CN115041177A - Catalyst with functions of adsorbing and oxidizing nitrogen oxides and preparation method and application thereof - Google Patents
Catalyst with functions of adsorbing and oxidizing nitrogen oxides and preparation method and application thereof Download PDFInfo
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- CN115041177A CN115041177A CN202210804892.5A CN202210804892A CN115041177A CN 115041177 A CN115041177 A CN 115041177A CN 202210804892 A CN202210804892 A CN 202210804892A CN 115041177 A CN115041177 A CN 115041177A
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
- B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/83—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with rare earths or actinides
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9404—Removing only nitrogen compounds
- B01D53/9409—Nitrogen oxides
- B01D53/9413—Processes characterised by a specific catalyst
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- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
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Abstract
The invention provides a catalyst with nitrogen oxide adsorption and oxidation functions and a preparation method and application thereof, wherein the catalyst comprises Al 2 O 3 Support and LaCoO 3 Active ingredient, said LaCoO 3 The loading amount of the active components is 40-80 wt%. The preparation method comprises the following steps: (1) mixing lanthanum nitrate, cobalt nitrate, water and citric acid to obtain a first solution; (2) dropwise adding ammonia water into the first solution until the pH value of the solution is more than or equal to 9 to obtain a second solution; (3) mixing alumina and the second solution for impregnation treatment to obtain an impregnated sample; (4) carrying out vacuum rotary evaporation treatment on the dipped sample to obtain a gel sample; (5) and drying, roasting and granulating the gel sample in sequence to obtain the catalyst. The catalyst provided by the invention has the functions of adsorbing and oxidizing nitrogen oxides,is suitable for being used as a low-temperature PNA catalyst with high activity and high selectivity.
Description
Technical Field
The invention belongs to the technical field of automobile exhaust treatment, relates to a catalyst, and particularly relates to a catalyst with functions of nitrogen oxide adsorption and oxidation, and a preparation method and application thereof.
Background
With the rapid development of the automobile industry, nitrogen oxides contained in the tail gas of motor vehicles have become one of the main atmospheric pollutants at present, and the harm of the nitrogen oxides to the environment is increasingly significant. In this regard, a common solution is to install a mobile denitration device at the exhaust emission site of the automobile.
However, in the cold start stage and the idling running process of the vehicle, the temperature of the tail gas is too low, and the common catalyst cannot work normally. For example, for NSR (lean NO) x Storage reduction technology) catalyst, lean burn stage to NO x The storage of (a) is primarily dependent on the nitrate storage pathway, and the rate of NO oxidation in this process is often an important rate-determining step. At low temperatures, the NO oxidation reaction, although thermodynamic equilibrium favors the reaction, is kinetically limited so that the rate is very slow, with NO oxidation rates below 200 ℃ typically being less than 10% for catalysts below 200 ℃, resulting in NSR catalysts that do not oxidize NO at low temperatures x The collection efficiency of (2) is difficult to improve. Urea-SCR (Selective catalytic reduction denitration technology) is another denitration technology widely applied and relies on NH released by decomposition of Urea as a reducing agent source 3 And the lower limit of the decomposition temperature is 180 ℃. At temperatures below 180 ℃ due to the absence of reducing agents, on NO x It is difficult to improve the removal efficiency of (2).
In response to the above problems, PNA (passive nitrogen oxide adsorption technology) is considered to be an effective countermeasure. The working principle of PNA is summarized mainly as high efficiency trapping NO at low temperature, and NO after temperature rise x After the operating temperature of the reduction catalyst, NO is released x At the same time, regeneration of the adsorption sites is completed. In addition, the complex composition and temperature variation range of the exhaust gas also impose higher tolerance requirements on the PNA material.
The research and development aiming at the PNA material at present mainly comprises three main types of noble metal/oxide, noble metal/molecular sieve and non-noble metal systems, wherein, researchers have reported flexible index on non-noble metal PNA materials. However, considering the factors of high cost of noble metals, limited resources and the like, the development of efficient non-noble metal PNA materials is a great trend of the development of PNA materials in the future.
Therefore, how to develop a low-temperature PNA catalyst with high activity and high selectivity, which has the functions of adsorbing nitrogen oxides and oxidizing nitrogen oxides, is a problem to be solved by those skilled in the art.
Disclosure of Invention
The invention aims to provide a catalyst with nitrogen oxide adsorption and oxidation functions, a preparation method and application thereof, wherein the catalyst is suitable for being used as a low-temperature PNA catalyst with high activity and high selectivity.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a catalyst for adsorbing and oxidizing nitrogen oxides, the catalyst comprising Al 2 O 3 Support and LaCoO 3 An active component.
The LaCoO 3 The amount of active ingredient loaded is in the range of from 40 to 80 wt%, and may be, for example, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt% or 80 wt%, although not limited to the recited values, and other values not recited within the range of values are equally applicable.
In the present invention, the LaCoO is 3 The loading amount of the active component is specifically the proportion of the mass of the active component in the total mass of the catalyst, and needs to be controlled within a reasonable range. When the loading is less than 40 wt%, the activity and selectivity of the catalyst are not ideal; when the loading is more than 80 wt%, the activity and selectivity of the catalyst are improved in a limited range, and the preparation cost is high.
The invention is realized by adding Al 2 O 3 LaCoO loaded on carrier 3 The active component, especially the loading capacity of the active component, is limited, the catalyst which has the functions of adsorbing and oxidizing nitrogen oxides is prepared, and when the catalyst is used for adsorbing the nitrogen oxides passively, nitrogen oxides are generatedThe storage efficiency of the material can reach 80 percent at most.
Preferably, the Al 2 O 3 The carrier comprises gamma-Al 2 O 3 And (3) a carrier.
Preferably, the Al 2 O 3 The support has an average particle diameter of 8 to 12nm, and may be, for example, 8mm, 8.5mm, 9mm, 9.5mm, 10mm, 10.5mm, 11mm, 11.5mm or 12mm, but is not limited to the values listed, and other values not listed in the numerical range are also applicable.
In a second aspect, the present invention provides a method for preparing a catalyst as described in the first aspect, the method comprising the steps of:
(1) mixing lanthanum nitrate, cobalt nitrate, water and citric acid to obtain a first solution;
(2) dropwise adding ammonia water into the first solution obtained in the step (1) until the pH value of the solution is more than or equal to 9 to obtain a second solution;
(3) carrying out impregnation treatment on the mixed alumina and the second solution obtained in the step (2) to obtain an impregnated sample;
(4) carrying out vacuum rotary evaporation treatment on the dipping sample obtained in the step (3) to obtain a gel sample;
(5) and (4) drying, roasting and granulating the gel sample obtained in the step (4) in sequence to obtain the catalyst.
According to the invention, the catalyst with nitrogen oxide adsorption and oxidation is finally obtained through sequentially mixing, pH adjustment, impregnation, vacuum rotary evaporation, drying, roasting and granulation, the preparation process is simple and efficient, and large-scale production and application are easy to realize.
In the present invention, the pH of the second solution obtained in step (2) is 9 or more, and may be, for example, 9, 9.5, 10, 10.5 or 11, but is not limited to the values listed, and other values not listed in the range of the values are also applicable.
According to the invention, ammonia water is dripped into the first solution until the pH value of the solution is more than or equal to 9, so that the citric acid in the solution can fully exert the complexing effect, and the rapid formation of a gel sample in the subsequent vacuum rotary evaporation treatment process is promoted.
Preferably, the specific order of mixing in step (1) is: firstly, dissolving lanthanum nitrate and cobalt nitrate in water, stirring uniformly, and then adding citric acid into the solution.
Preferably, in step (1), the mixing ratio of lanthanum nitrate, cobalt nitrate and citric acid is n (lanthanum nitrate): n (cobalt nitrate): n (citric acid): 1 (1.5-1.7), and may be, for example, 1:1:1.5, 1:1:1.52, 1:1:1.54, 1:1:1.56, 1:1:1.58, 1:1:1.6, 1:1:1.62, 1:1:1.64, 1:1:1.66, 1:1:1.68 or 1:1:1.7, but is not limited to the enumerated values, and other non-enumerated values in the numerical range are also applicable.
In the present invention, the mixing ratio of lanthanum nitrate, cobalt nitrate and citric acid specifically refers to the ratio of the amounts of the respective raw material substances.
Preferably, the concentration of the aqueous ammonia in step (2) is 20 wt% to 30 wt%, and for example, it may be 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt% or 30 wt%, but it is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the first solution is further stirred for 20-40min before the dropwise addition in step (2), such as 20min, 22min, 24min, 26min, 28min, 30min, 32min, 34min, 36min, 38min or 40min, but not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the impregnation treatment in step (3) comprises an equal volume impregnation treatment or an excess impregnation treatment, and more preferably an excess impregnation treatment.
Preferably, the dipping sample is further stirred for 40-80min after the dipping treatment in step (3), such as 40min, 45min, 50min, 55min, 60min, 65min, 70min, 75min or 80min, but not limited to the values listed, and other values not listed in the range of the values are also applicable.
The method adopts excessive dipping treatment and combines the subsequent stirring of a dipping sample, thereby further promoting the uniformity of dipping, improving the dispersibility of the surface active component of the obtained catalyst and improving the catalytic activity and selectivity of the catalyst.
Preferably, the vacuum rotary evaporation treatment in step (4) is performed in a vacuum rotary evaporator, and the absolute vacuum degree is 0.02-0.04MPa, and may be, for example, 0.02MPa, 0.022MPa, 0.024MPa, 0.026MPa, 0.028MPa, 0.03MPa, 0.032MPa, 0.034MPa, 0.036MPa, 0.038MPa or 0.04MPa, but not limited to the enumerated values, and other non-enumerated values in the numerical range are also applicable.
Preferably, the vacuum rotary evaporation treatment in the step (4) comprises a first rotary evaporation treatment and a second rotary evaporation treatment which are sequentially performed.
Preferably, the temperature of the first rotary evaporation treatment is 55-65 ℃, for example 55 ℃, 56 ℃, 57 ℃, 58 ℃, 59 ℃, 60 ℃, 61 ℃, 62 ℃, 63 ℃, 64 ℃ or 65 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, a sample in a gel state is formed after the first rotary evaporation treatment.
Preferably, the temperature of the second rotary evaporation treatment is 75-85 ℃, for example, 75 ℃, 76 ℃, 77 ℃, 78 ℃, 79 ℃, 80 ℃, 81 ℃, 82 ℃, 83 ℃, 84 ℃ or 85 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the time of the second rotary evaporation treatment is 10-20min, for example, 10min, 11min, 12min, 13min, 14min, 15min, 16min, 17min, 18min, 19min or 20min, but is not limited to the enumerated values, and other non-enumerated values in the numerical range are also applicable.
Preferably, the drying in step (5) is specifically: the gel samples and the roto-retort were transferred directly to an oven for drying.
Preferably, the drying temperature in step (5) is 100-140 ℃, for example, 100 ℃, 105 ℃, 110 ℃, 115 ℃, 120 ℃, 125 ℃, 130 ℃, 135 ℃ or 140 ℃, but not limited to the enumerated values, and other non-enumerated values in the range of the values are also applicable.
Preferably, the drying time in step (5) is 20-30h, such as 20h, 21h, 22h, 23h, 24h, 25h, 26h, 27h, 28h, 29h or 30h, but not limited to the recited values, and other values not recited in the range of values are also applicable.
Preferably, the solid obtained after drying in step (5) is ground into a powder.
Preferably, the calcination in step (5) is carried out in an atmosphere of flowing air, and the air flow rate is 250-350mL/min, such as 250mL/min, 260mL/min, 270mL/min, 280mL/min, 290mL/min, 300mL/min, 310mL/min, 320mL/min, 330mL/min, 340mL/min or 350mL/min, but not limited to the values listed, and other values not listed in this range are equally applicable.
Preferably, the roasting of step (5) includes a first roasting treatment and a second roasting treatment which are sequentially performed.
Preferably, the temperature increase rate of the first baking treatment is 0.5 to 1.5 ℃/min, and may be, for example, 0.5 ℃/min, 0.6 ℃/min, 0.7 ℃/min, 0.8 ℃/min, 0.9 ℃/min, 1 ℃/min, 1.1 ℃/min, 1.2 ℃/min, 1.3 ℃/min, 1.4 ℃/min, or 1.5 ℃/min, but is not limited to the values listed, and other values not listed within the range of values are equally applicable.
Preferably, the temperature of the first baking treatment is 250-350 ℃, and may be, for example, 250 ℃, 260 ℃, 270 ℃, 280 ℃, 290 ℃, 300 ℃, 310 ℃, 320 ℃, 330 ℃, 340 ℃ or 350 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the first calcination treatment is carried out for a time of 2.5 to 3.5 hours, for example, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, 3 hours, 3.1 hours, 3.2 hours, 3.3 hours, 3.4 hours or 3.5 hours, but not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the temperature increase rate of the second baking treatment is 4 to 6 ℃/min, and may be, for example, 4 ℃/min, 4.2 ℃/min, 4.4 ℃/min, 4.6 ℃/min, 4.8 ℃/min, 5 ℃/min, 5.2 ℃/min, 5.4 ℃/min, 5.6 ℃/min, 5.8 ℃/min, or 6 ℃/min, but is not limited to the values listed, and other values not listed within the range of values are also applicable.
Preferably, the temperature of the second baking treatment is 620-680 ℃, such as 620 ℃, 630 ℃, 640 ℃, 650 ℃, 660 ℃, 670 ℃ or 680 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
The invention sets the highest temperature of roasting to be lower 620-680 ℃, thereby not only improving the abundance of oxygen defects in the catalyst, but also reducing the preparation cost and improving the economic benefit.
Preferably, the second calcination treatment is carried out for 4 to 6 hours, for example, 4 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, 5 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours or 6 hours, but not limited to the recited values, and other values not recited in the range of the values are also applicable.
The invention adopts two-stage stepwise temperature rise roasting, and particularly limits the temperature rise rate, temperature and time of each stage of roasting treatment, promotes the uniform decomposition of nitrate, and improves the binding force between active components and a carrier, thereby further improving the activity and selectivity of the catalyst and prolonging the service life of the catalyst.
Preferably, the granulation in the step (5) comprises tabletting, crushing and screening which are sequentially carried out.
Preferably, the average particle size of the catalyst particles obtained by the granulation in step (5) is 40-60 mesh, for example, 40 mesh, 42 mesh, 44 mesh, 46 mesh, 48 mesh, 50 mesh, 52 mesh, 54 mesh, 56 mesh, 58 mesh or 60 mesh, but not limited to the recited values, and other values not recited in the range of the values are also applicable.
As a preferable technical solution of the second aspect of the present invention, the preparation method comprises the steps of:
(1) dissolving lanthanum nitrate and cobalt nitrate in water, uniformly stirring, and adding citric acid into the solution to obtain a first solution; the mixing ratio of the lanthanum nitrate, the cobalt nitrate and the citric acid is n (lanthanum nitrate), n (cobalt nitrate) and n (citric acid) 1:1 (1.5-1.7);
(2) stirring the first solution obtained in the step (1) for 20-40min, and then dropwise adding ammonia water with the concentration of 20-30 wt% until the pH value of the solution is more than or equal to 9 to obtain a second solution;
(3) performing excessive dipping treatment on the mixed alumina and the second solution obtained in the step (2), and stirring for 40-80min to obtain a dipped sample;
(4) performing vacuum rotary evaporation treatment on the impregnated sample obtained in the step (3) in a vacuum rotary evaporator, wherein the absolute vacuum degree is 0.02-0.04MPa, and the specific steps are as follows: firstly, carrying out first rotary steaming treatment at 55-65 ℃ until a sample in a gel state is formed, and then heating to 75-85 ℃ to carry out second rotary steaming treatment for 10-20min to obtain a gel sample;
(5) directly transferring the gel sample and the rotary evaporation bottle obtained in the step (4) to an oven at the temperature of 100-140 ℃ for drying for 20-30h, and grinding the obtained solid into powder; roasting the obtained powder in a flowing air atmosphere with the flow rate of 250-350mL/min, specifically: firstly heating to 250-350 ℃ at the speed of 0.5-1.5 ℃/min for roasting for 2.5-3.5h, and then heating to 620-680 ℃ at the speed of 4-6 ℃/min for roasting for 4-6 h; and tabletting, crushing and screening the roasted sample in sequence to obtain the catalyst particles of 40-60 meshes.
In a third aspect, the present invention provides the use of a catalyst as described in the first aspect, including the use of said catalyst for passive adsorption of nitrogen oxides.
Compared with the prior art, the invention has the following beneficial effects:
the invention is realized by adding Al 2 O 3 LaCoO loaded on carrier 3 The catalyst has the advantages that the catalyst has both nitrogen oxide adsorption and oxidation functions, and the storage efficiency of nitrogen oxide can reach 80% at most when the catalyst is used for passive nitrogen oxide adsorption.
Drawings
FIG. 1 shows LaCoO obtained in example 1 3 /Al 2 O 3 TEM images of the catalyst;
FIG. 2 shows LaCoO obtained in example 8 3 /Al 2 O 3 TEM images of the catalyst;
FIG. 3 shows LaCoO obtained in example 9 3 /Al 2 O 3 TEM images of the catalyst.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The embodiment provides a catalyst with nitrogen oxide adsorption and oxidation functions and a preparation method thereof, wherein the preparation method comprises the following steps:
(1) first 10.568g of La (NO) 3 ) 3 ·6H 2 O and 7.104g of Co (NO) 3 ) 2 ·6H 2 Dissolving O in 100mL of deionized water, stirring uniformly, and adding 7.693g of citric acid into the solution to obtain a first solution; the mixing ratio of the lanthanum nitrate, the cobalt nitrate and the citric acid is n (lanthanum nitrate), n (cobalt nitrate) and n (citric acid) 1:1: 1.64;
(2) stirring the first solution obtained in the step (1) for 30min, and then dropwise adding ammonia water with the concentration of 25 wt% until the pH value of the solution is 10 to obtain a second solution;
(3) mixing 4g of gamma-alumina and the second solution obtained in the step (2) for excessive impregnation treatment, and stirring for 60min to obtain an impregnated sample;
(4) performing vacuum rotary evaporation treatment on the impregnated sample obtained in the step (3) in a vacuum rotary evaporator, wherein the absolute vacuum degree is 0.03MPa, and the method specifically comprises the following steps: performing first rotary evaporation treatment at 60 ℃ until a sample in a gel state is formed, and then heating to 80 ℃ for performing second rotary evaporation treatment for 15min to obtain a gel sample;
(5) directly transferring the gel sample obtained in the step (4) and the rotary steaming bottle to a 120 ℃ oven for drying for 24h, and grinding the obtained solid into powder; roasting the obtained powder in a flowing air atmosphere with the flow rate of 300mL/min, and specifically: firstly heating to 300 ℃ at the speed of 1 ℃/min and roasting for 3h, and then heating to 650 ℃ at the speed of 5 ℃/min and roasting for 5 h; sequentially tabletting, crushing and screening the roasted sample to obtain 50-mesh 60 wt% LaCoO 3 /Al 2 O 3 Catalyst particles.
Example 2
The embodiment provides a catalyst with nitrogen oxide adsorption and oxidation functions and a preparation method thereof, wherein the preparation method comprises the following steps:
(1) first 10.568g of La (NO) 3 ) 3 ·6H 2 O and 7.104g of Co (NO) 3 ) 2 ·6H 2 Dissolving O in 100mL of deionized water, uniformly stirring, and then adding 7.693g of citric acid into the solution to obtain a first solution; the mixing ratio of the lanthanum nitrate, the cobalt nitrate and the citric acid is n (lanthanum nitrate), n (cobalt nitrate) and n (citric acid) 1:1: 1.64;
(2) stirring the first solution obtained in the step (1) for 20min, and then dropwise adding ammonia water with the concentration of 20 wt% until the pH value of the solution is 9 to obtain a second solution;
(3) mixing 4g of gamma-alumina and the second solution obtained in the step (2) for excessive impregnation treatment, and stirring for 40min to obtain an impregnated sample;
(4) performing vacuum rotary evaporation treatment on the impregnated sample obtained in the step (3) in a vacuum rotary evaporator, wherein the absolute vacuum degree is 0.02MPa, and the method specifically comprises the following steps: performing first rotary evaporation treatment at 55 ℃ until a sample in a gel state is formed, and then heating to 75 ℃ to perform second rotary evaporation treatment for 20min to obtain a gel sample;
(5) directly transferring the gel sample obtained in the step (4) and the rotary steaming bottle into an oven at 100 ℃ for drying for 30h, and grinding the obtained solid into powder; roasting the obtained powder in a flowing air atmosphere with the flow rate of 250mL/min, and specifically: firstly heating to 250 ℃ at the speed of 0.5 ℃/min and roasting for 3.5h, and then heating to 620 ℃ at the speed of 4 ℃/min and roasting for 6 h; sequentially tabletting, crushing and screening the roasted sample to obtain 40-mesh 60 wt% LaCoO 3 /Al 2 O 3 Catalyst particles.
Example 3
The embodiment provides a catalyst with nitrogen oxide adsorption and oxidation functions and a preparation method thereof, wherein the preparation method comprises the following steps:
(1) first 10.568g of La (NO) 3 ) 3 ·6H 2 O and 7.104g of Co (NO) 3 ) 2 ·6H 2 Dissolving O in 100mL of deionized water, stirring uniformly, and adding 7.693g of citric acid into the solution to obtain a first solution; what is needed isThe mixing ratio of the lanthanum nitrate, the cobalt nitrate and the citric acid is n (lanthanum nitrate), n (cobalt nitrate) and n (citric acid) 1:1: 1.64;
(2) stirring the first solution obtained in the step (1) for 40min, and then dropwise adding ammonia water with the concentration of 30 wt% until the pH value of the solution is 11 to obtain a second solution;
(3) mixing 4g of gamma-alumina and the second solution obtained in the step (2) for excessive impregnation treatment, and stirring for 80min to obtain an impregnated sample;
(4) performing vacuum rotary evaporation treatment on the impregnated sample obtained in the step (3) in a vacuum rotary evaporator, wherein the absolute vacuum degree is 0.04MPa, and the method specifically comprises the following steps: firstly, carrying out first rotary evaporation treatment at 65 ℃ until a sample in a gel state is formed, and then heating to 85 ℃ for carrying out second rotary evaporation treatment for 10min to obtain a gel sample;
(5) directly transferring the gel sample obtained in the step (4) and the rotary steaming bottle into an oven at 140 ℃ for drying for 20h, and grinding the obtained solid into powder; roasting the obtained powder in a flowing air atmosphere with the flow rate of 350mL/min, and specifically: firstly heating to 350 ℃ at the speed of 1.5 ℃/min, roasting for 2.5h, and then heating to 680 ℃ at the speed of 6 ℃/min, and roasting for 4 h; sequentially tabletting, crushing and screening the roasted sample to obtain 60-mesh 60 wt% LaCoO 3 /Al 2 O 3 Catalyst particles.
Example 4
This embodiment provides a catalyst with both nitrogen oxide adsorption and oxidation and a preparation method thereof, wherein the preparation method is the same as that of embodiment 1 except for the operation of dropping ammonia water in the step (2), and thus the details are not repeated herein.
Example 5
This embodiment provides a catalyst with both nitrogen oxide adsorption and oxidation and a preparation method thereof, wherein the preparation method is the same as that of embodiment 1 except that the excess impregnation in step (3) is changed to the equal volume impregnation, and the rest of the steps and conditions are the same, so that the detailed description thereof is omitted.
Example 6
The embodiment provides a catalyst with nitrogen oxide adsorption and oxidation functions and a preparation method thereof, wherein the preparation method is characterized in that the highest temperature of roasting in the step (5) is changed into 700 ℃; the rest of the steps and conditions are the same as those in example 1, and thus are not described herein.
Example 7
This example provides a catalyst with both nitrogen oxide adsorption and oxidation, and a preparation method thereof, except that the calcination process in step (5) is changed to: heating to 650 ℃ at the speed of 3 ℃/min and roasting for 8 h; the rest of the steps and conditions are the same as those in example 1, and thus are not described herein.
Example 8
The present embodiment provides a catalyst with both nitrogen oxide adsorption and oxidation and a preparation method thereof, except that the step (1) is changed to: 7.045g of La (NO) first 3 ) 3 ·6H 2 O and 4.736g Co (NO) 3 ) 2 ·6H 2 Dissolving O in 100mL of deionized water, stirring uniformly, and adding 5.129g of citric acid into the solution to obtain a first solution; changing the gamma-alumina in the step (3) into 6 g; the rest of the steps and conditions are the same as those in example 1, and thus are not described herein.
This example finally gives 40% by weight of LaCoO 3 /Al 2 O 3 A catalyst.
Example 9
The present embodiment provides a catalyst with both nitrogen oxide adsorption and oxidation and a preparation method thereof, except that the step (1) is changed to: first 14.09g of La (NO) 3 ) 3 ·6H 2 O and 9.472g of Co (NO) 3 ) 2 ·6H 2 Dissolving O in 100mL of deionized water, stirring uniformly, and adding 10.257g of citric acid into the solution to obtain a first solution; changing the gamma-alumina in the step (3) into 2 g; the rest of the steps and conditions are the same as those in example 1, and thus are not described herein.
This example finally gives 80% by weight of LaCoO 3 /Al 2 O 3 A catalyst.
Comparative example 1
This comparative example provides a catalyst and a method for preparing the same, except that step (1) is changed to: 3.523g of La (NO) first 3 ) 3 ·6H 2 O and 2.368g Co (NO) 3 ) 2 ·6H 2 Dissolving O in 100mL of deionized water, stirring uniformly, and adding 2.564g of citric acid into the solution to obtain a first solution; changing the gamma-alumina in the step (3) into 8 g; the rest of the steps and conditions are the same as those in example 1, and thus are not described herein.
This comparative example finally gives 20% by weight of LaCoO 3 /Al 2 O 3 A catalyst.
Comparative example 2
This comparative example provides a catalyst and a method of making the same, the method comprising the steps of:
(1) first 99.2mg of Pt (NH) 3 ) 4 (NO 3 ) 2 Dissolving in 50mL of deionized water, stirring uniformly, adding 4.95g of gamma-alumina into the solution for excessive impregnation treatment, and stirring for 60min to obtain an impregnated sample;
(2) carrying out vacuum rotary evaporation treatment on the impregnated sample obtained in the step (1) in a vacuum rotary evaporator at the absolute vacuum degree of 0.03MPa and the temperature of 60 ℃ to remove redundant moisture;
(3) transferring the solid obtained in the step (2) to a 100 ℃ oven for drying for 12h, grinding the solid into powder, and roasting the powder in a flowing air atmosphere with the flow rate of 300mL/min, wherein the heating rate is 5 ℃/min, the roasting temperature is 500 ℃, and the roasting time is 3 h; sequentially tabletting, crushing and screening the roasted sample to obtain 50-mesh 1 wt% Pt/Al 2 O 3 Catalyst particles.
LaCoO obtained in examples 1, 8 and 9 3 /Al 2 O 3 TEM images of the catalyst are shown in fig. 1, fig. 2 and fig. 3, respectively.
As can be seen from fig. 1-3: in LaCoO 3 The loading of the active component is in the range of 40-80 wt%, and LaCoO 3 /Al 2 O 3 Al in catalyst 2 O 3 The average particle diameter of the carrier is 8-12nm, and the agglomeration phenomenon of the catalyst nano particles is gradually increased along with the gradual increase of the loading amount of the active component.
The catalysts obtained in examples 1 to 9 and comparative examples 1 to 2 were subjected to the following evaluation tests, respectively:
(1) evaluation test of NOx adsorption Performance
The NOx adsorption performance evaluation experiment was carried out using 300mg of the catalyst in a quartz tube reactor having an inner diameter of 4 mm. Before the adsorption experiment, the catalyst was heated to 500 ℃ at 300mL/min and 10% O 2 /5％H 2 O/N 2 Pretreating for 1h in the atmosphere; after the pretreatment is finished, the reactor is naturally cooled to 120 ℃, the bypass is switched to be added with 200ppm NO, and the mixture is introduced into the reactor to be adsorbed for 90min after the concentration of the NO is stable.
(2) Nox temperature programmed desorption experiment (NOx-TPD)
The NOx-TPD test was continuously conducted after the NOx adsorption performance evaluation test, and the catalyst after adsorption in an NO-containing atmosphere for 90min was maintained at 120 ℃ at 10% O of 250mL/min 2 /5％H 2 O/N 2 Purging in the atmosphere for 1 h; followed by a temperature program from 120 ℃ to 720 ℃ at a rate of 10 ℃/min.
The adsorption and desorption performance parameters of the catalysts obtained in examples 1 to 9 and comparative examples 1 to 2 are shown in Table 1.
TABLE 1
In table 1, the specific meanings of nse (nox storage efficiency) are: nitrogen oxide storage efficiency; the specific meaning of NSC (NOx storage capacity) is: nitrogen oxide storage capacity; NDE (NOx sorbent effect) has the following specific meanings: the nitrogen oxide desorption efficiency.
(3) Evaluation test of NO Oxidation Property
NO oxidation performance evaluation experiments were also carried out using 300mg of catalyst in a quartz tube reactor having an internal diameter of 4 mm. Before the NO oxidation performance evaluation experiment is carried out, the temperature of the reactor is firstly raised to 500 ℃, and 200ppmNO/10 percent O is introduced into a bypass 2 /5％H 2 O/N 2 Setting the flow of the mixed gas to be 250 mL/min; introducing into the reactor after the concentration of the mixed gas is stable, maintaining for 1h, naturally cooling, and setting each test temperature and staying for 60-90min in the processTables 2-1 and 2-2; NO Oxidation Rate by calculation of NO at the end of the residence time at each temperature 2 The ratio/NOx is obtained.
TABLE 2-1
Tables 2 to 2
It can be seen that the invention is achieved by the use of Al 2 O 3 LaCoO loaded on carrier 3 The catalyst has the advantages that the catalyst has both nitrogen oxide adsorption and oxidation functions, and the storage efficiency of nitrogen oxide can reach 80% at most when the catalyst is used for passive nitrogen oxide adsorption.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.
Claims (10)
1. A catalyst with nitrogen oxide adsorption and oxidation functions, which is characterized by comprising Al 2 O 3 Support and LaCoO 3 An active ingredient;
the LaCoO 3 The loading amount of the active components is 40-80 wt%.
2. The catalyst of claim 1, wherein the Al is 2 O 3 The carrier comprises gamma-Al 2 O 3 A carrier;
preferably, the Al 2 O 3 The average particle diameter of the carrier is 8-12 nm.
3. A process for the preparation of a catalyst according to claim 1 or 2, characterized in that it comprises the following steps:
(1) mixing lanthanum nitrate, cobalt nitrate, water and citric acid to obtain a first solution;
(2) dropwise adding ammonia water into the first solution obtained in the step (1) until the pH value of the solution is more than or equal to 9 to obtain a second solution;
(3) carrying out impregnation treatment on the mixed alumina and the second solution obtained in the step (2) to obtain an impregnated sample;
(4) carrying out vacuum rotary evaporation treatment on the dipping sample obtained in the step (3) to obtain a gel sample;
(5) and (4) drying, roasting and granulating the gel sample obtained in the step (4) in sequence to obtain the catalyst.
4. The method according to claim 3, wherein the mixing in step (1) is performed in the following order: firstly, dissolving lanthanum nitrate and cobalt nitrate in water, uniformly stirring, and then adding citric acid into the solution;
preferably, the mixing ratio of lanthanum nitrate, cobalt nitrate and citric acid in the step (1) is n (lanthanum nitrate): n (cobalt nitrate): n (citric acid): 1 (1.5-1.7).
5. The production method according to claim 3 or 4, wherein the concentration of the aqueous ammonia in the step (2) is 20 wt% to 30 wt%;
preferably, the first solution is stirred for 20-40min before the dropwise addition in the step (2);
preferably, the impregnation treatment in the step (3) comprises an equal volume impregnation treatment or an excess impregnation treatment, and further preferably an excess impregnation treatment;
preferably, the dipping sample is stirred for 40-80min after the dipping treatment in the step (3).
6. The production method according to any one of claims 3 to 5, wherein the vacuum rotary evaporation treatment in the step (4) is carried out in a vacuum rotary evaporator with an absolute vacuum degree of 0.02 to 0.04 MPa;
preferably, the vacuum rotary evaporation treatment in the step (4) comprises a first rotary evaporation treatment and a second rotary evaporation treatment which are sequentially carried out;
preferably, the temperature of the first rotary evaporation treatment is 55-65 ℃;
preferably, a sample in a gel state is formed after the first rotary evaporation treatment;
preferably, the temperature of the second rotary evaporation treatment is 75-85 ℃;
preferably, the time of the second rotary evaporation treatment is 10-20 min.
7. The method according to any one of claims 3 to 6, wherein the drying in step (5) is specifically: directly transferring the gel sample and the rotary evaporation bottle into an oven for drying;
preferably, the temperature for drying in step (5) is 100-140 ℃;
preferably, the drying time of the step (5) is 20-30 h;
preferably, the solid obtained after drying in step (5) is ground into a powder.
8. The method as claimed in any one of claims 3 to 7, wherein the baking in step (5) is performed in an atmosphere of flowing air with an air flow rate of 250-350 mL/min;
preferably, the roasting of the step (5) comprises a first roasting treatment and a second roasting treatment which are sequentially carried out;
preferably, the temperature rise rate of the first roasting treatment is 0.5-1.5 ℃/min;
preferably, the temperature of the first roasting treatment is 250-350 ℃;
preferably, the time of the first roasting treatment is 2.5-3.5 h;
preferably, the temperature rise rate of the second roasting treatment is 4-6 ℃/min;
preferably, the temperature of the second roasting treatment is 620-680 ℃;
preferably, the time of the second roasting treatment is 4-6 h;
preferably, the granulation in the step (5) comprises tabletting, crushing and screening which are sequentially carried out;
preferably, the average particle size of the catalyst particles obtained by the granulation in the step (5) is 40-60 meshes.
9. The method according to any one of claims 3 to 8, characterized in that it comprises the following steps:
(1) dissolving lanthanum nitrate and cobalt nitrate in water, uniformly stirring, and adding citric acid into the solution to obtain a first solution; the mixing ratio of the lanthanum nitrate, the cobalt nitrate and the citric acid is n (lanthanum nitrate), n (cobalt nitrate) and n (citric acid) 1:1 (1.5-1.7);
(2) stirring the first solution obtained in the step (1) for 20-40min, and then dropwise adding ammonia water with the concentration of 20-30 wt% until the pH value of the solution is more than or equal to 9 to obtain a second solution;
(3) performing excessive dipping treatment on the mixed alumina and the second solution obtained in the step (2), and stirring for 40-80min to obtain a dipped sample;
(4) performing vacuum rotary evaporation treatment on the impregnated sample obtained in the step (3) in a vacuum rotary evaporator, wherein the absolute vacuum degree is 0.02-0.04MPa, and the specific steps are as follows: performing first rotary evaporation treatment at 55-65 ℃ until a sample in a gel state is formed, and then heating to 75-85 ℃ for performing second rotary evaporation treatment for 10-20min to obtain a gel sample;
(5) directly transferring the gel sample and the rotary evaporation bottle obtained in the step (4) to an oven at the temperature of 100-; roasting the obtained powder in a flowing air atmosphere with the flow rate of 250-350mL/min, specifically: firstly heating to 250-350 ℃ at the speed of 0.5-1.5 ℃/min and roasting for 2.5-3.5h, and then heating to 620-680 ℃ at the speed of 4-6 ℃/min and roasting for 4-6 h; and tabletting, crushing and screening the roasted sample in sequence to obtain the catalyst particles of 40-60 meshes.
10. Use of a catalyst according to claim 1 or 2, wherein the use comprises use of the catalyst for passive nitrogen oxide adsorption.
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