A method for preparing a catalyst capable of catalyzing decomposition of ozone in high humidity

Abstract

The application discloses a preparation method of a catalyst capable of catalyzing high-humidity ozone decomposition, and the corresponding nickel nitrate and iron nitrate solutions are uniformly titrated in an alkaline environment through a coprecipitation preparation technology; nitrogen protection is adopted to prevent CO2 from participating in the reaction and interfering with octanoate intercalation hydrotalcite, and the whole titration process is protected by nitrogen, and the reaction temperature, solution pH, titration rate and stirring rate need to be controlled; after the titration is completed, the wet-cake-shaped solid phase is collected through suction filtration and washing; the required solid-phase catalyst is obtained through drying treatment; and according to the use requirements, the solid-phase catalyst is ground and sieved to meet the actual requirements. Finally, through a unique pretreatment process, the catalyst is converted into a special structure of NiOOHFe-OAa, and is used for catalyzing high-humidity high-concentration ozone decomposition for a long time. The catalyst can stably catalyze high-concentration ozone decomposition for a long time under high air speed and high humidity conditions, has excellent catalytic performance and excellent moisture resistance, and can meet the catalytic ozone decomposition work under various environments.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalytic decomposition of polluted gas, and particularly relates to a preparation method of a catalyst capable of catalyzing decomposition of high-humidity ozone. BACKGROUND

[0002] Ozone is a double-edged sword. Ozone in the stratosphere blocks most of the ultraviolet light, protecting the normal survival of near-surface organisms and playing a vital role in human survival. However, near-surface ozone is an air pollutant that significantly affects human health and the ecological system. Due to its strong oxidation potential, it can adversely affect the growth of plant, insect and soil microbial communities, threatening the terrestrial ecosystem and biodiversity. In addition, long-term inhalation of low-concentration ozone can cause respiratory and cardiopulmonary diseases; a large amount of ozone is generated when indoor printers and other instruments are working, and indoor ozone also causes secondary organic aerosol pollution that harms human health. In view of these considerations, it is urgent to develop ozone removal technology.

[0003] At present, the elimination technologies for ozone mainly include thermal decomposition method, activated carbon adsorption method, electromagnetic wave radiation method and catalytic decomposition method. Among them, the catalytic decomposition method is considered to be the most ideal ozone treatment method due to its high efficiency, economy and safety. The catalysts used for catalytic decomposition of ozone can be divided into two categories: noble metals and transition metal oxides. The noble metal catalysts have high catalytic efficiency and good humidity resistance, but their preparation cost is high; in comparison, the transition metal oxide catalysts have lower preparation cost and excellent catalytic activity, and are therefore widely considered to be the most ideal catalytic material. Among the transition metal oxides, manganese element has become a research hotspot due to its high activity, relatively simple preparation and low cost. These characteristics make manganese oxides attract much attention in the field of ozone decomposition. However, oxygen vacancies are easily occupied by water molecules, which leads to subsequent work focusing on improving the hydrophobicity of manganese oxides. So far, there are still many problems in the manganese oxide catalysts for catalytic decomposition of ozone, such as complex preparation process and the need for further improvement of hydrophobicity.

[0004] Patent CN110152720B relates to a method for preparing an ozone catalyst and the ozone catalyst obtained by the method. The method includes activating a modified 5A molecular sieve support in an inert gas, then loading a metal onto it to finally prepare the ozone catalyst. The ozone catalyst prepared by this method has good formability, wear resistance, and a long service life. However, this method has a complex preparation process and high cost, requiring further improvement. Meanwhile, patent CN202210021356.8 relates to a method for preparing a nickel-manganese-iron ternary layered double hydroxide and its metal oxide catalyst. This method has a simple preparation process but suffers from reduced activity under high humidity conditions and low ozone concentration, requiring further improvement in the moisture resistance of this type of catalyst.

[0005] In conclusion, addressing high humidity and high concentration ozone pollution near the ground is the core challenge in this field. Developing easily prepared catalysts applicable to various scenarios is an important measure to eliminate near-ground ozone pollution and has significant implications for protecting human health and maintaining ecosystem stability. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention discloses a method for preparing a catalyst capable of catalyzing the decomposition of ozone in high humidity, comprising the following steps:

[0007] S1: Dissolve nickel nitrate and ferric nitrate in deionized water in a ratio of 2:1 to 3:1 to obtain solution A;

[0008] S2: Dissolve sodium octanoate and sodium hydroxide in deionized water in a ratio of 2:1 to 4:1 to obtain alkaline solution B;

[0009] S3: Dissolve solutions A and B under ultrasonic treatment at 25-50℃ for 0.5-1.5 hours;

[0010] S4: Solution A and solution B are titrated into the reaction vessel at a fixed rate. The reaction vessel is completely sealed during the titration process, and nitrogen gas is introduced to prevent carbon dioxide from interfering with the reaction. The stirring rate and temperature are kept constant during titration, and the pH value of the reaction solution in the reactor is controlled by adding pure sodium hydroxide alkaline solution.

[0011] S5: After titration, the suspension is aged, then filtered and washed with deionized water until the filtrate is neutral. The solid phase is then collected.

[0012] S6: The solid phase obtained in S5 is dried, pressed into tablets, and sieved to obtain octanoic acid-intercalated nickel-iron hydrotalcite.

[0013] S7: Ozone pretreatment of octanoic acid-intercalated nickel-iron hydrotalcite with a concentration of 100-200 ppm and a flow rate of 1 L / min or higher.

[0014] Furthermore, in step S4, the titration rates of solutions A and B should be kept at the same rate, and the titration rate should be maintained at 1-2 ml / min. The total flow rate of nitrogen gas should not be less than 10 ml / min. The temperature during the titration process should be maintained at 60-80℃, and the stirring speed should be maintained at more than 250 rpm. At the same time, the concentration of the pure sodium hydroxide alkaline solution should be controlled at 4-6 mol / L until the pH of the reaction solution is maintained between 9 and 11.

[0015] Furthermore, in step S5, the aging temperature is 60–80°C and the aging time is 4–6 hours; furthermore, in step S6, a vacuum oven is used for drying to prevent carbon dioxide from affecting the catalyst preparation process, the drying temperature is 70–80°C and the drying time is at least 24 hours; at the same time, the sieve size should be 40–60 mesh.

[0016] The beneficial effects of this invention are:

[0017] (1) This invention can effectively decompose high humidity and high concentration ozone, making it applicable to diverse scenarios and having higher practical production value;

[0018] (2) The present invention has low cost, simple process, easy process parameters, and is easy to industrialize;

[0019] (3) This invention does not require calcination, which greatly reduces the energy consumption of preparation, and the preparation process is simple;

[0020] (4) This invention is the first to use pretreatment technology to promote the reorganization and change of catalyst structure, which greatly improves the stability of catalyst. The pretreatment is a short-time ozone oxidation pretreatment process with high humidity, high concentration and high space velocity. When the catalyst color changes completely from green to black, the treatment is completed. This causes hydrogen loss on the catalyst surface and the material structure to change to form NiOOHFe-OAa structure, which generates unique hydrogen vacancies. Hydrogen vacancies have excellent decomposition activity for ozone as active sites. Hydrogen vacancies are a kind of material surface defect. As active sites, they can enhance the material's moisture resistance and reduce the competitive adsorption of reaction intermediates and water on active sites during the reaction process. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0022] Figure 1 This is a flowchart of embodiment 1 of the present invention;

[0023] Figure 2 This is a comparison chart of the ozone conversion effects of Example 1 and Example 3 under a relative humidity of 60%.

[0024] Figure 3 This is a comparison chart of the ozone conversion effects of Example 1 and Example 3 under a relative humidity of 90%. Detailed Implementation

[0025] Example 1

[0026] This embodiment discloses a method for preparing a catalyst capable of catalyzing the decomposition of ozone in high humidity. An octanoate-intercalated hydrotalcite ozone catalyst (NiOOH3Fe1-OAa) with a nickel-iron molar ratio of 3:1 is prepared. Nickel nitrate and iron nitrate are dissolved in 50 ml of deionized water at a molar ratio of 3:1 to form a 1 mol / L salt solution A. 5 mol of sodium octanoate and 0.8 mol of sodium hydroxide are dissolved in 50 ml of deionized water to form solution B. A 4 mol / L sodium hydroxide solution C is prepared. Solutions A, B, and C are ultrasonically vibrated at 240 W, maintaining a temperature of 30°C for 40 min. After ultrasonication, solutions A and B are added dropwise to 50 ml of deionized water at a constant rate of 2 ml / min. The reaction solution is heated in a constant-temperature water bath to maintain a reaction temperature of 80°C, and stirred using a magnetic stirrer at a speed of 350 rpm. The pH of the reaction solution was monitored in real time using a pH detector, and the pH was kept constant at 10 ± 0.5 by adding solution C dropwise. After titration, the reaction solution was aged at a constant temperature of 70℃ for 6 hours. Nitrogen gas was purged at a rate of 20 ml / min throughout the titration and aging process to prevent interference from carbon dioxide. After aging, the solution was washed and filtered until the pH of the filtrate reached 7. The filtered wet cake-like solid phase was then dried in a vacuum oven at 70℃ for 24 hours. The dried solid phase was then pulverized and sieved to obtain a 40-mesh catalyst for pretreatment. The catalyst was fixed in a reaction bed, and ozone at a flow rate of 1000 ml / min and a concentration of 150 ppm was introduced until the catalyst completely changed color and remained as a residue, yielding the NiOOH3Fe1-OAa catalyst. This catalyst catalyzes the decomposition of ozone. XRD characterization analysis of the prepared catalyst is as follows: Figure 2 It was found that octanoic acid ion intercalation into nickel-iron hydrotalcite forms a hydrotalcite-like layered structure, but due to surface defects caused by pretreatment, the catalyst crystallization state is poor.

[0027] In this embodiment, a low-humidity (RH=65%) ozone catalytic decomposition experiment was conducted on a nickel-iron layered double hydroxide catalyst (NiOOH3Fe1-OAa) with an octanoate intercalation at a nickel-iron molar ratio of 3:1. 0.05 g of the Ni3Fe1-OAa-LDH catalyst was weighed and placed in a 4 mm quartz reaction tube, which was then placed in a temperature-controlled device. The gas flow rate in this experiment was 700 ml / min. The volume hourly space velocity was 840 L / (g·h), the ozone inlet concentration was 100 ppm, and the relative humidity was 60%. The ozone removal efficiency is shown in the figure below.Figure 2 As shown in the figure, the catalyst Ni3Fe1-OAa-LDH has the best catalytic decomposition efficiency for ozone at a relative humidity of 60%, and can completely decompose ozone gas.

[0028] Example 2

[0029] In this embodiment, an octanoic acid intercalated layered double hydroxide ozone catalyst (NiOOH2Fe1-OAa) with a nickel-iron molar ratio of 2:1 was prepared by dissolving nickel nitrate and iron nitrate in 100 ml of deionized water to form a 0.5 mol / L salt solution A. 0.8 mol of sodium octanoate and 1 mol of sodium hydroxide were dissolved in 100 ml of deionized water to form solution B. A 5 mol / L sodium hydroxide solution C was prepared. Solutions A, B, and C were ultrasonically vibrated at 400 W, maintaining a temperature of 50°C for 60 min. After ultrasonication, solutions A and B were added dropwise to 100 ml of deionized water at a constant rate of 1.5 ml / min. The reaction solution was heated in a constant-temperature water bath to maintain a reaction temperature of 85°C, and stirred using a magnetic stirrer at a speed of 500 rpm. The pH value of the reaction solution was monitored in real time using a pH detector, and the pH was maintained at 10.5 ± 0.5 by adding solution C dropwise. After titration, the reaction solution was aged at a constant temperature of 80℃ for 7 hours. Nitrogen gas was purged at a rate of 30 ml / min throughout the titration and aging process to prevent interference from carbon dioxide. After aging, the solution was washed and filtered until the pH of the filtrate reached 7. The resulting wet cake-like solid phase was then dried in a vacuum oven at 80℃ for 24 hours. The dried solid phase was then pulverized and sieved to obtain a 40-mesh catalyst for pretreatment. The catalyst was then fixed in a reaction bed, and ozone at a flow rate of 900 ml / min and a concentration of 200 ppm was introduced until the catalyst completely changed color and remained as a residue, yielding the NiOOH2Fe1-OAa catalyst, which catalyzes the decomposition of ozone.

[0030] Example 3

[0031] In this embodiment, a non-differential intercalated layered double hydroxide ozone catalyst (NiOOH3Fe1) with a nickel-iron molar ratio of 3:1 was prepared. Nickel nitrate and iron nitrate were dissolved in 50 ml of deionized water at a molar ratio of 3:1 to form a 1 mol / L salt solution A. 0.25 mol of sodium carbonate and 0.8 mol of sodium hydroxide were dissolved in 50 ml of deionized water to form solution B. A 4 mol / L sodium hydroxide solution C was prepared. Solutions A, B, and C were ultrasonically vibrated at 240 W, maintaining a temperature of 30°C for 40 min. After ultrasonication, solutions A and B were added dropwise to 50 ml of deionized water at a constant rate of 2 ml / min. The reaction solution was heated in a constant-temperature water bath to maintain a reaction temperature of 80°C, and stirred using a magnetic stirrer at a speed of 250 rpm. The pH value of the reaction solution was monitored in real time using a pH detector, and the pH was maintained at 10 ± 0.5 by adding solution C dropwise. After titration, the reaction solution was aged at a constant temperature of 70℃ for 6 hours. Nitrogen was not introduced during the entire titration and aging process to ensure the preparation was not affected by carbon dioxide. After aging, the solution was washed and filtered until the pH of the filtrate reached 7. The filtered wet cake-like solid phase was then dried in a vacuum oven at 70℃ for 24 hours. The dried solid phase was then pulverized and sieved to obtain a 40-mesh catalyst for catalyst pretreatment. The catalyst was fixed in a reaction bed, and ozone at a flow rate of 100 ml / min and a concentration of 160 ppm was introduced until the catalyst completely changed color and remained as a residue, yielding the NiOOH3Fe1 catalyst, which catalyzes the decomposition of ozone.

[0032] In this embodiment, a low-humidity (RH=65%) ozone catalytic decomposition experiment was conducted on the prepared nickel-iron non-intercalated nickel-iron hydrotalcite catalyst (NiOOH3Fe1) with a nickel-iron molar mass ratio of 3:1.

[0033] 0.05 g of NiOOH3Fe1-LDH catalyst was weighed and placed in a 4 mm quartz reaction tube, which was then placed in a temperature-controlled device. The gas flow rate in this experiment was 700 ml / min. The volume hourly space velocity was 840 L / (g·h), the ozone inlet concentration was 100 ppm, and the relative humidity was 60%. The ozone removal efficiency graph is shown below. Figure 2 It can be seen that the catalyst Ni3Fe1-OAa-LDH can completely catalytically decompose ozone gas at a relative humidity of 60%.

[0034] Example 4

[0035] In this embodiment, a high humidity (RH=90%) ozone catalytic decomposition experiment was conducted on the nickel-iron layered double hydroxide catalyst (NiOOH3Fe1-OAa) with an octanoate intercalation prepared in Example 1 and having a nickel-iron molar mass ratio of 3:1.

[0036] 0.05 g of Ni3Fe1-OAa-LDH catalyst was weighed and placed in a 4 mm quartz reaction tube, which was then placed in a temperature-controlled device. The gas flow rate in this experiment was 700 ml / min. The volume hourly space velocity was 840 L / (g·h), the ozone inlet concentration was 100 ppm, and the relative humidity was 90%. The ozone removal efficiency is shown in the figure below. Figure 3 As shown, the ozone gas conversion rate of the Ni3Fe1-OAa-LDH catalyst can reach over 98% at a relative humidity of 90%. This demonstrates that the Ni3Fe1-OAa-LDH catalyst possesses excellent moisture resistance and can achieve catalytic decomposition of ozone under high humidity conditions.

[0037] Example 5

[0038] In this embodiment, the non-intercalated nickel-iron hydrotalcite catalyst (NiOOH3Fe1) with a nickel-iron molar mass ratio of 3:1 prepared in Example 1 was subjected to a high humidity (RH=90%) ozone catalytic decomposition experiment.

[0039] 0.05 g of NiOOH3Fe1-LDH catalyst was weighed and placed in a 4 mm quartz reaction tube, which was then placed in a temperature-controlled device. The gas flow rate in this experiment was 700 ml / min. The volume hourly space velocity was 840 L / (g·h), the ozone inlet concentration was 100 ppm, and the relative humidity was 90%. The ozone removal efficiency is shown in the figure below. Figure 3 As shown, the Ni3Fe1-LDH catalyst achieves only a 60% conversion rate for ozone gas at a relative humidity of 90%. This indicates that the moisture resistance of the unintercalated material is relatively poor compared to the octanoic acid intercalated material, making it unable to efficiently catalyze the decomposition of ozone gas in high humidity conditions.

[0040] The principle of this invention is as follows: First, nickel-iron hydrotalcite morphology is prepared by titrating nickel nitrate and ferric nitrate under alkaline conditions. Nitric acid is easily replaced by other anions, making octanoic acid ions more prone to intercalation into the hydrotalcite-like structure. Nitrogen gas is used to protect it from carbon dioxide interference, and sodium octanoic acid solution is added dropwise to facilitate the reaction, allowing it to intercalate into the interlayer of the nickel-iron hydrotalcite. During this process, stirring is used to achieve a uniform reaction. After thorough mixing, a certain amount of sodium hydroxide solution is added during titration to adjust the reaction environment to alkaline, synthesizing an alkaline hydrotalcite catalyst. After the reaction, aging allows the catalyst particle size to grow, resulting in a catalyst with superior crystallinity. Subsequently, filtration and washing are performed to remove impurity ions dissolved in the reaction solvent. The obtained wet cake is then dried in a vacuum oven, avoiding interference from carbon dioxide during the drying process. This process enabled the successful intercalation of octanoic acid ions into nickel-iron hydrotalcite, forming a hydrophobic layer on its surface and achieving superior moisture resistance. The obtained solid catalyst underwent pretreatment to promote the dehydrogenation reaction, exposing more unsaturated oxygen sites and obtaining the catalyst NiOOHFe-OAa, which can stably catalyze the decomposition of ozone in high humidity and high concentration for a long time.

[0041] The preferred embodiments of the present invention disclosed above are only for the purpose of illustrating the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation described.

Claims

1. A method for preparing a catalyst for the catalytic decomposition of ozone in high humidity, characterized in that, Includes the following steps: S1: Dissolve nickel nitrate and ferric nitrate in deionized water at a ratio of 2:1 to 3:1 to obtain solution A; S2: Dissolve sodium octanoate and sodium hydroxide in deionized water in a ratio of 2:1 to 4:1 to obtain alkaline solution B; S3: Dissolve solutions A and B under ultrasonic treatment at 25-50℃ for 0.5-1.5 hours; S4: Titrate solutions A and B into the reaction vessel at a fixed rate. The reaction vessel is completely sealed during the titration process, and nitrogen gas is introduced to prevent carbon dioxide from interfering with the reaction. The temperature and stirring rate are kept constant during titration, and the pH value of the reaction solution in the reactor is controlled by adding pure sodium hydroxide alkaline solution. The concentration of the pure sodium hydroxide alkaline solution used to control the pH is 4-6 mol / L until the pH of the reaction solution is maintained between 9 and 11. S5: After titration, the suspension is aged, then filtered and washed with deionized water until the filtrate is neutral. The solid phase is then collected. S6: The solid phase obtained in S5 is dried, pressed into tablets, and sieved to obtain octanoic acid-intercalated nickel-iron hydrotalcite. S7: Ozone pretreatment of nickel-iron hydrotalcite with octanoic acid anion intercalation at a concentration of 100-200 ppm and a flow rate of 1 L / min or higher is carried out; the treatment is completed when the catalyst color changes completely from green to black, which causes hydrogen loss on the catalyst surface and transforms the material structure to form a NiOOHFe-OAa structure.

2. The method for preparing a catalyst for the catalytic decomposition of ozone in high humidity according to claim 1, characterized in that, In step S4, the titration rates of solutions A and B should be kept at the same rate, and the titration rate should be maintained at 1 to 2 mL / min. The total flow rate of nitrogen gas should be no less than 10 mL / min. The temperature during the titration process should be maintained at 60 to 80 ℃, and the stirring speed should be maintained at more than 250 rpm during the titration process.

3. The method for preparing a catalyst for the catalytic decomposition of ozone in high humidity according to claim 1, characterized in that, The aging temperature in S5 is 60 ~ 80 ℃, and the aging time is 4 ~ 6 h.

4. The method for preparing a catalyst for the catalytic decomposition of ozone in high humidity according to claim 1, characterized in that, In step S6, a vacuum oven is used for drying to prevent carbon dioxide from affecting the catalyst preparation process. The drying temperature is 70-80℃ and the drying time is at least 24 hours. At the same time, the sieve size should be 40-60 mesh.

5. The application of the catalytic high humidity ozone decomposition catalyst prepared by the method described in any one of claims 1-4 in ozone decomposition.

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