Preparation method and application of plasma catalyst

Abstract

The invention discloses a preparation method and application of a plasma catalyst, and belongs to the field of environmental catalytic materials. Aiming at the problems of insufficient micro discharge quantity, low energy efficiency, easy catalyst deactivation and the like in the existing plasma catalysis technology, the invention provides the hollow fibrous perovskite type titanate composite catalyst. According to the catalyst, a carrier is prepared by combining a coaxial electrostatic spinning technology with a gradient calcination process, and then a transition metal active component is loaded, so that the plasma discharge intensity and the pollutant degradation efficiency are remarkably enhanced.

Description

Technical Field

[0001] This invention belongs to the field of environmental catalytic materials, specifically relating to a hollow fibrous perovskite catalyst and its preparation method, as well as the application of the catalyst in the synergistic catalytic removal of nitrogen oxides (NOx) and volatile organic compounds (VOCs) by low-temperature plasma (NTP). Background Technology

[0002] Nitrogen oxides (NO) x ) and volatile organic compounds (VOCs) as PM 2.5 And O3 is an important precursor, and their synergistic emission reduction is PM2.5. 2.5 The key to synergistic governance of NO and O3. NO in flue gas from furnaces and kilns in industries such as cement, steel, and chemicals. x It usually coexists with VOCs, and with the increase of NO in the coal-fired industry x With increased efforts to reduce emissions, industrial flue gas is a major contributor to NOx emissions. x The key to emission reduction is to control VOCs emissions in flue gas, which is also an essential way to reduce the total VOCs emissions in my country.

[0003] Low-temperature plasma (NTP) can break complex chemical bonds and initiate physical and chemical reactions at low temperatures, making it a potential technology for the synergistic control of multiple pollutants. In the NTP system, oxygen free radicals •O and their derivatives O3 are the main reactive species involved in oxidation reactions. They can oxidize VOCs into CO2 and H2O, and can also oxidize NO to NO2 through reactions such as •O + NO + M → NO2 + M and O3 + NO → NO2 + O2, thereby further converting it into nitrogen gas through selective catalytic reduction. In NTP reaction systems, the active species are closely related to discharge characteristics; higher discharge intensity and density are more conducive to the generation of active substances. Within a certain range, the higher the dielectric constant of the reactor packing material, the higher the discharge intensity (Chen et al., Journal of Hazardous Materials, 2022, 427, 128150). Moreover, when the pore size of the packing medium is larger than the Debye radius of the plasma, micro-discharges will occur in the pores, further enhancing the discharge intensity (Zhang et al., Applied Catalysis B: Environmental, 2016, 185, 56-67). Therefore, based on the above theoretical foundations, this invention designs the structure of the plasma catalyst to prepare a packing material with a high dielectric constant and abundant micron-sized pores to generate more active species and improve the removal efficiency of pollutants.

[0004] Currently, the design and preparation of plasma catalysts mainly focus on changing the catalyst structure or active components to enhance the adsorption and catalytic capabilities of the materials, thereby improving the plasma catalytic efficiency, such as CN117599802A, CN120285989A, CN117643885A, and CN119857490A. Although the intrinsic activity and adsorption performance of the catalysts have been improved, the number of micro-discharges and the discharge characteristics of the plasma have not been increased, thus failing to effectively improve the energy efficiency of plasma catalysis. Summary of the Invention

[0005] To address the problems of insufficient micro-discharge quantity, low energy efficiency, and easy catalyst deactivation in existing plasma catalysis technologies, this invention provides a hollow fibrous perovskite-type plasma catalyst. Through coaxial electrospinning combined with gradient calcination, the dielectric constant of the support and the micron-level pores are synergistically controlled, and transition metal active components are loaded, significantly improving plasma discharge intensity and pollutant degradation efficiency.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a plasma catalyst, the method comprising the following steps:

[0008] Step 1: Prepare the inner layer spinning solution: Dissolve the polymer in an organic solvent to form a solution with a mass concentration of 5-10%, which will be used to prepare the inner layer spinning solution;

[0009] Step 2: Preparation of outer spinning solution: Mix the nitrate precursor of A required for the perovskite titanate ATiO3 to be prepared with tetrabutyl titanate, then add polyvinylpyrrolidone and ethanol and stir for 20-30 hours to obtain the outer spinning solution.

[0010] Step 3: Coaxial electrospinning: The inner and outer spinning solutions are pushed into the spinning equipment, and the inner and outer spinning solutions are electrospinned under high pressure through a coaxial nozzle to form composite fibers.

[0011] Step 4: Gradient calcination: The coaxial electrospun composite fiber is first calcined to remove the template, and then crystallized to prepare hollow fibrous perovskite titanate ATiO3.

[0012] Step 5: Loading the active component: Immerse the hollow fibrous titanate ATiO3 support prepared in step 4 into a solution prepared with transition metal salt, then sonicate in a water bath for 2-4 hours, let it stand for 10-12 hours, and then calcine to obtain the plasma catalyst.

[0013] In the above preparation method: the polymer in step 1 is paraffin oil, mineral oil or polyacrylonitrile, and the organic solvent is N,N-dimethylformamide.

[0014] In the above preparation method: the perovskite titanate A in step 2 is at least one of Sr, Ba, Pr, and Bi; and the molar ratio of A:Ti is 1~5:1~5; the viscosity of the outer spinning solution is 20-50 cP.

[0015] In the above preparation method: the molar ratio of A:Ti in step 2 is 1~3:1~3.

[0016] In the above preparation method: in step 3, the inner spinning solution propulsion rate is 0.05-0.1 ml / min, the outer spinning solution propulsion rate is 0.1-0.3 ml / min, the needle diameter in coaxial electrospinning is 0.5-2 mm, the voltage is 12-15 kV, and the receiving plate temperature is 80-110℃; during coaxial electrospinning, the temperature is 30±5℃, the relative humidity is 40%-80%, and the spinning collection distance is 25±5 cm.

[0017] In the above preparation method: the conditions for calcination to remove the template in step 4 are to first raise the temperature to 400-500℃ at 1~5℃ / min and then hold it for 1~3h; the conditions for crystallization are to first raise the temperature to 800-900℃ at 3~8℃ / min and then hold it for 3~8h.

[0018] In the above preparation method: in step 5, the transition metal salt is one or two of the nitrate, acetate, and chloride salts of iron, manganese, copper, cerium, and cobalt; the solvent used in the solution prepared by the transition metal salt is water and ethylene glycol in a mass ratio of 1~3:1~3.

[0019] In the above preparation method: the total loading of active components in step 5 is 5-15 wt%, and the calcination temperature is increased to 400-600℃ at 5℃ / min and held for 6-8 hours.

[0020] A plasma catalyst, prepared by the above method, preferably having an outer diameter of 5-15 μm, an inner diameter of 3-10 μm, and a dielectric constant of 200-10000.

[0021] In the technical solution of the present invention, the catalyst prepared by the method is used in the fields of plasma-co-catalytic removal of gaseous pollutants and synthesis of chemical raw materials. More preferably, the catalyst is filled in a dielectric barrier discharge reactor for use in the field of plasma catalysis.

[0022] Furthermore, the catalyst is filled into a dielectric barrier discharge reactor for use in the field of plasma catalysis, particularly for the removal of nitrogen oxides (NOx) and volatile organic compounds (VOCs).

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) The hollow fibrous perovskite-type titanate composite catalyst prepared by the present invention can improve the abundance of micron-sized pores in the hollow channels and between the fibers. In addition, the titanate matrix has the characteristic of high dielectric constant, which can significantly enhance the discharge intensity and micro-discharge of the dielectric barrier discharge reactor, thereby increasing the number of active species.

[0025] (2) The hollow fibrous perovskite titanate composite catalyst prepared by the present invention has hollow channels that can promote gas diffusion and provide abundant adsorption sites. The loaded active components enhance the abundance of active sites, which can not only effectively improve the treatment effect of nitrogen oxides and volatile organic compounds in the plasma catalytic system, but also effectively suppress the emission of by-products during the plasma reaction process.

[0026] (3) The hollow fibrous structure and fiber network structure of the present invention can effectively resist airflow erosion, are more stable, and have a longer lifespan than powder catalysts. Attached Figure Description

[0027] The accompanying drawings, together with the embodiments of the present invention, are used to explain the present invention and do not constitute a limitation thereof.

[0028] Figure 1 This is a schematic diagram of the hollow fibrous perovskite titanate composite catalyst prepared in this invention.

[0029] The network perovskite structure is specifically illustrated on a macroscopic scale, exhibiting a hollow fibrous structure with a continuous, long-range fibrous morphology.

[0030] Perovskite nanofibers are specifically illustrated at the microscale. They are fibrous with a distinct hollow structure, and the stacked fibers form a micron-sized structure.

[0031] The perovskite hollow fiber structure is specifically a single hollow fiber filament. The hollow fiber is micron-sized and has metal active sites loaded on its inner and outer surfaces.

[0032] The perovskite crystal structure is specifically illustrated at the atomic scale, forming an ABO3 perovskite-type structure.

[0033] Figure 2 This is a schematic diagram of the synthesis route of the composite catalyst prepared in this invention.

[0034] Figure 3 This is a SEM image of the catalyst prepared in Example 1 of this invention.

[0035] Figure 4 This is a comparison of the discharge characteristics of the catalyst prepared in Example 1 of the present invention.

[0036] Figure 5 This is a comparison of the ozone production of the catalyst prepared in Example 1 of the present invention.

[0037] Figure 6 This is a performance comparison of the catalyst prepared in Example 3 of the present invention. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The embodiments of the present invention are not limited thereto; for process parameters not specifically specified, conventional techniques can be referred to. If those skilled in the art, inspired by this application, design similar structural methods and embodiments without departing from the spirit of this application, such designs should fall within the protection scope of this application.

[0039] Example 1

[0040] Step 1: Dissolve polyacrylonitrile (PAN) in N,N-dimethylformamide (DMF) to prepare an 8wt% solution, and stir magnetically for 6 hours until transparent to obtain the inner layer spinning solution.

[0041] Step 2: Take Sr(NO3)2 and tetrabutyl titanate (Sr:Ti=1:1 molar ratio), add polyvinylpyrrolidone (PVP, 10wt%) and ethanol (20vol%), stir for 24h until the viscosity is 35cP, and obtain the outer spinning solution.

[0042] Step 3: Perform coaxial electrospinning with the following parameters: inner layer feed rate, 0.08 ml / min; outer layer feed rate, 0.2 ml / min; needle diameter: 1.0 mm; voltage: 14 kV; receiving plate temperature: 100℃; ambient temperature: 30℃, humidity: 60%, collection distance: 25 cm.

[0043] Step 4: Perform gradient calcination. In the first stage, the temperature is increased to 450℃ at 2℃ / min and held for 2h (to remove PAN / PVP). In the second stage, the temperature is increased to 850℃ at 5℃ / min and held for 5h to obtain SrTiO3 hollow fibers (outer diameter 10μm, inner diameter 6μm, dielectric constant 5000).

[0044] Step 5: Loading of Cu / Ce active components. Copper nitrate and cerium nitrate (Cu:Ce = 3:1 molar ratio) were dissolved in a mixed solution of water and ethylene glycol (volume ratio 1:1). SrTiO3 fibers were impregnated with the solution in equal volume, and the mixture was ultrasonically treated in a water bath for 2 hours and then allowed to stand for 11 hours. The solution was then calcined at 500℃ for 7 hours with a heating rate of 5℃ / min. The total Cu-Ce loading was 10wt%, resulting in the final hollow fiber Cu-Ce / SrTiO3 catalyst.

[0045] Catalyst performance evaluation: First, the discharge characteristics and the yield of active species O3 of hollow fibrous SrTiO3 and solid SrTiO3 prepared in step four were compared (see...). Figure 4 and Figure 5 The waveform diagrams showed that the micro-discharge density of hollow fibrous SrTiO3 was significantly better than that of solid SrTiO3, and the ozone production was also higher. 0.2 g of the catalyst prepared in step five was placed in the discharge region of the plasma reactor, and toluene gas at a concentration of 100 ppm was introduced into the reactor. Different energy densities (0~500 J / L) were adjusted to degrade toluene, and the toluene concentration at the reactor outlet was recorded. As the energy density increased, the toluene concentration at the reactor outlet tended to stabilize, and ultimately the toluene removal rate of hollow fibrous Cu-Ce / SrTiO3 was >95%, significantly higher than the 68% without catalyst filling.

[0046] Example 2

[0047] Step 1: Dissolve paraffin oil in N,N-dimethylformamide to prepare a 10wt% solution, and stir magnetically for 5 hours until transparent to obtain the inner spinning solution.

[0048] Step 2: Take Ba(NO3)2 and tetrabutyl titanate (Ba:Ti=1:1 molar ratio), add polyvinylpyrrolidone (PVP, 5wt%) and ethanol (20vol%), stir for 24h until the viscosity is 30cP, and obtain the outer spinning solution.

[0049] Step 3: Perform coaxial electrospinning with the following parameters: inner layer feed rate, 0.1 ml / min; outer layer feed rate, 0.15 ml / min; needle diameter: 1.0 mm; voltage: 14 kV; receiving plate temperature: 90℃; environmental control temperature: 30℃, humidity: 60%, collection distance: 20cm.

[0050] Step 4: Perform gradient calcination. In the first stage, the temperature is increased to 450℃ at 2℃ / min and held for 2h. In the second stage, the temperature is increased to 850℃ at 5℃ / min and held for 5h to obtain BaTiO3 hollow fibers (outer diameter 12±2μm, inner diameter 8±1μm, dielectric constant 5200).

[0051] Step 5: Loading of Cu-Ce active components. Copper nitrate and cerium nitrate (Cu:Ce = 3:1 molar ratio) were dissolved in a mixed solution of water and ethylene glycol (volume ratio 1:1). BaTiO3 fibers were impregnated with an equal volume of the solution, ultrasonicated in a water bath for 2 hours, and then allowed to stand for 11 hours. The solution was then calcined at 500℃ for 7 hours with a heating rate of 5℃ / min. The total Cu-Ce loading was 10wt%, resulting in the final hollow fiber Cu-Ce / BaTiO3 catalyst.

[0052] Catalyst performance evaluation: 0.15 g of catalyst was packed into a dielectric barrier discharge reactor, and different energy densities (100~600 J / L) were adjusted to treat a simulated gas of 500 ppm acetone.

[0053] Catalyst type Acetone removal rate <![CDATA[O3 decomposition rate]]> <![CDATA[Example 2 (Cu-Ce / BaTiO3)]]> 96% 90% Comparative example (MnOx / cordierite) 60% 40%

[0054] Example 3

[0055] Hollow fiber Fe-Mn / SrTiO3 catalyst was prepared, with the hollow fiber SrTiO3 support prepared using the same method as in Example 1. The Fe-Mn bimetallic active components were loaded as follows: Fe(NO3)3 and Mn(CH3COO)2 (Fe / Mn = 1:2 molar ratio) were dissolved in a mixed solution of water and ethylene glycol (volume ratio 1:1), and the hollow fiber SrTiO3 support was impregnated with an equal volume. After ultrasonication in a water bath for 4 hours, the solution was allowed to stand for 12 hours. The solution was then calcined at 500℃ for 6 hours with a heating rate of 5℃ / min. The total Fe-Mn loading was 10wt%, yielding the final hollow fiber Fe-Mn / SrTiO3 catalyst.

[0056] Catalyst performance evaluation: At room temperature, 0.25 g of the above catalyst was placed in a quartz-medium plasma reactor, and different energy densities (100~500 J / L) were adjusted to simultaneously treat simulated waste gas with NO 1000 ppm and toluene 100 ppm (O2 5% and N2 balance gas), at a temperature of 30℃ and a space velocity of 60,000 h⁻¹. The trends of NO and toluene removal rates with energy density are shown below. Figure 6 The results showed that the final hollow fibrous Fe-Mn / SrTiO3 achieved a stable toluene removal rate of over 98% and a NO conversion rate of around 60%, which were significantly higher than the efficiency without catalyst packing.

[0057] Example 4

[0058] Hollow fiber Mn-Ce / PrTiO3 catalyst was prepared. In the preparation process of the hollow fiber PrTiO3 support, the outer spinning solution was Pr(NO3)3 + tetrabutyl titanate (molar ratio 1:1), with 8wt% PVP and ethanol (20 vol%) added, and stirred for 24 h until the viscosity reached 45 cP. The remaining steps were the same as in Example 2. The operation of loading the Mn-Ce bimetallic active components was as follows: Mn(NO3)2 and Ce(NO3)3 (Mn / Ce = 1:4 molar ratio) were dissolved in a mixed solution of water and ethylene glycol (volume ratio 1:1), and the hollow fiber PrTiO3 support was impregnated with an equal volume. After ultrasonication in a water bath for 4 h, it was allowed to stand for 12 h. The temperature was increased to 600℃ at 5℃ / min and calcined for 6 h. The total Mn-Ce loading was 12wt%, and the final hollow fiber Mn-Ce / PrTiO3 catalyst was obtained.

[0059] Catalyst performance evaluation: At room temperature, 0.25g of the above catalyst was placed in a quartz-medium plasma reactor, and different energy densities (100~600J / L) were adjusted to treat simulated waste gas containing 800ppm NO and 300ppm acetone (O2 5% and N2 balance gas). The performance comparison at a temperature of 30℃, a space velocity of 100,000 h⁻¹, and an energy density of 500J / L is as follows:

[0060] Catalyst type NO conversion rate Acetone degradation rate <![CDATA[CO2 selectivity]]> <![CDATA[Example 4 (Fe-Mn / PrTiO3)]]> 52% 98% 96% <![CDATA[Pure PrTiO3]]> 35% 72% 68% Blank (no fill) 28% 65% 60%

Claims

1. A method for preparing a plasma catalyst, characterized by The method comprises the following steps: Step 1: preparing the inner layer spinning solution: dissolving the high molecular polymer in the organic solvent to form a solution with a mass concentration of 5-10%, thereby obtaining the inner layer spinning solution; Step 2: preparing the outer layer spinning solution: mixing the nitrate precursor of A required by the perovskite titanate ATiO3 to be prepared with tetrabutyl titanate, and then adding polyvinylpyrrolidone and ethanol for stirring, thereby obtaining the outer layer spinning solution; Step 3: coaxial electrospinning: pushing the inner layer spinning solution and the outer layer spinning solution into the spinning equipment, and forming the composite fiber through coaxial nozzle high-voltage electrospinning of the inner and outer spinning solutions; Step 4: gradient calcination: calcining the coaxial electrospun composite fiber to remove the template, and then crystallizing, thereby obtaining the hollow fibrous perovskite titanate ATiO3; Step 5: loading active components: immersing the hollow fibrous titanate ATiO3 carrier prepared in step 4 into a solution of transition metal salt, and then performing water bath ultrasonic treatment for 2-4 h, standing for 10-12 h, and calcining after standing, thereby obtaining the plasmonic catalyst.

2. The method of claim 1, wherein: In step 1, the high molecular polymer is paraffin oil, mineral oil or polyacrylonitrile, and the organic solvent is N,N-dimethylformamide.

3. The method of claim 1, wherein: In step 2, the perovskite titanate A is at least one of Sr, Ba, Pr and Bi; and the molar ratio of A:Ti is 1-5:1-5; and the viscosity of the outer layer spinning solution is 20-50 cP.

4. The method of claim 3, wherein: In step 2, the molar ratio of A:Ti is 1-3:1-3.

5. The method of claim 1, wherein: In step 3, the pushing rate of the inner layer spinning solution is 0.05-0.1 ml / min, the pushing rate of the outer layer spinning solution is 0.1-0.3 ml / min, the needle diameter in the coaxial electrospinning is 0.5-2 mm, the voltage is 12-15 kV, and the receiving plate temperature is 80-110℃; the temperature during the coaxial electrospinning is 30±5℃, the relative humidity is 40%-80%, and the spinning collection distance is 25±5 cm.

6. The method of claim 1, wherein: In step 4, the conditions for calcining to remove the template are first increasing to 400-500℃ at 1-5℃ / min and then maintaining the temperature for 1-3 h; and the conditions for crystallization are first increasing to 800-900℃ at 3-8℃ / min and then maintaining the temperature for 3-8 h.

7. The method of claim 1, wherein: In step 5, the transition metal salt is one or two of the nitrate, acetate and chloride of iron, manganese, copper, cerium and cobalt; and the solvent used for the solution of the transition metal salt is water and ethylene glycol with a mass ratio of 1-3:1-3.

8. The method of claim 1, wherein: In step 5, the total loading amount of the active components is 5-15 wt%, and the calcination temperature is increased to 400-600℃ at 5℃ / min and maintained for 6-8 h.

9. A plasma catalyst, characterized by: The catalyst fiber has an outer diameter of 5-15 μm, an inner diameter of 3-10 μm and a dielectric constant of 200-10000.

10. The catalyst prepared by the method of claim 1 is used in the fields of plasma synergistic catalytic removal of gaseous pollutants and synthesis of chemical raw materials, and is further preferably filled in a dielectric barrier discharge reactor for use in the field of plasma catalysis.

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