CN106964360B - Medium-low temperature catalytic decomposition of N2Catalyst of O, preparation method and application - Google Patents
Medium-low temperature catalytic decomposition of N2Catalyst of O, preparation method and application Download PDFInfo
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Abstract
Medium-low temperature catalytic decomposition of N2The catalyst of O comprises an active oxide inner core and a porous inert oxide shell layer, wherein the active oxide inner core is composed of an active component Co3O4The porous inert oxide shell layer is formed into SiO2‑NxOyIn which N isxOyIs ZrO2Or CeO2The weight percentage of each component is as follows: co3O410‑40wt％，ZrO2Or CeO20.1-3 wt%, and the balance of SiO2. The invention has the advantages of good activity of the catalyst and long service life.
Description
Technical Field
The invention belongs to a medium-low temperature catalytic decomposition method for N2O catalyst, preparation method and application.
Background
With the development of chemical synthesis industries such as nitric acid, nylon 66 and the like and the continuous consumption of fossil fuels, N in the atmosphere is caused2The O concentration continues to rise. N is a radical of2O has a greenhouse potential of CO2310 times higher than that of the conventional method, is an important greenhouse gas, and N is2O can be stable in the troposphere and, when transported to the stratosphere, can cause ozone layer destruction. Thus, N2The elimination technology of O becomes an important part of the research of the atmospheric pollution control nowadays.
N studied in the near future2In the O-removing method, N is directly catalytically decomposed2O to O2And N2Thus, the development of a stable and highly active catalyst is currently N2The main direction of O catalytic decomposition studies. Currently for N2The research on the catalysts for O direct catalytic decomposition method focuses on noble metal catalysts, molecular sieve catalysts and metal oxide catalysts, wherein the metal oxide catalysts have low costThe catalyst is cheap and environment-friendly, the preparation method is simple and feasible, the composition is easy to modulate, and the catalyst has higher catalytic activity and is favored by scientific researchers.
Chinese patent document CN102513117A discloses a composite oxide composed of copper oxide and cerium oxide, which utilizes the synergistic effect formed by the composite oxide of cerium and copper oxide to greatly improve the material N2Activity and stability of O catalytic decomposition reactions. The shell company in patent document CN105408006A proposes a supported cobalt-based catalyst prepared by coprecipitation method, and adds an alkali metal promoter to the supported cobalt-based catalyst, so that the prepared catalyst has good activity under low temperature condition, and can maintain good physical properties and catalytic activity even in the presence of a small amount of water in the reaction atmosphere.
However, the above metal oxide catalyst has a fatal disadvantage that the material active metal oxide contact interface is small, and the active metal oxide nanoparticles are easily detached from the carrier and aggregated with each other under the conditions of long-period high-temperature reaction or the presence of water and oxygen in the reaction atmosphere, sintering of the active oxide occurs and the deactivation phenomenon is caused.
Disclosure of Invention
In order to solve the problems, the invention aims to provide a medium-low temperature catalytic decomposition N catalyst with good activity and long service life2O catalyst, preparation method and application.
In order to achieve the purpose, the technical scheme for preparing the metal oxide catalyst provided by the invention is as follows: first, monodisperse Co with particle size below 12nm is synthesized3O4Nano particles, then carrying out in-situ assistant modification on the active particles (the assistant is ZrO)2Or CeO2) Porous SiO of2Coating with shell to form Co with rich mesoporous channels3O4Inner core, SiO2A shell layer sphere-like core-shell catalyst. The contact interface of the active metal oxide is enlarged by utilizing the porous pore channel of the shell layer; the core-shell structure with the geometric configuration of the material is utilized to improve the high-temperature and hydrothermal stability of the internal active nano particles and enhance the structural stability and catalytic performance of the nitrous oxide catalytic decomposition material under the actual working condition. The coated nano material is used at the medium and low temperatureThe decomposition reaction of nitrous oxide at the temperature of less than 500 ℃ can reduce the using amount of active metal oxide, improve the sintering resistance of active metal oxide nano particles, and improve the activity and the service life of the catalyst.
The catalyst comprises an active oxide inner core and a porous inert oxide shell layer, wherein the active oxide inner core is composed of an active component Co3O4The porous inert oxide shell layer is formed into SiO2-NxOyIn which N isxOyIs ZrO2Or CeO2The weight percentage of each component is as follows:
Co3O410-40wt％，ZrO2or CeO20.1-3 wt%, and the balance of SiO2。
The specific surface area of the catalyst is 250-480m2g-1The size of the active oxide inner core is 9-12nm, the thickness of the coating porous inert oxide shell layer is 6-20nm, and the particle size of the integral core-shell coating structure is 21-50 nm.
The preparation steps of the catalyst of the invention are as follows:
(1) taking an ethanol water solution as a solvent, preparing a mixed solution of cobalt salt and hexamethylenetetramine, adding a polyvinylpyrrolidone dispersing agent with the same mass as the cobalt salt, and stirring until the cobalt salt and the polyvinylpyrrolidone dispersing agent are completely dissolved;
(2) dropwise adding H into the solution prepared in the step (1)2O2Water solution, sealing the reaction system after the transparent solution system becomes turbid gradually, raising the operation temperature to 55-80 ℃, and keeping vigorous stirring for 12-72h to obtain highly uniformly dispersed Co3O4A nanoparticle sol;
(3) in the presence of ZrO2Or CeO2Dissolving zirconium nitrate or cerium nitrate in ethyl orthosilicate to prepare a mixed solution;
(4) according to the composition of the catalyst, in-situ dropping the ethyl orthosilicate ethanol mixed solution prepared in the step (3) into the nano-particle sol prepared in the step (2), adding ammonia water, continuing to react for 24-72h, and performing high-speed centrifugal separation on the obtained suspension;
(5) drying the centrifugal precipitate at 60-100 ℃, calcining at high temperature for 2-6h under the condition of 500-700 ℃ in the calcining atmosphere to remove organic residues, and obtaining the cobalt-based core porous oxide coated catalyst.
The volume fraction ratio of the absolute ethyl alcohol to the deionized water in the ethyl alcohol aqueous solution in the step (1) is as follows: anhydrous ethanol: deionized water 1.5-2.5: 1.
the cobalt salt in the step (1) is composed of inorganic cobalt salt and organic cobalt salt, wherein the inorganic cobalt salt and the organic cobalt salt are matched according to the mole fraction of 0.5-3: 1. Wherein the inorganic cobalt salt is cobalt nitrate or cobalt chloride, and the organic cobalt salt is cobalt acetate or cobalt acetylacetonate.
The optimum concentration range of the cobalt ions in the mixed solution is 0.01-0.015 mol/L.
The optimal concentration range of the hexamethylenetetramine in the mixed solution in the step (1) is 0.17-0.30 mol/L.
H in the step (2)2O2The addition amount of the (B) is that 15-20m L3 wt% H is dripped into each liter of mixed solution2O2An aqueous solution.
The addition amount of the tetraethoxysilane in the step (3) is as follows: co per liter3O4Adding 15-60m L of tetraethoxysilane into the metal oxide nano particle sol.
The volume ratio of the ethyl orthosilicate to the ethanol in the step (3) is 1: 5-10.
The addition amount of the ammonia water in the step (4) is as follows: co per liter3O4Adding 28 wt% ammonia water 10-20m L into the metal oxide nano particle sol.
The calcining atmosphere in the step (5) can be static air, flowing air or flowing nitrogen atmosphere.
The application conditions of the catalyst of the invention are as follows:
in a fixed bed reactor, N2The O catalytic decomposition conditions are as follows: the reaction pressure is normal pressure, the raw material gas is fed in and discharged from the top, and N is contained in the raw material gas2O volume concentration of 0.1-0.35%, NO2Volume concentration of 0.35% or less, O2Volume concentration of 1% -4%, H2The volume concentration of O is 0.5-2 percent, and the airspeed is 10000h-1-20000h-1Operating temperature 200℃-500℃。
The raw material gas is flue gas of a gas-fired boiler or waste gas generated in nitric acid production.
The invention has the advantages and beneficial effects that:
1) the catalyst prepared by the invention has a typical monodisperse core-shell structure (figure 1), high catalytic activity and N2The complete conversion temperature of O decomposition is low;
2) the metal cobalt salt in the preparation method is composed of inorganic-organic complex salt, and can stabilize cobalt colloidal particles in an oil-water system. Meanwhile, the hexamethylenetetramine has dispersing and oxidation assisting effects in a solution system, so that the conversion temperature of the cobalt salt to the metal oxide thereof can be greatly reduced;
3) the zirconium nitrate or cerium nitrate added in the preparation method can be doped in the shell in the cross-linking process of the tetraethoxysilane to form SiO2-MOx(M ═ one of Zr or Ce) shell layer.
4) Co of the invention3O4The nano particles are anchored in the shell space and cannot migrate freely, the dispersion state of the active component can be maintained, the configuration characteristics of the active component core are stabilized, and the migration and agglomeration of the nano particles are prevented;
5) the porous shell layer is coated on the surface of the active oxide, so that the contact reaction interface of the active component is increased, and meanwhile, the limited domain structure of the shell layer pore canal can prevent the condensation and adsorption of water vapor on the surface of the core in the reaction atmosphere, keep the continuous adsorption and desorption of the active sites on nitrous oxide molecules, and effectively improve the stability of the catalyst in a water-containing system;
6) SiO of the invention2A small amount of variable valence metal oxides of Zr or Ce are doped in the shell layer, and can provide additional lattice oxygen or oxygen cavities in the core-shell limited reaction space, promote the desorption of oxygen transition states on adjacent cobalt sites, and accelerate the catalytic cycle of the reaction sites.
7) The catalyst of the invention has excellent low-temperature catalytic activity. Under the condition that the test reaction pressure is normal pressure, the industrial waste gas N of the raw material nitric acid2O volume concentration of 0.1-0.35%, NO2Volume concentration of 0.35% or less, O2The volume concentration is 1%-4％，H2The volume concentration of O is 0.5-2 percent, and the total airspeed is 15000h-1Under the operating conditions of (1), the catalyst can completely catalyze and decompose N below 440 DEG C2O, N required for the same kind of supported catalyst or unsupported catalyst2The complete conversion temperature of O is 50-70 ℃; the catalyst of the invention has stable activity in the working condition of nitric acid industrial waste gas: the test catalyst is tested under the working condition of nitric acid industrial waste gas, the temperature is 400 ℃, and the total space velocity is 25000 h-1Under the condition, the fixed bed is continuously operated for 50 hours, and the deactivation rate is less than 2.8 percent.
Drawings
FIG. 1 shows the catalytic decomposition of N obtained after calcination in example 42High-resolution transmission electron microscope images of the O-coated metal oxide catalyst.
Detailed Description
The present invention is further illustrated by specific examples. It should be understood that these examples are only for illustrating the present invention and do not limit the scope of the present invention.
Example 1:
(a) weighing 1.82g Co (NO)3)2·6H2O、1.61g Co(acac)2(Co ion total amount of 0.0125mol, mole fraction ratio of inorganic salt and organic salt of 1: 1) and 35.1g (0.25mol) of hexamethylenetetramine were added to a 2:1 ethanol aqueous solution of 1L in volume ratio, and stirred to mix, and 3.43g of polyvinylpyrrolidone was added to the mixed solution until dissolution was complete. (b) 3 wt% H of 15m L was continuously added to the mixed solution2O2And (3) after the solution system gradually turns black, heating to 60 ℃, and violently stirring for 72 hours to obtain highly uniformly dispersed cobaltosic oxide nanoparticle suspension. (c) 0.014g of Zr (NO)3)2·5H2Dissolving O in 210m L ethanol, adding 30m L ethyl orthosilicate to obtain a mixed solution of ethyl orthosilicate and zirconium nitrate and ethanol, (d) dropwise adding the mixed solution prepared in the step (c) into the suspension prepared in the step (b) in situ, adding 10m L ammonia water, continuing to react for 48h, (e) performing high-speed centrifugal separation on the obtained final suspension at 13000 r/min, drying at 60 ℃, calcining at 600 ℃ for 4h in a flowing air atmosphere to remove organic residues, and cooling to obtain the coated structure metal oxide catalyst1. Co in the obtained product3O426 wt% of ZrO20.1 wt% of SiO2The mass percentage content is 73.9 wt%.
Grinding the prepared catalyst and screening 40-60-mesh particles to perform a nitrous oxide decomposition reaction activity test, wherein the test reaction conditions are as follows: the composition of the nitric acid industrial waste gas is N2O volume concentration 0.1%, NO2Volume concentration 0.35%, O2Volume concentration of 1%, H2The volume concentration of O is 0.1 percent, and the reaction space velocity is 12000h-1Under the operating conditions of (1) and (2), the testing temperature ranges from 200 ℃ to 500 ℃, and the catalytic activity is tested by using gas chromatography every 20 ℃ in the temperature programming process. The activity test results are given below, with the catalyst reaching complete conversion at 440 ℃.
TABLE 2 results of nitrous oxide decomposition reaction with different catalysts as a function of reaction temperature
Grinding the prepared catalyst and screening 40-60-mesh particles to perform a nitric acid industrial tail gas atmosphere nitrous oxide decomposition stability test, wherein the test reaction conditions are as follows: the pressure is normal pressure, the temperature is 400 ℃, and the nitric acid industrial waste gas consists of N2O volume concentration 0.35%, NO2Volume concentration of 0.35%, O2Volume concentration of 3%, H2The volume concentration of O is 1 percent, and the total airspeed is 10000h-1Under the condition, the reaction is continuously operated on a fixed bed for 50 hours, the conversion rate of the catalyst to the nitrous oxide at the initial stage of the reaction is 85.4 percent, and the deactivation rate at the end of the reaction is 2.6 percent.
Example 2:
(a) 1.19g CoCl was weighed2·6H2O、2.49g Co(Ac)2·4H2O (Co ion total substance amount 0.015mol, inorganic salt and organic salt molar fraction ratio 0.5: 1) and 42.2g (0.3mol) of hexamethylenetetramine were added to a 2.5:1 ethanol aqueous solution of 1L in a volume ratio of 2.5:1, stirred and mixed, and 3.66g of polyvinylpyrrolidone was added to the mixed solution until dissolution was completed, (b) 20m L of polyvinylpyrrolidone was continuously added to the mixed solution3wt％H2O2And (3) after the solution system gradually turns black, heating to 55 ℃, and stirring vigorously for 12 hours to obtain highly uniformly dispersed cobaltosic oxide nanoparticle suspension. (c) 0.32g of Zr (NO)3)2·5H2Dissolving O in 150m L ethanol, adding 15m L ethyl orthosilicate to obtain ethyl orthosilicate zirconium nitrate ethanol mixed solution, (d) dropwise adding the mixed solution prepared in the step (c) into the suspension prepared in the step (b) in situ, adding 20m L ammonia water, continuing to react for 24h, (e) performing high-speed centrifugal separation on the obtained final suspension at 13000 r/min, drying at 80 ℃, calcining at 500 ℃ for 2h in a static air atmosphere to remove organic residues, and cooling to obtain a coated structure metal oxide catalyst 23O440 wt% of ZrO23 weight percent of SiO2The mass percentage content is 57 wt%.
Grinding the prepared catalyst and screening 40-60-mesh particles to perform a nitrous oxide decomposition reaction activity test, wherein the test reaction conditions are as follows: the nitric acid industrial waste gas has the composition of N2O volume concentration 0.2%, NO2Volume concentration 0.2%, O2Volume concentration of 2%, H2The volume concentration of O is 0.5 percent, and the reaction space velocity is 20000h-1Under the operating conditions of (1) and (2), the testing temperature ranges from 200 ℃ to 500 ℃, and the catalytic activity is tested by using gas chromatography every 20 ℃ in the temperature programming process. The activity test results are given below, with the catalyst reaching complete conversion at 440 ℃.
The prepared catalyst is ground and screened to obtain particles of 40-60 meshes, and then the nitric acid industrial tail gas atmosphere nitrous oxide decomposition stability test is carried out, the test conditions are the same as those of example 1, the reaction is continuously operated on a fixed bed for 50 hours, the nitrous oxide conversion rate of the catalyst at the initial stage of the reaction is 70.9%, and the deactivation rate at the end of the reaction is 2.8%.
Example 3:
(a) weighing 1.82g Co (NO)3)2·6H2O、1.61g Co(acac)2(Co ion total amount of 0.0125mol, mole fraction ratio of inorganic salt and organic salt of 1: 1) and 28.1g (0.2mol) of hexamethylenetetramine were added to a 2:1 ethanol aqueous solution of 1L in volume ratio, and stirred to mix, and 3.43g of polyvinylpyrrolidone was added to the mixed solution until dissolution was complete. (b) 3 wt% H of 18m L was continuously added to the mixed solution2O2And (3) after the solution system gradually turns black, heating to 70 ℃, and violently stirring for 24 hours to obtain highly uniformly dispersed cobaltosic oxide nanoparticle suspension. (c) 0.25g of Zr (NO)3)2·5H2Dissolving O in 210m L ethanol, adding 30m L ethyl orthosilicate to obtain a mixed solution of ethyl orthosilicate and zirconium nitrate and ethanol, (d) dropwise adding the mixed solution prepared in the step (c) into the suspension prepared in the step (b) in situ, adding 15m L ammonia water, continuing to react for 48h, (e) performing high-speed centrifugal separation on the obtained final suspension at 13000 r/min, drying at 100 ℃, calcining at 600 ℃ for 5h in a flowing air atmosphere to remove organic residues, and cooling to obtain a coated structure metal oxide catalyst 33O429 wt% of ZrO22 weight percent of SiO2The mass percentage content is 69 wt%.
Grinding the prepared catalyst and screening 40-60-mesh particles to perform a nitrous oxide decomposition reaction activity test, wherein the test reaction conditions are as follows: the nitric acid industrial waste gas has the composition of N2O volume concentration 0.3%, NO2Volume concentration 0.1%, O2Volume concentration of 3%, H2The volume concentration of O is 2 percent, and the reaction space velocity is 10000h-1Under the operating conditions of (1) and (2), the testing temperature ranges from 200 ℃ to 500 ℃, and the catalytic activity is tested by using gas chromatography every 20 ℃ in the temperature programming process. The activity test results are given below, with the catalyst reaching complete conversion at 400 ℃.
The prepared catalyst is ground and screened to obtain particles of 40-60 meshes, and then the nitric acid industrial tail gas atmosphere nitrous oxide decomposition stability test is carried out, the test conditions are the same as those of example 1, the reaction is continuously operated on a fixed bed for 50 hours, the nitrous oxide conversion rate of the catalyst at the initial stage of the reaction is 98.9%, and the deactivation rate at the end of the reaction is 2.0%.
Example 4:
(a) 2.20g Co (NO) are weighed out3)2·6H2O、0.63g Co(Ac)2·4H2O (Co ion total substance amount 0.01mol, inorganic salt and organic salt molar fraction ratio 3: 1) and 23.4g (0.17mol) of hexamethylenetetramine were added to a 1.5:1 ethanol aqueous solution of 1L in a volume ratio of 1.5:1, stirred and mixed, and 2.71g of polyvinylpyrrolidone was added to the mixed solution until dissolution was completed, (b) 3 wt% H of 15m L was continuously added to the mixed solution2O2And (3) after the solution system gradually turns black, heating to 80 ℃, and violently stirring for 48 hours to obtain highly uniformly dispersed cobaltosic oxide nanoparticle suspension. (c) 0.28g of Zr (NO)3)2·5H2Dissolving O in 300m L ethanol, adding 60m L tetraethoxysilane into the ethanol to obtain tetraethoxysilane zirconium nitrate ethanol mixed solution, (d) dropwise adding the mixed solution prepared in the step (c) into the suspension prepared in the step (b) in situ, adding 10m L ammonia water, continuing to react for 72h, (e) performing high-speed centrifugal separation on the obtained final suspension at 13000 r/min, drying at 100 ℃, calcining at 700 ℃ for 6h in flowing nitrogen atmosphere to remove organic residues, and cooling to obtain the coated structure metal oxide catalyst 43O410 wt% of ZrO21 weight percent of SiO2The mass percentage content is 89 wt%.
Grinding the prepared catalyst and screening 40-60-mesh particles to perform a nitrous oxide decomposition reaction activity test, wherein the test reaction conditions are as follows: the nitric acid industrial waste gas has the composition of N2O volume concentration 0.35%, NO2Volume concentration 0.01%, O2Volume concentration of 4%, H2The volume concentration of O is 1.5 percent, and the reaction space velocity is 14000h-1Under the operating conditions of (1) and (2), the testing temperature ranges from 200 ℃ to 500 ℃, and the catalytic activity is tested by using gas chromatography every 20 ℃ in the temperature programming process. The activity test results are given below, with the catalyst reaching complete conversion at 440 ℃.
The prepared catalyst is ground and screened to obtain particles of 40-60 meshes, and then the nitric acid industrial tail gas atmosphere nitrous oxide decomposition stability test is carried out, the test conditions are the same as those of example 1, the reaction is continuously operated on a fixed bed for 50 hours, the nitrous oxide conversion rate of the catalyst at the initial stage of the reaction is 90.6%, and the deactivation rate at the end of the reaction is 2.4%.
Example 5:
(a) 2.39g of CoCl were weighed out2·6H2O、1.25g Co(Ac)2·4H2O (Co ion total substance amount 0.015mol, inorganic salt and organic salt molar fraction ratio 2: 1) and 42.2g (0.3mol) hexamethylenetetramine were added to a 2.5:1 ethanol aqueous solution of 1L in volume ratio, and stirred to mix, and 3.66g polyvinylpyrrolidone was added to the mixed solution until dissolution was completed, (b) 3 wt% H of 20m L was continuously added to the mixed solution2O2And (3) after the solution system gradually turns black, heating to 55 ℃, and violently stirring for 18h to obtain highly uniformly dispersed cobaltosic oxide nanoparticle suspension. (c) 0.24g of Ce (NO)3)2·6H2Dissolving O in 150m L ethanol, adding 20m L ethyl orthosilicate to obtain a mixed solution of ethyl orthosilicate and cerous nitrate and ethanol, (d) dropwise adding the mixed solution prepared in the step (c) into the suspension prepared in the step (b) in situ, adding 20m L ammonia water, continuing to react for 24h, (e) performing high-speed centrifugal separation on the obtained final suspension at 13000 r/min, drying at 70 ℃, calcining at 500 ℃ for 2h in a static air atmosphere to remove organic residues, and cooling to obtain the coated structure metal oxide catalyst 53O438 percent of CeO by weight23 weight percent of SiO2The mass percentage content is 59 wt%.
Grinding the prepared catalyst and screening 40-60-mesh particles to perform a nitrous oxide decomposition reaction activity test, wherein the test reaction conditions are as follows: the nitric acid industrial waste gas has the composition of N2O volume concentration 0.3%, NO2Volume concentration 0.01%, O2The volume concentration is 2.5 percent，H2The volume concentration of O is 2 percent, and the reaction space velocity is 18000h-1Under the operating conditions of (1) and (2), the testing temperature ranges from 200 ℃ to 500 ℃, and the catalytic activity is tested by using gas chromatography every 20 ℃ in the temperature programming process. The activity test results are given below, with the catalyst reaching complete conversion at 400 ℃.
The prepared catalyst is ground and screened to obtain particles of 40-60 meshes, and then the nitric acid industrial tail gas atmosphere nitrous oxide decomposition stability test is carried out, the test conditions are the same as those of example 1, the reaction is continuously operated on a fixed bed for 50 hours, the nitrous oxide conversion rate of the catalyst at the initial stage of the reaction is 100%, and the deactivation rate at the end of the reaction is 1.9%.
Example 6:
(a) weighing 1.82g Co (NO)3)2·6H2O、1.61g Co(acac)2(Co ion total amount of 0.0125mol, mole fraction ratio of inorganic salt and organic salt of 1: 1) and 28.1g (0.2mol) of hexamethylenetetramine were added to a 2:1 ethanol aqueous solution of 1L in volume ratio, and stirred to mix, and 3.43g of polyvinylpyrrolidone was added to the mixed solution until dissolution was complete. (b) 3 wt% H of 18m L was continuously added to the mixed solution2O2And (3) after the solution system gradually turns black, heating to 70 ℃, and violently stirring for 32 hours to obtain highly uniformly dispersed cobaltosic oxide nanoparticle suspension. (c) 0.19g of Ce (NO)3)2·6H2Dissolving O in 210m L ethanol, adding 30m L ethyl orthosilicate to obtain a mixed solution of ethyl orthosilicate and cerous nitrate and ethanol, (d) dropwise adding the mixed solution prepared in the step (c) into the suspension prepared in the step (b) in situ, adding 15m L ammonia water, continuing to react for 48h, (e) performing high-speed centrifugal separation on the obtained final suspension at 13000 r/min, drying at 80 ℃, calcining at 600 ℃ for 5h in a flowing air atmosphere to remove organic residues, and cooling to obtain a coated structure metal oxide catalyst 6. Co in the obtained product3O427 wt% of CeO22 weight percent of SiO2Mass percentage ofIt was 71% by weight.
Grinding the prepared catalyst and screening 40-60-mesh particles to perform a nitrous oxide decomposition reaction activity test, wherein the test reaction conditions are as follows: the nitric acid industrial waste gas has the composition of N2O volume concentration 0.35%, NO2Volume concentration 0.35%, O2Volume concentration of 3%, H2The volume concentration of O is 1 percent, and the reaction space velocity is 10000h-1Under the operating conditions of (1) and (2), the testing temperature ranges from 200 ℃ to 500 ℃, and the catalytic activity is tested by using gas chromatography every 20 ℃ in the temperature programming process. The activity test results are given below, with the catalyst reaching complete conversion at 400 ℃.
The prepared catalyst is ground and screened to obtain particles of 40-60 meshes, and then the nitric acid industrial tail gas atmosphere nitrous oxide decomposition stability test is carried out, the test conditions are the same as those of example 1, the reaction is continuously operated on a fixed bed for 50 hours, the nitrous oxide conversion rate of the catalyst at the initial stage of the reaction is 100%, and the deactivation rate at the end of the reaction is 1.1%.
Example 7:
(a) weighing 1.46g Co (NO)3)2·6H2O、1.25g Co(Ac)2·4H2O (Co ion total substance amount 0.01mol, inorganic salt and organic salt molar fraction ratio 1: 1) and 23.4g (0.17mol) of hexamethylenetetramine were added to a 1.5:1 ethanol aqueous solution of 1L in a volume ratio 1.5:1, stirred and mixed, and 2.71g of polyvinylpyrrolidone was added to the mixed solution until dissolution was completed, (b) 3 wt% H of 15m L was continuously added to the mixed solution2O2And (3) after the solution system gradually turns black, heating to 80 ℃, and violently stirring for 64h to obtain highly uniformly dispersed cobaltosic oxide nanoparticle suspension. (c) 0.15g of Ce (NO)3)2·6H2Dissolving O in 300m L ethanol, adding 60m L tetraethoxysilane into the ethanol to obtain a mixed solution of tetraethoxysilane, cerous nitrate and ethanol, dropwise adding the mixed solution prepared in the step (c) into the suspension prepared in the step (b) in situ, adding 12m L ammonia water into the mixed solution, and continuously reacting for 72h, wherein the obtained final suspension passes through 130 hAnd (3) performing high-speed centrifugal separation at the speed of 00 r/min, drying at 90 ℃, calcining at the high temperature of 700 ℃ in flowing nitrogen atmosphere for 6 hours to remove organic residues, and cooling to obtain the coated metal oxide catalyst 7. Co in the obtained product3O413 w% of CeO21 weight percent of SiO2The mass percentage content is 86 wt%. .
Grinding the prepared catalyst and screening 40-60-mesh particles to perform a nitrous oxide decomposition reaction activity test, wherein the test reaction conditions are as follows: the nitric acid industrial waste gas has the composition of N2O volume concentration 0.2%, NO2Volume concentration 0.35%, O2Volume concentration 3.5%, H2The volume concentration of O is 2 percent, and the reaction space velocity is 15000h-1Under the operating conditions of (1) and (2), the testing temperature ranges from 200 ℃ to 500 ℃, and the catalytic activity is tested by using gas chromatography every 20 ℃ in the temperature programming process. The activity test results are given below, with the catalyst reaching complete conversion at 400 ℃.
The prepared catalyst is ground and screened to obtain particles of 40-60 meshes, and then the nitric acid industrial tail gas atmosphere nitrous oxide decomposition stability test is carried out, the test conditions are the same as those of example 1, the reaction is continuously operated on a fixed bed for 50 hours, the nitrous oxide conversion rate of the catalyst at the initial stage of the reaction is 100%, and the deactivation rate at the end of the reaction is 1.6%.
The texture and structural parameters of each porous silica-coated active metal oxide catalyst prepared in examples 1 to 7 are shown in table 1.
TABLE 1 porous silica coated active Metal oxide catalyst texture and structural parameters
Claims (12)
1. Medium-low temperature catalytic decomposition of N2The catalyst comprises an active oxide inner core and a porous inert oxide shell layer, wherein the active oxide inner core is composed ofBecomes an active component Co3O4The porous inert oxide shell layer is formed into SiO2-NxOyIn which N isxOyIs ZrO2Or CeO2The weight percentage of each component is as follows:
Co3O410-40wt％，ZrO2or CeO20.1-3 wt%, and the balance of SiO2；
The specific surface area of the catalyst is 250-480m2g-1The size of the active oxide inner core is 9-12nm, the thickness of the shell layer for coating the porous inert oxide is 6-20nm, and the particle size of the integral core-shell coating structure is 21-50 nm; the medium and low temperature means the temperature is less than 500 ℃;
the preparation method of the catalyst is characterized by comprising the following steps:
(1) taking an ethanol aqueous solution as a solvent, preparing a cobalt salt, mixing the cobalt salt with hexamethylenetetramine to form a mixed solution, adding a polyvinylpyrrolidone dispersing agent with the same mass as the cobalt salt, and stirring until the cobalt salt and the polyvinylpyrrolidone dispersing agent are completely dissolved;
(2) dropwise adding H into the solution prepared in the step (1)2O2Water solution, sealing the reaction system after the transparent solution system becomes turbid gradually, raising the operation temperature to 55-80 ℃, and keeping vigorous stirring for 12-72h to obtain highly uniformly dispersed Co3O4A nanoparticle sol;
(3) in the presence of ZrO2Or CeO2Dissolving zirconium nitrate or cerium nitrate and tetraethoxysilane in ethanol to prepare a mixed solution;
(4) according to the composition of the catalyst, in-situ dropping the ethyl orthosilicate ethanol mixed solution prepared in the step (3) into the nano-particle sol prepared in the step (2), adding ammonia water, continuing to react for 24-72h, and performing high-speed centrifugal separation on the obtained suspension;
(5) drying the centrifugal precipitate at 60-100 ℃, calcining at high temperature for 2-6h in the calcining atmosphere at 500-700 ℃ to remove organic residues, and obtaining the cobalt-based core porous oxide coated catalyst;
the cobalt salt is composed of inorganic cobalt salt and organic cobalt salt, wherein the inorganic cobalt salt and the organic cobalt salt are matched according to the molar ratio of 0.5-3: 1.
2. The medium-low temperature catalytic decomposition of N as claimed in claim 12The catalyst of O is characterized in that the volume part ratio of absolute ethyl alcohol to deionized water in the ethyl alcohol aqueous solution in the step (1) is as follows: anhydrous ethanol: deionized water 1.5-2.5: 1.
3. the medium-low temperature catalytic decomposition of N as claimed in claim 12The catalyst of O is characterized in that the inorganic cobalt salt is cobalt nitrate or cobalt chloride, and the organic cobalt salt is cobalt acetate or cobalt acetylacetonate.
4. The medium-low temperature catalytic decomposition of N as claimed in claim 12O, characterized in that the concentration of cobalt ions in the mixed solution in the step (1) is in the range of 0.01-0.015 mol/L.
5. The medium-low temperature catalytic decomposition of N as claimed in claim 12O, characterized in that the concentration of the hexamethylenetetramine in the mixed solution in the step (1) is in the range of 0.17-0.30 mol/L.
6. The medium-low temperature catalytic decomposition of N as claimed in claim 12O catalyst, characterized in that H in step (2)2O2The addition amount of the (2) is that 15-20m L3 wt% H is dripped into each liter of the mixed solution in the step (1)2O2An aqueous solution.
7. The medium-low temperature catalytic decomposition of N as claimed in claim 12The catalyst of O is characterized in that the addition amount of the tetraethoxysilane in the step (3) is as follows: co per liter3O4Adding 15-60m of ethyl orthosilicate L into the nano-particle sol.
8. The medium-low temperature catalytic decomposition of N as claimed in claim 12O catalyst, characterized in that the volume ratio of the ethyl orthosilicate and the ethanol in the step (3) is 1：5～10。
9. The medium-low temperature catalytic decomposition of N as claimed in claim 12The catalyst of O is characterized in that the addition amount of the ammonia water in the step (4) is as follows: co per liter3O4And adding 28 wt% of ammonia water 10-20m L into the nano particle sol.
10. The medium-low temperature catalytic decomposition of N as claimed in claim 12O, characterized in that the calcining atmosphere in the step (5) is any one of static air, flowing air or flowing nitrogen atmosphere.
11. The medium-low temperature catalytic decomposition of N as claimed in claim 12The application of the catalyst of O is characterized by comprising the following steps:
in a fixed bed reactor, N2The O catalytic decomposition conditions are as follows: the reaction pressure is normal pressure, the raw material gas is fed in and discharged from the top, and N is contained in the raw material gas2O volume concentration of 0.1-0.35%, NO2Volume concentration of 0.35% or less, O2Volume concentration of 1% -4%, H2The volume concentration of O is 0.5-2 percent, and the airspeed is 10000h-1-20000h-1The operation temperature is 200-500 ℃.
12. The medium-low temperature catalytic decomposition of N as claimed in claim 112The application of the catalyst of O is characterized in that the raw material gas is gas boiler flue gas or nitric acid production waste gas.
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| CN103263928A (en) * | 2013-05-17 | 2013-08-28 | 南京工业大学 | Composite oxide catalyst for low and medium-temperature decomposition of N2O and preparation method thereof |
| CN104226312A (en) * | 2013-06-20 | 2014-12-24 | 北京化工大学 | Core-shell structure catalyst, and preparation method and application thereof |
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| WO2017064711A1 (en) * | 2015-10-13 | 2017-04-20 | Newrocket Ltd. | Hypergolic system |
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