CN116328757B - A hollow metal oxide @TiO2 core-shell structure catalyst and its preparation method and application - Google Patents
A hollow metal oxide @TiO2 core-shell structure catalyst and its preparation method and application Download PDFInfo
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Abstract
本发明公开了一种空心金属氧化物@TiO2核壳结构催化剂及其制备方法与应用，属于催化剂材料制备和环保领域。所述催化剂以空心金属氧化物为内核，TiO2为外壳。采用廉价易得，价态多变的过渡金属氧化物为活性组分，以碳球为模板剂，设计以高比表面积的空心金属氧化物作内核，提高其催化活性，降低催化反应温度，同时利用SO2在TiO2上稳定性差，容易分解的特点，以TiO2作外壳。操作步骤简单，容易控制，未使用昂贵药剂，也没有任何有毒的添加剂。通过调节催化剂空腔尺寸，活性组分组成，核壳比例等，调控CO+NO和CO+O2竞争反应，促进CO催化还原NO反应，抑制CO氧化反应，并改善催化剂的耐硫性。The invention discloses a hollow metal oxide @ TiO2 core-shell structure catalyst and a preparation method and application thereof, and belongs to the field of catalyst material preparation and environmental protection. The catalyst has a hollow metal oxide as a core and TiO2 as a shell. A cheap, easily available, and valence-variable transition metal oxide is used as an active component, and a carbon ball is used as a template agent. A hollow metal oxide with a high specific surface area is designed as a core to improve its catalytic activity and reduce the catalytic reaction temperature. At the same time, the characteristics of poor stability and easy decomposition of SO2 on TiO2 are utilized, and TiO2 is used as a shell. The operation steps are simple and easy to control, and no expensive agents are used, and there are no toxic additives. By adjusting the catalyst cavity size, active component composition, core-shell ratio, etc., the competitive reaction of CO+NO and CO+ O2 is regulated, the catalytic reduction reaction of CO to NO is promoted, the CO oxidation reaction is inhibited, and the sulfur resistance of the catalyst is improved.
Description
Technical Field
The invention belongs to the field of catalyst material preparation and environmental protection, and particularly relates to a hollow metal oxide@TiO 2 core-shell structure catalyst and a preparation method and application thereof.
Background
Nitrogen oxides are one of the harmful atmospheric pollutants, mainly derived from thermal power generation, boiler combustion, automobile exhaust and the like, and can cause environmental hazards such as ozonolysis, acid rain, photochemical smog and the like. The steel sintering flue gas and the coke oven flue gas contain a large amount of NOx, and the catalytic reduction of NOx by using CO existing in the flue gas is the most economical way, but when the high-concentration O 2 exists, CO is easier to react with O 2, and SO 2 in the flue gas is easy to deactivate the catalyst, SO that the NOx conversion rate is obviously reduced. Therefore, the adsorption behavior of reactants on the catalyst can be effectively regulated and controlled through the selection of active components and the structural design of the catalyst, the CO catalytic reduction NO reaction is promoted, and the sulfur tolerance is improved.
In recent years, hollow-structure and core-shell catalyst materials have received great attention, and have become a research hotspot in the field of catalysis. The hollow material has unique advantages in catalysis due to the characteristics of high specific surface area, high porosity, high permeability, low density and the like, and the selectivity of the catalytic reaction can be improved by precisely controlling the size of the spherical shell aperture. CN106179471A discloses a spherical hollow catalyst for preparing hydrogen by reforming ethanol water vapor and a preparation method thereof, wherein carbon spheres are used as hard templates, a template-free hydrothermal crystallization method is adopted to synthesize the hollow Beta molecular sieve catalyst for preparing the hydrogen by reforming the ethanol water vapor, the ethanol conversion rate is 95.8% -99.8% at 300-600 ℃, and the hydrogen selectivity is 63% -69%. The core-shell components of the core-shell structure material are easy to produce synergistic effect, and the regulation and control of the catalytic performance are realized through the regulation of the core and shell components and the proportion and the regulation of the particle size and the shell thickness. CN104226374A discloses a supported oxide coated metal core-shell catalyst and a preparation method thereof, wherein raw gas contains 1% of CO and 1%O 2, the airspeed is 15000 mL.h -1·g-1, and the CO conversion rate reaches 80% -90% at 250 ℃.
Disclosure of Invention
Due to the characteristics of low cost, easy availability, multiple valence states and the like, transition metal oxides are commonly used as catalysts for CO oxidation and CO catalytic reduction of NO. Aiming at the influence of O 2 and SO 2 on the NO conversion rate in the CO catalytic reduction NO reaction, the invention provides a hollow metal oxide@TiO 2 core-shell structure catalyst and a preparation method thereof, wherein carbon spheres are used as a template agent, hollow metal oxide with high specific surface area is used as an inner core, the activity of CO catalytic reduction NO is improved, the catalytic reaction temperature is reduced, meanwhile, the characteristic of poor stability and easy decomposition of SO 2 on TiO 2 is utilized, tiO 2 is designed as an outer shell, and the sulfur resistance of the catalyst is improved. The invention has simple operation steps, easy control, no expensive medicament and no toxic additive. The sulfur tolerance of the catalyst is improved by adjusting the size of the catalyst cavity, the composition of active components, the proportion of core-shell and the like, regulating the competition reaction of CO+NO and CO+O 2, inhibiting the CO oxidation reaction.
In one aspect of the invention, a hollow metal oxide@TiO 2 core-shell structure catalyst is provided, wherein the hollow metal oxide is used as an inner core, and the TiO 2 is used as an outer shell.
Optionally, the specific surface area of the catalyst is 300-800 m 2/g, the cavity size of the inner core is 50-500 nm, the mass ratio of the core shell to the shell is 1 (0.01-0.6), and the thickness of the shell is 10-30 nm.
Optionally, the metal element in the hollow metal oxide is selected from at least one of Ce, fe, cu, mn, co, ni, sn, al.
According to one aspect of the present invention, there is provided a method for preparing the catalyst according to any one of claims 1 to 3, comprising the steps of:
(1) Dissolving a soluble carbon source in deionized water, cooling to room temperature after hydrothermal crystallization reaction, centrifugally separating, and drying to obtain powdery carbon spheres;
(2) Preparing a metal oxide source solution, namely adding a surfactant, a pore-forming agent and a complexing agent into an aqueous solution containing soluble metal salt, and uniformly stirring;
(3) Dispersing carbon spheres in deionized water to obtain a suspension, mixing the suspension with a metal oxide source solution, adjusting the pH value to 9-10, stirring, washing and drying;
(4) The preparation method of the hollow metal oxide@TiO 2 core-shell structure catalyst comprises the steps of dispersing a metal oxide precursor coated on the surface of a carbon sphere in deionized water, adding an auxiliary agent, dropwise adding a soluble titanium source, stirring for 0.5-2 h, standing for aging, washing, filtering, drying and roasting.
Optionally, in the step (1), the soluble carbon source is at least one selected from glucose, sucrose and fructose, and the solid-to-liquid ratio of the soluble carbon source to deionized water is 1:1-20;
The reaction temperature of the hydrothermal crystallization reaction is 120-190 ℃ and the reaction time is 3-18 h;
the drying condition is that the drying is carried out for 4-12 hours at 60-120 ℃;
the particle size of the powdery carbon spheres is 50-500 nm.
Optionally, in the step (2), the soluble metal cation is at least one of Ce ion, fe ion, cu ion, mn ion, co ion, ni ion, sn ion, and Al ion, and the anion is at least one of nitrate, sulfate, carbonate, acetate, and chloride ion, and the concentration of the soluble metal cation is 0.001-0.1 mol/L;
the mass ratio of the soluble metal salt to the surfactant, the pore-forming agent and the complexing agent is 1 (1 multiplied by 10 -3～1×10-1)：(5×10-3～1×10-1)：(5×10-3～1×10-1);
The surfactant is at least one of dodecyl ammonium sulfate or hexadecyl sodium sulfonate, the pore-forming agent is at least one of ammonium bicarbonate, benzoic acid or hexadecyl trimethyl ammonium bromide, and the complexing agent is at least one of hexamethylenetetramine or ethylenediamine tetraacetic acid.
Optionally, in the step (3), the solid-to-liquid ratio of the carbon spheres to the deionized water is 1:30-100, and the volume ratio of the suspension to the metal oxide source solution is 1:1-5.
The stirring condition is that stirring is carried out for 2-24 hours at 40-90 ℃, and the drying condition is that drying is carried out for 4-12 hours at 60-120 ℃;
In the step (3), alkali liquor is adopted to adjust the pH value, and the alkali liquor is at least one selected from 1-3 mol/L sodium hydroxide, 1-3 mol/L potassium hydroxide, 15-25% ammonia water and 10-30% urea.
Optionally, in the step (4), the mass ratio of the metal oxide precursor, the auxiliary agent and the soluble titanium source coated on the surface of the carbon sphere is 1 (5 multiplied by 10 -3～1.5×10-1)：(1×10-2 -1);
The auxiliary agent is at least one selected from citric acid, sodium citrate and ethylene glycol;
The soluble titanium source is tetrabutyl titanate, and the concentration of titanium ions in the mixed solution obtained in the step (4) is 1 multiplied by 10 -4～1×10-2 mol/L;
The standing and ageing time is 2-24 hours, the drying condition is that the drying is carried out for 4-12 hours at 60-120 ℃, the roasting temperature is 400-600 ℃, and the roasting time is 3-6 hours.
Optionally, the standing and aging time is selected from 4h, 6h, 8h, 10h, 12h, 15h, 16h, 18h, 20h, 22h, or any value between any two points.
Optionally, the firing temperature is selected from 420 ℃, 450 ℃, 470 ℃, 480 ℃, 500 ℃, 530 ℃, 550 ℃, 580 ℃, or any value between any two points;
The roasting time is selected from 3.5h, 4h, 4.5h, 5h and 5.5h, or any value between any two points.
According to one aspect of the invention, the catalyst and the application of the catalyst prepared by the preparation method in the CO catalytic reduction NO reaction are provided.
Optionally, the reaction temperature of the CO catalytic reduction NO reaction is 100-300 ℃, the space velocity is 10000-50000 h -1, the raw material gas is 0.05-1.0% of CO concentration, 0.01-0.1% of NO concentration and N 2 is used as balance gas.
The invention has the characteristics and beneficial effects that:
1. The size of the carbon spheres prepared by the method can be controlled by adjusting hydrothermal crystallization conditions, the solid-liquid ratio controls the size of crystal grains, and the addition of the pore-forming agent improves the specific surface area of the metal oxide, so that the hollow metal oxide@Ti 2 core-shell structure catalyst with different cavity sizes and high specific surface area can be obtained.
2. The hollow metal oxide @ TiO 2 core-shell structure catalyst prepared by the method can be a single metal oxide or a multi-component composite metal oxide.
3. The preparation method of the hollow metal oxide@TiO 2 core-shell structure catalyst has the advantages of simple operation steps, easy control, no expensive medicament and no toxic additive.
4. The hollow metal oxide@TiO 2 core-shell structure catalyst prepared by the method can be used for CO catalytic reduction NO reaction, and the coated TiO 2 shell structure can obviously improve the sulfur resistance of the catalyst.
Drawings
FIG. 1 shows the results of evaluating the catalytic activity of CO catalytic reduction of NO using the catalyst obtained in example 1.
Detailed Description
The following detailed description of the invention is merely a preferred embodiment of the invention and is not intended to limit the scope of the invention. All equivalent changes and modifications of the invention are intended to fall within the scope of the invention.
Example 1
1. The preparation method of the carbon spheres comprises the steps of stirring and dissolving 8g of glucose in 80ml of deionized water to form a clear solution, then placing the clear solution in a hydrothermal reaction kettle, keeping the temperature at 175 ℃ for 8 hours, cooling to obtain brown turbid liquid, centrifugally separating, drying the turbid liquid at 70 ℃ for 8 hours, and grinding to obtain brown carbon sphere powder, wherein the particle size of the carbon spheres is 150-200 nm.
2. The metal oxide source solution is prepared by weighing 18g of aluminum nitrate, 1.8g of ferric nitrate, 2.1g of cerium nitrate dissolved in 500mL of deionized water, and adding 0.5g of sodium dodecyl sulfate, 0.9g of ammonium bicarbonate and 0.6g of hexamethylenetetramine.
3. The preparation method of the carbon sphere surface coated metal oxide precursor comprises the steps of dispersing 0.2g of carbon sphere in 30mL of deionized water in an ultrasonic manner, mixing with a metal oxide source solution, adding 25% ammonia water to adjust the pH value to 10, continuously stirring for 12h at 60 ℃, cooling to room temperature, washing, filtering, and drying at 60 ℃ for 8h to obtain the precursor of the carbon sphere surface coated Fe 2O3-CeO2-Al2O3.
4. The preparation method of the hollow metal oxide @ TiO 2 core-shell structure catalyst comprises the steps of dispersing 5g of a precursor coated with Fe 2O3-CeO2-Al2O3 on the surface of a carbon sphere in 150ml of deionized water in an ultrasonic manner, adding 0.5g of sodium citrate, slowly dropwise adding 1.6g of tetrabutyl titanate, continuously stirring for 1h, standing and aging for 8h, washing and filtering, drying at 80 ℃ for 6h, roasting at 500 ℃ for 4h, and obtaining the hollow Fe 2O3-CeO2-Al2O3@TiO2 core-shell structure catalyst, wherein the specific surface area is 524.67m 2/g, the cavity size of an inner core is about 200nm, the mass ratio of the core to the shell is 1:0.08, and the thickness of the shell is about 20nm.
Example 2
1. 6.5G of glucose is stirred and dissolved in 70ml of deionized water to form a clear solution, then the clear solution is placed in a hydrothermal reaction kettle, the temperature is kept at 180 ℃ for 7 hours, a brown turbid liquid is obtained after cooling, the brown turbid liquid is dried at 60 ℃ for 8 hours after centrifugal separation, and the brown carbon sphere powder is obtained after grinding, wherein the particle size of the carbon sphere is 200-250 nm.
2. The metal oxide source solution is prepared by weighing 18g of aluminum sulfate, 1.8g of manganese acetate and 2.1g of cerium nitrate, dissolving in 500mL of deionized water, and adding 0.6g of sodium hexadecyl sulfonate, 1.2g of benzoic acid and 0.9g of ethylenediamine tetraacetic acid.
3. The preparation method of the carbon sphere surface coated metal oxide precursor comprises the steps of dispersing 0.3g of carbon sphere in 50mL of deionized water in an ultrasonic manner, mixing with a metal oxide source solution, adding 2.5mol/L sodium hydroxide to adjust the pH value to 10, continuously stirring for 5 hours at 80 ℃, cooling to room temperature, washing, filtering, and drying at 120 ℃ for 4 hours to obtain the precursor of the carbon sphere surface coated MnO 2-CeO2-Al2O3.
4. The preparation method of the hollow metal oxide@TiO 2 core-shell structure catalyst comprises the steps of dispersing 5g of a precursor coated with MnO 2-CeO2-Al2O3 on the surface of a carbon sphere in 200ml of deionized water in an ultrasonic manner, adding 0.3g of citric acid, slowly dropwise adding 2g of tetrabutyl titanate, continuously stirring for 1.5h, standing for aging for 12h, washing, filtering, drying at 100 ℃ for 5h, roasting at 500 ℃ for 4h, and obtaining the hollow MnO 2-CeO2-Al2O3@TiO2 core-shell structure catalyst, wherein the specific surface area is 489.03m 2/g, the cavity size of an inner core is about 250nm, the mass ratio of the core to the shell is 1:0.1, and the thickness of the shell is about 25nm.
Example 3
1. The preparation method of the carbon spheres comprises the steps of stirring and dissolving 10g of glucose in 80ml of deionized water to form a clear solution, then placing the clear solution in a hydrothermal reaction kettle, keeping the temperature at 170 ℃ for 9 hours, cooling to obtain brown turbid liquid, centrifuging and separating, drying the turbid liquid at 60 ℃ for 10 hours, and grinding to obtain brown carbon sphere powder, wherein the particle size of the carbon spheres is 100-150 nm.
2. The metal oxide source solution is prepared by weighing 12g of ferric chloride, 2g of cerium carbonate dissolved in 500mL of deionized water, adding 0.6g of sodium dodecyl sulfate, 1.5g of cetyl tetramethyl ammonium bromide and 0.6g of hexamethylenetetramine.
3. The preparation method of the carbon sphere surface coated metal oxide precursor comprises the steps of dispersing 0.5g of carbon sphere in 100mL of deionized water in an ultrasonic manner, mixing with a metal oxide source solution, adding a 30% urea solution, adjusting the pH value to 10, continuously stirring for 18h at 40 ℃, cooling to room temperature, washing, filtering, and drying at 60 ℃ for 10h to obtain the precursor of the carbon sphere surface coated CeO 2-Fe2O3.
4. The preparation method of the hollow metal oxide @ TiO 2 core-shell structure catalyst comprises the steps of dispersing 5g of a precursor coated with CeO 2-Fe2O3 on the surface of a carbon sphere in 250ml of deionized water by ultrasonic, adding 0.5g of sodium citrate, slowly dropwise adding 1.2g of tetrabutyl titanate, continuously stirring for 2 hours, standing and aging for 6 hours, washing and filtering, drying at 100 ℃ for 5 hours, roasting at 500 ℃ for 4 hours, and obtaining the hollow CeO 2-Fe2O3@TiO2 core-shell structure catalyst, wherein the specific surface area is 665.88m 2/g, the cavity size of an inner core is about 150nm, the mass ratio of the core to the shell is 1:0.06, and the thickness of the shell is about 12nm.
Example 4
1. The preparation method of the carbon spheres comprises the steps of stirring and dissolving 8g of glucose in 80ml of deionized water to form a clear solution, then placing the clear solution in a hydrothermal reaction kettle, keeping the temperature at 165 ℃ for 10 hours, cooling to obtain brown turbid liquid, centrifugally separating, drying the turbid liquid at 120 ℃ for 4 hours, and grinding to obtain brown carbon sphere powder, wherein the particle size of the carbon spheres is 100-150 nm.
2. The metal oxide source solution is prepared by weighing 18g of ferric nitrate and dissolving in 500mL of deionized water, adding 0.5g of sodium dodecyl sulfate, 1.5g of cetyl tetramethyl ammonium bromide and 0.9g of ethylenediamine tetraacetic acid.
3. The preparation method of the precursor for coating the metal oxide on the surface of the carbon sphere comprises the steps of dispersing 0.2g of carbon sphere in 50mL of deionized water in an ultrasonic manner, mixing with a metal oxide source solution, adding 2.5mol/L potassium hydroxide solution, regulating the pH value to 10, continuously stirring for 2 hours at 90 ℃, cooling to room temperature, washing, filtering, and drying at 60 ℃ for 10 hours to obtain the precursor for coating the Fe 2O3 on the surface of the carbon sphere.
4. The preparation method of the hollow metal oxide @ TiO 2 core-shell structure catalyst comprises the steps of dispersing 5g of a precursor coated with Fe 2O3 on the surface of a carbon sphere in 200ml of deionized water by ultrasonic, adding 0.5g of ethylene glycol, slowly dropwise adding 1.6g of tetrabutyl titanate, continuously stirring for 2 hours, standing for aging for 4 hours, washing, filtering, drying at 100 ℃ for 6 hours, roasting at 500 ℃ for 4 hours, and obtaining the hollow Fe 2O3@TiO2 core-shell structure catalyst, wherein the specific surface area is 390.23m 2/g, the cavity size of an inner core is about 150nm, the mass ratio of the core to the shell is 1:0.08, and the thickness of the shell is about 25nm.
Test case
The catalytic activity of CO catalytic reduction of NO was evaluated using the catalyst obtained in example 1 as an example, as shown in the following graph. The reaction temperature is 100-300 ℃, the space velocity is 30000h -1, the concentration of CO is 0.65%, the concentration of NO is 0.6%, N 2 is used as balance gas, and the test result is shown in figure 1.
While the application has been described in terms of preferred embodiments, it will be understood by those skilled in the art that various changes and modifications can be made without departing from the scope of the application, and it is intended that the application is not limited to the specific embodiments disclosed.
Claims (8)
1. The preparation method of the hollow metal oxide@TiO 2 core-shell structure catalyst is characterized by comprising the following steps of:
(1) Dissolving a soluble carbon source in deionized water, cooling to room temperature after hydrothermal crystallization reaction, centrifugally separating, and drying to obtain powdery carbon spheres;
(2) Preparing a metal oxide source solution, namely adding a surfactant, a pore-forming agent and a complexing agent into an aqueous solution containing soluble metal salt, and uniformly stirring;
(3) Dispersing carbon spheres in deionized water to obtain a suspension, mixing the suspension with a metal oxide source solution, adjusting the pH value to 9-10, stirring, washing and drying;
(4) Dispersing a metal oxide precursor coated on the surface of a carbon sphere in deionized water, adding an auxiliary agent, dropwise adding a soluble titanium source, stirring for 0.5-2 h, standing for ageing, washing, filtering, drying and roasting;
the particle size of the powdery carbon spheres is 50-500 nm;
the pore-forming agent is at least one selected from ammonium bicarbonate, benzoic acid or cetyltrimethylammonium bromide;
In the step (1), the solid-to-liquid ratio of the soluble carbon source to the deionized water is 1:1-20;
in the step (3), the solid-to-liquid ratio of the carbon spheres to deionized water is 1:30-100;
in the step (4), the solid-liquid ratio of the precursor of the metal oxide coated on the surface of the carbon sphere to deionized water is 1:10-150;
The catalyst takes hollow metal oxide as an inner core and TiO 2 as an outer shell;
The specific surface area of the catalyst is 300-800 m 2/g, the cavity size of the inner core is 50-500 nm, the mass ratio of the core to the shell is 1 (0.01-0.6), and the thickness of the shell is 10-30 nm.
2. The production method according to claim 1, wherein the metal element in the hollow metal oxide is at least one selected from Ce, fe, cu, mn, co, ni, sn, al.
3. The method according to claim 1, wherein in the step (1), the soluble carbon source is at least one selected from glucose, sucrose, and fructose;
The reaction temperature of the hydrothermal crystallization reaction is 120-190 ℃ and the reaction time is 3-18 h;
And the drying condition is that the drying is carried out for 4-12 hours at 60-120 ℃.
4. The preparation method according to claim 1, wherein in the step (2), the soluble metal cations are at least one selected from Ce ion, fe ion, cu ion, mn ion, co ion, ni ion, sn ion, and Al ion, and the anions are at least one selected from nitrate, sulfate, carbonate, acetate, and chloride ion, and the concentration of the soluble metal cations is 0.001 to 0.1mol/L;
The mass ratio of the soluble metal salt to the surfactant, the pore-forming agent and the complexing agent is 1 (1 multiplied by 10 -3~1×10-1)：(5×10-3~1×10-1)：(5×10-3~1×10-1);
the surfactant is at least one of ammonium dodecyl sulfate or sodium hexadecyl sulfonate, and the complexing agent is at least one of hexamethylenetetramine or ethylenediamine tetraacetic acid.
5. The method according to claim 1, wherein in the step (3), the volume ratio of the suspension to the metal oxide source solution is 1:1-5;
the stirring condition is that stirring is carried out for 2-24 hours at 40-90 ℃, and the drying condition is that drying is carried out for 4-12 hours at 60-120 ℃;
in the step (4), the mass ratio of the metal oxide precursor to the auxiliary agent and the soluble titanium source coated on the surface of the carbon sphere is 1 (5 multiplied by 10 -3~1.5×10-1)：(1×10-2 -1);
the auxiliary agent is at least one selected from citric acid, sodium citrate and ethylene glycol, and the soluble titanium source is tetrabutyl titanate.
6. The preparation method of the ceramic tile according to claim 1, wherein in the step (4), the standing aging time is 2-24 hours, the drying condition is 60-120 ℃ and is 4-12 hours, the roasting temperature of the roasting is 400-600 ℃ and the roasting time is 3-6 hours.
7. The method for preparing the catalyst according to any one of claims 1-6, wherein the catalyst is used for CO catalytic reduction of NO.
8. The application of claim 7, wherein the reaction temperature of the CO catalytic reduction NO reaction is 100-300 ℃, the space velocity is 10000-50000 h -1, the raw material gas component is that CO concentration is 0.05-1.0%, NO concentration is 0.01-0.1%, and N 2 is used as balance gas.
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| CN112221488A (en) * | 2020-11-04 | 2021-01-15 | 西南化工研究设计院有限公司 | Novel core-shell structure catalyst for synergistic denitration and demercuration and preparation method thereof |
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| CN112221488A (en) * | 2020-11-04 | 2021-01-15 | 西南化工研究设计院有限公司 | Novel core-shell structure catalyst for synergistic denitration and demercuration and preparation method thereof |
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