Multi-effect oxidation type perovskite catalyst, and preparation method and application thereof

Abstract

The present application belongs to the field of tail gas catalysis, and particularly relates to a multi-effect oxidation type perovskite catalyst as well as a preparation method and application thereof. x / LaAg y MO3, wherein M is one of manganese, iron, cobalt and copper, wherein the relative proportion of x, y is the relative proportion of the silver doping content in the lanthanum-based perovskite catalyst and the dissolved silver content in the lanthanum-based perovskite catalyst, x, y≠0 and both are greater than 0. The Ag nanoparticles dissolved on the surface of the catalyst have a promoting effect on the oxidation of C3H6. The single catalyst prepared by the method of the present application simultaneously completes the oxidation removal of four pollutants, which greatly simplifies the diesel vehicle tail gas treatment process. Moreover, the catalyst has the advantages of high catalytic activity, strong hydrothermal stability, low and easily obtained material cost, and good practical application value and prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of tail gas catalysis, and particularly relates to a multi-effect oxidation type perovskite catalyst and a preparation method and application thereof. BACKGROUND

[0002] Shipping, as a key industry of fossil fuel consumption, its tail gas emission is one of the important sources of global air pollution. The main pollutants emitted by ships include carbon dioxide (CO2), nitrogen oxides (NOx), particulate matter (PM), carbon monoxide (CO) and hydrocarbons (HC) and the like. Due to the wide range of exhaust gas temperature, large exhaust gas volume, and the particularity of shipping, the space in the ship is compact, and the energy supply is limited, so the development and application of ship aftertreatment technology is relatively slow.

[0003] The exhaust gas temperature and fuel quality of medium and high speed ships are similar to those of land diesel vehicles. In terms of medium and high speed ship emission control, many exhaust gas aftertreatment technologies are derived from the control technology of land diesel vehicles.

[0004] With the increasingly stringent emission standards for diesel engines, the diesel engine exhaust aftertreatment process is becoming more and more complex. At present, for land trucks using low-sulfur fuel, the classic exhaust treatment process is: engine exhaust → DOC (diesel oxidation catalyst) → CDPF (diesel particulate filter) → urea injection → SCR (selective catalytic reduction) → ASC (ammonia slip catalyst) → discharge. If CO and HC catalytic oxidation can be achieved in the normal temperature range (250-500℃) of medium and high speed ship engines, and carbon soot catalytic combustion can be achieved at a lower temperature by adjusting the NO2 / NOx ratio, the CDPF in the diesel engine aftertreatment process can have the catalytic oxidation function of DOC, which will effectively simplify the diesel engine exhaust treatment process. However, there are few studies on single catalyst for simultaneously catalyzing and oxidizing CO, HC, NO and soot in diesel engine exhaust.

[0005] Precious metals are considered to be the preferred catalyst for CO, HC and NO oxidation reactions in DOC due to their high catalytic activity. Recent research reports that single-atom structure catalysts and cluster structure catalysts with completely dispersed metal surface states have been prepared, and it is found that single-atom dispersion of precious metals can promote CO oxidation, but cannot be used for HC oxidation, while catalysts with precious metal clusters on the surface have good oxidation activity for HC and CO. In the current emission treatment catalysts, the oxidation reactions of CO, HC and NO are carried out on the surface of metal nanoparticle-loaded oxides.

[0006] In view of the high cost problem of noble metal catalysts, in recent years, the research of some cheap and easily available non-noble metal catalysts has also made great progress. Perovskite is a very promising catalytic material with low cost and good thermal stability. Because perovskite has the structural characteristics of flexible adjustment of A and B sites, the noble metal is doped into the A or B site of perovskite, which reduces the formation energy of oxygen vacancies, increases the flowability of active oxygen, and improves the NO oxidation activity.

[0007] Currently, few people report that noble metals exist in perovskite in the form of surface dissolution and structural doping, and a catalyst can simultaneously remove four pollutants of CO, HC, soot and NO. For example: CN 113559850 A discloses a manganese-based composite oxide catalyst for diesel vehicle exhaust treatment and a preparation method and use thereof, especially the cooperative purification of HC, CO and NO in diesel vehicle exhaust.

[0008] CN 110327916 A discloses an amorphous manganese oxide catalyst with high activity for oxidizing diesel vehicle soot particles and NO. The prepared amorphous manganese oxide catalyst has the characteristics of large specific surface area, small particle size and mesoporous structure. The catalyst can be used for catalytic oxidation of soot and NO in diesel vehicle exhaust respectively.

[0009] Although the above-mentioned catalysts can simultaneously catalyze the oxidation of two or three pollutants and have high activity, the research and development of a catalyst that can simultaneously remove four pollutants and has low cost and good thermal stability still has great challenges. Based on the above reasons, it has important economic and practical significance to research and develop a catalyst that realizes the simultaneous oxidation of multiple pollutants by two forms of Ag in perovskite. SUMMARY

[0010] The purpose of the present application is to overcome the shortcomings in the prior art and provide a multi-effect oxidation type perovskite catalyst, a preparation method and application thereof.

[0011] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0012] represented by the following formula: Ag x / LaAg y MO3, wherein M is one of manganese, iron, cobalt and copper, wherein the relative ratio of x, y is the relative ratio of the silver doping content in the lanthanum-based perovskite catalyst to the dissolved silver content in the lanthanum-based perovskite catalyst, x, y≠0 and both are greater than 0.

[0013] Preferably, Ag x / LaAg y MO3, x / y = 3-13:2.

[0014] Preferably, Ag x / LaAg y MO3 wherein x / y = 8:2.

[0015] The present application also includes a preparation method of the multi-effect oxidation perovskite catalyst, which adopts the following steps:

[0016] (1) adding a complexing agent into deionized water, continuing to stir after the complexing agent is completely dissolved;

[0017] (2) under the condition of continuous stirring, adding soluble salts of metal ions into the mixed solution obtained in step (1), wherein the metal ions are La, Ag and transition metal M, and continuing to stir after the soluble salts are completely dissolved; the transition metal M is one of manganese, iron, cobalt and copper;

[0018] (3) under the condition of continuous stirring, slowly adding ammonia water into the mixed solution obtained in step (2), and titrating to a certain pH to form solution A;

[0019] (4) placing the solution A on a rotary evaporator, and evaporating to dryness under water; and after drying, obtaining substance B;

[0020] (5) grinding the substance B, and placing it in a muffle furnace for calcination, so as to obtain a catalyst for multi-effect oxidation of diesel vehicle exhaust.

[0021] The complexing agent is any two of ethylenediamine tetraacetate, diethylene triamine pentaacetate, sodium nitrilotriacetate, citric acid and ethylenediamine tetraacetate.

[0022] The soluble salts of La, the soluble salts of Ag and the soluble salts of transition metal in step (2) are nitrate or hexahydrate nitrate.

[0023] The molar ratio of La, Ag and transition metal M in step (2) is 95-85:5-15:100; the pH in step (3) is 6.5-8; the evaporation temperature in step (4) is 60-80 DEG C; and after the substance B is ground, it can pass through a 20-60 mesh sieve and then be calcined in step (5).

[0024] The present application also includes an application of the multi-effect oxidation perovskite catalyst according to claim 1, which is characterized by being applied to catalytic oxidation of carbon monoxide, nitrogen monoxide, hydrocarbon and soot in diesel vehicle exhaust.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] The present application provides a catalyst which can simultaneously oxidize soot, CO, NO and C3H6 in diesel exhaust within the exhaust temperature range. The content of Ag element is regulated to realize two existing forms of Ag in perovskite: surface dissolution or structural doping.

[0027] The Ag nano-particles dissolved from the surface of the catalyst promote the oxidation of C3H6. The single catalyst prepared by the method of the application simultaneously completes the oxidation removal of four pollutants, which greatly simplifies the diesel vehicle exhaust treatment process. Moreover, the catalyst has the advantages of high catalytic activity, strong hydrothermal stability, low-cost and easily-obtained material, and good practical application value and prospect.

[0028] Specifically, the application has the advantages of preferentially catalyzing and oxidizing CO and NO at low temperature, and realizing the catalytic oxidation removal of HC and Soot within the diesel engine exhaust temperature range; the method is simple and easy to implement, and the raw materials are low-cost and easily obtained; the promotion effect of Ag doping on the lanthanum-based perovskite catalyst is closely related to the oxygen activation of Ag itself and the structure adjustment of perovskite and metal interaction; the silver nano-clusters on the surface of the catalyst are beneficial to the conversion of gaseous oxygen into active oxygen, and also help the catalytic oxidation of C3H6 pollutants; the catalyst still has high catalytic effect in the presence of 5%-10% water vapor. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is the NO oxidation spectrum of the lanthanum-based perovskite catalyst doped with different Ag contents prepared by the application;

[0030] Figure 2 is the catalytic oxidation spectrum of Soot of the lanthanum-based perovskite catalyst doped with different Ag contents prepared by the application under the atmosphere of NO+O2;

[0031] Figure 3 is the catalytic oxidation spectrum of C3H6 of the lanthanum-based perovskite catalyst doped with different Ag contents prepared by the application under the atmosphere of O2;

[0032] Figure 4 is the catalytic oxidation spectrum of CO of the lanthanum-based perovskite catalyst doped with different Ag contents prepared by the application under the atmosphere of O2;

[0033] Figure 5 is the conversion rate spectrum of the multi-effect synergistic catalytic oxidation of CO, NO, C3H6 and Soot of the lanthanum-based perovskite catalyst doped with different Ag contents prepared by the application.

[0034] Figure 6 is the high-resolution transmission electron microscopy (HRTEM) image of the lanthanum-based perovskite catalyst doped with different Ag contents prepared by the application. DETAILED DESCRIPTION

[0035] In order for those skilled in the art to better understand the technical solutions of the application, the application will be further described in detail below with reference to the drawings and the best embodiment.

[0036] Embodiment one: a preparation method of a multi-effect oxidation type perovskite catalyst, the specific steps are as follows:

[0037] (1) 100 ml of deionized water is added with a complexing agent, the complexing agent is ethylenediamine tetraacetate (EDTA-2Na) and citric acid, after complete dissolution, stirring for 20 min;

[0038] (2) Under the condition of continuous stirring, the mixed solution obtained in step (1) is added with lanthanum nitrate hexahydrate, silver nitrate and cobalt nitrate hexahydrate, after complete dissolution, stirring for 45 min; the molar ratio of metal ion: EDTA-2Na: citric acid is 5:1:6; the molar ratio of lanthanum nitrate hexahydrate, silver nitrate and cobalt nitrate hexahydrate is 98:2:100;

[0039] (3) Under the condition of continuous stirring, ammonia water is slowly added dropwise to the mixed solution obtained in step (2), and the solution A is formed after titration to pH 7.5;

[0040] (4) The solution A is placed on a rotary evaporator, and rotary evaporation is carried out at 75℃ until dryness and anhydrous, and after drying, substance B is obtained;

[0041] (5) After grinding substance B through a 40 mesh sieve, it is placed in a muffle furnace, calcined at 300℃ for 1 hour and at 700℃ for 6 hours under air atmosphere, and the catalyst for multi-effect oxidation of diesel vehicle exhaust is obtained, which is LaAg 2.0 CoO3.

[0042] Embodiment two: synthesis and application of a catalyst with two existence forms of Ag in perovskite for simultaneous oxidation of multiple pollutants, the basic steps are the same as those of embodiment one, except that the molar ratio of lanthanum nitrate hexahydrate, silver nitrate and cobalt nitrate hexahydrate in step (2) is 95:5:100; and then the steps are the same as those of embodiment one, and the multi-effect catalytic diesel vehicle exhaust catalyst Ag 3.0 / LaAg 2.0 CoO3.

[0043] Embodiment three: synthesis and application of a catalyst with two existence forms of Ag in perovskite for simultaneous oxidation of multiple pollutants, the basic steps are the same as those of embodiment one, except that the molar ratio of lanthanum nitrate hexahydrate, silver nitrate and cobalt nitrate hexahydrate in step (2) is 90:10:100; and then the steps are the same as those of embodiment one, and the multi-effect catalytic diesel vehicle exhaust catalyst Ag 8.0 / LaAg 2.0 CoO3.

[0044] Example 4: Synthesis and application of a catalyst with two forms of Ag in perovskite to achieve simultaneous oxidation of multiple pollutants, the basic steps are the same as example 1, the difference is that in step (2), the molar ratio of lanthanum nitrate hexahydrate, silver nitrate and cobalt nitrate hexahydrate is 85:15:100; then the steps are the same as example 1, and a multi-effect catalytic diesel vehicle exhaust catalyst Ag 13.0 / LaAg 2.0 CoO3.

[0045] Comparative Example 1: Synthesis and application of a lanthanum-cobalt perovskite catalyst without Ag, the basic steps are the same as example 1, the difference is that in step (2), the molar ratio of lanthanum nitrate hexahydrate and cobalt nitrate hexahydrate is 1:1, without silver nitrate; then the steps are the same as example 1, and a multi-effect catalytic diesel vehicle exhaust catalyst LaCoO3 is obtained.

[0046] The catalysts prepared in examples 1-4 and comparative example 1 were tested in a fixed bed reactor, the catalyst dosage was 0.1 g, the soot was 0.01 g, the catalyst particle size was 40-60 mesh, the flue gas concentration was NO: 100-2000 ppm, C3H6: 100-2000 ppm, O2 concentration: 15 vol.%, N2: balance, total gas volume: 400 mL min-1, and the reaction temperature was 100-600℃.

[0047] Figure 1 is the NO oxidation profile of the Ag-doped lanthanum-based perovskite catalyst prepared by the present application, the results show that with the increase of Ag content, the NO conversion rate moves to low temperature, and the conversion rate shows a gradual rising trend;

[0048] Figure 2 is the catalytic oxidation of soot under NO+O2 atmosphere of the Ag-doped lanthanum-based perovskite catalyst prepared by the present application; the oxidation T max emperature of soot shows a trend of first decreasing and then increasing with the increase of Ag content. The experimental results show that when the Ag content is 10% (example 3), the catalyst shows the best NO and soot catalytic activity;

[0049] Figure 4 is the catalytic oxidation of C3H6 under O2 atmosphere of the Ag-doped lanthanum-based perovskite catalyst prepared by the present application; the results show that LaAg 2.0 CoO3 and Ag 8.0 / LaAg 2.0 CoO3 have significant differences in the catalytic oxidation of propylene, the T90 temperature difference of the two samples for the oxidation of C3H6 is nearly 80℃;

[0050] Figure 3is a graph of the catalytic oxidation of CO under O2 atmosphere by the Ag-doped lanthanum-based perovskite catalyst prepared in the present application; the results show that LaAg 2.0 CoO3and Ag 8.0 / LaAg 2.0 CoO3all have good low-temperature catalytic oxidation activity of CO, and Ag 8.0 / LaAg 2.0 CoO3has better catalytic oxidation performance;

[0051] Figure 5 is a graph of the conversion rate of the multi-effect synergistic catalytic oxidation of CO, NO, C3H6 and soot by the Ag-doped lanthanum-based perovskite catalyst prepared in the present application; the graph shows that the catalyst Ag 8.0 / LaAg 2.0 CoO3has good performance in the synergistic removal of the four pollutants; CO is first oxidized, and when almost all of the CO is converted, the oxidation of C3H6 begins, indicating that CO preferentially occurs at low temperature; the conversion rate of NO decreases at each temperature point, because NO2 has stronger oxidation ability than O2.

[0052] Figure Six is a high-resolution transmission electron microscope (HRTEM) graph of the lanthanum-based perovskite catalyst doped with different Ag contents prepared in the present application. The HRTEM characterizes two forms of Ag in the catalyst; at low doping amounts, the oxidation state ion (Ag+) is the main form of existence (Example 1), and as the Ag content increases, silver clusters of different sizes are dissolved on the surface (Examples 2-4); a thin film-shaped decoration is observed on the surface of the silver clusters of 20-30 nm in size, and the catalyst with the Ag-O-Co structure at the interface, especially Ag 8.0 / LaAg 2.0 CoO3, has excellent catalytic activity.

[0053] The above description is only the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, several improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. The application of a multi-effect perovskite oxidation catalyst, characterized in that, It is used for the catalytic oxidation of carbon monoxide, nitrogen monoxide, hydrocarbons, and soot in diesel vehicle exhaust. The multi-effect oxidized perovskite catalyst is represented by the following formula: Agx / LaAgyMO3, where M is one of manganese, iron, cobalt, and copper, and the relative ratio of x and y is the relative ratio of the silver doping content in the lanthanum-based perovskite catalyst to the dissolved silver content in the lanthanum-based perovskite catalyst. x, y ≠ 0 and both are greater than 0; in Agx / LaAgyMO3, x / y = 3-13:2; The preparation method of the multi-effect oxidation perovskite catalyst includes the following steps: (1) adding a complexing agent to deionized water, and continuing to stir after the complexing agent is completely dissolved; the complexing agent is any two of ethylenediaminetetraacetic acid, diethylenetriaminepentacarboxylic acid, sodium aminotriacetate, citric acid, and ethylenediaminetetraacetic acid; (2) While continuously stirring, add a soluble salt of metal ions to the mixed solution obtained in step (1), wherein the metal ions are La, Ag and transition metal M, and continue stirring after complete dissolution; the transition metal M is one of manganese, iron, cobalt and copper. (3) While stirring continuously, ammonia water is slowly added dropwise to the mixed solution obtained in step (2), and solution A is formed after titration to a certain pH. (4) Place solution A on a rotary evaporator and evaporate until dry and anhydrous. After drying, substance B is obtained. (5) Grind substance B and then calcine it in a muffle furnace to obtain a catalyst for multi-effect oxidation of diesel vehicle exhaust gas.

2. The multi-effect perovskite catalyst according to claim 1, characterized in that, In Agx / LaAgyMO3, x / y = 8:

2.

3. The method for preparing the multi-effect perovskite oxide catalyst according to claim 1, characterized in that, The soluble salts of La, Ag, and transition metals in step (2) are nitrates or nitrate hexahydrates.

4. The method for preparing the multi-effect perovskite oxide catalyst according to claim 1, characterized in that, In step (2), the molar ratio of La, Ag and transition metal M is 95-85:5-15:

100.

5. The method for preparing the multi-effect perovskite oxide catalyst according to claim 1, characterized in that, In step (3), the pH is 6.5-8; in step (4), the rotary evaporation temperature is 60-80℃; in step (5), substance B is ground and then roasted through a 20-60 mesh sieve.

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