Catalyst with Cu-N vacancy defect, preparation method of catalyst and application of catalyst in catalytic ozonolysis

Abstract

The invention discloses a catalyst with a Cu-N vacancy defect, a preparation method of the catalyst and application of the catalyst in catalytic ozonolysis. The catalyst is of a nickel-iron hydrotalcite structure and contains Cu and N; in the catalyst, the molar ratio of Ni to Fe is (2.9-3.1): 1, the content of Cu accounts for 3-18% of the total amount of substance of Ni and Fe, and a Cu-N vacancy defect is formed between Cu and N. The formation of the Cu-N vacancy defect increases the oxygen vacancy content, so that the catalyst has excellent ozonolysis performance, and the obtained catalyst has excellent moisture resistance and shows excellent ozonolysis efficiency under dry and wet air conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to a catalyst with Cu-N vacancy defects, a preparation method thereof and application in catalytic ozone decomposition, and belongs to the technical field of catalysts. BACKGROUND

[0002] Ozone (O3) pollution has become a global environmental problem, and its concentration increases significantly under high-temperature conditions in summer, which has multiple negative impacts on the human respiratory system (such as increased incidence of asthma) and the ecological system (such as reduced crop yields). The catalytic decomposition method has the advantages of high efficiency, low cost, no secondary pollution, and low reaction temperature, and is currently the most promising method for addressing ozone pollution. The key to the catalytic decomposition method is to develop a highly efficient and stable ozone decomposition catalyst.

[0003] Layered double hydroxides (LDHs), also known as hydrotalcites, have a wide range of cation types, adjustable interlayer compensating anions, and mature synthesis methods, which make LDH materials have a large number of host-guest components and nanostructures with multifunctional physical and chemical properties. As a result, hydrotalcites have been widely studied and applied as catalyst materials, composite materials, and other materials, and have shown obvious advantages in the field of ozone catalytic decomposition.

[0004] Oxygen vacancies have been proven to be active sites for ozone decomposition reactions. Jia et al. increased the oxygen vacancy content on the surface of OMS-2 by doping Cu, which improved the ozone decomposition performance under humid conditions. In addition, hydrotalcite materials with hydroxyl groups as the main active sites can avoid the reduction of activity caused by competitive adsorption of water molecules, effectively compensating for the shortcoming of insufficient oxygen vacancies, and can adapt to ozone decomposition under various complex conditions. Studies have shown that Ni3Fe-LDH prepared by the coprecipitation method has an ozone decomposition efficiency of 89% under the conditions of 40 ppm ozone, 65% relative humidity, and 840 L·g -1 ·h -1 However, there is still much room for improvement in the ozone decomposition efficiency of the catalyst, especially under high humidity and high air velocity conditions, where the ozone decomposition efficiency will be greatly reduced. SUMMARY

[0005] The present application relates to a catalyst with Cu-N vacancy defects, a preparation method thereof and application in catalytic ozone decomposition, and belongs to the technical field of catalysts.

[0006] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows: A catalyst with Cu-N vacant defects, which is a nickel-iron hydrotalcite structure (i.e. a layered hydroxide containing nickel-iron elements of a hydrotalcite structure) and contains Cu and N; in the catalyst, the molar ratio of Ni and Fe is (2.9-3.1):1, the content of Cu is 3-18% of the total amount of substance of Ni and Fe, and Cu-N vacant defects are formed between Cu and N.

[0007] Preferably, Cu-N vacant defects are formed between Cu + -N bonds and Cu 2+ -N bonds.

[0008] The preparation method of any of the above-mentioned catalysts with Cu-N vacant defects is to mix urea with a solution containing nickel, iron and copper, and after hydrothermal reaction, cooling, suction filtration and drying.

[0009] Preferably, in the solution, the nickel source is one or more of nickel sulfate, nickel chloride, nickel nitrate and nickel acetate; the iron source is one or more of ferrous sulfate, ferrous chloride, ferric nitrate and ferric acetate; the copper source is one or more of copper sulfate, copper chloride, copper nitrate and copper acetate; the solvent is deionized water.

[0010] Preferably, the amount of urea is 3-8 times the total amount of substance of nickel and iron in the solution, and the pH is controlled at 9-10.

[0011] Preferably, the hydrothermal reaction conditions are 120-150 DEG C for 8-24 h.

[0012] Preferably, the drying conditions are 50-70 DEG C for 10-48 h.

[0013] The application of any of the above-mentioned catalysts with Cu-N vacant defects in catalyzing the decomposition of ozone in an ozone-containing gas.

[0014] Preferably, the humidity of the ozone-containing gas is 0-90%.

[0015] A method for increasing the content of oxygen vacancies in a nickel-iron hydrotalcite catalyst, which is to add urea and copper-containing substances in the preparation of a nickel-iron hydrotalcite catalyst, and to use Cu-N vacant defects formed between Cu and N to increase the content of oxygen vacancies, and in the obtained catalyst, the content of Cu is 3-18% of the total amount of substance of Ni and Fe.

[0016] The beneficial effects of the present application are: The catalyst has a larger specific surface area, and contains both hydroxyl groups and oxygen vacancies as active sites, and the presence of Cu-N vacancy defects increases the oxygen vacancy content, greatly improves the ozone decomposition efficiency, and the presence of Cu-N vacancy defects also improves the moisture resistance of the catalyst, so that the ozone decomposition efficiency under humid conditions is also improved. Under the condition of 60% relative humidity, the ozone removal rate is as high as 98%~100% in 3h, and under the condition of 60% relative humidity, the ozone decomposition efficiency is close to 100% in 72h. -1 ·h -1 , 60% relative humidity, the ozone removal rate is as high as 98%~100% in 3h, and under the condition of 60% relative humidity, the ozone decomposition efficiency is close to 100% in 72h. -1 ·h -1 , 60% relative humidity, the ozone removal rate is as high as 98%~100% in 3h, and under the condition of 60% relative humidity, the ozone decomposition efficiency is close to 100% in 72h. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 XRD patterns of different catalysts prepared in examples and comparative examples; Figure 2 SEM images of NiFe-LDH (a) and 15CuNiFe-LDH (b); Figure 3 XPS spectra of NiFe-LDH and 15CuNiFe-LDH; Figure 4 Hydroxyl radical and oxygen vacancy EPR spectra of NiFe-LDH (a) and 15CuNiFe-LDH (b); Figure 5 Performance test chart of the prepared material. DETAILED DESCRIPTION

[0018] Example 1: 2.8218g of nickel nitrate hexahydrate, 0.8987g of ferrous sulfate heptahydrate, 0.1562g of copper nitrate trihydrate and 3.8827g of urea were weighed and dissolved in 150mL of deionized water, and stirred for 20min; pour the solution into a 200mL polytetrafluoroethylene reaction kettle, and react at 120℃ for 12h; after taking out the reaction kettle, cool it to room temperature naturally, and filter the material to neutral with deionized water; put the wet cake-shaped solid into a 60℃ oven and dry overnight to obtain a 5% Cu (recorded as the percentage of Cu in the total amount of matter of nickel and iron, the same below) doped catalyst (recorded as 5CuNiFe-LDH).

[0019] Example 2: Weigh 2.8218 g of nickel nitrate hexahydrate, 0.8987 g of ferrous sulfate heptahydrate, 0.3124 g of copper nitrate trihydrate and 3.8827 g of urea, dissolve them in 150 mL of deionized water, stir for 20 min; pour the solution into a 200 mL polytetrafluoroethylene reactor, react at 120°C for 12 h; after taking out the reactor, cool it to room temperature naturally, filter the material to neutral with deionized water; put the wet cake-shaped solid into a 60°C oven and dry overnight to obtain a 10% Cu-doped catalyst (denoted as 10CuNiFe-LDH).

[0020] Example 3: Weigh 2.8218 g of nickel nitrate hexahydrate, 0.8987 g of ferrous sulfate heptahydrate, 0.4686 g of copper nitrate trihydrate and 3.8827 g of urea, dissolve them in 150 mL of deionized water, stir for 20 min; pour the solution into a 200 mL polytetrafluoroethylene reactor, react at 120°C for 12 h; after taking out the reactor, cool it to room temperature naturally, filter the material to neutral with deionized water; put the wet cake-shaped solid into a 60°C oven and dry overnight to obtain a 15% Cu-doped catalyst (denoted as 15CuNiFe-LDH).

[0021] Example 4: Weigh 2.8218 g of nickel nitrate hexahydrate, 0.8987 g of ferrous sulfate heptahydrate, 0.6248 g of copper nitrate trihydrate and 3.8827 g of urea, dissolve them in 150 mL of deionized water, stir for 20 min; pour the solution into a 200 mL polytetrafluoroethylene reactor, react at 120°C for 12 h; after taking out the reactor, cool it to room temperature naturally, filter the material to neutral with deionized water; put the wet cake-shaped solid into a 60°C oven and dry overnight to obtain a 20% Cu-doped catalyst (denoted as 20CuNiFe-LDH).

[0022] Comparative Example 1: Weigh 2.8218 g of nickel nitrate hexahydrate, 0.8987 g of ferrous sulfate heptahydrate, and 3.8827 g of urea, dissolve them in 150 mL of deionized water, stir for 20 min; pour the solution into a 200 mL polytetrafluoroethylene reactor, react at 120°C for 12 h; after taking out the reactor, cool it to room temperature naturally, filter the material to neutral with deionized water; put the wet cake-shaped solid into a 60°C oven and dry overnight to obtain a catalyst (denoted as NiFe-LDH).

[0023] Comparative Example 2: Weigh 4.4091 g of iron nitrate hexahydrate and 1.39 g of ferrous sulfate heptahydrate and dissolve in 20 mL of deionized water, stir for 20 min to obtain solution A; weigh 1.3333 g of sodium hydroxide and 1.0611 g of sodium carbonate and dissolve in 20 mL of deionized water, stir for 20 min to obtain solution B; slowly drop solution A and solution B into 40 mL of deionized water at the same time, stir for five hours in an 80°C oil bath; naturally cool to room temperature, filter the material to neutral with deionized water; put the wet cake-shaped solid into a 60°C oven to dry overnight to obtain a NiFe-LDH-C catalyst.

[0024] Comparative Example 3: Weigh 4.4091 g of nickel nitrate hexahydrate, 1.39 g of ferrous sulfate heptahydrate, and 0.7248 g of copper nitrate trihydrate and dissolve in 20 mL of deionized water, stir for 20 min to obtain solution A; weigh 1.3333 g of sodium hydroxide and 1.0611 g of sodium carbonate and dissolve in 20 mL of deionized water, stir for 20 min to obtain solution B; slowly drop solution A and solution B into 40 mL of deionized water at the same time, stir for five hours in an 80°C oil bath; naturally cool to room temperature, filter the material to neutral with deionized water; put the wet cake-shaped solid into a 60°C oven to dry overnight to obtain a 15% Cu-doped NiFe-LDH-C catalyst (denoted as 15CuNiFe-LDH-C).

[0025] Comparative Example 4: Weigh 8.8182 g of nickel nitrate hexahydrate and 2.78 g of ferrous sulfate heptahydrate and dissolve in 35 mL of deionized water, stir for 10 min to obtain solution A; weigh 3.2 g of sodium hydroxide and add to 15 mL of deionized water, stir to dissolve to obtain solution B; drop solution B into solution A and stir vigorously; pour the solution into a 200 mL polytetrafluoroethylene reaction kettle, react at 180°C for 24 h; after taking out the reaction kettle, naturally cool to room temperature, filter the material to neutral with deionized water; put the wet cake-shaped solid into a 60°C oven to dry overnight to obtain a Na-NiFe-LDH-H catalyst.

[0026] Comparative Example 5: Weigh 8.8182 g of nickel nitrate hexahydrate, 2.78 g of ferrous sulfate heptahydrate, and 1.4496 g of copper nitrate trihydrate and dissolve in 35 mL of deionized water, stir for 10 min to obtain solution A; weigh 3.2 g of sodium hydroxide and add to 15 mL of deionized water, stir to dissolve to obtain solution B; drop solution B into solution A and stir vigorously; pour the solution into a 200 mL polytetrafluoroethylene reaction kettle, react at 180°C for 24 h; after taking out the reaction kettle, naturally cool to room temperature, filter the material to neutral with deionized water; put the wet cake-shaped solid into a 60°C oven to dry overnight to obtain a 15% Cu-doped Na-NiFe-LDH-H catalyst (denoted as Na-15CuNiFe-LDH-H).

[0027] Figure 1For the XRD patterns of different catalysts prepared in the examples and comparative examples, the crystallinity of XRD becomes weaker with the increase of the content of vacancy adjuster Cu, the peak intensity of 20CuNiFe-LDH is the weakest, and tends to be amorphous, so the effect is not as good as 15CuNiFe-LDH.

[0028] Figure 2 For the SEM patterns of NiFe-LDH and 15CuNiFe-LDH, it can be seen that the catalyst morphology changes obviously after adding the vacancy adjuster copper, the size is larger, and the specific surface area is also improved.

[0029] Figure 3 For the XPS patterns of NiFe-LDH and 15CuNiFe-LDH, from the a area of Figure 3 The basic composition of all elements can be observed, and the N 1s peak of 15CuNiFe-LDH is slightly enhanced. From the b, c area of Figure 3 It can be seen that the binding energy has no obvious change before and after the doping of vacancy adjuster Cu. From the d area of Figure 3 It can be seen that the oxygen vacancy content of 15CuNiFe-LDH is increased and the hydroxyl content is reduced compared with NiFe-LDH. From the e area of Figure 3 It can be seen that the binding energy position of N 1s shifts to the high position, which confirms the successful addition of vacancy adjuster Cu and the formation of Cu-N bond with N, which helps to produce more vacancies and further decompose ozone. From the f area of Figure 3 Cu + The content is 36%, which is higher than the 24% of Cu 2+ , indicating that the Cu-N bond is mainly in the form of Cu + -N bond.

[0030] Figure 4 For the EPR patterns of NiFe-LDH and 15CuNiFe-LDH, from Figure 4 It can be seen that 15CuNiFe-LDH can also moderately increase the oxygen vacancy content on the basis of moderately reducing the hydroxyl content. This characterization as direct evidence is consistent with the XPS results, further verifying the conclusion.

[0031] Application effect evaluation.

[0032] The catalyst evaluation device (i.e. ozone catalytic decomposition experiment is used to test the ozone conversion rate) is built, and the silica hose is connected in sequence to the air generator, mass flow meter, ozone generator, humidification gas washing bottle, U-shaped quartz glass reaction tube, ozone detector and tail gas absorption bottle.

[0033] Turn on the air generator and adjust the airflow to 60L / h, turn on the ozone generator and adjust the ozone concentration to about 50ppm.

[0034] 50 mg of molded catalyst was loaded into the quartz glass reaction tube and supported at the bottom with quartz wool. After the gas flow stabilized, the gas path was switched to the pipeline containing the catalyst, the reaction timer was started, and the ozone concentration at the outlet was recorded periodically.

[0035] Figure 5 The performance test graphs of the prepared catalyst are shown below. Figure 5 As shown in region a, under the same test conditions, 15CuNiFe-LDH exhibits the highest ozone removal efficiency and significantly improved moisture resistance. Figure 5 The middle b region shows a comparison of dry and wet atmosphere switching experiments for 15CuNiFe-LDH and NiFe-LDH. It was observed that the ozone decomposition efficiency of both 15CuNiFe-LDH and NiFe-LDH was 100% under dry gas conditions. However, when switching to wet gas, the activity of NiFe-LDH decreased significantly, while 15CuNiFe-LDH still maintained an ozone decomposition efficiency of about 99%. This indicates that the addition of the vacancy regulator Cu (forming Cu-N vacancy defects) can significantly improve the ozone decomposition efficiency under wet gas conditions. Figure 5 Region c represents the ozone decomposition efficiency after adding Cu using both the co-precipitation and hydrothermal methods (adding sodium hydroxide instead of urea). It was observed that the Cu-doped catalyst prepared by the traditional co-precipitation method showed a significant decrease in performance. Furthermore, the material prepared by the hydrothermal method using sodium hydroxide instead of urea also exhibited poor performance, indirectly confirming that the formation of Cu-N bonds in 15CuNiFe-LDH improves the catalytic effect of the material. Figure 5 As can be seen from region d, at an airspeed of 850 L·g -1 ·h -1 Under 60% relative humidity, 15CuNiFe-LDH achieved nearly 100% ozone decomposition efficiency in 72 hours.

[0036] 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 catalyst having Cu-N vacancy defects, characterized in that, The catalyst has a nickel-iron hydrotalcite structure and contains Cu and N; in the catalyst, the molar ratio of Ni to Fe is (2.9-3.1):1, the content of Cu is 3-18% of the total amount of Ni and Fe, and Cu-N vacancy defects are formed between Cu and N.

2. The catalyst with Cu-N vacancy defects according to claim 1, characterized in that, Cu forms between Cu and N + -N bond and Cu 2+ -N key.

3. The method for preparing the catalyst with Cu-N vacancy defects according to any one of claims 1-2, characterized in that, It involves mixing urea with a solution containing nickel, iron, and copper, reacting it hydrothermally, and then cooling, filtering, and drying the mixture.

4. The method for preparing the catalyst with Cu-N vacancy defects according to claim 3, characterized in that, In the solution, the nickel source is one or more of nickel sulfate, nickel chloride, nickel nitrate, and nickel acetate; The iron source is one or more of ferrous sulfate, ferrous chloride, ferric nitrate, and ferric acetate; The copper source is one or more of copper sulfate, copper chloride, copper nitrate, and copper acetate; The solvent is deionized water.

5. The method for preparing the catalyst with Cu-N vacancy defects according to claim 3, characterized in that, The amount of urea used should be 3-8 times the total amount of nickel and iron in the solution, and the pH should be controlled at 9-10.

6. The method for preparing the catalyst with Cu-N vacancy defects according to claim 3, characterized in that, The hydrothermal reaction conditions are: 120-150℃, 8-24h.

7. The method for preparing the catalyst with Cu-N vacancy defects according to claim 3, characterized in that, The drying conditions are: 50-70℃, 10-48h.

8. The application of the catalyst with Cu-N vacancy defects according to any one of claims 1-2 in the catalytic decomposition of ozone in ozone-containing gases.

9. The application according to claim 8, characterized in that, The humidity level containing ozone gas is 0-90%.

10. A method for increasing the oxygen vacancy content in a nickel-iron hydrotalcite catalyst, characterized in that, The process involves adding urea and copper-containing substances to the preparation of nickel-iron hydrotalcite catalysts. This utilizes the formation of Cu-N vacancy defects between Cu and N to increase the oxygen vacancy content. In the resulting catalyst, the Cu content is 3-18% of the total amount of Ni and Fe.

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