reactant feed consisted of toluene with a mass concentration of 1000 ppm, and balance gases of O2 and N2 with a mass concentration of 20 vol%. The total gas flow rate was controlled at 60 mL / min, the space velocity was 36000 mL / (g·h), and the reaction temperature was 50–370 °C. Toluene was thermally catalytically oxidized and decomposed to produce CO2 and H2O.

[0058] Depend on Figure 6 As can be seen, compared with single-component Co3O4 catalysts and single-component CeO2 catalysts, the mesoporous Co3O4 / CeO2 nanosheets prepared in this invention exhibit abundant active centers due to their porous structure. The toluene catalytic performance of Co3O4 / CeO2 nanosheets is significantly better than that of single-component catalysts, and they also exhibit excellent low-temperature reduction properties.

Claims

1. The application of two-dimensional porous Co3O4 / CeO2 nanosheets as a catalyst for the thermocatalytic oxidative decomposition of toluene; characterized in that, 0.1 g of two-dimensional porous Co3O4 / CeO2 nanosheet catalyst was placed in a quartz tube reactor with a diameter of 10 mm. The reactant feed consisted of toluene with a mass concentration of 1000 ppm, 20% O2 and 80% N2 as balance gases. The total gas flow rate was controlled at 60 mL / min, the space velocity was 36000 mL / (g•h), and the reaction temperature was 50–370 °C. Toluene was thermally catalytically oxidized and decomposed to produce CO2 and H2O. The preparation method of the two-dimensional porous Co3O4 / CeO2 nanosheets includes the following steps: Step 1: Under room temperature and stirring conditions, the reducing agent D-glucose, raw materials Co(NO3)2•6H2O and Ce(NO3)3•6H2O are dissolved in water, and then the precipitant urea is added. Stirring is continued to obtain the precursor solution. Step 2: The precursor solution obtained in Step 1 is placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene. After hydrothermal reaction at 140–200℃ for 16–24 h, the supernatant is discarded. The lower precipitate is washed alternately by centrifugation with deionized water and anhydrous ethanol, dried at 60–80℃, ground, and then calcined in a tube furnace at 350–550℃ for 2–5 h. The calcination temperature is increased at a rate of 1℃ / min to obtain two-dimensional porous Co3O4 / CeO2 nanosheets.

2. The application as described in claim 1, characterized in that, The total amount of Co(NO3)2•6H2O and Ce(NO3)3•6H2O in molar ratio to urea is 1:50 to 3:

10.

3. The application as described in claim 1, characterized in that, The molar ratio of Co(NO3)2•6H2O and Ce(NO3)3•6H2O is 1:2 to 16:1.

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