KR20050028941A - Method for manufacturing double layer coated pd only three way catalyst - Google Patents

Abstract

To provide a method for manufacturing a double layer coated Pd-only three-way catalyst, wherein a completed catalyst maintains more improved nitrogen oxide removal performance and heat resistance by high porosity of second coating layer and is capable of greatly reducing a consumption amount of expensive Pd(palladium) compared with an existing manufacturing method. In a method for manufacturing a high porous double layer coated Pd-only three-way catalyst having high durability and high performance by preparing first catalyst slurry and second catalyst slurry using Pd(palladium), alumina, cerium oxide, mixed solution and so on, primarily coating the first catalyst slurry on a ceramic monolith carrier, and secondly coating the second catalyst slurry on the dried and fired ceramic monolith carrier after drying and firing the primarily coated ceramic monolith carrier, the method for manufacturing the double layer coated Pd-only three-way catalyst is characterized in that the second catalyst slurry is prepared by reducing alumina impregnated with a Pd solution, preparing a mixture by mixing cerium oxide, Ce-Zr composite oxide(Ce.Zr)O2, Ce-Zr-Y composite oxide(Ce.Zr.Y)O2 and cerium carbonate(Ce(CO3)2) in a weight ratio of 15:60:15:10 to 15:50:20:15, adding the prepared mixture to the reduced Pd solution impregnated alumina in an amount of 15 to 25 g/L for the total carrier apparent volume, adding praseodymium oxide to the resulting mixture in an amount of 2 to 5 g/L for the total carrier apparent volume, and adding one selected from (LaCe)(FeCo)O3 and (LaSr)(FeCo)O3 that are metal oxide(perovskite) to the mixed solution in an amount of 15 to 25 g/L for the total carrier apparent volume after reacting the mixed solution.

Description

Method for manufacturing double layer coated Pd only three way catalyst

The present invention relates to a method for producing a palladium _tertiary catalyst having a double layer coating structure, using alumina (Al ₂ O ₃ ), cerium oxide (CeO ₂ ), and a mixed solution as an additive. In the process of preparing the catalyst slurry, instead of the conventional method using only cerium oxide, a cerium oxide, a cerium-zirconium composite oxide, and a cerium-zirconium-yttrium composite oxide are used together in the primary catalyst slurry, and the above-mentioned oxidation is performed in the secondary catalyst slurry. Cerium carbonate ((Ce (CO ₃ ) ₂ ) is additionally used for cerium and cerium-zirconium composite oxide and cerium-zirconium-yttrium composite oxide, and then praseodymium oxide (PrO ₂ ) is added to the mixed solution. was added and the reaction after which the metal oxide (a perovskite) of (LaCe) (FeCo) O ₃ and (LaSr) (FeCo) O, by prepared by _three appropriate amount was added to a selected one of meat in the finished catalyst a secondary coating layer Siege More while having improved NOx removal performance and heat relates to a method of producing a three-way catalytic palladium double-layer coating structure that can be produced the amount of the expensive palladium significantly lower than the conventional method.

In general, a three way catalyst refers to a catalyst that removes these compounds by simultaneously reacting with hydrocarbon-based compounds, carbon monoxide and nitrogen oxides (NOx), which are harmful components of the exhaust gas, and conventionally, mainly Pt / Rh, Pd / Three-way catalysts of Rh or Pt / Pd / Rh systems have been used.

However, the catalyst as described above uses rhodium (Rh) as an element for reducing nitrogen oxides in the exhaust gas, and this rhodium has a problem in terms of cost and heat resistance.

Thus, a palladium tertiary catalyst (single layer coating structure) using only palladium (Pd) without rhodium has been developed and known [Republic of Korea Patent Publication No. 235029, US Patent No. 6,043,188], the manufacturing method is as follows. .

First, the palladium solution is impregnated with alumina (Al ₂ O ₃ ) and then reduced.

Next, cerium oxide (CeO ₂ ) and a mixed solution are added to the reduction product, and then the pH is adjusted to react, and the catalyst is milled to form a slurry.

Thereafter, ceramic monolith is immersed in the catalyst slurry prepared as described above, coated, dried and calcined to complete the palladium tertiary catalyst.

However, in response to tightened exhaust gas regulations, in recent years, high performance and high heat resistance of catalysts have been required. Due to the high performance and high heat resistance of these catalysts, the use of precious metals as catalyst materials has increased. The price of the catalyst is gradually rising.

Therefore, it remains a challenge to develop a method for preparing a high porosity three-way catalyst that can reduce the amount of precious metals while having excellent nitrogen oxide removal performance and heat resistance of the finished catalyst as compared to the conventional one.

Therefore, the present invention has been invented to solve the above problems, in the process of preparing the primary and secondary catalyst slurry for high porosity bilayer coating with excellent durability and performance, instead of using the conventional cerium oxide method Cerium oxide and cerium-zirconium composite oxide and cerium-zirconium-yttrium composite oxide are used together in the primary catalyst slurry, and the cerium oxide and cerium-zirconium composite oxide and cerium-zirconium-yttrium composite oxide are used in the secondary catalyst slurry. Cerium carbonate ((Ce (CO ₃ ) ₂ ) is further used, followed by addition of prasedium oxide (PrO ₂ ), and after addition and reaction of the mixed solution, a metal oxide (perovskite) (LaCe). ) (FeCo) O ₃ and (LaSr) (FeCo) O ₃ was prepared by adding appropriate amounts of a selected one of, the finished catalyst is more secondary enhanced removal of nitrogen oxides by the meat of the porous coating layer performance There is provided a method of manufacturing a three-way catalyst of palladium can be manufactured greatly reduces double-layer coating structure in comparison to the amount of palladium is expensive to conventional method while having heat resistance.

Hereinafter, the present invention will be described in detail.

The present invention is to prepare a primary and secondary catalyst slurry using palladium, alumina, cerium oxide, mixed solution and the like, and then the primary catalyst slurry is first coated on a ceramic monolith carrier, and the secondary catalyst slurry is In the method of manufacturing a high durability and high performance high porosity double layer coating structure palladium tertiary catalyst by secondary coating on the dried and calcined ceramic monolith carrier after the primary coating,

The secondary catalyst slurry, after reducing the alumina impregnated with a palladium solution, and then to the cerium oxide: cerium-zirconium composite oxide (CeZr) O ₂ : cerium-zirconium-yttrium composite oxide (CeZrY) ₂ : The ratio of cerium carbonate ((Ce (CO ₃ ) ₂ ) is added in a weight ratio of 15: 60: 15: 10 to 15: 50: 20: 15 and added at 15 to 25 g / l based on the total carrier apparent volume. Praseodymium oxide was added at a concentration of 2 to 5 g / l based on the total carrier apparent volume, followed by addition of the mixed solution and reaction with (LaCe (FeCo) O ₃ as a metal oxide (perovskite). (LaSr) (FeCo) O _{3 It} is characterized in that it is prepared by adding 15 to 25g / l relative to the total volume of the carrier.

Hereinafter, the present invention will be described in more detail.

The present invention relates to a method for producing a high porosity palladium tertiary catalyst having a double layer coating structure in which the finished catalyst can be produced by significantly reducing the amount of expensive palladium compared to the conventional manufacturing method while having improved nitrogen oxide removal performance and heat resistance. will be.

In the three-way catalyst production method of the present invention, among the platinum (Pt), palladium (Pd), and rhodium (Rh) used as the catalyst material, it is excellent in automobile exhaust gas purification effect, and particularly excellent in removing nitrogen oxides and having only excellent heat resistance. A three-way catalyst is prepared and prepared by double coating a ceramic monolith.

That is, in order to manufacture a palladium tertiary catalyst having a double-layer coating structure, a separate first and second catalyst slurry was prepared, and then, the ceramic monolith carrier was immersed in the first catalyst slurry, and then first coated, dried and calcined, The secondary coating slurry is subjected to a secondary coating process by dipping the primary coated ceramic monolith carrier in a slurry (meat washcoat).

Referring to the step-by-step description of the palladium three-way catalyst production method according to the present invention.

First, in order to prepare a primary catalyst slurry, a bulk of cerium oxide (CeO ₂ ), cerium-zirconium composite oxide (Ce.Zr) O ₂ , and alumina (Al ₂ O ₃ ) are used as a first step. A cerium-zirconium-yttrium composite oxide (Ce.Zr.Y) O ₂ is added, praseodymium oxide (PrO ₂ ) is added thereto, followed by a step of adding a mixed solution.

At this time, the cerium oxide (CeO ₂ ), cerium-zirconium composite oxide (Ce.Zr) O ₂ and cerium-zirconium-yttrium composite oxide (Ce.Zr.Y) O ₂ are mixed and added to each other, for a structural reason. This is to induce stabilization to improve the heat resistance of the catalyst and to improve the porosity.

Here, the ratio of the cerium oxide (CeO ₂ ): cerium-zirconium composite oxide (Ce.Zr) O ₂ : cerium-zirconium-yttrium composite oxide (Ce.Zr.Y) O ₂ is 25:60:15 to 20. The mixture is added in a weight ratio of: 60: 20, but it is not preferable because the degree of contribution to the improvement of heat resistance is insufficient if it is out of the above range.

In addition, the mixture of cerium oxide (CeO ₂ ), cerium-zirconium composite oxide (Ce.Zr) O _2, and cerium-zirconium-yttrium composite oxide (Ce.Zr.Y) O ₂ may be used in relation to the apparent volume of the entire carrier. Although it adds at -25 g / L, it is unpreferable since it is weak beyond the addition range, and the grade of heat resistance improvement is weak.

The praseodymium oxide (PrO ₂ ) is added in a powder state, which stabilizes cerium (Ce) on the catalyst to control the adsorption and oxygen storage capacity of carbon monoxide (CO) to effectively remove nitrogen oxides (NOx). .

At this time, the Praseodymium oxide (PrO ₂ ) is added at 2 ~ 5g / ℓ with respect to the apparent volume of the entire carrier, if a small amount of less than the above range is a problem that the effect of improving the heat resistance and nitrogen oxide purification efficiency is less In addition, the addition of more than the above range is not preferred because there is a problem that the price compared to the effect is increased.

The mixed solution is a mixture of barium oxide, lanthanum oxide, acetic acid and water, and barium oxide is 2 to 4 g / l based on the total volume of the carrier, and lanthanum oxide is 0.5 to 2 g / l relative to the apparent volume of the carrier. It is preferable to add in order to improve the heat resistance of alumina and the characteristic of cerium oxide.

In addition, acetic acid is preferably 10 to 20 g / l relative to the apparent volume of the entire carrier, and the pH is preferably 4.5 or less for the control of the viscosity in preparing the catalyst slurry for the next coating.

On the other hand, in the second step, the mixture obtained in the first step is milled while controlling the slurry reaction and particle size by the ball mill method, and finely ground to 90% or more of the total particles having a particle size of 7 μm or less. .

At this time, when milling the particle size outside the above range there is a problem that the reduction in activity and durability is reduced.

As a result of the milling step, a catalyst slurry having a solid content of 30 to 50% and a viscosity of 200 to 400 cpsi is obtained.

A third step, the first metal oxide in order to improve the removal performance of the nitrogen oxide to the catalyst slurry obtained in the second step (perovskite) is (LaCe) (FeCo) O ₃ and (LaSr) (FeCo) O ₃ of The selected one is added at 15-25 g / l relative to the apparent volume of the total carrier to prepare the final primary catalyst slurry.

In the fourth process, the ceramic monolith carrier is immersed in the primary catalyst slurry prepared through the first to third processes, followed by primary coating, followed by drying and firing.

The coating of the present invention is a double coating method using a segregation effect, which can maximize the efficiency of the catalyst by locating the components in the necessary portion using the compound state having the property of agglomeration with each other and the catalytic performance The effect can be improved.

In other words, in the coating of the present invention, the desired component is coated on the desired position as much as possible in the form of dipping by the method of adding each component and selecting an appropriate starting material of the component.

In addition, the drying step is carried out for 2 hours at a temperature of 150 ℃ in a drying furnace, the firing step is carried out for 4 hours at a temperature of 450 ~ 550 ℃ in an electric furnace.

At this time, when the drying and firing conditions are out of the above range, cracking of the coating layer occurs, and there is a problem that harmful compounds are formed, which is not preferable.

The following describes the process of preparing a secondary catalyst slurry and coating the secondary catalyst slurry with a primary coated ceramic monolith carrier to complete the palladium tertiary catalyst.

First, in order to prepare a secondary catalyst slurry, in a fifth step, a palladium (Pd) solution is impregnated into alumina (Al ₂ O ₃ ), and then a step of reducing the same using a thermosetting method is performed.

As an example of the heat-purifying method, heat-cleaning treatment is performed for 3 hours at a temperature of 500 ° C.

In a sixth process, bulk cerium oxide (CeO ₂ ), cerium-zirconium composite oxide (CeZr) O ₂ , cerium-zirconium-yttrium composite oxide (CeZrY) O ₂ and cerium carbonate ((Ce ( CO ₃ ) ₂ ) is added, and praseodymium oxide (PrO ₂ ) is added thereto, followed by adding a mixed solution.

In this case, the cerium oxide (CeO ₂ ), cerium-zirconium composite oxide (CeZr) O ₂ , cerium-zirconium-yttrium composite oxide (CeZrY) O ₂ and cerium carbonate ((Ce (CO ₃ ) ₂ ) ) Are mixed and added to each other to induce structural stabilization to improve the heat resistance of the catalyst and to form high porosity.

Here, the cerium oxide (CeO ₂ ): cerium-zirconium composite oxide (CeZr) O ₂ : cerium-zirconium-yttrium composite oxide (CeZrY) O ₂ : cerium carbonate ((Ce (CO ₃ ) ₂ ) Is added in a weight ratio of 15: 60: 15: 10 to 15: 50: 20: 15, but it is not preferable because it is insufficient to contribute to the improvement of heat resistance if it is out of the above range.

And the cerium oxide (CeO ₂ ), cerium-zirconium composite oxide (Ce.Zr) O ₂ , cerium-zirconium-yttrium composite oxide (Ce.Zr.Y) O _2, and cerium carbonate ((Ce (CO ₃ ) ₂ ). ) Is added in an amount of 15 to 25 g / l based on the total volume of the whole carrier, but it is not preferable because it is difficult to expect improvement in heat resistance outside this addition range.

The praseodymium oxide (PrO ₂ ) is added in a powder state, which stabilizes cerium (Ce) on the catalyst to control the adsorption and oxygen storage capacity of carbon monoxide (CO) to effectively remove nitrogen oxides (NOx). .

At this time, the Praseodymium oxide (PrO ₂ ) is added at 2 ~ 5g / ℓ with respect to the apparent volume of the entire carrier, if a small amount of less than the above range is a problem that the effect of improving the heat resistance and nitrogen oxide purification efficiency is less In addition, the addition of more than the above range is not preferred because there is a problem that the price compared to the effect is increased.

The mixed solution is a mixture of barium oxide, lanthanum oxide, acetic acid and water, and barium oxide is 2 to 4 g / l based on the total volume of the carrier, and lanthanum oxide is 0.5 to 2 g / l relative to the apparent volume of the carrier. It is preferable to add in order to improve the heat resistance of alumina and the characteristic of cerium oxide.

In addition, acetic acid is preferably 10 to 20 g / l relative to the apparent volume of the entire carrier, and the pH is preferably 4.5 or less for the control of the viscosity in preparing the catalyst slurry for the next coating.

In the seventh step, the mixture obtained in the sixth step is milled while controlling the slurry reaction and particle size by a ball mill method, and the fine particles are finely ground to have 90% or more of the particles having a particle size of 7 μm or less.

At this time, when milling the particle size outside the above range there is a problem that the reduction in activity and durability is reduced.

As a result of the milling step, a catalyst slurry having a solid content of 30 to 50% and a viscosity of 200 to 400 cpsi is obtained.

The eighth step, the second the (LaCe) (FeCo) O ₃ and (LaSr) 7 step catalyst slurry the metal oxide in order to improve the removal performance of the nitrogen oxide in (a perovskite) obtained in (FeCo) O ₃ of The selected one is added at 15-25 g / l relative to the apparent volume of the total carrier to produce the final secondary catalyst slurry.

In a ninth step, the first monolayer coated ceramic monolith carrier is immersed in the second catalyst slurry prepared through the fifth to eighth steps, followed by a second coating, followed by drying and firing.

The drying step is carried out for 2 hours at a temperature of 150 ℃ in a drying furnace, the firing step is carried out for 4 hours at a temperature of 450 ~ 550 ℃ in an electric furnace.

At this time, when the drying and firing conditions are out of the above range, there is a problem that cracks of the coating layer occur and harmful compounds are formed, which is not preferable.

In this way, when the three-way catalyst is prepared according to the production method of the present invention made up of the above-mentioned steps, the amount of expensive palladium that is used while the finished catalyst has improved nitrogen oxide removal performance and heat resistance, It can be greatly reduced.

The method for producing a three-way catalyst having a low palladium content as described above can be widely used in the production of catalysts for automobile exhaust gas purification and industrial catalysts.

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

Example

In order to compare the conventional palladium oxide catalyst using palladium (Pd) at 7.0 g / l relative to the total carrier apparent volume, in this embodiment, palladium (Pd) is used at 4.0 g / l relative to the total carrier apparent volume. A palladium tertiary catalyst having a multilayer coating structure was prepared.

First, in order to prepare a primary catalyst slurry, first, 50 g of alumina (Al ₂ O ₃ ), ₃ g of bulk cerium oxide (CeO ₂ ), 9 g of cerium-zirconium compound oxide (CeZr) O _2, and cerium-zirconium A mixture of 3 g of yttrium composite oxide (Ce.Zr.Y) O ₂ was added, followed by 3.0 g of praseodymium (PrO ₂ ).

In addition, a solution containing 2.8 g of barium oxide, 0.67 g of lanthanum oxide, 13.5 g of acetic acid, and 187.5 ml of water was added thereto, and the pH was adjusted to 4.2 using acetic acid.

Then, the particle size was milled to 9 μm or less by a ball mill method, and then (LaCe (FeCo) O ₃ , which is a metal oxide (perovskite), was 22.5 g / g based on the total volume of the whole carrier. After additionally added in the form of powder, the final size of the final catalyst slurry having a solid content of 40% and a viscosity of 300 cpsi was obtained by milling so that the final particle size of 7 μm or less was 94% of the total particles.

Here, the ceramic monolith carrier was dipped and coated, and then dried in a drying furnace at a temperature of 150 ° C. for 2 hours, and then fired in an electric furnace at a temperature of 500 ° C. for 4 hours.

Next, to prepare a secondary catalyst slurry, first, a solution containing 4.0 g of palladium (Pd) was impregnated in 50 g of alumina (Al ₂ O ₃ ), and then reduced by thermal purification for 3 hours at a temperature of 500 ° C. I was.

Next, 2.5 g of bulk cerium oxide (CeO ₂ ), 7.5 g of cerium-zirconium compound oxide (Ce.Zr) O ₂ , ₃ g of cerium-zirconium-yttrium compound oxide (Ce.Zr.Y) O ₂ , 2.25 g of cerium carbonate ((Ce (CO ₃ ) ₂ )) was added and mixed, and 3.0 g of prasedium oxide (PrO ₂ ) was added thereto.

In addition, a solution containing 2.8 g of barium oxide, 0.67 g of lanthanum oxide, 13.5 g of acetic acid, and 187.5 ml of water was added thereto, and the pH was adjusted to 4.2 using acetic acid.

Then, the particle size was milled to 9 μm or less by a ball mill method, and then (LaCe (FeCo) O ₃ , which is a metal oxide (perovskite), was 17.5 g / g based on the total volume of the whole carrier. After the powder was added in the form of L, the final particle size of 7 µm or less was milled to 94% of the total particles, thereby obtaining a final secondary catalyst slurry having a solid content of 40% and a viscosity of 300 cpsi.

The first coated ceramic monolith carrier was dipped and coated therein, and then dried in a drying furnace at a temperature of 150 ° C. for 2 hours and calcined at 500 ° C. in an electric furnace for 4 hours, thereby forming a three-layer palladium tertiary catalyst. To complete.

Comparative example

In order to compare the palladium (Pd) to the oxidation catalyst of the low palladium content of the present invention using 4.0 g / l of the total carrier apparent volume, in the comparative example, palladium (Pd) was 7.0 g / l of the total carrier apparent volume. The used palladium terpolymer was prepared by a known method.

First, a solution containing 7.0 g of palladium (Pd) was impregnated into 100 g of alumina (Al ₂ O ₃ ), and then hydrazine hydrate (hydrazinehydrate) was added dropwise to 1.66 ml per 1 g of palladium.

Then, 30 g of cerium oxide (CeO ₂ ) was added, and a solution containing 5.6 g of barium oxide, 1.33 g of lanthanum oxide, 27.3 g of acetic acid, and 375 ml of water was added thereto, and the pH was adjusted to 4.2 using acetic acid.

In addition, the final catalyst slurry having a solid content of 40% and a viscosity of 300 cpsi was obtained by milling the particle size having a particle size of 7 μm or less by 94% of all particles by a ball mill method.

Here, the ceramic monolith carrier was dipped and coated, and then dried at a temperature of 150 ° C. for 2 hours in a drying furnace, and calcined at 500 ° C. in an electric furnace for 4 hours, thereby completing a single layered palladium terpolymer.

The catalyst prepared according to the above Example and Comparative Example was tested and the results are shown in Table 1 below.

In Table 1, the low temperature activation temperature is a 50% purification temperature means that the lower the measured temperature, the better the purification efficiency of hydrocarbons, carbon monoxide, nitrogen oxides, the three-way characteristic is high to indicate the removal performance of the three components The better the property is.

In addition, 950 degreeC aging is the result of having carried out for 140 hours in the atmosphere of 950 degreeC electric furnace in air | atmosphere.

As a result of the comparative test, as shown in Table 1, the three-way catalyst prepared according to the embodiment of the present invention, despite the significantly reduced palladium content compared to the comparative example prepared, purifying hydrocarbons, carbon monoxide, nitrogen oxides Efficacy and removal performance was found to be superior to the three-way catalyst of the comparative example.

In this way, when the three-way catalyst is produced through the production method of the present invention, the amount of the expensive palladium can be significantly reduced compared to the conventional production method while the finished catalyst has more improved nitrogen oxide removal performance and heat resistance.

As described above, according to the method for preparing a palladium three-way catalyst having a double layer coating structure according to the present invention, the finished catalyst has a high porosity double layer coating structure capable of further improving the catalytic performance, and further improved nitrogen oxides. Palladium three-way of the high porosity double layer coating structure according to the present invention has the effect of reducing the use of expensive palladium while removing performance and heat resistance significantly compared to the existing manufacturing method, due to the economical effect of manufacturing cost reduction The catalyst production method can be widely used in the production of catalysts for automobile exhaust gas purification and industrial catalysts.

Claims (1)

Palladium, alumina, cerium oxide, mixed solution and the like to prepare a primary and secondary catalyst slurry, then the primary catalyst slurry is first coated on a ceramic monolith carrier, the secondary catalyst slurry is the primary coating In the method of producing a high durability and high performance high pore double layer coating structure palladium terpolymer catalyst by secondary coating on the dried and calcined ceramic monolith carrier, The secondary catalyst slurry, after reducing the alumina impregnated with a palladium solution, and then to the cerium oxide: cerium-zirconium composite oxide (CeZr) O ₂ : cerium-zirconium-yttrium composite oxide (CeZrY) ₂ : The ratio of cerium carbonate ((Ce (CO ₃ ) ₂ ) is added in a weight ratio of 15: 60: 15: 10 to 15: 50: 20: 15 and added at 15 to 25 g / l based on the total carrier apparent volume. Praseodymium oxide was added at a concentration of 2 to 5 g / l based on the total carrier apparent volume, followed by addition of the mixed solution and reaction with (LaCe (FeCo) O ₃ as a metal oxide (perovskite). (LaSr) (FeCo) O _{3 A} method for producing a palladium tertiary catalyst having a double-layer coating structure, characterized in that the addition of 15 to 25g / L based on the total volume of the carrier.