CN104971735B - A kind of efficient diesel car tail gas refining oxidation catalyst and its preparation method and application - Google Patents

Abstract

The present invention relates to a high-efficiency diesel vehicle tail gas purification oxidation catalyst and its preparation method and application. The active component of the catalyst is Cu-Mn-Ce-Zr composite oxide, and the catalyst has a mesopore structure. , The loading amount of Ce is 30-40%, the loading amount of Mn is 60-70%, the loading amount of Cu is 0-10%, and the loading amount of Zr is 0-3%.

Description

A high-efficiency diesel vehicle exhaust purification oxidation catalyst and its preparation method and application

technical field

The invention belongs to the technical field of catalytic materials, in particular to a non-noble metal mesoporous composite oxide catalyst for highly efficient catalytic oxidation of CO, C ₃ H ₆ , and C ₃ H ₈ for purifying diesel vehicle exhaust and a preparation method thereof.

Background technique

As a highly efficient and energy-saving power machine, diesel vehicles are widely used in real life. However, toxic gases such as CO, CH compounds, NOx and soot particles in the exhaust gas of diesel engines also seriously endanger the environment and human health. Therefore, with the continuous increase in the number of diesel vehicles and strict regulations on diesel vehicle exhaust emissions, the post-treatment technology for diesel vehicle exhaust has also developed rapidly.

Diesel vehicle oxidation catalyst (DOC) oxidizes CO, CH and SOF into CO ₂ and H ₂ O through the oxidation of the catalyst, so as to achieve the purpose of reducing pollutant emissions. The catalyst does not need to be regenerated, so DOC is currently the most widely used diesel Vehicle exhaust after-treatment technology. Non-noble metal DOC catalysts, such as: Cu-based compounds, Ce-based compounds, perovskite oxides, etc., generally have the problem of low catalyst activity; while noble metal catalysts are still the main active components of DOC, such as: Pt, Pd, etc., they It has excellent catalytic oxidation performance for CO and CH compounds in diesel vehicle exhaust, but its high catalytic activity is also prone to produce sulfate, causing sulfur poisoning and deactivation of the catalyst. In addition, the high cost of noble metal-based catalysts also limits its promotion to a certain extent.

Therefore, it is of great scientific significance to study high-efficiency non-precious metal-based catalysts with high water resistance and high sulfur resistance for the catalytic oxidation of CO and CH compounds in automobile exhaust, and it is also the development trend of DOC materials in the future.

Contents of the invention

In view of the deficiencies in the prior art, the purpose of the present invention is to provide a highly efficient non-noble metal mesoporous composite oxide catalyst, which can not only realize the catalytic oxidation of CO, C ₃ H ₆ and C ₃ H ₈ at a lower temperature, but also has Excellent resistance to water vapor poisoning, and the catalyst also has excellent reusability.

Here, on the one hand, the present invention provides a highly efficient diesel vehicle exhaust purification oxidation catalyst, the active component of the catalyst is Cu-Mn-Ce-Zr composite oxide, the catalyst is a mesoporous structure, by mass , the loading amount of Ce is 30-40%, the loading amount of Mn is 60-70%, the loading amount of Cu is 0-10%, and the loading amount of Zr is 0-3%.

The active component of the catalyst of the invention is a non-noble metal composite oxide, and the cost is relatively low. There is a synergistic catalytic action mechanism between multivalent metal oxide catalysts, which can further improve the catalytic effect. The catalyst of the invention can not only realize the catalytic oxidation of CO, C ₃ H ₆ and C ₃ H ₈ at a relatively low temperature, but also has excellent resistance to water vapor poisoning, and meanwhile, the catalyst also has excellent reusability.

Preferably, the loading amount of Zr is 1-3%.

Preferably, the mesopore diameter of the catalyst is 5-20 nm, and the specific surface area is 90-250 m ² /g. The catalyst of the invention has a large specific surface area and abundant mesopore structure, can increase the effective contact area and improve the catalytic effect.

On the other hand, the present invention also provides the preparation method of above-mentioned catalyst, comprises the following steps:

(1) Weigh the metal salts of each metal in the Cu-Mn-Ce-Zr composite oxide and dissolve them in an appropriate amount of water to prepare a uniform solution of mixed salts;

(2) Add the precipitating agent dropwise to the homogeneous solution of the mixed salt obtained in step (1) under stirring at 40-80°C, and react until the precipitation is complete;

(3) separating, washing and drying the precipitate of step (2) to obtain a precursor;

(4) Calcining the obtained precursor at 400-500° C. for 2-4 hours to obtain the catalyst.

The preparation process of the present invention does not require relatively harsh conditions such as high temperature, high pressure, and hydrothermal conditions, and can be carried out at a temperature of 40°C to 80°C. The preparation process of the method is simple, the reaction parameters are easy to control, the source of raw materials is wide, and it is easy to popularize.

Preferably, in step (1), the cerium salt is cerium nitrate, cerium sulfate and/or cerium carbonate; the manganese salt is potassium permanganate, manganese sulfate and/or manganese acetate; the copper salt is copper acetate and/or copper nitrate the zirconium salt is zirconium nitrate and/or zirconium sulfate.

Preferably, in step (1), the concentration of the cerium salt in the homogeneous mixed salt solution is 0.02-0.2 mol/L.

Preferably, in step (2), the precipitation agent is at least one of hydrogen peroxide, ammonium carbonate solution, and ammonia solution, preferably hydrogen peroxide.

Preferably, in step (2), the concentration of hydrogen peroxide is 0.1-0.2 mol/L.

In another aspect, the present invention also provides the application of the above-mentioned catalyst in the efficient catalytic removal of CO, C ₃ H ₆ and C ₃ H ₈ in diesel vehicle exhaust.

_The catalyst enables complete oxidation _of CO, _C3H6 and _C3H8 at a temperature less than 250°C.

Description of drawings

Fig. 1 a is the TEM photo of the non-noble metal Ce-Mn mesoporous composite oxide catalyst prepared in embodiment one;

Fig. 1 b is the EDS picture of the non-noble metal Ce-Mn mesoporous composite oxide catalyst prepared in embodiment one;

Fig. 2 is the SEM and element distribution picture of the non-noble metal Cu-Mn-Ce mesoporous composite oxide catalyst prepared in Example 2;

Fig. 3 is the reaction of the non-noble metal Ce-Mn mesoporous composite oxide catalyst in the first example in the N ₂ /H ₂ O/O ₂ atmosphere at a temperature range of 30-400°C to CO, C ₃ H ₆ , C ₃ H ₈ Catalytic oxidation effect diagram;

Fig. 4 is the reaction of the non-noble metal Ce-Mn mesoporous composite oxide catalyst in the N ₂ /H ₂ O/O ₂ atmosphere in the temperature range of 30-400°C to CO, C ₃ H ₆ , C ₃ H ₈ The cycle catalytic oxidation effect diagram;

Fig. 5 is a diagram of the cycle test results of the non-noble metal Cu-Mn-Ce mesoporous composite oxide catalyst in the N ₂ /H ₂ O/O ₂ atmosphere in Example 2;

Fig. 6 is the N ₂ adsorption-desorption curve and pore size distribution diagram of Ce-Mn mesoporous composite oxide catalyst and Cu-Mn-Ce mesoporous composite oxide catalyst in an example of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the drawings and the following embodiments. It should be understood that the drawings and the following embodiments are only used to illustrate the present invention rather than limit the present invention.

The present invention provides a high-efficiency diesel vehicle exhaust purification oxidation catalyst (DOC), the active component of the catalyst is a non-noble metal composite oxide, and the non-noble metal is a transition metal with variable valence, which can be Ce, Mn, Cu, Fe , Co, Zr, Ti any two or more, for example, the active component of the catalyst can be Ce-Mn, Cu-Ce, Fe-Cu, Ce-Co, Cu-Ce-Mn, Fe-Ce-Mn , Co-Ce-Mn, Cu-Mn-Ce-Zr, Cu-Mn-Ce-Ti composite oxides, etc.

In one embodiment, the active component of the catalyst is a Cu-Mn-Ce-Zr composite oxide, wherein by mass, the loading amount of Ce is 30-40%, and the loading amount of Mn is 60-70%, The loading amount of Cu is 0 to 10% (preferably 1 to 10%), and the loading amount of Zr is 0 to 3% (preferably 1 to 3%).

In the non-noble metal composite oxide of the present invention, there is a synergistic catalytic action mechanism among the multivalent metal oxide catalysts, thereby improving the catalytic effect.

The catalyst of the present invention has a large specific surface area and abundant mesoporous structure, for example, the mesopore diameter can be 5-20nm, and the specific surface area can be 90-250m ² /g (see Figure 6). This can increase the effective contact area and improve the catalytic effect.

The catalysts of the present invention can be prepared by coprecipitation. In one example, the following steps are included:

Step 1. Weigh an appropriate amount of metal salt, dissolve it in an appropriate amount of water, and stir (for example, stir in a water bath at 40-80°C for 0.5-1 hour) to make it dissolve uniformly;

Step 2. Measure the precipitating agent (hydrogen peroxide/ammonium carbonate solution/ammonia solution), and slowly add it dropwise to the homogeneous solution of the mixed salt obtained in the above step 1 under stirring at 40-80°C;

Step 3, separate by suction filtration, wash 2-4 times with deionized water, and dry the obtained precipitate (for example, dry in an oven at 40-80°C for 12-24h);

Step 4. Calcining the obtained precursor at 400-500° C. for 2-4 hours to obtain a composite metal oxide catalyst.

In step 1, the corresponding metal salt used can be water-soluble inorganic or organic metal salt known in the art, for example, cerium salt can be cerium nitrate, cerium sulfate or cerium carbonate, manganese salt can be potassium permanganate, manganese sulfate Or manganese acetate, the copper salt can be copper acetate or copper nitrate, and the zirconium salt can be zirconium nitrate.

In step 1, in the prepared homogeneous mixed salt solution, the concentration of the cerium salt may be 0.02-0.2 mol/L.

In step 2, the precipitation agent can be at least one of hydrogen peroxide, ammonium carbonate solution, and ammonia solution, preferably hydrogen peroxide. When _hydrogen peroxide is used, the concentration of H2O2 can be _0.1-0.2mol /L. The volume of hydrogen peroxide can be: 1-5L of hydrogen peroxide is used per 1 mol of cerium salt.

In step 2, after the hydrogen peroxide is added dropwise, the reaction can be continued for 10-14 hours to complete the precipitation.

In one example, the method of using the non-precious metal compound oxide catalyst of the present invention for efficient catalytic removal of CO in diesel vehicle exhaust, C ₃ H ₆ and C ₃ H ₈ is as follows: take a certain amount of catalytic material in the reactor , the simulated diesel vehicle exhaust gas is passed into the reactor, and the diesel vehicle exhaust gas includes CO, C ₃ H ₆ , C ₃ H ₈ , N ₂ and O ₂ , with O ₂ as the oxidant, Ce-Mn, Cu -Mn-Ce and Cu-Mn-Ce-Zr oxides are used as catalysts, the heating rate is 5°C per minute, and the CO, C ₃ H ₆ , C ₃ H in the exhaust gas of diesel vehicles are treated in the temperature range of 30°C to 400°C ₈ for catalytic oxidation.

Preferably, the CO content in the diesel vehicle exhaust may be 5000ppm, the C ₃ H ₆ may be 400ppm, and the C ₃ H ₈ may be 200ppm. Preferably, the content of O ₂ may be 5(V)%-20(V)%, and the content of water vapor may be 0(V)%-10(V)%. Preferably, the amount of the catalyst used may be 0.2 g.

Tests show that the catalyst of the present invention can achieve complete oxidation of CO, C ₃ H ₆ and C ₃ H ₈ at low temperature (<250° C.), and has good water resistance and repeated use performance during the oxidation process. Under the same evaluation conditions, its comprehensive performance is superior to all kinds of diesel vehicle exhaust oxidation catalysts reported so far, and it has good application and promotion value.

The present invention uses mesoporous composite oxides Mn-Ce, Cu-Mn-Ce and Cu-Mn-Ce-Zr as catalysts to catalyze and oxidize CO, C ₃ H ₆ , and C ₃ H ₈ in diesel vehicle exhaust. The advantages are:

1. The preparation process does not require relatively harsh conditions such as high temperature, high pressure, and hydrothermal, and can be carried out at a temperature of 40°C to 80°C;

2. The prepared mesoporous composite oxide catalyst has excellent oxidation ability to CO, C ₃ H ₆ and C ₃ H ₈ in diesel vehicle exhaust at relatively low temperature;

3. The prepared mesoporous composite oxide catalyst has good water resistance and reusability in the oxidation process of CO, C ₃ H ₆ , and C ₃ H ₈ in diesel vehicle exhaust;

4. The preparation process of this method is simple, the reaction parameters are easy to control, the source of raw materials is wide, and it is easy to popularize;

5. Non-precious metal DOC catalyst with low cost.

Examples are given below to describe the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above contents of the present invention all belong to the present invention scope of protection. The specific process parameters and the like in the following examples are only an example of the appropriate range, that is, those skilled in the art can make a selection within the appropriate range through the description herein, and are not limited to the specific values exemplified below.

Preparation Example

Embodiment one

Weigh 0.007mol potassium permanganate and 0.003mol cerium nitrate hexahydrate, and dissolve them in 40mL deionized water under stirring in a water bath at 80°C to form a uniform solution; measure 10mL hydrogen peroxide and add dropwise to the above homogeneous solution After 12 hours of oxidation-reduction reaction, vacuum filtration, washing with a large amount of water, drying in an oven at 80°C to obtain a precursor, calcining in a muffle furnace at 550°C for 4 hours to obtain a non-precious metal mesoporous composite oxide catalyst, Recorded as: Ce-Mn.

Figure 1a and Figure 1b are TEM and EDS photographs of the _CeMnOx catalyst prepared in this example. It can be seen from Figure 1a and Figure 1b that the material has a good pore structure, and the prepared material contains elements Mn, Ce and O.

Embodiment two

Weigh 0.005mol of copper acetate, 0.01mol of manganese acetate and 0.005mol of cerium nitrate, and dissolve them in 50mL of deionized water while stirring in a water bath at 40°C to form a uniform solution; measure 20mL of hydrogen peroxide and add it dropwise to the above homogeneous solution And keep stirring, after reacting for 12 hours, vacuum filtration, washing with a large amount of water, drying in an oven at 60°C to obtain a precursor, and calcining in a muffle furnace at 550°C for 4 hours to obtain a non-precious metal mesoporous composite oxide catalyst, which is recorded as: Cu-Mn-Ce.

Fig. 2 is the SEM and elemental distribution diagram of the Cu-Mn-Ce catalyst prepared in this example. It can be seen from Figure 2 that the material has a good pore structure, and the elements Mn, Cu, Ce and O are uniformly distributed throughout the material.

Embodiment three

A synthesis process similar to that of Example 2 was adopted, except that 0.0015 mol of zirconium nitrate was added to the precursor solution to prepare a Cu-Mn-Ce-Zr mesoporous composite oxide catalyst.

Effect Example

In order to verify the catalytic removal effect of the non-precious metal mesoporous composite oxide catalyst of the present invention on CO, C ₃ H ₆ , and C ₃ H ₈ in diesel vehicle exhaust, a specially simulated diesel vehicle exhaust condition was designed and carried out under laboratory conditions. Experiment below.

Embodiment four

The 0.2g Ce-Mn catalyst prepared by the method of Example 1 is loaded into the fixed-bed reactor, and the following mixed gas is introduced at room temperature: the concentration of CO is 5000ppm, the concentration of C ₃ H ₆ is 400ppm, and the concentration of C ₃ H ₈ The concentration is 200ppm, the concentration of _O2 is 10(V)%, and the total flow rate is 200mL/min.

The catalytic oxidation effect of the catalyst Ce-Mn on CO, C ₃ H ₆ , and C ₃ H ₈ in diesel vehicle exhaust was tested in the temperature range of 30-400°C. The test results are listed in Table 1.

Embodiment five

The 0.2g Cu-Mn-Ce catalyst prepared by the method of Example 2 is loaded into the fixed-bed reactor, and the following mixed gas is introduced at room temperature: the concentration of CO is 5000ppm, the concentration of C ₃ H ₆ is 400ppm, and the concentration of C ₃ H The concentration of ₈ is 200ppm, the concentration of _O2 is 10(V)%, and the total flow rate is 200mL/min.

The catalytic oxidation effect of the catalyst Cu-Mn-Ce on CO, C ₃ H ₆ , and C ₃ H ₈ in diesel vehicle exhaust was tested in the temperature range of 30-400°C. The test results are listed in Table 1.

Embodiment six

In the fixed bed reactor, the Cu-Mn-Ce-Zr catalyst of 0.2g prepared by the method of embodiment three is loaded into, and the following mixed gas is passed into at room temperature: the concentration of CO is 5000ppm, the concentration of C ₃ H ₆ is 400ppm, C The concentration of ₃ H ₈ is 200 ppm, the concentration of O ₂ is 10(V)%, and the total flow rate is 200 mL/min.

The catalytic oxidation effect of the catalyst Cu-Mn-Ce-Zr on CO, C ₃ H ₆ , and C ₃ H ₈ in diesel vehicle exhaust was tested in the temperature range of 30-400°C. The test results are listed in Table 1.

The test result of table 1 embodiment four, five, six

Embodiment seven

Catalyst Ce-Mn is preferred, and its water resistance is tested:

The 0.2g Ce-Mn catalyst prepared by the method of Example 1 is loaded into the fixed-bed reactor, and the following mixed gas is introduced at room temperature: the concentration of CO is 5000ppm, the concentration of C ₃ H ₆ is 400ppm, and the concentration of C ₃ H ₈ The concentration is 200ppm, the concentration of O ₂ is 10(V)%, the concentration of H ₂ O is 0(V) and 8(V)%, and the total flow rate is 200mL/min.

The catalytic oxidation effect of the catalyst Ce-Mn on CO, C ₃ H ₆ , and C ₃ H ₈ in diesel vehicle exhaust was tested in the temperature range of 30-400°C. The test results are shown in Figure 3.

Embodiment eight

Catalysts Ce-Mn and Cu-Mn-Ce are preferred, and their recycling performance is tested:

0.2g of Ce-Mn or Cu-Mn-Ce catalyst prepared by the method of Example 1 or Example 2 is loaded into the fixed-bed reactor, and mixed gas is introduced at room temperature: the concentration of CO is 5000ppm, C ₃ H ₆ The concentration of C 3 H 8 is 400ppm, the concentration of C ₃ H ₈ is 200ppm, the concentration of O ₂ is 10(V)%, the concentration of H ₂ O is 8(V)%, and the total flow rate is 200mL/min.

The repeated use effect of catalyst Ce-Mn on the catalytic oxidation of CO, C ₃ H ₆ , and C ₃ H ₈ in diesel vehicle exhaust was tested in the temperature range of 30-400°C. After the test, the catalyst was recovered directly, and the cyclic catalytic test was continued under the same conditions. The test results are shown in Figure 4.

The repeated use effect of the catalyst Cu-Mn-Ce on the catalytic oxidation of CO, C ₃ H ₆ , and C ₃ H ₈ in diesel vehicle exhaust was tested in the temperature range of 30-400°C. After the test, the catalyst was recovered directly, and the cyclic catalytic test was continued under the same conditions. The test results are shown in Figure 5.

In summary, the non-noble metal mesoporous composite oxide catalyst of the present invention can achieve efficient catalytic removal of CO, C ₃ H ₆ , and C ₃ H ₈ in diesel vehicle exhaust in a relatively low temperature range (<250°C). The catalyst has excellent low-temperature catalytic effect and water vapor poisoning resistance, and also has excellent recycling performance, and its raw material cost is low, and the preparation process is simple and convenient. ₃ H ₆ , C ₃ H ₈ are of great significance and practical value.

Claims (6)

1. an efficient diesel vehicle exhaust CO, C ₃ H ₆ and C ₃ H ₈ purification oxidation catalyst, it is characterized in that, the active component of described catalyzer is Cu-Mn-Ce composite oxide, and described catalyzer is medium Pore structure, by mass, the loading of Ce is 30-40%, the loading of Mn is 60-70%, the loading of Cu is 1-10%, and the sum of the loadings of Ce, Mn and Cu is 100%. The temperature at which the catalyst completely oxidizes CO, C ₃ H ₆ and C ₃ H ₈ is less than 250°C, the mesopore diameter of the catalyst is 5-20 nm, and the specific surface area is 90-250 m ² /g. Prepared by: (1) Weigh the metal salts of each metal in the Cu-Mn-Ce composite oxide and dissolve them in an appropriate amount of water to prepare a uniform solution of the mixed salt; (2) Add hydrogen peroxide dropwise to the homogeneous solution of the mixed salt obtained in step (1) under stirring at 40-80°C, and react until the precipitation is complete; (3) separating, washing and drying the precipitate in step (2) to obtain the precursor; (4) Calcining the obtained precursor at 400-500° C. for 2-4 hours to obtain the catalyst. 2. The catalyst according to claim 1, characterized in that, in step (1), the cerium salt is cerium nitrate, cerium sulfate and/or cerium carbonate; the manganese salt is potassium permanganate, manganese sulfate and/or manganese acetate ; the copper salt is copper acetate and/or copper nitrate. 3. The catalyst according to claim 1, characterized in that, in step (1), the concentration of the cerium salt in the homogeneous mixed salt solution is 0.02-0.2 mol/L. 4. The catalyst according to claim 1, characterized in that, in step (2), the concentration of hydrogen peroxide is 0.1-0.2mol/L. 5. The application of the high-efficiency diesel vehicle exhaust purification oxidation catalyst according to any one of claims 1 to 4 in efficient catalytic removal of CO, C ₃ H ₆ and C ₃ H ₈ in diesel vehicle exhaust. 6. The application according to claim 5, characterized in that, the temperature at which the catalyst completely oxidizes CO, C ₃ H ₆ and C ₃ H ₈ is less than 250°C.