A MOFs-derived cobalt-based porous carbon material catalyst for catalytic decomposition of ozone and its preparation method

Abstract

The present invention discloses a MOFs-derived cobalt-based porous carbon material catalyst for catalytic decomposition of ozone and a preparation method thereof. The catalyst uses a cobalt-based organic framework compound as a precursor and forms a MOFs-derived porous carbon material through different high-temperature calcinations. The advantages of the present invention are that a cobalt-based carbon material with a high specific surface area, a micro-nano hierarchical pore structure, and rich Co-N composite active sites can be obtained using the MOFs structure as a precursor, which has good moisture resistance and stability, and can achieve complete decomposition of ozone at room temperature, 50% humidity, and within 7 hours, and is particularly suitable for the purification and treatment of high-humidity O3-containing tail gas in sewage treatment plants.

Description

Technical Field

[0001] The present invention belongs to the technical fields of environmental protection catalytic materials and air pollution control, and relates to a MOFs (metal-organic framework)-derived cobalt-based porous carbon material catalyst and a preparation method thereof, which are applicable to catalytically decomposing high-concentration ozone (O3) into oxygen (O2) under relatively high humidity conditions. Background Art

[0002] Ozone, with the chemical formula O3, is a pale blue gas with a fishy smell. Ozone has extremely strong oxidizing properties and can react with all elements in the periodic table except noble metals, fluorine, and inert gases.

[0003] In the surface atmosphere, ozone is mainly generated by the photochemical reaction between volatile organic compounds (VOCs) and nitrogen oxides (NO x ). In recent years, the large consumption of fossil fuels and the rapid development of industry have led to a significant increase in the emissions of VOCs and NO x , and the ozone concentration in the atmosphere has been rising year by year. At the same time, as a highly efficient oxidant, ozone's strong oxidizing properties are often used in industry to treat pollutants, and the main products are non-toxic and harmless gases such as CO2 and H2O, which are environmentally friendly. Therefore, it is widely used in sewage treatment, air purification, disinfection, and other fields. However, due to the low utilization rate of ozone during the pollutant treatment process, a large amount of unreacted ozone is discharged into the atmosphere, further increasing the ozone concentration in the atmosphere. When people are exposed to ozone with a concentration exceeding 0.40 mg / m 3 , symptoms such as headache, dry throat, and damaged respiratory mucosa will appear, and even life and health will be threatened. Therefore, the purification of ozone is of great significance for environmental improvement and the protection of people's life and health.

[0004] The catalytic decomposition method is an ideal method for ozone decomposition, which can completely remove ozone at room temperature, and has the advantages of high catalytic ozone decomposition efficiency, no energy consumption, and no secondary pollutants. Commonly used catalysts mainly include noble metals, transition metal oxides, molecular sieve-based catalysts, metal-organic framework compounds (MOFs), etc.

[0005] Patent CN1990102A proposed a nano Au / TiO2 catalyst with Au as the catalyst active component and TiO2 as the carrier; CN 202111543639.0 invented a noble metal catalyst with a double metal oxide as the carrier and about 1 wt% of Pd and Ag as the active centers. However, the active components of noble metal catalysts such as Au and Pd are expensive, and water vapor will severely inhibit the process of catalytically decomposing ozone by them, and they generally have the disadvantage of poor moisture resistance, so their application scope is limited.

[0006] Transition metal oxide catalysts use manganese oxides as the main active component and can be doped with transition metals and alkali metal oxides as secondary active components to achieve the catalytic decomposition of ozone. For example, Patent CN201410237627.9 introduces a catalyst with cerium-manganese oxides as the active component, which exhibits high catalytic decomposition activity of ozone and good moisture resistance under high space velocity and high humidity environmental conditions, but has poor stability. The competitive adsorption of water molecules and ozone molecules at the active sites causes the catalyst to easily lose its activity.

[0007] Molecular sieve-based catalysts use molecular sieves as carriers, have a large specific surface area, can provide more active sites for catalytic materials, and improve the activity of the catalyst. However, they have the disadvantage of poor stability and are difficult to be applied industrially. For example, the catalytic material described in Patent CN201410284947.X uses a composite material mainly composed of porous activated carbon and molecular sieves as the carrier and is loaded with one or more non-noble metal oxides as the active component. The ability to catalytically decompose ozone can reach more than 95% under normal temperature and normal humidity conditions, but it has poor stability and the catalyst cannot maintain high catalytic activity for a long time.

[0008] Patent CN202210750112.3 introduces the metal-organic framework structures of different manganese MOFs materials. The manganese source is mixed with the organic ligand and reacted under high temperature and high pressure to obtain Mn-MOFs materials, which have a good effect on ozone degradation and can achieve efficient ozone degradation for 72 consecutive hours within a large humidity fluctuation range (10% ≤ RH ≤ 90%). However, the applicable ozone concentration is less than or equal to 625 ppb, and it only has a good decomposition effect on low-concentration ozone. Although metal-organic framework (MOFs) catalysts have the advantages of a large specific surface area and abundant catalytic sites, their organic frameworks are easily oxidized by ozone and its decomposition products, resulting in the collapse of the overall structure of the material, and the catalytic activity decreases or even completely deactivates.

[0009] At present, the development and application of ozone catalytic decomposition catalysts are seriously insufficient and cannot meet the efficient decomposition of high-humidity and high-space-velocity ozone. There is an urgent need to develop an ozone decomposition catalyst with better moisture resistance, activity, and stability. The present invention proposes a solution for this. Summary of the Invention

[0010] The purpose of the present invention is to overcome the problems existing in the existing catalysts and provide a MOFs-derived cobalt-based porous carbon material catalyst for catalytically decomposing ozone under high humidity and its preparation method. For the high-humidity ozone tail gas emitted when treating pollutants in sewage treatment plants and the ozone existing in enclosed spaces such as photocopying rooms and aircraft cabins, this catalyst can completely eliminate ozone pollution at room temperature and has good stability at the same time.

[0011] The invention provides a MOF-derived cobalt-based porous carbon material catalyst for catalytic decomposition of ozone. The catalyst is a porous carbon material composed of cobalt, metal M, and carbon, which is obtained by carbonizing a MOF material precursor. It inherits the high specific surface area and porosity of the MOF material and has abundant catalytic sites. At the same time, the connection between the organic ligand and the metal can effectively improve the dispersion of the metal sites, thus significantly enhancing the interaction between the active center and ozone, and endowing the catalyst with better activity.

[0012] The invention provides a MOF-derived cobalt-based porous carbon material catalyst for catalytic decomposition of ozone under high humidity conditions. The porous carbon material is used as the carrier, and cobalt is used as the main active component, and other doped metals M are used as auxiliary active components. The metal M is selected from one or more combinations of manganese, cerium, iron, nickel, silver, vanadium, palladium, and copper, and the molar ratio of cobalt to metal M is 1:0.25 to 1.

[0013] The invention provides a MOF-derived cobalt-based porous carbon material catalyst for catalytic decomposition of ozone under high humidity conditions. The preparation method includes the following steps:

[0014] (1) Dissolve the organic ligand in a solvent and stir to dissolve to obtain a mixed solution 1;

[0015] (2) Dissolve the cobalt salt and metal M salt in a solvent and stir to dissolve to obtain a mixed solution 2;

[0016] (3) Add the mixed solution 1 in step (1) to the mixed solution 2 in step (2), stir and mix evenly to obtain a mixed solution 3;

[0017] (4) React the mixed solution 3 obtained in step (3) at a certain temperature for a period of time;

[0018] (5) Centrifuge, wash, and dry the mixed solution after the reaction in step (4) to obtain a cobalt-based heterometallic organic framework compound;

[0019] (6) Calcinate the cobalt-based heterometallic composite MOFs in step (5) at a high temperature in an inert atmosphere for a period of time to obtain a micro-nano cobalt-based heterometallic porous carbon material.

[0020] In step (2), the cobalt salt and metal M salt are selected from one or both of nitrates and acetates;

[0021] In step (3), the reaction temperature is 25 to 140 °C, the reaction time is 6 to 24 hours, and the drying time is 12 to 24 hours;

[0022] In step (5), the detergent used for washing is one or more of water, ethanol, methanol, and (N,N-dimethylformamide) DMF; the drying time is 12 to 24 hours; the inert atmosphere for calcination is one of nitrogen, argon, and helium, the calcination temperature is 400 to 1000 °C, and the calcination time is 1 to 10 hours.

[0023] Advantages of the present invention:

[0024] 1. The catalyst prepared by the present invention forms a porous carbon structure by introducing a MOFs structure, has a high specific surface area and porosity, and at the same time exposes abundant Co-N active centers after calcination, increasing the binding probability of ozone and active sites and improving the catalytic efficiency. Due to the hydrophobic characteristics of the carbon material, this preparation method improves the water resistance of the catalytic material, enabling the catalyst to exhibit excellent moisture resistance activity under high humidity conditions.

[0025] 2. This catalyst has a wide range of applications. At room temperature, with an airspeed of 10,000 - 400,000 h -1 , and a reaction humidity of RH = 0 - 50%, it can achieve complete catalytic decomposition of O3 when the O3 concentration is 0 - 80 ppm and can still maintain good catalytic activity at higher humidity. For example, the catalyst in Example 1 can decompose ozone at room temperature under high humidity (RH = 50%) and ultra-high airspeed (360,000 h -1 ), can effectively resist the destructive effect of ozone on the structure of general catalysts, inhibit the competitive adsorption of water molecules, and the ozone conversion rate can still remain above 98% after 10 hours. Description of the drawings

[0026] Figure 1 is the X-ray diffraction pattern of the catalysts prepared in Examples 1 - 5 and the comparative example.

[0027] Figure 2 is the curve of the conversion rate of catalytic decomposition of ozone by the catalysts prepared in Examples 1 - 5 and the comparative example changing with time.

[0028] Figure 3 are the scanning electron microscope and transmission electron microscope images of the precursors, the comparative example, and the catalysts prepared in some examples. (a-1) SEM images of ZIF-67, (a-2) Co-NC, (a-3) CoMn-NC, and (a-4) CoCe-NC samples, and (b-1, c-1) transmission electron microscope images of ZIF-67, (b-2, c-2) Co-NC, (b-3, c-3) CoMn NC, and (b-4, c-4) CoCe-NC samples. Detailed implementation manners

[0029] The present invention will be further described below by way of examples. However, it is not limited to the following examples.

[0030] Example 1

[0031] The CoMn-NC catalyst was prepared according to the following steps: Dissolve 5.5 grams of 2-methylimidazole in 60 milliliters of water, stir to dissolve to obtain mixture 1; Dissolve 0.45 grams of cobalt nitrate hexahydrate and 0.118 grams of manganese nitrate tetrahydrate in 3 milliliters of water, stir to dissolve to obtain mixture 2; Add mixture 1 to mixture 2, stir and mix evenly to obtain mixed solution 3; Stir mixed solution 3 at room temperature for 6 hours; Centrifuge, wash, and dry the reacted mixed solution 3 overnight at 80 °C to obtain the cobalt-based heterometallic organic framework ZIF-67-Mn; Calcinate ZIF-67-Mn in a tubular furnace for 2 hours, the calcination atmosphere is N2 atmosphere, and the calcination temperature is 600 °C to obtain CoMn-NC.

[0032] After granulating the prepared CoMn-NC catalyst, it was loaded into a quartz reaction tube. After mixing the gases, they were introduced into the reaction tube and reacted in the reactor. The ozone concentration in the reaction system was 40 ppm, the humidity was 50% (air was the balance gas), and the volumetric space velocity of the mixed gas was 360,000 h -1 Ozone decomposition was carried out under the condition. At room temperature as the reaction temperature, data was recorded every 10 seconds. It was obtained that: at 50% humidity, the ozone conversion rate could still remain above 98% after 10 hours.

[0033] Example 2

[0034] The CoCe-NC catalyst was prepared according to the following steps: Dissolve 5.5 grams of 2-methylimidazole in 60 milliliters of water, stir to dissolve to obtain mixture 1; Dissolve 0.45 grams of cobalt nitrate hexahydrate and 0.204 grams of cerium nitrate hexahydrate in 3 milliliters of water, stir to dissolve to obtain mixture 2; Add mixture 1 to mixture 2, stir and mix evenly to obtain mixed solution 3; Stir mixed solution 3 at room temperature for 6 hours; Centrifuge, wash, and dry the reacted mixed solution 3 overnight at 80 °C to obtain the cobalt-based heterometallic organic framework ZIF-67-Ce; Calcinate ZIF-67-Ce in a tubular furnace for 2 hours, the calcination atmosphere is N2 atmosphere, and the calcination temperature is 600 °C to obtain CoCe-NC.

[0035] After granulating the prepared CoCe-NC catalyst, it was loaded into a quartz reaction tube. After mixing the gases, they were introduced into the reaction tube and reacted in the reactor. The ozone concentration in the reaction system was 40 ppm, the humidity was 50% (air was the balance gas), and the volumetric space velocity of the mixed gas was 360,000 h -1 Ozone decomposition was carried out under the condition. At room temperature as the reaction temperature, data was recorded every 10 seconds. It was obtained that: at 50% humidity, the ozone conversion rate remained at 94.29% after 10 hours.

[0036] Example 3

[0037] The CoFe-NC catalyst was prepared according to the following steps: Dissolve 5.5 grams of 2-methylimidazole in 60 milliliters of water, stir to dissolve to obtain mixture 1; Dissolve 0.45 grams of cobalt nitrate hexahydrate and 0.190 grams of iron(III) nitrate nonahydrate in 3 milliliters of water, stir to dissolve to obtain mixture 2; Add mixture 1 to mixture 2, stir and mix evenly to obtain mixed solution 3; Stir mixed solution 3 at room temperature for 6 hours; Centrifuge, wash, and dry the reacted mixed solution 3 overnight at 80 °C to obtain the cobalt-based heterometallic organic framework ZIF-67-Fe; Calcinate ZIF-67-Fe in a tube furnace for 2 hours, with a calcination atmosphere of N2 and a calcination temperature of 600 °C to obtain CoFe-NC.

[0038] After granulating the prepared CoFe-NC catalyst, it was loaded into a quartz reaction tube. After mixing the gases, they were introduced into the reaction tube and reacted in the reactor. The ozone concentration in the reaction system was 40 ppm, the humidity was 50% (air as the balance gas), and the volumetric space velocity of the mixed gas was 360,000 h -1 Ozone decomposition was carried out under these conditions. At a reaction temperature of room temperature, data was recorded every 10 seconds. It was obtained that at 50% humidity, the ozone conversion rate was 87.39% after 10 hours.

[0039] Example 4

[0040] The CoNi-NC catalyst was prepared according to the following steps: Dissolve 5.5 grams of 2-methylimidazole in 60 milliliters of water, stir to dissolve to obtain mixture 1; Dissolve 0.45 grams of cobalt nitrate hexahydrate and 0.137 grams of nickel nitrate hexahydrate in 3 milliliters of water, stir to dissolve to obtain mixture 2; Add mixture 1 to mixture 2, stir and mix evenly to obtain mixed solution 3; Stir mixed solution 3 at room temperature for 6 hours; Centrifuge, wash, and dry the reacted mixed solution 3 overnight at 80 °C to obtain the cobalt-based heterometallic organic framework ZIF-67-Ni; Calcinate ZIF-67-Ni in a tube furnace for 2 hours, with a calcination atmosphere of N2 and a calcination temperature of 600 °C to obtain CoNi-NC.

[0041] After granulating the prepared CoNi-NC catalyst, it was loaded into a quartz reaction tube. After mixing the gases, they were introduced into the reaction tube and reacted in the reactor. The ozone concentration in the reaction system was 40 ppm, the humidity was 50% (air as the balance gas), and the volumetric space velocity of the mixed gas was 360,000 h -1 Ozone decomposition was carried out under these conditions. At a reaction temperature of room temperature, data was recorded every 10 seconds. It was obtained that at 50% humidity, the ozone conversion rate was 78.55% after 10 hours.

[0042] Example 5

[0043] The CoAg-NC catalyst was prepared as follows: 5.5 g of 2-methylimidazole was dissolved in 60 mL of water and stirred until dissolved to obtain mixture 1; 0.45 g of cobalt(II) nitrate hexahydrate and 0.080 g of silver nitrate were dissolved in 3 mL of water and stirred until dissolved to obtain mixture 2; mixture 1 was added to mixture 2 and stirred until evenly mixed to obtain mixed solution 3; mixed solution 3 was stirred at room temperature for 6 hours; the reacted mixed solution 3 was centrifuged, washed, and dried overnight at 80 °C to obtain cobalt-based heterometallic organic framework ZIF-67-Ag; ZIF-67-Ag was calcined in a tube furnace for 2 hours under a N2 atmosphere at a calcination temperature of 600 °C to obtain CoAg-NC.

[0044] The prepared CoAg-NC catalyst was granulated and loaded into a quartz reaction tube. After the gases were mixed, they were passed into the reaction tube and reacted in the reactor. The ozone concentration in the reaction system was 40 ppm, the humidity was 50% (air as the balance gas), and the volumetric space velocity of the mixed gas was 360,000 h -1 Ozone decomposition was carried out under these conditions. At a reaction temperature of room temperature, data was recorded every 10 seconds. It was found that at 50% humidity, the ozone conversion rate was 71.78% after 10 hours.

[0045] Comparative Example

[0046] The Co-NC catalyst was prepared as follows: 5.5 g of 2-methylimidazole was dissolved in 60 mL of water and stirred until dissolved to obtain mixture 1; 0.45 g of cobalt(II) nitrate hexahydrate was dissolved in 3 mL of water and stirred until dissolved to obtain mixture 2; mixture 1 was added to mixture 2 and stirred until evenly mixed to obtain mixed solution 3; mixed solution 3 was stirred at room temperature for 6 hours; the reacted mixed solution 3 was centrifuged, washed, and dried overnight at 80 °C to obtain cobalt-based heterometallic organic framework ZIF-67; ZIF-67 was calcined in a tube furnace for 2 hours under a N2 atmosphere at a calcination temperature of 600 °C to obtain Co-NC.

[0047] The prepared Co-NC catalyst was granulated and loaded into a quartz reaction tube. After the gases were mixed, they were passed into the reaction tube and reacted in the reactor. The ozone concentration in the reaction system was 40 ppm, the humidity was 50% (air as the balance gas), and the volumetric space velocity of the mixed gas was 360,000 h -1 Ozone decomposition was carried out under these conditions. At a reaction temperature of room temperature, data was recorded every 10 seconds. It was found that at 50% humidity, the ozone conversion rate was 64.32% after 10 hours, which could not meet the requirement of decomposing ozone efficiently and stably for a long time.

Claims

1. Application of a MOFs-derived cobalt-based porous carbon material, characterized in that, As a catalyst, it is used to catalytically decompose ozone into oxygen. In the reaction system, the ozone concentration is 40 ppm, the humidity is 50%, air is the balance gas, and the volumetric space velocity of the mixed gas is 360,000 h -1 , and ozone decomposition is carried out under normal temperature conditions; The preparation method of the MOFs-derived cobalt-based porous carbon material comprises the following steps: (1) Dissolve the organic ligand in a solvent and stir to dissolve to obtain a mixture 1; (2) Dissolve the cobalt salt and the doped metal M salt in a solvent and stir to dissolve to obtain a mixture 2; (3) Add the mixture 1 in step (1) to the mixture 2 in step (2), stir and mix evenly to obtain a mixture 3; (4) React the mixture 3 obtained in step (3) at a certain temperature for a period of time; (5) Centrifuge, wash and dry the mixture after the reaction in step (4) to obtain a cobalt-based doped metal-organic framework compound; (6) Calcinate the cobalt-based doped metal-organic framework compound in step (5) at a high temperature for a period of time under an inert atmosphere condition to obtain the MOFs-derived cobalt-based porous carbon material; The metal M is selected from one or more combinations of manganese, cerium, iron, nickel, silver, vanadium, palladium, and copper, and the molar ratio of cobalt to the metal M is 1: 0.25 to 1.

2. The application according to claim 1, wherein In step (2), the cobalt salt and the metal M salt are selected from one or both of nitrates and acetates for use.

3. The application according to claim 1, wherein In step (4), the reaction temperature is 25 to 140 °C and the reaction time is 6 to 24 hours.

4. The application according to claim 1, characterized in that, In step (5), the detergent used for washing is one or more of water, ethanol, methanol, and DMF; the drying time is 12 to 24 hours; in step (6), the inert atmosphere is one of nitrogen, argon, and helium, the calcination temperature is 400 to 1000 °C, and the calcination time is 1 to 10 hours.

5. The application according to claim 1, characterized in that, The organic ligand in step (1) is the organic ligand corresponding to different MOFs, and the MOFs include ZIF-9, ZIF-12, ZIF-21, ZIF-67, and Co-BDC.

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