An ozone decomposition catalyst with excellent low temperature activity and water resistance and its preparation method and application

Abstract

The present invention discloses an ozone decomposition catalyst with excellent low temperature activity and water resistance, and a preparation method and application thereof, which belongs to the field of ozone catalytic removal. The catalyst is a highly active nitrogen-doped MnO2 catalyst and a highly dispersed loaded noble metal catalyst, wherein the active component of the loaded catalyst is selected from at least one of Pd and Ag. The catalyst has a high activity at 600,000 h. ‑1 , 25 ℃, 15ppmO3, high relative humidity (RH=95%), it has excellent ozone decomposition activity and stability. The catalyst is expected to be used in the field of near-ground, sewage ozone oxidation exhaust purification or aircraft cabin ozone catalytic removal.

Description

Technical Field

[0001] The invention relates to an ozone decomposition catalyst with excellent low-temperature activity and water resistance, a preparation method thereof and application in removing ozone near the ground or in an aircraft cabin, and belongs to the field of ozone catalytic removal. Background Art

[0002] Ozone is composed of three oxygen atoms and is an allotrope of oxygen. Its molecular structure is C 2v Symmetrical isosceles triangle, the distance of OO bond is 0.128nm, and the bond angle is 116.49°. Ozone, as a strong oxidant, can react with most substances at low temperature. In acidic solution, the oxidizing property of ozone is second only to fluorine, atomic oxygen and hydroxyl radicals, and it can react with all elements in the periodic table except inert gases, fluorine and precious metals. Ozone is distributed in the stratosphere and near the ground. Its existence is a double-edged sword for human production and life and even the natural environment of the earth. On the one hand, the content of ozone in the stratosphere 10 to 50 km from the surface is about 50ppm. When exposed to long-wave ultraviolet radiation, an ozone molecule will decompose into an oxygen molecule and an oxygen atom; when exposed to short-wave ultraviolet radiation, the oxygen molecule will decompose into two oxygen atoms, and the oxygen atom can combine with another oxygen molecule to regenerate ozone. This process makes the oxygen and ozone content in the atmosphere in a dynamic balance, and can also absorb ultraviolet rays to protect organisms. On the other hand, the increase in ground-level ozone concentration has caused great harm to the health of animals, plants and humans. It is also one of the main components of "smog". On hot sunny days, the ozone content will increase significantly. Even relatively low levels of ozone will have an impact on health. Affected groups include asthma patients, children, the elderly and outdoor workers. In addition, people who lack certain nutrients such as vitamin C and E are more affected when exposed to ozone. High concentrations of ozone can cause cardiovascular disease, respiratory dysfunction, neurotoxicity, memory loss, decreased vision, impaired human immune function, lymphocyte lesions, and accelerated human aging.

[0003] There are two main sources of ozone in the troposphere, natural sources and anthropogenic sources. Natural sources refer to inputs from the stratosphere and emissions from plants in nature. Anthropogenic ozone is produced by a series of photochemical reactions under light caused by volatile organic compounds (VOCs) and nitrogen oxides (NOx) emitted into the atmosphere by human activities such as transportation, petrochemicals, thermal power generation, and biomass combustion. Ozone in indoor environments mainly comes from outdoors, but machines such as copiers, laser printers, electrostatic air filters, and electrostatic precipitators also produce ozone during operation. The ozone content in the cabin of an airplane on a long flight should not be underestimated. In 2005, the World Health Organization issued the "Air Quality Guidelines", which stipulates that the average ozone concentration within a maximum of 8 hours per day must be lower than 100μg·m -3 In 2015, the U.S. Environmental Protection Agency (EPA) established primary and secondary standards for the concentrations of six major pollutants, including ozone, that may be harmful to public health and the environment. The ozone concentration requirement is that the maximum daily average concentration over 8 hours should not exceed 0.07 ppm. In 2012, the National Environmental Quality Standard "Ambient Air Quality Standard" (GB3095-2012) jointly issued by my country's Ministry of Environmental Protection and the General Administration of Quality Supervision, Inspection and Quarantine stipulates that the average daily ozone concentration within 8 hours should not exceed 100 μg·m -3 (primary standard) and 160 μg·m -3 (Secondary standard). my country's "Special Requirements for Air Purifiers with Antibacterial, Sterilizing and Purifying Functions for Household and Similar Electrical Appliances" (GB21551.3-2010) also stipulates that the harmful substances produced by air purifiers: the ozone concentration (5 cm from the air outlet) shall not exceed 100 μg / m 3 .

[0004] At present, there have been many relevant research reports on methods for ozone removal and decomposition. Common methods include: catalytic decomposition, thermal decomposition, activated carbon adsorption, solution absorption, plasma decomposition, electromagnetic wave radiation decomposition, etc. So far, the catalytic decomposition method with the advantages of safety, economy, and efficiency is still the most ideal and potential ozone decomposition method. O3 decomposition catalysts usually need to efficiently decompose O3 at room temperature or even low temperature, high humidity and high air velocity. The presence of water vapor often occupies active sites, thereby reducing the O3 decomposition activity of the catalyst. Low temperature and high air velocity conditions also place very strict requirements on the catalyst. Therefore, it is very important to develop catalysts with high activity and high moisture resistance at room temperature or even sub-zero temperatures. Summary of the invention

[0005] The object of the present invention is to provide an ozone decomposition catalyst which can decompose ozone efficiently at room temperature and has a long service life by using N-doped manganese dioxide as an ozone decomposition catalyst and a catalyst carrier, and loading precious metal Pd.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned catalyst, in which the raw materials are widely available and the preparation process is simple and easy.

[0007] In order to achieve the above invention objectives, the present invention includes the following specific technical solutions:

[0008] A catalyst comprises a carrier and an active component; the carrier is nitrogen-doped manganese dioxide (N-MnO2); and the active component is selected from Pd and / or Ag.

[0009] Optionally, the loading amount of the active component is 0.01 wt.% to 10 wt.% of the catalyst.

[0010] Optionally, when the active component is selected from Pd and Ag, the molar ratio of Ag to Pd is 0.1-10.

[0011] Optionally, the loading amount of the active component is 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 6wt%, 7wt%, 8wt% or 9wt% of the catalyst, or any value between any two of the above points.

[0012] Optionally, the nitrogen doping amount in the carrier is 0.5% to 5%.

[0013] The present invention also provides a method for preparing the catalyst, which comprises immersing an equal volume of nitrogen-doped manganese dioxide in a solution I containing an active component precursor, and calcining the solution to obtain the catalyst.

[0014] Optionally, the active component precursor is selected from at least one of metal acetate and nitrate; the solvent of the solution I is deionized water; the concentration of the solution I is 0.5 to 3 mol / L;

[0015] The mass volume ratio of the nitrogen-doped manganese dioxide to solution I is 5 to 20 (g:mL).

[0016] Optionally, the calcination temperature is 100-600° C. and the calcination time is 2-10 hours.

[0017] Optionally, the nitrogen-doped manganese dioxide is prepared by any one of method a, method b or method c:

[0018] Method a: calcining MnO2 at 100-500°C in NH3 atmosphere for 2-8 hours; preferably, MnO2 is prepared by a solid state method;

[0019] Method b: Nitrogen-doped MnO2 was prepared by in-situ hydrothermal method using raw materials containing manganese acetate, urea and PVP;

[0020] Method c: In the presence of NH4 + It is prepared by liquid phase heat treatment of MnO2 in an aqueous solution.

[0021] Optionally, the method b is to react an aqueous solution containing manganese acetate, urea and PVP at 150-200° C. for 2-10 hours; centrifugally separate the generated precipitate, wash it with water, wash it with alcohol, dry it, and calcine it at 300-500° C. for 2-4 hours.

[0022] Optionally, the molar ratio of manganese acetate, urea and PVP is 0.5-15; and the reactor of method b is a hydrothermal reactor.

[0023] Optionally, the method c is to add MnO2 to a mixture containing NH4 + The mixture is stirred vigorously at 400-800 r / min for 2-10 hours in an aqueous solution at 40-80°C; centrifuged, washed with water and alcohol, and dried at 50-150°C for 2-12 hours.

[0024] Optionally, the MnO2 and NH4 + The molar ratio is 1 to 10.

[0025] The present invention also provides the use of the catalyst and the catalyst prepared by the preparation method in ozone decomposition.

[0026] Optionally, the catalyst is suitable for a space velocity of 300,000 to 1,000,000 h -1 , ozone decomposition under the conditions of temperature 25~200℃, humidity RH=95%, and O3 concentration 0~30ppm.

[0027] Optionally, a use of nitrogen-doped manganese dioxide in ozone decomposition.

[0028] As an embodiment of the present invention, a method for preparing nitrogen-doped manganese dioxide uses potassium permanganate (KMnO4) and divalent manganese salt as raw materials, grinds them for reaction, heats them for reaction, obtains manganese dioxide by a solid-state method, and further introduces nitrogen atoms.

[0029] Optionally, the divalent manganese salt is selected from one of manganese sulfate (MnSO4), manganese nitrate (MnAc2), manganese acetate (Mn(NO3)2), manganese chloride (MnCl2) and manganese carbonate (MnCO3).

[0030] Optionally, the molar ratio of potassium permanganate to divalent manganese salt is 0.5 to 2.5.

[0031] Optionally, after sufficient grinding and reaction, the mixture is placed in an oven for heating reaction, and the obtained solid is centrifuged and washed with water to obtain manganese dioxide (MnO2); the heating reaction temperature is 40-100°C, which can be selected as 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C, or any value between any two of the above points; the heating reaction time is 2-8h, which can be selected as 2h, 3h, 4h, 5h, 6h, 7h or 8h, or any value between any two of the above points.

[0032] Optionally, nitrogen atoms are introduced into manganese dioxide using any of methods (a), (b) or (c):

[0033] (a) MnO2 is heat treated in an atmosphere containing N atoms.

[0034] The heat treatment atmosphere is selected from at least one of N2 or NH3; the heat treatment temperature is 100-500°C, which can be selected as 100°C, 200°C, 300°C, 400°C or 500°C, or any value between any two of the above points; the heat treatment time is 1-4 hours.

[0035] (b) Prepared by in situ hydrothermal method.

[0036] Manganese acetate tetrahydrate (MnAc2·4H2O) is added to deionized water containing ethylene glycol, and stirred and dissolved thoroughly, wherein ethylene glycol is used as a dispersant; the molar ratio of ethylene glycol to manganese acetate is 0.5-2.5. Then urea and PVP are added to the mixed solution stirred evenly, and the mixture is stirred evenly at room temperature; the molar ratio of urea to manganese acetate is 0.5-15, and the molar ratio of urea to PVP is 1-10; the average molecular weight of PVP is 3500-13000000, which can be selected as 3600, 5500, 10100, 58000 or 1300000. The mixed solution stirred evenly is transferred to a hydrothermal reactor, the reaction temperature is 120-200°C, and the reaction time is 2-10 hours. The generated precipitate is centrifuged, washed with water and alcohol, dried, and then roasted in an air atmosphere, the roasting temperature is 200-500°C, and the roasting time is 2-6 hours.

[0037] (c) Prepared by ion exchange method.

[0038] Take an appropriate amount of MnO2 and mix it with an aqueous solution of ammonium salt, where MnO2 and NH4 + The molar ratio of NH4 is 1 to 10. At a certain temperature, + K in the MnO2 pore structure +Exchange. The type of ammonium salt can be selected from NH4Ac solution, (NH4)2CO3 solution, (NH4)2SO4 solution, NH4Cl solution, urea aqueous solution or melamine aqueous solution; the concentration of the ammonium salt solution is 10g / L~200g / L. The temperature of the solution is controlled at 40~80℃, and the reaction time is 2~10 hours. Then, the obtained solid is centrifuged, washed with water and alcohol several times, and dried at 105℃ for 12h. The dried sample is calcined in an air atmosphere at a calcination temperature of 200~500℃ and a calcination time of 2~6 hours.

[0039] The beneficial effects of the present invention include but are not limited to: the preparation method is mild and simple, without high temperature and high pressure, and the ion types and concentrations in the manganese dioxide pore structure are adjusted by doping with non-metallic elements, thereby improving the interaction between precious metals and manganese oxides and making oxygen desorption easier. The ozone decomposition performance of manganese oxide catalysts is effectively improved, especially the long-term stability performance under low temperature, high space velocity and high relative humidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The X-ray diffraction patterns of the catalysts in Examples 1, 2 and Comparative Example 2 are shown.

[0041] Figure 2 Schematic diagram of the catalytic decomposition of ozone by the catalysts in Examples 1 and 2 and Comparative Examples 1 and 2 under different humidity conditions.

[0042] Figure 3 This is a schematic diagram of the stability of the catalyst prepared in Example 2 in catalytic decomposition of ozone. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below through specific examples, but this should not be construed as limiting the scope of the above claims in the present invention to the following examples.

[0044] Example 1

[0045] Weigh 5g potassium permanganate and 12g manganese acetate, put the two solid powders into a quartz mortar, mix them evenly, and grind them thoroughly for 1h. Then put the obtained solid into an oven and react at 60°C for 4h, then centrifuge and wash the obtained solid with deionized water and ethanol solution. Put the obtained solid into a round-bottom flask, add 150mL of 1mol / L ammonium chloride solution, and stir it thoroughly to mix it evenly. At the same time, put the round-bottom flask into a 50°C water bath and continue stirring for 6h. Then continue to centrifuge and wash with deionized water and ethanol solution, and put it into an oven at 105°C for 12h. The dried solid is placed in a muffle furnace and calcined at 350°C for 4h in an air atmosphere to obtain a nitrogen-doped manganese dioxide catalyst, named NH4-MnO2 catalyst.

[0046] Example 2

[0047] Weigh 2 g of the NH4-MnO2 catalyst described in Example 1 and impregnate it with a 150 mg / mL palladium nitrate solution by an equal volume impregnation method, with a loading content of 1 wt% of precious metal Pd. After impregnation for 4 h, the catalyst was placed in an oven at 105°C and dried for 12 h. The dried solid was placed in a muffle furnace and calcined at 350°C for 4 h in an air atmosphere. The obtained catalyst was named Pd-NMnO2 catalyst.

[0048] Example 3

[0049] Weigh 2g of the NH4-MnO2 catalyst described in Example 1, and co-impregnate it with a mixed solution of palladium nitrate and silver nitrate with concentrations of 150mg / mL and 200mg / mL, respectively, by an equal volume impregnation method, and load 1wt% of precious metal Pd and precious metal Ag. After impregnation for 4h, the catalyst was placed in an oven at 105°C and dried for 12h. The dried solid was placed in a muffle furnace and calcined at 350°C for 4h in an air atmosphere. The obtained catalyst was named PdAg-NMnO2 catalyst.

[0050] Comparative Example 1

[0051] Weigh 5g potassium permanganate and 12g manganese acetate, put the two solid powders into a quartz mortar, mix them evenly, and grind them thoroughly for 1h. Then put the obtained solid into an oven and react at 60℃ for 4h. Then, wash the obtained solid with deionized water and ethanol solution by centrifugation, and put it into an oven at 105℃ to dry for 12h. The dried solid is placed in a muffle furnace and calcined at 350℃ for 4h in an air atmosphere to obtain a manganese dioxide catalyst, named S-MnO2 catalyst.

[0052] Comparative Example 2

[0053] Weigh 2g of the S-MnO2 catalyst described in Comparative Example 1, and impregnate it with a 150mg / mL palladium nitrate solution by an equal volume impregnation method, with a loading content of 1wt% of precious metal Pd. After impregnation for 4h, the catalyst was placed in an oven at 105°C and dried for 12h. The dried solid was placed in a muffle furnace and calcined at 350°C for 4h in an air atmosphere. The obtained catalyst was named Pd-MnO2 catalyst.

[0054] Comparative Example 3

[0055] Weigh 2g of the S-MnO2 catalyst described in Comparative Example 1, and co-impregnate a mixed solution of palladium nitrate and silver nitrate with concentrations of 150mg / mL and 200mg / mL, respectively, by an equal volume impregnation method, and load 1wt% of precious metal Pd and precious metal Ag. After impregnation for 4h, the catalyst was placed in an oven at 105°C and dried for 12h. The dried solid was placed in a muffle furnace and calcined at 350°C for 4h in an air atmosphere. The obtained catalyst was named PdAg-MnO2 catalyst.

[0056] Test Example 1

[0057] The X-ray diffraction patterns of the catalysts in Examples 1, 2 and Comparative Example 2 were measured. Figure 1 According to the XRD standard card (JCPDS NO.29-1020), the diffraction peaks at 12.745°, 18.059°, 28.737°, and 37.620° correspond to the {110}, {200}, {310}, and {211} crystal planes of cryptomelane-type manganese dioxide, respectively, indicating that the main phase of the catalyst after nitrogen doping and noble metal loading is still α-MnO2 with a rich pore structure. The lack of diffraction peaks of the corresponding noble metals indicates that the dispersion of the noble metals is good.

[0058] Test Example 2

[0059] Comparison of the catalytic decomposition of ozone by the catalysts in Examples 1, 2, and 3 with those in Comparative Examples 1, 2, and 3 under different humidity conditions. Figure 2 The experimental conditions are as follows: the reaction gas is air as the balance gas, and the ozone concentration is 15±1ppm; in a dry atmosphere, the temperature is 30℃, the relative humidity RH=0, and the air velocity is 600Lg -1 h -1 , catalyst dosage 0.15g; humid atmosphere, temperature 30℃, relative humidity RH=95%, space velocity 600Lg -1 h -1 , the catalyst dosage is 0.15g. The reaction is carried out under the same reaction conditions for 2 hours. Figure 2 It can be seen that the catalytic activity of the N-doped manganese dioxide carrier is better than that of the undoped catalyst under both low and high humidity conditions. After loading the precious metal, the activity of the manganese dioxide catalyst is further improved, effectively improving the performance of manganese oxide under high humidity conditions.

[0060] Test Example 3

[0061] Taking the catalyst in Example 2 as an example, the stability and life of the catalyst's ability to catalyze ozone decomposition were investigated. Figure 3The setting conditions are that the reaction gas is air as the balance gas, the ozone concentration is 15±1ppm; the temperature is 30℃, the relative humidity is <5%RH, and the air velocity is 600Lg -1 h -1 , catalyst dosage 0.15g; humid atmosphere, temperature 30℃, relative humidity>90%RH, air velocity 600Lg -1 h -1 , the catalyst dosage is 0.15g. The relative humidity in the reaction conditions is adjusted every 2 to 4 hours. After the reaction exceeds 80 hours, the conversion rate of the catalyst under high humidity conditions can still be maintained at about 80%, and when the relative humidity is reduced, the performance of the catalyst can be fully restored to 100%.

[0062] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A catalyst, characterized in that The catalyst comprises a carrier and an active component, wherein the active component is loaded on the carrier; the carrier is nitrogen-doped manganese dioxide; the active element in the active component is selected from Pd and / or Ag; The loading amount of the active noble metal element component is 0.01wt.% to 10wt.% of the catalyst; When the active component is selected from Pd and Ag, the molar ratio of Ag to Pd is 0.1 to 10; The nitrogen doping amount in the carrier is 0.5% to 5%; The catalyst is prepared by the following steps: An equal volume of nitrogen-doped manganese dioxide is impregnated in a solution I containing an active component precursor, and calcined to obtain the catalyst; The nitrogen-doped manganese dioxide is prepared by any one of method a, method b or method c: Method a: calcining MnO2 at 100-500°C in NH3 atmosphere for 2-8 hours; Method b: manganese acetate is used as a manganese source and urea is used as a nitrogen source, which are added to a solution containing PVP and prepared by an in-situ hydrothermal method; Method c: In the presence of NH4 + It is prepared by liquid phase heat treatment of MnO2 in an aqueous solution.

2. The catalyst according to claim 1, characterized in that After testing the water absorption rate of nitrogen-doped manganese dioxide, a precursor solution with a solution concentration of 10 to 200 mg / mL is prepared, wherein the active component precursor is selected from at least one of metal acetates and nitrates; the solvent of the solution I is deionized water; the concentration of the solution I is 0.5 to 3 mol / L; and the carrier is immersed in the precursor solution for 2 to 6 hours according to the calculated amount of the required precious metal component. The mass volume ratio of the nitrogen-doped manganese dioxide to solution I is 5 to 20 (g:mL).

3. The catalyst according to claim 1, characterized in that The calcination temperature is 100-600° C. and the calcination time is 2-10 hours.

4. The catalyst according to claim 1, characterized in that The method b is to react an aqueous solution containing manganese acetate, urea and PVP at 150-200° C. for 2-10 hours; and calcine the generated precipitate at 300-500° C. for 2-4 hours; The molar ratio of manganese acetate, urea and PVP is 0.5-15.

5. The catalyst according to claim 1, characterized in that The method c is to add MnO2 into a solution containing NH4 + in an aqueous solution at 40 to 80° C. with a stirring rate of 400 to 800 r / min for 2 to 10 hours; Centrifugal separation, water washing, alcohol washing, drying at 50-150°C for 2-12 hours; The MnO2 and NH4 + The molar ratio is 1 to 10.

6. Use of the catalyst according to any one of claims 1 to 5 in ozone decomposition; The catalyst is heated at a space velocity of 300,000 to 1,000,000 h -1 , application in ozone decomposition under the conditions of temperature 25~200℃, humidity RH=95%, and O3 concentration 0~30ppm.

7. Application of nitrogen-doped manganese dioxide in ozone decomposition; The nitrogen-doped manganese dioxide is the nitrogen-doped manganese dioxide described in claim 1; The nitrogen-doped manganese dioxide is heated at a space velocity of 300,000 to 1,000,000 h -1 It is used for ozone decomposition under the conditions of temperature 25-200℃, humidity RH=0, and O3 concentration 0-30ppm.

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