Three-dimensional urchin-shaped catalyst and preparation method thereof

Abstract

The invention discloses a three-dimensional sea-urchin-shaped Na / Co3O4 catalyst and a preparation method thereof, the catalyst has a three-dimensional sea-urchin-shaped hierarchical morphology, is composed of radially arranged nanorods, is spherical as a whole and has a diameter of 5-10 [mu] m, and the nanorods are formed by self-assembly of Co3O4 nanoparticles. According to the preparation method, firstly, a Co3O4 carrier assembled by radial nanorods is synthesized through a hydrothermal method, alkali metal sodium is loaded on the Co3O4 carrier through an impregnation method, and the method does not need complex equipment, is simple in process and low in cost, is suitable for efficient catalytic elimination of diesel vehicle tail gas soot particles and has a large-scale application prospect.

Description

TECHNICAL FIELD

[0001] The present application discloses a three-dimensional urchin-like Na / Co3O4 catalyst and a preparation method thereof. BACKGROUND

[0002] Compared with gasoline engines, diesel engines have been widely used in the field of transportation and industry due to their high thermal efficiency, low fuel consumption and long service life. However, the soot particles emitted from diesel engine exhaust are one of the main sources of air pollution, and the carcinogenic substances such as benzopyrene and polycyclic aromatic hydrocarbons adsorbed on the surface of the soot particles pose a serious threat to human health and the ecological environment. At present, the aftertreatment scheme combining diesel particulate filter (DPF) with catalytic combustion technology is considered as the most effective soot purification method, but its large-scale application is limited by the development of high-performance catalysts. Soot catalytic combustion involves a three-phase reaction of gas (O2)-solid (catalyst)-solid (soot), and the catalytic performance is mainly limited by the synergistic regulation of the contact efficiency of soot particles and catalyst and the intrinsic redox capacity of the catalyst.

[0003] Transition metal oxide catalysts have attracted much attention in the field of soot catalytic combustion due to their variable valence and excellent redox properties. Among them, cobalt-based catalysts exhibit outstanding oxidation capacity through the cyclic transformation of Co³⁺ / Co²⁺, but their activity is limited by the contact efficiency of soot particles and active sites on the catalyst surface and high-temperature stability. In recent years, Co3O4 catalysts with hierarchical structure constructed by morphology regulation have been shown to effectively improve the contact efficiency of soot, but they still face the challenges of insufficient active oxygen species migration rate and limited low-temperature activity. SUMMARY

[0004] Therefore, the present application provides a three-dimensional urchin-like Na / Co3O4 catalyst and a preparation method thereof. The catalyst maintains high activity while having excellent hydrothermal stability and sulfur resistance, providing a new idea for efficient purification of diesel engine exhaust soot.

[0005] The technical scheme of the present application comprises a three-dimensional urchin-like Na / Co3O4 catalyst, which has a three-dimensional urchin-like hierarchical morphology composed of radially arranged nanorods, and the whole is spherical with a diameter of 5-10 μm, wherein the nanorods are composed of self-assembled Co3O4 nanoparticles.

[0006] The present application also provides a preparation method of the above-mentioned three-dimensional urchin-like Na / Co3O4 catalyst, which comprises the following steps: Step 1: Synthesis of Co3O4 carrier with radially arranged nanorods by hydrothermal method; Step 2: loading alkali metal sodium on the Co3O4 carrier by impregnation method, wherein the impregnation solution is a sodium nitrate NaNO3 solution, and the sodium nitrate NaNO3 solution is prepared by dissolving sodium nitrate NaNO3 in deionized water according to a molar ratio of Na / Co of 10%-50%.

[0007] The step 1 comprises: mixing a raw cobalt source, a precipitant, and a solvent to obtain a mixed solution; and stirring the mixed solution at room temperature to prepare a precursor solution. transferring the precursor solution into a polytetrafluoroethylene high-pressure reaction kettle, hydrothermally reacting, cooling to room temperature, centrifugally collecting precipitates, drying, and calcining in an air atmosphere to finally obtain the urchin-like Co3O4 carrier.

[0008] Preferably, the cobalt source is cobalt nitrate hexahydrate; the precipitant is urea; and the solvent is deionized water.

[0009] The hydrothermal reaction condition is 100 °C for 16 hours, and the calcination parameter is 5 °C / min to 500 °C for 3 hours.

[0010] The step 2 comprises: dropwise impregnating the sodium nitrate NaNO3 impregnation solution onto the surface of the Co3O4 carrier, and obtaining an impregnated sample after the impregnation solution fully penetrates the carrier. drying and calcining the impregnated sample to finally obtain the three-dimensional urchin-like Na / Co3O4 catalyst.

[0011] After the sodium nitrate NaNO3 impregnation solution is dropwise impregnated onto the surface of the Co3O4 carrier, ultrasonic dispersion treatment is performed for 5-15 minutes.

[0012] The impregnated sample is dried under the following conditions: constant temperature at 80 °C in an oven for 12-36 h.

[0013] Preferably, the calcination condition is 5 °C / min to 500 °C for 3 hours in an air atmosphere, and the air flow rate is 50 mL / min.

[0014] The application provides a three-dimensional urchin-shaped Na / Co3O4 catalyst and a preparation method thereof. The method is a synergistic regulation of hydrothermal synthesis and impregnation process, and a composite catalyst with hierarchical structure and high active site density is constructed. The urchin-shaped morphology significantly improves the contact efficiency of the catalyst and soot particles, and the radial nanorod array provides abundant mesoporous channels to promote reaction mass transfer; the introduction of Na regulates the Co3+ / Co2+ ratio and induces the formation of surface oxygen vacancies through electron transfer effect, thereby enhancing the activation ability of chemisorbed oxygen. In addition, the synergistic effect of Na and Co can optimize the conversion path of NO to NO2, realize the efficient transformation of the soot combustion reaction path from "gas-solid-solid" to "gas-gas-solid" through the strong oxidizing property of gaseous NO2, and significantly reduce the reaction activation energy.

[0015] The method is simple in process, good in repeatability, and free of harmful by-product generation in the reaction process, and meets the industrial application requirements of soot purification catalysts.

[0016] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the disclosure of the application. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Scanning electron microscope photos of three-dimensional urchin-shaped Co3O4 catalysts prepared in the examples; (wherein Figure A is a scanning electron microscope photo of the three-dimensional urchin-shaped Co3O4 catalyst prepared in Example 1; Figure B is a scanning electron microscope photo of the three-dimensional urchin-shaped 10% Na / Co3O4 catalyst prepared in Example 2; Figure C is a scanning electron microscope photo of the three-dimensional urchin-shaped 20% Na / Co3O4 catalyst prepared in Example 2; Figure D is a scanning electron microscope photo of the three-dimensional urchin-shaped 30% Na / Co3O4 catalyst prepared in Example 2; Figure E is a scanning electron microscope photo of the three-dimensional urchin-shaped 40% Na / Co3O4 catalyst prepared in Example 2; and Figure F is a scanning electron microscope photo of the three-dimensional urchin-shaped 50% Na / Co3O4 catalyst prepared in Example 2.) Figure 2 XRD spectrum of the three-dimensional urchin-shaped Na-loaded Co3O4 catalyst prepared in Examples 1-2. DETAILED DESCRIPTION

[0018] The exemplary embodiments will be described in detail hereinbelow with reference to the drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples of systems consistent with some aspects of the present application as detailed in the appended claims.

[0019] To address the limitations of cobalt-based catalysts via Co³⁺ / Co²⁺ in terms of contact efficiency between soot particles and active sites on the catalyst surface, as well as high-temperature stability, this invention first provides a three-dimensional sea urchin-like Na / Co3O4 catalyst. This catalyst exhibits a three-dimensional sea urchin-like hierarchical morphology, composed of radially arranged nanorods, forming an overall spherical shape with a diameter of 5-10 μm. The nanorods are self-assembled from Co3O4 nanoparticles. The nanorods in the catalyst are radially arranged along the center to form a micron-sized sea urchin-like spherical morphology, with an average pore size of 20-80 nm and a specific surface area of ​​5-18 m² / g. The catalyst exhibits distinct Co3O4 characteristic diffraction peaks and good crystallinity. The nanorods are formed by the self-assembly of Co3O4 particles with a diameter of approximately 20 nm. Figure 1 A); XRD pattern ( Figure 2 The results showed that the catalyst had characteristic diffraction peaks of spinel-type Co3O4 (JCPDS 42-1467) and good crystallinity. No diffraction peaks of Na species were observed, indicating that sodium was highly dispersed on the support surface and did not form an independent crystalline phase.

[0020] This invention also provides a method for preparing a three-dimensional sea urchin-like Na / Co3O4 catalyst, comprising the following steps: Step 1: Synthesize Co3O4 support with radial nanorod assembly via hydrothermal method; 1) Preparation of precursor solution: Cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and urea (CO(NH2)2) were dissolved in deionized water at a certain molar ratio, and the solution was magnetically stirred for 30 min until a pink transparent solution was formed. The molar ratio of the cobalt source to the precipitant (1:1-1:6) plays a key regulatory role in the morphology of the precursor: the alkaline environment (CO3²⁻, NH4⁺, OH⁻) generated by urea hydrolysis can induce the directional growth of β-CoOOH nanorod precursors.

[0021] 2) The precursor solution was transferred to a hydrothermal reactor for hydrothermal reaction; the precursor solution was transferred to a polytetrafluoroethylene-lined high-pressure reactor and hydrothermally reacted at 100 °C for 16 hours. After natural cooling, the precipitate was collected by centrifugation, dried at 80 °C for 12 hours, and then calcined in air at 5 °C / min to 500 °C for 3 hours to obtain a sea urchin-like Co3O4 support.

[0022] 3) The hydrothermal products are washed, centrifuged, dried, and calcined. Step 2: Load alkali metal sodium using the impregnation method; 1) The alkali metal Na was loaded onto the calcined product obtained in step 1 by impregnation and then dried; 2) The dried product is calcined in a tube furnace under air to obtain the three-dimensional urchin-like Na / Co3O4 catalyst.

[0023] Specifically, sodium nitrate (NaNO3) is dissolved in deionized water at a Na / Co molar ratio of 10%-50% to prepare an impregnation solution (1 mL of solution per gram of Co3O4), and ultrasonic dispersion is performed for 15 minutes to ensure uniformity. The solution is impregnated drop by drop onto the surface of the carrier, and stirring is performed for 30 minutes to allow the solution to penetrate fully. The impregnated sample is dried at 80°C for 12 hours, and then calcined at 500°C under an air atmosphere at a temperature increase rate of 5°C / min for 3 hours, with an air flow rate of 50 mL / min, to remove residual nitrate and stabilize the dispersion state of the sodium species. The reaction ratio of the Na / Co molar ratio of 10%-50% is defined as the loading amount of Na on the Co3O4 carrier.

[0024] This method synthesizes a Co3O4 carrier with radial nanorod assemblies by a hydrothermal method. The unique morphology not only provides abundant surface active sites, but also improves the diffusion and anchoring efficiency of soot particles through the gaps in the nanorod array. Further, the sodium modification regulates the electronic structure of the Co3O4 surface, strengthens the oxidation ability of the Co³⁺-O⁻ active site, and promotes dynamic contact at the reaction interface using the mobility of Na⁺.

[0025] The introduction of alkali metal Na can adjust the Co³⁺ proportion on the Co3O4 surface through an electron donor effect, enhance the oxygen vacancy concentration and the activation ability of chemisorbed oxygen, and the low melting point characteristic can promote the dynamic contact between soot and the catalyst.

[0026] The catalyst prepared as described above is used in the catalytic combustion reaction of soot particles, and has high catalytic activity, in which soot particles can be completely removed at less than 400°C.

[0027] To better illustrate the technical means and product effects of the present application, the preferred embodiments of the present application are described below.

[0028] Example 1 4.36 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 2.40 g of urea (CO(NH2)2) are dissolved in 96 mL of deionized water, and magnetic stirring is performed for 30 min until the solution is pink and clear and transparent. The mixed solution is transferred to a 150 mL polytetrafluoroethylene-lined reaction kettle, and hydrothermal reaction is performed in a 100°C oven for 16 h. After the reaction is completed, natural cooling is performed, and the purple precipitate is collected by centrifugation at a rotation speed of 8000 revolutions per minute for 5 minutes. The precipitate is washed with deionized water and ethanol three times each, and dried at 80°C for 12 h. Subsequently, the dried sample is placed in a tube furnace, and calcined at 500°C under an air atmosphere at a temperature increase rate of 5°C / min for 3 h to obtain urchin-like Co3O4 carriers.

[0029] In the above preparation method, urea acts as a precipitant, providing an alkaline medium under high temperature and pressure. The alkaline medium in the urea hydrolysate includes CO3. 2- NH 4+ and OH - These elements have a crucial influence on nucleation and subsequent crystal growth, thus controlling the morphology of the product. For example... Figure 1 As shown, the urchin-like Co3O4 support prepared in this embodiment is as follows: Figure 1 As shown in Figure A, the synthesized Co3O4 support exhibits a complete sea urchin-like structure, with nanorods arranged radially from a central point. The nanorods have a diameter of approximately 50 nm, and the overall spherical structure has a diameter of approximately 7 μm. Table 1 shows the activity test results of the three-dimensional sea urchin-like Co3O4 catalyst in catalytic combustion of soot particles, compared with the combustion temperature (T) of pure soot particles without a catalyst. 10 T 50 and T 90 Compared to 461 °C, 552 °C and 594 °C respectively, the T of the urchin-shaped Co3O4 catalyst... 10 T 50 and T 90 The combustion temperatures were 274 °C, 327 °C and 359 °C, respectively, which significantly reduced the combustion temperature of the soot. This is attributed to the strong redox ability and special microstructure of Co3O4.

[0030] Table 1 Catalytic activity of the prepared soot combustion catalyst Example 2 Using the Co3O4 prepared in Example 1 as a carrier, the corresponding mass of NaNO3 was weighed according to the molar ratio of Co3O4 to sodium nitrate (NaNO3) of 1:0.1 (Na / Co molar ratio 10%), 1:0.2 (Na / Co molar percentage 20%), 1:0.3 (Na / Co molar percentage 30%), 1:0.4 (Na / Co molar percentage 40%), and 1:0.5 (Na / Co molar percentage 50%).

[0031] Taking 30% Na / Co3O4 as an example: Take 4.15 mmol of Co3O4 support and add 0.415 mmol of NaNO3. Dissolve NaNO3 in 1 mL of deionized water, sonicate for 15 min, and add it dropwise and evenly to the Co3O4 powder while stirring until the slurry is homogeneous. After the mixture is allowed to stand at room temperature for 2 h, it is dried at 80°C for 12 h, and then calcined in air at 500°C for 3 h at a heating rate of 5 °C / min to finally obtain the 30% Na / Co3O4 catalyst.

[0032] The preparation method of the remaining load (10%, 20%, 40%, 50%) is the same, only adjust the amount of NaNO3. As Figure 1 A-F, the prepared catalysts all present urchin-like spheres with a diameter of about 7 μm, in which the nanorods are radially arranged from the center to each direction. The morphology of the low content Na loaded catalysts (10%Na / Co3O4, 20%Na / Co3O4) has no obvious change, indicating that the morphology of Co3O4 is not destroyed by Na loading under this condition. However, with the increase of the loading amount of sodium, the integrity of the morphology is destroyed, as Figure 1 F shows that some rod-like structures on the surface of the catalyst have been broken, and a large number of broken rod-like structures have gathered on the surface of the catalyst.

[0033] Figure 2 XRD diffraction patterns of Co3O4 and Na / Co3O4 catalysts are shown. The diffraction peaks of the catalysts are located at 2θ = 19.2°, 31.5°, 37.2°, 45.2°, 59.7° and 65.6°, which are highly consistent with the characteristic peaks of Co3O4 phase (marked as “▼”, JCPDS card No. 42-1467). The peak position of the prepared Na / Co3O4 catalyst is consistent with that of Co3O4, indicating that Na is highly dispersed on the surface of the Co3O4 carrier and does not affect the spinel structure of Co3O4. In Figure 2 no other diffraction peaks are observed, which may be due to the good dispersion of Na on the surface of the Co3O4 carrier. With the increase of the Na-Co ratio, the half-peak width of the Co3O4 diffraction peak becomes wider and the peak intensity decreases, indicating that the addition of Na inhibits the crystallization of Co3O4 to some extent. Compared with the 10%Na / Co3O4 catalyst, the peak at about 37.2° in the cobalt spinel lattice plane (311) is lower, especially the diffraction peak position of the lattice plane (211) of the 30%Na / Co3O4 catalyst decreases from 37.2° to 36.8°, which is due to the entry of Na into the Co3O4 lattice, thereby increasing the lattice spacing.

[0034] Table 2 is a test table of the activity of three-dimensional urchin-like Na loaded Co3O4 catalysts for catalytic combustion of soot particles. With the increase of the loading amount of alkali metal Na, the activity of the catalysts shows a trend of first increasing and then decreasing, among which the 30%Na / Co3O4 shows the best catalytic activity of soot, T 10 , T 50 and T 90 are 268 °C, 301 °C and 326 °C respectively, indicating that the appropriate loading of Na can significantly improve the catalytic combustion activity of soot.

[0035] Table 2 catalytic activity of the prepared soot combustion catalysts Example 3 Evaluation method of catalyst activity: using gas chromatography detection system, the catalyst adopts fixed bed mode Specific steps: the weighed three-dimensional sea urchin-shaped Na loaded Co3O4 catalyst and soot particles are placed on the weighing paper, stirred uniformly with a medicine spoon, and then the catalyst is placed in a 6 mm quartz reaction tube, wherein the gas flow is controlled at 50 mL / min, the volume content of NO in the gas is 2000 ppm, the volume content of O2 is 10%, and the balance is Ar; the temperature rising rate is controlled at about 2 °C / min.

[0036] Evaluation method: the oxidation ability of the catalyst is represented by the combustion temperature of the soot particles, wherein the ignition temperature (T 10 ), the temperature corresponding to the maximum combustion rate (T 50 ), and the burnout temperature (T 90 ) represent the temperature points corresponding to 10%, 50%, and 90% of the completion of soot combustion, respectively. The calculation method is to integrate the CO2 and CO curves generated by the combustion of carbon black in the programmed temperature oxidation reaction, and the temperature points corresponding to 10%, 50%, and 90% of the sum of the CO2 and CO integral areas are T 10 , T 50 , and T 90 , respectively. Wherein S CO2 m represents the CO2 selectivity of the catalyst at the maximum combustion rate of soot. The results of the catalytic combustion of pure soot particles are shown in Table 3. As can be seen from Table 2 and Table 3, in the absence of a catalyst, the combustion temperature of pure soot is relatively high. In particular, the 30% Na / Co3O4 catalyst involved in the present application exhibits excellent performance in soot catalytic combustion, with high active oxygen species concentration, strong NO x conversion ability, good stability, and good water and sulfur resistance. It shows that the three-dimensional sea urchin-shaped Na loaded Co3O4 catalyst prepared in the present application has high catalytic activity for the catalytic combustion of soot particles.

[0037] Table 3 Catalytic combustion activity of pure soot particles Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. Various modifications and variations can be made to the embodiments of the application without departing from the spirit or scope of the application. This application is intended to cover any alternatives, modifications, or equivalents, which include known or customary practice within the art to which this application pertains. The specification and examples are to be considered exemplary only, with the true scope and spirit of the application indicated by the claims.

[0038] It should be understood that the application is not limited to the precise construction which has been described above and which shown in the drawings, and that various modifications and changes can be made by those skilled in the art without departing from the scope of the application. The scope of the application should be limited only by the appended claims.

Claims

1. A three-dimensional sea urchin-like Na / Co304 catalyst, characterized in that, The catalyst has a three-dimensional urchin-like hierarchical morphology, which is composed of radially arranged nanorods, and the whole is spherical with a diameter of 5-10 μm, wherein the nanorods are self-assembled by Co3O4 nanoparticles.

2. The method for preparing the three-dimensional sea urchin-like Na / Co3O4 catalyst according to claim 1, characterized in that, The method comprises the following steps: Step 1: synthesizing a Co3O4 carrier with radially arranged nanorods by a hydrothermal method; Step 2: loading alkali metal sodium on the Co3O4 carrier by an impregnation method, wherein the impregnation solution is a sodium nitrate NaNO3 solution, and the sodium nitrate NaNO3 solution is prepared by dissolving sodium nitrate NaNO3 in deionized water according to a molar ratio of Na / Co of 10%-50%.

3. The method for preparing the three-dimensional sea urchin-like Na / Co3O4 catalyst according to claim 2, characterized in that, The step 1 comprises: Mixing a cobalt source, a precipitator and a solvent to obtain a mixed solution; stirring the mixed solution at room temperature to prepare a precursor solution; Transferring the precursor solution into a polytetrafluoroethylene high-pressure reaction kettle, hydrothermally reacting, cooling to room temperature, centrifuging to collect the precipitate, drying, and calcining in an air atmosphere to finally obtain a urchin-like Co3O4 carrier.

4. The method for preparing the three-dimensional sea urchin-like Na / Co3O4 catalyst according to claim 3, characterized in that, The cobalt source is cobalt nitrate hexahydrate; the precipitator is urea; and the solvent is deionized water, wherein the molar ratio of cobalt nitrate hexahydrate to urea is 1:1-1:

6.

5. The method for preparing the three-dimensional sea urchin-like Na / Co3O4 catalyst according to claim 3, characterized in that, The hydrothermal reaction condition is 100℃ for 16 hours; and the calcination parameter is 5℃ / min to 500℃ for 3 hours.

6. The method for preparing the three-dimensional sea urchin-like Na / Co3O4 catalyst according to claim 2, characterized in that, The step 2 comprises: Dropping the sodium nitrate NaNO3 impregnation solution onto the surface of the Co3O4 carrier, and obtaining an impregnated sample after the impregnation solution fully penetrates the carrier; Drying and calcining the impregnated sample to finally obtain a three-dimensional urchin-like Na / Co3O4 catalyst.

7. The method for preparing the three-dimensional sea urchin-like Na / Co3O4 catalyst according to claim 6, characterized in that, After the sodium nitrate NaNO3 impregnation solution is dropped onto the surface of the Co3O4 carrier, ultrasonic dispersion treatment is performed for 5-15 minutes.

8. The method for preparing the three-dimensional sea urchin-like Na / Co3O4 catalyst according to claim 6, characterized in that, The impregnated sample is dried under the following conditions: 80℃ constant temperature in an oven for 12-36h.

9. The method for preparing the three-dimensional sea urchin-like Na / Co3O4 catalyst according to claim 6, characterized in that, The calcination condition is 5℃ / min to 500℃ in an air atmosphere for 3 hours, and the air flow rate is 50mL / min.

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