CN110813301A - High-dispersion supported perovskite catalyst and preparation method and application thereof - Google Patents

Abstract

The invention discloses a highly dispersed supported perovskite catalyst and a preparation method and application thereof. The catalyst is composed of a catalyst carrier and catalytic active components, wherein the carrier is γ-Al ₂ O ₃ , and the catalytic active components are LaCoO ₃ and LaCo One of _0.96 Pt _0.04 O ₃ , and the catalyst active component is loaded in an amount of 10wt%-15wt%. The catalyst is prepared by combining the sol-gel method and the equal volume impregnation method. The advantages of this preparation method are that the operation is simple, the dispersibility of the active components is high, and the activity of the catalyst is fully increased. It is applied to the field of diesel exhaust purification. The emission of particulate matter is reduced, so as to achieve the purpose of reducing air pollution.

Description

A kind of highly dispersed supported perovskite catalyst and its preparation method and application

technical field

The invention belongs to the technical field of diesel engine exhaust gas purification catalysts, and more particularly relates to a preparation method and application of a highly dispersed supported perovskite catalyst for diesel engine exhaust gas purification, which is applied to the catalytic oxidation of soot particles in diesel engine exhaust gas.

Background technique

At present, diesel engines are widely used in heavy-duty long-distance transportation because of their high stability and high efficiency. However, a series of harmful gases such as particulate matter, carbon monoxide, hydrocarbons, nitrogen oxides, etc. have been produced. decline, while seriously threatening the environment and human health. Therefore, it is urgent to treat automobile exhaust emitted by diesel engines, and improving the development of efficient and stable exhaust emission treatment technology is the key to solving such problems. Particulate matter filter (DPF) is currently one of the most recognized and effective vehicle exhaust aftertreatment technologies. It is a filter with a special structure made of some high-temperature resistant materials as the base, which can adsorb particulate matter inside the filter body by means of adsorption, and then restore the performance of the material through a regeneration device, so as to achieve the effect of particulate matter purification. The efficiency of DPF filtering particulate matter can reach about 65%-90%. However, its disadvantage is that as the working time of DPF increases, the deposition of trapped particulate matter increases, causing an increase in back pressure. If it exceeds a certain limit, the service life of the filter will be greatly reduced. Therefore, it is necessary to regularly remove particulate matter to restore working status. As a result, catalytic regeneration technology has been developed, which inevitably leads people to focus on the research and development of efficient and stable catalysts.

According to previous research, noble metal catalysts and rare earth metal catalysts have great advantages in the catalytic oxidation of particulate matter, but it is well known that noble metals are expensive, and a series of side reactions in the exhaust process will lead to catalyst failure. , the expected effect cannot be achieved. Perovskite catalysts are the most studied so far and have the advantages of low price and high stability, and are widely used in the field of diesel exhaust purification.

The ideal perovskite oxide is a cubic crystal, the A-site alkaline earth metal is coordinated with the neighboring atom 12, and the B-site transition metal element is coordinated with the oxygen element 6 to form a regular octahedral structure. A large number of studies have shown that the B-site metal ion acts as an active center, which determines the catalytic activity of the catalyst. Ming Caibing et al. prepared B-substituted LaCo1-xRexO _3-δ (x=0.04) type perovskite composite oxide catalyst Re (Pt, Pd, Rh, Au, Ag) by sol-gel method, and found that the catalyst The catalytic activity was significantly improved. However, the size of perovskite oxide nanoparticles in the traditional sense is large, about 100-200 nm, and the overall surface area is small, which cannot form good contact with soot particles, and cannot give full play to the advantages of such catalysts. Therefore, choosing to develop a supported perovskite catalyst has great application prospects. Usually, supported catalysts help to improve the specific surface area of traditional perovskite catalysts, so that they can more fully contact particles and improve the catalytic activity of particles. .

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a highly dispersed supported perovskite catalyst and a preparation method and application thereof, namely to provide a highly efficient supported perovskite with low raw material cost, good stability and high dispersibility In order to overcome the shortcomings of low specific surface area of traditional perovskite catalysts, the preparation method of the combination of equal volume impregnation method and sol-gel method greatly improves the uniformity of loading, overcomes the agglomeration of nanoparticles, reduces the the nanoparticle size. This method can not only improve the specific surface area of the active components of the catalyst, but also satisfy the close contact between the active components and soot particles during the catalytic oxidation process, further improve the effect of automobile exhaust purification, and reduce the environmental damage caused by air pollution. and threats to human health.

The technical purpose of the present invention is achieved through the following technical solutions:

A highly dispersed supported perovskite catalyst is composed of a catalyst carrier and a catalyst active component, wherein the carrier is γ-Al ₂ O ₃ , and the catalyst active component is LaCoO ₃ or LaCo _0.96 Pt _0.04 O ₃ (that is, LaCo _0.96 One of Pt _0.04 O _3-δ ), the loading of the catalyst active component is 8wt%-15wt% (that is, the catalyst active component mass/catalyst carrier mass), preferably 10-15%.

The preparation method of the above-mentioned highly dispersed supported perovskite catalyst is carried out according to the following steps:

Step 1, according to the catalyst active component distribution ratio, carry out the batching of lanthanum nitrate, cobalt nitrate or lanthanum nitrate, cobalt nitrate, platinum nitrate and evenly disperse in distilled water, then add citric acid in an equal molar ratio to the total metal ions and disperse evenly to form immersion liquid;

In step 1, magnetic stirring is used for dispersion, and the rotating speed is 300-500 rpm or ultrasonic waves are used for dispersion, and the time is 5-10 min.

In step 1, two ions (lanthanum+cobalt) and citric acid are in an equimolar ratio, or three ions (lanthanum+cobalt+platinum) and citric acid are in an equimolar ratio.

Step 2, weigh the catalyst carrier according to the loading amount of the catalyst active component and place it in the impregnation solution obtained in step 1, and carry out equal volume impregnation at room temperature, so that the metal element is loaded on the catalyst carrier to obtain an impregnated sample;

In step 2, the solution prepared according to the principle of the equal volume immersion method is immersed in equal volume at room temperature of 20-25° C. for 12-24 hours.

In step 3, the impregnated sample obtained in step 2 is heated to form a wet gel, that is, the temperature is raised to 60-80 °C at a heating rate of 1-5 °C/min for 1-5 h to form a wet gel; and then the wet gel is formed at a temperature of 1-5 °C The temperature was raised to 100-120 °C at a heating rate of The high-dispersion supported perovskite catalyst can be obtained by heating at a heating rate of 10 °C/min to 700-800 °C for heat preservation treatment, and then naturally cooling to room temperature 20-25 °C with the furnace.

In step 3, an oven or a crucible is selected for heating, and the atmosphere is air to obtain wet gel and dry gel in sequence.

In step 3, a muffle furnace is selected for high temperature heat treatment, and air is used as the atmosphere.

In step 3, the temperature is raised to 70-80°C at a heating rate of 3-5°C/min for 3-5 hours to form a wet gel; then the temperature is raised to 110-120°C at a heating rate of 3-5°C/min, and the temperature is kept for 7 hours. -10h to form a dry gel.

In step 3, the holding time for completely decomposing the citric acid is 1-5 hours, preferably 2-4 hours, the holding temperature is 350-400°C, and the heating rate is 8-10°C/min.

In step 3, the temperature is raised to 700-800°C with a heating rate of 5-10°C/min for 1-5 hours, preferably 3-5 hours, the holding temperature is 750-800°C, and the heating rate is 8-10°C/ min.

The invention adopts the same volume of impregnation to synthesize the supported catalyst, which can improve the dispersibility of the catalyst on the surface of the carrier, reduce the agglomeration of the catalyst nanoparticles, fully contact the soot particles, and improve its catalytic activity. Compared with the prior art, the sample prepared by doping Pt at the B site of the present invention has higher catalytic performance, and when the loading amount of the catalyst active component is 10 wt %, the catalytic activity is better.

Description of drawings

Fig. 1 is the XRD diffraction pattern of the sample of the embodiment of the present invention.

FIG. 2 is the TEM and HRTEM photographs of the sample obtained in Example 1 of the present invention.

FIG. 3 is the TEM and HRTEM photographs of the sample obtained in Example 2 of the present invention.

FIG. 4 is the TEM and HRTEM photographs of the sample obtained in Example 3 of the present invention.

FIG. 5 is the TEM and HRTEM photographs of the sample obtained in Example 4 of the present invention.

FIG. 6 is a graph of the conversion rate calculated according to the thermogravimetric test data according to an embodiment of the present invention.

Detailed ways

The technical solutions of the present invention will be further described below through specific embodiments. According to the reference Tang Guoqi, Zhang Chunfu, Sun Changshan, Yan Bin, Yang Guoxiang, Dai Wei, Tian Baoliang. Research progress of activated alumina carrier [J]. Advances in Chemical Industry, 2011(30):1756-1765 for γ-Al ₂ O ₃ Preparation and water absorption measurement are as follows: 10-20g of pseudo-boehmite is placed in a muffle furnace, heated to 400-600°C at a heating rate of 3-5°C/min, and continuously calcined at 400-600°C After 3-5h, the furnace is cooled down at room temperature of 20-25°C after firing, and the muffle furnace is opened, and white powder is obtained after taking it out, which is γ-Al ₂ O ₃ . Weigh 5-10g into the beaker, slowly add distilled water to the beaker until it reaches the thin and thick state, record the total weight as 7.3078g, the calculated water absorption rate of γ-Al ₂ O ₃ is 0.6842, and in the muffle furnace is air atmosphere.

Example 1

1. Weigh 0.433g of lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O) and 0.291g of cobalt nitrate (Co(NO ₃ ) ₃ ·6H ₂ O), dissolve them in 1.676ml of distilled water, and then add them to the mixed solution Add 0.42028g of citric acid, stir until mixed uniformly; slowly add 2.4583g of alumina (γ-Al ₂ O ₃ ) to it.

2. Immersion: Immerse the above solution for 24h.

3. Drying: transfer the above solution to a crucible, keep at 80°C for 5 hours, and keep at 120°C for 12 hours to obtain a dry gel.

4. Sintering: transfer the above xerogel to a muffle furnace, calcine in an air atmosphere, heat up to 400°C at a rate of 3°C/min, and heat up to 800°C at a rate of 10°C/min after holding for 3 hours. After 5 h of calcination, a 10 wt% LaCoO ₃ /γ-Al ₂ O ₃ supported perovskite catalyst was prepared.

Example 2

1. Weigh 0.433g lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O), 0.279g cobalt nitrate (Co(NO ₃ ) ₃ ·6H ₂ O), 0.05872g platinum nitrate (Pt(NO ₃ ) ₂ and dissolve In 1.7193ml of distilled water, 0.42028g of citric acid was added to the mixed solution, and the mixture was stirred until it was evenly mixed; 2.5128g of alumina (γ-Al ₂ O ₃ ) was slowly added to it.

2. Immersion: Immerse the above solution for 24h.

3. Drying: transfer the above solution to a crucible, keep at 80°C for 5 hours, and keep at 120°C for 12 hours to obtain a dry gel.

4. Sintering: transfer the above xerogel into a muffle furnace, calcine in an air atmosphere, heat up to 400°C at a rate of 3°C/min, and heat up to 800°C at a rate of 10°C/min after holding for 3 hours , 10wt% LaCo _0.96 Pt _0.04 O _3-δ /γ-Al ₂ O ₃ supported perovskite catalyst was obtained after calcination for 5h.

Example 3

1. Weigh 0.433 g of lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O) and 0.291 g of cobalt nitrate (Co(NO ₃ ) ₃ ·6H ₂ O), dissolve them in 1.0624 ml of distilled water, and then add them to the mixed solution. Add 0.42028g of citric acid, stir until mixed uniformly; slowly add 1.6389g of alumina (γ-Al ₂ O ₃ ) to it.

2. Immersion: Immerse the above solution for 24h.

3. Drying: transfer the above solution to a crucible, keep at 80°C for 5 hours, and keep at 120°C for 12 hours to obtain a dry gel.

4. Sintering: transfer the above xerogel into a muffle furnace, calcine in an air atmosphere, heat up to 400°C at a rate of 3°C/min, and heat up to 800°C at a rate of 10°C/min after holding for 3 hours , 15wt% LaCoO ₃ /γ-Al ₂ O ₃ supported perovskite catalyst was prepared after calcination for 5 h.

Example 4

1. Weigh out 0.866g lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O), 0.5588g cobalt nitrate (Co(NO ₃ ) ₃ ·6H ₂ O), 0.1174g platinum nitrate (Pt(NO ₃ ) ₂ and dissolve it In 2.2925ml of distilled water, 0.8404g of citric acid was added to the mixed solution, and the mixture was stirred until uniform; 3.3507g of alumina (γ-Al ₂ O ₃ ) was slowly added to it.

2. Immersion: Immerse the above solution for 24h.

3. Drying: transfer the above solution to a crucible, keep at 80°C for 5 hours, and keep at 120°C for 12 hours to obtain a dry gel.

4. Sintering: transfer the above xerogel into a muffle furnace, calcine in an air atmosphere, heat up to 400°C at a rate of 3°C/min, and heat up to 800°C at a rate of 10°C/min after holding for 3 hours , 15wt% LaCo _0.96 Pt _0.04 O _3-δ /γ-Al ₂ O ₃ supported perovskite catalyst was obtained after calcination for 5h.

The catalyst prepared by the present invention is characterized, as shown in Fig. 1, the diffraction peak of the catalyst carrier (γ-Al ₂ O ₃ ) can be seen obviously, and only the weak peak of perovskite can be detected, which is It is fully confirmed that the perovskite catalyst synthesized according to the examples is highly dispersed on the support surface. With reference to Figures 2 and 5, it can be seen that the catalyst activity of each example is uniformly distributed on the catalyst carrier, and the dispersibility of Example 1 and Example 2 is higher, and the particle size of the catalytically active component of each example is maintained At about 5nm (ie, 4-6nm), it is beneficial to increase the specific surface area of the catalyst, so as to be in close contact with the soot particles to improve the catalytic activity.

The invention adopts the TG/DSC thermogravimetric analyzer equipment of Mettler toledo company. The main body of the thermogravimetric analyzer is a furnace body, which is a heating body. It operates under a certain temperature program, and different dynamic conditions can be passed through the furnace. Atmospheres (such as N ₂ , Ar, He and other protective atmospheres, O ₂ , air and other oxidative atmospheres and other special atmospheres, etc.), or test in vacuum or static atmosphere. During the test process, the high-precision balance connected to the lower part of the sample holder senses the current weight of the sample at any time, and transmits the data to the computer, and the computer draws the curve (TG curve) of the sample weight versus temperature/time. When the weight of the sample changes (the reasons include decomposition, oxidation, reduction, adsorption and desorption, etc.), it will appear as a weight loss (or weight gain) step on the TG curve. The temperature region in which it occurs, and the loss/gain ratio is quantitatively calculated. The present invention selects an atmosphere (volume ratio) with O ₂ : N ₂ of 1:9 for testing in the testing process, weighs 20 mg of the sample, and heats it up from 50 ℃ to 900 ℃ at a heating rate of 10 ℃/min in an air flow of 100 ml/min. °C to test. Convert the tested data to conversion rate to obtain the result in Figure 6 (that is, during the heating process, the catalyst and the passing atmosphere undergo catalytic oxidation and the conversion rate is calculated).

It can be found from Fig. 6 that Example 1 and Example 2 show faster conversion rate, so it shows that when the loading amount of catalyst active component is 10wt%, the catalyst activity is higher, in contrast, the loading amount is At 15wt%, the catalyst activity is low. In addition, Example 2 has a faster conversion rate than Example 1, indicating that the catalyst obtained in Example 2 has the highest activity, that is, the activity of the catalyst is improved after the incorporation of platinum element, that is, the incorporated element partially replaces the ideal calcium. The B site in the titanium oxide oxide has significantly improved catalytic activity and high dispersion performance, showing its application in the catalytic oxidation of soot particles in diesel engine exhaust.

By adjusting the process parameters according to the content of the present invention, the preparation of the perovskite catalyst can be realized, and the performance is basically consistent with that of the embodiment. The present invention has been exemplarily described above. It should be noted that, without departing from the core of the present invention, any simple deformation, modification, or other equivalent replacements that can be performed by those skilled in the art without any creative effort fall into the scope of the present invention. the scope of protection of the invention.

Claims (10)

1. The high-dispersion supported perovskite catalyst is characterized by consisting of a carrier of the catalyst and an active component of the catalyst, wherein the carrier is gamma-Al₂O₃The active component of the catalyst is LaCoO₃Or LaCo_0.96Pt_0.04O₃In the catalyst, the loading amount of the active component of the catalyst is 8-15 wt%, and the particle size of the active component of the catalyst is kept between 4 and 6 nm.

2. A highly dispersed supported perovskite catalyst as claimed in claim 1, wherein the loading of the active component of the catalyst is in the range of 10 to 15%.

3. A preparation method of a high-dispersion supported perovskite catalyst is characterized by comprising the following steps:

step 1, mixing lanthanum nitrate and cobalt nitrate or lanthanum nitrate, cobalt nitrate and platinum nitrate according to the active component ratio of a catalyst, uniformly dispersing the mixture in distilled water, adding citric acid with the molar ratio equal to the total metal ions, and uniformly dispersing the mixture to form an impregnation solution;

step 2, weighing a catalyst carrier according to the loading amount of the active components of the catalyst, placing the catalyst carrier into the impregnation liquid obtained in the step 1, and performing equal-volume impregnation at room temperature to load the metal elements onto the catalyst carrier to obtain an impregnated sample;

step 3, heating the impregnated sample obtained in the step 2 to form wet gel, namely heating to 60-80 ℃ at the heating rate of 1-5 ℃/min and preserving the heat for 1-5h to form wet gel; then heating to 120 ℃ at the heating rate of 1-5 ℃/min, and preserving the heat for 5-10h to form dry gel; then raising the temperature to 350-450 ℃ at the temperature raising speed of 5-10 ℃/min for heat preservation so as to completely decompose the citric acid, raising the temperature to 700-800 ℃ at the temperature raising speed of 5-10 ℃/min for heat preservation treatment, and naturally cooling to the room temperature of 20-25 ℃ along with the furnace so as to obtain the high-dispersion load type perovskite catalyst.

4. The process for preparing a highly dispersed supported perovskite catalyst as claimed in claim 3, wherein in the step 1, the dispersion is carried out by magnetic stirring at a rotation speed of 300 to 500rpm or by ultrasonic dispersion for 5 to 10 min.

5. The process for preparing a highly dispersed supported perovskite catalyst as claimed in claim 3, wherein in the step 2, the catalyst is immersed at room temperature of 20-25 ℃ for 12-24h at constant volume.

6. The preparation method of a highly dispersed supported perovskite catalyst as claimed in claim 3, wherein in step 3, heating is performed by using an oven or a crucible in an atmosphere of air to obtain a wet gel and a dry gel in sequence; the high-temperature heat treatment is carried out by using a muffle furnace and taking air as an atmosphere.

7. The preparation method of the highly dispersed supported perovskite catalyst as claimed in claim 3, wherein in the step 3, the temperature is raised to 70-80 ℃ at a temperature raising rate of 3-5 ℃/min and is kept for 3-5h to form wet gel; then the temperature is raised to 110-120 ℃ at the heating rate of 3-5 ℃/min, and the temperature is kept for 7-10h to form xerogel.

8. The process for preparing a highly dispersed supported perovskite catalyst as claimed in claim 3, wherein in the step 3, the holding time for completely decomposing citric acid is 1 to 5 hours, preferably 2 to 4 hours, the holding temperature is 350 ℃ and 400 ℃, and the temperature rising rate is 8 to 10 ℃/min.

9. The method for preparing a highly dispersed supported perovskite catalyst as claimed in claim 3, wherein in step 3, the temperature is raised to 700-800 ℃ at a temperature raising rate of 5-10 ℃/min for 1-5 hours, preferably 3-5 hours, the temperature is raised to 750-800 ℃ at a temperature raising rate of 8-10 ℃/min.

10. Use of a highly dispersed supported perovskite catalyst as claimed in claim 1 or 2 for the catalytic oxidation of soot particulates in diesel exhaust.

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