KR100551792B1 - Preparation method of ceria for purifying automotive exhaust gas - Google Patents

Abstract

The present invention relates to a method for preparing ceria for automobile exhaust gas purification, comprising a sol-type compound prepared by mixing an aqueous solution of cerium nitrate-zirconium nitrate with one or two or more precursors selected from lanthanum, neodymium, and samarium precursors. The present invention relates to a method of manufacturing ceria for automobile exhaust gas purification, which is capable of providing ceria having improved oxygen adsorption / desorption rate due to the high pore structure in which oxygen is easily adsorbed / desorbed.

Such a manufacturing method of the present invention includes a first step of preparing an aqueous solution of cerium nitrate-zirconium nitrate salt having a pH of 2 to 6 by adding an aqueous citric acid solution to an aqueous solution to which cerium nitrate salt and zirconium nitrate salt are added; A second step of producing a precipitated solid from a solution prepared by mixing a yttrium precursor with one or two or more selected ones of lanthanum, neodymium, and samarium precursors and solving the precipitated solids to prepare a sol compound having a pH of 2 to 4; A third step of mixing the aqueous solution of the first step with the sol compound of the second step to obtain a suspension, and adding a precipitation derivative thereto to produce a primary product; And a fourth step of drying and firing the primary product of the third step.

Car, exhaust gas purification, ceria, catalyst, high porosity, oxygen absorption / desorption speed improvement

Description

Preparation method of ceria for automobile exhaust gas purification {Preparation method of ceria for purifying automotive exhaust gas}             

1 is a process flowchart showing a method of manufacturing ceria according to the present invention;

Figure 2 is a graph showing the pore distribution of Examples 1 to 3 and Comparative Examples according to the prior art according to the present invention.

The present invention relates to a method for preparing ceria for automobile exhaust gas purification, comprising a sol-type compound prepared by mixing an aqueous solution of cerium nitrate-zirconium nitrate with one or two or more precursors selected from lanthanum, neodymium, and samarium precursors. The present invention relates to a method of manufacturing ceria for automobile exhaust gas purification, which is capable of providing ceria having improved oxygen adsorption / desorption rate due to the high pore structure in which oxygen is easily adsorbed / desorbed.

In general, the catalyst for the purification of automobile exhaust gases reacts with the exhaust gases to convert harmful gases such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) into nitrogen (N ₂ ), carbon dioxide (CO ₂ ), and water (H _2). O) and converts to.

Such catalysts usually have a structure in which a wash coat is coated on a cordierite honeycomb base, where the wash coat is a combination of metal oxide compounds of ceramic components.

The components of the washcoat include alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), zirconia (ZrO ₂ ), and lanthanum (La ₂ O ₃ ). Especially, ceria and zirconia are oxygen absorbing materials. Oxygen is adsorbed / desorbed according to the air-fuel ratio.

That is, the oxygen storage material of the washcoat is to help the oxidation of hydrocarbons and carbon monoxide by releasing oxygen when oxygen is insufficient, and to maintain the reduction effect of nitrogen oxide by occluding oxygen when oxygen is excessive. .

Recently, with the improvement of engine electronic control technology, the exhaust gas conditions are always kept close to the theoretical air-fuel ratio to maximize the purification performance of the catalyst.

However, on the other hand, conditions outside the theoretical air-fuel ratio near the operating conditions, i.e., when the operating region in the catalyst is not λ ≒ 1, are not excluded.

In this situation, the catalyst is affected by the oxygen adsorption / desorption rate, not the oxygen storage amount, in order to maintain performance.

For example, when the fuel is cut in the state of rapid deceleration, the air-fuel ratio is rapidly lean, and the ceria of the catalyst rapidly absorbs oxygen and moves to the oxidation state.

However, if the ceria does not quickly release oxygen occupied when entering the theoretical air-fuel ratio range, the catalyst is deoxidized and the purification performance of nitrogen oxide deteriorates.

Therefore, at this time, the oxygen adsorption / desorption rate becomes a more important factor than the oxygen storage amount of ceria.

However, the ceria of the conventional manufacturing method has limited the adsorption / desorption speed of oxygen from the fine pore structure of several tens to 100 nm, and thus is limited in responding to changes in driving conditions such as fuel cuts of automobiles. There was a phenomenon that eventually, the exhaust gas purification performance deteriorated.

Nevertheless, studies to improve the rate of adsorption / desorption of ceria have been very insufficient until now, and thus, a method for improving the rate of oxygen adsorption / desorption of ceria is urgently needed.

Accordingly, the present invention has been invented to solve the above problems, sol form prepared by mixing a cerium nitrate-zirconium nitrate aqueous solution with one or two or more precursors selected from lanthanum, neodymium and samarium precursors to the yttrium precursor The present invention provides a method for preparing ceria for automobile exhaust gas purification, which can provide ceria with improved oxygen adsorption / desorption rate due to the high pore structure of oxygen adsorption / desorption, which is prepared by mixing the compounds. There is this.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The present invention relates to a method for producing ceria for automobile exhaust gas purification, the method of producing a cerium nitrate-zirconium nitrate aqueous solution having a pH of 2 to 6 by adding an aqueous citric acid solution to an aqueous solution containing cerium nitrate and zirconium nitrate salts. A process for preparing a sol compound having a pH of 2-4 by adding polyethylene glycol to a precipitated solid produced by mixing one or two or more selected ones of lanthanum, neodymium and samarium precursors with yttrium precursor and adding sodium hydroxide or potassium hydroxide thereto And a third step of mixing the aqueous solution of the first step and the sol compound of the second step to obtain a suspension, and adding potassium hydroxide thereto to produce a primary product, and the first step of the third step. The tea product is dried at a temperature of 70-95 ℃ for 1-5 hours, and then fired at 500 ℃ while reducing the moisture content in an atmosphere of 5% moisture at firing. Followed by calcination and is characterized in that it comprises a fourth step of firing drive 2 to 800 ℃.

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In particular, the second step is to produce a precipitate solid by adding an aqueous solution of sodium hydroxide or potassium hydroxide to a solution of 1 molar concentration prepared by using a yttrium precursor and a lanthanum precursor in a molar ratio of 1: 0.5 to 1, respectively, and then solvated. It is characterized in that to prepare a sol compound.

In another embodiment, the second process may be performed by adding an aqueous solution of sodium hydroxide or potassium hydroxide to a solution of 1 molar concentration prepared by using a yttrium precursor and a neodymium precursor in a molar ratio of 1: 0.5 to 1, respectively to generate a precipitated solid. And then sollation to prepare a sol compound.

In another embodiment, the second process may include sodium hydroxide or potassium hydroxide in a solution of 1 molar concentration prepared by using a yttrium precursor, a lanthanum precursor, and a samarium precursor at a molar ratio of 1: 0.5 to 1: 0.25 to 0.5, respectively. It is characterized in that the addition of an aqueous solution to produce a precipitate solid and then sollation to prepare a sol compound.

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Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

The present invention relates to a method for producing ceria used in the production of a catalyst for automobile exhaust gas purification, and more particularly, to a method for producing ceria having improved oxygen adsorption / desorption rate.

The method for producing ceria according to the present invention is described in detail for each process as follows.

1 is a process flowchart showing a method of manufacturing ceria according to the present invention.

First, as a first step, citric acid aqueous solution is added to an aqueous solution in which cerium nitrate salts and zirconium nitrate salts are dissolved, thereby preparing an aqueous solution of cerium nitrate-zirconium nitrate salt having a pH of 2 to 6.

Here, the cerium nitrate salt and the zirconium nitrate salt are respectively added in a weight ratio of 25:75 to 75:25, and an aqueous solution of 1 mol of citric acid is added to the aqueous solution in which they are dissolved, thereby producing a cerium nitrate salt and zirconium nitrate salt having a pH of 2 to 6. Prepare in aqueous solution.

At this time, when the pH of the aqueous solution is out of the above range, citric acid is not decomposed well, there is a problem to produce a precipitate is not preferred.

Next, the second step is to prepare an additive, the additive is prepared by mixing one or more precursors selected from the lanthanum (La), neodymium (Nb) and samarium (Sm) precursor to the yttrium (Y) precursor A sol compound prepared by producing a precipitated solid from a solution via precipitation and then solvating this solid.

Preferably, sodium hydroxide (NaOH) or potassium hydroxide as a precipitant in a solution of 1 molar concentration prepared by using a yttrium (Y) precursor and a lanthanum (La) precursor in a molar ratio of 1: 0.5 to 1, respectively, in the second step. A suitable amount of an aqueous solution of (KOH) is added dropwise to obtain a solid, and a sol compound having a pH of 2 to 4 is obtained through a sol process in which an anionic surfactant of polyethylene such as polyethylene glycol is added thereto.

At this time, when the use ratio of the yttrium precursor and the lanthanum precursor is out of the above range, there is a problem that the performance of the catalyst is lowered, which is not preferable.

In addition, when the pH of the sol compound is out of the above range, it is difficult to form the sol compound and there is a problem that the compound aggregates, which is not preferable.

Alternatively, in another embodiment, sodium hydroxide or potassium hydroxide may be used as a precipitant in a solution of 1 molar concentration prepared by using a yttrium (Y) precursor and a neodymium (Nd) precursor in a molar ratio of 1: 0.5 to 1, respectively. A suitable amount of the aqueous solution is added dropwise to obtain a solid, and a sol compound having a pH of 2 to 4 is obtained through a sol process in which an anionic surfactant of polyethylene such as polyethylene glycol is added thereto.

At this time, when the use ratio of the yttrium precursor and the neodymium precursor is out of the above range, there is a problem that the catalytic performance is lowered, which is not preferable.

On the other hand, in another embodiment, 1 mole prepared by using a yttrium (Y) precursor, a lanthanum (La) precursor and a samarium (Sm) precursor in a molar ratio of 1: 0.5 to 1: 0.25 to 0.5, respectively An appropriate amount of an aqueous solution of sodium hydroxide or potassium hydroxide is added dropwise to the solution of the concentration to obtain a solid content, and a sol compound having a pH of 2 to 4 is obtained through a sol process in which an anionic surfactant of polyethylene such as polyethylene glycol is added thereto.

At this time, when the use ratio of the yttrium precursor, the lanthanum precursor and the samarium precursor is out of the above range, there is a problem that it is difficult to obtain a compound having a uniform composition, which is not preferable.

Next, as a third step, a cerium nitrate salt-zirconium nitrate salt aqueous solution obtained through the first step and a sol compound obtained through the second step are mixed to obtain a suspension, and a precipitate derivative such as potassium hydroxide is added to the mixed product. Is added to produce the primary product.

Here, since the sol compound precursor is the base and cerium ions and zirconium ions form a complex compound through a substitution reaction, cerium ions and zirconium ions are effectively substituted through this third process, thereby improving the performance of the final catalyst. It can be activated.

Next, the fourth step is a final step, in which the primary product obtained through the third step is dried and calcined under appropriate conditions to obtain a final ceria composite oxide having large particle characteristics in the suspension. .

Through the whole process, each additive component is mixed with the final compound in an optimal combination state as a sol compound, and finally forms as a solid metal oxide or cerium-zirconium oxide and solid solution.

This depends on the heat treatment conditions in the calcination process of the primary product, the primary product is dried for 1 to 5 hours at a temperature of 70 ~ 95 ℃ in the drying process of the fourth process, the first 5% moisture in the firing process After slowly calcining to 500 ° C. while reducing the water content to 0% in the atmosphere of 2 ° C., the final product was calcined to 800 ° C. in the second place.

In carrying out the drying and firing processes of the fourth process, if the heat treatment conditions are not described above, crystals of the product are separated and thus the performance of the catalyst is degraded.

In this way, according to the above-described manufacturing method of the present invention, in the preparation of the catalyst, the primary product together with the final product may be more easily attached to a supporter, and may be used. It is possible to manufacture a ceria having a high porosity structure that is excellent in heat resistance compared to oxides and easily adsorbs and desorbs oxygen.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by Examples.

Examples 1 to 3

Each embodiment is prepared according to the production method of the present invention, each with different additives.

First, 300 g of cerium nitrate salt was completely dissolved in 1 L of water, and then 150 g of zirconium nitrate salt was further dissolved, and 0.5 L of an aqueous solution of 1 mol of citric acid was added thereto to prepare an aqueous solution of pH 4.

Then, in order to prepare the additive, a solution of 1-moral concentration prepared using a yttrium precursor and a lanthanum precursor in a molar ratio of 1: 0.7 for Example 1, and a yttrium precursor and a neodymium precursor for Example 2 were each 1: A 1 molar concentration solution prepared using a molar ratio of 0.7, and yttrium, lanthanum and samarium precursors in the case of Example 3 in a molar ratio of 1: 0.7: 0.4, respectively, was prepared.

Subsequently, potassium hydroxide was added to each of the above solutions in an appropriate amount to obtain a solid, and polyethylene glycol was further added to obtain a sol compound having a final pH of 2 to 4 as an additive.

Thereafter, the aqueous solution of cerium nitrate-zirconium nitrate was mixed with the sol compound to obtain a suspension, and 0.1 mol of potassium hydroxide was added thereto to obtain a primary product.

Thereafter, the primary product was dried at a temperature of 90 ° C. for 4 hours, and then slowly calcined to 500 ° C. while reducing the water content in an atmosphere of 5% moisture, and then calcined to 800 ° C. to obtain a final product (Example 1 to 1). 3) was prepared.

Comparative example

Ceria was prepared according to a conventional manufacturing method (oxide production by a solid-phase reaction method), and cerium composite oxide was prepared from a mixed solution at a ratio corresponding to a chemical equivalence ratio using a cerium nitrate and zirconium nitrate solution.

Comparative Example is a metal oxide of Cex Zr (1-xy) MyO ₂ structure formed after calcination at 800 ° C. at a pressure of 1 bar or more in a closed reactor by adding a small amount of metal compounds such as yttrium, scandium, and rare earth (where M is a small amount Is a compound of x = 0.65 and y = 0.3, which are recognized to have high performance in the product of the conventional manufacturing process.

2 is a graph showing the pore distribution of the products according to Examples 1 to 3 and Comparative Examples. As can be seen from this, the products of Examples 1 to 3 are products of Comparative Examples according to the prior art. Compared with the high pore structure, oxygen adsorption / desorption is easy.

On the other hand, to confirm the adsorption / desorption rate of oxygen in Examples 1 to 3 and Comparative Examples, 5g of reactant was put in the reactor and oxygen containing 1% oxygen and 1.5% oxygen at 1Hz conversion rate of oxygen desorption The amount was measured, and the following Table 1 shows the result.

Looking at the measurement results, as shown in Table 1, it can be seen that the amount of oxygen adsorbed and desorbed in the ceria of Examples 1 to 3 prepared according to the present invention compared to the comparative example.

In this way, according to the method for producing a vehicle exhaust gas purifying ceria according to the present invention, by admixing the sol-type additives with an aqueous solution of cerium nitrate-zirconium nitrate salt at an appropriate pH, it is easy to adsorption / desorption of oxygen The tool bath makes it possible to produce ceria with improved oxygen adsorption / desorption rate.

As described above, according to the present invention, a sol-type compound prepared by mixing a cerium nitrate salt-zirconium nitrate aqueous solution with one or two or more precursors selected from lanthanum, neodymium, and samarium (Sm) precursors By producing by mixing, there is an effect that it is possible to provide a ceria with improved oxygen adsorption / desorption rate due to the high pore structure of oxygen adsorption / desorption easy.

Claims (6)

In the method of manufacturing a ceria for automobile exhaust purification, A first step of preparing an aqueous solution of cerium nitrate-zirconium nitrate salt having a pH of 2 to 6 by adding an aqueous citric acid solution to an aqueous solution to which the cerium nitrate salt and the zirconium nitrate salt are added; A compound for preparing a sol compound having a pH of 2 to 4 by mixing polyethylene precursor to a precipitated solid produced by mixing one or two or more selected ones of lanthanum, neodymium and samarium precursors with yttrium precursor and adding sodium hydroxide or potassium hydroxide thereto 2 step; A third step of mixing the aqueous solution of the first step with the sol compound of the second step to obtain a suspension, and adding potassium hydroxide thereto to produce a primary product; After drying the primary product of the third process for 1 to 5 hours at a temperature of 70 ~ 95 ℃, the first firing up to 500 ℃ while reducing the water content in the atmosphere of 5% moisture at the time of firing and then up to 800 ℃ 2 A fourth step of firing into a car; Method for producing a vehicle exhaust gas purification ceria comprising a. The method according to claim 1, In the second step, a solution of sodium or potassium hydroxide is added to a solution of 1 molar concentration prepared by using a yttrium precursor and a lanthanum precursor in a molar ratio of 1: 0.5 to 1, respectively, to generate a precipitated solid, which is then solated by sol Method for producing ceria for automobile exhaust gas purification, characterized in that to prepare a compound. The method according to claim 1, In the second step, an aqueous solution of sodium hydroxide or potassium hydroxide is added to a solution of 1 molar concentration prepared by using a yttrium precursor and a neodymium precursor in a molar ratio of 1: 0.5 to 1, respectively, to generate a precipitate solid, and then sol Method for producing ceria for automobile exhaust gas purification, characterized in that to prepare a compound. The method according to claim 1, In the second step, the solids precipitated by adding an aqueous solution of sodium hydroxide or potassium hydroxide to a solution of 1 molar concentration prepared by using a yttrium precursor, a lanthanum precursor, and a samarium precursor in a molar ratio of 1: 0.5 to 1: 0.25 to 0.5, respectively. The method for producing ceria for automobile exhaust gas purification, characterized in that to produce a sol compound by producing a sol compound after. delete delete

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