Cerium monatomic catalyst, preparation method and application thereof

Abstract

The invention discloses a cerium monatomic catalyst as well as a preparation method and application thereof, and belongs to the technical field of sewage treatment. The method comprises the following steps: firstly, preparing a nitrogen-doped carbon substrate, and then putting the nitrogen-doped carbon substrate in an atomic layer deposition reaction chamber for pretreatment to remove impurities and moisture on the surface of the nitrogen-doped carbon substrate, so as to obtain a pretreated carbon substrate; then, cerium acetylacetonate is used as a Ce precursor and introduced into an atomic layer deposition reaction chamber to be subjected to pulse treatment at a certain temperature and pressure, the cerium acetylacetonate is chemically adsorbed on the pretreated carbon substrate, and a plurality of cycles are performed to enable Ce atoms to be deposited on the surface of the pretreated carbon substrate, so that a deposited catalyst is obtained; and finally, purging, washing and the like are carried out. The catalyst prepared by the method disclosed by the invention can utilize active metal sites to the greatest extent, is environment-friendly, and has a wide application prospect in an environmental catalytic oxidation process.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and specifically relates to a cerium single-atom catalyst, a preparation method and application thereof. Background Art

[0002] With the development of industrial civilization and the prosperity of social economy, a large amount of industrial wastewater and domestic wastewater are discharged into water bodies. In particular, new pollutants that are difficult to degrade, such as aromatic and antibiotic pollutants, are often detected in natural water, which brings great challenges to the control of water pollution and the recycling of water resources. Heterogeneous catalytic ozonation relies on the active species produced by ozone decomposition on the catalyst surface to destroy stubborn organic pollutants in water, and has been widely used to strengthen sewage treatment.

[0003] Compared with traditional metal-loaded catalysts, single-atom catalysts have gradually been applied to cutting-edge research fields in wastewater treatment and degradation of difficult-to-degrade organic matter due to their inherent advantages such as the highest utilization efficiency of isolated metal atoms, clear catalytic sites, and adjustable coordination structures.

[0004] The existing research reports on water treatment catalysts include:

[0005] Application No. 202110949161.5 discloses a platinum-based single-atom catalyst for water treatment and a preparation method thereof. The method uses porous ceramics as a carrier, platinum-based single atoms as catalytically active components, and vinyl silane as a surface modifier. The method is prepared by a steam in-situ growth method. Kaolin, aluminum source powder, activated carbon powder, straw powder, and a forming agent solution are extruded and formed, and a porous ceramic carrier is obtained by roasting. The porous ceramic carrier is then immersed in a surface modifier solution for reaction and dried to obtain a surface-modified porous ceramic carrier. The surface-modified porous ceramic carrier is then adsorbed with an active component precursor solution, and after drying, the active component precursor is reduced to a platinum-based single-atom catalyst for water treatment by a steam in-situ growth method. The catalyst can efficiently catalyze and reduce water pollutants such as p-nitrophenol, methyl orange, and methylene blue.

[0006] Application No. 202210384284.3 discloses a silver-based water treatment single-atom catalyst and a preparation method thereof, wherein the method uses zirconium hydrogen phosphate to adsorb a silver source solution, and then mixes it with butyl acrylate-styrene-acrylonitrile (ASA) resin, prepares the ASA material by melt blending, and then carbonizes the ASA material at high temperature under a nitrogen atmosphere, and finally reduces it under a hydrogen atmosphere to generate a silver-based water treatment single-atom catalyst. Based on the mass of the ASA resin, the mass percentage of zirconium hydrogen phosphate is 5% to 10%, and the mass percentage of the silver source is 0.01% to 0.1%.

[0007] The above-mentioned single-atom catalysts in the prior art still have technical problems in actual use: easy deactivation, easy agglomeration during the preparation process, and low catalytic activity.

[0008] This shows that the prior art needs to be further improved. Summary of the invention

[0009] One of the purposes of the present invention is to provide a method for preparing a cerium single-atom catalyst, which has the advantages of simple operation, low catalyst deactivation, strong catalytic ability, etc., and has a good effect in sewage treatment.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A method for preparing a cerium single atom catalyst comprises the following steps:

[0012] a. dissolving a certain amount of zinc nitrate hexahydrate and 2-methylimidazole in methanol, mixing, stirring and standing to obtain a suspension; centrifuging the suspension, collecting the precipitate, washing and drying the precipitate to obtain a precursor; placing the precursor in a tube furnace under an inert atmosphere for carbonization treatment to obtain a nitrogen-doped carbon matrix;

[0013] b. placing the nitrogen-doped carbon substrate in an atomic layer deposition reaction chamber for pretreatment to remove impurities and moisture on its surface, thereby obtaining a pretreated carbon substrate;

[0014] c. Cerium acetylacetonate is used as a Ce precursor, introduced into an atomic layer deposition reaction chamber and heated to 180-250° C., and the pressure is maintained at 0.1-2 Torr. The cerium acetylacetonate is pulse-treated for 40-150 seconds and chemically adsorbed on the pretreated carbon substrate. Several cycles are performed to deposit Ce atoms on the surface of the pretreated carbon substrate to obtain a deposited catalyst.

[0015] d. Introduce inert gas to purge the atomic layer deposition reaction chamber, blow excess raw materials and by-products out of the atomic layer deposition reaction chamber, wash and dry the deposited catalyst, and obtain the catalyst.

[0016] The beneficial technical effects directly brought about by the above technical solution are:

[0017] In the above technical scheme, firstly, a ZIF-8 metal organic framework with high specific surface area and porosity is obtained by mixing zinc nitrate hexahydrate and 2-methylimidazole; then, impurities are removed by high-temperature calcination in an inert gas to obtain a nitrogen-doped carbon matrix that is often used as a carrier; then, cerium acetylacetonate is chemically adsorbed on the surface of the pretreated carbon matrix through pulse treatment, so that the thickness can be controlled at the atomic level, and one atomic layer is deposited in each reaction cycle. This high-precision control makes the prepared single atomic layer extremely uniform and consistent.

[0018] In the above-mentioned method for preparing a cerium single-atom catalyst, in step a, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:1.5-10, the mixture is stirred for 0.5-1.5 hours, and allowed to stand for 20-30 hours.

[0019] In the above-mentioned method for preparing a cerium single-atom catalyst, in step a, an inert atmosphere is maintained by filling nitrogen into a tubular furnace, the calcination temperature of the tubular furnace is 600-1000°C, the heating rate is 5-8°C / min, and the calcination is 2-4h.

[0020] In the above-mentioned method for preparing a cerium single-atom catalyst, in step a, the precipitate is washed 2 to 4 times and dried at a temperature of 50 to 70°C.

[0021] In the above-mentioned method for preparing a cerium single-atom catalyst, in step b, the vacuum degree in the atomic layer deposition reaction chamber is 2-8 Pa for pretreatment.

[0022] In the above-mentioned method for preparing a cerium single-atom catalyst, in step c, the heating temperature in the atomic layer deposition reaction chamber is 230° C., the pulse treatment is performed for 100 seconds, and 10 cycles are performed to deposit Ce atoms on the surface of the pretreated carbon substrate.

[0023] Another object of the present invention is to provide a cerium single-atom catalyst, which is prepared using the above-mentioned method for preparing a cerium single-atom catalyst.

[0024] Another object of the present invention is to provide an application of a cerium single-atom catalyst in catalyzing ozone oxidation of refractory organic matter.

[0025] Furthermore, the above application is the use of cerium single-atom catalyst as a heterogeneous catalyst in the catalytic oxidation of wastewater ozone.

[0026] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0027] (1) The cerium single-atom catalyst prepared by the present invention has a large number of metal single-atom active sites (such as Figure 1), its electron unsaturation effect can efficiently catalyze the decomposition of ozone into higher-order active oxidative species. Compared with ozone, the highly active species produced have lower selectivity, which greatly improves the degradation efficiency of difficult-to-degrade pollutants, thereby improving the treatment effect of sewage.

[0028] (2) The preparation method of the present invention is based on a brand-new single-atom technology. The rare earth metal material is specially treated in the form of a single atom so that it can be attached to a carbon matrix and can be directly used for catalytic ozone oxidation. The nitrogen-doped carbon matrix of the present invention is generated by calcining and carbonizing a metal skeleton, has good adsorption properties, and can produce a synergistic effect with transition metals, thereby significantly improving the effect of sewage treatment.

[0029] (3) The single-atom catalyst of the present invention adopts a brand-new single-atom technology. By fixing rare earth metals on a carbon matrix in the form of single atoms, it successfully achieves 100% utilization of metal atoms and achieves a complete "atomic economy". Compared with traditional catalysts, single-atom catalysts can increase the utilization rate of ozone while ensuring the same catalytic effect. At the same time, the catalyst has a high-efficiency sewage treatment capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be further described below in conjunction with the accompanying drawings:

[0031] Figure 1 This is a spherical aberration electron microscope of the Ce single atom nitrogen-doped carbon material prepared by the present invention;

[0032] Figure 2 The C / C0 of the catalysts of Example 1, Comparative Example 2 at different times. DETAILED DESCRIPTION

[0033] The present invention proposes a cerium single-atom catalyst, a preparation method and an application thereof. In order to make the advantages and technical solutions of the present invention clearer and more specific, the present invention is further described below in conjunction with specific embodiments.

[0034] The raw materials described in the present invention can be purchased through commercial channels.

[0035] A method for preparing a cerium single atom catalyst comprises the following steps:

[0036] a. Dissolve a certain amount of zinc nitrate hexahydrate and 2-methylimidazole in methanol, wherein the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:1.5-10, mix and stir for 0.5-1.5 hours and stand for 20-30 hours to obtain a suspension; centrifuge the suspension, collect the precipitate, wash the precipitate 2-4 times, and dry it at a temperature of 50-70° C. to obtain a precursor; place the precursor in a tubular furnace under an inert atmosphere for carbonization treatment, the calcination temperature is 600-1000° C., the heating rate is 5-8° C. / min, and the calcination is 2-4 hours to obtain a nitrogen-doped carbon matrix.

[0037] b. placing the nitrogen-doped carbon substrate in an atomic layer deposition reaction chamber at a vacuum degree of 2 to 8 Pa for pretreatment to remove impurities and moisture on its surface, thereby obtaining a pretreated carbon substrate;

[0038] c. Cerium acetylacetonate is used as a Ce precursor, introduced into an atomic layer deposition reaction chamber and heated to 180-250° C., and the pressure is maintained at 0.1-2 Torr. The cerium acetylacetonate is pulse treated for 40-100 seconds and chemically adsorbed on the pretreated carbon substrate. Several cycles are performed to deposit Ce atoms on the surface of the pretreated carbon substrate to obtain a deposited catalyst.

[0039] d. Introduce inert gas to purge the atomic layer deposition reaction chamber, blow excess raw materials and by-products out of the atomic layer deposition reaction chamber, wash and dry the deposited catalyst, and obtain the catalyst.

[0040] The present invention will be further described below in conjunction with specific embodiments:

[0041] Embodiment 1:

[0042] A method for preparing a cerium single atom catalyst comprises the following steps:

[0043] Step 1: Dissolve 2.975 g of zinc nitrate hexahydrate and 6.568 g of 2-methylimidazole in 100 mL of methanol, mix and stir for 1 hour, let stand for 24 hours, centrifuge the suspension to collect the precipitate, wash three times with methanol, and dry at 60°C overnight to obtain a precursor; calcine the precursor in a tubular furnace at 1000°C (5°C / min) in a nitrogen atmosphere for 3 hours to obtain a nitrogen-doped carbon matrix.

[0044] Step 2: Place the nitrogen-doped carbon substrate in an atomic layer deposition (ALD) reaction chamber, and evacuate the chamber to a vacuum level below 5 Pa for pretreatment to remove impurities and moisture on the surface.

[0045] Step 3: Use cerium acetylacetonate as a Ce precursor, introduce it into an atomic layer deposition (ALD) reaction chamber and heat it to 180°C. The pressure of the atomic layer deposition (ALD) reaction chamber is 0.5 Torr. Pulse the Ce precursor for 80 seconds and chemically adsorb it on the carbon substrate. Perform 5 cycles to deposit Ce atoms on the pretreated carbon substrate surface to obtain a deposited catalyst.

[0046] Step 4: Introduce nitrogen gas for purging for 120 seconds to purge excess reaction precursors and by-products out of the atomic layer deposition (ALD) reaction chamber, wash the deposited catalyst three times with methanol and dry it at 60° C. overnight to obtain a cerium single atom catalyst.

[0047] Embodiment 2:

[0048] The difference from Example 1 is that in step three, cerium acetylacetonate is used as a Ce precursor, introduced into an atomic layer deposition (ALD) reaction chamber and heated to 230°C. The pressure of the atomic layer deposition (ALD) reaction chamber is 1 Torr. The Ce precursor is pulse-treated for 100 seconds and chemically adsorbed on the carbon substrate. Ten cycles are performed to deposit Ce atoms on the pretreated carbon substrate surface to obtain a deposited catalyst.

[0049] In step 4, nitrogen gas was introduced for purging for 130 seconds to purge excess reaction precursors and by-products out of the atomic layer deposition (ALD) reaction chamber, and the deposited catalyst was washed three times with methanol and dried at 60° C. overnight to obtain a cerium single atom catalyst.

[0050] The spherical aberration electron microscope of the cerium single atom catalyst prepared in this example is as follows Figure 1 shown.

[0051] Embodiment 3:

[0052] The difference from Example 1 is that in step three, cerium acetylacetonate is used as a Ce precursor, introduced into an atomic layer deposition (ALD) reaction chamber and heated to 250°C. The pressure of the atomic layer deposition (ALD) reaction chamber is 2 Torr. The Ce precursor is pulse-treated for 150 seconds and chemically adsorbed on the carbon substrate. 15 cycles are performed to deposit Ce atoms on the pretreated carbon substrate surface to obtain a deposited catalyst.

[0053] In step 4, nitrogen gas was introduced for purging for 150 seconds to purge excess reaction precursors and by-products out of the atomic layer deposition (ALD) reaction chamber, and the deposited catalyst was washed three times with methanol and dried at 60° C. overnight to obtain a cerium single atom catalyst.

[0054] Embodiment 4:

[0055] A method for preparing a cerium single atom catalyst comprises the following steps:

[0056] Step 1: Dissolve 2.975 g of zinc nitrate hexahydrate and 6.568 g of 2-methylimidazole in 100 mL of methanol, mix and stir for 1 hour, let stand for 24 hours, centrifuge the suspension to collect the precipitate, wash three times with methanol, and dry at 60°C overnight to obtain a precursor; calcine the precursor in a tubular furnace at 600°C (8°C / min) in a nitrogen atmosphere for 4 hours to obtain a nitrogen-doped carbon matrix.

[0057] Step 2: Place the nitrogen-doped carbon substrate in an atomic layer deposition (ALD) reaction chamber, and evacuate the chamber to a vacuum level below 5 Pa for pretreatment to remove impurities and moisture on the surface.

[0058] Step 3: Use cerium acetylacetonate as a Ce precursor, introduce it into an atomic layer deposition (ALD) reaction chamber and heat it to 180°C. The pressure of the atomic layer deposition (ALD) reaction chamber is 0.5 Torr. Pulse the Ce precursor for 80 seconds and chemically adsorb it on the carbon substrate. Perform 5 cycles to deposit Ce atoms on the pretreated carbon substrate surface to obtain a deposited catalyst.

[0059] Step 4: Introduce nitrogen gas for purging for 120 seconds to purge excess reaction precursors and by-products out of the atomic layer deposition (ALD) reaction chamber, wash the deposited catalyst three times with methanol and dry it at 60° C. overnight to obtain a cerium single atom catalyst.

[0060] Comparative Example 1:

[0061] A commercial CeO2 catalyst.

[0062] Comparative Example 2:

[0063] Step 1: Dissolve 2.975 g zinc nitrate hexahydrate and 6.568 g 2-methylimidazole in 100 mL methanol, mix and stir for 1 hour, let stand for 24 hours, centrifuge the suspension to collect the precipitate, wash it three times with methanol, and dry it at 60° C. overnight to obtain a precursor;

[0064] Step 2: calcine the precursor in a tube furnace at 1000° C. (5° C. / min) under a nitrogen atmosphere for 3 h to obtain a CN catalyst without further treatment.

[0065] Comparative Example 3:

[0066] Step 1: directly using commercial multi-walled carbon nanotubes as the carbon matrix;

[0067] Step 2: Cerium acetylacetonate is used as a Ce precursor, introduced into an atomic layer deposition (ALD) reaction chamber and heated to 180°C. The pressure of the atomic layer deposition (ALD) reaction chamber is 0.5 Torr. The Ce precursor is pulsed for 80 seconds and chemically adsorbed on the carbon substrate. Five cycles are performed to deposit Ce atoms on the surface of the carbon substrate to obtain a deposited catalyst.

[0068] Step 3: Introduce nitrogen gas for purging for 120 seconds to purge excess reaction precursors and by-products out of the atomic layer deposition (ALD) reaction chamber, wash the deposited catalyst three times with methanol and dry it at 60° C. overnight to obtain a cerium single atom catalyst.

[0069] Comparative Example 4:

[0070] A method for preparing a cerium single atom catalyst comprises the following steps:

[0071] Step 1: Dissolve 2.975 g of zinc nitrate hexahydrate and 6.568 g of 2-methylimidazole in 100 mL of methanol, mix and stir for 1 hour, let stand for 24 hours, centrifuge the suspension to collect the precipitate, wash three times with methanol, and dry at 60°C overnight to obtain a precursor; calcine the precursor in a tubular furnace at 1000°C (5°C / min) in a nitrogen atmosphere for 3 hours to obtain a nitrogen-doped carbon matrix.

[0072] Step 2: Dissolve 1.311 g of cerium nitrate hexahydrate and the above-mentioned carbon matrix in 100 ml of methanol, mix and stir the two for 1 hour, let stand for 3 hours, collect the precipitate by centrifugation, wash three times with methanol, dry at 60°C overnight, and finally calcine at 800°C (5°C / min) in a tubular furnace under a nitrogen atmosphere for 3.5 hours to obtain Ce-CN.

[0073] The application of the catalysts prepared in the above examples and comparative examples was further studied, and they were applied to the activity evaluation method of catalytic ozone oxidation, and the specific steps were as follows:

[0074] Semi-continuous catalytic ozonation experiment was carried out in a round-bottom flask. Ozone was produced by an ozone generator and pre-operated for 20 minutes before the start to achieve a constant gaseous ozone concentration. The concentration of ozone was controlled by controlling the working current of the ozone generator. After stabilization, 100 mg of the catalyst of the comparative example (1-4) and the embodiment (1-4) and 500 ml of ibuprofen solution with a mass concentration of 10 mg / L were stirred and mixed in a round-bottom flask. The experiment was run for 60 minutes, wherein sampling and filtration were performed at 0, 5, 10, 15, 20, 30, 40, and 60 minutes, and quenched with N2. Finally, the concentration of ibuprofen was detected by high performance liquid chromatography to evaluate the catalytic activity of the catalyst.

[0075] The calculation method of ibuprofen degradation efficiency is shown in formula (1):

[0076]

[0077] The above evaluation results are Figure 2 It can be seen that the ibuprofen removal rate reached 85% at 20 minutes by using the single-atom catalyst prepared in Examples 1 to 4 of the present invention to catalyze the degradation of ibuprofen by ozone; at 60 minutes, the ibuprofen removal rate reached more than 99% by using Examples 1 to 3 of the present invention, and the degradation efficiency of the embodiments for ibuprofen was about 85%; while the removal rate of ibuprofen by catalyzing the oxidative degradation of ozone using the commercially available CeO2 catalyst in Comparative Example 1 was only 50%; the removal rate of ibuprofen by catalyzing the oxidative degradation of ozone using the catalyst in Comparative Example 2 was 77%, and the removal rates of ibuprofen by catalyzing the oxidative degradation of ozone using the catalyst in Comparative Examples 3 and 4 were 52% and 65%, respectively, indicating that the activity of the catalyst prepared by the present invention is better than that of the catalyst in the comparative example.

[0078] In summary, the preparation method of a cerium single atom catalyst proposed in the present invention can prepare a catalyst with high activity and stability, can maximize the utilization of active metal sites, is environmentally friendly, and has broad application prospects in environmental catalytic oxidation processes; and due to the customizability of the single atom coordination structure, some unique oxidation behaviors may occur in the catalytic ozonation process, which is of great significance for the degradation of organic pollutants.

[0079] Parts not described in the present invention can be implemented by referring to the existing technology.

[0080] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit of the present application, appropriate changes and modifications to the above embodiments should fall within the scope of protection of the claims of the present application.

Claims

1. A method for preparing a cerium single atom catalyst, characterized in that: The following steps are involved: a. dissolving a certain amount of zinc nitrate hexahydrate and 2-methylimidazole in methanol, mixing, stirring and standing to obtain a suspension; centrifuging the suspension, collecting the precipitate, washing and drying the precipitate to obtain a precursor; placing the precursor in a tube furnace under an inert atmosphere for carbonization treatment to obtain a nitrogen-doped carbon matrix; b. placing the nitrogen-doped carbon substrate in an atomic layer deposition reaction chamber for pretreatment to remove impurities and moisture on its surface, thereby obtaining a pretreated carbon substrate; c. Cerium acetylacetonate is used as a Ce precursor, introduced into an atomic layer deposition reaction chamber and heated to 180-250° C., and the pressure is maintained at 0.1-2 Torr. The cerium acetylacetonate is pulse-treated for 40-150 seconds and chemically adsorbed on the pretreated carbon substrate. Several cycles are performed to deposit Ce atoms on the surface of the pretreated carbon substrate to obtain a deposited catalyst. d. Introduce inert gas to purge the atomic layer deposition reaction chamber, blow excess raw materials and by-products out of the atomic layer deposition reaction chamber, wash and dry the deposited catalyst, and obtain the catalyst.

2. The method for preparing a cerium single atom catalyst according to claim 1, characterized in that: In step a, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:1.5-10, the mixture is stirred for 0.5-1.5 hours, and then allowed to stand for 20-30 hours.

3. The method for preparing a cerium single atom catalyst according to claim 1, characterized in that: In step a, nitrogen is charged into the tubular furnace to maintain an inert atmosphere, the calcination temperature of the tubular furnace is 600-1000° C., the heating rate is 5-8° C. / min, and the calcination time is 2-4 hours.

4. The method for preparing a cerium single atom catalyst according to claim 1, characterized in that: In step a, the precipitate is washed 2 to 4 times and dried at a temperature of 50 to 70°C.

5. The method for preparing a cerium single atom catalyst according to claim 1, characterized in that: In step b, the vacuum degree in the atomic layer deposition reaction chamber is 2-8 Pa for pretreatment.

6. The method for preparing a cerium single atom catalyst according to claim 1, characterized in that: In step c, the heating temperature in the atomic layer deposition reaction chamber is 230° C., the pulse treatment is performed for 100 seconds, and 10 cycles are performed to deposit Ce atoms on the surface of the pretreated carbon substrate.

7. A cerium single atom catalyst, characterized in that: The catalyst is prepared by the method for preparing a cerium single atom catalyst as described in any one of claims 1 to 6.

8. Use of the cerium single atom catalyst according to claim 7 in catalytic ozone oxidation of refractory organic matter.

9. The use according to claim 8, characterized in that: The application is the use of cerium single-atom catalyst as a heterogeneous catalyst in the catalytic oxidation of wastewater ozone.

Images