CN108465469B

CN108465469B - Co-doped modified spherical SrMnO3Perovskite type oxide catalyst and preparation method and application thereof

Info

Publication number: CN108465469B
Application number: CN201810211072.9A
Authority: CN
Inventors: 黄学辉; 陈魁; 尹芷琳; 潘洪云; 洪静
Original assignee: Wuhan University of Technology WUT
Current assignee: Wuhan University of Technology WUT
Priority date: 2018-03-14
Filing date: 2018-03-14
Publication date: 2021-04-20
Anticipated expiration: 2038-03-14
Also published as: CN108465469A

Abstract

The invention relates to Co-doped modified spherical SrMnO₃A perovskite type oxide catalyst, a preparation method and application thereof. The catalyst has a spherical microstructure formed by stacking nano rods, and is prepared by spherical gamma-MnO₂Calcining manganese source, strontium source and cobalt source in molten liquid of sodium chloride-potassium chloride, adding water, stirring at constant temperature, performing solid-liquid separation, drying, and grinding. The invention has the advantages of simple and easily obtained raw materials, low production cost, simple preparation process and short period, and experiments show that the spherical catalyst has good thermal stability and low-temperature catalytic activity on CO in automobile exhaust.

Description

Co-doped modified spherical SrMnO3Perovskite type oxide catalyst and preparation method and application thereof

Technical Field

The invention relates to the technical field of catalysts, in particular to Co-doped modified spherical SrMnO₃A perovskite type oxide catalyst, a preparation method and application thereof.

Background

In recent years, the automobile industry in China is rapidly developed, the quantity of automobiles kept is continuously increased, the pollution of pollutants discharged by the automobiles to the atmosphere is increasingly intensified, and automobile exhaust is one of the main reasons for deteriorating the quality of the urban atmospheric environment in China. Automobile exhaust not only seriously harms human health, but also causes acid rain and urban photochemical smog to destroy ecological environment, so that the purification of the automobile exhaust is increasingly concerned by people.

The chemical general formula is ABO₃The rare earth perovskite type composite oxide catalyst has good three-way catalytic activity, is low in price compared with noble metal catalysts, has strong high-temperature stability compared with common metal oxides, and becomes automobile exhaustThe hot spot of catalyst research. ABO₃The catalytic performance of (a) depends on the a and B ions and their oxidation states, the a site cation (rare earth) is generally catalytically inactive providing only thermal stability, while the B site cation (transition metal) is the active component. It is possible to improve the catalytic performance of such oxide catalysts by partial doping because the ionic valence is changed and oxygen vacancy is generated by partial substitution of the a-site or the B-site thereof to change the catalytic activity thereof.

The traditional preparation methods of the perovskite catalyst comprise a template method, a sol-gel method, a solid phase method and the like, but the methods generally have the defects of high calcination temperature, high energy consumption, long preparation period and the like. Therefore, the development of a perovskite type oxide catalyst with low energy consumption, simple operation and better catalytic performance is one of the problems to be solved in the preparation of the perovskite type catalyst.

The perovskite oxide catalyst with the spherical structure has relatively high specific surface area, so that the amount of adsorbed gas is increased, the reaction activity is enhanced, and the catalytic performance of the catalyst is improved. Therefore, the invention selects the lune-shaped gamma-MnO₂As a precursor, the spherical Sr-Mn-O system perovskite type oxide catalyst with similar morphology is prepared.

Disclosure of Invention

The invention aims to overcome the defects of the existing perovskite catalyst preparation method and provide Co-doped modified spherical SrMnO₃A perovskite type oxide catalyst, a preparation method and application thereof. The invention takes acanthosphere-shaped gamma-MnO₂As a precursor, preparing spherical SrMn with similar morphology by using a molten salt growth method_1-XCo_XO₃The perovskite catalyst has good catalytic performance on CO in automobile exhaust and good thermal stability. The invention also has the advantages of simple synthesis method, low energy consumption, short period and the like, and has better application prospect. In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

co-doped modified spherical SrMnO₃Perovskite type oxide catalyst stacked by numerous nanorodsIs spherical with a particle diameter of 4-12 μm, and the perovskite oxide catalyst has a chemical formula of SrMn_1-XCo_XO₃Wherein 0 ≦ X ≦ 0.5.

The Co-doped modified spherical SrMnO₃A process for preparing a perovskite-type oxide catalyst comprising the steps of:

(a) strontium source and spinous spherical gamma-MnO₂Mixing with cobalt source, adding sodium salt and potassium salt, and mixing to obtain mixture;

(b) heating the mixture for calcining, adding deionized water after the mixture is cooled, stirring at constant temperature, then carrying out solid-liquid separation, washing and grinding the obtained solid to obtain Co-doped modified spherical SrMnO₃A perovskite type oxide catalyst.

In the above scheme, the strontium source is strontium nitrate, the cobalt source is cobalt nitrate or a hydrate thereof, the sodium salt is sodium chloride, and the potassium salt is potassium chloride. Experiments show that the shape and performance of the prepared sample are greatly influenced by selecting other raw materials, for example, the shape of the sample is greatly influenced by changing sodium salt and potassium salt into potassium nitrate or sodium nitrate, and the sample contains a heterogeneous phase if the molten salt and other raw materials are the same nitrate.

In the scheme, the strontium source and the thorn-ball-shaped gamma-MnO are counted by mole number₂The addition ratio of the cobalt source to the cobalt source is 1 (1-X), X, and the addition amounts of the sodium salt and the potassium salt are 8-12 times of that of the strontium source, wherein X is less than or equal to 0.5 and 0.

Further, the gamma-MnO may be a lune₂From equimolar MnSO₄Or a hydrate thereof with (NH)₄)₂S₂O₈Uniformly mixing in deionized water, carrying out hydrothermal reaction at 80-100 ℃ for 18-30h, carrying out solid-liquid separation, washing, drying at constant temperature of 60-80 ℃, and grinding to obtain the catalyst.

In the scheme, the temperature of the mixture is increased from room temperature to 700-800 ℃ at the temperature increasing rate of 3-5 ℃/min, and then the mixture is subjected to heat preservation and calcination for 2-6 h.

In the scheme, deionized water with the mass of 12-18 times of that of the mixture obtained by calcination is added into the mixture, and the mixture is heated to 40-60 ℃ and then stirred for 1.8-2.2h at constant temperature.

In the scheme, the solid obtained by solid-liquid separation is washed by deionized water and ethanol in sequence, then dried for 10-18h at 60-80 ℃, and then ground into powder with the particle size of 4-12 um.

The Co-doped modified spherical SrMnO₃The perovskite type oxide catalyst is used for catalyzing CO in automobile exhaust.

Compared with the prior art, the invention has the following beneficial effects:

(1) spherical SrMn other than La-based perovskite catalyst is synthesized_1-XCo_XO₃The oxide is proved by experiments to enable the complete conversion temperature of CO to be lower than that of SrMnO₃The reduction is remarkable, and the thermal stability is better;

(2) in the spherical perovskite type oxide catalyst SrMn_1-XCo_XO₃In the method, crystal lattices generate distortion to cause crystal lattice defects due to the doping of cobalt ions, more oxygen vacancies are generated to form active oxygen, and the defects have good promoting effect on the purification of automobile exhaust, so that better catalytic performance is obtained;

(3) sodium chloride, potassium chloride and the like are used as molten salts, reactants are in the molten liquid at 700-800 ℃, a favorable environment is provided for diffusion among ions, and the spinous spherical gamma-MnO synthesized by a hydrothermal method₂As a precursor, spherical SrMn with similar morphology is synthesized_1-XCo_XO₃The catalyst enables the shape of the catalyst to be controllable;

(4) the raw materials used in the preparation process are cheap and easy to obtain, the preparation process is simple, and the synthesis period is short.

Drawings

FIG. 1 shows a raw material lunette-shaped γ -MnO synthesized in example 1 of the present invention₂XRD pattern of (a);

FIG. 2 shows a raw material lunette-shaped γ -MnO synthesized in example 1 of the present invention₂FE-SEM picture of (b);

FIG. 3 shows a spherical SrMnO prepared in example 2 of the present invention₃FE-SEM image of perovskite type oxide catalyst;

FIG. 4 shows spherical SrMn prepared in example 6 of the present invention_0.7Co_0.3O₃Perovskite type oxideFE-SEM picture of catalyst;

FIG. 5 is a XRD contrast of spherical perovskite oxide catalysts prepared in examples 1-6 of the present invention;

FIG. 6 is a graph showing the comparative catalytic oxidation activity of spherical perovskite-type oxide catalysts prepared in examples 1 to 6 of the present invention with respect to CO in automobile exhaust.

Detailed Description

In order to make those skilled in the art fully understand the technical solutions and advantages of the present invention, the following embodiments are further described.

Example 1

Spherical SrMnO₃The perovskite type oxide catalyst is prepared by the following steps:

(1) taking a clean beaker, measuring 120mL of deionized water by using a measuring cylinder, pouring into the beaker, and slowly adding 64mmol of MnSO while stirring₄·H₂O, continuously stirring at room temperature for 10-30min to completely dissolve, and slowly adding 64mmol (NH)₄)₂S₂O₈And continuously stirring for 10-15min until the solid is completely dissolved.

(2) Transferring the solution obtained in the last step into a stainless steel reaction kettle with a polytetrafluoroethylene lining, heating to 90 ℃, carrying out constant-temperature hydrothermal reaction for 24 hours, cooling to room temperature, removing supernatant, carrying out suction filtration, washing the solid product with deionized water for multiple times, then placing the solid product into a constant temperature box with the temperature of 70 ℃, drying for 24 hours, and finally grinding the dried sample into powder to obtain the luniform gamma-MnO₂。

(3) Weighing 2.12g of anhydrous strontium nitrate and 0.87g of gamma-MnO obtained in step (2)₂5.85g of sodium chloride and 7.46g of potassium chloride. Weighing anhydrous strontium nitrate and gamma-MnO₂Grinding in mortar, adding sodium chloride and potassium chloride, and grinding. And putting the ground mixture into a crucible, then integrally transferring the crucible into a muffle furnace, heating the crucible to 700 ℃ from room temperature at the heating rate of 5 ℃/min, carrying out heat preservation and calcination at the temperature for 4h, and then cooling the crucible to the room temperature.

(4) Dissolving the calcined product in 30mL of deionized water, heating to 50 ℃, and stirring at constant temperature for 2hCooling to room temperature, removing supernatant, performing multiple suction filtration and washing, drying the obtained solid in a thermostat at 70 ℃ for 12h, and grinding to obtain spherical SrMnO₃A perovskite type catalyst.

FIG. 1 shows a spiked spherical γ -MnO prepared in step (2) of this example₂XRD pattern of (a). As can be seen from FIG. 1, the spiked spherical gamma-MnO₂No impurity phase is generated. FIG. 2 shows a spiked spherical γ -MnO prepared in step (2) of this example₂FE-SEM photograph of (1 μm) scale bar. As can be seen from FIG. 2, the spinous spherical γ -MnO₂Is formed by stacking countless nano rods. The spherical SrMnO prepared in this example₃The XRD pattern of the perovskite catalyst product is shown in FIG. 5, from which FIG. 5 it is known as hexagonal SrMnO₃The perovskite phase of (P63/mmc) has a sharp XRD pattern peak, which shows that the sample has a good crystalline form.

To fully understand the spherical SrMnO prepared in this example₃The catalytic oxidation activity of the perovskite catalyst on CO is correspondingly tested, and the specific method and the result are as follows:

with 93 vol% Ar, 5 vol% O₂And 2 vol% of CO to simulate automobile exhaust. 0.1g of SrMnO prepared in example 1 was mixed with anhydrous ethanol₃Uniformly coating sample powder on 0.2g of quartz glass fiber cotton, placing the quartz glass fiber cotton into a quartz tube with the inner diameter of 8mm, ensuring that the sample is at the middle position, placing the quartz tube into a miniature fixed quartz bed reactor, and introducing simulated automobile exhaust (the total flow is 438mL/min, and the space velocity is 12000 h) into the quartz tube^-1). The sample is heated by an electric furnace, and the testing temperature range is 100-350 ℃. The FID detector in the gas chromatograph is used for detecting the reacted gas, and the oxidation catalytic performance of the sample on CO is determined, and the result is shown in FIG. 6. As can be seen from FIG. 6, the spherical SrMnO prepared in this example₃The perovskite catalyst has the catalytic performance of 7.7% at 175 ℃ and 84.3% at 300 ℃ on CO in automobile exhaust, and the catalytic performance is not ideal enough.

Example 2

Example 2 is essentially the same procedure as example 1, except that: the calcining temperature in the step (3) is increased from 700 ℃ to 750 ℃, and the calcining time is kept unchanged.

Example 3

Example 3 is essentially the same procedure as example 1, except that: the calcining temperature in the step (3) is increased from 700 ℃ to 750 ℃, and the calcining time is increased from 4h to 6 h.

Spherical SrMnO prepared in examples 2 and 3₃The XRD pattern of the perovskite catalyst is shown in figure 5. As can be seen from FIG. 5, the catalyst products obtained in examples 2 and 3 are hexagonal SrMnO₃(P63/mmc) perovskite phase.

Spherical SrMnO prepared in examples 2 and 3 was treated in the same manner as in example 1₃The perovskite-type catalyst was subjected to a catalytic oxidation activity test of CO, and the results are shown in fig. 6. As can be seen from FIG. 6, the catalytic performance of the catalyst product prepared in example 2 on CO in automobile exhaust reaches 12.4% at 175 ℃ and 98.7% at 300 ℃; the catalytic performance of the catalyst product prepared in example 3 on CO in automobile exhaust reaches 30.3% at 175 ℃ and 99.8% at 300 ℃. Comparative examples 1 to 3 found that the spherical SrMnO obtained in example 3₃The perovskite catalyst has relatively good catalytic effect on CO at low temperature, and is obviously better than the other two catalysts at the temperature below 175 ℃. This corresponds to the more prominent peak in the XRD contrast pattern (figure 5) for the catalyst of example 3.

FIG. 3 shows spherical SrMnO prepared in example 2₃FE-SEM spectrum of perovskite type catalyst, wherein the scale bar of a-1 is 1um, and the scale bar of a-2 is 100 nm. As can be seen from FIG. 3, the morphology of the product is spherical and is formed by stacking numerous nanorods. This indicates that SrMnO was prepared₃Product and acanthosphere-like gamma-MnO₂Has similar appearance, also indicates that the gamma-MnO with the raw material thorny ball shape controlled is realized₂The morphology of the product is controlled.

Example 4

Spherical SrMn with Co doping amount of 30%_0.7Co_0.3O₃The perovskite catalyst is prepared by the following steps:

(1) taking a clean beaker, measuring 120ml of deionized water by using a measuring cylinder, pouring into the beaker, and slowly stirring while stirringSlowly adding 64mmol of MnSO₄·H₂O, continuously stirring at room temperature for 10-30min until the solid is completely dissolved, and slowly adding 64mmol (NH)₄)₂S₂O₈And continuously stirring for 10-15min until the materials are completely dissolved.

(2) Transferring the solution into a stainless steel reaction kettle with a polytetrafluoroethylene lining, heating to 90 ℃, carrying out constant-temperature hydrothermal reaction for 24h, cooling to room temperature, removing supernatant, carrying out suction filtration, washing a product with deionized water for multiple times, placing the product in a constant temperature box with the temperature of 70 ℃ for drying for 24h, and finally grinding a dried sample into powder to obtain the lunulate gamma-MnO₂。

(3) 2.12g of anhydrous strontium nitrate and 0.61g of γ -MnO obtained in step (2) were weighed₂0.87g of cobalt nitrate hexahydrate, 5.85g of sodium chloride and 7.46g of potassium chloride. Weighing anhydrous strontium nitrate and gamma-MnO₂And cobalt nitrate hexahydrate are put into a mortar and ground uniformly, and then sodium chloride and potassium chloride are added and fully ground. Putting the ground mixture into a crucible, putting the crucible into a muffle furnace, heating the crucible to 750 ℃ from room temperature at a heating rate of 5 ℃/min, carrying out heat preservation and calcination for 4h at the temperature, and then cooling the crucible to room temperature.

(4) The calcined product was dissolved in 30mL of deionized water, heated to 50 ℃ and stirred for 2h at constant temperature. Cooling to room temperature, removing supernatant, vacuum filtering, washing, drying at 70 deg.C for 12 hr, and grinding to obtain spherical SrMn_0.7Co_0.3O₃A perovskite catalyst.

The spherical SrMn prepared in this example_0.7Co_0.3O₃The XRD pattern of the perovskite catalyst is shown in fig. 5. From FIG. 5, the catalyst is similar to hexagonal SrMnO₃(P63/mmc) perovskite phase.

The spherical SrMn obtained in example 4 was treated in the same manner as in example 1_0.7Co_0.3O₃The perovskite catalyst was tested for catalytic oxidation activity of CO and the results are shown in figure 6. As can be seen from fig. 6, the catalytic performance of the catalyst was 2.4% at 125 ℃ and 97.3% at 150 ℃, thereby illustrating that it exhibited high catalytic performance at a relatively low temperature.

Example 5

Example 5 is essentially the same as example 4 except that: the raw material dosage and the calcining process are changed, 2.12g of anhydrous strontium nitrate and 0.78g of gamma-MnO are weighed₂0.29g of cobalt nitrate hexahydrate, 5.85g of sodium chloride and 7.46g of potassium chloride, and the temperature rise rate during calcination was changed to 3 ℃/min. The product thus obtained is spherical SrMn_0.9Co_0.1O₃A perovskite catalyst.

Example 6

Example 6 is essentially the same procedure as example 4, except that: the heating rate was changed to 3 deg.C/min. The product thus obtained is spherical SrMn_0.7Co_0.3O₃A perovskite catalyst.

SrMn obtained in examples 5 and 6_0.9Co_0.1O₃And SrMn_0.7Co_0.3O₃The XRD pattern of the catalyst is shown in fig. 5. As can be seen from FIG. 5, both catalysts are hexagonal-like SrMnO₃(P63/mmc) perovskite phase.

The two spherical perovskite catalysts obtained in examples 5 and 6 were subjected to CO catalytic oxidation activity tests in accordance with the method of example 1, and the results are shown in FIG. 6. As can be seen from FIG. 6, SrMn was prepared in example 5_0.9Co_0.1O₃The catalytic performance of the catalyst is 58.8% at 125 ℃ and 94.6% at 150 ℃; SrMn prepared in example 6_0.7Co_0.3O₃The catalytic performance of the catalyst was 98.5% at 125 ℃ and 100% at 150 ℃.

SrMn prepared in example 6_0.7Co_0.3O₃The FE-SEM image of the catalyst is shown in FIG. 4, wherein the scale bar of b-1 is 1um, and the scale bar of b-2 is 100 nm. FIG. 4 shows that the morphology of the catalyst is spherical, the particle size is 4-12 μm, and the catalyst is formed by stacking countless nanorods. In contrast to fig. 3, it was found that the product of fig. 4 was packed more compactly.

From the above results, it is understood that the spherical SrMnO can be used₃Co doping of the perovskite oxide catalyst did effectively improve the catalytic activity of the catalyst on CO in automobile exhaust, and the product SrMn of example 6_0.7Co_0.3O₃Shows good low-temperature catalytic activity and high-temperature stability.

Claims

1. Co-doped modified spherical SrMnO₃A perovskite-type oxide catalyst characterized by: the catalyst is stacked into a sphere by countless nano rods, and the chemical formula of the catalyst is SrMn_1-XCo_XO₃Wherein 0 < X ≦ 0.5; the preparation method of the catalyst comprises the following steps:

(b) heating the mixture for calcining, adding deionized water after the mixture is cooled, stirring at constant temperature, then carrying out solid-liquid separation, washing and grinding the obtained solid to obtain Co-doped modified spherical SrMnO₃A perovskite-type oxide catalyst;

the strontium source is strontium nitrate, the cobalt source is cobalt nitrate or a hydrate thereof, the sodium salt is sodium chloride, and the potassium salt is potassium chloride; the thorn ball-shaped gamma-MnO₂From equimolar MnSO₄Or a hydrate thereof with (NH)₄)₂S₂O₈Uniformly mixing in deionized water, carrying out hydrothermal reaction at 80-100 ℃ for 18-30h, carrying out solid-liquid separation, washing, drying at constant temperature of 60-80 ℃, and grinding to obtain the catalyst.

2. The Co-doped modified spherical SrMnO of claim 1₃A perovskite-type oxide catalyst characterized by: the particle size of the catalyst is 4-12 μm.

3. The Co-doped modified spherical SrMnO of claim 1₃A perovskite-type oxide catalyst characterized by: strontium source and thorn-ball-shaped gamma-MnO in terms of mole number₂The adding amount ratio of the cobalt source is 1 (1-X), X, and the adding amount of the sodium salt and the potassium salt is 8-12 times of that of the strontium source.

4. The Co-doped modified spherical SrMnO of claim 1₃Perovskite type oxideA catalyst, characterized by: the mixture is heated from room temperature to 700 ℃ and 800 ℃ at the heating rate of 3-5 ℃/min, and then the mixture is calcined for 2-6h under the condition of heat preservation.

5. The Co-doped modified spherical SrMnO of claim 1₃A perovskite-type oxide catalyst characterized by: adding deionized water 12-18 times the weight of the mixture obtained by calcination, heating to 40-60 ℃, and stirring at constant temperature for 1.8-2.2 h.

6. The Co-doped modified spherical SrMnO of claim 1₃A perovskite-type oxide catalyst characterized by: washing the solid obtained by solid-liquid separation with deionized water and ethanol in sequence, drying at 60-80 deg.C for 10-18h, and grinding into powder with particle size of 4-12 μm.

7. Co-doped modified spherical SrMnO of any one of claims 1-2₃The perovskite type oxide catalyst is used for catalyzing CO in automobile exhaust.