Method for photocatalytic degradation of hfc-134a by synergistic effect of light and heat

Abstract

The application belongs to the technical field of materials, and provides a method for photothermal synergistic catalytic degradation of tetrafluoroethane HFC-134a, which comprises the following steps: placing a manganese dioxide catalyst in a reactor, heating the reactor, introducing a reaction gas, and then performing light irradiation, and the method is completed; the manganese dioxide catalyst is at least one of alpha-MnO2, beta-MnO2, gamma-MnO2, delta-MnO2 and epsilon-MnO2. Through the design of oxygen vacancy-acid site double active centers, a 99.8% degradation rate is achieved within 10 min at 220 DEG C and normal pressure; a modular photothermal reactor is used on the equipment side, and light-heat field coupling and gas chromatography online sampling are completed in the same cavity, so that the problems of low energy utilization rate and large temperature gradient caused by traditional 'light-heat separation' are solved; on the process side, a four-variable coupling model of 'light intensity-temperature-humidity-oxygen concentration' is established, the degradation conditions are optimized, and a degradation model is established.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a method for photothermal synergistic catalytic degradation of tetrafluoroethane HFC-134a. Background Technology

[0002] Waste refrigerant disposal is a crucial issue in environmental science and technology. With the large-scale application of synthetic refrigerants, the amount of waste refrigerants generated is constantly increasing, and their environmental harm is becoming increasingly significant. HFC-134a (tetrafluoroethane), a widely used fluorinated refrigerant, has a significant greenhouse effect, with a global warming potential (GWP) as high as 1430, posing a serious threat to the environment. Existing waste refrigerant degradation technologies, such as incineration pyrolysis, plasma methods, and catalytic decomposition, generally suffer from drawbacks such as high energy consumption, high cost, and the potential for secondary environmental problems caused by degradation products.

[0003] Photothermal synergistic catalysis technology has attracted widespread attention due to its ability to simultaneously utilize the synergistic effect of light and heat energy to achieve efficient degradation under mild conditions. This technology combines the advantages of photocatalysis and thermocatalysis, significantly improving the degradation efficiency of refrigerants, reducing energy consumption, and enhancing catalyst stability through the synergistic effect of light and heat energy. MnO2, as a typical transition metal oxide, has attracted much attention due to its abundant resources, low cost, chemical stability, and unique catalytic activity. Different crystal forms of MnO2 have different crystal structures, surface morphologies, and chemical compositions, resulting in significant differences in their catalytic performance. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a method for photothermal synergistic catalytic degradation of tetrafluoroethane (HFC-134a), and the method provided by the present invention has a high degradation rate of HFC-134a.

[0005] This invention provides a method for photothermal synergistic catalytic degradation of tetrafluoroethane (HFC-134a), comprising:

[0006] The manganese dioxide catalyst is placed in a reactor, the reactor is heated, a reaction gas is introduced, and then the mixture is irradiated with light to obtain the product.

[0007] The manganese dioxide catalyst is at least one of α-MnO2, β-MnO2, γ-MnO2, δ-MnO2, and ε-MnO2.

[0008] The reactant gases comprise the following volume percentages: tetrafluoroethane (HFC-134a): 0.5%–5%; water vapor (H2O): 2%–20%; oxygen (O2): 10%–50%; the remainder being inert carrier gas, up to 100% of the total volume.

[0009] In some specific embodiments, the light source is a 300 W xenon lamp with a luminous intensity of 1.6~3.5 W / cm². 2 .

[0010] In some specific embodiments, the heating temperature is 200~240℃.

[0011] In some specific embodiments, the reaction is carried out in a photothermal synergistic catalytic reaction device, which sequentially includes a gas distribution system, a photothermal reaction system, and a chromatographic detection system; the photothermal reaction system includes a light source disposed above the reactor, a heating plate for heating the reactor, and a pressure gauge for determining the airtightness of the reactor; the reactor is a cavity reactor equipped with a quartz window; the chromatographic detection system is a gas chromatograph; the gas distribution system includes a nitrogen source, an oxygen source, and a tetrafluoroethane source.

[0012] In some specific embodiments, the volume ratio of HFC-134a:H2O:O2:N2 in the reaction gas is 1:10:40:100.

[0013] In some specific embodiments, after placing the manganese dioxide catalyst in the reactor, the reactor is set to a vacuum state with a vacuum degree of 100 kPa and maintained for 30 min.

[0014] In some specific embodiments, the α-MnO2 nanowires have a diameter of 20 nm and a length of 1 μm; the β-MnO2 nanorods have a diameter of 100 nm and a length of 500 nm; the γ-MnO2 urchin-like morphology is formed by the self-assembly of radially arranged nanowires with a diameter of 50 nm, and the overall diameter of the urchin-like morphology can reach 4 μm; the δ-MnO2 flower-like morphology is formed by the curling and stacking of ultrathin nanosheets with a thickness of 10 nm, and the overall particle size distribution is 1 μm; the ε-MnO2 spherical aggregate morphology is formed by the fusion of primary particles with a particle size of 30 nm through the interface, and the average diameter is 1.6 μm.

[0015] In some specific embodiments, the manganese dioxide catalyst is α-MnO2 and δ-MnO2.

[0016] In some specific embodiments, the heating temperature is 220°C, and the light source is a 300 W xenon lamp with a luminous intensity of 3.5 W / cm². 2 .

[0017] In some specific embodiments, the manganese dioxide catalyst is prepared by a hydrothermal method or a calcination method.

[0018] Compared with the prior art, the present invention provides a method for photothermal synergistic catalytic degradation of tetrafluoroethane (HFC-134a), comprising: placing a manganese dioxide catalyst in a reactor, heating the reactor, introducing a reaction gas, and then irradiating it with light; wherein the manganese dioxide catalyst is at least one selected from α-MnO2, β-MnO2, γ-MnO2, δ-MnO2, and ε-MnO2; wherein the reaction gas comprises the following volume percentages: tetrafluoroethane (HFC-134a): 0.5%–5%; water vapor (H2O): 2%–20%; oxygen (O2): 10%–50%; the remainder being an inert carrier gas, up to 100% of the total volume. This invention achieves a 99.8% degradation rate within 10 minutes at 220 °C and atmospheric pressure through a dual active center design of oxygen vacancy and acidic sites. On the equipment side, a modular photothermal reactor is used to complete photo-thermal field coupling and online gas chromatography sampling within the same chamber, solving the problems of low energy utilization and large temperature gradient caused by traditional "photo-thermal separation". On the process side, a four-variable coupling model of "light intensity-temperature-humidity-oxygen concentration" is established to optimize the degradation conditions and establish a degradation model. Attached Figure Description

[0019] Figure 1 The XRD patterns of the α-MnO2, β-MnO2, γ-MnO2, δ-MnO2 and ε-MnO2 catalysts prepared in Example 1 of this invention are shown below.

[0020] Figure 2 SEM images of the α-MnO2, β-MnO2, γ-MnO2, δ-MnO2 and ε-MnO2 catalysts prepared in Example 1 of this invention;

[0021] Figure 3 These are TEM images of the α-MnO2, β-MnO2, γ-MnO2, δ-MnO2 and ε-MnO2 catalysts prepared in Example 1 of this invention;

[0022] Figure 4 Comparison of N2 adsorption-desorption isotherms of the α-MnO2, β-MnO2, γ-MnO2, δ-MnO2 and ε-MnO2 catalysts prepared in Example 1 of this invention;

[0023] Figure 5 The UV-Vis diffuse reflectance spectra of the α-MnO2, β-MnO2, γ-MnO2, δ-MnO2 and ε-MnO2 catalysts prepared in Example 1 of this invention are shown.

[0024] Figure 6 Comparison of band gap spectra of the α-MnO2, β-MnO2, γ-MnO2, δ-MnO2 and ε-MnO2 catalysts prepared in Example 1 of this invention;

[0025] Figure 7 The X-ray photoelectron spectra of the α-MnO2, β-MnO2, γ-MnO2, δ-MnO2 and ε-MnO2 catalysts prepared in Example 1 of this invention are shown below.

[0026] Figure 8 The hydrogen temperature-programmed reduction curves of the α-MnO2, β-MnO2, γ-MnO2, δ-MnO2 and ε-MnO2 catalysts prepared in Example 1 of this invention are shown.

[0027] Figure 9 The oxygen temperature-programmed desorption curves of the α-MnO2, β-MnO2, γ-MnO2, δ-MnO2 and ε-MnO2 catalysts prepared in Example 1 of this invention are shown.

[0028] Figure 10 The ammonia temperature-programmed desorption curves of the α-MnO2, β-MnO2, γ-MnO2, δ-MnO2 and ε-MnO2 catalysts prepared in Example 1 of this invention are shown.

[0029] Figure 11 This is a diagram of the photothermal synergistic catalytic reaction device in Embodiment 2 of the present invention;

[0030] Figure 12 The graph shows the relationship between the removal rate and time of the photothermal synergistic degradation of tetrafluoroethane by the α-MnO2, β-MnO2, γ-MnO2, δ-MnO2 and ε-MnO2 catalysts prepared in Example 2 of this invention.

[0031] Figure 13 This is a stability diagram of the photothermal synergistic degradation of tetrafluoroethane by the α-MnO2 and δ-MnO2 catalysts prepared in Example 3 of this invention;

[0032] Figure 14 This is a graph showing the effect of oxygen concentration and humidity on the activity of the α-MnO2 and δ-MnO2 catalysts prepared in Example 4 of this invention during the photothermal synergistic degradation of tetrafluoroethane.

[0033] Figure 15 This is a graph showing the effect of light intensity on the activity of the δ-MnO2 catalyst prepared in Example 5 of this invention during the photothermal synergistic degradation of tetrafluoroethane.

[0034] Figure 16 This is a graph showing the effect of system temperature on the activity of the δ-MnO2 catalyst prepared in Example 6 of the present invention during the photothermal synergistic degradation of tetrafluoroethane. Detailed Implementation

[0035] This invention provides a method for the photothermal synergistic catalytic degradation of tetrafluoroethane (HFC-134a). Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and fall within the scope of this invention. The method and application of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the method and application described herein without departing from the content, spirit, and scope of this invention to implement and apply the technology of this invention.

[0036] This invention pioneers a four-variable coupled process involving temperature, light intensity, water vapor content, and oxygen concentration, solving the problems of high energy consumption, high cost, and secondary pollution inherent in existing waste refrigerant degradation technologies. This invention systematically explores the application of photothermal synergistic catalysis technology in waste refrigerant degradation by constructing a three-part system: a replaceable oxide catalyst, a photothermal coupled reactor, and a multi-field synergistic process involving temperature, humidity, light, and oxygen.

[0037] This invention provides a method for photothermal synergistic catalytic degradation of tetrafluoroethane (HFC-134a), comprising:

[0038] The manganese dioxide catalyst is placed in a reactor, the reactor is heated, a reaction gas is introduced, and then the mixture is irradiated with light to obtain the product.

[0039] The manganese dioxide catalyst is at least one of α-MnO2, β-MnO2, γ-MnO2, δ-MnO2, and ε-MnO2.

[0040] The present invention first prepares a manganese dioxide catalyst.

[0041] In some specific embodiments, the manganese dioxide catalyst is prepared by a hydrothermal method or a calcination method.

[0042] On one hand, this invention provides a method for preparing α-MnO2, β-MnO2, γ-MnO2, δ-MnO2, and ε-MnO2 catalysts, including hydrothermal and calcination methods. The specific preparation steps are as follows:

[0043] (1) Manganese sulfate hydrate and potassium permanganate were dissolved in ultrapure water, and 68% concentrated nitric acid was added to the precursor solution to carry out hydrothermal reaction. The hydrothermal temperature was 100 °C and the reaction time was 24 h. Finally, α-MnO2 was obtained by calcination in air.

[0044] (2) Manganese sulfate hydrate and ammonium persulfate were dissolved in ultrapure water and stirred evenly. The precursor solution was then subjected to a hydrothermal reaction at a temperature of 140 °C for 12 h. Finally, β-MnO2 was obtained by vacuum drying.

[0045] (3) Dissolve manganese sulfate hydrate and ammonium persulfate in ultrapure water, stir evenly, and then carry out hydrothermal reaction of the precursor solution at a hydrothermal temperature of 90 °C for 24 h. Finally, vacuum dry to obtain γ-MnO2.

[0046] (4) Dissolve manganese sulfate hydrate and potassium permanganate in ultrapure water, stir evenly, and then carry out hydrothermal reaction of the precursor solution at 160 °C for 24 h. Finally, vacuum dry to obtain δ-MnO2.

[0047] (5) Manganese sulfate hydrate and sodium bicarbonate were dissolved separately in ultrapure water. 7 mL of anhydrous ethanol was added to the manganese salt solution as a dispersant, and then the sodium bicarbonate solution was slowly added dropwise to the mixture. The mixture was stirred at room temperature for 2 h to form a precursor precipitate. The precipitate collected by centrifugation was dried and then calcined in air to obtain ε-MnO2.

[0048] In a particularly preferred embodiment, the specific preparation steps are as follows:

[0049] (1) Dissolve 0.53 g manganese sulfate hydrate and 1.25 g potassium permanganate in 80 mL of ultrapure water respectively. Add 2 mL of 68% concentrated nitric acid to the precursor solution for hydrothermal reaction at 100 °C for 24 h. Finally, calcine in air to obtain α-MnO2.

[0050] (2) Dissolve 1.69 g of manganese sulfate hydrate and 2.28 g of ammonium persulfate in 80 mL of ultrapure water, stir evenly, and then carry out hydrothermal reaction of the precursor solution at 140 °C for 12 h. Finally, vacuum dry to obtain β-MnO2.

[0051] (3) Dissolve 3.37 g of manganese sulfate hydrate and 4.57 g of ammonium persulfate in ultrapure water, stir evenly, and then carry out hydrothermal reaction of the precursor solution at a hydrothermal temperature of 90 °C for 24 h. Finally, vacuum dry to obtain γ-MnO2.

[0052] (4) Dissolve 0.27 g manganese sulfate hydrate and 1.5 g potassium permanganate in ultrapure water, stir evenly, and then carry out hydrothermal reaction of the precursor solution at 160 °C for 24 h. Finally, vacuum dry to obtain δ-MnO2.

[0053] (5) Dissolve 0.34 g of manganese sulfate hydrate and 1.68 g of sodium bicarbonate in 70 mL of ultrapure water. Add 7 mL of anhydrous ethanol to the manganese salt solution as a dispersant. Then, slowly add the sodium bicarbonate solution dropwise to the mixture. Stir at room temperature for 2 h to form a precursor precipitate. After centrifugation, the precipitate was dried and calcined in air to obtain ε-MnO2.

[0054] The present invention does not limit the specific preparation parameters mentioned above; those known to those skilled in the art are acceptable.

[0055] The raw materials for preparing manganese dioxide catalysts of different crystal forms described in this invention include manganese sulfate hydrate, potassium permanganate, nitric acid, ammonium persulfate, sodium bicarbonate, and anhydrous ethanol, etc.

[0056] Five different crystal forms of manganese dioxide catalysts can achieve efficient degradation of tetrafluoroethane under photothermal synergistic catalysis, among which δ-MnO2 and α-MnO2 show the best performance.

[0057] In some specific embodiments, the α-MnO2 nanowires have a diameter of 20 nm and a length of 1 μm; the β-MnO2 nanorods have a diameter of 100 nm and a length of 500 nm; the γ-MnO2 urchin-like morphology is formed by the self-assembly of radially arranged nanowires with a diameter of 50 nm, and the overall diameter of the urchin-like morphology can reach 4 μm; the δ-MnO2 flower-like morphology is formed by the curling and stacking of ultrathin nanosheets with a thickness of 10 nm, and the overall particle size distribution is 1 μm; the ε-MnO2 spherical aggregate morphology is formed by the fusion of primary particles with a particle size of 30 nm through the interface, and the average diameter is 1.6 μm.

[0058] In some specific embodiments, the manganese dioxide catalyst is α-MnO2 and δ-MnO2.

[0059] The prepared MnO2 catalyst was placed in a photothermal reactor, the reactor was evacuated to a vacuum state and maintained for 30 minutes. After confirming that the reactor was airtight by observing the change in the pressure gauge, subsequent operations were carried out.

[0060] According to the present invention, the reaction is carried out in a photothermal synergistic catalytic reaction device, which sequentially includes a gas distribution system, a photothermal reaction system, and a chromatographic detection system. The photothermal reaction system includes a light source positioned above the reactor, a heating plate for heating the reactor, and a pressure gauge for determining the reactor's airtightness. The reactor is a cavity reactor equipped with a quartz window. The chromatographic detection system is a gas chromatograph. The gas distribution system includes a nitrogen source, an oxygen source, and a tetrafluoroethane source; a gas collection bag is particularly preferred. The inventors periodically extract 10 μL gas samples from the reactor using an airtight needle.

[0061] After being mixed according to a set ratio, the mixture, carrying water vapor, enters the photothermal reaction system. In this system, a heating plate precisely controls the temperature of the reactor, while a xenon lamp irradiates the catalyst through a quartz window, achieving a synergistic coupling of light and heat energy. The exhaust gas is directly fed into a gas chromatography detection system, where a hydrogen ion flame detector and a thermal conductivity detector quantitatively detect the concentration of HFC-134a before and after degradation, obtaining real-time data on the HFC-134a degradation rate. After the airtightness test is completed, the gas distribution system's inlet valve is opened, and the mixed reaction gas is introduced according to a preset ratio. Once the system pressure stabilizes at atmospheric pressure, the heating plate is turned on to raise the temperature to the set reaction temperature. After the temperature stabilizes, the xenon lamp is turned on for illumination, initiating the photothermal synergistic catalytic degradation reaction.

[0062] According to the present invention, the reaction gas comprises the following volume percentages: tetrafluoroethane (HFC-134a): 0.5% to 5%; water vapor (H2O): 2% to 20%; oxygen (O2): 10% to 50%; the remainder being inert carrier gas, up to 100% of the total volume.

[0063] In some preferred embodiments, the reactant gas comprises the following volume percentages:

[0064] Tetrafluoroethane (HFC-134a): 1%–3%; water vapor (H2O): 5%–15%; oxygen (O2): 20%–40%; the remainder is inert carrier gas, up to 100% by volume. Nitrogen is preferred as the inert carrier gas, but other inert gases that do not participate in the catalytic reaction and are well known to those skilled in the art may also be used.

[0065] In some preferred embodiments, the reactant gas comprises the following volume percentages:

[0066] Tetrafluoroethane (HFC-134a): 1%; water vapor (H2O): 10%; oxygen (O2): 40%; the remainder is nitrogen, up to 100% by volume. The inert carrier gas does not participate in the catalytic reaction and will not interfere with the degradation process and results.

[0067] To achieve efficient degradation, this invention uses a mixed gas with a gas concentration ratio of HFC-134a:H2O:O2:N2 = 1:10:40:100.

[0068] This invention uses a gas collection bag to prepare HFC-134a gas with a volume concentration of 0.66%–10%; specifically, it can be 0.66%, 1%, 2%, 3%, 5%, or a range between the two.

[0069] In each experiment, 50 ml of reaction gas was extracted and injected into the photocatalytic window reactor. The system was heated, and after the heating temperature stabilized to the preset value, the light source was turned on to start the degradation reaction. During the reaction, a quantitative amount of reaction gas was extracted from the sampling port with a gas-tight needle at regular intervals, and the concentration of HFC-134a was detected by gas chromatography. The degradation rate of HFC-134a at different reaction times was calculated based on the peak area.

[0070] In some specific embodiments, the heating temperature is 200~240℃; specifically, it can be 200℃, 210℃, 220℃, 230℃, 240℃, or any range between two of the above values. In some specific embodiments, the light source is a 300 W xenon lamp with a light intensity of 1.6~3.5 W / cm²; specifically, it can be 1.6 W / cm², 2.0 W / cm², 2.5 W / cm², 3.0 W / cm², 3.5 W / cm², or any range between two of the above values. This invention, through the synergistic effect of photothermal energy, significantly improves the degradation efficiency of HFC-134a compared to single heating catalysis or single photocatalysis, achieving near-complete degradation in a short time under normal pressure and 220℃ conditions.

[0071] In some preferred embodiments, the heating temperature is 220°C, and the light source is a 300 W xenon lamp with a luminous intensity of 3.5 W / cm². 2 Within the above-mentioned preferred parameter range, the present invention can achieve a degradation rate of 99.8% for HFC-134a within 10 minutes, with catalytic performance far exceeding the degradation effect under other temperature and light intensity conditions. At the same time, the catalyst has good stability and can maintain excellent degradation activity even after multiple cycles of reaction.

[0072] During the reaction, 10 μL gas samples were periodically extracted from the reactor using a gas-tight needle, and the gas concentration was determined using a gas chromatograph. The conversion rate of HFC-134a was calculated by combining the peak area obtained from the chromatographic analysis with the formula, thereby evaluating the activity of the catalyst.

[0073] The parameters are as follows: Al2O3 (30 m × 0.53 mm × 20 μm) column; nitrogen as carrier gas, constant pressure mode of 0.05 MPa; injection method of six-way valve, split flow rate of 80 mL / min, column temperature of 150 ℃, FID detector, 200 ℃; detector gas makeup gas of 25 mL / min, hydrogen of 30 mL / min, and air of 300 mL / min; injection volume of 10 μL.

[0074] The formula is as follows: X HFC134a =(C0-C t ) / C0*100%, where C0 is the initial HFC- 134a concentration, C t HFCs with different reaction times - 134a concentration.

[0075] In some specific embodiments, the photothermal synergistic catalytic reaction device includes a photothermal reactor, a gas chromatograph, a gas-tight needle, a gas collection bag, and a xenon lamp light source. The photothermal reactor is used to carry out the catalytic reaction, the gas chromatograph is used to measure the gas concentration, the gas-tight needle is used to extract gas samples, the gas collection bag is used to prepare the reaction gas, and the xenon lamp provides illumination as a light source.

[0076] Through in-depth research and repeated experiments, the inventors have creatively discovered that the key influencing factors for the photothermal synergistic catalytic degradation of HFC-134a encompass multiple aspects, primarily including the oxygen concentration in the reaction system, ambient humidity, light intensity, and overall system temperature. Changes in these key parameters significantly affect the final catalytic degradation effect. By scientifically and systematically controlling these core factors, the reaction conditions of the degradation process can be effectively optimized, thereby significantly improving the degradation efficiency of the target pollutant and the overall treatment effect.

[0077] Compared with the prior art, the beneficial technical effects achieved by the present invention include:

[0078] (1) A process model with four variables synergistically controlled by temperature, humidity, light, and oxygen was established. Through single-variable control experiments, the quantitative influence trend of each parameter on the degradation rate was clarified, and the optimal process window was determined: the system temperature of 220 ℃ is the optimal temperature; the activity with H2O is higher than that without H2O; and the activity is within the range of 1.6-3.5 W / cm². 2 The light intensity within the specified range is positively correlated with the degradation rate; the activity with O2 is significantly higher than that without O2. Furthermore, it provides directly applicable combinations of process conditions, under optimal conditions (220 ℃, H2O content, O2 content, 3.5 W / cm³). 2 Under light intensity, HFC-134a was nearly completely degraded (99.8%) within 10 minutes, providing theoretical support and technical solutions for the efficient degradation of waste refrigerants.

[0079] (2) The δ-MnO2 and α-MnO2 catalysts used in this invention have abundant oxygen active sites and acidic sites, and exhibit excellent degradation performance under photothermal synergistic catalysis. The degradation rate can reach 99.8% within 10 min, and the activity did not decrease significantly after six cycles of stability testing, demonstrating good cycle stability. This proves that the method and catalyst have good experimental repeatability and operational stability.

[0080] (3) Using in-situ infrared spectroscopy characterization technology, the degradation pathway and transformation mechanism of HFC-134a under thermocatalysis and photothermal synergistic catalysis were dynamically tracked, revealing the photothermal synergistic catalytic mechanism. Irradiation can promote the formation of oxygen vacancies on the catalyst surface and accelerate the generation of ·OH free radicals, thereby significantly improving the CF bond breaking efficiency, providing an important reference for the design and optimization of photothermal synergistic catalysts.

[0081] (4) The photothermal synergistic catalytic degradation method of the present invention is simple to operate, has mild conditions, does not require extreme conditions such as high temperature and high pressure, has broad industrial application prospects, and can effectively solve the problem of environmental pollution caused by waste refrigerant.

[0082] It should be understood that the expression “one or more of…” individually includes each of the objects described after the expression, as well as various different combinations of two or more of the described objects, unless otherwise understood from the context and usage. The expression “and / or” combined with three or more described objects should be understood to have the same meaning, unless otherwise understood from the context.

[0083] The terms “including,” “having,” or “containing,” including the use of their grammatical synonyms, should generally be understood as open-ended and non-restrictive, for example, not excluding other unstated elements or steps, unless otherwise specifically stated or understood from the context.

[0084] The "range" disclosed in this invention is given in the form of a lower limit and an upper limit. There can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges defined in this way are composable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 100-180 and 12-24 are listed for specific parameters, it is also expected that ranges of 100-180 and 12-24 are also expected. Furthermore, if the listed minimum range values ​​are 1 and 2, and the listed maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0085] In this invention, unless otherwise specified, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this invention, and "0-5" is simply a shortened representation of these numerical combinations.

[0086] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0087] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items.

[0088] In this invention, unless otherwise specified, the term "two kinds" as used in this specification means "at least two kinds".

[0089] In this invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0090] It should be understood that the order of the steps or the order in which certain actions are performed is not important as long as the invention remains operational. Furthermore, two or more steps or actions can be performed simultaneously.

[0091] The use of any and all instances or exemplary language such as “e.g.” or “including” in this document is merely intended to better illustrate the invention and is not intended to limit the scope of the invention unless the claims are made. No language in this specification should be construed as indicating that any unclaimed element is essential to the practice of the invention.

[0092] Furthermore, the numerical ranges and parameters used to define the present invention are approximate values, and the relevant values ​​in the specific embodiments have been presented as precisely as possible. However, any value inevitably contains standard deviations due to individual test methods. Therefore, unless explicitly stated otherwise, it should be understood that all ranges, quantities, values, and percentages used in this disclosure are modified with the word "approximately". Here, "approximately" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a specific value or range.

[0093] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0094] The embodiments and comparative examples of this invention describe some examples, in which the embodiments illustrate certain implementations of the invention. However, this does not mean that the effects of the invention can only be achieved in these examples.

[0095] To further illustrate the present invention, the following describes in detail a method for photothermal synergistic catalytic degradation of tetrafluoroethane HFC-134a provided by the present invention, in conjunction with embodiments.

[0096] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0097] Example 1: Preparation and Characterization of Catalysts

[0098] This embodiment provides five methods for preparing manganese dioxide catalysts with different crystal forms: α-MnO2, β-MnO2, γ-MnO2, δ-MnO2, and ε-MnO2. The specific preparation methods include the following steps:

[0099] Step 1: First, weigh 0.53 g of manganese sulfate hydrate (MnSO4·H2O) and 1.25 g of potassium permanganate (KMnO4) and dissolve them in 80 mL of deionized water. Then, add 2 mL of 68% concentrated nitric acid (HNO3) and stir magnetically for 60 min to form a homogeneous precursor solution. Transfer this mixture to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and perform hydrothermal crystallization in a constant temperature oven at 100 ℃ for 24 h. After the reaction, allow it to cool naturally. The product is then separated by centrifugation and washed three times with deionized water and anhydrous ethanol to remove residual ions. Subsequently, it is treated in a vacuum drying oven at 80 ℃ for 12 h and finally calcined in a muffle furnace at 400 ℃ in air atmosphere for 4 h to obtain pure phase α-MnO2 nanomaterials.

[0100] Step 2: Dissolve 1.69 g of manganese sulfate hydrate and 2.28 g of ammonium persulfate ((NH4)2S2O8) in 80 mL of deionized water. Stir magnetically for 60 min until completely dissolved, then transfer to a high-pressure reactor and carry out a hydrothermal reaction at 140 ℃ for 12 h. The product is then centrifuged, washed with deionized water, and vacuum dried at 60 ℃ to obtain β-MnO2.

[0101] Step 3: Dissolve 3.375 g of manganese sulfate hydrate and 4.575 g of ammonium persulfate in 80 mL of distilled water, stir for 60 min to mix evenly, then heat the mixture to 90 °C in a 100 mL autoclave and maintain it for 24 h. Finally, obtain γ-MnO2 by centrifugation, washing and drying.

[0102] Step 4: Dissolve 0.275 g of manganese sulfate hydrate and 1.5 g of potassium permanganate in 80 mL of distilled water and mix well. Heat the mixture to 160 °C in an autoclave and maintain it for 24 h. Obtain δ-MnO2 by centrifugation, washing and drying.

[0103] Step 5: Dissolve 0.338 g of manganese sulfate hydrate and 1.68 g of sodium bicarbonate (NaHCO3) separately in 70 mL of deionized water. Add 7 mL of anhydrous ethanol to the manganese salt solution as a dispersant, and then slowly add the sodium bicarbonate solution dropwise to the mixture. Stir at room temperature for 2 h to form a precursor precipitate. The precipitate collected by centrifugation is dried at 80 ℃ for 12 h and then calcined at 400 ℃ in air for 4 h to complete the crystal transformation, obtaining ε-MnO2 microspheres.

[0104] The α-MnO2, β-MnO2, γ-MnO2, δ-MnO2 and ε-MnO2 catalysts were characterized in a series of ways, and their XRD patterns are shown in the figure. Figure 1 As shown, there are significant differences in the exposed major crystal planes of manganese dioxide with different crystal forms. SEM and TEM images are shown below. Figure 2 and Figure 3 As shown. By Figure 2 It can be seen that manganese dioxide with different crystal forms has different morphological characteristics. (From...) Figure 3 As can be seen, the results are consistent with the scanning electron microscopy characterization results. Figure 4 The N2 adsorption-desorption isotherms for catalysts with different crystal forms show that the specific surface areas of the five crystal forms differ significantly, and the pore size distribution is mainly mesoporous. Figure 5 The UV-Vis diffuse reflectance spectra of the five catalysts clearly show that all five crystalline forms of manganese dioxide exhibit significant light absorption capabilities in the wavelength range of 200-900 nm. Figure 6 The band gap spectra of manganese dioxide with different crystal forms are shown. Figure 7 The images show the X-ray photoelectron spectra of five catalysts, among which δ-MnO2 and α-MnO2 have high oxygen vacancy densities and abundant adsorbed oxygen species. Figure 8 , Figure 9 and Figure 10 The figures show the temperature-programmed reduction curves for hydrogen, the temperature-programmed desorption curve for oxygen, and the temperature-programmed desorption curve for ammonia, respectively. It can be seen that δ-MnO2 and α-MnO2 have abundant oxygen active sites and acidic sites.

[0105] Example 2: Catalyst Activity Test

[0106] This embodiment provides a method for photothermal synergistic catalytic degradation of tetrafluoroethane (HFC-134a), mainly including the following steps:

[0107] First, 0.3 g of each catalyst (α-MnO2, β-MnO2, γ-MnO2, δ-MnO2, and ε-MnO2) was weighed and placed in the photothermal reactor. The reaction apparatus is as follows: Figure 11 As shown. The reactor was evacuated to a vacuum and maintained for 30 minutes. The airtightness of the reactor was confirmed by observing the pressure gauge changes. A gas collection bag was used to prepare HFC-134a gas with a volume concentration of 0.66%, where the gas concentration ratio was HFC-134a:H2O:O2:N2 = 1:10:40:100. For each experiment, 50 ml of the reaction gas was extracted and injected into the photocatalytic window reactor. The system temperature was adjusted to 220 ℃ using a heating plate. After the temperature reached the target value, the light source was turned on. The light source was a 300 W xenon lamp with a light intensity of 3.5 W / cm². 2 During the reaction, 10 μL gas samples were drawn from the reactor every 1 minute using a gas-tight needle, and the gas concentration was determined using gas chromatography. The peak areas obtained from chromatographic analysis were used to calculate the conversion rate of HFC-134a, thereby evaluating the catalyst activity. Figure 12 It can be seen that δ-MnO2 and α-MnO2 exhibit the best performance, with a degradation rate of 99.8% within 10 min.

[0108] Example 3

[0109] This embodiment provides δ-MnO2 and α-MnO2 catalysts, prepared using the same method as in Example 1, and tested using the same methods and reaction conditions as in Example 2. 0.3 g of each catalyst (δ-MnO2 and α-MnO2) was weighed and placed in a photothermal reactor. The reaction apparatus is as follows: Figure 11 As shown. The reactor was evacuated to a vacuum and maintained for 30 minutes. The airtightness of the reactor was confirmed by observing the pressure gauge changes. A gas collection bag was used to prepare HFC-134a gas with a volume concentration of 0.66%, where the gas concentration ratio was HFC-134a:H2O:O2:N2 = 1:10:40:100. For each experiment, 50 ml of the reaction gas was extracted and injected into the photocatalytic window reactor. The system temperature was adjusted to 220 ℃ using a heating plate. After the temperature reached the target value, the light source was turned on. The light source was a 300 W xenon lamp with a light intensity of 3.5 W / cm². 2During the reaction, 10 μL of gas was drawn from the reactor through a gas-tight needle at 1-minute intervals, and the gas concentration was measured using a gas chromatograph. Six cycles of this experiment were performed on δ-MnO2 and α-MnO2. Figure 13 It can be seen that neither δ-MnO2 nor α-MnO2 showed significant activity decay after cyclic experiments, demonstrating excellent stability.

[0110] Comparative Example 1

[0111] This comparative example describes the degradation of HFC-134a under conditions of absence of O2 and presence of H2O.

[0112] This comparative example provides δ-MnO2 and α-MnO2 catalysts, prepared using the same methods as in Example 1, and tested using the same methods and reaction conditions as in Example 2. 0.3 g of each catalyst (δ-MnO2 and α-MnO2) was weighed and placed in a photothermal reactor. The reaction apparatus is as follows: Figure 11 As shown. The reactor was evacuated to a vacuum and maintained for 30 min. A gas concentration of 0.66% HFC-134a was prepared using a gas collection bag, with a gas concentration ratio of HFC-134a:H2O:O2:N2 = 1:10:40:100. For each experiment, 50 ml of the reaction gas was extracted and injected into the photocatalytic window reactor. The system temperature was adjusted to 220 ℃ using a heating plate. Once the target temperature was reached, the light source was turned on. The light source was a 300 W xenon lamp with a light intensity of 3.5 W / cm². 2 During the reaction, 10 μL of gas was drawn from the reactor every 1 minute using a gas-tight needle, and the gas concentration was measured using a gas chromatograph. Only the oxygen concentration and humidity in the reaction system were varied. The results are as follows: Figure 14 As shown, the results indicate that the degradation rate when both O2 and H2O are present is higher than that when only O2 or only H2O are present, demonstrating the key synergistic effect of O2 and H2O in the photothermal synergistic process.

[0113] Comparative Example 2

[0114] This comparative example describes the degradation of HFC-134a under different light intensities.

[0115] This comparative example provides a δ-MnO2 catalyst, prepared using the same method as in Example 1, and tested using the same methods and reaction conditions as in Example 2. 0.3 g of the catalyst (δ-MnO2) was weighed and placed in a photothermal reactor. The reaction apparatus is as follows: Figure 11As shown. The reactor was evacuated to a vacuum and maintained for 30 min. A gas concentration of 0.66% HFC-134a was prepared using a gas collection bag, with a gas concentration ratio of HFC-134a:H2O:O2:N2 = 1:10:40:100. For each experiment, 50 ml of the reaction gas was extracted and injected into the photocatalytic window reactor. The system temperature was adjusted to 220 ℃ using a heating plate. Once the target temperature was reached, the light source was turned on using a 300 W xenon lamp. During the reaction, 10 μL of gas was extracted from the reactor every 1 min using a gas-tight needle, and the gas concentration was measured using a gas chromatograph. Only the light intensity in the reaction system was varied, set to 0 and 2.0 W / cm², respectively. 2 2.5 W / cm 2 3.0 W / cm 2 and 3.5 W / cm 2 The result is as follows Figure 15 As shown, the results indicate that HFC-134a hardly degrades in the absence of light, at a degradation rate of 2.0–3.5 W / cm². 2 Within the specified range, the degradation rate is positively correlated with light intensity, with the optimal light intensity being 3.5 W / cm². 2 This indicates that light exposure promotes the degradation of HFC-134a.

[0116] Comparative Example 3

[0117] This comparative example describes the degradation of HFC-134a under different system temperatures.

[0118] This comparative example provides a δ-MnO2 catalyst, prepared using the same method as in Example 1, and tested using the same methods and reaction conditions as in Example 2. 0.3 g of the catalyst (δ-MnO2) was weighed and placed in a photothermal reactor. The reaction apparatus is as follows: Figure 11 As shown. The reactor was evacuated to a vacuum and maintained for 30 min. A gas concentration of 0.66% HFC-134a was prepared using a gas collection bag, with a gas concentration ratio of HFC-134a:H2O:O2:N2 = 1:10:40:100. For each experiment, 50 ml of the reaction gas was extracted and injected into the photocatalytic window reactor. The system temperature was adjusted to 220 ℃ using a heating plate. After reaching the target temperature, the light source was turned on using a 300 W xenon lamp. During the reaction, 10 μL of gas was extracted from the reactor every 1 min using a gas-tight needle, and the gas concentration was determined using a gas chromatograph. The temperature in the reaction system was changed. When there was no light, the temperature was set to 250 ℃, 270 ℃, 290 ℃, 310 ℃, and 330 ℃; when the light intensity was 3.5 W / cm², the temperature was adjusted accordingly. 2The temperatures were set to 25 ℃, 100 ℃, 140 ℃, 180 ℃, 220 ℃, and 260 ℃, respectively. The results are as follows... Figure 16 As shown, the results indicate that under pure thermal catalysis, even at a temperature of 330 °C, the degradation rate of HFC-134a within 10 min is only about 50%, far lower than that of the photothermal synergistic mode (99.8%), demonstrating the significant photothermal synergistic effect. Furthermore, with a light intensity set to 3.5 W / cm²... 2 Under the given conditions, when the temperature was further increased to 260 °C, the reaction rate of the catalyst only increased slightly, indicating that under high temperature conditions, the reactant conversion rate and reaction rate may reach an equilibrium point, and further increasing the temperature has a limited effect on increasing the reaction rate.

[0119] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for photothermal synergistic catalytic degradation of tetrafluoroethane (HFC-134a), characterized in that, include: The manganese dioxide catalyst is placed in a reactor, the reactor is heated, a reaction gas is introduced, and then the mixture is irradiated with light to obtain the product. The manganese dioxide catalyst is at least one of α-MnO2, β-MnO2, γ-MnO2, δ-MnO2, and ε-MnO2. The reactant gases comprise the following volume percentages: tetrafluoroethane (HFC-134a): 0.5%–5%; water vapor (H2O): 2%–20%; oxygen (O2): 10%–50%; the remainder being inert carrier gas, up to 100% of the total volume.

2. The method according to claim 1, characterized in that, The light source is a 300 W xenon lamp with a luminous intensity of 1.6~3.5 W / cm². 2 .

3. The method according to claim 2, characterized in that, The heating temperature is 200~240℃.

4. The method according to claim 1, characterized in that, The reaction is carried out in a photothermal synergistic catalytic reaction device, which sequentially includes a gas distribution system, a photothermal reaction system, and a chromatographic detection system. The photothermal reaction system includes a light source positioned above the reactor, a heating plate for heating the reactor, and a pressure gauge for determining the reactor's airtightness. The reactor is a cavity reactor equipped with a quartz window. The chromatographic detection system is a gas chromatograph. The gas distribution system includes a nitrogen source, an oxygen source, and a tetrafluoroethane source.

5. The method according to claim 1, characterized in that, The volume ratio of HFC-134a:H2O:O2:N2 in the reaction gas is 1:10:40:

100.

6. The method according to claim 1, characterized in that, After placing the manganese dioxide catalyst in the reactor, the reactor was set to a vacuum state with a vacuum degree of 100 kPa and maintained for 30 min.

7. The method according to claim 1, characterized in that, The α-MnO2 nanowires have a diameter of 20 nm and a length of 1 μm; the β-MnO2 nanorods have a diameter of 100 nm and a length of 500 nm; the γ-MnO2 urchin-like morphology is composed of radially arranged nanowires with a diameter of 50 nm that self-assemble, and the overall diameter of the urchin-like morphology can reach 4 μm; the δ-MnO2 flower-like morphology is formed by the curling and stacking of ultrathin nanosheets with a thickness of 10 nm, and the overall particle size distribution is 1 μm; the ε-MnO2 spherical aggregate morphology is formed by the fusion of primary particles with a particle size of 30 nm through the interface, and the average diameter is 1.6 μm.

8. The method according to claim 1, characterized in that, The manganese dioxide catalyst is α-MnO2 and δ-MnO2.

9. The method according to claim 3, characterized in that, The heating temperature is 220℃, and the light source is a 300 W xenon lamp with a light intensity of 3.5 W / cm². 2 .

10. The method according to claim 1, characterized in that, The manganese dioxide catalyst is prepared by hydrothermal method or calcination method.

Images